CA2179042C - Method and apparatus for forming aperiodic gratings in optical fibers - Google Patents
Method and apparatus for forming aperiodic gratings in optical fibersInfo
- Publication number
- CA2179042C CA2179042C CA002179042A CA2179042A CA2179042C CA 2179042 C CA2179042 C CA 2179042C CA 002179042 A CA002179042 A CA 002179042A CA 2179042 A CA2179042 A CA 2179042A CA 2179042 C CA2179042 C CA 2179042C
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- Prior art keywords
- refractive index
- beams
- light
- aperiodic
- wavelength
- Prior art date
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- 238000000034 method Methods 0.000 title claims abstract description 11
- 239000013307 optical fiber Substances 0.000 title abstract description 6
- 239000000463 material Substances 0.000 claims abstract description 4
- 230000003287 optical effect Effects 0.000 claims description 21
- 238000002310 reflectometry Methods 0.000 claims description 11
- 238000000926 separation method Methods 0.000 claims description 2
- 239000000835 fiber Substances 0.000 abstract description 28
- 230000006870 function Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 230000000737 periodic effect Effects 0.000 description 5
- 230000003595 spectral effect Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 230000002452 interceptive effect Effects 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000001066 destructive effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium dioxide Chemical compound O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 description 2
- 230000010363 phase shift Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 206010034972 Photosensitivity reaction Diseases 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000036211 photosensitivity Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
- G02B6/02133—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating using beam interference
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S359/00—Optical: systems and elements
- Y10S359/90—Methods
Abstract
A method and apparatus for simultaneously exposing an optical fiber (32), made of a material which has a refractive index that can b e permanently changed by exposure to light of a predetermined intensity at a predetermined wavelength, to two writing light beams (268 , 272) which intersect and interfere in a predetermined region (30) of the fiber (32) so as to create an interference pattern along a longi tudinal axis of the fiber (32), for a time long enough to form a permanent refractive index variation in the waveguide. Each of said two writing beams have a predetermined number of wavelengths, each wavelength being sufficiently different from each other so as to cause said refract ive index variation to be an aperiodic variation. Also, each wavelength represents a Fourier component of the desired aperiodic refracti ve index variation.
Description
WO95117705 i~ ~9042 PCT/US94~110~59 DesGription M-thod an~ Apparatu~ f or Forming Aperiodic Gr~ting~ in Optical FiDer~
5 T~ ;~-1 FiQld This invention relates to Bragg gratings and, more particularly, to aperiodic gratings in optical f ibers .
B~C}.y ~ ' Art 10Reflective gratings, as is known, have .us applications in the areas of optical sensing and signal prorPcc;n~. Also, it is known to impress refractive index (or Bragg) reflection gratings, having a uniform spatial periodicity, in the core of 15 a germania doped optical fiber, as is ti; CCIlCCPd in U. S . Patent Nos . 4, 807, 950 and 4, 725, 110 both to Glenn et al. A Bragg grating having a uniform spatial periodicity of refractive index variations or peL LuLl,a~ions acts as a narrow wavelength band 20 reflector at wavelengths equal to twice the grating spacing ( i . e ., the spacing between successive index perturbations ) .
Also, the width of the ref lection peak is detPrm; nP-l by the amplitude of the refractive index 25 variations or p~,LLuLLaLions (i.e., the "strength" of the grating) and the effective length of the grating ( i . e ., the length over which the incident light has dissipated to substantially zero).
In particular, for low amplitude index 30 variations (i.e., "weak" gratings), the width of the reflection peak is very narrow because, as the input light is incident on successive pertubations, due to the small change in refractive index, only a small portion of the incident light is ref lected . Thus, 35 the source light is only slightly depleted. As a W095117705 ~ ! ~ r 21 79042 PCT/Us94/110ss result, the total reflected light compri~es a sm~ll ~mount of light reflected from many successive perturbations which add coherently tdue to their spacing) to produce a strong reflected signal at the peak ref lection wavelength ( i . e ., twice the grating spacing~. It should be understood that the effective (optical) length of the grating, i. e., the length it takes for the light to completely dissipate, is not ~rPcsArily equal to (and is generally shorter than) its physical length.
However, as the wavelength of the source light changes from twice the grating spacing (where peak reflectivity occurs), destructive interference quickly begins to occur between light beams reflected from the various peL~uL~c,tions due to phase differences cau5ed because the spacing between successive perturbations are no longer egual to half the incident wavelength.
Conversely, for large amplitude index variations (i.e., "strong" gratings) a large amount of light is reflected from each grating. Thus, the input light is significantly depleted by each peL LuL},~.tion. Consequently, the effective length of the grating is much shorter than with weak gratings.
As a result, the input wavelength may deviate more from twice the grating spacing before destructive interf erence begins to occur . Thus, the width of the reflection peak for strong gratings is typically wider than that f or weak gratings .
As is known, the formation of gratings in a fiber is the result of a photo-refractive effect.
In particular, when the core of a photosensitive fiber is exposed to ultra-violet radiation at a wavelength near 250 nanometers, a p~rr~n~nt change in the refractive index is produced. The magnitude of the change is related to the intensity of the incident radiation and the time of exposure. As WO 9S/17705 ~ 2 1 7 ~ 0 4 2 PCT/US941110~9 tl;ccllcsP~ in the aforementioned patents, a grating with a unif orm spatial periodicity can be produced by allowing two n~ ;n;~l ly plane optical waves to interfere within the core of the fiber, thereby 5 producing an interference pattern therein. The uniform sinusoidal intensity variation of the interference pattern ~ludu. es a grating having a uni~orm spatial period of refractive index variation6 similar to the sinusoidal variations of lO the interference pattern.
However, while having a narrow ref lection band is useful for some applications, there may be other applications which contemplate the use of a filter function which is wider than that achievable with 15 the aforementioned strong gratings, or has a different shape than merely a simple single peak narrow ref lection band .
Therefore it would be desirable to provide a Bragg grating having a ref lectivity prof ile which is 20 not merely a narrow band single peak.
D;~cl~_ .. of Invention Objects of the invention include provision of a Bragg grating having a selectable filter-function profile.
According to a first aspect of the present invention a method of impressing an aperiodic grating includes the steps of taking an optical waveguide made of a material which has a refractive index that can be pPrr-nPntly changed by ~ /O~ULe to light of a predetPrmi nPd intensity at a predetermined wavelength and simultaneously exposing the waveguide to two writing light beams which intersect and interfere in a prP~4PtPrm;nPd region of the waveguide so as to create an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a pPrr-nPnt W095117705 ,; ~ ~ 21 79042 PCTruS94/llOS9 refractive index variation in the waveguide, each o~
the two writing beams have a prede~P~m; nPrl number of wavelengths, each wavelength is sufficiently different from each other so as to cause the refractive index variation to be an aperiodic variation .
According further to the first aspect of the invention, each of the wavelengths in the step of exposing comprises a Fourier, -nPnt of the aperiodic refractive index variation, According to a second aspect of the present invention, an apparatus for impressing an aperiodic grating into a region of an optical waveguide, includes light source means, for providing a predetPrm;nP~l number of source beams, each beam having a predetPrminPd wavelength; wavelength combining means for combining the source beams into a ~ingle beam; beamsplitting means for splitting the single beam into at least two writing beams; and beam directing means for directing the writing beams so as to intersect on a region of the waveguide, thereby creating an interf erence pattern along a longitudinal axis of the waveguide for a time long enough to form a pPrr-nPnt refractive index variation in the waveguide, the wavelengths associated with the source beams are sufficiently different from each other so as to cause the refractive index variation to be an aperiodic variation .
According further to the second aspect of the invention the light source means includes broadband light source means for providing a broadband source light having a plurality of wavelengths and wavelength separation means, f or separating the broadband light into the predetPrm; nP~ number of beams .
:; ;
W095/17705 ~ 2 1 79042 PCT/US94/11059 The invention represents signif icant ~ ,uLuvl ~5 over the prior art Bragg gratings by providing a method and apparatus f or making an aperiodic refractive index variation ( i . e., an aperiodic grating) along the length of an optical waveguide such as an optical fiber. Such aperiodic gratings allow for the reflectivity profile of the grating to be tailored to match some specific pretlt~tt~rm;n~d wavelength profile characteristic. In one ~ nt, the periodicity of refractive index variation, and hence the grating, is varied by changing the wavelength, the amplitude, and/or the phase of the interfering beams, and/or their angle of intersection within the fiber. By adjusting these parameters of the writing beams it is possible to sequentially build-up the desired variation in periodicity by a process of Fourier synthesis.
Thus, each interference pattern is a Fourier -Ir~t of the overall aperiodic index variation.
In an alternative t~mho~l;r ~, an aperiodic grating is written with all the Fourier ~ l Ls, or a portion thereof, simultaneously, by using a spectral filter which separates-out the desired wavelengths, alters the amplitude of each wavelength in a prt~ tt~rm;nt~l manner (and/or phase shifts of each wavelength), and recombines the individual Fourier c ^nts into a single beam which is then used to write the grating. In the former technique, the writing is done sequentially and in the latter te~hn;trlt~ the Fourier components are; ~.:ssed simultaneously .
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary ~ s thereof as illustrated in the Rt -nying drawings.
WO 95/17705 s 1~ 2 1 7 9 0 4 2 PCTIUS94/1l059 Brie~ D~s_ription of Dr~wing3 Fig. 1 is a schematic block diagram showing amplitude and phase modulation to write an aperiodic grating, in accordance with the present invention.
Fig . 2 is a blown-up 6ide view of a f iber and two beams which intersect and interf ere in a region of the f iber.
Fig. 3 is a plurality of waveforms in illustrations (a), (b), (c), (d), (e), showing a plurality of Fourier ~ -nontS of refractive index variation along a longitudinal axis of a waveguide and a resultant summation of these _ _-nPnts which exists after all the ~ s are written into a f iber, in accordance with the present invention .
Fig . 4 is a graph of the ref lectivity prof ile associated with the aperiodic grating of Fig. 3, illustration (e), in acuu~d~llce with the present invention .
Fig. 5 is a block diagram of an alternative Pmho~ nt of the present invention having ~^~nnin~
mirrors to adjust the angle of intersection where the grating is written in the fiber, in accordance with the present invention.
Fig . 6 is a blown-up view of the s~^Ann i n~
mirror and optical elements of the -mhotlir L of Fig. 5, in accordance with the present invention.
Fig. 7 is a schematic block diagram of an alternative _mho~l i L of the present invention using simultaneously writing all the Fûurier ~ -^nts to form an aperiodic grating, in accordance with the present invention.
Best Mode for Carrying out the Inv~ntion Referring now to Fig. 1, a tunable wavelength laser 10 provides a source beam 12 having a wavelength based on a signal on a line 14 from a controller 16 (tli C~ cs-^d hereinafter) . The light 12 _ _ _ _ .
W0 95/17705 ~ 2 1 7 9 0 4 2 PC~/US94/11059 is incident on an amplitude modulator 18, e.g., an ele~;~, v ~ic amplitude modulator or a spatial light modulator. The amplitude modulator 18 adjusts the amplitude of the input light signal 12 and provides a light signal 20 having an amplitude in response to an amplitude control 6ignal on a line 21 from the controller 16.
The amplitude adjusted light signal 20 is incident on a beamsplitter 22, which passes a predetPrmin~l percentage, e.g., 5096, of the input light 20 as a passed light 24 and reflects the L~ in;n~ portion as a reflected light 25. The passed light 24 is incident on a mirror 26 which provides a reflected beam 28. The beam 28 is incident on a region 30 of an optical fiber 32, e.g.
a g~rr - n i A -doped s i 1 ica-core f iber .
The reflected beam 25 is incident on a phase modulator 34, e.g., an ele~ Lic phase modulator, which provides an output beam 36 being phase shifted from the input beam 25 in Lc:~ullSe to a signal on a line 38 from the controller 16. The phase shifted beam 36 is incident on a mirror 40 which provides a reflected beam 42. The reflected beam 42 is also incident on the region 30 of the optical fiber 32 and intersects with and interferes with the beam 28.
Alternatively, a f ixed phase modulator may be used if desired, such as a phase plate. It should be understood that the phase modulator 34 may alternatively be placed in the path of the beams 24, 28, or 42.
The controller comprises known electronic, digital and/or analog circuitry, or it may likely be a digital computer, having the appropriate signal prQcPfi~in~ and memory capability to provide the functions fli ~c~ cl herein.
As fl i ~c~ d hereinbef ore, and in the aforementioned US Patents to Glenn et al, a Bragg W0 95/17705 , , ~ 2 1 7 9 0 4 2 PCT/US94/llOss --grating is ~-mht~lAt~-l into the core of an optical f iber by interf ering two coherent beams in the region of the f iber core where the grating is desired. The resulting interference pattern i8 a standing wave which exists along the fiber length (or longitudinal axis) which causes a cv~L~ in~
spatially periodic variation in refractive index along the longitudinal axis of the fiber (t~; Ccllcst~d hereinbefore). The spatial periodicity if the refractive index variation (and hence the grating) is a function of the wavelength of the two incident light beams 28, 42 . To aid in altering each ~ -nt of the refractive index, the amplitude and pha6e of each ~-o~nr~nent may be adjusted, however, this i5 not required, provided the source is wavelength variable. Also, instead of the amplitude modulator 18, the laser source 10 may have variable output power which is controlled by the controller 16 .
Referring now to Fig. 2, the beams 28,42 are either collimated or focussed to a line (using cylindrical lenses-not shown) and intersect at the region 30 of the core of the fiber 32. The region 30 is where the periodic interference pattern is formed which creates the periodic variation of refractive index .
Ref erring now to Fig . 3, we have f ound that by performing successive writings of interference patterns having different amplitude, phase and fre~uency of spatial variations (and thereby producing CUL r ~,-yv.,dingly different periodic refractive index variations), an aperiodic refractive index profile can be created, thereby allowing for filter shapes other than a single narrow band reflection filter.
In particular, if each of the refractive index ~rofi es along the longitudlnal or z-axis of the WO 95117705 ,3, '~ 2 1 7 9 0 4 2 PCT,US94/ll059 .
fiber indicated in Fig. 3, illusts. (a)-(d) are written successively into the core of the fiber, then the resultant p~-n~nt refractive index variation profile i8 as indicated in Fig. 3, illust.
(e), which is simply the sum of the individual Fourier ~ ~s (in Fig. 3, illusts . (a) - (d) ) .
Such an index variation profile provides a wide bandwidth filter profile 60, shown in Fig. 4.
Using the principle of superposition, each of the waveforms 50-56 of Fig. 3 , illusts. (a) - (d), respectively, reflects a narrow wavelength band of light related to the grating spacing, and are indicated by the individual profiles 62-66, respectively . Thus, when each of these wavef orms are i~ ecsed in the fiber core, the resultant filter profile is the broadband filter function 60.
It should be understood that other filter function profiles may be created by using different Fourier-^-lt refractive index variation waveforms.
Also, ,as is known, the reflectivity profile (e.g., Fig. 4) is the Fourier transform of the refractive index prof ile when the amplitude of the variation is small (i.e., for "weak" gratings), e.g., Fig. 3, illust. (e)). For more information regarding this Fourier transform relatinn~hir see H.
Kogelnik, "Filter Response of Nonuniform Almost Periodic Structures", Bell System Tech. Journal, Vol. 55, No. l (Jan. 1976). Thus, one can obtain the desired aperiodic refractive index variation profile by taking the inverse Fourier transform of the desired reflectivity characteristic and taking the Fourier transform of the resultant aperiodic index profile (with respect to length), to determine the individual refractive index Fourier ^ntS
needed to be written to create such a reflectivity function .
_ g _ WO95/17705 ~ 21 79042 PCrNS94lll059 Referring again to Fig. 1, to create the refractive index profile 58 shown in Fig. 3, illust.
(e), the controller 16 controls the tunable laser 10, the amplitude modulator 18, and the phase modulator 34 to create each of the Fourier c~ --,t6 of the wavcform6 50-56 of Fig. 3, illu6ts. (a) - (d), 6equentially in time.
More 6pecifically, the controller 15 sets the wavelength of the tunable laser 10, the level of attenuation of the amplitude modulator 18, and the amount of phase delay of the phase modulator 34 to provide the beam6 28,42 with the appropriate amplitude and phase so as to create the refractive index waveform 12 of Fig. 3, illust. (a). These condition6 are held con6tant for a prede~rm;nF-~l period of time long enough to write thi6 refractive index variation pattern p~rr-n~ntly into the core of the fiber 32, 6imilar to that tlicc~ d in the aforementioned U. S. Patents. The amount of time, a6 i6 known, varie6 from seconds to minutes rl~r~n~;nq on the photo-sensitivity of the fiber and intensity of the exposing radiation.
Next, the controller adjusts the wavelength of the tunable la6er 10, the amplitude modulator 18, and the pha6e modulator 34 60 a6 to provide the beam6 28,34 with the appropriate amplitude, phase, and wavelength to create the refractive index variation waveform 52 of Fig. 3, illust. (b), in the fiber 32. These 6ettings are retained for sufficient length6 of time and at a 6ufficient intensity so as to provide a permanent index variation as indicated by the waveform 52 of Fig. 3, illust. (b).
A similar process is performed to create the refractive index variation waveforms 54,56 of Fig.
3, illusts. (c), (d), in the ~ame region 30 of the W095/17705 ~ 2 1 79042 PCT/US94/llO~i9 fiber 32. The result is an overall refractive index profile such as that shown in Fig. 3, illust. (e).
Referring now to Fig. 5, as is known, the spatial periodicity of refractive index variation i5 also a function of the angle e of ; nricl~n~e of the two interfering beams on the fiber 32. Using this effect, the beams 24,36 are incident on c~nn;n~
mirrors 100 ,102 which pivot about axes 104 ,106, respectively ( instead of being incident on the stationary mirrors 26,40, l;ccllcs~l hereinbefore with Fig. 1). Also, for this ~mhorl;- L, the laser source need not be a variable wavelength source and the amplitude and phase modulation is not required, however, may still be used to vary additional variables, if desired.
Referring now to Figs. 5 and 6, the mirror 100 provides a reflected collimated beam 108 having an angle ~ relative to the angle of the mirror 100.
The beam 108 is incident on a lens 110 which focusses and directs light entering the lens from various different angles to provide output light 112 having substantially parallel central rays. The light 112 is incident on a collimating lens 114, which collimates and directs the light 112 as an output light 116 to a region 30 of the fiber 32 which is located at the focal plane of the lens 114.
The distance between where the light 108 leaves the mirror 100 and the lens 110 is equal to the f ocal length f 1 of the lens 110 . The distance between the lens 114 and the fiber 32 is equal to the focal length f2 of the lens 114. Also, the distance between the lens 110 and the lens 114 is equal to the sum of the two focal lengths fl,f2 of the lenses 110,114, respectively. To have a change in the angle ~ cause the same change in the angle e onto the fiber, the focal lengths fl, f2 should be wo 95/17705 ' ~ , 2 1 7 9 0 4 2 PCT/US94/11059 the same; however, this i5 not required for the invention to operate.
Referring to Fig. 5, a similar arrangement exists between the adjustable mirror 102 and the fiber 32. In particular, a light 120 is reflected from the mirror 102 and is incident on a focussing and redirecting lens 122 which provides a focussed output light 124 (similar to the focussed beam 112 of Fig. 6). The focussed light 124 is incident on a lo collimating lens 126 which provides a collimated light beam 128 onto the region 30 of the fiber 32.
Ref erring now to Fig . 7, a broadband laser source 200 provides a beam 201, having a broad wavelength band which includes wavelengths of the desired Fourier spectrum. The beam 201 is incident on a diffraction grating 202, which, as is known, diffracts light so as to spatially separate various wavelengths existing in the light beam 201. In particular, the diffraction grating 202 provides a diffracted light 204, having a wavelength of A1.
The diffraction grating also provides a beam 206, having a wavelength of A2, and a beam 208, having a wavelength of A3. More wavelengths may be used if des ired .
The beams 204-208 are incident on a focussing lens 210 which converts the collimated beams 204-208 to focussed beams 212-216, respectively, having substantially parallel central ray6 (a6 i6 indicated in Fig. 5).
The beams 212-216 are incident on an amplitude modulator 220, e.g., a spatially varying transparency or a spatial light modulator. The 6patial light modulator 220 alter6 the inten6ity of the beams 212-216 in a selective manner based on the location that a given light is incident on the modulator 220. The spatial light modulator provides amplitude adjusted light beams 222-226 in ~,yullse .
WO95/17705 21 79042 PCT/US91/110~i9 .
to a control signals on lines 228 from a controller 230. The controller 230 is similar to the controller 56 discussed hereinbefore and sets the value of the amplitude of each of the beams 222-226 used to make the grating. Alternatively, the spatial light modulator 220 may be a passive transparency sheet having varying regions of opagueness.
The beams 222-226 are incident on a lens 240 which collimates the beams 234-238 as the beams 242-248, respectively, and directs the beams onto a common region of a diffraction grating 250. The diffraction grating 250, combines the beams 242-248 to a single output beam 252.
The optical ~ 7ts of the diffraction grating 202, the lenses 210,240, the amplitude and phase modulators 220,232, and the grating 250, essentially make up a spectral filter which adjusts the amplitude and phase of the individual Fourier ^~7ts of the desired aperiodic refractive index variation. Also, the lenses 210,240 are in essentially the same conf iguration as that of Fig.
6.
The beam 252 is incident on a beamsplitter 260 similar to the beamsplitter 22 (Fig. 1), r7~ie~l7~^s^d hereinbefore. The beamsplitter 260 passes a beam 262 and reflects the L~ ininj portion of the input beam 252 as the beam 264. The beam 262 is incident on a mirror 266, which provides a reflected beam 268 onto the region 30 of the fiber 32. The reflected beam 264 is incident on a mirror 270, which provides a reflected beam 272 onto the region 30 of the fiber 32. The beams 268,272 intersect in the region 30 of the fiber 32 similar to that shown in Fig. 2 for the beams 28, 42 .
3 5 The _mho~7; - t shown on Fig . 7 provides simultaneous writing of all the Fourier spectral Ls that make-up the desired refractive index Wo 95117705 t , ~ 2 1 7 9 0 4 2 PCr/USs4/11Oss ~`
waveform profile. This embodiment has the advantage of reduced time to write the desired aperiodic grating as well as being less susceptible to stability vibration and air current problems associated with performing repeated writing in a segucntial fa6hion. In particular, the distances between mirrors and the orientations of the lenses and mirrors relative to each other must remain precisely f ixed in order f or the multiple sequential spectral Fourier ~ Ls to provide the desired C hi ner~l refractive index waveform.
It should be understood that when the wavelengths are closely spaced, there will actually be some overlap of the focussed beams 212-216.
Thus, the modulator 220 should be placed close to the focal points of the beams 212-216, as indicated in Fig. 7.
Also, i~ phase modulation is desired, the amplitude adjusted beams 222-226 may be incident on a phase modulator (not shown), e.g., an electro-optic modulator located between the amplitude modulator 220 and the lens 240. In that case, the mirrors 210,240 may be cylindrical, the beams 222-226 may be focussed to a line, the phase modulator would modulate a portion of each focussed line, an optical element (not shown) would split each beam ~nd another optical element would direct the beams onto the fiber. Also in that case, the controller 230 would set the amount of phase shift in each beam and the optical elements 260,266,270 would not be used .
Instead of using the single broadband source 200 and the diffraction grating 202, a plurality of single wavelength sources (not shown) may be used to provide the beams 204-208, each being incident on the lens 210.
5 T~ ;~-1 FiQld This invention relates to Bragg gratings and, more particularly, to aperiodic gratings in optical f ibers .
B~C}.y ~ ' Art 10Reflective gratings, as is known, have .us applications in the areas of optical sensing and signal prorPcc;n~. Also, it is known to impress refractive index (or Bragg) reflection gratings, having a uniform spatial periodicity, in the core of 15 a germania doped optical fiber, as is ti; CCIlCCPd in U. S . Patent Nos . 4, 807, 950 and 4, 725, 110 both to Glenn et al. A Bragg grating having a uniform spatial periodicity of refractive index variations or peL LuLl,a~ions acts as a narrow wavelength band 20 reflector at wavelengths equal to twice the grating spacing ( i . e ., the spacing between successive index perturbations ) .
Also, the width of the ref lection peak is detPrm; nP-l by the amplitude of the refractive index 25 variations or p~,LLuLLaLions (i.e., the "strength" of the grating) and the effective length of the grating ( i . e ., the length over which the incident light has dissipated to substantially zero).
In particular, for low amplitude index 30 variations (i.e., "weak" gratings), the width of the reflection peak is very narrow because, as the input light is incident on successive pertubations, due to the small change in refractive index, only a small portion of the incident light is ref lected . Thus, 35 the source light is only slightly depleted. As a W095117705 ~ ! ~ r 21 79042 PCT/Us94/110ss result, the total reflected light compri~es a sm~ll ~mount of light reflected from many successive perturbations which add coherently tdue to their spacing) to produce a strong reflected signal at the peak ref lection wavelength ( i . e ., twice the grating spacing~. It should be understood that the effective (optical) length of the grating, i. e., the length it takes for the light to completely dissipate, is not ~rPcsArily equal to (and is generally shorter than) its physical length.
However, as the wavelength of the source light changes from twice the grating spacing (where peak reflectivity occurs), destructive interference quickly begins to occur between light beams reflected from the various peL~uL~c,tions due to phase differences cau5ed because the spacing between successive perturbations are no longer egual to half the incident wavelength.
Conversely, for large amplitude index variations (i.e., "strong" gratings) a large amount of light is reflected from each grating. Thus, the input light is significantly depleted by each peL LuL},~.tion. Consequently, the effective length of the grating is much shorter than with weak gratings.
As a result, the input wavelength may deviate more from twice the grating spacing before destructive interf erence begins to occur . Thus, the width of the reflection peak for strong gratings is typically wider than that f or weak gratings .
As is known, the formation of gratings in a fiber is the result of a photo-refractive effect.
In particular, when the core of a photosensitive fiber is exposed to ultra-violet radiation at a wavelength near 250 nanometers, a p~rr~n~nt change in the refractive index is produced. The magnitude of the change is related to the intensity of the incident radiation and the time of exposure. As WO 9S/17705 ~ 2 1 7 ~ 0 4 2 PCT/US941110~9 tl;ccllcsP~ in the aforementioned patents, a grating with a unif orm spatial periodicity can be produced by allowing two n~ ;n;~l ly plane optical waves to interfere within the core of the fiber, thereby 5 producing an interference pattern therein. The uniform sinusoidal intensity variation of the interference pattern ~ludu. es a grating having a uni~orm spatial period of refractive index variation6 similar to the sinusoidal variations of lO the interference pattern.
However, while having a narrow ref lection band is useful for some applications, there may be other applications which contemplate the use of a filter function which is wider than that achievable with 15 the aforementioned strong gratings, or has a different shape than merely a simple single peak narrow ref lection band .
Therefore it would be desirable to provide a Bragg grating having a ref lectivity prof ile which is 20 not merely a narrow band single peak.
D;~cl~_ .. of Invention Objects of the invention include provision of a Bragg grating having a selectable filter-function profile.
According to a first aspect of the present invention a method of impressing an aperiodic grating includes the steps of taking an optical waveguide made of a material which has a refractive index that can be pPrr-nPntly changed by ~ /O~ULe to light of a predetPrmi nPd intensity at a predetermined wavelength and simultaneously exposing the waveguide to two writing light beams which intersect and interfere in a prP~4PtPrm;nPd region of the waveguide so as to create an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a pPrr-nPnt W095117705 ,; ~ ~ 21 79042 PCTruS94/llOS9 refractive index variation in the waveguide, each o~
the two writing beams have a prede~P~m; nPrl number of wavelengths, each wavelength is sufficiently different from each other so as to cause the refractive index variation to be an aperiodic variation .
According further to the first aspect of the invention, each of the wavelengths in the step of exposing comprises a Fourier, -nPnt of the aperiodic refractive index variation, According to a second aspect of the present invention, an apparatus for impressing an aperiodic grating into a region of an optical waveguide, includes light source means, for providing a predetPrm;nP~l number of source beams, each beam having a predetPrminPd wavelength; wavelength combining means for combining the source beams into a ~ingle beam; beamsplitting means for splitting the single beam into at least two writing beams; and beam directing means for directing the writing beams so as to intersect on a region of the waveguide, thereby creating an interf erence pattern along a longitudinal axis of the waveguide for a time long enough to form a pPrr-nPnt refractive index variation in the waveguide, the wavelengths associated with the source beams are sufficiently different from each other so as to cause the refractive index variation to be an aperiodic variation .
According further to the second aspect of the invention the light source means includes broadband light source means for providing a broadband source light having a plurality of wavelengths and wavelength separation means, f or separating the broadband light into the predetPrm; nP~ number of beams .
:; ;
W095/17705 ~ 2 1 79042 PCT/US94/11059 The invention represents signif icant ~ ,uLuvl ~5 over the prior art Bragg gratings by providing a method and apparatus f or making an aperiodic refractive index variation ( i . e., an aperiodic grating) along the length of an optical waveguide such as an optical fiber. Such aperiodic gratings allow for the reflectivity profile of the grating to be tailored to match some specific pretlt~tt~rm;n~d wavelength profile characteristic. In one ~ nt, the periodicity of refractive index variation, and hence the grating, is varied by changing the wavelength, the amplitude, and/or the phase of the interfering beams, and/or their angle of intersection within the fiber. By adjusting these parameters of the writing beams it is possible to sequentially build-up the desired variation in periodicity by a process of Fourier synthesis.
Thus, each interference pattern is a Fourier -Ir~t of the overall aperiodic index variation.
In an alternative t~mho~l;r ~, an aperiodic grating is written with all the Fourier ~ l Ls, or a portion thereof, simultaneously, by using a spectral filter which separates-out the desired wavelengths, alters the amplitude of each wavelength in a prt~ tt~rm;nt~l manner (and/or phase shifts of each wavelength), and recombines the individual Fourier c ^nts into a single beam which is then used to write the grating. In the former technique, the writing is done sequentially and in the latter te~hn;trlt~ the Fourier components are; ~.:ssed simultaneously .
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary ~ s thereof as illustrated in the Rt -nying drawings.
WO 95/17705 s 1~ 2 1 7 9 0 4 2 PCTIUS94/1l059 Brie~ D~s_ription of Dr~wing3 Fig. 1 is a schematic block diagram showing amplitude and phase modulation to write an aperiodic grating, in accordance with the present invention.
Fig . 2 is a blown-up 6ide view of a f iber and two beams which intersect and interf ere in a region of the f iber.
Fig. 3 is a plurality of waveforms in illustrations (a), (b), (c), (d), (e), showing a plurality of Fourier ~ -nontS of refractive index variation along a longitudinal axis of a waveguide and a resultant summation of these _ _-nPnts which exists after all the ~ s are written into a f iber, in accordance with the present invention .
Fig . 4 is a graph of the ref lectivity prof ile associated with the aperiodic grating of Fig. 3, illustration (e), in acuu~d~llce with the present invention .
Fig. 5 is a block diagram of an alternative Pmho~ nt of the present invention having ~^~nnin~
mirrors to adjust the angle of intersection where the grating is written in the fiber, in accordance with the present invention.
Fig . 6 is a blown-up view of the s~^Ann i n~
mirror and optical elements of the -mhotlir L of Fig. 5, in accordance with the present invention.
Fig. 7 is a schematic block diagram of an alternative _mho~l i L of the present invention using simultaneously writing all the Fûurier ~ -^nts to form an aperiodic grating, in accordance with the present invention.
Best Mode for Carrying out the Inv~ntion Referring now to Fig. 1, a tunable wavelength laser 10 provides a source beam 12 having a wavelength based on a signal on a line 14 from a controller 16 (tli C~ cs-^d hereinafter) . The light 12 _ _ _ _ .
W0 95/17705 ~ 2 1 7 9 0 4 2 PC~/US94/11059 is incident on an amplitude modulator 18, e.g., an ele~;~, v ~ic amplitude modulator or a spatial light modulator. The amplitude modulator 18 adjusts the amplitude of the input light signal 12 and provides a light signal 20 having an amplitude in response to an amplitude control 6ignal on a line 21 from the controller 16.
The amplitude adjusted light signal 20 is incident on a beamsplitter 22, which passes a predetPrmin~l percentage, e.g., 5096, of the input light 20 as a passed light 24 and reflects the L~ in;n~ portion as a reflected light 25. The passed light 24 is incident on a mirror 26 which provides a reflected beam 28. The beam 28 is incident on a region 30 of an optical fiber 32, e.g.
a g~rr - n i A -doped s i 1 ica-core f iber .
The reflected beam 25 is incident on a phase modulator 34, e.g., an ele~ Lic phase modulator, which provides an output beam 36 being phase shifted from the input beam 25 in Lc:~ullSe to a signal on a line 38 from the controller 16. The phase shifted beam 36 is incident on a mirror 40 which provides a reflected beam 42. The reflected beam 42 is also incident on the region 30 of the optical fiber 32 and intersects with and interferes with the beam 28.
Alternatively, a f ixed phase modulator may be used if desired, such as a phase plate. It should be understood that the phase modulator 34 may alternatively be placed in the path of the beams 24, 28, or 42.
The controller comprises known electronic, digital and/or analog circuitry, or it may likely be a digital computer, having the appropriate signal prQcPfi~in~ and memory capability to provide the functions fli ~c~ cl herein.
As fl i ~c~ d hereinbef ore, and in the aforementioned US Patents to Glenn et al, a Bragg W0 95/17705 , , ~ 2 1 7 9 0 4 2 PCT/US94/llOss --grating is ~-mht~lAt~-l into the core of an optical f iber by interf ering two coherent beams in the region of the f iber core where the grating is desired. The resulting interference pattern i8 a standing wave which exists along the fiber length (or longitudinal axis) which causes a cv~L~ in~
spatially periodic variation in refractive index along the longitudinal axis of the fiber (t~; Ccllcst~d hereinbefore). The spatial periodicity if the refractive index variation (and hence the grating) is a function of the wavelength of the two incident light beams 28, 42 . To aid in altering each ~ -nt of the refractive index, the amplitude and pha6e of each ~-o~nr~nent may be adjusted, however, this i5 not required, provided the source is wavelength variable. Also, instead of the amplitude modulator 18, the laser source 10 may have variable output power which is controlled by the controller 16 .
Referring now to Fig. 2, the beams 28,42 are either collimated or focussed to a line (using cylindrical lenses-not shown) and intersect at the region 30 of the core of the fiber 32. The region 30 is where the periodic interference pattern is formed which creates the periodic variation of refractive index .
Ref erring now to Fig . 3, we have f ound that by performing successive writings of interference patterns having different amplitude, phase and fre~uency of spatial variations (and thereby producing CUL r ~,-yv.,dingly different periodic refractive index variations), an aperiodic refractive index profile can be created, thereby allowing for filter shapes other than a single narrow band reflection filter.
In particular, if each of the refractive index ~rofi es along the longitudlnal or z-axis of the WO 95117705 ,3, '~ 2 1 7 9 0 4 2 PCT,US94/ll059 .
fiber indicated in Fig. 3, illusts. (a)-(d) are written successively into the core of the fiber, then the resultant p~-n~nt refractive index variation profile i8 as indicated in Fig. 3, illust.
(e), which is simply the sum of the individual Fourier ~ ~s (in Fig. 3, illusts . (a) - (d) ) .
Such an index variation profile provides a wide bandwidth filter profile 60, shown in Fig. 4.
Using the principle of superposition, each of the waveforms 50-56 of Fig. 3 , illusts. (a) - (d), respectively, reflects a narrow wavelength band of light related to the grating spacing, and are indicated by the individual profiles 62-66, respectively . Thus, when each of these wavef orms are i~ ecsed in the fiber core, the resultant filter profile is the broadband filter function 60.
It should be understood that other filter function profiles may be created by using different Fourier-^-lt refractive index variation waveforms.
Also, ,as is known, the reflectivity profile (e.g., Fig. 4) is the Fourier transform of the refractive index prof ile when the amplitude of the variation is small (i.e., for "weak" gratings), e.g., Fig. 3, illust. (e)). For more information regarding this Fourier transform relatinn~hir see H.
Kogelnik, "Filter Response of Nonuniform Almost Periodic Structures", Bell System Tech. Journal, Vol. 55, No. l (Jan. 1976). Thus, one can obtain the desired aperiodic refractive index variation profile by taking the inverse Fourier transform of the desired reflectivity characteristic and taking the Fourier transform of the resultant aperiodic index profile (with respect to length), to determine the individual refractive index Fourier ^ntS
needed to be written to create such a reflectivity function .
_ g _ WO95/17705 ~ 21 79042 PCrNS94lll059 Referring again to Fig. 1, to create the refractive index profile 58 shown in Fig. 3, illust.
(e), the controller 16 controls the tunable laser 10, the amplitude modulator 18, and the phase modulator 34 to create each of the Fourier c~ --,t6 of the wavcform6 50-56 of Fig. 3, illu6ts. (a) - (d), 6equentially in time.
More 6pecifically, the controller 15 sets the wavelength of the tunable laser 10, the level of attenuation of the amplitude modulator 18, and the amount of phase delay of the phase modulator 34 to provide the beam6 28,42 with the appropriate amplitude and phase so as to create the refractive index waveform 12 of Fig. 3, illust. (a). These condition6 are held con6tant for a prede~rm;nF-~l period of time long enough to write thi6 refractive index variation pattern p~rr-n~ntly into the core of the fiber 32, 6imilar to that tlicc~ d in the aforementioned U. S. Patents. The amount of time, a6 i6 known, varie6 from seconds to minutes rl~r~n~;nq on the photo-sensitivity of the fiber and intensity of the exposing radiation.
Next, the controller adjusts the wavelength of the tunable la6er 10, the amplitude modulator 18, and the pha6e modulator 34 60 a6 to provide the beam6 28,34 with the appropriate amplitude, phase, and wavelength to create the refractive index variation waveform 52 of Fig. 3, illust. (b), in the fiber 32. These 6ettings are retained for sufficient length6 of time and at a 6ufficient intensity so as to provide a permanent index variation as indicated by the waveform 52 of Fig. 3, illust. (b).
A similar process is performed to create the refractive index variation waveforms 54,56 of Fig.
3, illusts. (c), (d), in the ~ame region 30 of the W095/17705 ~ 2 1 79042 PCT/US94/llO~i9 fiber 32. The result is an overall refractive index profile such as that shown in Fig. 3, illust. (e).
Referring now to Fig. 5, as is known, the spatial periodicity of refractive index variation i5 also a function of the angle e of ; nricl~n~e of the two interfering beams on the fiber 32. Using this effect, the beams 24,36 are incident on c~nn;n~
mirrors 100 ,102 which pivot about axes 104 ,106, respectively ( instead of being incident on the stationary mirrors 26,40, l;ccllcs~l hereinbefore with Fig. 1). Also, for this ~mhorl;- L, the laser source need not be a variable wavelength source and the amplitude and phase modulation is not required, however, may still be used to vary additional variables, if desired.
Referring now to Figs. 5 and 6, the mirror 100 provides a reflected collimated beam 108 having an angle ~ relative to the angle of the mirror 100.
The beam 108 is incident on a lens 110 which focusses and directs light entering the lens from various different angles to provide output light 112 having substantially parallel central rays. The light 112 is incident on a collimating lens 114, which collimates and directs the light 112 as an output light 116 to a region 30 of the fiber 32 which is located at the focal plane of the lens 114.
The distance between where the light 108 leaves the mirror 100 and the lens 110 is equal to the f ocal length f 1 of the lens 110 . The distance between the lens 114 and the fiber 32 is equal to the focal length f2 of the lens 114. Also, the distance between the lens 110 and the lens 114 is equal to the sum of the two focal lengths fl,f2 of the lenses 110,114, respectively. To have a change in the angle ~ cause the same change in the angle e onto the fiber, the focal lengths fl, f2 should be wo 95/17705 ' ~ , 2 1 7 9 0 4 2 PCT/US94/11059 the same; however, this i5 not required for the invention to operate.
Referring to Fig. 5, a similar arrangement exists between the adjustable mirror 102 and the fiber 32. In particular, a light 120 is reflected from the mirror 102 and is incident on a focussing and redirecting lens 122 which provides a focussed output light 124 (similar to the focussed beam 112 of Fig. 6). The focussed light 124 is incident on a lo collimating lens 126 which provides a collimated light beam 128 onto the region 30 of the fiber 32.
Ref erring now to Fig . 7, a broadband laser source 200 provides a beam 201, having a broad wavelength band which includes wavelengths of the desired Fourier spectrum. The beam 201 is incident on a diffraction grating 202, which, as is known, diffracts light so as to spatially separate various wavelengths existing in the light beam 201. In particular, the diffraction grating 202 provides a diffracted light 204, having a wavelength of A1.
The diffraction grating also provides a beam 206, having a wavelength of A2, and a beam 208, having a wavelength of A3. More wavelengths may be used if des ired .
The beams 204-208 are incident on a focussing lens 210 which converts the collimated beams 204-208 to focussed beams 212-216, respectively, having substantially parallel central ray6 (a6 i6 indicated in Fig. 5).
The beams 212-216 are incident on an amplitude modulator 220, e.g., a spatially varying transparency or a spatial light modulator. The 6patial light modulator 220 alter6 the inten6ity of the beams 212-216 in a selective manner based on the location that a given light is incident on the modulator 220. The spatial light modulator provides amplitude adjusted light beams 222-226 in ~,yullse .
WO95/17705 21 79042 PCT/US91/110~i9 .
to a control signals on lines 228 from a controller 230. The controller 230 is similar to the controller 56 discussed hereinbefore and sets the value of the amplitude of each of the beams 222-226 used to make the grating. Alternatively, the spatial light modulator 220 may be a passive transparency sheet having varying regions of opagueness.
The beams 222-226 are incident on a lens 240 which collimates the beams 234-238 as the beams 242-248, respectively, and directs the beams onto a common region of a diffraction grating 250. The diffraction grating 250, combines the beams 242-248 to a single output beam 252.
The optical ~ 7ts of the diffraction grating 202, the lenses 210,240, the amplitude and phase modulators 220,232, and the grating 250, essentially make up a spectral filter which adjusts the amplitude and phase of the individual Fourier ^~7ts of the desired aperiodic refractive index variation. Also, the lenses 210,240 are in essentially the same conf iguration as that of Fig.
6.
The beam 252 is incident on a beamsplitter 260 similar to the beamsplitter 22 (Fig. 1), r7~ie~l7~^s^d hereinbefore. The beamsplitter 260 passes a beam 262 and reflects the L~ ininj portion of the input beam 252 as the beam 264. The beam 262 is incident on a mirror 266, which provides a reflected beam 268 onto the region 30 of the fiber 32. The reflected beam 264 is incident on a mirror 270, which provides a reflected beam 272 onto the region 30 of the fiber 32. The beams 268,272 intersect in the region 30 of the fiber 32 similar to that shown in Fig. 2 for the beams 28, 42 .
3 5 The _mho~7; - t shown on Fig . 7 provides simultaneous writing of all the Fourier spectral Ls that make-up the desired refractive index Wo 95117705 t , ~ 2 1 7 9 0 4 2 PCr/USs4/11Oss ~`
waveform profile. This embodiment has the advantage of reduced time to write the desired aperiodic grating as well as being less susceptible to stability vibration and air current problems associated with performing repeated writing in a segucntial fa6hion. In particular, the distances between mirrors and the orientations of the lenses and mirrors relative to each other must remain precisely f ixed in order f or the multiple sequential spectral Fourier ~ Ls to provide the desired C hi ner~l refractive index waveform.
It should be understood that when the wavelengths are closely spaced, there will actually be some overlap of the focussed beams 212-216.
Thus, the modulator 220 should be placed close to the focal points of the beams 212-216, as indicated in Fig. 7.
Also, i~ phase modulation is desired, the amplitude adjusted beams 222-226 may be incident on a phase modulator (not shown), e.g., an electro-optic modulator located between the amplitude modulator 220 and the lens 240. In that case, the mirrors 210,240 may be cylindrical, the beams 222-226 may be focussed to a line, the phase modulator would modulate a portion of each focussed line, an optical element (not shown) would split each beam ~nd another optical element would direct the beams onto the fiber. Also in that case, the controller 230 would set the amount of phase shift in each beam and the optical elements 260,266,270 would not be used .
Instead of using the single broadband source 200 and the diffraction grating 202, a plurality of single wavelength sources (not shown) may be used to provide the beams 204-208, each being incident on the lens 210.
It should be understood that although various beam6 have been described as collimated, the invention will work equally well if the beams are focussed to a line. In that case, cylindrical lenses 5 (not shown) should be used, however, the drawings in - Figs. 2, 6, and 7 of the beams would not change.
Also, it should be understood that the Fourier I s of the desired aperiodic refractive index variation have frequencies which are very close to each other, i . e., not harmonics of each other.
Further, the invention will work equally well with waveguides other than an optical f iber, such as a planar waveguide~ provided the waveguide is made of a material having an index of refraction which can be p~mr~-nently changed by exposing the waveguide to light of a pre~lPr~rm;npd intensity at a predetPrm; nP~l wavelength.
Still further, for the ~mho~ of Fig. 7, instead of using the beam splitter 260 to split the beam 252 into two writing beams 268,272, a pair of the spectral filters and diffraction gratings 202, 250 may be used each producing a beam which is directed onto the fiber 32 to form the grating.
Also, it should be understood that the Fourier I s of the desired aperiodic refractive index variation have frequencies which are very close to each other, i . e., not harmonics of each other.
Further, the invention will work equally well with waveguides other than an optical f iber, such as a planar waveguide~ provided the waveguide is made of a material having an index of refraction which can be p~mr~-nently changed by exposing the waveguide to light of a pre~lPr~rm;npd intensity at a predetPrm; nP~l wavelength.
Still further, for the ~mho~ of Fig. 7, instead of using the beam splitter 260 to split the beam 252 into two writing beams 268,272, a pair of the spectral filters and diffraction gratings 202, 250 may be used each producing a beam which is directed onto the fiber 32 to form the grating.
Claims (21)
We Claim:
1. A method of impressing an aperiodic grating, comprising the steps of:
obtaining an optical waveguide made of a material which has a refractive index that can be permanently changed by exposure to light of a predetermined intensity at a predetermined wavelength; and simultaneously exposing the waveguide to two writing light beams which intersect and interfere in a predetermined region of the waveguide so as to create an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a permanent refractive index variation in the waveguide, each of said two writing beams having a predetermined number of wavelengths, each wavelength being sufficiently different from each other so as to cause said refractive index variation to be an aperiodic variation.
obtaining an optical waveguide made of a material which has a refractive index that can be permanently changed by exposure to light of a predetermined intensity at a predetermined wavelength; and simultaneously exposing the waveguide to two writing light beams which intersect and interfere in a predetermined region of the waveguide so as to create an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a permanent refractive index variation in the waveguide, each of said two writing beams having a predetermined number of wavelengths, each wavelength being sufficiently different from each other so as to cause said refractive index variation to be an aperiodic variation.
2. The method of claim 1 wherein each of said wavelengths in said step of exposing comprises a Fourier component of said aperiodic refractive index variation.
3. The method of claim 1 further comprising a step of modulating the amplitude of a predetermined number of said wavelengths.
4. The method of claim 1 wherein said aperiodic refractive index variation exhibits a broadband reflectivity profile.
5. An apparatus for impressing an aperiodic grating into a region of an optical waveguide, comprising:
light source means, for providing a predetermined number of source beams, each beam having a predetermined wavelength;
wavelength combining means, for combining said source beams into a single beam;
beamsplitting means for splitting said single beam into at least two writing beams; and beam directing means for directing said writing beams so as to intersect on a region of the waveguide, thereby creating an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a permanent refractive index variation in the waveguide, the wavelengths associated with said source beams being sufficiently different from each other so as to cause said refractive index variation to be an aperiodic variation.
light source means, for providing a predetermined number of source beams, each beam having a predetermined wavelength;
wavelength combining means, for combining said source beams into a single beam;
beamsplitting means for splitting said single beam into at least two writing beams; and beam directing means for directing said writing beams so as to intersect on a region of the waveguide, thereby creating an interference pattern along a longitudinal axis of the waveguide for a time long enough to form a permanent refractive index variation in the waveguide, the wavelengths associated with said source beams being sufficiently different from each other so as to cause said refractive index variation to be an aperiodic variation.
6. The apparatus of claim 5, wherein said light source means comprises:
broadband light source means for providing a broadband source light having a plurality of wavelengths; and wavelength separation means, for separating said broadband light into said predetermined number of source beams.
broadband light source means for providing a broadband source light having a plurality of wavelengths; and wavelength separation means, for separating said broadband light into said predetermined number of source beams.
7. The apparatus of claim 5, further comprising amplitude modulation means, for independently modulating the amplitude of each of said source beams.
8. The apparatus of claim 7, further comprising signal processing means for providing an amplitude modulation signal to said amplitude modulation means and for determining the desired amplitude of each of said source beams.
9. The apparatus of claim 5, wherein said aperiodic variation exhibits a broadband reflectivity profile.
10. An apparatus for impressing an aperiodic grating into a region of an optical waveguide, comprising:
variable wavelength light source means, for providing a variable wavelength source light;
beamsplitting means for splitting said source light into at least two writing beams;
beam directing means for directing said writing beams so as to intersect on a region of the optical waveguide, thereby creating an interference pattern along a longitudinal axis of the waveguide, for a time long enough to form a permanent refractive index variation in the waveguide; and signal processing means for providing a wavelength control signal to said variable wavelength light source means, for setting different successive wavelengths, each wavelength forming a different refractive index variation, so as to create a total refractive index variation which is an aperiodic variation.
variable wavelength light source means, for providing a variable wavelength source light;
beamsplitting means for splitting said source light into at least two writing beams;
beam directing means for directing said writing beams so as to intersect on a region of the optical waveguide, thereby creating an interference pattern along a longitudinal axis of the waveguide, for a time long enough to form a permanent refractive index variation in the waveguide; and signal processing means for providing a wavelength control signal to said variable wavelength light source means, for setting different successive wavelengths, each wavelength forming a different refractive index variation, so as to create a total refractive index variation which is an aperiodic variation.
11. The apparatus of claim 10, further comprising amplitude modulation means, for independently modulating the amplitude of said source light.
12. The apparatus of claim 11, further comprising signal processing means for providing an amplitude modulation signal to said amplitude modulation means and for determining the desired amplitude of said source light.
13. The apparatus of claim 10, further comprising phase modulation means, for independently modulating the phase of at least one of said writing beams.
14. The apparatus of claim 13, further comprising signal processing means for providing a phase modulation signal to said phase modulation means and for determining the phase relationship between said writing beams.
15. The apparatus of claim 10, wherein said aperiodic variation exhibits a broadband reflectivity profile.
16. An apparatus for impressing an aperiodic grating into a region of an optical waveguide, comprising:
light source means, for providing a source light having a predetermined wavelength;
beamsplitting means for splitting said source light into at least two writing beams;
variable beam directing means for directing said writing beams so as to intersect on a region of the optical waveguide at a predetermined angle of incidence thereon, thereby creating an interference pattern along a longitudinal axis of the waveguide, for a time long enough to form a permanent refractive index variation in the waveguide; and signal processing means for providing a wavelength control signal to said variable beam directing means, for setting different successive angles of incidence, each angle causing a different refractive index variation to form, so as to create a total refractive index variation which is an aperiodic variation.
light source means, for providing a source light having a predetermined wavelength;
beamsplitting means for splitting said source light into at least two writing beams;
variable beam directing means for directing said writing beams so as to intersect on a region of the optical waveguide at a predetermined angle of incidence thereon, thereby creating an interference pattern along a longitudinal axis of the waveguide, for a time long enough to form a permanent refractive index variation in the waveguide; and signal processing means for providing a wavelength control signal to said variable beam directing means, for setting different successive angles of incidence, each angle causing a different refractive index variation to form, so as to create a total refractive index variation which is an aperiodic variation.
17. The apparatus of claim 16, further comprising amplitude modulation means, for independently modulating the amplitude of said source light.
18. The apparatus of claim 17, further comprising signal processing means for providing an amplitude modulation signal to said amplitude modulation means and for determining the desired amplitude of said source light.
19. The apparatus of claim 16, further comprising phase modulation means, for independently modulating the phase of at least one of said writing beams.
20. The apparatus of claim 19, further comprising signal processing means for providing a phase modulation signal to said phase modulation means and for determining the phase relationship between said writing beams.
21. The apparatus of claim 16, wherein said aperiodic variation exhibits a broadband reflectivity profile.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/169,796 US5388173A (en) | 1993-12-20 | 1993-12-20 | Method and apparatus for forming aperiodic gratings in optical fibers |
| US08/169,796 | 1993-12-20 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2179042A1 CA2179042A1 (en) | 1995-06-29 |
| CA2179042C true CA2179042C (en) | 1998-01-06 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002179042A Expired - Lifetime CA2179042C (en) | 1993-12-20 | 1994-09-30 | Method and apparatus for forming aperiodic gratings in optical fibers |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5388173A (en) |
| EP (1) | EP0736201B1 (en) |
| JP (1) | JP3059761B2 (en) |
| CA (1) | CA2179042C (en) |
| DE (1) | DE69411590T2 (en) |
| ES (1) | ES2119372T3 (en) |
| WO (1) | WO1995017705A2 (en) |
Families Citing this family (99)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5363239A (en) * | 1992-12-23 | 1994-11-08 | At&T Bell Laboratories | Method for forming spatially-varying distributed Bragg reflectors in optical media |
| US5559907A (en) * | 1994-02-17 | 1996-09-24 | Lucent Technologies Inc. | Method of controlling polarization properties of a photo-induced device in an optical waveguide and method of investigating structure of an optical waveguide |
| GB2286898B (en) * | 1994-02-26 | 1997-08-20 | Northern Telecom Ltd | Chirped distributed Bragg grating optical fibre filters on flexible plates |
| US6314220B1 (en) | 1995-03-13 | 2001-11-06 | Templex Technology, Inc. | Segmented complex fiber gratings |
| US5552882A (en) * | 1995-03-28 | 1996-09-03 | Lyons; Donald R. | Methods of and apparatus for calibrating precisely spaced multiple transverse holographic gratings in optical fibers |
| US5633966A (en) * | 1995-04-07 | 1997-05-27 | Sumitomo Electric Industries, Ltd. | Method of forming refractive index distribution in light transmission path, and optical filter and method of using the same |
| US5748814A (en) * | 1995-11-16 | 1998-05-05 | Institut National D'optique | Method for spatially controlling the period and amplitude of Bragg filters |
| US5903689A (en) * | 1995-11-16 | 1999-05-11 | Institut National D'optique | Method for spatially controlling the period and amplitude of BRAGG filters |
| CA2239730A1 (en) * | 1995-12-12 | 1997-06-19 | British Telecommunications Public Limited Company | Formation of a refractive index grating |
| US5629998A (en) * | 1996-01-29 | 1997-05-13 | Corning Incorporated | Method and apparatus for writing photosensitive grating using Lloyd's mirror |
| US5668901A (en) * | 1996-02-14 | 1997-09-16 | Corning Incorporated | Low reflectivity fiber bragg grating with rectangular reflection function |
| TW358167B (en) * | 1996-03-25 | 1999-05-11 | Corning Inc | Method of forming a grating in an optical waveguide |
| US5863449A (en) * | 1996-03-29 | 1999-01-26 | The Whitaker Corporation | Method for forming optical interferometer |
| US6195483B1 (en) * | 1996-09-30 | 2001-02-27 | The United States Of America As Represented By The Secretary Of The Navy | Fiber Bragg gratings in chalcogenide or chalcohalide based infrared optical fibers |
| US5822479A (en) * | 1997-01-24 | 1998-10-13 | Northern Telecom Limited | Writing diffraction gratings with interference fringe patterns |
| AUPO512697A0 (en) * | 1997-02-14 | 1997-04-11 | Indx Pty Ltd | Improvements in a system for writing gratings |
| US6093927A (en) * | 1997-06-09 | 2000-07-25 | Trw Inc. | Automated precision wavelength control for fiber optic Bragg grating writing |
| FR2768819B1 (en) * | 1997-09-25 | 1999-12-17 | Alsthom Cge Alcatel | GREAT LENGTH BRAGG NETWORKS |
| US6404956B1 (en) * | 1997-10-02 | 2002-06-11 | 3M Intellectual Properties Company | Long-length continuous phase Bragg reflectors in optical media |
| US6728444B2 (en) * | 1997-10-02 | 2004-04-27 | 3M Innovative Properties Company | Fabrication of chirped fiber bragg gratings of any desired bandwidth using frequency modulation |
| US6768825B2 (en) | 1998-05-06 | 2004-07-27 | Weatherford/Lamb, Inc. | Optical sensor device having creep-resistant optical fiber attachments |
| AUPP381698A0 (en) * | 1998-05-29 | 1998-06-25 | University Of Sydney, The | Electro-, magneto- or acousto- optically controlled UV writing set up for bragg grating fabrication |
| AU739506B2 (en) * | 1998-05-29 | 2001-10-11 | University Of Sydney, The | Electro- magneto- or acousto- optically controlled UV writing set up for bragg grating fabrication |
| AUPP425898A0 (en) * | 1998-06-22 | 1998-07-16 | University Of Sydney, The | An improved grating writing system |
| KR100322121B1 (en) * | 1998-10-13 | 2002-03-08 | 윤종용 | Apparatus for fabricating long-period grating filter |
| US7065298B1 (en) | 1998-11-17 | 2006-06-20 | Intel Corporation | Code-based optical networks, methods, and apparatus |
| US6982996B1 (en) | 1999-12-06 | 2006-01-03 | Weatherford/Lamb, Inc. | Large diameter optical waveguide, grating, and laser |
| US6621957B1 (en) | 2000-03-16 | 2003-09-16 | Cidra Corporation | Temperature compensated optical device |
| US6249624B1 (en) | 1998-12-04 | 2001-06-19 | Cidra Corporation | Method and apparatus for forming a Bragg grating with high intensity light |
| US6298184B1 (en) | 1998-12-04 | 2001-10-02 | Cidra Corporation | Method and apparatus for forming a tube-encased bragg grating |
| US6763043B2 (en) * | 1998-12-04 | 2004-07-13 | Cidra Corporation | Tunable grating-based dispersion compensator |
| US6792009B2 (en) | 1998-12-04 | 2004-09-14 | Cidra Corporation | Tunable grating-based channel filter parking device |
| US6834142B2 (en) * | 1998-12-04 | 2004-12-21 | Cidra Corporation | Optical grating-based filter |
| WO2000041014A1 (en) * | 1998-12-30 | 2000-07-13 | Alpha And Omega Imaging, Llc | Distributed bragg reflectors with preferred properties in optical fibers |
| US6084998A (en) * | 1998-12-30 | 2000-07-04 | Alpha And Omega Imaging, Llc | System and method for fabricating distributed Bragg reflectors with preferred properties |
| GB9905196D0 (en) * | 1999-03-05 | 1999-04-28 | Fujitsu Telecommunications Eur | Aperiodic gratings |
| GB2385943B (en) * | 1999-03-05 | 2003-11-05 | Nanovis Llc | Mach-Zehnder interferometer with aperiodic grating |
| US6993222B2 (en) * | 1999-03-05 | 2006-01-31 | Rj Mears, Llc | Optical filter device with aperiodically arranged grating elements |
| TR200100429T1 (en) * | 1999-03-10 | 2002-11-21 | Ishikawajima-Harima Heavy Industries Co., Ltd. | Hot rolled steel plate production device and method |
| US6140660A (en) | 1999-03-23 | 2000-10-31 | Massachusetts Institute Of Technology | Optical synthetic aperture array |
| CA2272008A1 (en) * | 1999-05-11 | 2000-11-11 | Francois Trepanier | Device and method for recording an interference pattern in a photosensitive medium |
| US6313771B1 (en) | 1999-11-17 | 2001-11-06 | Templex Technology, Inc. | Codes, methods, and apparatus for optical encoding and decoding |
| JP2001215351A (en) * | 2000-02-04 | 2001-08-10 | Toyota Gakuen | Dielectric constant multiplex period structure element and its design method and manufacturing method |
| US6614959B1 (en) * | 2000-07-27 | 2003-09-02 | Ciena Corporation | Methods of writing apodized fiber gratings and associated apparatuses |
| US6594410B2 (en) | 2000-08-26 | 2003-07-15 | Cidra Corporation | Wide range tunable optical filter |
| US7386204B1 (en) | 2000-08-26 | 2008-06-10 | Cidra Corporation | Optical filter having a shaped filter function |
| JP2002090556A (en) * | 2000-09-20 | 2002-03-27 | Sumitomo Electric Ind Ltd | Optical waveguide type diffraction grating element, method for manufacturing optical waveguide type diffraction grating element, multiplexing and demultiplexing module and optical transmission system |
| US6453108B1 (en) | 2000-09-30 | 2002-09-17 | Cidra Corporation | Athermal bragg grating package with course and fine mechanical tuning |
| US6594288B1 (en) | 2000-11-06 | 2003-07-15 | Cidra Corporation | Tunable raman laser and amplifier |
| US6594081B2 (en) | 2000-12-29 | 2003-07-15 | Cidra Corporation | Actuator mechanism for tuning an optical device |
| US6778733B2 (en) | 2001-01-05 | 2004-08-17 | Teraxion Inc. | Lithographic fabrication of phase mask for fiber Bragg gratings |
| WO2002075391A2 (en) * | 2001-03-16 | 2002-09-26 | Cidra Corporation | Optical grating-based filter |
| US6739154B2 (en) * | 2001-04-24 | 2004-05-25 | Corning Incorporated | Method for manufacturing optical gratings |
| US6904201B1 (en) * | 2001-05-09 | 2005-06-07 | Intel Corporation | Phase-controlled fiber Bragg gratings and manufacturing methods |
| WO2002101889A2 (en) * | 2001-06-12 | 2002-12-19 | Nufern | Compression-tunable fiber laser and compression-resistant optical fiber for lasers |
| US6904200B2 (en) | 2001-09-14 | 2005-06-07 | Fibera, Inc. | Multidimensional optical gratings |
| US6718092B2 (en) | 2001-09-14 | 2004-04-06 | Fibera, Inc. | Frequency detection, tuning and stabilization system |
| US6748138B2 (en) * | 2001-09-14 | 2004-06-08 | Fibera, Inc. | Optical grating fabrication |
| US6807339B1 (en) | 2001-09-14 | 2004-10-19 | Fibera, Inc. | Wavelength division multiplexing and de-multiplexing system |
| TW582062B (en) * | 2001-09-14 | 2004-04-01 | Sony Corp | Laser irradiation apparatus and method of treating semiconductor thin film |
| US20030121289A1 (en) * | 2002-01-02 | 2003-07-03 | Benda John A. | Long period fiber Bragg gratings written with alternate side IR laser illumination |
| US7062126B2 (en) * | 2002-06-07 | 2006-06-13 | Kersey Alan D | Tunable optical filter having large diameter optical waveguide with bragg grating and being configured for reducing the bulk modulus of compressibility thereof |
| US7068897B2 (en) * | 2002-06-10 | 2006-06-27 | Cidra Corporation | Method for restoring or increasing photosensitivity in hydrogen or deuterium loaded large diameter optical waveguide |
| TW538258B (en) * | 2002-07-16 | 2003-06-21 | Ind Tech Res Inst | Grating interferometer device with tunable resolution |
| US7900836B2 (en) * | 2002-08-20 | 2011-03-08 | Illumina, Inc. | Optical reader system for substrates having an optically readable code |
| US7164533B2 (en) * | 2003-01-22 | 2007-01-16 | Cyvera Corporation | Hybrid random bead/chip based microarray |
| US7126755B2 (en) * | 2002-09-12 | 2006-10-24 | Moon John A | Method and apparatus for labeling using diffraction grating-based encoded optical identification elements |
| US7441703B2 (en) * | 2002-08-20 | 2008-10-28 | Illumina, Inc. | Optical reader for diffraction grating-based encoded optical identification elements |
| US7923260B2 (en) | 2002-08-20 | 2011-04-12 | Illumina, Inc. | Method of reading encoded particles |
| US7901630B2 (en) * | 2002-08-20 | 2011-03-08 | Illumina, Inc. | Diffraction grating-based encoded microparticle assay stick |
| US7872804B2 (en) * | 2002-08-20 | 2011-01-18 | Illumina, Inc. | Encoded particle having a grating with variations in the refractive index |
| EP1535241A1 (en) | 2002-08-20 | 2005-06-01 | Cyvera Corporation | Diffraction grating-based optical identification element |
| US7508608B2 (en) * | 2004-11-17 | 2009-03-24 | Illumina, Inc. | Lithographically fabricated holographic optical identification element |
| US20050227252A1 (en) * | 2002-08-20 | 2005-10-13 | Moon John A | Diffraction grating-based encoded articles for multiplexed experiments |
| US7092160B2 (en) * | 2002-09-12 | 2006-08-15 | Illumina, Inc. | Method of manufacturing of diffraction grating-based optical identification element |
| WO2004025563A1 (en) * | 2002-09-12 | 2004-03-25 | Cyvera Corporation | Diffraction grating-based encoded micro-particles for multiplexed experiments |
| WO2004024328A1 (en) | 2002-09-12 | 2004-03-25 | Cyvera Corporation | Method and apparatus for aligning elongated microbeads in order to interrogate the same |
| US20100255603A9 (en) | 2002-09-12 | 2010-10-07 | Putnam Martin A | Method and apparatus for aligning microbeads in order to interrogate the same |
| US20040191637A1 (en) * | 2003-03-25 | 2004-09-30 | Gregory Steckman | Method for packaging thermally compensated filters |
| US6853772B2 (en) * | 2003-05-13 | 2005-02-08 | 3M Innovative Properties Company | Fiber grating writing interferometer with continuous wavelength tuning and chirp capability |
| US6915044B2 (en) * | 2003-07-15 | 2005-07-05 | 3M Innovative Properties Company | Tunable talbot interferometers for fiber bragg grating writing |
| JP2005055508A (en) * | 2003-08-05 | 2005-03-03 | Fujikura Ltd | Method and device for manufacturing grating type optical components, and optical components produced using the method and device |
| US20060057729A1 (en) * | 2003-09-12 | 2006-03-16 | Illumina, Inc. | Diffraction grating-based encoded element having a substance disposed thereon |
| US7433123B2 (en) * | 2004-02-19 | 2008-10-07 | Illumina, Inc. | Optical identification element having non-waveguide photosensitive substrate with diffraction grating therein |
| WO2006020363A2 (en) * | 2004-07-21 | 2006-02-23 | Illumina, Inc. | Method and apparatus for drug product tracking using encoded optical identification elements |
| US7604173B2 (en) * | 2004-11-16 | 2009-10-20 | Illumina, Inc. | Holographically encoded elements for microarray and other tagging labeling applications, and method and apparatus for making and reading the same |
| WO2006055735A2 (en) | 2004-11-16 | 2006-05-26 | Illumina, Inc | Scanner having spatial light modulator |
| WO2006055736A1 (en) | 2004-11-16 | 2006-05-26 | Illumina, Inc. | And methods and apparatus for reading coded microbeads |
| US7623624B2 (en) * | 2005-11-22 | 2009-11-24 | Illumina, Inc. | Method and apparatus for labeling using optical identification elements characterized by X-ray diffraction |
| US7830575B2 (en) * | 2006-04-10 | 2010-11-09 | Illumina, Inc. | Optical scanner with improved scan time |
| CA2548029A1 (en) * | 2006-05-23 | 2007-11-23 | Itf Laboratories Inc. | Method and system for writing fiber bragg grating having apodized spectrum on optical fibers |
| WO2009005746A1 (en) * | 2007-06-29 | 2009-01-08 | Allview Research Llc | Writing a diffractive structure |
| US8049885B1 (en) * | 2008-05-15 | 2011-11-01 | Ondax, Inc. | Method and apparatus for large spectral coverage measurement of volume holographic gratings |
| US7986407B2 (en) | 2008-08-04 | 2011-07-26 | Ondax, Inc. | Method and apparatus using volume holographic wavelength blockers |
| US8369017B2 (en) * | 2008-10-27 | 2013-02-05 | Ondax, Inc. | Optical pulse shaping method and apparatus |
| CA2839071C (en) * | 2009-03-04 | 2017-10-17 | Imricor Medical Systems, Inc. | Mri compatible medical device temperature monitoring system and method |
| US9599565B1 (en) | 2013-10-02 | 2017-03-21 | Ondax, Inc. | Identification and analysis of materials and molecular structures |
| US9587983B1 (en) | 2015-09-21 | 2017-03-07 | Ondax, Inc. | Thermally compensated optical probe |
| US10768361B1 (en) * | 2018-08-03 | 2020-09-08 | Facebook Technologies, Llc | System for monitoring grating formation |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2442652A1 (en) * | 1974-09-06 | 1976-03-18 | Siemens Ag | ARRANGEMENT FOR TUNABLE OPTICAL WAVE CONDUCTOR COMPONENTS |
| CA1149209A (en) * | 1980-07-09 | 1983-07-05 | Paolo G. Cielo | Evanescent-wave fiber reflector |
| EP0191063B1 (en) * | 1984-08-13 | 1992-05-13 | United Technologies Corporation | Method for impressing grating within fiber optics |
| USH474H (en) * | 1985-10-25 | 1988-06-07 | United States Of America | Optical transversal fiber with reflective taps |
| US4749248A (en) * | 1985-11-06 | 1988-06-07 | American Telephone And Telegraph Company At&T Bell Laboratories | Device for tapping radiation from, or injecting radiation into, single made optical fiber, and communication system comprising same |
| US5006716A (en) * | 1989-02-22 | 1991-04-09 | Research Corporation Technologies, Inc. | Method and system for directional, enhanced fluorescence from molecular layers |
| US5042897A (en) * | 1989-12-26 | 1991-08-27 | United Technologies Corporation | Optical waveguide embedded light redirecting Bragg grating arrangement |
| US5007705A (en) * | 1989-12-26 | 1991-04-16 | United Technologies Corporation | Variable optical fiber Bragg filter arrangement |
| US5237576A (en) * | 1992-05-05 | 1993-08-17 | At&T Bell Laboratories | Article comprising an optical fiber laser |
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1993
- 1993-12-20 US US08/169,796 patent/US5388173A/en not_active Expired - Lifetime
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1994
- 1994-09-30 EP EP95904045A patent/EP0736201B1/en not_active Expired - Lifetime
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- 1994-09-30 CA CA002179042A patent/CA2179042C/en not_active Expired - Lifetime
- 1994-09-30 WO PCT/US1994/011059 patent/WO1995017705A2/en active IP Right Grant
- 1994-09-30 DE DE69411590T patent/DE69411590T2/en not_active Expired - Lifetime
- 1994-09-30 JP JP07517406A patent/JP3059761B2/en not_active Expired - Lifetime
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| DE69411590T2 (en) | 1998-11-12 |
| WO1995017705A3 (en) | 1995-09-08 |
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| EP0736201A1 (en) | 1996-10-09 |
| JP3059761B2 (en) | 2000-07-04 |
| EP0736201B1 (en) | 1998-07-08 |
| ES2119372T3 (en) | 1998-10-01 |
| WO1995017705A2 (en) | 1995-06-29 |
| JPH09506981A (en) | 1997-07-08 |
| CA2179042A1 (en) | 1995-06-29 |
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