CA2148317C - Optical circulator - Google Patents
Optical circulatorInfo
- Publication number
- CA2148317C CA2148317C CA002148317A CA2148317A CA2148317C CA 2148317 C CA2148317 C CA 2148317C CA 002148317 A CA002148317 A CA 002148317A CA 2148317 A CA2148317 A CA 2148317A CA 2148317 C CA2148317 C CA 2148317C
- Authority
- CA
- Canada
- Prior art keywords
- pair
- light
- dividing
- optical circulator
- birefringent crystal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on magneto-optical elements, e.g. exhibiting Faraday effect
- G02F1/093—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on magneto-optical elements, e.g. exhibiting Faraday effect used as non-reciprocal devices, e.g. optical isolators, circulators
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3083—Birefringent or phase retarding elements
Abstract
The optical circulator according to the present invention comprises two birefringent crystal end-plates, non-reciprocal Faraday rotators inserted between birefringent crystal plates, and a pair of matched birefringent crystal plates disposed between the rotators. The first birefringent crystal end-plate functions as a dividing and combining means for dividing a beam into two beams of orthogonal electric filed vectors from different paths into one on the same path. The pair of matched birefringent crystal plates serve as beam path determining means shifting a beam to a different direction depending on the direction of the electric filed vector and the propagation. The pair of crystal plates are substantially identical but oppositely oriented, such that the pair of means have opposite beam shifted directions.
Description
21~8317 Optical Circulator Field of the Invention The present invention relates to an optical circu~ator for use in optical S CC,~ ical;on~, Background of the Invention A practical way to double the bit c~lyil~g capacity of an ~ Aisting unidirection~l 10 fiber optic comm~mic~tion link is by the use of optical circulators. An optical circulator is a passive, non-reciprocal device which permits full duplex con....~- çation on a single fiber optic link. Thus, a typical fiber optic cc ~tiQn link opelal ng on two fibers can be quickly and economically converted to a bi-directior~1 single fiber co....~ cation link by in.~t~llin~ an optical circulator at each end ofthe link.
One ofthe major advantages of optical circulators over more tr~ition~l 3 dB
couplers is that the loss penalty is much lower. Using a 3 dB coupler at each end of a fiber link, there is an insertion loss of at least 6 dB. For conl-e.i~;on.~ which operate near their detection limits, this additional 6 dB loss could make bi-directi~n~l co.. ~ icalion 20 i~ vlival)lv.
In a real optical circulator insertion loss and cross-talk are two i ll~)oll~ll col-~idf ~ ~lions. Insertion loss is the diLr~vl~vllce in power b~lnven light l~ ed into the optical circulator and the power that exits the device. Insertion loss is largely due to 25 absorption of light and to illl~vlrvvl po1~ri7~tion separation.
Prior art optical circulators are de3vlil,ed in U.S. Pat. No. 4,650,289, issued to K~l~.dhal~; U.S. Pat. No. 4,464,022, issued to Emkey; and in U.S. Pat. No. 4,859,014, issued to Schmitt et al. However, insertion loss and/or cross-talk in optical circulators 21~8317 made as desclilJed in these l~ft;rences are ~n~ccept~bly high for many commllniç~tions applic~tion~ Ther~ror~, a need exists for an optical circulator having lower insertion loss and cross-talk than that found in present optical circulators.
One factor that cGnl,il,ules to lower insertion loss and cross-talk in the optical circulator of the present invention than in prior optical circulators is the use of l"~er, ;"~e-.
crystals instead oftM~litiQn~l po1G-;~I;on spitting cubes results in much more co"lp'ete pol~ri7~tion of incident random~y polarized light.
A more recent prior art optical circulator that uses b--~r. ;nge .l clystals in contact with other elpmpntc such as polarization rolalols, is U.S. Pat. No. 5,204,771 issued April 20, 1993 in the name of Koga. Although this invention appears to pe ru~ its intPntled fimction adequately, precise l""lch;"~ of optical colllpone~ such as waveplates is re~luir~d; this precision ".~ .hil~p is found to be difficult and thus costly. This requht;lllellt of ",~ g reciprocal ro~lcl~ is obviated in the present invention which ovel-iollles this problem by ~ a centrally dis~,osed split pair of bil~r~ l crystal plates.
It is Ihelerore an object ofthe invention, to ovel-iollle many ofthe limit~q~tions of known prior art devices.
Summary of the Invention In accordal~ce with the invention, there is provided, an optical circulator colll~ g first means for sepalaling a beam of light into two polarized beams having ortho~n~l po1~ri7~tion states, and for conlbilfing two sepalaled orthogonally polarized beams; second means for sepalaL~g a beam of light into two pol~i~;ed beams having orthogonal pol~ri7~tion states, and for collll)il~ng two sepal~led orthogon~lly polarized beams; a pair of ~ul~t~llially identic~l oppositely onented bil~rl ;n~.~1 crystal plates Gl;f--~lled to shift one oftwo orth(-~on~lly p~ i7ed beams in a first direction and the other 2148~1~
oriented to shi~ one oftwo orthogonally p~lqri7ed beams in a first direction and the other of the two orthogonally pol~ .ed beams in a second direction, said means being disposed inte~ iAIe the first and second sep~alh~g and cGln~ ing means; and, a pair of non-reciprocal pol~ri7~tiQn rol~ling means, one means in said pair being disposed between the 5 pair of bir~r,;,~ge~t crystal plates and one of said sepala~ g and coml)illil~g means, the other means in said pair of non-lecipl~cal polari_ation l'OI~ling means being disposed between the other of said Se~alalihg and COllll)~n~ , means and said pair of bir~in,~nt crystal plates.
0 In accordallce with the invention there is further provided, an optical circulator for lights from ;I~CG...;~ and outgoing ports circularly, colll~lishl~.
a first dividing and COlllbll~lng means for dividing a beam into two beams of orthogonal electric filed vectors and for coml~ilfing two beams from dilrelenl paths into one on the same path; a pair of beam path dele~ ...;.~ing means ncljnc~ ly coupled for introducing a 15 beam to a di~eltnl direction d~pelNI~ on the direction ofthe electric filed vector and the propagation, each means in said pair being sul~ llially idçntic~l but oppositely oriented, such that the pair of means have opposite beam shi~ing directions; a second dividing and colllbilfing means for dividing a beam into two beams of orthogonal electric field vectors and for collll)inil~g two beams of orthogon~l electric filed vectors from di~t;r~lll paths into 20 one on the same path, said first dividing and collll)hling means, said beam path d~lt;....;~.;,~
means and said second dividing and collll)illillg means being optically coupled to allow light to propagate from the first dividing and collll~inil~g means to the beam path detell.lil~ing means and to the second dividing and col~ g means; a first polarization rotation means b~weell said first dividing and cG..~l)il-il~g means and said beam path 25 del~. ..~;..;l~p means for rolaling two orthogon~l pol~iLalion vectors in a same direction and IllA;l~ , an orthogQn~l r~l~stion~hip; and, a second po1~ri7~tiorl rotating means between said beam path delt;~ means and said second dividing and collll)hfing means for rol~ling two orthogon~l polsri7~tion vectors in a same direction to --A;.~1~i.- thereb il,lAil~ g an orthogonal rÇlption~hir _ Brief Description of the Drawings F.x~n~pl~ty embodL-le.lts of invention will be dçsc~ ibed in conjunction with the dl`awill~s, in which:
5 Fig. 1 is a prior art is a pel~e~tive view sl,owLIg an optical non-reciprocal optical circulator;
Fig. 2a is a pel~e.,livt; view sllowing a first embodiment of an optical circulator ofthe present invention;
Fig. 2b is a pel~e-ilive view from another end ofthe optical circulator shown in Fig. 2a;
10 Fig. 2c is a cLawing sllu~.ing polarized light in a path A accor~ing to the first embodiment of the invention;
Fig. 2d is a d.~wing i,howil~g pol~i~ed light in a path B acco.dil~g to the first embodiment ofthe invention;
Fig. 3a is a pe ~e~ilive view shuwLIg a second embodiment of an optical circulator ofthe 15 present invention;
Fig. 3b is a pe.spe~ilive view from another end ofthe optical circulator shown in Fig. 3a;
Fig. 3c is a drawing showing polarized light in a path A accolding to the secondembodiment of the invention;
Fig. 3d is a dl~wing showing polarized light in a path B according to the second20 embodiment ofthe invention;
Fig. 4a is a pel~e~;live view sLuwL~g a third embodiment of an optical circulator of the present invention;
Fig. 4b is a pel~,l.e~ilive view from another end ofthe optical circulator shown in Fig. 4a;
Fig. 4c is a dlawing sLowL~g pols ;~.çd Iight in a path A accoldhlg to the third embodiment 25 oftheinvention;
Fig. 4d is a dlawing showing pol~ri7.ed light in a path B accordil-g to the third embodiment of the invention;
Fig. 5a is a pel~e;liv-e view showing a fourth embodiment of an optical circulator ofthe present invention;
21~8317 Fig. 5b is a dlawh~g sh~ wing polq i7ed light in a path A acco,.ling to the fourth embodill,~"l of the invention;
Fig. 5c is a dl~wil g shuwil,g polC ;,.ed light in a path B accG~ g to the fourth embodiment ofthe i"~enliol~
5 Fig. 6a is a pe,*e~ e view ~l~uwh~g a f~h embodiment of an optical circulator ofthe present invention;
Fig. 6b is a drawing showing polarized light in a path A accordh~g to the f~h embodiment of the invention;
Fig. 6c is a drawing showil~g pol~ d Iight in a path B acconJil,~ to the f~ch embodiment 10 oftheinvention;
Fig. 7a is a perspective view ~howil g a sixth embodiment of an optical circulator of the present invention;
Fig. 7b is a dlawh~g i~llowll g polarized light in a path A accor~ing to the sixth embodiment of the invention; and, 15 Fig. 7c is a drawing showing polarized light in a path B accoldh~g to the sixth embodiment ofthe invention.
Detailed Description Turning now to Fig. 1, a prior art optical circulator 21 is constructed of a first through third double refraction crystal plates 22 through 24 disposed along the proceedin~
direction of light with a plcdclr- .,.;l~ed interval; a rotator 25 ofthe first group h~se, led between the first double refraction crystal plate 22 and the second refracted crystal plate 23; a rotator 26 ofthe second group inserted between the second double refraction crystal plate 23 and the third refracted crystal plate 24; light h~co,~ g and o~ltgoing ports 27 and 28 disposed on the first double refraction crystal plate 22; and a light inco",ing and outgoing port 29 di;,yosed on the third double refraction crystal plate 24. The rotator 25 ofthe first group consists of reciprocal and non-reciprocal r~lalo,~ that rotate electric field vibration directions of light up to an id~ntic~l angle; a first reciprocal rotator 31 rotates 21~8~17 clockwise to 45 degrees, and a first reciprocal rotator 32 rotates coullLt;l-,lockwise to 45 degrees, and a first non-reciprocal rotator 33 rotates to 45 degrees.
Disadvantages have been found in ~ Iri~ g this device 21. For insl~ce, a 5 high level of accuracy is rt4uiltd in II~A~C~ g the r~ ol~ 31 and 32;
The rotator 26 of the second group is constructed similarly to rotator 25 of thefirst group, colnl,lisil g a second reciprocal rotator 41 r~laling clockwise to 45 degrees, a second reciprocal rotator 42 rola~ g counterclockwise to 45 degrees, and a second non-10 reciprocal rotator 43 lol~ g to 45 degree. As with the rolalol~ 31 and 32, 41 and 42must be m~tc.h~d to within a high level of ac.iul~cy, such precision ,..~ of ~ m~nts tends to be difficult to achieve and as a result incr~ses the cost of m~mlf~ctlltin~ the device.
The various embodiments ofthe present invention desclibed heleallel overcome this limit~tion.
A First Embodiment The first embodiment ofthe optical circulator ofthis invention is de3vlibed wither~rence to Figs 2a to 2d. R~feleilce numerals acci~n~d to elem~ntc in the prior art device shown in Fig. 1 and those AC:~ gJ~ed to ~ x in the following embodiments shown in Figs. 2 to 7 do not intentions1ly collt;~,olld to same plr ..~l1s The optical circulator 200 is constructed of a first through fourth double refraction crystal plates 21, 23a, 23b, and 25 disposed along the proceedin~ direction of light with a predetermined interval. Plates 21 and 25 will her~lle be rerelled to as end-plates; plates 23a and 23b will be left;lled to as central-plates. Plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, and plate 25 is "c" units wide; where a=c and b = ~a. A non-21~8317 reciprocal rotator 22 is il,selled belweel the first crystal end-plate 21 and central-plates 23a and 23b. A second non-reciplocal rotator 24 is interposed bt;lween the second end-plate 25 and the central-plates 23a and 23b. Light ;I~CQ~ and outgoing ports 1 and 3 are disposed on oulwaldly facing endface 10 ofthe first crystal end-plate 21, and a light S hlco~ g and oulgohlg port 2 is disposed on an oulw~dly facing endface 20 of crystal end-plate 25. The rol~lol~ 22 and 24 in the form of Faraday lotdllng Pl~""~"ls rotate electric field vibrations of light up to an identi5~l angle of 45.
The operation ofthe optical circulator will be ~ ed with l~felel-ce to Figs. 2a 10 to 2d. The positive direction ofthe Z-axis is the direction that goes from the side ofthe light h~co~ ng and oulgoil~g ports 1 and 3 to the side ofthe light in~",;~p and out going ports 2, this direction being from front left to rear right in Fig. 2a. The direction from bottom to top is the rcl~d direction ofthe Y-axis.
Calcite or rutile crystals are preferably used for the above double refraction crystal plates. The non-lecip~cal r~lalol~ 22 and 24 are prer~l~ly Faraday lulallng ~l~mpnts using Y.I.G crystal or Bi-added thin film crystals. The composition of the Bi-added thin film crystals include a co",hil-AIion of, for c ~Ic, (YbTbBi)3Fe50l2 and (GdBi)3(GeAlGa)5Ol2, or of Y.I.G. and Y3~BixFe5Ol2.
In this embo~limP.nt, the direction that separates ordilldly light and extraordinary light in the double refraction crystal plates 21, 23a, 23b and 25 is set so that the direction that the central plates differs from the directions ofthe first and last end-plates 21 and 25 re~e~ rely.
Next operations of the optical circulator 200 are e pl~ ed Fig. 2a is a view of polarized light in a path A going from the light incoll~, and outgoin~ port 1 to the light incolllillg and oulgoh~g port 2 as viewed from the side ofthe il-co",;l~g light. ( the side of the h~con~ing and oulgoing port 1). States Z10, Z12, Z14 through Z20 are in~lic~ted in _ 21~8317 Figs 2c and 2d and coincide with çntlf~ces 10, 12 through 20 in Fig. 2a, traveling along the Z-axis. Light injected from the light incolll.llg and oul~ing port 1, is in a state Z10 and is separated into light Ll l and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light Ll l is ordin~y light (O-ray) relative to the first double 5 refraction crystal plate 21 and light L12 is extraordilld y (E-ray). The light is pol~ri~ed at right angles and ~,il,r~les along a 45 degree axis to the X and Y directions as shown by Z12. The electric field ~ibl~lion of light Ll l and light L12 which are pel~ r to each other, proceed in the same direction as a result ofthe light Ll l and L12 passing through the non-reciprocal Faraday rotator 22. The state ofthe pol~ri~ion at this time is shown 10 by Z14; Ll l and L12 having been rotated 45 degrees by 22, L11 at Z14 is oriented ho. ;~.o~ ly along the X-axis and L12 is oriented vertically along the Y-axis. The double refraction central-plates 23a and 23b are so ~I~ged that the light L11 is shifted by 23b, L12 passing through 23a ~JI~cl~A~ ed at endface 16 shown by state Z16. Next non-reciprocal rotator 24 rotates both Ll l and L12 by 45 degrees in a clockwise direction 15 shown by state Z18. The ~ibl~lions ofthe two lights Ll l and L12 cross at the in,Ection edge face 18 ofthe fourth double refraction crystal plate 25 where they are con~ ed at port 2 on face 20 illustrated by state Z20.
Next, l~r~ to Figs. 2b and 2d polz.i~ed light at light path B going from the 20 light incoming and oul~;-~g port 2 to the light incoll~g and OUlgOillg port 3 as viewed from the side ofthe o.l~ g light (the side ofthe light incGIllll~g and oulgoil~ port 3).
The light injected from the light incollling and oulgoing port 2 is in a Z20 state, and is sep~led into light Ll l and light L12 on the X-Y plane by the fourth double refraction crystal plate 25. The light Ll l is ol~y light (O-ray) relative to the fourth double 25 reIiu~lioll crystal plate 25, and the light L12 is extrao-~il~y light ~-ray). Each light is pol~ri7:ed at right angles, vil~l~lh~g 45 degrees to the X and Y axes as shown by Z18.
Thelealler, the two lights Lll and L12 (in state 18) will pass through the non-reciprocal Faraday rotator 24 being rotated in the same counter clockwise direction as in its previous path from endface 16 to endface 18. Thus lights L11 and L12 will have the direction of polarization rotated clockwise by 45 degrees. After passing through the rotator 24 the lights Ll l and L12 shown by state Z16 are ho~ l and vertically oriented. The ho~ ;~o~Al beam Ll l becollles shifted by crystal 23a and L12 passes through un~ ged as seen at endface 14 in state Z14. Faraday rotator 22 rotates both beams clockwise by 45 5 degrees seen in state Z12; and the beams are cGnll)illed at port 3 which is disposed in a di~elt;lll location from port 1, by crystal 21 at endface 10 illu~llaled in state Z10.
As ~ .!A;..çd above, accolJ~g to this optical circulator 200, a non-reciprocal circuit can be realized such that the light ill;e ~e~ from the light inCGI~ g and oulgoillg 10 port 1 will pass out from the light i~ nin~ and ~ulgoi~lg port 2, and the light injected from the light incoming and oulgomg port 2 will not pass out from the light incoming and olllgQ;..~ port 1, but from the light ilu~ln;.~ and oul~oi~lg port 3.
The Second Embodiment Next, an f ~ nAI;on is given of an optical circulator accordil~ to the second embodiment of the present invention, with rerelellce to Figs. 3a, 3b, 3c, and 3d.
Fig. 3a is a view of polarized light in a path A going from the light ;..co..~in~ and o~lgoil~
port 1 to the light incoming and oulgoillg port 2 as viewed from the side ofthe il~co~;np 20 light. ( the side of the i~co.~ -g and oulgoillg port 1). These states Z10, Z11, Z12, Z14 through Z20 are indicated in Figs 3c and 3d and coill.,;de with en(lf~cçs 10, 11, 12 through 20 in Fig. 2a, ll~veLI~, along the Z-axis. Light injected from the light illCOIllillg and oulgoi~ port 1, is in a state Z10 and is sep~aled into light Ll l and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light Ll l is ordil~y light (O-25 ray) relative to the first double refraction crystal plate 21 and light L12 is extraold~(E-ray). The light is polarized at right angles and vibrates in the X and Y directions as shown by Zl l . The electric field vibration of light Ll l and light L12 which are pe~ .n-l..i..l~r to each other, proceed in the same direction as a result ofthe light L11 and L12 passing through the reciprocal rotator in the form of a v~avepldle 35. The state ofthe 30 pol~ri7~tion at this time is shown by Z12; Ll and L2 having been rotated 4S degrees _ 214~317 clockwise by 35, lights L11 and L12 then pass through a Faraday rotator 22 and are rotated a further 45 degrees clockwise. L12 at Z14 is oriented ho~ lly along the X^
axis and Ll l is oriented vertically along the Y-axis. The state of the polarization at this time is shown by Z14; The double refraction central-plates 23a and 23b are so arranged 5 that the light L12 is shifted by 23b, L11 passing through 23a ~ .h~l~ged at endface 16 shown by state Z16. Next, non-reciprocal rotator 24 rotates both L11 and L12 by 45 degrees in a clockwise direction shown by state Z18. The vibrations ofthe two lights L11 and L12 cross at the injection edge face 18 ofthe fourth double refraction crystal plate 25 where they are conll)i~d at port 2 on face 20 illustl~led by state Z20. As in the first 10 embo~lim~nt~ the plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, and plate 25 is "c" units wide; where a=b and c = ~a.
Next, light il~ected from the light i~.co...;l~g and ol~l~in~ port 2 following a path B, is in a state Z20 is sep&,~led into light Ll l and light L12 on the X-Y plane by a fourth double refraction crystal plate 25. The light L12 is ordi~y light (O-ray) relative to the fourth double refraction crystal plate 25 and light L11 is extraol Ih~& y (E-ray). The light is polarized at right angles and vibrates at 45 degrees to the X and Y directions as shown by Z18. The electric field vibration of light L11 and light L12 which are pc;l~ d~ r to each other, proceed in the same direction as a result ofthe light L11 and L12 passing through the non-reciprocal Faraday rotator 24. The state ofthe polali~lion at this time is shown by Z16;. The double r~cLoll central-plates 23a and 23b are so ~l~lged that the ho. ;~ lly oriente~ light L11 is shi~ed by 23b, L12 passing through 23a . ~n~.hAI~oed at endface 14 shown by state Z14. After passing through non-reciprocal Faraday rotator 22, L11 and L12 are rotated 45 degrees, L11 and L12 at Z12 are oriented 45 degrees offthe X-Y axes. Reciprocal rolali,~ waveplates 35 rotate L11 and L12 counter clockwise so that L11 is holi~onlal and L12 is vertical along the X and Y axes re~ecliv~ly illustrated by state Z11. The two lights are coll~ ed by the first crystal plate 21 shown by state Z10.
2148~17 The Third Embodiment Rerelling now to Figs. 4a through 4d, the third embodiment of the invention is shown. Fig. 4a is a view of polarized light in a path A going from the light incollling and 5 outgoing port 1 to the light incoll~ng and oulgo..lg port 2 as viewed from the side of the incoming light. ( the side ofthe incolllil g and o~ P port 1 of circulator 400). States Z10, Zl l, Z12, Zl4 through Z20 are in-lic~ted in Figs 4c and 4d and coin~;de with çn-lf~ces lO, l l, 12 through 20 in Fig. 2a, traveling along the Z-axis. Light in;~cted from the light i~lcolllillg and ol~lgoi.~g port 1, is in a state Z10 and is sep~led into light L11 10 and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light L11 is ordil~y light (O-ray) relative to the first double refraction crystal plate 21 and light L12 is extraoldil~y (E-ray). The light is polarized at right angles and ~,;I,I~les in the X
and Y directions as shown by Z11. The electric field vil~l~lion of light L11 and light L12 which are pel~,~n~lic~ r to each other, proceed in the same direction as a result of the light 15 Ll l and Ll2 passing through the non-reciprocal rotator in the form of a Faraday rotator 22. The state ofthe polali~ion at this time is shown by Zl4; Ll and L2 having been rotated 45 degrees clockwise by 22 then pass through the double refraction central-plates 23a and 23b; the plates are so ~ ged that the light Ll l is shifted by 23b, L12 passing through 23a ~ d at endface 16 shown by state Z16. Next, a fourth double 20 refraction crystal plate 25 is oriented to shift L12, Ll l passing through u~-r~ ped shown by state Z20. Next, the vil~l~liolls ofthe two lights Ll l and Ll2 cross at the injection edge face 20 ofthe fi~h double refraction crystal plate 43 where they are combined at port 2 on face 22 illustrated by state Z22.. The plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, plate 25 is "c" units wide; and plate 43 is "a~' units wide where d=a+c 25 and b = ~/ a.
The states of lights Ll l and L12 along path B from port 2 to port 3 are clearlyillustrated in Fig. 4d.
2148~17 The Fourth Embodiment With the eAce~tion ofthe two double refraction crystal central-plates 23c and 23d being oriPnte~l dirrclelltly from 23a and 23b in earlier embo-limPnte, this circulator 500 is eSS~ ;AIIy the same as the circulator 200 shown and desc~ il,e~ with rcrelence to Figs. 2a, 5 2b, 2c, and 2d.
R~r~. . ;,-p now to Figs. 5a, 5c, and 5d, the circulator 500 in 5a is shown having two double refraction central-plates 23c and 23d oriPnted 45 degrees to the X-Y axes.
Thus, in operation, in states Z14 to Z16, light is dirccled diLrelc~ltly by 23c and 23d than 10 by 23a and 23b in device 200. The cAll~ldil~y colllpollclll of light L12 is shifted 45 degrees to the X-Y axes in state Z16. The Faraday rotators and the end-plates function in a similar manner as they do in circuldlor 200, desclil~ed hclclofolc. In this embodiment a=c and b=~a.
The Fifth embodiment Referring now, to Fig. 6, light pr~p~ting through the circulator 500 suffers less from polAri7~tion mode disycl~lon (PMD) than in the circulators shown in the previous embo~limPnte due to this circulator's sylll lætly. Improvements in PMD in the circulator 500 are a result ofthe two orthogQn~lly pola,i~cd beams llavelil~g along a same path 20 length within the device; thus a=dandb=c; as well, a=d=~b .
The operation ofthe circulator 600 can be understood with rcrelcllce to Figs. 6a, 6b, and 6c. The polari_ation states of light traveling from port 1 to port 2 at interf~cçs Z10 to Z20 are PYP.mplifiP~d in Fig. 6b. The polalization states of light traveling from port 2 to 25 port 3 at intçrf~cçs Z20 to Z10 are e~ ed in Fig. 6c. It should be noted that in lr~els~g state Z14 to Z16, L12 is shifted as same ~lis~ ce as Ll l in traversing state Z17a to Z17b, thus the path length Ira~eled by Ll l is sul~sl~llially the same as that for L12.
- 21~8317 The Sixth Embodiment ~ an alternative embodiment a circulator 700 is shown similar in most re~ecl~ to circulator 600. However, circulator 700 inf 1lldes two ad~lition~l double refraction crystal plates 72 and 73 adjac-.nt end-plates 21 and 25 res~eiLively.S Adv~nt~eo~l~ly, by adding the double refraction crystal plates 72 and 73, ports 1 and 3 are disposed along the endface 10 along a same hol~o~ l line, i.e. sharing the same Y-axis coordillale, thus the task of ~ ~ the ports 1 and 3 and m~mlf~ct~lrin~ the device becollles simplified.
The operation ofthe circulator 700 is similar in many re~ecls to that of cil~;ulalor 600 however, crystal plates 72 and 73 pel~llll ~ddition~ hif~in~ The states of pol~ri7~tion from ports 1 to 2 and 2 to 3 are illustrated in Figs. 7b and 7c respectively. the f~ .e~,~;ons ofthe crystal plates 21, 72, 63a, 63b, 73, and 25 are such that a=b=e=fand d=c.
Of course, llunlelous other embo-lim~nt~ may be envisaged, without dep~l~lg from the spirit and scope ofthe invention. For c s~ ple the device in accordance with this invention can be m~nllf~chlred having more than three ports.
One ofthe major advantages of optical circulators over more tr~ition~l 3 dB
couplers is that the loss penalty is much lower. Using a 3 dB coupler at each end of a fiber link, there is an insertion loss of at least 6 dB. For conl-e.i~;on.~ which operate near their detection limits, this additional 6 dB loss could make bi-directi~n~l co.. ~ icalion 20 i~ vlival)lv.
In a real optical circulator insertion loss and cross-talk are two i ll~)oll~ll col-~idf ~ ~lions. Insertion loss is the diLr~vl~vllce in power b~lnven light l~ ed into the optical circulator and the power that exits the device. Insertion loss is largely due to 25 absorption of light and to illl~vlrvvl po1~ri7~tion separation.
Prior art optical circulators are de3vlil,ed in U.S. Pat. No. 4,650,289, issued to K~l~.dhal~; U.S. Pat. No. 4,464,022, issued to Emkey; and in U.S. Pat. No. 4,859,014, issued to Schmitt et al. However, insertion loss and/or cross-talk in optical circulators 21~8317 made as desclilJed in these l~ft;rences are ~n~ccept~bly high for many commllniç~tions applic~tion~ Ther~ror~, a need exists for an optical circulator having lower insertion loss and cross-talk than that found in present optical circulators.
One factor that cGnl,il,ules to lower insertion loss and cross-talk in the optical circulator of the present invention than in prior optical circulators is the use of l"~er, ;"~e-.
crystals instead oftM~litiQn~l po1G-;~I;on spitting cubes results in much more co"lp'ete pol~ri7~tion of incident random~y polarized light.
A more recent prior art optical circulator that uses b--~r. ;nge .l clystals in contact with other elpmpntc such as polarization rolalols, is U.S. Pat. No. 5,204,771 issued April 20, 1993 in the name of Koga. Although this invention appears to pe ru~ its intPntled fimction adequately, precise l""lch;"~ of optical colllpone~ such as waveplates is re~luir~d; this precision ".~ .hil~p is found to be difficult and thus costly. This requht;lllellt of ",~ g reciprocal ro~lcl~ is obviated in the present invention which ovel-iollles this problem by ~ a centrally dis~,osed split pair of bil~r~ l crystal plates.
It is Ihelerore an object ofthe invention, to ovel-iollle many ofthe limit~q~tions of known prior art devices.
Summary of the Invention In accordal~ce with the invention, there is provided, an optical circulator colll~ g first means for sepalaling a beam of light into two polarized beams having ortho~n~l po1~ri7~tion states, and for conlbilfing two sepalaled orthogonally polarized beams; second means for sepalaL~g a beam of light into two pol~i~;ed beams having orthogonal pol~ri7~tion states, and for collll)il~ng two sepal~led orthogon~lly polarized beams; a pair of ~ul~t~llially identic~l oppositely onented bil~rl ;n~.~1 crystal plates Gl;f--~lled to shift one oftwo orth(-~on~lly p~ i7ed beams in a first direction and the other 2148~1~
oriented to shi~ one oftwo orthogonally p~lqri7ed beams in a first direction and the other of the two orthogonally pol~ .ed beams in a second direction, said means being disposed inte~ iAIe the first and second sep~alh~g and cGln~ ing means; and, a pair of non-reciprocal pol~ri7~tiQn rol~ling means, one means in said pair being disposed between the 5 pair of bir~r,;,~ge~t crystal plates and one of said sepala~ g and coml)illil~g means, the other means in said pair of non-lecipl~cal polari_ation l'OI~ling means being disposed between the other of said Se~alalihg and COllll)~n~ , means and said pair of bir~in,~nt crystal plates.
0 In accordallce with the invention there is further provided, an optical circulator for lights from ;I~CG...;~ and outgoing ports circularly, colll~lishl~.
a first dividing and COlllbll~lng means for dividing a beam into two beams of orthogonal electric filed vectors and for coml~ilfing two beams from dilrelenl paths into one on the same path; a pair of beam path dele~ ...;.~ing means ncljnc~ ly coupled for introducing a 15 beam to a di~eltnl direction d~pelNI~ on the direction ofthe electric filed vector and the propagation, each means in said pair being sul~ llially idçntic~l but oppositely oriented, such that the pair of means have opposite beam shi~ing directions; a second dividing and colllbilfing means for dividing a beam into two beams of orthogonal electric field vectors and for collll)inil~g two beams of orthogon~l electric filed vectors from di~t;r~lll paths into 20 one on the same path, said first dividing and collll)hling means, said beam path d~lt;....;~.;,~
means and said second dividing and collll)illillg means being optically coupled to allow light to propagate from the first dividing and collll~inil~g means to the beam path detell.lil~ing means and to the second dividing and col~ g means; a first polarization rotation means b~weell said first dividing and cG..~l)il-il~g means and said beam path 25 del~. ..~;..;l~p means for rolaling two orthogon~l pol~iLalion vectors in a same direction and IllA;l~ , an orthogQn~l r~l~stion~hip; and, a second po1~ri7~tiorl rotating means between said beam path delt;~ means and said second dividing and collll)hfing means for rol~ling two orthogon~l polsri7~tion vectors in a same direction to --A;.~1~i.- thereb il,lAil~ g an orthogonal rÇlption~hir _ Brief Description of the Drawings F.x~n~pl~ty embodL-le.lts of invention will be dçsc~ ibed in conjunction with the dl`awill~s, in which:
5 Fig. 1 is a prior art is a pel~e~tive view sl,owLIg an optical non-reciprocal optical circulator;
Fig. 2a is a pel~e.,livt; view sllowing a first embodiment of an optical circulator ofthe present invention;
Fig. 2b is a pel~e-ilive view from another end ofthe optical circulator shown in Fig. 2a;
10 Fig. 2c is a cLawing sllu~.ing polarized light in a path A accor~ing to the first embodiment of the invention;
Fig. 2d is a d.~wing i,howil~g pol~i~ed light in a path B acco.dil~g to the first embodiment ofthe invention;
Fig. 3a is a pe ~e~ilive view shuwLIg a second embodiment of an optical circulator ofthe 15 present invention;
Fig. 3b is a pe.spe~ilive view from another end ofthe optical circulator shown in Fig. 3a;
Fig. 3c is a drawing showing polarized light in a path A accolding to the secondembodiment of the invention;
Fig. 3d is a dl~wing showing polarized light in a path B according to the second20 embodiment ofthe invention;
Fig. 4a is a pel~e~;live view sLuwL~g a third embodiment of an optical circulator of the present invention;
Fig. 4b is a pel~,l.e~ilive view from another end ofthe optical circulator shown in Fig. 4a;
Fig. 4c is a dlawing sLowL~g pols ;~.çd Iight in a path A accoldhlg to the third embodiment 25 oftheinvention;
Fig. 4d is a dlawing showing pol~ri7.ed light in a path B accordil-g to the third embodiment of the invention;
Fig. 5a is a pel~e;liv-e view showing a fourth embodiment of an optical circulator ofthe present invention;
21~8317 Fig. 5b is a dlawh~g sh~ wing polq i7ed light in a path A acco,.ling to the fourth embodill,~"l of the invention;
Fig. 5c is a dl~wil g shuwil,g polC ;,.ed light in a path B accG~ g to the fourth embodiment ofthe i"~enliol~
5 Fig. 6a is a pe,*e~ e view ~l~uwh~g a f~h embodiment of an optical circulator ofthe present invention;
Fig. 6b is a drawing showing polarized light in a path A accordh~g to the f~h embodiment of the invention;
Fig. 6c is a drawing showil~g pol~ d Iight in a path B acconJil,~ to the f~ch embodiment 10 oftheinvention;
Fig. 7a is a perspective view ~howil g a sixth embodiment of an optical circulator of the present invention;
Fig. 7b is a dlawh~g i~llowll g polarized light in a path A accor~ing to the sixth embodiment of the invention; and, 15 Fig. 7c is a drawing showing polarized light in a path B accoldh~g to the sixth embodiment ofthe invention.
Detailed Description Turning now to Fig. 1, a prior art optical circulator 21 is constructed of a first through third double refraction crystal plates 22 through 24 disposed along the proceedin~
direction of light with a plcdclr- .,.;l~ed interval; a rotator 25 ofthe first group h~se, led between the first double refraction crystal plate 22 and the second refracted crystal plate 23; a rotator 26 ofthe second group inserted between the second double refraction crystal plate 23 and the third refracted crystal plate 24; light h~co,~ g and o~ltgoing ports 27 and 28 disposed on the first double refraction crystal plate 22; and a light inco",ing and outgoing port 29 di;,yosed on the third double refraction crystal plate 24. The rotator 25 ofthe first group consists of reciprocal and non-reciprocal r~lalo,~ that rotate electric field vibration directions of light up to an id~ntic~l angle; a first reciprocal rotator 31 rotates 21~8~17 clockwise to 45 degrees, and a first reciprocal rotator 32 rotates coullLt;l-,lockwise to 45 degrees, and a first non-reciprocal rotator 33 rotates to 45 degrees.
Disadvantages have been found in ~ Iri~ g this device 21. For insl~ce, a 5 high level of accuracy is rt4uiltd in II~A~C~ g the r~ ol~ 31 and 32;
The rotator 26 of the second group is constructed similarly to rotator 25 of thefirst group, colnl,lisil g a second reciprocal rotator 41 r~laling clockwise to 45 degrees, a second reciprocal rotator 42 rola~ g counterclockwise to 45 degrees, and a second non-10 reciprocal rotator 43 lol~ g to 45 degree. As with the rolalol~ 31 and 32, 41 and 42must be m~tc.h~d to within a high level of ac.iul~cy, such precision ,..~ of ~ m~nts tends to be difficult to achieve and as a result incr~ses the cost of m~mlf~ctlltin~ the device.
The various embodiments ofthe present invention desclibed heleallel overcome this limit~tion.
A First Embodiment The first embodiment ofthe optical circulator ofthis invention is de3vlibed wither~rence to Figs 2a to 2d. R~feleilce numerals acci~n~d to elem~ntc in the prior art device shown in Fig. 1 and those AC:~ gJ~ed to ~ x in the following embodiments shown in Figs. 2 to 7 do not intentions1ly collt;~,olld to same plr ..~l1s The optical circulator 200 is constructed of a first through fourth double refraction crystal plates 21, 23a, 23b, and 25 disposed along the proceedin~ direction of light with a predetermined interval. Plates 21 and 25 will her~lle be rerelled to as end-plates; plates 23a and 23b will be left;lled to as central-plates. Plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, and plate 25 is "c" units wide; where a=c and b = ~a. A non-21~8317 reciprocal rotator 22 is il,selled belweel the first crystal end-plate 21 and central-plates 23a and 23b. A second non-reciplocal rotator 24 is interposed bt;lween the second end-plate 25 and the central-plates 23a and 23b. Light ;I~CQ~ and outgoing ports 1 and 3 are disposed on oulwaldly facing endface 10 ofthe first crystal end-plate 21, and a light S hlco~ g and oulgohlg port 2 is disposed on an oulw~dly facing endface 20 of crystal end-plate 25. The rol~lol~ 22 and 24 in the form of Faraday lotdllng Pl~""~"ls rotate electric field vibrations of light up to an identi5~l angle of 45.
The operation ofthe optical circulator will be ~ ed with l~felel-ce to Figs. 2a 10 to 2d. The positive direction ofthe Z-axis is the direction that goes from the side ofthe light h~co~ ng and oulgoil~g ports 1 and 3 to the side ofthe light in~",;~p and out going ports 2, this direction being from front left to rear right in Fig. 2a. The direction from bottom to top is the rcl~d direction ofthe Y-axis.
Calcite or rutile crystals are preferably used for the above double refraction crystal plates. The non-lecip~cal r~lalol~ 22 and 24 are prer~l~ly Faraday lulallng ~l~mpnts using Y.I.G crystal or Bi-added thin film crystals. The composition of the Bi-added thin film crystals include a co",hil-AIion of, for c ~Ic, (YbTbBi)3Fe50l2 and (GdBi)3(GeAlGa)5Ol2, or of Y.I.G. and Y3~BixFe5Ol2.
In this embo~limP.nt, the direction that separates ordilldly light and extraordinary light in the double refraction crystal plates 21, 23a, 23b and 25 is set so that the direction that the central plates differs from the directions ofthe first and last end-plates 21 and 25 re~e~ rely.
Next operations of the optical circulator 200 are e pl~ ed Fig. 2a is a view of polarized light in a path A going from the light incoll~, and outgoin~ port 1 to the light incolllillg and oulgoh~g port 2 as viewed from the side ofthe il-co",;l~g light. ( the side of the h~con~ing and oulgoing port 1). States Z10, Z12, Z14 through Z20 are in~lic~ted in _ 21~8317 Figs 2c and 2d and coincide with çntlf~ces 10, 12 through 20 in Fig. 2a, traveling along the Z-axis. Light injected from the light incolll.llg and oul~ing port 1, is in a state Z10 and is separated into light Ll l and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light Ll l is ordin~y light (O-ray) relative to the first double 5 refraction crystal plate 21 and light L12 is extraordilld y (E-ray). The light is pol~ri~ed at right angles and ~,il,r~les along a 45 degree axis to the X and Y directions as shown by Z12. The electric field ~ibl~lion of light Ll l and light L12 which are pel~ r to each other, proceed in the same direction as a result ofthe light Ll l and L12 passing through the non-reciprocal Faraday rotator 22. The state ofthe pol~ri~ion at this time is shown 10 by Z14; Ll l and L12 having been rotated 45 degrees by 22, L11 at Z14 is oriented ho. ;~.o~ ly along the X-axis and L12 is oriented vertically along the Y-axis. The double refraction central-plates 23a and 23b are so ~I~ged that the light L11 is shifted by 23b, L12 passing through 23a ~JI~cl~A~ ed at endface 16 shown by state Z16. Next non-reciprocal rotator 24 rotates both Ll l and L12 by 45 degrees in a clockwise direction 15 shown by state Z18. The ~ibl~lions ofthe two lights Ll l and L12 cross at the in,Ection edge face 18 ofthe fourth double refraction crystal plate 25 where they are con~ ed at port 2 on face 20 illustrated by state Z20.
Next, l~r~ to Figs. 2b and 2d polz.i~ed light at light path B going from the 20 light incoming and oul~;-~g port 2 to the light incoll~g and OUlgOillg port 3 as viewed from the side ofthe o.l~ g light (the side ofthe light incGIllll~g and oulgoil~ port 3).
The light injected from the light incollling and oulgoing port 2 is in a Z20 state, and is sep~led into light Ll l and light L12 on the X-Y plane by the fourth double refraction crystal plate 25. The light Ll l is ol~y light (O-ray) relative to the fourth double 25 reIiu~lioll crystal plate 25, and the light L12 is extrao-~il~y light ~-ray). Each light is pol~ri7:ed at right angles, vil~l~lh~g 45 degrees to the X and Y axes as shown by Z18.
Thelealler, the two lights Lll and L12 (in state 18) will pass through the non-reciprocal Faraday rotator 24 being rotated in the same counter clockwise direction as in its previous path from endface 16 to endface 18. Thus lights L11 and L12 will have the direction of polarization rotated clockwise by 45 degrees. After passing through the rotator 24 the lights Ll l and L12 shown by state Z16 are ho~ l and vertically oriented. The ho~ ;~o~Al beam Ll l becollles shifted by crystal 23a and L12 passes through un~ ged as seen at endface 14 in state Z14. Faraday rotator 22 rotates both beams clockwise by 45 5 degrees seen in state Z12; and the beams are cGnll)illed at port 3 which is disposed in a di~elt;lll location from port 1, by crystal 21 at endface 10 illu~llaled in state Z10.
As ~ .!A;..çd above, accolJ~g to this optical circulator 200, a non-reciprocal circuit can be realized such that the light ill;e ~e~ from the light inCGI~ g and oulgoillg 10 port 1 will pass out from the light i~ nin~ and ~ulgoi~lg port 2, and the light injected from the light incoming and oulgomg port 2 will not pass out from the light incoming and olllgQ;..~ port 1, but from the light ilu~ln;.~ and oul~oi~lg port 3.
The Second Embodiment Next, an f ~ nAI;on is given of an optical circulator accordil~ to the second embodiment of the present invention, with rerelellce to Figs. 3a, 3b, 3c, and 3d.
Fig. 3a is a view of polarized light in a path A going from the light ;..co..~in~ and o~lgoil~
port 1 to the light incoming and oulgoillg port 2 as viewed from the side ofthe il~co~;np 20 light. ( the side of the i~co.~ -g and oulgoillg port 1). These states Z10, Z11, Z12, Z14 through Z20 are indicated in Figs 3c and 3d and coill.,;de with en(lf~cçs 10, 11, 12 through 20 in Fig. 2a, ll~veLI~, along the Z-axis. Light injected from the light illCOIllillg and oulgoi~ port 1, is in a state Z10 and is sep~aled into light Ll l and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light Ll l is ordil~y light (O-25 ray) relative to the first double refraction crystal plate 21 and light L12 is extraold~(E-ray). The light is polarized at right angles and vibrates in the X and Y directions as shown by Zl l . The electric field vibration of light Ll l and light L12 which are pe~ .n-l..i..l~r to each other, proceed in the same direction as a result ofthe light L11 and L12 passing through the reciprocal rotator in the form of a v~avepldle 35. The state ofthe 30 pol~ri7~tion at this time is shown by Z12; Ll and L2 having been rotated 4S degrees _ 214~317 clockwise by 35, lights L11 and L12 then pass through a Faraday rotator 22 and are rotated a further 45 degrees clockwise. L12 at Z14 is oriented ho~ lly along the X^
axis and Ll l is oriented vertically along the Y-axis. The state of the polarization at this time is shown by Z14; The double refraction central-plates 23a and 23b are so arranged 5 that the light L12 is shifted by 23b, L11 passing through 23a ~ .h~l~ged at endface 16 shown by state Z16. Next, non-reciprocal rotator 24 rotates both L11 and L12 by 45 degrees in a clockwise direction shown by state Z18. The vibrations ofthe two lights L11 and L12 cross at the injection edge face 18 ofthe fourth double refraction crystal plate 25 where they are conll)i~d at port 2 on face 20 illustl~led by state Z20. As in the first 10 embo~lim~nt~ the plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, and plate 25 is "c" units wide; where a=b and c = ~a.
Next, light il~ected from the light i~.co...;l~g and ol~l~in~ port 2 following a path B, is in a state Z20 is sep&,~led into light Ll l and light L12 on the X-Y plane by a fourth double refraction crystal plate 25. The light L12 is ordi~y light (O-ray) relative to the fourth double refraction crystal plate 25 and light L11 is extraol Ih~& y (E-ray). The light is polarized at right angles and vibrates at 45 degrees to the X and Y directions as shown by Z18. The electric field vibration of light L11 and light L12 which are pc;l~ d~ r to each other, proceed in the same direction as a result ofthe light L11 and L12 passing through the non-reciprocal Faraday rotator 24. The state ofthe polali~lion at this time is shown by Z16;. The double r~cLoll central-plates 23a and 23b are so ~l~lged that the ho. ;~ lly oriente~ light L11 is shi~ed by 23b, L12 passing through 23a . ~n~.hAI~oed at endface 14 shown by state Z14. After passing through non-reciprocal Faraday rotator 22, L11 and L12 are rotated 45 degrees, L11 and L12 at Z12 are oriented 45 degrees offthe X-Y axes. Reciprocal rolali,~ waveplates 35 rotate L11 and L12 counter clockwise so that L11 is holi~onlal and L12 is vertical along the X and Y axes re~ecliv~ly illustrated by state Z11. The two lights are coll~ ed by the first crystal plate 21 shown by state Z10.
2148~17 The Third Embodiment Rerelling now to Figs. 4a through 4d, the third embodiment of the invention is shown. Fig. 4a is a view of polarized light in a path A going from the light incollling and 5 outgoing port 1 to the light incoll~ng and oulgo..lg port 2 as viewed from the side of the incoming light. ( the side ofthe incolllil g and o~ P port 1 of circulator 400). States Z10, Zl l, Z12, Zl4 through Z20 are in-lic~ted in Figs 4c and 4d and coin~;de with çn-lf~ces lO, l l, 12 through 20 in Fig. 2a, traveling along the Z-axis. Light in;~cted from the light i~lcolllillg and ol~lgoi.~g port 1, is in a state Z10 and is sep~led into light L11 10 and light L12 on the X-Y plane by a first double refraction crystal plate 21. The light L11 is ordil~y light (O-ray) relative to the first double refraction crystal plate 21 and light L12 is extraoldil~y (E-ray). The light is polarized at right angles and ~,;I,I~les in the X
and Y directions as shown by Z11. The electric field vil~l~lion of light L11 and light L12 which are pel~,~n~lic~ r to each other, proceed in the same direction as a result of the light 15 Ll l and Ll2 passing through the non-reciprocal rotator in the form of a Faraday rotator 22. The state ofthe polali~ion at this time is shown by Zl4; Ll and L2 having been rotated 45 degrees clockwise by 22 then pass through the double refraction central-plates 23a and 23b; the plates are so ~ ged that the light Ll l is shifted by 23b, L12 passing through 23a ~ d at endface 16 shown by state Z16. Next, a fourth double 20 refraction crystal plate 25 is oriented to shift L12, Ll l passing through u~-r~ ped shown by state Z20. Next, the vil~l~liolls ofthe two lights Ll l and Ll2 cross at the injection edge face 20 ofthe fi~h double refraction crystal plate 43 where they are combined at port 2 on face 22 illustrated by state Z22.. The plate 21 is "a" units wide, plates 23a and 23b are "b" units wide, plate 25 is "c" units wide; and plate 43 is "a~' units wide where d=a+c 25 and b = ~/ a.
The states of lights Ll l and L12 along path B from port 2 to port 3 are clearlyillustrated in Fig. 4d.
2148~17 The Fourth Embodiment With the eAce~tion ofthe two double refraction crystal central-plates 23c and 23d being oriPnte~l dirrclelltly from 23a and 23b in earlier embo-limPnte, this circulator 500 is eSS~ ;AIIy the same as the circulator 200 shown and desc~ il,e~ with rcrelence to Figs. 2a, 5 2b, 2c, and 2d.
R~r~. . ;,-p now to Figs. 5a, 5c, and 5d, the circulator 500 in 5a is shown having two double refraction central-plates 23c and 23d oriPnted 45 degrees to the X-Y axes.
Thus, in operation, in states Z14 to Z16, light is dirccled diLrelc~ltly by 23c and 23d than 10 by 23a and 23b in device 200. The cAll~ldil~y colllpollclll of light L12 is shifted 45 degrees to the X-Y axes in state Z16. The Faraday rotators and the end-plates function in a similar manner as they do in circuldlor 200, desclil~ed hclclofolc. In this embodiment a=c and b=~a.
The Fifth embodiment Referring now, to Fig. 6, light pr~p~ting through the circulator 500 suffers less from polAri7~tion mode disycl~lon (PMD) than in the circulators shown in the previous embo~limPnte due to this circulator's sylll lætly. Improvements in PMD in the circulator 500 are a result ofthe two orthogQn~lly pola,i~cd beams llavelil~g along a same path 20 length within the device; thus a=dandb=c; as well, a=d=~b .
The operation ofthe circulator 600 can be understood with rcrelcllce to Figs. 6a, 6b, and 6c. The polari_ation states of light traveling from port 1 to port 2 at interf~cçs Z10 to Z20 are PYP.mplifiP~d in Fig. 6b. The polalization states of light traveling from port 2 to 25 port 3 at intçrf~cçs Z20 to Z10 are e~ ed in Fig. 6c. It should be noted that in lr~els~g state Z14 to Z16, L12 is shifted as same ~lis~ ce as Ll l in traversing state Z17a to Z17b, thus the path length Ira~eled by Ll l is sul~sl~llially the same as that for L12.
- 21~8317 The Sixth Embodiment ~ an alternative embodiment a circulator 700 is shown similar in most re~ecl~ to circulator 600. However, circulator 700 inf 1lldes two ad~lition~l double refraction crystal plates 72 and 73 adjac-.nt end-plates 21 and 25 res~eiLively.S Adv~nt~eo~l~ly, by adding the double refraction crystal plates 72 and 73, ports 1 and 3 are disposed along the endface 10 along a same hol~o~ l line, i.e. sharing the same Y-axis coordillale, thus the task of ~ ~ the ports 1 and 3 and m~mlf~ct~lrin~ the device becollles simplified.
The operation ofthe circulator 700 is similar in many re~ecls to that of cil~;ulalor 600 however, crystal plates 72 and 73 pel~llll ~ddition~ hif~in~ The states of pol~ri7~tion from ports 1 to 2 and 2 to 3 are illustrated in Figs. 7b and 7c respectively. the f~ .e~,~;ons ofthe crystal plates 21, 72, 63a, 63b, 73, and 25 are such that a=b=e=fand d=c.
Of course, llunlelous other embo-lim~nt~ may be envisaged, without dep~l~lg from the spirit and scope ofthe invention. For c s~ ple the device in accordance with this invention can be m~nllf~chlred having more than three ports.
Claims (12)
1. An optical circulator for transmitting lights from incoming and outgoing ports circularly, comprising.
a first dividing and combining means for dividing a beam into two beams of orthogonal electric filed vectors and for combining two beams from different paths into one on the same path;
a pair of beam path determining means adjacently coupled for introducing a beam to a different direction depending on the direction of the electric filed vector and the propagation each means in said pair being substantially identical but oppositely oriented, such that the pair of means have opposite beam shifting directions;
a second dividing and combining means for dividing a beam into two beams of orthogonal electric field vectors and for combining two beams of orthogonal electric filed vectors from different paths into one on the same path, said first dividing and combining means, said beam path determining means and said second dividing and combining means being optically coupled to allow light to propagate from the first dividing and combining means to the beam path determining means and to the second dividing and combining means;
a first polarization rotation means between said first dividing and combining means and said beam path determining means for rotating two orthogonal polarization vectors in a same direction and maintaining an orthogonal relationship; and, a second polarization rotating means between said beam path determining means and said second dividing and combining means for rotating two orthogonal polarization vectors in a same direction to maintain thereby maintaining an orthogonal relationship.
a first dividing and combining means for dividing a beam into two beams of orthogonal electric filed vectors and for combining two beams from different paths into one on the same path;
a pair of beam path determining means adjacently coupled for introducing a beam to a different direction depending on the direction of the electric filed vector and the propagation each means in said pair being substantially identical but oppositely oriented, such that the pair of means have opposite beam shifting directions;
a second dividing and combining means for dividing a beam into two beams of orthogonal electric field vectors and for combining two beams of orthogonal electric filed vectors from different paths into one on the same path, said first dividing and combining means, said beam path determining means and said second dividing and combining means being optically coupled to allow light to propagate from the first dividing and combining means to the beam path determining means and to the second dividing and combining means;
a first polarization rotation means between said first dividing and combining means and said beam path determining means for rotating two orthogonal polarization vectors in a same direction and maintaining an orthogonal relationship; and, a second polarization rotating means between said beam path determining means and said second dividing and combining means for rotating two orthogonal polarization vectors in a same direction to maintain thereby maintaining an orthogonal relationship.
2. An optical circulator as defined in claim 1, wherein the pair of beam path determining means is comprised of two oppositely oriented birefringent crystal plates, each having opposite beam shifted directions.
3. An optical circulator as defined in claim 2, wherein the first and second polarization rotation means are non-reciprocal rotators.
4. An optical circulator as defined in claim 3, wherein the non-reciprocal rotators comprise Faraday elements.
5. An optical circulator as defined in claim 2, wherein the first dividing and combining means comprise double refraction crystal plates.
6. An optical circulator as defined in claim 5, further comprising a reciprocal rotating element disposed between one of the first and second dividing and combining means and the pair of substantially identical oppositely oriented birefringent crystal plates.
7. An optical circulator as defined in claim 2, wherein the pair of substantially identical oppositely oriented birefringent crystal plates are oriented to shift one of two orthogonally polarized beams in a first direction and the other of the two orthogonally polarized beams in a second direction.
8. An optical circulator as defined in claim 2, comprising a second pair of substantially identical oppositely oriented birefringent crystal plates disposed between said first pair of birefringent crystal plates and one of said first and second polarization rotating means, said first pair and said second pair of birefringent plates being substantially identical.
9. An optical circulator as defined in claim 8 comprising means for rotating incoming light by 90 degrees, said means disposed between said first and second pair of birefringent crystal plates.
10. An optical circulator as defined in claim 9, further comprising a pair of birefringent crystals, a first crystal of the pair being adjacent to the first dividing and combining means and the second crystal of said pair being adjacent to the second dividing and combining means, said pair of crystals for further shifting redirecting light in such as manner as to align incoming and outgoing light at one end of the circulator at different ports that are aligned with one of a horizontal and vertical axis of the device.
11. An optical circulator, comprising:
first and second non-reciprocal polarization elements having first and second side surfaces;
a first birefringent crystal having first and second side surfaces, the second side surface being disposed against the first side surface of the first non-reciprocal polarization element;
a second birefringent crystal having first and second side surfaces, the second side surface being disposed against the first side surface of the second non-reciprocal polarization element; and first beam path determining means adjacently coupled for introducing a beam to a different direction depending on the direction of the electric filed vector and the propagation, said beam path determining means being comprised of substantially identical but oppositely oriented birefringent crystals for beam shifting in opposite directions, said crystals having endfaces being disposed between second side surfaces of the first and second non-reciprocal polarization elements, wherein light propagates through from a first port on the first side of the first birefringent crystal to a second port on the first side of the second birefringent crystal, and wherein light propagates through from a second port on the first side of the second birefringent crystal to a third port on the first side of the first birefringent crystal.
first and second non-reciprocal polarization elements having first and second side surfaces;
a first birefringent crystal having first and second side surfaces, the second side surface being disposed against the first side surface of the first non-reciprocal polarization element;
a second birefringent crystal having first and second side surfaces, the second side surface being disposed against the first side surface of the second non-reciprocal polarization element; and first beam path determining means adjacently coupled for introducing a beam to a different direction depending on the direction of the electric filed vector and the propagation, said beam path determining means being comprised of substantially identical but oppositely oriented birefringent crystals for beam shifting in opposite directions, said crystals having endfaces being disposed between second side surfaces of the first and second non-reciprocal polarization elements, wherein light propagates through from a first port on the first side of the first birefringent crystal to a second port on the first side of the second birefringent crystal, and wherein light propagates through from a second port on the first side of the second birefringent crystal to a third port on the first side of the first birefringent crystal.
12. An optical circulator comprising:
first means for separating a beam of light into two polarized beams having orthogonal polarization states, and for combining two separated orthogonally polarized beams;
second means for separating a beam of light into two polarized beams having orthogonal polarization states, and for combining two separated orthogonally polarized beams;
a pair of substantially identical oppositely oriented birefringent crystal plates oriented to shift one of two orthogonally polarized beams in a first direction and the other of the two orthogonally polarized beams in a second direction, said means being disposed intermediate the first and second separating and combining means; and, a pair of non-reciprocal polarization rotating means, one means in said pair being disposed between the pair of birefringent crystal plates and one of said separating and combining means, the other means in said pair of non-reciprocal polarization rotating means being disposed between the other of said separating and combining means and said pair of birefringent crystal plates.
first means for separating a beam of light into two polarized beams having orthogonal polarization states, and for combining two separated orthogonally polarized beams;
second means for separating a beam of light into two polarized beams having orthogonal polarization states, and for combining two separated orthogonally polarized beams;
a pair of substantially identical oppositely oriented birefringent crystal plates oriented to shift one of two orthogonally polarized beams in a first direction and the other of the two orthogonally polarized beams in a second direction, said means being disposed intermediate the first and second separating and combining means; and, a pair of non-reciprocal polarization rotating means, one means in said pair being disposed between the pair of birefringent crystal plates and one of said separating and combining means, the other means in said pair of non-reciprocal polarization rotating means being disposed between the other of said separating and combining means and said pair of birefringent crystal plates.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002148317A CA2148317C (en) | 1995-05-01 | 1995-05-01 | Optical circulator |
| US08/442,368 US5574596A (en) | 1995-05-01 | 1995-05-16 | Optical circulator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002148317A CA2148317C (en) | 1995-05-01 | 1995-05-01 | Optical circulator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2148317A1 CA2148317A1 (en) | 1996-11-02 |
| CA2148317C true CA2148317C (en) | 1998-05-05 |
Family
ID=4155764
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002148317A Expired - Fee Related CA2148317C (en) | 1995-05-01 | 1995-05-01 | Optical circulator |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5574596A (en) |
| CA (1) | CA2148317C (en) |
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- 1995-05-01 CA CA002148317A patent/CA2148317C/en not_active Expired - Fee Related
- 1995-05-16 US US08/442,368 patent/US5574596A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2148317A1 (en) | 1996-11-02 |
| US5574596A (en) | 1996-11-12 |
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