WO1991000535A1 - A wavelength demultiplexer - Google Patents

A wavelength demultiplexer Download PDF

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Publication number
WO1991000535A1
WO1991000535A1 PCT/GB1990/001024 GB9001024W WO9100535A1 WO 1991000535 A1 WO1991000535 A1 WO 1991000535A1 GB 9001024 W GB9001024 W GB 9001024W WO 9100535 A1 WO9100535 A1 WO 9100535A1
Authority
WO
WIPO (PCT)
Prior art keywords
filter
channel
wavelengths
optical
waveguides
Prior art date
Application number
PCT/GB1990/001024
Other languages
French (fr)
Inventor
David John Mccartney
Simon Thomas Nicholls
Original Assignee
British Telecommunications Public Limited Company
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by British Telecommunications Public Limited Company filed Critical British Telecommunications Public Limited Company
Publication of WO1991000535A1 publication Critical patent/WO1991000535A1/en

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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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29313—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response
    • G02B6/29314—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response by moving or modifying the diffractive element, e.g. deforming
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • 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
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29395—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device configurable, e.g. tunable or reconfigurable

Definitions

  • a first channel, having one or more selected wavelengths, is reflected by the filter and is incident on a second optical waveguide, and a second channel having all other wavelengths is transmitted by the filter.
  • Light in the second channel may then be collected by a third optical waveguide.
  • a first lens is required.
  • a second lens is necessary to focus the second channel onto the third optical waveguide.
  • GB 2096350A discloses a demultiplexer in which the second channel is reflected back through the filter and first lens to a third optical fibre.
  • a wavelength demultiplexer for splitting an optical signal having a plurality of wavelengths into a first channel having one or more wavelengths, and a second channel having the remaining wavelengths comprising a filter capable of reflecting one channel and transmitting the other channel a first optical waveguide for directing the optical signal onto the filter a second optical waveguide for receiving the reflected channel reflection means for reflecting the transmitted channel back through the filter and into a third optical waveguide for receiving the transmitted channel; characterised in that the filter is a position tuned filter and there is included a positioning means for varying the position of the grating relative to the optical waveguides whereby the wavelength or wavelengths of the first channel may be selected.
  • the present invention provides a readily tunable wavelength demultiplexer.
  • the filter is a volume reflection grating.
  • the reflected channel will thus comprise the first channel having one or more wavelengths, and the transmitted channel will comprise the second channel having the remaining wavelengths.
  • the volume reflection grating is a holographic reflection grating capable of reflecting different wavelengths at different points along the grating.
  • the holographic reflection filter may be formed from dichromated gelatin.
  • the filter may be a transmission filter.
  • the reflected channel will thus comprise the second channel having remaining wavelengths, and the transmitted channel will comprise the first channel having the one or more wavelengths.
  • the transmission filter may comprise, for example, a position tuneable multilayer thin film filter or a scanning Fabry-Perot filter.
  • the first, second and third waveguides are all mounted in a single head unit. This further eases the alignment of the waveguides relative to one another, as once the waveguides have been aligned and mounted in the head unit, their positions relative to one another are fixed and parallel to one another.
  • the first, second and third waveguides may each be formed from silica, titanium in-diffused lithuim niobate or other suitable materials. Conveniently, however, the first, second and third waveguides are each optical fibres.
  • the single head unit may then comprise a fibre connector ferrule.
  • the focussing means in the demultiplexer according to the present invention results in the collimation of the optical signal, the first channel and the second channel and allows the distances between the waveguides, the filter and the reflecting means to be longer than when no focussing means is included. This is because light exiting an optical waveguide diverges, and thus does not remain substantially collimated over a long distance.
  • the apparatus of the present invention requires only one focussing means in order to collimate each of the optical signal, the first channel and the second channel. This is in contrast to the prior art described above in which two focussing means are required.
  • the elimination of a focussing means leads to further simplification in the alignment of the components, and in the apparatus itself.
  • the focussing means may be a graded refractive index (GRIN) lens, but preferably it is a rod lens as a rod lens has a wider wavelength range of use than a GRIN lens.
  • GRIN graded refractive index
  • the first, second and third waveguides may be butted against the end of the rod lens, and secured in fixed position relative to the rod lens.
  • the rod lens may thus form part of the single head unit in which the waveguides are mounted.
  • Figure 1 is a schematic representation of one embodiment of an apparatus according to the present invention comprising a reflection grating
  • Figures 3a and 3b are schematic side and end views of the optical waveguides of the apparatus of Figure 1 or 2;
  • FIGs 6 and 7 illustrate the performance of the apparatus illustrated in Figure 2.
  • an apparatus for splitting an optical signal according to the present invention is shown.
  • the apparatus is shown.
  • holographic reflection grating 22 made from dichromated gelatin, a rod lens 23, a broadband mirror 24, input fibre 25, output fibres 26 and 27, and a fibre connector ferrule 28.
  • An optical signal having a plurality of wavelengths - - for example, is guided by fibre 25 and is incident on lens 23 which focusses it onto the holographic reflection grating 22.
  • the first optical channel 22 reflects a first optical channel having a selected single wavelength back through lens 23 and into fibre 27.
  • the first optical channel has a single selected wavelength, it could equally comprise more than one wavelength, for example ⁇ + ⁇ g, depending on the response characteristics of the grating
  • a second optical channel having the remaining wavelengths is transmitted by grating 22 and is incident on broadband mirror 24.
  • Mirror 24 is inclined at an angle relative tb grating 22 such that the second channel is reflected back by the mirror 24 through lens
  • the fibres 25, 26, 27 are held in a fixed position relative to one another by fibre connector ferrule 28.
  • the ends of the fibres 25, 26 and 27 abutt and are fixed to the end face 29 of lens 23.
  • the lens 23, ferrule 28 and fibres 25, 26 and 27 thus form a single unit. This eases the problems of alignment of the components forming the apparatus and reduces the number of components.
  • the filter is a transmission filter, 32.
  • the apparatus 31 works on the same principle as that of apparatus 21 of Figure 1.
  • the filter 32 transmits the first channel having a selected single wavelength or a selected range of wavelengths, and reflects the second channel having the remaining wavelengths.
  • Figures 3a and 3b an arrangement of the fibres 25, 26 and 27 within the ferrule 28 is shown.
  • Figures 4 and 5 show the performance of a position tunable holographic reflection filter showing the coupling efficiency versus position for wavelengths 1290nm and 1545nm near the extremes of the filter tuning range for the embodiments of Figure 1.
  • Figure 4 shows the reflected channel.
  • Figure 5 the transmitted channel.
  • Figures 6 and 7 show the performance of a position tunable thin film transmission filter for the same wavelengths as Figures 4 and 5, namely 1290nm and 1545nm.
  • Figure 6 shows the transmitted channel.
  • Figure 7 the reflected channel.
  • optical is intended to refer to that part of the electromagnetic spectrum which is generally known as the visible region together with those parts of the infrared and ultraviolet regions at each end of the visible region which are capable of being transmitted by dielectric optical waveguides such as optical fibres.

Abstract

The apparatus (21) comprises a position tuned volume reflection grating (22), a lens (23), and a broadband mirror (24). An optical signal having a plurality of wavelengths is guided by optical fibre (25) onto lens (23). Lens (23) collimates the signal and focusses it onto filter (22). Grating (22) reflects back a first optical channel having a selected single wavelength back through lens (23) and into fibre (27). A second channel having the remaining wavelengths is transmitted by grating (22), and then reflected back through filter (22) and lens (23) by mirror (24) and into fibre (26). Fibres (25, 26, 27) are held in a fixed position relative to one another by fibre connector ferrule (28) in which they are mounted.

Description

A WAVELENGTH DEMULTIPLEXER
This invention relates to a wavelength demultiplexer for splitting an optical signal having a plurality of wavelengths into a first channel having one or more wavelengths, and a second channel having the remaining wavelengths.
It is known to split an optical signal having a plurality of wavelengths by directing the optical signal from a first optical waveguide onto a filter. A first channel, having one or more selected wavelengths, is reflected by the filter and is incident on a second optical waveguide, and a second channel having all other wavelengths is transmitted by the filter. Light in the second channel may then be collected by a third optical waveguide. In order to focus the optical signal onto the filter, and the first channel onto the second waveguide, a first lens is required. A second lens is necessary to focus the second channel onto the third optical waveguide.
GB 2096350A discloses a demultiplexer in which the second channel is reflected back through the filter and first lens to a third optical fibre.
According to the present invention there is provided a wavelength demultiplexer for splitting an optical signal having a plurality of wavelengths into a first channel having one or more wavelengths, and a second channel having the remaining wavelengths comprising a filter capable of reflecting one channel and transmitting the other channel a first optical waveguide for directing the optical signal onto the filter a second optical waveguide for receiving the reflected channel reflection means for reflecting the transmitted channel back through the filter and into a third optical waveguide for receiving the transmitted channel; characterised in that the filter is a position tuned filter and there is included a positioning means for varying the position of the grating relative to the optical waveguides whereby the wavelength or wavelengths of the first channel may be selected. The present invention provides a readily tunable wavelength demultiplexer.
Preferably, the filter is a volume reflection grating. The reflected channel will thus comprise the first channel having one or more wavelengths, and the transmitted channel will comprise the second channel having the remaining wavelengths.
Conveniently, the volume reflection grating is a holographic reflection grating capable of reflecting different wavelengths at different points along the grating. By varying the relative positions of the first optical waveguide and the reflection grating, the wavelength or wavelengths of the first channel may be selected. The holographic reflection filter may be formed from dichromated gelatin.
Such gratings are well known, and are described, for example in the paper: "Optic letters Vol 10 p 303-305, June 1985" by D J McCartney, D.B Payne and S S Duncan.
Alternatively, the filter may be a transmission filter. The reflected channel will thus comprise the second channel having remaining wavelengths, and the transmitted channel will comprise the first channel having the one or more wavelengths. The transmission filter may comprise, for example, a position tuneable multilayer thin film filter or a scanning Fabry-Perot filter.
Preferably, the first, second and third waveguides are all mounted in a single head unit. This further eases the alignment of the waveguides relative to one another, as once the waveguides have been aligned and mounted in the head unit, their positions relative to one another are fixed and parallel to one another. The first, second and third waveguides may each be formed from silica, titanium in-diffused lithuim niobate or other suitable materials. Conveniently, however, the first, second and third waveguides are each optical fibres. The single head unit may then comprise a fibre connector ferrule.
Advantageously, the demultiplexer further comprises focussing means for focussing the optical signal emerging from the first waveguide onto the filter, and for focussing the first and second - 3 -
channels onto the second and third waveguides respectively. The inclusion of the focussing means in the demultiplexer according to the present invention results in the collimation of the optical signal, the first channel and the second channel and allows the distances between the waveguides, the filter and the reflecting means to be longer than when no focussing means is included. This is because light exiting an optical waveguide diverges, and thus does not remain substantially collimated over a long distance.
The apparatus of the present invention requires only one focussing means in order to collimate each of the optical signal, the first channel and the second channel. This is in contrast to the prior art described above in which two focussing means are required. The elimination of a focussing means leads to further simplification in the alignment of the components, and in the apparatus itself.
The focussing means may be a graded refractive index (GRIN) lens, but preferably it is a rod lens as a rod lens has a wider wavelength range of use than a GRIN lens. To further simplify the alignment of the components, the first, second and third waveguides may be butted against the end of the rod lens, and secured in fixed position relative to the rod lens. The rod lens may thus form part of the single head unit in which the waveguides are mounted.
The invention will now be described by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of one embodiment of an apparatus according to the present invention comprising a reflection grating;
Figure 2 is a schematic representation of a second embodiment of the present invention comprising a transmission filter;
Figures 3a and 3b are schematic side and end views of the optical waveguides of the apparatus of Figure 1 or 2;
Figures 4 and 5 illustrate the performance of the apparatus illustrated in Figure 1.
Figures 6 and 7 illustrate the performance of the apparatus illustrated in Figure 2. Referring to Figure 1, an apparatus for splitting an optical signal according to the present invention is shown. The apparatus
21 comprises a holographic reflection grating 22 made from dichromated gelatin, a rod lens 23, a broadband mirror 24, input fibre 25, output fibres 26 and 27, and a fibre connector ferrule 28. An optical signal having a plurality of wavelengths - - for example, is guided by fibre 25 and is incident on lens 23 which focusses it onto the holographic reflection grating 22. The grating
22 reflects a first optical channel having a selected single wavelength back through lens 23 and into fibre 27. Although in this example, the first optical channel has a single selected wavelength, it could equally comprise more than one wavelength, for example λ^+λg, depending on the response characteristics of the grating
22. A second optical channel having the remaining wavelengths is transmitted by grating 22 and is incident on broadband mirror 24. Mirror 24 is inclined at an angle relative tb grating 22 such that the second channel is reflected back by the mirror 24 through lens
23 and into fibre 26. The fibres 25, 26, 27 are held in a fixed position relative to one another by fibre connector ferrule 28. The ends of the fibres 25, 26 and 27 abutt and are fixed to the end face 29 of lens 23. The lens 23, ferrule 28 and fibres 25, 26 and 27 thus form a single unit. This eases the problems of alignment of the components forming the apparatus and reduces the number of components.
Referring now to Figure 2, a second embodiment of the present invention is illustrated. The apparatus 31 is similar to that illustrated in Figure 1 and equivalent parts have been given the same reference numerals. In this embodiment the filter is a transmission filter, 32. The apparatus 31 works on the same principle as that of apparatus 21 of Figure 1. Here, however, the filter 32 transmits the first channel having a selected single wavelength or a selected range of wavelengths, and reflects the second channel having the remaining wavelengths.
Referring to Figures 3a and 3b an arrangement of the fibres 25, 26 and 27 within the ferrule 28 is shown. Figures 4 and 5 show the performance of a position tunable holographic reflection filter showing the coupling efficiency versus position for wavelengths 1290nm and 1545nm near the extremes of the filter tuning range for the embodiments of Figure 1. Figure 4 shows the reflected channel. Figure 5 the transmitted channel.
Figures 6 and 7 show the performance of a position tunable thin film transmission filter for the same wavelengths as Figures 4 and 5, namely 1290nm and 1545nm. Figure 6 shows the transmitted channel. Figure 7 the reflected channel.
In this specification, the term "optical" is intended to refer to that part of the electromagnetic spectrum which is generally known as the visible region together with those parts of the infrared and ultraviolet regions at each end of the visible region which are capable of being transmitted by dielectric optical waveguides such as optical fibres.

Claims

1. A wavelength demultiplexer for splitting an optical signal having a plurality of wavelengths into a first channel having one or more wavelengths, and a second channel having the remaining wavelengths comprising: a filter capable of reflecting one channel and transmitting the other channel; a first optical waveguide for directing the optical signal onto the filter; a second optical waveguide for receiving the reflected channel; reflection means for reflecting the transmitted channel back through the filter and into a third optical waveguide for receiving the transmitted channel; characterised in that the filter is a position tuned filter and there is included a positioning means for varying the position of the grating relative to the optical waveguides whereby the wavelength or wavelengths of the first channel may be selected.
2. Apparatus as claimed in claim 1 wherein the first, second and third waveguides are all mounted in a single head unit.
3. Apparatus as claimed in claim 1 or claim 2 wherein the first, second and third waveguides are each optical fibres.
4. Apparatus as claimed in any of the preceding claims further comprising focussing means for focussing the optical signal emerging from the first waveguide onto the filter, and for focussing the first and second channels onto the second and third waveguides respectively.
5. Apparatus as claimed in claim 4 wherein the focussing means is a rod lens.
6. Apparatus as claimed in claim 5 wherein the first, second and third waveguides abutt and are fixed to the rod lens.
7. Apparatus as claimed in any one of the preceding claims wherein the reflecting means is a broadband mirror positioned at an angle relative to the filter.
8. Apparatus as claimed in any one of the preceding claims wherein the filter is a reflection grating.
9. Apparatus as claimed in claim 8 wherein the reflection grating is a volume holographic reflection grating capable of reflecting different wavelengths at different points along the grating.
10. Apparatus as claimed in claim 10 wherein the holographic reflection filter is formed from dichromated gelatin.
11. Apparatus as claimed in any one of claims 1 to 7 wherein the filter is a transmission filter.
12. Apparatus as claimed in claim 11 wherein the transmission filter is a position tuneable multilayer thin film filter.
13. Apparatus as claimed in claim 11 wherein the transmission filter is a scanning Fabry-Perot device.
PCT/GB1990/001024 1989-07-04 1990-07-03 A wavelength demultiplexer WO1991000535A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8915307.6 1989-07-04
GB898915307A GB8915307D0 (en) 1989-07-04 1989-07-04 A wavelength demultiplexer

Publications (1)

Publication Number Publication Date
WO1991000535A1 true WO1991000535A1 (en) 1991-01-10

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GB (1) GB8915307D0 (en)
WO (1) WO1991000535A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001014921A1 (en) * 1999-08-25 2001-03-01 Lightchip, Inc. Wavelength division multiplexer/demultiplexer using homogeneous refractive index lenses and transmission grating
WO2001018578A1 (en) * 1999-09-08 2001-03-15 Lightchip, Inc. Wavelength division multiplexer and demultiplexer using polymer lenses
US6608719B1 (en) 2000-03-24 2003-08-19 Wuhan Research Institute Of Posts And Telecommunications, Mii Comb wavelength division multiplexer

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2096350A (en) * 1981-03-20 1982-10-13 Western Electric Co Wavelength-selective optical coupling device
JPS59185309A (en) * 1983-04-05 1984-10-20 Matsushita Electric Ind Co Ltd Optical multiplexer/demultiplexer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2096350A (en) * 1981-03-20 1982-10-13 Western Electric Co Wavelength-selective optical coupling device
JPS59185309A (en) * 1983-04-05 1984-10-20 Matsushita Electric Ind Co Ltd Optical multiplexer/demultiplexer

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
12th European Conference on Optical Communications, Barcelona, 22-25 September 1986, ECOC '86, Technical Digest, Vol. I, D.J. McCARTNEY et al.: "A Review of the Performance of Two Types of Position Tuned Filters for use in the 1200 - 1600nm Range", pages 133-136 *
Applied Optics, Vol. 26, No. 3, 1 February 1987, Optical Society of America, (New York, US), S.R. MALLINSON: "Wavelength Selective Filters for Single-Mode Fiber WDM Systems usings Fabry-Perot Interferometers", pages 430-436 *
PATENT ABSTRACTS OF JAPAN, Vol. 8, No. 121 (P-278) (1558), 7 June 1984; & JP-A-5928124 (Mitsubishi Denki K.K.) 14 February 1984 *
PATENT ABSTRACTS OF JAPAN, Vol. 9, No. 48 (P-338) (1991), 28 February 1985; & JP-A-59185309 (Matsushita Denki Sangyo K.K.) 20 October 1984 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6298182B1 (en) 1997-12-13 2001-10-02 Light Chip, Inc. Wavelength division multiplexing/demultiplexing devices using polymer lenses
WO2001014921A1 (en) * 1999-08-25 2001-03-01 Lightchip, Inc. Wavelength division multiplexer/demultiplexer using homogeneous refractive index lenses and transmission grating
WO2001018578A1 (en) * 1999-09-08 2001-03-15 Lightchip, Inc. Wavelength division multiplexer and demultiplexer using polymer lenses
US6608719B1 (en) 2000-03-24 2003-08-19 Wuhan Research Institute Of Posts And Telecommunications, Mii Comb wavelength division multiplexer

Also Published As

Publication number Publication date
GB8915307D0 (en) 1989-08-23
AU6039690A (en) 1991-01-17

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