GB2217870A - Optical coupler - Google Patents

Optical coupler Download PDF

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Publication number
GB2217870A
GB2217870A GB8809954A GB8809954A GB2217870A GB 2217870 A GB2217870 A GB 2217870A GB 8809954 A GB8809954 A GB 8809954A GB 8809954 A GB8809954 A GB 8809954A GB 2217870 A GB2217870 A GB 2217870A
Authority
GB
United Kingdom
Prior art keywords
transparent
optical
optical fibre
division multiplexer
diffraction grating
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.)
Withdrawn
Application number
GB8809954A
Other versions
GB8809954D0 (en
Inventor
John Philip Dakin
Jeffrey John Purcell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Plessey Co Ltd
Original Assignee
Plessey Co Ltd
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 Plessey Co Ltd filed Critical Plessey Co Ltd
Priority to GB8809954A priority Critical patent/GB2217870A/en
Publication of GB8809954D0 publication Critical patent/GB8809954D0/en
Publication of GB2217870A publication Critical patent/GB2217870A/en
Withdrawn legal-status Critical Current

Links

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
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
    • 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
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29326—Diffractive elements having focusing properties, e.g. curved gratings
    • 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
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29328—Diffractive elements operating in reflection
    • 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
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4246—Bidirectionally operating package structures

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optical Transform (AREA)

Abstract

An optical wavelength-division multiplexer/demultiplexer device comprises a transparent light guiding structure 1 which is recessed 4 for receiving one end of an optical fibre 5. In operation of the device as a demultiplexer a divergent beam of broadband light emerging from the end of the optical fibre is reflected by a mirrored surface 6 and is guided by the transparent structure 1 onto a reflective diffraction grating 7 which separates or disperses the spectral components of the incident broadband light to provide along an edge 9 a spectrum of spectral components. In operation of the device as a multiplexer a number of spectral components of broadband light incident on the edge 9 are reflected by areas 12 of a disc 10 of a shaft encoder/decoder and are guided in substantially parallel relationship by the structure 1 on to the diffraction grating 7 which combines the components and focuses them on to the aforesaid end of the optical fibre 5. <IMAGE>

Description

IMPROVEMENTS RELATING TO OPTICAL WAVELENGTH-DIVISION MULTIPLEXER S XDEMULTIPLEXER S This invention relates to optical wavelength-division multiplexers/demultiplexers for use in optical sen sing systems, for example, and relates more specifically to such multiplexers/ demultiplexers utilising optical fibres.
Hitherto, optical fibre wavelength-division multiplexers/ demultiplexers have included bulk optic light dispersive arrangements or multiple dichroic mirror assemblies for the purpose of providing spatial separation of the operating spectral bands.
However, such multiplexers/demultiplexers may tend to be unnecessarily complex and expensive and have disadvantages as regards alignment time and environmental sensitivity.
According to the present invention therefore there is provided an optical wavelength-division multiplexer/demultiplexer device comprising a transparent light guiding structure which is recessed or otherwise adapted for receiving one end of an optical fibre, in which in operation of the device as a demultiplexer a divergent beam of broadband light emerging from the end of the optical fibre is guided by the transparent structure on to a reflective diffraction grating which is formed on an external convex surface of the transparent structure and which separates or disperses the spectral components of the incident broadband light to provide along an edge or equivalent of said structure a spectrum of spectral components and in which in operation of the device as a multiplexer a number of spectral components of broadband light incident on said edge or equivalent of the transparent structure are guided in substantially parallel relationship by said structure on to said diffraction grating which combines said components and focusses them on to said end of the optical fibre.
In carrying out the present invention the transparent light guiding structure may comprise a relatively thin block or plate 9f transparent material which is sandwiched between two similarly shaped plates bonded to said structure but having a lower refractive index than that of the light guiding structure or, alternatively, the structure may be sandwiched between similarly shaped plates of the same material as the transparent structure but bonded to the structure with cement having a lower refractive index than the structure material. In this way the light transmitted between the end of the optical fibre, the reflective diffraction grating and the edge along which the spectrum of spectral components is provided is contained substantially within -the structure, thereby reducing light losses to a minimum.
The end of the optical fibre may be received within a channel of rectangular (e.g. square) cross-section provided at one end of the transparent light guiding structure having side plates bonded thereto with the closed end of the channel defining an oblique mirror or otherwise reflective (e.g. totally internally reflective in a prismatic insert) surface which reflects light emerging from the optical fibre generally backwards towards that end of the structure where the reflective diffraction grating is formed on the external convex surface of the structure so as to reflect light received from the optical fibre to the opposite end of the structure having a narrow edge along which the separated spectral components of broadband light will be distributed.
In an alternative embodiment of the invention the optical fibre may be so orientated that light emerging from the end thereof is directed on to the diffraction grating without the intervention of the mirrored surface just above referred to.
The optical wavelength division multiplexer/demultiplexer structure according to the present invention may form part of an optical shaft encoder/decoder arrangement for sensing the position of the encoder/decoder shaft which in turn may be representative of some parameter required to be monitored and/or measured.
By way of example the present invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a wavelength-division multiplexer/demultiplexer device operatively associated with a shaft encoder in an optical sensing system; Figure 2 is a perspective view of a transparent light guiding structure forming part of the device according to Figure 1; Figure 3 shows a wavelength-division multiplexer/demultiplexer device similar to that shown in Figure 1 but provided with an array of optical fibres appertaining to respective spectral components of broadband light; and, Figure 4 shows an optical shaft encoder/decoder sensing system incorporating a wavelength-division multiplexer/ demultiplexer device and a pulsed broadband light source.
Referring to Figures 1 and 2 of the drawings the wavelength- division multiplexer/demultiplexer device shown comprises a micro machined plate 1 of transparent material sandwiched between two similarly shaped plates 2 and 3 and bonded thereto to provide a unitary or monolithic structure. The material of the plates 2 and 3 may have a lower refractive index than the material of the plate 1 or, alternatively, the material of the plates 2 and 3 may be the same as that of plate 1 but with cement having a lower refractive index than the plate 1 being used to bond the plates together.
The plate 1 is provided with a slot 4 the sides of which are closed by the plates 2 and 3 to define a channel of rectangular (e.g.
square) cross section which receives the end of an optical fibre 5.
The closed end of this channel has an oblique mirrored surface 6.
In operation of the multiplexer/demultiplexer device as a wavelength-division demultiplexer broadband light propagates along the optical fibre 5 and emerges as a divergent light beam from the end thereof and is reflected generally backwards by the mirrored surface 6 through the plate 1 on to a reflective diffraction grating 7 formed on an external convex surface 8 of the plate 1, the relative refractive indexes of the plate 1 and the plates 2 and 3 or of the plate 1 and the plate bonding cement serving to ensure that substantially all of the broadband light emerging from the optical fibre 5 is contained within the light guiding structure.
As the divergent beam of broadband light falls on the reflective diffraction grating 7 the light is separated by the grating into its spatial wavelength components which are reflected in parallel relationship through the plate l to the linear edge surface 9 of the plate 1 where they appear as a spectrum of spatially separated components.
The multiplexer/demultiplexer device is operatively associated with a shaft encoder/decoder the code disc 10 of which is arranged to be angularly rotated by a shaft 11 through an angle dependent upon a parameter being sensed. The code disc may comprise a reflective type disc having thereon a predetermined pattern of arcuate reflective areas, such as those shown at 12, at various radial positions on the surface of the disc. As can be seen in Figure 2 of the drawings, the code disc 10 is located closely adjacent and in parallel relationship with the linear edge surface 9 of the plate 1.
Consequently, certain spectral components of the broadband light emerging from the plate 1 at the surface 9 will be reflected back on to the surface 9 by reflective code areas on the code disc according to the angular position of the shaft 11 and the code disc 11. The reflected spectral components will pass back through the plate 1 and will be combined and focussed by the diffraction grating 7 on to the mirrored surface 6 which will then reflect the combined spectral components on to the end of the optical fibre 5. This combined light may then be demultiplexed as by a further device of the - form shown in Figure 2 in order to separate the spectral components for detection and/or decoding purposes in order to ascertain the angular position of the shaft and thereby the value of the particular parameter of which the angular position of the shaft is representative.
It may here be mentioned that the mirrored surface 6 could be dispensed with by arranging that the end of the optical fibre 5 is positioned to direct the light beam emerging therefrom on to the reflective diffraction grating. However, this arrangement may result in undue bending of the optical fibre 5 if the entry of the optical fibre into the plate 1 and the location of the diffraction grating 7 are not to encroach on the shaft encoder disc end of the multiplexer/demultiplexer device.
Referring lastly to the Figure 4 optical sensing system, the wavelength division multiplexer/demultiplexer and reflective - shaft encoder indicated at 14 are similar to those illustrated in Figure 1. A pulsed broadband light source 15 is arranged to produce pulses of broadband light 16 which propagate along an optical fibre 17 and into the optical fibre 5 through an optical directional coupler 18. The broadband light will be demultiplexed into its different spectral components by the diffraction grating 7 within the multiplexer/demultiplexer device 19 and selected wavelength components will be reflected back into the device according to the angular position of the code disc 10 and shaft 11 of the shaft encoder.These reflected components will be multiplexed by the diffraction grating within device 19 before being transmitted by the optical fibre 5 to the directional coupler 18 which directs the multiplexed reflected components into a further multiplexer/demultiplexer 20 which may be similar to that shown in Figure 3. After the demultiplexing of the input the separated components are fed along the optical fibres 21-25 to respective optical detectors 26-30 (e.g. photodiodes) which produce electrical outputs indicative of the angular position of the shaft 11 of the shaft encoder.
This pulsed light source arrangement when compared with a continuous light source arrangement has the advantage that a timegate (or electronic switch which is opened at the interval when pulse echoes return from the disc) may be incorporated, to ensure that the received optical power in a given spectral band is not contaminated by light from the source that reaches the detector as a result of undesirable reflections from optical connectors, for example, within the system.
It should be understood that although the code disc 10 of the shaft encoder in the arrangements described above with reference to Figures 1, 3 and 4 is of the reflective type it could alternatively be of the transmissive type in which case respective rows of optical fibres could be positioned on opposite sides of the code disc. In this case, two identical optical wavelength division multiplexers/demul tiplexers would be arranged, in mirror-image location, at opposite sides of the coded disc.

Claims (9)

1. An optical wavelength-division multiplexer/demultiplexer device comprising a transparent light guiding structure which is recessed or otherwise adapted for receiving one end of an optical fibre, in which in operation of the device as a demultiplexer a divergent beam of broadband light emerging from the end of the optical fibre is guided by the transparent structure on to a concave reflective diffraction grating which is carried by said transparent structure and which separates or disperses the spectral components of the incident broadband light to provide along an edge or equivalent of said structure a spectrum of spectral components, and in which in operation1 of the device as a multiplexer a number of spectral components of broadband light incident on said edge or equivalent of the transparent structure are guided in substantially parallel relationship by said structure on to said diffraction grating which combines said componerits and focuses them on to said end of the optical fibre.
2. An optical wavelength-division multiplexer/demultiplexer device as claimed in claim 1, in which the concave reflective diffraction grating is formed on an external convex surface of the transparent structure.
3. An optical wavelength-division multiplexer/demultiplexer device as claimed in claim 1 or claim 2, in which the transparent light guiding structure comprises a relatively thin block or plate of transparent material which is sandwiched between two similarly shaped plates bonded to the transparent structure but having a lower refractive index than that of the light guiding structure.
4. An optical wavelength-division multiplexer/demul tiplexer device as claimed in claim 1 or claim 2, in which the transparent structure is -sandwiched between similarly shaped plates of the same material as the transparent structure but bonded to the structure with cement having a lower refractive index than the structure material.
5. An optical wavelength-division multiplexer/demultiplexer device as claimed in claim 3 or claim 4, in which the end of the optical fibre is received within a channel of rectangular (e.g. square) cross-section provided at one end of the transparent light guiding structure having side plates bonded thereto with the closed end of the channel defining an oblique mirror or other reflective surface which reflects light emerging from the optical fibre generally backwards towards the end of the structure where the concave reflective diffraction grating is located so as to reflect light received from the optical fibre to the opposite end of the structure having a narrow edge along which the separated spectral components of broadband light will be distributed.
6. An optical wavelength-division multiplexer/demultiplexer device as claimed in claim 3 or claim 4, in which the optical fibre is so orientated that light emerging from the end thereof is directed directly on to the diffraction grating.
7. An optical shaft encoder/decoder arrangement including an optical wavelength-division multiplexer/demultiplexer device as claimed in any preceding claim.
8. An optical wavelength -division multiplexer/demultiplexer device substantially as hereinbefore described with reference to the accompanying drawings.
9. An optical shaft encoder/decoder arrangement substantially as hereinbefore described with reference to the accompanying drawings.
GB8809954A 1988-04-27 1988-04-27 Optical coupler Withdrawn GB2217870A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8809954A GB2217870A (en) 1988-04-27 1988-04-27 Optical coupler

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8809954A GB2217870A (en) 1988-04-27 1988-04-27 Optical coupler

Publications (2)

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GB8809954D0 GB8809954D0 (en) 1988-06-02
GB2217870A true GB2217870A (en) 1989-11-01

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6388803B1 (en) * 2000-03-02 2002-05-14 Agere Systems Guardian Corp. Article comprising a broad band optical amplifier
WO2005006044A1 (en) * 2003-07-09 2005-01-20 Sinvent As Optical multiplexer/demultiplexer and channel equaliser
WO2014001074A1 (en) * 2012-06-27 2014-01-03 Nico Correns Monolithic spectrometer arrangement

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6388803B1 (en) * 2000-03-02 2002-05-14 Agere Systems Guardian Corp. Article comprising a broad band optical amplifier
WO2005006044A1 (en) * 2003-07-09 2005-01-20 Sinvent As Optical multiplexer/demultiplexer and channel equaliser
WO2014001074A1 (en) * 2012-06-27 2014-01-03 Nico Correns Monolithic spectrometer arrangement
US9625317B2 (en) 2012-06-27 2017-04-18 Nico Correns Monolithic spectrometer arrangement

Also Published As

Publication number Publication date
GB8809954D0 (en) 1988-06-02

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