GB2153546A - Optical filtering devices - Google Patents

Optical filtering devices Download PDF

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Publication number
GB2153546A
GB2153546A GB8402761A GB8402761A GB2153546A GB 2153546 A GB2153546 A GB 2153546A GB 8402761 A GB8402761 A GB 8402761A GB 8402761 A GB8402761 A GB 8402761A GB 2153546 A GB2153546 A GB 2153546A
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GB
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Patent type
Prior art keywords
filters
filter
series
layers
body
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Withdrawn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
GB8402761A
Inventor
James Allister Mcquoid
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.)
Pilkington Perkin Elmer Ltd
Original Assignee
Pilkington Perkin Elmer 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

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B6/00Light guides
    • G02B6/24Coupling light guides
    • G02B6/26Optical coupling means
    • G02B6/28Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293Optical 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
    • G02B6/29346Optical 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 wave or beam interference
    • G02B6/29361Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
    • G02B6/29362Serial cascade of filters or filtering operations, e.g. for a large number of channels
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B27/00Other optical systems; Other optical apparatus
    • G02B27/10Beam splitting or combining systems
    • G02B27/1073Beam splitting or combining systems characterized by manufacturing or alignment methods
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B27/00Other optical systems; Other optical apparatus
    • G02B27/10Beam splitting or combining systems
    • G02B27/1086Beam splitting or combining systems operating by diffraction only
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B27/00Other optical systems; Other optical apparatus
    • G02B27/10Beam splitting or combining systems
    • G02B27/14Beam splitting or combining systems operating by reflection only
    • G02B27/145Beam splitting or combining systems operating by reflection only having sequential partially reflecting surfaces
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B6/00Light guides
    • G02B6/24Coupling light guides
    • G02B6/26Optical coupling means
    • G02B6/28Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293Optical 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
    • G02B6/29346Optical 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 wave or beam interference
    • G02B6/29361Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
    • G02B6/29362Serial cascade of filters or filtering operations, e.g. for a large number of channels
    • G02B6/29364Cascading by a light guide path between filters or filtering operations, e.g. fibre interconnected single filter modules

Abstract

An optical (de)multiplexer optionally has a body (3) containing a series of reflection filters, e.g. parallel holographic filters (1 to 6), which selectively reflect different narrow wavebands but transmit other wavebands to the next filter so as to separate a multi-waveband input light signal (N lambda ) into respective narrow waveband output signals ( lambda 1 to lambda 6). The filters may be sandwiched between spacers (7 to 13) formed by substrates carrying e.g. the holographic layers which have been stacked and secured together and then cut at appropriate angles to give the body (B) with suitably inclined filters. <IMAGE>

Description

SPECIFICATION Improvements in or relating to optical filtering devices This invention concerns improvements in or relating to optical filtering devices and relates more particularly to wavelength selective devices for use in demultiplexing or multiplexing systems.

It has previously been proposed to provide in a multiplexer/demultiplexer a reflective grating ar ranged so that, in demultiplexing mode, a beam of incident light having a plurality of wavelengths im pinges on the grating to be reflected therefrom as a plurality of angularly separated beams of different respective wavelengths which are received at respective spatially separated detector positions.

Such grating arrangements can be rather inefficient in terms of light usage, and also tend to be rather complex and lacking in compactness.

According to the present invention there is provided an optical filtering device comprising a series of wavelength selective reflection filters adapted to reflect different respective narrow wavebands but to transmit through the filter other wavebands reflected by other filters of the series, and arranged so that the wavebands transmitted through a reflection filter are received by the next reflection filter of the series. Such a device can be used in demultiplexing mode so that a multi-waveband input light signal, usually in the form of a collimated light beam, is incident on the first reflection filter which reflects out the respective narrow waveband to which that first filter is tuned but transmits through to the next reflection filter the other wave bands in the input signal.This next filter reflects out its respective tuned waveband but passes on the other wavebands, and subsequent filters do likewise. Preferably the filters are holographic reflectors.

The filters are preferably disposed in substantially parallel relationship and angled with respect to a predetermined direction. In demultiplexing mode that direction may be the direction of travel of the input beam, and the filters may, for exam ple, be angled at 45 degrees to that direction. The filters are preferably separated by transparent spacer elements which sandwich the filter in a solid body. Conveniently, these spacer elements may be substrates carrying layers in which the filters are formed, and these substrates can be stacked and secured together, and the body cut from the stack.

The invention further provides, from this aspect, a method of making an optical filtering device comprising the steps of stacking and securing together a series of substantially flat transparent substrates carrying respective wavelength selective filter layers adapted to reflect different respective narrow wavebands but to transmit through the filter layer other wavebands reflected by other filter layers in the series, thereby to form a solid stack with filter layers sandwiched between substrates and disposed in substantially parallel relationship, and cutting from that solid stack a body having filter layers at a desired angle to a face of the body.

Conveniently the body is substantially of rectangular parallelepiped form. The filter layers are preferably holographic and in this case, prior to stacking, the wavelength selective filter layers may be produced by exposing photosensitive layers on the substrates to interfering coherent light beams so as to produce reflection holograms in the layers.

An apparatus and method in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic representation of an optical filtering device, and Figure 2 is a schematic illustration of a manner of making the device of Figure 1.

Referring to Figure 1, the device comprises a body B of rectangular parallelepiped form containing a series of wavelength-selective reflection filters 1, 2, 3, 4, 5, 6 each adapted to reflect a respective predetermined narrow wavelength band and to transmit other wavebands which are reflected by subsequent filters in the series. The filters are basically planar and disposed in parallel relationship, being sandwiched between transparent elements 7, 8, 9, 10, 11, 12, 13 which space the filters apart in the solid body.A light input fibreoptic cable 14 is optically connected with an input end face 15 of the body and feeds into it as a collimated light beam á light input signal having a plurality of wavelength bands indicated as NA. The filters 1 to 6 are disposed in series along, and angled at 45 degrees relative to, the direction of travel of the light input beam so that each filter reflects off the respective wavelength band to which it is tuned to travel substantially at right angles to the light input direction. A series of receiving fibreoptic cables 16, 17, 18, 19, 20 and 21 are optically connected to an output face 22 of the body at positions to receive the light reflected from the respective filters.Thus the first filter 1 reflects light over a narrow waveband 1 into the receiving fibre-optic link 16 but transmits other wavebands through the filter. The second filter 2 receives the light transmitted through the first filter and reflects a narrow waveband 2 into the receiving fibre-optic link 17 but transmits other wavebands through the filter to the next filter, and so on. In this manner, each filter reflects its respective waveband from the input signal into its respective associated receiver while transmitting the remaining wavebands onwards.

The input signal NA is thus separated or demultiplexed into its component wavebands Xl, X2, X3, X4, X5 and X6 which travel as output signals along the respective fibre-optic links 16, 17, 18, 19, 20 and 21.

The filters 1 to 6 are uniform conformal holograms constructed in a manner known per se by causing interference between an incident collimated coherent light beam and a return beam reflected from a back mirror so as to produce fringes which are recorded in a photosensitive coating layer, preferably of dichromated gelatine, or a transparent substrate, prefereably of glass, the interference fringes extending generally parallel to the substrate surface. The layer may, if necessary, be subjected to further processing in order to enhance or permanently record the refractive index variations in the layer that thereby form the hologram. The hologram construction is effected in a manner such that the respective filters selectively reflect, i.e. are tuned to, the different required respective narrow wavelength bands.The planar transparent substrates carrying the holographic layers form the transparent spacing elements 7 to 12 in the eventual device.

The device shown in Figure 1 is made in a manner schematically illustrated in Figure 2. The holographic filters 1 to 6 with their respective plate-like flat substrates 7 to 12 are stacked on top of one another and cemented together, and a final cover plate 13 is cemented on top of the final filter 6. The body B of the device can then be cut from the stack as indicated by the broken line, the cuts being made at angles to the faces of the stack appropriate to the required angle of the filters 1 to 6 to the input and output faces 15 and 22 in the finished device.It will be appreciated that this angle may conveniently be 45 degrees as described above, but that other angles could be employed if desired, the input and output fibre-optic links then being suitably relatively inclined to achieve the required reception, after reflection, and the filters being tuned to effect selective reflection of the required respective narrow waveband at the angle involved.

It will further be appreciated that the receiving fibre-optic links 16 to 21 may lead to respective detectors or could be replaced by respective detectors arranged directly against the output face 22. It will also be understood that the number of filters shown and described, namely six, is given by way of illustration and example, and that the device may have as many filters as required for the number of channels to be separated, with a corresponding number of receivers. A device as described above can be very compact so that, for example, a thirty channel unit may have a body a few centimeters long.It will be appreciated that the final reflector in the device could, if desired, be a total reflector which simply reflects all that remains of the input signal into the final receiver, or alternatively the final receiver could be located against the end face of the body opposite the input face 15 to receive directly what remains of the input signal after transmission through the series of reflection filters.

The wavelengths over which the device operates may, but need not necessarily, be in the visible part of the electromagnetic spectrum, and the terms light', "optical' and the like when used herein are to be construed accordingly. The wavelengths involved could, for example, be in the ultra-violet or the infra-red and, as a particular illustrative example, the working range could be about 1.2 to 1.6 microns wavelength with a device having filters tuned to reflect respectively at 1.2, 1.3, 1.4, 1.5 and 1.6 microns.

A device as described above with holographic filters can operate with low loss throughput of the input light beam, i.e. the filters can each reflect the respective required narrow waveband and transmit the other wavebands with high efficiency. Such holographic filters are therefore highly desirable. It will be understood, however, that other types of wavelength selective filter, such as conventional interference filters, could be used, but with possi ble forfeit of efficiency.

It will also be understood that having the filters in parallel disposition can contribute to the compactness of the device and also to the simplicity and ease of manufacture, since the transparent spacer elements can be of planar plate-like form, and can conveniently be the substrates on which the filters are formed. However, if such compactness and simplicity is not of concern, the filters need not be parallel but could be relatively angled with wedge-shaped spacer elements between them and could, for example, be in alternating oppositely inclined disposition so that the output signals emerge from opposite faces of the block in alternation along the series of filters, the respective receivers then being located correspondingly.

It will further be understood that a device as described above could be used in reverse mode as a multiplexer to combine respective wavelength channels fed in through the links 16 to 21 into a multiple wavelength output through the link 14.

Claims (10)

1. An optical filtering device comprising a series of wavelength selective reflection filters adapted to reflect different respective narrow wavebands but to transmit through the filter other wavebands reflected by other filters of the series, and arranged so that the wavebands transmitted through a reflection filter are received by the next reflection filter of the series.
2. A device according to Claim 1 in which the filters are holographic reflectors.
3. A device according to Claim 1 or Claim 2 in which the filters are disposed in substantially parallel relationship and angled with respect to a predetermined direction.
4. A device according to any preceding ciaim in which the filters are separated by transparent spacer elements which sandwich the filters in a solid body.
5. A device according to Claim 5 in which the spacer elements are substrates carrying layers in which the filters are formed.
6. A method of making an optical filtering device comprising the steps of stacking and securing together a series of substantially flat transparent substrates carrying respective wavelength selective filter layers adapted to reflect different respective narrow wavebands but to transmit through the filter layer other wave bands reflected by other filter layers in the series, thereby to form a solid stack with filter layers sandwiched between substrate and disposed in substantially parallel relationship, and cutting from that solid stack a body having filter layers at a desired angle to a face of the body.
7. A method according to Claim 6 in which the body is substantially of rectangular parallelepiped form.
8. A method according to Claim 6 or Claim 7 comprising the step of producing the wavelength selective filter layers by exposing photosensitive layers on the substrates to interfering coherent light beams so as to produce reflection holograms in the layers.
9. A optical filtering device substantially as described herein with reference to Figure 1 of the accompanying drawing.
10. A method of making an optical filtering device substantially as described herein with reference to Figure 2 of the accompanying drawing.
GB8402761A 1984-02-02 1984-02-02 Optical filtering devices Withdrawn GB2153546A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8402761A GB2153546A (en) 1984-02-02 1984-02-02 Optical filtering devices

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8402761A GB2153546A (en) 1984-02-02 1984-02-02 Optical filtering devices

Publications (1)

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GB2153546A true true GB2153546A (en) 1985-08-21

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GB8402761A Withdrawn GB2153546A (en) 1984-02-02 1984-02-02 Optical filtering devices

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GB (1) GB2153546A (en)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2591764A1 (en) * 1985-12-18 1987-06-19 Smiths Industries Plc optical multiplexing system and method of use of this system
EP0240000A2 (en) * 1986-04-02 1987-10-07 Hewlett-Packard Company Apparatus for separating electromagnetic waves
FR2635590A1 (en) * 1988-08-18 1990-02-23 Kis Photo Ind Device for separating a white light beam into a plurality of elementary beams of particular color
EP0359658A2 (en) * 1988-09-12 1990-03-21 Fujitsu Limited Optical base material and optical product using the same and method of manufacturing the optical base material
US4995702A (en) * 1986-10-31 1991-02-26 Seiko Epson Corporation Projection-type display device
US6394607B1 (en) 1996-03-12 2002-05-28 Seiko Epson Corporation Polarized light separation device, method of fabricating the same and projection display apparatus using the polarized light separation device
US6404550B1 (en) 1996-07-25 2002-06-11 Seiko Epson Corporation Optical element suitable for projection display apparatus
EP1265081A2 (en) * 2001-06-06 2002-12-11 Agilent Technologies Inc., A Delaware Corporation Multi-axis interferometer with integrated optical structure and method for manufacturing rhomboid assemblies
US6751373B2 (en) 2001-04-10 2004-06-15 Gazillion Bits, Inc. Wavelength division multiplexing with narrow band reflective filters
WO2005059595A2 (en) 2003-12-15 2005-06-30 Leica Microsystems Cms Gmbh Device for the production of a light beam having several wavelengths
USRE39243E1 (en) 1996-12-18 2006-08-22 Seiko Epson Corporation Optical element, polarization illumination device, and projector
US7280570B2 (en) 2003-12-15 2007-10-09 Leica Microsystems Device for generating a light beam including multiple wavelengths
WO2009046814A1 (en) * 2007-10-02 2009-04-16 Carl Zeiss Microimaging Gmbh Mirror cascade for bundling a plurality of light sources and laser scanning microscope
JP4799420B2 (en) * 2003-12-15 2011-10-26 ライカ ミクロジュステムス ツェーエムエス ゲーエムベーハー Light beam generating apparatus including a plurality of wavelengths

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB232602A (en) *
GB2014752A (en) * 1978-01-31 1979-08-30 Nippon Telegraph & Telephone Element for use in optical multiplexer or de-multiplexer
GB2071866A (en) * 1980-03-13 1981-09-23 Marconi Co Ltd Colour selective holographic reflector
GB2089521A (en) * 1980-12-04 1982-06-23 Philips Nv Colour television camera having colour separating prism system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB232602A (en) *
GB2014752A (en) * 1978-01-31 1979-08-30 Nippon Telegraph & Telephone Element for use in optical multiplexer or de-multiplexer
GB2071866A (en) * 1980-03-13 1981-09-23 Marconi Co Ltd Colour selective holographic reflector
GB2089521A (en) * 1980-12-04 1982-06-23 Philips Nv Colour television camera having colour separating prism system

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2591764A1 (en) * 1985-12-18 1987-06-19 Smiths Industries Plc optical multiplexing system and method of use of this system
EP0240000A2 (en) * 1986-04-02 1987-10-07 Hewlett-Packard Company Apparatus for separating electromagnetic waves
EP0240000A3 (en) * 1986-04-02 1989-08-30 Hewlett-Packard Company Apparatus for separating electromagnetic waves
US4995702A (en) * 1986-10-31 1991-02-26 Seiko Epson Corporation Projection-type display device
FR2635590A1 (en) * 1988-08-18 1990-02-23 Kis Photo Ind Device for separating a white light beam into a plurality of elementary beams of particular color
EP0356349A1 (en) * 1988-08-18 1990-02-28 KIS PHOTO INDUSTRIE S.a.r.l. Device for separating a white-light beam into a plurality of elementary beams with predetermined colours
WO1990002355A1 (en) * 1988-08-18 1990-03-08 Kis Photo Industrie Device for separating a white light beam into a plurality of elementary beams of determined colour
EP0359658A2 (en) * 1988-09-12 1990-03-21 Fujitsu Limited Optical base material and optical product using the same and method of manufacturing the optical base material
EP0359658A3 (en) * 1988-09-12 1991-05-08 Fujitsu Limited Optical base material and optical product using the same and method of manufacturing the optical base material
US6394607B1 (en) 1996-03-12 2002-05-28 Seiko Epson Corporation Polarized light separation device, method of fabricating the same and projection display apparatus using the polarized light separation device
US6404550B1 (en) 1996-07-25 2002-06-11 Seiko Epson Corporation Optical element suitable for projection display apparatus
USRE39243E1 (en) 1996-12-18 2006-08-22 Seiko Epson Corporation Optical element, polarization illumination device, and projector
USRE40251E1 (en) 1996-12-18 2008-04-22 Seiko Epson Corporation Optical element, polarization illumination device, and projector
US6751373B2 (en) 2001-04-10 2004-06-15 Gazillion Bits, Inc. Wavelength division multiplexing with narrow band reflective filters
EP1265081A3 (en) * 2001-06-06 2004-07-28 Agilent Technologies Inc., A Delaware Corporation Multi-axis interferometer with integrated optical structure and method for manufacturing rhomboid assemblies
EP1619525A1 (en) * 2001-06-06 2006-01-25 Agilent Technologies Inc., A Delaware Corporation Multi-axis interferometer with integrated optical structure and method for manufacturing rhomboid assemblies
EP1265081A2 (en) * 2001-06-06 2002-12-11 Agilent Technologies Inc., A Delaware Corporation Multi-axis interferometer with integrated optical structure and method for manufacturing rhomboid assemblies
WO2005059595A3 (en) * 2003-12-15 2005-11-24 Leica Microsystems Device for the production of a light beam having several wavelengths
US7280570B2 (en) 2003-12-15 2007-10-09 Leica Microsystems Device for generating a light beam including multiple wavelengths
WO2005059595A2 (en) 2003-12-15 2005-06-30 Leica Microsystems Cms Gmbh Device for the production of a light beam having several wavelengths
JP4799420B2 (en) * 2003-12-15 2011-10-26 ライカ ミクロジュステムス ツェーエムエス ゲーエムベーハー Light beam generating apparatus including a plurality of wavelengths
WO2009046814A1 (en) * 2007-10-02 2009-04-16 Carl Zeiss Microimaging Gmbh Mirror cascade for bundling a plurality of light sources and laser scanning microscope

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