GB2295247A - Optical waveguide grating filter having two or three gratings - Google Patents

Optical waveguide grating filter having two or three gratings Download PDF

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Publication number
GB2295247A
GB2295247A GB9523489A GB9523489A GB2295247A GB 2295247 A GB2295247 A GB 2295247A GB 9523489 A GB9523489 A GB 9523489A GB 9523489 A GB9523489 A GB 9523489A GB 2295247 A GB2295247 A GB 2295247A
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United Kingdom
Prior art keywords
waveband
optical
grating
optical waveguide
blazed
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Granted
Application number
GB9523489A
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GB9523489D0 (en
GB2295247B (en
Inventor
Kevin Christopher Byron
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Nortel Networks Ltd
Original Assignee
Northern Telecom Ltd
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Filing date
Publication date
Priority claimed from GB9423105A external-priority patent/GB9423105D0/en
Application filed by Northern Telecom Ltd filed Critical Northern Telecom Ltd
Priority to GB9523489A priority Critical patent/GB2295247B/en
Publication of GB9523489D0 publication Critical patent/GB9523489D0/en
Publication of GB2295247A publication Critical patent/GB2295247A/en
Application granted granted Critical
Publication of GB2295247B publication Critical patent/GB2295247B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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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
    • G02B6/29316—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
    • G02B6/29317—Light guides of the optical fibre type
    • G02B6/29319—With a cascade of diffractive elements or of diffraction operations
    • G02B6/2932—With a cascade of diffractive elements or of diffraction operations comprising a directional router, e.g. directional coupler, circulator
    • 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
    • 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
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/124—Geodesic lenses or integrated 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
    • G02B6/29323—Coupling to or out of the diffractive element through the lateral surface of the light guide
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
    • H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
    • 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
    • G02B6/29346—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 wave or beam interference
    • G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
    • G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Plasma & Fusion (AREA)
  • Optical Communication System (AREA)
  • Optical Integrated Circuits (AREA)

Description

OPTICAL WAVEGUIDE GRATING FILTER This invention relates to optical waveguide grating filters and in particular to such filters that exhibit a relatively high degree of isolation between stop and pass bands.
A transmission type filter with a defined pass-band can be constructed in a length of single mode optical waveguide by creating in the waveguide two Bragg gratings providing stop-bands respectively on the long-wavelength side and the short wavelength side of the intended pass-band. These two Bragg gratings may be normally reflective Bragg gratings whose elements extend in parallel planes normal to the waveguide axis, in which case their stop-bands are created by reflection of light within those wavebands reversing the direction of propagation of the guided light. Alternatively, they may be blazed Bragg gratings whose grating elements extend in parallel planes inclined at an oblique angle to the waveguide axis, in which case their stop-bands are created by mode conversion of light propagating in the waveguide from the guided mode into an unguided, and hence radiating, mode or group of modes. By way of example, normally reflective Bragg gratings may be made in optical fibre waveguides by the method described in US 4,725,110, and blazed Bragg gratings by the method described in US 5,042,897. A transmission type filter of this type may be constructed to provide an isolation of about 30 dB between its stop and pass bands. A similar degree of isolation can be obtained in a reflective type filter in single mode waveguide by the use of a single normally reflective Bragg grating.
The present invention is directed to the provision of a filter affording the possibility of improved isolation.
According to one aspect of the present invention there is provided a single mode optical waveguide filter which includes the series combination comprising two optical waveguide blazed Bragg gratings optically in tandem with an optical waveguide normally reflective Bragg grating, wherein the periodicities of the three Bragg gratings are such that the blazed gratings are spectrally selectively mode coupling respectively over spectrally separated wavebands k1 and k2, while the normally reflective grating is spectrally selectively reflecting over a waveband k3 which at least compasses the spectral waveband separating waveband Xi from waveband ?, 2, and wherein the series combination is optically coupled with one port of an optical circulator or one port of a 4-port 3dB coupler.
It may be noted that the improved isolation afforded by such a structure is generated at least in part by the fact that the light transmitted by the filter makes a full double passage through each of the two blazed Bragg gratings.
Such improved isolation may for instance be required in filters for use in association with optical waveguide amplifiers for separating wanted signal from spontaneous emission noise. Another illustrative application is in wavelength division multiplexed (WDM) systems extending between one or more optical transmitters and receivers, and where the wavelength spacing of the multiplexed channels is found to be such that the side-lobes of a normally reflective Bragg filter designed for one channel register with, or at least extend into, the spectral bands of other channels. It will be appreciated that in some circumstances the presence of one of the side-lobes presents a problem, while that of the other does not. In such circumstances one of the blazed Bragg gratings can clearly be dispensed with.
Accordingly the invention also provides a single mode optical waveguide filter which includes the series combination comprising an optical waveguide blazed Bragg grating optically in tandem with an optical waveguide normally reflective Bragg grating, wherein the periodicities of the two Bragg gratings are such that the blazed grating is spectrally selectively mode coupling over spectral waveband B1, while the normally reflective grating is spectrally selectively reflecting over a waveband kB a side lobe of which extends into spectral waveband . 1, and wherein the series combination is optically coupled with one port of an optical circulator or one port of a 4-port 3dB coupler.
There follows a description of optical fibre filters embodying the invention in preferred forms. The description refers to the accompanying drawings in which: Figure 1 schematically depicts a length of single mode fibre in which there is a series combination of two blazed Bragg gratings in tandem with a normally reflective Bragg grating; Figure 2 schematically depicts the spectral transmission characteristics of the series combination of the two blazed Bragg gratings of Figure 1; Figure 3 schematically depicts the spectral reflection characteristics of the normally reflective grating of Figure 1; Figures 4 and 5 schematically depict the fibre of Figure 1 optically coupled respectively with a three-port optical circulator and with a four-port 3dB tapered fused coupler, and Figure 6 depicts a filter comprising a 3dB tapered fused fibre coupler with the arrangement of three Bragg gratings as in Figure 1 in both fibres on one side of its coupling region.
Referring to Figure 1, in the core 1 of a single mode fibre 2 are photoinduced two blazed Bragg gratings 3 and 4, and a normally reflective grating 5. The periodicities of blazed gratings 3 and 4 are such as to provide them with wavebands . i and k2 (Figure 2) over which they respectively couple light from the propagating mode guided by optical fibre 2 into radiating modes whose power is dissipated. Accordingly, for a single passage of light through the two blazed gratings 3 and 4, they provide a spectral transmission characteristic as depicted by curve 20.
Curve 39 shows the corresponding spectral reflection characteristic for the normally reflective Bragg grating 5. This Bragg grating, on its own, functions in reflection as a spectrally selective band-pass reflector reflective over a waveband 3, but typically the construction of such filters is liable to produce a spectral characteristic with side-bands 30a and 30b.
The construction of the Bragg grating 5 is such that the spectral waveband A3 over which it is selectively reflective at least compasses the waveband separating waveband B1 from waveband B2. and may be, as depicted in Figure 3, slightly larger than this. The wavebands S1 and 2 of Bragg gratings 3 and 4 are preferably chosen to compass respectively the side-bands 30a and 30b. In this way, light launched into optical fibre 2 from the end nearest grating 3, the combination exhibits a spectral reflection characteristic in which the spectral discrimination of curve 30 provided by the spectral reflective characteristic of grating 5 is twice enhanced by the spectral discrimination of curve 20 provided by the spectral transmission characteristic of gratings 3 and 4.
For use as a transmission type filter, the end of the combination nearer grating 3 is connected to a circulator 40 as depicted in Figure 4, or to one port of a 4-port 3dB optical coupler 50 as depicted in Figure 5. This coupler 50 may conveniently be constituted by a single mode tapered fused optical fibre type 3dB coupler. The arrangement of Figure 5 provides an additional 6dB loss which can be avoided by a Mach Zhender type arrangement as depicted in Figure 6 in which identical grating elements 3,4 and 5 are located in both fibres of a 3dB tapered fused coupler 60. In the case of the normally reflective gratings 5, it will be appreciated the light reflected by these gratings will interfere, and hence the phase relationship between the two reflected signals is critical in ensuring that when they interfere, they do so in a manner that directs substantially no output power back into the input port. Such a phase relationship can be ensured by the method described in the specification of United Kingdom Patent Application No. 2 283 831 that involves creating the gratings in both fibres simultaneously at a point in the coupler where the two fibres remain tacked together in side-by-side contact so that the resulting gratings are automatically formed optically equidistant from the coupling region of the coupler.

Claims (10)

  1. CLAIMS 1. A single mode optical waveguide filter which includes the series combination comprising two optical waveguide blazed Bragg gratings (3,4) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the three Bragg gratings are such that the blazed gratings are spectrally selectively mode coupling respectively over spectrally separated wavebands kl and A2, hile the normally reflective grating is spectrally selectively reflecting over a waveband A which at least compasses the spectral waveband separating waveband Xl from waveband A2, and wherein the series combination is optically coupled with one port of an optical circulator (40).
  2. 2. A single mode optical waveguide filter which includes the series combination comprising two optical waveguide blazed Bragg gratings (3,4) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the three Bragg gratings are such that the blazed gratings are spectrally selectively mode coupling respectively over spectrally separated wavebands A1 and A2 hile the normally reflective grating is spectrally selectively reflecting over a waveband AB which at least compasses the spectral waveband separating waveband ? l from waveband A2, and wherein the series combination is optically coupled with one port of a 4-port 3dB coupler (50).
  3. 3. An optical fibre filter including a 3dB tapered fused optical fibre coupler (60) having an optical coupling region formed between a pair of single mode fibres, on one side of which coupling region, in both fibres is formed the series combination comprising two optical fibre blazed Bragg gratings (3,4) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the three Bragg gratings are such that the blazed gratings are spectrally selectively mode coupling respectively over spectrally separated wavebands l and A 2, hile the normally reflective grating is spectrally selectively reflecting over a waveband ? WX which at least compasses the spectral waveband separating waveband B1 from waveband A2.,
  4. 4. A single mode optical waveguide filter which includes the series combination comprising an optical waveguide blazed Bragg grating (3) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the two Bragg gratings are such that the blazed grating is spectrally selectively mode coupling over spectral waveband A1, hile the normally reflective grating is spectrally selectively reflecting over a waveband k3 a side lobe of which extends into spectral waveband k1. and wherein the series combination is optically coupled with one port of an optical circulator (40).
  5. 5. A single mode optical waveguide filter which includes the series combination comprising an optical waveguide blazed Bragg grating (3) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the two Bragg gratings are such that the blazed grating is spectrally selectively mode coupling over spectral waveband A1, hile the normally reflective grating is spectrally selectively reflecting over a waveband . 3 a side lobe of which extends into spectral waveband . 1, and wherein the series combination is optically coupled with one port of a 4-port 3dB coupler (50).
  6. 6. An optical fibre filter including a 3dB tapered fused optical fibre coupler (60) having an optical coupling region formed between a pair of single mode fibres, on one side of which coupling region, in both fibres is formed the series combination comprising an optical fibre blazed Bragg grating (3) optically in tandem with an optical waveguide normally reflective Bragg grating (5), wherein the periodicities of the two Bragg gratings are such that the blazed grating is spectrally selectively mode coupling over spectral waveband A1, while the normally reflective grating is spectrally selectively reflecting over a waveband Ax a side lobe of which extends into spectral waveband A1.
  7. 7. An optical fibre filter as claimed in any preceding claim, wherein the Bragg gratings are photo-induced gratings.
  8. 8. An optical fibre filter substantially as hereinbefore described with reference to the accompanying drawings.
  9. 9. A method of operating an optical transmission system which method of operation includes transmission of optical signals from at least one transmitter to at least one receiver through one or more filters as claimedQn any preceding claim.
  10. 10. A method of filtering an optical signal wherein the signal is fed through an optical circulator (40) or 4-port 3dB coupler (50) and into an optical transmission path and traverses a first filter (3,4) in the path effective to remove at least some unwanted wavelengths by reflecting them out of the transmission path, passing the signal to a second filter (5) effective to reflect the wanted signal back through the first filter whereby to further remove unwanted wavelength from the transmission path before being fed back through the optical circulator or 4-port 3dB coupler.
GB9523489A 1994-11-16 1995-11-16 Optical waveguide grating filter Expired - Fee Related GB2295247B (en)

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Application Number Priority Date Filing Date Title
GB9423105A GB9423105D0 (en) 1994-11-16 1994-11-16 Optical wave grating filter
GB9523489A GB2295247B (en) 1994-11-16 1995-11-16 Optical waveguide grating filter

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GB2295247A true GB2295247A (en) 1996-05-22
GB2295247B GB2295247B (en) 1996-11-27

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998036302A1 (en) * 1997-02-14 1998-08-20 Aofr Pty. Ltd. Optical devices and methods
WO1999000683A1 (en) * 1997-06-27 1999-01-07 The University Of Sydney Narrow transmission bandpass filters utilising bragg grating assisted mode conversion
US5915052A (en) * 1997-06-30 1999-06-22 Uniphase Telecommunications Products, Inc. Loop status monitor for determining the amplitude of the signal components of a multi-wavelength optical beam
US5982964A (en) * 1997-06-30 1999-11-09 Uniphase Corporation Process for fabrication and independent tuning of multiple integrated optical directional couplers on a single substrate
US6020986A (en) * 1997-11-21 2000-02-01 Jds Uniphase Corporation Programmable add-drop module for use in an optical circuit
US6031849A (en) * 1997-11-14 2000-02-29 Jds Uniphase Corporation High power three level fiber laser and method of making same
US6151157A (en) * 1997-06-30 2000-11-21 Uniphase Telecommunications Products, Inc. Dynamic optical amplifier
AU731587B2 (en) * 1997-02-14 2001-04-05 Aofr Pty Limited Optical devices and methods
US6226424B1 (en) 1997-09-19 2001-05-01 Uniphase Telecommunications Products, Inc. Integrated wavelength-select transmitter

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5210807A (en) * 1992-06-29 1993-05-11 The United States Of America As Represented By The Secretary Of The Navy Variable wide band fiber optic delay line
EP0572169A1 (en) * 1992-05-29 1993-12-01 AT&T Corp. Article comprising an otpical waveguide with in-line refractive index grating
GB2275347A (en) * 1993-02-19 1994-08-24 Univ Southampton Optical waveguide grating formed by transverse optical exposure

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0572169A1 (en) * 1992-05-29 1993-12-01 AT&T Corp. Article comprising an otpical waveguide with in-line refractive index grating
US5210807A (en) * 1992-06-29 1993-05-11 The United States Of America As Represented By The Secretary Of The Navy Variable wide band fiber optic delay line
GB2275347A (en) * 1993-02-19 1994-08-24 Univ Southampton Optical waveguide grating formed by transverse optical exposure

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998036302A1 (en) * 1997-02-14 1998-08-20 Aofr Pty. Ltd. Optical devices and methods
AU731587B2 (en) * 1997-02-14 2001-04-05 Aofr Pty Limited Optical devices and methods
WO1999000683A1 (en) * 1997-06-27 1999-01-07 The University Of Sydney Narrow transmission bandpass filters utilising bragg grating assisted mode conversion
US6463194B1 (en) 1997-06-27 2002-10-08 The University Of Sydney Narrow transmission bandpass filters utilizing bragg grating assisted mode conversion
US5915052A (en) * 1997-06-30 1999-06-22 Uniphase Telecommunications Products, Inc. Loop status monitor for determining the amplitude of the signal components of a multi-wavelength optical beam
US5982964A (en) * 1997-06-30 1999-11-09 Uniphase Corporation Process for fabrication and independent tuning of multiple integrated optical directional couplers on a single substrate
US6151157A (en) * 1997-06-30 2000-11-21 Uniphase Telecommunications Products, Inc. Dynamic optical amplifier
US6226424B1 (en) 1997-09-19 2001-05-01 Uniphase Telecommunications Products, Inc. Integrated wavelength-select transmitter
US6031849A (en) * 1997-11-14 2000-02-29 Jds Uniphase Corporation High power three level fiber laser and method of making same
US6020986A (en) * 1997-11-21 2000-02-01 Jds Uniphase Corporation Programmable add-drop module for use in an optical circuit

Also Published As

Publication number Publication date
GB9523489D0 (en) 1996-01-17
GB2295247B (en) 1996-11-27

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732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 20041116