WO1998019406A1 - Improvements in optical polarisation scrambling - Google Patents

Improvements in optical polarisation scrambling Download PDF

Info

Publication number
WO1998019406A1
WO1998019406A1 PCT/GB1997/002939 GB9702939W WO9819406A1 WO 1998019406 A1 WO1998019406 A1 WO 1998019406A1 GB 9702939 W GB9702939 W GB 9702939W WO 9819406 A1 WO9819406 A1 WO 9819406A1
Authority
WO
WIPO (PCT)
Prior art keywords
polarisation
modulator
optical phase
amplitude
phase modulator
Prior art date
Application number
PCT/GB1997/002939
Other languages
French (fr)
Inventor
Ian Haxell
Original Assignee
Alcatel Alsthom Compagnie General D'electricite
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 Alcatel Alsthom Compagnie General D'electricite filed Critical Alcatel Alsthom Compagnie General D'electricite
Publication of WO1998019406A1 publication Critical patent/WO1998019406A1/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/532—Polarisation modulation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  in optical waveguides, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
    • G02F1/0139—Polarisation scrambling devices; Depolarisers

Definitions

  • the present invention relates to optical polarisation scrambling and more particularly but not exclusively, to an integrated polarisation scrambling device
  • SOP state of polarisation
  • a polarisation scrambler comprising an optical phase modulator which requires no misalignment in polarisation state to that which emerges from an amplitude modulator waveguide
  • the polarisation scrambler comprises a birefringent element arranged to receive light from the optical phase modulator having a launch angle which substantially bisects the fast and slow axis of the birefringent element
  • the birefringent element is adjusted to one half of the phase modulation period of the optical phase modulator
  • phase modulation depth ⁇ of the optical phase modulator is substantially 0 38275 x pi radians
  • the amplitude modulator is a Mach Zehnder modulator
  • the present invention makes use of the relative ease with which Mach Zehnder amplitude modulators and phase modulators may be integrated onto a substrate such as L1NDO3
  • the polarisation scrambler is constructed by launching the phase modulated light into a birefringent element
  • the birefringent element causes polarisation state changes in each side band depending on its optical frequencx
  • launch angle and phase modulation depth are of sufficient magnitude then complete depola ⁇ sation may be achieved
  • Figure 1 is a block diagram of a polarisation scrambler in accordance with the present invention, and.
  • FIG. 2 is a more detailed illustration of the polarisation scrambler of Figure 1 Detailed description
  • depolarisation is achieved by launching phase modulated light into a birefringent element 1.
  • the birefringent element may readily be constructed from a length of polarisation maintaining fibre which can be obtained from manufacturers such as Corning, 3M or LYCOM
  • the launch angle to the birefringent elements slow axis must be tightly controlled to be 45 degrees. If the phase modulation depth and birefringence are of sufficient magnitude then complete depolarisation will occur.
  • the phase modulator 2 creates a series of spectral lines with power spectral density given by the following expression:
  • FIG. 2 illustrates the polarisation scrambler in more detail
  • the polarisation scrambler comprises a Mach Zehnder amplitude modulator 3 and a phase modulator 2 integrated on a L1NDO3 substrate
  • This integrated device is available from manufacturers such as Uniphase Telecommunications Products
  • the device receives light from for example a semiconductor laser 4
  • the driver amplifiers 5 and 6 for the Mach Zehnder modulator 3 and the phase modulator 2 respectively are arranged so that the electrical level is sufficient to amplitude modulate the light beam to the desired exstmction and phase modulate the light to the required modulation depth respectiveh
  • An oscillator 7 is provided to control the operation of the phase modulator and which operates at a frequency of double that of the bit rate fk. of electrical data from a data source 8 used to drive the Mach Zehnder modulator 3
  • Incident light propagates through the combined Mach Zehnder - phase modulator device At this point the light is broadened by the phase modulator 2 at a modulating frequency of twice the bit rate of the data
  • the emerging light propagates through the output fibre tail 9 where it is aligned with the slow axis of the fibre It then encounters a 45 degree rotation brought about at the splice 10 with the birefringent fibre 1 (the slow axes are 45 degrees out of alignment)
  • the splice alignment can be achieved initially by visual alignment of the optical fibre stress rods with anv splicing rig (not shown) which has angular torsional alignment of the fibre
  • Exact adjustment can be achieved using either a polarisation extinction meter without phase modulation or a degree of polarisation meter when phase modulation is applied
  • the birefringent delay is 1/4 f then the first odd order side bands will emerge from the birefringent fibre 1 orthogonal to the fundamental as is shown in the figure
  • the drive level to the phase modulator 2, and therefore the phase modulation depth is then adjusted so that the power levels in the odd order side bands are equal to the even order Alternatively, it can be adjusted correctly using a degree of polarisation meter.
  • the integrated design has an advantage of cost, reliability, space and insertion loss over a discrete amplitude modulator and polarisation scrambler
  • the device may also offer advantages in line- width broadening over the discrete design for complete polarisation

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Integrated Circuits (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

A polarisation scrambler is provided which includes an optical phase modulator (2) and an amplitude waveguide (3). The optical phase modulator (2) requires no misalignment in polarisation state to that which emerges from the amplitude modulator waveguide (3). In particular, the polarisation scrambler comprises an optical phase modulator (2), and an amplitude modulator waveguide (3) integrated on a single substrate, with an output fibre (9) coupled to a birefringent fibre (1).

Description

IMPROVEMENTS IN OPTICAL POLARISATION SCRAMBLING
Field of Invention
The present invention relates to optical polarisation scrambling and more particularly but not exclusively, to an integrated polarisation scrambling device
Background of Invention
The effects of polarisation dependent hole-burning and polarisation dependent loss can be reduced by modulating the state of polarisation (SOP) of an arbitraπly polarised optical signal being launched into the transmission path periodically through a predetermined sequence of polarisation states The sequence of polarisation states is selected such that on average the launched modulated signal excites substantially all possible polarisation states with substantially equal probability
One arrangement which is known to us is to add a polarisation scrambler after an optical amplitude modulator to depolarise the signal light Since polarisation scramblers require 45 degree optical alignment to the waveguide this necessarily means that the polarisation scrambler cannot be an integrated optical device with the amplitude modulator
Summary of the Invention
According to the present invention there is provided a polarisation scrambler comprising an optical phase modulator which requires no misalignment in polarisation state to that which emerges from an amplitude modulator waveguide
Preferablv the two devices are integrated on a single substrate Preferably, the polarisation scrambler comprises a birefringent element arranged to receive light from the optical phase modulator having a launch angle which substantially bisects the fast and slow axis of the birefringent element
Preferably, the birefringent element is adjusted to one half of the phase modulation period of the optical phase modulator
Preferably the phase modulation depth β of the optical phase modulator is substantially 0 38275 x pi radians
Preferably, the amplitude modulator is a Mach Zehnder modulator
The present invention makes use of the relative ease with which Mach Zehnder amplitude modulators and phase modulators may be integrated onto a substrate such as L1NDO3 The polarisation scrambler is constructed by launching the phase modulated light into a birefringent element The birefringent element causes polarisation state changes in each side band depending on its optical frequencx When the birefringence, launch angle and phase modulation depth are of sufficient magnitude then complete depolaπsation may be achieved
Brief Description of the Drawings
An example of the present invention will now be described with reference to the accompanying drawings, in which
Figure 1 is a block diagram of a polarisation scrambler in accordance with the present invention, and.
Figure 2 is a more detailed illustration of the polarisation scrambler of Figure 1 Detailed description
Referring to Figure 1 , depolarisation is achieved by launching phase modulated light into a birefringent element 1. The birefringent element may readily be constructed from a length of polarisation maintaining fibre which can be obtained from manufacturers such as Corning, 3M or LYCOM The launch angle to the birefringent elements slow axis must be tightly controlled to be 45 degrees. If the phase modulation depth and birefringence are of sufficient magnitude then complete depolarisation will occur.
The phase modulator 2 creates a series of spectral lines with power spectral density given by the following expression:
Figure imgf000005_0001
where β represents the phase modulation depth Jn = nth order Bessel function
If the birefringent element 1 is adjusted to one half of the phase modulation period (with a launch angle bisecting the fast and slow axes) then alternate spectral lines will emerge with orthogonal states of polarisation. To reduce the degree of polarisation to zero then all that is required for the power in each of the orthogonal states to be equal. This will occur when the following expression is met for sinusoidal phase modulation:
Figure imgf000005_0002
= ∑ J P) This can be shown to occur when the phase modulation depth, β=0 38275* radians
Figure 2 illustrates the polarisation scrambler in more detail The polarisation scrambler comprises a Mach Zehnder amplitude modulator 3 and a phase modulator 2 integrated on a L1NDO3 substrate This integrated device is available from manufacturers such as Uniphase Telecommunications Products The device receives light from for example a semiconductor laser 4 The driver amplifiers 5 and 6 for the Mach Zehnder modulator 3 and the phase modulator 2 respectively are arranged so that the electrical level is sufficient to amplitude modulate the light beam to the desired exstmction and phase modulate the light to the required modulation depth respectiveh An oscillator 7 is provided to control the operation of the phase modulator and which operates at a frequency of double that of the bit rate fk. of electrical data from a data source 8 used to drive the Mach Zehnder modulator 3
Incident light propagates through the combined Mach Zehnder - phase modulator device At this point the light is broadened by the phase modulator 2 at a modulating frequency of twice the bit rate of the data The emerging light propagates through the output fibre tail 9 where it is aligned with the slow axis of the fibre It then encounters a 45 degree rotation brought about at the splice 10 with the birefringent fibre 1 (the slow axes are 45 degrees out of alignment) The splice alignment can be achieved initially by visual alignment of the optical fibre stress rods with anv splicing rig (not shown) which has angular torsional alignment of the fibre Exact adjustment can be achieved using either a polarisation extinction meter without phase modulation or a degree of polarisation meter when phase modulation is applied
If the birefringent delay is 1/4 f then the first odd order side bands will emerge from the birefringent fibre 1 orthogonal to the fundamental as is shown in the figure The drive level to the phase modulator 2, and therefore the phase modulation depth, is then adjusted so that the power levels in the odd order side bands are equal to the even order Alternatively, it can be adjusted correctly using a degree of polarisation meter.
The amount of birefringence required can be approximated by the following expression
4Δ/ '
where τ - differential group delay , and. Δ/ = bit rate (fh)
The integrated design has an advantage of cost, reliability, space and insertion loss over a discrete amplitude modulator and polarisation scrambler The device may also offer advantages in line- width broadening over the discrete design for complete polarisation

Claims

CLAIMS:
1 A polarisation scrambler comprising an optical phase modulator and an amplitude waveguide in which the optical phase modulator requires no misalignment in polarisation state to that which emerges from the amplitude modulator waveguide.
2. A polarisation scrambler according to claim 1 , further comprising a birefringent element arranged to receive light from the optical phase modulator having a launch angle which substantially bisects the fast and slow axis of the birefringent element
3 A polarisation scrambler according to claim 2, in which the birefringent element is adjusted to one half of the phase modulation period of the optical phase modulator
4 A polarisation scrambler according to claim 2 or 3. in which the phase modulation depth β of the optical phase modulator is substantially 0 38275 x pi radians
5 A polarisation scrambler according to any preceding claim, in which the optical phase modulator and amplitude waveguide are integrated on a single substrate
6 A polarisation scrambler according to claim 5, in which the substrate is LiNb03 or GaAs
7 A polarisation scrambler according to any preceding claim, in which the amplitude modulator is a Mach Zehnder modulator
PCT/GB1997/002939 1996-10-25 1997-10-24 Improvements in optical polarisation scrambling WO1998019406A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9622245A GB2318646A (en) 1996-10-25 1996-10-25 Optical polarisation scrambling
GB9622245.0 1996-10-25

Publications (1)

Publication Number Publication Date
WO1998019406A1 true WO1998019406A1 (en) 1998-05-07

Family

ID=10801949

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1997/002939 WO1998019406A1 (en) 1996-10-25 1997-10-24 Improvements in optical polarisation scrambling

Country Status (2)

Country Link
GB (1) GB2318646A (en)
WO (1) WO1998019406A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100371750C (en) * 2002-04-09 2008-02-27 奥普林克通信公司 Depolarizer

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2789827A1 (en) * 1998-11-19 2000-08-18 Cit Alcatel SUPPRESSION OF THE BRILLOUIN EFFECT BY AMPLITUDE MODULATION AND POLARIZATION INTERFERENCE
FR2786638A1 (en) * 1998-11-26 2000-06-02 Cit Alcatel SUPPRESSION OF THE RAMAN EFFECT BY MODULATING POLARIZATION

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0668672A1 (en) * 1994-02-18 1995-08-23 Alcatel Submarcom Optical communication system with polarisation scrambler
EP0781001A1 (en) * 1995-12-21 1997-06-25 PIRELLI CAVI S.p.A. Modulated and depolarized optical signal transmitter
EP0809368A1 (en) * 1996-05-23 1997-11-26 Alcatel Submarine Networks Optical amplifier optical communication system with gain dependent on the input signal polarization

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4384760A (en) * 1980-12-15 1983-05-24 Bell Telephone Laboratories, Incorporated Polarization transformer
US5611005A (en) * 1996-04-26 1997-03-11 Lucent Technologies, Inc. High-speed polarization scrambler with adjustable chirp

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0668672A1 (en) * 1994-02-18 1995-08-23 Alcatel Submarcom Optical communication system with polarisation scrambler
EP0781001A1 (en) * 1995-12-21 1997-06-25 PIRELLI CAVI S.p.A. Modulated and depolarized optical signal transmitter
EP0809368A1 (en) * 1996-05-23 1997-11-26 Alcatel Submarine Networks Optical amplifier optical communication system with gain dependent on the input signal polarization

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
HABBAB I M I ET AL: "Polarization-switching techniques for coherent optical communications", JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 6, no. 10, October 1988 (1988-10-01), pages 1537 - 1548, XP000009769 *
HEISMANN F: "Compact electro-optic polarization scramblers for optically amplified lightwave systems", JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 14, no. 8, August 1996 (1996-08-01), pages 1801 - 1814, XP000630976 *
SANTORO M A ET AL: "Polarization scrambling using a short piece of high-birefringence optical fiber and a multifrequency laser diode", JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 12, no. 2, February 1994 (1994-02-01), pages 288 - 293, XP000469791 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100371750C (en) * 2002-04-09 2008-02-27 奥普林克通信公司 Depolarizer

Also Published As

Publication number Publication date
GB9622245D0 (en) 1996-12-18
GB2318646A (en) 1998-04-29

Similar Documents

Publication Publication Date Title
CA2200236C (en) High-speed polarization scrambler with adjustable chirp
EP0630122B1 (en) Apparatus and method employing fast polarization modulation to reduce effects of polarization hole burning and polarization dependent loss
US8761607B2 (en) Optical system for reducing stimualted brillouin scattering by controllably changing polarization direction of an optical signal
US6459518B1 (en) Optical transmitting apparatus
US5995685A (en) Optical modulator and an optical modulating method
US5365531A (en) Apparatus and method for initializing an optical-fiber laser for mode locking
CA2229516C (en) Compensation of dispersion
EP0639900B1 (en) Improved apparatus and method employing polarization modulation to reduce effects of polarization hole burning and/or polarization dependent loss
JPH09197354A (en) Synchronous polarization and phase modulation using periodic waveform including complicated higher harmonic for high-performance optical transmission system
WO1988003278A1 (en) Optical signal modulation device
US5911016A (en) Polarization scrambler and integrated optical circuit making use thereof
EP0867743A3 (en) Optical fiber modulator having an optical fiber having poled portion serving as an electrooptic element and method for making same
JP3249884B2 (en) Apparatus and method for modulating polarized light signal
WO1998019406A1 (en) Improvements in optical polarisation scrambling
US5619364A (en) Depolarized source for high power operation of an integrated optical modulator
Heismann et al. High-speed polarization scrambler with adjustable phase chirp
US6333808B1 (en) Optical signal scrambling
US5808768A (en) Optical telecommunications system
JP3485226B2 (en) Polarization scrambling method and polarization modulator
US6947617B2 (en) Polarized wave scrambler and optical signal transmission apparatus
EP1043848A2 (en) Improvements in or relating to optical signal scrambling
JPH0843776A (en) Optical modulator
EP0200889A3 (en) Electro-optical deviator for a laser

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FI FR GB GR IE IT LU MC NL PT SE

121 Ep: the epo has been informed by wipo that ep was designated in this application
NENP Non-entry into the national phase

Ref country code: JP

Ref document number: 1998520179

Format of ref document f/p: F

122 Ep: pct application non-entry in european phase