WO2021247771A1 - Mesure précise pour la diffusion de brillouin à ondes acoustiques guidées - Google Patents

Mesure précise pour la diffusion de brillouin à ondes acoustiques guidées Download PDF

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Publication number
WO2021247771A1
WO2021247771A1 PCT/US2021/035545 US2021035545W WO2021247771A1 WO 2021247771 A1 WO2021247771 A1 WO 2021247771A1 US 2021035545 W US2021035545 W US 2021035545W WO 2021247771 A1 WO2021247771 A1 WO 2021247771A1
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WO
WIPO (PCT)
Prior art keywords
laser
gawbs
noise
light
arrangement
Prior art date
Application number
PCT/US2021/035545
Other languages
English (en)
Inventor
Fatih Yaman
Eduardo Rodriguez
Shinsuke Fujisawa
Hussam BATSHON
Kohei Nakamura
Takanori Inoue
Yoshihisa Inada
Takaaki Ogata
Original Assignee
Nec Laboratories America, Inc.
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
Priority claimed from US17/336,280 external-priority patent/US12034482B2/en
Application filed by Nec Laboratories America, Inc. filed Critical Nec Laboratories America, Inc.
Priority to JP2022574505A priority Critical patent/JP7504233B2/ja
Publication of WO2021247771A1 publication Critical patent/WO2021247771A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
    • G01M11/333—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face using modulated input signals
    • 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
    • G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
    • G02B6/4401—Optical cables
    • G02B6/4415—Cables for special applications
    • G02B6/4427—Pressure resistant cables, e.g. undersea cables
    • 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
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/077—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using a supervisory or additional signal
    • H04B10/0775—Performance monitoring and measurement of transmission parameters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2537—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to scattering processes, e.g. Raman or Brillouin scattering
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/63—Homodyne, i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal

Definitions

  • optical communications systems employing optical fiber have become the backbone of modem communications and an enabling technology for innumerable contemporary services.
  • optical fiber facilities and supporting components located undersea (i.e., submarine).
  • systems, methods, and structures according to aspects of the present disclosure employ a homodyne receiver which advantageously simplifies measurement processing and avoids any dynamic range limitations by suppressing a large carrier.
  • systems, methods, and structures according to aspects of the present disclosure determine an accurate estimation of noise level(s) as compared to the carrier by utilizing a secondary laser.
  • systems, methods and structures according to aspects of the present disclosure determine an accurate measurement of GAWBS noise even over short lengths of optical fiber while - at the same time - simultaneously providing a measurement of both polarization components of GAWBS noise.
  • systems, methods and structures according to aspects of the present disclosure advantageously suppress the large carrier by using band-pass filters, which dramatically improve the dynamic range of the measurement. Additionally, systems, methods, and structures according to aspects of the present disclosure employ a secondary laser that advantageously allows for an accurate calibration of noise level as compared to the carrier - without sacrificing dynamic range. Finally, systems, methods, and structures according to aspects of the present disclosure provide the simultaneous measurement of both polarization components of GAWBS which is a most important check of such measurements.
  • FIG. 1 shows a schematic diagram of a simplified illustrative example heterodyne measurement method using an RF spectrum analyzer according to the prior art
  • FIG. 3 shows a plot of Power Spectral Density vs. Frequency showing a comparison of back-to-back measurements illustrating the impact of a Band Pass Filter (BPF) according to aspects of the present disclosure
  • FIGs comprising the drawing are not drawn to scale.
  • undersea optical fiber cable - such cables include a plurality of fibers each fiber configured to convey additional data/traffic.
  • the data carrying capacity of an optical fiber cable such as an undersea cable is proportional to the number of individual optical fibers comprising the cable.
  • ASE amplified-spontaneous emission
  • a narrow linewidth laser is first launched into a fiber under test (FUT).
  • Output is directed to a photodiode after combining with a second narrow linewidth laser.
  • the illustrative configuration may include amplifiers and/or filters to condition the signal.
  • GAWBS noise is generated in all polarizations, and this configuration shown in the figure measures GAWBS noise only in a polarization that is aligned with the polarization of the local oscillator (in FIG 1 this duty is assigned to laser2). Accordingly, to measure GAWBS in both polarization(s) the PC needs to be adjusted carefully to measure total GAWBS in two separate measurements. Third, even narrow linewidth lasers have laser phase noise that is large enough to affect the measurement of the GAWBS. Using two separate lasers means doubling such noise level, which will reduces the sensitivity of the measurement. Finally, employing two separate lasers means that their frequencies are not locked. That means, frequency and phase drift between the two lasers need to be digitally estimated and removed, which adds one more possible route for affecting the measurement sensitivity.
  • FIG. 2 shows a schematic diagram of an illustrative measurement arrangement according to aspects of the present disclosure.
  • a PC is included in the signal path - it is not necessary.
  • a contemporary coherent receiver is a ubiquitous device in optical communication and a hybrid in the coherent receiver takes as input the local oscillator (LO) and the signal.
  • LO local oscillator
  • the beating in the 4 quadratures are detected by 4 balanced photo-diodes.
  • the beating signals are passed through RF band-pass filters and. after filtering, the 4 beating signals are sampled by an ADC. Note that all the phase, amplitude and polarization information regarding the signal with respect to the LO is contained in these 4 beating signals.
  • BPFs located after the coherent receiver improve the sensitivity of our measurement configuration. They advantageously allow the shifting of the dynamic range of the measurement to that range exhibiting GAWBS noise, and it also removes noise from ASE-ASE beating.
  • GAWBS noise extends to about 1 GHz away from the CW laser, which is oftentimes referred to as the carrier.
  • the optical BPF’s located after the erbium-doped fiber amplifiers (EDFAs) filter out ASE noise, however, in practice it is difficult to find ASE filters having band-pass bandwidths as narrow as 2 GHz. Typically they tend to be as wide as 50 GHz.
  • one advantage of using BPFs is that it allows for using practical and low cost optical BPFs, while also allowing the use of a low sampling rate ADC, at the same time preventing deterioration from out-of-band ASE noise.
  • GAWBS noise can extend further or less than 1 GHz.
  • the BPFs higher rejection edge can be reduced or increased as required according to the FUT.
  • the ratio of the GAWBS noise peaks to the carrier level is typically larger than 60 dB. This means the measurement noise floor should be close to 80 dB below the carrier level to exhibit a sufficient precision - which is difficult to achieve. As such, this is - in effect - a limitation of the dynamic range. As a solution, the DC portion can be rejected which contains the carrier power.
  • FIG 3 shows an example of a measurement, where the FUT is removed and the carrier and the noise floor in the back-to-back configuration. Without the BPF, there is a large DC contribution which comes from the DC with higher noise floor. Suppressing the DC with a BPF shows that the noise floor is reduced but the DC carrier can no longer be measured within the same measurement.
  • the GAWBS noise power is only meaningful relative to the carrier. With the carrier removed from the measurement, how can we relate the measured GAWBS noise level to the carrier level? Even though one can calibrate this in separate measurements, it is better to have a self-calibrating scheme, where instabilities or drifts between separate measurements which can inject further uncertainties into the measurements can be avoided.
  • Laser-cal is another narrow-band laser which is combined with the original laser before entering the FUT.
  • the power level of the Laser-cal is adjusted to be about 30 dB below the Laser.
  • Its polarization in general can be totally arbitrary as compared to the Laser however, to simplify the digital processing, it can advantageously be aligned to the Laser. This can simply be obtained by using PM components for combining the two lasers.
  • Frequency of Laser-cal is shifted with respect to the laser in such a way that it is outside of the bandwidth where the GAWBS tones are measured, but just inside the passband of the BPFs.
  • FIG 4 shows how the signal will appear in a spectral domain.
  • GAWBS window As shown in FIG 4 as the window that contains all the GAWBS tones desired to be measured. For transmission systems what matters is the total GAWBS noise power experienced by the signal.
  • the GAWBS tones typically have a maximum around 100-300 MHz, and beyond that the power of the tones decreases away from the carrier.
  • the Laser-cal and GAWBS can be simultaneously measured without requiring such a large dynamic range as before.
  • the power level of the GAWBS tones can be compared to the Laser-cal which can be used to as a calibration point to relate the GAWBS power to the carrie r power.
  • Laser-cal is not locked to the carrier. That means its frequency and phase will drift compared to the carrier within the measurement time window.
  • all we need is the total power of the Laser-cal, and we are not interested in its instantaneous frequency. Therefore, we can keep the measurement window almost arbitrarily long to improve sensitivity as needed, so long as any frequency drift is not too large that it would overlap with the GAWBS window. Such is the case for most commonly used lasers for communications.
  • the measurement is no longer limited by the dynamic range of the measuring equipment, while we can directly calibrate the GAWBS power to the carrier.
  • FIG 5 shows a laser spectrum in a back-to-back configuration, i.e., the
  • the signal is received by the ADC.
  • a power spectral density (PSD) can be calculated. If the received power is comparable to the equipment noise floor, the noise floor can also be measured and removed from the PSD. In addition, measurement set up has a frequency dependent response, that response can also be measured and removed as well.
  • FIG 6(A) shows the PSD after the PSD obtained after 48-km-long single mode fiber.
  • the ADC noise floor was measured without signal, and subtracted from the signal PSD.
  • this example shown in the figure is for the signal with the polarization that is aligned with that of the carrier. Since GAWBS creates a symmetric spectrum around DC, only the positive spectrum is shown. It can be clearly seen that laser phase noise has a large contribution to the PSD especially for lower frequencies. For accurate estimation of GAWBS noise, this contribution should be accurately estimated and removed.
  • FIG 6(B) shows PSD after the laser phase noise is removed.
  • the criterion for choosing the GAWBS window is such that it includes all the GAWBS peaks that are higher than 20 dB below the highest GAWBS peak.
  • FIG 7 shows the measurement result after FUT, which is the same as that shown in FIG 6(B), however, in FIG 7 the Laser-cal is also shown.
  • the power level of the Laser-cal was 29 dB lower than power level of the carrier. It is located nominally 900 MHz away from the carrier, which is just outside of the GAWBS bandwidth and inside the passband of the BPF.
  • the Laser-cal is a narrow linewidth laser similar to the carrier, however it appears broadened as it is not frequency/phase locked to the carrier. Within the measurement time, Laser-cal’ s phase and frequency drift with respect to the carrier. However, since we are only interested in its power, we just integrate the total power under the Laser-cal. Therefore, we do not need any signal processing to remove frequency variations of either the carrier or the Laser-cal. Note that in FIG 7, only the polarization components parallel to the carrier is shown. In general the Laser-cal may not be parallel to the carrier. In that case, one needs to add all the power of the Laser-cal in both polarization components.
  • FIG 2 shows the measurement configuration in which our measurement also includes contribution from ASE.
  • the span length is not too long ⁇ 80km, the contribution of ASE would be below the instrument noise floor, and it can be neglected.
  • GAWBS can advantageously be measured reliably for fibers as short as just a few kilometers. Being able to measure GAWBS for such short sections of fiber allows for estimating GAWBS from short samples of prototypes which reduces the cost of new fiber and cable development.
  • GAWBS noise is created by acoustic modes in the fiber.
  • ROm modes only creates GAWBS noise that is parallel in polarization to the carrier, and this contribution is known as the polarized contribution.
  • Tr2m generates GAWBS noise that is both parallel and orthogonal to the carrier, and this contribution is known as the unpolarized contribution.
  • Tr2m contributes twice as much to the orthogonal polarization as the polarized contribution. Therefore, we can use this relation as a “sanity” check on our measurements if we can separate the GAWBS noise into two contributions that are parallel and orthogonal to the carrier, which our invention can do in a single process.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Optical Communication System (AREA)

Abstract

Des aspects de la présente invention concernent des systèmes, des procédés et des structures permettant la mesure précise de la diffusion de Brillouin à ondes acoustiques guidées dans des systèmes et des installations de transmission par fibres optiques.
PCT/US2021/035545 2020-06-03 2021-06-02 Mesure précise pour la diffusion de brillouin à ondes acoustiques guidées WO2021247771A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2022574505A JP7504233B2 (ja) 2020-06-03 2021-06-02 導波音響波型ブリルアン散乱の正確な測定

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US202063704927P 2020-06-03 2020-06-03
US63/704,927 2020-06-03
US202163141068P 2021-01-25 2021-01-25
US63/141,068 2021-01-25
US17/336,280 US12034482B2 (en) 2021-06-01 Accurate measurement for guided acoustic-wave Brillouin scattering
US17/336,280 2021-06-01

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20150168253A1 (en) * 2012-06-13 2015-06-18 Omnisens Sa Sensing system and methods for distributed brillouin sensing
US20150377656A1 (en) * 2013-03-29 2015-12-31 Filippo Bastianini Apparatus for interrogating distributed stimulated brillouin scattering optical fibre sensors using a quickly tuneable brillouin ring laser
JP2019161246A (ja) * 2018-03-07 2019-09-19 国立大学法人東北大学 デジタルコヒーレント伝送システム
KR102048459B1 (ko) * 2018-05-21 2019-11-25 한국과학기술연구원 이벤트 고속 검출 및 정밀 측정이 가능한 이중 브릴루앙 분포형 광섬유 센싱 시스템 및 브릴루앙 산란을 사용한 센싱 방법
JP2019203859A (ja) * 2018-05-25 2019-11-28 日本電信電話株式会社 ブリルアン周波数シフトを測定する装置及び方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20150168253A1 (en) * 2012-06-13 2015-06-18 Omnisens Sa Sensing system and methods for distributed brillouin sensing
US20150377656A1 (en) * 2013-03-29 2015-12-31 Filippo Bastianini Apparatus for interrogating distributed stimulated brillouin scattering optical fibre sensors using a quickly tuneable brillouin ring laser
JP2019161246A (ja) * 2018-03-07 2019-09-19 国立大学法人東北大学 デジタルコヒーレント伝送システム
KR102048459B1 (ko) * 2018-05-21 2019-11-25 한국과학기술연구원 이벤트 고속 검출 및 정밀 측정이 가능한 이중 브릴루앙 분포형 광섬유 센싱 시스템 및 브릴루앙 산란을 사용한 센싱 방법
JP2019203859A (ja) * 2018-05-25 2019-11-28 日本電信電話株式会社 ブリルアン周波数シフトを測定する装置及び方法

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