Nec Corporation

Nec Laboratories America, Inc.

Yue-Kai Huang

Ezra Ip

Fatih Yaman

Shaoliang Zhang

Ting Wang

Philip N Ji

Junqiang Nochur Hu

Giovanni Milione

Dayou Qian

Shuji Murakami

Ming-Fang Huang

Yoshihisa Inada

Eduardo Rodriguez

Jiakai Yu

Robert Saperstein

Weiyang Mo

Narayan Prasad

Neda Cvijetic

Yoshiaki Aono

Takanori Inoue

Yue Tian

Kohei Nakamura

Yaowen Li

Tsutomu Tajima

Hussam Batshon

Shalabh Gupta

Shinsuke Fujisawa

Ben Wu

Shaoling Zhang

Yechi Ma

Philip Nan Ji

Disclosed is a forward phase method using regular narrow line width CW laser, to cover the acoustic band with reduced processing speed, while tolerant laser frequency drift. A narrow linewidth CW laser is used to launch its power into an optical fiber at a transmitter side. At a receiver side, another narrow linewidth CW laser is used to coherently detect the received signal. The detected signal, which includes both X and Y polarizations, each having in-phase and quadrature to represent a 'complex' channel, are connected to an ADC's inputs. Signal processing following the ADC inputs and extracts the phase change of the acoustic band.

Laser frequency drift compensation in forward distributed acoustic sensing

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS) systems, methods, and structures that advantageously sense/monitor intra-data center operations using self-coherent detection. Advantageously, sensing signal(s) and data signal(s) are optically multiplexed such that the sensing signal(s) are generated and detected using the same optoelectronic components as data generation and detection while requiring only minimal changes to transponder arrangements and no additional bandwidth to digital-to-analog converters (DAC) or analog-to-digital converters (ADC).

Distributed fiber optic sensing enabled self-coherent detection for data centers

Aspects of the present disclosure describe systems and methods that advantageously enable vibration-induced optical phase measurement at a centralized optical line terminal (OLT) in a PON architecture. In sharp contrast to existing distributed fiber sensing systems and methods, the optical phase measurements of the present disclosure do not rely on back scattering mechanisms and maintain a sufficient optical signal to noise ratio (OSNR) even after round-trip splitting loss in the PON.

Vibration sensing over passive optical networks (PONs) using forwarding optical phase retrieval and time-domain multiplexed (TDM) switching

Earthquake detection via fiber sensing is provided using using a supervisory path of submarine cables wherein the supervisory system/path of a submarine optical cable conveys portion(s) of an optical signal back to an origin location periodically—i.e., at every repeater location. Advantageously, since it is known where a returning signal is coming from, a resolution equivalent to an undersea span length may be determined—which is sufficient for wide area disturbances such as earthquakes. The returned signal is sufficiently strong such that the signal-to-noise ratio of a returned/received signal is not limited by the ASE noise of the amplifiers. The returned signal is much larger as compared to a normal distributed acoustic sensing (DAS) return signal since the return signal according to aspects of the present disclosure is directed backward via an optical coupler/reflector/circulator having a much larger coupling ratio as compared to normal Rayleigh back scattering utilized in DAS.

Fiber sensing using supervisory path of submarine cables

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS)/distributed acoustic sensing (DAS) systems, methods, and structures exhibiting a sensitivity enhancement via MIMO sampling and phase recombination.

Distributed acoustic sensing sensitivity enhancement using MIMO sampling and phase recombination

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS) systems, methods, and structures that advantageously provide DFOS and WDM communications over amplified, multi-span optical WDM optical telecommunications facilities using all Raman amplification and coding schemes. Our all-Raman amplification operates stably—without isolators—and provides sufficient gain to compensate for fiber span loss for both DFOS signals and WDM channel signals—at the same time. Furthermore, our inventive techniques employ signal coding, such as MB-TGD-OFDR for DAS, and we operate our DFOS operation power at a much lower power level as compared to pulse interrogation techniques. With improved OSNR and reduced power using signal coding along with our distributed Raman amplification, our DFOS systems can co-exist with WDM communication channels on the same amplified multi-span fiber optic links over great distances.

Long distance distributed fiber optic sensing (DFOS) and WDM communications over repeated fiber spans using all-raman amplification and coding schemes

Aspects of the present disclosure directed to frequency drift compensation for coded-DAS systems that use chirped pulses as a probe signal. Our inventive approach estimates timing jitter by correlating the amplitude of the estimated Rayleigh impulse response of every frame with a reference frame, and then re-aligns each frame by the estimated timing jitter. As the amount of timing jitter varies within a frame, every frame is divided into blocks where all samples have similar timing jitter, and perform timing jitter estimation and compensation on a block-by-block, frame-by-frame basis using an overlap-and-save method. Tracking of a slowly changing channel is enabled by allowing the reference frame to be periodically updated.

Frequency-drift compensation in chirped-pulse-based distributed acoustic sensing

Aspects of the present disclosure describe improved distributed acoustic sensing using dynamic range suppression of optical time domain reflectometry either by using a feedback loop comprising optical and electrical elements or using a nonlinear element in the electrical domain after coherent detection. When using a feedback loop, the amplitude of the periodic waveform of coherent OTDR can be inverted. This allows optical pre-compensation of the received optical signal before coherent detection with the goal of minimizing amplitude dynamic range. Alternatively, a nonlinear element in the electrical domain can reduce amplitude dynamic range before sampling by analog-to-digital converters (ADC).

Distributed acoustic sensing using dynamic range suppression

Aspects of the present disclosure describe systems, methods. and structures for vibration detection using phase recovered from an optical transponder with coherent detection. Advantageously, our systems, methods, and structures leverage contemporary digital coherent receiver architecture in which various adaptive DSP operations performed to recover transmitted data track optical phase. The phase is extracted at low overhead cost, allowing a digital coherent transponder to perform vibration detection/monitoring as an auxiliary function to data transmission. Demonstration of vibration detection and localization based on the extraction of optical phase from payload-carrying telecommunications signal using a coherent receiver in a bidirectional WDM transmission system is shown and described.

Vibration detection using phase recovered from an optical transponder with coherent detection

Aspects of the present disclosure are directed to laser interferometric systems, methods, and structures exhibiting superior laser phase noise tolerance particularly in seismic detection applications wherein laser requirements are advantageously relaxed by employing a novel configuration wherein the same laser which generates an outgoing signal is coherently detected using the same laser as local oscillator and fiber turnarounds are employed that result in the cancellation and/or mitigation of undesired mechanical vibration.

Laser noise reduction for laser interferometry

Aspects of the present disclosure are directed to alternative repeater design(s) that advantageously improve signal-to-noise of distributed acoustic sensing (DAS) systems using coherent detection of Rayleigh backscatter in multi-span links including inline amplification that may be employed—for example—in undersea submarine systems. The repeater designs incorporate Rayleigh combine units (RCU) and Rayleigh drop units (RDU) to reduce Rayleigh backscatter loss as Rayleigh signal(s) is/are routed to a link that propagates the backscatter signal in an opposite direction relative to interrogation pulse(s).

Repeater design for distributed acoustic sensing on multispan fiber links

A spatial averaging method for a coherent distributed acoustic sensing (DAS) system that employs differential beating and polarization combining of signals for two locations along a length of optical sensing fiber to determine phase change in-between every location along the length of the optical sensing fiber and a moving average using polarization combining output to reduce any Rayleigh fading before phase determination.

Spatial averaging method for coherent distributed acoustic sensing

A distributed optical fiber sensing (DOFS)/distributed acoustic sensing (DAS) method employing polarization diversity combining and spatial diversity combining for a DOFS/DAS system wherein the polarization diversity combining determines a temporal average product for each beating product, determines one having a max average power, rotates that one having max average power for its phase shift to produce a reference, determines a phase difference for each beating product as compared to the reference, compensates any phase difference such that all beating products exhibit a well-aligned phase; and combining the beating products; and wherein the spatial diversity combining uses the combined beating products for each location, determines a temporal average power, determines a location having a greatest average power; and combines the results and provides an indicia of the combined result(s).

Polarization diversity combining method in coherent DAS maintaining phase continuity

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS) systems, methods, and structures that advantageously overcome problems encountered when operating DFOS systems over operational telecommunications facilities namely, cross-phase modulation, and uneven amplitude profiles through the use of a novel constant amplitude coded DFOS employing suppressed out-of-band signaling.

Suppressed out-of-band level for increasing loss margin and stable ABC operation of coded DFOS system

Aspects of the present disclosure describe Rayleigh fading mitigation via short pulse coherent distributed acoustic sensing with multi-location beating-term combination. In illustrative configurations, systems, methods, and structures according to the present disclosure employ a two stage modulation arrangement providing short interrogator pulses resulting in a greater number of sensing data points and reduced effective sectional length. The increased number of data points are used to mitigate Rayleigh fading via a spatial combining process, multi-location-beating combining (MLBC) which uses weighted complex-valued DAS beating results from neighboring locations and aligns phase signals of each of the locations, before combining them to produce a final DAS phase measurement. Since Rayleigh scattering is a random statistic, the MLBC process allows capture of different statics from neighboring locations with correlated vibration/acoustic signal. The combined DAS results minimize a total Rayleigh fade, in both dynamic fading and static fading scenarios.

Growing community of inventors

Princeton, NJ, United States of America

Yue-Kai Huang