As the ultra-high frequency nature of lightwave corresponds to great potential in wideband signal processing, nextgeneration electronic information systems of surveillance, radar and communications is promised with photonic signal processing systems. However, the sophisticated photonic systems suffer from various hardware defects, which severely limit the performance of signal processing. By introducing the emerging deep learning technology into the photonic system, the hardware defects can be recovered by the trained neural networks. Using different modified neural networks, we have demonstrated high-accuracy photonic analog-to-digital converters, Brillouin instantaneous frequency measurement, and high-fidelity photonic radar receivers. The demonstrated systems with simple configurations can outperform the conventional photonic processing system with complex configurations. Note that the adoption of neural networks may cause additional time delay to the signal flow. Photonic neural network accelerators (PNNs) become a promising solution to realize real-time signal processing. We propose and experimentally demonstrate several system architectures of photonic convolutional neural networks. The photonic dot product unit architecture implements the basic operation in convolution neural networks. And an optical patching scheme is demonstrated to enhances the power efficiency of the input ports in PNNs. Performance evaluations show that the proposed PNN architectures possess potential advantages of energy efficiency and computational power. We believe that, by combining the technical advantages of photonic signal processing and PNN acceleration, intelligent photonic signal processing systems with high-performance real-time wideband signal processing capabilities can be realized. Moreover, the large-scale photonic integration technology promises the fabrication of such hybrid systems in the future.
We propose a novel method to multiply the pulse repetition rate of actively mode-locked fiber laser (AMLL) by spectrum-slicing and time-division-multiplexing for photonic analog-to-digital converters (PADC). Self-phase modulation (SPM) is employed to broaden the spectrum in order to obtain more parallel channels. The SPM induces additional phase jitter that degrades PADC’s performance. We theoretically and experimentally show phase jitter can be effectively reduced by precise control of the tunable true-time delay array. Sampling clock of 40 GHz or higher with low phase jitter is achieved based on 10-GHz AMLL, which can be used to realize high performance PADC.
This paper introduces a novel pulse-compression optical time domain reflectometer (OTDR) by utilizing linear frequency modulation (LFM) pulse-compression technology. The working principle of the pulse-compression OTDR is demonstrated. The spatial resolution is determined by the sweeping range of the pulsed LFM instead of the pulse width, which solves the dilemma of spatial resolution and measurement range in the conventional OTDR. A preliminary experiment of the pulse-compression OTDR is performed, providing 55 cm spatial resolution and 5.4 km measurement range under 2 μs pulse, 221 MHz LFM sweeping range, and 100 kHz linewidth laser diode. It is expectable to achieve a spatial resolution of less than 1 cm and dozens-kilometer measurement range by tens of GHz LFM sweeping ranges via microwave photonics.
KEYWORDS: Computing systems, Passive optical networks, Network architectures, Optical engineering, Reliability, Time division multiplexing, Field programmable gate arrays, Telecommunications, Data transmission, Control systems
A passive optical network (PON) based real-time Ethernet (PONRTE), which can take advantage of PON features such as broad bandwidth, high reliability, and easy maintenance to satisfy the determination and real-time requirements of high performance industrial applications, is proposed. The protocol model and network architecture having a compatible physical layer and MAC layer with Ethernet passive optical network are presented for the proposed PONRTE. A fixed periodic time slot allocation mechanism including a synchronic time division multiplexing transmission and an asynchronic data transmission is adopted to guarantee the determination and real-time of the communication. A simple and easy to implement time synchronization approach, where the starting time of the first transmission slot of an access node is synchronized by a relative time synchronization while the starting time of subsequent slots is determined by the fixed period and a dynamic time synchronization, is designed to support the fixed time slot allocation mechanism and avoid the collision in PONRTE. A 100 Mb/s PONRTE experimental testbed with 16 access nodes and a time allocation period of 240 μs is demonstrated. The results show that the experimental PONRTE can work stably and reliably with a frame loss ratio less than 10 −7 .
A novel scheme is proposed to measure Brillouin gain spectrum in an optical fiber combining Brillouin gain and loss
effects. A dual-parallel Mach-Zehnder modulator is used to generate upshifted afterward downshifted single sideband
with suppressed carrier by periodically chopping the dc bias. The two successive single sidebands serve as Brillouin
pump and probe waves to amplify and absorb the carrier wave for lock-in detecting of the net Brillouin gain between
Brillouin gain and loss effects. The signal-to-noise ratio of the cost-effective measurement system with fewer optical
devices is twofold enhanced. Distributed strain sensing ability with a nominal spatial resolution of 1.6 cm is
experimentally demonstrated by utilization of this scheme into a Brillouin optical correlation domain analysis system.
We have demonstrated distributed discrimination of strain and temperature by localizing and scanning both the
Stimulated Brillouin scattering (SBS) and the Brillouin dynamic grating (BDG) along a polarization maintaining fiber,
with elongated measurement range. The localization and scanning is performed by a correlation domain technique,
whose measurement range is restricted by the distance between consecutive correlation peaks. To overcome this
restriction, we applied a temporal gating scheme to the system, enlarging the measurement range from ~8 m to ~500 m.
Here, we report the results confirming the effectiveness of this scheme in a system operated by a single laser source and
demonstrate strain-temperature discrimination when strain or temperature is applied to segments on the 500-m-long fiber
under test.
We propose a single-ended distributed temperature or strain sensor based on stimulated Brillouin scattering (SBS) in a
polarization-maintaining (PM) optical fiber. Pump and probe waves with orthogonal polarization states enter one fiber
end and generate SBS assisted by a polarization beam splitter and a PM isolator at the other fiber end. Unlike the
previously-reported method, neither an optical filter nor a sophisticated beat-lock-in detection is necessary. Single-ended
distributed sensing of temperature or strain is experimentally demonstrated with the measurement range and the spatial
resolution of 200 m/16 cm, 56 m/5 cm, or 5.6 m/5 mm, respectively.
We propose and demonstrate a novel method to discriminate strain and temperature by simultaneous measurements of
birefringence and Brillouin frequency shift in a PANDA-type polarization-maintaining fiber. A high-accuracy
discrimination of 3~4 με and 0.02~0.03 °C is realized.
The distribution of temperature-induced changes in Brillouin frequency shift and that of birefringence-determined
frequency deviation in the spectrum of SBS-generated dynamic grating in a PMF have been measured with 1.2-meter
spatial resolution and 110-meter measurement range. Synchronously controlled sinusoidal frequency-modulations are
applied into two laser sources that are used for pump (probe) light and readout light, respectively, enabling distributed
generation and detection of the dynamic grating.
We propose Brillouin optical correlation-domain reflectometry (BOCDR), which can measure the strain and/or
temperature distribution along an optical fiber by controlling the interference of continuous lightwaves. In pulse-based
conventional Brillouin optical time-domain reflectometry (BOTDR), it is difficult to achieve a spatial resolution less than
1 m in principle, and the measurement time is as long as 5-10 minutes. On the contrary, the continuous-wave-based
BOCDR can exceed the limit of 1-m resolution, and realize much faster measurement and random access to measuring
position. A 40-cm spatial resolution was experimentally demonstrated with 50-Hz sampling rate.
We investigate the influence of the intrinsic thermal stress in optical fibers on their Brillouin gain spectra (BGS). We apply our newly-proposed modal analysis based on two-dimensional finite element method (2D-FEM) to a single-mode optical fiber (SMF) and a PANDA polarization-maintaining fiber (PMF) that are drawn from preforms of the same design except the stress applying parts in PMF. We evaluate both the optical and the acoustic effective velocities and their corresponding fields, and then quantify the BGS of the fibers. The BGS of the two fibers are measured for comparison and the measured results are in good agreement with the calculated ones. The difference in the feature of BGS between the two fibers is found dominantly originated from the effect upon the acoustic velocity due to 2D intrinsic thermal stress in the PMF.
The repetition rate multiplication based on the temporal fractional Talbot effect is one of the solutions to realize the high-repetition frequency optical pulse. In this paper, varying even-multiplications due to the theoretical different group velocity dispersions (GYDs) of the linearly chirped fiber Bragg grating (LCFBG) are calculated by another way. The characteristics of repetition-rate-multiplied pulse tram caused by different values of deviation of GVD are discussed. And the range within which the deviation of GVD must be limited during the fabricating of LCFBG for the case of M=4 is 5% when the FWHM of the original pulse train is 12 PS. The cascaded multiplication of repetition-rate using the same or different GVD LCFBGs are also theoretically explained.
The repetition-rate multiplication of a pulse train outside the laser cavity by using all-pass filters is discussed. Schemes based on the phase responses of optical all-pass filters for multiplying the repetition-rate of an optical pulse train are presented and the design of the required all-pass filters is also presented. These methods, in principle, can produce a uniform pulse train with a multiplied pulse repetition-rate without energy loss. The error analyses of these methods are discussed and the error ranges ofthe parameters are given.
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