Wavelet convolutional neural network for robust and fast temperature measurements in Brillouin optical time domain reflectometry.

In this paper, a wavelet convolutional neural network (WNN) consisting of a one-dimensional (1D) convolutional neural network and a self-adaptive wavelet neural network has been proposed and demonstrated experimentally for temperature measurement in a Brillouin optical time domain reflectometry (BOTDR) system. Based on the analysis of the system noise, it follows the Gaussian white noise distribution along the time-related sensing distance. The impact of the noise in time-domain on the measured Brillouin gain spectra (BGSs) could be neglected, so that the BGSs in the fiber can be regarded as a series of 1D input data of the proposed WNN. Different self-adaptive wavelet activation functions connected to each output of the full-connection network are adopted to realize the multi-scaled analysis and the scale translation, which can obtain more local characteristics in frequency-domain. The output extracted by the WNN is Brillouin frequency shift (BFS), which presents linearity correlation to the actual temperature. Considering the multi-parameters including different frequency ranges, signal-to-noise-ratios (SNRs), BFSs and spectral widths (SWs), a general model of the proposed WNN is trained to handle more extreme cases, in which it doesn't require retraining for different single-mode (SM) optical fibers in BOTDR sensing system. The performances of the WNN are compared with other two techniques, the Lorentzian curve fitting based on Levenberg-Marquardt (LM) algorithm and the basic neural network (NN) containing input and output layers together with two hidden layers. Both the simulated and measured results show that the WNN has better robustness and flexibility than the LM and the NN. Besides, the computational accuracy of the WNN is improved and the fluctuation of that is slighter, especially when the SNR is less than 11 dB. Moreover, the WNN takes approximately 0.54 s to measure the temperature from the 18,000 collected BGSs transmitted through the 18 km SM optical fiber. The calculating time of the WNN is greatly reduced by three orders of magnitude in comparison with that of the LM, and is comparable to that of the NN. It proves that the proposed WNN may provide a feasible or even better scheme for the robust and fast temperature measurement in BOTDR system.

Multi-parameter measurement of a multi-point high-frequency vibration signal in an OFDR system.

The phase cross-correlation function of an optical frequency domain reflectometry (OFDR) system is proposed to detect a multi-point vibration event, which is verified in detail by theoretical simulation and experiment. An OFDR system based on a non-tunable laser source with digital sweep frequency is developed. It is verified experimentally that the location and frequency resolution of multi-point high-frequency vibration can be detected by analyzing the phase cross-correlation function of the sensing signal. High-frequency signals of 50 kHz and 20 kHz are located and separated on the 8 km optical fiber. The frequency resolution is 1.26 kHz, and the minimum spatial error is 11.5 m.

Higher-order-mode assisted silicon-on-insulator 90 degree polarization rotator.

We propose and analyze a 90 degrees polarization rotator based on wave coupling through an intermediate, multimode, axially uniform waveguide. The coupling efficiency of the x- and y-polarized fundamental modes between the horizontal and vertical rectangular waveguides is remarkably enhanced with the help of the TE(01) mode in the multimode waveguide. The polarization rotator has a very short (21-microm) conversion length with a 17.22 dB extinction ratio. It also exhibits a 68-nm bandwidth for polarization conversion efficiency above 90%.

Data quality dependencies in microring-based DPSK transmitter and receiver.

An ultra-small silicon-based microring modulator and filter were proposed to generate and demodulate NRZ DPSK at 10 Gb/s. In this paper, we analyze performance dependencies of the modulator and demodulator under different operating conditions, such as variable laser linewidth, phase shift, demodulator offset and receiver bandwidth. Data quality of the microring-based DPSK transceiver can be optimized with eye-opening improvement of up to 7 dB. Transmission performance of the all-microring-based DPSK signal over a 70-km single mode fiber is compared to that of DPSK using a Mach-Zehnder modulator and a delay-line interferometer.

Coupled-ring-resonator-based silicon modulator for enhanced performance.

A compact silicon coupled-ring modulator structure is proposed. Two rings are coupled to each other, and only one of these rings is actively driven and over-coupled to a waveguide, which enables high modulation speed. The resultant notch filter profile is steeper than that of the single ring and has exhibited a smaller resonance shift and lower driving electrical power. Simulation results include: (i) potentially 60-Gb/s non-return-to-zero (NRZ) data modulation and over 20-dB extinction ratio can be achieved by shifting the active ring by a 20 GHz resonance shift, (ii) the frequency chirp of the modulated signals can be adjusted by varying the coupling coefficient between the two rings, and (iii) dispersion tolerance at 0.5-dB power penalty is extended from 18 to 85 ps/nm, for a 40-Gb/s NRZ signal.

Microring-based modulation and demodulation of DPSK signal.

Ultra-small modulator and demodulator for 10 Gb/s differential phase-shift-keying (DPSK), using silicon-based microrings, are proposed. A single-waveguide microring modulator with over-coupling between ring and waveguide generates a DPSK signal, while a double-waveguide microring filter enables balanced DPSK detection. These modulator and demodulator are characterized. A trade-off between pattern dependence of the Duobinary signal and alternate-mark inversion signal power in demodulator design is discussed. Power penalty of the proposed approach is 0.8 dB relative to baseline using conventional modulation and demodulation techniques.

Embedded ring resonators for microphotonic applications.

We propose a new type of optical resonator that consists of embedded ring resonators (ERRs). The resonators exhibit unique amplitude and phase characteristics and allow designing compact filters, modulators, and delay elements. A basic configuration of the ERRs with two rings coupled in a point-to-point manner is discussed under two operating conditions. An ERR-based microring modulator shows a high operation speed up to 30 GHz. ERRs with distributed coupling are briefly described as well.

Monolithic modulator and demodulator of differential quadrature phase-shift keying signals based on silicon microrings.

Silicon microring resonators are proposed to achieve ultrasmall differential quadrature phase-shift keying modulators and demodulators operated at 20 Gb/s, which may require a dramatically reduced chip size. The modulators are characterized in terms of the carrier transit time and misalignment of the driving signals, while the demodulation performance is analyzed in terms of the bandwidth and frequency detuning of the demodulator. A bit-error rate of <10(-9) is achieved using all microring-based devices in the back-to-back case.