High-speed Optical Signal Processing Research Articles

Phase noise of Kerr soliton dual microcombs.

Dissipative Kerr soliton microcombs are believed to be a promising technique to build a dual-comb source for applications including precision laser metrology, fast laser spectroscopy, and high-speed optical signal processing. In this Letter, we conduct a detailed experimental investigation on the phase coherence between two on-chip Kerr soliton microcombs, where the underlying physical and technical origins that lead to the mutual phase noise between microcombs are analyzed. Moreover, the techniques of 2-point locking and optical frequency division are explored to enhance the dual-microcomb phase coherence, and we demonstrate the best phase noise down to -50 dBc/Hz at 1-Hz offset, -90 dBc/Hz at 1-kHz offset, and -120 dBc/Hz at 1-MHz offset. Our study provides a basic reference for both fundamental studies and practical applications of Kerr soliton dual microcombs that entail high mutual phase coherence.

Graphene-enhanced polarization-insensitive all-optical wavelength conversion based on four-wave mixing.

All-optical wavelength conversion technology based on four-wave mixing (FWM) effect is a promising development need of the modern high-speed optical signal processing system. In this work, we report on the polarization insensitive four-wave mixing based on graphene for all optical wavelength conversion. To overcome the polarization sensitivity of FWM, a dual-pump configuration was proposed based on the combination of graphene and the optical fibers. Our experimental results illustrate that by using the dual pump configuration, the FWM-based wavelength conversion efficiency, can be enhanced by graphene with about 8 dB when the state of polarization of the two pumps are parallel. This proposed all-optical wavelength converter based on graphene may provide a new approach for the next generation optical communications and signal processing.

InAs/InP quantum dot mode-locked laser with an aggregate 12.544 Tbit/s transmission capacity.

Chip-scale optical frequency comb sources are ideal compact solutions to generate high speed optical pulses for applications in wavelength division multiplexing (WDM) and high-speed optical signal processing. Our previous studies have concentrated on the use of quantum dash based lasers, but here we present results from an InAs/InP quantum dot (QDot) C-band passively mode-locked laser (MLL) for frequency comb generation. By using this single-section QDot-MLL we demonstrate an aggregate line rate of 12.544 Tbit/s 16QAM data transmission capacity for both back-to-back (B2B) and over 100-km of standard single mode fiber (SSMF). This finding highlights the viability for InAs/InP QDot lasers to be used as a low-cost optical source for large-scale networks.

Design and analysis of an optical three-input AND gate using a photonic crystal fiber.

In this paper, a three-input AND logic gate is employed using a 2D photonic crystal T-shaped waveguide using a silicon in an air medium. In contrast to other gates, the key functions of employing an AND gate are recognition, error correction, code conversion, data encryption/decryption, and arithmetic operations. The proposed footprint is 8.4µm×5.4µm, which is a modest size. The performance of the proposed AND gate is investigated by employing the finite-difference time-domain approach, and the outputs are validated at wavelength (λ) of 1.55 µm. The outcomes clearly show the higher contrast ratio (CR) of 24.533 dB, and the worst case CR of is 8.6 dB; transmission efficiency values for minimum and maximum values are 19.6% and 142%; reaction time is 26 fs; insertion loss is 1.52 dB; and bit rate is 38.4 Tbps, which can be used in high-speed optical signal processing. The suggested circuit's primary objective is to consume minimal space and possess high CR.

On-chip silicon photonic controllable 2\u2009\xd7\u20092 four-mode waveguide switch

Multimode optical switch is a key component of mode division multiplexing in modern high-speed optical signal processing. In this paper, we introduce for the first time a novel 2 × 2 multimode switch design and demonstrate in the proof-of-concept. The device composes of four Y-multijunctions and 2 × 2 multimode interference coupler using silicon-on-insulator material with four controllable phase shifters. The shifters operate using thermo-optic effects utilizing Ti heaters enabling simultaneous switching of the optical signal between the output ports on four quasi-transverse electric modes with the electric power consumption is in order of 22.5 mW and the switching time is 5.4 µs. The multimode switch exhibits a low insertion loss and a low crosstalk below − 3 dB and − 19 dB, respectively, in 50 nm bandwidth in the third telecom window from 1525 to 1575 nm. With a compact footprint of 10 µm × 960 µm, this device exhibits a relatively large width tolerance of ± 20 nm and a height tolerance of ± 10 nm. Furthermore, the conceptual principle of the proposed multimode switch can be reconfigurable and scalable in multifunctional on-chip mode-division multiplexing optical interconnects.

New approach to design D-flip flop and two bit down counter using optical micro-ring resonator for high speed data processing

Optical switches play a key role in the field of high-speed optical fiber communication and signal processing. Present work shows the design and implementation of D-flip flop and a two-bit optical counter using optical micro ring resonator (OMRR). The design of the proposed model is developed by considering nonlinear material-based resonators. Here, three OMRR based optical switches are used to design the D-flip flop circuit thereafter two-bit optical counter is implemented using the modeled D-flip flop. The mathematical model of the D-flip flop circuit is provided in the Z-domain by unit delay signal processing approach. The effectiveness of the proposed D flip flop and two-bit down counter circuit is described in the present work. The accuracy and feasibility of the circuits are determined by estimating various performance parameters during simulation.

CMOS-compatible high-index doped silica waveguide with an embedded silicon-nanocrystal strip for all-optical analog-to-digital conversion

Passive all-optical signal processors that overcome the electronic bottleneck can potentially be the enabling components for the next-generation high-speed and lower power consumption systems. Here, we propose and experimentally demonstrate a CMOS-compatible waveguide and its application to the all-optical analog-to-digital converter (ADC) under the nonlinear spectral splitting and filtering scheme. As the key component of the proposed ADC, a 50 cm long high-index doped silica glass spiral waveguide is composed of a thin silicon-nanocrystal (Si-nc) layer embedded in the core center for enhanced nonlinearity. The device simultaneously possesses low loss (0.16 dB/cm at 1550 nm), large nonlinearity (305  W−1/km at 1550 nm), and negligible nonlinear absorption. A 2-bit ADC basic unit is achieved when pumped by the proposed waveguide structure at the telecom band and without any additional amplification. Simulation results that are consistent with the experimental ones are also demonstrated, which further confirm the feasibility of the proposed scheme for larger quantization resolution. This demonstrated approach enables a fully monolithic solution for all-optical ADC in the future, which can digitize broadband optical signals directly at low power consumption. This has great potential on the applications of high-speed optical communications, networks, and signal processing systems.

Analysis of an I/O metal grating coupler for organic membrane photonic integrated circuits

We propose organic membrane photonic integrated circuits (OMPICs), which can collectively integrate various optical elements into a thin film and can realize wearable devices and high-speed optical signal processing by making more flexible photonic integrated circuits. In OMPICs, vertical grating couplers are effective as input and output ports. In this study, we propose three types of structure: an SU-8/Cytop grating coupler, a metal grating coupler, and a modified metal grating coupler with a metal mirror and an SU-8/Cytop distributed Bragg reflector. We analyze the optical coupling efficiency in each case.

Nonlinear Optics in Hydrogenated Amorphous Silicon

Nonlinear photonic circuits with the ability to generate and process signals all-optically have emerged in the past decade with superior performance to electronic chips. In particular, crystalline silicon has become a leading platform for integrated nonlinear optics. More recently, hydrogenated amorphous silicon emerged as a promising alternative to crystalline silicon due to its large nonlinearity. In this paper, we review recent research on nonlinear optical interactions in and applications of hydrogenated amorphous silicon nanophotonic devices. This new material platform enables the capability of multilayer CMOS-compatible photonic-integrated circuits with low-power requirements for high-speed optical signal processing.

All-Optical Signal Processing Techniques for Flexible Networks

This tutorial highlights challenges and opportunities in achieving efficient flexible optical networks. Optical signal processing may potentially increase network flexibility because of its functions’ transparency, tunability, and reconfigurability. We review recent advances in high-speed optical signal processing techniques that might enable flexible networks. Various optical approaches that enable key functions are discussed, including format conversion, increases in spectral efficiency, and phase-sensitive operations. We also discuss the potential utilization of basic enabling technologies, such as optical frequency combs and optical nonlinear devices.

Low-Cost AWG-Based Fundamental Frequency Mode-Locked Semiconductor Laser for Multichannel Synchronous Ultrashort Pulse Generation

We report a low-cost arrayed waveguide grating (AWG) based mode-locked semiconductor laser designed for multichannel synchronous ultrashort pulse generation. Both the fabrication process and chip characterization results are discussed in detail. By deploying a bundle active-passive photonic integration technique, only one regrowth step is required to monolithically integrate a semiconductor optical amplifier array, an AWG, and a common saturable absorber on a single InP substrate. Combined with a shallow ridge waveguide structure common for both active and passive sections and formed in a single dry etching process, our process allows the fabrication of the monolithic photonic integrated circuit chip in a much simplified process. The fabricated device demonstrated multichannel mode-locking operation at a repetition frequency of 4.1 GHz in a fundamental mode-locking regime under both passive mode-locking and synchronous hybrid mode-locking conditions. Timing jitter as low as 1 ps was obtained, and preliminary pulse chirping characteristics were analyzed by a frequency-resolved optical gating technique. The exhibited performance makes our device a promising candidate as a multichannel ultrashort pulse optical source for future cost-effective high-speed optical networking and signal processing applications.

Efficient frequency comb generation in AlGaAs-on-insulator

The combination of nonlinear and integrated photonics has recently seen a surge with Kerr frequency comb generation in micro-resonators as the most significant achievement. Efficient nonlinear photonic chips have myriad applications including high speed optical signal processing, on-chip multi-wavelength lasers, metrology, molecular spectroscopy, and quantum information science. Aluminium gallium arsenide (AlGaAs) exhibits very high material nonlinearity and low nonlinear loss when operated below half its bandgap energy. However, difficulties in device processing and low device effective nonlinearity made Kerr frequency comb generation elusive. Here, we demonstrate AlGaAs-on-insulator as a nonlinear platform at telecom wavelengths. Using newly developed fabrication processes, we show high-quality-factor (Q>100,000) micro-resonators with integrated bus waveguides in a planar circuit where optical parametric oscillation is achieved with a record low threshold power of 3 mW and a frequency comb spanning 350 nm is obtained. Our demonstration shows the huge potential of the AlGaAs-on-insulator platform in integrated nonlinear photonics.

High-Speed Optical Signal Processing System Based on DSP for Neutral Beam Injector on EAST

Neutral Beam Injection (NBI) is one of the main plasma heating methods in nuclear fusion devices. To prevent the device from irreversible damage, all the status signal acquisition and transmission must meet high voltage isolation, fast-reaction and high reliability requirements. DSP performs well at complicated algorithms computing and meets the real-time requirements, but it is poor at parallel processing. FPGA is good at combination logic and sequential logic control. To meet the EAST-NBI control system experimental operational requirements, DSP and FPGA architecture is taken in this design, which converts the optical signal to high-precision analog signal to output. This paper analyzes the requirement of high-speed optical signal processing system based on DSP for EAST-NBI and introduces the detail modules designs, including seven modules: optical signal receiving and conversion interface circuit, FPGA decoding interface circuit, OMAP processing interface circuit, DAC interface circuit, Ethernet interface circuit, serial port interface circuit and amplification interface circuit.

All-Optical Signal Processing

Optical signal processing brings together various fields of optics and signal processing - namely, nonlinear devices and processes, analog and digital signals, and advanced data modulation formats - to achieve high-speed signal processing functions that can potentially operate at the line rate of fiber optic communications. Information can be encoded in amplitude, phase, wavelength, polarization and spatial features of an optical wave to achieve high-capacity transmission. We revisit advances in the key enabling technologies that led to recent research in optical signal processing for digital signals that are encoded in one or more of these dimensions. Various optical nonlinearities and chromatic dispersion have been shown to enable key sub-system applications such as wavelength conversion, multicasting, multiplexing, demultiplexing, and tunable optical delays. We review recent advances in high-speed optical signal processing applications in the areas of equalization, regeneration, flexible signal generation, and optical control information (optical logic and correlation).

Ultra compact slow light photonic crystal directional coupler design with elliptical rods

We propose a novel design for a photonic crystal waveguide coupler, which uses elliptical shaped rods with refractive index equal to 3.4 arranged in square lattice. We investigate the performance of slow light in this photonic crystal coupler. By providing a slow-light region using elliptical cells, a coupling length of just 2.58μm is achieved at optical wavelength. This is extremely small coupling length then previously reported. The proposed structure would offer significant potential for novel compact high-speed optical signal processing devices.

High-speed optical coherence tomography signal processing on GPU

The signal processing speed of spectral domain optical coherence tomography (SD-OCT) has become a bottleneck in many medical applications. Recently, a time-domain interpolation method was proposed. This method not only gets a better signal-to noise ratio (SNR) but also gets a faster signal processing time for the SD-OCT than the widely used zero-padding interpolation method. Furthermore, the re-sampled data is obtained by convoluting the acquired data and the coefficients in time domain. Thus, a lot of interpolations can be performed concurrently. So, this interpolation method is suitable for parallel computing. An ultra-high optical coherence tomography signal processing can be realized by using graphics processing unit (GPU) with computer unified device architecture (CUDA). This paper will introduce the signal processing steps of SD-OCT on GPU. An experiment is performed to acquire a frame SD-OCT data (400A-lines×2048 pixel per A-line) and real-time processed the data on GPU. The results show that it can be finished in 6.208 milliseconds, which is 37 times faster than that on Central Processing Unit (CPU).

1-GHz All-Optical Flip-Flop Operation of Conventional Cylindrical-Shaped Single-Mode VCSELs Under Low-Power Optical Injection

All-optical set-reset flip-flop operations of conventional circular cylindrical-shaped 1.55-μm wavelength single-mode vertical-cavity surface-emitting lasers (VCSELs) have been demonstrated at a switching frequency of 1 GHz based on polarization bistability observed via injection current variation. The energy of set and reset pulses was lower than 4.5 fJ at a bias current of the VCSEL of 4 mA. Polarization bistable VCSELs will be useful for high-speed optical signal processing applications.

Trigonometric Transforms for High-Speed Optical Networks: All-Optical Architectures and Optical OFDM

In this paper, it is shown that the use of real trigonometric transforms can advantageously replace the Fourier transform in optical communication systems, for both all-optical and electronic signal processing. All-optical discrete Hartley transform (DHT) and discrete Cosine transform (DCT) architectures for high-speed optical signal processing, filtering and data compression are given and compared to fiber Fourier processing. A trigonometric transform-based orthogonal frequency division multiplexing (OFDM) transmission system is also presented. The modulation/demodulation is performed by using the fast Hartley transform (FHT) algorithm. The simplified scheme and the real processing make it suitable for direct detection optical systems.

Ultra high-speed optical signal processing based on single SOA at 60 Gb/s

The paper shows the design of all-optical logic gates OR, AND, NOT, NOR, XNOR, XOR at ultra high speed by using SOA. The simulations of all logic gates are obtained by XGM and FWM in SOA at 40 Gb/s and 60 Gb/s. The OR, AND, NOR logic between two data sources are obtained using a pump signal, while another logic XNOR using two data. The NOT, XOR obtained using FWM and XGM combined. Thus realization of these logics at 40 Gb/s and 60 Gb/s will lead revolution growth in optical signal processing for high-speed operation.

Analysis of Noise Effects in Long Semiconductor Optical Amplifiers

In this letter, we address one of the essential processes to consider in long Semiconductor Optical Amplifiers (SOAs) analysis, which is the noise. Particularly, we investigate the impact of noise effects on the SOA behavior by measuring the gain, the optical signal to noise ratio and the noise figure, referring to numerical simulations. Although its gain dynamics provide very attractive features of high speed optical signal processing, we show that the noise is strong in long SOAs and can limit the performance of the structure. In order to remedy this, we show that using high bias current at moderate input signal power is recommended.