Coherent Optical Detection Research Articles

Laser-Phase-Fluctuation-Insensitive Optical Coherent Detection Scheme for Radio-over-Fiber System

Laser-phase-fluctuation-insensitive optical coherent detection scheme with two-tone local light and digital signal processing technique for a radio-over-fiber (RoF) signal is proposed and experimentally demonstrated. Data recovery with the error vector magnitude of less than 14% rms is successfully performed for 10- and 2.5-Gbaud 25-GHz-band QPSK RoF signals. In addition, bit error rate of less than 10$^{-5}$ is also verified for 10-Gbaud 25-GHz-band QPSK RoF signal after 20-km fiber-optic transmission even if the light source with the linewidth of more than 10 MHz in the transmitter is used.

Photonic generation for multichannel THz wireless communication.

We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.

Optical serial coherent analyzer of radio-frequency (OSCAR).

Optical serial coherent analyzer of radio-frequency is a novel scheme that enables fast-scanning microwave signal measurements in a large bandwidth. The measurements are performed based on serial channelization realized by using a fast scanning laser source as the local oscillator to down-convert the to-be-measured radio-frequency (RF) signals. Optical coherent detection effectively removes interferences induced by RF's self-beating and guarantees the accuracy of measurements. In the experimental demonstration, instantaneous multi-frequency measurements and vector information acquisition of RF signals can be achieved by this scheme within 2.8 μs over 14 GHz bandwidth.

Interleaved and partial transmission interleaved optical coherent orthogonal frequency division multiplexing

A novel group of interleaved orthogonal frequency division multiplexing (IL-OFDM) and partial transmission IL-OFDM (PT-IL-OFDM) schemes are proposed for optical coherent detection. In the interleaved operation, the odd (or even) subcarriers of an OFDM symbol are reserved (closed). Such an interleaved arrangement can gain the tolerance toward phase noise induced interchannel interference (PN-ICI). Meanwhile, the peak to average power ratio (PAPR) of an OFDM signal can be significantly reduced. However, half of the capacity is sacrificed for the interleaved operation. By exploring the time domain symmetry property of IL-OFDM, the concept of PT-IL-OFDM is proposed to double the capacity of IL-OFDM. Consequently, PT-IL-OFDM can gain the merits of low PAPR and a high tolerance toward PN-ICI without capacity sacrifice. Numerical simulation verified the advanced properties of IL-OFDM and PT-IL-OFDM.

SDN and OpenFlow for Dynamic Flex-Grid Optical Access and Aggregation Networks

We propose and discuss the extension of software-defined networking (SDN) and OpenFlow principles to optical access/aggregation networks for dynamic flex-grid wavelength circuit creation. The first experimental demonstration of an OpenFlow1.0-based flex-grid λ-flow architecture for dynamic 150 Mb/s per-cell 4 G Orthogonal Frequency Division Multiple Access (OFDMA) mobile backhaul (MBH) overlays onto 10 Gb/s passive optical networks (PON) without optical network unit (ONU)-side optical filtering, amplification, or coherent detection, over 20 km standard single mode fiber (SSMF) with a 1:64 passive split is also detailed. The proposed approach can be attractive for monetizing optical access/aggregation networks via on-demand support for high-speed, low latency, high quality of service (QoS) applications over legacy fiber infrastructure.

Multiband Carrierless Amplitude Phase Modulation for High Capacity Optical Data Links

Short range optical data links are experiencing bandwidth limitations making it very challenging to cope with the growing data transmission capacity demands. Parallel optics appears as a valid short-term solution. It is, however, not a viable solution in the long-term because of its complex optical packaging. Therefore, increasing effort is now put into the possibility of exploiting higher order modulation formats with increased spectral efficiency and reduced optical transceiver complexity. As these type of links are based on intensity modulation and direct detection, modulation formats relying on optical coherent detection can not be straight forwardly employed. As an alternative and more viable solution, this paper proposes the use of carrierless amplitude phase (CAP) in a novel multiband approach (MultiCAP) that achieves record spectral efficiency, increases tolerance towards dispersion and bandwidth limitations, and reduces the complexity of the transceiver. We report on numerical simulations and experimental demonstrations with capacity beyond 100 Gb/s transmission using a single externally modulated laser. In addition, an extensive comparison with conventional CAP is also provided. The reported experiment uses MultiCAP to achieve 102.4 Gb/s transmission, corresponding to a data payload of 95.2 Gb/s error free transmission by using a 7% forward error correction code. The signal is successfully recovered after 15 km of standard single mode fiber in a system limited by a 3 dB bandwidth of 14 GHz.

Multiplier-Free Phase Recovery With Polar-domain Multisymbol-Delay-Detector

We present a highly efficient carrier phase recovery module for coherent optical detection of single-carrier advanced modulation formats with differential precoding. Remarkably, we eliminate all multipliers from the multisymbol-delay-detector (MSDD) carrier recovery system, without incurring performance penalty relative to the previously shown complex-domain MSDD. We also introduce a novel polyblock hardware parallelization method for the MSDD, eliminating the “distant feedback” parallelization penalty of decision-feedback-based carrier recovery methods, such as MSDD. Simulations indicate extremely high nonlinear phase noise tolerance for the new polar MSDD carrier recovery system for 16-QAM 2000 km transmission. The ultralow-complexity CR is simulated and electrically demonstrated in real-time at 25 Gbaud symbol rate over FPGA HW for single-carrier QPSK and 16-QAM constellations, respectively.

Demonstrating Doubly-Differential Quadrature Phase Shift Keying in the Optical Domain

We report for the first time the experimental demonstration of doubly differential quadrature phase shift keying (DDQPSK) using optical coherent detection. This method is more robust against high frequency offsets (FO) than conventional single differential quadrature phase shift keying (SDQPSK) with offset compensation. DDQPSK is shown to be able to compensate large FOs (up to the baud rate) and has lower computational requirements than other FO compensation methods. DDQPSK is a simple algorithm to implement in a real-time decoder for optical burst switched network scenarios. Simulation results are also provided, which show good agreement with the experimental results for both SDQPSK and DDQPSK transmissions.

Photonic time stretch preprocessor employing coherent detection in analog-to-digital converter

The performance of analog-to-digital converter (ADC) can be greatly enhanced by preprocessing the high-speed RF signal using the photonic time stretch technique. In order to accumulate more dispersion to stretch the optical pulses in time domain, we used the large dispersion photonic crystal fiber (PCF) as the stretched medium. However, the length of used fiber is so long, the optical signal becomes the weak signal before the digitizer as a result. We propose a new implementation of the time stretch analog-to-digital conversion system that overcomes the disadvantage from the direct detection. It is shown that the weak signal can be recovered by using the coherent optical detection and the conversion gain is very high. Real-time analog-to-digital conversion at 1.56TSa/s is demonstrated.

Ultrahigh sampling rate photonic time stretch analog-to-digital converter employing phase modulation

The performance of analog-to-digital converter (ADC) can be greatly enhanced by preprocessing the ultrafast analog signal using the photonic time-stretch technique. In the previous time-stretch ADC, the amplitude modulation is adopted. The amplitude of stretched signal has nonuniformity after the time-stretch preprocessing and the power of stretched signal is very weak, this will influence on recovering distortionless stretched signal, increase the difficult of detector and sampling. In this paper, we propose the photonic time-stretch ADC employing the phase modulation and the optical coherent detection to eliminate the nonuniformity phenomenon on the amplitude and increase power of stretched signal by adjusting the local oscillation (LO) power. The sampling rate of the ADC can reach 1.56TSa/s by using large dispersion photonic crystal fiber (PCF).

Chromatic dispersion estimation methods using polynomial fitting in PDM-QPSK or other multilevel-format coherent optical systems

We propose a polynomial fitting algorithm based method for non-data-aided chromatic dispersion (CD) estimation in single carrier (SC) coherent optical systems with arbitrary modulation formats, and compare it with our previously proposed CD estimation method which is also based on the polynomial fitting algorithm but requires special modulation formats thus is a data-aided CD estimation method for systems with PDM-QPSK or other multilevel modulation formats. For the data-aided CD estimation method, an extra chirp-free OOK signal is transmitted. The curve of the average phase at the frequency±f as a function of the frequency f is measured at the coherent receiver. The accumulated CD is then estimated with a polynomial fitting algorithm. In the simulation of a 50Gbaud 50%-RZ OOK system through 12.5×80km standard single mode fiber (SSMF), the estimation errors are within±50ps/nm in 20 tests when the launch power is from −5dBm to −1dBm. Non-data-aided CD estimation for arbitrary modulation formats is achieved by measuring the differential phase between frequency f±fs/2 (fs is the symbol rate) in digital coherent receivers. The estimation errors are within±200ps/nm, in a 50Gbaud PDM-QPSK system through 10×80km SSMF with the launch power from −3dBm to −1dBm. The estimation accuracy can be potentially improved by averaging multiple results. The data-aided CD estimation method has an inherently bigger estimation range than that of the newly proposed non-data-aided method, while the newly proposed non-data-aided method can tolerate a much larger frequency offset between the transmitter and the local oscillator. These methods are promising for future optical fiber networks with dynamic optical routing and coherent detection.

光电多功能检测仪光学系统设计

An optical system of optical multi-functions detector was designed,which combined multiple detection functions such as laser beam quality analysis,photoelectric auto-collimator,laser auto-collimator,optical coherence detection as one.Its operating wavelength range was300~1 700nm,alignment accuracies was 2″and angular resolution was 0.1″.One kind of parallel light beam expanding system and three-axis system that had a long focus was designed,and a kind of removable toric lens telephoto with a central plane was adopted.The objective lens diameter was 75 mm,extend to 400 mm diameter.It enabled the optical system to achieve consistency,outgoing laser pointing and integrated multi-parameter detection and had high degree of integration.Furthermore,it used the optical design software ZEMAX for system simulation and optimization.As a result,the modulation transfer functions at 50lp/mm for the position of the focal length corresponding to different wavelengths are greater than 0.2nin the whole field of view.Then,a functional prototype was successfully developed,and processing equipment was tested after adjustment.Finally,the results show that it can get clear and accurate images in the focus range.The system satisfies the command of test requirements.

光束特性对声光偏转相干光探测效率的影响

光束特性对声光偏转相干光探测效率的影响

Optical and millimeter-wave radio seamless MIMO transmission based on a radio over fiber technology

Multi-input multi-output (MIMO) transmission of two millimeter-wave radio signals seamlessly converted from polarization-division-multiplexed quadrature-phase-shift-keying optical signals is successfully demonstrated, where a radio access unit basically consisting of only optical-to-electrical converters and a radio receiver performs total signal equalization of both the optical and the radio paths and demodulation with digital signal processing (DSP). Orthogonally polarized optical components that are directly converted to two-channel radio components can be demultiplexed and demodulated with high-speed DSP as in optical digital coherent detection. 20-Gbaud optical and radio seamless MIMO transmission provides a total capacity of 74.4 Gb/s with a forward error correction overhead of 7%.

Coherent Radio-Over-Fiber and Millimeter-Wave Radio Seamless Transmission System for Resilient Access Networks

We propose a millimeter-wave (MMW) coherent radio-over-fiber (RoF) transmission system for application to an access network with a direct broadband last-mile wireless connection to an optical fiber network. The coherent RoF system comprises an optical two-tone RoF signal generator with an advanced modulation format for high-throughput transmission and employs a digital-signal-processing-aided coherent detection technique for MMW radio, which is a technique similar to that of optical digital coherent detection. As proof of concept, a 20-GBd quadrature phase-shift keying RoF transmission over 20 km of optical fiber before a radio transmission over 20 m of air is demonstrated. The results of the radio transmissions using Cassegrain-type antenna pairs with a gain of 50 dBi are consistent with theoretical estimations; this suggests the possibility of developing a midrange transmission system using a high-power MMW amplifier.

Linear Technique for Discrimination of Optically Coded Waveforms Using Optical Frequency Combs

We have demonstrated a novel coherent optical detection architecture that serves as a matched filter and successfully discriminates between various encoded optical waveforms with high confidence. The waveforms are produced by encoding the spectral phase of an optical frequency comb with codes from a Walsh-Hadamard set. The encoded optical waveforms are decoded with a coherent detection technique implemented using an optical frequency comb as a set of local oscillators, an interferometer, and a pair of differential balanced photodetectors. The use of only linear optical devices in the receiver results in a higher sensitivity compared to the use of nonlinear optical thresholding and gating techniques. Decoding is demonstrated at power levels of ~ 25 μW, which are much lower than previously reported. Possible applications of the receiver architecture include laser radar and optical communications in an optical code-division multiple access network.

A complex-weighted, decision-aided, maximum-likelihood carrier phase and frequency-offset estimation algorithm for coherent optical detection

We present a symbol-by-symbol coherent optical receiver, which employs a novel, complex-weighted, decision-aided, maximum-likelihood (CW-DA-ML) carrier phase and frequency offset estimator. The CW-DA-ML carrier estimator uses a CW transversal filter to generate a carrier reference phasor, and the filter weights are automatically adapted on-line by linear regression on the observed signals. A complete modulo-R reduced frequency offset estimation (FOE) range of ± R/2 is achieved, independent of modulation format, where R is the symbol rate. Carrier phase and frequency tracking is achieved rapidly. The acquisition speed of frequency offset in quaternary phase-shift keying (4-PSK) signals is more than 5 times faster than that of differential FOE. A constant penalty of approximately 1 dB at bit-error rate of 10(-4) is demonstrated for all frequency offsets in 4-PSK signals with laser-linewidth-symbol-duration product of 8 × 10(-5).

Nonlinear Shannon Limit in Pseudolinear Coherent Systems

In this paper, we develop a general first-order perturbation theory of the propagation of a signal in an optical fiber in the presence of amplification and Kerr nonlinearity, valid for arbitrary pulse shapes. We obtain a general expression of the sampled signal after optical filtering, coherent detection, and optimal sampling. We include intrachannel and as well as interchannel nonlinear effects. We obtain simplified expressions in the case in which the accumulated dispersion is high (equivalent to the far-field limit in paraxial optics). This general theory is applied in detail to the special case of spectral-efficient sinc pulses. This exercise shows that the characteristics of the neighboring wavelength-division multiplexed channels are essential in determining the nonlinear impairments.

Study of Quantum Communication System with Coherent Light

In this paper， we introduced a system of coherent optical detection with homodyne， which implementing coherent optical communication，our own design based on the principle of coherent optical communication. IN the system, PCI6111E was useed as a data acquisition(DAQ) module. Alice and Bob’s control procedure by their computers under the LabVIEW. The synchronous detection and DAQ were carried out on the system. The signals were processed, displayed and measured. The Experimental results show that by light-synchronization and LabVIEW procedure control, each function module work together in cooperation, include Alice’s acousto-optic modulator and electro-optical modulator, Bob’s data acquisition and phase adjustment by PZT. The coherent optical information could be transitted by Alice and real-time demodulated by Bob.

Highly-sensitive coherent optical detection of M-ary frequency-shift keying signal

We demonstrate M-ary frequency-shift keying (FSK) optical modulation and digital coherent detection, aiming at applications to space communications, where high receiver sensitivity is the most crucial consideration. The proposed FSK transmitter and receiver are based on the coherent orthogonal frequency-division multiplexing (OFDM) technique and feature simple configuration and low computational complexity. By offline bit-error rate measurements using a 256-FSK signal without the forward error-correction code, we obtain the receiver sensitivity as high as 3.5 photons per bit at the bit-error rate of 10(-3). The experimental result is in good agreement with simulations.