Coherent Heterodyne Detection Research Articles

Demonstration of an 8-Gbit/s QPSK coherent underwater wireless optical communication link using coherent heterodyne detection under scattering conditions

Demonstration of an 8-Gbit/s QPSK coherent underwater wireless optical communication link using coherent heterodyne detection under scattering conditions

Interference fading suppression with a multi-subcarrier pulse in a distributed acoustic sensor

A low-complexity multi-subcarrier pulse generation scheme is proposed to suppress the interference fading in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) based distributed acoustic sensor (DAS) with heterodyne coherent detection. The multi-subcarrier pulse is generated in the digital domain based on the proper clipping operation of a sine signal. The localization and recovery of the disturbance signal are realized by the spectrum extraction and rotated vector sum (SERVS) method. The experimental results show that the occurrences of interference fading can be significantly reduced. The intensity fluctuation is reduced from ∼75 dB to ∼25 dB. Multiple disturbance signals are successfully demodulated to verify the effectiveness of the proposed method.

Blast-Assisted Subsurface Characterisation Using a Novel Distributed Acoustic Sensing Setup Based on Geometric Phases.

A novel DAS setup based on geometric phases in coherent heterodyne detection is applied for the first time to the characterisation of the Earth's subsurface. In addition, an optimisation of the proposed setup in terms of its spatial resolution is also presented for the first time. The surface waves are generated by strong blasts of 25 kg of explosives at a dedicated test site. A 10 km dark fiber link in the vicinity of the test site connected to the test setup records the resulting strain signals. The spike-free and low-noise strain data thus obtained minimize post-processing requirements, making the setup a candidate for real-time seismic monitoring. An analysis of the dispersion characteristics of the generated surface waves is performed using a recently reported optimised seismic interferometric technique. Based on the dispersion characteristics, the shear wave velocities of the surface waves as a function of the depth profile of the Earth's crust are determined using an optimised evolutionary algorithm.

Heterodyne coherent detection of phase modulation in a mid-infrared unipolar device.

Phase modulation is demonstrated in a quantum Stark effect modulator designed to operate in the mid-infrared at wavelength around 10 µm. Both phase and amplitude modulation are simultaneously resolved through the measurement of the heterodyne signal arising from the beating of a quantum cascade laser with a highly stabilized frequency comb. The highest measured phase shift is more than 5 degrees with an associated intensity modulation of 5 %. The experimental results are in full agreement with our model in which the complex susceptibility is precisely described considering the linear voltage dependent Stark shift of the optical resonance.

Phase-sensitive optical time domain reflectometry based on geometric phase measurement

A phase-sensitive optical time domain reflectometer based on coherent heterodyne detection of geometric phase in the beat signal of light, is reported for the first time to our knowledge. The use of the geometric phase to extract strain makes it immune to polarisation diversity fading. This is because a polarisation mismatch between the interfering beams is not a hindrance to its measurement. The geometric phase is calculated using the amplitude of the beat signal and individual beam intensities without any need for phase unwrapping. It is measured per beat period and can be equated with the traditionally measured dynamic phase with appropriate scaling. The results show that the system based on the geometric phase successfully measures strain, free from polarisation mismatch fading and phase unwrapping errors, providing a completely novel solution to these problems.

Quantitative detection of multi-frequency disturbance signal by ϕ-OTDR system

Recently, the combination of pattern recognition technology and distributed fiber sensing systems has become increasingly common, so whether the disturbance signal can be well recovered has become increasingly important. To verify the recovery and linear response of a distributed fiber optic sensing system to multi-frequency disturbance signals, a heterodyne coherent detection system for phase-sensitive optical time-domain reflectometry is developed. The output beat signal is extracted using the digital in-phase/quadrature demodulation algorithm. The signal can be precisely located on a 7 km length range, and the disturbance signal can be restored well through the phase information. Not only the superposition signal composed of the same signal but also that composed of different kinds of signals can be successfully restored. A fast Fourier transform algorithm is used to obtain the frequency information of the superimposed signal. Combined with the use of a finite impulse response filter, the superposed signal is decomposed according to its frequency components, which perfectly restores the two signals before they are superimposed. In addition, their amplitude is highly linear with the driving voltage of the piezoelectric transducer. The system can fully retain the details of each frequency component in the recovery of multi-frequency disturbance signals. More importantly, in field experiments, the disturbance behavior is well recovered, which has broad prospects in the application of perimeter security.

Performance Analysis of Mixed Rayleigh and F Distribution RF-FSO Cooperative Systems with AF Relaying

This paper proposes a dual-hop mixed radio frequency-free-space optical (RF-FSO) cooperative system with amplify-and-forward (AF) relaying. The RF link is subject to Rayleigh fading and the FSO link is assumed to follow F-distributed fading with pointing error. The different types of detection, including intensity modulation with direct detection (IM/DD) and coherent heterodyne detection (HD), are considered. The closed-form expressions for the cumulative distribution function (CDF), the moment generating function (MGF), and the moments of end-to-end signal-to-noise ratio (SNR) are derived. Furthermore, closed-form expressions for the outage probability, average bit error rate (BER), and ergodic capacity are presented. Asymptotic outage probability expressions are derived to obtain additional insights into the system performance. It is shown that the HD technique exhibits better performance than an IM/DD technique. The system performance is deteriorated by atmospheric turbulence and pointing error. Finally, analytical results are confirmed by Monte Carlo simulations.

Analytical performance assessment of FSO links over cascaded Snedecor’s [formula omitted] turbulence channels in the presence of pointing errors

The performance of free-space optical (FSO) links over cascaded Snedecor’s F turbulence channels with pointing errors is investigated in this paper. To this end, we derive exact analytical expressions for the probability distribution function (PDF) and the cumulative distribution function (CDF) of the irradiance fluctuations in the presence of pointing errors. We also provide exact analytical expressions for the PDF, the CDF, the moment generating function (MGF), the moments, and the scintillation index (SI) of the received signal-to-noise ratio (SNR) assuming both intensity modulation/direct detection (IM/DD) and coherent heterodyne detection. The derived statistical expressions for the SNR are further utilized to derive exact analytical and asymptotic expressions for the outage probability, the average symbol error rate (SER) of various modulation techniques, and the average ergodic capacity. The derived asymptotic expressions give insights into the diversity gain of the system. The derived expressions are verified by Monte-Carlo simulations.

An adaptive algorithm for performance enhancement of long-haul MMW/RoF system for next generation mobile communications

Radio over fibre (RoF) and millimetre wave (MMW) are regarded as the most promising solutions to provide high-capacity, long-distance data transport between base stations and core network in the future heterogeneous radio access networks that support both cloud and edge computing paradigms. In this paper, we propose an adaptive algorithm to optimise and determine a set of important link parameters for a MMW/RoF integrated system based on 10 Gb/s QPSK modulation format and heterodyne coherent detection. We develop analytical models of main components and derive a closed-form expression of system performance such as Q, SNR and BER. The adaptive algorithm is successfully applied to determine important link parameters including laser power, local oscillator power, optical amplifier location and gains so that the overall performance could be enhanced at an acceptable level corresponding to the varied propagation length from 200 km to 300 km. BERs of well below the 10-9.

Optical polarization division multiplexing fiber-wireless integration system at Ka-band based on a low-cost dual-drive MZM.

In this paper, a low-cost dual-drive Mach-Zehnder modulator (DDMZM) based 40 Gbit/s polarization division multiplexing (PDM) fiber-wireless-integration system at Ka-band is experimentally demonstrated. Since the DDMZM is biased at the quadrature point for electro-to-optical (E/O) conversion, a high-power direct current (DC)/radio frequency (RF) component will appear within the received signal bandwidth. This high-power component becomes a narrowband interference due to the phase noise of lasers, which will lead to the incorrect convergence of the constant-modulus algorithm (CMA) during equalization at the receiver side. In order to deal with the broadened DC component, twin-single-sideband (twin-SSB) signal with bandwidth interleave and RF-pilot based phase noise compensation scheme are adopted. Enabled by the combination of optical PDM technique and heterodyne coherent detection, a 40 Gbit/s PDM twin-SSB Nyquist-shaped quadrature-phase-shift-keying (QPSK) signal transmitting over 20-km single mode fiber (SMF) and 1-m 2×2 multiple-input multiple-output (MIMO) wireless distance is achieved with the bit error rate (BER) below the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3.

100 Gbit/s/λ DMT-PON System Based on Intensity Modulation and Heterodyne Coherent Detection

Due to the high receiver sensitivity and linear detection of coherent reception compared to direct detection (DD), the cost-efficient and low-complexity coherent detection based passive optical network (PON) with data rate beyond 100 Gbit/s has drawn great attention. In this letter, we demonstrate a 100 Gbit/s/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> discrete multitone (DMT) PON enabled by intensity modulation and heterodyne coherent detection in simulation. In order to compensate the phase noise, both common phase error (CPE) and RF-pilot (RFP) based schemes are considered and compared. According to the simulation results, the power budgets of our proposed system after 10-km and 20-km single mode fiber (SMF) transmission based on CPE scheme without dispersion management are 32.5-dB and 30.5-dB, while for RFP based scheme, 35-dB and 32.9-dB power budgets can be obtained for 10-km and 20-km SMF transmission, respectively. Our proposed system provides a low cost and low complexity coherent solution for single-wavelength 100 Gbit/s PON.

Heterodyne coherent tracking technology for inter-satellite laser link during direct sunlight

There is a possibility that the angle of the laser link between two geosynchronous orbit satellites and the incident direction of sunlight will be small during the periods of the vernal equinox and autumnal equinox. At these times, the sunlight is incident to the receiving detector along the receiving channel of the laser terminal on the satellite, which easily causes the signal laser to be submerged in the background light. This study analyzed the influence of direct sunlight on a laser terminal, and a tracking scheme for heterodyne coherent detection using two four-quadrant detectors was designed. The explanations of the analysis and experimental results show that this scheme has a sufficient signal-to-noise ratio for tracking during direct sunlight. Experimental verification was carried out, with a solar simulator used to simulate the solar illumination. The laser terminal could track and communicate stably under direct irradiation by the sun, with a tracking accuracy that was better than 1 μrad (1 σ), and a bit error rate that was better than 10-7 at 1 Gbps. These research results could be applied to different link scenarios such as an inclined geosynchronous orbit and low earth orbit constellation.

Distributed optical fiber hydrophone based on Φ-OTDR and its field test.

In this letter, a distributed optical fiber hydrophone (DOFH) based on Φ-OTDR is demonstrated and tested in the field. The specially designed sensitized optical cable with sensitivity up to -146 dB rad/µPa/m is introduced, and an array signal processing model for DOFH is constructed to analyze the equivalence and specificity of the distributed array of acoustic sensors. In the field test, a 104-meter-long optical cable and a Φ-OTDR system based on heterodyne coherent detection (Het Φ-OTDR) is utilized, and underwater acoustic signal spatial spectrum estimation, beamforming and motion trajectory tracking with high accuracy can be realized. As far as we know, this is the first report on the field trial of DOFH based on Φ-OTDR. The DOFH has the potential to achieve an array range of tens of kilometers, with elements spaced up to the meter level and flexible configuration, which has a broad application prospect for marine acoustic detection.

Probabilistic shaping with pre-equalization in W-band MM-wave communication system with heterodyne coherent detection

Abstract In this paper, an 85 GHz MM-wave signal is demonstrated in the fiber and MM-wave converged system in W-band. It is known to us, this is the first experimental demonstration that the pre-equalizaiton (PE) and probabilistic shaping (PS) techniques are applied to the fiber and MM-wave converged system. BER of 4.4 × 10−3 is achieved by using those method after 4-m wireless transmission and 25-km Standard single mode fiber (SSMF).

Investigation and comparison of sensitivity of LiDAR to laser physical parameters at 750 m using different detection techniques

In this paper, the different detection techniques are investigated- Direct Detection and Coherent Heterodyne Detection on FMCW LiDAR system using Optisystem package. The results of investigations done are included to see the influence of laser physical parameters- Active Length, Active Layer Width and Reflectivity on LiDAR performance parameters- Power Received, SNR at photodetector output and beam parameters- Beam Diameter and Beam Divergence. This investigation is done using DFB laser and FP laser in place of CW laser in different reference models for different detection techniques. The optimised values of laser physical parameters are obtained where the DFB Laser and FP Laser provide the same performance as that of the CW Laser.

A real-time three-dimensional coherent ladar demonstration: System structure, imaging processing, and experiment result

A new real-time, high-precision three-dimensional (3D) laser radar with a coherent system is presented. A self-designed arbitrary waveform generator (AWG), an electro-optic modulator, and an optical filter are proposed to generation a linear frequency modulated continuous waveform (FMCW) with a bandwidth of 2.4 GHz and pulse repetition frequency (PRF) of 100kHz. The heterodyne coherent detection and Micro-Electro-Mechanical System (MEMS) scanner are implemented with high sensitivity and fast 3D imaging. At the same time, multi-phase FFT algorithm is proposed to realize the frequency calculation with real-time. In this paper, we present the system structure, signal processing, and the experimental results in detail. The system achieves static 3D target and dynamic target imaging verification, and the experiment result validates the performance of system for real-time 3D imaging. It acquires 3D imaging at 40 frames per second (fps), which can satisfy the demand of high imaging speed requirements for special situation.

Performance analysis of a DCO-CO-OFDM optical transmission system with distributed Raman amplifier using coherent heterodyne receiver

A novel analytical approach is developed to evaluate the bit error rate performance (BER) of a DC biased optical coherent orthogonal frequency division multiplexing (DCO−CO-OFDM) transmission system with distributed Raman amplifier using single mode fiber (SMF) considering intensity modulation and coherent heterodyne detection. Analytical expressions are developed for optical SNR (OSNR) at the output of the fiber link along with IF-SNR and output SNR to evaluate the conditional BER performance for a given output of DCO-OFDM demodulator. Average BER is evaluated by averaging the conditional BER over the pdf of the output of DCO-OFDM demodulator. Results are evaluated in terms of average BER with different systems parameter viz. input signal power, pump power, local oscillator power, modulation index, number of OFDM sub-channel, fiber length and data rate. Results show that DCO−CO-OFDM optical transmission system offers better performance compared to CO-OFDM optical transmission reported earlier. It is further noticed that performance of an optical OFDM transmission link can be significantly improved by increasing the number of OFDM subcarrier and DC bias level. The results are found to be in conformity with the results of CO-OFDM reported earlier.

Nonlinear compensation in W-band MM-wave communication system with heterodyne coherent detection

Abstract In this paper, we experimentally demonstrate the transmission of 45 Gb/s/λ 16QAM OFDM signal in the W-band MM-wave and fiber converged system. To the best of our knowledge, it is reported for the first time that parallel Volterra nonlinear compensation (VNC) method is applied in the W-band heterodyne detection millimeter wave (MMW) and fiber converged system. By using this method, BER of 3.4 × 10−3 is achieved after 25 km standard single mode fiber (SSMF) and 4 m wireless transmission.

Optical I/Q modulation utilizing dual-drive MZM for fiber-wireless integration system at Ka-band.

In this Letter, a fiber-wireless integration system at Ka-band adopting heterodyne coherent detection is proposed and experimentally demonstrated. Optical I/Q up-conversion is realized with a low-cost dual-drive Mach-Zehnder modulator (DD-MZM) instead of the traditional I/Q nested MZM. To avoid non-convergence during constant-modulus-algorithm-based equalization, DC elimination is applied to suppress the ultra-high peak in the frequency domain after frequency down-conversion and symbol-phase-average-processing-based coarse phase noise estimation. Using DD-MZM for optical I/Q modulation, transmission, and reception of single polarization, 20-Gbit/s quadrature phase shift keying (QPSK) over 40-km single-mode fiber (SMF) and 5-m free space at Ka-band is demonstrated.

Compact polarization diversity Kramers-Kronig coherent receiver on silicon chip.

We design and fabricate a compact silicon photonic integrated circuit (PIC) for polarization diversity heterodyne coherent detection. This PIC integrates two optical gratings for fiber coupling and polarization diversity, two germanium single-ended photodetectors (PDs), and three multimode interferometers (MMIs) for power splitting and optical hybrid. The device is highly compact with a footprint of 0.68mm × 0.9mm. We test this PIC with heterodyne detection experiments of polarization division multiplexed (PDM) 32Gbaud quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals. The signal-signal beat interference due to square-law detection is separately mitigated with the Kramers-Kronig (KK) scheme for each of the two orthogonal polarizations. To our best knowledge, we report the first PDM-KK coherent receiver in PIC with a capability of detecting 256Gb/s 16QAM signals, which shows the most compact size among the silicon coherent receivers ever reported.