High-speed Optical Receiver Research Articles

High stability visible-light photoresponse of flexible heterostructures based on LaCoO3 epitaxial films

The research of high-speed photodetector and high-speed optical receiver garners significant attention due to their indispensable properties in many fields including high-temperature event monitoring, security, and ad hoc network wireless communication. Inorganic perovskite oxides LaCoO3 films showcase an extensive prospect in this area owing to their remarkable photoconductive effect. Up to present, however, LaCoO3 films are mostly grown on rigid instead of flexible substrates, greatly limiting their applications to wearable optoelectronic sensors. In this work, we fabricated some flexible LaCoO3 thin films to study their photoresponse. By inserting SrTiO3 and BaTiO3 as buffer layers, we find that LaCoO3 thin films could epitaxially grow on the fluorphlogopite surface and show a stable photoresponse to visible-light. Nevertheless, we also found that the epitaxial strain and the content of surface-adsorbed oxygen could impact the photoconductivity. The mechanical strain generated by bending the fluorphlogopite substrate has been confirmed to has a tunable effect on the photoresponse. Moreover, with the fatigue tests of 105 bending cycles, the flexible LaCoO3 thin films maintain a good photoresponse without any essentially weakening, proving a superior mechanical durability and stability. This work not only indicates the feasibility of the LaCoO3 films applied for flexible photodetectors but also opens a path for other perovskite films applications for flexible substrate.

Threshold-programmable loss-of-signal detection circuit with temperature compensation

It is a challenge to implement a loss-of-signal (LOS) circuit with a wide threshold voltage range that is insensitive to temperature. This paper presents a new wide-range threshold-programmable LOS detector with full temperature compensation for application in 25Gb/s high-speed optical communication receivers. The wide-range programmable threshold voltage of the LOS detector is achieved by adjusting the threshold voltage of the peak detector and the gain of the variable gain amplifier (VGA). The detection accuracy is obviously improved by using offset self-cancellation technology for the comparator (COMP) and temperature compensation technology for the VGA and the peak detector. The LOS detector has been fabricated in 0.18 um BICMOS process and occupies 0.03mm2. The programmable threshold voltage range is 11∼130mV for the 25Gb/s non-return-to-zero code, the hysteresis is 2dB, and the max detection error is 4mV. The LOS detector consumes 2.18mW from 1.8V supply voltage.

Monolithic Integrated Optical Receiver With a Metal Reflector-Assisted Surface Grating Coupler

High-speed optical receivers with high-efficiency power collection capability are highly demanded in an optical wireless communication system to achieve high sensitivity due to the power-limited eye safety regulation. A cascaded aperture optical receiver enabled by a waveguide photodetector and a grating coupler is a promising candidate because of its advantage of optimizing the electrical performance and the light collection independently. Here, we propose using a metal reflector (MR)-assisted grating coupler to increase the coupling efficiency further. A sensitivity-enhanced monolithic integrated optical receiver with an MR-assisted grating coupler is realized for the first time, which is demonstrated on the Indium Phosphide membrane on Silicon platform. The maximum −3 dB bandwidth and the external responsivity of the waveguide photodetector inside the proposed optical receiver are 52.2 GHz and 0.31 A/W, respectively. A back-to-back receiver sensitivity of −4.75 dBm for a 10 Gb/s OOK signal at the 7% FEC limit is achieved. With the enhancement of an MR, the achieved sensitivity is calculated to be 1.5 dB higher based on the measured results compared with the cascaded aperture optical receiver without an MR on the same platform.

High-Speed SiGe BiCMOS Detector Enabling a 28 Gbps Quasi-Coherent Optical Receiver

This brief presents a high-speed detector targeting quasi-coherent optical receivers operating up to 28 Gbps data rates. The circuit consists of a balanced rectifier based on diode-connected heterojunction bipolar transistors (HBTs) together with tailored input and output filtering networks. The rectifier is buffered by a linear DC-coupled single-ended to differential amplifier providing a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50\,\Omega $ </tex-math></inline-formula> output interface. The design was fabricated in a commercial 130 nm SiGe BiCMOS technology with f textsubscript t/f textsubscript max of 250/340 GHz, and was tested on a quasi-coherent receiver setup. Optical receiver sensitivity better than −28 dBm and −26 dBm (FEC-limited BER of 1E-3) is demonstrated, respectively, at 25 and 28 Gbps data rates. To the best of the author’s knowledge, the reported circuit represents the fastest envelope detector published to date.

Reliability‐based quantization for soft decoding of LDPC codes in short‐reach optical links

Efficient quantizer design is vital in high-speed optical receivers. In this paper, the authors propose a three-level (1.5-bit) reliability-based quantizer for low-complexity soft decoding of low-density parity-check (LDPC) codes, and show that it outperforms a conventional quantizer employing eight levels (3 bits). Different approaches for obtaining the quantization thresholds are discussed, and it is shown that the achievable channel capacity with the proposed quantizer is within 0.4 dB of the Shannon limit of the unquantized channel. Rate-compatible LDPC codes are also designed tailored to the asymmetric optical channel terminated with the proposed reliability-based quantizer, and it is shown that the resulting quantizer-aware LDPC codes significantly outperform other existing codes of similar rates.

Generalized weighted bit-flipping LDPC decoding for asymmetric optical channels

Efficient low-complexity and low-latency forward error correction (FEC) decoding is vital in high-speed optical receivers. The weighted bit-flipping (WBF) decoding algorithm is a low-complexity and high-performance iterative decoder for low-density parity-check (LDPC) codes, devised for symmetric Gaussian channels. In this paper, we present a generalization of the WBF algorithm and its variants to discrete and continuous asymmetric optical channels which have signal-dependent noises. We have employed a fully analytical approach to derive the generalized WBF decoders, and show that they can achieve a net coding gain within 0.5 dB of that of the soft-decision near-optimal decoding.

Colloidal PbS Quantum Dots for Visible-to-Near-Infrared Optical Internet of Things

The emergence of optical Internet of Things (optical-IoT) for sixth-generation (6G) networks has been envisaged to relieve the bandwidth congestion in the conventional radio frequency (RF) channel, and to support the ever-increasing number of smart devices. Among the plethora of device innovations deemed essential for fortifying the development, herein we report on the visible-to-near-infrared color-conversion luminescent-dyes based on lead sulphide quantum dots (PbS QDs), so as to achieve an eye-safe high-speed optical link. The solution-processed PbS QDs exhibited strong absorption in the visible range, radiative recombination lifetime of 6.4 $\mu$ s, as well as high photoluminescence quantum yield of up to 88%. Our proof-of-principle demonstration based on an orthogonal frequency-division multiplexing (OFDM) modulation scheme established an infrared data transmission of 0.27 Mbit/s, readily supporting an indoor optical-IoT system, and shed light on the possibility for PbS-integrated transceivers in supporting remote access control of multiple nodes. We further envisaged that our investigations could find applications in future development of solution-processable PbS-integrated luminescent fibers, concentrators, and waveguides for high-speed optical receivers.

Organic photovoltaics for simultaneous energy harvesting and high-speed MIMO optical wireless communications

We show that organic photovoltaics (OPVs) are suitable for high-speed optical wireless data receivers that can also harvest power. In addition, these OPVs are of particular interest for indoor applications, as their bandgap is larger than that of silicon, leading to better matching to the spectrum of artificial light. By selecting a suitable combination of a narrow bandgap donor polymer and a nonfullerene acceptor, stable OPVs are fabricated with a power conversion efficiency of 8.8% under 1 Sun and 14% under indoor lighting conditions. In an optical wireless communication experiment, a data rate of 363 Mb/s and a simultaneous harvested power of 10.9 mW are achieved in a 4-by-4 multiple-input multiple-output (MIMO) setup that consists of four laser diodes, each transmitting 56 mW optical power and four OPV cells on a single panel as receivers at a distance of 40 cm. This result is the highest reported data rate using OPVs as data receivers and energy harvesters. This finding may be relevant to future mobile communication applications because it enables enhanced wireless data communication performance while prolonging the battery life in a mobile device.

Distortion losses of high-speed single-photon avalanche diode optical receivers approaching quantum sensitivity.

The high internal gain of single-photon avalanche diodes (SPADs) operating in Geiger mode allows the quantum limit of detection to be approached. This offers a significantly improved sensitivity for optical communication over existing photodiodes. A fully integrated CMOS SPAD array receiver (RX) is presented which achieves 500 Mb s-1 four-level pulse amplitude modulation in a visible light communication link within 15.2 dB of the quantum limit. However, SPAD dead time induces around 5.7 dB of transient distortion which restricts error performance and data rate. We propose a model describing a discrete photon counting system which exhibits this nonlinear behaviour and compare it to practical measurements with the RX. A unipolar intensity modulated optical signal is considered, as opposed to bipolar electric fields in conventional radio frequency wireless systems. Intermodulation between the DC and harmonic components of the data-carrying waveform is investigated, and the resulting degradation of signal-to-noise-and-distortion ratio and bit error rate is evaluated. The model is developed as a tool for understanding distortion to ultimately allow rectification through RX architecture, modulation scheme, coding and equalization techniques. This article is part of the theme issue 'Optical wireless communication'.

Advanced Design of Schottky Photodiodes in Bulk CMOS for High Speed Optical Receivers

This paper provides theoretical insight on how circular Schottky photodiodes in bulk CMOS can be optimized for certain integrated receiver applications. An optimal photodiode size is analytically demonstrated and the effects of a metal plate reflector are simulated using a transfer-matrix method, both for frontside and backside illumination. Finally, a distributed circuit model is presented, which deviates from the classical lumped model for large photodiodes or sheet resistances. The presented methodologies can also be extended to other types of photodetectors.

All-Si Large-Area Photodetectors With Bandwidth of More Than 10 GHz

We report high-speed large-area silicon photodetectors (PDs) that were fabricated on silicon-on-insulator (SOI) substrates. These coplanar interdigital PDs were fabricated with finger spacing in the 0.5– $5~\mu \text{m}$ range. One of the detectors, which had an area of $2300~\mu \text{m}^{{2}}$ , achieved a bandwidth as high as 14.1 GHz under a bias voltage of −10 V at a wavelength of 850 nm. Meanwhile, the device with the maximum area of $4300~\mu \text{m}^{{2}}$ also achieved a 7.9-GHz bandwidth, suggesting our detectors are highly suitable for high-speed 850-nm optical receiver and, especially, for large area receiving applications. We established a new transition time and resistor–capacitor ( RC ) equivalent circuit model to analyze and calculate the 3-dB frequency of the coplanar interdigital PD; the model results were well-matched with the measurement results.

Sensitivity Calculations of High-Speed Optical Receivers Based on Electron-APDs

Sensitivity of high-speed optical receivers is heavily influenced by the performance of the optical detectors used in the receivers, the data rate, and the target bit-error-rate (BER). A simulation model for sensitivity of optical receivers based on electron-avalanche photodiodes (e-APDs) is presented. It allows for the optimization of avalanche width and operating voltage to achieve the optimum receiver sensitivity for given bit rate and target BER. The effects modelled include inter-symbol interference (ISI), various dark current components (tunnelling, diffusion, and generation), current impulse duration, avalanche gain, and amplifier's noise. The model was demonstrated through simulations of Indium Arsenide (InAs) e-APDs. For $10^{-12}$ target BER, the receiver's sensitivities were found to be −30.6, −22.7, −19.2, and −16.6 dBm, for 10, 25, 40, and 50 Gb/s data rate, respectively. Desirable avalanche properties of InAs e-APDs are counteracted by detrimental effects of high dark currents. Hence InAs e-APDs with lower dark currents are required to be more competitive with other optical detector technologies for high-speed optical receivers. The data reported in this article is available from the ORDA digital repository (DOI: 10.15131/shef.data.9959468).

МОДУЛЯТОР СВІТЛОВОГО ПОТОКУ З ВІДОМОЮ ФОРМОЮ ОПТИЧНОГО ІМПУЛЬСУ

The article describes the developed and tested luminous flux modulator (LFM). LFM is designed to identify and study the dynamic distortions of optoelectronic devices (OED) with high temporal resolution. Such OED are capable to register optical radiation at fast processes (for example: pulse action of ionic beams, laser influence, electric discharges).The basis of the LFM's work is the mechanical principle of modulation, which makes it possible to preserve the shape of the optical signal with controlled changes in the duration of the optical signal. In addition, the applied LFM scheme allows a change in the spectral composition of optical radiationIn the implemented device, the optical signal has a trapezoidal shape, which makes it possible to determine quite simply the quantities that characterize the dynamic distortions of the OED (transient response, relaxation time, etc.).The modulator allows you to adjust the duration of trapezoidal optical pulses in the range from 0.69 ms (t1) to 0.11 ms (t2). In this case, the duration of the front and the cut are, respectively, τF1 = 54.8 μs and τC1 = 65.7 μs for t1; τF2 = 8.73 μs and τC2 = 10.5 μs for t2.The LFM was tested using OED based on a photoelectric multiplier (PMT), which, as is known, is considered to be a high-speed optical receiver. The experiment was carried out in two modes of operation of the power amplifier: in quasi-static and in dynamic modes. In quasi-static mode, with a controllably longer duration of the optical pulse (&gt;&gt; 1 s) and no dynamics of the process, the true form of the optical signal was obtained. In the dynamic mode, a signal was recorded whose shape is distorted with respect to the quasi-static signal, which indicates the presence of dynamic distortions.The received result testifies to the efficiency of the luminous flux modulator, allows to register and study the dynamic distortions of optoelectronic devices.

Forward-biased nanophotonic detector for ultralow-energy dissipation receiver

Generally, reverse-biased photodetectors (PDs) are used for high-speed optical receivers. The forward voltage region is only utilized in solar-cells, and this photovoltaic operation would not be concurrently obtained with high efficiency and high speed operation. Here we report that photonic-crystal waveguide PDs enable forward-biased high-speed operation at 40 Gbit/s with keeping high responsivity (0.88 A/W). Within our knowledge, this is the first demonstration of the forward-biased PDs with high responsivity. This achievement is attributed to the ultracompactness of our PD and the strong light confinement within the absorber and depleted regions, thereby enabling efficient photo-carrier generation and fast extraction. This result indicates that it is possible to construct a high-speed and ultracompact photo-receiver without an electrical amplifier nor an external bias circuit. Since there is no electrical energy required, our estimation shows that the consumption energy is just the optical energy of the injected signal pulse which is about 1 fJ/bit. Hence, it will lead to an ultimately efficient and highly integrable optical-to-electrical converter in a chip, which will be a key ingredient for dense nanophotonic communication and processors.

Stability analysis and compensation technique for low-voltage regulated cascode transimpedance amplifier

Stability of low voltage regulated cascode (RGC) transimpedance amplifier (TIA) with level shifter path is analyzed and criterions for a well-behaved time response are derived. It is shown that there is a trade-off between the amplifier bandwidth and stability in this topology. Improving bandwidth by increasing transconductance of transistors leads to ringing in the step response of the amplifier and finally its instability. To add a degree of freedom to design of the low-voltage RGC circuit for high-speed optical receivers, a compensation technique is proposed in this paper and employed in a TIA circuit, designed in a 0.18 μm CMOS technology. Post layout simulation results show a gain of 52 dBΩ and bandwidth of 3 GHz in presence of a 2 pF photo-detector (PD) capacitance and with power consumption of 4.3 mW. The results show that the proposed technique enhances bandwidth of the low-voltage RGC circuit by about 40%, while preserving its stability and well-behaved time response.

A 10-Gb/s Optical Receiver With Sub-Microampere Input-Referred Noise

High-speed optical receivers realized in low-cost technology often suffer from unfavorable performance, dictated by the transimpedance limit, the key design constraint of shunt-shunt feedback transimpedance amplifier (TIA). In this letter, we propose a novel TIA architecture to overcome the transimpedance limit, achieving both low noise and high gain that are not realizable in a conventional topology. A 10-Gb/s optical receiver with sub-microampere input-referred noise current is implemented in a mature 0.18- $\mu \text{m}$ CMOS technology. Wire-bonded with a commercial III–V p-i-n photodiode, the receiver demonstrates the state-of-the-art input-referred noise current of 0.97 $\mu $ Arms and a total transimpedance gain of 68.3 dB $\Omega $ while consuming 45 mA from 1.8-V power supply. Finally, the proposed architecture is applicable to 10 Gb/s beyond to realize low-noise high-gain optical receivers.

Method to increase the working frequency of digital carrier synchronization module for high-speed digital coherent optical receivers

A digital carrier synchronization module with high working frequency is indispensable for high-speed digital coherent optical receivers to recover the transmitted symbols. We proposed a method to increase the working frequency of the digital carrier synchronization (DCS) module based on the commonly used M’th power algorithms. Parallel architecture can increase the throughput of digital signal processing (DSP) modules for a given working frequency. pipelined architecture (PA) leads to a reduction in the critical path, and thus it can be exploited to increase the throughput of DSP modules by increasing the working frequency. It is demonstrated that in PA the working frequency is not limited by the computation time of the M’th power subfunction with the highest complexity because it is feedforward and thus pipelining registers can be introduced to reduce the critical path inside it. Instead, the phase unwrapping subfunction (PUS) becomes the bottleneck of the working frequency because it requires the immediately preceding result and cannot be implemented in PA, which results in the longest critical path among the DCS module. To solve this problem, we propose a feedforward look-up-table-based PUS design that can greatly reduce the critical path and increase the working frequency. Experimental DCS implementation in a Xilinx Virtex7 field programmable gate array shows that with this method the working frequency of the DCS module for quadrature phase-shift keying (QPSK) signals can be increased by 63.8%. Furthermore, using experimental and simulation data, it is demonstrated that the performance of the DCS module with increased working frequency is close to that of the off-line DCS algorithms for QPSK signals.

On the performance of joint iterative detection and decoding in coherent optical channels with laser frequency fluctuations

The joint iterative detection and decoding (JIDD) technique has been proposed by Barbieri et al. (2007) with the objective of compensating the time-varying phase noise and constant frequency offset experienced in satellite communication systems. The application of JIDD to optical coherent receivers in the presence of laser frequency fluctuations has not been reported in prior literature. Laser frequency fluctuations are caused by mechanical vibrations, power supply noise, and other mechanisms. They significantly degrade the performance of the carrier phase estimator in high-speed intradyne coherent optical receivers.This work investigates the performance of the JIDD algorithm in multi-gigabit optical coherent receivers. We present simulation results of bit error rate (BER) for non-differential polarization division multiplexing (PDM)-16QAM modulation in a 200Gb/s coherent optical system that includes an LDPC code with 20% overhead and net coding gain of 11.3dB at BER=10−15. Our study shows that JIDD with a pilot rate ⩽5% compensates for both laser phase noise and laser frequency fluctuation. Furthermore, since JIDD is used with non-differential modulation formats, we find that gains in excess of 1dB can be achieved over existing solutions based on an explicit carrier phase estimator with differential modulation. The impact of the fiber nonlinearities in dense wavelength division multiplexing (DWDM) systems is also investigated. Our results demonstrate that JIDD is an excellent candidate for application in next generation high-speed optical coherent receivers.

A Low-Noise Design Technique for High-Speed CMOS Optical Receivers

A careful comparison between alternative topologies to realize low-noise wideband TIAs is carried out in this work. In order to break the tradeoff between noise and bandwidth, the proposed front-end uses two stages, i.e. a low-noise narrowband transimpedance interface followed by an equalizer aimed at restoring the required bandwidth. The technique is especially effective for white noise components. The core first-stage amplifier exploits current reuse for minimum power consumption and is optimized for colored noise reduction. A net 4 × noise power reduction is achieved if compared with a design approach based on a traditional shunt-feedback TIA with the same bandwidth. A complete receiver, interfacing a commercial photodiode, and including the proposed two-stage front-end (TSFE), a limiting amplifier and a wideband output buffer has been realized in 65 nm CMOS. Optical communications tailored to 100GBASE-LR4 standard, which is specified for mid-to-long range transmissions at a channel rate of 25 Gb/s, are targeted. Realized prototypes show a sensitivity of -11.9 dBm at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> with a PRBS31 input pattern and a transimpedance gain of 83 dBΩ, while tolerating an overall input capacitance of 160 fF. To the best of the authors' knowledge, this is the best sensitivity performance achieved by 25-Gb/s optical receivers in CMOS, comparable to state-of-the-art BiCMOS realizations.

Research of High-Speed and Stable Photodetector of Monolithic Optocoupler Chip

Designed and fabricated a monolithically integrated high-speed optical receiver module optocoupler chip, which contains “Nwell-Pepitaxial-Psub” model for the photoelectric detector (PD), the transimpedance amplifier (TIA) and the subsequent processing circuits. Clarify the circuit structure of the TIA and the adjustable gain theory. Detailed analysis the frequency response of the PD models and simulated the PD theoretical analysis. Simulation results showed that when the temperature is constant and the photocurrent change from 5uA to 80uA, the response speed of the PD and TIA module change quickly. When the photocurrent (Iph) unchanged and the test temperature (T) change from -25℃ to 125℃, the delay time does not exceed 10ns. Tape-out with the 1P3M 0.35um BCD process and the test results showed when the T is 25℃ and the Iph is 20uA, the delay time of the whole chip are 155ns and 205ns. When the T is125℃ and the Iphh kept constant, the delay time of the whole chip are 153ns and 220ns.The results show that the photodetector design with high-speed response capability, combined with the TIA gain adjusted in real time, the high-speed monolithic integration optocouplers can be established.