Direct Detection Optical Receiver Research Articles

저궤도 위성 간 레이저 통신을 위한 직접수신 광수신기 구조 연구

저궤도 위성 네트워크를 통해 전세계에 통신 서비스를 제공하는 방안에 대한 관심이 높아지고 있다. 저궤도 위성 네트워크에서 노드 간 데이터를 주고받기 위해서는 레이저 통신 기술이 필요하다. 위성 간 레이저 통신 링크는 전송 거리가 매우 길어서 링크 연결을 위해 광수신기의 수신 감도가 중요하다. 본 논문에서는 저궤도 위성 간 레이저 통신 링크 구현에 적합한 광수신기 구조를 제안한다. 저궤도 위성 간 레이저 링크 시스템의 특성을 고려하여 링크 버짓을 계산하고 요구되는 수신감도를 도출한다. 도출된 수신감도 충족을 위한 avalanche photodiode (APD)기반 광수신기와 광섬유 전치증폭기 기반 광수신기의 성능을 평가하고 최대 전송 거리 분석을 통해 저궤도 위성간 링크에 적용 가능성을 확인한다.

Performance Analysis of a Multiple Subcarrier Modulated FSO Communication System using Direct Detection Optical Receiver under the Effect of Weak Atmospheric Turbulence

AbstractIn this paper, an analytical approach is presented to evaluate the bit error rate (BER) of a free space optical (FSO) link with radio frequency (RF) multiple subcarrier modulation, taking into account the effect of weak atmospheric turbulence considering a direct detection optical receiver followed by RF synchronous demodulator for each sub-channel. Analysis is carried out to find a closed-form expression for conditional BER at the output of the RF demodulators conditioned on a given value of atmospheric turbulence-induced fading and intermodulation distortion (IMD). The average BER for each sub-channel is then found by averaging the conditional BER over the probability density function of the atmospheric turbulence modeled as log-normal distribution. Degradations of BER due to atmospheric turbulence are evaluated for several values of system parameters like number of RF subcarrier, turbulence variance, link distance, data rate and power penalty suffered by the system due to atmospheric turbulence and IMD. For a given system bandwidth, it is found that the maximum power penalty occurs when the subcarrier number is around four and the performance gradually improves with increase in the number of subcarrier. For example, at a system bandwidth of 20 GHz with subcarrier number 4, the power penalty at a BER of 10–9 is found to be 30 dB for a link distance of 3.6 km, whereas the power penalty reduces to 13 dB when the number of subcarrier is increased to 32.

Performance Analysis of a STBC FDM FSO Communication System with Direct Detection Receiver under Turbulent Condition

Abstract Weather conditions are severely degraded the performance of FSO communication link. Atmospheric turbulence is one of the important weather conditions that degrade the performance even under clear sky condition. In this paper, we provide a noble analytical approach to evaluate the performance of STBC coded FDM FSO communication system with direct detection optical receiver under turbulent condition. Analysis is carried out to find the channel capacity of RF subcarrier modulation taking into consideration the effect of strong atmospheric turbulence which is modeled as gamma-gamma distribution and the probability density function of the conditional CNR, conditioned on a given turbulence-induced fading is derived considering equal gain receive diversity combining technique with direct detection optical receiver followed by RF synchronous demodulation. Results are evaluated numerically in terms of average CNR, BER and channel capacity for several system parameters like turbulence variance, link distance, data rate, etc.

Online digital offset mismatch compensation for high-speed time-interleaved ADC in real-time optical OFDM receiver.

The time-interleaved analog-to-digital converter (TI-ADC) is a good option to realize high-speed data conversion for both single-carrier and multi-carrier optical communication systems. Offset mismatch is one of its drawbacks, which causes distortion in the sampled data and degrades the bit error rate (BER) performance of communication systems. In this article, a low-complexity online digital offset mismatch compensation (OMC) scheme based on time-domain averaging is proposed and implemented with a commercial off-the-shelf field programmable gate array (FPGA) chip for high-speed optical OFDM communications. The proposed OMC scheme is experimentally demonstrated in real-time direct-detection optical OFDM receiver with a 5 GS/s TI-ADC. The experimental results show that the BER performance can be improved by more than an order of magnitude, by using the proposed OMC scheme, for both 16- and 64-QAM modulation formats. The receiver sensitivity can be improved by more than 5-dB in terms of the received optical power at the BER of 1e-3. What's more, the real-time measured BER performance is similar to that of by using offline DSP approaches and has good stability during the measurement period. Numerical simulations are performed under additive white Gaussian noise (AWGN) channel to fully verify the performance of the OMC scheme. It exhibits that the error floor in BER performance can be eliminated by using the OMC scheme and a negligible signal-to-noise ratio (SNR) penalty can be achieved compared with that of offset mismatch-free case.

90-Gb/s NRZ Optical Receiver in Silicon Using a Fully Differential Transimpedance Amplifier

We present the design and implementation of a 90 -Gb/s non-return-to-zero (NRZ) direct detection optical receiver that consists of a low-noise transimpedance amplifier (TIA), fabricated in a 55-nm SiGe BiCMOS technology, and a Ge photodiode integrated into a Silicon Photonic integrated circuit. Low-noise broadband operation is achieved using a fully differential TIA that provides the photodiode reverse bias. 50-, 56-, and 64-Gb/s NRZ operation is demonstrated at bit-error ratios (BERs) below $10^{-12}$ at sensitivities of $-$ 12.3-, $-$ 11.2-, and $-$ 11.1-dBm optical modulation amplitude (OMA) while consuming 128, 141, and 157 mW, respectively. Furthermore, a BER below $10^{-12}$ is achieved at 80 Gb/s with a sensitivity of $-$ 6.1 dBm (OMA) at 165 mW, and operation below KP4-FEC $({2.4 \times {10}^{-4}})$ is demonstrated up to 90 Gb/s with a sensitivity of $-$ 7.1 dBm (OMA) while consuming 222 mW. All BERs were measured in real time and without DSP or equalization to compensate the receiver. The presented receiver achieves the best reported sensitivities up to 90 Gb/s, at the second-lowest power consumption, and is the first reported integrated optical RX up to 90 Gb/s that is tested in real time without any equalization or DSP to compensate the receiver. The presented optical receiver is ideally suited for upcoming short-reach applications.

Optical Communication Using Linear Sums of Optical Receiver Modes: Proof of Concept

We demonstrate the feasibility of an optical communication system that transmits linear sums of optical receiver modes (ORMs) as optical signals called ORM signals. The ORMs are inherent modes of conventional direct-detection optical receivers for wavelength-division multiplexing systems. Two lowest order ORMs are used to build ORM signals having distinct received voltage waveforms from each other. The optical receiver used has a Fabry–Perot filter as its optical filter and a fourth-order Bessel filter as its electrical filter. With these filters, corresponding ORMs are evaluated numerically and the ORM signals are generated using digital-to-analog converters. The received voltage waveforms after the receiver electrical filter are in good agreement with our analysis.

Statistical analysis and performance evaluation of optical array receivers for deep-space optical communications under random tracking errors

Telescope array receiver is a viable architecture for Earth-based reception in a deep-space optical communication system. In this paper, effects of random tracking errors on the performance of optical array receivers for an inter-planetary deep-space optical communications link between Earth and Mars is investigated. The paper has two major parts. In the first part, statistical analysis and mathematical modeling of the impact of tracking errors on general direct-detection optical communication receivers is presented. The analytical results show that tracking errors could severely degrade the performance of optical receivers; hence, these need to be compensated, especially in a deep-space link. In the second part, design and analysis of a closed-loop tracking subsystem for telescope array receivers operating in a deep-space link is presented. An end-to-end simulation platform for communication between Earth and Mars is implemented that incorporates direct-detection array receivers and the proposed tracking subsystems to alleviate the effects of random tracking errors. Extreme channel conditions, i.e., maximum distance, strong background noise and turbulence conditions are modeled to evaluate the performance bounds. Simulations results depict that in worst-case channel conditions, the proposed architecture mitigates the impact of tracking errors to be within reasonable limits. Comparison of achievable data rates show that in the presence of random tracking errors, replacement of a large telescope (10m diameter) with an array of relatively smaller-sized telescopes (i.e., 100, 1m telescopes) results in acceptable performance loss (i.e., <13%). Hence, performance degradation due to tracking errors does not pose a major limitation in employing array architecture in deep-space communication. The presented analysis further strengthens the viability of array architecture compared to a monolithic, large telescope for deep-space communications.

Integrated fiber optical receiver reducing the gap to the quantum limit

Experimental results of a single-photon avalanche diode (SPAD) based optical fiber receiver integrated in 0.35 µm PIN-photodiode CMOS technology are presented. To cope with the parasitic effects of SPADs an array of four receivers is implemented. The SPADs consist of a multiplication zone and a separate thick absorption zone to achieve a high photon detection probability (PDP). In addition cascoded quenchers allow to use a quenching voltage of twice the usual supply voltage, i.e. 6.6 V instead of 3.3 V, in order to increase the PDP further. Measurements result in sensitivities of −55.7 dBm at a data rate of 50 Mbit/s and −51.6 dBm at 100 Mbit/s for a wavelength of 635 nm and a bit-error ratio of 2 × 10−3, which is sufficient to perform error correction. These sensitivities are better than those of linear-mode APD receivers integrated in the same CMOS technology. These results are a major advance towards direct detection optical receivers working close to the quantum limit.

Theoretical Comparative Analysis of BER in Multi-Channel Systems With Strip and Photonic Crystal Silicon Waveguides

We present a comparative analysis of the performance of multi-channel photonic systems containing strip or photonic crystal (PhC) silicon (Si) waveguides in the presence of white Gaussian noise. Specifically, we consider a multi-wavelength optical signal propagating either in a strip single-mode Si photonic waveguide (Si-PhW) or in a Si PhC waveguide (Si-PhCW), each channel consisting of a CW nonreturn-to-zero ON–OFF keying modulated signal. The output signal is demultiplexed and the signal in each channel is analyzed using direct-detection optical receivers. We describe the propagation of the optical signal in the Si-PhW and Si-PhCW using a linearized model and validate our main results by employing a rigorous theoretical model that incorporates all relevant linear and nonlinear optical effects and the mutual interaction between free-carriers and the optical field. The bit error rate (BER) of the transmitted signal is calculated by using both a time- and frequency-domain Karhunen–Loeve expansion method. Our analysis suggests that due to enhanced nonlinear effects, for comparable optical power, a similar BER is achieved in a PhC waveguide about $100\times$ shorter than a strip one, with a particularly strong signal degradation being observed in the slow-light regime of the Si-PhCW.

Calculation of Bit Error Rates in Optical Systems With Silicon Photonic Wires

A theoretical approach to calculate the bit error rate (BER) in optical systems containing silicon photonic wires (Si-PhWs) is presented. Specifically, the optical link consists of a single-mode silicon-on-insulator strip waveguide followed by a direct-detection optical receiver containing an optical filter, an ideal square-law photodetector, and an electrical filter. We assume that the optical input consists of a superposition of a nonreturn-to-zero ON–OFF keying modulated optical signal and an additive white Gaussian noise, the BER of the transmitted optical signal being calculated using the time domain Karhunen–Loève expansion method. The propagation of the optical signal in the Si-PhW is described by employing both a rigorous theoretical model that incorporates all relevant linear and nonlinear optical effects and the mutual interaction between the free carriers and the optical field, as well as a linearized model valid in the low-noise power regime. These analytical and computational tools are then used to comprehensively investigate the influence of the parameters characterizing the waveguide and optical signal on the transmission BER.

Joint Probability Density Functions for Direct-Detection Optical Receivers

We derive joint probability density functions (JPDFs) for two adjacent data from direct-detection optical receivers in dense wavelength-division multiplexing systems. We show that the decision using two data per bit can increase the receiver sensitivity compared with the conventional decision. Our JPDFs can be used for software-defined optical receivers enhancing the receiver sensitivities for intensity-modulated channels.

Accuracy of Gaussian Approach for the Performance Evaluation of Direct-Detection Receiver with Partially Polarized Noise

We investigate the accuracy of a Gaussian approach (GA) developed to estimate the performance of a direct-detection optical receiver with arbitrary optical and electrical filtering and in the presence of partially polarized noise due to polarization-dependent loss (PDL). The accuracy is assessed by comparison of the performance estimates obtained from the GA with the estimates obtained from a rigorous method (RM) based on the calculation of the moment-generating function of the current at the optical receiver output. We show that the GA has a good accuracy when considering the variation of the optical filter bandwidth, extinction ratio, degree of polarization of the noise (DOP), and angle between signal and noise polarizations. However, it fails to predict the receiver sensitivity within 2 dB of the RM when DOP is greater than 0.7 and signal and noise polarizations are orthogonal in the Jones space. Nevertheless, it is shown that the GA provides receiver sensitivity estimates with good accuracy in most cases of long-haul optical communication systems influenced by PDL, where the typical average DOP is below 0.15. Due to its simplicity, shorter computation time, and good accuracy, the GA is a good tool to assess the performance of such optical systems.

Direct-detection optical cdma receiver with interference estimation and double optical hardlimiters

This paper proposes a new channel interference cancellation technique using interference estimation and double optical hardlimiters (DHLs) for direct-detection optical code-division multiple-access systems. In the proposed system, when the output of the DHL is 0, the proposed system outputs 0. When the output of the DHL is 1, the proposed system reconstructs the interference and estimates whether the output 1 is owing to the interference or the transmitted signal. It is shown that the proposed system is effective to reduce the effects of the channel interference. Moreover, it is shown that the proposed system can improve the error floor of the systems with DHL.

Bit error probability reduction in direct detection optical receivers using RZ coding

We analyze the bit error probability reduction for direct detection ON-OFF keying optical receivers using return-to-zero (RZ) coding instead of the nonreturn-to-zero (NRZ) format. For the same average optical power, RZ is shown to outperform NRZ, even when employing the same receiver bandwidth. Results are given for receivers whose noise variance is i) dominated by a signal-independent term (e.g., simple pin diode receivers), ii) dominated by a signal-dependent term (e.g., optically preamplified receivers), and iii) made up of two equally important contributions [e,g,, avalanche photodiode (APD) receivers]. Based on semianalytic simulations including intersymbol interference, we show that the achievable RZ sensitivity gain is typically less for dominating signal-independent noise than for dominating signal-dependent noise, where it amounts to about 3 dB. We also quantitatively discuss the influence of the optical pulse shape on the achievable RZ coding gain, and show that finite extinction ratios can significantly reduce that gain, especially when the RZ signals are produced by direct-modulation methods.

A novel analytical approach to the evaluation of the impact of fiber parametric gain on the bit error rate

We present in this paper a novel accurate method to analyze the performance of an optical link where the amplified spontaneous emission noise, enhanced by a fiber nonlinear phenomenon called parametric gain, is the limiting factor. Our method allows us to compute the exact error probability given a generic noise spectral density at the input of a direct detection optical receiver, using arbitrary optical and electrical filters. We compare our results with those predicted using the standard Gaussian technique (based on the Q factor), showing that this approximation may lead to significant errors. Our method is then used to evaluate the impact of parametric gain on a realistic long-haul multiwavelength link operating at 10 Gb/s, showing both the system limitation imposed by this phenomenon and the inaccuracy of the Q factor method.

Single- and multiple-pulse noncoherent detection statistics associated with partially developed speckle

Single- and multiple-pulse detection statistics are presented for aperture-averaged direct detection optical receivers operating against partially developed speckle fields. A partially developed speckle field arises when the probability density function of the received intensity does not follow negative exponential statistics. The case of interest here is the target surface that exhibits diffuse as well as specular components in the scattered radiation. An approximate expression is derived for the integrated intensity at the aperture, which leads to single- and multiple-pulse discrete probability density functions for the case of a Poisson signal in Poisson noise with an additive coherent component. In the absence of noise, the single-pulse discrete density function is shown to reduce to a generalized negative binomial distribution. The radar concept of integration loss is discussed in the context of direct detection optical systems where it is shown that, given an appropriate set of system parameters, multiple-pulse processing can be more efficient than single-pulse processing over a finite range of the integration parameter n.

Gain equalization of EDFA cascades

Investigates the impact of wavelength-dependent erbium-doped fiber amplifier (EDFA) gain spectrum on multichannel direct-detection lightwave transmission systems employing multiple amplifiers. An analysis is presented which quantifies the constraints imposed by received power imbalance, signal-to-noise ratio (SNR), and receiver sensitivity on an EDFA cascade. Expressions are derived which relate the system constraints to the EDFA gain imbalance, bit rate, number of channels, and receiver dynamic range. Results demonstrate that when four-wave mixing (FWM) is compensated in an 11-channel system, received power imbalance can impose a significant constraint on transmission distance when the EDFA gain imbalance is greater than 1 dB or when bit rate is less than 1.8 Gb/s. In addition, performance of the preemphasis gain equalization technique is studied for multichannel systems employing APD or p-i-n/FET direct-detection optical receivers. Simple expressions are derived which can be used to quantify the increase in transmission distance obtained when employing preemphasis equalization. Results indicate that equalization of the received power spectrum can provide a two- to four-fold increase in the transmission distance when using APD receivers, compared to a one- to two-fold improvement with p-i-n/FET receivers. Analytic results are compared with results obtained by proven simulation methods and found to be in good agreement.

Performance analysis of optical receivers with space diversity reception

The performance of digital and analogue direct-detection optical receivers with space diversity reception is analysed. The cumulative probability distribution of the received signal is calculated for M-branch selection diversity and equal-gain combining diversity receivers. For a given probability of detection, the permissible threshold detection level is shown to increase with the number of diversity branches. The improvement in carrier-to-noise ratio (CNR) is shown to be higher for selection diversity compared to combining diversity detection. Optimum diversity array spacing is calculated; this shows the practicality of space diversity systems.

Exact expression for Prabhu upper bound for digital communication systems with noise and interference

The authors first present an exact expression for the Prabhu general upper bound on error probability of the canonical binary system with noise and interference in terms of a modified Bessel function. This bound is tighter than the modified Chernoff bound and simpler than a recent approximation. Secondly, the new expression is used to evaluate the error rate of an optically preamplified direct-detection optical receiver and is shown to provide tighter estimates of the error probability than either the Chernoff or modified Chernoff bounds for amplifier gains of practical interest.

Jitter in the square synchroniser on direct detection optical communications. Part 2: comparison with Franks and Bubrouski's results

For part I see ibid. p. 209. The increasing use of very high bit rate direct detection optical systems with the need for more and more precise clock recovery circuit (CRC) is a justification for the study of CRC performance. In a previous paper, this study was developed for the square synchroniser but its validation needs to be confirmed. In this paper, this confirmation is effected by comparing the results established in that paper with Franks and Bubrouski&apos;s work. A relevant outcome of this comparison is that the study of the square synchroniser performance in the direct detection optical receiver can be regarded as a generalisation of the Franks and Bubrouski&apos;s study.