The sensitivity of photoconductor receivers for long-wavelength optical communications

We calculate the sensitivity of In0.53Ga0.47As photoconductor receivers for use in moderate to high bit-rate lightwave transmission applications. It is found that the noise of photoconductive receivers is dominated at all bit ratesB < 4Gbit/s by Johnson noise in the conductive channel. Nevertheless, the total noise current decreases approximately linearly with photoconductive gain, and therefore the sensitivity of photoconductive receivers can be comparable to high-sensitivity p-i-n photodiode receivers. The sensitivity of practical photoconductive receivers compares most favorably with p-i-n receivers in the bit-rate range of 500-2 Gbit/s. However, receivers employing high-speed In0.53Ga0.47As/InP avalanche photodiodes are expected to be more sensitive than photoconductive receivers over the entire bit-rate range considered. In this analysis, we consider the effects of slow photoconductor response on receiver sensitivity, and find that the limited gain-bandwidth product of practical photoconductors increases the complexity of the receiver circuit by necessitating equalization, resulting in a decrease in receiver sensitivity and dynamic range.     

Effect of chirping-induced waveform distortion on the performanceof direct detection receivers using traveling-wave semiconductor opticalpreamplifiers

The influence of chirping-induced waveform distortion on the performance of multigigabit-per-second traveling-wave semiconductor optical amplifier (TWSOA)/p-i-n direct detection receivers is evaluated. The results are based on a novel method of evaluating the probability of error in the presence of the signal-spontaneous and spontaneous-spontaneous beat noise components. Laser chirping causes the dependence of the receiver sensitivity on the fiber dispersion coefficient×length product DL to be different for TWSOA/p-i-n and avalanche photodiode (APD) receivers. Compared to the APD receiver, the sensitivity of the TWSOA/p-i-n receiver degrades less quickly. So for cases of practical interest, the TWSOA/p-i-n receiver is more tolerant of chirping-induced waveform distortion     

Investigation of manufacturing variations of planar InP/InGaAs avalanche photodiodes for optical receivers

Planar InP/InGaAs avalanche photodiodes are widely used for high-speed optical receivers in optical fiber communication systems. Even though these avalanche photodiodes offer the excellent characteristics in high-speed operation, the performance metrics are affected by manufacturing parameter variations considerably. In this paper, the effects of manufacturing variations on the device performance are investigated. In order to build a photodiode model, the test structures were fabricated and the measured current-voltage characteristics were compared with the simulated data to verify the model. After the model verification, the variations of the breakdown voltage and punch-through voltage according to the different manufacturing parameters such as multiplication layer width and charge sheet density are examined. Based on the results, the manufacturability of the avalanche photodiodes can be improved by analyzing the manufacturing variations.     

Power penalty due to decision-time jitter in receivers using avalanche photodiodes

Power penalties on receiver sensitivity due to the presence of timing jitter are derived for receivers incorporated with PIN detectors and with avalanche photodiodes. It is shown that the presence of timing jitter will lower the optical gain of the avalanche photodiodes and will reduce the improvement in receiver sensitivity of using avalanche photodiodes over PIN detectors. Using computer simulation on results of transmission experiments it is shown that the receiver sensitivity can be degraded by several decibels owing to the presence of timing jitter in the Anritsu pulse pattern generator and/or error detector.     

Sensitivity penalty calculation for burst-mode receivers using avalanche photodiodes

This paper presents the sensitivity penalty for burst-mode receivers using avalanche photodiodes. The analysis takes into account detailed avalanche photodiode statistics, additive Gaussian noise, intersymbol interference and dc offsets in the receiver channel. The penalty has been calculated via comparison of bit-error rates (BERs), obtained using numerical integration, both in continuous- and burst-mode operation. Sensitivity penalties for burst-mode operation as a function of the mean avalanche gain are presented. The Gaussian approximation systematically underestimates the burst-mode penalty. It is shown that the penalty depends upon both the type of avalanche photodiode (APD) and the required BER. Optimum avalanche gains maximizing the sensitivity of the receiver are given. The influence of dc-offsets upon the sensitivity is studied. Furthermore, it is shown that the impulse response of the filters used to extract the decision threshold profoundly impacts the receiver performance. Finally, some important guidelines for the design of high sensitivity and wide dynamic range burst-mode receivers are given.     

Reduction of spectral noise density in p-i-n-HEMT lightwavereceivers

The spectral noise density of a lightwave receiver is computed from known physical parameters of the photodiode and the high-electron-mobility transistor (HEMT). Low noise is achieved for an appropriate choice of device parameters. The results are applied to circuits built with readily available commercial HEMTs and p-i-n photodiodes. They also predict the superior noise performance of cooled receivers which cannot be readily derived from previous work     

Transmission and signal processing techniques for gigabit lightwave systems

The technology of optical-fiber transmission systems has advanced rapidly within recent years; a number of laboratories having reported gigabit transmission over 100-km spans. These developments have placed increasing emphasis on the associated signal processing functions such as timing extraction and regeneration. This paper will review laser, fiber, and receiver requirements for high-speed systems and describe two recent lightwave transmission experiments featuring distributed feedback lasers, low-loss dispersion-shifted fiber, germanium avalanche photodiode receivers, and gallium arsenide logic devices.     

The effect of nonuniform gain on the multiplication noise of InP/InGaAsP/ InGaAs avalanche photodiodes

We have investigated the effect of spatial gain uniformity on the multiplication noise of InP/InGaAsP/InGaAs avalanche photodiodes (APD's) with separate absorption, "grading," and multiplication regions. APD's with localized regions of high gain exhibit higher excess noise factors and poorer Performance in lightwave receivers than those with uniform gain.     

Photoconductor receiver sensitivity

The various contributions to photoconductor (PC's) noise are calculated and are used to determine the sensitivity of digital photoconductor receivers for use in lightwave communication systems. We find that Johnson noise is the most significant source of noise current up to bit rates as high as 4 Gbit/s, above which FET channel noise becomes dominant. In comparing the results obtained for ideal photoconductive receivers with receivers employing p-i-n photodetectors, we find that the sensitivities of both circuits are comparable, provided that low-capacitance p-i-n receivers are employed. In contrast, we find that avalanche photodiode receivers have higher sensitivities than either photoconductor or p-i-n receivers over the entire bit-rate range considered. It is concluded that equalization necessary for photoconductor receiver operation at high bit rates due to a limited gain-bandwidth product significantly degrades the sensitivity of the receiver.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the Various receiver designs.     

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the various receiver designs.     

Effect of the nonlinear gain in semiconductor lasers on theperformance of multigigabit-per-second lightwave systems

The implications on performance of the functional form of the nonlinear gain in single-mode semiconductor lasers are studied for multigigabit-per-second, intensity-modulation, direct-detection lightwave systems. Compared to a previously used functional dependence on the photon and carrier densities, a new result due to G. Agrawal (1988) can, depending on the fiber dispersion and gain compression factor, yield quite different receiver sensitivities     

Gain-bandwidth-limited response in long-wavelength avalanche photodiodes

The gain-bandwidth(GB)-limited response of In0.53Ga0.47As/ InP heterostructure avalanche photodiodes (APD's) and related devices used in long-wavelength digital optical receivers is calculated. We find that these diodes, as currently designed, are useful at bit ratesB lsim 2Gbit/s when employed in conjunction with high-sensitivity optical receivers. Response at higher bit rates may be obtained depending on the details of device design. On the other hand, use of poor-quality receivers that require moderate-to-high values of optimum gain can significantly degrade the performance of heterostructure APD's at high bit rates due to GB limitations. We also show that APD receiver bandwidth can be expressed in terms of the sensitivity obtained using the receiver in conjunction with a p-i-n photodiode. It is found that the response speed of optimized receivers is lowest for an APD effective ionization rate ratio ofk = 0.5.     

Optical receiver for VHF multichannel video transmission

Optical receivers for multichannel TV transmission in the VHF band are analyzed and tested from the viewpoints of linearity, sensitivity, and frequency response. Photodiodes and avalanche photodiodes are compared for use as a front-end detector. Optimization of the preamplifiers is studied in terms of both configurations and biasing conditions. Improvement of frequency characteristics, using a Percival coil, is also investigated. It is concluded that a receiver using a photodiode can attain as high a sensitivity as and a greater linearity (around 5 dB) than one using an avalanche photodiode     

Effect of avalanche build-up time on avalanche photodiode sensitivity

A calculation method for the receiver sensitivity of an avalanche photodiode is considered, taking into account avalanche build-up time and carrier transit time, in addition to the CR time constant. Actual receiver performance is estimated in a high data rate region of up to 10 Gbits/s for germanium avalanche photodiodes, applying the measured avalanche build-up time.     

Avalanche photodiodes on silicon photonics

Silicon photonics technology has drawn significant interest due to its potential for compact and high-performance photonic integrated circuits.The Ge-or Ⅲ-Ⅴ material-based avalanche photodiodes integrated on silicon photonics provide ideal high sensitivity optical receivers for telecommunication wavelengths.Herein,the last advances of monolithic and hetero-geneous avalanche photodiodes on silicon are reviewed,including different device structures and semiconductor systems.     

Ge-on-SOI-Detector/Si-CMOS-Amplifier Receivers for High-Performance Optical-Communication Applications

In this paper, an overview and assessment of high-performance receivers based upon Ge-on-silicon-on-insulator (Ge-on-SOI) photodiodes and Si CMOS amplifier ICs is provided. Receivers utilizing Ge-on-SOI lateral p-i-n photodiodes paired with high-gain CMOS amplifiers are shown to operate at 15 Gb/s with a sensitivity of -7.4 dBm (BER=10^-12) while utilizing a single supply voltage of only 2.4 V. The 5-Gb/s sensitivity of similar receivers is constant up to 93 degC, and 10-Gb/s operation is demonstrated at 85 degC. Error-free (BER<10^-12) operation of receivers combining a Ge-on-SOI photodiode with a single-ended high-speed receiver front end is demonstrated at 19 Gb/s, using a supply voltage of 1.8 V. In addition, receivers utilizing Ge-on-SOI photodiodes integrated with a low-power CMOS IC are shown to operate at 10 Gb/s using a single 1.1-V supply while consuming only 11 mW of power. A perspective on the future technological capabilities and applications of Ge-detector/Si-CMOS receivers is also provided     

High-sensitivity and wide-dynamic-range 10 Gbit/s APD/preamplifieroptical receiver module

InAlAs avalanche photodiodes (APD) and SiGe-HBT preamplifier 10 Gbit/s optical receiver modules have been developed. The measured back-to-back minimum sensitivity and the optical overload with a pseudorandom binary sequence of 2³¹ - 1 at a bit error rate of 10^-9 are -29.5 and +0.4 dBm, respectively. The dynamic range is 29.9 dB. These results show the highest sensitivity and the widest dynamic range yet reported for 10 Gbit/s APD receivers     

High-frequency properties of avalanche multiplication of photocarriers in structures with negative feedback

The high-frequency characteristics of photosensitive avalanche Si-SiC structures were studied. It is shown that their high-speed operation is substantially superior to that of silicon avalanche photodiodes. A theoretical analysis of the high-frequency properties of avalanche photodiodes is carried out and analytical expressions for the gain-bandwidth product are obtained. It is shown that this product is not a universal parameter for a metal-insulator-semiconductor structure with a negative feedback, since, for high amplification factors, the effective value of the relation of the impact-ionization coefficients for different types of charge carriers in such structures turns out to be significantly different from that in avalanche photodiodes.     

Performance of smart lightwave receivers with linear equalization

Signal processing techniques can be used to reduce linear and nonlinear distortion in high-speed lightwave systems caused by fiber dispersion and nonideal responses of optoelectronic and electronic components. The improvement in the performance of 2.5 and 10 Gb/s intensity modulation, direct detection systems is assessed for receivers which utilize an analog taped delay line equalizer to compensate for signal distortion. Synchronous and fractionally spaced equalizers are evaluated. Smart receivers that jointly optimize the decision time, decision threshold, and equalizer tap weights under a minimum bit error ration criterion are considered. This yields the optimum system performance and allows consideration of both reduced distortion and enhanced noise arising from the signal processing. The effectiveness of the equalization is determined as a function of several important system parameters. Three-tap and five-tap synchronous equalizers yield virtually the same improvement in receiver sensitivity. Depending on the system, a five-tap fractionally spaced equalizer with half-bit-period tap spacing may or may not be significantly more effective than a three-tap synchronous equalizer