Optimization of InP APDs for high-speed lightwave systems

Abstract

Abstract-Calculations based on a rigorous analytical model are carried out to optimize the width of the indium phosphide avalanche region in high-speed direct-detection avalanche photodiode-based optical receivers. The model includes the effects of intersymbol interference (ISI), tunneling current, avalanche noise, and its correlation with the stochastic avalanche duration, as well as dead space. A minimum receiver sensitivity of 28 dBm is predicted at an optimal width of 0.18 m and an optimal gain of approximately 13, for a 10 Gb/s communication system, assuming a Johnson noise level of 629 noise electrons per bit. The interplay among the factors controlling the optimum sensitivity is confirmed. Results show that for a given transmission speed, as the device width decreases below an optimum value, increased tunneling current outweighs avalanche noise reduction due to dead space, resulting in an increase in receiver sensitivity. As the device width increases above its optimum value, the receiver sensitivity increases as device bandwidth decreases, causing ISI to dominate avalanche noise and tunneling current shot noise.

On the Use of Gaussian Approximation in Analyzing the Performance of Optical Receivers

“…For its relevance to the present paper, we begin by briefly reviewing the probabilistic model for the conditional receiver outputs, À 0 and À 1 , developed using the PI and PD methods to determine their BERs; these BERs are termed BER I and BER D . Both the mean and variance of R n , denoted by n and 2 n , respectively, are shown in [7] to be proportional to the average number of photons per bit, n 0 . Additionally, they are both exponentially decreasing with the bit order n. More precisely [7],…”

“…Both the mean and variance of R n , denoted by n and 2 n , respectively, are shown in [7] to be proportional to the average number of photons per bit, n 0 . Additionally, they are both exponentially decreasing with the bit order n. More precisely [7],…”

“…A closed-form expression for the BER can be found by first conditioning on the past bit pattern; then the BER is calculated by averaging the conditional BER over all possible past bit patterns. This approach, denoted here by the bit-patterndependent (PD) approach, was adopted by Ong et al [7], [8] in which the receiver output, conditional on the present and all the past bits, is approximated by a Gaussian random variable. The validity of this approximation has been verified for large number of incident photons [9].…”

InGaAsN as absorber in APDs for 1.3 micron wavelength applications

“…The upper limit of these APD gain-bandwidth products (~150 GHz) is mainly due to the minimum InP multiplication layer thickness required to avoid excessive band-to-band tunnelling current [1]. Although In 0.52 Al 0.48 As (lattice-matched to InP) offers a slightly larger band gap (1.4 eV) compared to InP (1.35 eV) and hence a thinner In 0.52 Al 0.48 As multiplication layer for the same tunnelling current level, the gain-bandwidth products of In 0.53 Ga 0.47 As /In 0.52 Al 0.48 As APD are still limited to ~180 GHz [2].…”

Avalanche Photodiodes in High-Speed Receiver Systems

“…Ong et al (Ong et al, 2009) replaced this with the more realistic assumption that the receiver output, conditional on the state of the present bit and the entire past bit stream, is a Gaussian random variable. This enables one to compute the BER conditional on the entire past bit stream, and then average the resulting patternspecific BERs over all possible past bit patterns to obtain the overall average BER.…”