Noise and Regeneration in Semiconductor Waveguides With Saturable Gain and Absorption

Abstract

Abstract-We have modeled the noise properties of a novel waveguide device with regenerative properties. The device consists of alternating sections of saturable gain and absorption, which give a nonlinear power transfer function. We investigate the relative intensity noise spectra and signal-to-noise ratio after the device by both a small-signal analysis and large-signal simulation, and we show that the gain saturation gives noise redistribution at the mark level. We also examine the influence of the nonlinearity on the noise probability density function and show that the standard approximations of Gaussian and noncentral 2 distributions do not give a satisfying description. The strength and weaknesses of the limiting cases of static transfer functions and linear noise transfer as well as the small-signal analysis are examined in the case of bit-error-rate estimation in a cascade of regenerators. The interplay between increased nonlinearity and noise is investigated and we show that the increased nonlinearity achieved by additional device sections can improve the cascadability although more amplified spontaneous emission noise is added.

Modeling of bit error rate in cascaded 2R regenerators

“…The latter part will constitute the increase in BER at the particular regenerator considered. A more correct transformation of the PDF using the nonlinear transfer function would give a non-Gaussian distribution [6], [9] at the output of the regenerator. The PDF can then no longer be described using only the mean value and variance but has to be described in detail through the cascade of regenerators, including the convolution with the amplifier noise and the nonlinear transformation.…”

Output Power PDF of a Saturated Semiconductor Optical Amplifier: Second-Order Noise Contributions by Path Integral Method

“…We have previously measured and calculated the probability density functions (PDFs) after amplification in a saturated SOA [11]. The calculations of the PDFs were based on statistical simulations, standard assumptions like Gaussian or noncentral -distributions, or used models [12] that are not able to describe the nonlinear noise redistribution shown in experiments [11], [13]. Large-signal simulations can, in principle, include the nonlinear redistribution, but it is difficult Manuscript to reach far out in the tails of the distributions, i.e., to simulate the rare occurrences of errors corresponding to low BERs.…”

Steep and adjustable transfer functions of monolithic SOA-EA 2R regenerators

“…It is clearly seen that the concatenation of an additional pair gives a stronger nonlinearity with a larger ER and threshold steepness, i.e., a large change in output power for a small change in input power at the regenerator threshold, i.e., the point where It should be noted that the additional gain section also introduces more noise, and hence, an increase in the noise figure [5]. In order to reduce this effect, the first SOA in the device should have as large a gain as possible [11].…”

“…This drawback can be remedied by combining the saturable absorber with a section of saturable gain in the form of a semiconductor optical amplifier (SOA) [3]. We have earlier proposed [4], [5] an integrated component for 2R regeneration consisting of an SOA and an EA and concatenated sections thereof, as shown in Fig. 1.…”