Gain suppression in semiconductor lasers: The influence of dynamic carrier temperature changes

Abstract

An analytic expression for the gain suppression coefficient of semiconductor laser in terms of carrier temperature and other material parameters is presented. The expression is derived from a density matrix formulation of gain in diode lasers based on a dynamic carrier heating model. We find that in the single mode approximation the theoretical estimate of the gain suppression coefficient is of the order 10−23 m3 in agreement with experimental values. This supports recent direct experimental demonstrations that dynamic carrier heating, rather than spectral hole burning provides the dominant contribution to nonlinear gain in semiconductor lasers.

Review on the chirping characteristics of directly modulated laser diodes under high transmission speeds in optical fiber networks

“…When the laser operates above threshold, g is suppressed and clamped just under gth due to the gain suppression effect. The gain suppression reasons can be attributed to many physical mechanisms, including intraband relaxation processes of injected carriers when the laser is biased above threshold (Ahmed & Yamada, 1998), spectral hole burning (Adams, 1983), nonlinear absorption (Bowers et al, 1985), carrier diffusion (Furuya et al, 1978), and dynamic carrier heating effects (Gomatam & DeFonzo, 1988). The phase condition determines the frequency of the laser light (vlaser), which requires the optical wave to be reflected in phase after completing a round-trip in the cavity and is given by (Farghal, 1999) .…”

“…The relationship between intensity and frequency modulation is known as "frequency chirp" (Agrawal, 2012). In digital transmission systems, lasers with a large differential gain can increase the frequency chirp, which meets the requirement of 40-Gbps shortreach data communication links (Gomatam & DeFonzo, 1988;Yousuf & Najeeb-ud-din, 2018a). The frequency chirp usually results in changes in pulse width and shifts in the output wavelength.…”

“…There are several reasons why gain suppression may occur, which include various physical mechanisms. These mechanisms are intraband relaxation processes of injected carriers when the laser is biased above the threshold (Ahmed & Yamada, 1998), spectral hole burning (Adams, 1983), nonlinear absorption (Bowers et al, 1985), carrier diffusion (Furuya et al, 1978), and dynamic carrier heating effects (Gomatam & DeFonzo, 1988). It is important to investigate the effects of laser parameters such as α-factor and gain suppression coefficient ε on frequency chirp induced by directly modulated LDs, particularly at high modulation bit rates.…”

Impact of linewidth enhancement factor and gain suppression on chirp characteristics of high-speed laser diode and performance of 40 Gbps optical fiber links

“…The gain suppression suppresses the carrier-photon resonance and increases the damping rate of relaxation oscillations, which then reduces the transient chirp and introduces adiabatic chirp [20,25]. The gain suppression was attributed to many physical mechanisms, including intraband relaxation processes of injected carriers [26], spectral hole burning [27], nonlinear absorption [28], carrier diffusion [29], and dynamic carrier heating effects [30].…”