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Chinese Journal of Lasers

Improving the Filter and Bistable Characteristics of Distributed-Feedback Semiconductor Optical Amplifiers Based on Linearly Variable Current Injection

Xin-Hong Jia, Guang-Qiong Xia

Published Jan 1, 2005• 0 citations

Abstract

The distributed-feedback semiconductor optical amplifiers(DFB-SOAs) possess the dual functions of amplifier and filter due to the built-in grating.If the input power is close to saturation value,dispersive optical bistability occurs as a consequence of the positive feedback loop informed among the optical intensity in active-layer,effective mode refractive index,and resonance amplification frequency.By introducing spatial phase-shift and chirp,the filter and bistable performances can be improved.A novel configuration based on linearly variable current injection is proposed to improve the filter and bistable characteristics of the DFB-SOAs.The coupled mode equation and carrier rate equation are used to perform characteristic comparisons of this configuration with phase-shifted and chirped DFB-SOAs.The results show that,this method not only enhances the on-off switching ratio,but also has similar transmission spectra with phase-shift effect method,and similar bistable features,such as the wide-band and the flat upper branch of the hysteresis,with chirp effect method.

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The distributed-feedback semiconductor optical amplifiers(DFB-SOAs) possess the dual functions of amplifier and filter due to the built-in grating.If the input power is close to saturation value,dispersive optical bistability occurs as a consequence of the positive feedback loop informed among the optical intensity in active-layer,effective mode refractive index,and resonance amplification frequency.By introducing spatial phase-shift and chirp,the filter and bistable performances can be improved.A novel configuration based on linearly variable current injection is proposed to improve the filter and bistable characteristics of the DFB-SOAs.The coupled mode equation and carrier rate equation are used to perform characteristic comparisons of this configuration with phase-shifted and chirped DFB-SOAs.The results show that,this method not only enhances the on-off switching ratio,but also has similar transmission spectra with phase-shift effect method,and similar bistable features,such as the wide-band and the flat upper branch of the hysteresis,with chirp effect method.

We use spatial chirp of the built-in grating to improve optical bistability on reflection from distributed feedback semiconductor laser amplifiers. We show that improvements in the on-off switching ratio occur because spatial chirp greatly affects the saturation behavior of the reflectivity resonances, allowing access to states of low reflection during bistable switching. We also show that spatial chirp modifies the spectral range of the variety of hysteresis shapes that occur on reflection. In doing so, we discover a new type of hysteresis loop that reveals a qualitative difference between the loop-shaped hystereses occurring near the two edges of the stop band. With spatial chirp, the new hysteresis loop can exhibit an on-off switching ratio in excess of 100000.

Dispersive optical bistability in a Fabry-Perot, a distributed feedback (DFB), or a distributed Bragg reflector (DBR), semiconductor laser amplifier has recently attracted much attention, because of its potential in the operation of highly functional optical devices. While the steady-state operation of bistable diode laser amplifiers are well understood, studies of the dynamic properties have been limited to switching time, critical slowing down and output spiking measurements[1-3]. Little attention has been paid to the dynamic frequency chirp which is associated with the turn-on spike at the onset of light injection. Such frequency chirp exists because in dispersive bistability the Fabry-Perot resonance (or the DBR/DFB transmission peak) sweeps through the injected wavelength as a result of alight induced refractive index change. In this paper, we report on a theoretical analysis and the first experimental observation of this dynamic chirp in a Fabry-Perot type nonlinear semiconductor laser amplifier. It is found that the magnitude of the chirp depends on the input power, which in turn is related to critical slowing down.

We investigate the bistable response of a traveling-wave semiconductor optical amplifier (SOA) connected bidirectionally to a distributed feedback (DFB) laser diode. By contrast to dispersive DFB amplifiers, bistability is possible for a broad wavelength range of the injected optical signal. A theoretical analysis clarifies the origin of the phenomenon and the conditions under which it occurs. Numerical simulations and experimental results confirm the theoretical analysis. Experimentally obtained step heights up to 25 dB and widths of the bistability domain of 1-4 dB have been found

Optical bistability (OB) behavior in quarter-wave-shift (QWS) distributed coupling coefficient (DCC) distributed feedback (DFB) semiconductor laser amplifiers (SLApsilas) is investigated. The simulations are based on a modified transfer-matrix method, which considers grating non-uniformities along the structure as well as gain saturation effect. Switching characteristics, including structural dependence of OB in QWS DCC DFB SLApsilas is demonstrated in the steady state regime. Time-dependent analysis of OB is performed as well, and the dynamics of optical switching is demonstrated.