An all-semiconductor-optical-amplifier loop device with a multimode interference (MMI) coupler was fabricated with the deep UV cryo-etching technique. Efficient power-dependent switching was observed. With continuous-wave signals, nonlinear switching occurred due to the combined effect of the nonlinear coupling in the MMI coupler and the lateral wave field redistribution caused by the loop structure. Simulation results showed good agreement in trend with the experimental data.

Nonlinear switching effects in a GaAs-AlGaAs allsemiconductor optical-amplifier loop device with a multimode interference waveguide amplifier (MMIWA) for closing the loop was investigated experimentally and numerically. The miniaturized device, designed to imitate a nonlinear optical loop mirror (NOLM), has a latency more than one hundred times smaller than that of a NOLM. Also, because it used an MMIWA for replacing a coupler in a conventional NOLM, its operation was quite different from that previously reported. In CW signal operation, the nonlinear switching behavior resulted from the combined effect of nonlinear coupling in the MMIWA and the amplification and lateral field redistribution of the signal through the loop structure. Efficient self-switching and cross-polarized switching were observed. Numerical simulations showed consistent trends in varying device parameters.

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Gain saturation and the induced refractive index variation in semiconductor optical amplifiers (SOAs) have been widely used for many optoelectronics operations, including frequency conversion, phase conjugation, switching, modulation, and laser mode locking. In this paper, we report the experimental and numerical results of using gain saturation in SOAs for all-optical switching and novel laser mode locking configurations. For all-optical switching, we fabricated an all-SOA nonlinear optical loop mirror and implemented efficient power-dependent switching in both cw and pulse modes. Also, numerical modeling was also conducted to show consistent trends with experimental data. For novel laser mode-locking configurations, we demonstrated numerically efficient operation of mode-locked semiconductor laser with multi-mode interference SOA structures. With the nonlinear coupling process, it was found that efficient pulse compression could be achieved, implying that stable mode locking is feasible. Also, with a ring cavity colliding-pulse mode locking can be implemented.

Figure 3(a) shows the SOA bias current dependence of the recovery time. The probe wavelength is fixed at 1550 nm and ECL output power is at 5.5 dBm. The gain recovery time changes from 45 ps to 13 ps corresponding to bias current from 200 mA to 700 mA. Afterwards the speed is limited by the resolution of our measurement setup. Figure 3(b) shows the probe wavelength dependence of gain recovery time at a constant injection current (I = 600 mA). The ECL output power is kept at 3 dBm when operated at different wavelength. With constant input powers for both the pump and probe, the gain recovery is fastest at the device gain peak and slower at the higher and lower wavelengths. This again shows that to increase the SOA gain is essential to obtain very high speed all optical operations. The proposed two-section operation makes it possible to easily obtain -100 Gbit/s all optical devices.