H Ju

All-optical logic based on ultrafast gain and index dynamics in a semiconductor optical amplifier

We investigate nonlinear carrier dynamics in a multiquantum-well semiconductor optical amplifier (SOA) in the context of ultrafast all-optical logic. A rate-equation model is presented that accounts for two-photon absorption, free-carrier absorption, self- and cross phase modulation, carrier heating, spectral, spatial hole burning, and self- and cross polarization modulation. The nonlinear refractive index dynamics is investigated theoretically and experimentally. We find nonlinear phase changes larger than /spl pi/ radians, which recovers on a timescale in the order of 1 ps. We also investigate a nonlinear AND gate that consists of an SOA that is placed in an asymmetric Mach-Zehnder interferometer. We show that the gate can be operated using 800-fJ optical pulses with duration of 200 fs while having a contrast ratio larger than 11 dB.

SOA-based all-optical switch with subpicosecond full recovery

We investigate all-optical switching in a multi-quantum-well semiconductor optical amplifier-based nonlinear polarization switch using optical pulses with duration of 200 fs at a central wavelength of 1520 nm. We show full recovery of the switch within 600 fs, in both the gain and absorption regime. We discuss the switching and recovery mechanisms using numerical simulations that are in qualitatively good agreement with our experimental data.

Ring-laser optical flip-flop memory with single active element

We present a novel optical flip-flop configuration that consists of two unidirectional ring lasers with separate cavities but sharing the same active element unidirectionally. We show that in such a configuration light in the lasing cavity can suppress lasing in the other cavity so that this system forms an optical bistable element. Essential for obtaining the bistability is the presence of an additional feedback circuit that is shared by both lasers. We show experimentally that the flip-flop can be optically set and reset, has a contrast ratio of 40 dB and allows low optical power operation. We also present a model based on roundtrip equations. Good agreement between theory and experiments is obtained.

Simulation of mode-locking by nonlinear polarization rotation in a semiconductor optical amplifier

We present a theoretical investigation of a mode locked laser that has a semiconductor optical amplifier (SOA) in its ring cavity. A mode-locked train of narrow pulses is obtained by combining nonlinear polarization rotation in the SOA and a polarization filter whose polarization axis is set such that the tail of optical pulses is removed in each cavity round-trip. The pulse narrowing process is demonstrated numerically and good qualitative agreement with experiments in our previous work is achieved. The pulse performance is largely determined by the ultrafast SOA gain dynamics and the cavity dispersion. Our simulation shows that the laser can produce a pulse train of subpicosecond pulsewidth at a repetition rate of 28 GHz for a moderate SOA current level. We observe that the laser can switch itself on or off depending on the initial pulse.

All-Optical Switching and Wavelength Conversion Based on Ultrafast Nonlinearities in Semiconductor Optical Amplifiers

We investigate all-optical switching and wavelength conversion based on ultrafast nonlinearities in a multi-quantum-well semiconductor optical amplifier. We present a rate equation model that accounts for two-photon absorption, free-carrier absorption, self- and cross phase modulation, carrier heating, spectral, spatial hole burning and self- and cross polarization modulation. We demonstrate optical AND gate operation using a semiconductor optical amplifier placed in an asymmetric March-Zehnder interferometer and we show that the gate can be operated using 800 fJ optical pulses with duration of 200 fs. We also investigate wavelength conversion based on ultrafast nonlinear polarization rotation. We found a conversion efficiency of 12 dB for control pulse energies of 10 pJ.

Eight state optical flip-flop based on coupled unidirectional ring lasers with optical feedback

An eight-state optical flip-flop based on coupled unidirectional ring lasers with optical feedback is demonstrated. The flip-flop exhibits low power operation since it contains only one gain medium. The contrast ratio is over 35 dB.

Digital optical signal processing for telecommunication applications

Optical packet switching has received considerable attention over the last few years. In this paper we discus how optical signal processing can play a role in photonic packet routing. Two examples are given. Firstly we discuss ultrafast wavelength switching at 160 Gbit/s in a single semiconductor optical amplifier. Secondly, an integrated photonic flip-flop is discussed. Finally a discussion is given about potential opportunities and limitations of optics in packet switched nodes.

Simulation of mode-locked ring laser based on nonlinear polarization rotation in a semiconductor optical amplifier

We investigate numerically the generation of sub-picosecond optical pulses using a semiconductor optical amplifier (SOA) and a linear polarizer placed in a ring laser configuration. Nonlinear polarization rotation in the SOA is employed as the passive mode-locking mechanism. In particular attention is paid to the pulse narrowing process. We find that pulses as short as 300 femtoseconds can be generated if the dispersion is completely compensated. Our results are well in agreement with experimental results.