P. W. Smith

Ultrafast all‐optical switching in a dual‐core fiber nonlinear coupler

We report the first demonstration of a nonlinear coupler switch capable of substantially complete all‐optical switching at subpicosecond rates with no light‐induced thermal effects.

Passive mode locking of a semiconductor diode laser

By using a GaAs/GaAIAs multiple-quantum-well sample as a saturable absorber in an external resonator, we have passively mode locked a GaAs laser to obtain pulses as short as 1.6 psec, the shortest pulses ever observed to our knowledge from a mode-locked diode laser in a regulator pulse train.

Mode locking of semiconductor diode lasers using saturable excitonic nonlinearities

Multiple-quantum-well (MQW) structures of GaAs and GaAlAs have been used for passive mode locking of commercial GaAs semiconductor diode lasers. We present an extended discussion of this application of the sensitive room-temperature excitonic absorption saturation in MQW material. We review the criteria for passive mode locking and discuss two methods—carrier diffusion and proton bombardment—for reducing the aborption recovery time without destroying the excitonic nonlinearity. A simple probabilistic theory is derived for the effect of bombardment on the excitonic effects that is in order-of-magnitude agreement with experiment. We have performed experiments using MQW material to mode lock a GaAs laser. A continuous train of pulses as narrow as 1.6 psec has been obtained with a pulse-repetition rate of 2 GHz.

Fast nonlinear optical response from proton‐bombarded multiple quantum well structures

Proton bombardment is shown to shorten the recovery time of the excitonic absorption in GaAs/GaAlAs multiple quantum well saturable absorbers. The response time can be reduced from 30 ns to 150 ps without affecting the absorption characteristics or the saturation energy.

Nonlinear Optical Properties Of GaAs/GaAlAs Multiple Quantum Well Material: Phenomena And Applications

Semiconductor microstructures whose dimensions are comparable to atomic dimensions and whose interfaces are atomically smooth exhibit novel optical properties not encountered in the parent compounds. Quantum well structures, which consist of ultrathin semiconductor layers alternately grown one on the other, possess remarkable optical nolinearities and electro-optical properties with potential applications in optoelectronics. In this paper we review our studies of GaAs/AIGaAs quantum well structures (QWS). We briefly discuss the physics of absorption in QWS at room temperature, and we describe the mechanisms of saturation of excitonic absorption and refraction and that of electroabsorption in QWS. Finally, we review the applications of these effects to optical processing and optoelectronic devices.

On the role of photonic switching in future communications systems

The reasons for the growing interest in developing photonic switching and signal processing devices for future communications applications are examined. The foreseeable fundamental and technological limits for photonic switching technology are outlined, and areas in which photonics can be expected to be superior to other technologies are identified. Some examples of current research on electrooptic and all-optical switching elements are presented, and future prospects for photonic switching are discussed.

Chapter 5 Nonlinear Optical Properties of Multiple Quantum Well Structures for Optical Signal Processing

Publisher Summary This chapter discusses the nonlinear optical properties of multiple quantum well structures for optical signal processing. Two properties of quantum wells that are relevant for nonlinear optical devices are: first, quantum wells show optical absorption saturation associated with the remarkably distinct room-temperature excitonic resonance. Second, they show a large electricfield dependence of the absorption, both associated with the excitonic transition and also directly with the transition between two-dimensional subbands. All these effects are seen near the optical absorption edge. The work reviewed here is primarily, from recent experiments on GaAs/AlCaAs multiple quantum well structures (MQWS). The chapter discusses the linear absorption in MQWS with a particular emphasis on room-temperature effects. It presents the measurements of nonlinear optical effects in MQWS, including absorption saturation and four-wave mixing. Further, the experimental and theoretical studies of electroabsorption in MQWS are reviewed, and the example of a new category of devices that exploits both the absorption saturation and electroabsorption is discussed.

Fast Multiple Quantum Well Absorber for Mode Locking of Semiconductor Lasers

Passive mode locking of a semiconductor diode laser using GaAs/ GaAlAs multiple quantum well (MQW) material as a saturable absorber has been reported recently [1]. The strong room-temperature excitonic absorption line in this material [2] saturates at relatively low powers, and it can be matched to the GaAs laser wavelength. Such mode-locked lasers are potentially important sources for future ultra-fast photonic signal processing.