T. G. Chang

Comparison of Sagnac and Mach-Zehnder ultrafast all-optical interferometric switches based on a semiconductor resonant optical nonlinearity

We present a theoretical analysis of recently demonstrated ultrafast all-optical interferometric switching devices (based on Sagnac and Mach-Zehnder interferometers) that use a large optical nonlinearity in a resonant regime. These devices achieve ~10-ps switching windows and do not require high-energy optical control pulses. We theoretically analyze and compare one Sagnac and two Mach-Zehnder switching configurations.

DEMONSTRATION OF ULTRAFAST, ALL-OPTICAL, LOW CONTROL ENERGY, SINGLE WAVELENGTH, POLARIZATION INDEPENDENT, CASCADABLE, AND INTEGRATABLE SWITCH

A new type of ultrafast all optical switch based on a Mach–Zehnder interferometer is demonstrated with a 10 ps switching window which requires only 0.65 pJ of control pulse energy. The optical nonlinearity which is utilized is associated with the gain compression of semiconductor optical amplifiers, and the switching turnoff transition does not depend on the slow amplifier recovery time. Both data and control pulses are at the same wavelength of 1.313 μm, and are not polarized orthogonal to each other. The device configuration and the semiconductor amplifiers allow for small scale integration and data output cascadability.

Nonlinear-index-of-refraction measurement in a resonant region by the use of a fiber Mach–Zehnder interferometer

The nonlinear index of refraction in a resonant region has been determined by the use of a fiber-based Mach--Zehnder interferometer to measure the temporal fringe shift between two signals. The measurement technique is direct and does not require additional amplitude information for the extraction of the nonlinear index of refraction. This technique has been used to measure the temporal response of an InGaAsP semiconductor optical amplifier at 1.313 µm.

Polarization-insensitive terabit optical demultiplexer for TDMA networks

We have developed a demultiplexer known as a Colliding Pulse Mach- Zehnder (CPMZ) suitable for OTDM systems capable of ultrafast all- optical demultiplexing and address recognition. Recently we have demonstrated a polarization and wavelength independent device, called a Terabit Optical Demultiplexer, which is capable of all-optical demultiplexing of Tbit/s pulse train with 650 fJ of switching energy, and which can be integrated on a chip. This device has achieved a 10 ps switching window. Both devices are wavelength compatible with all of the low loss transmission windows of optical fibers.

A simple method to characterize dynamic parameters of semiconductor waveguide amplifiers

Semiconductor optical amplifiers (SOA) are indispensable both for optical time domain multiplexed (OTDM) and wavelength division multiplexed (WDM) optical networks. To fully utilize the potential of SOAs, evolution of a short optical pulse inside SOAs is important. To understand the pulse propagation dynamics, one must know small signal gain, carrier recombination time, linewidth enhancement factor, saturation energy, the differential gain coefficient, and other parameters. Here, we present a pump-probe technique to simultaneously measure these five quantities. The technique is insensitive to pulse shaping and broadening in the SOA, which occurs to the optical pulse propagating through the SOA.

Ultrafast all-optical wavelength and polarization independent demultiplexer

Recent developments in all-optical switching devices based on the interferometric principle are very promising for optical communication systems, especially those based on optical time division multiplexing system (OTDM), where a user is allowed to transmit or receive a data in a assigned time slot within a given time frame. One such device based on a Sagnac interferometer is called a Terahertz Optical Asymmetric Demultiplexer (the TOAD). Another device based on a Mach-Zehnder interferometer is a Symmetric Mach-Zehnder (SMZ). Both devices utilize large optical nonlinearities in the resonance regime of the semiconductor, therefore it is possible to operate these devices with a very small optical control pulse energy. The currently demonstrated TOAD can be switched with 0.8 pJ, and the SMZ with 11 pJ. We still can reduce the control pulse energy by optimizing and employing other nonlinear optical materials. The most critical problem associated with a slow recovery time of the resonance nonlinearities has been solved by a special geometrical location of a nonlinear optical element in the Sagnac interferometer, and two control pulses to do independent on and off switching operation for the Mach-Zehnder. We demonstrated a 10 ps switching window by counter-propagating the control and data pulses in the Mach-Zehnder interferometer using 0.65 pJ of control pulse energy. This device is advantageous in its superior rejection capability of the control signal. In terms of the possibility of integration, this device is expected to be a much simpler design than the previously demonstrated systems. Also the utilized optical nonlinear elements are semiconductor optical amplifiers, the data signal can be larger than the input. This may facilitate cascadability and fan-out capability.