Ararat Yesayan

Optimized grating-frustrated coupler.

A complete theoretical analysis of a modified grating-frustrated coupler with a second grating in the input channel is presented. We show that this second grating allows for a reduction to zero of backreflected light and transmits all the radiation near the Bragg wavelength to a drop port.

NONRECIPROCAL DIFFRACTION BY SPATIAL MODULATION OF ABSORPTION AND REFRACTION

Linear diffraction gratings that provide strongly asymmetric diffraction without surface modulation are created and studied. The spatial phase shift of the refractive-index grating relative to the absorption grating is the origin of nonreciprocal behavior.

Zero backreflection condition for a grating-frustrated coupler

A complete theoretical analysis of a modified grating-frustrated coupler involving a second grating in an input channel is presented. We show that this second grating allows for improved performance of the device, especially in terms of backreflected light. The condition for zero backreflection is found analytically, and a physical interpretation of the results is given.

Mode locking of a ring cavity semiconductor diode laser

We report new results on the generation and characterization of picosecond pulses from a self-mode-locked semiconductor diode laser. The active medium (InGaAs, 830-870 nm) is a semiconductor optical amplifier whose facets are cut at angle and AR coated. The amplifier is inserted in a three-minor ring cavity. Mode locking is purely passive; it takes place for specific alignment conditions. Trains of counterpropagating pulses are produced, with pulse duration varying from 1 .2 to 2 ps. The spectra of the counterpropagatmg pulses do not fully overlap; their central wavelengths differ by a few nm. The pulse repetition rate has been varied from 0.3 to 3 GHz. The pulses have been compressed to less than 500-fs duration with a grating pair. We discuss some of the potential physical mechanisms that could be involved in the dynamics of the mode-locked regime. Hysteresis in the LI curve has been observed. To characterize the pulses, we introduce the idea of a Pulse Quality Factor, where the pulse duration and spectral width are calculated from the second-order moments of the measured intensity autocorrelation and power spectral density.