Optical phased arrays can achieve inertialess, high-resolution, flexible beam steering required by a broad range of applications, such as laser radar, free space optical communication and interconnect, and laser projection displays. In this paper, we study the SOI and GaAs waveguide optical phased arrays (WOPAs) comparatively. The principle of the phase shifter is investigated based on the thermo-optic effect in silicon waveguides and electro-optic effect in GaAs waveguides. The propagation properties of optical field in the two kinds of WOPAs are studied numerically, including the guided modes, the propagation of optical field in single waveguide and the coupling properties of optical field in waveguide arrays. We also analyze the performance of the two kinds of WOPAs. Silicon WOPAs show superiorities of low propagation loss and wide beam scanning range, while GaAs WOPAs show superiorities of fast beam scanning speed. This research provides a valuable reference for the chip design of optical phased arrays.
The photorefractive adaptive optical heterodyne detection system (PAOHDS) is proposed. The dynamic properties of
mutually pumped phase conjugate (MPPC), the key technology to the PAOHDS, are studied theoretically. The
three-dimensional distribution of MPPC refraction index grating in time and length axis is simulated numerically. The
dependence of dynamic properties of MPPC on the intensity of the fanning light is presented.The stronger the intensity
of the fanning light is, the less response time for MPPC is. The dependence of dynamic properties of MPPC on the
coupling strength is presented. The greater the coupling strength is, the less response time for MPPC is. These results
provide theoretical basis to reduce response time of PAOHDS.
A numerical solution, travelling-wave-like spatial soliton is obtained by using
travelling-wave transform along with numerical methods to solve the photorefractive nonlinear
equation, and its necessary forming conditions are presented. The evolution properties of the
travelling-wave-like spatial soliton in the photorefractive crystal are investigated. The results
show that travelling-wave-like spatial soliton can not only keep its shape invariably, but also
translate its energy transversely. It is possible for controllable deflection of the spatial soliton. The
deflection angle depends on the magnitude of the transverse phase modulation coefficient. These
properties of the multi-soliton coherent interactions can be potentially applied in optical
The experimental results of the nonlinear photoconductive semiconductor switches triggered by laser diode were reported. A new phenomenon of carrier accumulation effect in the nonlinear PCSS was found. The roles of bias voltage and laser pulse on carrier accumulation have been studied. The results indicate that the number of carriers can be controlled by adjusting the bias voltage, optical pulse or using the other methods. Therefore, the nonlinear PCSS can be controlled.
The effect of bias voltage on the characteristic of GaAs photoconductive semiconductor switches (PCSS) was investigated theoretically and experimentally. The outputs of the switches for different bias voltages were obtained by solving the basic equations of transient model of PCSS. With a bias voltage of 2400V and triggered by a laser diode, the high gain PCSS switched a electric pulse with voltage up to 1700V. The simulated results agree with the experiment observations well. A new phenomenon of carriers accumulation effect was found.
This research has focused on modeling of optically triggered, high gain nonlinear GaAs switches. A complete model with dynamics of deep level trap, carries, direct band-gap recombination radiation and heat involved has been constructed. The various generation and recombination mechanism have been discussed and presented. Photo-ionization, thermal emission of deep level traps, intrinsic impact ionization, standard Shockley-Read-Hall recombination, direct band-gap recombination and Auger recombination have been considered.
The design and performance of a stable Ti:sapphire regenerative amplifier. 7 mJ (800 nm) per pulse at the repetition rate 10 Hz, has been described. The resonator consists of one concave mirror (R equals 4000 mm) and one plane mirror, spaced at a distance of 1.76 m. The two mirrors are coated for high reflection centered at 800 nm. Two Pockel cells, one broadband waveplate and polarizer are used to switch a pulse into and out of the resonator. The Ti:sapphire crystal rod is 6X6X14 mm with an absorption coefficient of 2.6 cm-1 at 490 nm and both sides is cut at Brewster's angle. The pump source is frequency double Nd:YAG laser. For regenerative amplifier, the pump energy which we usually use is 64 mJ per pulse. The seed pulse is from a self-mode-locked Ti:sapphire laser that provides 400 mW of outpower with pulse duration about 80 - 100 fs. After stretching the pulse to about 200 - 300 ps by using the grating stretcher, we inject the pulse into the regenerative amplifier and obtain 7 mJ output energy in single pulse, a net gain of up to 106. This laser system is a pre-amplifier for high energy amplifier.