Based on the four-wave mixing mechanism and light fanning effect, a mutually pumped phase conjugator(MPPC) model
is proposed to analyze the variation of MPPC output response with time for different scattering seed value. It shows that
preset grating can enhance the fan light intensity when it satisfies Bragg condition and also can shorten MPPC response
time. In experiment the bird-wings MPPC is done with or without the preset grating and the variation of MPPC
reflectivity with time is obtained in two cases, and simulation conclusion is in agreement with the experimental result.
These results have importance for applications of MPPC on optical heterodyne detection.
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.
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 theoretical model of a photorefractive optical switch, which is implemented by adjusting the wavelength and space-phase of the read-out beam to control the diffraction direction of volume grating in a photorefractive crystal, is proposed. For N channel optical switch, each channel include n dissimilar wavelength carrying information with distinct space-phase, and any wavelength can turn into any other N-1 channel controlled by space-phase. In order to obtain this device, multiple holograms be recorded in a photorefractive crystal, performing an optical database accessible either by wavelength or by space-phase multiplexing. The holograms were written in a Fe doped LiNbO3 using an Ar+ laser with its three wavelength. The diffraction direction depended on wavelength and space-phase of the read-out beam, which agrees with the theoretical prediction and indicates that photorefractive crystal possesses excellent optical switching properties. It is demonstrated that the diffraction direction of the volume grating is relevant to the wavelength and space-phase of read-out beam; this property can be used to implement the all-optical switch.
The properties of light scattering from air bubbles in water have recently attracted considerable attention, but in practical applications such as in underwater detection, submarine imaging etc., we must take account of light scattering from various sizes of particles suspended in water. The situation of air bubbles and particles co-exist in water was studied in the first time. It is known that an air bubble in water is an example of a scatterer for which the refractive index of core (gas) is less than that of surroundings, which differs significantly from that for particles in water. Consequently, the forward light scattering characteristics of both air bubbles and typical particulate assemblages in the ocean are estimated with Mie theory, the result are analyzed and compared to validate the influence of particles on forward light scattering of air bubbles in the ocean. A preliminary laboratory experiment is also carried out to investigate the properties of forward light scattering (scattering angle less than 4 degrees) caused by particles and air bubbles and to illustrate the differences of light scattering between them.
Based on the programmable phase modulation technique with a multi-channel optical wave-guide array, a novel method used for collimated laser precision scanning was presented. Optical system and control circuit have been designed for the multi-channel optical wave-guide array. Theoretical analysis and experimental result shows that the
method can be used for small angle adjusting and big angle scanning of collimated laser in free space light communication.
Optical waveguide array are attractive for high-speed, wide-angle optical beam steering or deflection, but optical waveguide arrays radiate undesirable sidelobes. It is shown that suppression of sidelobes can be accomplished by configuring array elements in nonuniform pattern. Tow kinds of arrangement of linear changed spaced optical waveguide array are discussed. Sidelobes can be suppressed deeply. Especially, the light path area ratio can be improved
to 71.9% by using symmetrical structure array. Steering characteristic shown that the maximum steering degree of 240(-3dB) can be obtained by nonuniform spaced optical waveguide array.
In steady state and two dimensions the distributions of the nonlinear refractive index in a photorefective crystals under the conditions of supporting low intensity spatial solitons are studied. It is shown that steady state spatial bright solitons of modulated ThM00 mode Gaussian waveform can form and induce planar array waveguides in photorefractive crystal. The effects of modulating conditions, the intensity of spatial solitons and the external bias electric field on profile of refractive index of the array waveguides is investigated.
We propose a novel method of transform spectral measurement, based on the diffraction of light through the side of a waveguide fabricated in photorefractive crystal where a holographic grating is recorded by holography. The optical spectrum can be obtained by Fourier transform for the interference pattern, which is formed by lights diffracted from counter-propagating mode in the waveguide. Changing the periodic length of the holographic Bragg grating recorded in the waveguide can widen the range of measurable spectrum. This spectral measurement method is well suited as high- resolution wavelemeter, terminal network spectrum monitor and spectral measurement advice for fiber-grating sensor.
We start from Kukhtarav equations and Gauss's law which describe the photorefrective effect in a photorrefractive medium in which electroncs are the sole charge carries, plus the wave equation for the slowly varying amplitude of the optical field , In steady state and two dimensions the distributions of the nonlinear refractive index in a photorefective cystals under the conditions of supporting low intensity spatial solitons are studied theoretically. It is shown that steady state spatial bright solitons of TEMn0(n=2,2,3...)modes and modulated TEMn0 mode Gaussian waveform can form and induce planar array waveguides in photorefractive crystal.