A. S. Trushin

Investigation in acousto-optic laser stabilization for crystal resonator-based optoelectronic oscillators

Abstract. Potentialities are investigated for using acousto-optic cells based on a TeO2 crystal to stabilize a microwave signal generated by an optoelectronic oscillator. Bulk acoustic waves at two radio frequencies (RF) near 60 MHz are launched in the two identical cells providing a required locking on of a microwave signal. Differences between RF signals are up to 400 kHz to follow quality factor of the optic resonator typically in the range of 5×108. Critical alignment of the two cells is performed thanks to an extraordinary polarized laser beam launched at a very low Bragg angle of light incidence. Moreover, the system is operating for any resonator to be inserted into the optoelectronic oscillator with a Q factor in the range of 2×107−1011.

Photoluminescence of Yb Doped ZnTe

The photoluminescence from ZnTe : Yb films grown on (100) GaAs by MBE was studied at different temperatures (4.2-350) K. The efficient Yb 3+ -related emission in ZnTe was observed up to room temperature. The analysis of the fine structure of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f 13 levels for the dominant complex center based on Yb ion.

Influence of the thickness of CdTe and ZnTe layers on cathodoluminescence spectra of strained CdTe/ZnTe superlattices with quantum-dot layers

The influence of the thickness of ZnTe barrier layers on the cathodoluminescence spectra of strained CdTe/ZnTe superlattices containing layers of quantum dots with an average lateral size of approximately 3 nm has been investigated. In samples with thick barrier layers (30, 15 nm), the cathodoluminescence spectra of quantum dots exhibit one band with a maximum at E = 2.03 eV. It has been revealed that, at a barrier layer thickness of ∼3 nm, the luminescence band is split. However, at a ZnTe layer thickness of 1.5 nm, the luminescence spectrum also contains one band. The experimental results have been interpreted with allowance made for the influence of elastic biaxial strains on the energy states of light and heavy holes in the CdTe and ZnTe layers. For the CdTe/ZnTe heterostructure with quantum dots in which the thickness of the deposited CdTe layer is 1.5 monolayers and the thickness of the barrier layer is 100 monolayers, the cathodoluminescence spectrum contains 2LO-phonon replicas. This effect has been explained by the resonance between two-phonon LO states and the difference between the energy states in the electronic spectrum of wetting layer fragments.

Acousto-optic interaction in TeO2 and LiNbO3 devices with surface generation of bulk acoustic waves

In this paper, a theoretical and experimental study is presented related to light interaction with bulk acoustic waves generated from a surface of piezoelectric LiNbO3 and TeO2 crystals. A paratellurite acousto-optic cell was designed and developed on base of conversion of acoustic modes during a reflection from a tilted surface in the cell. An intrinsic shear acoustic wave was excited along [001] axis in the material by means of two metal electrodes deposited on the (001) crystal facet. After the reflection, the shear wave propagated along [001] axis and then it was converted into the [110] mode with the velocity 617 m/s. A prototype acousto-optic device based on XY-cut of LiNbO3 is also described in the paper. Experimental investigation of the devices proved that the diffraction efficiency about 1% was obtained in the paratellurite crystal and also about 2% in the lithium niobate at 1.0 Watt of driving electric power. In this way, a possibility has been demonstrated of a non-traditional acoustic wave ge...

Laser stabilized by acousto-optic cells for optoelectronic oscillators

We investigate application of acousto-optic cells based on a TeO2 crystal to stabilize a microwave signal generated by an optoelectronic oscillator (OEO) based on a MgF2 resonator. Bulk acoustic waves at two radio frequencies (RF) near 60 MHz are launched in the two identical cells providing a required locking on of a microwave signal. When quality factor of the optic resonator is typically of the order 108, difference between RF signals are up to 2 MHz. We send an extraordinary polarized laser beam on ultrasound at very low Bragg angle of light incidence. It helps to perform a critical alignment of the two cells.

Acoustic wave velocities in two-dimensional composite structures based on acousto-optical crystals

Sound velocities in two-dimensional composite structures based on isotropic and anisotropic acousto-optical crystals have been determined by numerical simulations. The isotropic materials are represented by fused quartz (SiO2) and flint glass, while anisotropic materials include tetragonal crystals of paratellurite (TeO2) and rutile (TiO2) and a trigonal crystal of tellurium (Te). It is established that the acoustic anisotropy of periodic composite structures strongly depends on both the chemical composition and geometric parameters of components.

Comparison of two methods of laser stabilization for optoelectronic oscillators

In order to stabilize the signal delivered by an optoelectronic oscillator (OEO) [1-5], it is necessary to lock the signal of the laser on the resonance. The laser wavelength must be stabilized onto one of the resonator’s resonances to be able to maintain a stable performance of the oscillator. We first present the Pound Drever hall method that has been used to realize this setup. As an alternative method, we have also investigate another technique based on the use of acousto-optic cells (AOC). It is presented on part 3 of this paper.

Acousto-optic interaction in the lithium niobate crystal upon the surface excitation of the bulk acoustic wave

The interaction of light with the bulk acoustic wave that is excited from the surface of the lithium niobate crystal is experimentally studied. A prototype of the acousto-optic device that employs the XY-cut crystal and the optimized (Y-13°)-cut crystal is presented. Diffraction efficiencies of 1 and 2 %/W are obtained for the first and second prototypes, respectively. It is demonstrated that the polarization characteristics of the device differ from the conventional characteristics by the dependence on the structure of the acoustic beam. An original method for the excitation of the ultrasonic beam can be used in the acousto-optic devices for light control.

Electric phase delays in tunable acousto-optic filters applying extended transducers

The paper examines operation of wide angle tunable acousto-optic filters applying multiple transducers. The analysis was carried out for a tellurium dioxide device with a large transducer consisting of 7 identical sections connected in series. It was found that the sections of the transducer generated acoustic waves with a phase shift. This shift was caused by time delay when a driving electric signal propagated over the sections. The phase shift between adjacent sections was dependent on frequency of a driving electric signal, while a total phase delay between side sections of the transducer depended on a number of connected sections. Experimental investigation of the filter was performed at the driving frequencies 100-240 MHz. The measured total time delay between side sections of the transducer was equal to 1.6 ns, while the delay between adjacent sections was limited to 0.23 ns. It was proved that presence of the phase shifts influenced on spectral transmission characteristics of the tunable acousto-optic filter and also on relative intensity of side lobes.