Acoustic-optic Modulator Research Articles

Waveguide-type optical passive ring resonator gyro using phase modulation spectroscopy technique

We report the first demonstration of silica waveguide optical passive ring resonator gyro (OPRG) based on the phase modulation spectroscopy technique. The ring resonator is composed of a 6-cm-long silica waveguide. Observed from the resonance curve, the free spectral range (FSR) of the resonator, the full width at half maximum (FWHM) of the resonance curve, the finesse (F) of the resonator, and the resonance depth are 3.4 GHz, 62 MHz, 54.8, and 70%, respectively. The detection sensitivity of this OPRG will be 7.3×10–5 rad/s. In the experiments, there is an acoustic-optical modulator (AOM) in each light loop. We lock the lasing frequency at the resonance frequency of the silica waveguide ring resonator for counterclockwise (CCW) lightwave; the frequency difference between the driving frequencies of the two AOMs is equivalent to the Sagnac frequency difference caused by gyro rotation. Thus, the gyro output is observed.

Optimization of Doubly<tex>$Q$</tex>-switched Lasers With Both an Acoustic-Optic Modulator and a Cr<tex>$^4+$</tex>-Doped Saturable Absorber

By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a doubly Q-switched laser with both an AO modulator and a Cr /sup 4+/ -doped saturable absorber (SA). These coupled rate equations are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined,and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter, the optimal normalized SA parameters and the normalized parameters of the AO Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power and the normalized pulsewidth are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the SA, the AO Q-switch,the resonator and the spatial distributions of the intracavity photon density. Sample calculations for a diode-pumped Nd/sup 3/+:YVO/sub 4/ laser with both an AO modulator and a Cr/sup 4+/ :YAG SA are presented to demonstrate the use of the curves and the related formulas.

Optimization of the slowly actively Q-switched laser

By taking into account turnoff time of the slowly active Q-switch, the coupled equations of a slowly actively Q-switched laser are given. These rate equations are solved numerically. The key parameters of an optimally coupled actively Q-switched laser with the turnoff time are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter which maximizes the output energy, and the corresponding normalized energy, normalized peak power and normalized pulse width. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium and the resonator. In addition, the importance of including turnoff time of the slowly active Q-switch is also shown. The optimal calculations for an actively Q-switched Nd:YVO 4 laser with acoustic–optic modulator are presented to demonstrate the use of the curves and the related formulas.

A laser diode system for 40K-87Rb atomic cooling

We have developed a semiconductor laser system used in 40K-87Rb trapping and cooling experiment. The laser diode system is composed of three external cavity diode lasers and four injection diode lasers and a tapered amplifier. Four laser beams used for 40K and 87Rb cooling and repump lights are obtained by using acoustic optic modulators to offset the frequencies from the three external cavity diode lasers. Four light beams with different frequencies are injected into four slave lasers for injection locking. Then Rb cooling light, K cooling light and K repump light are injected into a semiconductor tapered amplifier in a master oscillator-power configuration. This configuration is flexible and stable and can simultaneously produce the cooling and repump light for 40K and 87Rb trapping and cooling experiment.

Modeling of a diode-pumped acousto optically Q-switched intracavity doubling <inline-formula><math display="inline" altimg="none" overflow="scroll"><mrow><mi>Nd</mi><mo>:</mo><msub><mi>GdVO</mi><mn>4</mn></msub><mo>∕</mo><mi>KTP</mi></mrow></math></inline-formula> green laser

A model based on rate equations that consider the spatial distribution of photon density and inversion population density, as well as the turnoff time of an acoustic-optical modulator, is developed to perform accurate predictions of the characteristics of a green laser. Numerical solutions are consistent with the experimental results of a diode-pumped acousto optical Q-switched intracavity-frequency-doubled Nd:GdVO4/KTP green laser.

Diode-pumped Actively Q-switched Nd:GdVO4 Green Laser with Periodically Poled KTP

A diode-pumped actively Q-switched Nd:GdVO4 green laser with periodically poled KTP (PPKTP) and Acoustic-optic (AO) modulator has been realized. The dependences of pulse energy, pulse width, and peak power on incident pump power are measured. At the pump power of 4.1 W and repetition rate of 10 kHZ, we can obtain a 19.2 ns pulse with pulse energy of 0.11 mJ and peak power of 5.8 kW, which are almost three times of that in the conventional KTP green laser, respectively. A rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the Gaussian spatial distribution of the intracavity photon density is taken into account. The numerical solutions of the rate equations agree with the experimental results.

Pulse Width Reduction in Diode-Pumped Nd:GdVO4 Laser with AO and GaAs Double Q-Switches

By considering the Gaussian spatial distribution of the intracavity photon density, we introduce the rate equations of a diode-pumped Nd:GdVO4 laser doubly Q-switched by acoustic-optic (AO) modulator and GaAs saturable absorber. These rate equations are solved numerically, and the dependence of pulse width on incident pump power is obtained. Meanwhile, a diode-pumped doubly Q-switched Nd:GdVO4 laser with AO and GaAs is realized. This laser can generate a shorter and more symmetric pulse when compared with purely AO and passive Q-switching. The experimental results are in agreement with the theoretical calculations.

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with Cr4+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a Cr4+:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO4 laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO4 laser with both an acoustic-optic (AO) modulator and a Cr4+:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.

Compression of pulse duration in a laser-diode, end-pumped, double Q-switched laser

By considering the Guassian transversal distribution of intracavity photon density and the longitudinal distribution of photon density along the cavity axis as well as the influence of the turn-off time of the acousto-optic Q switch, we introduce the coupled rate equations of a laser-diode, end-pumped, double Q-switched laser with an acousto-optic modulator and GaAs saturable absorber. In addition the thermal effect of the gain medium is taken into account. These coupled rate equations are solved numerically, and the dependence of pulse width on incident pump power at different pulse repetition rates is obtained for the generated output pulses. It is shown that the pulse duration is obviously shorter in contrast to the actively Q-switched Nd:YVO4 laser with an acoustic-optic modulator, and the maximum compression ratio of the pulse width is more than 60%. In the experiment a laser-diode, end-pumped, double Q-switched Nd:YVO4 laser with both an acousto-optic modulator and GaAs is realized, and the experimental results agree with the numerical solutions.

Theoretical and experimental study of a laser-diode-pumped actively Q-switched intracavity-frequency-doubling Nd:YVO4/KTP laser with acousto-optic modulator

By considering the Guassian spatial distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic Q -switch, the coupled rate equations of actively Q -switched intracavity frequency-doubling Nd:YVO 4 /KTP laser with acoustic-optic modulator are given. These coupled rate equations are solved numerically, and the dependences of pulse width, single-pulse energy and peak power on incident pump power are obtained for the generated-green-laser pulses. In the experiment, a laser-diode end-pumped actively Q -switched Nd:YVO 4 /KTP laser with acoustic-optic-modulator is realized and the experimental results agree with the numerical solutions.

Theoretical and experimental study of a laser-diode-pumped actively Q-switched Nd:YVO 4 laser with acoustic–optic modulator

By considering the Gaussian spatial distribution of the intracavity photon density and initial population-inversion density as well as the longitudinal distribution of the photon density along the cavity axis and turnoff time of the acoustic–optic Q-switch, the coupled equations of an LD-pumped actively Q-switched Nd:YVO 4 laser with acoustic–optic modulator are given. These coupled rate equations are solved numerically on a computer, and the dependences of pulse width, single-pulse energy and peak power on incident pump power are obtained. In the experiment, a laser-diode-pumped actively Q-switched Nd:YVO 4 laser with acoustic–optic modulator is realized, and the experimental results are in fair agreement with the numerical solutions.

음향광변조기를 이용한 고분해능의 헤테로다인 간섭식 열팽창 측정기술

열팽창계수의 정확한 측정은 재료과학이나 공업기술 분야에서 가장 중요한 요구량 중의 하나이다. 음향광변조기(AOM)를 이용한 고분해능 간섭식 열팽창계를 제작하여 성능검사를 하였다. 이 계는 이중광로 헤테로다인 간섭계와 복사열 전기로로 구성되어, 정밀한 변위의 측정과 시료의 신속한 가열 및 냉각이 가능토록 하였다. 또한 레이저의 주파수 안정화를 위하여 2차 맥놀이 주파수를 이용한 3종모드 안정화 He-Ne 레이저를 제작하였으며, 이때의 주파수 안정도는 5<TEX>$\times$</TEX><TEX>$10^{-9}$</TEX>이었다. 제작된 계의 길이 측정은 실온에서 1100k온도영역에서 나노미터 정도의 정밀도를 주었다. The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be <TEX>$5{\times}10^{-9}$</TEX>. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

Frequency-domain differential phase-shift keying (FD-DPSK) of ultra fast laser pulses

Frequency-domain differential phase-shift-keying (DPSK) using ultrafast laser pulses has been demonstrated. Spectral coding based on acoustic optical modulator pulse shaping is used for modulation, and the ultrafast pulse characterization based on spectral interferometry is used for demodulation. The encoded differential phase pattern is successfully retrieved after transmission over 4-km dispersion-shifted fiber, which induces substantial nonlinear distortions.

Design and fabrication of CMOS optical modulator

This study describes a micromachined optical modulator with electrostatic actuation, fabricated by the conventional CMOS process. The optical modulator is operated by the interaction of fixed stationary gratings and movable sliding gratings. The period of the gratings is determined by the slide of the movable part, allowing different diffraction patterns of reflected light. In addition, 100% modulation in the first order can act as an optical switch. All procedures following the CMOS process require a simple post-process. Maskless dry etching was the only requirement of the post-process to obtain a high-aspect-ratio microstructure, and only a low voltage of 20 V was necessary to drive the actuator of the optical modulator. The micromachined optical modulator proposed herein is smaller and weighs less than commercially available acoustic optical modulators.

Comment on “Manipulating the frequency-entangled states by an acoustic-optical modulator”

A recent theoretical paper [1] proposes a scheme for entanglement swapping utilizing acousto-optic modulators without requiring a Bell-state measurement. In this comment, we show that the proposal is flawed and no entanglement swapping can occur without measurement.

Manipulating the frequency-entangled states by an acoustic-optical modulator

In this paper, we describe how to realize conditional frequency entanglement swapping and to produce probabilistically a three-photon frequency entangled state from two pairs of frequency entangled states by using an acoustic-optical modulator. Both schemes are very simple and may be implementable in practice.

Quantum key distribution using different-frequency photons

In this paper, we present a scheme for quantum key distribution, in which different-frequency photons are used to encode the key. These different-frequency photons are produced by an acoustic-optical modulator and two kinds of narrow filters. This scheme may be implementable in practice.

Structural, optical, and surface acoustic wave properties of epitaxial ZnO films grown on (011̄2) sapphire by metalorganic chemical vapor deposition

High-quality ZnO films are receiving increased interest for use in low-loss high-frequency surface acoustic wave (SAW) devices, acousto-optic and optical modulators, as buffer layers for III-nitride growth, and as the active material in ultraviolet solid state lasers. In this work, high quality epitaxial ZnO films were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition. The structural, piezoelectric, and optical properties of the ZnO films on R sapphire have been investigated. The epitaxial relationship between ZnO and R-Al2O3 was found to be (112̄0) ZnO∥(011̄2) Al2O3, and [0001] ZnO∥[01̄11] Al2O3. The interface between as-grown ZnO and R sapphire was atomically sharp and semicoherent, as evaluated by transmission electron microscopy. On annealing the films at temperatures above 850 °C, a solid state reaction occurred between ZnO and Al2O3, resulting in the formation of ZnAl2O4 (spinel) at the interface. A 15–20 nm spinel layer formed when the ZnO film was annealed at 850 °C for 30 min, whereas a 150 nm layer formed when the film was annealed at 1000 °C for 150 min. To prevent this reaction from occurring, the maximum process temperature should be below 750 °C. The surface acoustic wave properties of the piezoelectric ZnO were evaluated by fabricating SAW devices on (112̄0) ZnO/(011̄2) Al2O3. An effective electromechanical coupling coefficient, keff2, of 6% was achieved for a 1.5 μm thick ZnO film, which is close to the value for bulk single-crystal ZnO. The photoluminescence spectra were obtained both at room temperature and at 11 K. The full width at half maximum of the 3.363 eV band edge emission photoluminescence peak measured at 11 K was 6 meV, which is close to that for single-crystal ZnO. We also evaluated the anisotropic absorption characteristics of the (112̄0) ZnO film, which can be used for a high contrast ultraviolet light modulator.

Absolute frequency stabilization of an injection-seeded optical parametric oscillator

A method is described that provides absolute frequency stabilization and calibration of the signal and idler waves generated by an injection-seeded optical parametric oscillator (OPO). The method makes use of a He-Ne stabilized transfer cavity (TC) to control the frequencies of the cw sources used to seed both the pump laser and OPO cavity. The TC serves as a stable calibration source for the signal and idler waves by providing marker fringes as the seed laser is scanned. Additionally, an acoustic-optic modulator (AOM) is used to shift the OPO seed laser's frequency before locking it onto the TC. The sidebands of the AOM are tunable over more than one free spectral range of the TC, thereby permitting stabilization of the signal and idler waves at any frequency. A ±25-MHz residual error in the absolute frequency stabilities of the pump, signal, and idler waves is experimentally demonstrated, which is roughly 30% of the 160-MHz near-transform-limited linewidths of the signal and idler pulses.

Modulated laser source for monitoring the stability of detectors employing photomultipliers

Light from an argon high stability laser is used together with an acoustic-optic modulator to provide constant energy calibration pulses to the photomultiplier tubes in an experimental setup. This solution is proposed as the most appropriate when many (up to one/two hundred) of PMTs must be monitored and controlled for gain stability. In our case, gain changes should be limited to 1% which means a still better reproducibility for both the intensity and the width of the calibrator light pulses. In this paper we motivate our choice, present a simple crystal controlled pulse generator which assures the required long-term width stability and give the results obtained in several experimental runs.