Reflective diffractive beam splitter for laser interferometers

The first realization of a reflective 50/50 beam splitter based on a dielectric diffraction grating suitable for high-power laser interferometers is reported. The beam splitter is designed to operate at a wavelength of 1064 nm and in s polarization. To minimize the performance degradation of the device that is due to fabrication fluctuations, during the design process special attention was paid to achieve high fabrication tolerances especially of groove width and depth. Applying this beam splitter to high-power laser interferometers, such as future gravitational wave detectors, will avoid critical thermal lensing effects and allow for the free choice of substrate materials.     

基于DSP的频谱分析型激光多普勒信号处理器的研究

为了提高激光测速系统中信号处理速度,获取更高的测量精度和实时检测能力,本文从硬件结构、传输策略和试验结果入手,提出了利用DSP芯片作为频率分析处理器的多普勒测速系统.通过对A/D控制策略,光电数据采集压缩,DMA传输和DSP处理器中的FFT谱分析和频谱校正算法的研究和对数变频模式模拟电压信号测量试验,实现了多普勒信号处理器在显示采样频率为7MHz,速度显示间隔为0.3ms的实时检测和频率细化能力.     

Photodynamic effects in laser Doppler anemometry

The first observations of photodynamic effects in laser Doppler anemometry are reported, consisting in the fact that the result of a measurement of the Doppler shift of the frequency of light scattered by a particle depends on the action of the probe light beams on the particle. Pis’ma Zh. Tekh. Fiz. 24, 53–58 (September 12, 1998)     

Design and fabrication of continuous-profile diffractive micro-optical elements as a beam splitter

An optimization algorithm that combines a rigorous electromagnetic computation model with an effective iterative method is utilized to design diffractive micro-optical elements that exhibit fast convergence and better design quality. The design example is a two-dimensional 1-to-2 beam splitter that can symmetrically generate two focal lines separated by 80 microm at the observation plane with a small angle separation of +/- 16 degrees. Experimental results are presented for an element with continuous profiles fabricated into a monocrystalline silicon substrate that has a width of 160 microm and a focal length of 140 microm at a free-space wavelength of 10.6 microm.     

Rational design of a diffractive homogenizer for a laser beam

The problem of designing a diffractive optical element (DOE) that produces a uniform-intensity beam from a spatially variable source is considered. Under the thin-lens approximation, the DOE is fully characterized by a phase function. Fresnel approximation is used to simplify the relationship between the input amplitude, the phase function, and the image intensity. The case where the light source has partial coherence is considered. A simple design procedure based on a lenslet array is proposed. It is shown that under certain physical assumptions, this `engineering' solution leads to an effective design capable of producing a uniform intensity from a time-varying, non-uniform source.     

Plane-wave theory of a Michelson laser coupler with a dielectric slab beam splitter

The plane-wave theory for the transmittance and absorbtance of a perfectly aligned Michelson coupler with a dielectric slab beam splitter is presented. It is shown that the transmittance and absorbtance vary sinusoidally and in quadrature. As a result of this quadrature relationship, the maximum transmittance occurs at a setting of the translatable coupler mirror at which the absorbtance is not at an extremum, and so the curve of output power as a function of coupler setting is asymmetrical with respect to the setting yielding maximum transmittance. Experimental measurements of the output power of a far-infrared HCN laser as a function of the coupler setting confirm this asymmetry, which seems to have been overlooked or ignored in previous studies.     

Polarization-selective beam splitter based on a highly efficient simple binary diffraction grating

A polarization beam splitter (PBS) based on a giant-reflection to zero-order (GIRO) grating is presented. The GIRO grating is a simple binary diffraction grating with parameters chosen such that the excited optical modes in the grating interfere constructively and destructively at the respective interfaces. This interference results in high-zero-order reflection (>99%) with a high polarization-selective extinction ratio (+/-30 dB). The grating shows a low aspect ratio. The GIRO PBS is theoretically and experimentally shown to be an adequate PBS for use as an optical isolator in combination with a quarter-wave plate in a CO2-laser system.     

Polarization beam splitter based on honeycomb-lattice photonic crystal ring resonators

A new polarization beam splitter is proposed based on a photonic crystal ring resonator (PCRR) composed of honeycomb-lattice cylindrical silicon rods in air. By shrinking the width of the bus waveguide and adjusting the radii of two nearest-neighbor center rods of the PCRR, an unpolarized beam can be separated well into TE and TM polarization states, respectively, at the backward and forward output ports. Simulation results obtained by the two-dimensional finite-difference time-domain technique show that the insertion losses are 3.58 dB and 3.08 dB, and the polarization extinction ratios are 21.42 dB and 28.53 dB for TE and TM polarization, respectively, at a 1566.7 nm center wavelength. The excess loss is less than 0.34 dB and its dimensions are roughly 43.2 μm × 27.52 μm. These findings offer potential practical applications in high-density photonic integrated circuits.     

Absorbing beam splitter in a Michelson interferometer

The equality of the reflected and the transmitted irradiances by a beam splitter that consists of a thin absorbing coating (typically a metallic film) on a transparent plate is considered. The absorption and the phase difference between the reflected and transmitted fields are also studied. The lack of reversibility of this beam splitter introduces an asymmetry that is discussed for a Michelson interferometer.     

Metrological analysis of two-component systems for laser doppler anemometry of turbulent flows

A metrological analysis of three- and two-channel two-component laser Doppler anemometry measurements of turbulent flow parameters is made on the basis of information theory and parametric optimization. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 18–21, January, 1996.     

Metallized photoresist grating as a polarizing beam splitter

We propose and demonstrate the use of a simple holographic relief photoresist grating covered with an aluminum film as a reflecting polarizing beam splitter. The polarizing effects were achieved as a result of the nonsinusoidal profile of the grating. The best parameters of the gratings for optimizing the polarizing-beam-splitting properties were found by the introduction of the experimental profiles in diffraction calculation software. Theoretical and experimental results are presented, confirming the feasibility of the element.     

Speckle reduction in laser projection systems by diffractive optical elements

In laser projection systems the observer in the far field of the image points on the screen will recognize serious speckle noise. There are many methods to reduce or eliminate speckles in the near field by reducing or eliminating temporal or spatial coherence of the laser. But for the far field it is hardly possible to change the coherence properties of laser sources so that speckles will disappear. We propose a new method for eliminating speckles in the far field by using a diffractive optical element. The intensity modulation depth in the far-field speckle pattern can be reduced to a few percent while good beam quality is preserved.     

Performance evaluation of a bigrating as a beam splitter

The design of a bigrating for use as a beam splitter is presented. It is based on a rigorous formulation of plane-wave scattering by a bigrating that is composed of two individual gratings oriented in different directions. Numerical results are carried out to optimize the design of a bigrating to perform 1 x 4 beam splitting in two dimensions and to examine its fabrication and operation tolerances. It is found that a bigrating can be designed to perform two functions: beam splitting and polarization purification.     

Beam splitter and beam bends based on self-collimation effect in two-dimensional photonic crystals

Basing on the self-collimation effect of photonic crystals, one-to-two beam splitter, beam bend and one-to-three beam splitter are, respectively, designed by introducing a different line defect along the same direction. From the equal-frequency contour plot which is calculated by the plane wave expansion method, we obtain the frequency and the propagate direction of the self-collimated beam. The self-collimated beam propagation in photonic crystals with different line defects is simulated by the two-dimensional finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. The simulation results show that one-to-two beam splitter, beam bend and one-to-three beam splitter can be realized by appropriately arranging the line defect along the proper direction. Such devices can greatly enhance photonic crystals for use in high-density optical integrated circuits.     

Beam splitter for a wide-angle Michelson Doppler imaging interferometer

The design and construction of a hexagonal interferometer beam splitting prism is described in which the light falls onto the all-dielectric partially reflecting coating at an angle of 300 with respect to the normal. For a beam that undergoes one transmission and one reflection by the device, the average effective transmittance 1/2 (T(parallel)R(parallel) + T(perpendicular)R(perpendicular)) in the 0.55-0.75-microm spectral region is approximately 0.23. This quantity is not strongly dependent on the plane of polarization of the incident light, nor on small changes of the angle of incidence from the design angle of 30 degrees. Ways to improve further the performance of the beam splitter are indicated. Coating designs for other angles of incidence are also given.     

Design of a nonpolarizing beam splitter based on the form birefringence of a subwavelength grating inside a glass cube

We propose a design concept to design a nonpolarizing beam splitter with a compact sandwich structure that has a subwavelength grating. The design is based on effective-medium theory and rigorous coupled-wave analysis. The simulation shows that a subwavelength grating inside a glass cube can eliminate the polarization effect.