Vibration transducer using an ultrashort Fabry-Perot cavity

We report here on the development of an optical transducer for mechanical vibration, making use of an ultrashort Fabry-Perot cavity. The noise level measured by a cavity 150 μm long is ~1.3 × 10(-16) m/√Hz at ~1 kHz, which was obtained without a frequency-stabilization system. It was, however, large compared with the shot noise.     

Properties of an optical time-division demultiplexing module using serialized nonlinear optical loop mirrors

Abstract

In this paper, the properties of the demultiplexing module using the serialized nonlinear optical loop mirrors have been investigated. The noise of the demultiplexing output has been discussed in detail. The influences of the switches' settings on the noise and the properties of the bit error rate of each demultiplexing channel have also been investigated. It is shown that the power penalty of the demultiplexing module in a serial structure using the nonlinear optical loop mirrors is much lower than that in the parallel structure and it will be very small if the settings of the loop mirrors are carefully chosen     

Measuring the polarization characteristics of birefringent optical fibers using an interference technique

A simple method based on the interference of coherently excited modes is proposed for measuring the orientations of birefringence axes and determining the level of polarized mode excitation in single-mode birefringent fibers. The exact determination of these characteristics is achieved by introducing the dimensionless coefficients of modulation and transmission dependent on the analyzer rotation angle. The proposed technique, in contrast to the conventional methods, does not require the use of special excitation conditions at the fiber entrance.     

Low-loss birefringent spectral filters comprising three identical retarders

Basic fan or folded arrangements comprising three identical retarders in cascade between parallel or crossed polarizers are presented for constructing birefringent spectral filters without an internal polarizer. The retarders' axes are oriented with an angle increment of theta or -theta preferably with /theta/ 相似文献   

Quantum non-demolition measurements using cold atoms in an optical cavity

Abstract

In this paper we present a theoretical analysis of a recent quantum non-demolition experiment in optics using cold atoms in a magneto-optical trap as a nonlinear medium. A signal beam and a meter beam from two independent lasers are coupled within a A-type three-level scheme in the D1 line of ⁸⁷Rb atoms. The experimental results for the relevant quantum correlations of the fields represent up to now the best achievement for a single back-action evading measurement. Moreover, they are found to be in remarkably good agreement with the theoretical predictions from a fully quantum model for three-level atoms in a doubly resonant cavity.     

External cavity lasers using stripe mirrors with different mirror width

We present the study of an external cavity laser using a stripe mirror and a grating for the optical feedback. As the most important parameter in this system, the width of the stripe mirror has been systematically studied, which strongly affects the device performances. Furthermore, the size of the focused laser spots and the distance between the spots of adjacent modes have been obtained. The measured results agree with the theoretical calculation very well. These parameters are very important for the design and construction of this kind of external cavity lasers.     

Measurements of birefringent media properties using optical vortex birefringence compensator

We present some applications of the optical vortex birefringence compensator, based on the C polarization type singularities generated using two Wollaston compensators. The theory and experimental results of birefringent media properties measurements are presented. The possibility of the simultaneous measurement of both the azimuth angle and the phase retardance has been analyzed and experimentally verified.     

Metrological characteristics of an optical heterodyne transducer

Literature on the correct definition and utilization of the metrological characteristics of an optical heterodyne transducer operating as an integral part of a laser Doppler velocimeter is reviewed briefly.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 42–46, November, 1993.     

Modal properties of an external diode-laser-array cavity with diffractive mode-selecting mirrors

Coupled mode theory is used to describe the behavior of an external laser cavity consisting of a diode laser array and a diffractive mode-selecting mirror. The mirror is designed to establish a uniform-amplitude, uniform-phase fundamental mode. Coupled mode theory is then used to study the behavior of higher-order modes. We show that the maximum discrimination against higher-order modes occurs when the round-trip cavity length satisfies certain Talbot relations. In addition, this high modal discrimination can be maintained for arrays with large numbers of lasers without incurring significant loss in the fundamental mode.     

Microcontroller-based performance enhancement of an optical fiberlevel transducer

A proposed digital microcontrolled transducer for liquid-level measurement is based on two optical fibers from which the cladding was removed in suitably spaced zones at known distances. A 1-m full-scale, 6.25-mm resolution prototype was made and tested. The adopted hardware and software strategies assure a low-cost, high-static, and dynamic performance, good reliability, and the possibility of remote control. These features were confirmed by the experimental tests carried out on gasoline     

Magnetic crosstalk compensation for an optical current transducer

In this paper, we analyze the errors associated with magnetic crosstalk within point type, or unlinked, optical current transducers (OCTs) working in a three-phase electric current transmission systems. For many practical conductor arrangements, the magnetic crosstaIk may introduce errors unacceptable for the accuracy requirements demanded from the OCT. A solution to this problem is devised around a unique compensation method which solves, in real time, a set of linear equations, each representing the instantaneous output signal from one phase current sensor     

Capacitive transducer for relative position error galvo mirrors

A transducer was designed to sense small angular displacements of servo-controlled galvo mirrors in rotary optical storage devices. The transducer is differential in nature, and operates on the principle of linear electrical capacitance variation with area overlap of uniquely shaped capacitor plates. These capacitive plates lie in planes normal to the axis of rotation, and consist of many electrically connected wedge-shaped projections aligned radially to the center of rotation. A prototype was fabricated and tested. For optical storage devices, experimentally determined characteristic curves show sufficient linearity and repeatability for relative position error (RPE) feedback applications, at plate spacings of 0.15 mm or less. A design change, for further extending the linear range of the characteristic curve of the transducer beyond RPE feedback requirements, is described. A circuit design to produce voltage variations proportional to differential capacitance changes in the transducer is discussed, and peak-to-peak signal-to-noise ratio is conservatively approximated at 2×10⁴ with 10 kHz bandwidth     

Generation of high-order optical vortices using directly machined spiral phase mirrors

We report on the generation of high-order optical vortices by spiral phase mirrors (SPMs). The mirrors are produced by direct machining with a diamond tool and are shown to produce high-quality optical vortices with topological charges ranging from 1 to upwards of 100 at a wavelength of 532 nm. The direct machining technique is flexible and offers the promise of high-precision, large-diameter SPMs that are compatible with high optical powers.     

Misalignment correction for optical interconnects using vertical cavity semiconductor optical amplifiers

In board-to-board optical interconnects, the misalignment between the board and the backplane connections can cause both optical loss and interchannel cross talk. A vertical cavity semiconductor optical amplifier (VCSOA) is proposed to correct optical misalignment in an optical connector between the board and the backplane. Angular or lateral misalignment can be corrected with the designed module. The correction ability is determined by the acceptance angle of the VCSOA, which was characterized to be 9.4 degrees full angle at a 3 dB gain drop for a 30 microW optical signal at 1 GHz. The lateral misalignment correction ability is 0.16f, where f is the focal length of the mini lens to converge the input light onto the VCSOA.     

Linearization of transducer signals using an analog-to-digitalconverter

A simple method for linearizing analog electrical signals and transducer outputs as they are being converted to a digital format is described. It is based on the ratiometric property inherent to the analog-to-digital converter. The method gives satisfactory results in many cases, and the resulting circuits are simple and easily adjusted. It can be applied to correct the output of a digital readout meter and can provide a convenient alternative to digital linearization of signals     

Reflected optical harmonics from dielectric mirrors

Optical second and third harmonics were generated in reflection from commercially available laser dielectric mirrors. Although most dielectric coatings on laser mirrors are centrosymmetric, the inversion symmetry is broken at the dielectric-air interface. When intense femtosecond laser pulses are reflected off the dielectric mirrors, a second-order dipole contribution to surface second-harmonic generation can exist and is detected. More dramatically, at a laser fluence of ～10 GW/cm(2) the normally much weaker electric-dipole-allowed third-harmonic generation that originated in the bulk accentuates the second-harmonic generation. These reflected harmonics are, in some cases, nonnegligible in many sensitive experiments.     

一款低频Janus-Helmholtz顺性腔换能器

Janus-Helmholtz(JH)顺性腔换能器是在传统的JH换能器腔内加入顺性管堆,通过调节占空比实现谐振频率及带宽的控制。在顺性腔的设计中采用了压缩系数为3.2×10-8 Pa-1的顺性管,通过ATILA仿真软件对Janus-Helmholtz顺性腔换能器在不同占空比下的声发射性能进行预计且与测试结果进行对比,发现在占空比为12%时,可在300~700 Hz的频带内实现190 d B的声源级,且可实现600 Hz以下频段全向辐射。