Tomoaki Eiju

Phase-only modulation using a twisted nematic liquid crystal television

We used a commercially available liquid crystal television display unit as a spatial optical phase-only modulator. To do this, we removed the integral polarizers from the unit and double passed the light under modulation through it. We found that it was possible to obtain continuous phase modulation from 0 to PI with essentially no change in the state of polarization of the output light and absorption changes of <2.5%. We wrote computer-generated phase-only holograms on the LCTV and reconstructed them optically.

Optimization of twisted nematic liquid crystal panels for spatial light phase modulation

Abstract To optimize a twisted nematic liquid crystal panel for large phase modulation, it is necessary to optimize the angles of the polarizer and analyzer. We determine the Jones matrix of a panel and find these optimum angles by computer simulations. They compare well to the experimental results.

Reconfigurable free-space optical interconnections with a phase-only liquid-crystal spatial light modulator

A range of space-invariant and space-variant holographic optical interconnections are demonstrated with the aid of a nematic liquid-crystal panel that is capable of nearly continuous phase modulation. Results on fan-out, nearest-neighbor/next-nearest-neighbor interconnects, and 8-bit perfect shuffle are presented. The diffraction efficiencies are close to 15% of incident light in all cases.

High resolution adaptive optics using an interference phase loop

Abstract The Interference Phase Loop is an interferometer with feedback of the output intensity to a phase modulator in one of the inteferometer arms. When a spatial optical phase modulator is used, the modulator phase distribution approximates to the conjugate of the spatial phase distribution in the interferometer, and so the device has potential for application in adaptive optics. We have implemented an interference phase loop using a high-resolution liquid crystal spatial light modulator (PAL-SLM) and a common path radial shearing interferometer. We show how the system can be analysed in simple terms, derive some design and operating criteria, and demonstrate diffraction-limited real-time aberration correction of arbitrary input wavefronts using the system. Because of the nature of the interferometer used, our system has the potential to operate in white light.

Microscopic laser Doppler velocimeter for blood velocity measurement

A high-resolution laser Doppler velocimeter with small measurement volume is described. This instrument uses a novel frequency shifter incorporating a moving glass prism that gives stable frequency shifts up to 7 kHz and determines the velocity measurement range, which is 0.1 to 7 mm/s. The instrument has been used to measure blood flow velocities in microvessels and results are presented that demonstrate the capabilities of the system.

Analysis of a joint transform correlator using a phase-only spatial light modulator

A theoretical analysis of a joint transform correlator that uses a phase-only spatial light modulator to input joint transform plane intensity data into the second Fourier transform system is presented. It is shown that this correlator produces signals that differ from, but are related to, the mathematical correlation between the test and reference input images. An undesirable characteristic of the correlator is that the form of the output signals depends on both the intensity-to-phase transfer characteristic of the phase modulator and the intensities of the input images. However, apodization of the joint transform intensity distribution by the reciprocal of the intensity distribution of the reference image Fourier transform can overcome this problem, and results in a correlator with narrow matching output peaks and high discrimination, in which the autocorrelation peak can be eliminated. Theoretical results are demonstrated by computer simulation.

Grating interferometer with extremely high stability, suitable for measuring small refractive index changes.

We describe here a grating interferometer with extremely high stability and which can be used as a differential refractometer. The instrument uses heterodyne techniques to achieve high sensitivity. We present an analysis of the operation of the system and results which show that it has a long term stability of the order of 1/1500 wavelength over 2 h.

Novel holographic shearing interferometer for measuring lens lateral aberration.

A new type of holographic shearing interferometer for measuring lens lateral aberrations is described. In this interferometer a vertical tilt is introduced between the output beams so that the output fringes directly map out the lateral aberration curve of the lens being tested. In addition to this we improve the precision of the interferometer by making it a multiple-beam system through the use of multiple-exposure holograms. The theory of operation of the interferometer is described, and results obtained with an experimental system are presented.

Joint Transform Correlator Using a Phase Only Spatial Light Modulator

A Joint Transform Optical Correlator is described which uses a phase only spatial light modulator for input of the Joint Transform plane information into the second stage of the correlator. This, combined with suitable apodizing of the Joint Transform plane intensity distribution, brings several advantages including high optical efficiency, good signal-to-noise ratio, and the ability to correct system aberrations.

Straightness measurements with a reflection confocal optical system—an experimental study

Straightness measurement is an important technique in the field of mechanical engineering. We previously proposed a novel optical method for measuring straightness of motion using reflection confocal optics. The advantage of this method in comparison with the transmission optical systems of others [Opt. Laser Technol. 6, 166 (1974)] is that the lateral displacements in the two axes perpendicular to the optical axis and the rotation angles around all three axes can be measured simultaneously. We demonstrate straightness measurements using reflection confocal optics and show these measurements to be in good agreement with the theory.