Abstract: A Fabry-Perot filter device for selectively transmitting three wavelength bands of infrared radiation, including a reference light band, wherein the filter device comprises a fixed mirror formed on a substrate; a movable mirror arranged opposite to the fixed mirror with a gap formed therebetween so that the movable mirror is displaced with respect to the fixed mirror by applying an external force; a fixed electrode formed on the fixed mirror; and a movable electrode formed on the movable mirror and arranged opposite to the fixed electrode wherein the movable electrode is displaced by applying a potential difference across the fixed and movable electrodes so that the width of the gap is varied in at least three steps, whereby at least three wavelength bands of infrared radiation are selectively transmitted through the filter device.

Abstract: A Fabry-Perot filter device for selectively transmitting three wavelength bands of infrared radiation, including a reference light band, wherein the filter device comprises a fixed mirror formed on a substrate; a movable mirror arranged opposite to the fixed mirror with a gap formed therebetween so that the movable mirror is displaced with respect to the fixed mirror by applying an external force; a fixed electrode formed on the fixed mirror; and a movable electrode formed on the movable mirror and arranged opposite to the fixed electrode wherein the movable electrode is displaced by applying a potential difference across the fixed and movable electrodes so that the width of the gap is varied in at least three steps, whereby at least three wavelength bands of infrared radiation are selectively transmitted through the filter device.

Abstract: A Fabry-Perot filter device for selectively transmitting three wavelength bands of infrared radiation, including a reference light band, wherein the filter device comprises a fixed mirror formed on a substrate; a movable mirror arranged opposite to the fixed mirror with a gap formed therebetween so that the movable mirror is displaced with respect to the fixed mirror by applying an external force; a fixed electrode formed on the fixed mirror; and a movable electrode formed on the movable mirror and arranged opposite to the fixed electrode wherein the movable electrode is displaced by applying a potential difference across the fixed and movable electrodes so that the width of the gap is varied in at least three steps, whereby at least three wavelength bands of infrared radiation are selectively transmitted through the filter device.

Abstract: A needle-shaped terminal, i.e., a probe tip, is brought into extremely close proximity with an object being measured. This probe tip is formed from an optically active material and in itself is electrically non-conductive, so that it has no electrical influence whatsoever on the object being measured. When optical pulses are beamed onto this probe tip, the probe tip becomes an electric conductor and a current flows between it and the object being measured, so that the electric potential of the object can be measured. This facilitates previously impossible measurements of high-speed electric waveforms. It also facilitates high spatial resolution monitoring and control of probe tip position and characterization of measurement sites, and enables highly reliable measurements to be made inexpensively.

Abstract: This invention relates to a distributed feedback semiconductor laser which achieves distributed feedback by gain coupling by providing periodical changes in the thickness of the active layer (5) or the absorptive layer, and aims to achieve light distributed feedback mainly of periodical perturbation of the gain factor by diminishing the periodical perturbation of refractive index caused by the changes in the thickness of the active layer (5) or the absorptive layer. This invention is characterized by a refractive index canceling structure comprising a combination of layers (6) and (7) of different refractive indices to cancel periodical changes in refractive index caused by the periodical structure of the active layer (5) or the absorptive layer.

Abstract: A photodiode having a GaInAs light-absorbing layer on an InP substrate which can reduce temperature dependence of the spectral responsivity as well as enable the optical power measurement with less dependence on the incident light spectral width by using a material with smaller composition ratio of Ga for the light-absorbing layer to extend the absorption edge toward the longer wavelengths.

Abstract: A distributed feedback semiconductor laser having a diffractive grating on an active layer in order to generate stimulated emission by recombing electrons with positive holes thereon by the light distributed feedback. This laser can achieve precisely single wavelength longitudinal mode lasing as a thin buffer layer is grown on the surface of the semiconductor layer which has been etched with irregular pattern corresponding to the diffractive grating while the corrugated pattern is being maintained intact and an active layer is grown on the surface thereof in a manner to fill in the valleys of the corrugated pattern as much as possible so that a diffractive grating is formed on the active layer and light distributed feedback is caused mainly by the periodic perturbation of gain coefficients stimulated by the diffractive grating.

Abstract: This invention enables low voltage operation and improves matching in velocities of the radio frequency and of light by lowering effective index and to thereby expand modulation frequency bandwidth by structuring an optical modulator where a substrate of the material of which refractive index changes by an application of electric field description, and the insulating buffer layers are eliminated from the regions other than the electrodes. By structuring the modulator in a manner to satisfy the prescribed conditions with dimensions of each unit, the light can be matched in complete phase matching (group velocity matching) with radio frequency while characteristic impedance of the electrodes is fixed at a desired value.

Abstract: An optical frequency synthesizer and/or sweeper, whereby a coherent optical output light is obtained by using a wavelength stabilized laser and an optical phase locked loop wherein the frequency of the output has the characteristics of high accuracy, high stability and narrow spectral line width. The optical phase locked loop comprises a tunable laser, an optical frequency multiplier, an optical frequency shifter and an optical heterodyne detector, wherein the optical phase locked loop is capable of precisely outputting an arbitrary wavelength by feeding back an output optical frequency.

Abstract: An optical frequency synthesizer and/or sweeper, whereby a coherent optical output light is obtained by using a wavelength stabilized laser and an optical phase locked loop wherein the frequency of the output has the characteristics of high accuracy, high stability and narrow spectral line width. The optical phase locked loop comprises a tunable laser, an optical frequency multiplier, an optical frequency shifter and an optical heterodyne detector, wherein the optical phase locked loop is capable of precisely outputting an arbitrary wavelength by feeding back an output optical frequency.

Abstract: An optical frequency analyzer for measuring an optical frequency spectrum with high accuracy, high resolving power and high stability by heterodyne detecting the incident light with the aid of a local oscillator, wherein the local oscillator comprises an optical frequency synthesizer/sweeper or a marker signal attached tunable laser. The optical frequency analyzer can be modified to measure the incident light itself as the object of measurement or light emerging from the object of measurement can be the incident light.

Abstract: Light relative to non-modulated output light emitted from a semiconductor laser is applied to an absorption cell. Frequency modulating signals are converted into amplitude modulation signals of the output light through a modulating means by utilizing absorptive properties of the absorption cell. Transmissive light outputs of the absorption cell are synchronously rectified by a lock in amplifier, and an electric current supplied to the semiconductor laser is controlled so that the output signals of the lock in amplifier are arranged to be a predetermined value. The wavelength of the output light is locked to the absorption line of the standard substance in the absorption cell. Advantageously, the invention stabilizes the instantaneous value of the oscillation frequency.

Abstract: In order to accurately measure time interval Tx from time t.sub.j to time t.sub.k, the pulse widths of a start interpolation pulse and a stop interpolation pulse must be measured accurately. The invention uses two time-to-voltage converters, one for the start interpolation pulse and the other for the stop interpolation pulse, to convert these pulses to corresponding voltage signals to thereby measure the pulse widths. These converters each comprises a high speed circuit which comprises a current switch, a capacitor, a constant current source and a diode. Advantageously, even though the start and stop interpolation pulses occur close to each other, the pulses can be measured accurately. Also, even though the pulses occur at short intervals, the time interval Tx can be measured accurately.

Abstract: An optical scanning device comprising a transmission or reflection hologram disk, wherein recording beams, such as an object and a reference beam which are used in preparing holograms, and a reconstructing beam which is used in reconstructing or scanning, are spherical waves having different wavelengths; and wherein the sources of recording beams and reconstructing beams are located at different positions for enabling the beams to fall obliquely on the hologram disk to cause a reconstructed image on a focusing or scanning plane to be subjected to linear aberration free scanning. The incident angle of the reconstructing beam on the hologram disk meets the Bragg condition for high diffraction efficiency.

Abstract: A coil arrangement for producing a static magnetic field comprising a central coil and two outer coils disposed on opposite sides of the central coil. The positions and dimensions of the coils are so selected that each term contained in the Taylor series of the function of the magnetic field in the axial direction (z axis) of the coil arrangement in minimized. The current density in the central portion of the central coil is made to be higher than at other portions. The inventive coil arrangement is smaller in size, lighter in weight, and consumers a smaller amount of power than the prior art for the same magnetic strength and with a better homogeneous magnetic field.

Abstract: In measuring a number of echo signal, which normally attenuate chronologically, in a single pulse sequence, such as in multi-echo method or a multi-slice method, each echo signal is received and suitably amplified by a reception amplifier having predetermined levels of gain for different time periods during which the successive echo signals are processed such that the echo signals received at a data collection unit are all of substantially the same amplitude regardless of where they appear in the time sequence. The predetermined levels of gains are obtained by false scanning prior to actual image scanning and calculation and storing in a memory. As a result, the echo signals can be received within a dynamic range which is smaller than using the conventional system.

Abstract: An NMR imaging domain is required to have a uniform distribution of static magnetic field. However, it is very difficult to generate a uniform magnetic field for an entire imaging domain, which is usually a spherical domain. The invention advantageously, exploits the requirement that to obtain imaging the static magnetic field need only be uniform as the slicing part. Thus, sufficient uniformity of static magnetic field is obtained in the invention by providing one or more shim coils to a static magnetic field generating coil and selectively controlling current to be applied to each shim coil in relation to data defining the imaging domain.

Abstract: In a nuclear magnetic resonance imaging device, a pulse sequence is selected and a variance or standard deviation of a calculated image for T1, T2, .rho. is determined as a function of scan parameters from the theoretical equation of signal intensity in the pulse sequence and the variance in the values for T1, T2, .rho. to be measured and the original image. Scan parameters, with which the total sum of variance or standard deviation of the calculated image takes a minimum value, are determined as optimum values. An image is obtained from the optimum scan parameters to obtain a plurality of original images. A calculated image for T1, T2, .rho. is determined, based on the original images, whereby a calculated image of high quality is simultaneously obtained.

Abstract: An object which can provide a reference for measuring the intensity of a primary magnetic field, is positioned in the vicinity of a subject being examined. A variation in the primary magnetic field intensity is detected, based on a frequency shift of data observed of the object, and is used to control the primary magnetic field intensity, or reference frequency for phase detection, or to correct image data. In this manner image quality is prevented from being degraded due to the variation of the primary magnetic field intensity.

Abstract: An NMR imaging apparatus which generates NMR signals cleared of foreign noises by adding a noise detecting coil, for detecting mainly the foreign noises, to an intrinsic detecting coil for detecting the NMR signals and by producing a difference from the outputs of the two detecting coils. As a result, the foreign noises can be eliminated simply and effectively without requiring expensive shielded rooms.