Abstract: An optical pickup head for operating on an information recording medium includes a light source for emitting a light beam. A transparent base plate has opposite surfaces formed with a semitransparent film and a hologram respectively. The semitransparent film is exposed to the light beam emitted from the light source, and reflects a portion of the light beam emitted from the light source. The portion of the light beam which is reflected by the semitransparent film forms a forward light beam. A condenser optical system serves to focus the forward light beam on the information recording medium. The forward light beam is reflected at the information recording medium, and forms a backward light beam. The backward light beam successively passes through the condenser optical system, the semitransparent film, and the transparent base plate, and then reaches the hologram. The hologram generates a backward +1-order diffraction light beam from the backward light beam.

Abstract: A phase lock type semiconductor laser comprising: an array type semiconductor laser main body which includes a plurality of line-shaped active layers having wave guides disposed in parallel with each other, these active layers having waveguide modes optically coupled with each other, and a reflection-type light diffraction element executing a light return or feedback in such a manner that only a specific wavelength beam among emitted beams of coupling modes which are emitted from one end surface of the semiconductor laser main body in terms of a line-shaped light source can be directly focused on the same one end surface of the semiconductor laser main body in a line-shaped.

Abstract: An optical pick-up for an optical disk has a semiconductor laser having an optical axis for generating a laser beam. An objective lens focuses the laser beam onto an optical disk disposed in the path of the optical axis of the semiconductor laser. A wavelength between the semiconductor laser and the objective lens has a plurality of input grating couplers for coupling the laser beam reflected from the optical disk into the waveguide for propagating beams in a plurality of directions. A plurality of output grating couplers radiate the propagated beams from the waveguide. A plurality of photodetectors detect the radiated beams from the output grating couplers.

Abstract: An optical pick-up device includes a semiconductor laser for emitting a laser beam, a focusing lens for focusing the laser beam emitted from the laser onto the surface of an optical medium, a holographic optical element having an anisotropic refractive index and located between the laser and the focusing lens, and a photodetector for receiving a diffracted laser beam from the holographic optical element. The holographic optical element, which may be formed of a liquid crystal or a lithium niobate crystal, transmits therethrough in an undiffracted manner the laser beam emitted from the semiconductor laser and diffracts only the reflected laser beam which has reflected off of the optical medium.

Abstract: A digital loop filter is used in a phase-tracking circuit which is adaptable to a phase-comparison radio navigation system such as the DECCA (registered trademark) system. The digital loop filter includes a feedback circuit which receives a digital input signal from the digital loop filter and outputs a digital output signal and which feeds back and adds the digital output signal to the digital input signal after a predetermined delay. It also includes a feed-forward circuit which multiplies the digital input signal by a predetermined constant (B) and adds the resultant signal to the digital output signal of the feedback circuit to generate a digital output signal. A multiplier for multiplying the digital output signal of the feed-forward circuit by a second predetermined constant (C) to generate a digital output signal of the digital loop filter is also provided.

Abstract: A hyperbolic navigation receiver locates ships, and the like, by phase-locking the output signal of the voltage-controlled oscillator or voltage-controlled phase shifter of respectively provided tracking loop filters corresponding to the incoming signals from a master and slave station. The voltage-controlled oscillator or voltage-controlled phase shifter is caused to produce an output signal which is a multiple frequency of the incoming signal. Phase discrimination of the output signals is undertaken without the use of a multiplier.

Abstract: A liquid crystal light valve projection type image display apparatus comprises an electro-optic element and a Schlieren optical system. The electro-optic element has a liquid crystal layer having a dielectric and optical anisotropy. An electric field having a spatial intensity distribution according to an image signal is applied to said liquid crystal at a spatial period, so that a spatially phase-modulated phase diffraction grating is formed in the liquid crystal layer. Thus, a projected image in enlarged form is obtained. The fact that the electric field with a spatial period is applied to the liquid crystal leads to a constant light diffraction angle, and the modulation of the diffraction light intensity in the applied electric field enables an image corresponding to the input image signal to be projected at high light utilization.