Abstract: An optical waveguide having a light receiving end and a propagation mode with a double-hump shaped optical field distribution at the light receiving end to receive light into the optical waveguide. The light incident on the light receiving end typically has a single-hump shaped optical field distribution. Overlap in the optical field distribution of the incident light and the optical field distribution of the propagation mode of the optical waveguide causes the light to be received by the optical waveguide. Alternatively, the optical waveguide can have a propagation mode with a single-hump shaped optical field distribution at the light receiving end, and the incident light can have a double-hump shaped optical field distribution at the light receiving end.

Abstract: A Faraday rotator which includes a magnetic optical element and a magnetic field generating unit. The magnetic optical element has an optical path extending therethrough. The magnetic field generating unit is positioned so as not to obstruct the optical path, and generates a uniform magnetic field in the magnetic optical element. The magnetic field generating unit can include a first magnet unit and a second magnet unit. The first magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The second magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The magnetic field generated by the second magnet unit is perpendicular to the magnetic field generated by the first magnet unit and combines with the magnetic field generated by the first magnet unit to produce a uniform magnetic field in the magnetic optical crystal.

Abstract: An optical fiber comprises a core line, which includes a core and a cladding, and a cover. The core line is twisted 90.degree. clockwise and counterclockwise alternately at predetermined intervals (for example, every 30 meters). The twisted portion in the core line is equal to or shorter than 1 m, and is more preferably only several centimeters long. Since the optical fiber has residual birefringence, there exist two principal axes of birefringence, that is, a fast axis f and a slow axis s in the core line. Since the core line is 90.degree. twisted at the twisted portion, the two principal axes of the consequent portion exchange their direction compared with the two principal axes of the antecedent portion. Thus, twisting the core line effectively shortens the sustaining distance of the birefringence of the optical fiber, and exchanging the directions of the two principal axes successfully suppresses the polarized wave dispersion.

Abstract: The invention comprises an interferometer for detecting rotation in which a single light beam is split by a first polarizing beam splitter into two linearly, orthogonally polarized beams and introduced to opposite ends of a linear polarization maintaining fiber optic loop formed of a Kerr medium optical fiber material having a 90.degree. twist therein. Upon exiting the opposite ends of the loop, the two beams are recombined by the first polarizing beam splitter into a single beam. The recombined light beam is seperated from the input light beam and is passed through a quarter-wave plate which converts the linear polarization to circular polarization. The circularly polarized beam is then passed through a second polarizing beam splitter to form two separate beams of distinct intensity dependent upon the two distinct circular polarizations contained in the incident beam. The two light beams are introduced to a balanced detector whereupon the difference in intensity of the two light beams is detected.

Abstract: The present invention relates to a laser device. A laser resonator is formed of a positive dispersion region, a negative dispersion region, the first and second dispersion regions having the same dispersion amount, a first mode synchronous light modulator, a second mode synchronous light modulator, and a light gain medium. A light propagation path is formed by arranging in the light propagating order the first mode synchronous light modulator, the positive dispersion region, the second mode synchronous light modulator, and the negative dispersion region. The light gain medium is arranged in any place in the light transmission path. Control unit varies a relative phase in modulation between the first mode synchronous light modulator and the second mode synchronous light modulator. The simplified structure can suppress the device manufacturing cost and control the oscillation wavelength.

Abstract: An interferometric measurement scheme utilizing squeezed light wherein an input pulse is split into two consecutive input pulses separated by a time interval that is less than the inverse spectral width of GAWBS. The two pulses are further split into first and second pairs of pulses and are caused to propagate in opposite directions through a fiber optic interferometer loop and are recombined upon exiting the loop. The recombined pulses are caused to pass through a .pi. phase modulator which modulates one of the two pulses. The output is then introduced to a balanced detector where the detected signal of the two is averaged such that GAWBS noise is cancelled.

Abstract: An optical transmitter is disclosed of the type having direct phase-shift and self-homodyne intensity modulation (DPSH-IM) applied to thereto. A periodic signal having the period corresponding to one time slot of a modulation current pulse for a laser diode is superimposed, together with the modulation current pulse, on a bias current to improve the transmission waveform.

Abstract: An optical detector having a detection surface and a mirror sized and positioned relative to the surface so as to receive and return light which is reflected off of the detecting surface within the response time of the system.

Abstract: A mode locked fiber ring laser comprising an optical fiber, an output mirror, a partially reflective/partially transmissive mirror and a unidirectional attenuator. The unidirectional attenuator comprises, in sequence, a first linear polarizer, with its polarization axes at 0.degree., a first quarter wave plate with its axis at .theta..degree., a non-reciprocal rotator for rotating the polarization of incident light by .gamma..degree., a second quarter wave plate with its axis accented at (.theta.+.gamma.+90).degree. and a second linear polarizer with its polarization axis at .gamma..degree.. The parameters .theta. and .gamma. are selected to provide a desired relative phase shift between counter-propagating beams in the fiber and to attenuate the beam in one of the directions so as to create an additive pulse mode-locked (APM) type passive mode locking system.

Abstract: An optical amplifier is disclosed which, in an optical amplifier adapted such that signal light and pump light are propagated through an optical waveguide structure (2, 2') therein made of an optically nonlinear material to thereby achieve optical parametric amplification or four-wave mixing optical amplification of the signal light, is provided with means for attenuating idler light to be generated within the optical waveguide structure. The optical amplifier has an advantage that phase matching between the pump light and the signal light is easily achieved and thus an optical amplifier operative over a broad frequency band can be realized.

Abstract: In spectrum measuring equipment the light to be measured is separated by a double-image polarizing element into two polarized wave components whose planes of polarization cross each other perpendicular and which have different optical axes. The two polarized wave components are applied to a dispersing element so that their planes of polarization intersect the direction of light separation at .+-.45.degree. thereto, respectively. The sum of optical powers of the two polarized wave components separated by the dispersing element is measured by a photodetector, so that spectrum measurement independent of the polarization of the light to be measured can be achieved.

Abstract: A method of modulating a semiconductor laser, a method of stabilizing a self-homodyne optical interferometer and a light modulation apparatus using a semiconductor laser is provided for use, for example, in various optical communication systems. To avoid the adverse affect on a semiconductor laser of wavelength chirping and to facilitate high-speed direct modulation, a predetermined short pulse current is superimposed on a bias current to drive a semiconductor laser, thereby phase-modulating the output light at a high speed, eliminating the phase deviation at the output of the light interferometer of the self-homodyne-type and achieving a stable output from the semiconductor laser. The average intensity of the output light is obtained, thereby applying a feedback to a wavelength of the input light or to a difference in an optical path length of the optical interferometer itself in accordance with the average intensity of the output light in order to correct the phase bias when modulating the intensity.

Abstract: Spatial phase modulating transparent masks comprising two or more portions having two different optical paths and their production processes are disclosed. The transparent masks are particularly useful as an exposure mask in the production of phase-shifted, distributed feedback (DFB) semiconductor lasers for a single-mode operation. A process for the formation of phase-shifted diffraction gratings or corrugations which comprises exposing a substrate, through the above transparent mask, to exposure radiation is also disclosed. According to the present invention, the phase-shifted diffraction gratings can be easily and directly produced with a high accuracy and reliability.

Abstract: An optical device is provided for dividing light depending on an optical wavelength thereof. The device includes a single input optical fiber and an output fiber array consisting of a plurality of optical fibers, and spectroscopic grating and a tetrahedral dispersion-dividing prism disposed on an optical path between the input and the output fibers. The prism has a face defining a dispersion-dividing part consisting of a plurality of step-like V-shaped grooves each having an apex with an angle of 60.degree. and two inclined surfaces, so that a light beam, the position of which is shifted depending on the wavelength thereof, hits the grooved face, and within the region of one groove, the light beam is reflected first at one of the inclined surfaces and then reflected at the other surface so as to change the direction of the light beam.

Abstract: A polarization rotation compensator and an optical isolator using the same are described. The optical isolator comprises a first birefringent wedge plate; a polarization rotation compensator composed of a combination of a half-wave plate whose principal axis is inclined at an angle of .theta./2 with respect to the plane of polarization of the incident light and a quarter-wave plate whose principal axis is inclined at an angle of .theta. with respect to the plane of polarization of the incident light; a Faraday rotator; and a second birefringent wedge plate; wherein the Faraday rotator, quarter wavelength plate, and half-wavelength plate are respectively arranged in the order of propagation of the backward light or of the forward light.

Abstract: An optical switch including a first polarization converter and a second polarization converter which is provided in series with the first polarization converter.The first and second converters are able to select as emitted light one of two perpendicular polarized light components of incident light having a desired wavelength (.lambda..sub.0) in a polarized state. The first polarization converter converts the incident light having wavelength .lambda..sub.0 into a polarized light component corresponding to one of two points positioned on opposite sides of a Poincar/e/ sphere. The two points on the Poincar/e/ sphere are obtained by rotating the incident light +90.degree. or -90.degree.. The incident light is rotated around an axis perpendicular to an axis passing through a point corresponding to the incident light on the Poincar/e/ sphere and the center of the Poincar/e/ sphere.

Abstract: A polarizing element comprising a transparent flat plate having at least two parallel surfaces, a polarizing separate layer provided on a portion of one parallel surface of the transparent flat plate and an optical reflecting material provided on a portion of the other parallel surface of the transparent flat plate.

Abstract: Disclosed is a laser light source device having a laser and an external resonator, wherein as a base, a Faraday rotator is provided at the laser side front of a reflection plane of the resonator so that clockwise and counter-clockwise circular polarizations which have frequencies slightly different to each other are generated, and if a laser such as a semiconductor laser having an eigen-mode having a linear polarization is applied, elements which rotate a polarization by 90 degrees by one emission-and-return through the element, for example, quarter-wave plates, are arranged, The device does not need a strong magnetic field or a strong electric field, and can easily generate lights which are a constant strength. Thus the device can be miniaturized and a high efficiency obtained.

Abstract: A Faraday rotator assembly includes a Faraday rotator of an optically transparent magnetic material; a device for applying a first magnetic field to the Faraday rotator, which field saturates the Faraday rotator with reversible magnetization; and a device for applying a second magnetic field to the Faraday rotator, the field having a direction different from that of the device for applying the first magnetic field to the Faraday rotator. The magnetization in the Faraday rotator is maintained in a saturation state by the second magnetic field at least during the reversal of the direction of the first magnetic field. The angle of the Faraday rotation of the Faraday rotator is reversed by reversing the direction of the first magnetic field.

Abstract: An optical device, such as an optical isolator or an optical modulator, comprises a 45.degree. Faraday rotator or an electrooptic crystal which is interposed between tapered plates of birefringent material for separating and combining polarized light. The tapered plates are made of rectile or calcite. The optical device is polarization independent, and it can be miniaturized with less components than prior art optical devices. The optical isolator also allows one hundred percent of light in the forward direction to pass through it. The optical modulator can be used as a voltage senser.