Hitachi Metals, Ltd.

Hitachi, Ltd.

Satoshi Makio

Masayoshi Sato

Yasunori Furukawa

Tsuyoshi Miyai

Toshiki Sugawara

Shigeru Takeda

Kohei Ito

Fumio Nitanda

Hironari Matsumoto

Hidenobu Ishida

Kenchi Ito

Kazuhiko Hosomi

Akio Miyamoto

Kazutami Kawamoto

Masazumi Sato

Yasuhiro Furukawa

The present invention provides: (1) a compensator that compensates a wide range of amount of dispersion of light in a wide bandwidth band; and (2) a variable dispersion slope compensator applicable to the case where a transmission path suitable for a wavelength division multiplexing transmission system produces a wavelength dispersion slope.

Variable dispersion compensator

A dispersion compensator is applicable to a WDM optical transmission system and features low loss, wideband usage, and minimum ripple. The dispersion compensator is constructed so that the light emitted from a collimator will be reflected from an etalon of a 100% single-side reflectance by arranging the etalon and a mirror in parallel or with a slight angle and then enter another collimator. Elements for achieving variable dispersion compensation by changing temperature using a heater, for example, are also provided. In addition, these dispersion compensating elements are provided in multi-stage form and the angle of the mirror and the reflectance of the etalon are optimized. Thus, it becomes possible to realize a dispersion compensator applicable to a WDM optical transmission system and featuring low loss, wideband usage, and minimum ripple.

The dispersion compensator with an etalon and a mirror arranged in parallel or at a slight angle with respect to each other is constructed so that emitted light from a collimator is reflected by the etalon multiple times and then enters another collimator. The dispersion compensator also has dispersion compensating units that change temperature using a heater or equivalent in order to render the amount of dispersion variable. In addition, these dispersion compensating units are provided in multi-stage form, and the angle of the mirror, the amplitude reflectance of the etalon, and temperature are optimized to offer polygonal dispersion characteristics. This realizes a practical, variable dispersion compensator suitable for a wavelength division multiplex optical transmission system and capable of shifting a variable amount of dispersion to the plus or minus side.

An optical switch comprising one input optical fiber, two output optical fibers, a stationary mirror for reflecting a light beam from the input optical fiber to cause it to enter into one output optical fiber, a movable mirror moving into and out of an optical path of a light beam from the input optical fiber, and a means for driving the movable mirror; whereby when the driving means drives the second mirror to a position at which it interrupts the optical path, a light beam from the input optical fiber is reflected by the movable mirror so that it enters into the other output optical fiber.

Optical switch and its production method, and optical path-switching apparatus comprising optical switch

In a second harmonic, single-mode laser having a resonator including a Cr-doped fluoride laser crystal, first and second wavelength-selecting elements and a nonlinear optical crystal between a pair of laser mirrors, a wavelength-selecting width of the first wavelength-selecting element is {fraction (1/30)} or less of that of the second wavelength-selecting element, the first wavelength-selecting element is provided with a reflection coating having a reflectivity of 10-30% to the oscillated laser beam, such that the wavelength selection width of the first wavelength-selecting element is 0.02-0.03 nm, a wavelength interval in the oscillation wavelength range of the first wavelength-selecting element is 0.8-1.3 nm, and a wavelength selection width of the second wavelength-selecting element is 1.0-1.6 nm.

Second harmonic, single-mode laser

The free spectral range dependent on the length of an oscillator is put in a relation of integral times with respect to the free spectral range dependent on the length of at least a nonlinear optical crystal or a wavelength selection SHG output element. Thereby, reduced noise in the output of a second-harmonic generator is intended.

Reduced-noise second-harmonic generator and laser application device

A second harmonic generator comprising a semiconductor laser as an excitation light source and a resonator having a solid laser crystal excited by the excitation light source, a control element for controlling the wavelength of a first oscillation wave generated from the solid laser crystal and a nonlinear crystal for wavelength converting the first oscillation wave as a fundamental wave into a second harmonic wave as a second oscillation wave, wherein the components of the resonator are arranged in the order of a first laser mirror, solid laser crystal, wavelength control element, nonlinear crystal and second laser mirror from the input side of the excitation light.

Second harmonic generator and laser applied units

A laser having, a resonator structure including a wavelength variable laser crystal containing a fluoride and an optical part for controlling the wavelength of radiation from the laser crystal, a device to excite the laser crystal, a device for detect reflected light from the optical part as a sample beam, and a device to stabilize the output of a laser beam from the resonator structure based on the sample beam.

Laser and laser applied units

A second harmonic generating apparatus including a semiconductor laser serving as a pumping source, a resonator structure for oscillating a first radiation wave generated by LiSAF (Cr:LiSrAlF.sub.6 : Lithium strontium aluminum fluoride with chromium added) crystal which is a solid-state laser crystal which is excited by the pumping source, a control element for controlling the wavelength of the first oscillation wave, and a nonlinear crystal for performing wavelength conversion into second harmonic which is a second oscillation wave, with the first oscillation wave serving as a fundamental wave, the nonlinear crystal being provided in the resonator. A higher efficiency and reliability of the second harmonic generating apparatus is achieved.

Second harmonic generating apparatus and apparatus employing laser

A laser apparatus including a laser crystal composed of a fluoride which contains chromium (Cr), a resonator which includes the laser crystal, a means for exciting the laser crystal, a first laser beam produced from light which is emitted from the laser crystal and oscillated in the laser resonator, and at least one optical component which is inserted in said resonator; wherein an aperture in the resonator is substantially five or more times the diameter of the first laser beam. A small, low-power SHG laser light source is achieved.

Laser apparatus and apparatus employing laser

Using an LiTaO.sub.3 or LiNbO.sub.3 substrate, a proton exchange layer in a grid pattern, namely sprout areas of polarization inversion, is firstly, formed on the surface of said substrate and, after formation of the pattern, heat treatment is executed at a temperature of 200.degree. C. or more and for a holding time of 10 minutes or less. By maintaining the temperature gradient up to said heat treatment point at 50.degree. C./min. or steeper and by maintaining the temperature decrease rate from said heat treatment point at 50.degree. C./min. or faster, polarization inverted areas are formed downwards from the proton exchanged areas, while in addition to making the top ends of said polarization inverted areas into an acute angle, the depth/weight ratio of the polarization inverted grids being formed is made to exceed 1, thus enabling the production of a high-efficiency SHG element.

Second harmonic generating element and the production method thereof

0.1% or more of Mg by weight is added to lithium tantalate monocrystal materials wherein the amount of Fe is restricted to 10 ppm by weight or less to improve light transmittance in the short wavelength range of blue light and to shift the fundamental absorption edge to the shorter wavelength.

Lithium tantalate monocrystal, monocrystal substrate, and photo element

A Faraday rotator device containing (a) a Faraday rotator, (b) a wire winding encircling the Faraday rotator for changing the magnetization state of the Faraday rotator, and (c) a hollow yoke surrounding the Faraday rotator and the wire winding for forming a substantially closed magnetic circuit together with the Faraday rotator, the hollow yoke having an opening in each of front and rear walls in alignment with the Faraday rotator for permitting a light to pass through the hollow yoke and the Faraday rotator. The optical switch containing a pair of polarizers disposed on front and rear sides of the Faraday rotator device, the magnetization direction of the Faraday rotator being reversible to change the optical path. The hollow yoke is made of a soft magnetic material or a semi-hard magnetic material.

Faraday rotator device and optical switch containing same

An optical isolator comprising a cylindrical magnet magnetized in a direction parallel to the axis of rotational symmetry thereof, a Faraday rotator disposed in a center space of the cylindrical magnet, a pair of beam splitters capable of serving as a polarizer or an analyzer arranged on both sides of said Faraday rotator with inclination of 45.degree. relative to each other, characterized in that the outer diameter Do, the inner diameter Di and the length L of the cylindrical magnet are in the range defined by ##EQU1## where .alpha.=Do/Di. In the case of a multi-stage optical isolator, the Faraday rotators and the beam splitters are arranged alternately in tandem, and any two adjacent cylindrical magnets are arranged with their magnetic poles of the same polarity facing each other.

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Kumagaya, Japan

Satoshi Makio