Fdk Corporation

Other

Fujitsu Corporation

Hidenori Nakada

Hirotaka Kawai

Isao Kojima

Yuko Ota

Tsugio Tokumasu

Teruhisa Sahashi

Hiroaki Ono

Nobuhiro Fukushima

Keisuke Ikeda

Hiromitsu Umezawa

Shohei Abe

Shusuke Wada

Taro Nakamura

Ikuo Maeda

Hideo Takeshita

Youichi Suzuki

Mototsugu Goto

An input/output port, a birefringent element, variable polarization rotator, and a reflector are arranged along an optical axis in the order named. The variable polarization rotator includes permanent magnets for applying a fixed magnetic field to a Faraday rotator in an in-plane direction to magnetically saturate the Faraday rotator and a solenoid coil for applying a variable magnetic field to the Faraday rotator in a direction of the optical axis. A fixed magnetic field is applied in the &#x3c;211&#x3e; direction, in which the Faraday rotator is likely to be magnetically saturated. The Faraday rotator can be saturated with a low magnetic field of about 100 Oe. The permanent magnets may employ ferrite permanent magnets, which have weak magnetic forces. A variable magnetic field may also be reduced. Therefore, an air-core coil can be used.

Reflection type variable optical attenuator

A low-cost compact optical attenuator structure has an input port and an output port for optical signals arranged side by side; a reflecting member arranged to face both ports to reverse light from the input side on an optical path folded 180&#xb0;; a birefringence crystal splits incident light into two polarization components, a converging lens converges the incident light, a fixed Faraday rotator having a variable rotation angle arranged in that order in the optical path. The partial reflecting member that transmits a portion of incident light to the rear side thereof, an optical sensor at the rear side of the reflecting member, optical guide means guide only the transmitted light from the input port side to the optical sensor, and optical detection signals of the optical sensor are used as optical input monitoring signals.

Optical attenuator

A variable optical filter comprises a first polarizer, a first phase difference element operable to generate a phase difference, a variable Faraday rotator operable to impart a variable Faraday rotation, a second phase difference element operable to generate a phase difference, and a second polarizer, wherein said polarizers, said variable Faraday rotator, and said phase difference elements are arranged in the mentioned order along the optical axis, and wherein when the angles formed by the optic axes of said first and second phase difference elements and the transmitted polarization azimuth of the first polarizer are assumed respectively to be &#x3c6;and &#x3c6;, these &#x3c6;and &#x3c6;are set to different angles.

Variable optical filter

A reflection-type variable optical attenuator comprises: a main attenuator unit including a first birefringent crystal plate, a Faraday rotational angle varying unit, and a second birefringent crystal plate arranged in this order; an input port and an output port that are arranged on a side of one end of the main attenuator unit; and a two-point reflection-type optical path varying reflector that is arranged on a side of the other end of the main attenuator unit. Light that comes in from the input port makes a round trip in the main attenuator unit and goes out through the output port.

Reflective variable light attenuator

Optical devices including a Faraday rotation devices improved in wavelength and temperature characteristics and an optical attenuator reduced in wavelength dependence and temperature-dependent loss. The Faraday rotation device has permanent magnets magnetized in an axial direction of through-holes, and Faraday elements having a same Faraday rotation direction with respect to a same magnetization direction. The permanent magnets are directed in the same magnetization direction along an optical path, where part of the Faraday elements are accommodated in the through-hole of the permanent magnet, and the remaining Faraday elements are arranged between the magnets, whereby the Faraday elements are to be applied by magnetic fields in opposite directions. For a device variable in Faraday rotation angle, an electromagnet is provided. An input fiber collimator and polarizer are provided on an input side of with the Faraday elements while an analyzer and output fiber collimator are on an output side.

Faraday rotation device and optical device using same

Farady rotation device and optical device comprising it

A variable optical gain equalizer in accordance with one embodiment of the present invention comprises a variable branching ratio beam splitter having a variable polarization rotator, the variable branching ratio beam splitter branching an input light beam into two light beams at an arbitrary power ratio, through control of the rotation angle of the polarization direction by the variable polarization rotator; an optical filter presenting different filter characteristics to the two branched output light beams; and a polarization coupler for polarization coupling the two light beams that have passed through the optical filter, wherein the rotation angle of the polarization direction is controlled by the variable polarization rotator so as to vary the spectra of the output light beams.

Variable optical gain equalizer and variable branching ratio beam splitter

Disclosed is a Faraday rotator capable of reducing the temperature dependence on a Faraday rotation angle, thereby enhancing the temperature characteristic, particularly, in a service environment in which the magnetization direction is variable, and an optical device using the Faraday rotator. The Faraday rotator includes a Faraday element which rotates the polarization plane of polarized light rays passing through the Faraday element when an external magnetic field is applied to the Faraday element. In this Faraday rotator, assuming that an angle between a magnetization direction of the Faraday element and a light ray direction is taken as &agr;, the amount of the temperature-dependent change in Faraday rotation angle is reduced by applying the external magnetic field in a direction in which a first amount of the change in Faraday rotation angle due to the temperature dependence on the angle &agr; and a second amount of the change in Faraday rotation angle due to the temperature dependence on the Faraday effect satisfy a relationship in which the sign of the first amount is plus or minus, the sign of the second amount is minus or plus, and the absolute value of one of the first and second amounts is less than twice the absolute value of the other amount, more preferably, substantially equal to the absolute value of the other amount.

Faraday rotator

A Faraday rotation angle varying apparatus for controlling a Faraday rotation angle of a light beam passing through a garnet single crystal having a Faraday effect by applying external magnetic fields to the garnet single crystal in two or more of directions and varying a synthetic magnetic field synthesized from the external magnetic fields is disclosed. According to an aspect of the present invention, the garnet single crystal has the (111) plane polished and the light beam is allowed to pass through the garnet single crystal along the &lt;111&gt; direction of the garnet single crystal perpendicular to the (111) plane. A displacement path of a synthetic vector of the external magnetic fields is within a fan-shaped range (peripheral lines of the fan-shape inclusive) of a stereographic projection chart of the garnet single crystal with the (111) plane taken as the center of the chart. The fan-shaped range is surrounded by two lines connecting a point indicating the (111) plane positioned at the center of the stereographic projection chart to two positions apart 10.degree. rightward and leftward from a point indicating one of crystal planes equivalent to the (110) plane positioned on the outermost peripheral circle of the stereographic projection chart.

Growing community of inventors

Aichi, Japan

Hidenori Nakada