Nippon Telegraph and Telephone Corporation

Other

Kuninori Hattori

Hiroshi Takahashi

Toshikazu Hashimoto

Yusuke Nasu

Yohei Sakamaki

Yasuyuki Inoue

Kenji Yokoyama

Takashi Goh

Motohaya Ishii

Katsunari Okamoto

Manabu Oguma

Motohiro Nakahara

Koichi Arishima

Akimasa Kaneko

Shin Sumida

Senichi Suzuki

Yasuaki Hashizume

Fumiaki Hanawa

Fumihiro Ebisawa

Hiroaki Yamada

Takashi Yoshida

An optical 90-degree hybrid circuit includes: first and second optical splitters for receiving and splitting a first and second light beam into two, respectively; a first optical coupler for generating an interfering light beam by multiplexing one of the light beams split by the first optical splitter and the second optical splitter; and a second optical coupler for generating an interfering light beam by multiplexing another one of the light beams split by the first optical splitter and the second optical splitter. The first optical splitter includes an optical coupler configured to output two light beams having equal phases, and the second optical splitter includes an optical coupler configured to output two light beams having a phase difference of 90 degrees.

Optical 90-degree hybrid circuit

The present invention provides an optical 90-degree hybrid circuit for reducing wavelength dependency of an IQ phase difference. An optical 90-degree hybrid circuit according to the present invention comprises a first demultiplexing optical coupler including a first and second input port, a second demultiplexing optical coupler including a third and fourth input port, first and second arm waveguides connected to the first and second input port, each having the same length, a third and fourth arm waveguides connected to the third and fourth input port, each having the same length, a 90-degree phase shift section installed in one of the first to fourth arm waveguides, a first optical coupler connected to the first and third arm waveguide, and a second optical coupler connected to the second and fourth arm waveguide, the light is inputted into the first and fourth input port or into the second and third input port.

An optical 90-degree hybrid circuit includes a first demultiplexing optical coupler having two or more first input ports and two or more first output ports, a second demultiplexing optical coupler having two or more second input ports and two or more second output ports, two first arm waveguides connected to the first output ports, two second arm waveguides connected to the second output ports, a 90-degree phase shift section installed in one of the four arm waveguides, a first optical coupler and a second optical coupler connected to the first arm waveguides and the second arm waveguides, a first optical waveguide for connecting an optical splitter and the first input ports, and a second optical waveguide for connecting the optical splitter and the second input ports, wherein an optical length of the first optical waveguide is different from that of the second optical waveguide.

In an optical interferometer, polarization dependence attributable to the optical path difference has conventionally been eliminated by inserting a half-wave plate at the center of the interferometer. However, light induced by polarization coupling produced in directional couplers used in the optical interferometer causes interference having different interference conditions from those of the normal light. Polarization rotators that effect any one of 90&#xb0; rotation and &#x2212;90&#xb0; rotation of all states of polarization of incoming light are inserted in the optical interferometer, and thereby the interference conditions of light induced by polarization coupling are made the same as those of the normal light. Each of the polarization rotators is implemented by using two half-wave plates and by varying an angle of combination of these half-wave plates. Alternatively, each of the polarization rotators is implemented through a combination of one half-wave plate and a waveguide having birefringence properties.

Waveguide-type optical interferometer

A demodulator is provided for a multilevel differential phase shift keyed signal, capable of eliminating polarization dependence due to birefringence and polarization coupling-induced light resulting from a waveguide structure, and also, polarization dependence due to dynamic birefringence produced at the time of driving a variable phase adjuster. The demodulator is configured of an optical delay line interferometer of a waveguide interference type. The S/N ratio of a demodulated signal in the demodulator formed by the optical delay line interferometer can be also improved. Further, both the polarization dependence and the temperature dependence of the optical delay line interferometer can be reduced. The disposition of a polarization converter and groves filled with a temperature compensation material makes it possible to provide a circuit configuration suitable for eliminating the polarization dependence and the temperature dependence of the optical delay line interferometer.

Optical delay line interferometer

In a light waveguide circuit including a plurality of waveguides having different length, a material (,) having a temperature coefficient of a refractive index including a symbol different from that of a temperature coefficient of an effective refractive index of the waveguide (,) is charged into a groove (,) formed by removing the upper clad and the core from the waveguide (,), or a groove (,) formed by removing the upper clad, the core and the lower clad from the waveguide (,). A difference in length of the removed portions between adjacent waveguides is proportional to a difference in length of the waveguides which were not removed and remained.

Optical waveguide circuit, its manufacturing method and optical waveguide module having the optical waveguide circuit

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Atsugi, Japan

Kuninori Hattori