Nippon Telegraph and Telephone Corporation

Manabu Oguma

Tsutomu Kitoh

Hiroshi Takahashi

Takayuki Mizuno

Yuichiro Ikuma

Kenya Suzuki

Yasuyuki Inoue

Yusuke Nasu

Osamu Moriwaki

Toshikazu Hashimoto

Takashi Saida

Yohei Sakamaki

Takashi Go

Yoshinori Hibino

Shin Kamei

Akira Himeno

Kaname Jinguji

Makoto Jizodo

Yasuaki Hashizume

Kenichi Suzuki

Toshio Watanabe

Masamichi Fujiwara

Hiromasa Tanobe

Katsunari Okamoto

Masayuki Itoh

Takashi Yamada

Ikuo Ogawa

Shogo Yamanaka

Yoshiyuki Doi

Koichi Takiguchi

Shunichi Souma

Kuninori Hattori

Naoto Yoshimoto

Tsutomu Kitou

Masaki Koutoku

Masaki Kotoku

A wavelength monitoring apparatus includes a wavelength monitoring circuit. The wavelength monitoring circuit includes: a split circuit that splits an input optical signal into two; an optical delay circuit that applies a delay time difference to the two split optical signals; and a two-input two-output optical multiplexer/demultiplexer circuit that outputs a result of applying multiplexing interference to the optical signals to which the delay time difference has been applied. The wavelength monitoring apparatus further includes photoelectric conversion elements that perform photoelectric conversions on the two optical signals output from the wavelength monitoring circuit so as to output electrical signals. The wavelength monitoring apparatus is configured to obtain the wavelength of the optical signal, by calculating a ratio between two electrical outputs of the photoelectric conversion elements and referring to a correspondence table indicating wavelengths of optical signals input to the wavelength monitoring circuit and ratios between electrical outputs.

Wavelength monitoring device and controlling method thereof

An object is to improve crosstalk between ports while keeping an interposer circuit small. In an interposer circuit that includes a first surface connected to an optical circuit, a second surface that is connected to a fiber block and is located opposite to the first surface in parallel with the first surface, and a plurality of connection waveguides connected to a plurality of input/output waveguides included in the optical circuit and a plurality of input/output fibers included in the fiber block, the connection waveguides each have a straight shape, and an angle (θ) formed between the first surface and each of the connection waveguides is the same as an angle (φ) formed between the second surface and each of the connection waveguides.

Interposer circuit

To provide an optical 90-degree hybrid formed of a silicon waveguide capable of suppressing an optical loss and a phase error, and facilitating electronic packaging and optical packaging. In the optical 90-degree hybrid circuit including two optical branching units facing each other and two optical coupling units facing away from each other, four arm waveguides are arranged including bent waveguides each of which guides an output light of the optical branching unit to the optical coupling unit, and is formed in a curved shape.

Optical 90 degree hybrid circuit

A wavelength monitoring circuit obtains a light output proportional to only an input optical signal, independent of wavelength, by adding a light split circuit to the configuration in the related art, or changing the light split circuit to a light trifurcation circuit. In addition, wavelength monitoring with high accuracy is possible while improving the resistance to noise. The extraction of the light output proportional to only the input optical signal is performed by a light split circuit for input light at the top stage of the wavelength monitoring circuit or a light split circuit for interference in a stage in the middle of the circuit. The changed light split circuit causes the MZI included in the wavelength monitoring circuit to operate in a state of losing the balance of the configuration or the optical signal level, and increases the signal level near the bottom portion of the transmission characteristics.

Wavelength monitoring circuit

The invention provides a planar optical waveguide circuit capable of preventing part of the input signal light that has not been combined in the waveguide and propagates as leaked light from interfering with the output signal. A planar optical waveguide circuit having an optical waveguide embedded in a cladding layer includes: a plurality of parallel output optical waveguides configured to emit light from a same end face; a groove having a reflective interface formed at an angle of +45 degrees relative to the output optical waveguides and configured to reflect leaked light propagating in the cladding layer; and a groove having a reflective interface formed at an angle of &#x2212;45 degrees, the reflective interface formed at an angle of +45 degrees, the output optical waveguide, and the reflective interface formed at &#x2212;45 degrees being arranged repeatedly in that order.

Planar optical waveguide circuit

Provided is an optical wavelength multi/demultiplexing circuit with a high rectangular transmission loss spectrum that is able to secure loss flatness of a transmission band, maintain/reduce a guard bandwidth of wavelength channel spacing, and broaden a transmission bandwidth. The circuit uses a multimode waveguide for a connecting part between a field modulation device and an AWG. The field modulation device is constituted by a common input waveguide, an optical branching unit, optical delay lines, a multiplex interference unit, and a mode converter/multiplexer.

Optical multi/demultiplexing circuit

A polarization multiplex optical transmitter circuit can provide compensation for the transmission PDL while reducing decrease in transmission power. The polarization multiplex optical transmitter circuit includes a beam divider circuit configured to divide light outputted from a light source, optical phase shifters provided in at least one of two waveguides connected to output terminals of the beam divider circuit, a light wave synthesizer circuit connected to the two waveguides, first and second optical transmitters coupled to two output terminals of the light wave synthesizer circuit, a polarization multiplexer configured to synthesize two output polarized waves from the first and second optical transmitters, and a polarization rotator provided between the first and second optical transmitters and the polarization multiplexer and coupled to at least one of the first and second optical transmitters.

Polarization multiplexed optical transmitter circuit and polarization multi/demultiplexed optical transceiver circuit

A multiplexer/demultiplexer that functions as an extremely small AWG optical filter in order to prepare a miniaturized and low-cost transceiver module necessary to realize a high speed transceiver for Ethernet (registered trademark). An optical multiplexer/demultiplexer includes: at least one input waveguide, a first slab waveguide, an arrayed waveguide group, a second slab waveguide, and at least one output waveguide. Each of the waveguides of the arrayed waveguide group has: a first bent part of which a waveguide extending direction changes 180 degrees or more; and a second bent part of which a waveguide extending direction changes 180 degrees or more in a direction opposite to a direction of the change of the first bent part.

Optical multiplexer/demultiplexer

The present invention relates to an optical coupling/splitting device that realizes the splitting of a down-signal and the coupling of up-signals by the same optical device, and reduces coupling losses of the up-signal. An optical coupling/splitting device in the present invention comprises an optical coupling/splitting means for coupling a plurality of up-signals in a multi-mode for output and splitting a down-signal in a single mode for output, and a two-way optical propagation means for propagating the up-signal that is output from the optical coupling/splitting means in a multi-mode for output and propagate the down-signal in a single mode to be output to the optical coupling/splitting means.

Optical coupling/splitting device, two-way optical propagation device, and optical-transmit-receive system

An optical wavelength multi/demultiplexer having transmission characteristics with a higher rectangular degree than a conventional one includes an AWG and two-stage lattice circuit. An example of a two-stage lattice circuit according to the present invention includes an input waveguide, a third optical coupler, a third and fourth arm waveguides, a second optical coupler, a first and second arm waveguides, a first optical coupler, and output waveguides. The optical path length differences between the third and fourth arm waveguides and between the first and second arm waveguides are designed to be &#x394;L. The path passing the third and first arm waveguides differs by 2&#xb7;&#x394;L in optical length from that the fourth and second arm waveguides. The paths passing the third and second arm waveguides and passing the fourth and first arm waveguides differ by &#x394;L from that passing the fourth and second arm waveguides.

Optical wavelength multi/demultiplexer

When a conventional synchronized AWG is employed to extend a transmission passband, an increase in loss near the optical center frequency can not be avoided. Because of passband width limit, a problem has existed in that the synchronized AWG could not be applied for a large, complicated communication system wherein a signal light passes a number of points. Therefore, an optical wavelength multiplexing/demultiplexing circuit of the present invention is a synchronized AWG, which includes an optical splitter arranged in an interference circuit that is connected on the side of one slab waveguide. The splitting ratio of the optical splitter varies, depending on the optical frequency, and the value becomes minimum near the optical center frequency of the synchronized AWG. The optical splitter is operated so that the splitting ratio is comparatively great at optical frequencies distant from the optical center frequency.

Optical wavelength multiplexing/demultiplexing circuit, optical module using optical wavelength multiplexing/demultiplexing circuit, and communication system

A Mach-Zehnder interferometer circuit () is provided with two couplers () and two arm waveguides () connecting the couplers with each other, each fabricated on a substrate, in which a polarization rotation device () is disposed in a groove dividing each of the two arm waveguides into two, the polarization rotation device () for converting vertically polarized light into horizontally polarized light, and birefringence is adjusted by performing laser irradiation or the like partially into at least one of the two arm waveguides such that a difference between birefringence values divided by an optical wavelength to be used is within a range of 2 m-0.2 to 2 m+0.2 (m is an integer including zero), the birefringence values being those integrated linearly along the respective two arm waveguides in an optical signal travelling direction.

Polarization-independent waveguide-type optical interference circuit

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

The present invention discloses an interferometer optical switch that can carry out switching over a broad band and has a high extinction ratio and large fabrication tolerance. The interferometer optical switch employs a phase generating coupler, the phase difference of the output of which has wavelength dependence, as at least one of the optical multi/demultiplexing device included in the interferometer optical switch. A wavelength insensitive interferometer optical switch is implemented by making the sum 2&#x3c0;{&#x3c6;(&#x3bb;)+&#x3c6;&#x394;(&#x3bb;)+&#x3c6;(&#x3bb;)} constant regardless of the wavelength, where &#x3c6;(&#x3bb;) is the phase produced by the first optical multi/demultiplexing device, 2&#x3c0;&#x3c6;&#x394;(&#x3bb;) is the phase difference of the optical delay line with an optical path length difference of &#x394;L, and 2&#x3c0;&#x3c6;(&#x3bb;) is the phase produced by the second optical multi/demultiplexing device.

Interferometer optical switch and variable optical attenuator

An optical multi/demultiplexing circuit includes at least one phase generating optical coupler and an optical delay line coupled to the phase generating optical coupler. The phase generating optical coupler consists of at least one input and at least two outputs. At least one of the phase generating optical coupler has a wavelength dependent or frequency dependent output phase difference in the passband of the circuit so that it can change the transmittance characteristics of the optical multi/demultiplexing circuit.

Growing community of inventors

Atsugi, Japan

Manabu Oguma