Nec Corporation

Nippon Electric Co., Ltd.

Kazuhisa Kaede

Ikuo Mito

Isamu Takano

Mitsuhiro Kitamura

Kohroh Kobayashi

Masahiko Fujiwara

Minoru Shikada

Naoki Shimosaka

Shigeo Matsushita

Shigetoki Sugimoto

Hiroyoshi Rangu

Ro Ishikawa

An optical transmission system that can perform not only amplification of optical signal level but also dispersion pre-equalization, as the signals are optical. In this invention, optical power level of an optical signal propagating through the dispersion medium is amplified in the optical amplifier. The signal becomes the optical signal a. A phase modulator driving circuit outputs a signal corresponding to the envelope signal of the optical signal a. An optical phase modulator phase-modulates the input optical signal a, outputs an optical signal d for which signal optimum dispersion pre-equalization is performed.

Optical trunk transmission system and an optical repeater circuit

The object of this invention is to offer an optical transmission system that can perform not only amplification of optical signal level but also dispersion pre-equalization, as the signals are optical. In this invention, optical power level of an optical signal propagating through the dispersion medium 101a is amplified in the optical amplifier 102, the signal becomes the optical signal a. The phase modulator driving circuit 104 outputs a signal corresponding to the envelope signal of the optical signal a. The optical phase modulator 103 charged the signal phase-modulates the input optical signal a, outputs the optical signal d which is performed dispersion pre-equalization to dispersion medium 101b.

An optical timing extraction circuit is capable of extracting an optical clock signal of greater than tens of Gb/sec from a NRZ modulated signal. The light intensity level of a light signal modulated in intensity by an NRZ signal is amplified to a level sufficient to cause the optical Kerr effect, and combined with a CW light from a semiconductor laser which is modulated in frequency by the amplified light signal in an optical converting circuit by utilizing the optical Kerr effect. This frequency-modulated light is passed through a narrow band-pass optical filter to cause a signal intensity-modulated pulsed light at each intensity changing point of the modulated signal. Next, after the pulsed light is amplified up to a required optical intensity level, it is passed through another narrow band-pass optical filter, which is an optical tank for extracting the optical clock, to extract an optical clock signal.

Optical timing extraction circuit

A multi-wavelength light amplifier comprises a light amplifier for amplifying a wavelength division multiplex signal with accompanying generation of spontaneous emission. An optical coupler is provided for coupling light from the light amplifier to a wavelength filter, such as Fabry-Perot filter. The filter has a plurality of spectral peaks of transmittance and corresponding valleys of reflectance, with the spectral peaks and valleys corresponding respectively to the wavelengths of the multiplex signal. The optical coupler further provides coupling of light reflected from the wavelength filter to an optical sink by which the undesired spontaneous emission is absorbed.

Light amplifier for multi-wavelength signals

An optical amplifying apparatus is disclosed which includes an optical amplifier for amplifying a signal light, a narrow-band optical filter for removing a spontaneous light emitted from the signal light, two photodetectors for detecting, transmitting and reflecting lights of the narrow-band optical filter, and a controller for controlling a gain of the optical amplifier by comparing intensities of the transmitting and reflecting lights in accordance with the detected signals supplied from the photodetectors.

Optical amplifying apparatus

The invention relates to an optical wavelength drop-and-insert device including two sets of input/output optical fibers attached to two terminals on each of a first and second polarization beam splitter. The first polarization beam splitter splits incoming light into two linearly orthogonal polarizations which are transmitted via a first and second polarization preserving fiber through a first and second quarter wave plate for changing the subject beams into circular polarization. An optical filter is included to transmit or reflect light from the quarter wave plates according to a wavelength based transmission/reflection characteristic. The second polarization beam splitter then acts as a combiner for the circularly polarized light which is received via a third and fourth polarization preserving fibers and then is transmitted via an output optical fiber. The second polarization beam splitter splits incoming light into two orthgonal polarizations via an incoming optical fiber for two way operation. A second embodiment of the invention uses a first and second optical filter which can be a Fabry Perot or Bragg diffraction grating type optical fiber.

Wavelength drop-and-insert device

There are disclosed a method and apparatus for stabilizing an oscillation frequency separation among a plurality of laser devices wherein a plurality of laser devices are controlled to radiate output lights each having a predetermined frequency so that a frequency separation is stabilized. Reference pulses are produced in an optical resonator which has periodic resonant frequencies and receives a frequency sweep signal, and beat signals are produced in accordance with the combination of the frequency sweep signal and oscillation frequencies of the plurality of laser devices. The reference signals and beat signals thus produced are processed to produce error signals which are time differences between the producing times of the both signals. The plurality of laser devices are controlled to be driven such that the error signals become a predetermined value.

Method and apparatus for an oscillation frequency separation among a

An optical wavelength-division switching system comprises means for reproducing an electric signal for each channel from a wavelength division multiplexed optical signal, and means for converting the electric signal to a modulated optical signal. The means for reproducing the electric signal can be composed of an optical heterodyne or homodyne detection system, while the means for converting the electric signal can be composed of a distributed feedback laser diode having an optical frequency modulating characteristic so that the number of channels is much increased with the decrease of crosstalk.

Optical wavelength-division switching system with coherent optical

A frequency-stabilized semiconductor laser oscillator in which a control signal derived from a modulation signal is applied to a second optical waveguide adjacent the first optical waveguide in order to make the overall optical path between both waveguides constant despite variations in the refractive index of the optical path in the first optical waveguide. The control signal may be a current signal derived by shifting the phase of the variation of the current of the modulation signal with respect to time, or a voltage signal derived by shifting the phase of the variation of the voltage of the modulation signal with respect to time. If a current control signal is used, the compensation mechanism is an increase in the carrier density in a second optical waveguide. If a voltage control signal is used, the compensation mechanism is an electro-optic variation of the refractive index in the second optical waveguide.

Frequency-stabilized semiconductor laser oscillator

An optical coupler formed on a substrate including a plurality of input and output guide channels and an immediate mixing guide channel connecting the input and output guide channels wherein the optical coupler comprises substantially V-shaped grooves on the substrate disposed in the ends of the input and output guide channels for receiving optical fibers.

Planar, optical star coupler for optical fibers

A buried heterostructure laser diode and method for making the same wherein an active layer is provided in a semiconductor region forming a mesa stripe, and, except for the top surface portion of the mesa stripe, the side surface portion of the mesa stripe and the remainder are covered by a current-blocking layer. Furthermore, a current-confining layer covers only this current-blocking layer, and a clad layer covers the current-blocking layer and the top surface portion of the mesa stripe.

Buried heterostructure laser diode

A multichannel light switch including a cylindrical-shaped light-focusing transmission body having a length equal to an odd multiple of one quarter of the pitch of light beam undulation within the body and having a total reflection coating applied to one end face thereof, which is normal to the axis of the transmission body. A stationary optical fiber bundle is arranged opposite to the other end face of the transmission body and is in parallel to the axis thereof. For light-path switching between the optical fibers, the transmission body is adapted to be displaced in a radial direction or to be rotated in a plane normal to the axis thereof.

Growing community of inventors

Tokyo, Japan

Kazuhisa Kaede