Abstract: An optical circulator outputs an optical signal entered through its port A from its port B. A fiber collimator makes the optical signal spread out from the port B of the optical circulator into a collimated beam and applies it to a beam splitter. The beam splitter is disposed at an angle of 45° to the optical axis. Around of the beam splitter, total reflection mirrors are disposed in three directions per angle of 90° except for the direction in which the fiber collimator is disposed. The distance between the total reflection mirrors and the beam splitter is adjustable.

Abstract: An optical gate according to the invention comprises a polarization divider to divide an optical signal into two orthogonal polarization components and to output them as a first polarization component which precedes in the time base and a second polarization component which follows the first one in the time base; a semiconductor optical amplifier to modulate the phase of the second polarization component output from the polarization divider according to a control light; an assist light supplier to supply to the semiconductor optical amplifier an assist light to help the recovery of the refractive index variation of the semiconductor optical amplifier caused by the control light; a polarization combiner to combine the first and second polarization components of the optical signal transmitting on the semiconductor optical amplifier so as to adjust them in the same time location; and a polarization extractor to extract a predetermined polarization direction component from the output from the polarization combine

Abstract: A ring resonator comprises a ring waveguide (12) of a first relative refractive index difference having a narrow part (12a), and an optical waveguide (14) of a second relative refractive index difference smaller than the first relative refractive index difference. The optical waveguide is disposed adjacent to the narrow part to optically couple with the narrow part.

Abstract: An optical delay unit comprises a periodic wavelength demultiplexer having M (M is a natural number) input ports including a signal input port, M output ports including a signal output port, and periodic input/output characteristics for wavelengths between the M input ports and the M output ports, and (M−1) optical paths to connect each of the (M−1) output ports in which the signal output port is excluded from the M output ports of the periodic wavelength demultiplexer with any of the (M−1) input ports in which the signal input port is excluded from the M input ports of the periodic wavelength demultiplexer.

Abstract: An object of this invention is to improve coupling efficiency of a silica optical waveguide having a high relative refractive index difference and a single mode optical fiber. A silica optical waveguide (10) consists of a single mode optical waveguide, and its core (12) is originally a rectangle. A width of the core (12) of the silica optical waveguide (10) is tapered at a predetermined length part (16) connecting to an optical fiber (20). A thickness of the core (12) in the tapered part (16) is constant.

Abstract: An object of this invention is to compensate group delay or group velocity dispersion. An optical circulator (12) outputs an optical signal (10) entered through its port A from its port B. A fiber collimator (14) makes the optical signal spread out from the port B of the optical circulator (12) into a collimated beam and applies it to a beam splitter (16). The beam splitter (16) is disposed at an angle of 45° to the optical axis. Around of the beam splitter (16), total reflection mirrors (18, 20, and 22) are disposed in three directions per angle of 90° except for the direction in which the fiber collimator (14) is disposed. The distance between the total reflection mirrors (18, 20, and 22) and the beam splitter (16) is adjustable.

Abstract: An optical signal processor is disclosed comprising a first optical path having a first electroabsorption optical modulator to be applied with a constant voltage and to absorb light of a signal wavelength, a second optical path having a fixed phase relation with the first optical path relative to a probe wavelength, a probe light introducer for dividing probe light of the probe wavelength into two portions and feeding them respectively into the first and second optical paths, an original signal light introducer for introducing original signal light of the signal wavelength into the first electroabsorption optical modulator, and a combiner for combining both light of the probe wavelength passed through the first and second paths.

Abstract: An optical gate according to the invention comprises a polarization divider to divide an optical signal into two orthogonal polarization components and to output them as a first polarization component which precedes in the time base and a second polarization component which follows the first one in the time base; a semiconductor optical amplifier to modulate the phase of the second polarization component output from the polarization divider according to a control light; an assist light supplier to supply to the semiconductor optical amplifier an assist light to help the recovery of the refractive index variation of the semiconductor optical amplifier caused by the control light; a polarization combiner to combine the first and second polarization components of the optical signal transmitting on the semiconductor optical amplifier so as to adjust them in the same time location; and a polarization extractor to extract a predetermined polarization direction component from the output from the polarization combine

Abstract: A nonlinear optical element is disclosed for reducing intensity noise of both mark level and space level, and being stable, miniaturized and low-priced. Signal light enters a semiconductor waveguide layer (14). The semiconductor waveguide layer (14) has a band gap wavelength shorter than a wavelength of the signal light. A diffraction grating (12), having a Bragg wavelength close to the wavelength of the signal light, is disposed adjacent to the semiconductor waveguide layer (14). DC voltage is applied to the semiconductor waveguide layer (14).

Abstract: An chromatic dispersion compensator according to the invention is composed of a wavelength converter for converting a wavelength of a lightwave carrying an input signal into a conversion wavelength, a wavelength dispersion medium for giving different chromatic dispersion according to each wavelength to optical signal of the conversion wavelength output from the wavelength converter, a photodetector for converting optical signal of the conversion wavelength output from the chromatic dispersion medium into an electric signal, and a controller for controlling the conversion wavelength for a predetermined component in the output of the photodetector. In optical receivers, input signal light is transmitted through the above chromatic dispersion compensator and then demodulated into a data.

Abstract: An optical processor comprising, a semiconductor saturable absorber; a current source for injecting a current to the semiconductor saturable absorber; a signal light introducer for introducing a signal light to the saturable absorber; a control light introducer for introducing a control light having a wavelength not longer than the wavelength of the signal light into the semiconductor saturable absorber; an assist light introducer for introducing an assist light having a wavelength longer than the wavelength of the signal light into the semiconductor saturable absorber; and a signal light extractor for extracting the signal light after treatment by the semiconductor saturable absorber.

Abstract: An optical short pulse reshaping device capable of effectively eliminating noise from or reshaping of input optical short pulses of a pulse width of picosecond order shorter than a carrier life time. The device comprises: a semiconductor laser element, means for injecting an electric current to the semiconductor laser element for obtaining an oscillation state of the semiconductor laser element, means for injecting into the semiconductor laser element input optical short pulses of a wavelength shorter than that of the oscillation light of said semiconductor laser element, and means for taking out optical short pulses emitted from the semiconductor laser element in distinction from its oscillation output light.

Abstract: There is disclosed a reshaping device for optical short pulses to effectively perform reshaping of and eliminate noise from an optical short pulse of a pulse width of pico second order less than a carrier life time. Input optical short pulses are applied to a saturable absorption element, while an assist light of a wavelength longer than that of the input optical signal pulses is also applied to the saturable absorption element to accelerate, by stimulated emission, recombination of excited electrons and holes produced in the saturable absorption element in response to the input optical signal pulses, so that the input optical signal pulses reshaped are derived from the saturable absorption element.

Abstract: A multiple quantum well structure which permits substantially uniform injection of carriers from the outside into respective quantum well layers of the multiple quantum well and a semiconductor device employing such a multiple quantum well structure. A multiple quantum well structure is formed by laminating at least two pairs of quantum well layers each having a thickness substantially equal to the de Broglie's wave-length of electrons and barrier layers of an energy gap greater than that of the quantum well layers, and the multiple quantum well structure is doped with at least one of p-type and n-type impurities in a manner to slope the energy band of the entire multiple quantum well structure so that carriers injected thereinto are distributed uniformly throughout it.

Abstract: A semiconductor device with a strained-layer superlattice is disclosed, in which a first semiconductor and a second semiconductor of a lattice constant smaller than that of the first semiconductor are stacked on a clad layer of a lattice constant substantially intermediate between those of the first and second semiconductors to form the strained-layer superlattice. The lattice constant of the strained-layer superlattice in the direction of its plane in the free space is nearly equal to the lattice constant of the clad layer. A third semiconductor of a lattice constant substantially equal to that of the clad layer is laminated between the first and second semiconductors stacked one on the other.

Abstract: A quantum well structure is disclosed, which is comprised of a quantum well layer of a thickness substantially equal to the de Broglie wavelength of electrons and carrier confinement layers of an energy gap greater than that of the quantum well layer. A second material of a lattice constant different from that of a first material primarily for the quantum well layer is disposed in the quantum well layer to provide a phase shift in the period of the crystal lattice of the first material, thereby forming energy levels in the forbidden band of the quantum well layer. A semiconductor device which employs such a quantum well structure and is so constructed as to utilize its physical phenomenon which is caused by the energy levels in the forbidden band. In concrete terms, the present invention has its feature in allowing ease in the fabrication of an intermediate infrared or blue light emitting device, for instance.

Abstract: A distributed feedback semiconductor device is disclosed which has a diffraction grating disposed near a light emitting active layer, a double hetero structure with the active layer sandwiched between n- and p-type semiconductors and n- and p-side electrodes for injection a current into the active layer, one of the n- and p-side electrodes being divided into a plurality of electrodes, and in which a current is injected into the active layer across the n- and p-side electrodes for laser oscillation to obtain output light. A first current source is connected to each of electrodes into which one of the n- and p-side electrodes is divided, and a second current source is connected to the divided electrodes via resistors, for injecting a current into the active layer in a desired ratio. The first and second current sources are controlled in accordance with the light emitting state of the active layer.

Abstract: A distributed feedback semiconductor laser with monitor is disclosed, in which the energy gap of a light absorbing layer provided on the window region alone is smaller than the energy gap of the light emitting layer, and in which an independent pn junction isolated from the pn junction in the laser region is provided in or at one edge of the light absorbing layer on the window region.

Abstract: A semiconductor device with a distributed Bragg reflector is disclosed, in which periodic corrugations are formed between two semiconductor layers along the direction of travel of light. In accordance with the present invention, the periodic corrugations are formed by grid-like layers of a refractory material. The refractory material is an insulator, a refractory metal or a laminate member of an insulator and a refractory metal.

Abstract: A distributed feedback semiconductor laser with monitor is disclosed, in which the energy gap of a cap layer formed on the laser region and the window region is smaller than the energy gap of the light emitting layer, and in which a pn junction isolated from a pn junction in the laser region is provided in the cap layer on the window region.