Mitsubishi Denki Kabushiki Kaisha

Mitsubishi Denki K.k.

Kunihiko Isshiki

Akihiro Shima

Wataru Susaki

Takashi Murakami

Toshitaka Aoyagi

Yasunori Miyazaki

Hitoshi Watanabe

An optical amplifier includes a plurality of pump light sources, an intensity modulator that modulates intensity of a pump light to be output from any one of the pump light sources, at a predetermined frequency; a photoelectric converter that converts a part of the wavelength-division multiplexed signal light Raman-amplified by the pump light to electrical signals; a gain modulation signal detector that extracts a gain modulation signal having a component of the frequency from the electrical signals; and a controller that controls only the intensity of pump lights that are output from the pump light source, of which intensity is modulated at the frequency to control Raman amplification gain so that an amplitude of the gain modulation signal becomes a predetermined value. The intensities of pump lights output from individual pump light sources are sequentially controlled to obtain a predetermined value of the Raman amplification gain.

Optical amplifier and optical communication system

An efficient, wavelength independent, small optical amplifier includes an optical transmitter, a signal light inputter supplying light to the optical transmitter, an amplified light fiber connected to the optical transmitter, an excitation source supplying pump light to the light amplified fiber, an optical filter connected between the light amplified fiber and the excitation source for reflecting the signal light and transmitting the pump light, and an outputter for outputting the amplified signal light. The amplifier may also include another light amplified fiber connected to the optical transmitter, another excitation source, and another optical filter for further amplifying the signal light amplified by the light amplified fiber. The wavelengths output by the excitation sources may differ to provide more efficient amplification. The signal light may include different wavelengths, resulting in a wavelength dependency of gain for the amplifier. In order to compensate for this wavelength dependency, the material, the length, the dopant level, and/or the core diameter used for the light amplified fibers may differ, again the wavelength of the excitation sources may differ, and the optical filters may only pass different certain wavelengths. Portions fed by the respective terminal may be integrated to reduce the number of elements and size of the amplifier.

Optical amplifier

In an optical modulator including a laser light source emitting laser light and a modulator, a modulation signal source for applying a modulation signal to the modulator, a signal processor for producing and outputting a signal in response to a change in the modulation signal, and a driving current source for generating a driving current applied to the laser light. Wavelength chirping modulation reverse to the wavelength chirping occurring in the modulator is produced in the light emitted from the laser by modulation of the driving current whereby wavelength chirping produced by the modulator is at least partially cancelled and wavelength chirping of the light output from the modulator is reduced.

Optical modulator

A double heterojunction semiconductor laser according to the invention includes first and third cladding layers sandwiching an active layer. The third cladding layer includes a mesa opposite a light emitting region of the active layer. The mesa is confined by a current blocking layer. A cap layer that is part of the mesa is used as a dopant diffusion source to dope a light emitting region of the active layer heavily. A second cladding layer may be present between the active layer and third cladding layer having the same conductivity type as the third cladding layer adjacent the light emitting region but the opposite conductivity type elsewhere. A semiconductor laser according to the invention may also include a stripe groove structure. The semiconductor lasers include pnpn structures outside the light emitting region and in window structures adjacent the facets of the semiconductor laser for suppressing leakage currents, thereby increasing laser efficiency and reducing threshold current while increasing power output.

Semiconductor laser

A method of producing a semiconductor light emitting device includes forming a stripe-shaped mesa on a surface of a semiconductor substrate; epitaxially growing a multiple layer structure including at least a first cladding layer, an active layer, a second cladding layer, and a cap layer so that the active layer and cap layer have mesas corresponding to the mesa of the substrate; depositiong photoresist on the cap layer to form a flattened surface; removing the photoresist to expose the mesa of the cap layer; removing a portion of the cap layer using the photoresist remaining on the cap layer as a mask to make the surface of the cap layer approximately flat; depositing a thin film to be used as a mask for proton or ion bombardment on the cap layer and on the remaining photoresist; removing the remaining photoresist and the thin film on the remaining photoresist; and bombarding the cap layer with protons and ions using the remaining thin film on the cap layer as a mask to produce higher resistivity regions adjacent the remaining thin film than directly below the remaining thin film. Therefore, highly reliable semiconductor laser devices having good and uniform characteristics can be realized.

Method for producing semiconductor light emitting device

Semiconductor laser manufacturing method

A multi-quantum well laser having a self-aligned structure which limits catastophic optical damage by producing window regions near the facets without significantly decreasing the efficiency of the laser. The semiconductor laser includes at least a first conductivity type lower cladding layer, an active layer including a multi-quantum well structure, a second conductivity type first upper cladding layer, a first conductivity type current blocking layer, and a second conductivity type second upper cladding layer successively disposed on a first conductivity type semiconductor substrate. The current blocking layer has a central elongate stripe shaped current confinement groove extending between the laser facets which stabilizes the transverse mode and confines current to a channel-like region in the active layer. First conductivity type dopant impurities form disordering regions located adjacent the facets which invade and disorder the multi-quantum well active layer to create disordered active layer regions. Second conductivity type dopant impurities form separating regions located adjacent the faects which separate the current blocking layer and the disordering regions to prevent current leakage between the current blocking layer and the disordering regions.

Semiconductor laser device

A semiconductor laser device in which the thickness of an active layer is made smaller than or equal to 0.04 .mu.m only in regions near the laser light emitting facets and the active layer in the other inner region is made to have a sufficient thickness not to cause a conspicuous deterioration in quality of the layer, that is, a thickness larger than 0.04 .mu.m.

A semiconductor light emission device includes: a first conductivity type semiconductor substrate which has a pair of confronting resonator end surfaces and a hollow section provided thereon. The hollow section is arranged in a direction vertical the direction in which the resonator end surfaces confront each other. A second conductivity type current blocking layer having a flat upper surface is provided on the entire upper surface of the semiconductor substrate. A stripe groove is provided in the current blocking layer extending in a direction between the resonator end surfaces in such a manner that the groove reaches only within the current blocking layer at the hollow section and reaches the semiconductor substrate through the current blocking layer at portions outside the hollow section. A first conductivity type lower clad layer is provided on the entire upper surface of the current blocking layer so as to embed the stripe groove. A first or second conductivity type active layer is provided on the entire upper surface of the lower clad layer, and a second conductivity type upper clad layer is provided on the entire upper surface of the active layer.

Internal current confinement type semiconductor light emission device

Laser light guided by a coupled waveguide (formed by difference in refractive index between n-type and p-type AlGaAs clad layers (2) and (4) and an undoped AlGaAs active layer (3) and difference in refractive index between the p-type AlGaAs clad layers (4) and (7) and a p-type AlGaAs waveguide layer (6)) is guided only by the p-type AlGaAs waveguide layer (6) in the vicinity of end surfaces (40, 42), not to be coupled with the undoped AlGaAs active layer (3). Therefore, surface regions of the end surfaces (40, 42) reflecting the laser light are formed by the p-type AlGaAs clad layers (4, 7) and the p-type AlGaAs waveguide layer (6) being larger in forbidden bandwidth.

Growing community of inventors

Itami, Japan

Kunihiko Isshiki