A light amplifier using a semiconductor, in which an elongated single semiconductor PN junction is used for amplifying an input light injected at an input face provided at one end of the PN junction along the junction plane of the PN junction. The semiconductor PN junction is driven by bias signals applied at a common ohmic electrode and a plurality of ohmic electrodes respectively provided at opposite sides of the PN junction with respect to the junction plane. A plurality of the ohmic electrodes are sequencially arranged overlying the PN junction in a longitudinal direction and are electrically isolated from one another, so that a plurality of discrete regions are provided in the PN junction corresponding to the respective electrodes. Two adjacent regions are employed as one unitary region and are driven by predetermined different forward bias currents to bias one of the two regions as an amplifying region and the other of the two regions as a saturable absorbing region. The amplifying region is disposed at the input side while the saturable absorbing region is disposed at the output side in each unitary region. The respective unitary regions are connected in cascade to provide a plurality of the unitary regions.
A semiconductor laser device comprising a laser-oscillating optical waveguide composed of a control region which functions to absorb light and main regions which function to oscillate laser light, said control region being positioned in the center portion of said optical waveguide and said main regions being positioned on both ends of said control region, wherein said laser device further comprises a shunting means by which the ratio of the current Ig flowing to said control region to the total current It injected into said laser device is set to meet the inequality (1): ##EQU1## wherein Lg is the length of said control region and Lt is the length of said optical waveguide.
A launch quasi-optical amplifier including a photonic bandgap crystal, designed to operate within a specific frequency range. The photonic bandgap crystal is populated with active devices that are coupled to the alternate layers, or defects, in the crystal to compensate for the absorption in the alternate layers thereby creating a negative absorption coefficient. The photonic bandgap crystal is operable as an amplifier when the active devices are amplifiers, and as a wave source when the active devices are oscillators.
Light is amplified in a semiconductor laser structure through which a current is passed and (a) the wavelength of the light is greater than the wavelength of maximum gain of the laser structure, or (b) injection locking is avoided, or (c) the current is controlled so as at least partly to compensate for the decrease in the monitored light output at a wavelength or over a wavelength range distinct from that of the emitted amplified signal. In this way relatively high input powers can be amplified.
For a reversed bias double heterostructure diodes, particularly GaAs diodes, electroabsorption can be obtained with reverse bias and light emission can be obtained with forward bias. However bulk absorption is large at wavelengths close to the band edge, where light emission occurs. Thus light emission through a modulator at zero bias is low. By providing for the light emulsion to be at a larger wavelength than that corresponding to the band edge high modulation efficiencies can be obtained. This is achieved by suitably doping the emitter differently as compared with the modulator so that light emission occurs at wavelengths greater than that at the fundamental energy gap.
A semiconductor optical amplifier device includes an active layer, an n-type InP substrate, an n-type InP clad layer, a p-type InP clad layer, p-electrodes and n-electrodes. The active layer is made of, e.g., InGaAsP, and includes a saturable absorption region and optical amplification regions. A common modulated current is injected into each optical amplification region through the p-electrode. A modulated current is injected into the saturable absorption region through the p-electrode independently of the optical amplification region. The active layer receives injection light produced by adding additional noise light to an externally applied light signal, and emits output light produced by amplifying the injection light.
