Abstract: A method for selecting a light source for optical communication system comprises the steps of: measuring time division chirping characteristics and optical response waveforms of the light source responding to a fixed strength random pulse signal; performing a simulation of a transmission process based on measured data; computing a selection parameter as an index for determining a dispersion tolerance quality of the light source according to a computed post-transmission waveform of an optical signal that propagated through an optical fiber path; and deciding the dispersion tolerance quality of the light source based on values of the selection parameter. There is no need for providing the usual facilities required for dispersion tolerance evaluation such as EDFA, optical fibers, wavelength filter, receiving disk and error rate detector and the like and the time required for selection is significantly reduced.

Abstract: An optical device including a substrate, a distributed feedback (DFB) semiconductor laser formed on the substrate and including a diffraction grating having an asymmetrical &lgr;/4 phase shift region, the diffraction grating extending along an optical axis of the DFB semiconductor laser, and a field absorbing modulator integrated with the DFB semiconductor laser on the substrate for modulating a light wave emitted from the DFB semiconductor laser, the optical modulator having a facet reflection rate between 0.01 and 0.02% at an output end thereof, the difraction grating having a □L value between 1 and 1.2 The proper combinations of the □L value of the diffraction grating and the reflection rate of the output facet of the modulator of the DFB semiconductor laser can fabricate the source for integrating the modulator having the excellent quality with a higher yield and lower cost.

Abstract: A Peltier cooler is situated in a module casing, and combined with a metallic block, on which a lens is mounted. A thermistor, an electroabsorption modulator integrated DFB laser (a laser unit), a monitoring photosensor are mounted on the metallic block. A signal line of a co-planar structure which is connected with a signal input pin supplied with an external signal is laid on a ceramic substrate, under which a pedestal is formed. A part of the ceramic substrate on the pedestal is removed, and an amplifier is mounted on the pedestal in condition that it approximates to the laser unit. The laser unit is connected with the amplifier by an Au wire, and the amplifier is connected with the signal line by another Au wire. According to the aforementioned configuration, an electrical length between the signal pin and the laser unit can be shortened, and a compact optical communication module having an excellent performance in a high bit rate communication can be provided.

Abstract: Disclosed is an electroabsorption-type optical modulator, which includes a semiconductor substrate; and a semiconductor buffer layer, a semiconductor optical absorption layer and a semiconductor cladding layer which are layered in order on the semiconductor substrate. The absorption of a light wave supplied to an end of the semiconductor optical absorption layer is controlled by changing the intensity of an electric field applied to the semiconductor optical absorption layer. The semiconductor optical absorption layer has a first region with an absorption-edge wave length shorter than that of a second region of the semiconductor optical absorption layer.

Abstract: A driving apparatus for causing an optical modulator to output modulated light, which has a PIN structure composed of a buffer layer, a light absorption layer and a clad layer and wherein an absorbed amount of light waves inputted to the light absorption layer varies in response to an applied voltage applied in the reverse direction to the PIN structure, includes a voltage waveform converter for deforming an input signal waveform so as to correct the non-linear characteristics of the absorbed amount with respect to the applied voltage of the optical modulator or a level shifting circuit for shifting a voltage level of the input signal to a forward voltage side to the PIN structure within a built-in voltage to correct the displacement of a cross point of an eye pattern of modulated output light outputted from the optical modulator of the electrical field absorption type.

Abstract: In an electroabsorption optical intensity modulator, a semiconductor buffer, a first semiconductor cladding layer, a semiconductor optical absorption layer, a second semiconductor cladding layer and a semiconductor cap layer are formed on a semiconductor substrate. Also, a first electrode is formed on the second semiconductor cap layer, and a second electrode is formed on a second surface of the semiconductor substrate. The semiconductor optical absorption layer includes a first semiconductor optical absorption layer element having a first absorption edge wavelength and a second semiconductor optical absorption layer element having a second absorption edge wavelength different from the first absorption edge wavelength.

Abstract: A semiconductor optical modulator is provided, which is capable of stable modulation operation against the detune fluctuation. This modulator includes a semiconductor optical absorption layer formed on or over a semiconductor substrate, and a pair of electrodes arranged at each side of the absorption layer for applying an electric field to the absorption layer. A detune is determined in such a way that a changing rate in refractive-index of the absorption layer generated on application of a fixed biasing electric-field to the absorption layer increases from its initial value at the time no biasing electric-field is applied.

Abstract: In a semiconductor Mach-Zehnder modulator, when a phase modulator portion 113 and other passive areas (incident light waveguide path 111, a branch portion 112, a joint portion 114 and an output light waveguide path 115) are formed, a buffer layer 102, a waveguide layer 103 and a clad layer 104 are successively and selectively formed on a semiconductor substrate 101. At this time, a pair of masks having a gap therebetween are used as a selective growth mask. The phase modulator portion 113 is formed in the gap portion of the masks, and the passive areas are formed in the other portions. The band gap and the layer thickness can be partially or locally varied by adjusting the width of the masks and the gap portion.

Abstract: A Mach-Zehnder modulator has a first waveguide path, a second waveguide path and first and second phase modulator sections respectively formed in the first and second waveguide paths. Those two waveguide paths have different equivalent refractive indexes so that with no modulation electric signal applied to the first and second phase modulator sections, lights waveguided through the first and second phase modulator sections have a phase difference of (2N+1).pi. (N: 0 or a positive integer). No voltage or a constant voltage is applied to the second phase modulator section, and a modulation signal is applied to the electrode of the first phase modulator section. When a voltage of 0 is applied to the first phase modulator section, a light OFF state is acquired, and when a voltage of V.pi. is applied to the first phase modulator section, a light ON state is acquired. Therefore, negative chirping is generated at the light ON time and the light OFF time.