Abstract: An optical A/D converter according to the present invention includes an optical splitter that splits an analog input signal light into plurals, a plurality of Mach-Zehnder interferometers to which each of the signal lights split by the optical splitter is input, and plurality of optical/electrical conversion unit that convert each signal lights output from each Mach-Zehnder interferometer into a digital electrical signal, in which each Mach-Zehnder interferometer includes optical intensity-to-phase conversion unit that optically convert intensity of the input signal light into an amount of phase shift and the amount of phase shift differs for each Mach-Zehnder interferometer. Then, it is possible to provide a high speed and low power consuming optical demodulation circuit.

Abstract: The present invention has an object to provide an optical modulation device and an optical modulation method that achieve an excellent spectral efficiency with a simple and compact configuration and low power consumption. An optical modulation device according to an exemplary aspect of the present invention includes a CW light source (11), a coupler (12), optical modulators (14a) and (14b), an optical frequency shifter (15b), a serial-to-parallel converter (21), and a delay circuit (24a). The serial-to-parallel converter (21) divides a data signal having a bit rate B into two data strings having a bit rate B/2, and extracts a clock signal (CLK). The delay circuit (24a) temporally synchronizes the two data strings. CW light emitted from the CW light source is split into two beams by the coupler (12). The optical modulators (14a) and (14b) generate optical signals by modulating the two split light beams according to the data strings.

Abstract: The present invention provides an external resonator-type wavelength tunable laser device that can properly fulfill a wavelength tuning function even with the use of a planar wavelength tunable reflector involving a considerable level of residual reflection. The external resonator-type wavelength tunable laser device includes a planar reflection structure enabling a reflection spectral peak wavelength to be varied and a semiconductor element as a semiconductor gain medium. The semiconductor gain medium is composed of a multiple quantum well in which product ?·L of optical confinement constant ? and semiconductor gain medium length L (?m) of a gain layer is at least 25 ?m and at most 40 ?m and in which gain peak wavelength ?0 (nm) observed during carrier injected with a maximum modal gain equal to an internal loss of the semiconductor gain medium is larger than ?3·?R/2+(?c+35) and smaller than (?(?·L)/7+8)·?R+(?(?·L)+?c+45).

Abstract: In an external cavity wavelength tunable laser device including an external cavity (20) which includes a semiconductor optical amplifier (2) and performs laser oscillation operation by feeding back external light, a wavelength tunable mirror (7) having at least a single peak reflection spectrum characteristic within a laser wavelength tuning range is placed on one end of the external cavity (20), and a Fabry Perot mode interval determined by the effective length of the external cavity (20) is not less than 1/10 times and not more than 10 times the reflection band full width half maximum of the wavelength tunable mirror (7).

Abstract: The invention provides a semiconductor optical modulator including a two-step mesa optical waveguide having a first clad layer (101); a mesa-like core layer (102) formed over the first clad layer (101); and a second clad layer (103) formed into a mesa shape over the core layer (102), and having a mesa width smaller than that of the core layer (102). The two-step mesa optical waveguide includes a multi-mode optical waveguide region to which an electric field is applied or into which an electric current is injected, and a single-mode optical waveguide region to which the electric field is not applied and into which the electric current is not injected. When the mesa width of the core layer in the multi-mode optical waveguide region is defined as Wmesa1, and the mesa width of the core layer in the single-mode optical waveguide region is defined as Wmesa2, Wmesa1>Wmesa2 is satisfied.

Abstract: In an external cavity wavelength tunable laser device including an external cavity (20) which includes a semiconductor optical amplifier (2) and performs laser oscillation operation by feeding back external light, a wavelength tunable mirror (7) having at least a single peak reflection spectrum characteristic within a laser wavelength tuning range is placed on one end of the external cavity (20), and a Fabry Perot mode interval determined by the effective length of the external cavity (20) is not less than 1/10 times and not more than 10 times the reflection band full width half maximum of the wavelength tunable mirror (7).

Abstract: In an external cavity wavelength tunable laser device including an external cavity (20) which includes a semiconductor optical amplifier (2) and performs laser oscillation operation by feeding back external light, a wavelength tunable mirror (7) having at least a single-peak reflection spectrum characteristic within a laser wavelength tuning range is placed on one end of the external cavity (20), and a Fabry-Perot mode interval determined by the effective length of the external cavity (20) is not less than 1/10 times and not more than 10 times the reflection band full width half maximum of the wavelength tunable mirror (7).

Abstract: The present invention provides an external resonator-type wavelength tunable laser device that can properly fulfill a wavelength tuning function even with the use of a planar wavelength tunable reflector involving a considerable level of residual reflection. The external resonator-type wavelength tunable laser device includes a planar reflection structure enabling a reflection spectral peak wavelength to be varied and a semiconductor element as a semiconductor gain medium. The semiconductor gain medium is composed of a multiple quantum well in which product ?·L of optical confinement constant ? and semiconductor gain medium length L (?m) of a gain layer is at least 25 ?m and at most 40 ?m and in which gain peak wavelength ?0 (nm) observed during carrier injected with a maximum modal gain equal to an internal loss of the semiconductor gain medium is larger than ?3·?R/2+(?c+35) and smaller than (?(?·L)/7+8)·?R+(?(?·L)+?c+45).

Abstract: In an external resonator type semiconductor wavelength tunable laser apparatus using a wavelength tunable mirror or a wavelength tunable filter which uses a refractive index change of liquid crystal, a resonant frequency is set as FR, when a response of the refractive index change to a drive voltage frequency of liquid crystal becomes maximum. A frequency F1 of a drive AC power supply voltage to control the refractive index of liquid crystal is set to a frequency largely different from FR. A wavelength tunable mirror or a wavelength tunable filter is driven with a signal in which a dither AC signal F2 of a frequency close to the FR and an AC power supply voltage are superimposed. A PD to monitor a light output from the laser controls an amplitude of the drive AC power voltage such that an amplitude of the dither AC signal F2 become minimum. Thus, high laser mode stability is realized.

Abstract: A semiconductor optical waveguide-A having an optical amplification function and a semiconductor optical waveguide-B having a light control function are integrated together on the same substrate. A facet of the semiconductor optical waveguide-A facing an isolation trench and a facet of the semiconductor optical waveguide-B facing the isolation trench are configured as a composite optical reflector/optical connector using an optical interference. The facet of the semiconductor optical waveguide-A achieves an optical reflectivity not higher than the reflectivity corresponding to a cleaved facet and not smaller than several percent, and an optical coupling coefficient of not lower than 50% between the semiconductor optical waveguide-A and the semiconductor optical waveguide-B.

Abstract: The reflectance of a semiconductor optical amplifier (1) on the side where an external cavity is formed is 0.1% at most. The finesse value obtained by dividing the period of the transmission characteristic of the wavelength selection filter (3) by the half value width of the transmission characteristic is 4 or more and 25 or less. Even when the reflectance of a cavity side end face (1bb) of the semiconductor optical amplifier (1) is about 0.1%, a wavelength accuracy of ±1.5 GHz can be achieved by setting the finesse to 4 or more. In addition, a wavelength accuracy of about ±0.5 GHz can be achieved by setting the finesse to 8 or more. In order to suppress insertion loss, it is preferable to set the finesse of the FP etalon to 25 or less. This makes it possible to implement an external cavity wavelength tunable laser with high wavelength accuracy.

Abstract: In an external cavity wavelength tunable laser device including an external cavity (20) which includes a semiconductor optical amplifier (2) and performs laser oscillation operation by feeding back external light, a wavelength tunable mirror (7) having at least a single-peak reflection spectrum characteristic within a laser wavelength tuning range is placed on one end of the external cavity (20), and a Fabry-Perot mode interval determined by the effective length of the external cavity (20) is not less than 1/10 times and not more than 10 times the reflection band full width half maximum of the wavelength tunable mirror (7).

Abstract: Only the light at an overlapping wavelength of the transmission characteristics of at least two wavelength selecting filters is looped, and at least one of the wavelength selecting filters varies a selected wavelength. Since a loss due to the optical filters is small and there is not a loss caused by a highly reflecting film, the output of an external-resonator variable-wavelength laser can be increased. Optical circuit component (8) divides light input from external device (1) into at least two ports. Loop waveguide (11) interconnects at least ports (9, 10) divided by optical circuit component (8) in the form of a loop. At least two first wavelength selecting filters (12, 13) are inserted in series in a path of loop waveguide (11), and have periodic transmission characteristics on a frequency axis which are different from each other. At least one of first wavelength selecting filters (12, 13) varies the selected wavelength.

Abstract: Input ports (103a, 103b) formed from fundamental mode waveguides are provided at one end of a multimode waveguide (104). Further, an output port (105) formed from a fundamental mode waveguide is provided at the other end of the multimode waveguide (104). The multimode waveguide (104) has a width wider than those of the input ports (103a, 103b) and the output port (105), and provides modes including multimode to the waveguide. The multimode waveguide (104) is embedded with a buried layer (200). Both of the end faces of the multimode waveguide (104) are made to be planes equivalent to a (100) plane or planes inclined from these planes. In a case of inclined planes, the planes are made to be planes inclined to a direction that the waveguide region spreads toward a stacked direction of the semiconductor layers.

Abstract: Input ports (103a, 103b) formed from fundamental mode waveguides are provided at one end of a multimode waveguide (104). Further, an output port (105) formed from a fundamental mode waveguide is provided at the other end of the multimode waveguide (104). The multimode waveguide (104) has a width wider than those of the input ports (103a, 103b) and the output port (105), and provides modes including multimode to the waveguide. The multimode waveguide (104) is embedded with a buried layer (200). Both of the end faces of the multimode waveguide (104) are made to be planes equivalent to a (100) plane or planes inclined from these planes. In a case of inclined planes, the planes are made to be planes inclined to a direction that the waveguide region spreads toward a stacked direction of the semiconductor layers.