Abstract: A light source for generating many precisely spaced wavelength channels, based on the periodic modulation of light. CW light is periodically amplitude modulated and then coupled to a non-linear fiber where it undergoes additional modulation by the process of self-phase modulation or other non-linear effects. In a general embodiment of the multi-wavelength source (MWS), an optical modulator driven by a periodic electromagnetic signal imposes periodic amplitude modulation on light from a single longitudinal mode CW laser. The light is then coupled to a non-linear medium with an intensity dependent refractive index where it generates higher order spectral sidebands by the process of self-phase modulation and/or other non-linear effects. The frequency spacing between the spectral components is equal to the repetition rate of the modulation. The shape of the spectrum (i.e.

Abstract: A cladding-pumped fiber structure is disclosed in which mode mixing of pump light injected into the fiber is induced by index modulation. In one embodiment, the index modulation is created by a stress-inducing region disposed in the cladding which simultaneously maintains the polarization within the core to produce a polarization-maintaining fiber useful for multi-mode and laser applications.

Abstract: A pulse width modulation and intensity modulation signal generating unit, based on input data, performs pulse width modulation and intensity modulation and generates a light emission instruction signal. An error amplifier forms a negative feedback loop together with a semiconductor laser and a light reception device which monitors light output of the semiconductor laser, the error amplifier controlling forward current of the semiconductor laser so that a light reception signal proportional to the light output of the semiconductor laser is equal to the light emission instruction signal. A current driving unit causes a driving current, according to the light emission instruction signal, to flow through the semiconductor laser as the forward current thereof, the driving current being generated so as to control driving of the semiconductor laser with a current of the difference or sum with the control current of the negative feedback loop.

Abstract: The present invention provides a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section. The method comprises the following steps. The laser section is supplied with a direct current which is equal to or larger than a threshold current for allowing the laser section to show a laser emission when the modulator section is supplied with a pulse signal for allowing the modulator section to show a pulse modulation so as to allow a light emitted directly from a facet of the laser section to show a transmission through a light wavelength dispersion medium within which the light on transmission shows a dispersion in wavelength. An intensity of the light having shown the dispersion in wavelength is measured to find a coefficient of variation in intensity of the light, wherein the variation is due to wavelength chirping.

Abstract: A high-speed optical modulator module which includes: a lead frame having an outer lead frame and an inner lead frame, the outer lead frame for receiving a high-speed signal; a substrate, in which a metal base having a matching impedance device, and a submount having a laser diode thereon, are formed; a first multi-bonding wire for electrically connecting the inner lead frame of the lead frame to one end of the matching impedance device; a second multi-bonding wire for electrically connecting the other end of the matching impedance device to one end of the metal base; and a dual-bonding wire for electrically connecting the other end of the metal base to the laser diode. The matching impedance device includes a matching resistor and a compensation capacitor connected in parallel. The module is formed by packaging and sealing the components other than the outer lead frame.

Abstract: A harmonically and regeneratively mode-locked laser pulse oscillator having a clock extraction circuit for picking up from a fragment of a laser output a clock signal corresponding to a high-order integer multiple of the fundamental frequency determined by the cavity length of the laser, a phase shifter and an electric amplifier for driving an optical modulator disposed in the laser cavity at the frequency of the clock signal. The laser pulse oscillator has a phase-locked loop including a phase comparator for detecting the phase difference between the clock signal and an external signal fed from a synthesizer with its frequency fixed, a fiber stretcher for controlling the cavity length such that the repetition rate frequency of the laser pulse oscillator is locked to the external signal, and an electric filter and electric amplifier for expanding and contracting the fiber length by feeding back the phase difference detected by the phase comparator to the fiber stretcher.

Abstract: An injection-locked semiconductor laser process that improves the modulation bandwidth and reduces the broadband noise of an injection-locked semiconductor laser. Injection locking of a semiconductor laser can significantly improve its broadband modulation characteristics. By adjusting the frequency offset between the master laser and the slave laser, improved modulation bandwidth of the modulation response can be emphasized. The intrinsic modulation bandwidths can be enhanced above the theoretical limit for the free-running laser. The improved modulation characteristics are accompanied by reduced broadband relative intensity noise.

Abstract: A device and a method for driving an electro-absorption optical modulator for receiving carrier light emitted from a light source and outputting signal light subjected to intensity modulation according to the absorption of the carrier light. A bias circuit generates a bias voltage determined so that the optical modulator has a given chirping parameter. A driving circuit generates a modulating signal corresponding to an input signal, superimposes the modulating signal on the bias voltage, and supplies the superimposed signal to the optical modulator. A control circuit controls at least one parameter selected from a parameter group including the amplitude and duty of the modulating signal and the power of the carrier light, based on the bias voltage. It can be possible to provide a method of and a device for driving an optical modulator capable of arbitrarily setting a chirping parameter.

Abstract: A DFB laser is provided with a top electrode divided symmetrically into two or three in-line separate elements through which a bias current is applied with a symmetrical distribution and through which a modulation current is applied in push-pull with a temporal asymmetry.

Abstract: A driving method for a tunable semiconductor laser which is remarkably effective for realizing high speed and stable wavelength switching is presented. Generally, when a single longitudinal mode laser oscillation wavelength of a tunable semiconductor laser diode comprising an active region and a wavelength control region is switched from .lambda..sub.1 to .lambda..sub.2, a wavelength control current (.lambda.-Control) supplied to the wavelength control region is switched from I.sub.1 to I.sub.2. In the driving method according to the present invention, an active layer current (Active) supplied to the active region is temporarily decreased below a predetermined value during a predetermined period, in order to temporarily stop the single longitudinal mode laser oscillation of the laser diode.

Abstract: A GCL is formed on a first major surface of a semi-insulating InP substrate. Specifically, an InGaAsP active layer, an InGaAsP waveguide path and a striped grating having two phase shift portions are formed on the first major surface of the InP substrate. An EA modulator is formed on a second major surface of the semi-insulating InP substrate. Specifically, a p-InP layer, an MQW structure of 100-layer, an n.sup.- -InP layer and an n.sup.+ -InP layer are formed on the second major surface of the InP substrate. The first major surface and second major surface of the InP substrate are inclined to each other by a few degrees.

Abstract: A register using a single pin to provide two or more control signals (e.g., clock and data signals). The present invention decodes a three state input waveform to generate a clock/write signal and uses a three state clock waveform to generate a clock/read data signal. The present invention generally comprises a three-level receiver, a latch and an output driver to form a one-pin bidirectional interface used with a shift register. To write, the interface converts a three-level input signal into separate clock and data signals which drive the shift register. To read, the interface converts a bi-level input signal into a three-level output signal representing the output of the shift register. As a result, the present invention allows the programming of a device such as an erasable programmable read only memory (EPROM) in a clock chip while utilizing the fewest number of pins.

Abstract: A variable wavelength light source is provided with a laser of which the oscillating state can be changed over between two oscillating states accompanied by a change of an oscillation wavelength, and an optical selection element for selecting an output light in one of the two oscillating states of the laser. The optical selection element is capable of changing over which of the output lights in the two oscillating states of the laser is to be selected. Also, by using a laser in which the oscillation wavelength in the respective oscillating states can be changed, the wavelength variation ranges in the both oscillating states can be used.

Abstract: A semiconductor photonic integrated circuit and a manufacturing method thereof involving a selective-area growth technique using a set of insulating film patterning masks formed on a semiconductor substrate. The mask width and the mask-to-mask open space width are variable but numerically limited. A single crystal growth process is carried out to form on the same substrate a plurality of contiguous bulk semiconductor layers or quantum well layers differing from one another in terms of growth layer thickness or composition. The differences in energy level between these layers are utilized so that semiconductor photonic integrated devices of different functions are formed on the substrate.

Abstract: Laser modulation control apparatus and methods which provide direct control of the transmitted optical extinction ratio of a semiconductor laser. A relatively low frequency and low amplitude pilot tone is superimposed on the signal used to drive the laser. Setting the amplitude of the pilot tone to a fixed fraction of the laser modulation current causes the transmitted optical power to vary a fixed fraction of the optical data amplitude at the pilot tone frequency. By using feedback to control the laser modulation current, the amplitude of the variation can be maintained at a desired value, which in turn maintains the transmitted optical data amplitude at a constant value, regardless of variations due to operating temperature or laser aging. A separate control loop is employed to maintain the average optical power at a fixed value. Since the optical data amplitude and the average optical power remain constant, the optical extinction ratio is also constant. Alternate embodiments are disclosed.

Abstract: A semiconductor light source for an optical transmitter which includes at least one DC supply unit and at least one AC supply unit, comprises a DC signal source connected to the DC supply unit in order to supply a drive signal thereto; and an AC signal source connected to the AC supply unit in order to supply a control signal thereto; wherein turning on or off an optical output by the semiconductor light source is controlled by using a control signal having the same electric polarity as the drive signal.

Abstract: A semiconductor laser of the present invention includes a semiconductor laser structure having a waveguide extending along a resonance direction, an active layer provided at least partly in the waveguide, and a control unit for controlling the excited state of the semiconductor laser structure to change the relationship between wavelengths or propagation constants and threshold gains for transverse electric (TE) mode and transverse magnetic (TM) mode of the laser structure. The waveguide is designed such that threshold gains for the TE mode and the TM mode can be alternately made minimum under the control of the control unit.

Abstract: An ultraviolet laser source which can stably emits ultraviolet light having a sufficient output and low coherence, as a light source for an exposure unit, for a long period of time, is compact, and allows easy maintenance. The laser source is constituted by 10.times.10 laser elements, i.e., a total of 100 laser elements. Each laser element includes a laser beam emitting section for emitting light having a long wavelength, i.e., visible or infrared light, and a wavelength converting section for converting the emitted laser beam into ultraviolet light. The laser beam emitting section includes a semiconductor laser, and a solid-state laser. The wavelength converting section contains a nonlinear crystal for converting the wavelength of incident light and outputting the resultant light.

Abstract: An intracavity modulated pulsed laser and methods of using the same. In one preferred form, an intracavity modulated pulsed laser comprises an amplification medium, a pulsed pumping source, a beam modulator, and two mirrors, one totally reflective and one partially reflective for generating at least one laser output burst comprising a plurality of sub-pulses having variably controllable peak powers. In another preferred form, a non-linear crystal is utilized to double the frequency of each laser output burst. In still another preferred form, a fluorescence feedback control circuit is utilized to control the beam modulator.

Abstract: A modulated cavity including a cavity; a modulation source; and a modulator located with said cavity and in electrical communication with said modulation source. The modulation source overdrives the modulator with a period of modulation T.sub.mod substantially equal to T.sub.roundtrip (n+(p/q)).sup.-1. n, p, and q are integers. T.sub.roundtrip is the period of a pulse making one round-trip in the cavity. In one embodiment of the invention p and q are relatively prime. In another embodiment of the invention the optical response of the modulator includes the qth harmonic of (1/T.sub.mod). In yet another embodiment of the invention p/q is an integer. In still yet another embodiment of the invention p/q is a rational number.

Abstract: A non-linear semiconductor optical device includes an active waveguide with a multiple quantum well construction in the active region. The device is supplied with a drive current at the material transparency current with respect to an optical pump. An optical non-linearity appears with respect to input radiation having a wavelength below that of the bandgap equivalent wavelength of the active region (.lambda.<.lambda.g), the effect being achieved at relatively low optical input powers. The non-linearity is fast enough that a switching device incorporating the invention, in use as a demultiplexer, has potential to be used at bit rates approaching the Tbit/s range. In a demultiplexer embodiment, the non-linearity may be exploited in a directional coupler, an optical pump being used intermittently to control cross-over of an incoming TDM data signal so as to "pick off" a selected channel. Other applications include optical logic devices.

Abstract: An optical communications source has a laser optically coupled with an external optical modulator (25). The laser has a long optical cavity and a narrow spectral bandwidth Bragg reflector (24) so that the longitudinal mode separation of the laser emission is small compared with the spectral bandwidth of the reflector. This makes the laser operate multi-mode, but without any significant dispersion penalty.

Abstract: An optical semiconductor device comprises a stripe-mesa structure provided on a semi-insulating substrate. The stripe-mesa structure comprises an undoped light absorption layer sandwiched by cladding layers, and by burying layers on both sides. With this structure, the device capacitance is decreased to provide wide bandwidth and ultra-high speed operation properties. This device can be applied to an optical modulator, an integrated type optical modulator, and an optical detector.

Abstract: A high power laser source having a preselected broad bandwidth, including a master oscillator providing a single-mode laser beam, a resonant electro-optical modulator and a source of radio-frequency (rf) modulation voltage, to produce a modulator output beam having sidebands spaced on each side of the nominal frequency of the single-mode laser beam. The bandwidth and the number of modes may be varied by controlling the voltage applied to the modulator. At least one additional modulator in series with the first provides for the addition of other sidebands overlaying those generated with just one modulator. In another embodiment of the invention, the modulator is installed in a PC MOPA (phase conjugated master oscillator power amplifier) configuration to provide modulation only on the return path of the beam from a phase conjugation device having a stimulated Brillouin scattering (SBS) medium.

Abstract: A dual cavity laser having a positively mode-locked structure capable of double increasing the repetition rate of output light. The dual cavity laser includes an amplitude modulator to simultaneously generate two modulating signals with opposite phases. The dual cavity laser has a simply modified structure from that of the conventional single cavity laser to have two resonators, so that it can have a repetition rate corresponding to two times that of the single cavity laser. One of the resonators may have an adjusted optical property so as to obtain two kinds of output optical pulses with different optical properties.

Abstract: A device and method for measuring a difference frequency having a simple structure and utilizing optogalvanic effect for measuring a difference frequency when carbon dioxide laser light of a single wavelength is varied in frequency by a measuring object. When a part of frequency varied laser light is mixed with an original frequency of laser light by self-mixing in a laser resonator, a strength of the laser light in the resonator is modulated to a difference frequency between the original frequency and the variation frequency. Since a current change in response to strength of light is generated by the optogalvanic effect in the laser resonator, when a frequency of optogalvanic current change is measured, the difference frequency can be measured.

Abstract: An apparatus for generating a laser beam modulated on the basis of an information signal, which comprises a circuit for generating a first information signal, a circuit for generating a second information signal, independent of the first information signal, a circuit for driving a semiconductor laser on the basis of the first and the second information signals, wherein the driving circuit comprises first and second switching elements which operate supplementarily with each other, one of the first and second switching elements switches a drive current to the semiconductor laser, and wherein the first information signal is provided into a control terminal of the first switching element and the second information signal is provided into a control terminal of the second switching element.

Abstract: An ultrashort pulse laser apparatus of the this invention includes (1) a laser medium, (2) a laser resonator which stores the laser medium and externally extracts a laser beam, and (3) an excitation source for outputting an excitation energy to the laser resonator to excite the laser medium. The laser resonator includes (i) a plurality of resonant mirrors disposed on both sides of the laser medium to form a resonant optical path, and (ii) a phase dispersion compensation unit which includes two optical members respectively arranged on two light input/output surface sides of the laser medium on the resonant optical path and compensates phase dispersion of light in the resonant optical path. That is, the laser medium is disposed in the optical path between the two optical members of the phase dispersion compensation unit.

Abstract: Intelligent fiberoptic/laser diode transmitter/controller modules and methods of operating and manufacturing the same are disclosed. During calibration procedures for the modules, a laser diode is characterized over a defined operating temperature range. Characteristic data and/or curves defining the operational characteristics of the laser diode over the range of operating conditions (temperature, power supply) are stored in non-volatile memory such as EEPROM. During operation, an embedded microcontroller together with analog to digital converters, digital to analog converters and other associated circuitry, dynamically control the operational parameters (e.g. modulation and bias current) based on the current operating conditions (temperature, power supply). The operating conditions are used as an index into the non-volatile memory containing operational data tables as well as predicted "end-of-life" data.

Abstract: A laser diode driver with automatic power control in which start-up characteristics are controlled to avoid unsafe power levels at a driven laser is disclosed. The laser diode driver according to the invention produces a bias control signal that controls a bias current source such that the bias current supplied to the laser is maintained below a predetermined level during a start-up period.

Abstract: An optical pulse sequence is generated by applying a repetitive optical signal to an optical modulator connected in the laser cavity of a mode-locked laser. The pulse sequence in the laser cavity is then output. The repeat period of the repetitive optical signal is set to be equal to, or an integer multiple of, the cavity round-trip time. The laser is thereby driven to output pulses in bit positions corresponding to the non-zero pulses of the input repetitive optical signal. In one example, the output pulse sequence is used to control an optical switch to provide an OTDM programmable multiplexer using optical signals.

Abstract: A rare-earth doped, lithium niobate, diffusion Bragg reflector laser having a simplified structure and improved efficiency is disclosed. The laser has a pump source, a wavelength division multiplexer, a substrate of lithium niobate doped with at least one rare earth element and having a feedback element, and a grating reflector. The grating reflector is formed from portions of an optical fibre and abuts one end of the doped substrate, such that the grating reflector and the feedback element of the doped substrate form a cavity for the laser. The doped substrate may include phase or amplitude modulators for FM or AM mode-locking operation.

Abstract: A linearized external modulator transmitter with improved dynamic range includes a limiter and a subtractor, which each receive one or more time-varying input signals. The limiter generates a first signal with an amplitude that is confined to a range bounded by preset positive and negative levels, wherein, between the preset levels, the transmitter has an optical power output that is linearly related to the input signal. The first signal is passed through a predistortion circuit connected to an external modulator as well as into the subtractor, which generates a signal equal to the amount by which the input signal exceeds, either positively or negatively, the limited first signal. The subtractor sends the excess signal to a tunable gain circuit connected to a laser. The laser is connected to the external modulator, which generates the optical power output of the transmitter. The transmitter can be adapted to include dual sets of inputs--e.g.

Abstract: An optical pulse generator comprises a resonant source of optical radiation, a modulator, and a source of modulating signals, wherein the modulator is operative to mode lock the resonant source and phase modulate the optical radiation in accordance with the modulating signals in such a manner as to produce dark pulses in the optical radiation.

Abstract: An optical semiconductor device includes a semiconductor laser diode having a first electrode for receiving a current for driving the laser diode, and a grounding electrode; a modulator for modulating light emitted from the semiconductor laser diode, the modulator having a second electrode for receiving a current for driving the modulator, and a grounding electrode connected to the grounding electrode of the semiconductor laser diode; a first resistor having a terminal connected to the first electrode of the laser diode; a second resistor connected between the second electrode of the modulator and the grounding electrode of the modulator; and a third resistor having a first terminal connected to the grounding electrode of the modulator and a grounded second terminal.

Abstract: An optical pulse source includes a gain-switched semiconductor laser diode (1). Light from a continuous wave source (3) is optically coupled into the laser cavity. Light output from the laser cavity passes through an electro-optic amplitude modulator (2). Synchronised modulating signals are applied to the semiconductor diode and to the amplitude modulator. The source outputs short low-jitter optical pulses and is suitable for use, for example, in a broadband optical network operating at high bit rates of 100 Gbit/s or more, or in an optical interconnect.

Abstract: A wavelength-tunable laser device has an active part comprising an active laser region for generating a laser emission with a predetermined emission wavelength, and a tuning part comprising a tuning region allocated to the active laser region and capable of tuning the emission wavelength of the laser light emitted by the active region. The active part is charged with a chronologically variable modulation current that controls the intensity of the emitted laser emission, and the tuning part is charged with an electrical tuning current for controlling the emission wavelength of the emitted laser light. The active part controls the intensity of the emitted laser light and the tuning part is charged with an electrical tuning current for controlling the emission wavelength of the emitted laser light. The tuning current that is supplied to the tuning part and controls the emission wavelength of the emitted laser light is directly derived from the chronologically variable modulation current.

Abstract: A light absorption modulator includes a semiconductor substrate of a first conductivity type; a first cladding layer of the first conductivity type disposed on the substrate; an optical waveguide disposed on the first cladding layer and including a multiple quantum well optical waveguide layer through which light travels and first and second light confinement layers respectively disposed on opposed surfaces of the optical waveguide layer to confine light in the optical waveguide layer; and a second cladding layer of a second conductivity type, opposite the first conductivity type, disposed on the optical waveguide, one of the first and second cladding layers being n type, the one of the first and second light confinement layers that contacts the n type cladding layer being p type, and light traveling through the optical waveguide layer being modulated by applying an electric field to the optical waveguide layer.

Abstract: A laser light generator includes an adder 12 which adds an optical frequency modulation signal Sm onto a d.c. voltage for driving a laser diode 10 for continuous laser oscillation, and applies the sum signal to the laser diode 10 to drive it. An light output from the laser diode 10 is introduced to an optical intensity controller 14 that is controlled by a control signal prepared by adjusting the optical frequency modulation signal Sm both in phase and in amplitude by a phase adjusting circuit 16 and an amplitude adjusting circuit 18. The optical intensity controller 14 may be an electroabsorption modulator that changes its transmissivity in response to an output voltage of the circuit 18. Quantities of adjustment by the circuits 16 and 18 are determined so that fluctuation in transmissivity of the optical intensity controller 14 suppresses intensity fluctuation of the light output of the laser diode 10.

Abstract: In a laser diode which forms read and write functions upon an electro-optic memory, a drive circuit provides power modulation during the read function and sufficient power to perform a write function. During a read function, transistors connected in an emitter coupled switch pair modulate the power delivered to the laser diode. At the emitters of each transistors are a pair of Schottky diodes which enhance the switching speeds of the transistors. Logic is provided to completely turn on the read switch during the time the write switch is on in order to provide sufficient power to the laser diode in order to perform a write function.

Abstract: The modulation bandwidth of a long-cavity semiconductor laser and a multi-frequency long-cavity semiconductor laser is increased by electronic precompensation of the modulation input. The modulation bandwidth may be further increased by having the modulated amplifier and the desired output as far apart as possible.

Abstract: A laser imaging apparatus comprising:a laser diode which is always operable in a linear lasing region;an amplitude modulator for amplitude modulating said laser diode for a digital image signal applied to said laser diode, when said digital image signal has a code value in a first range of code values in the mid to high range of signal code values; anda high speed pulse width modulator for pulse width modulating said laser diode when said digital signal, which is applied to said laser diode, has a code value in a second range of code values below said first range of code values, said laser diode being operated at a constant predetermined power level which is above the threshold power level of said laser diode.

Abstract: An optical clock regenerator using a laser includes an optical modulator for mode locking in a laser resonator. The optical modulator is driven by an intensity-modulated optical signal. When an intensity-modulated optical data pulse train including a clock frequency component close to a frequency n (n is an integer) times or one-nth times a resonance frequency of the laser resonator is input to the optical modulator, the laser outputs clock pulse light locked by the frequency n times or one-nth times a clock frequency of the optical data pulse train. The optical data pulse train and the laser resonator are spatially separated from each other.

Abstract: A stabilized solid-state laser in a thermal imaging system in which a laser diode pumps the solid-state laser and a modulator modulates the laser beam according to graphical data to be recorded in a thermally sensitive medium, as is used in the graphics industry. The solid-state laser is stabilized against relaxation oscillations induced in the laser by modulated light reflected back from the thermally sensitive medium. The light reflected from the medium is allowed to reenter the solid-state laser, but the optical output of the solid-state laser is sampled in the frequency band in which relaxation oscillations occur. The detected intensity is then used in a feedback circuit to control the intensity of the diode laser that is optically pumping the solid-state laser. Thereby, the data modulation does not cause the solid-state laser to oscillate, and neither a Faraday rotator nor use of a diffracted beam is required.

Abstract: A modulation drive current control loop for a digitally modulated laser diode uses the small signal, square-law portion of an RF signal diode detection circuit to adjust the magnitude of laser modulation drive current, and compensate for variations in temperature and aging of the laser diode. Operating the RF signal detector diode as a non-switched device, in its square-law region, provides several advantages over large signal, switched, linear region devices. When a detector diode is operated in the large signal, switched, linear region, its output depends upon the reduced slope beyond the `knee` region of the curve, so that the diode functions essentially as a switch. In such a large signal detection mode, the diode conducts during only a portion of the input cycle, with its output voltage following peaks of the input signal waveform in accordance with a linear relationship between input voltage and output voltage.

Abstract: A modulating circuit for a semiconductor optical modulator is composed of a driver 3 DC-coupled to an optical modulator 2, a load resistor 4 connected in parallel to the modulator 2, and a constant current source 5 connected in parallel to the optical modulator 2 for drawing out the photo-current generated in the optical modulator 2 by absorption of light emitted from a semiconductor laser. The modulating circuit can perform light intensity modulation with low wavelength chirping using a driver DC-coupled to the optical modulator 2. The drawing out current is approximately equal to or more than an average of photo-current which is generated in the optical modulator 2 by light absorption at the time of modulation.

Abstract: An optical device includes a semiconductor optical modulator element (46) which is connected to an end of a signal line (42) in form of a microstrip high-frequency line and whose other electrode is connected to a ground electrode (48) by a bonding wire (50). The signal line (42) includes first and second line portions (42a, 42b). The first line portion (42a) nearer to the entrance of a high-frequency signal has a width W1 determined to adjust its characteristic impedance to 50.OMEGA. and a length L1 equal to an integer multiple of 1/4 of its own guide wavelength. The second line portion (42b) has a width W2 determined to adjust its impedance to an intermediate value between the impedance of the optical modulator element 46 and the impedance of the first line portion (42a), and a length L2 equal to an integer multiple of 1/4 of its own guide wavelength.

Abstract: The invention provides a circuit for amplitude modulating an optical signal with an N-state electrical signal where N is greater than or equal to 2, the circuit comprising a modulator having a first input for receiving the optical signal to be modulated and a second input for receiving a modulating electrical signal. According to the invention, the circuit comprises, upstream from the second input, shaping component having an input receiving the N-state electrical signal and having an output that switches from one of the N states to another of the N states in response to the N-state electrical signal taking up a level that is greater than a predetermined threshold, and switching from the other state to the one of the N states in response to the N-state electrical signal taking up a level that is less than the predetermined threshold, the predetermined threshold being associated with the pair of states, and having a level that lies between and is different from the respective levels taken by the two states.

Abstract: In an optical semiconductor device including a DFB laser and a light absorption modulator, a semi-insulating semiconductor layer is disposed between a carrier blocking layer and a upper cladding layer, the upper cladding layer having an opposite conductivity type from that of the semiconductor substrate and disposed on a buried waveguide and the carrier blocking layer. The capacitance between the carrier blocking layer and the upper cladding layer is reduced. Therefore, mutual interference between the DFB laser and the light absorption modulator through the carrier blocking layer is reduced.

Abstract: A method of frequency stabilizing a semiconductor laser. The method includes the steps of detecting a heterodyne beat note by optically mixing a leakage field of an optical resonator and a frequency modulated output of the semiconductor laser and detecting a phase of the heterodyne beat note by mixing the heterodyne beat note in quadrature with a radio frequency reference signal. The method further includes the steps of filtering the detected phase of the heterodyne beat note, scaling the filtered detected phase of the heterodyne beat note, and modulating the semiconductor laser with the scaled detected phase of the heterodyne beat note and the radio frequency modulation reference signal.