Abstract: A color mixing system is proposed for use in an optical-fiber laser-diode assembly comprising at least two semiconductor laser diodes, optical fiber light input and output couples, a system of spatial superposition of laser beams of different wavelength with at least one semi-transparent mirror, and a system for electronic control of light power in monochromatic light components to be mixed. The electronic control system makes it possible to produce a plurality of different colors. The basic colors, i.e., blue, green, and red, are produced by respective laser diode assemblies provided with means for adjusting output light power on each individual assembly. The electronic system contains a microprocessor connected to a pulse width modulation unit capable of modulating the duration and shape of the light pulse emitted from the laser diode. This allows for selecting a required ratio of energetic brightnesses of light beams produced by individual laser diode assemblies.

Abstract: The cavity of the invention has a pumping source, a ring cavity, a planar convex lens, an optical gain medium, and/or a nonlinear medium. The laser cavity is formed by two mirrors with the same curvature. The curving surfaces of the two mirrors are coupled by a manner of face to face, whereby a space is defined as the ring cavity. The planar-convex lens is located between the pump beam and the ring cavity to work together with the two mirrors of the ring cavity to focus the pump beam. The pumping light enters the ring cavity at a desired distance of d mm from the mirror axis. The laser light also enters the ring cavity in a propagating direction nearly parallel to the mirror axis. Due to the two curving surfaces of the two mirrors, the light beam is reflected back and forth to form the 3-D figure-“8” light path. The optical gain medium and the nonlinear medium are located between the two mirrors on the light path.

Abstract: A semiconductor laser device comprises a semiconductor laser, a photo-diode, a first input terminal and a second input terminal. A sample hold circuit, having a first switch and a capacitor, is provided between the first input terminal and the semiconductor laser. A second switch is provided between the second input terminal and the semiconductor laser. A drive current is supplied to the semiconductor laser based on a light radiation level command signal input to the first input terminal. A constant current is generated based on a signal input through the second input terminal. In a sampling mode, the first and second switches are turned ON, and thus, a control current, which is obtained by subtracting the constant current from the drive current, is sampled by the sample hold circuit. In a holding mode, one of a bias current, obtained based on the control current and the constant current, or the drive current are supplied to the semiconductor laser, in accordance with ON/OFF of the second switch.

Abstract: Disclosed is a laser optical system including a multiline laser source that emits a laser beam having a plurality of peak wavelengths, an imaging optical system that converges the laser beam emitted from the multiline laser source to form beam spots of respective peak wavelengths on an object surface, and a correcting optical system that makes beam spots have the same diameter for at least two selected peak wavelengths. The correcting optical system adjusts a diameter of a laser beam incident on the imaging optical system such that the diameter of the incident laser beam becomes smaller as the wavelength of laser beam becomes shorter.

Abstract: There is disclosed a mode-locked optical fiber laser stabilizing apparatus for stabilizing the length of the optical fiber laser resonator by feedbacking the optical signals to the laser resonator, in the direction where the signal reflected by the optical fiber loop mirror is detected as an error signal to minimize the signal, and method thereof.

Abstract: A variation in optical output of a semiconductor luminous device outputting an optical signal to an optical fiber which is caused due to a variation in ambient temperature and an end of a life thereof capable of being compensated for without measuring the optical output. An output variation quantity H0(Ta) of the semiconductor luminous device due to the ambient temperature Ta is operated in a step S2. In a step S4, an output reduction quantity ST of the semiconductor luminous device obtaining by accumulating an output reduction ST thereof per unit time due to a deterioration of the device is provided. In a step S5, it is judged that a life of the device reaches an end when the output reduction ST exceeds a reference value ST0. When the former fails to exceed the latter, a variation quantity IH(Ta) of a drive current command value due to the ambient temperature Ta and a current reduction quantity IST(ST, dST) determined due to a deterioration of the device are operated in a step S6.

Abstract: The quality of a multi-channel signal launched into an optical fiber may be degraded by active device distortion as well as non-linear fiber effects. Active device distortion in the form of clipping distortion and interferometric noise are reduced by a laser bias control circuit that does not require significant delay of the main RF signal. An information carrying signal, with periodic high amplitude peaks, drives the RF input of a laser as well as the input of a laser bias control circuit. The laser bias control circuit directly modulates the laser with a low frequency signal that is proportional to the frequency of occurrence and intensity of peaks in the information carrying signal that are likely to cause the laser to clip.

Abstract: A gas laser includes a control to modify the distribution of the intensity of the laser light over the laser beam cross section produced in the lasing gas within at least one laser tube by at least two electrodes and a voltage supply unit by means of which a voltage can be fed to electrodes. A discharge area forms in the lasing gas and this can be affected by adjusting the amplification profile of the laser over the excitation cross section of the laser tube.

Abstract: The problem of the disclosed technology is that, in a wavelength locking optical system, a resonator is formed between a wavelength deviation detection device and a facet of a laser diode, which makes a control signal unstable.

Abstract: A light source (27) comprises a header (30), electrical conductors (31), (32), (33), a light sensor (40), a laser (39), a can (28), a convex lens (36), and an external control circuit (34). A window (35) is defined in an inclined top of the can (28), and the convex lens (36) is mounted within the window (35). A convex surface of the inclined convex lens (36) faces away from the light sensor (40). The laser (39) and the light sensor (40) are separately mounted on the header (30). The electrical conductors (31), (32), (33) electrically connect with the control circuit (34). The convex lens (36) has a pre-determined curvature such that emitted light beams of the laser (39) reflected from the lens (36) converge onto the light sensor (40). Accordingly, the reflected light beams (52) received by the light sensor (40) are accurately proportional to the emitted light power of the laser (39).

Abstract: A wavelength control circuit includes a temperature control loop monitoring the ambient temperature of an LD device and driving an electronic heating and cooling device so that the temperature is constant on the basis of a difference signal between a signal value corresponding to the temperature and a reference signal. In a wavelength control loop, the wavelength of a light signal from the light emitting device is monitored by a wavelength monitor and the electronic heating and cooling device is controlled so that the wavelength is uniform. At power on, the temperature is controlled by the temperature control loop to control LD device wavelength. After the temperature control loop is stabilized, a control is performed with both the temperature control loop and the wavelength monitor.

Abstract: A drive current Ip used to control the light output from a laser diode LD is controlled by using an output Vsft from a level shift circuit 3. By inserting the level shift circuit 3 between a drive source (V+) and a switch buffer 5, the lower limit (V+)−(V−) of the drive voltage in the circuit is lowered to enable the laser diode drive circuit to be driven at a lower voltage and to achieve a reduction in power consumption.

Abstract: A method and apparatus for controlling the extinction ratio and average output power of an optical device is disclosed. The method includes calculating a ratio of a first slope of a first characteristic curve to a second slope of a second characteristic curve. A modulation current is calculated based on the ratio.

Abstract: The laser drive device of this invention includes a laser, first and second current sources, a current amplifier, and first and second transistors. When the first transistor is OFF, a first current from the first current source is supplied to the current amplifier, where the current is amplified to generate a laser current to be supplied to the laser. Thus, the laser is turned ON. During this time, the second transistor is ON, allowing a second current to flow from a power supply node into the second current source. When the first transistor is ON, the entire or part of the first current flows into the second current source through the first transistor. This reduces the current supplied to the current amplifier and thus the laser current, resulting in turning OFF the laser. During this time, the second transistor is OFF. The values of the first and second currents are determined by a set current value.

Abstract: A method of controlling an optical device includes inputting a dither current to the optical device, calculating a ratio of a first slope of a first characteristic curve to a second slope of a second characteristic curve, and calculating a modulation current based on the ratio.

Abstract: An optical module includes a first level detecting part having a semi-transparent structure and receiving a light signal emitted from a light-emitting element, a second level detecting part receiving the light signal which penetrates through the first level detecting part and passes through an optical filter, and a control part controlling an operation temperature of the light-emitting element on the basis of electric signals output from the first and second level detecting parts.

Abstract: To more precisely output signals of optical recording media, a semiconductor laser element is mounted in a concave portion on the surface of a semiconductor substrate so that the optical axis of signal detecting light emitted from the semiconductor laser element is substantially parallel to the surface of the semiconductor substrate, and the light emitted from the semiconductor laser element is reflected at the side surface of the concave portion that is opposed to the signal detecting light emitting side of the semiconductor laser element in a direction substantially perpendicular to the surface of the semiconductor substrate. A light receiving portion for signal detection is provided in an area outside the concave portion on the surface of the semiconductor substrate where the semiconductor laser element is mounted.

Abstract: The control of output power of a laser beam generated by a laser system is accomplished on a tool by tool basis, using a position setting of an optical attenuator in conjunction with a repetition rate parameter of the laser beam. Two tables of data points representative of output power of the laser beam as a function of laser frequency and attenuation are generated. A scale factor is determined based on one of the tables, and is used to scale data stored in the other. The scaled data is then used to determine settings necessary to obtain the required output power of the laser beam. The tables are configured to have increased granularity around maximum usage region of the laser frequency and attenuation working range. As a result, the process can be done with high accuracy and within a reasonable time.

Abstract: This invention relates to a light source (10) for producing a binary light signal of constant average power. The light source (10) includes a laser (12) and a current supply for supplying a current to the laser (12). The current has a slowly varying bias component (33) and a modulation component (35), each of which are independently controlled by the current supply so as to keep the average output power of the laser (12) constant when the temperature of the laser (12) changes during use. The current is controlled so as to keep the bias current just above the threshold current, the threshold current being inferred from previously obtained data values. An optical sensor is provided to monitor the average optical power output of the laser (12), and the modulation current is controlled by a feedback loop so as to keep the average optical output power constant.

Abstract: A semiconductor laser control method and a semiconductor laser control apparatus allow an outgoing radiation power of a semiconductor laser to be accurately stabilized to a desired value even if a characteristic of the semiconductor laser changes due to temperature variations or deterioration of life. The characteristic of a semiconductor laser is measured by a semiconductor laser characteristic detection unit and a target value is corrected by a target value correction unit based on a threshold current and differential quantum efficiency obtained from the measurement result. A power control unit controls the semiconductor laser by comparing the corrected target value with the output of a power detection unit, making it possible to achieve a desired outgoing radiation power of the semiconductor laser with high accuracy even if the threshold current or differential quantum efficiency of the semiconductor laser changes due to temperature variations or deterioration of life.

Abstract: A scalable high power laser system includes a plurality of parallel connected modular power amplifier arms, coupled to a common master oscillator to provide a high average power laser system with a scalable output power level, particularly suitable for laser weapon systems with varying power level output applications. Adaptive optics devices are provided in order to provide pre-compensation of phase front distortions due to the modular amplifier arms as well as encode the wave front of the laser beam with a phase conjugate of atmospheric aberrations.

Abstract: The problem of gain tilt in an optically amplified WDM system is avoided by using SBS (Stimulated Brillouin Scattering) to limit the power levels of the individual WDM channels at the outputs of at least selected amplifiers in the transmission path. The SBS limits the power by the creation of a dynamic amplitude Bragg reflective grating. Alternative mode of creating such gratings are also described, one relying upon the Kerr effect, and another relying on creating a thermal grating in a medium, such as a liquid crystal that exhibits a refractive index that is strongly temperature sensitive.

Abstract: There is provided a beam homogenizer which can unify the energy distribution of a linear laser beam in a longitudinal direction. In the beam homogenizer including cylindrical lens groups for dividing a beam, and a cylindrical lens and a cylindrical lens group for condensing the divided beams, the phases, in the longitudinal direction, of linear beams passing through individual cylindrical lenses of the cylindrical lens group for condensing the divided beams are shifted, and then, the beams are synthesized, so that the intensity of interference fringes of the linear beam on a surface to be irradiated is made uniform.

Abstract: A molecular fluorine (F2) laser is provided wherein the gas mixture includes molecular fluorine for generating an emission spectrum including two or three closely spaced lines around 157 nm. An optical method and means are provided for selecting an emission line from among the plurality of closely spaced emission lines of the molecular fluorine laser gas volume and broadening the spectrum of said selected emission line. This approach of broadening the spectrum reduces the coherence length of the output beam. As a result, speckle may be reduced or avoided in microlithography applications.

Abstract: A laser oscillation device, which has an optical fiber where laser ion is doped; an excitation emission element that generates one laser beam including multiple wavelength components by exciting the laser ion in the optical fiber by light emission; a total reflection element that is located at one end of the optical fiber and reflects uniformly laser beam with multiple wavelengths; a separation optical element that is located at another end of the optical fiber and separates laser beam into beams with multiple wavelengths; and a plurality of partial reflection element that reflect separately laser beams with multiple wavelengths separated by the separation optical element.

Abstract: A quantum absorber is provided having transitions that include a first transition between a first lower quantum state and an upper quantum state, and a second transition between a second lower quantum state and the upper quantum state. The first transition and the second transition have energies that correspond to frequencies of &ohgr;1 and &ohgr;2, respectively. The lower quantum states differ in energy by an energy difference subject to a total a.c. Stark shift. Incident electro-magnetic radiation is generated. The incident electro-magnetic radiation includes main frequency components and additional frequency components. The main frequency components are at frequencies of &OHgr;1 and &OHgr;2, equal to &ohgr;1 and &ohgr;2, respectively, and differ in frequency by a frequency difference. The additional frequency components collectively have a spectrum. The quantum absorber is irradiated with the incident electro-magnetic radiation.

Abstract: An optical amplifier includes an optical feedback resonant laser cavity (OFRC) including a power dependent loss element (PDLE) having the characteristic that as the incident laser power on the PDLE increases the cavity loss decreases. The OFRC with the PDLE provides optical gain control or optical power control for a WDM amplifier or a single channel power equalization amplifier (PEA), respectively. A 1×N×N WADM node incorporating more than one of these amplifiers, at least some of which commonly share a pump source, and a method for controlling a transient power change in a single channel optical amplifier or reducing a DC gain error in a WDM optical amplifier that are subject to dynamically variable operating conditions at an input of the amplifier, are also disclosed.

Abstract: A laser diode pump for fiber amplifiers, such as erbium-doped fiber amplifiers (EDFAs), reduces spurious reflections in the signal frequencies by providing a laser pump system that is dissipative at these signal frequencies. Reflections from the pump system are reduced, or eliminated by using an output facet that is currently coated to be reflective at pump frequencies, but anti-reflective, or transmissive, at the signal frequencies. In one embodiment, material layers of aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2) are used.

Abstract: A temperature compensation apparatus for controlling an output power of a laser diode according to a temperature variation of the laser diode, and a method therefor. An error voltage between a voltage corresponding to the output power of the laser diode and a reference voltage is generated. The error voltage is output as a control voltage corrected based on the output power and is applied to the laser diode. When the level of the error voltage overflows or underflows in a first up/down counter, the control voltage based on the luminous efficiency of the laser diode is output by applying the corrected control voltage to the laser diode while interlocking the first up/down counter with a second up/down counter. Accordingly, it is possible to stabilize the luminous efficiency and reduce control error of the laser diode.

Abstract: An oscillator for isolating a transverse electromagnetic (TEM) zero—zero mode pulsed laser beam includes a laser pumping diode that is mounted on a base to induce a multi-mode laser beam from a lasing medium. As initially induced, the multi-mode laser beam is directed along a path and is characterized by a beating signal which has a frequency that is based on amplitude variations of laser pulses in the multi-mode laser beam. Electronics detect this beating signal and generates a responsive error signal. With closed loop control, the error signal is used to advance a straightedge toward the path of the multi-mode laser beam to remove transverse modes from the multi-mode laser beam with the straightedge. This advancement continues until the error signal is a null and the zero—zero mode pulsed laser beam is thereby isolated.

Abstract: A laser device comprises a non-collinear optical parametric generator (OPG) and a pump wave source (4). The OFG comprises a non-linear crystal (1) fixedly mounted within the generator wherein the relative orientations of the pump wave (3) and each generated wave (5) to an optic axis (2) of the non-linear crystal (1) are substantially such that a point of inflexion is produced in a tuning curve of wavelength versus pump wave orientation of one of the generated waves, such that a broadband spectral output is obtained. This device has many applications including an amplifier for an input seed wave in which the crystal dose not have to be rotated to match the wavelength of the seed wave; or as part of a continuously tuneable narrowband source.

Abstract: The bias current of the semiconductor laser 4 is adjusted corresponding to the amplitude of the modulation. A transmit signal is presented to the input 1, then amplified by an amplifier 2 and transmitted to the laser 4 via a blocking capacitor 3. A check photodiode 5 is optically coupled to the laser and a set of four resistors 6, 7, 8, 9 forms a bridge. A differential amplifier 10 having its inputs connected to the bridge ensures the supply of bias current through an inductance 11 intended to inhibit the passing of the modulation signal. A peak detector 12 measures the peak amplitude of the signal that drives the laser to check the conductance of a transistor 14 which operates in the variable conductance mode and is branched parallel to the branch 7 of the resistor bridge to modify the balance of the bridge and thus the value of the power transmitted by the laser.

Abstract: A diode pumped, multi axial mode, intracavity doubled laser has at least two resonator mirrors that define a resonator cavity. A Nd:YVO4 laser crystal and a LBO doubling crystal are positioned in the resonator cavity. A diode pump source supplies a pump beam to the laser crystal and produces a laser crystal beam with at least three axial modes that are incident on the doubling crystal. A frequency doubled output beam is generated with an output power of at least 1 watt.

Abstract: A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

Abstract: A wavelength stabilized laser system includes a laser that produces a laser light having an amplitude and a wavelength that varies as a function of a temperature of the laser. A temperature control device controls the temperature of the laser. A beam splitter deflects a portion of the laser light. A first detector receives the portion of the laser light from the beam splitter and provides a first signal representing the amplitude of the laser light. A filter has a gain that is a function of the wavelength of the laser light. The filter receives the laser light and outputs a filtered light having an amplitude that varies with the wavelength of the laser light. A second detector provides a second signal representing the amplitude of the filtered light. A sealed housing contains the laser, the first and second detectors and the filter. The housing has a window.

Abstract: At least one monitor laser having an associated monitor diode. The monitor diode is connected to an electronic circuit that controls the monitor laser, while correspondingly driving the semiconductor lasers in parallel, in such a way that an electrical signal from the monitor diode constantly has a preset value. This value and a nominal signal corresponding to the nominal value of the optical power of the monitor laser are used to form a correction variable. If a current flowing through a semiconductor laser exceeds the current through the monitor laser, weighted by the correction variable, then the power of the semiconductor laser is reduced. In this manner, the transmitting device is of simple construction and at the same time avoids unacceptably high powers in the semiconductor lasers.

Abstract: The invention relates to a method and a circuit arrangement for a laser control loop with automatic adaptation to the monitoring signal polarity. Use is made of a single-phase method which consists in that a signal produced by the monitor during the starting phase of the laser control loop is compared with a reference value, and in accordance with the result of the comparison the signal produced by the monitor is fed directly or inverted to the comparator for controlling the light power of the laser during the starting phase of the laser control loop. A signal is produced which initially feeds the comparator for controlling the light power the inverted monitoring signal, or directly feeds the monitoring signal, in a fashion always independent of the monitoring signal polarity, but dependent on the polarity of a reference value, and feeds it in a non-inverted fashion in the case of a monitoring signal running up to the reference value.

Abstract: A wavelength-stabilized laser system includes a laser that produces a laser light. The laser light has an amplitude and a wavelength that varies with the temperature of the laser and/or a bias signal provided to the laser. A temperature control device controls the temperature of the laser. A first detector outputs a first signal representing an amplitude of a laser light. A filter receives the laser light and outputs a filtered light having an amplitude that varies with the wavelength of the laser light. A second detector outputs a second signal representing the amplitude of the filtered light. An electromagnetic radiation source transmits electromagnetic radiation through the filter and through a diverging lens. A third detector receives the electromagnetic radiation that passes through the diverging lens. The second detector may be between the diverging lens and the third detector. The third detector outputs a third signal representing an amplitude of the electromagnetic radiation.

Abstract: A technique of stabalizing during operation a gas mixture with a gas composition initially provided within a discharge chamber of an excimer or molecular fluorine gas discharge laser includes monitoring a temporal pulse shape of the laser beam and adjusting and/or determining the status of the gas mixture based on the monitored temporal pulse shape. The monitored temporal pulse shape is preferably compared with a reference temporal pulse shape. The difference or deviation between the monitored temporal pulse shape and a reference temporal pulse shape is calculated. The amount of and intervals between gas replenishment actions are determined based on the calculated deviation. The energy of the beam is also monitored and the driving voltage and gas actions are adjusted to stabilize the energy, energy stability and/or energy dose.

Abstract: Power control for a laser is performed on at least a per-packet basis, rather than a per-pulse basis, and that end-of-life detection may similarly be performed. This is achieved by accumulating the current generated by a photodiode in response to the light signal generated by the laser, subtracting therefrom a preset threshold current which is similarly modulated in response to the data signal used to drive the laser, and comparing the resulting difference to the value prior to having begun accumulating and subtracting. The result of the comparison, which may be filtered, is used to control the driver of the laser or as an indicator, e.g., for use in end-of-life detection.

Abstract: Disclosed is a laser diode protecting circuit adapted to prevent a laser diode from producing an excessive emission when the laser diode is driven at low temperature, thereby assuring that the laser diode will not be damaged or degraded in terms of its characteristic. When the laser diode is started at low temperature, a laser diode protecting circuit has a power monitor circuit for monitoring backward power of the laser diode and a laser diode current limiting circuit for limiting the laser diode current when the backward power becomes equal to the set power. When the laser diode temperature subsequently rises and the backward power falls below the set power, an automatic current control circuit performs automatic current control in such a manner that the laser diode current attains a set current value.

Abstract: An optical transmitter (200) in a cable television system (100) includes an uncooled laser diode (250) and a thermal compensation circuit (FIG. 2). The thermal compensation circuit includes a voltage controlled attenuator (220) located between the transmitter input (205), at which an electrical information signal is received, and the laser diode (250). The thermal compensation circuit also includes a thermistor (230) that is situated physically near the laser diode (250) and that is characterized by a resistance that varies with temperature. The thermistor (230) is coupled to a controller (225) for sensing thermistor resistance changes, which are indicative of changes in the laser diode temperature, and for selectively controlling the attenuator (220) to attenuate the level of the electrical information signal.

Abstract: An improved optically pumped atomic frequency standard in which excitation light intensity entering the resonance cell is controlled and maintained independently of the optical pump.

Abstract: A scalable high power laser system includes a plurality of parallel connected modular power amplifier arms, coupled to a common master oscillator to provide a high average power laser system with a scalable output power level, particularly suitable for laser weapon systems with varying power level output applications. Adaptive optics devices are provided in order to provide pre-compensation of phase front distortions due to the modular amplifier arms as well as encode the wave front of the laser beam with a phase conjugate of atmospheric aberrations.

Abstract: There is provided an improvement on homogeneity of annealing performed utilizing radiation of a laser beam on a silicon film having a large area. In a configuration wherein a linear laser beam is applied to a surface to be irradiated, optimization is carried out on the width and number of cylindrical lenses forming homogenizers 103 and 104 for controlling the distribution of radiation energy density in the longitudinal direction of the linear beam. For example, the width of the cylindrical lenses forming the homogenizers 103 and 104 is set in the range from 0.1 mm to 5 mm, and the number of the lenses is chosen such that one lens is provided for every 5 mm-15 mm along the length of the linear laser beam in the longitudinal direction thereof. This makes it possible to improve homogeneity of the radiation energy density of the linear laser in the longitudinal direction thereof.

Abstract: An apparatus for stabilizing the wavelength of light emitted by a laser or light source comprising a divider for dividing a sample of emitted light into a first and second portion; a first photodetector configured to measure an intensity of the first portion and a second photodetector configured to measure an intensity of the second portion, the second photodetector configured to receive the emitted light via an optical frequency discriminator, such as a dielectric coating, wherein the optical frequency discriminator is configured to modify the intensity of the emitted light at the second photodetector as a function of an optical frequency of the emitted light; and a processor configured to maintain a desired level corresponding to a ratio of the intensity measured by the first photodetector and the intensity measured by the second photodetector, so as to provide a feedback control signal to adjust the wavelength of the emitted light.

Abstract: The frequency standard comprises a quantum absorber, a source of incident electro-magnetic radiation, a detector, a frequency difference controller, a spectrum controller and a frequency standard output. The quantum absorber has transitions including a first transition between a first lower quantum state and an upper quantum state, and a second transition between a second lower quantum state and the upper quantum state. The first transition and the second transition have energies that correspond to frequencies of &ohgr;1 and &ohgr;2, respectively. The lower quantum states differ in energy by an energy difference subject to a total a.c. Stark shift. The source of incident electro-magnetic radiation is arranged to irradiate the quantum absorber. The incident electro-magnetic radiation includes main frequency components at frequencies of &OHgr;1 and &OHgr;2, equal to &ohgr;1 and &ohgr;2, respectively, and additionally includes additional frequency components collectively having a spectrum.

Abstract: The present invention is a method and apparatus for controlling a drive current of an optical transmitter having a laser. A sensing circuit generates a sensing signal responsive to an intensity of an optical radiation emitted by the laser. An error circuit is coupled to the sensing circuit to generate an error quantity in response to the sensing signal. An updating circuit is coupled to the error circuit to update a control quantity based on the error quantity synchronously with an input signal. The control quantity controls the drive current.

Abstract: A semiconductor laser device with reduced threshold current and power consumption. Reflectivity Rr at a rear face of an optical cavity of the laser is set as large as possible. A monitor photodiode used for controlling an output form the laser is provided on a mount at a position to detect the main laser beam emitted from the front face of the optical cavity.

Abstract: The invention concerns a method of reducing the amplitude noise of solid lasers (e.g. Nd-YAG, Nd:YAlO, Nd:YLF, Nd:YVO.sub.3, etc.) with resonator-internal frequency doubling (for example by KTP, LBO, BBO, KNbO3, LiNbO.sub.3, etc.). According to the invention, some of the frequency-doubled ejected laser radiation or the fundamental wave radiation is guided onto a photodetector (in particular a photodiode) whose electrical output signal undergoes bandpass filtering which filters out a frequency range typical of the noise. This output signal, optionally after rectification, quadrature and/or integration, is then subjected to temperature regulation or control which corrects the temperature of the frequency-doubling crystal such that the output signal is minimized after the bandpass filter and thus the amplitude noise of the laser radiation is minimized.