Abstract: An optical transmitter is disclosed. In accordance with some embodiments of the present disclosure, an optical transmitter may comprise a vertical-cavity surface-emitting laser (VCSEL) and a VCSEL driver. The VCSEL driver may comprise an input stage configured to receive a voltage signal and a low-impedance output stage comprising an input coupled to the input stage and a low-impedance output coupled to the VCSEL and configured to provide a modulated output current to the VCSEL.

Abstract: A laser driver apparatus, system, and method include a single laser driver. One or more threshold levels and one or more undershoot levels can be digitally combined into a single output with respect to the single laser driver to reduce the output capacitance of the single laser driver and minimize circuit power, resulting in a faster and higher fidelity signal thereof. A decoder (e.g., thermometer decoding) can also be provided, wherein the threshold level(s) and the undershoot level(s) are thermometer decoded via the decoder.

Abstract: Embodiments of the present invention use an external cavity laser source with dual input terminals, such as bias current for a gain section, and a voltage signal for a modulator section. An aspect of the present invention provides an ultra-low frequency noise external cavity frequency modulated (FM) semiconductor laser source frequency stabilized by a dual electronic feedback circuitry applied to semiconductor gain section and a modulation section. A further aspect of the present invention provides an optical frequency discriminator based on homodyne phase demodulation using an unbalanced Michelson interferometer with fiber optics delay and a symmetrical 3×3 optical coupler.

Abstract: A laser drive device capable of easily reducing influence of bias light emission and thereby preventing variation in threshold current. A light amount of a laser beam emitted from a laser diode is detected by a photodiode. A drive current supplied to the laser diode is controlled according to the detected light amount to thereby control the amount of light emitted from the laser diode to a plurality of set light amounts. A threshold current is calculated according to the detected light amount and the drive current. The light amounts are changed and selected, and threshold currents calculated with respect to respective set light amounts are compared. A light amount corresponding to a difference in threshold current not less than a predetermined value is set as a set light amount for use in light amount control of the laser diode.

Abstract: A method or algorithm to control a driving current supplied to a semiconductor laser diode (LD) is disclosed. the method first prepares the look-up-table (LUT) that stores a set of parameters, ? and ?, for evaluating the modulation current Im by the equation of Im=?×Ib+?, where Ib is determined by the auto-power-control (APC) loop. In a practical operation of the LD, the APC loop determines Ib, while, Im is calculated according to the equation above by reading above two parameters corresponding to the current temperature of the LD from the LUT.

Abstract: Apparatus and systems create differential drive signals suitable for HAMR data recording. A laser diode differential driver provides heating current pulses at a time ?1. The pulses energize a laser diode to pre-heat the magnetic medium to be written. Some embodiments duplicate portions of the laser diode circuit architecture to create a magnetic write head differential driver. The write head driver provides write current pulses to a magnetic write head in one direction with ?1 timing and in the opposite direction with ?2 timing. Both drivers utilize sets of reference voltages capable of being switched to one terminal or the other of the element to be driven. In the laser diode case, the common mode is split between the anode and cathode sections of the driver. A feedback element is added between the cathode and anode sections to provide current accuracy independent of the electrical characteristics of the selected laser diode.

Abstract: An optical power stabilizing device is adapted to stabilize optical power of a light emitting device having a forward voltage, and includes a current generating circuit that generates a pulse-wave driving current to drive light emission of the light emitting device, an optical-type feedback circuit that outputs a first feedback voltage according to detected optical power of the light emitting device, an electrical-type feedback circuit that outputs a second feedback voltage according to the forward voltage, and a pulse wave generating circuit that generates a pulse-wave signal to control the current generating circuit according to one of the first feedback voltage and the second feedback voltage.

Abstract: Techniques and devices based on optical resonators made of nonlinear optical materials and nonlinear wave mixing to generate optical combs that are stabilized relative to an atomic reference.

Abstract: A laser system comprising a laser configured to generate a laser beam, a power supply arranged to provide a drive power to the laser, a photodetector arranged to detect the power of the laser beam and provide a detection signal from the power of the laser beam and a feedback loop arranged to form a feedback signal by subtracting a target signal from the detection signal wherein the feedback signal has a high bandwidth, amplify the feedback signal and adjust the drive power according to the amplified feedback signal, thereby reducing noise in the laser beam.

Abstract: A method and apparatus for stabilizing the seed laser in a laser produced plasma (LPP) extreme ultraviolet (EUV) light system are disclosed. In one embodiment, the cavity length of the laser may be adjusted by means of a movable mirror forming one end of the cavity. The time delay from the release of an output pulse to the lasing threshold next being reached is measured at different mirror positions, and a mirror position selected which results in a cavity mode being aligned with the gain peak of the laser, thus producing a minimum time delay from an output pulse of the laser to the next lasing threshold. A Q-switch in the laser allows for pre-lasing and thus jitter-free timing of output pulses. Feedback loops keep the laser output at maximum gain and efficiency, and the attenuation and timing at a desired operating point.

Abstract: An image display device including a laser light source device that includes: laser elements of different output wavelengths; a pulse signal generating unit that generates pulse signals based on a video signal; a laser driving unit that drives the laser elements in synchronization with the pulse signals; an optical combining system that combines laser beams, outputs a combined laser beam, and retrieves part of the combined laser beam; a light amount measuring unit that measures a light amount of a retrieved laser beam; and a light amount adjusting unit that causes the laser driving unit to individually adjust a light amount for the each laser element based on a measurement value, wherein the pulse signal generating unit operates in a light amount measuring mode so that emission timings would not coincide one another, and the light amount measuring unit individually measures a light amount of the each laser element.

Abstract: A thin beam laser crystallization apparatus for selectively melting a film deposited on a substrate is disclosed having a laser source producing a pulsed laser output beam, the source having an oscillator comprising a convex reflector and a piano output coupler; and an optical arrangement focusing the beam in a first axis and spatially expanding the beam in a second axis to produce a line beam for interaction with the film.

Abstract: A semiconductor laser driving device that drives a semiconductor laser with a driving current output from a driving current output terminal is disclosed. The semiconductor laser driving device includes a driving current monitoring terminal configured to output a driving current monitoring current having a value of 1/? of the driving current; a current-voltage conversion resistor connected to the driving current monitoring terminal and configured to convert the driving current monitoring current having the value of 1/? of the driving current into a corresponding driving current monitoring voltage; and a detector configured to generate a reference voltage and detect whether the corresponding driving current monitoring voltage has reached the reference voltage.

Abstract: In one embodiment, a system includes a master oscillator for generating a primary laser signal. A plurality of amplifiers amplifies a plurality of secondary laser signals and generates a plurality of amplified laser signals. A plurality of actuators adjusts a position, a beam angle, a path length, and a phase of the plurality of amplified laser signals. At least one control module controls the plurality of actuators that adjust the position, the beam angle, the path length, and the phase of the plurality of amplified laser signals. A combiner receives the amplified laser signals to generate a combined laser output signal. At least one filter samples the combined laser output signal to generate a plurality of phase errors as feedback for the control module to control at least one of the position, the beam angle, or the path length for the plurality of amplified laser signals.

Abstract: A method and apparatus for active voltage regulation in optical modules utilize a voltage regulator to change the supply voltage provided to laser diode driver and receiver electronics to optimize module performance over temperature. The ambient temperature of the module is monitored. The outputs of the voltage regulator are controlled to provide voltages that are optimized with respect to temperature for the integrated circuits in the optical module. This control is implemented via a temperature sensitive feedback or a control input from a microcontroller with a temperature monitor input. The supply voltage is optimized to minimize the voltage required to achieve acceptable performance at a given temperature. Minimizing the supply voltage lengthens the lifetime of the integrated circuit and the optical module. The voltage regulator provides higher than standard supply voltages to a laser diode driver to compensate for higher laser voltage at low temperatures.

Abstract: A driver device for a laser includes a control device configured to generate a control current, an NPN differential amplifier connected to the control device and configured to superimpose a modulation current onto the control current to generate a combined current, and a laser activation switch coupled to the output of the NPN differential amplifier, the laser activation switch operating the laser utilizing the combined current. Also described herein is a communication system including a driver device.

Abstract: A method for operating a laser device, which has a laser-active solid-state body including a preferably passive Q switch, in which pumped light is applied to the laser device in order to generate a laser pulse. The laser device and/or an optical link between the laser device and a pumped light source supplying the pumped light is at least partially acted upon by an optical test pulse in order to check the integrity of a/the optical link between the laser device and a pumped light source supplying the pumped light.

Abstract: A laser diode drive circuit includes a power supply circuit connected to an anode of a laser diode to supply a variable voltage to the laser diode, and a drive current control circuit connected to a cathode of the laser diode to control a current of the laser diode. The power supply circuit generates a start-up voltage which is equal to the sum of the maximum drive voltage that is larger than the drive voltage and a predetermined first reference voltage, acquires a cathode voltage of the laser diode while the start-up voltage is generated, generates a voltage by lowering from the start-up voltage so as to diminish the difference between the acquired cathode voltage and the first reference voltage, and the first reference voltage is the minimum cathode voltage necessary to supply a predetermined current to the laser diode by the drive current control circuit.

Abstract: A safety and interlock circuit for use with devices which could cause injury if an error condition causes improper operation. A control program executing on a processor monitors a variety of device conditions, including pulse over-duration threshold, diode over-current threshold, pulse lock-out duration, temperature threshold, and pulse repetition frequency limit, and prevents the laser from firing if an error condition is detected. In addition, the error conditions are logged in a persistent memory to facilitate subsequent diagnosis and correction.

Abstract: A laser driver circuit having a differential circuit and an output circuit includes a control circuit receiving a regulated supply voltage that also supplies the differential circuit as an input signal. The control circuit generates a feedback voltage across a first resistor to cause a first current to flow in the first resistor having a current value equal or proportional to the modulation current value. The laser driver circuit includes an operational amplifier receiving the feedback voltage and a reference voltage indicative of a desired modulation current value and to generate the regulated supply voltage. The control circuit and the operational amplifier form a feedback control loop to adjust the regulated supply voltage to regulate the feedback voltage to be equal to the reference voltage, thereby regulating the modulation current value to the desired modulation current value.

Abstract: A semiconductor laser driver includes a light detection circuit to detect a quantity of light as a detected light emission intensity and output the detected light emission intensity to the control circuit, and a control circuit to control a light emission intensity for the semiconductor laser based on the detected light emission intensity and on a predetermined light emission intensity setting value. The light detection circuit includes a photoelectric conversion element to convert the quantity of light emitted from the semiconductor laser into an electrical current and output the converted electrical current, a current magnification setting circuit to amplify the electrical current output from the photoelectric conversion element to a predetermined amplified current at one of multiple different predetermined magnifications, a detection resistor to convert the amplified current output from the current magnification setting circuit into a voltage and output the voltage as the detected light emission intensity.

Abstract: A power supply for laser systems is configured with a DC power source having an output source voltage, an energy accumulator operatively connected to the output of the DC power source, and a pump. Coupled between the accumulator and source is a first DC to DC stage with at least one switched-mode power converter which is operative to charge the accumulator with voltage. The charged voltage may be same or different from the source voltage. The power supply further includes a second DC to DC stage with at least one switched-mode power converter coupled between the accumulator and pump and operative to discharge accumulator to the same or different output voltage. The DC to DC converters are configured so that current pulses at the input of the pump each have a peak value greater than the power source current.

Abstract: A laser machining control system includes a laser diode, a laser power controller connected to the laser diode, a light transmission-reflection element positioned on a light path of a laser light beam to a workpiece, and an output power meter. The output power meter detects the laser light beam being reflected by the transmission-reflection element element and measures an output power of the laser diode. The output power meter gives a signal to the laser power controller if there is a power loss of the laser light beam, and the laser power controller adjusts the voltage and the current input to the laser diode in compensation.

Abstract: According to the repetition frequency control device, a master laser outputs a master laser light pulse the repetition frequency of which is controlled to a predetermined value. A slave laser outputs a slave laser light pulse. A reference comparator compares a voltage of a reference electric signal the repetition frequency of which is the predetermined value and a predetermined voltage with each other, thereby outputting a result thereof. A measurement comparator compares a voltage based on a light intensity of the slave laser light pulse and the predetermined voltage with each other, thereby outputting a result thereof. A phase difference detector detects a phase difference between the output from the reference comparator and the output from the measurement comparator. A loop filter removes a high-frequency component of an output from the phase difference detector.

Abstract: Systems and methods are provided for generating an accurate, stable measurement for a laser bias current. The average current and the extinction ratio are controlled using a dual control loop. The transfer function between the laser and a monitor photo diode (MPD) is characterized. A laser driver control module predicts the average power that will be measured using the MPD relative to the data being transmitted, and this information is used to control a laser driver.

Abstract: A method and apparatus for stabilizing the seed laser in a laser produced plasma (LPP) extreme ultraviolet (EUV) light system are disclosed. In one embodiment, the cavity length of the laser may be adjusted by means of a movable mirror forming one end of the cavity. The time delay from the release of an output pulse to the lasing threshold next being reached is measured at different mirror positions, and a mirror position selected which results in a cavity mode being aligned with the gain peak of the laser, thus producing a minimum time delay from an output pulse of the laser to the next lasing threshold. A Q-switch in the laser allows for pre-lasing and thus jitter-free timing of output pulses. Feedback loops keep the laser output at maximum gain and efficiency, and the attenuation and timing at a desired operating point.

Abstract: The present disclosure relates to an optical power monitoring circuit including an automatic power control (APC) loop and a microcontroller unit (MCU), and a method for monitoring the same. The APC loop comprises a laser diode (LD) and a feedback loop to maintain a laser optical power. The MCU is configured to (i) monitor a bias current using a current sense circuit, (ii) monitor a rate of change of the bias current with time, and (iii) adjust a target power of the APC loop. By monitoring the bias current and the rate of change, and comparing them against thresholds, the target power can be adjusted by the MCU, to prevent roll-over in the laser diode, damage to the laser, and/or a hard failure in the data links that use the laser.

Abstract: The luminance of a laser diode is a function of laser diode drive current. The luminance is also a function of other factors, such as age and temperature. A laser projection device includes laser diodes to generate light in response to a commanded luminance, and also includes photodiodes to provide a measured luminance. The commanded luminance and measured luminance are compared, and drive currents for the laser diodes are adjusted to compensate for changes in laser diode characteristics.

Abstract: An optical transmitter is disclosed, where the optical transmitter shows an emission wavelength kept stable in one of grid wavelengths of the WDM system during the boot of the transmitter. The optical transmitter includes an LD, a TEC to control a temperature of the LD, and a controller. Detecting the flag to enable the optical output, the controller increases the driving current of the LD concurrently with the decrease of the temperature of the TEC to compensate the self-heating of the LD due to the driving current.

Abstract: A method of fabricating a semiconductor laser device by forming a semiconductor structure at least part of which is in the form of a mesa structure having a flat top. The steps include depositing a passivation layer over the mesa structure, forming a contact opening in the passivation layer on the flat top of the mesa structure; and depositing a metal contact portion, with the deposited metal contact portion contacting the semiconductor structure via the contact opening. The contact opening formed through the passivation layer has a smaller area than the flat top of the mesa structure to allow for wider tolerances in alignment accuracy. The metal contact portion comprises a platinum layer between one or more gold layers to provide an effective barrier against Au diffusion into the semiconductor material.

Abstract: A solid-state laser apparatus may include: a master oscillator configured to output laser light having at least one longitudinal mode, the master oscillator being capable of changing the spectral linewidth of the laser light output therefrom; at least one amplifier located downstream of the master oscillator on an optical path; a wavelength converter located downstream of the amplifier on the optical path; a detector configured to detect the spectrum of the laser light; and a controller configured to control the spectral linewidth of the laser light output from the master oscillator based on a detection result of the detector.

Abstract: A laser oscillator control device includes a controller having a transmitter section and a receiver section; a laser oscillator having a transmitter section and a receiver section and communicating with the controller via a communication line; wherein the laser oscillator control device outputs a control signal from the controller to the laser oscillator, based on a status signal indicating operational state of the laser oscillator sent from the laser oscillator to the controller. The controller has an alternating signal transmitter circuit that generates an alternating signal that changes at a predetermined period, and sends this alternating signal to the laser oscillator, and the laser oscillator has a return signal transmitter circuit which generates a return signal that changes periodically in correspondence to the alternating signal from the controller, and sends this return signal to the controller.

Abstract: A projection apparatus includes at least one laser diode and a laser diode junction temperature estimator to estimate the junction temperature of the at least one laser diode. Laser diode current drive values are modified in response to the estimated laser junction temperature. The modification of laser diode current drive values may occur as frequently as once per pixel.

Abstract: The present invention provides a laser apparatus capable of improving a scan speed and achieving a scan rate equal to or more than 1 MHz, and an optical tomographic imaging apparatus using the laser apparatus as a light source. The laser apparatus includes a ring resonator, the ring resonator having a structure in which a first modulator, a normal dispersion region, a second modulator and an anomalous dispersion region are arranged in this order, and in this arrangement, a gain medium is included, and being configured so that modulation with respect to the second modulator can be caused to be phase modulation by periodically superimposing phase modulation on modulation with respect to the first modulator.

Abstract: An optoelectronic swept-frequency semiconductor laser coupled to a microfabricated optical biomolecular sensor with integrated resonator and waveguide and methods related thereto are described. Biomolecular sensors with optical resonator microfabricated with integrated waveguide operation can be in a microfluidic flow cell.

Abstract: Disclosed is a semiconductor laser driving unit that outputs a driving current for driving a semiconductor laser. A value of a correction current is set in such a manner as to determine a rising characteristic and/or a falling characteristic of an output of the driving current in accordance with a value of the driving current.

Abstract: Dual laser-power-level control and calibration system for burst-mode and continuous-mode transmitter. A first signal path receives a transmit signal that also drives the transmit laser, and a second signal path receives the output of a monitor diode. The first and second signal paths include filtering so that the two signal paths have a similar frequency response. The upper and lower excursions in both signal paths are compared, and the power levels of the optical transmitter are adjusted based on those comparisons. Embodiments with one control loop and two control loops are disclosed.

Abstract: Average-power control loops and methods through laser supply voltage closed-loop control. In accordance with one of the methods, a switching converter is coupled to provide power to a first terminal of a laser diode, a programmable current source is coupled to control the average current through a laser diode, an average power control circuit is coupled to a monitor diode to monitor the average power out of a laser diode and to control the programmable current source to maintain a desired average power out of a laser diode, and the output of the switching converter is adjusted responsive to the headroom of the programmable current source to limit the output of the switching converter to a voltage that will still assure adequate operation of the current source. Various embodiments are disclosed.

Abstract: A laser diode driving device (1) of the present invention includes: a variable DC power supply (3) for outputting a voltage for driving laser diodes (LD1 to LDn); a current driving element (4) for causing a current If to flow; a current control section (5) for controlling (i) turning on and off of the current driving element (4) and (ii) the amount of the current If; and a power supply control section (7) for controlling an output voltage of the variable DC power supply (3). The power supply control section (7) controls, on the basis of If-Vf characteristic data (D2), voltage drop characteristic data (D3), and Vds setting data (D4) all stored in a memory section (8), the output voltage of the variable DC power supply (3) so that the current driving element (4) has a constant inter-terminal voltage regardless of the amount of the current If.

Abstract: An optical device includes: a light source that emits laser beams; a detecting unit that detects the laser beams and converts light amounts of the detected laser beams into voltage values; a first storage unit that stores in advance a light amount to be output for each of the laser beams and the voltage value; a second storage unit that stores in advance a value indicating light use efficiency of an optical system that guides the laser beams to a surface to be scanned for scanning; a calculating unit that calculates a target voltage value for each of the laser beams based on the light amount and the voltage value and also on the value indicating the light use efficiency; and a control unit that controls emission power for each of the laser beams so that the voltage value output from the detecting unit approaches the target voltage value.

Abstract: An optical transmission module includes a bias current driver circuit adapted to input bias current set in response to a temperature of a laser diode to the laser diode, a modulation current driver circuit adapted to input modulation current set in response to the temperature of the laser diode to the laser diode, and a decision circuit adapted to decide whether or not an error of optical output power of the laser diode detected by a light reception device with respect to a target value of the optical output power of the laser diode at the set bias current and the set modulation current is equal to or higher than a threshold value. The modulation current driver circuit inputs, while the error is equal to or higher than the threshold value, correction modulation current higher than the set modulation current to the laser diode.

Abstract: Various examples of feed-forward systems that reduce phase noise in a laser field generated by a laser. These include feed-forward systems that utilize phase and/or frequency discriminators, filters, integrators, voltage controlled oscillators (VCOs), current controlled oscillators (CCOs), phase modulators, and/or amplitude modulators. It also includes systems that use both feed-forward and feedback phase noise reduction systems, tunable semiconductor lasers, and multiple, sequential feed-forward systems.

Abstract: One embodiment of the invention includes an optical system. The optical system includes an optical cavity comprising a plurality of reflectors. The optical system also includes optics configured to provide a first optical signal and a second optical signal into respective inputs of the optical cavity to be substantially concurrently resonated within the optical cavity. The first and second optical signals can have distinct wavelengths.

Abstract: A laser device includes a seed laser, an amplifier, a detector, and an optical element arranged to direct radiation emitted by the seed laser towards a plasma generation site. The optical element is arranged to direct towards the detector amplified spontaneous emission radiation which has been emitted by the seed laser and has been reflected from a droplet of fuel material. The detector is arranged to trigger generation of a laser radiation pulse by the seed laser when the reflected amplified spontaneous emission radiation is detected.

Abstract: A semiconductor laser drive apparatus comprises a bias current setting section (232) which sets a bias current value on the basis of the drive temperature so that the temperature characteristic of the bias current value with respect to the drive temperature may be a linear function having a slope except zero and a drive current setting section (233) for setting the drive current value on the basis of the drive temperature so that the temperature characteristic of the drive current value with respect to the drive temperature may be a function having a slope except zero. The temperature characteristic of the bias current and that of the drive current are functions different from each other. With this, low cost, space-saving, and power-saving of a semiconductor laser are achieved, and a semiconductor laser drive apparatus enabling a good transmission characteristic on the reception side and a high optical output over the whole drive temperature range when driving the semiconductor laser can be provided.

Abstract: A high-power laser unit capable of accurately correcting laser output from low to rated outputs, even when the laser unit has a laser power monitor which may be affected by environmental factors inside or outside the laser unit, by effectively reducing environmental factors. The laser unit has a laser power monitor for measuring laser output, and a laser controller for correcting the laser output by correcting an amount of excitation energy to a laser power supply so that a measurement value coincides with a laser output command value. The laser unit has a laser output commanding part for generating a laser output command. When it is not necessary to correct the laser output command, the laser output command is converted into an excitation energy command value and sent to the power supply. Otherwise, an output correcting part of the laser controller corrects the laser output command.

Abstract: An active laser guarding system 1 comprises at least one screen 3 provided with at least two spaced apart conductors 7, 9 each defining a respective electrically conductive path that is electrically separate from the other. The screen 3 comprises material, at least between the two conductors 7, 9, which is arranged to carbonize when struck by a laser beam to form a further conductive path 19 which extends between, and electrically connects, the two conductors 7, 9. The system 1 further comprises a detector 15 operative to detect the further conductive path 19 so formed, the detector 15 being operative to generate a laser deactivation signal response to detecting the further conductive path 19.

Abstract: A laser and amplifier combination delivers a sequence of optical pulses at a predetermined pulse-repetition frequency PRF. An interferometer generates a signal representative of the carrier-envelope phase (CEP) of the pulses at intervals corresponding to the PRF. The signal includes frequency components from DC to the PRF. The signal is divided into high and low frequency ranges. The high and low frequency ranges are sent to independent high frequency and low frequency control electronics, which drive respectively a high-frequency CEP controller and a low frequency controller for stabilizing the CEP of pulses in the sequence.

Abstract: A DC-DC converter is disclosed having an input configured to receive an input signal and an output configured to present an output signal at a different voltage than the input signal. The converter also includes at least one inductor and at least one capacitor. Two or more transistors fingers are provided such that at least one of the two or more transistor fingers comprises two or more switching transistors, each of which has an input, an output, a control input. An activation controller connect to at least one of the two or more switching transistors, the activation controller to configured to control whether the at least one of the two or more switching transistors is active or non-active. Also disclosed is a buck-boost converter with numerous controlled switches that establish the converter in either buck-boost mode, buck mode or boost mode.

Abstract: A disclosed laser diode driving device drives laser diodes with driving currents obtained by adding switch currents to corresponding bias currents and includes a common switch current generating circuit configured to generate a common switch current according to an input signal; switch current generating circuits provided for the corresponding laser diodes and configured to generate the switch currents based on the common switch current and input signals; switches configured to control the output of the switch currents to the corresponding laser diodes according to input signals; bias current generating circuits configured to generate the bias currents and output the generated bias currents to the corresponding laser diodes; and a control unit configured to detect the light intensities of the respective laser diodes and to control the common switch current generating circuit, the switch current generating circuits, and the switches to adjust the light intensities of the respective laser diodes.