Abstract: Embodiments herein describe an ASIC design where certain portions of the laser driver are controllable by the user. In one embodiment, the ASIC may include one or more pins which provide a connection interface where the user can electrically connect a sense resistor that corresponds to the particular laser being used. The remaining portions of the laser driver are implemented in the ASIC, thereby giving the user the flexibility to adapt the laser driver to her selected laser while having the advantages that come from using an ASIC.

Abstract: In some implementations, an electrical drive circuit may include a first optical load terminal to receive an anode of a first optical load. The electrical drive circuit may include a junction section that includes a first electrical junction and a second optical load terminal to receive a cathode of the first optical load and an anode of a second optical load. The electrical drive circuit may include a third optical load terminal to receive a cathode of the second optical load; a first switch connected between the third optical load terminal and a common ground; a coupling capacitor connected between the first electrical junction and a second electrical junction; a second switch connected between the second electrical junction and the common ground; and an inductor connected from a second branch of the second electrical junction and between the second electrical junction and the common ground.

Abstract: Embodiments of this application disclose a laser diode drive circuit and a LiDAR. The laser diode drive circuit includes a laser diode and a charging and discharging circuit. A cathode of the laser diode is grounded. The charging and discharging circuit is in a one-to-one correspondence with the laser diode, and includes an energy storage element, a first switch element, and a second switch element. The energy storage element is connected to an anode of the laser diode via the first switch element, and the energy storage element is grounded via the first switch element and the second switch element in sequence.

Abstract: A pulsed laser diode driver includes a refresh circuit configured to generate a refresh current using a received input voltage. A current amplitude of the refresh current is controlled by the refresh circuit based on a voltage level of a source voltage received by the refresh circuit. A source capacitor of the pulsed laser diode driver is configured to receive the refresh current and to develop the source voltage therefrom. An inductor of the pulsed laser diode driver has a first terminal that is directly electrically connected to the source capacitor. One or more switches of the pulsed laser diode driver are configured to control a current flow through the inductor to produce a high-current pulse through a laser diode that corresponds to a peak current of a resonant waveform developed at an anode of the laser diode.

Abstract: The DML driver includes: a post driver which supplies a driving current to the LD; and a pre-driver which drives the post driver in response to a modulated signal. The pre-driver has a transistor, a peaking inductor, a peaking inductor, a group delay inhibition inductor, and a peaking capacitor.

Abstract: In some implementations, an electrical drive circuit may generate a rectangular optical pulse using cathode pre-charge and cathode-pull compensation. The electrical drive circuit may include an anode and a cathode to connect an optical load, a switch, a first source connected between the anode and a ground, a rectifier connected between the cathode and the switch, a capacitor connected in parallel with the rectifier, a second source connected to the ground, and an inductor connected between the switch and the second source. In some implementations, when the switch is closed and the optical load is connected, a first current is provided to the optical load through the first source, the rectifier, and the switch, and a second current is provided to the optical load through the first source, the capacitor, and the switch, where a rise time of the first current complements a fall time of the second current.

Abstract: A light source device including a light emitting unit in which multiple light emitting elements including vertical cavity surface emitting lasers are arranged is intended to curb temperature rise. A light source device according to the present technology includes a light emitting unit in which multiple light emitting elements including vertical cavity surface emitting lasers are arranged, and a driving unit that, regarding the light emitting element in the light emitting unit, causes multiple light emitting elements to be caused to emit light in a light emission target period to emit light in a time-divided manner in the light emission target period. By adopting time-division light emission, the number of light emitting elements that are caused to emit light simultaneously is reduced.

Abstract: A high-side driver method for a laser of a Lidar, including: transforming a first input signal into a second input signal between a first voltage value and a second voltage value, by a level translation module; stepping down a first voltage signal according to a first voltage difference to obtain a second voltage signal, by a low-dropout linear regulator; generating a first control signal, by the first pre-driver module; generating a pulse current for driving the laser, by the first power switching transistor.

Abstract: A laser transmission system includes: a modulation module, a voltage-current conversion module, an electro-optic conversion module, an optic-electro conversion module, and a control module. The modulation module is configured to modulate an input voltage, and output a first voltage. An average value of the first voltage within a first duration is 0. The voltage-current conversion module is configured to output a first current based on the first voltage. The electro-optic conversion module is configured to output an optical signal corresponding to the first current. The optic-electro conversion module is configured to receive the optical signal from the analog optical fiber, and output a second voltage based on the optical signal. The control module is configured to determine an average value of the second voltage, and determine an electro-optic conversion coefficient of the electro-optic conversion module based on the average value of the second voltage.

Abstract: The present disclosure relates to the technical field of optical communication, and particularly to a laser emitting system, including a burst signal controller, a transfer switch, a power supply, a laser device and a bypass circuit, the burst signal controller is connected with the transfer switch and used for sending a burst control signal to the transfer switch, and the transfer switch is used for connecting the power supply to the laser device or the bypass circuit according to the burst control signal. The establishment time of an optical signal of a laser device can be shortened by using the laser emitting system of the present disclosure.

Abstract: A driving device that includes a temperature monitoring circuit, a headroom voltage monitoring circuit, a power supply voltage monitoring circuit, and a control unit. The temperature monitoring circuit detects a temperature of a drive circuit that drives a light emitting element in a test light emission period of the light emitting element. The headroom voltage monitoring circuit detects a headroom voltage of the drive circuit in the test light emission period. The power supply voltage monitoring circuit detects a power supply voltage supplied to the light emitting element in the test light emission period. The control unit adjusts the power supply voltage in the test light emission period according to an input/output potential difference of the light emitting element varying depending on the temperature of drive circuit so as to obtain a headroom voltage necessary and sufficient for causing a prescribed drive current to flow through the light emitting element.

Abstract: A method for operating a light emitting diode arrangement with at least one light emitting diode includes the steps of: a) determining at least one instantaneous current-voltage value pair; b) matching the instantaneous current-voltage value pair with an original current-voltage value pair; and c) determining an updated current feed based on the matching and driving the light emitting diode with the updated current feed.

Abstract: Disclosed is a pulse radar apparatus including a clock generator generating a transmission clock signal, a reception clock signal, and a sensitivity adjustment interval signal, a transmitter radiating a transmission pulse based on the transmission clock signal, and a receiver receiving a first pulse and a second pulse, which are associated with the transmission pulse, with different sensitivities based on the reception clock signal and the sensitivity adjustment interval signal.

Abstract: A pulsed laser diode driver includes a refresh circuit configured to generate a refresh current using a received input voltage. A current amplitude of the refresh current is controlled by the refresh circuit based on a voltage level of a source voltage received by the refresh circuit. A source capacitor of the pulsed laser diode driver is configured to receive the refresh current and to develop the source voltage therefrom. An inductor of the pulsed laser diode driver has a first terminal that is directly electrically connected to the source capacitor. One or more switches of the pulsed laser diode driver are configured to control a current flow through the inductor to produce a high-current pulse through a laser diode that corresponds to a peak current of a resonant waveform developed at an anode of the laser diode.

Abstract: A printing system is disclosed which comprises a writing module, and a member having an imaging surface configured to carry a polymer and movable relative to the writing module. The writing module is configured to direct onto the imaging surface a plurality of individually controllable light beams that are spaced from one another in a direction transverse to the direction of movement of the imaging surface, incidence of a light beam on a spot on the imaging surface serving to soften or liquefy the polymer carried by the imaging surface at the spot. The polymer softened or liquefied at the spot can transfer to a substrate or serve as an adhesive on the imaging surface. The writing module comprises a plurality of integrated electronic modules each having an array of individually controllable light sources, each light source producing a respective one of the light beams.

Abstract: In some implementations, an electrical drive circuit may generate a rectangular optical pulse using cathode pre-charge and cathode-pull compensation. The electrical drive circuit may include an anode and a cathode to connect an optical load, a switch, a first source connected between the anode and a ground, a rectifier connected between the cathode and the switch, a capacitor connected in parallel with the rectifier, a second source connected to the ground, and an inductor connected between the switch and the second source. In some implementations, when the switch is closed and the optical load is connected, a first current is provided to the optical load through the first source, the rectifier, and the switch, and a second current is provided to the optical load through the first source, the capacitor, and the switch, where a rise time of the first current complements a fall time of the second current.

Abstract: A light sensor having a control complexity reducing mechanism is provided. When light is emitted to a photodiode by both of an ambient light source and a light-emitting component, a first coarse count value is counted by a counter and then is sampled and held by a first sample and hold circuit. When light is emitted to the photodiode by only the ambient light source, a second coarse count value is counted by the counter and then is sampled and held by a second sample and hold circuit. After the coarse count values are held, the counter performs a fine counting operation on light intensity of the light emitted by both of the ambient light source and the light-emitting component to generate a first fine count value, and on light intensity of the light emitted by only the ambient light source to generate a second fine count value.

Abstract: A light source device that includes a first resistor that is connected to a given potential, a light emitting element that is connected in series to the first resistor, a second resistor that is connected to the given potential, and a first current source that is connected in series to the second resistor and that is configured to supply a freely-selected current within a given range are included. A first voltage is taken out from a first connection part where the first resistor and the light emitting element are connected to each other and a second voltage is taken out from a second connection part where the second resistor and the first current source are connected to each other.

Abstract: A circuit includes a controller circuit configured to receive an output voltage of a converter and adjust a switching frequency of the converter in response to a status of an output load and an output load sensing circuit configured to determine the status of the output load and provide the peak current to the controller circuit. The output load sensing circuit may include a first timer configured to provide a delayed first signal to a peak current control in response to the output load being a heavy load. A second timer may be configured to provide a delayed second signal to the peak current control in response to the output load being a light load. The peak current control may be configured to adjust a peak current based on the received first signal and the second signal and configured to provide the peak current to the controller circuit.

Abstract: The present disclosure relates to systems and methods that facilitate compliance of a laser device with a laser safety threshold. An example method includes receiving, from a sensing circuit, an operating voltage that is indicative of a charge of a capacitive element of a laser pulser circuit. The method also includes comparing a first voltage indicative of the operating voltage and a second voltage indicative of a reference voltage. The method additionally includes providing an output value based on the comparing. The method yet further includes evaluating compliance with the laser safety threshold based on the output value.

Abstract: The invention provides an optical system and method for outputting a modulated signal comprising a single multimode interference (MMI) device having at least two inputs configured with a fixed phase and an output, wherein the output modulated signal is controlled by modulating the input power of at 5 least one of the inputs. The invention only requires a single MMI device to operate as the relative phase between the two inputs are fixed relative each other and one of the inputs can be used to modulate the output by modulating the power at a single input. In further embodiments, the invention shows how correct phases can be set by a single MMI device. Thus, no more than two 10 MMIs are required in conjunction with phase or amplitude modulating elements to fully generate a BPSK or QPSK signal.

Abstract: Embodiments of the disclosure provide control systems and methods for controlling a pulsed laser diode and a sensing device including a pulsed laser diode. An exemplary control system includes a distance detector configured to generate a distance signal indicating a distance between the pulsed laser diode and an object reflecting pulsed laser beams emitted by the pulsed laser diode. The control system may also include a controller configured to dynamically control power supplied to the pulse laser diode based on the distance signal.

Abstract: An optoelectronic device includes a laser diode having a cathode terminal and an anode terminal, which is connected to a driving voltage. A driver is coupled to drive current pulses through the laser diode from the anode terminal to the cathode terminal. A discharge switch has a first switch terminal connected to the cathode terminal and a second switch terminal connected to a discharge voltage, which is equal to or greater than the driving voltage, and is configured, when closed, to raise the cathode terminal to the discharge voltage. A switch control circuit has an input connected to the cathode terminal and an output connected to close the discharge switch in response to the current pulses occurring at the input.

Abstract: A method for a calibration of at least one laser diode, in particular at least one laser diode of a laser projection device. The at least one laser diode is calibrated on the basis of a comparison of at least one currently acquired characteristic value of the at least one laser diode with at least one characteristic value, stored in at least one database, of a model laser diode that is at least substantially identical in construction to the at least one laser diode.

Abstract: An optoelectronic device includes a driver die including drive circuits and first bond pads on a front surface of the driver die. An emitter die is mounted on the front surface of the driver die and includes one or more vertical emitters and second bond pads connected to the vertical emitters. An encapsulation layer contains the emitter die and has an inner surface adjacent to the front surface of the driver die. Conductive vias extend through the encapsulation layer and have inner ends connected to the first bond pads and outer ends at an outer surface of the encapsulation layer. A redistribution layer is disposed over the outer surface of the encapsulation layer and includes conductive traces, each of which is connected to at least one terminal selected from a group of terminals consisting of the second bond pads and the outer ends of the conductive vias.

Abstract: A circuit includes a laser diode and a switched-capacitance charge pump coupled to control the laser diode. The charge pump can include a capacitor and a switching circuit that is capable of triggering a charge and discharge of the capacitor. The switching circuit can include a switch and an inverting circuit.

Abstract: The invention relates to a measuring apparatus for characterizing the electrical resistance of a measurement object, comprising an electric energy source having two poles, a voltage measuring device having two measuring inputs, four connecting contacts for the connection of four contact electrodes, and a switching device for the variable electrical pairwise connection of each one of the poles and measuring inputs to each one of the connecting contacts, forming different wiring configurations, wherein the measuring device is configured to carry out at least two measuring sequences with different wiring configurations and to determine the series resistance of the measurement object by incorporating the current and voltage signals acquired in these wiring configurations.

Abstract: An optical line terminal receives a sequence of optical power test transmissions from an optical network unit, wherein the sequence of optical power test transmissions includes a first plurality of consecutive optical transmissions, a second plurality of consecutive optical transmissions, and a third plurality of consecutive optical transmissions. The optical line terminal decides whether the optical network unit is malfunctioning based on an extinction ratio and an average transmit power, wherein the extinction ratio is based on the first plurality of consecutive optical transmissions and the second plurality of consecutive optical transmissions, and the average transmit power is based on the third plurality of consecutive optical transmissions.

Abstract: A driver circuit configured to increase or decrease a drive current flowing to a light emitting element in accordance with an input signal, the driver circuit including: an output terminal configured to be electrically connected between a bias current source and the light emitting element, and configured to draw an output current inward; a shunt circuit configured to generate a first current in accordance with the input signal; and a waveform shaping circuit configured to detect a rising transition of a voltage of the output terminal and generate a second current based at least in part on a result of detection, wherein the first current and the second current constitute the output current, Wherein the first current increases when the input signal increases, and decreases when the input signal decreases, and wherein the voltage of the output terminal rises when the output current decreases.

Abstract: Embodiments of the present disclosure provide a pixel circuit, an array substrate, a display device and a controlling method thereof. The pixel circuit includes: a pixel display unit consisted of n sub-pixel display units, n?3; and a data signal control unit coupled to the pixel display unit, n data lines for driving the pixel display unit and a control line. The data signal control unit is configured to, under a condition that a first control signal is input through the control line, couple the n sub-pixel display units to the n data lines for driving the n sub-pixel display units respectively; and when a second control signal is input through the control line, couple one of the n data lines for driving the pixel display unit to at least one of the n sub-pixel display units in the pixel display unit.

Abstract: The invention relates to a laser assembly, wherein, in one embodiment, the laser assembly (1) comprises a plurality of laser groups (2) each having at least one semiconductor laser (20). Furthermore, the laser assembly (1) contains a plurality of photothyristors (3), each laser group (2) being clearly assigned one of the photothyristors (3). The photothyristors (3) are each connected electrically in series with the associated laser group (2) and/or integrated in the associated laser group (2). Furthermore, the photothyristors (3) are each optically coupled to the associated laser group (2). A dark breakdown voltage (Ut) of each photothyristor (3) lies above an intended operating voltage (Ub) of the associated laser group (2).

Abstract: Disclosed is a pixel driving circuit, comprising a driving control circuit, a first driving circuit and a second driving circuit. The driving control circuit is configured to control one of the first driving circuit and the second driving circuit to be turned on under the condition the first scanning line outputs an effective voltage signal, and control the other of the first driving circuit and the second driving circuit to be turned on under the condition the second scanning line outputs an effective voltage signal. The first driving circuit is configured to drive the light emitting circuit to emit light under control of the driving control circuit. The second driving circuit is configured to drive the light emitting circuit to emit light under control of the driving control circuit.

Abstract: A tunable optical source includes a substrate, a light source disposed on the substrate, and a wavelength selecting element configured to select light of a specific wavelength as output light, from light emitted from the light source, in accordance with a control signal. On the substrate, a wavelength filter including multiple output ports and a photodetector are disposed. The wavelength filter is configured to receive a part of the output light and to output light beams to the respective output ports. The photodetector is configured to receive the light beam output from one of the output ports. The tunable optical source further includes an inspection waveguide connecting to the photodetector at one end, and an inspection light input unit for inputting inspection light provided at the other end of the inspection waveguide.

Abstract: The amount of current provided to a laser diode of an optical network transceiver device is monitored, the amount of current reaching a threshold limit is detected, and the power output of the optical network transceiver device is monitored. Based at least in part on the detection that the amount of current has reached the threshold limit and the monitored power output of the optical network transceiver device, a likelihood of failure of the optical network transceiver device is predicted.

Abstract: An optical communication apparatus includes: a light-receiving device that receives an optical signal transmitted from another optical communication apparatus through an optical fiber and converts the optical signal into an electrical signal; a first measurement circuit that measures an average power and a modulation power of the optical signal based on the electrical signal; a light-emitting device that transmits the optical signal to the another optical communication apparatus by emitting light in accordance with a driving current; a driver that causes the light-emitting device to transmit the optical signal according to a transmission signal by controlling the driving current based on the transmission signal; and a processor that adjusts the driving current based on the average power and the modulation power.

Abstract: A system for dynamically adjusting a bias voltage for a laser diode or a light emitting diode is provided. An output voltage of the laser diode is measured and a level of a supply voltage applied to the laser diode is adjusted to change the bias voltage to the laser diode to manage power usage and avoid saturation of the laser diode. Also, a junction temperature of a laser diode may be estimated by mapping a measured output voltage and known current to device characteristic data based on temperature and the supply voltage adjusted in order to bias the laser diode to compensate for a temperature change. Further, data indicating an intensity level of data to be rendered by the laser diode is used to adjust the second supply voltage to bias the laser diode in advance of rendering the data.

Abstract: Disclosed is a frequency characteristic adjusting circuit disposed between an optical circuit element and a drive circuit driving the optical circuit element. The frequency characteristic adjusting circuit includes a capacitor, and two or more series circuits having a resistor and a switch, the two or more series circuits being connected in parallel with the capacitor, where resistance with respect to the switch that is turned on is changed according to an output voltage of the drive circuit by changing ON or OFF of the switch such that electric charge at a contact point between the optical circuit element and the capacitor is adjusted to be constant regardless of the output voltage of the drive circuit.

Abstract: A slider configured for heat-assisted magnetic recording includes a laser diode optically coupled to a waveguide of the slider. A power supply is coupled to the laser diode. A preamplifier is coupled to the power supply. The preamplifier is configured to monitor a forward voltage across the laser diode while operating the laser diode at a constant current during a write operation, detect a change in the forward voltage indicative of laser power instability, and generate a signal in response to detecting the forward voltage change.

Abstract: A headlamp with a light source, an electrical power source and several states controlling power sources and light beams is presented. The first state corresponds to at least one activated state in which the electrical power source is coupled to a light source to generate a light beam. The second state corresponds to a deactivated state where the electrical power source is not coupled to a light source and no light beam is generated. The third state corresponds to a locked state in which the electrical power source is not coupled to a light source and no light beam is generated; Also included is a switching mechanism to receive a first and a second physical user input through one switching element. A processor is coupled to the switching mechanism and is used to select one among the first, second and third states in response to the physical user inputs.

Abstract: In some embodiments, an apparatus includes an optical detector that can sample asynchronously an optical signal from an optical component that can be either an optical transmitter or an optical receiver. In such embodiments, the apparatus also includes a processor operatively coupled to the optical detector, where the processor can calculate a metric value of the optical signal without an extinction ratio of the optical signal being measured. The metric value is proportional to the extinction ratio of the optical signal. In such embodiments, the processor can define an error signal based on the metric value of the optical signal and the processor can send the error signal to the optical transmitter such that the optical transmitter modifies an output optical signal.

Abstract: According to one embodiment, a current outputting circuit includes an output node, a first circuit outputting a first signal and a second signal based on an input signal, the first and second signals having phases of complementary relationship, and a second circuit outputting an output current from the output node based on the first and second signals. The second circuit includes a first current source with a first terminal and a second terminal, the first terminal being connected to a first power source, and a first transistor with a third terminal, a fourth terminal and a fifth terminal, the first signal being input to the third terminal, the fourth and fifth terminals sandwiching a first current path controlled by the first signal, the fourth terminal being connected to the second terminal, the fifth terminal being connected to the output node. The second signal is input to the fifth terminal.

Abstract: Disclosed are batteries and methods of manufacturing batteries with improved energy densities. In some embodiments, a first cathode current collector and a first anode current collector are provided on a first side of a substrate. A second cathode current collector and a second anode current collector are provided on a second side of the substrate. A laser is used to form: a first channel through the substrate between the first cathode current collector and the second cathode current collector, and a second channel through the substrate between the first anode current collector and the second anode current collector. A cathode interconnection is formed, via the first channel, between the first cathode current collector and the second cathode current collector. An anode interconnection is formed, via the second channel, between the first anode current collector and the second anode current collector.

Abstract: An EUV light source is disclosed which may comprise a plurality of targets, e.g., tin droplets, and a system generating pre-pulses and main-pulses with the pre-pulses for irradiating targets to produce expanded targets. The system may further comprise a continuously pumped laser device generating the main pulses with the main pulses for irradiating expanded targets to produce a burst of EUV light pulses. The system may also have a controller varying at least one pre-pulse parameter during the burst of EUV light pulses. In addition, the EUV light source may also include an instrument measuring an intensity of at least one EUV light pulse within a burst of EUV light pulses and providing a feedback signal to the controller to vary at least one pre-pulse parameter during the burst of EUV light pulses to produce a burst of EUV pulses having a pre-selected dose.

Abstract: An optical semiconductor device includes: an electric-optic conversion element that is provided with a diode; and a driving circuit that drives the diode in a forward direction, the driving circuit including a first switching circuit that is provided with a first switch, and a second switching circuit that is provided with a second switch, wherein the first switching circuit constitutes a first signal line that charges the electric-optic conversion element with an electric charge by bringing the first switch into an ON state and the second switch into an OFF state, and the second switching circuit constitutes a second signal line that discharges the electric charge stored in the electric-optic conversion element by bringing the second switch into an ON state and the first switch into an OFF state.

Abstract: There is provided a light source apparatus including at least one light emitting diode (LED) string including at least one light emitting diode and at least one inductance unit generating an induced current according to a change in a current applied to the light emitting diode, a main switch controlling power applied to the LED string according to an on/off switching operation, and a capacitor charged with a voltage of the power applied to the LED string when the main switch is switched on and applying the charged voltage to the LED string when the main switch is switched off.

Abstract: A method and apparatus for powering up and powering down a laser diode and its driver are disclosed. The disclosed method and apparatus enable the use of deep sub-micron CMOS technology to build a laser diode driver (LDD), while ensuring the low voltage limits prescribed by such technology are not exceeded. Building an LDD with deep sub-micron CMOS technology pushes circuit integration further ahead, bringing cost of LDDs and required board circuits down.

Abstract: A light emitting device includes: a light emitting element; and a light variable resistive element which is connected to the light emitting element in parallel and is provided at a position which is irradiated with light emitted from the light emitting element, wherein the light variable resistive element has a characteristic in which a resistance value decreases as an amount of irradiation light increases.

Abstract: A control apparatus for driving a laser diode comprises an output connection for connecting the laser diode, a regulation device for generating an output signal, a detector device which is designed to determine a regulation variable when the regulation device provides the output signal and the laser diode is connected to the output connection. The control apparatus furthermore comprises a computer device for providing a control signal for the regulation device, wherein the computer device provides the control signal independently of the regulation variable. The regulation device is designed in such a way that it generates a level for the output signal depending on the control signal and the determined regulation variable.

Abstract: A light emitting device includes: a light emitting element; and a temperature variable resistive element which is connected to the light emitting element in parallel and is provided so that heat of the light emitting element can be conducted, wherein the temperature variable resistive element has a characteristic in which a resistance value decreases as a temperature increases.

Abstract: A voltage mode laser diode driver selectively turns on and off a laser diode. An output stage has an output node configured to be connected to one of the terminals of the laser diode. Depending upon implementation, an active swing controller drives the output stage in a manner that substantially prevents inductive kickback from causing the output node voltage to swinging above the voltage level at the voltage output of the power supply, or swing below ground. The output stage provides a discharge path around the laser diode to shunt current associated with the inductive kickback, and substantially eliminates ringing on the output node of the output stage while the laser diode is off. A power supply controller adjusts the voltage level of the voltage output of the power supply so that current through the laser diode when on and emitting light is substantially equal to a predetermined desired current.