JP2008192717A - Laser light source device, projector and monitor device, and semiconductor laser driving method - Google Patents

Abstract

In a laser light source device using a semiconductor laser, output efficiency is improved.
A laser light source device according to the present invention provides a semiconductor laser with a pulsed drive voltage having a peak value equal to or higher than a laser oscillation start voltage corresponding to a laser oscillation start current of the semiconductor laser. And a semiconductor laser driving circuit for driving the semiconductor laser by applying. The semiconductor laser drive circuit is a bias having a voltage value that is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before the start of application of the pulsed drive voltage to the semiconductor laser. A voltage is applied to the semiconductor laser.
[Selection] Figure 1

Description

  The present invention relates to a laser light source device, a projector and a monitor device, and a semiconductor laser driving method.

  Conventionally, an ultra-high pressure mercury lamp (UHP) has been generally used as a light source for a projector that enlarges and projects an image. However, UHP requires several minutes to reach the maximum luminance, so there are various problems such as difficulty in instantaneous lighting, relatively short life, and insufficient color reproducibility range. Was. Therefore, in recent years, a technique using a semiconductor laser as a light source is being developed (see, for example, Patent Document 1).

  A semiconductor laser starts laser oscillation and emits laser light by applying a drive voltage to a laser diode constituting the semiconductor laser so that a drive current having a current value equal to or greater than the laser oscillation start current flows. Is. However, applying a DC drive voltage to the laser diode is not desirable for extending the life. Therefore, normally, a pulsed drive voltage is applied to the laser diode to flow a pulsed drive current. The output light quantity of the laser light emitted from the semiconductor laser is controlled by adjusting the pulse height of the drive voltage and the pulse width of the drive voltage.

  Here, since the rising speed of the waveform of the drive current that flows when a pulsed drive voltage is applied to the semiconductor laser is slow due to the characteristics of the laser diode itself and the parasitic elements of the wiring, the desired output light quantity In order to obtain the above, there is a problem that it is necessary to apply a driving voltage having an excessive voltage value to flow a desired driving current, resulting in poor efficiency.

  In the field of optical communications, in order to realize a steep rise in drive current, a DC bias voltage is applied to the laser diode in advance, and a DC bias current (current slightly smaller than the laser oscillation start current) just before laser oscillation starts. It is considered that the rising speed of the drive current is increased by passing the current (for example, see Patent Document 2).

  However, when a laser light source device using a semiconductor laser is applied to a lighting application such as a projector, the output of the desired laser light needs to be several tens of times larger than that in the case of optical communication. For this reason, for example, a laser diode that constitutes a semiconductor laser has a large output and a very large laser oscillation start current.

  In such a laser light source apparatus using a semiconductor laser, if the above-described optical communication method is used to solve the above-described problem, a very large DC bias current will flow and the efficiency will deteriorate. There is. In addition, the DC bias current becomes a loss, and heat generated by the loss becomes very large, and there is a problem that the cooling device becomes very large for cooling the heat generation.

JP-A-2005-99160 JP 2002-270948 A

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a technique capable of improving output efficiency in a laser light source device using a semiconductor laser.

In order to solve at least a part of the above problems, the present invention may be configured as the following laser light source device. That is,
A laser light source device that emits laser light,
A semiconductor laser;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A bias voltage having a voltage value is applied to the semiconductor laser.

  In the laser light source device of the present invention, a bias voltage is applied for a certain period immediately before the application of a pulsed drive voltage is started and the semiconductor laser is driven. As a result, the steep rise of the drive current can be realized as in the case of applying the DC bias voltage described in the prior art, so that the output efficiency can be improved as compared with the case where no bias voltage is applied. It is.

  Also, since a DC bias voltage is not applied but only a bias voltage is applied for a certain period of time, loss generated when a DC bias voltage is applied is reduced, and heat generation due to this loss is reduced. Therefore, it is possible to improve the output efficiency with respect to the input power of the semiconductor laser. Furthermore, the reduction of the heat generation due to this loss also allows the cooling device for cooling the heat generation to be downsized.

  Here, the bias voltage may be a voltage value corresponding to a current having a current value of 90% or less of the laser oscillation start current. The predetermined period may be in the range of 0.5 microsecond to 2 microseconds.

  In this way, it is possible to easily set a bias voltage that can realize a steep rise of the drive current.

  The semiconductor laser drive circuit may omit application of the bias voltage when the pulse length of the pulsed drive voltage is five times or more of the predetermined period. .

  According to the above, in the case where the pulse length of the pulsed drive voltage is 5 times or more of the predetermined period, it is possible to reduce the loss generated by applying the bias voltage.

The present invention may be configured as a projector as follows. That is,
A projector that projects an image according to an input image signal,
A laser light source device for emitting laser light;
A projection unit that projects light modulated according to the image signal,
The laser light source device
A semiconductor laser;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A bias voltage having a voltage value is applied to the semiconductor laser.

  With such a configuration, the subject can be illuminated brightly with a high-power laser beam, so that a high-luminance image can be projected.

Further, the present invention may be configured as the following monitor device. That is,
A monitor device for outputting a photographed subject,
A laser light source device for emitting laser light;
A diffusion element for diffusing the light emitted from the laser light source device;
An imaging unit that images a subject illuminated by the diffusing element,
The laser light source device
A semiconductor laser;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A bias voltage having a voltage value is applied to the semiconductor laser.

  With such a configuration, the subject can be illuminated brightly with a high-power laser beam, so that a clear image can be taken.

In addition, the present invention can be configured as the following semiconductor laser driving method. That is,
A semiconductor laser driving method for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to a laser oscillation starting current of the semiconductor laser to the semiconductor laser,
A bias voltage having a voltage value equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before the application of the pulsed drive voltage to the semiconductor laser is started. And applying to the semiconductor laser.

  In the above method, a bias voltage is applied for a certain period immediately before the application of a pulsed drive voltage is started and the semiconductor laser is driven. As a result, the steep rise of the drive current can be realized as in the case of applying the DC bias voltage described in the prior art, so that the output efficiency of the semiconductor laser is improved as compared with the case where no bias voltage is applied. It is possible.

  Also, since a DC bias voltage is not applied but only a bias voltage is applied for a certain period of time, loss generated when a DC bias voltage is applied is reduced, and heat generation due to this loss is reduced. Therefore, it is possible to improve the output efficiency of the semiconductor laser. Furthermore, the reduction of the heat generation due to this loss also allows the cooling device for cooling the heat generation to be downsized.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment (laser light source device):
B. Second embodiment (monitor device):
C. Third embodiment (projector):
D. Variation:

A. First embodiment (laser light source device):
FIG. 1 is a schematic configuration diagram of a laser light source device 100 as a first embodiment of the present invention. As illustrated, the laser light source device 100 includes a semiconductor laser 110 and a filter 120 that constitute a laser light source that emits laser light, a semiconductor laser driving circuit 130 that drives the semiconductor laser 110, and an optical sensor 140. .

  The semiconductor laser 110 is configured by one laser diode or a laser diode array having a plurality of laser diodes.

  When the drive voltage DPv applied from the semiconductor laser drive circuit 130 is applied to the semiconductor laser 110, a drive current DPi corresponding to the drive voltage DPv flows, and when the drive current DPi is larger than a laser oscillation start current described later, Oscillates and emits laser light.

  The filter 120 blocks light having an unnecessary wavelength out of the laser light emitted from the semiconductor laser 110 and passes only light having the required wavelength, thereby increasing the purity of the wavelength of the laser light LB emitted from the laser light source device 100. .

  The semiconductor laser drive circuit 130 includes a switch circuit 132 and a switch control circuit 134.

  The switch circuit 132 includes, for example, two switches S1 and S2 and one diode D1. The switch circuit 132 is input to the switch circuit 132 as described later by turning on / off the two switches S1 and S2 in accordance with the two switch control signals CTLS1 and CTLS2 input from the switch control circuit 134. A pulsed drive voltage DPv based on the two drive voltage generation voltages V 1 and V 2 (<V 1) is generated and applied to the semiconductor laser 110. The two drive voltage generation voltages V1 and V2 are generated by a voltage generation circuit such as a DC / DC converter, for example, and input to the switch circuit 132.

  The switch control circuit 134 outputs two switch control signals CTLS1 and CTLS2 according to the sensor signal input from the optical sensor 140.

  Here, the optical sensor 140 detects the amount of light blocked by the filter 120 (light having an unnecessary wavelength), and outputs a sensor signal corresponding to the detected amount of light. The light blocked by the filter 120 and the light that has passed through the filter 120 (light having a required wavelength) have a correlation with each output light amount. If the light amount of unnecessary wavelength light is known, the light having the required wavelength is obtained. Can be estimated.

  Therefore, the switch control circuit 134 responds to the sensor signal input from the optical sensor 140 so that the output light amount of the laser light LB emitted from the laser light source device 100 becomes a predetermined output light amount set in advance. The pulse widths of the two switch control signals CTLS1 and CTLS2 are adjusted.

  As described above, the semiconductor laser drive circuit 130 switches on / off the two switches S1, S2 of the switch circuit 132 based on the two switch control signals CTLS1, CTLS2 output from the switch control circuit 134. A pulsed drive voltage DPv based on the two drive voltage generation voltages V 1 and V 2 input to the circuit 132 is generated and applied to the semiconductor laser 110 to drive the semiconductor laser 110.

  Here, the two drive voltage generation voltages V1 and V2 are set to voltages described below.

  FIG. 2 is an explanatory diagram showing an output light amount with respect to a drive current flowing through a laser diode constituting the semiconductor laser 110 and a drive voltage corresponding to the drive current.

  The first drive voltage generation voltage V1 is a voltage equal to or higher than the laser oscillation start voltage Vst corresponding to the laser oscillation start current Ist, and is a current (hereinafter referred to as “laser oscillation current”) that provides a desired light output light quantity Pt. The voltage corresponding to Idv (hereinafter referred to as “laser oscillation voltage”) Vdv is set.

  The second drive voltage generation voltage V2 is a voltage higher than the operation start voltage Vdon at which the laser diode starts operating as a diode and starts to flow, and is smaller than the laser oscillation start current Ist and does not cause laser oscillation. (Hereinafter referred to as “bias current”.) The voltage at which Ibs flows (hereinafter referred to as “bias voltage”) Vbs is set. Here, in order to simplify the description, the forward voltage Vf of the diode D1 is omitted. The actual V2 is a voltage obtained by adding Vf to Vbs. Specifically, for example, since the laser oscillation start current Ist usually varies about ± 10%, even if the laser oscillation start current Ist varies, the bias current Ibs is biased to prevent laser oscillation. The current Ibs is preferably set to 90% or less of the laser oscillation start current Ist.

  FIG. 3 is an explanatory diagram showing the drive voltage DPv applied to the semiconductor laser 110 by the semiconductor laser drive circuit 130 and the drive current DPi flowing through the semiconductor laser 110 based on the drive voltage DPv.

  As shown in FIG. 3A, the switch control circuit 134 (FIG. 1) outputs a pulse signal having a pulse width Wdv as the first switch control signal CTLS1 for controlling the first switch S1, as shown in FIG. For convenience of explanation, the rising times of the first switch control signal CTLS1 shown in FIG. The switch control circuit 134 outputs a pulse signal having a cycle Tdv as a second switch control signal CTLS2 for controlling the second switch signal S2, as shown in FIG. However, the second switch control signal CTLS2 rises at times t0 and t3 that are a fixed period Wbs before the rise times t1 and t4 of the first switch control signal CTLS1 and falls at the fall time of the switch control signal CTLS1, that is, This is a pulse signal with a pulse width (Wbs + Wdv) that falls from the time t1, t4 at the same timing as the time t2, t5 after the elapse of a period equal to the pulse width Wdv of the switch control signal S1.

  In the period from time t0 to time t1, only the second switch control signal SCLT2 rises, so only the switch S2 is turned on. As a result, as shown in FIG. 3C, the drive voltage DPv is the second drive voltage generation voltage V2, that is, the bias voltage Vbs (strictly, the voltage equal to the forward voltage of the diode D1 from the bias voltage Vbs). The voltage of the lowered value) is applied to the semiconductor laser 110, and a bias current Ibs corresponding to the bias voltage Vbs flows to the semiconductor laser 110 as shown in FIG. Here, as described above, since the bias current Ibs is a current that does not cause laser oscillation, the semiconductor laser 110 operates as a semiconductor but cannot perform laser oscillation (hereinafter also referred to as “idling state”). ) And does not emit laser light.

  In the period from time t1 to time t2, since both the two switch control signals SCLT1 and SCLT2 rise, both the switch S1 and the switch S2 are turned on. However, as described above, since the second drive voltage generation voltage V2, that is, the bias voltage Vbs is smaller than the first drive voltage generation voltage V1, that is, the laser oscillation voltage Vdv, the diode D1. Is in a reverse bias state. As a result, as shown in FIG. 3C, only the first drive voltage generation voltage V1, that is, the laser oscillation voltage Vdv, is applied to the semiconductor laser 110 as the drive voltage DPv, as shown in FIG. As described above, a laser oscillation current Idv corresponding to the laser oscillation voltage Vdv flows through the semiconductor laser 110. As a result, a laser oscillation current Idv rising from the bias current Ibs flows through the semiconductor laser 110, and during this period, the semiconductor laser 110 performs laser oscillation and emits laser light with an output light amount corresponding to the laser oscillation current Idv.

  In addition, since both the two switch control signals SCLT1 and SCLT2 are falling during the period from time t2 to t3, both the switch S1 and the switch S2 are turned off. As a result, no voltage is applied to the semiconductor laser 110 as the drive voltage DPv as shown in FIG. 3C, and no current flows through the semiconductor laser 110 as shown in FIG. Thus, the semiconductor laser 110 does not oscillate and does not emit laser light during this period.

  Since the operation after time t3 is a repetition from time t0 to time t3, description thereof is omitted.

  As described above, the laser diode of the semiconductor laser 110 is in the period from time t1 to time t2 (which is a period equal to the pulse width Wdv of the first switch control signal CTLS1, hereinafter also referred to as “laser oscillation period”). Since the bias voltage Vbs is applied during the period from the previous time t0 to t1 (equal to the fixed period Wbs, hereinafter also referred to as “bias period”), the bias current Ibs is set so as not to cause laser oscillation. The rise of the drive current DPi can be made steep compared to the case where no current is passed before the laser oscillation period (indicated by a broken line in FIG. 3D). As a result, the efficiency of the optical output of the semiconductor laser with respect to the drive current can be increased.

  In addition, since the bias current is supplied only during a certain period (bias period) immediately before the laser oscillation period, the current loss is reduced by reducing the current loss as compared with the case where the DC bias current as described in the prior art is supplied. Since heat generation due to loss can be suppressed, a cooling device for heat dissipation can be simplified.

  If the length of the bias period for supplying the bias current Ibs, that is, the fixed period Wbs for applying the bias voltage Vbs is 0.5 microseconds, the rise time of the bias current Ibs can be secured. Further, even if the length of the fixed period Wbs is 2 microseconds or more, the rising speed of the drive current during laser oscillation hardly changes and the current loss increases. Therefore, the length of the fixed period Wbs for applying the bias voltage Vbs is preferably set in the range of 0.5 microseconds to 2 microseconds.

  Further, as described above, the length of the laser oscillation period corresponding to the pulse width Wdv of the first switch control signal CLTS1 varies depending on the set output light amount. When the length of the bias period corresponding to the fixed period Wbs immediately before the period is sufficiently long, for example, when the length is five times or more, the influence of the rising of the drive current becomes small, and the laser In this case, the application of the bias voltage may be omitted because the necessity of flowing a bias current before the oscillation starts is reduced.

B. Second embodiment (monitor device):
FIG. 4 is a schematic configuration diagram of a monitor device 400 as a second embodiment of the present invention. The monitor device 400 includes a device main body 410 and an optical transmission unit 420. The apparatus main body 410 includes the laser light source apparatus 100 of the first embodiment described above.

  The light transmission unit 420 includes two light guides 421 and 422 on the light sending side and the light receiving side. Each of the light guides 421 and 422 is a bundle of a large number of optical fibers, and can send laser light to a distant place. The laser light source device 100 is disposed on the incident side of the light guide 421 on the light transmission side, and the diffusion plate 423 is disposed on the emission side thereof. The laser light emitted from the laser light source device 100 is transmitted to the diffusion plate 423 provided at the tip of the light transmission unit 420 through the light guide 421 and is diffused by the diffusion plate 423 to irradiate the subject.

  An imaging lens 424 is also provided at the tip of the light transmission unit 420, and reflected light from the subject can be received by the imaging lens 424. The received reflected light travels through the light guide 422 on the receiving side and is sent to a camera 411 as an imaging means provided in the apparatus main body 410. As a result, the camera 411 can capture an image based on the reflected light obtained by irradiating the subject with the laser light emitted from the laser light source device 100.

  According to the monitor device 400 configured as described above, the high-power laser light source device 100 can irradiate the subject, so that the camera 411 can clearly capture an image.

C. Third embodiment (projector):
FIG. 5 is a schematic configuration diagram of a projector 500 as a third embodiment of the invention. In the drawing, a casing constituting the projector 500 is omitted for simplification. The projector 500 includes a red laser light source device 501R that emits red light, a green laser light source device 501G that emits green light, and a blue laser light source device 501B that emits blue light.

  The laser light source devices 501R, 501G, and 501B of the respective colors have the same configuration as the laser light source device 100 of the first embodiment described above except that the laser light beams LBr, LBg, and LBb of the corresponding colors are emitted. is doing.

  In addition, the projector 500 is a liquid crystal light valve (modulation) that modulates the laser beams LBr, LBg, and LBb of each color emitted from the laser light source devices 501R, 501G, and 501B of each color according to image signals sent from a personal computer or the like. Image) formed by the liquid crystal light valves 504R, 504G, and 504B, the cross dichroic prism 506 that combines the light emitted from the liquid crystal light valves 504R, 504G, and 504B and guides the light to the projection lens 507. And a projection lens 507 as a projection optical system for enlarging and projecting the image on the screen 510.

  Further, in order to make the illuminance distribution of the laser light emitted from each of the laser light source devices 501R, 501G, and 501B uniform, the projector 500 places the integrator optical system 502R on the optical path downstream side of each of the laser light source devices 501R, 501G, and 501B. , 502G, and 502B are provided, and the liquid crystal light valves 504R, 504G, and 504B are illuminated by the light having a uniform illuminance distribution. For example, the integrator optical systems 502R, 502G, and 502B are configured using a rod lens, a lens array, an optical element such as a hologram element, a field lens, and the like.

  The three color lights modulated by the liquid crystal light valves 504R, 504G, and 504B are incident on the cross dichroic prism 506. This prism is formed by bonding four right-angle prisms, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are arranged in a cross shape on the inner surface thereof. These dielectric multilayer films combine the three color lights to form light representing a color image. The synthesized light is projected onto the screen 510 by the projection lens 507, which is a projection optical system, and an enlarged image is displayed.

  According to the projector 500 configured as described above, since the high-power laser light source devices 501R, 501G, and 501B can be used, a high-luminance image can be displayed.

D. Variation:
As mentioned above, although the various Example of this invention was described, it cannot be overemphasized that this invention is not limited to these Examples, and can take a various structure in the range which does not deviate from the meaning. For example, the following modifications are possible.

(1) The present invention can be applied as a semiconductor laser resonance structure without distinction between an internal resonance type and an external resonance type. Also, the structure of the laser diode constituting the semiconductor laser can be applied regardless of whether it is a surface emitting type or an edge emitting type.
The

(2) In the above embodiment, the semiconductor laser drive circuit 130 is configured by the switch circuit 132 and the switch control circuit 134, and the switch circuit 132 is configured by the two switches S1 and the one diode D1. However, the present invention is not limited to this, and as the drive voltage DPv, the laser oscillation voltage Vdv is output during a period in which a pulsed drive voltage is applied (laser oscillation period), and during a certain period (bias period) immediately before the laser oscillation period. Any configuration is possible as long as the configuration can output the bias voltage Vbs.

  (3) The projector 500 of the third embodiment is a so-called three-plate type liquid crystal projector. Instead of this, the laser light source device is turned on in a time-sharing manner for each color so that only one light valve is used. A single-plate liquid crystal projector having a configuration that enables display may be used. Also, it can be used as a scanning projector that displays an image by scanning a laser beam modulated in accordance with an image signal.

It is a schematic block diagram of the laser light source apparatus 100 as 1st Example of this invention. 3 is an explanatory diagram showing a light emission output with respect to a drive current flowing in a laser diode constituting the semiconductor laser 110 and a drive voltage corresponding to the drive current. FIG. It is explanatory drawing which shows the drive current DPi which flows into the semiconductor laser 110 based on the drive voltage DPv applied to the semiconductor laser 110 by the semiconductor laser drive circuit 130. It is a schematic block diagram of the monitor apparatus 400 as 2nd Example of this invention. It is a schematic block diagram of the projector 500 as 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Laser light source device 110 ... Semiconductor laser 120 ... Filter 130 ... Semiconductor laser drive circuit 132 ... Switch circuit 134 ... Switch control circuit 140 ... Optical sensor 400 ... Monitor apparatus 410 ... Device main body 411 ... Camera 420 ... Optical transmission part 421,422 ... light guide 423 ... diffusing plate 424 ... imaging lens 500 ... projector 501B ... blue laser light source device 501G ... green laser light source device 501R ... red laser light source device 502R, 502G, 502B ... integrator optical system 504R, 504G, 504B ... liquid crystal light Valve 506 ... Cross dichroic prism 507 ... Projection lens 510 ... Screen

Claims (7)

A laser light source device,
A semiconductor laser that emits laser light;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A laser light source device, wherein a bias voltage having a voltage value is applied to the semiconductor laser. The laser light source device according to claim 1,
The laser light source device, wherein the bias voltage is a voltage value corresponding to a current having a current value of 90% or less of the laser oscillation start current. The laser light source device according to claim 1 or 2,
The laser light source device according to claim 1, wherein the predetermined period is in a range of 0.5 microseconds to 2 microseconds. A laser light source device according to any one of claims 1 to 3,
The semiconductor laser driving circuit omits application of the bias voltage when the pulse length of the pulsed driving voltage is five times or more of the predetermined period. apparatus. A projector that projects an image according to an input image signal,
A laser light source device;
A projection unit that projects light modulated according to the image signal,
The laser light source device
A semiconductor laser that emits laser light;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A projector that applies a bias voltage having a voltage value to the semiconductor laser. A monitor device for outputting a photographed subject,
A laser light source device;
A diffusion element for diffusing the light emitted from the laser light source device;
An imaging unit that images a subject illuminated by the diffusing element,
The laser light source device
A semiconductor laser that emits laser light;
A semiconductor laser driving circuit for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to the laser oscillation starting current of the semiconductor laser to the semiconductor laser; Prepared,
The semiconductor laser drive circuit is equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before starting to apply the pulsed drive voltage to the semiconductor laser. A monitoring apparatus, wherein a bias voltage having a voltage value is applied to the semiconductor laser. A semiconductor laser driving method for driving the semiconductor laser by applying a pulsed driving voltage having a peak value equal to or higher than a laser oscillation starting voltage corresponding to a laser oscillation starting current of the semiconductor laser to the semiconductor laser,
A bias voltage having a voltage value equal to or higher than the operation start voltage of the semiconductor laser and smaller than the laser oscillation start voltage in a certain period immediately before the application of the pulsed drive voltage to the semiconductor laser is started. And applying to the semiconductor laser. A method for driving a semiconductor laser.

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