WO2010004749A1 - 波長変換レーザ光源、これを備えたプロジェクションディスプレイ装置、液晶ディスプレイ装置及びレーザ光源 - Google Patents
波長変換レーザ光源、これを備えたプロジェクションディスプレイ装置、液晶ディスプレイ装置及びレーザ光源 Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/37—Non-linear optics for second-harmonic generation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/355—Non-linear optics characterised by the materials used
- G02F1/3558—Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/12—Picture reproducers
- H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
- H04N9/3141—Constructional details thereof
- H04N9/315—Modulator illumination systems
- H04N9/3161—Modulator illumination systems using laser light sources
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
- G02F1/3544—Particular phase matching techniques
- G02F1/3546—Active phase matching, e.g. by electro- or thermo-optic tuning
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
- H01S3/0092—Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
- H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/105—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
- H01S3/1053—Control by pressure or deformation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
- H01S3/109—Frequency multiplication, e.g. harmonic generation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/1306—Stabilisation of the amplitude
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/1312—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation by controlling the optical pumping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
- H01S3/2383—Parallel arrangements
- H01S3/2391—Parallel arrangements emitting at different wavelengths
Definitions
- the present invention relates to a wavelength conversion laser light source that converts the wavelength of laser light emitted from a laser light source by a nonlinear optical effect, a projection display device including the same, a liquid crystal display device, and a laser light source.
- visible light such as green light is obtained by converting the wavelength of light oscillated from an Nd: YAG laser or Nd: YVO 4 laser using a nonlinear optical effect, or ultraviolet light obtained by further converting green light.
- Nd: YAG laser or Nd: YVO 4 laser using a nonlinear optical effect
- ultraviolet light obtained by further converting green light.
- Many wavelength conversion laser light sources for obtaining laser light have been developed and put into practical use. These converted lights are used for applications such as laser processing and laser display.
- FIG. 1 A general configuration example of a conventional wavelength conversion laser light source using a nonlinear optical effect is shown in FIG.
- a nonlinear optical crystal having a birefringence LiB 3 O 5 (lithium triborate: LBO), KTiOPO 4 (potassium titanyl phosphate: KTP), CsLiB 6 O 10 (cesium lithium borate: CLBO), LiNbO 3 (lithium niobate: PPLN), LiTaO 3 (lithium tantalate: PPLT) or the like having a domain-inverted structure has been used.
- LiB 3 O 5 lithium triborate: LBO
- KTiOPO 4 potassium titanyl phosphate: KTP
- CsLiB 6 O 10 cesium lithium borate: CLBO
- LiNbO 3 lithium niobate: PPLN
- LiTaO 3 lithium tantalate: PPLT
- the wavelength conversion laser light source 100 includes a fundamental wave light source 101, a condenser lens 108, a wavelength conversion element (nonlinear optical crystal) 109, a recollimator lens 111, a wavelength separation mirror 113, and a temperature of the wavelength conversion element 109.
- a temperature holding device 116 such as a heater for keeping the temperature constant, a control device 115 for controlling the laser output, and a temperature controller 122 for controlling the temperature of the nonlinear optical crystal disposed in the control device 115 are included.
- the fundamental light source 101 a fiber laser using a Nd: YAG laser, a Nd: YVO 4 laser, a Yb-doped fiber, or the like having a wavelength of 1.06 ⁇ m is often used.
- the laser light having a wavelength of 1.06 ⁇ m oscillated from the fundamental wave light source 101 is condensed on the nonlinear optical crystal 109 by the condenser lens 108.
- the refractive index of the nonlinear optical crystal 109 with respect to light having a wavelength of 1.06 ⁇ m and the refractive index with respect to light having a wavelength of 0.532 ⁇ m to be generated coincide with each other, which is called phase matching.
- the refractive index of a crystal changes depending on the temperature condition of the crystal itself, it is necessary to keep the temperature of the crystal constant. For this reason, the nonlinear optical crystal itself is disposed in the temperature holding device 116 and held at a temperature corresponding to the type of crystal.
- FIG. 2 schematically shows a control loop that monitors green light as light after wavelength conversion and controls the output to be constant.
- the control loop 250 shown in FIG. 2 controls the fundamental wave output 260 from the fundamental wave light source 101 by controlling the input current 240 to the fundamental wave light source 101.
- the fundamental wave output 260 is incident on the wavelength conversion element 109 made of a nonlinear optical crystal whose temperature is kept constant under the control of the element temperature control unit 280.
- green light 270 is output from the wavelength conversion element 109.
- APC auto power control
- the polarization direction of the fundamental wave oscillated from the fundamental wave light source 101 and the wavelength of the fundamental wave oscillated from the fundamental wave light source 101 are also important factors for wavelength conversion.
- Patent Document 3 discloses a method for reducing output noise when mitigating oscillation is performed by monitoring outputs of a fundamental wave and a second harmonic.
- Patent Document 4 in a wavelength conversion laser light source using a wavelength conversion element that takes type-II phase matching, each polarization component of the fundamental wave is acquired and used to drive the phase difference adjusting means provided in the resonator. A feedback method has been proposed.
- the conventional control loop has a problem that it cannot cope with a change in polarization or a wavelength even in a steady state, in addition to the problem that it cannot cope with the state of relaxation oscillation that has been pointed out conventionally.
- JP 2004-157217 A JP 2000-305120 A JP 2004-348052 A Japanese Patent Laid-Open No. 5-188421
- An object of the present invention is to provide a wavelength conversion laser light source capable of performing stable and efficient wavelength conversion, a projection display device including the same, a liquid crystal display device, and a laser light source.
- a wavelength conversion laser light source has a fundamental light source that emits fundamental light and a nonlinear optical effect, and converts the fundamental light into harmonic light having a different wavelength.
- a wavelength conversion element that receives light of a specific polarization direction included in the fundamental wave light emitted from the fundamental wave light source, converts the light amount into an electrical signal, and outputs from the wavelength conversion element
- a second light receiver for receiving the harmonic light to be converted and converting the light amount into an electric signal, a temperature holding unit for keeping the temperature of the wavelength conversion element constant, and an electric signal from the second light receiver
- a second control for controlling the light quantity of the fundamental wave light based on an electric signal from the first light receiver. Fundamental wave control When, and a, and a temperature control unit for performing a third control for controlling the holding temperature of the temperature holding unit based on the electric signal from the second receiver.
- this wavelength conversion laser light source receives light of a specific polarization direction included in the fundamental wave light emitted from the fundamental wave light source by the first light receiver, converts the light amount into an electric signal, and converts it into the electric signal. Based on this, the fundamental wave control unit controls the light amount or wavelength of the fundamental wave light emitted from the fundamental wave light source. Thereby, since the fundamental wave light can be appropriately adjusted according to the change in the polarization component of the fundamental wave light, a wavelength conversion laser light source capable of performing stable and efficient wavelength conversion can be realized.
- FIG. 3A shows a schematic configuration of a measuring apparatus that measures the amount of change in the polarization direction of the fundamental light.
- FIG. 3B shows the amount by which the polarization direction of the fundamental wave light measured using the measuring device shown in FIG. 3A changes.
- FIG. 3A shows schematic structure of the wavelength conversion light source to which the control method of the harmonic output light which concerns on one embodiment of this invention is applied.
- FIG. 3 drawing shows the control loop to which the control method of the harmonic output light which concerns on one embodiment of this invention is applied.
- FIG. 8A is a plot diagram for explaining the temperature control method of the wavelength conversion element in the harmonic output light control method according to one embodiment of the present invention.
- FIG. 8B is a plot diagram for explaining the temperature control method of the wavelength conversion element in the harmonic output light control method according to one embodiment of the present invention.
- FIG. 8C is a plot diagram for explaining the temperature control method of the wavelength conversion element in the harmonic output light control method according to one embodiment of the present invention.
- 8D is a plot diagram for explaining the temperature control method of the wavelength conversion element in the harmonic output light control method according to one embodiment of the present invention. It is a plot figure which shows the output stability at the time of applying the control method of the harmonic output light which concerns on one embodiment of this invention. It is explanatory drawing which shows schematic structure of the wavelength conversion light source to which the control method of the other harmonic output light in one embodiment of this invention is applied. It is explanatory drawing which shows the control loop in the control method of the other harmonic output light in one embodiment of this invention. It is a schematic diagram which shows schematic structure of the control system for adjusting the oscillation wavelength which concerns on one embodiment of this invention.
- DELTA shift
- FIG. 3A shows a schematic configuration of a measuring apparatus 300 that measures the amount of change in the polarization direction of the fundamental light.
- FIG. 3B shows the result of measuring the amount by which the polarization direction of the fundamental wave light emitted from the fundamental wave light source 101 changes using the measurement apparatus 300 shown in FIG. 3A.
- the measurement apparatus 300 includes a fundamental wave light source 101, a polarizing prism 301, and a power meter 303 including a light receiving unit 302.
- the fundamental light 105 emitted from the fundamental light source 101 enters the polarizing prism 301 and is linearly polarized. Only a predetermined polarization component in the linearly polarized light is incident on the light receiving unit 302 of the power meter 303.
- the power meter 303 measures the amount of output fluctuation based on the amount of light received incident on the light receiving unit 302.
- the graph of FIG. 3B plots the amount of output fluctuation with respect to the measurement time, that is, the amount by which the polarization direction changes.
- control A control A that can cope with elements that are difficult to adjust by the conventional control method such as change in polarization direction and change in wavelength even if the control margin is reduced.
- FIG. 4 is a schematic diagram showing a schematic configuration of a wavelength conversion laser light source 200 according to an embodiment of the present invention.
- the wavelength conversion laser light source 200 is a configuration example for realizing the control A.
- the wavelength conversion laser light source 200 includes a fundamental wave light source (light source) 201, a dichroic mirror 206, a beam splitter 207, a polarization filter 403, a light receiver (photodiode) 404, a condensing lens 208, wavelength conversion, and the like.
- An element (including a nonlinear optical crystal) 209, a recollimating lens 211, a beam splitter 213, a light receiver (photodiode) 212, and the like are provided.
- a part of the fundamental wave 205 oscillated from the fundamental wave light source (light source) 201 is transmitted through the beam splitter 207 by 1% of the light amount, and the remaining 99% is reflected.
- the fundamental wave 205 reflected by the beam splitter 207 is input to the wavelength conversion element 209.
- the fundamental wave 205 is wavelength-converted by the wavelength conversion element 209 and converted to green light as the second harmonic.
- the fundamental wave light source 201 a fiber laser light source using a Yb-doped fiber is used.
- the fiber laser light source has an advantage that an oscillation wavelength and a spectrum width can be arbitrarily determined. Therefore, the conversion efficiency from the fundamental wave to the harmonic can be greatly improved by narrowing the spectrum width.
- the fundamental wave light 205 generated from the fundamental wave light source 201 is condensed by a condenser lens 208 onto a wavelength conversion element 209 including a nonlinear optical crystal.
- a condenser lens 208 onto a wavelength conversion element 209 including a nonlinear optical crystal.
- an Mg: LiNbO 3 crystal element (MgLN element) having a domain-inverted structure is used as the nonlinear optical crystal.
- the fundamental wave that has passed through the beam splitter 207 and passed through the polarizing filter 403 is monitored, and feedback control is performed.
- the polarizing filter 403 transmits only the polarization component that contributes to wavelength conversion in the fundamental wave 205 transmitted through the beam splitter 207. Then, the light of the polarization component transmitted through the polarization filter 403 is monitored by a light receiver (photodiode) 404.
- the light receiver 404 can monitor the polarization fluctuation as a change in intensity simultaneously with the change in the intensity of the fundamental wave 205 and convert it into an electric signal. This electrical signal is fed back to the control device 215 as intensity information of the fundamental wave 205. In the present embodiment, feedback control is performed based on the feedback information so that the intensity of a predetermined polarization component becomes constant as in loop 2 of FIG. 5 described later (APC: Auto Power Control). ).
- the wavelength conversion laser light source 200 is provided on the lower surface of the wavelength conversion element 209, and includes a temperature holding unit 216 for maintaining the wavelength conversion element 209 at a constant temperature.
- a temperature holding unit 216 As the temperature holding unit 216, a Peltier element is used.
- the second harmonic wave 210 (green light) generated by the wavelength conversion by the wavelength conversion element 209 is converted into a parallel light beam by the recollimating lens 211, and a part thereof is received by the light receiver 212 via the beam splitter 213. Is done.
- the light receiver 212 monitors the intensity of the second harmonic wave 210 generated by the wavelength conversion element 209, converts the intensity into an electric signal (green light intensity information), and outputs the electric signal.
- the temperature of the temperature holding unit 216 that holds the temperature of the wavelength conversion element 209 is controlled based on the intensity information of the second harmonic 210 monitored by the light receiver 212 (loop 3 in FIG. 5). As a result, when the intensity of the second harmonic 210 varies due to a change in the wavelength of the fundamental wave, the temperature of the wavelength conversion element 209 can be changed in accordance with the change in the wavelength of the fundamental wave.
- loop 2 and loop 3 feedback control using only the above two loops (loop 2 and loop 3) can be controlled only by a parameter having a large time constant of temperature with respect to fluctuations in the output of the second harmonic 210. For this reason, it is difficult to make the output of the second harmonic 210 constant.
- the control by the loop 1 is performed in the state where the control of the loop 2 and the loop 3 in FIG. 5 is stopped.
- the current for driving the fundamental wave is controlled based on the electric signal indicating the intensity information of the second harmonic 210.
- the feedback control of the loop 1 it is possible to make the output of the second harmonic 210 constant even when a parameter having a large time constant is set as a control target. That is, the output fluctuation of the second harmonic 210 can be reduced by operating a plurality of loops in a time division manner as in the present control A.
- FIG. 6 is a timing chart showing an example of the switching timing of the controlled object. This timing chart indicates whether each loop is operating or at rest with respect to the operating status of the wavelength conversion laser light source 200.
- the control for making the output of the fundamental wave 205 constant (loop 2) and the control for optimizing the temperature of the wavelength conversion element 209 (loop 3) are operated at the same timing. This is because the two loops of the loop 2 and the loop 3 do not cause a problem such as runaway even if operated simultaneously.
- the feedback control according to the present embodiment is not limited to this. That is, if the operation timing of the loop 1 and the operation timing of the loop 2 and the loop 3 are operated at different timings, it is not always necessary to operate the two loops of the loop 2 and the loop 3 at the same timing. It may be started and ended at different timings.
- the operation time of the loop 3 is preferably about 10 seconds to 1 minute.
- the control of the loop 2 and the loop 3 is once ended.
- the operation time of the loop 1 can be sufficiently followed by about 0.1 to 10 seconds.
- the loop 1 that feeds back to the current value input to the fundamental light source is operated again based on the harmonic light output.
- the temperature of the wavelength conversion element 209 is always adjusted with respect to environmental changes such as ambient temperature and wavelength fluctuation of the fundamental wave light.
- the optimal value can be kept. Therefore, the output margin of the fundamental wave light required when the temperature of the wavelength conversion element 209 is kept constant without changing, that is, the margin of the current value input to the fundamental wave light source can be reduced, and the apparatus can be controlled with simple control. There is an effect that the size and power consumption can be reduced.
- this control can be applied by using the time-averaged value of the output of the harmonic light for feedback control. it can.
- FIG. 7 is a schematic diagram showing a control system for adjusting the temperature of the wavelength conversion element 209 used in the loop 3.
- the wavelength conversion element 209 is held on the temperature holding unit 216, and the temperature of the wavelength conversion element 209 is indirectly monitored by monitoring the temperature of the temperature holding unit 216 with the thermistor 703.
- the temperature signal from the thermistor 703 and the light intensity signal 712 of the wavelength-converted light are converted into a digital value by the A / D converter 704 and stored in the register 705.
- a table of element temperatures with respect to the harmonic output is stored in the EEPROM 706 together with a current value to be input to the fundamental light source 201 in advance.
- the set value data of the harmonic light output is transferred to the MPU 707.
- the temperature controller 711 includes a power source 708, a thermistor 703, an A / D converter 704 that converts a temperature signal from the thermistor 703 into a digital value, and a temperature signal that has been converted to a digital value by the A / D converter 704.
- Register 705 for storing, output-temperature set value conversion table, EEPROM 706 for storing input current value necessary in advance, MPU 707 to which data of harmonic output set value is transferred from controller 215, temperature holding unit from power supply 708
- a switch 709 for performing PWM (Pulse Width Modulation) control on the current waveform supplied to 216 is included.
- the wavelength conversion element 209 has a polarization inversion structure (Mg: LiNbO 3 having a polarization inversion structure in this embodiment), and the holding temperature of the wavelength conversion element 209 is 50 ° C.
- FIG. 8A to 8D show an example of a temperature adjustment method of the wavelength conversion element 209.
- FIG. 8A to 8D show an example of a temperature adjustment method of the wavelength conversion element 209.
- the control temperature of the wavelength conversion element 209 is wobbling ⁇ ⁇ t (° C.) around the center temperature Tc (° C.).
- the harmonic output when the element temperature is Tc + ⁇ t (° C.) is P (Tc + ⁇ t), the harmonic output when Tc (° C.) is P (Tc), and the harmonic output when Tc ⁇ t (° C.) is P (T When Tc ⁇ t), as shown in FIG. 8A, when P (Tc ⁇ t) ⁇ P (Tc) ⁇ P (Tc + ⁇ t), an operation of increasing Tc is performed. As shown in FIG. 8B, when P (Tc + ⁇ t) ⁇ P (Tc)> P (Tc ⁇ t), control is performed to maintain Tc. On the other hand, when P (Tc ⁇ t)> P (Tc)> P (Tc + ⁇ t) as shown in FIG.
- ⁇ t is preferably in the range of 0.1 to 0.2 ° C.
- the wobbling period is 5 to 10 seconds.
- P (Tc ) Will be difficult to search for the maximum point.
- ⁇ t is equal to or lower than 0.1 ° C., it is easy to be affected by disturbance during temperature detection. Therefore, by setting the above range, it is possible to perform a constant output operation while keeping output fluctuation small. effective.
- the temperature control method is not limited to this method.
- the output characteristic curve with respect to the temperature is kept waiting at a position where the output peak value is 80% to 90%, and (P (T pv ) in the figure) from the output fluctuation amount therefrom, from the fundamental wave
- P (T pv ) in the figure) from the output fluctuation amount therefrom, from the fundamental wave A method of calculating a deviation from the temperature at which the conversion efficiency to the harmonic light becomes maximum and correcting the temperature of the wavelength conversion element 209, so-called hill-climbing control, can also be applied.
- FIG. 9 is a plot diagram showing the output fluctuation amount with respect to the operation time when the output control method of the present embodiment is applied to the wavelength conversion laser light source 200. This is compared with FIG. 3B to verify the effect of the present embodiment.
- the output decrease due to the change of the polarization component of the fundamental wave is as large as 8% or more, and the output decrease due to the wavelength fluctuation of the fundamental wave is also 2% after 3500 seconds from the start of operation. It was about.
- the output control method of the present embodiment is applied, as shown in FIG. 9, the decrease in output due to the change in the polarization component of the fundamental wave is reduced to only about 1%. It can be seen that the decrease in output due to wave wavelength fluctuation is substantially zero.
- control method effectively suppresses the output fluctuation caused by the change of the polarization component of the fundamental wave and the wavelength fluctuation of the fundamental wave.
- the improvement of the stability of control and the improvement of the reliability of a wavelength conversion laser light source are realizable.
- the output of the wavelength converted light is controlled to be constant by adjusting the oscillation wavelength of the fundamental light source 201 (Control B).
- FIG. 10 is a schematic diagram showing a configuration of the laser light source 1000 proposed in the control B.
- the fundamental wave light source 201 includes a semiconductor laser 102 that emits excitation light, a double-clad rare earth-doped fiber 103 that absorbs the excitation light emitted from the semiconductor laser 102 and emits the fundamental light, and a double-clad A narrow-reflection band fiber grating 104b and a wide reflection-band fiber grating 104a, which are arranged at both ends of the rare-earth doped fiber 103 and determine the wavelength of the fundamental light emitted from the fundamental light source 201, and the semiconductor laser 102.
- a residual pumping light processing mechanism (not shown) that absorbs the pumping light that has not been absorbed by the double-clad rare earth-doped fiber 103 of the pumping light, and a polarization direction of the fundamental light emitted from the fundamental light source 201 are linear.
- a polarization unifying mechanism (not shown) to make the direction
- An actuator 1001 for applying stress to the fiber grating in the band, and one end of the fiber grating 104b in the narrow reflection band is held by the actuator 1001, and the basic force is applied to the fiber grating 104b in the narrow reflection band by the actuator 1001.
- the wavelength of the wave light is changed.
- a part of the fundamental wave 205 oscillated from the fundamental wave light source (fiber laser) 201 is transmitted through the beam splitter 207 by 1% of the light amount, and the remaining 99% is reflected.
- the reflected fundamental wave 205 is input to the wavelength conversion element 209.
- the input fundamental wave 205 is wavelength-converted by the wavelength conversion element 209 and converted to green light as harmonic light.
- the fundamental wave 205 is monitored by the light transmitted through the beam splitter 207.
- light in a state where only one polarization component is extracted by the polarization filter 403 is observed by a light receiver (photodiode) 404.
- the light receiver 404 can monitor the polarization fluctuation as a change in intensity simultaneously with the change in the intensity of the fundamental wave 205.
- the fundamental wave oscillated from the fundamental wave light source 201 is monitored by the light receiver 404 and the intensity information is fed back to the control device 215.
- the fundamental light source capable of changing the wavelength of the fundamental wave light is a distributed feedback semiconductor laser light source including a distributed feedback mirror unit, and the wavelength of the fundamental wave light is changed by changing a current input to the distributed feedback mirror unit. It is good also as a structure to change.
- a distributed feedback type semiconductor laser light source that has a distributed feedback mirror section and generates light that is the source of the fundamental wave light, an excitation light source that emits excitation light, and A laser medium that amplifies the intensity of the light emitted from the distributed feedback semiconductor laser light source by absorbing the excitation light, and changing the current input to the distributed feedback mirror unit, thereby changing the wavelength of the fundamental light You may use the light source of the structure to change.
- control B As in the case of the control A described above, feedback control is performed based on the information fed back to the control device so that the intensity of a certain polarization component becomes constant (APC: Auto Power Control, Loop 2 (Fig. 11)).
- Control A the temperature of the temperature holding unit 216 that controls the temperature of the wavelength conversion element 209 is controlled based on the intensity information of the green light monitored by the light receiver 212.
- this control B the temperature is held.
- the temperature of the part 216 is constant at a predetermined temperature.
- the fundamental wavelength is adjusted to the element temperature determined by the temperature holding unit 216 using the actuator 1001 that fixes the fiber grating 104b (loop 3). That is, the fundamental wave input in the polarization direction that contributes to wavelength conversion is controlled to be constant (loop 2 in FIG. 11), and the wavelength of the fundamental wave, which is another variation factor of green light, is changed (FIG. 11). 3), the idea is to cope with fluctuations in the output of green light.
- the amount of current to be input to the fundamental light source 201 cannot be determined based on the amount of green light. For this reason, trouble occurs when setting a desired green light output. Therefore, in the present control A, the control of the loop 2 and the loop 3 in FIG. 11 is stopped, and the feedback to the current for driving the fundamental wave is performed based on the green light intensity signal (loop 1 in FIG. 11). By inserting, green light output can be made constant even when green output is set. That is, the fluctuation of the green light can be reduced by operating a plurality of loops in a time division manner.
- this control when a rectangular wave modulated light output is emitted or when dealing with a pulsed laser light, this control can be applied by using a value obtained by averaging the output for time feedback control. it can.
- FIG. 12 is a schematic diagram showing a control system 1200 for adjusting the oscillation wavelength used in the loop 3.
- One end of the fiber grating (FBG) 104b that determines the oscillation wavelength is held on the actuator 1001, and the stress applied to the FBG 104b is determined by the voltage applied to the actuator 1001.
- a green light intensity signal 1201 generated by wavelength conversion is converted into a digital value by the A / D converter 1202 and stored in the register 1203.
- a table of the voltage applied to the actuator 1001 with respect to the harmonic output, that is, the stress applied to the FBG, is stored in advance in the EEPROM 1204 together with the necessary input current to the excitation LD.
- the harmonic output set value data is transferred to the MPU 1205.
- the MPU 1205 acquires stress data to the FBG with respect to the harmonic output stored in the EEPROM 1204, and compares and calculates the current value of the green light intensity signal stored in the register 1203.
- a power source 1206 is a power source supplied to the actuator 1001, and the signal converter 1207 converts the PWM signal into an analog voltage signal to control the actuator 1001.
- the actuator 1001 that can be used in this embodiment may be an electromagnetic coil or a piezoelectric element, but the stress applied to the FBG can be controlled by the voltage, and the voltage It is preferable to use an actuator 1001 using an electromagnetic coil from the viewpoint that the stress can be monitored by the value.
- a DBR (Distributed Bragg Reflector) laser which is a type of wavelength tunable semiconductor laser
- a method of optical amplification using an optical fiber amplifier or the like using a DBR laser as a seed light can be employed.
- FIG. 13 shows a plot of the output fluctuation amount with respect to the operation time of the wavelength conversion laser light source 1000 in the control B.
- the output fluctuation amount is within 1%.
- the output fluctuation caused by the wavelength fluctuation of the fundamental wave and the output fluctuation caused by the change of the polarization component of the fundamental wave It can be seen that it is possible to significantly reduce.
- the fundamental oscillation wavelength which is faster than the temperature time response of the wavelength conversion element, is targeted for control, the control response speed can be improved compared to the control A.
- the plot diagram shown in FIG. 9 when the control A is applied it can be seen that there is an effect of further suppressing the output fluctuation with respect to the wavelength remaining about 1% by applying the control B.
- the wavelength conversion laser light source having the configuration shown in Control A and Control B of the present embodiment, it is possible to detect an output change due to disturbance with respect to the polarization direction of the fundamental wave, the wavelength of the fundamental wave, and the temperature of the wavelength conversion element. Therefore, the stability of the output control is improved and the reliability of the apparatus is improved.
- control method of the first embodiment is applied to an internal resonator type wavelength conversion laser light source.
- FIG. 14 shows a schematic configuration of an internal resonator type wavelength conversion laser light source 1400 according to the present embodiment.
- the internal resonator type wavelength conversion laser light source 1400 includes a power supply device 1403, a control device 1402, an output setting device 1401, an excitation light source (fundamental wave light source, laser diode) 1405, a collimator lens 1406, a condensing lens 1407, and a solid-state laser element 1409. , Resonance mirrors 1408 and 1412, a dielectric multilayer mirror 1413, a light receiving element 1416 including a polarizer 1415, a temperature controller 1404, harmonic reflection mirrors 1414 and 1417, a light receiving element 1418, and the like.
- Excitation light emitted from an excitation light source (laser diode) 1405 is excited by being incident on a solid-state laser element 1409 using a collimator lens 1406 and a condenser lens 1407.
- the solid-state laser element 1409 and the wavelength conversion element 1410 are arranged in a resonator composed of resonance mirrors 1408 and 1412.
- the fundamental wave oscillated from the solid-state laser element 1409 resonates in the resonator and oscillates.
- the generated fundamental wave is incident on the wavelength conversion element 1410, and a part thereof is converted into the second harmonic.
- the resonant mirror 1408 and the output mirror 1412 have high reflectivity at the wavelength of the fundamental wave light, and in particular, for the 1412 from which light is output, the dielectric multilayer so that the second harmonic has low reflectivity (high transmittance).
- a film is formed.
- the light emitted from the laser resonator is almost the second harmonic, but a slight fundamental wave is also emitted.
- the second harmonic wave emitted from the emission mirror 1412 is passed through the dielectric multilayer film mirror 1413, and the fundamental wave component is separated from the second harmonic wave.
- the fundamental wave reflected from the dielectric multilayer mirror 1413 and separated from the second harmonic is incident on a light receiving element 1416 having a polarizer 1415, and the amount of light is monitored.
- the second harmonic component passes through the dielectric multilayer mirror 1413, is reflected by the harmonic reflection mirrors 1414 and 1417, and is emitted outside the light source as output light 1419. At this time, part of the second harmonic passes through the harmonic reflection mirror 1417.
- the harmonic wave that has passed through the harmonic reflection mirror 1417 is received by the light receiving element 1418 to monitor the amount of the harmonic wave.
- a quasi-phase-matched LiNbO 3 element having a periodically poled structure is used as the wavelength conversion element.
- the periodically poled LiTaO 3 or KTiOPO 4 crystal having an oxygen octahedral structure in the basic structure is also used. You may use the quasi phase matching wavelength conversion element which formed the structure.
- an element using a crystal substrate in which Mg, Ce, or the like is added to the crystal system to suppress a change in the optical refractive index may be used.
- the fundamental light intensity signal received by the light receiving element 1416 and the harmonic light intensity signal received by the light receiving element 1418 are sent to the control device 1402.
- the control device 1402 controls a current signal sent from the power supply device 1403 to the excitation light source 1405 based on the fundamental and harmonic light intensity signals and the input value set by the output setting device 1401. Further, the temperature of the wavelength conversion element 1410 is adjusted by a temperature controller 1404.
- the fundamental wave incident on the light receiving element 1416 passes through the polarizer 1415 and is only a predetermined polarization component.
- the cause of the output fluctuation is Predicted to be in the fundamental light source.
- the fundamental light source There are three possible causes for the output reduction due to the fundamental light source: heat generation of the solid-state laser element, output reduction of the excitation light source, and mode change of the oscillated fundamental wave.
- excitation light source fundamental wave light source
- APC Auto Power Control
- the cause of the output fluctuation Can be predicted to be caused by the wavelength conversion element.
- the output can be recovered by optimizing the element temperature using the method described with reference to FIGS. 8A to 8D in the first embodiment. it can.
- the light intensity signal of the predetermined polarization component detected by the light receiving element 1416 and the phase of the harmonic light intensity signal detected by the light receiving element 1418 are coincident (synchronized) or inverted (asynchronized). For example, if the phases of both signals are in the range of 0 ⁇ 45 degrees, it can be judged that they are in agreement (synchronized), and if the phases of both signals are in the range of 180 ⁇ 45 degrees, they are reversed ( Asynchronous).
- FIG. 15B shows a control loop of the wavelength conversion laser light source according to the present embodiment.
- the residual fundamental wave and the harmonic wave (green light) output from the output mirror are compared in phase information of the intensity, and are fed back in the loop 2 based on the information indicating the synchronous / asynchronous of the intensity change, or the loop 3 Determine whether to give feedback.
- loop 2 feedback is made to the input current value to the excitation light source 1405.
- the loop 3 feedback is performed in the form of element temperature. At this time, it is important to execute the present embodiment that the feedback operation is not performed unless the light quantity of the harmonic (green light) is changed with respect to the fluctuation of the light quantity of the remaining fundamental wave. .
- Loop 1 is a loop used for comparing the input current value and the harmonic (green light) output when setting the output or at regular intervals. Also in the present embodiment, an example of the control target switching timing used in the first embodiment can be used as it is. In the timing chart of FIG. 6, it is shown whether each loop is operating or at rest with respect to the operating state of the wavelength conversion laser light source.
- APC control for feeding back the light output value to the input current value (loop 1) is performed, and when the light output is determined, the time division control is started.
- the control for making the fundamental wave output constant (loop 2) and the control for optimizing the temperature of the wavelength conversion element (loop 3) are operated at the same timing. This is because the two loops of the loop 2 and the loop 3 do not cause a problem such as runaway even if operated simultaneously.
- the feedback control according to the present embodiment is not limited to this. That is, if the operation timing of the loop 1 and the operation timing of the loop 2 and the loop 3 are operated at different timings, it is not always necessary to operate the two loops of the loop 2 and the loop 3 at the same timing. It may be started and ended at different timings.
- the operation time of the loop 3 is preferably about 10 seconds to 1 minute. Then, after operating the loop 2 and the loop 3 for a certain period of time, the control of the loop 1 and the loop 2 is temporarily terminated to release the loop, and again, based on the harmonic (green light) output, to the input current value
- the loop 1 to be fed back is operated.
- the operation time of the loop 1 can be sufficiently followed by about 0.1 seconds to 10 seconds. In this way, by dividing the time for operating the loop 1 and the time for operating the loop 2 and the loop 3, the element temperature is always kept at an optimum value with respect to environmental changes such as environmental temperature and wavelength fluctuation of the fundamental wave light. be able to. As a result, there is an effect of improving the stability of control and improving the reliability of the light source.
- the fundamental light output margin (input current value margin) required when the element temperature is constant can be reduced.
- the wavelength conversion laser device can be reduced in size and power consumption.
- a configuration of a wavelength conversion laser light source capable of further enhancing the effect on the problems of output stabilization and low power consumption by the control described in the first and second embodiments will be described.
- FIG. 16 shows a schematic diagram of a wavelength conversion laser light source proposed in the present embodiment.
- FIGS. 17 and 18 show the relationship between the difference ( ⁇ T) between the thermistor temperature at which the wavelength conversion efficiency is maximum, the temperature monitored by the thermistor, and the fundamental light quantity required to obtain the set harmonic output.
- ⁇ T difference between the thermistor temperature at which the wavelength conversion efficiency is maximum
- the temperature monitored by the thermistor the fundamental light quantity required to obtain the set harmonic output.
- the wavelength conversion laser light source 1600 includes a fundamental wave light source 1601, a condenser lens 1603, a wavelength conversion element 1604, a Peltier element 1605, a thermistor 1606, a collimator lens 1607, a wavelength separation mirror 1608, an optical branching mirror 1610, A temperature control circuit 1611, a photodiode 1612, and a constant light amount control circuit are provided.
- the fundamental wave light 1602 emitted from the fundamental wave light source 1601 is incident on a wavelength conversion element 1604 using a nonlinear optical crystal, and a part of the fundamental wave light 1602 is converted into wavelength converted light 1609.
- the fundamental wave light source 1601 is a fiber laser
- the fundamental wave light 1602 is infrared light in the 1 ⁇ m band
- the wavelength converted light 1609 is green light that is the second harmonic of the infrared light.
- the wavelength conversion element 1604 is a quasi phase matching wavelength conversion element made of LiNbO 3 to which 5 mol% of Mg having a domain-inverted structure with a period of 7 ⁇ m is added.
- the element length of the wavelength conversion element 1604 is 20 mm.
- the fundamental wave light 1602 and the wavelength converted light 1609 emitted from the wavelength conversion element 1604 are separated by a wavelength separation mirror 1608, and the obtained wavelength converted light 1609 is divided into an optical branching mirror 1610 (wavelength converted light transmittance of about 1 to 10%). ) Part of the light is incident on the photodiode 1603 and the light quantity of the wavelength converted light 1609 is monitored.
- constant light intensity control is performed based on the monitored value. If the wavelength-converted light 1609 increases from the desired light amount, the fundamental light 1602 is reduced. If the wavelength-converted light 1609 decreases from the desired light amount, the light amount for controlling the drive current of the fundamental light source 1601 to increase the fundamental light 1602.
- a constant control circuit 1613 is provided to control the monitor value of the wavelength converted light 1609 to be constant.
- the fundamental wave light source 1601 includes a temperature control circuit 1611 that adjusts the temperature of the wavelength conversion element 1604 using the thermistor 1606 and the Peltier element 1605 based on a value obtained by monitoring the amount of fundamental wave light.
- the means for monitoring the amount of fundamental wave light is not shown in FIG. 16, but a configuration in which a part of the fundamental wave light before entering the wavelength conversion element is reflected by a branch mirror and received by a photodiode may be used.
- the fundamental wave light source is a light source in which the increase / decrease in the drive current coincides with the increase / decrease in the oscillating fundamental light amount
- a means for monitoring the drive current may be substituted. In this case, it is possible to reduce the number of photodiodes used, which is preferable because the cost can be further reduced.
- the total light quantity of the fundamental wave light and the wavelength converted light emitted from the wavelength conversion element substantially matches the fundamental light quantity incident on the wavelength conversion element, and the fundamental light quantity emitted from the wavelength conversion element and the fundamental light incident on the wavelength conversion element.
- the increase or decrease in quantity is consistent. In the control of the present embodiment, it is only necessary to know the increase / decrease in the amount of fundamental wave incident on the wavelength conversion element. Therefore, means for monitoring the amount of fundamental wave emitted from the wavelength conversion element may be used instead. In this case, it is preferable because a large amount of fundamental wave light oscillated by the fundamental wave light source can be incident on the wavelength conversion element. Thereby, wavelength conversion with higher efficiency is possible.
- the light amount for wavelength conversion is monitored, and the light amount constant control is performed by increasing / decreasing the light amount of the fundamental wave so that the value becomes constant.
- the light amount constant control is performed by increasing / decreasing the light amount of the fundamental wave so that the value becomes constant.
- a fundamental light amount that is three times as high is set as a threshold value a
- a basic light amount that is 1.1 times the reference basic light amount is set as a threshold value b.
- the wavelength conversion element 1604 is cooled (S15). Then, it is determined again whether the light quantity is within the controllable range (S11), and thereafter the same processing is repeated. That is, if the light amount is not within the controllable range (NO in S11), it is determined whether ⁇ T ⁇ 0 (S13). If ⁇ T ⁇ 0 (YES in S13), the wavelength conversion element 1604 is heated, and if ⁇ T is negative (NO in S13), the wavelength conversion element 1604 is cooled. Then, after reaching the range of ⁇ T where the light quantity can be controlled, the start-up operation is terminated and switched to the normal operation (S12).
- the fundamental light quantity is larger than the threshold value a (S21). If it is equal to or less than the threshold value a (NO in S21), temperature constant control is performed (S22). On the other hand, if the fundamental wave light amount is larger than the threshold value a (YES in S21), the wavelength conversion element 1604 is heated (S23). Next, it is determined whether or not the fundamental wave light amount has increased (S24). If an increase in the fundamental wave light amount (YES in S24), it means an increase in the deviation between TM 0 and TM (absolute value of [Delta] T), it cools the wavelength conversion element 1604 (S25).
- control for making the wavelength-converted light quantity constant needs to be always performed during normal operation.
- the thermistor temperature hunting increases. In this case, the heating and cooling energy required for temperature adjustment increases, a higher-output fundamental wave light source is required, and the cost increases.
- the difference between the threshold value “a” and the threshold value “b” serving as a reference for determining whether the fundamental wave light amount has increased or decreased is too large, the possibility of erroneous determination of increase or decrease in the fundamental light amount increases.
- the increase / decrease of the fundamental wave light amount can be accurately determined, and the temperature can be adjusted at a higher speed.
- the average value of the required fundamental wave light amount can also be lowered, so that the output margin value of the fundamental light source can be kept low. As a result, it is possible to reduce the power and cost of the wavelength conversion laser light source.
- the threshold value a and the threshold value b are set, and the temperature control and the constant temperature control for eliminating ⁇ T are switched and executed. Thereby, it is possible to continue driving the laser light source without interrupting the constant light amount control. Furthermore, since energy required for heating or cooling the wavelength conversion element can be reduced, stable harmonic output can be realized with low power consumption.
- control method can be used as temperature control under constant light intensity control.
- the start-up operation as in the case of the control C, the start-up operation as shown in the flow of FIG. 20 is performed until the TM reaches a range where the light quantity can be controlled constant. Then, after reaching the range of ⁇ T in which constant light amount control is possible, the operation is switched to normal operation.
- the wavelength conversion element When ⁇ T is negative at the start of start-up, the wavelength conversion element is heated as the start-up operation, and the operation is switched to normal operation within a range in which ⁇ T can be controlled with a constant light amount and ⁇ T is negative.
- the wavelength conversion element is heated when the fundamental light amount is larger than the threshold value c so as to converge at the point A shown in FIG. 21, and the wavelength conversion element is cooled when the fundamental light amount is less than or equal to the threshold value c.
- the control process can be reduced compared with the case of converging to the point B, higher speed control can be realized.
- the wavelength conversion element at a temperature higher than the temperature of the installation environment.
- Control D can instantly determine whether TM has shifted to a higher temperature side or a lower temperature side than point A. Thereby, compared with the above-mentioned control C, since a control process can be reduced, higher-speed temperature control is realizable. As a result, it is possible to greatly narrow the range in which the temperature of the fundamental wave path itself in the TM and the wavelength conversion element fluctuates, and the following points are excellent in comparison with the control C.
- the energy required for heating or cooling for temperature control of the wavelength conversion element can be greatly reduced.
- this laser light source is used for an image display device, an image display device in which color shift is suppressed can be realized.
- measurement errors due to wavelength shift can be reduced.
- the allowable variation range of ⁇ T (hereinafter, ⁇ T allowable range) can be expanded by the following method.
- ⁇ T allowable range By expanding the ⁇ T allowable range, it becomes possible to use temperature measuring means with lower accuracy, and it is possible to use temperature adjusting means with lower heating / cooling capacity, thereby further reducing the cost.
- the temperature adjusting means can be omitted by greatly expanding the allowable range of the temperature measured by the thermistor, further cost reduction of the wavelength conversion laser light source can be realized.
- the wavelength conversion element 1604 Like the wavelength conversion laser light source 2400 shown in FIG. 22, in the wavelength conversion element 1604, a part of the fundamental wave light 1602 is absorbed, and a thermal resistance adjusting material 2401 is provided between the fundamental wave light 1602 optical path in the wavelength conversion element 1604 and the thermistor 1606. With this configuration, it is possible to widen an allowable range that can cope with a change in the external temperature of the wavelength conversion laser light source.
- a temperature difference is generated between the thermistor 1606 and the optical path of the fundamental wave light 1602 in the wavelength conversion element 1604 in proportion to the magnitude of the fundamental wave light.
- the temperature difference is shifted to the low temperature side, which is indicated by a broken line 2501. It will change to a curve.
- the slope of the change in wavelength conversion efficiency with respect to the change in ⁇ T when ⁇ T is negative is gentler than that when ⁇ T is positive.
- the temperature control is performed so as to converge to the point A ′, the allowable range of ⁇ T is expanded.
- ⁇ T when ⁇ T is negative, if ⁇ T decreases, the amount of absorption of the fundamental wave light increases, and the temperature difference between the fundamental wave light path in the wavelength conversion element and the TM increases, so the fundamental wave light path in the wavelength conversion element.
- the temperature decrease amount at is smaller than the temperature decrease amount of TM.
- the width in which the temperature of the fundamental wave path in the wavelength conversion element varies is narrower than the width in which TM varies.
- ⁇ T around 0.7 ° C.
- ⁇ T constant light control is possible in the range of ⁇ T from around 1 ° C to -1.9 ° C. It becomes.
- the configuration of the present embodiment is preferable to the method of shortening the element length in that the effect of expanding the ⁇ T allowable range is large without causing a significant decrease in wavelength conversion efficiency. For this reason, a wavelength conversion laser light source with lower power consumption can be realized.
- the thermal resistance of the thermal resistance adjusting material 2401 is set to a lower value, and the thermal resistance adjusting material 2401 is thickened. And a method of increasing the absorptance of the fundamental wave light 1602.
- both the slopes of the fundamental light quantity with respect to ⁇ T between the left curve 2601a and the right curve 2601b are made negative. be able to.
- the value of the fundamental wave light amount for obtaining the same wavelength-converted light amount has ⁇ T that is two or more.
- both the slopes of the fundamental wave amounts with respect to ⁇ T of the left curve 2601a and the right curve 2601b can be made negative.
- the oscillation wavelength of the fundamental wave light may momentarily shift and shift from the left curve 2601a to the right curve 2601b.
- both the increase / decrease in ⁇ T and the slope of the increase / decrease in the amount of fundamental wave light are negative, and therefore it is possible to suppress the runaway of temperature control.
- the slope of increase / decrease of the fundamental wave light quantity with respect to ⁇ T can be further moderated as shown by a one-dot broken line 2701 in FIG.
- the example shown in FIG. 25 does not include the thermal resistance adjusting material 2401 between the fundamental light path and the thermistor. While the ⁇ T allowable width 2702a in the configuration is about 1.4 ° C., when the thermal resistance adjusting material 2401 is provided, the ⁇ T allowable width 2702b can be expanded to about 8.9 ° C. Here, it goes without saying that the allowable width can be further increased by increasing the amount of heat generated by absorption of the fundamental wave light and further expanding the thermal resistance between the thermistor and the fundamental wave light path.
- the temperature allowable width 2702a in the case where the thermal resistance adjusting material 2401 is not provided is the desired wavelength conversion light amount with the fundamental light quantity being maximized (constant) when the thermal resistance adjusting material 2401 is provided. Agrees with the difference 2702c in ⁇ T obtained. For this reason, it is preferable to adjust the thermal resistance of the thermal resistance adjusting material 2401 so that the ⁇ T allowable width 2702b is wider than the ⁇ T difference 2702c.
- the thermal resistance adjusting member 2401 preferably has a value obtained by dividing the thermal conductivity [W / m / K] by the thickness (distance between the wavelength conversion element and the thermistor) [m] of 15 ⁇ 10 4 or less.
- the thermal resistance adjusting material 2401 preferably has a value obtained by dividing the thermal conductivity [W / m / K] by the thickness (distance between the wavelength conversion element and the thermistor) [m] of 5 ⁇ 10 4 or less.
- the excitation light amount required when the light amount is constant with respect to the temperature change of the wavelength conversion element changes similarly to the light amount of the fundamental wave light required when the light amount is constant in the laser light source 1600 (FIGS. 18 and 19).
- the same control can be performed by controlling the excitation light amount. That is, by monitoring the excitation light amount that increases or decreases with the change of ⁇ T, the temperature control of the wavelength conversion element can be performed while applying constant light amount control even in the configuration of the internal resonator type wavelength conversion light source shown in the second embodiment. Can be done.
- This wavelength conversion laser light source 2800 is configured such that the wavelength conversion element 1604 is installed in the wavelength conversion laser light source 2800 via the thermal resistance adjusting material 2401, and temperature adjusting means such as a thermistor and a Peltier element are omitted.
- the external temperature of the wavelength conversion laser light source 2800 is “T”
- the temperature of the wavelength conversion laser light source 2800 that maximizes the wavelength conversion efficiency is “T 0 ”.
- the TM and TM 0 shown in the case of using the configuration of FIG. 16 is replaced with T and T 0, respectively, the difference between T and T 0 With [Delta] T, similar to the configuration of FIG. 16
- the control C and the control D can be performed.
- the amount of fundamental wave light necessary for making the output constant with respect to the change in ⁇ T exhibits the same characteristics as those shown in FIG. Further, by using the thermal resistance adjusting material 2401, the characteristics shown in FIGS. 23 to 25 are obtained. In other words, even if the temperature of the laser light source decreases, the fundamental light amount is increased, and the temperature of the fundamental light path is increased with respect to the laser light source, thereby greatly reducing the temperature drop of the fundamental light path. Yes.
- the allowable range of the thermistor temperature is greatly increased compared to the conventional one. It shows that it becomes possible. Even if the temperature at the position measured by the thermistor drops, the fundamental wave light is increased and the temperature of the fundamental wave path is increased by increasing the temperature of the fundamental wave path to the thermistor. Because it can be done. Similarly, in the present embodiment, even if the temperature of the laser light source is lowered, the fundamental light amount is increased, and the temperature of the fundamental light path is increased with respect to the laser light source, thereby greatly reducing the temperature drop of the fundamental light path. Can be reduced.
- ⁇ T is the difference between the thermistor temperature at which the wavelength conversion efficiency is maximum and the temperature monitored by the thermistor, and the heat between the fundamental wave path using the thermal resistance adjusting material 2401 and the laser light source.
- the amount of heat generation, the thermal resistance between them, and the wavelength conversion so that the temperature difference between the external temperature of the wavelength conversion laser light source 2800 and the fundamental wave path is 120 ° C.
- Design a temperature that maximizes the conversion efficiency of the device Even when the external temperature of the wavelength conversion laser light source 2800 is 0 ° C., the amount of fundamental wave light is 1.5 times that when the wavelength conversion efficiency is maximum, and the external temperature of the wavelength conversion laser light source 2800 and the fundamental wave optical path And the temperature difference becomes 180 ° C. That is, even if the external temperature of the wavelength conversion laser light source 2800 varies from 0 ° C. to 60 ° C., the temperature of the wavelength conversion element can be kept substantially constant at 180 ° C.
- the wavelength conversion element 2305 is directly installed on the laser light source 2900 with the thermal resistance adjusting material 2401 interposed therebetween.
- the difference between T and T 0 is ⁇ T
- the thermal resistance between the fundamental wave path using the thermal resistance adjusting material 2401 and the laser light source is adjusted, and the results are shown in FIGS. It has a configuration that satisfies the relationship.
- a heat transfer material (a material having a high thermal conductivity.
- metal aluminum (237 W / m / K), copper (390 W / m / K) between the heat resistance adjusting material and the wavelength conversion element. ), Silver (420 W / m / K, etc.), the contact area between the thermal resistance adjusting material and the wavelength conversion element can be increased, and the influence of individual variations in contact thermal resistance can be reduced. Become. As a result, individual variations in thermal resistance between the wavelength conversion element and the thermistor can be reduced.
- thermo resistance adjusting material By providing a heat transfer material between the thermistor and the thermal resistance adjusting material, it is possible to further reduce individual variations in thermal resistance between the wavelength conversion element and the thermistor. It is possible to suppress the individual variation of the thermistor temperature at which the wavelength conversion efficiency is maximized, and it is possible to improve the yield and reliability of the wavelength conversion laser light source. As a result, a structure in which a heat transfer material is provided between the thermistor or the wavelength conversion element and the heat resistance adjusting material is preferable.
- the effect of installing the thermal resistance adjusting material between the wavelength conversion element and the thermistor or between the wavelength conversion element and the casing of the wavelength conversion laser light source has been shown.
- the configuration including the thermal resistance adjusting material between the wavelength conversion element and the thermistor or the laser light source according to the present embodiment is not limited to the above configuration, and when the input constant control is performed with the wavelength conversion laser light source having the same configuration. It can also be applied to. The effect is shown below.
- FIG. 27 shows the amount of wavelength-converted light with respect to ⁇ T when constant input control is performed with a conventional wavelength-converted laser light source.
- reference numerals 3001, 3002, and 3003 are plots of wavelength converted light amounts using the fundamental light amount (or excitation light amount: hereinafter referred to as input light amount) as a parameter.
- the relationship between ⁇ T and the wavelength-converted light amount when the minimum input light amount (hereinafter referred to as the minimum light amount) at which the wavelength-converted light amount is 1 or more is shown by a solid line 3001, and the broken line 3002 when the wavelength-converted light amount is 1.1 times the minimum light amount. And indicated by a dotted line 3003 when the minimum light quantity is 1.2 times.
- the ⁇ T range (3004) in which one or more wavelength conversion light amounts can be obtained is when the input light amount is maximum, that is, the curve indicated by the dotted line 3003 is It coincides with the range where the wavelength conversion light quantity becomes 1 or more, and is about 1 ° C. (0.5 ° C. to ⁇ 0.5 ° C.).
- FIG. 28 is a wavelength conversion laser light source provided with a thermal resistance adjusting material 2401 between the wavelength conversion element and the thermistor, or between the wavelength conversion element and the housing of the wavelength conversion laser light source. It is the plot figure which showed the wavelength conversion light quantity with respect to (DELTA) T at the time of performing.
- a solid line 3101 indicates the relationship between ⁇ T and the wavelength converted light amount when the input light amount is the minimum light amount.
- a broken line 3102 indicates the relationship between ⁇ T and the wavelength converted light amount when the input light amount is 1.1 times the minimum light amount.
- a dotted line 3103 indicates the relationship between ⁇ T and the wavelength converted light amount when the input light amount is 1.2 times the minimum light amount.
- the temperature difference between the wavelength conversion element and the thermistor or wavelength conversion laser light source casing increases.
- the temperature at which the wavelength conversion efficiency is maximized is shifted to the lower temperature side as the input light quantity is larger.
- the ⁇ T range 3104 in which the wavelength conversion light quantity shown in FIG. 28 is 1 or more is 1.6 ° C. (0.1 ° C. to ⁇ 1.5 ° C.). It can be seen that the magnification is about 1.6 times that of the conventional wavelength conversion laser light source.
- the broken line 3102 having a smaller input light quantity has a larger wavelength conversion light quantity than the dotted line 3103 having a larger input light quantity.
- the thermal resistance adjusting material 2401 is placed between the wavelength conversion element and the thermistor, or between the wavelength conversion element and the laser light source so that the dotted line 3101 has a larger wavelength conversion light amount than the broken line 3102. It is preferable to adjust the thermal resistance.
- a range of ⁇ T in which a wavelength converted light quantity greater than a predetermined light quantity can be obtained. Can be bigger. That is, the average output can be made constant over a wider temperature range.
- a wavelength conversion laser light source that exhibits the above-described effects can be realized at low cost, and is therefore preferably used for a laser pointer or the like. be able to.
- the pulse duty (pulse oscillation time / pulse period) can be adjusted so that the average light amount of the wavelength converted light becomes 1.
- the pulse When used in a laser pointer or an image display device, it is desirable to drive the pulse at a high speed so that flickering of the output cannot be visually recognized by human eyes, and it is preferable that the frequency is at least 60 Hz or more. In this case, it is possible to realize a wavelength conversion laser light source having a constant average output over a wide temperature range.
- the average output can be made constant over a wide temperature range. For this reason, the output margin of the fundamental wave light (the margin of the input current value) can be reduced, and the wavelength conversion laser light source can be reduced in size and power consumption by simple control.
- FIG. 30 is a schematic diagram of an optical engine of a projector system using the laser proposed in the first to third embodiments as a light source.
- a two-dimensional image display apparatus 1700 according to the present embodiment is an example in which the wavelength conversion laser light source of each of the first to third embodiments is applied to an optical engine of a liquid crystal three-plate projector.
- FIG. 31 is a schematic diagram showing a configuration example of a liquid crystal display to which the wavelength conversion laser light source of each of the first to third embodiments is applied.
- FIG. 32 is a schematic diagram showing a configuration example of a laser light source with a fiber to which the wavelength conversion laser light source of each of the first to third embodiments is applied.
- the two-dimensional image display device 1700 includes an image processing unit 1702, a laser output controller (controller) 1703, an LD power source 1704, red, green, and blue laser light sources 1705R, 1705G, 1705B, beam forming rod lenses 1706R, 1706G, 1706B, a relay.
- Lenses 1707R, 1707G, 1707B, folding mirrors 1708G, 1708B, two-dimensional modulation elements 1709R, 1709G, 1709B for displaying an image, polarizers 1710R, 1710G, 1710B, a combining prism 1711, and a projection lens 1712 are included. .
- the green laser light source 1705G is controlled by a laser output controller 1703 and an LD power source 1704 that control the output of the green light source.
- Laser light from each light source (red, green, blue laser light sources 1705R, 1705G, 1705B) is shaped into a rectangle by beam forming rod lenses 1706R, 1706G, 1706B, and then 2 of each color through relay lenses 1707R, 1707G, 1707B.
- the dimension modulation elements 1709R, 1709G, and 1709B are illuminated.
- the two-dimensionally modulated images of each color are combined by the combining prism 1711 and projected onto the screen from the projection lens 1712 to display an image.
- the green laser light source 1705G is a system in which the laser resonator is closed in the fiber. As a result, it is possible to suppress a decrease in output over time and output fluctuation due to an increase in the loss of the resonator due to dust from the outside or misalignment of the reflecting surface.
- the image processing unit 1702 generates a light amount control signal that varies the output of the laser light in accordance with the luminance information of the video signal 1701 input from a TV, a video device, a PC, or the like, and sends the light amount control signal to the laser output controller 1703. Plays the role of sending out. In this way, the contrast can be improved by controlling the amount of light according to the luminance information.
- the laser output controller 1703 pulse-drives the laser and changes the duty ratio of the laser lighting time (lighting time / (lighting time + non-lighting time)) to change the average light amount.
- Various control methods PWM control can be used.
- the green light source used in the projector system may emit green laser light having a wavelength of 510 nm to 550 nm. With this configuration, green laser output light with high visibility can be obtained, and a color expression close to the primary color can be expressed as a display with good color reproducibility.
- the two-dimensional image display apparatus includes a screen, a plurality of laser light sources, and a scanning unit that scans the laser light sources.
- the laser light sources emit light sources that emit at least red, green, and blue, respectively.
- at least the green light source may be configured using any of the wavelength-converted laser light sources shown in the first to third embodiments.
- This configuration makes it possible to obtain green laser output light with high visibility, so that it can be used for a display with good color reproducibility and can express colors closer to the primary color.
- the spatial modulation element a two-dimensional modulation element using a transmission type liquid crystal or a reflection type liquid crystal, a galvano mirror, a mechanical micro switch MEMS (Micro Electro Mechanical System) represented by DMD (Digital Mirror Device), or the like is used. Of course it is possible.
- a transmission type liquid crystal or a reflection type liquid crystal a galvano mirror, a mechanical micro switch MEMS (Micro Electro Mechanical System) represented by DMD (Digital Mirror Device), or the like.
- DMD Digital Mirror Device
- a PANDA fiber (polarization)
- maintaining maintaining
- abduction reduction when a two-dimensional modulation device using liquid crystal is used, it is preferable to use a polarization maintaining fiber because the modulation characteristic and the polarization characteristic are greatly related.
- a liquid crystal display including a light guide plate member 1808 for converting to a surface light source and illuminating the entire surface of the liquid crystal panel, a polarizing plate / diffusion member 1809 for aligning the polarization direction and removing uneven illumination, a liquid crystal panel 1810, and the like It is also possible to implement 1800. That is, the wavelength conversion laser light source shown in the first, second, and third embodiments can be used as a backlight light source of a liquid crystal display.
- the laser apparatus provided with the wavelength conversion laser light source of the present invention shown in the first to third embodiments can be used as a laser light source 1900 with a fiber for operation.
- This laser light source 1900 with a fiber for operation includes a laser light source, a control unit for controlling the output from the laser light source, an output setting unit 1902 for setting the output, an output connector 1903 for outputting the laser light source, and a region to be irradiated with the laser light.
- a delivery fiber 1904 for guiding, a handpiece 1905, and the like are provided.
- the wavelength conversion laser light source of the present application By applying the wavelength conversion laser light source of the present application to a laser display (image display device), a laser liquid crystal backlight, or a surgical laser light source as described above, the output control stability of the light source can be improved. The effect of expanding the operating temperature and improving the reliability can be obtained.
- a quasi phase matching LiNbO 3 element having a periodically poled structure is used, but this embodiment is not limited to this, and the basic structure has an oxygen octahedron structure.
- a quasi-phase matching wavelength conversion element in which a periodically poled structure is formed in a LiTaO 3 or KTiOPO 4 crystal may be used, and Mg, Ce, or the like is added to these commonly used crystal systems to produce an optical refractive index. You may use the element using the crystal substrate which suppressed the change.
- a quasi-phase-matched wavelength conversion element with a periodically poled structure has the same polarization direction of the incident fundamental wave as that of the outgoing harmonic, but is sensitive to the temperature of the wavelength conversion element and the fluctuation of the fundamental wave wavelength. Therefore, by adopting the configuration / control method proposed in this application, it is possible to detect the output change due to disturbance to each component and control for each element, which is greater than improving the time stability of harmonic output. An effect can be obtained.
- a nonlinear optical crystal having an oxygen octahedron structure in its basic structure such as a potassium titanyl phosphate (KTiOPO 4 : KTP) crystal
- KTiOPO 4 potassium titanyl phosphate
- a domain-inverted structure can be formed, and the absorption factor for visible light is as high as 0.01 cm ⁇ 1 or more, but the absorption factor for infrared light is as low as about 0.002 cm ⁇ 1 to 0.004 cm ⁇ 1 .
- the amount of light of the second harmonic that is visible light is constant and the amount of absorption is also constant, and thus heat is generated by absorption of the second harmonic. Therefore, the effect of the present invention cannot be obtained. Therefore, it is preferable to use a material with an increased absorption rate of infrared light. As a result, the temperature difference between the fundamental wave optical path in the wavelength conversion element and the thermistor is increased, and the ⁇ T allowable range is further increased.
- the temperature control means (the thermistor 206, Peltier 205, and temperature control circuits 102 and 813 are shown in the first and second embodiments) of the wavelength conversion element are omitted, and the temperature control is free. It is also possible to use a laser light source. In addition, since heating and cooling of the fundamental wave path portion can be adjusted at higher speed, it is possible to realize a laser light source with a stable temperature and a stable output wavelength. For this reason, by using this laser light source, it is possible to realize an image display device without color misregistration and a measurement device with little measurement error due to wavelength misalignment.
- a wavelength conversion element with a domain-inverted structure formed in a nonlinear optical crystal implements a heat cycle by installing a non-insulator on the surface that intersects the polarization direction where the domain-inverted wall (boundary where the polarization direction changes) is exposed Then, our own investigation showed that the absorptance of infrared light (wavelength 800nm-1800nm) increased.
- the coating on the surface intersecting with the polarization direction is made of a conductive coating material, a coating material A having an electrical resistivity of 1 ⁇ 10 8 ⁇ ⁇ cm, and an electrical resistivity of 2 ⁇ .
- the coating material B of 10 11 ⁇ ⁇ cm, the SiO 2 film formed by RF sputtering, and the SiO 2 film formed by CVD were subjected to 100 heat cycles of 0 to 80 ° C.
- a non-insulator coat with a rate of 1 ⁇ 10 8 ⁇ ⁇ cm or less it can be seen that the infrared light absorptance is increased by heat cycle.
- the SiO 2 film formed by RF sputtering also has the effect of increasing the absorption rate of infrared light due to the occurrence of DC drift. Moreover, about a heat cycle, even if it is 100 cycles or less, there exists an effect
- the method for increasing the infrared light absorptance of the present embodiment is to perform a process for increasing the infrared light absorptance in a state where a periodically poled structure is formed and a quasi phase matching wavelength conversion element is formed. Therefore, it is easy to form a domain-inverted structure, which is a more preferable method.
- a wavelength conversion laser light source includes a fundamental light source that emits fundamental light, and a wavelength conversion element that has a nonlinear optical effect and converts the fundamental light into harmonic light of different wavelengths.
- a first light receiver that receives light in a specific polarization direction included in the fundamental light emitted from the fundamental light source and converts the light amount into an electrical signal; and harmonic light output from the wavelength conversion element Based on the electrical signal from the second light receiver that converts the light amount into an electrical signal, a temperature holding unit that keeps the temperature of the wavelength conversion element constant, and the second light receiver.
- a first control for controlling the amount of fundamental light emitted from the fundamental light source and a second control for controlling the amount of fundamental light based on an electrical signal from the first light receiver are performed.
- this wavelength conversion laser light source receives light of a specific polarization direction included in the fundamental wave light emitted from the fundamental wave light source by the first light receiver, converts the light amount into an electric signal, and converts it into the electric signal. Based on this, the fundamental wave control unit controls the light amount or wavelength of the fundamental wave light emitted from the fundamental wave light source. Thereby, since the fundamental wave light can be appropriately adjusted according to the change in the polarization component of the fundamental wave light, a wavelength conversion laser light source capable of performing stable and efficient wavelength conversion can be realized.
- the first control for stabilizing the harmonic light is performed by receiving the light quantity of the harmonic light with the second light receiver and feedback-controlling the light quantity of the fundamental light.
- a second control for stabilizing the fundamental wave in the polarization direction that contributes to wavelength conversion by receiving light of a specific polarization direction included in the fundamental wave light with a first light receiver and feedback-controlling the light amount of the fundamental wave light. Is going. This further stabilizes the harmonic light.
- the second light receiver receives the amount of harmonic light and feedback-controls the holding temperature of the temperature holding unit, and performs a third control to appropriately respond to the change in the wavelength of the fundamental wave with the temperature of the wavelength conversion element. ing.
- the first to third controls it is possible to realize a wavelength conversion laser light source capable of performing stable and efficient wavelength conversion.
- the first to third controls are controlled by the fundamental wave control unit so that the execution timing of the first control does not overlap with the execution timings of the second control and the third control. And it is preferable to implement intermittently by the said temperature control part.
- the first control can be controlled in a shorter time than the second control and the third control.
- time-division control is performed intermittently so that the execution timing of the first control does not overlap with the execution timings of the second control and the third control. Accordingly, the basic polarization direction that contributes to wavelength conversion at a timing that does not overlap with the execution timing of the first control while appropriately controlling the light amount of the fundamental wave light with reference to the light amount of the harmonic light at the timing of the first control.
- the temperature of the wavelength conversion element can be adjusted according to the wavelength variation of the fundamental light (third control). Therefore, it is possible to realize a wavelength conversion laser light source that can perform wavelength conversion more stably and efficiently.
- the temperature control unit supplies a current to the temperature holding unit based on a temperature measurement unit that measures the temperature of the wavelength conversion element and a measurement signal from the temperature measurement unit, and holds the temperature. And a temperature controller that controls the holding temperature of the unit to be constant.
- the third control can be accurately performed by configuring the temperature control unit as described above.
- the temperature controller adjusts the holding temperature of the temperature holding unit by wobbling at ⁇ ⁇ t (° C.) around the center temperature Tc (° C.).
- P (Tc + ⁇ t), P (Tc), and P (Tc ⁇ t) where P (Tc + ⁇ t), P (Tc), and P (Tc ⁇ t) are P (Tc + ⁇ t (° C.), Tc (° C.), and Tc ⁇ t (° C.), respectively. If Tc ⁇ t) ⁇ P (Tc) ⁇ P (Tc + ⁇ t), Tc is increased.
- Tc Tc is maintained, and P (Tc ⁇ When ⁇ t)> P (Tc)> P (Tc + ⁇ t), it is preferable to supply a current to the temperature holding unit so as to decrease Tc.
- the third control can be easily and accurately performed by the wobbling by the temperature controller as in the above configuration.
- the range of ⁇ t in which the temperature controller performs wobbling is preferably 0.1 ° C. to 0.2 ° C.
- the temperature controller can perform appropriate wobbling.
- the wobbling period by the temperature controller is preferably 5 seconds to 10 seconds.
- the temperature controller can perform appropriate wobbling.
- a second light receiver that receives the harmonic light output from the wavelength conversion element and converts the light amount into an electric signal, and a temperature holding unit that holds the temperature of the wavelength conversion element constant.
- the fundamental wave control unit controls the amount of fundamental light emitted from the fundamental light source based on an electrical signal from the second light receiver, and the first light reception.
- the first control is performed to stabilize the harmonic light by receiving the light amount of the harmonic light with the second light receiver and feedback-controlling the light amount of the fundamental light.
- a second control for stabilizing the fundamental wave in the polarization direction that contributes to wavelength conversion by receiving light of a specific polarization direction included in the fundamental wave light with a first light receiver and feedback-controlling the light amount of the fundamental wave light. Is going. This further stabilizes the harmonic light.
- the third control is performed so as to cope with a case where the wavelength of the fundamental wave light is changed, thereby deviating from the wavelength of the fundamental wave light optimum for the temperature of the wavelength conversion element held at a constant temperature.
- third control is performed to stabilize the wavelength of the fundamental wave light by receiving the light amount of the harmonic light with the second light receiver and feedback-controlling the wavelength of the fundamental wave light.
- a wavelength conversion laser light source capable of performing stable and efficient wavelength conversion.
- the fundamental wave control unit may perform the first to third so that the execution timing of the first control does not overlap the execution timing of the second control and the third control. It is preferable to carry out the control intermittently.
- the time-sharing control By performing the time-sharing control intermittently so that the execution timing of the first control and the execution timing of the second control and the third control do not overlap as in the above configuration, while properly controlling the light amount of the fundamental wave light based on the light amount of the harmonic light at the first control timing, the fundamental wave in the polarization direction that contributes to wavelength conversion is stabilized at a timing that does not overlap with the execution timing of the first control. (Second control) and the wavelength of the fundamental wave light can be stabilized (third control). Thereby, the wavelength conversion laser light source which can perform wavelength conversion more stably and efficiently can be realized.
- the fundamental light source includes a semiconductor laser that emits excitation light, a double-clad rare earth-doped fiber that absorbs excitation light emitted from the semiconductor laser and emits the fundamental light, and the double-clad rare-earth doped fiber
- the third control can be performed easily and accurately by using the fundamental wave light source having the above configuration.
- the fundamental light source is a distributed feedback semiconductor laser light source including a distributed feedback mirror unit, and the wavelength of the fundamental light is changed by changing a current input to the distributed feedback mirror unit. It is preferable that
- the third control can be performed easily and accurately by using the fundamental wave light source having the above configuration.
- the fundamental wave light source has a distributed feedback mirror unit, and generates a light that is a source of the fundamental wave light, a distributed feedback semiconductor laser light source that emits excitation light, and the excitation light.
- a laser medium that amplifies the intensity of light emitted from the distributed feedback semiconductor laser light source by absorption, and the wavelength of the fundamental wave light is changed by changing a current input to the distributed feedback mirror unit It is preferable that
- the third control can be easily and accurately performed.
- the above configuration further includes a temperature control unit that controls a holding temperature of the temperature holding unit, the temperature control unit measuring a temperature of the wavelength conversion element, and a measurement signal from the temperature measurement unit And a temperature controller for supplying a current to the temperature holding unit and controlling the holding temperature of the temperature holding unit to be constant.
- the temperature of the wavelength conversion element can be reliably kept constant.
- a thermal resistance adjusting material for providing a difference between the temperature of the wavelength conversion element and the temperature measured by the temperature measurement unit is provided between the wavelength conversion element and the temperature measurement unit. It is preferable that
- the permissible range that can cope with the change in the external temperature of the wavelength conversion laser light source can be expanded.
- the thermal resistance adjusting material and the wavelength conversion element, the housing of the wavelength conversion laser light source, or the temperature measurement unit are configured to transmit the contact thermal resistance between the members uniformly. It is preferable that a heat material is provided.
- the permissible range that can cope with the change in the external temperature of the wavelength conversion laser light source can be expanded.
- the contact area between the thermal resistance adjusting material and the wavelength conversion element can be increased, and the influence of individual variations in contact thermal resistance can be reduced.
- the wavelength conversion element is made of an optical crystal mainly having an oxygen octahedron structure as a basic structure, and the optical crystal has a periodicity for matching the phases of the fundamental light and the harmonic light.
- a domain-inverted structure is preferably formed.
- the wavelength conversion element having the above configuration is optimal for this wavelength conversion laser light source.
- the said wavelength conversion element is covered with the coating
- the wavelength conversion element covered with the coating material having the above-described structure increases the absorption rate of infrared light, and the temperature of the fundamental wave path portion of the wavelength conversion element can be easily adjusted.
- the second control when the phase of the electrical signal output from the first light receiver is synchronized with the phase of the electrical signal output from the second light receiver, the second control is selectively performed.
- the third control when the phase of the electric signal output from the first light receiver and the phase of the electric signal output from the second light receiver are asynchronous, the third control is selectively executed. It is preferable.
- the second control depends on whether the phase of the electrical signal output from the first light receiver is synchronized with the phase of the electrical signal output from the second light receiver.
- Appropriate control is possible by selectively executing the third control. That is, when the above two phases are synchronized, it can be predicted that the output fluctuation of the harmonic light is caused by the fundamental light source, so the second control for stabilizing the fundamental wave in the polarization direction contributing to wavelength conversion. Is effective. On the other hand, when both of the above phases are asynchronous, it can be predicted that the output fluctuation of the harmonic light is not the fundamental light wavelength suitable for the temperature of the wavelength conversion element.
- the third control for adjusting the wavelength or the wavelength of the fundamental light is effective.
- a projection display device includes a wavelength conversion laser light source having any one of the above configurations, and a two-dimensional light modulation element that receives the harmonic light emitted from the wavelength conversion laser light source to form an image. And a projection lens that projects an image formed by the two-dimensional modulation element.
- a projection display device with high image quality and low power consumption can be realized by using the above-described wavelength conversion laser light source capable of performing stable and efficient wavelength conversion.
- a liquid crystal display device includes the wavelength-converted laser light source having any one of the above-described structures and a liquid crystal panel that receives light emitted from the light source unit and forms an image.
- a liquid crystal display device with high image quality and low power consumption can be realized by using the wavelength conversion laser light source capable of performing stable and efficient wavelength conversion.
- a laser light source includes the wavelength conversion laser light source having any one of the above-described configurations, and a delivery fiber that guides the harmonic light output from the wavelength conversion laser light source to an irradiation target region. Yes.
- a highly reliable and low power consumption laser light source with a fiber can be realized by using the wavelength conversion laser light source capable of performing stable and efficient wavelength conversion.
- the wavelength conversion laser light source of the present invention is useful for a wavelength conversion laser light source including a fundamental wave light source whose polarization characteristics and oscillation wavelength of the fundamental wave are easily changed, and can be applied to a laser display device having high color reproducibility. It becomes possible.
Abstract
Description
以下、本発明の実施の形態について、図3ないし図13を参照しながら説明する。
本発明の他の実施の形態について図14及び図15を参照し、以下に説明する。
本発明の他の実施の形態に係る波長変換レーザ光源について図16ないし図29を参照し以下に説明する。
図18に示すように、例えば、所定の波長変換光量を得るために、必要な基本波光量が最低となる点(ΔT=0)における基本波光量(以下、基準基本波光量とする)の1.3倍の基本波光量を閾値aとし、当該基準基本波光量の1.1倍の基本波光量を閾値bとする。
図21に示すように、所定の波長変換光量を得るために、必要な基本波光量が最低となる点(ΔT=0)における基本波光量(以下、基準基本波光量とする)の1.15倍の基本波光量を閾値cとし、常に、基本波光量が閾値cに近づくように波長変換素子を加熱/冷却する場合について説明する。
以下に、その効果を示す。
本発明の他の実施の形態について、図30ないし図32を参照し、以下に説明する。
Claims (20)
- 基本波光を出射する基本波光源と、
非線形光学効果を有し、前記基本波光を異なる波長の高調波光に変換する波長変換素子と、
前記基本波光源から出射される基本波光に含まれる特定の偏光方向の光を受光してその光量を電気信号に変換する第1の受光器と、
前記波長変換素子から出力される高調波光を受光してその光量を電気信号に変換するする第2の受光器と、
前記波長変換素子の温度を一定に保持する温度保持部と、
前記第2の受光器からの電気信号に基づいて前記基本波光源から出射される基本波光の光量を制御する第1の制御、および、前記第1の受光器からの電気信号に基づいて前記基本波光の光量を制御する第2の制御をそれぞれ行う基本波制御部と、
前記第2の受光器からの電気信号に基づいて前記温度保持部の保持温度を制御する第3の制御を行う温度制御部と、を含むことを特徴とする波長変換レーザ光源。 - 前記第1の制御の実施タイミングと、前記第2の制御および前記第3の制御の実施タイミングとが重複しないように、前記第1ないし第3の制御が前記基本波制御部および前記温度制御部により間欠的に実施されることを特徴とする請求項1に記載の波長変換レーザ光源。
- 前記温度制御部は、
前記波長変換素子の温度を計測する温度計測部と、
前記温度計測部からの計測信号に基づいて、前記温度保持部に電流を供給し、前記温度保持部の保持温度を一定に制御する温度コントローラと、を含んでいることを特徴とする請求項1または2に記載の波長変換レーザ光源。 - 前記温度コントローラは、中心温度Tc(℃)を中心にして±Δt(℃)でウォブリングすることによって、前記温度保持部の保持温度を調整するものであり、
前記波長変換素子の温度がTc+Δt(℃)、Tc(℃)およびTc-Δt(℃)のときの前記高調波光の光量をそれぞれP(Tc+Δt)、P(Tc)およびP(Tc-Δt)としたとき、
P(Tc-Δt)<P(Tc)<P(Tc+Δt)の場合はTcを上昇させ、
P(Tc+Δt)<P(Tc)>P(Tc-Δt)の場合はTcを維持させ、
P(Tc-Δt)>P(Tc)>P(Tc+Δt)の場合はTcを低下させるよう、前記温度保持部に電流を供給することを特徴とする請求項3に記載の波長変換レーザ光源。 - 前記温度コントローラがウォブリングを行う前記Δtの範囲は、0.1℃~0.2℃であることを特徴とする請求項4に記載の波長変換レーザ光源。
- 前記温度コントローラによる前記ウォブリングの周期が、5秒~10秒であることを特徴とする請求項4または5に記載の波長変換レーザ光源。
- 基本波光を出射する基本波光源と、
非線形光学効果を有し、前記基本波光を異なる波長の高調波光に変換する波長変換素子と、
前記基本波光源から出射される基本波光に含まれる特定の偏光方向の光を受光してその光量を電気信号に変換する第1の受光器と、
前記波長変換素子から出力される高調波光を受光してその光量を電気信号に変換するする第2の受光器と、
前記波長変換素子の温度を一定に保持する温度保持部と、
前記第2の受光器からの電気信号に基づいて前記基本波光源から出射される基本波光の光量を制御する第1の制御、前記第1の受光器からの電気信号に基づいて前記基本波光の光量を制御する第2の制御、および前記第2の受光器からの電気信号に基づいて前記基本波光の波長を制御する第3の制御をそれぞれ行う前記基本波制御部と、を含むことを特徴とする波長変換レーザ光源。 - 前記基本波制御部は、前記第1の制御の実施タイミングと、前記第2の制御および前記第3の制御の実施タイミングとが重複しないように、前記第1ないし第3の制御を間欠的に実施することを特徴とする請求項7に記載の波長変換レーザ光源。
- 前記基本波光源は、
励起光を発する半導体レーザと、
前記半導体レーザから発せられた励起光を吸収し、前記基本波光を発するダブルクラッド希土類添加ファイバと、
前記ダブルクラッド希土類添加ファイバの両端に配置され、当該基本波光源から発せられる前記基本波光の波長を決定する、狭反射帯域のファイバグレーティングおよび広反射帯域のファイバグレーティングと、
前記狭反射帯域のファイバグレーティングに応力を付加するアクチュエータと、を含み、
前記アクチュエータが前記狭反射帯域のファイバグレーティングに与える応力により前記基本波光の波長が変化することを特徴とする請求項7または8に記載の波長変換レーザ光源。 - 前記基本波光源は、分布帰還ミラー部を含む分布帰還型半導体レーザ光源であり、前記分布帰還ミラー部へ投入する電流を変化させることにより、前記基本波光の波長が変化することを特徴とする請求項7または8に記載の波長変換レーザ光源。
- 前記基本波光源は、
分布帰還ミラー部を有し、前記基本波光の元となる光を発生する分布帰還型半導体レーザ光源と、
励起光を発する励起光源と、
前記励起光を吸収することで前記分布帰還型半導体レーザ光源が発する光の強度を増幅させるレーザ媒質と、を含み、
前記分布帰還ミラー部へ投入する電流を変化させることで、前記基本波光の波長が変化することを特徴とする請求項7または8に記載の波長変換レーザ光源。 - 前記温度保持部の保持温度を制御する温度制御部をさらに含み、
前記温度制御部は、
前記波長変換素子の温度を計測する温度計測部と、
前記温度計測部からの計測信号に基づいて、前記温度保持部に電流を供給し、前記温度保持部の保持温度を一定に制御する温度コントローラと、を備えていることを特徴とする請求項7ないし11の何れか1項に記載の波長変換レーザ光源。 - 前記波長変換素子の温度と前記温度計測部で計測される温度との間に差を設けるための熱抵抗調節材が、前記波長変換素子と前記温度計測部との間に設けられていることを特徴とする請求項3ないし6および12の何れか1項に記載の波長変換レーザ光源。
- 前記熱抵抗調節材と、
前記波長変換素子、前記波長変換レーザ光源の筐体、または前記温度計測部と、の間に、
部材間の接触熱抵抗を均一にするための伝熱材が設けられていることを特徴とする請求項13記載の波長変換レーザ光源。 - 前記波長変換素子は、基本構造に酸素八面体構造を主とする光学結晶からなり、
前記光学結晶には、前記基本波光と前記高調波光との位相を整合させるための周期的分極反転構造が形成されていることを特徴とする請求項1ないし14の何れか1項に記載の波長変換レーザ光源。 - 前記波長変換素子は、前記周期的分極反転構造の分極方向と直交する面が電気抵抗率1×108Ω・cm以上の被覆材で覆われていることを特徴とする請求項15記載の波長変換レーザ光源。
- 前記第1の受光器から出力される電気信号の位相と前記第2の受光器から出力される電気信号の位相とが同期しているときには前記第2の制御が選択的に実行される一方、
前記第1の受光器から出力される電気信号の位相と前記第2の受光器から出力される電気信号の位相とが非同期のときには前記第3の制御が選択的に実行されることを特徴とする請求項2または8に記載の波長変換レーザ光源。 - 請求項1ないし17の何れか1項に記載の波長変換レーザ光源と、
前記波長変換レーザ光源から発せられた前記高調波光を受けて画像を形成する2次元光変調素子と、
前記2次元変調素子で形成された画像を投影する投影レンズと、を含むことを特徴とするプロジェクションディスプレイ装置。 - 請求項1ないし17の何れか1項に記載の波長変換レーザ光源を含む光源ユニットと、
前記光源ユニットから発せられた光を受けて画像を形成する液晶パネルと、を含むことを特徴とする液晶ディスプレイ装置。 - 請求項1ないし17の何れか1項に記載の波長変換レーザ光源と、
前記波長変換レーザ光源から出力された前記高調波光を照射対象領域へ導くデリバリファイバと、を含むことを特徴とするレーザ光源。
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