WO2011108256A1 - 波長変換装置およびそれを用いた画像表示装置 - Google Patents
波長変換装置およびそれを用いた画像表示装置 Download PDFInfo
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- 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
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Definitions
- the present invention relates to a wavelength conversion device that can efficiently convert fundamental light into harmonic light and an image display device using the same.
- red, green, and blue laser light sources that are the three primary colors of light are required.
- the red and blue high-power laser light sources are realized by semiconductor lasers
- the green high-power laser light sources are difficult to realize because it is difficult to construct a practically optimal material that can be configured as a semiconductor laser. Therefore, for example, a wavelength converter that converts the wavelength of fundamental wave light from a solid-state laser into a harmonic by a wavelength conversion element and outputs green high-power laser light has attracted attention, and development for mass production is underway.
- a solid-state laser refers to a configuration that obtains laser light using a laser medium, and includes, for example, a semiconductor laser-excited solid-state laser that is excited by a semiconductor laser.
- FIG. 15 is a plan view showing a schematic configuration of a conventional wavelength conversion device 100.
- a conventional wavelength conversion device 100 shown in FIG. 15 includes an excitation laser light source 110, a condenser lens 110c, a laser medium 120, a concave mirror 200, two resonator mirrors 130 (130a and 130b), and wavelength conversion. And an element 140.
- the excitation light 110 a emitted from the excitation laser light source 110 is condensed by the condenser lens 110 c and enters the laser medium 120.
- the laser medium 120 absorbs the excitation light 110a and generates the fundamental wave light 120a by the two resonator mirrors 130 (130a and 130b).
- the wavelength conversion element 140 is disposed between the two resonator mirrors 130 (130 a and 130 b) and converts the wavelength of the fundamental wave light 120 a into the harmonic light 160.
- Each component is fixedly disposed on the base 100a of the wavelength conversion device 100.
- one of the two resonator mirrors 130 (130 a and 130 b) that resonates the fundamental wave light 120 a uses the end surface 300 that is a curved surface of the concave mirror 200.
- the conventional wavelength conversion device 100 has a problem that the number of parts is large and the cost is high. Therefore, a configuration has been proposed in which the resonator mirror 130a is formed not on the end face 300 of the concave mirror 200 but on the end face of the wavelength conversion element 140 and the concave mirror 200 is removed.
- the resonator mirror 130 a is formed on the end face of the wavelength conversion element 140, compared with the conventional wavelength conversion device 100, the efficiency (hereinafter referred to as electricity) that is converted from the input power to the excitation laser light source into the harmonic light 160. There is a problem that the conversion efficiency to light is reduced.
- the wavelength conversion element In order to realize a low power consumption green laser light source with high conversion efficiency from electricity to light, it is necessary for the wavelength conversion element to efficiently convert from fundamental light to harmonic light.
- the image display device when the high-efficiency green laser light source obtained in this way is used, it is possible to display the image to be operated by stabilizing the output of the green laser light at a certain value. It is important to maintain the display of high quality.
- a plurality of green laser light sources using wavelength conversion elements are electrically controlled by a drive control device, and an image display device with high brightness and high image quality is proposed by a field sequential method (see, for example, Patent Document 2). ).
- the rise of the harmonic light obtained in this way was not steep. For this reason, there is a problem that it is difficult to obtain a high-luminance image display device if it is used as it is in an image display device. In addition, since the rise is not steep, there is a problem that it is difficult to control the gradation and it is difficult to obtain high image quality.
- the present invention solves the above-described conventional problems, and can provide a high-efficiency wavelength conversion device that can display a high-luminance and high-quality image even when used as it is in an image display device, and is suitable for downsizing and cost reduction.
- the purpose is to provide.
- a wavelength conversion device includes an excitation light source that generates excitation light, a laser medium that generates fundamental wave light using the excitation light, and a laser medium that sandwiches the laser medium to resonate the fundamental wave light.
- the laser medium is made of a material having a thermo-optic effect and a positive thermo-optic constant
- the pulse modulation signal generated by the driving unit includes an initial section including a rising edge of the pulse and the A residual interval that follows the initial interval, and the average signal strength of the initial interval is higher than the average signal strength of the residual interval.
- An image display device includes a spatial modulation element that spatially modulates incident light, and an illumination unit that includes a laser light source that emits light that illuminates the spatial modulation element from one main surface side;
- the illumination unit is configured to include a red laser light source that emits red laser light, a green laser light source that emits green laser light, and a blue laser light source that emits blue laser light, It is comprised with the solid-state laser light source containing this wavelength converter.
- An image display device emits a spatial modulation element that spatially modulates incident light, a red laser light source that emits red laser light, a green laser light source that emits green laser light, and a blue laser light.
- An illuminating unit that illuminates the spatial modulation element from one main surface side, and supplies a drive signal to the spatial modulation element based on an input image signal, thereby making the spatial modulation element field sequential
- a controller that sequentially emits the red, green, and blue laser light sources in synchronization with a drive signal supplied to the spatial modulation element.
- the green laser light source includes a wavelength conversion device.
- the wavelength conversion unit is composed of a solid-state laser light source, the wavelength conversion unit is made of an excitation light source that generates excitation light, and a material having a thermo-optic effect and a positive thermo-optic constant.
- a laser medium that generates a fundamental wave light by light, two resonator mirrors that are disposed with the laser medium sandwiched between them, and that is disposed between the two resonator mirrors to emit the fundamental wave light.
- FIG. 5C is a diagram illustrating an example of a pulse modulation signal
- FIG. 5C is a diagram illustrating parallelism of two resonator mirrors of the wavelength conversion device according to the first embodiment of the present invention
- FIG. 6 is a diagram schematically showing a state in which fundamental light propagates in a laser medium sandwiched between two resonator mirrors, in which (a) is a laser medium made of a material having a thermo-optic effect and a positive thermo-optic constant.
- (B) is a figure which shows the case of the laser medium which consists of material which does not have a thermo-optic effect as a comparative example.
- (A) is a figure which shows the structure of the laser resonator which has arrange
- (b) and (c) are the figures of FIG. The figure which shows typically the temperature distribution in the laser medium of the direction along the Y-axis of (a) when an excitation laser light source is modulated by the pulse modulation signal shown by (b).
- (A) is a sectional side view of the laser medium and the holding unit
- (b) is a front view of the laser medium and the holding unit
- (c) is a diagram showing the diameters of the laser medium and the excitation light
- (d) is The sectional side view which shows the example which inserted resin in the clearance gap between a laser medium and a holding part.
- the top view which shows schematic structure of the wavelength converter concerning Embodiment 2 of this invention. It is a figure which shows the optical output waveform when the output of a pumping light when driving a pumping laser light source with a rectangular current waveform by a drive unit and the output of a harmonic light are seen on the same time axis.
- the figure which shows an optical output waveform (b) is a figure which shows the optical output waveform of excitation light.
- (A) to (d) are diagrams showing excitation light output waveforms and harmonic light output waveforms when the excitation laser light source is driven with a current waveform in which the signal intensity at the rising portion of the pulse modulation signal is higher than the average signal intensity.
- (A), (b) is a figure which shows a harmonic light output waveform
- (c) is a figure which shows an excitation light output waveform
- (e) is for outputting the excitation light shown by (d)
- the figure which shows a pulse modulation signal (f) is a figure which shows another example of a pulse modulation signal.
- FIG. 6 is a plan view showing a schematic configuration of an image display apparatus according to a fifth embodiment of the present invention.
- FIG. 9A is a diagram illustrating timings of laser light and an image drive signal when an image display apparatus according to a fifth embodiment of the present invention is modulated by a field sequential method, and
- FIG. (B) is a figure which shows the timing of the drive signal of each image of a spatial modulation element.
- the image display apparatus concerning Embodiment 5 of this invention, it is a figure which shows an optical output waveform
- (a) is a figure which shows the time waveform of the harmonic light output of G light source
- (b) is the harmonic light output of (a).
- the figure which shows the time waveform of the excitation light output for (a) The figure which shows the example which divided
- the figure which shows a pumping light output waveform and a harmonic light output waveform when the signal intensity of the rising part of the pulse modulation signal shown in Embodiment 1 of this invention drives a pumping laser light source with a current waveform higher than average signal strength.
- FIG. 4C is a diagram illustrating a time waveform of a drive signal of the spatial modulation element.
- FIG. 7A is a diagram illustrating timings of a laser beam and an image drive signal when an image display apparatus according to a sixth embodiment of the present invention is modulated by a field sequential method.
- FIG. The figure which shows timing, (b) is a figure which shows the timing of the drive signal of each image of a spatial modulation element.
- the top view which shows schematic structure of the conventional wavelength converter.
- FIG. 1A is a plan view showing a schematic configuration of the wavelength conversion device 10 according to the first embodiment of the present invention
- FIG. 1B is an excitation of the wavelength conversion device 10 according to the first embodiment of the present invention
- FIG. 1C is a diagram illustrating an example of a pulse modulation signal for driving the laser light source 11
- FIG. 1C is a diagram illustrating the parallelism of the two resonator mirrors of the wavelength conversion device 10 according to the first embodiment of the present invention. It is.
- the wavelength conversion device 10 includes an excitation laser light source 11 as an excitation light source, a laser medium 12, and two resonator mirrors 13 (13a and 13b).
- the wavelength conversion element 14 and the drive unit 15 are provided.
- the excitation laser light source 11 generates excitation light 11a
- the laser medium 12 generates fundamental wave light 12a by the excitation light 11a.
- the excitation laser light source 11 is, for example, a semiconductor laser that generates 808 nm laser light
- the laser medium 12 is a YVO4 crystal doped with 1% Nd that absorbs 808 nm light.
- the coating on the surface of the two resonator mirrors 13 has a reflectivity of 99% or more for 1064 nm light, for example. Furthermore, the coating of the resonator mirror 13a has a transmittance of 95% or more for 532 nm light, and the coating of the resonator mirror 13b has a transmittance of 95% for 808 nm light, for example. That's it.
- the two resonator mirrors 13 (13a, 13b) are arranged with the laser medium 12 sandwiched in the incident direction of the excitation light 11a to resonate the fundamental wave light 12a.
- the wavelength conversion element 14 is disposed between the two resonator mirrors 13 (13 a and 13 b) and converts the wavelength of the fundamental wave light 12 a into the harmonic light 16. Then, the driving unit 15 drives the excitation laser light source 11 with, for example, the pulse modulation signal in FIG. Each component is fixedly disposed on the base 10 a of the wavelength conversion device 10.
- the laser medium 12 is made of a material having a thermooptic effect and a positive thermooptic constant. Excitation light 11 a generated by the excitation laser light source 11 enters the laser medium 12.
- the laser medium 12 generates a temperature distribution in a direction perpendicular to the optical axis 13c of the excitation light 11a by the excitation light 11a. In other words, the temperature of the laser medium 12 in the vicinity of the optical axis 13c of the excitation light 11a is higher than that at a position away from the optical axis 13c of the excitation light 11a, and there is a temperature difference in a direction perpendicular to the optical axis 13c. A temperature distribution is formed.
- thermo-optic effect Since the laser medium 12 has a thermo-optic effect, the temperature difference causes a refractive index difference in a direction perpendicular to the optical axis 13c of the excitation light 11a, and the laser medium 12 has a lens effect ( Hereinafter referred to as “thermal lens effect”).
- thermo lens effect since the thermo-optic constant of the laser medium 12 is positive, the thermal lens effect due to the thermo-optic effect is optically similar to that of a convex lens. Since the fundamental wave light 12a is converged by the action of the convex lens generated by the thermal lens effect, the fundamental wave light 12a resonates stably with the two resonator mirrors 13a and 13b.
- the driving unit 15 When the driving unit 15 performs pulse modulation driving of the excitation laser light source 11, the signal intensity I1 at the rising portion of the pulse modulation signal is higher than the average signal intensity Iave of the pulse modulation signal as shown in FIG. It is configured to drive with signal strength.
- the drive unit 15 generates the pulse modulation signal shown in FIG. 1B and drives the excitation laser light source 11 in pulses.
- the pulse modulation signal shown in FIG. 1B has an initial period P1 including a rising edge of a pulse and a remaining period P2 following the initial period P1.
- the initial section P1 and the remaining section P2 have a rectangular wave shape, and the signal intensity I1 of the initial section P1 is higher than the signal intensity I2 of the remaining section P2.
- the average signal strength of the initial section P1 is equal to the signal strength I1
- the wavelength conversion device 10 can solve the problem of the rise time during modulation (that is, the problem that the rise of the harmonic light is not steep during pulse driving), and when used in an image display device, Blank time can be reduced. Thereby, a high-intensity and high-quality image can be displayed, and a highly efficient wavelength conversion device 10 suitable for downsizing and cost reduction can be realized.
- FIG. 2 is a diagram schematically showing how the fundamental wave light 12a propagates in a laser medium sandwiched between two resonator mirrors 13 (13a, 13b).
- FIG. 2 (a) has a thermo-optic effect.
- FIG. 2B is a diagram showing the case of the laser medium 121 made of a material having no thermo-optic effect as a comparative example. .
- the fundamental wave light 12a propagates in the laser medium 12 while spreading.
- this fundamental wave light 12a propagates through the laser medium 12, and a part of the fundamental wave light 12a is absorbed by the laser medium 12 to produce a thermal lens effect.
- the fundamental light 12a that has propagated as divergent light by acting as if the convex lens 12d indicated by the broken line in FIG. It propagates as light and reaches the other resonator mirror 13a.
- the fundamental wave light 12a a part of which is reflected by the resonator mirror 13a, travels backward in the same path and reaches the resonator mirror 13b.
- a stable laser resonator is formed by the laser medium 12 and the two resonator mirrors 13a and 13b sandwiching the laser medium 12.
- the fundamental light 12a spreads as it is in the laser medium 121.
- the fundamental wave light 12a propagates between the two resonator mirrors 13a and 13b as diverging light, the laser medium 121 and the two resonator mirrors 13a and 13b sandwiching the laser medium 121 form a laser resonator. Instead, the fundamental light 12a diverges.
- FIG. 3A shows a laser resonator in which a laser medium 12 having a thermo-optic effect and a wavelength conversion element 14 for converting fundamental wave light 12a into harmonic light 16 are arranged between two resonator mirrors 13a and 13b.
- the fundamental wave light 12a is repeatedly reflected between two flat resonator mirrors 13a and 13b without being diverged by the convex lens 12d formed by the thermal lens effect of the laser medium 12, and sandwiches the laser medium 12 and the laser medium 12 2
- the two resonator mirrors 13a and 13b constitute a laser resonator stably.
- FIG. 3 (b) and 3 (c) show the directions along the Y axis in FIG. 3 (a) when the excitation laser light source 11 is modulated by the pulse modulation signal shown in FIG. 1 (b). It is a figure which shows typically the temperature distribution in the laser medium.
- FIG. 3B shows the temperature distribution of the laser medium 12 when the light at the beginning of the pulse modulation signal passes.
- the temperature distribution TP1 is the temperature distribution of the laser medium 12 when the initial section P1 of the pulse modulation signal shown in FIG.
- the temperature distribution TP10 is a temperature distribution of the laser medium 12 when the head portion of a pulse modulation signal having a normal rectangular waveform passes, and is shown as a comparative example.
- the temperature distribution TP2 is a temperature distribution of the laser medium 12 when light in a portion other than the leading portion of the pulse modulation signal (that is, the remaining section P2 of the pulse modulation signal shown in FIG. 1B) passes. It is.
- the laser medium 12 has a refractive index of n, and the laser medium. If the temperature of 12 is T, it is necessary that the thermo-optic constant (dn / dT)> 0.
- the Nd: YVO4 crystal used as the laser medium 12 of the wavelength conversion device 10 according to the first embodiment has a thermo-optic constant of 3.0 ⁇ 10 ⁇ 6 / K. This produces the effect of a convex lens.
- an Nd: GdVO4 crystal or the like that has a positive thermo-optic constant of 4.7 ⁇ 10 ⁇ 6 / K. Since the Nd: GdVO4 crystal has a larger refractive index change due to temperature, the effect of the convex lens is further increased.
- the laser medium is not a single crystal but may be a ceramic such as YAG.
- the Nd concentration can be increased to about 10%, the absorption rate of the ceramics against the incident excitation light can be increased, and a compact wavelength conversion device can be realized. Further, by increasing the absorption rate by setting the Nd concentration from 2% to 10%, the thermal lens effect becomes conspicuous, and the wavelength conversion device has a faster rise time during modulation.
- the amount of heat generated can also be increased by using ceramic as the laser medium, or by increasing the concentration of the additive to 3% or more, or increasing the amount of impurities such as Fe remaining in the crystal. The effect can be remarkable. Therefore, the wavelength conversion device 10 has a fast rise time during modulation. In other words, it is possible to realize the wavelength conversion device 10 in which the rise of the harmonic light during pulse driving is steep.
- pulse modulation and increasing the absorptance of the laser medium 12 may be used alone or in combination.
- the intensity of the excitation light 11a required when the pulse modulation signal rises varies depending on the parallelism of the two resonator mirrors 13a and 13b. This is because, when the parallelism of the two resonator mirrors 13a and 13b is high, the fundamental wave light 12a resonates appropriately, so that even if the thermal lens effect due to the thermo-optic effect of the laser medium 12 is small, the harmonic light 16 is steep. This is because the intensity rises, but when the parallelism is low, the fundamental light 12a does not resonate favorably, and thus the intensity of the harmonic light 16 does not rise steeply.
- the drive unit 15 sets the parallelism of the two resonator mirrors 13a and 13b to ⁇ (min) and the energy of the initial section P1 in the pulse modulation signal to E (joule), 3.33 ⁇ + 1 ⁇ E ⁇ 3.78 ⁇ + 3 (1)
- E the energy of the initial section P1 is obtained by using the average signal intensity I1 (watts) of the initial section P1 and the pulse width T1 (seconds) of the initial section P1.
- the pulse width T1 of the initial period P1 of the pulse modulation signal is short, a higher signal intensity I1 is necessary. Conversely, if the pulse width T1 of the initial period P1 can be made long, It shows that the signal intensity I1 can be suppressed. Therefore, in the image display apparatus using the present embodiment as a light source, the signal intensity I1 is determined in consideration of the maximum value of current that can be supplied by the circuit, and the initial value is determined based on the signal intensity I1 and the above equation (1). It is necessary to determine the pulse width T1 of the section P1.
- the laser medium 12 uses, for example, an Nd: YVO 4 crystal having a large thermo-optic constant.
- an AlGaAs semiconductor laser locked at a wavelength of 808 nm is used as the excitation laser light source 11.
- a wavelength selection unit 11d (shown by a broken line in FIG. 1A) such as a diffraction grating is disposed opposite to the rear end face 11b of the excitation laser light source 11, and the rear side of the excitation laser light source 11 is arranged.
- a part of a laser beam (not shown) from the end face 11b is wavelength-selected by a wavelength selector 11d such as a diffraction grating, and is incident on the rear-side end face 11b and returned. Thereby, the wavelength is locked to 808 nm by the wavelength of the laser beam selected and returned.
- a wavelength selection element may be formed in the chip of the excitation laser light source 11.
- the excitation laser light source 11 may be formed of a distributed feedback laser.
- the excitation laser light source 11 may be constituted by a distributed Bragg reflector laser.
- the wavelength change due to the temperature change of the excitation light 11a can be reduced, and a stable output of the harmonic light 16 can be obtained. Further, as will be described later, since the blank time does not increase under the influence of temperature and can be reduced and held, the wavelength conversion device 10 with more stable output can be realized.
- the excitation light 11 a emitted from the excitation laser light source 11 is condensed by the condenser lens 11 c and is incident on the end surface 12 e of the laser medium 12.
- the laser medium 12 is excited by the excitation light 11a to generate fundamental wave light 12a having a wavelength of 1064 nm.
- the fundamental wave light 12a propagates while being amplified in the laser medium 12, and is incident on the wavelength conversion element 14 in a slightly converged state as shown in FIG. 1A due to the thermal lens effect of the laser medium 12.
- the wavelength conversion element 14 converts a part of the fundamental wave light 12a into green harmonic light 16 having a wavelength of 532 nm, which is the second harmonic wave, by the nonlinear optical effect, and outputs it as output light from one end face 14a.
- the laser medium 12 uses a Nd: YVO4 crystal having a thickness of 2 mm and doped with 1% of Nd.
- the wavelength conversion element 14 is made of PPMgLN having a thickness of 0.5 mm.
- one resonator mirror 13b is constituted by an end face 12e of the laser medium 12, and the other resonator mirror 13a is a wavelength conversion element. 14 end faces 14a.
- This configuration eliminates the need for a new resonator mirror, so that a compact wavelength converter 10 can be realized.
- Both end surfaces of the laser medium 12 and the wavelength conversion element 14 are coated with, for example, dielectric multilayer films 131, 132, 133, and 134.
- the dielectric multilayer film 131 is formed so as to have a high reflectance with respect to wavelengths of 1064 nm and 532 nm and no reflection with respect to a wavelength of 808 nm.
- the dielectric multilayer films 132 and 133 are formed so as to be non-reflective with respect to a wavelength of 1064 nm.
- the dielectric multilayer film 134 is formed to have a high reflectance with respect to a wavelength of 1064 nm and non-reflection with respect to a wavelength of 532 nm.
- the excitation light 11a is efficiently incident on the laser resonator composed of the two resonator mirrors 13a and 13b with little loss and the output harmonic light 16 is efficiently output with little loss.
- the fundamental wave light 12a oscillates stably in a laser resonator composed of two resonator mirrors 13a and 13b.
- FIG. 4A is a side sectional view of the laser medium and the holding unit
- FIG. 4B is a front view of the laser medium and the holding unit
- FIG. 4C is a diagram illustrating the diameters of the laser medium and the excitation light
- FIG. 4D is a side sectional view showing an example in which resin is inserted into the gap between the laser medium and the holding portion. The structure of the laser medium and the like will be described with reference to FIGS. 1 (a) and 4 (a) to 4 (d).
- the distribution of the refractive index change generated by the thermo-optic effect caused by the excitation light 11a incident on the laser medium 12 is preferably axially symmetric with respect to the optical axis of the excitation light 11a. This is because if the refractive index change distribution is axially symmetric, the thermal lens effect due to the thermo-optic effect is prevented from being distorted with respect to the optical axis of the excitation light 11a, compared to the case where the refractive index change distribution is not axially symmetric. This is because the beam of the fundamental wave light 12a resonated by the two resonator mirrors 13a and 13b can be further prevented from being distorted. By suppressing the distortion of the beam of the fundamental wave light 12a, the harmonic light 16 can be obtained with high efficiency.
- the laser medium 12 is formed in a cylindrical shape whose axis is parallel to the incident direction of the excitation light 11a, and further, the laser medium 12
- the holding portion 12f that holds the cylinder is made to have a cylindrical hollow portion. And the holding part 12f can escape the heat which generate
- the diameter D of the laser medium 12 is not more than 5 times the beam diameter d of the excitation light 11a, the thermal resistance between the heat generating portion of the laser medium 12 and the holding part 12f due to absorption of the excitation light 11a can be reduced.
- the temperature rise of the entire laser medium 12 can be suppressed. Therefore, it is possible to suppress a decrease in conversion efficiency from the excitation light 11a to the fundamental wave light 12a due to a temperature rise of the entire laser medium 12.
- a temperature difference is formed in the region through which the fundamental wave light 12a of the laser medium 12 passes, and the fundamental wave light 12a. It is necessary to produce a thermal lens effect. For that purpose, in the region where the fundamental wave light 12a passes, it is preferable that the temperature difference between the beam center of the fundamental wave light 12a and the outside of the beam is large. On the other hand, if the temperature of the laser medium 12 increases, the conversion efficiency from the excitation light 11a to the fundamental wave light 12a decreases, so the temperature of the entire laser medium 12 should be low. Therefore, it is preferable that the heat dissipation performance from the laser medium 12 to the holding portion 12f is high.
- the holding portion 12f is formed of metal.
- metal For example, copper, iron, aluminum, zinc or the like can be used. Since metal has high thermal conductivity, the temperature of the entire laser medium 12 can be efficiently reduced, and the temperature rise of the entire laser medium 12 can be reduced.
- a resin 12g such as heat transfer grease is provided in the gap in order to improve the adhesion between the laser medium 12 and the holding part 12f. It is preferable that it is inserted in. By doing so, the heat transfer between the laser medium 12 and the holding part 12f can be increased, and the temperature rise of the entire laser medium 12 can be suppressed.
- a metal capable of improving adhesion such as indium plating, may be used.
- the thermal conductivity of the laser medium 12 is low.
- Nd: YVO4 which has a thermal conductivity of 5.32 W / m ⁇ K, lower than Nd: YAG, as the laser medium 12, rather than Nd: YAG, which has a thermal conductivity of 14 W / m ⁇ K. .
- the laser medium 12 and the wavelength conversion element 14 may be arranged adjacent to or along the optical axis 13c.
- FIG. 5 is a plan view showing a schematic configuration of the wavelength conversion device 20 according to the second embodiment of the present invention.
- the wavelength conversion device 20 shown in FIG. 5 is similar to the wavelength conversion device 10 shown in FIG. 1A, and includes an excitation laser light source 11, a laser medium 12, and two resonator mirrors 13 (13a and 13b).
- a wavelength conversion element 14 and a drive unit 15 are provided.
- the laser medium 12 is made of a material having a thermooptic effect and a positive thermooptic constant, and the excitation light 11 a is incident on the laser medium 12.
- the fundamental wave light 12a is resonated by the two resonator mirrors 13a and 13b, and a temperature distribution having a temperature difference in a direction perpendicular to the optical axis 13c is generated. This temperature distribution causes the fundamental wave light 12a to resonate. Stabilize.
- the driving unit 15 performs pulse modulation driving of the excitation laser light source 11
- the signal intensity I1 at the rising portion of the pulse modulation signal is higher than the average signal intensity Iave of the pulse modulation signal as shown in FIG. It is configured to drive with signal strength.
- the pulse modulated signal shown in FIG. 1B has an initial interval P1 and a remaining interval P2.
- the initial interval P1 and the residual interval P2 have a rectangular wave shape, so the average signal strength of the initial interval P1 is equal to the signal strength I1, and the average of the residual interval P2 The signal strength is equal to the signal strength I2. Therefore, the average signal strength of the initial section P1 is higher than the average signal strength of the remaining section P2.
- the wavelength conversion device 20 shown in FIG. 5 has a configuration in which the laser medium 12 and the wavelength conversion element 14 are joined along the optical axis 13c. . That is, the end face of the laser medium 12 on which the dielectric multilayer film 132 is laminated and the end face of the wavelength conversion element 14 on which the dielectric multilayer film 133 is laminated are joined together by, for example, a light transmissive adhesive.
- the laser medium 12 and the wavelength conversion element 14 may not be joined, and may simply be disposed adjacently along the optical axis 13c.
- the wavelength converter 20 shown in FIG. 5 further includes a photodetector 17 that receives the fundamental light 18, unlike the wavelength converter 10 shown in FIG.
- the fundamental light 18 that slightly leaks from the resonator mirror 13 a is reflected by the dichroic mirror 17 a and detected by the photodetector 17.
- the detection signal of the photodetector 17 is electrically fed back to the drive unit 15 through the wiring 17b.
- the drive unit 15 is configured to change the modulation intensity of the excitation laser light source 11 in accordance with the output waveform of the fundamental wave light 18.
- the driving unit 15 can feed back the output of the fundamental wave light 18 and drive the excitation laser light source 11 so as to eliminate the difference in characteristics due to individual differences between the laser medium 12 and the resonator mirror 13. Furthermore, since the fundamental wave light 18 that is invisible to the eye, for example, an infrared laser beam having a wavelength of 1064 nm is not emitted to the outside of the wavelength conversion device 20, a safer wavelength conversion device 20 can be realized.
- FIG. 6 is a diagram showing an optical output waveform when the output of the excitation light 11a and the output of the harmonic light 16 are viewed on the same time axis when the driving unit 15 drives the excitation laser light source 11 with a rectangular current waveform.
- FIG. 6A is a diagram showing a light output waveform of the harmonic light 16
- FIG. 6B is a diagram showing a light output waveform of the excitation light 11a.
- the optical axis 13c The temperature distribution in the vertical plane changes with time and is not constant. Therefore, it takes a little time for the temperature to rise until the thermal lens effect occurs in the laser medium 12, and it takes a little time for the fundamental wave light 12a to oscillate. Therefore, the harmonic light 16 that is the output light of the wavelength conversion device 20 is not generated until the fundamental light 12a oscillates, so that a blank time TB shown in the state S1 occurs.
- the excitation laser light source 11 has a signal intensity I1 at the rising portion of the pulse modulation signal as shown in FIG. What is necessary is just to drive by signal strength higher than intensity
- FIGS. 7A and 7B are diagrams showing a harmonic light output waveform and a pump light output waveform and a harmonic light output waveform when the pumping laser light source 11 is driven with a current waveform.
- FIG. 7C and FIG. 7D are diagrams showing excitation light output waveforms.
- FIG. 7E is a diagram showing a pulse modulation signal for outputting the excitation light shown in FIG.
- FIG. 7F is a diagram showing another example of the pulse modulation signal.
- the excitation light output waveform is a rectangular wave
- the excitation light 11a shown in FIG. When the laser medium 12 is excited, the conventional blank time is eliminated as shown by the solid line in FIG.
- the excitation light output waveform is a rectangular wave
- the rise of the harmonic light output waveform is not steep as shown by the broken line in FIG. 7C
- the excitation light 11a shown in FIG. When the laser medium 12 is excited, the rise of the harmonic light output waveform becomes steep as shown by the solid line in FIG.
- the drive unit 15 When the drive unit 15 (FIG. 5) generates the pulse modulation signal shown in FIG. 1B and drives the excitation laser light source 11 (FIG. 5), the excitation light 11a shown in FIG. 7B is output. Is done.
- the driving unit 15 When the driving unit 15 generates the pulse modulation signal shown in FIG. 7E and drives the excitation laser light source 11, the excitation light 11a shown in FIG. 7D is output.
- the pulse modulation signal shown in FIG. 7 (e) has an initial interval P1 and a residual interval P2, similarly to the pulse modulation signal shown in FIG. 1 (b). However, unlike the pulse modulation signal shown in FIG. 1B, the pulse modulation signal shown in FIG. 7E has a triangular waveform in the initial period P1.
- the signal intensity Ip at the time of rising is maximum, and then decreases linearly to the signal intensity I2.
- the excitation laser light source 11 may be driven so that CW (continuous wave) light is superimposed on the excitation light 11a shown in FIGS. 7B and 7D. That is, when the driving unit 15 performs pulse modulation driving of the excitation laser light source 11, as illustrated in FIG. 7F, the driving unit 15 outputs a signal in which a DC (direct current) signal is superimposed on the pulse modulation signal. Alternatively, the excitation laser light source 11 may be driven. At this time, the signal intensity Idc of the DC signal may be set to a signal intensity that does not exceed the threshold value at which the fundamental light 12a oscillates.
- the drive unit 15 may generate a signal in which a DC signal is superimposed on the pulse modulation signal shown in FIG.
- FIG. 8A is a diagram illustrating the wavelength conversion device 25 according to the fourth embodiment of the present invention
- FIG. 8B is a diagram illustrating a pulse modulation signal generated by the drive unit 15, and
- FIG. FIG. 8D shows the curvature of the condenser lens 11c and the beam diameter of the excitation light 11a.
- the wavelength conversion device 25 according to the fourth embodiment of the present invention has a configuration in which a liquid lens is used as the condenser lens 11c, and the drive unit 15 and the condenser lens 11c are connected by a wiring 11e. Other configurations are the same as those of the wavelength conversion device 20 shown in FIG.
- the liquid lens is a lens in which the shape of the unevenness changes according to the voltage applied to the liquid part.
- the beam diameter of the excitation light 11a incident on the laser medium 12 can be changed at high speed.
- the driving unit 15 performs pulse modulation driving of the excitation laser light source 11 with the pulse modulation signal shown in FIG. 8B
- the beam diameter of the excitation light 11a incident on the laser medium 12 is pulse modulated.
- the curvature of the liquid lens is increased so that it becomes smaller than the average beam diameter of the excitation light 11a when the rising portion of the signal is incident, and is larger than the average beam diameter of the excitation light 11a when the falling portion of the pulse modulation signal is incident. Reduce the curvature of the liquid lens.
- the driving unit 15 sets the curvature of the liquid lens 11c to the first curvature value x1 as shown in FIG. 8C. As a result, the excitation light 11a is formed into a beam having a diameter d1. Further, as shown in FIG. 8D, the drive unit 15 sets the curvature of the liquid lens 11c to the second curvature value x2 that is smaller than the first curvature value x1 in the remaining section P2. As a result, the excitation light 11a is formed into a beam having a diameter d2. Since x1> x2, d1 ⁇ d2.
- the excitation light 11a is formed into a beam that is more converged in the initial interval P1 than in the remaining interval P2. Therefore, in the initial section P1, the temperature rise of the laser medium 12 at the incident position of the excitation light 11a can be made steeper.
- FIG. 9 is a plan view showing a schematic configuration of the image display device 30 according to the fifth embodiment of the present invention.
- an image display device 30 according to the fifth embodiment includes an image display device including a spatial modulation element 31 and an illumination device 33 that illuminates the spatial modulation element 31 from one main surface 32.
- the light source of the illumination device 33 includes a plurality of laser light sources 34.
- the laser light source 34 uses laser light sources 34R, 34G, and 34B that emit at least red laser light, green laser light, and blue laser light, respectively. Consists of configuration.
- the laser light source that emits at least green laser light includes the wavelength converter of any one of the wavelength converters 10, 20, and 25 described in the first to fourth embodiments. Is used.
- the illumination device 33 of the image display device 30 includes a plurality of laser light sources 34.
- the illumination device 33 includes a red laser light source (hereinafter referred to as “R light source”) 34R that emits red laser light (hereinafter referred to as “R light”) 34r, a green laser light (hereinafter referred to as “G light”).
- R light source red laser light source
- G light green laser light
- B light source blue laser light source
- the G light source 34G is a solid-state laser light source 34S including any one of the wavelength conversion devices 10, 20, and 25 described in the first to fourth embodiments, and as shown in FIG. A drive unit 15 is included.
- the controller 40 supplies a drive signal to the spatial modulation element 31 based on an image signal input from the outside, and drives the spatial modulation element 31 by a field sequential method (described later). Further, the control unit 40 sequentially emits the R light source 34R, the solid-state laser light source 34S (G light source 34G), and the B light source 34B in synchronization with the drive signal supplied to the spatial modulation element 31.
- the R light 34r, G light 34g, and B light 34b emitted from the plurality of laser light sources 34R, 34G, and 34B are converted into parallel light by the collimator 33a, and one light beam 33d is obtained by the two dichroic mirrors 33b and 33c. Is output from the lighting device 33.
- the luminous flux 33d is mixed by the diffusing plate 35, converted into an enlarged laser beam 36, and incident on the polarization beam splitter 38 by the field lens 37. Then, the light is reflected by the reflection surface 38 a of the polarization beam splitter 38 and is applied to one main surface 32 of the spatial modulation element 31.
- the laser light 36 is modulated by the image signal by the spatial modulation element 31, passes through the polarization beam splitter 38 again, and is projected onto a screen (not shown) or the like by the projection lens 39.
- the image display device 30 capable of displaying a high-luminance and high-quality image can be realized.
- the spatial modulation element 31 may be a reflective liquid crystal display panel. With this configuration, it is possible to realize the image display device 30 with high light utilization efficiency and low power consumption. Note that even if the image display device 30 is configured using a DMD (trademark of Texas Instruments) or a transmissive liquid crystal panel as the spatial modulation element 31, the light use efficiency is similarly high, and operation with low power consumption is realized. be able to.
- DMD trademark of Texas Instruments
- FIG. 10 is a diagram showing the timing of the laser beam and the image drive signal when the image display device 30 according to the fifth embodiment of the present invention is modulated by the field sequential method
- FIG. FIG. 10B is a diagram illustrating the timing of the driving signal of each image of the spatial modulation element 31.
- the rising of the R light 34r, the G light 34g, and the B light 34b is caused by the control unit 40 in accordance with normal field sequential modulation, respectively.
- the R image, the G image, and the B image are driven in synchronism with rising edges of the drive signals.
- the light output within one pulse varies, it may be difficult to accurately control the tone of the image tone.
- FIG. 11 is a diagram showing a light output waveform in the image display device 30 according to the fifth embodiment of the present invention.
- FIG. 11A is a diagram showing a time waveform of the harmonic light output of the G light source 34G.
- FIG. 11B is a diagram showing the time waveform of the excitation light output for the harmonic light output shown in FIG. 11A, and
- FIG. 11C is the same as the harmonic light output shown in FIG. It is a figure which shows the divided example.
- FIG. 12 shows the excitation light output waveform and the harmonic light output when the excitation laser light source is driven with a current waveform in which the signal intensity at the rising portion of the pulse modulation signal shown in Embodiment 1 of the present invention is higher than the average signal intensity.
- FIG. 12A is a diagram illustrating a waveform
- FIG. 12A is a diagram illustrating a harmonic light output waveform
- FIG. 12B is a diagram illustrating an excitation light output waveform.
- FIG. 12B a current waveform in which the signal intensity at the rising portion of the pulse modulation signal is higher than the average signal intensity (that is, as shown in FIG. 1B, the average signal intensity I1 in the initial period P1).
- the excitation laser light source 11 is driven with a current waveform higher than the average signal intensity I2 in the remaining section P2, the temperature rises early in the laser medium 12, and the thermal lens effect appears quickly and remarkably.
- the output waveform of the harmonic light rises sharply.
- FIGS. 12 (a) and 12 (b) the driving method using a normal rectangular waveform and the rise of the harmonic light thereby are shown by broken lines for comparison.
- control unit 40 drives the drive signal of the spatial modulation element 31 and the drive signal of the solid-state laser light source 34S in synchronization with each other, and controls the drive unit 15 to generate a normal rectangular waveform.
- the excitation laser light source 11 of the solid-state laser light source 34S may be driven, and the excitation laser light source 11 of the solid-state laser light source 34S may be controlled to rise earlier than the rise of the drive signal of the spatial modulation element 31.
- FIG. 13 is a diagram showing the temporal relationship between the drive signal and the harmonic light output of the spatial modulation element 31 and the solid-state laser light source 34S
- FIG. 13 (a) is a diagram showing the time waveform of the harmonic light output
- FIG. 13B is a diagram showing the time waveform of the excitation light output
- FIG. 13C is a diagram showing the time waveform of the drive signal of the spatial modulation element 31.
- the period of the time waveform of the drive signal of the spatial modulation element 31 and the drive signal of the solid-state laser light source 34S is synchronized, and the rise of the solid-state laser light source 34S is It is earlier than the rise of the drive signal of the spatial modulation element 31. That is, the control unit 40 outputs a drive signal to the spatial modulation element 31 after outputting a drive start control signal to the drive unit 15 of the solid-state laser light source 34S. Therefore, when the drive signal of the spatial modulation element 31 rises, the laser medium 12 heated by the output of the excitation light 11a has a sufficient thermal lens effect, so that the harmonic light output also rises. As a result, the solid-state laser light source 34S outputs G light 34g as the G light source 34G and is modulated in accordance with the drive signal in the spatial modulation element 31, so that gradation control becomes easy.
- control unit 40 may be configured to drive the spatial modulation element 31 at a frequency of 180 Hz or more and 1000 Hz or less. Normally, flickering of the screen is not felt at 180 Hz or higher for human eyes, and color braking is not an issue at 360 Hz or higher. Note that in the case of modulation faster than 1000 Hz, signal processing becomes complicated, and such fast modulation is unnecessary.
- FIG. 14 is a diagram showing the timing of the laser light and the image drive signal when the image display device 30 according to the sixth embodiment of the present invention is modulated by the field sequential method
- FIG. FIG. 14B is a diagram showing the timing of the driving signal of each image of the spatial modulation element.
- a black period T0 during which the spatial modulation element 31 is not driven is provided between the drive signals corresponding to the respective color images of the spatial modulation element 31. Therefore, the control unit 40 outputs a drive start control signal to the drive unit 15 simultaneously with the fall of the drive signal corresponding to the R image of the spatial modulation element 31.
- the rising timing of the excitation light output can be made earlier by the black period T0 than the rising timing of the drive signal corresponding to the G image of the spatial modulation element 31.
- the light output of the G light 34g has reached a sufficiently high level at the rise of the drive signal corresponding to the G image of the spatial modulation element 31.
- the excitation light output is raised at the same time as the drive signal corresponding to the R image of the spatial modulation element 31 falls, but this is not restrictive.
- the control unit 40 may output the drive start control signal to the drive unit 15 by a predetermined time earlier than the fall of the drive signal corresponding to the R image of the spatial modulation element 31. Even in this case, since the output of the G light is small at the beginning of driving, the R image is not adversely affected.
- the predetermined time may be set to an upper limit value that does not adversely affect the R image.
- the control unit 40 can make the rise timing of the excitation light output as early as possible than the rise timing of the drive signal corresponding to the G image of the spatial modulation element 31. As a result, the light output of the G light 34g can be set to a higher level at the rising edge of the drive signal corresponding to the G image of the spatial modulation element 31.
- the output waveform of the excitation light is a rectangular wave shape, but is not limited thereto.
- the output waveform of the excitation light may be a waveform in which the intensity of the initial section including the rising is higher than the intensity of the remaining section. In this case, the rise of the light output of the G light 34g can be made more steep even more reliably.
- the image display device 30 may further include a photodetector 39 a that detects the laser light 36 at the outer end of the projection lens 39. Then, the control unit 40 temporally determines the relationship between the rise timing of the drive signal of the spatial modulation element 31 and the rise timing of the excitation laser light source 11 of the solid-state laser light source 34S based on the detection result of the photodetector 39a. It is good also as a structure controlled so that it may change.
- the image display device 30 with lower power consumption and easy gradation control can be realized for the reasons described below.
- a user who uses the image display device 30 may change the luminance of the image display device 30 according to the environment in which the image display device 30 is used. In bright places, the brightness of the image display device 30 may be increased in order to improve the visibility of the image. On the contrary, in dark places, the brightness of the image display device 30 may be lowered to reduce power consumption.
- scene control there is also a control technique called scene control that changes the output of a light source in accordance with the brightness of an image displayed by the image display device 30. If scene control is used, the power consumption of the light source can be reduced in the case of a dark image, so that the image display device 30 with low power consumption can be realized.
- the outputs of the R light source 34R, the G light source 34G, and the B light source 34B are reduced.
- the output of the excitation laser light source 11 of the solid-state laser light source 34S becomes small. If the output of the excitation laser light source 11 becomes small, the laser medium 12 of the solid-state laser light source 34S has a small thermal lens effect, and the rise of the output of the harmonic light is delayed.
- the control unit 40 of the image display device 30 determines whether or not the rise of the harmonic light output detected by the photodetector 39a is delayed with respect to the rise of the drive signal of the spatial modulation element 31, and is delayed.
- the drive unit 15 is controlled to advance the rise time of the output of the excitation laser light source 11 by the delay time of the rise of the harmonics.
- the optical output light pulse of the G light 34g and the drive time of the drive signal of the spatial modulation element 31 in the field sequential method become substantially the same, and the image display device 30 with low power consumption and easy gradation control. Can be realized.
- the excitation laser light source 11 is not limited to a laser light source that emits light having a wavelength of 808 nm.
- the laser medium 12 and an additive contained in the laser medium 12 may be a laser light source that emits light having a wavelength that efficiently absorbs light.
- the excitation light source is not limited to the excitation laser light source 11, and may be a light source such as a light emitting diode or a lamp that emits a wavelength at which the laser medium 12 and the additive contained in the laser medium 12 efficiently absorb light. .
- the additive to the laser medium 12 is not limited to Nd, and may be Yb, Pr, or the like.
- the wavelength of the light generated by the wavelength conversion element 14 is not limited to 532 nm.
- a desired wavelength may be obtained by appropriately using the laser medium 12, the additive of the laser medium 12, and the wavelength conversion element 14.
- an element for selecting a wavelength, an element for selecting a polarization, and an element for generating a pulse may be provided in the laser resonator.
- a wavelength conversion device includes an excitation light source that generates excitation light, a laser medium that generates fundamental wave light using the excitation light, and a laser medium that sandwiches the laser medium.
- the laser medium is made of a material having a thermo-optic effect and a positive thermo-optic constant, and the pulse modulation signal generated by the drive unit includes an initial period including a rising edge of a pulse. And a residual interval following the initial interval, and the average signal strength of the initial interval is higher than the average signal strength of the residual interval.
- the excitation light source generates excitation light.
- the laser medium generates fundamental wave light by excitation light.
- the two resonator mirrors are arranged with the laser medium interposed therebetween to resonate the fundamental wave light.
- the wavelength conversion element is arranged between the two resonator mirrors and converts the wavelength of the fundamental wave light into harmonic light.
- the drive unit generates a pulse modulation signal to drive the excitation light source in pulses.
- the laser medium is made of a material having a thermooptic effect and a positive thermooptic constant.
- the pulse modulation signal generated by the drive unit has an initial period including a rising edge of a pulse and a remaining period following the initial period, and the average signal strength of the initial period is higher than the average signal intensity of the remaining period.
- the power of the pumping light incident on the laser medium in the initial section of the pulse modulation signal is larger than the power of the pumping light in the remaining section.
- the heat generation amount of the laser medium in the initial section of the pulse modulation signal is larger than the heat generation amount in the remaining section.
- the driving unit drives the excitation light source in pulses
- the temperature of the laser medium is the lowest immediately before the pulse modulation signal is input, and gradually increases and becomes constant when the pulse modulation signal is input. .
- the heat generation amount of the laser medium in the initial section of the pulse modulation signal is larger than the heat generation amount in the remaining section, the temperature of the laser medium can be rapidly increased in the initial section of the pulse modulation signal. .
- the temperature of the laser medium can be increased sharply, the temperature difference between the position near the optical axis and the position away from the optical axis in the direction perpendicular to the optical axis of the fundamental light is pulsed in the initial section of the pulse modulation signal. Compared to the case where the average signal strength in the initial interval of the modulation signal is the same as the average signal strength in the remaining interval, it can be made larger. Since the laser medium has a thermo-optic effect, if a temperature difference occurs in a direction perpendicular to the optical axis of the fundamental light, a refractive index difference occurs in a direction perpendicular to the optical axis of the fundamental light, and the laser medium has a thermal lens effect. Will have.
- the laser medium is made of a material having a positive thermo-optic constant, if a temperature distribution having a temperature difference in a direction perpendicular to the optical axis of the fundamental wave light of the laser medium is formed, the heat of the laser medium
- the lens effect is an effect of a convex lens with respect to the fundamental wave light.
- the convex lens effect of the laser medium on the fundamental wave light is made larger in the initial section of the pulse modulated signal than in the case where the average signal intensity in the initial section of the pulse modulated signal is the same as the average signal intensity in the remaining section. Can do.
- the wavelength conversion element can convert the wavelength of the fundamental light into the harmonic light from the rising point of the pulse modulation signal.
- the wavelength conversion device can solve the problem of the rise time during modulation, that is, the problem that the rise of the harmonic light is not steep when driving the pulse. Time can be reduced. Thereby, a high-intensity and high-quality image can be displayed, and a highly efficient wavelength conversion device suitable for downsizing and cost reduction can be realized.
- the drive unit when the parallelism of the two resonator mirrors is ⁇ (minutes) and the energy in the initial section of the pulse modulation signal is E (joules), the drive unit is 3.33 ⁇ + 1 ⁇ It may be configured to generate a pulse modulation signal satisfying E ⁇ 3.78 ⁇ + 3.
- the intensity of the excitation light required when the pulse modulation signal rises changes depending on the parallelism of the two resonator mirrors. This is because, when the parallelism of the two resonator mirrors is high, the fundamental wave light resonates favorably, so even if the thermal lens effect due to the thermo-optic effect of the laser medium is small, the intensity of the harmonic light rises sharply but is parallel. This is because when the degree is low, the fundamental light does not resonate favorably, and the intensity of the harmonic light does not rise steeply.
- the drive unit when the parallelism of the two resonator mirrors is ⁇ (minutes) and the energy of the initial period in the pulse modulation signal is E (joules), the drive unit has 3.33 ⁇ + 1 ⁇ E ⁇ 3. A pulse modulation signal satisfying .78 ⁇ + 3 is generated. Therefore, since it is possible to obtain the necessary excitation light intensity according to the parallelism of the two resonator mirrors, the intensity of the harmonic light can be sharply raised.
- the laser medium may be formed in a cylindrical shape whose axis is parallel to the incident direction of the excitation light.
- the laser medium is formed in a cylindrical shape whose axis is parallel to the incident direction of the excitation light, the heat generated in the laser medium by the incidence of the excitation light is axisymmetric with respect to the optical axis of the excitation light. Can escape. Therefore, the temperature distribution can be formed symmetrically with respect to the axis, and the refractive index change distribution generated by the thermo-optic effect can be made axially symmetric.
- the thermal lens effect due to the thermo-optic effect can be prevented from being distorted with respect to the optical axis of the excitation light, compared to the case where the refractive index distribution is not axially symmetric, It is possible to further prevent distortion of the beam shape of the fundamental wave light resonated by the two resonator mirrors. By suppressing distortion of the beam shape of the fundamental wave light, harmonic light can be obtained with high efficiency.
- the above-described wavelength conversion device may further include a holding portion that has a cylindrical hollow portion and accommodates and holds the laser medium in the hollow portion.
- the cylindrical hollow portion is provided and the holding portion that holds and holds the laser medium in the hollow portion is provided, the heat generated in the laser medium is directed toward the holding portion to emit light of excitation light.
- Relief can be reliably made symmetrical with respect to the axis.
- the diameter of the laser medium may be not less than 2 times and not more than 5 times the diameter of the excitation light incident on the laser medium.
- the diameter of the laser medium is smaller than the diameter of the incident excitation light, the pumping light is scattered on the incident surface of the laser medium and the efficiency is lowered.
- the diameter of the laser medium is twice or more than the diameter of the pumping light, it is possible to eliminate the pumping of the pumping light on the incident surface of the laser medium.
- the diameter of the laser medium is not more than five times the diameter of the excitation light, the thermal resistance between the laser medium that generates heat by absorbing the excitation light and the holding part can be reduced. Therefore, the temperature rise of the entire laser medium can be suppressed. As a result, it is possible to suppress a decrease in the conversion efficiency from the excitation light to the fundamental light due to the temperature rise of the entire laser medium.
- the driving unit may generate a signal in which a direct current signal having a signal intensity that does not exceed a threshold value at which the laser medium generates the fundamental light is superimposed on the pulse modulation signal. Good.
- the drive unit generates a signal in which a direct current signal having a signal intensity that does not exceed the threshold value at which the laser medium generates fundamental light is superimposed on the pulse modulation signal. Therefore, the laser medium can be steadily heated by the excitation light generated by the superimposed DC signal. As a result, a temperature distribution having a temperature difference can be steadily formed in a plane perpendicular to the optical axis of the excitation light in the laser medium, and the rise of the harmonic light can be further accelerated by further reducing the blank time. Can do. Thereby, a high-intensity and high-quality image can be displayed, and a highly efficient wavelength conversion device suitable for downsizing and cost reduction can be realized.
- the driving unit drives the variable lens to generate the pulse
- the curvature of the variable lens is set to a first curvature value
- the curvature of the variable lens is set to a second curvature value smaller than the first curvature value. It is good also as a structure.
- the drive unit is disposed between the excitation light source and the laser medium, and drives a variable lens whose curvature can be changed.
- the driving unit sets the curvature of the variable lens to the first curvature value in the initial section of the pulse modulation signal, and sets the curvature of the variable lens to a second curvature value smaller than the first curvature value in the remaining section of the pulse modulation signal. Therefore, since the first curvature value is larger than the second curvature value, the diameter of the excitation light incident on the laser medium is smaller in the initial section than in the remaining section of the pulse modulation signal.
- one of the two resonator mirrors may be configured by an end surface of the laser medium, and the other resonator mirror may be configured by an end surface of the wavelength conversion element.
- This configuration eliminates the need for a new resonator mirror, thus realizing a compact wavelength converter.
- the laser medium and the wavelength conversion element may be arranged adjacent to or along the optical axis of the fundamental wave light.
- the above wavelength conversion device may be configured to further include a wavelength selection unit outside or inside the excitation laser light source.
- the wavelength converter further includes a fundamental light detector that receives the fundamental light emitted from the wavelength conversion element, and the drive unit converts an output waveform of the fundamental light received by the fundamental light detector. Accordingly, the intensity of modulation of the excitation light source may be changed.
- the drive unit changes the intensity of modulation of the excitation light source according to the output waveform of the fundamental light emitted from the wavelength conversion element, so that the difference in characteristics due to individual differences in the excitation light source is eliminated.
- the pulse modulation signal By generating the pulse modulation signal, the output of the harmonic light can be stabilized.
- the pulse modulation signal generated by the drive unit may have a maximum signal strength at the time of rising.
- the pulse modulated signal generated by the drive unit has the maximum signal intensity at the time of rising, so that the rising of the harmonic light can be accelerated more reliably.
- An image display device includes a spatial modulation element that spatially modulates incident light, and an illumination unit that includes a laser light source that emits light that illuminates the spatial modulation element from one main surface side;
- the illumination unit is configured to include a red laser light source that emits red laser light, a green laser light source that emits green laser light, and a blue laser light source that emits blue laser light, It is comprised with the solid-state laser light source containing this wavelength converter.
- a driving signal is supplied to the spatial modulation element based on an input image signal, the spatial modulation element is driven by a field sequential method, and the driving signal is supplied to the spatial modulation element
- a controller that sequentially emits the red, green, and blue laser light sources in synchronization with each other, and the controller supplies the spatial modulation element with a pulse drive rise of the excitation light source of the solid-state laser light source. It is good also as a structure made earlier than the rising of a signal.
- An image display device emits a spatial modulation element that spatially modulates incident light, a red laser light source that emits red laser light, a green laser light source that emits green laser light, and a blue laser light.
- An illuminating unit that illuminates the spatial modulation element from one main surface side, and supplies a drive signal to the spatial modulation element based on an input image signal, thereby making the spatial modulation element field sequential
- a controller that sequentially emits the red, green, and blue laser light sources in synchronization with a drive signal supplied to the spatial modulation element.
- the green laser light source includes a wavelength conversion device.
- the wavelength conversion unit is composed of a solid-state laser light source, the wavelength conversion unit is made of an excitation light source that generates excitation light, and a material having a thermo-optic effect and a positive thermo-optic constant.
- a laser medium that generates a fundamental wave light by light, two resonator mirrors that are disposed with the laser medium sandwiched between them, and that is disposed between the two resonator mirrors to emit the fundamental wave light.
- control unit may be configured such that the rising edge of the pulse driving of the excitation light source is the falling edge of the previous driving signal supplied to the spatial modulation element driven by a field sequential method. It is good also as a structure used simultaneously.
- control unit makes the rise of the pulse drive of the excitation light source coincide with the fall of the previous drive signal supplied to the spatial modulation element driven by the field sequential method.
- the rise of the harmonic light can be accelerated without adversely affecting the modulation of the laser light of other colors.
- control unit may be configured to drive the spatial modulation element at a frequency of 180 Hz or more and 1000 Hz or less.
- This configuration realizes a high-quality image display device that does not flicker on the screen and does not bother with color braking.
- the control unit further includes a harmonic light detector that detects the harmonic light spatially modulated by the spatial modulation element, and the control unit detects that the rise of the harmonic light detected by the harmonic light detector is the spatial modulation. A determination may be made as to whether or not it is delayed from the rise of the drive signal of the element, and if it is determined to be delayed, the pulse drive rise of the excitation light source may be accelerated.
- the spatial modulation element may be a reflective liquid crystal display panel.
- the wavelength conversion device of the present invention can solve the problem of the rise time during modulation, that is, the problem that the rise of the harmonic light is not steep during pulse driving, and can reduce the blank time when used in an image display device. Therefore, it is possible to produce a compact device by outputting the higher harmonic light. Further, when this wavelength conversion device is used, an image display device capable of displaying a high-luminance and high-quality image can be realized and useful.
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Abstract
Description
図1(a)は、本発明の実施の形態1にかかる波長変換装置10の概略構成を示す平面図、図1(b)は、本発明の実施の形態1にかかる波長変換装置10の励起用レーザ光源11を駆動するパルス変調信号の1例を示す図、図1(c)は、本発明の実施の形態1にかかる波長変換装置10の2つの共振器ミラーの平行度を説明する図である。
3.33θ+1<E<3.78θ+3 ・・・(1)
を満たすパルス変調信号を生成する。ここで、初期区間P1のエネルギーEは、初期区間P1の平均信号強度I1(ワット)と初期区間P1のパルス幅T1(秒)とを用いて、
E=I1×T1 ・・・(2)
で表される。したがって、この実施形態では、2つの共振器ミラー13a、13bの平行度に応じて、必要な励起光11aの強度を得ることが可能になっているため、高調波光16の強度を急峻に立ち上がらせることができる。
図5は、本発明の実施の形態2にかかる波長変換装置20の概略構成を示す平面図である。図5に示す波長変換装置20は、図1(a)に示す波長変換装置10と同様に、励起用レーザ光源11と、レーザ媒質12と、2つの共振器ミラー13(13a、13b)と、波長変換素子14と、駆動部15と、を備えている。
図7(a)~図7(d)は、本発明の実施の形態3にかかる波長変換装置20(図5)の、パルス変調信号の立ち上がり部分の信号強度I1が、平均信号強度Iaveより高い電流波形で励起用レーザ光源11を駆動したときの励起光出力波形と高調波光出力波形を示す図で、図7(a)、図7(b)は高調波光出力波形を示す図、図7(c)、図7(d)は励起光出力波形を示す図である。図7(e)は図7(d)に示される励起光を出力するためのパルス変調信号を示す図である。図7(f)はパルス変調信号の別の例を示す図である。
I1=(Ip+I2)/2
となる。したがって、初期区間P1の平均信号強度I1は、図1(b)に示されるパルス変調信号と同様に、残余区間P2の平均信号強度I2より大きくなっている。また、図7(e)に示されるパルス変調信号についても、上記式(1)および式(2)を適用することができる。
図8(a)は、本発明の実施の形態4にかかる波長変換装置25を示す図、図8(b)は、駆動部15が生成するパルス変調信号を示す図、図8(c)、図8(d)は、集光レンズ11cの曲率および励起光11aのビーム径を示す図である。本発明の実施の形態4にかかる波長変換装置25は、集光レンズ11cとして液体レンズを用いる構成で、駆動部15と集光レンズ11cとが配線11eで接続されている。その他の構成は、図5に示される波長変換装置20と同様である。液体レンズは液体部に印加される電圧に応じて、凹凸の形状が変化するレンズである。集光レンズ11cの作用をもつ液体レンズの凹凸を変化させれば、レーザ媒質12に入射する励起光11aのビーム径を高速に変化させることができる。これによって、例えば、駆動部15が図8(b)に示されるパルス変調信号により励起用レーザ光源11をパルス変調駆動する場合に、レーザ媒質12に入射する励起光11aのビーム径は、パルス変調信号の立ち上がり部分が入射する時には励起光11aの平均ビーム径より小さくなるよう、液体レンズの曲率を大きくし、パルス変調信号の立ち下がり部分が入射する時には励起光11aの平均ビーム径より大きくなるよう、液体レンズの曲率を小さくする。
図9は、本発明の実施の形態5にかかる画像表示装置30の概略構成を示す平面図である。図9に示すように、本実施の形態5の画像表示装置30は、空間変調素子31と、この空間変調素子31を一方の主面32から照明する照明装置33と、を備えた画像表示装置30である。この照明装置33の光源は、複数のレーザ光源34を含んで構成され、レーザ光源34は、少なくとも赤色レーザ光、緑色レーザ光および青色レーザ光をそれぞれ出射するレーザ光源34R、34G、34Bを用いた構成からなる。そして、レーザ光源34のうち、少なくとも緑色レーザ光を出射するレーザ光源が、実施の形態1~4で説明された波長変換装置10、20、25のいずれかの波長変換装置を含む固体レーザ光源34Sを用いた構成としている。
図14は、本発明の実施の形態6にかかる画像表示装置30がフィールドシーケンシャル方式により変調されるときのレーザ光と画像駆動信号とのタイミングを示す図で、図14(a)は、励起光を含むレーザ光の発光のタイミングを示す図、図14(b)は、空間変調素子の各画像の駆動信号のタイミングを示す図である。励起光出力の立ち上がりのタイミングを空間変調素子31の駆動信号の立ち上がりのタイミングより少し早くすることにより、G光34gの光出力の光パルスとフィールドシーケンシャル方式における空間変調素子31の駆動信号の立ち上がり時間を略同時とすることにより、階調制御を容易としている。
Claims (19)
- 励起光を発生する励起用光源と、
前記励起光により基本波光を発生するレーザ媒質と、
前記レーザ媒質を挟んで配置されて、前記基本波光を共振させる2つの共振器ミラーと、
前記2つの共振器ミラーの間に配置されて前記基本波光を高調波光に波長変換する波長変換素子と、
パルス変調信号を生成して前記励起用光源をパルス駆動する駆動部と、を備え、
前記レーザ媒質は、熱光学効果を有し熱光学定数が正である材料からなり、
前記駆動部により生成される前記パルス変調信号は、パルスの立ち上がりを含む初期区間と前記初期区間に続く残余区間とを有し、前記初期区間の平均信号強度が前記残余区間の平均信号強度よりも高いことを特徴とする波長変換装置。 - 前記2つの共振器ミラーの平行度をθ(分)、前記パルス変調信号の前記初期区間におけるエネルギーをE(ジュール)としたとき、前記駆動部は、
3.33θ+1<E<3.78θ+3
を満たすパルス変調信号を生成することを特徴とする請求項1に記載の波長変換装置。 - 前記レーザ媒質は、軸が前記励起光の入射方向に平行な円柱状に形成されていることを特徴とする請求項1または2に記載の波長変換装置。
- 円柱状の中空部を有し、前記レーザ媒質を前記中空部に収容して保持する保持部をさらに備えることを特徴とする請求項3に記載の波長変換装置。
- 前記レーザ媒質の直径は、前記レーザ媒質に入射する前記励起光の直径の2倍以上かつ5倍以下であることを特徴とする請求項4に記載の波長変換装置。
- 前記駆動部は、前記レーザ媒質が前記基本波光を発生するしきい値を超えない信号強度の直流信号を前記パルス変調信号に重畳した信号を生成することを特徴とする請求項1ないし5のいずれか1項に記載の波長変換装置。
- 前記励起用光源と前記レーザ媒質との間に配置され、曲率が変更可能な可変レンズをさらに備え、
前記駆動部は、前記可変レンズを駆動して、前記パルス変調信号の前記初期区間では前記可変レンズの曲率を第1曲率値に設定し、前記パルス変調信号の前記残余区間では前記可変レンズの曲率を前記第1曲率値より小さい第2曲率値に設定することを特徴とする請求項1ないし6のいずれか1項に記載の波長変換装置。 - 前記2つの共振器ミラーのうち、一方の共振器ミラーは、前記レーザ媒質の端面で構成され、他方の共振器ミラーは、前記波長変換素子の端面で構成されることを特徴とする請求項1ないし7のいずれか1項に記載の波長変換装置。
- 前記レーザ媒質と前記波長変換素子とが、前記基本波光の光軸に沿って隣接して配置され、または接合されていることを特徴とする請求項8に記載の波長変換装置。
- 前記励起用レーザ光源の外部または内部に、波長選択部をさらに備えたことを特徴とする請求項1ないし9のいずれか1項に記載の波長変換装置。
- 前記波長変換素子から出る前記基本波光を受光する基本波光検出器をさらに備え、
前記駆動部は、前記基本波光検出器により受光された前記基本波光の出力波形に応じて前記励起用光源の変調の強さを変えることを特徴とする請求項1ないし10のいずれか1項に記載の波長変換装置。 - 前記駆動部により生成される前記パルス変調信号は、立ち上がり時点の信号強度が最大であることを特徴とする請求項1ないし11のいずれか1項に記載の波長変換装置。
- 入射光を空間的に変調する空間変調素子と、
前記空間変調素子を一方の主面側から照明する光を出射するレーザ光源を有する照明部と、を備え、
前記照明部は、赤色レーザ光を出射する赤色レーザ光源、緑色レーザ光を出射する緑色レーザ光源および青色レーザ光を出射する青色レーザ光源を含んで構成され、
前記緑色レーザ光源は、請求項1ないし12のいずれか1項に記載の波長変換装置を含む固体レーザ光源で構成されていることを特徴とする画像表示装置。 - 入力される画像信号に基づき前記空間変調素子に駆動信号を供給して前記空間変調素子をフィールドシーケンシャル方式により駆動し、かつ、前記空間変調素子に供給する駆動信号に同期して前記赤色、緑色および青色レーザ光源を順に発光させる制御部をさらに備え、
前記制御部は、前記固体レーザ光源の前記励起用光源のパルス駆動の立ち上がりを前記空間変調素子に供給する駆動信号の立ち上がりよりも早くすることを特徴とする請求項13に記載の画像表示装置。 - 入射光を空間的に変調する空間変調素子と、
赤色レーザ光を出射する赤色レーザ光源、緑色レーザ光を出射する緑色レーザ光源および青色レーザ光を出射する青色レーザ光源を有し、前記空間変調素子を一方の主面側から照明する照明部と、
入力される画像信号に基づき前記空間変調素子に駆動信号を供給して前記空間変調素子をフィールドシーケンシャル方式により駆動し、かつ、前記空間変調素子に供給する駆動信号に同期して前記赤色、緑色および青色レーザ光源を順に発光させる制御部と、
を備え、
前記緑色レーザ光源は、波長変換装置を含む固体レーザ光源で構成され、
前記波長変換部は、
励起光を発生する励起用光源と、
熱光学効果を有し熱光学定数が正である材料からなり、前記励起光により基本波光を発生するレーザ媒質と、
前記レーザ媒質を挟んで配置されて、前記基本波光を共振させる2つの共振器ミラーと、
前記2つの共振器ミラーの間に配置されて前記基本波光を高調波光に波長変換する波長変換素子と、
前記励起用光源をパルス駆動する駆動部と、
を含み、
前記制御部は、前記励起用光源のパルス駆動の立ち上がりを前記空間変調素子に供給する駆動信号の立ち上がりよりも早くすることを特徴とする画像表示装置。 - 前記制御部は、前記励起用光源のパルス駆動の立ち上がりを、フィールドシーケンシャル方式により駆動している前記空間変調素子に供給する1つ前の駆動信号の立ち下がりと同時とすることを特徴とする請求項14または15に記載の画像表示装置。
- 前記制御部は、前記空間変調素子を180Hz以上かつ1000Hz以下の周波数で駆動することを特徴とする請求項14ないし16のいずれか1項に記載の画像表示装置。
- 前記空間変調素子により空間的に変調された前記高調波光を検出する高調波光検出器をさらに備え、
前記制御部は、前記高調波光検出器により検出された前記高調波光の立ち上がりが前記空間変調素子の駆動信号の立ち上がりより遅れているか否かを判定し、遅れていると判定すると、前記励起用光源のパルス駆動の立ち上がりを早めることを特徴とする請求項14ないし17のいずれか1項に記載の画像表示装置。 - 前記空間変調素子は、反射型液晶表示パネルであることを特徴とする請求項13ないし18のいずれか1項に記載の画像表示装置。
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JP2012503010A JP5524325B2 (ja) | 2010-03-02 | 2011-03-01 | 波長変換装置およびそれを用いた画像表示装置 |
US13/266,956 US8976203B2 (en) | 2010-03-02 | 2011-03-01 | Wavelength conversion device and image display apparatus using same |
CN201180001932.2A CN102414943B (zh) | 2010-03-02 | 2011-03-01 | 波长转换装置及利用该波长转换装置的图像显示装置 |
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JP2016048237A (ja) * | 2014-08-26 | 2016-04-07 | 株式会社トプコン | レーザ測量装置 |
JP2019135765A (ja) * | 2017-12-15 | 2019-08-15 | クリスティ デジタル システムズ ユーエスエイ インコーポレイテッド | 光パルスシステム |
WO2019220739A1 (ja) * | 2018-05-17 | 2019-11-21 | パナソニックIpマネジメント株式会社 | プロジェクタ光源変調装置及び変調方法 |
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JP5978612B2 (ja) * | 2011-07-13 | 2016-08-24 | ソニー株式会社 | 照明装置および表示装置 |
EP3102980B1 (en) * | 2014-02-03 | 2021-04-21 | IPG Photonics Corporation | High-power ultra-short pulse fiber laser-illuminated projector |
JP6631273B2 (ja) * | 2016-01-25 | 2020-01-15 | 株式会社リコー | 画像投射装置 |
JP6800221B2 (ja) * | 2016-05-13 | 2020-12-16 | ヌヴォトンテクノロジージャパン株式会社 | 光源装置及び照明装置 |
KR102636682B1 (ko) * | 2016-12-21 | 2024-02-15 | 엘지디스플레이 주식회사 | 표시장치와 그 구동방법 |
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US20120044280A1 (en) | 2012-02-23 |
US8976203B2 (en) | 2015-03-10 |
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JPWO2011108256A1 (ja) | 2013-06-20 |
JP5524325B2 (ja) | 2014-06-18 |
CN102414943B (zh) | 2014-05-07 |
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