JP2010177406A - Light source device and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source device of low power consumption, whose light conversion efficiency is less degraded even if the quantity of output light is adjusted, and to provide an image display device. <P>SOLUTION: A light source device comprises: a laser module 10 provided with a laser array chip 11 as a light-emitting element, an external mirror 17 as a resonator mirror, and a wavelength conversion element 16 to generate output light W2 that is wavelength-converted by passing a basic laser beam W1 generated between the laser array chip 11 and the external mirror 17 through the wavelength conversion element 16; and a controlling section 20 for driving the laser module 10 by a pulse-like driving signal 21. The controlling section 20 adjusts the quantity of the output light W2 by changing the pulse cycle 33 of the driving signal 21 of the laser module 10 according to a light-quantity controlling signal 23 that is input from the exterior. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light source device and an image display device.

  In recent years, in image display devices such as projectors, light bulbs such as liquid crystal panels are illuminated using RGB three-color solid light sources that can be made smaller, lower power consumption, and higher color gamut than conventional lamp light sources. The method to do is put into practical use. For example, an LED (Light Emitting Diode) light source or a laser light source has been put to practical use as the solid light source. However, the laser light source is particularly convenient because it has high directivity of light flux and can use light without waste. Since the laser light source can easily adjust the output light amount, it is possible to adjust the white balance by changing the RGB output light amount distribution, or to adjust the output light amount according to the viewing environment of the image. is there. As a method for adjusting the amount of output light, as shown in Patent Document 1, it is common to adjust by changing the absolute value of the driving current, that is, the amplitude of the driving power.

Japanese Patent Laid-Open No. 10-49901

  The following problems remain in the conventional technology. That is, the laser light source has a threshold value, and there is a characteristic that laser light does not oscillate below a certain value of driving power and output light cannot be obtained. Therefore, if the output light quantity is adjusted by adjusting the amplitude of the driving power, a phenomenon that the light conversion efficiency is lowered occurs. The output light amount here is a time average value of the optical power of the output light, and the light conversion efficiency is a value obtained by dividing the output light amount by the time average value of the input driving power. This phenomenon that the light conversion efficiency decreases becomes more pronounced as the amount of output light decreases. For example, if only a very small amount of light is output, most of the input drive power is consumed as power to exceed the threshold. Therefore, the light conversion efficiency is greatly reduced.

  The present invention is realized as the following forms or application examples so as to solve at least a part of the problems described above.

Application Example 1 A light source device according to this application example includes a light emitting element, a resonator mirror, and a wavelength conversion element, and the basic laser light generated between the light emitting element and the resonator mirror A light source device comprising: a laser module that generates output light that has been wavelength-converted through a conversion element; and a control unit that drives the laser module with a pulsed drive signal. The light amount of the output light is adjusted by changing a pulse period of the drive signal of the laser module in accordance with a light amount control signal.
According to this configuration, the output light amount is adjusted on a time average basis by changing the number of pulses within a certain time, so that the threshold value is reduced, and even if the output light amount is adjusted, the light conversion efficiency is reduced. Less power consumption.

Application Example 2 In the light source device according to the application example described above, the pulse width of the drive signal is constant.
This configuration is preferable because the output of the laser light in each pulse is equal, that is, the light conversion efficiency is constant regardless of the amount of output in principle.

Application Example 3 In the light source device according to the application example, the pulse width of the drive signal is controlled to be longer when the light amount instruction value of the light amount control signal is lower. To do.
According to such a configuration, when the output light amount is reduced and the pulse cycle is lengthened, it is possible to compensate for the rise of the output light being delayed due to the cooling effect between the pulses and the light conversion efficiency being lowered. .

Application Example 4 An image display device according to this application example includes the light source device according to the application example described above, and displays an image using light from the light source device.
According to such a configuration, since the light source device of the above application example is provided, it is possible to provide an image display device with low power consumption with little reduction in light conversion efficiency even when the output light amount is adjusted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
A first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, and FIG. FIG. 1 is an overall block diagram of a light source device according to the present embodiment, FIG. 2 is a top view of the laser module, and FIG. 3 is a side view of the laser module of FIG.
As shown in FIG. 1, the light source device according to this embodiment includes a control unit 20 and a laser module 10. The control unit 20 recognizes the output light amount from the light amount monitor signal 22 from the laser module 10, adjusts the drive signal 21 of the laser module 10, and performs feedback so that the output light amount matches the light amount instruction value of the light amount control signal 23. Control is in progress. That is, APC (Automatic Power Control) driving is performed.

  As shown in FIG. 2, the laser module 10 of the present embodiment includes a laser array chip 11 as a light emitting element, an external mirror 17 as a resonator mirror, and a wavelength conversion element 16. It is arranged on the table 2.

  The laser array chip 11 is a surface-emitting laser array chip that emits light in a direction perpendicular to the substrate surface, which is formed and cut out collectively on a GaAs substrate by a semiconductor process. A light emitting unit 11a is provided. The laser array chip 11 is supported by a support portion 13. Further, the support portion 13 is fixed to the fixing member 3 placed on the one end 2 a side on the base 2.

  Further, the peak wavelengths of the seven lights emitted from the light emitting unit 11a are substantially equal, and in this embodiment, 1060 nm. As shown in the enlarged view of FIG. 2, the light emitting portion 11a has a configuration in which an active layer 11c made of InGaAs is stacked on a DBR (Distributed Bragg Reflector) layer 11b in which AlGaAs and GaAs are periodically stacked. Yes. The DBR layer 11b functions as a mirror having a high reflectance.

  The external mirror 17 and the wavelength conversion element 16 are disposed on the optical path of the light emitted from the light emitting unit 11a. The external mirror 17 is an element having a structure in which a high-refractive index layer and a low-refractive index layer called VHG (Volume Holographic Grating) are periodically repeated, and only for light having a wavelength of the basic laser light W1 of 1060 nm. It acts as a selectively reflecting mirror and has a function of transmitting light of other wavelengths. The basic laser light W1 emitted from the light emitting unit 11a is selectively reflected by the external mirror 17, returned to the light emitting unit 11a, and then reflected again by the DBR layer 11b in the light emitting unit 11a. Thus, since a laser resonator structure is formed between the light emitting portion 11a and the external mirror 17, the basic laser light W1 is repeatedly reflected and amplified by passing through the active layer 11c to enter a laser oscillation state. .

  As the wavelength conversion element 16, PPLN (Periodically Poled Lithium Niobate), which is a nonlinear optical element, is used. As shown in FIG. 3, the wavelength conversion element 16 is provided on a support member 4 placed on the base 2 and is a basic laser. The position is adjusted so that the light W <b> 1 passes through substantially the center of the wavelength conversion element 16. In the present embodiment, the wavelength conversion element 16 is disposed between the light emitting unit 11 a and the external mirror 17. As shown in FIG. 3, a part of the basic laser light W <b> 1 emitted from the light emitting unit 11 a and directed to the external mirror 17 passes through the wavelength conversion element 16, thereby being half-wavelength light (530 nm), that is, secondary. It is converted into harmonic light. Since the external mirror 17 has transmission characteristics with respect to the wavelength of the second harmonic, the wavelength-converted second harmonic light is output to the outside through the external mirror 17 as output light W2. A part of the basic laser light W1 reflected by the external mirror 17 and returning to the light emitting unit 11a is also wavelength-converted, but this light is absorbed around the light emitting unit 11a and changed to heat. In the present embodiment, this light is absorbed without being used, but may be appropriately extracted using a wavelength selection filter or the like and used as the output light W2. In the present embodiment, the wavelength conversion element 16 is disposed in the laser resonator structure. However, the wavelength conversion element 16 may be disposed outside the laser resonator structure. In this case, since the basic laser light passes through the wavelength conversion element 16 only once, the wavelength-converted output light W2 is output only in one direction.

  The wavelength conversion efficiency (wavelength conversion efficiency) in the wavelength conversion element 16 has a non-linear characteristic. For example, the stronger the intensity (amplitude) of the basic laser light W1 incident on the wavelength conversion element 16, the higher the wavelength conversion efficiency. Get higher. However, the overall wavelength conversion efficiency in the wavelength conversion element 16 is about 40 to 70%. That is, not all of the basic laser light W1 emitted from the light emitting unit 11a is converted into the output light W2 that is the second harmonic.

  The output light W <b> 2 output to the outside passes through the beam splitter 19, a part of which is separated and enters the light receiving element 18. The light receiving element 18 outputs a current corresponding to the amount of incident light and sends it as a light amount monitor signal 22 to the control unit 20 through a monitor FPC (Flexible Printed Circuit) 15 connected to the light receiving element 18.

  The light emitting unit 11a is connected to the power supply FPC 14 by wire bonding 11d and further connected to the control unit 20. The control unit 20 supplies driving power to the light emitting unit 11 a through the power supply FPC 14 to drive the laser module 10.

  Next, a driving method of the light source device according to the present embodiment will be described with reference to FIGS. 4 to 7 while comparing with a conventional driving method. 4 is a diagram showing a conventional drive signal, FIG. 5 is a diagram showing the relationship between the drive power and the output light amount, FIG. 6 is a diagram showing the drive signal in the present embodiment, and FIG. 7 is the relationship between the drive power and the output light amount. FIG. The configuration of the light source device will be described with reference to FIGS.

  Since the wavelength conversion efficiency of the wavelength conversion element 16 increases as the instantaneous power of the basic laser light W1 increases, the laser module is driven by an intermittent signal, that is, a pulsed drive signal, rather than being driven by a constant signal. The light conversion efficiency of 10 is increased. The pulse period 33 is preferably very short so as not to be felt by the eyes, and is generally driven with a value of about several hundreds to 1 μs. The pulse period 33 and the pulse width 34 are determined so as to increase the light conversion efficiency depending on the characteristics of the laser array chip 11 and the wavelength conversion element 16 as light emitting elements.

  The conventional adjustment of the output light amount uses a method of controlling the output light amount by changing the pulse amplitude 31 of the drive signal as shown in FIG. 4, and the pulse period 33 is 1 μs and the pulse width 34 is 0.5 μs. To do. The relationship between the driving power and the output light quantity has a characteristic having a threshold value 32 of about 11.5 W as shown in FIG. In other words, even when power is applied up to 11.5 W, there is almost no light, and the output light quantity increases rapidly with more driving power.

  Here, the threshold value 32 does not mean that the output light quantity is zero, but some light is output, but this occurs because there are a plurality of light emitting units 11a and the threshold values 32 in the respective light emitting units 11a are different. It is a phenomenon. Here, as shown in FIG. 5, the slope of the output light amount is linearly approximated, and the drive power at the intersection with the line where the output light amount becomes 0 is set as the threshold value 32.

  In the present embodiment, the control unit 20 adjusts the output light amount in the range of 0.5W to 4W. For example, when the light amount control signal 23 is set to 4 W, the control unit 20 performs APC driving of the light source device by adjusting the amplitude of the drive signal 21 so that the light amount monitor signal 22 becomes a value corresponding to 4 W.

  As shown in FIG. 5, the driving power at this time was 42.6 W, and the light conversion efficiency was 9.4%. In this state, it can be seen that the light conversion efficiency is almost the maximum. However, when this light source device is used so that the output light amount is adjusted to 0.5 W, the driving power is 16.2 W, the light conversion efficiency is 3.1%, and the light conversion efficiency is lowered. .

  In contrast to the above-described conventional example, in the present embodiment, as shown in FIG. 6, by changing the pulse period 33 without changing the pulse width 34 of the drive signal 21, the time average value of the drive power is changed and the output light quantity is changed. Adjust. In the control unit 20, a pulse period 33 corresponding to the light amount control signal 23 is determined in advance, and is stored as a calculation formula in a memory in the control unit 20. The calculation formula of the pulse period 33 is set to an optimum value by a prior experiment. For example, in this embodiment, the following formula (1) is used.

Here, Tp is the pulse period 33 (μs), and Pv is the light quantity instruction value (W) of the light quantity control signal 23. Here, the pulse width 34 is set to 0.5 μs, which is equal to the conventional example.
In the equation (1), the pulse period 33 at the output light amount 4 W is 1 μs, and the driving conditions are the same as in the conventional example.

  When the output light quantity is adjusted by changing the light quantity control signal 23, the control unit 20 changes the pulse period 33 of the drive signal 21 according to the equation (1). At this time, the coefficient of the expression (1) is determined so that an output light amount substantially equal to the light amount control signal 23 is obtained. For example, when adjusting the output light amount to be 0.5 W, the pulse period 33 is set to about 3.3 μs from the equation (1). Under this condition, an output light amount of approximately 0.5 W can be obtained without changing the pulse amplitude 31.

Further, the control unit 20 adjusts the pulse amplitude 31 of the drive signal 21 so that the light quantity monitor signal 22 becomes a value corresponding to the light quantity control signal 23 and APC drives the light source device.
As a result of using such a driving method, the relationship between the driving power and the output light quantity is as shown in FIG. When adjusted and used so that the amount of output light is 0.5 W, the driving power is 12.9 W and the light conversion efficiency is 3.9%, which is an improvement over the conventional example. Further, the threshold value 32 is 8.8 W, which is lower than the conventional example.

  As in this embodiment, by adjusting the output light amount by increasing the pulse period 33 without changing the pulse width 34, the reduction in light conversion efficiency is reduced even if the output light amount is adjusted. A light source device with low power consumption can be provided. In this embodiment, the APC driving is performed by adjusting the pulse amplitude 31, but the APC driving may be performed by adjusting the driving power by adjusting the pulse period 33 and the pulse width 34.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a diagram showing drive signals in this embodiment, and FIG. 9 is a diagram showing the relationship between the drive power and the output light quantity.

The driving method of the present embodiment is a method of controlling by changing both the pulse period 33 and the pulse width 34 as shown in FIG.
Also in the present embodiment, the control unit 20 adjusts the output light amount in the range of 0.5W to 4W. The drive condition when the output light quantity is 4 W is the same as that of the first embodiment, but the output light quantity is adjusted by changing both the pulse period 33 and the pulse width 34 of the drive signal 21 as shown in FIG. In the control unit 20, a pulse period 33 and a pulse width 34 corresponding to the light amount control signal 23 are determined in advance, and are stored as calculation formulas in a memory in the control unit 20. The calculation formulas for the pulse period 33 and the pulse width 34 are set to optimum values by a prior experiment. For example, in this embodiment, the following formulas (2) and (3) are used.

Here, Tp is the pulse period 33 (μs), Pv is the light amount instruction value (W) of the light amount control signal 23, and Tw is the pulse width 34 (μs).
In the expressions (2) and (3), the pulse period 33 in the output light quantity 4W is 1 μs, the pulse width 34 is 0.5 μs, and the driving conditions are the same as in the conventional example, but the light quantity instruction value Pv is lower than 4W. In some cases, the driving condition is that the pulse width 34 becomes longer and the pulse period 33 becomes longer according to the pulse width 34.

  For example, when the output light quantity is adjusted to 0.5 W, the pulse period 33 is set to about 17.0 μs from the equation (2), and the pulse width 34 is set to 2.3 μs from the equation (3). Under this condition, an output light amount of approximately 0.5 W can be obtained without changing the pulse amplitude 31.

Further, the control unit 20 adjusts the pulse amplitude 31 of the drive signal 21 so that the light quantity monitor signal 22 becomes a value corresponding to the light quantity control signal 23 and APC drives the light source device.
As a result of using such a driving method, the relationship between the driving power and the output light quantity is as shown in FIG.

  When the output light amount is adjusted to 0.5 W, the driving power is 11.9 W, the light conversion efficiency is 4.2%, and the threshold value 32 is 6.8 W. It can be seen that the improvement is further improved compared to the first embodiment.

  In this embodiment, the APC drive is performed by adjusting the pulse amplitude 31, but the drive power may be adjusted by adjusting the pulse period 33 and the pulse width 34 to perform the APC drive.

   As in this embodiment, the pulse width 34 of the drive signal is controlled to be longer when the light intensity instruction value of the light intensity control signal 23 is lower, thereby reducing the output light intensity and extending the pulse period 33. Sometimes, it is possible to compensate that the rise of the output light is delayed due to the cooling effect between the pulses and the light conversion efficiency is lowered. In addition, due to the characteristics of the wavelength conversion element that absorbs laser light, the light conversion efficiency is reduced even when the temperature of the wavelength conversion element decreases, particularly when the average power of the basic laser light is small. Can be compensated. As a result, even if the output light quantity is adjusted, the decrease in light conversion efficiency is further reduced, so that a light source device with even lower power consumption can be provided.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to FIG.
In the present embodiment, a projector as an image display device including the light source device of the first and second embodiments will be described. FIG. 10 is a schematic configuration diagram of the projector according to the present embodiment.

  The projector (image display device) 100 according to the present embodiment includes a red laser light source device 101R, a green laser light source device 101G, and a blue laser light source device 101B that emit red light, green light, and blue light, respectively. The apparatus is the light source apparatus (laser module 10) of the first and second embodiments.

  The projector 100 emits light from the transmissive liquid crystal light valves (image forming apparatuses) 104R, 104G, and 104B and the liquid crystal light valves 104R, 104G, and 104B that modulate the color lights emitted from the laser light source devices 101R, 101G, and 101B, respectively. A projection lens (projection means) that magnifies and projects the image formed by the liquid crystal light valves 104R, 104G, and 104B and a cross dichroic prism (color synthesis means) 106 that synthesizes the light and guides it to the projection lens 107 107). Furthermore, the projector 100 includes uniformizing optical systems 102R, 102G, and 102B for making the illuminance distribution of the laser light emitted from the laser light source devices 101R, 101G, and 101B uniform, and the illuminance distribution is made uniform. The liquid crystal light valves 104R, 104G, and 104B are illuminated with light. In the present embodiment, the uniformizing optical systems 102R, 102G, and 102B are configured by, for example, a hologram 102a and a field lens 102b.

  The three color lights modulated by the respective liquid crystal light valves 104R, 104G, and 104B are incident on the cross dichroic prism 106. This prism is formed by bonding four right-angle prisms, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are arranged in a cross shape on the inner surface thereof. These dielectric multilayer films combine the three color lights to form light representing a color image. The synthesized light is projected onto the screen 110 by the projection lens 107, which is a projection optical system, and an enlarged image is displayed.

  In the projector 100 according to the present embodiment, the light source device 10 according to the first and second embodiments is used as the red laser light source device 101R, the green laser light source device 101G, and the blue laser light source device 101B. It is possible to realize a projector with little reduction in light conversion efficiency, that is, low power consumption.

  Although a transmissive liquid crystal light valve is used as the light modulator, a reflective light valve may be used, or a light modulator other than liquid crystal may be used. Examples of such a light valve include a reflective liquid crystal light valve and a DMD (Digital Micromirror Device). What is necessary is just to change suitably the structure of a projection optical system according to the kind of light valve used.

It is a block diagram of the light source device which concerns on embodiment of this invention. It is a top view of the laser module which concerns on embodiment of this invention. It is a side view of the laser module concerning the embodiment of the present invention. It is a figure which shows the conventional drive signal. It is a figure which shows the relationship between the conventional drive power and output light quantity. It is a figure which shows the drive signal which concerns on 1st Embodiment of this invention. It is a figure which shows the relationship between the drive electric power and output light quantity which concern on 1st Embodiment of this invention. It is a figure which shows the drive signal which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between the drive electric power and output light quantity which concern on 2nd Embodiment of this invention. It is a schematic block diagram of the projector which concerns on 3rd Embodiment of this invention.

  DESCRIPTION OF SYMBOLS 10 ... Laser module, 11 ... Laser array chip | tip, 16 ... Wavelength conversion element, 17 ... External mirror, 18 ... Light receiving element, 20 ... Control part.

Claims (4)

A light emitting element;
A resonator mirror,
A wavelength conversion element,
A laser module that generates basic laser light generated between the light emitting element and the resonator mirror, and outputs wavelength-converted output light through the wavelength conversion element;
A light source device comprising: a controller that drives the laser module with a pulsed drive signal;
The light source apparatus according to claim 1, wherein the control unit adjusts a light amount of the output light by changing a pulse period of the drive signal of the laser module in accordance with a light amount control signal from the outside.   The light source device according to claim 1, wherein a pulse width of the drive signal is constant.   2. The light source device according to claim 1, wherein the pulse width of the drive signal is controlled to be longer when the light intensity instruction value of the light intensity control signal is lower.   An image display device comprising the light source device according to claim 1, wherein an image is displayed using light from the light source device.

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