JP2008292784A - Laser light generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser light generating device which generates laser light with a desired wavelength as laser light for output by converting the wavelength of laser light. <P>SOLUTION: The laser light generating device includes a first wavelength converting element which receives laser light with a first wavelength generated by a laser diode 6 and converts the laser light into laser light with a second wavelength, a second wavelength converting element which receives the laser light with the second wavelength converted by the first wavelength converting element and converts the laser light into laser light for output, a filter 10 which is disposed in the optical path of the laser light for output wavelength-converted by the second wavelength converting element and cuts off laser light with an unnecessary wavelength, and a laser diode drive circuit 16 which supplies a driving current to the laser diode and is provided nearby the first wavelength converting element and second wavelength converting element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser light generator that converts the wavelength of laser light generated from a laser diode to generate laser light having a desired wavelength as output laser light.

  2. Description of the Related Art Optical disk apparatuses that can perform signal reading operations and signal recording operations by irradiating a signal recording layer provided on an optical disk with laser light emitted from an optical pickup device have become widespread.

  As an optical disk apparatus, an apparatus using an optical disk called CD or DVD has been widely used, but recently, an optical disk with improved recording density, that is, a Blu-ray standard or an HD DVD (High Density Digital Versatile Disk) standard. Products that use optical disks have been commercialized.

  In order to improve the density of the signal recorded on the optical disc, it is necessary to reduce the spot diameter of the laser beam irradiated on the signal surface of the optical disc, and for this purpose, it is necessary to shorten the wavelength of the laser beam. In general, an optical pickup device used in an optical disc apparatus incorporates a laser diode that generates laser light.

  The laser beam used for reproducing the signal recorded on the CD standard disc described above uses infrared light, and the laser beam used for reproducing the signal recorded on the DVD standard disc. Red light is used, and blue-violet light is used as the laser light used to reproduce signals recorded on Blu-ray standard and HD DVD (High Density Digital Versatile Disk) standard disks. .

  The laser diode that can generate the infrared, red, and blue-violet laser light described above has been developed and commercialized, but the laser diode that can generate the green laser light is commercialized. Is late.

The green laser light is used in projectors that project images to form the three primary colors of light and is considered to be used in ink-depositing devices because of its high visibility, but it produces green laser light. Since no laser diode has been developed, green laser light is obtained by converting the wavelength of the laser light. As such a wavelength conversion element for converting the wavelength of laser light, an anisotropic crystal such as Nd: YVO4 or a nonlinear optical crystal such as KTP crystal (KTiOP4) is generally used. (See Patent Document 1)
JP-A-7-58391

  When an anisotropic crystal such as YVO4 or a nonlinear optical crystal such as a KTP crystal is used as the wavelength conversion element, the conversion efficiency is highly dependent on the incident light wavelength, and in order to obtain a stable output laser beam, the incident light It is necessary to stabilize the wavelength. A major cause of the unstable wavelength of incident light is a temperature change, and a method of using a Peltier element is generally used as a method for suppressing such a temperature change as described in the patent literature.

A conventional technique will be described with reference to FIG. In FIG. 2, reference numeral 1 denotes a laser diode made of an AIGaAs crystal, which generates laser light having a wavelength of 808 nm. Reference numeral 2 denotes a YVO4 crystal on which the laser light emitted from the laser diode 1 is incident, and is configured to excite laser light having a wavelength of 1064 nm.

  Reference numeral 3 denotes a KTP crystal to which the laser beam having a wavelength converted by the YVO4 crystal 2 is incident, and is configured to convert the wavelength into a 532 nm (green) laser beam having a ½ wavelength. Reference numeral 4 denotes a filter provided in the output optical path of the green laser light output from the KTP crystal 3, which cuts off unnecessary wavelength laser light and outputs only the green laser light. is there.

  A Peltier element 5 is provided in the vicinity of the laser diode 1, the YVO4 crystal 2 and the KTP crystal 3, and serves to keep the temperature of the laser diode 1, the YVO4 crystal 2 and the KTP crystal constant.

  When the Peltier element is not used, if the conversion efficiency is used at a low temperature, the output level of the converted laser light is reduced. Therefore, an operation of supplying a large drive current to the laser diode 1 in order to increase the laser output. Done. Since a laser crystal is damaged when a large current exceeding the rating is supplied to the laser diode 1, the lifetime is shortened. Therefore, a current limiting circuit is generally provided.

  When the current limiting circuit is provided, the problem that the laser diode 1 is damaged and the lifetime is shortened can be solved, but the current limiting operation is performed, that is, a stable operation can be performed. There is a problem in that the laser beam is not emitted until. FIG. 3 is a characteristic diagram showing the relationship between temperature and light output, and stable laser light can be generated only in a narrow temperature range indicated by a solid line.

  The laser diode 1, the YVO4 crystal 2, the KTP crystal 3, and the like are arranged in a case constituting the laser light generator, and are supplied to the laser diode 1 and the case temperature when generating a predetermined amount of laser light. The relationship with the drive current is as shown in the characteristic diagram of FIG.

  As is clear from the characteristic diagram shown in FIG. 4, when the case temperature is in the range of 20 ° C. to 30 ° C., the magnitude of the drive current supplied to the laser diode 1 can be minimized. As is clear from the characteristic diagram shown in FIG. 3, by controlling the case temperature to 20 ° C. to 30 ° C., the laser beam can be emitted quickly and stable laser light can be emitted. Generation operation can be performed.

  In order to perform the above-described operation, the temperature of the laser diode 1, the YVO4 crystal 2 and the KTP crystal is made constant by using the Peltier element 5 described above, but only the apparatus cannot be reduced in size. There is a problem of becoming expensive.

  The present invention intends to provide a laser beam generator capable of solving such a problem.

The present invention provides a first wavelength conversion element that receives a first wavelength laser beam generated from a laser diode that generates a first wavelength laser beam and converts the wavelength of the laser beam to a second wavelength laser beam. A second wavelength conversion element that receives the laser light having the second wavelength converted by the first wavelength conversion element and converts the laser light into output laser light that is laser light having the third wavelength; A filter disposed in the output optical path of the output laser light wavelength-converted by the second wavelength conversion element, and a filter for blocking unnecessary laser light other than the output laser light; A laser diode drive circuit to be supplied is provided in the vicinity of the first wavelength conversion element and the second wavelength conversion element, and heat generated from the drive circuit is supplied to the first wavelength conversion element and the second wavelength conversion element. It is configured to transmit the second wavelength conversion element.

  Further, the present invention is characterized in that the first wavelength conversion element is constituted by an Nd: YVO4 crystal and the second wavelength conversion element is constituted by a KTP crystal.

  The present invention is characterized in that a monitor light-receiving element for detecting the intensity of the laser light is provided at a position where the output laser light wavelength-converted by the second wavelength conversion element is irradiated.

  Further, according to the present invention, a filter provided on the emission side of the second wavelength conversion element is disposed so as to be inclined with respect to the optical axis of the output laser beam, and a part of the output laser beam is reflected by the filter. It is characterized by being guided to the light receiving element for monitoring.

  The present invention is characterized in that a diffraction grating is provided between the laser diode and the wavelength conversion element, and the wavelength of the laser light that is the first wavelength is stabilized by operating the diffraction grating as a resonator. Is.

  The present invention also provides a laser diode that generates a laser beam having a first wavelength, a laser beam having a first wavelength that is generated from the laser diode, and the wavelength of the laser beam is changed to a laser beam having a second wavelength. A wavelength conversion element for conversion, and a filter disposed in the output optical path of the output laser light converted by the wavelength conversion element, and a filter for blocking unnecessary laser light other than the output laser light, the laser diode A laser diode drive circuit for supplying a drive current to the wavelength conversion element is provided in the vicinity of the wavelength conversion element, and heat generated from the drive circuit is transmitted to the wavelength conversion element.

  The present invention is characterized in that the wavelength conversion element is composed of PPLN or PPKTP.

  The laser beam generator of the present invention receives a first wavelength laser beam generated from a laser diode that generates a first wavelength laser beam and converts the wavelength of the laser beam into a second wavelength laser beam. A first wavelength conversion element and a second wavelength laser beam converted by the first wavelength conversion element are incident thereon, and the second laser beam is converted into an output laser beam that is a third wavelength laser beam. A laser that includes a wavelength conversion element and a filter that is disposed in an output optical path of the output laser light that has been wavelength-converted by the second wavelength conversion element, and that blocks unnecessary laser light other than the output laser light; A laser diode drive circuit for supplying a drive current to the diode is provided in the vicinity of the first wavelength conversion element and the second wavelength conversion element, and heat generated from the drive circuit is pre-heated. Since transmission is made to the first wavelength conversion element and the second wavelength conversion element, the temperature of the first wavelength conversion element and the second wavelength conversion element is set to a desired temperature, for example, a temperature at which the wavelength conversion operation can be accurately performed. The laser beam can be quickly raised, and as a result, a laser beam having a desired wavelength can be quickly generated from the laser beam generator.

  Further, the laser light generator of the present invention provides a diffraction grating in the optical path between the laser diode and the wavelength conversion element, and operates the diffraction grating as a resonator to change the wavelength of the laser light as the first wavelength. Since stabilization is achieved, the conversion efficiency of the wavelength conversion element can be increased, and as a result, power consumption can be reduced.

  FIG. 1 is a side view showing an embodiment of the laser beam generator of the present invention. In the figure, reference numeral 6 denotes a laser diode made of an AIGaAs crystal, which generates laser light having a first wavelength of 808 nm. Reference numeral 7 denotes a diffraction grating provided at a position where the first wavelength laser beam generated from the laser diode 6 is incident, and is composed of elements called VHG (Volume Holographic Grating) and VBG (Volume Bragg Grating). Has been. Such a VHG element has optical grooves periodically carved therein, and a laser beam having a predetermined wavelength, that is, a wavelength of 808 nm which is a wavelength of the laser beam generated from the laser diode 6 in this embodiment, is obtained. It is set to oscillate.

  The laser beam incident on the VHG element described above oscillates by reciprocating between a groove periodically engraved in the VHG element and an end face of the element piece constituting the laser diode 6. Although such an oscillating operation is well known, its description is omitted. An operation of fixing and stabilizing the wavelength of the laser beam having a wavelength of 808 nm generated from the laser diode 6 to the first wavelength by performing an oscillation operation in cooperation with the laser diode 6 and the VHG element as the diffraction grating 7 is performed. Is called.

  Reference numeral 8 denotes a YVO4 crystal on which the first wavelength laser beam fixed by the diffraction grating 7 is incident, and is configured to excite laser light having a second wavelength of 1064 nm.

  Reference numeral 9 denotes a KTP crystal into which the laser light whose wavelength has been converted by the YVO4 crystal 8 is incident, and is configured to convert the wavelength into a laser light having a third wavelength of 532 nm (green) which is a half wavelength. ing. Reference numeral 10 denotes a filter provided in the output optical path of the green laser light output from the KTP crystal 9, which serves to block the laser light of an unnecessary wavelength and output only the green laser light. is there.

  In the case of a conventional laser beam generator that does not include the diffraction grating 7, the first wavelength of the laser beam generated and emitted from the laser diode 6 changes in the range of 808 nm ± 10 nm, and the temperature characteristic is also 0.3 nm. There is a characteristic of changing at / ° C.

  Compared with such a conventional laser light generator, in the case of the laser light generator of the present invention having the diffraction grating 7, the first wavelength of the laser light generated and emitted from the laser diode 6 is in the range of 808 nm ± 1 nm. It is possible to obtain an excellent characteristic of changing at a low temperature. Further, the laser beam generator of the present invention has an advantage that the temperature characteristic can be suppressed to a slight change of 0.01 nm / ° C.

  Reference numeral 11 denotes a base constituting the laser beam generator, and a plurality of electrode terminals 12 are fixed thereto. Reference numeral 13 denotes a fixed substrate fixed to the base 11. The laser fixed substrate 14 to which the laser diode 6 is fixed is fixed and the diffraction grating 7 is fixed.

  Reference numeral 15 denotes a wavelength conversion element fixed substrate fixed to the fixed substrate 13, and the YVO4 crystal 8 and the KTP crystal 9 are fixedly arranged as shown. A laser diode driving circuit 16 is connected to the laser diode 6 by a lead wire (not shown) so as to supply a driving current to the laser diode 6 and is disposed in the wavelength conversion element fixed substrate 15. ing. That is, the heat generated from the laser diode drive circuit 16 is transmitted to the YVO4 crystal 8 and the KTP crystal 9 which are wavelength conversion elements.

17 is fixed to the base 11 and the laser diode 6 and diffraction grating 7.
, YVO4 crystal 8, KTP crystal 9 and the like, and the filter 10 is provided at a position where the output laser beam is irradiated. According to such a configuration, the output laser light converted to the third wavelength by the KTP crystal 9 is emitted in the direction of arrow A through the filter 10.

  The filter 10 is inclined as shown in the figure, and a reflection film for reflecting a part of the output laser beam is formed on the incident surface 10a. Reference numeral 18 denotes a monitor light receiving element fixed to the substrate 11, which is irradiated after the output laser light reflected from the incident surface 10 a of the filter 10 is reflected by the reflecting portion 17 a provided on the cover 17. It is arranged at the position.

  In such a configuration, a control signal output from a laser diode drive control circuit provided outside the laser light generator is supplied to the laser diode drive circuit 16 through the electrode terminal 12, and the laser diode drive circuit 16 outputs the laser diode. 6 is supplied with drive current.

  When such a drive current is supplied to the laser diode 6, a laser beam having a first wavelength, that is, a wavelength of 808 nm is generated from the laser diode 6. The laser beam generated in this way is irradiated to the diffraction grating 7 and reciprocates between the grooves formed in the diffraction grating 7 and the end faces of the element pieces constituting the laser diode 6; That is, an oscillation operation is performed. As a result, the wavelength of the laser light generated from the laser diode 6 can be fixed and stabilized at 808 nm which is the first wavelength.

  The laser beam having the first wavelength stabilized in this way is incident on the YVO4 crystal 8, and after being converted into a laser beam having a second wavelength of 1064 nm, it is incident on the KTP crystal 9. As a result, the laser light having the second wavelength of 1064 nm is converted into the laser light having the third wavelength of 532 nm (green) which is ½ wavelength by the KTP crystal 9 and emitted as the output laser light. It will be.

  Laser light emitted from the KTP crystal 9 as output laser light is emitted to the outside through the filter 10, and part of the laser light is incident on the incident surface 10 a of the filter 10 and the reflecting portion 17 a provided on the cover 17. The light is reflected and applied to the monitor light receiving element 18. Therefore, since the output level of the output laser beam can be monitored by the monitor light receiving element 18, the monitor signal obtained from the monitor light receiving element 18 is sent to the laser diode drive control circuit provided outside. By performing the feedback, an operation for controlling the output of the laser beam generated from the laser diode 6 to a desired level, that is, a so-called automatic output control operation can be performed.

  As described above, the laser light generation operation in this embodiment is performed. However, when the power supply operation is performed to generate the laser light, the heat generated from the laser diode driving circuit 16 is the YVO4 crystal 8 that is the wavelength conversion element. And transmitted to the KTP crystal 9, the temperature of the YVO4 crystal 8 and the KTP crystal 9 can be quickly raised to a temperature suitable for performing the wavelength conversion operation. As a result, the wavelength conversion operation for the input laser beam can be started quickly, and the laser beam having a desired wavelength can be generated in a short time as a laser beam generator.

In the embodiment described above, a laser diode that generates laser light having a wavelength of 808 nm is used as the laser diode 6, but a laser diode that generates laser light having a wavelength of 1064 nm can also be used as the laser diode 6. In such a case, since the laser light generated from the laser diode 6 is laser light having a first wavelength of 1064 nm, PPLN (Periodically-Poled) that converts the wavelength to 532 nm (green), which is the second wavelength, as the wavelength conversion element. Lithium Niobate) crystals or PPKTP (Periodically-Poled KTiOP4) crystals can be used.

  In this embodiment, YVO4 crystal, KTP crystal, PPLN crystal and PPKTP crystal are used as the wavelength conversion element. However, other crystal elements can be used. Further, in order to obtain green laser light, a laser diode having a wavelength of 808 nm or a laser diode having a wavelength of 1064 nm is used, but the wavelength is not limited.

  In this embodiment, the case where laser light having a wavelength of 532 nm, which is green, is obtained has been described. However, it is also possible to obtain laser light having other wavelengths.

It is a side view which shows one Example of the laser beam generator of this invention. It is the schematic which shows one Example of the conventional laser beam generator. It is a characteristic view for demonstrating the laser beam generator of this invention. It is a characteristic view for demonstrating the laser beam generator of this invention.

Explanation of symbols

6 Laser diode 7 Diffraction grating 8 YVO4 crystal 9 KTP crystal 10 Filter 11 Base 13 Fixed substrate 15 Fixed substrate for wavelength conversion element 16 Laser diode drive circuit 17 Cover 18 Monitor light receiving element

Claims (9)

A laser diode that generates a laser beam having a first wavelength, and a first wavelength converter that receives the laser beam having a first wavelength generated from the laser diode and converts the wavelength of the laser beam to a laser beam having a second wavelength A second wavelength conversion element that receives the laser light having the second wavelength converted by the first wavelength conversion element and converts the laser light into output laser light that is laser light having the third wavelength; And a laser light generator provided with a filter that is disposed in the output optical path of the output laser light wavelength-converted by the second wavelength conversion element and that blocks unnecessary laser light other than the output laser light. A laser diode driving circuit for supplying a driving current to the laser diode is provided in the vicinity of the first wavelength conversion element and the second wavelength conversion element; Laser light generating device characterized by the heat generated and so transmitted to the first wavelength conversion element and the second wavelength converting element from. 2. The laser beam generator according to claim 1, wherein the first wavelength conversion element is configured by an Nd: YVO 4 crystal, and the second wavelength conversion element is configured by a KTP crystal. 2. The laser beam generator according to claim 1, further comprising a monitor light-receiving element that detects the intensity of the laser beam at a position where the output laser beam wavelength-converted by the second wavelength conversion element is irradiated. . The filter provided on the emission side of the second wavelength conversion element is disposed so as to be inclined with respect to the optical axis of the output laser beam, and a part of the output laser beam is reflected by the filter to receive the monitor light. 4. The laser beam generator according to claim 3, wherein the laser beam generator is guided to an element. A diffraction grating is provided in an optical path between the laser diode and the first wavelength conversion element, and the wavelength of the laser light as the first wavelength is stabilized by operating the diffraction grating as a resonator. Item 2. The laser light generator according to Item 1. A laser diode that generates laser light of a first wavelength, and a wavelength conversion element that receives the laser light of the first wavelength generated from the laser diode and converts the wavelength of the laser light into laser light of a second wavelength; And a laser light generator provided with a filter disposed in the output optical path of the output laser light converted by the wavelength conversion element and blocking unnecessary laser light other than the output laser light, the laser A laser light generator characterized in that a laser diode drive circuit for supplying a drive current to the diode is provided in the vicinity of the wavelength conversion element, and heat generated from the drive circuit is transmitted to the wavelength conversion element. 7. The laser beam generator according to claim 6, wherein the wavelength conversion element is composed of a PPLN crystal or a PPKTP crystal. 7. The wavelength of the laser beam as the first wavelength is stabilized by providing a diffraction grating in the optical path between the laser diode and the wavelength conversion element and operating the diffraction grating as a resonator. The laser beam generator described in 1. The laser beam generator according to claim 2 or 7, wherein the output laser beam is green.

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