JPH04316386A - Harmonic wave generator - Google Patents

Abstract

PURPOSE:To reduce in size and manufacturing cost of a harmonic wave generator. CONSTITUTION:A semiconductor laser (LD) 13, a collimater lens 15, a mode matching lens 17 and a monolithic type resonator 53 are sequentially disposed on one Peltier element 55. A basic wave 27 emitted from the LD 13 is resonated in a triangular ring shape in the resonator 53, amplified, converted to a second harmonic wave, and emitted. Since the LD 13 and a nonlinear optical crystal 25 can be controlled by one element 55 to a temperature in which the wavelength of the wave 27 emitted from the LD 13 is brought into coincidence with the wavelength to be phase-matched by the crystal 25, a plurality of temperature controllers are eliminated to reduce in size and manufacturing cost a device.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generation device that converts a fundamental wave emitted from a semiconductor laser into harmonic waves within a resonator.

0002

[Background Art] In recent years, semiconductor lasers (hereinafter referred to as LD)
Various devices have been proposed in which a fundamental wave emitted from a nonlinear optical material is passed through a nonlinear optical material to obtain wavelength-converted second harmonics and third harmonics. In these devices, a nonlinear optical material is placed inside a resonator made up of a plurality of reflective surfaces, and the fundamental wave is confined and amplified within the resonator, thereby efficiently generating harmonic waves. The resonator can be a monolithic resonator in which a reflective film is provided on the end face of a nonlinear optical material to cause resonance inside the resonator, or a monolithic resonator in which a plurality of mirrors are arranged to form a resonator. External resonators arranged with materials are known.

FIG. 3 shows an example of a second harmonic generation device using an external resonator.

This second harmonic generation device 11 includes a semiconductor laser (hereinafter referred to as LD) 13, a collimating lens 15,
It is composed of a mode matching lens 17 and an external resonator 19. For example, the LD13 has a wavelength of 860 nm.
The fundamental wave 27 is emitted. The collimating lens 15 is L
The mode matching lens 17 serves to converge the fundamental wave 27 emitted from the D 13 and to match the resonance mode of the external resonator 19 with the incident beam.

The external resonator 19 includes spherical mirrors 21 and 23.
Inside thereof, a nonlinear optical crystal 25 made of a nonlinear optical material such as KNbO3 crystal is arranged.

In order to efficiently convert the fundamental wave 27 into the second harmonic 29, a Peltier element 31 is placed near the LD 13, and the wavelength of the emitted fundamental wave 27 is adjusted by keeping the LD 13 at a constant temperature. In addition, a Peltier element 33 is arranged near the nonlinear optical crystal 25 to control the temperature of the nonlinear optical crystal 25 so that a phase matching condition for the wavelength of the fundamental wave 27 is obtained.

A fundamental wave 27 emitted from the LD 13 passes through a collimating lens 15 and a mode matching lens 17, is irradiated onto a spherical mirror 21, and enters an external resonator 19. The incident fundamental wave 27 is transmitted to the spherical mirrors 21 and 23.
is reflected, resonates, and is amplified. Then, when passing through the nonlinear optical crystal 25, a part of it is converted into a second harmonic wave 29, which passes through the spherical mirror 23 and is output.

FIG. 4 shows an example of a second harmonic generator using a monolithic resonator.

[0009] This second harmonic generation device 35 includes the LD 13
, collimating lens 15, mode matching lens 17
and a nonlinear optical crystal 25. Two surfaces of the nonlinear optical crystal 25, on the left and right in the figure, are polished into spherical shapes.

The surface on the left side of the figure forms the incident surface of the fundamental wave 27, and this surface partially transmits the fundamental wave 27 and transmits the second harmonic 27.
9, a reflective spherical mirror 37 is formed. In addition, the surface on the right side in the figure serves as the output surface of the second harmonic wave 29,
A spherical mirror 39 that reflects the fundamental wave 27 and transmits the second harmonic 29 is formed on this surface. Further, the lower surface of the nonlinear optical crystal 25 in the drawing forms a plane mirror 41 that totally reflects the fundamental wave 27 and the second harmonic 29. A Peltier element 31 is disposed near the LD 13, and a Peltier element 33 is disposed near the nonlinear optical crystal 25, respectively, to control the LD 13 and the nonlinear optical crystal 25 to different temperatures.

The fundamental wave 27 emitted from the LD 13 passes through the collimating lens 15 and the mode matching lens 17, and enters the spherical mirror 37 of the nonlinear optical crystal 25. The incident fundamental wave 27 is reflected within a resonator constituted by a spherical mirror 39, a plane mirror 41, and a spherical mirror 37, resonates in a triangular ring shape, and is amplified. When passing through the nonlinear optical crystal 25 in the crystal axis direction, the fundamental wave 2
7 is converted into the second harmonic 29, and the spherical mirror 39
is transmitted and output. At this time, the temperature of the LD 13 and the nonlinear optical crystal 25 is controlled by the Peltier elements 31 and 33, the wavelength is stabilized and the phase is matched, and the wavelength is efficiently converted into the second harmonic 29.

0012

[Problems to be Solved by the Invention] However, in the conventional second harmonic generation device, since the temperatures to be controlled for the LD and the nonlinear optical material are different, it is necessary to provide one Peltier element for the LD and the nonlinear optical material. It was necessary to place them one by one. For this reason, not only a plurality of Peltier elements are required for one device, but also the number of temperature controllers corresponding to the number of elements is required, resulting in a high product cost.

Furthermore, when using a plurality of Peltier elements, it is necessary to arrange each Peltier element at a certain interval in order to dissipate heat from the Peltier elements, so it is necessary to downsize the device. was difficult.

[0014] Therefore, an object of the present invention is to provide a harmonic generation device that can efficiently generate harmonics by controlling an LD and a nonlinear optical material at a constant temperature, and that can reduce the size of the device and the product cost. Our goal is to provide the following.

[0015]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor laser for generating a fundamental wave, a resonator that confines the fundamental wave inside and makes it resonate, and a semiconductor laser disposed inside the resonator. The harmonic generation device is characterized in that temperature control of the semiconductor laser and the nonlinear optical material is performed by one Peltier element.

[0016] Furthermore, in a preferred embodiment of the present invention,
The resonator may be an external resonator or a monolithic resonator.

[0017]

[Operation] In the harmonic generator of the present invention, the LD and the nonlinear optical material are controlled to the same temperature by one Peltier element. Therefore, temperature control can be performed for one device by using only one Peltier element and one temperature controller, and product costs can be reduced. Furthermore, since only one Peltier element is used, there is no need to secure a large space for heat radiation, and the device can be made smaller.

The temperature conditions to control the LD and nonlinear optical material will now be explained with reference to FIG. 2.

FIG. 2 shows the temperature dependence of the wavelength at which phase matching can be achieved with the nonlinear optical material and the wavelength of the fundamental wave emitted from the LD. In the figure, the solid line shows the relationship between the wavelength and temperature at which phase matching can be achieved with the nonlinear optical material, and the broken line shows the relationship between the wavelength and temperature at which phase matching can be achieved with the nonlinear optical material.
This shows the relationship between the wavelength of the fundamental wave emitted from the temperature and the temperature.

As shown by the solid line, a nonlinear optical material kept at a certain temperature can achieve phase matching only for a fundamental wave having a specific wavelength λ corresponding to that temperature. When the temperature of the nonlinear optical material changes, the wavelength λ at which phase matching can be achieved also changes accordingly. Similarly, as shown by the broken line, the wavelength λ of the fundamental wave emitted from the LD also changes depending on the temperature.

[0021]The wavelength λ of the fundamental wave emitted from the LD at a certain temperature varies depending on the material of the LD, so L
By selecting the material D, it is possible to obtain a fundamental wave light source where the solid line and the broken line in FIG. 2 intersect. Therefore, for example, if they intersect at temperatures T1 and T2, by controlling the temperature to either T1 or T2, the wavelength λ of the fundamental wave emitted from the LD and the wavelength λ at which phase matching can be achieved by the nonlinear optical material can be set. The temperatures of the LD and the nonlinear optical material can be controlled by a single Peltier element.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a harmonic generator according to the present invention. Note that this embodiment is based on the second embodiment of the present invention.
Although this embodiment is applied to a harmonic generator, it can also be applied to a third harmonic generator.

[0023] This second harmonic generation device 51 includes the LD 13
, a collimating lens 15 , a mode matching lens 17 , and a monolithic resonator 53 are mounted on one Peltier element 55 . Note that although a monolithic resonator 53 is used in this embodiment, the present invention is not limited to this, and an external resonator may also be used.

As mentioned above, the LD 13 is one that can emit the fundamental wave 27 of a wavelength that matches the phase matching condition of the nonlinear optical material under a certain common temperature control, that is, the solid line and the broken line intersect in FIG. Those with characteristics are selected and used. In addition, the collimating lens 15 is
The mode matching lens 17 serves to converge the fundamental wave 27 emitted from the monolithic resonator 53 and to match the resonant mode within the monolithic resonator 53 with the incident beam.

The monolithic resonator 53 transmits a part of the fundamental wave 27 through one end face located in the crystal axis a direction where phase matching of the nonlinear optical crystal 25 can be achieved, and transmits the second harmonic wave 27.
The other end surface is a spherical mirror 37 that reflects the fundamental wave 27 and transmits the second harmonic 29, and one surface parallel to the crystal axis a is used as the fundamental wave mirror 39. 27 and the second harmonic 29, and one spherical mirror 37 reflects the fundamental wave 29.
The other spherical mirror 39 serves as the exit surface of the second harmonic 29.

[0026] As the nonlinear optical crystal 25, for example, KNbO3, KTiOPO4, KH2PO4
, LiNbO3, and the like can be used. Furthermore, the monolithic resonator 53 can also be formed using a block in which a transparent base material such as glass is bonded to the end face of a nonlinear optical crystal.

The Peltier element 55 controls the LD 13 and the nonlinear optical crystal 25 at a common temperature, and is arranged so as to be in contact with the LD 13 and the nonlinear optical crystal 25 along the optical axis of the fundamental wave 27 as shown in the figure. has been done.

In the above configuration, the temperature is such that the wavelength of the fundamental wave 27 emitted from the LD 13 matches the wavelength at which phase matching can be achieved in the nonlinear optical crystal 25, that is, the temperature T1 or T2 in FIG. Next, the temperatures of the LD 13 and the nonlinear optical crystal 25 are controlled by the Peltier element 55.

In this state, the fundamental wave 27 is emitted from the LD 13 and is made to enter the spherical mirror 37 of the resonator 53 from point A through the collimating lens 15 and the mode matching lens 17. The fundamental wave 27 propagates in the direction of the crystal axis a of the nonlinear optical crystal 25, is reflected at point B of the opposing spherical mirror 39, and heads toward the plane mirror 41. Then, it is reflected at the point C of the plane mirror 41 in the direction of the spherical mirror 37, and is reflected at the point A.
It returns to , is reflected at point A, and propagates again in the crystal axis a direction,
It overlaps with the original light, creating a traveling wave type resonance and being amplified.

When the fundamental wave 27 propagates between points A and B in the direction of the crystal axis a, a part of it becomes the second harmonic 29.
This second harmonic wave 29 is emitted from the spherical mirror 39.

By the Peltier element 55, T in FIG.
Since the temperature of the LD 13 and the nonlinear optical crystal 25 is controlled so that the temperature becomes 1 and T2, the wavelength of the fundamental wave 27 emitted from the LD 13 can be stabilized.
Furthermore, the phase matching conditions in the nonlinear optical crystal 25 can be controlled to match the wavelength of the fundamental wave 27.

[0032] In this way, since the temperature is controlled by a single Peltier element 55, there is no need to use a plurality of temperature controllers, and the product cost can be reduced. Further, unlike the case where a plurality of Peltier elements are used, there is no need to secure a large space for heat radiation and assemble each component, so the device can be made smaller.

Specific examples are shown below.

In the second harmonic generator 51 of the above embodiment, a KNbO3 crystal with a length of 7 mm in the crystal axis a direction is used as the nonlinear optical crystal 25, and both end faces in the crystal axis a direction are spherical with a radius of 5 mm. An optical film that reflects 93% of the fundamental wave with a wavelength of 860 nm is deposited on the incident side of the fundamental wave 27 to form a spherical mirror 37, and on the output side of the second harmonic 29, the fundamental wave is reflected by 99.9 nm. 9% reflection, wavelength 430n
A spherical mirror 39 was formed by depositing an optical film that transmits 90% or more of the second harmonic of m. As the LD 13, one that emits the fundamental wave 27 with a wavelength of 858 nm at room temperature was used.

Using this second harmonic generator 51, the LD 13 and the nonlinear optical crystal 25 are controlled by the Peltier element 55.
Set the temperature to 27.8 degrees, and send the fundamental wave 27 from LD13.
When the beam was emitted, a second harmonic wave 29 with a wavelength of 430 nm could be obtained.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
Since the temperatures of the semiconductor laser and the nonlinear optical material can be controlled by one Peltier element, the device can be made smaller and the product cost can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing an embodiment of a harmonic generator of the present invention.

[Figure 2] Wavelength and L at which phase matching can be achieved with nonlinear optical materials
Chart showing the temperature dependence of the wavelength of the fundamental wave emitted from D

[Fig. 3] A schematic side view showing an example of a conventional second harmonic generator.

FIG. 4 is a schematic side view showing another example of a conventional second harmonic generator.

[Explanation of symbols]

13 Semiconductor laser (LD) 15 Collimating lens 17 Mode matching lens 25 Nonlinear optical crystal 27 Fundamental wave 29 Second harmonic 37 Spherical mirror 39 Spherical mirror 41　Plane mirror 51 Second harmonic generator 53 Monolithic resonator 55 Peltier element

Claims (2)

[Claims] 1. A semiconductor laser for generating a fundamental wave, a resonator that confines the fundamental wave inside and makes it resonate, and a nonlinear optical material that is disposed within the resonator or constitutes the resonator itself. 1. A harmonic generation device comprising: temperature control of the semiconductor laser and the nonlinear optical material using one Peltier element. 2. The harmonic generation device according to claim 1, wherein the resonator is an external resonator or a monolithic resonator.