JPH04366820A - Higher harmonic generation device - Google Patents

Abstract

PURPOSE:To provide the higher harmonic generation device which can easily adjust the incidence position and incidence angle of a fundamental wave to a resonator. CONSTITUTION:The 2nd higher harmonic generation device 21 consists of an LD 23, collimator lens 25, mode matching lens 27, monolithic resonator 31, and mirror 29 for adjustment. The fundamental wave 33 emitted by the LD 23 is reflected by the mirror 29 for adjustment and made incident on the resonator 31 and the tilt angle and position of the mirror 29 are only finely adjusted to enable alignment adjustment and also lead a 2nd higher harmonic 37 out almost in parallel to the optical axis of the fundamental wave 33.

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 laser light source into harmonic waves within a monolithic resonator.

0002

2. Description of the Related Art In recent years, various devices have been proposed in which a fundamental wave emitted from a semiconductor laser or the like is passed through a nonlinear optical material to obtain wavelength-converted second 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 harmonics. 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. Recently, in order to downsize the device and improve the conversion efficiency to harmonics, the mainstream has shifted from external resonator type to monolithic type that resonates the fundamental wave inside a nonlinear optical material. It is being done.

FIG. 2 shows an example of a second harmonic generator using such a monolithic resonator.

The second harmonic generator 1 is composed of a semiconductor laser (hereinafter referred to as LD) 2, a collimator lens 3, a mode matching lens 4, and a nonlinear optical material 5 made of KNbO3 crystal or the like. The LD 2 emits a fundamental wave 9 having a wavelength of 860 nm, for example. The two surfaces of the nonlinear optical material 5, on the left and right sides in the figure, are polished into curved (usually spherical) shapes. And the plane on the left side of the figure is the fundamental wave 9
The fundamental wave 9 is partially transmitted through this surface.
A curved mirror 6 is formed to reflect the second harmonic 10. Further, the right side surface in the figure serves as an exit surface for the second harmonic wave 10, and a curved mirror 7 that reflects the fundamental wave 9 and transmits the second harmonic wave 10 is formed on this surface. Furthermore, the lower surface of the nonlinear optical material 5 in the figure has a fundamental wave 9 and a second wave.
A plane mirror 8 reflects all of the harmonics 10. Note that a Peltier element 11 for temperature control is provided below the nonlinear optical material 5 in the figure.

A fundamental wave 9 with a wavelength of 860 nm emitted from the LD 2 passes through a collimating lens 3 and a mode matching lens 4, enters a curved mirror 6 of a nonlinear optical material 5, and is then transmitted to a curved mirror 7, a plane mirror 8, and a curved mirror 6. It is reflected, resonated, and amplified within a ring resonator made up of. When the fundamental wave 9 passes through the nonlinear optical material 5 in a predetermined direction, a part thereof is converted into a second harmonic wave 10 having a wavelength of 430 nm, which is transmitted through the curved mirror 7 and output. If such a monolithic resonator is used, conversion to the second harmonic can be performed efficiently, and the second harmonic generation device can be downsized.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional harmonic generator, the incident position that enables resonance of the fundamental wave 9 to the monolithic resonator is extremely limited, and the incident position of the fundamental wave 9 is If there is even a slight deviation, both the reflection points and reflection angles on the curved mirrors 6 and 7 will be shifted, which causes the problem that the optical path will gradually deviate greatly from the resonance path and the resonance condition will no longer be satisfied. For this reason, it is necessary to align the resonator with high precision, but it is mechanically extremely difficult to finely adjust the arrangement of the nonlinear optical material 5 itself and various optical components.

Furthermore, while the fundamental wave 9 is incident on the curved mirror 6 of the nonlinear optical material 5 at a specific angle θ with respect to the crystal axis a, the wavelength-converted second harmonic 10 is incident on the curved mirror 6 of the nonlinear optical material 5. The crystal axis a is directed from the curved mirror 7 in the opposite direction to the above.
The light is refracted at an angle θ relative to the light beam and is emitted. For this reason, the incident direction of the fundamental wave 9 and the output direction of the second harmonic 10 are significantly bent, and in order to put the second harmonic generator into practical use, it is necessary to arrange various optical components in the same direction. This makes it difficult to assemble various optical components, and there are also problems in reducing the size of the device.

Therefore, an object of the present invention is to be able to adjust the incident position and incident angle of the fundamental wave with respect to the fundamental wave incident surface of a monolithic resonator with a simple structure, and more preferably to adjust the incident direction of the fundamental wave and the output of harmonics. An object of the present invention is to provide a harmonic generation device that can make the directions substantially parallel to each other.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the harmonic generation device of the present invention uses a monolithic resonator having a nonlinear optical material.
A mirror is disposed on the optical axis of the fundamental wave between the fundamental wave generating light source and the monolithic resonator so that the inclination angle with respect to the optical axis and/or the distance to the monolithic resonator can be adjusted. The present invention is characterized in that the incident position of the fundamental wave into the monolithic resonator is adjusted.

In a preferred embodiment of the present invention, the angle and position of the mirror are set so that the emission direction of the fundamental wave and the emission direction of the harmonic wave emitted from the monolithic resonator are substantially parallel. .

[0011]

In the present invention, a monolithic resonator is used, and a mirror is placed on the optical axis of the fundamental wave between the fundamental wave generating light source and the monolithic resonator. This mirror is
Since the tilt angle with respect to the optical axis and the distance from the monolithic resonator can be adjusted, by adjusting this mirror, the fundamental wave to the resonator can be adjusted without changing the installation position or installation angle of the resonator itself. The incident position can be adjusted. Therefore, alignment adjustment can be facilitated.

In a preferred embodiment of the present invention, the position and inclination angle of the mirror are adjusted so that the emission direction of the fundamental wave and the emission direction of the harmonic wave emitted from the light source substantially coincide. In this way, by matching the emission direction of the fundamental wave and the emission direction of the second harmonic, it is possible to arrange various optical components in the same direction in practical use and to facilitate assembly of the components. Furthermore, the design and installation of various information processing devices incorporating these as light sources can be facilitated.

[0013]

Embodiment FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generator. However, the present invention can also be applied to harmonic generators other than the second harmonic generator, such as third harmonic generators.

The second harmonic generation device 21 is constructed by sequentially arranging an LD 23 as a laser light source, a collimating lens 25, a mode matching lens 27, an adjustment mirror 29, and a monolithic resonator 31. LD2
3 is used in this embodiment, which emits a fundamental wave with a wavelength of 860 nm, single longitudinal and single transverse modes, and little astigmatism. Note that as the light source, it is also possible to use light emitted from a solid laser medium such as YAG or YLF excited by an LD. The collimating lens 25 is L
The fundamental wave 33 emitted from the D23 is made into a predetermined beam,
The mode matching lens 27 serves to match the resonant mode within the monolithic resonator 31 and the incident beam.

In this embodiment, the monolithic resonator 31 is formed using a nonlinear optical material 35 made of KNbO3 crystal, so that phase matching is achieved in a direction parallel to the crystal axis a. In addition to KNbO3 crystal, KTiOPO is also used as the nonlinear optical material 35.
Various nonlinear optical crystals such as 4, KH2PO4, LiNbO3, and organic nonlinear optical materials can be used.

In the monolithic resonator 31, both end faces of the nonlinear optical material 35 located in the direction of the crystal axis a are each processed into a spherical shape with a radius of curvature of 5 mm, and the fundamental wave 33 is incident on the incident surface of the fundamental wave 33 by 93%. A reflective film is deposited to form a spherical mirror 39, and a fundamental wave 33 is formed on the output surface of the second harmonic 37.
The spherical mirror 41 is formed by depositing a reflective film that reflects 99.9% of the second harmonic wave 37 and transmits 90% of the second harmonic wave 37. Further, the nonlinear optical material 35 is cut into a plane along the crystal axis a, and this plane is used as a plane mirror 43 that totally reflects both the fundamental wave 33 and the second harmonic 37. Note that a Peltier element 45 is installed below the monolithic resonator 31 in the figure to perform temperature control so as to meet phase matching conditions.

On the optical axis of the fundamental wave 33 between the mode matching lens 27 and the monolithic resonator 31, an adjustment mirror 29 consisting of a plane mirror that totally reflects the fundamental wave 33 and the second harmonic 37 is placed on the LD 23. The optical axis of the fundamental wave 33 is inclined at a predetermined angle θ1 = 3.2° with respect to the optical axis of the fundamental wave 33 emitted from the optical axis. This adjustment mirror 29 can appropriately adjust the predetermined angle θ1 with respect to the optical axis of the fundamental wave 33, and is also slidable in the direction of arrow G in FIG. Therefore, the predetermined angle θ1 with respect to the optical axis of the fundamental wave 33 and the monolithic resonator 31
By adjusting the distance between the monolithic resonator 31 and the monolithic resonator 31, the angle and position of incidence of the fundamental wave 33 on the monolithic resonator 31 can be easily adjusted. In this embodiment, the nonlinear optical material 35 is arranged at an angle of about 6.5 degrees with respect to the optical axis of the fundamental wave 33 emitted from the LD 23.

Using this second harmonic generator 21, the LD
23 emits a fundamental wave 33 with a wavelength of 860 nm. The emitted fundamental wave 33 is made into a predetermined beam by the collimating lens 25 and the mode matching lens 27, propagates, is reflected by the adjustment mirror 29, changes the direction of travel, and travels from point A of the spherical mirror 39 to the monolithic resonator. 3
1. At this time, the adjustment mirror 29 can adjust the inclination angle θ1 of the fundamental wave 33 with respect to the optical axis, and can also adjust the distance between the resonator 31 and the monolithic resonator 31 by sliding it in the direction of arrow G in the figure. The angle and position of incidence of the fundamental wave 33 on the spherical mirror 39 can be easily adjusted without moving the mirror itself. Therefore, alignment adjustment for enabling resonance can be facilitated.

The fundamental wave 3 is reflected by the adjustment mirror 29 and enters the resonator 31 from the point A of the spherical mirror 39.
3 propagates along the crystal axis a in the nonlinear optical material 35, is reflected at point B of the opposing spherical mirror 41, and heads toward point C of the plane mirror 43. The fundamental wave 33 is then reflected at point C of the plane mirror 43 and returned to point A of the spherical mirror 39, reflected at point A, propagated again along the crystal axis a, overlapped with the original light, and formed a traveling wave. resonance occurs. In this way, the fundamental wave 33 resonates within the monolithic resonator 31 along a triangular ring-shaped resonance path and is amplified. The fundamental wave 33 amplified in this way is at the point A-B.
When propagating in the crystal axis a direction between
nm, and this second harmonic 37
is emitted from the spherical mirror 41.

In this case, the inclination angle of the adjustment mirror 29 with respect to the optical axis of the fundamental wave 33 emitted from the LD 23 and the distance between the adjustment mirror 29 and the monolithic resonator 31 are initially set to pre-calculated values. By doing so, the angle and interval to be adjusted for the alignment can be extremely small, so that the fundamental wave 33 emitted from the LD 23
The emission direction of the second harmonic wave 37 can be made substantially parallel to the emission direction of the second harmonic wave 37. In the case of this embodiment, the angle θ1 of the adjustment mirror 29 with respect to the fundamental wave 33 is set to 3.2 degrees, and the inclination angle of the nonlinear optical material 35 with respect to the fundamental wave 33 is set to approximately 6.5 degrees. The emission direction of the second harmonic wave 37 is substantially parallel to the emission direction of the second harmonic wave 37. Therefore, various optical components can be arranged in the same direction to facilitate assembly of the components.

[0021]

[Effects of the Invention] As explained above, according to the present invention,
A mirror placed on the optical axis of the fundamental wave between the fundamental wave generating light source and the monolithic resonator makes it possible to easily adjust the incident position of the fundamental wave on the fundamental wave incident surface of the monolithic resonator. Therefore, alignment to satisfy the resonance conditions, which conventionally took a lot of effort, can be easily performed.

Furthermore, by adjusting the location and inclination angle of the mirror, the direction of emission of the fundamental wave emitted from the light source and the direction of emission of the second harmonic wave can be made substantially parallel. Therefore, various optical components can be arranged in the same direction to facilitate assembly of the components. In addition, when incorporating the light source into an optical information processing device, design and
Installation can be facilitated.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a harmonic generator of the present invention.

FIG. 2 is an explanatory diagram showing a conventional second harmonic generator.

[Explanation of symbols]

21 Second harmonic generator 23 Semiconductor laser (LD) 25 Collimating lens 27 Mode matching lens 29 Adjustment mirror 31 Monolithic resonator 33 Fundamental wave 35 Nonlinear optical materials

Claims (2)

[Claims] 1. In a harmonic generation device using a monolithic resonator having a nonlinear optical material, on the optical axis of the fundamental wave between a fundamental wave generation light source and the monolithic resonator, an inclination angle with respect to the optical axis is provided. and/or a harmonic generation device characterized in that a mirror is arranged so that the distance to the monolithic resonator can be adjusted, and the incident position of the fundamental wave to the monolithic resonator is adjusted by the mirror. 2. The angle and position of the mirror are set so that the optical axis of the fundamental wave and the optical axis of the harmonic wave emitted from the monolithic resonator are substantially parallel.
The harmonic generator described.