JP3133097B2 - Harmonic generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generator for converting a fundamental wave emitted from a semiconductor laser into a harmonic using a nonlinear optical material.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers (hereinafter referred to as LDs) have been developed.
Various devices have been proposed for obtaining a wavelength-converted second harmonic or a third harmonic by passing a fundamental wave emitted from a non-linear optical material through a nonlinear optical material. In these devices, a nonlinear optical material is arranged in a resonator composed of a plurality of reflection surfaces, and a fundamental wave is confined in the resonator and amplified, so that harmonics are efficiently generated. As the resonator, a monolithic resonator in which a reflection film is provided on the end face of the nonlinear optical material and resonates inside the resonator, and a plurality of mirrors are arranged to form a resonator, and the nonlinear optical It is known to arrange materials.

FIG. 5 shows an example of a conventional second harmonic generator using a monolithic resonator.

[0004] The second harmonic generator 11 is an LD 1
2, collimating lens 13, mode matching lens 1
4 and a monolithic resonator 15. The LD 12 emits a fundamental wave 16 having a wavelength of 860 nm, for example. The collimating lens 13 converts the fundamental wave 16 emitted from the LD 12 into a beam, and the mode matching lens 14 functions to match the resonance mode in the monolithic resonator 15 with the incident beam.

The monolithic resonator 15 is, for example, KN
One end face of the nonlinear optical material 17 made of a bO ₃ crystal or the like located in the direction of the crystal axis
A spherical mirror 19 partially transmitting to the second harmonic 18 and reflecting the second harmonic 18, and a spherical mirror 20 reflecting the other end of the fundamental wave 16 and transmitting the second harmonic 18. One surface parallel to the axis a is configured as a plane mirror 21 that totally reflects the fundamental wave 16 and the second harmonic 18, and one spherical mirror 19 forms an incident surface of the fundamental wave 16 and the other surface mirror. Of the second harmonic 18 forms an emission surface of the second harmonic 18.

In the second harmonic generator 11, the LD1
The fundamental wave 16 emitted from the collimator lens 1
3. From the spherical mirror 19 of the monolithic resonator 15 through the mode matching lens 14, the nonlinear optical material 1
7 is incident. This fundamental wave 16 corresponds to the nonlinear optical material 1
7 propagates in a direction parallel to the crystal axis a,
The light is reflected by the plane mirror 21 and the spherical mirror 19, resonated in a triangular ring shape, and amplified. When the light propagates in a direction parallel to the crystal axis a of the nonlinear optical material 17, a part of the light is converted into a second harmonic 18 and emitted through the spherical mirror 20.

[0007]

In such a second harmonic generator 11, in order to efficiently convert the fundamental wave 16 to the second harmonic 18, a monolithic resonator 15 is required.
Therefore, it is particularly important that the resonance condition of the fundamental wave 16 is satisfied and phase matching can be achieved. For this reason,
Positioning of LD 12, collimating lens 13, mode matching lens 14, monolithic resonator 15, etc., and spherical mirror 1 in monolithic resonator 15
It is necessary to make the processing accuracy of 9, 20, the flat mirror 21 and the like strict. Therefore, processing and assembling of each optical component become strict, and it has been difficult to improve manufacturing workability.

In order to obtain the second harmonic with a simpler configuration, the present applicant has developed a second harmonic generator comprising an external resonance type LD and a nonlinear optical material as shown in FIG. An apparatus has already been proposed (Japanese Utility Model Application No. 2-94777).
issue).

The second harmonic generator 31 reflects an end face on the left side in the figure of the nonlinear optical material 32 in the direction of the crystal axis where the phase matching can be achieved with respect to the fundamental wave 16 and the second harmonic 1
8 is a plane mirror 33 that transmits light, and the right end face in the figure is a plane 34 that transmits light to the fundamental wave 16. The external resonance type LD 35 is connected to the plane 3 of the nonlinear optical material 32.
4, the fundamental wave 16 is made to enter the plane 34, and the end face on the right side of the external resonance type LD 35 in the figure is a plane mirror 36 that reflects the fundamental wave 16.

Therefore, the second harmonic generator 31
Then, the fundamental wave 16 emitted from the external resonance type LD 35 is
Is incident from a plane 34 of the nonlinear optical material 32, is reflected by the plane mirror 33 of the nonlinear optical material 32, returns to the external resonance type LD 35, is reflected by the plane mirror 36 on the right side in the drawing of the external resonance type LD 35, A reciprocating resonance is made again toward the plane 34 of the nonlinear optical material 32 and amplified. And the fundamental wave 16 is the nonlinear optical material 3
When the light propagates in the direction of the crystal axis, the light is converted into the second harmonic wave 18 and emitted from the plane mirror 33.

However, the second harmonic generator 3
In 1, the fundamental wave 16 emitted from the external cavity LD35 spreads rapidly, the fundamental wave 16 when reaching the non-linear optical material 32 Ru spread. Generation efficiency of the second harmonic wave 18 by the nonlinear optical material 32 is proportional to the density of the light beam of the fundamental wave 16, the light beam Ru spread efficiency decreases.
Further, since the reflection surface of the nonlinear optical material 32 is the plane mirror 33, the reflected light does not return effectively, the resonator becomes a large loss, and the fundamental wave 16 is weakened.
There was also weak for that problem.

Accordingly, it is an object of the present invention to provide a second harmonic generator comprising two parts, an external resonance type LD and a nonlinear optical material, to increase the luminous flux density of the fundamental wave and to increase the generation efficiency of the second harmonic. To improve it.

[0013]

In order to achieve the above object, the present invention relates to a harmonic generator for converting a fundamental wave emitted from a semiconductor laser into a harmonic by a nonlinear optical material. One end face of the two end faces located in the matching direction is defined as a transmission plane for the fundamental wave, and the other end face is reflected on the fundamental wave.
Use a semiconductor laser stage as a spherical mirror that transmits harmonics
As the light emitting surface of adhered external cavity semiconductor lasers is close to or joined to the plane of the nonlinear optical material, said flat
The semiconductor laser stage is adhered to a surface, and an end face of the two end faces of the external resonance type semiconductor laser that faces the light emission face is a mirror for reflecting a fundamental wave.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

LD is, for example, GaAs, GaAlAs,
A semiconductor is formed using a material such as InGaAlP, and p
Generally, both ends of the -n junction surface are parallel plane mirrors, and light generated by flowing a current is resonated by the parallel plane mirrors to cause laser oscillation. The external resonance type LD used in the present invention does not resonate inside the semiconductor in this way, but means a laser that resonates between the semiconductor and a mirror disposed outside the semiconductor and performs laser oscillation as described above. Only one end face of the pn junction surface of a semiconductor made of a material is used as a plane mirror, and the other end face emits light substantially.
There is a flying etc. transmissive surfaces.

In the present invention, the non-linear optical materials include, for example, KNbO ₃ , KTiOPO ₄ , KH ₂ P
Non-linear optical crystals such as O ₄ and LiNbO ₃ and organic non-linear optical materials can be used. However, in order to reduce material costs and facilitate processing, a transparent substrate such as glass or plastic is bonded to these crystals. Blocks may be used. In this nonlinear optical material, one end face of two end faces positioned in the crystal axis direction where phase matching can be performed is a plane that transmits a fundamental wave generated from the external resonance type LD, and the other end face is a fundamental wave. Is a spherical mirror that reflects light and transmits light with respect to harmonics.

The harmonic generation device according to the present invention is configured such that an emission surface of the fundamental wave of the external resonance type LD is arranged close to or joined to a plane transmitting the fundamental wave of the nonlinear optical material. You. In this case, the assembly of the LD and a non-linear optical material, for drawers and reliable contact bonding of the electrodes, LD
After bonding to the appropriate platform, the platform each nonlinear optical material
How to adhere to the plan is adopted. In this case, in order to prevent the position of the LD is shifted due to shrinkage during curing of the adhesive, it is good preferable to use a base of symmetrical shape about the LD.

[0018] By the way, in the present invention, in the case of using an ordinary LD, for vertical mode is a multi-mode, noise due to longitudinal mode competition ing large. Therefore, an LD that emits a single-mode fundamental wave is preferably adopted as the LD. For example, by using a distributed reflection type (DBR) or a distributed feedback type (DFB), a vertical single mode including an external resonator is provided. be able to. Further, if a half-wave plate is interposed between the LD and the nonlinear optical material, noise can be reduced even in multi-mode oscillation. In this case, a normal LD can be used.

It is preferable that an antireflection film for a fundamental wave generated from the LD is provided on each joint surface between the nonlinear optical material and the LD. Further, it is preferable to provide an optical film that transmits a fundamental wave generated from the LD and reflects a higher harmonic wave on a joint surface between the nonlinear optical material and the LD.
By providing such an optical film, harmonics generated in the nonlinear optical material are transmitted through the LD and lost.
Of the non-linear optical material can be taken out from the spherical mirror side of the nonlinear optical material after being reflected by the optical film.

[0020]

In the harmonic generation device according to the present invention, the fundamental wave generated from the LD enters directly from one end face of the nonlinear optical material, is reflected by the spherical mirror located on the other end face of the nonlinear optical material, and is reflected in the LD direction. The laser beam is returned, reflected by a plane mirror located on the outer end face of the LD, and re-enters the nonlinear optical material, causing a reciprocal resonance. When the fundamental wave passes through the nonlinear optical material, it is converted into a harmonic. This harmonic is emitted through a spherical mirror made of a nonlinear optical material.

Although the fundamental wave emitted from the LD spreads rapidly in the nonlinear optical material, it is reflected and focused by the spherical mirror of the nonlinear optical material, so that the density of the light beam is increased and the loss of light is reduced. , It is possible to improve the generation efficiency of harmonics.

As described above, the harmonic generation device of the present invention
Simple structure consisting of LD, LD stage (semiconductor laser stage) and non-linear optical material enables miniaturization and cost reduction, and improves stability because there are no moving parts such as external mirrors and various lenses. I do.

[0023]

1 and 2 show an embodiment in which the present invention is applied to a second harmonic generator. However, the present invention is not limited to the second harmonic generator,
It can also be applied to a harmonic generator.

As shown in FIG. 1, the second harmonic generator 41 comprises an external resonance type LD 42 and a nonlinear optical material 43.
And an LD table 44.

The external resonance type LD 42 has one end face of the pn junction plane, that is, an end face on the right side in the drawing, as a plane mirror 45 for reflecting the fundamental wave 16 by a Bragg waveguide, thereby performing wavelength selection. A fundamental wave 16 having a wavelength of 860 nm in a single longitudinal mode is emitted. Also,
On one end surface of the pn junction surface, that is, on the left end surface in the figure, an anti-reflection film for preventing reflection of the fundamental wave 16 at an interface with an adhesive described later is deposited and used as an emission surface of the fundamental wave 16. .

The length of the nonlinear optical material 43 is 4.4.
Using a 6 mm KNbO ₃ crystal, the left end face in the figure located in the direction of the crystal axis where phase matching can be achieved is processed into a spherical surface having a radius of 4.5 mm. An optical film that transmits 90% of the second harmonic 18 having a wavelength of 430 nm was deposited to form a spherical mirror 47. The end face on the right side in the figure positioned in the crystal axis direction was processed into a flat surface 46, and an antireflection film for preventing reflection of the fundamental wave 16 at an interface with an adhesive described later was formed by vapor deposition.

The external resonance type LD 42 is bonded to the LD table 44 with its light incident surface coincident with one end face of the LD table 44, and the end faces of the LD table 44 and the LD 42 are bonded to the plane 46 of the nonlinear optical material 43. By doing so, it was integrated with the nonlinear optical material 43.

Then, as shown in FIG. 2, the LD 42, the LD base 44, and the nonlinear optical material 43 thus joined are
The temperature control of the LD 42 and the non-linear optical material 43 is performed by being mounted on the Peltier element 48. The second harmonic generator 41 has a very compact shape because the components are simple and integrated.

In the second harmonic generator 41, the LD4
2 is directly incident on the nonlinear optical material 43 from the light exit surface of the LD 42, is reflected by the spherical mirror 47 of the nonlinear optical material 43 and returns to the LD 42 direction. The fundamental wave 16 is amplified by taking a resonance path which is reflected by the plane mirror 45 forming the end face and enters the non-linear optical material 43 again.
When the light propagates in the crystal axis direction where phase matching can be achieved,
The light is converted into harmonics 18 and emitted from the spherical mirror 47.

In this case, the fundamental wave 16 emitted from the LD 42 spreads abruptly in the nonlinear optical material 43, but is reflected by the spherical mirror 47 to narrow the light beam. Loss due to the above can be reduced. Further, since the fundamental wave 16 generated in the LD 42 is directly confined between the spherical mirror 47 of the nonlinear optical material 43 and the plane mirror 45 of the LD 42 to resonate, a large power is obtained inside the resonator. Therefore, according to the second harmonic generator 41, the second harmonic 18 can be efficiently generated.

Actually, by using this second harmonic generator 41, a current is supplied to the external resonance type LD 42 and the wavelength is 860 nm.
When the fundamental wave 16 is generated, the nonlinear optical material 43
From the spherical mirror 47 of the second harmonic 18 having a wavelength of 430 nm.
Was observed to be emitted efficiently.

In the second harmonic generator 41, the bonding surface between the LD 42 and the nonlinear optical material 43 is
By interposing an optical film that reflects the harmonic wave 18 and transmits the fundamental wave 16, the second harmonic wave 18 generated by the nonlinear optical material 43 toward the LD 42 is reflected toward the spherical mirror 47. Therefore, the output of the second harmonic 18 can be further increased. In addition, by interposing a half-wave plate on the bonding surface between the LD 42 and the nonlinear optical material 43, noise can be reduced even when a normal multi-mode oscillation LD is used.

FIGS. 3 and 4 show another embodiment in which the present invention is applied to a second harmonic generator. In the following description of the embodiment, substantially the same parts as those of the embodiment of FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof will be omitted.

In the second harmonic generation device 51, a cylindrical shape symmetric about the LD 42 is used as the LD table 52. That is, the LD table 52 has a cylindrical shape, and a rectangular through-hole 53 is formed at the center thereof, and the LD 42 is inserted into the through-hole 53. And LD42
Are arranged so that their light emitting surfaces coincide with the end faces of the LD table 52, and are adhered to the inner periphery of the LD table 52. In this state, the LD table 52 and the LD 42 are adhered to the plane 46 of the nonlinear optical material 43 to form the second harmonic generator 51.

In this embodiment, since the LD table 52 has a symmetrical shape around the LD 42, the nonlinear optical material 43
When the adhesive is bonded to the flat surface 46, shrinkage of the adhesive at the time of curing occurs evenly, and it is possible to prevent the LD 42 from tilting and shifting the optical axis.

[0036]

[0037]

[0038]

As described above, according to the present invention,
The external stage type LD adhered to the LD stage is brought close to or joined to the nonlinear optical material, and the LD stage is irradiated with light from the nonlinear optical material.
A flat mirror for the fundamental wave is formed on the other end face of the non-linear optical material that is not in close proximity to or bonded to the non-linear optical material of the LD. By forming a spherical mirror that transmits the wave, the fundamental wave generated in the LD is directly confined between the mirrors and resonated, and converted into a harmonic in the nonlinear optical material. The density can be increased, the loss due to diffusion during reflection can be reduced, and harmonics can be generated and extracted efficiently.

Further, since the LD, the LD stage, and the nonlinear optical material have a simple structure, the entire apparatus is extremely compact, and the manufacturing cost can be significantly reduced. Further, since there are no movable parts such as various lenses and mirrors of an external resonator, stable performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment in which the present invention is applied to a second harmonic generator.

FIG. 2 is a side view showing a state where the second harmonic generation device of FIG. 1 is mounted on a Peltier device.

FIG. 3 is a partially cutaway side view showing another embodiment in which the present invention is applied to a second harmonic generator.

FIG. 4 is an end view of the second harmonic generator shown in FIG. 3 as viewed from the right side.
Figure

FIG. 5 is a side view showing an example of a conventional second harmonic generator.

FIG. 6 is a side view showing a second harmonic generation device previously proposed by the present applicant .

[Explanation of symbols]

Reference Signs List 16 fundamental wave 18 second harmonic 41 second harmonic generator 42 external resonance type semiconductor laser (external resonance type LD) 43 nonlinear optical material 44 semiconductor laser stage (LD stage) 45 plane mirror 46 plane 47 spherical mirror 48 Peltier element 51 second harmonic generator 52 semiconductor laser stage (LD stage )

Claims (4)

(57) [Claims] 1. A harmonic generator for converting a fundamental wave emitted from a semiconductor laser into a harmonic by a nonlinear optical material, wherein one of two end faces located in a direction in which the nonlinear optical material can be phase-matched. was a plane transparent to the fundamental wave, the reflection of the other end face to the fundamental wave, a spherical mirror transparent to harmonics, the semiconductor laser platform
As the light emitting surface of adhered external cavity semiconductor lasers is close to or joined to the plane of the nonlinear optical material, said plane
Wherein the semiconductor laser base is adhered to the external laser diode, and an end face of the two end faces of the external resonance type semiconductor laser which faces the light emitting face is a mirror for reflecting a fundamental wave. 2. The harmonic generator according to claim 1, wherein said external resonance type semiconductor laser emits a single mode fundamental wave. 3. The harmonic generator according to claim 1, wherein a half-wave plate is interposed between a light emitting surface of the external resonance type semiconductor laser and a plane of the nonlinear optical material. 4. An optical film transmitting a fundamental wave and reflecting a harmonic wave between a light emitting surface of the external resonance type semiconductor laser and a plane of the nonlinear optical material. 4. The harmonic generator according to 1, 2, or 3.