JPH095809A - Higher harmonic generator - Google Patents

Abstract

PURPOSE: To stably generate higher harmonic waves with high efficiency by inclining a basic wave to a resonance axis and making the basic wave incident on a resonator in such a manner that the basic wave enters the inside of the permissible width of the resonance of the resonator. CONSTITUTION: The second higher harmonic generator 101 is constituted by successively arranging an LD102 as a basic wave light source, a coupling optical system 103 consisting of a collimator lens, mode matching lens, etc., and the standing wave linear resonator 104. The optical axis 110 of the incident basic wave has an angle of, for example, 0.3 deg. to the resonance axis 111. A part of the basic wave 105 is not made incident on the resonator 104 and is reflected by an incident surface 109, by which the basic wave is made into directly reflected light 112. The optical axis 110 of the incident basic wave and the optical axis of the directly reflected light 112 have an angle of, for example, 0.2 deg. and, therefore, the light is not recondensed to the light emitting layer of the semiconductor laser (LD)102. The oscillation wavelength of the LD102 is, therefore, stable and since the oscillation spectral line width does not increase, the coupling efficiency of >=40% is obtd.

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 from a semiconductor laser into a harmonic by a non-linear optical material.

[0002]

2. Description of the Related Art FIG. 2 shows, as an example of a conventional harmonic generator, a second harmonic generator 2 using a standing wave linear resonator.
01 is shown. This second harmonic generator is a coupling optical system 20 including a semiconductor laser (hereinafter referred to as LD) 202, a collimator lens, a mode matching lens, and the like.
3. Non-linear optical crystal 206 such as KNbO ₃ single crystal using the resonance mirror 204 and one surface (exit surface 205) as the resonance mirror
And a standing wave linear resonator 207.

The LD 202 emits a fundamental wave 208 having a wavelength of 860 nm, for example. On the entrance surface 209 of the resonator, a film partially transmitting the fundamental wave and highly reflecting the harmonic wave is vapor-deposited to form a resonance mirror surface, and on the exit surface 205, a high reflection of the fundamental wave and the harmonic wave is formed. A highly transparent film is deposited to form the resonant mirror surface.

In the above structure, the fundamental wave 208 having a wavelength of 860 nm emitted from the LD 202 is coupled to the coupling optical system 203.
The light is focused by, is matched with the resonance mode, and is incident on the standing wave linear resonator 207. At this time, part of the fundamental wave 208 is not directly incident on the standing wave linear resonator 207 but becomes the directly reflected light 210 reflected by the incident surface 209, and is re-focused on the light emitting layer of the LD 202.

The incident fundamental wave optical axis 211 is arranged so as to coincide with the resonance axis 212, and the incident fundamental wave 208 has two incident mirror surfaces, an incident surface 209 and an outgoing surface 205.
And travels between them and resonates to be amplified. Return light 21 from the resonator that has passed through the incident surface 209 of the amplified fundamental wave 21
3 returns to the LD 202. When the fundamental wave 208 passes through the nonlinear optical crystal 206, a part of it has a wavelength of 430 nm.
Is converted into the second harmonic wave 214 and is emitted from the emission surface 205.

[0006]

However, in the above-described harmonic generator, the incident surface 209 of the resonator 207 is used.
When the reflected light 210 at the LD returns to the LD 202,
The oscillation frequency becomes unstable and the oscillation spectrum line width increases, and the coupling efficiency to the resonator 207 decreases. As a result, there is a problem that a sufficient resonance output cannot be obtained and only the unstable and weak second harmonic of about 10 μW can be obtained.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is a resonance constituted by a semiconductor laser as a fundamental wave light source and a plurality of resonance mirrors for resonating the fundamental wave. And a non-linear optical material arranged on the optical axis of the fundamental wave in the resonator, wherein the fundamental wave is tilted with respect to the resonance axis and is within the resonance allowable width of the resonator. (EN) Provided is a harmonic wave generator which is incident so as to enter.

In the present invention, the resonance axis is an optical axis that gives the maximum resonance output within the allowable resonance width, and is an optical axis that is uniquely determined when a resonator is composed of a plurality of resonance mirrors. Often equal to the axis through the center of the resonator.

The term "resonance allowable width" means that the resonance optical axis is parallel to the incident optical axis or is tilted in parallel with the incident optical axis. The range in which output is obtained.

In the present invention, the resonator is a standing wave linear resonator, and the resonance of the fundamental wave is between the resonance mirror on the incident side and the resonance mirror on the emitting side provided on one surface of the nonlinear optical material. What is done is that the configuration of the device is simplified,
It is preferable because adjustment of the optical axis and the like becomes easy. Further, by using one surface of the nonlinear optical material as the resonance mirror on the emitting side, it is possible to generate highly efficient harmonics with a simple configuration.

When the resonator is the standing wave linear resonator, the angle between the fundamental wave incident optical axis and the resonance axis is such that the radius of curvature of the incident surface (spherical surface) of the resonance mirror on the incident side is 5 mm.
0.15 ° to 0.4 ° is preferable. If it is smaller than 0.15 °, instability of the LD oscillation frequency and increase of the oscillation spectrum line width cannot be avoided, which is not preferable, and if it is larger than 0.4 °, the resonance output becomes less than 50% of the maximum resonance output, which is not preferable. Similarly, when the radius of curvature is 3 mm,
The angle is preferably 0.15 ° to 0.3 °.

Here, the angle between the incident optical axis of the fundamental wave and the resonance axis
The angle between the incident optical axis of the fundamental wave and the direct reflected light is 0.2 °
It is necessary to incline so that it is above. Let this angle be θ
Then, θ is the radius of curvature R of the resonance mirror,
From the incident surface (incident surface 109 of FIG. 1) of the resonant mirror
Distance L to the center of rotation of the resonator existing on the oscillation axis (L <L <
R) and the rotation angle (tilt angle) φ of the resonance axis, approximately θ = 2
It is expressed as (1-L / R) φ. θ is greater than 0.2 °
Φ> 1 / {10 (1-L / R)} because it needs to be
You. On the other hand, when the output is just 50% within the resonance allowable width,
Angle of inclination φ _t Then, 1 / {10 (1-L /
R)} <φ <φ_t Becomes

Since O <L <R, 0.1 ° <1 /
{10 (1-L / R)}, and 0.1 ° <φ <φ _t . However, when 1 / {10 (1-L / R)} ≧ φ _t , φ exceeds the resonance permissible width, and L cannot take such a value.

As the non-linear optical material, KNbO is used.
₃ , β-BaB ₂ O ₄ , KTiOPO ₄ , KH ₂ PO
₄ , non-linear optical crystals such as LiNbO ₃ and other organic non-linear optical materials can be used, but KNbO ₃ single crystal is preferable in terms of high conversion efficiency to the second harmonic and easy handling of the crystal.

Further, the present invention can be applied not only to the second harmonic but also to a generator of higher harmonics such as the third harmonic.

[0016]

In the present invention, the fundamental wave from the LD is tilted with respect to the resonance axis and is incident so as to fall within the resonance allowable width of the resonator, so that the directly reflected light not coupled to the resonator is LD. Avoiding the destabilization of the oscillation frequency of the LD and the increase of the oscillation spectrum line width due to re-focusing on the light emitting layer,
It is considered that the fundamental wave can be incident on the resonator with high coupling efficiency, which enables highly efficient wavelength conversion.

[0017]

EXAMPLES Examples will be described below. FIG. 1 shows an embodiment of a second harmonic generation device 101 to which the present invention is applied. The second harmonic generation device 101 is configured by sequentially arranging an LD 102 as a fundamental wave light source, a coupling optical system 103 including a collimator lens and a mode matching lens, and a standing wave linear resonator 104.
In this embodiment, the LD 102 has a wavelength of 860 nm and a single longitudinal-transverse mode with little astigmatism is used, and emits the fundamental wave 105. The fundamental wave 105 is collected by the coupling optical system 103, matched with the resonance mode, and incident on the standing wave linear resonator 104.

The standing wave linear resonator 104 in this embodiment is composed of a resonance mirror 106 having a spherical resonance mirror surface with a radius of curvature of 5 mm and a KNbO ₃ single crystal having one surface (emission surface 107) as a resonance mirror surface. The nonlinear optical crystal 108 is used. Incident surface 109 of standing wave linear resonator 104
95% or more of the fundamental wave and 90% of the harmonic wave
The reflection film is vapor-deposited to form a resonance mirror, and the exit surface 1
In 07, 99% or more of the fundamental wave is reflected and 9 of the harmonic wave is reflected.
A film having a transmission of 0% or more is deposited to form a resonance mirror.

In this structure, the incident fundamental wave optical axis 110
Forms an angle of 0.3 ° with the resonance axis 111, and a part of the fundamental wave 105 does not enter the standing wave linear resonator 104 but is reflected by the incident surface 109 to be directly reflected light 112. Since the incident fundamental wave optical axis 110 and the optical axis of the direct reflected light 112 form an angle of 0.2 °, they are not re-focused on the light emitting layer of the LD 102. Therefore, the oscillation wavelength of the LD 102 is stable,
Moreover, since the oscillation spectrum line width does not increase, a coupling efficiency of 40% or more was obtained.

As a result, a sufficient fundamental wave resonance output was obtained, and the second harmonic wave 113 having a wavelength of 430 nm and an output of 1 mW was obtained. Of the amplified fundamental wave, the resonance mirror 10
The return light 114 from the resonator that has passed through 6 is the LD 102.
The oscillation frequency of the LD 102 was stabilized by the return light 114, and the second harmonic (blue laser) output was maintained even at room temperature ± 10 ° C.

The resonator used in the present invention is not limited to a resonator in which a plurality of resonant mirrors and a nonlinear optical material are separate, but a monolithic type (integrally molded type) in which a resonant mirror is formed in the nonlinear optical material itself. ) Resonator is also applicable.

[0022]

As described above, according to the present invention,
The fundamental wave is tilted with respect to the resonance axis and is incident so as to fall within the resonance allowable width of the resonator, thereby coupling to the resonator due to destabilization of the oscillation frequency of the LD and increase of the oscillation spectrum line width. The decrease in efficiency can be avoided, and stable and highly efficient harmonic generation can be achieved. Moreover, since an element for controlling the directly reflected light such as an optical isolator is not required,
It also has the effect of enabling a compact and simple configuration.

[Brief description of drawings]

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

FIG. 2 is a side view showing an example of a conventional harmonic generator.

[Explanation of symbols]

 101: Second harmonic generation device 102: Semiconductor laser (LD) 103: Coupling optical system 104: Standing wave linear resonator 105: Fundamental wave 106: Resonant mirror 107: Emission surface 108: Nonlinear optical crystal 109: Incident surface 110 : Incident fundamental wave optical axis 111: resonance axis 112: direct reflected light 113: second harmonic 114: return light

Claims (2)

[Claims] 1. A semiconductor laser as a fundamental wave light source, a resonator constituted by a plurality of resonant mirrors for resonating the fundamental wave, and a nonlinear optical material arranged on the optical axis of the fundamental wave in the resonator. A harmonic generation device comprising: a fundamental wave which is inclined with respect to a resonance axis and is incident so as to fall within a resonance allowable width of a resonator. 2. The resonator is a standing wave linear resonator, and the resonance of the fundamental wave is one of a resonance mirror on the incident side and a nonlinear optical material.
The harmonic generation device according to claim 1, wherein the harmonic generation device is performed between the resonance mirror provided on the surface and on the exit side.