JPH0580379A - Second higher harmonic generation device - Google Patents

Abstract

PURPOSE:To stabilize the frequency of laser light as a fundamental wave projected from a semiconductor laser element. CONSTITUTION:A 2nd higher harmonic generating element 13 is arranged in the optical path of the laser light emitted from the front end surface of the semiconductor laser element 11 between a 1st resonator 12 and the resonator mirrors 12a, 12b of the 1st resonator 12, and a 2nd resonator 17 which has the same resonator length with the 1st resonator 12 and has resonator mirrors 17a, 17b lower in refractive index to the laser light emitted by the semiconductor laser element 11 than the resonator mirrors 12a, 12b of the 1st resonator 12 is arranged in the optical path of laser light emitted from the rear end surface; and the laser light emitted from the rear end surface of the semiconductor laser element 11 is resonated by the 2nd resonator 17 and then fed back to the semiconductor laser element 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a second harmonic generation device in which a semiconductor laser device, a resonator and a second harmonic generation device are combined.

[0002]

2. Description of the Related Art Recently, in order to obtain a short wavelength light required to increase the storage capacity of a storage device such as a CD (Compact Disc), semiconductor laser (hereinafter referred to as LD) light in the near infrared region (800 nm band) Second harmonic generation (Second Harmonic Gen
The second harmonic generation device that converts the laser light into a blue laser beam with a half wavelength using an eration (hereinafter referred to as SHG) element is under study.

There are various structures of the SHG element used in this second harmonic generation device, and they are roughly classified into a bulk crystal type and a waveguide type. By the way, there is a method of increasing the energy density of the LD light, which is the fundamental wave, as one of the methods to efficiently generate the second harmonic, but in the waveguide type SHG element, by confining the LD light in a narrow area in the waveguide, In order to improve efficiency, the bulk crystal type SHG element has a resonator structure as shown in FIG.

FIG. 1 is a schematic diagram showing a conventional second harmonic generator using a typical bulk crystal type SHG element. In the figure, 1 is a semiconductor laser element, 2 is a resonator, and 3 is an SHG element. Shows. The resonator 2 and the SHG element 3 are arranged with the optical isolator 4 interposed on the optical axis of the fundamental laser (LD) light emitted from the semiconductor laser element 1. LD light is an optical isolator 4
The light is incident on the resonator 2 via the.

The resonator 2 is provided on both sides of the SHG element 3 with the SHG element 3 interposed therebetween.
The resonator mirrors 2a and 2b having a high reflectance (90% or more) with respect to the LD light are arranged so as to face each other. The light passing through the optical isolator 4 is transmitted through the resonator mirror 2a, and then the resonator mirror 2a. , 2b and then repeatedly reflected by the resonator mirrors 2a, 2b, reciprocally reciprocated between the resonator mirrors 2a, 2b to resonate, the energy density is increased, and the SHG element 3 receives the second harmonic ( SH wave) is converted. The SH wave is transmitted through the resonator mirror 2b, further transmitted through the dichroic mirror 5 which is arranged on the same optical axis and inclined at a predetermined angle with respect to the optical axis, and is emitted.

On the other hand, a part of the LD light which has not been converted into the SH wave is reflected by the dichroic mirror 5 and is reflected by the total reflection mirror 6.
After passing through 7, the light enters the mirror on the light output end side of the optical isolator 4, and from there, the optical isolator 4 travels backward and is fed back to the semiconductor laser device 1. As a result, fluctuations in the frequency of the laser light emitted from the semiconductor laser device 1 itself are suppressed, and the frequency of the laser light emitted from the semiconductor laser device 1 is maintained stable.

[0007]

By the way, in such a conventional second harmonic generator, the resonator mirrors 2a and 2b in the resonator 2 are required to reflect the LD light and cause it to resonate. Although the reflectance is set high, when the reflectance of the resonator mirrors 2a and 2b is high, the width of the resonable frequency in the resonator 2 (referred to as the resonance half-value width) becomes narrow, and the light is emitted from the resonator 2. The emitted LD light is as shown in FIG.

FIG. 2 is a graph showing the relationship between the fluctuation width Δf of the LD light emitted from the resonator 2 and the resonator output P _{t. The} fluctuation width Δf is plotted on the horizontal axis and the resonator is plotted on the vertical axis. The output P _t is shown. As is clear from this graph, the emitted light in the resonance state can be obtained only within the very narrow fluctuation width Δf.

For this reason, for example, when the frequency of the LD light emitted from the semiconductor laser element 1 fluctuates significantly by the disturbance over the resonance half-width, the LD light is not emitted from the resonator 2 and the semiconductor laser element 1 is not emitted. Since the LD light in the resonance state to be returned cannot be obtained, the emission light characteristic from the semiconductor laser device 1 cannot be stabilized, and a vicious cycle in which fluctuations become even larger occurs, and stable SH waves cannot be obtained. There was a problem.

The present invention has been made in view of the above circumstances, and an object thereof is to surely obtain light for feedback to a semiconductor laser device and to obtain a stable second harmonic. Another object of the present invention is to provide a second harmonic generation device.

[0011]

A second harmonic generating device according to the present invention comprises a semiconductor laser element, a semiconductor laser element, and a resonator mirror, which face each other, and is emitted from the semiconductor laser element. A second resonator having a resonator for resonating the fundamental wave and a second harmonic wave generating element arranged between the resonator mirrors of the resonator and converting the fundamental wave resonated by the resonator into the second harmonic wave In the harmonic generator, a resonator mirror having the same resonator length as the resonator and having a reflectance with respect to a fundamental wave lower than that of the resonator mirror of the resonator is emitted from the semiconductor laser device. Another resonator for resonating the generated fundamental wave and returning it to the semiconductor laser device is provided.

[0012]

According to the present invention, the second harmonic wave generating element is arranged between the resonator mirrors to reflect the fundamental wave separately from the one resonator for generating the second harmonic wave by putting the fundamental wave into a resonance state. The resonator has a resonator mirror whose ratio is smaller than that of the resonator, and another resonator that resonates the fundamental wave to make it enter the semiconductor laser element by feedback is provided. Is smaller than the full width at half maximum of the resonance of the one resonator by a smaller value, and even if the laser light emitted from the semiconductor laser element fluctuates, the light for feedback can be reliably obtained and the second harmonic wave can be stably generated. It can be generated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 3 is a schematic diagram of a second harmonic generation device according to the present invention, in which 11 is a semiconductor laser element, 12 is a first resonator, and 17 is a second resonator. Laser light as a fundamental wave emitted from the front end face of the semiconductor laser device 11.
A bulk crystal type second harmonic generation element (SHG) located between the first resonator 12 and the resonator mirrors 12a and 12b of the first resonator 12 with an optical isolator 14 interposed on the optical axis of (LD light). An element) 13 is provided, and the LD light passes through the optical isolator 14 and enters the first resonator 12.

The first resonator 12 comprises resonator mirrors 12a and 12b, which are composed of a pair of concave mirrors, facing each other, and the LD light transmitted through the resonator mirror 12a receives the resonator mirror 12a.
The energy density is increased by being repeatedly reflected between a and 12b, converted into the second harmonic (SH wave) by the second harmonic generation element 13, and the first resonance occurs when the fundamental wave and SH wave are mixed. Bowl 12
The LD light is emitted by the filter 15, the LD light is removed by the filter 15, and only the SH wave is extracted.

On the other hand, an optical isolator 16 is placed on the optical axis of the LD light which is the fundamental wave emitted from the rear end face of the semiconductor laser device 11.
Also, the second resonator 17 is provided, and the LD light passes through the optical isolator 16 and is incident on the second resonator 17. The second resonator 17 has a slightly lower reflectance for LD light than the resonator mirrors 12a and 12b of the first resonator 12 described above.
a and 17b are made to face each other, and the light incident on this is repeatedly reflected by the resonator mirrors 17a and 17b, reciprocates between the resonator mirrors 17a and 17b, and is resonated to increase the energy density. After that, the light passes through the resonator mirror 17b and enters the total reflection mirror 18.

The total reflection mirrors 18, 19, 20 are arranged so as to be inclined with respect to each other by a predetermined angle, and the LD light in the resonant state emitted from the second resonator 12 is reflected by the total reflection mirrors 18, 19, 20. After that, it returns to the optical isolator 16 and is fed back to the semiconductor laser device 11 via the optical isolator 16 to fix the oscillation wavelength of the LD light oscillated from the semiconductor laser device 11.

Thus, in such a device of the present invention,
The reflectance of the second resonator 17 of the resonator mirrors 17a and 17b with respect to the LD light is set smaller than the reflectance of the resonator mirrors 12a and 12b of the first resonator 12, respectively. 17
The output of the LD light emitted after being resonated at
As shown in.

In the graph shown in FIG. 4, the horizontal axis represents the frequency fluctuation width Δf, and the vertical axis represents the second resonator output P _t . As is clear from this graph, the resonance half width of the fluctuation width Δf is remarkably wider than that of the conventional case shown in FIG. 2, and the LD emitted from the semiconductor laser device 11 is
Stable second resonator even if light fluctuates slightly due to disturbance
The output of 17, in other words, the LD light in the resonance state can be obtained, the LD light can be reliably returned to the semiconductor laser element 11, and the frequency of the LD light emitted from the semiconductor laser element 11 can be stabilized. It will be.

This will be described below with specific numerical values. The resonance half-width Δν of the first resonator 12 and the second resonator 17 is expressed by the following equation (1) using the frequency spacing FSR between modes and the finesse F of the resonator.

Δν = FSR / F (1)

The frequency spacing FSR between modes in the equation (1) is c / 2L
(C: speed of light, L: resonator length (optical path length)), and the finesse F of the resonator is given by πR ^1/2 (1-R) (R: reflectance of resonator mirror).

Now, for example, the resonator length of the first and second resonators 12 and 17 is 10 mm, and the resonator mirror reflectance of the first resonator is 95.
%, And the resonator mirror reflectance of the second resonator is 60%,
The inter-mode frequency interval FSR = 15 GHz, the finesse F ₁ = 61 of the first resonator, and the finesse F ₂ = 6.1 of the second resonator 17. Therefore, the resonance half-value width Δν ₁ of the first resonator is 216 MHz, the resonance half-value width Δν ₂ of the second resonator is 2.46 GHz, and the resonance half-value width of the second resonator is nearly 10 times that of the first resonator. .. In other words, from the second resonator 17 to the semiconductor laser device 11
The light to be returned to can be obtained in a wide range with respect to the frequency fluctuation Δf of the laser light (LD light) emitted from the semiconductor laser element 11.

The intensity of light to be returned to the semiconductor laser device 11 is 1 to 0.1% of the light output from the end face of the semiconductor laser device.
The optical output of the front end face on the first resonator 12 side is
When using the semiconductor laser device 11 of 100 mW, 1 to 0.
Light with an output of about 1 mW should be returned and incident.

Assuming that the laser light to the second resonator 17 side is obtained from the rear end face of the semiconductor laser element 11 as in the embodiment, when the optical output of the front end face is 100 mW, the optical output from the rear end face is usually It is about 5 mW. Therefore, the light obtained from the emission side of the second resonator 17 is given by the following equation (2) when the internal loss is (1-A).

P _t / P _i = (1-R) ² A / (1-RA) ² (2) where P _t : light intensity transmitted through the second resonator P _i : incident on the second resonator Light intensity

For example, the mirror reflectance R in the second resonator
Is 60% and (1-A) = 2%, _Pt / _Pi = 92%
Becomes Therefore, if the intensity of the incident light on the second resonator 17 is 5 mW, it is possible to return the light with the maximum output of about 4.5 mW, and the oscillation frequency of the semiconductor laser device 11 can be stabilized by using the second resonator 17. It is possible enough.

In the above embodiment, the LD light incident on the second resonator 17 is obtained from the rear end face of the semiconductor laser device 11, but the laser light emitted from the front end face of the semiconductor laser device 11 is described. Needless to say, the beam may be split by a beam splitter, and a part of the beam may be incident on the second resonator 17 to resonate, and then returned to the front end face.

[0028]

As described above, in the device of the present invention, the second harmonic generating element is arranged between the resonator mirrors, and the fundamental wave emitted from the semiconductor laser element is resonated to increase the energy density. The resonator has the same resonator length as that of the one resonator that is output after being converted to the second harmonic, and the reflectance of the resonator mirror with respect to the fundamental wave is lower than the reflectance of the mirror of the one resonator. Since another resonator that resonates the laser beam and makes it return and enter the semiconductor laser element is provided, the fundamental wave is stabilized if the fluctuation of the frequency of the fundamental wave emitted from the semiconductor laser element is within the resonance half-value width of the other resonator. The present invention has excellent effects such as high stability against external disturbances.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a conventional device.

FIG. 2 is a graph showing an output light output from a resonator.

FIG. 3 is a schematic diagram of the device of the present invention.

FIG. 4 is a graph showing an output light output from the second resonator.

[Explanation of symbols]

 11 Semiconductor laser device 12 First resonator 12a, 12b Resonator mirror 13 Second harmonic generation device 14 Optical isolator 15 Filter 16 Optical isolator 17 Second resonator 17a, 17b Resonator mirror 18, 19, 20 Total reflection mirror

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuharu Matsumoto 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A semiconductor laser device and a resonator mirror are arranged to face each other, and a resonator for resonating a fundamental wave emitted from the semiconductor laser device is disposed between the resonator mirror and the resonator mirror. , The second fundamental wave resonated by the resonator
In a second harmonic generation device having a second harmonic generation element for converting into a harmonic, the resonator has the same resonator length as the resonator, and the reflectance for the fundamental wave is the reflectance of the resonator mirror of the resonator. A second harmonic generation device having another resonator having a lower resonator mirror and resonating the fundamental wave emitted from the semiconductor laser element and returning it to the semiconductor laser element.