JPH06196779A - Light generator - Google Patents

Abstract

PURPOSE:To output a higher-harmonic wave very efficiently and stably by comprising a longitudinal mod of the combination of a multi-mode high output semiconductor laser and a grating. CONSTITUTION:A longitudinal spectrum comprises a multi-mode semiconductor laser 1 and a feed back grating 3 which has 1400-2000 channels per mm. Laser light emitted from an end face 4 of the semiconductor laser 1 is collimated by means of a collimator lens 2 and only the lights having a specific wave length are collected on the end face 4 of the semiconductor laser due to a wavelength dispersion effect of the grating 3 and those lights are fed back to an active layer 5 and then a wave length of the semiconductor laser is stabilized. Also, the longitudinal mode spectrum can be narrower, so green or blue higher-harmonic wave light can be obtained stably and very efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used in a high-density optical disk system, a solid-state laser using a semiconductor laser as an excitation light source, and a short-wavelength light source with high efficiency and stabilization.

[0002]

2. Description of the Related Art Obtaining green and blue light sources by highly efficient wavelength conversion using a semiconductor laser as an excitation light source is required for high density recording on an optical disk, image processing and the like.
The output light obtained here is required to have a transverse mode of Gaussian and can be condensed to near the diffraction limit, and have an output of several mW and stable in frequency and time.

In order to obtain a high-power short-wavelength light source of several tens of mW or more using a semiconductor laser as a light source, a quasi-phase matching (hereinafter referred to as QPM) type polarization inversion waveguide (Yamamoto et al., Optics. Letters Optics Letters V
ol.16, No.15, 1156 (1991)) or using a semiconductor laser with a single longitudinal mode spectrum as an excitation light source to insert a wavelength conversion element inside the resonator to obtain harmonics. The type is influential. Here, a QPM type polarization inversion waveguide will be described as an example of the nonlinear optical crystal.

At present, 1.1 mW of blue light is obtained by using a polarization inversion waveguide of the QPM system for an incident light intensity of 35 mW into the waveguide of a semiconductor laser. However, the QPM polarization inversion waveguide device has a wavelength tolerance of only 0.2 nm, the oscillation wavelength fluctuation with respect to the temperature change of the semiconductor laser is 0.2 nm / ° C, and the mode hop due to the returning light is about 1 nm, so the output is Only stable for a few seconds. Therefore, wavelength stabilization of the semiconductor laser is indispensable.

Further, by using an internal cavity type of a solid-state laser, green light having an excitation intensity of Nd: YVO ₄ of a semiconductor laser of about 3 mW with respect to 50 mW is obtained. However, the full width at half maximum of the absorption spectrum of the laser material is several nm in the case of Nd: YVO ₄ , and mode hops and multimodal longitudinal modes cause output noise. Therefore, wavelength stabilization of the semiconductor laser is indispensable.

As described above, in a light generator using a semiconductor laser whose longitudinal mode is a single mode as excitation light, a polarization inversion type waveguide short wavelength using as excitation light a semiconductor laser having a grating on the emitting side of the semiconductor laser is used. A light source (schematic configuration diagram in FIG. 5) and a short wavelength light source using an internal cavity type solid-state laser (schematic configuration diagram in FIG. 6) have been proposed.

In FIG. 5, 501 is a 0.83 μm band 50 mW class AlGaAs semiconductor laser, 502 is a collimating lens, 503 is a λ / 2 plate, 504 is a focusing lens with NA = 0.6, and 505 is the optical axis of the semiconductor laser. It is a grating installed with an inclination of θ. The grating 505 has a linear shape. The rear end surface 506 of the semiconductor laser 501 is provided with a high reflectance coat. The laser light with a wavelength of 830 nm reflected by the grating is rotated by the λ / 2 plate 503 in the deflection direction and is focused on the waveguide end face 507 by the focusing lens 504.
The light propagated through the polarization inversion waveguide 508 having a 3.7 μm polarization inversion layer is converted to a wavelength of 415 nm, and the waveguide end face 50
It is emitted from 9.

Similarly, in FIG. 6, 601 is 80
A 9 nm band 60 mW class AlGaAs semiconductor laser, 602 is a collimating lens, 603 is a focusing lens of f = 12.5 mm, and 604 is a grating installed at an angle of θ with respect to the optical axis of the semiconductor laser. The grating 604 has a linear shape. Depth for incident angle 30 °
When the pitch was 0.29 μm and the pitch was 0.83 μm, the diffraction efficiency was about 10%, and stable single mode oscillation was obtained. The light emitted from the end face 605 of the semiconductor laser is collimated by the collimator lens 6
The light is collimated by 02 and part of it is returned to the active layer 606 of the semiconductor laser by the grating 604, and the rest is reflected light (0th-order diffracted light), and the end surface 608 of Nd: YVO ₄ 607 is reflected by the focusing lens 603 with f = 12.5 mm. Is focused on. The fundamental wave resonating at the output mirror 609 and the end surface 608 of Nd: YVO ₄ is wavelength-converted by the nonlinear optical crystal 610 and emitted from the output mirror 609.

[0009]

At present, the output of a semiconductor laser capable of oscillating in a single longitudinal mode is about 100 mW, and the output of green or blue light obtained when these semiconductor lasers are used as excitation light is 10 mW. It is the following. However, green and blue light sources with a power of 10 mW or more, such as a light source for writing on an optical disk, are also required.

A semiconductor laser of 100 mW or more has a multimode longitudinal mode spectrum, and it is difficult to obtain a highly efficient and stable output.

An object of the present invention is to overcome the problems of the short wavelength light source in which the semiconductor laser and the polarization inversion waveguide or the solid-state laser are combined as described above, and to provide a highly efficient and stable harmonic output. .

[0012]

According to the present invention, (1) a semiconductor laser having a multimode longitudinal mode spectrum and a groove number of 1400 / mm or more and 2000 / m or more.
In order to obtain a stable and highly efficient light source, a feedback grating having a length of m or less is provided, the longitudinal mode spectrum of a semiconductor laser is locked by the grating, and the reflected light from the grating is used as an excitation light source for a solid-state laser crystal. To do.

The present invention also provides (2) a semiconductor laser having a multimode longitudinal mode spectrum and a groove number of 1400 / mm to 2000 / m.
In order to obtain a stable and highly efficient light source, a feedback grating having a length of m or less is provided, the longitudinal mode spectrum of a semiconductor laser is locked by the grating, and the reflected light from the grating is used as an excitation light source for a nonlinear optical crystal. To do.

[0014]

According to the present invention, a high output (100 mW or more) semiconductor laser having a multimode longitudinal mode is combined with a grating, and diffracted light from the grating can be returned to the semiconductor laser to stabilize the wavelength of light emitted from the semiconductor laser. Further, since the longitudinal mode spectrum can be narrowed, stable and highly efficient harmonic light of green or blue can be realized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration diagram including a multimode semiconductor laser of the present invention and a grating feedback.

In FIG. 1, 1 is a 0.83 μm band 200 mW class AlGaAs semiconductor laser, 2 is a collimating lens with NA = 0.55, and 3 is a grating installed at an angle of θ with respect to the optical axis of the semiconductor laser.

The laser light emitted from the end face 4 of the semiconductor laser is collimated by the collimating lens 2 with NA = 0.55, and only a specific wavelength is condensed on the end face 4 of the semiconductor laser by the wavelength dispersion effect of the grating 3. The wavelength of the semiconductor laser is stabilized by optical feedback to 5. The grating 3 has a linear shape having the following formula pitch d.

D = λ / (2sinθ) (1) λ is the oscillation wavelength of the LD, d is the pitch of the grating, and θ
Is the angle between the optical axis of the laser beam and the grating.

At this time, important parameters are (1) the reflectance of the end face 4 of the semiconductor laser, and (2) the relationship between the thickness of the active layer of the semiconductor laser and the pitch of the grating. FIG. 2 shows the relationship between the reflectance of the end face 4 and the relative noise intensity (RIN) when the amount of feedback of the semiconductor laser to the active layer by the grating is set to about several%.
At a reflectance of 0.5% or less, the amount of feedback due to the grating is small and the oscillation threshold value increases, so a high output cannot be obtained. Moreover, the change in the output was large with respect to the change in the feedback amount. 0.5%
With the above reflectance, oscillation easily occurs and the output is 200 m.
It is possible to take out up to about W and RI at that time
N was -150 dB / Hz or less. However, if the reflectance of the end face 4 is 2.5% or more, the locked state becomes unstable,
The lock disappeared at 5% or more. R at this time
IN was about -115 dB / Hz. As a result, it is found that the reflectance of the emitting end face 4 of the semiconductor laser is optimally 0.5% or more and 2.5% or less.

Next, the relationship between the thickness of the active layer of the semiconductor laser and the pitch of the grating will be shown. The length of the active layer of the semiconductor laser is about 600 μm, and the longitudinal mode interval at this time is about 0.2 nm. The wavelength dispersion effect of the grating with respect to 0.2 nm is obtained using the equation (1). The results are shown in Table 1.

[0021]

[Table 1]

From this result, the distance from the longitudinal mode next to the focusing position on the end face 5 of the semiconductor laser when using a collimating lens with NA = 0.55 was calculated. The results are also shown in Table 1. An experiment was actually conducted considering that the thickness of the active layer of the semiconductor laser is about 1 μm. Locked in single longitudinal mode, the pitch is 1400 lines / mm
The above was 2000 lines / mm or less. 2000 lines / mm
The reason that the above gratings did not lock was
This is because almost no diffraction efficiency is obtained for a wavelength of about 830 nm, and in order to make a multimode semiconductor laser in the wavelength of 830 nm a single mode, a grating with a pitch of 1400 lines / mm or more and 2000 lines / mm or less is used. Must be used.

Another important point here is that the reflected light from the grating of the semiconductor laser can be focused on the solid-state laser crystal or the nonlinear optical crystal. The width of the active layer of a 1 W class multimode semiconductor laser is 50 μm
As described above, even if the longitudinal mode spectrum is unified, high efficiency cannot be expected. The relationship between the output and the width of the active layer obtained for an LD output of 100 mW in the semiconductor laser pumped solid-state laser is shown in FIG. The output intensity obtained when excited by a semiconductor laser having an active layer width of 50 μm is about 85% of that of a single mode laser (active layer width, 4 μm).
However, when excited with an active layer width of 100 μm, the obtained output intensity was only about 30%. As a result, the width of the active layer must be 50 μm or less in order to obtain highly efficient solid-state laser oscillation.

In a semiconductor laser pumped solid-state laser,
Optimally when the multimode laser diode is locked,
The relationship between the LD output and the obtained solid state laser output is shown in FIG. It can be seen that twice the output is obtained compared to when it is not locked.

Although the semiconductor laser pumped solid-state laser has been described in the above embodiments, the grating feedback semiconductor laser shown in the above embodiments is also used in wavelength conversion by a nonlinear optical crystal such as a QPM type polarization inversion waveguide. The same effect as is obtained.

[0026]

INDUSTRIAL APPLICABILITY The present invention uses a light generation device equipped with a multimode semiconductor laser and a feedback grating as an excitation light source, and uses a nonlinear optical crystal such as a QPM polarization inversion waveguide and a solid-state laser to provide a stable and high-power green. Since a blue short-wavelength light source is realized, it is possible to realize a light source for an optical disk or a measurement that requires stable output with low noise, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a light generation device in which a multimode semiconductor laser of the present invention and a feedback grating are combined.

FIG. 2 is a diagram showing the relationship between the end face reflectance and the relative noise intensity of the semiconductor laser of the light generator of the present invention.

FIG. 3 is a diagram showing the relationship between the width of the active layer of the semiconductor laser of the light generator of the present invention and the output intensity.

FIG. 4 is a diagram showing an output intensity obtained from a solid-state laser with and without a feedback grating of a pumping multimode semiconductor laser.

FIG. 5 is a schematic configuration diagram of a short wavelength light source using a combination of a conventional semiconductor laser using grating feedback and a polarization inversion waveguide.

FIG. 6 is a schematic configuration diagram of a short wavelength light source by combining a conventional semiconductor laser using grating feedback and an internal cavity type solid state laser.

[Explanation of symbols]

1 semiconductor laser 2 collimating lens 3 grating 4 end face 5 active layer 501 semiconductor laser 502 collimating lens 503 λ / 2 504 focusing lens 505 grating 506 end face 507 end face 508 polarization reversal waveguide 509 end face 601 semiconductor laser 602 4 collimating lens 603 collimating lens 605 End face 606 Active layer 607 Nd: YVO ₄ 608 End face 609 Output mirror 610 Non-linear optical crystal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number in the agency FI Technical indication H01S 3/109 8934-4M 3/133 (72) Inventor Makoto Kato 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A semiconductor laser having a multimode longitudinal mode spectrum and a groove number of 1400 / mm or more 2000
A light generating device comprising a feedback grating of not more than 1 / mm, locking the longitudinal mode spectrum of a semiconductor laser by the grating, and using reflected light from the grating as an excitation light source for a solid-state laser crystal. 2. A semiconductor laser having a multimode longitudinal mode spectrum and a groove number of 1400 / mm or more 2000
A light generating device comprising a feedback grating of not more than 1 / mm, locking the longitudinal mode spectrum of a semiconductor laser by the grating, and using the reflected light from the grating as an excitation light source for a nonlinear optical crystal. 3. The light generating device according to claim 1, wherein in the semiconductor laser, the reflectance of the emitting end face is 0.5% or more and 2.5% or less. 4. The light generating device according to claim 1, wherein in the semiconductor laser, the width of the active layer is 50 μm or less.