JPH05323404A - Optical wavelength conversion element - Google Patents

Abstract

PURPOSE:To obtain wavelength converted waves of stable output and high intensity by providing a light shielding plate which shields the laser beam reflected at the end face of an optical waveguide formed in the direction where the laser beam of the basic wave is made incident diagonally. CONSTITUTION:The light shielding plate 15 is disposed in the position deviating from the optical path of the laser beam 11 heading toward the wavelength. conversion element 20 between a collimator lens 12 and a lambda/2 plate 13. This light shielding plate 15 is so disposed as to approach the laser beam 11 as far as possible within the range where the laser beam 11 is not shielded. The rear end face 20a of the wavelength conversion element 20 is diagonally cut overall including the end face 22a of the optical waveguide. The direction of the cut is set at the direction where the optical path of the reflected laser beam 11R is completely separated from the laser beam 11 heading toward the wavelength conversion element 20 and deviates to the light shielding plate 15 side. Then, the laser beam 11R reflected by the end face 22a of the optical waveguide is shielded by the light shielding plate 15 and is prevented from returning to the semiconductor laser 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength conversion device for converting a fundamental wave into a second harmonic or the like, and more particularly to a semiconductor laser as a fundamental wave light source and an optical waveguide type optical wavelength conversion element. The present invention relates to a light wavelength conversion device.

[0002]

2. Description of the Related Art Conventionally, non-linear optical materials have been used to
Various attempts have been made to convert the wavelength of laser light into a second harmonic wave (shorter wavelength). As a light wavelength conversion element that performs wavelength conversion in this way, specifically, a bulk crystal type, an optical waveguide type, and the like are known. In addition, this type of optical wavelength conversion element is often used in combination with a semiconductor laser.

As described above, in order to use the semiconductor laser as the fundamental wave light source and input the laser beam emitted from the fundamental laser to the optical wavelength conversion element of the optical waveguide type, the laser beam emitted from the semiconductor laser is used in the incident optical system. A method of squeezing and converging on the end face of the optical waveguide is often used.

[0004]

However, when the fundamental laser beam is input to the optical waveguide type optical wavelength conversion element as described above, the laser beam reflected by the end face of the optical waveguide returns to the semiconductor laser. It has been recognized that such incidents cause noise, and that the wavelength-converted wave output greatly changes due to a decrease in wavelength conversion efficiency due to fluctuations in the oscillation wavelength.

In order to prevent the problem due to this return light, it has been conventionally considered to superimpose a high frequency on the driving current of the semiconductor laser to make the semiconductor laser multi-mode. Such a method is effective for a so-called Cerenkov radiation type optical wavelength conversion element, which has a relatively wide fundamental wavelength allowable width for achieving phase matching between the fundamental wave and the wavelength-converted wave. It is difficult to apply to a waveguide-guided type optical wavelength conversion element that achieves phase matching between the fundamental wave of the wave mode and the wavelength conversion wave of the guided mode. In other words, in this waveguide-guided type optical wavelength conversion element, since the fundamental wave wavelength allowable width is narrow, only one mode of the multimodes of the semiconductor laser can be used for wavelength conversion, and therefore, apparently. The wavelength conversion efficiency is extremely low.

The present invention has been made in view of the above circumstances. A semiconductor laser of a single longitudinal mode is used as a fundamental wave light source, and an optical waveguide type is used as an optical wavelength conversion element. It is an object of the present invention to provide an optical wavelength conversion element capable of obtaining a high-intensity wavelength-converted wave with stable output by suppressing return light to the.

[0007]

An optical wavelength conversion device according to the present invention includes an optical waveguide made of a non-linear optical material as described above, and an optical wavelength conversion element for wavelength-converting a fundamental wave guided through the optical waveguide. And a single longitudinal mode semiconductor laser that emits a laser beam as a fundamental wave, and an optical system that converges the laser beam on the end face of the optical waveguide and makes it enter the optical waveguide. The end face of is formed in a direction in which the laser beam as the fundamental wave is obliquely incident, and a light-shielding plate that blocks the laser beam that is reflected by the end face of the optical waveguide and proceeds to the semiconductor laser side is provided. To do.

[0008]

As described above, when the end face of the optical waveguide is formed in the direction in which the laser beam as the fundamental wave is obliquely incident as described above, the laser beam reflected by this end face is converted from the semiconductor laser into the optical wavelength conversion element. It will follow a different optical path than the laser beam going to. Therefore, it is possible to partially or completely block the laser beam returning to the semiconductor laser side by disposing the light shielding plate as described above at a position where the laser beam traveling from the semiconductor laser to the light wavelength conversion element is not or hardly blocked. ..

If the returning light to the semiconductor laser can be eliminated or reduced in this way, noise or oscillation wavelength fluctuation due to the returning light can be suppressed even if a single longitudinal mode semiconductor laser is used as the fundamental wave light source. .. As a result, in this device, a wavelength-converted wave having a stable output can be obtained with high wavelength conversion efficiency. Further, since the device of the present invention does not convert the semiconductor laser into a multi-longitudinal mode, the utilization efficiency of the laser beam is kept high even when a waveguide-guided type is used as the optical wavelength conversion element. From the point of view, the wavelength conversion efficiency can be improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. 1 and 2 are respectively the first of the present invention.
3A and 3B show a planar shape and a side surface shape of an optical wavelength conversion device according to an example, and FIG. 3 is a perspective view thereof. As shown in the figure, this optical wavelength conversion device includes a semiconductor laser 10 as a fundamental wave light source, a collimator lens 12, and a λ / 2 plate 13
And an incident optical system including a condenser lens 14 and an optical waveguide type optical wavelength conversion element 20.

The optical wavelength conversion element 20 comprises a three-dimensional optical waveguide 22 made of a non-linear optical material embedded in a substrate 21 made of glass or plastic. In this example, 3,5-dimethyl-1- (4-nitrophenyl) pyrazole (hereinafter referred to as DMNP) disclosed in JP-A-62-210432 is used as the above-mentioned nonlinear optical material. On the other hand, the semiconductor laser 10 has a fundamental wavelength of 870.
A device that emits a laser beam 11 of nm is used. The light wavelength conversion element 20 and the semiconductor laser 10 are fixed to a common mount (not shown) with the optical waveguide 22 extending in the same direction as the beam emission axis of the semiconductor laser 10.

The front end face 20b including the end face 22b of the optical waveguide of the optical wavelength conversion element 20 transmits almost 100% of the laser beam 11 as a fundamental wave having a wavelength of 870 nm and the second harmonic wave 16 having a wavelength of 435 nm which will be described later. It has a coating. The rear end face 20a of the light wavelength conversion element 20 is coated with a laser beam 11 which is almost 100% transparent.

The laser beam 11 emitted from the semiconductor laser 10 is collimated by a collimator lens 12, and after passing through a λ / 2 plate 13 for adjusting its convergent spot shape and polarization direction to the shape of the optical waveguide 22. , Condensing lens 14
Is converged by and is converged on the end face 22a of the optical waveguide 22. As a result, the laser beam 11 enters the optical waveguide 22 through this end face 22a and travels there in the waveguide mode to the right in the figure. The laser beam 11 guided through the optical waveguide 22 is
The wavelength is halved by the DMNP that constitutes the optical waveguide 22.
It is converted into the second harmonic wave 16 of (= 435 nm). The second harmonic wave 16 propagates through the optical waveguide 22 in the guided mode. As an example, the phase matching is performed between the guided mode of the laser beam 11 in the optical waveguide 22 and the guided mode of the second harmonic wave 16 (in the case of the so-called guided-waveguide type). A beam obtained by mixing the laser beam 11 and the second harmonic wave 16 is emitted from the front end face 20b of the light wavelength conversion element 20. This emitted beam is passed through a filter (not shown) and the second harmonic wave 16
Only are retrieved and used.

Next, a structure for eliminating the returning light to the semiconductor laser 10 will be described. Collimator lens 12
Between the λ / 2 plate 13 and the λ / 2 plate 13 at a position deviated from the optical path of the laser beam 11 toward the light wavelength conversion element 20.
15 are arranged. This shading plate 15 is a laser beam
The laser beam 11 is arranged as close as possible to the laser beam 11 within a range that does not block 11. And the optical wavelength conversion element 20
The rear end face 20a of the above is also obliquely cut as a whole including the end face 22a of the optical waveguide. The direction of the oblique cut of the optical waveguide end face 22a is such that the optical path of the laser beam 11R reflected thereat is completely separated from the laser beam 11 directed to the optical wavelength conversion element 20 and is shifted to the light shielding plate 15 side.

Therefore, the laser beam 11R reflected by the end face 22a of the optical waveguide is blocked by the light shielding plate 15 and does not return to the semiconductor laser 10. If so, the semiconductor laser 10 does not generate noise due to the returning light, or the wavelength conversion efficiency does not decrease due to a change in the oscillation wavelength and a change in the phase matching condition. Therefore, in this device,
It is possible to stably obtain the high-intensity second harmonic wave 16 with a constantly high wavelength conversion efficiency.

Further, since the semiconductor laser 10 oscillates in a single longitudinal mode, there is no possibility that wavelengths other than light of a specific wavelength in the laser beam 11 cannot be wavelength-converted as in the case where the semiconductor laser is driven by high frequency superposition. From this point, the substantial wavelength conversion efficiency is improved.

In the present embodiment, the semiconductor laser 10
Are arranged so that the divergence angle of the laser beam 11 is minimized in the horizontal plane, and the optical waveguide end face 22a is cut in the horizontal plane so as to be oblique to the laser beam incident direction. Correspondingly, the light shielding plate 15 is also arranged so as to be displaced in the horizontal direction with respect to the optical path of the laser beam 11 which is directed to the light wavelength conversion element 20.

With this arrangement, the laser beam 11 and the laser beam 11R (reflected light), whose optical paths should be deviated from each other, have the smallest beam diameter in the plane in which the optical paths are deviated. Therefore, even if the oblique cut angle of the optical waveguide end face 22a is made relatively small, the laser beam 11R can be surely shielded while preventing the laser beam 11 from being vignetted by the light shielding plate 15. FIG. 4 clearly shows this. If the laser beams 11 and 11R have the beam diameters shown by the solid lines, the laser beam 11R can be blocked by the shading plate 15 arranged at the position shown in the figure, but if those beam diameters are large as shown by the broken lines. For example, while a part of the laser beam 11 heading for the light wavelength conversion element 20 is vignetted,
A part of the laser beam 11R is no longer blocked. Even if the beam diameter is large, if the oblique cut angle of the optical waveguide end face 22a is made large, the above-mentioned problems can be eliminated, but if this is done, the size of the device cannot be avoided.

It is also possible to eliminate the return light by simply displacing the optical path of the laser beam 11R from the optical path of the laser beam 11 without providing the light shielding plate 15 as described above.
However, when the laser beam 11 is converged on the optical waveguide end face 22a and is incident on the optical waveguide 22, it is necessary to converge the laser beam 11 into an extremely small spot, and the NA (numerical aperture) of the condenser lens 14 is small. A fairly large lens would be used. If this is the case, the distance between the condenser lens 14 and the end face 22a of the optical waveguide becomes extremely short, so it is very difficult to eliminate the return light with the above-mentioned configuration.

Further, in this embodiment, as described above, the laser beam 11 is applied to the rear end face 20a of the optical wavelength conversion element 20 in an amount of about 100.
%, The reflection of the laser beam 11 is suppressed to a small extent, and the effect of reducing the returning light can be obtained from this point as well.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 5, elements that are the same as the elements in FIG. 1 are given the same numbers, and duplicated description thereof will be omitted.

The optical waveguide type wavelength conversion device 30 of the second embodiment comprises a LiTaO ₃ substrate 31 on which a proton exchange optical waveguide 32 having a periodic structure of inversion domains is formed. And this optical wavelength conversion element 30 is
The direction N in which 32 extends is the beam emission axis M of the semiconductor laser 10.
On the other hand, they are arranged in an inclined state so as to satisfy Snell's law. That is, assuming that the refractive index of the optical waveguide 32 is n _w , sin θ ₁ = n _w sin θ ₂ in FIG.

Also in this embodiment, the same light-shielding plate 15 as in the first embodiment is provided, and the rear end face (including the optical waveguide end face 32a) 30a of the light wavelength conversion element 30 is the optical waveguide end face 32a. The optical path of the reflected laser beam 11R is completely separated from the laser beam 11 directed to the light wavelength conversion element 30 and is shifted toward the light shielding plate 15 side. Therefore, also in this case, the effect of preventing returning light can be obtained as in the first embodiment.

Although the optical waveguides 22 and 32 in the above-described embodiments are three-dimensional optical waveguides, the present invention is also applicable to the case of using an optical wavelength conversion element composed of a thin film optical waveguide. Furthermore, the present invention can be applied to an optical wavelength conversion device that obtains, for example, a sum frequency or a third harmonic other than the second harmonic.

[Brief description of drawings]

FIG. 1 is a plan view showing an optical wavelength conversion device according to a first embodiment of the present invention.

FIG. 2 is a side view showing the optical wavelength conversion device.

FIG. 3 is a perspective view of the optical wavelength conversion device.

FIG. 4 is a schematic diagram for explaining the difference in action depending on the direction of the oblique cut on the end face of the optical waveguide.

FIG. 5 is a plan view showing an optical wavelength conversion device according to a second embodiment of the present invention.

[Explanation of symbols]

 10 Semiconductor laser 11 Laser beam (fundamental wave) 12 Collimator lens 13 λ / 2 plate 14 Condenser lens 15 Light-shielding plate 16 Second harmonic 20, 30 Optical wavelength conversion element 22, 32 Optical waveguide 22a, 22b, 32a Optical waveguide End face of

Claims (2)

[Claims] 1. An optical wavelength conversion element having an optical waveguide made of a non-linear optical material, for converting a wavelength of a fundamental wave guided through the optical waveguide, and a semiconductor laser of a single longitudinal mode for emitting a laser beam as the fundamental wave. And an optical system for converging the laser beam on the end face of the optical waveguide and entering the optical waveguide, the end face of the optical waveguide is formed in a direction in which the laser beam obliquely enters. In addition, the light wavelength conversion device is provided with a light shielding plate that shields a laser beam that is reflected by the end face of the optical waveguide and travels toward the semiconductor laser. 2. The end face of the optical waveguide is arranged in a direction oblique to the incident direction of the laser beam within a plane where the divergence angle of the laser beam emitted from the semiconductor laser is minimized. The optical wavelength conversion device according to claim 1, wherein