JPH0769555B2 - Optical wavelength converter - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a wavelength converter for a laser light source. This has a very wide range of application as a short wavelength light source element such as an optical memory device, an optical information processing device typified by a laser printer, or a display device typified by a laser television. In particular, when it is applied to a semiconductor laser, it emits blue light, which is highly expected as a blue laser.

2. Description of the Related Art As an optical wavelength converter that applies a nonlinear optical effect, an element configuration as shown in FIG. 4 has already been proposed. this is,
An optical waveguide 52 is formed on the surface of a lithium niobate single crystal (LiNbO3) substrate 51 by an ion exchange method, and a mounting configuration example thereof is shown in FIG. This is because the light of the semiconductor laser 53 is narrowed down by the lens system 54 and the fundamental wave is applied to the end face 55 of the waveguide 52.
By injecting as 56, the second harmonic 57
Is generated.

Problems to be Solved by the Invention In such a configuration of the conventional example, since the optical waveguide 52 is formed on the surface of the substrate 51, the second harmonic is generated only on the substrate side and exits the emission surface 58. The subsequent beam cross-sectional shape was, for example, as shown in FIGS. 6 (a) and 6 (b).

More specifically, in the optical wavelength converter typified by this conventional example, since the second harmonic is generated over the entire length of the waveguide, this waveguide functions as a linear light source. Therefore, the light beam generated from this has a peculiar property that it is parallel in the direction perpendicular to the contour of the waveguide cross section, but spreads in other directions. This beam cross-sectional shape strongly depends on the waveguide cross-sectional shape, and a light beam having the cross-sectional shapes shown in FIGS. 6 (a) and 6 (c) has cross sections as shown in FIGS. 6 (b) and 6 (d). It is formed by a waveguide that has. Further, as these light beams advance, they change their shape into a more elongated belt shape or a shape in which a part of the ring is cut off.

Considering the current state of the application field, a circular light beam is generally used in optical application equipment. This is because the light density is concentrated in the central portion, so that the efficiency is good, and because it is the object of the rotation axis, it is easy to handle. In particular, in an optical memory device, it is indispensable to form a circular minute spot because of its characteristics. Therefore, after converting light of a semiconductor beam having an elliptical emission distribution into a circular beam by some optical means, It has been devised to obtain a circular spot of diffraction limit by focusing with a lens.

Now, considering the demand from such optical application equipment, assuming the configuration of the light source part by this optical wavelength converter, this peculiar light beam shape shows improved utilization efficiency, collimation optical system configuration, aberration correction It turns out that solving such a problem is extremely difficult. Further, a circular beam cannot be obtained with any waveguide shape, and such an optical wavelength converter cannot be said to be suitable as an element of a light source section.

Means for Solving the Problems In order to solve such problems, in the present invention, an optical wavelength converter is configured by forming an embedded waveguide inside a lithium niobate single crystal. That is, the fundamental wave is made incident on the waveguide from one end facet, and the second harmonic wave is radiated over the entire circumference.

Effect According to the present invention, since the second harmonic is generated over the entire circumference of the waveguide, an axially symmetric light beam can be obtained. further,
With a proper choice of waveguide shape, a nearly circular beam is obtained. The axially symmetric beam and the circular beam are extremely easy to handle due to the optical system configuration as described above, and are extremely useful as a short wavelength light source element for optical application equipment.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings. The same elements in the drawings are denoted by the same numbers.

One embodiment of the present invention is shown in FIG. Optical wavelength converter 1
Is configured by providing a buried waveguide 3 inside a lithium niobate single crystal 2.

Such a structure can be easily realized by, for example, a method of joining a lithium niobate single crystal having a waveguide on its surface to another lithium niobate single crystal.

The light of the semiconductor laser 4 which becomes a fundamental wave is condensed by the lens system 5 and enters the waveguide 3 from the first end face 6. When this propagates through the waveguide 3, the second harmonic wave 7 due to the nonlinear optical effect is generated in the direction of the angle θ that satisfies the phase matching condition. The second harmonic wave 7 has a wavelength half that of the fundamental wave and is radiated over the entire length and the entire circumference of the waveguide 3. Therefore, the waveguide 3 can be regarded as a short-wavelength linear light source, and when the cross-sectional shape is selected to be circular, a conical second harmonic wave is generated. Second cross section 8 of optical wavelength converter 1
Is processed into a conical shape to correct the angle θ,
The second harmonic wave 7 emitted from this becomes a circular beam having a substantially uniform light intensity distribution. As described above, this is an optimum beam that is easy to handle and has good utilization efficiency when applied to optical-related equipment.

Although FIG. 2 shows another embodiment of the present invention, the difference from the embodiment of the whole tree is that the second end face 9 is not conical to correct the radiation angle. Even with such a configuration, the characteristics of the obtained light beam are good,
It does not lower the industrial value of the present invention. That is, the light beam after exiting the second end surface 9 which is a flat surface is radial, but can be converted into the parallel ring-shaped light beam 11 by the condensing lens 10 arranged in close proximity.
This is also symmetrical about the axis like the circular light beam, and is therefore easy to handle. For example, as an application to an optical memory device,
Considering the case where the ring-shaped light beam 11 is narrowed down by the diaphragm lens 12, the minute light spot 13 formed is an extremely good circular light spot as in the case of a circular light beam.

Needless to say, it is desirable to provide the first end face 6 and the second end faces 8 and 9 with antireflection films suitable for the fundamental wave and the second harmonic, respectively. Further, not all the fundamental wave in the waveguide is converted into the second harmonic, so that the unconverted fundamental wave component is transmitted to the waveguide end face on the second end face side. It is preferable that this is processed by a local absorbing means or a scattering means so as not to leak into the output of the second harmonic. Alternatively, it is possible to positively use this fundamental wave. Considering the application to the optical memory device again, the second harmonic, which is a short wavelength, is suitable for writing and reading information, but as the detection light for controlling the position of this, or as the information erasing light, This fundamental wave can be used.

By taking the following measures, the output of the second harmonic wave can be increased and the beam diameter can be increased at the same time. An embodiment is shown in FIG. 3 and further description will be added.

The fundamental wave is transmitted to the first end face 6 of the optical wavelength converter 1,
Two-wavelength separating means 14 for reflecting the second harmonic is provided. Further, the second end facet is provided with a second two-wavelength separating means 15 which reflects the fundamental wave and transmits the second harmonic wave. The fundamental wave that has passed through the first two-wavelength separation means and is incident from the first end face is being propagated through the waveguide 3 (reciprocating).
As described above, the second harmonic wave 7 is generated due to the nonlinear optical effect. Now, the fundamental wave reaching the second end face is reflected by the second wavelength separating means 15,
Although it propagates through the waveguide in the opposite direction again (return path), the second harmonic wave 7'is also generated in this process by the same principle. The second harmonic wave 7 ′ is reflected by the first wavelength separating means 14 on the first end face 6 and travels toward the second end face 8. In this way, the second harmonics 7 and 7'generated in the forward and return paths
Meet at the second end face 8 and are emitted as one beam. As a result, the total light quantity of the second harmonic increases, and at the same time, the beam diameter of the second harmonic increases. It goes without saying that this is extremely useful for application to equipment. Waveguide loss,
Also, due to energy loss due to light wavelength conversion, the output of the second harmonic is lower in the return path than in the outward path, but its light intensity distribution and wave front are subject to axial adjustment, as described above. Its properties are good. In addition, the fundamental wave propagating on the return path is again transmitted through the lens system 5 to the semiconductor laser 4
In order to avoid returning to the light emitting point of (1), it is preferable to take appropriate measures such as providing a beam splitter 16 in a part of the lens system 5.

EFFECTS OF THE INVENTION As described above, according to the present invention, since the second harmonic is generated over the entire circumference of the waveguide, it is possible to form a good light beam having axial symmetry and circular shape. This is very useful when applied to optical-related equipment and has extremely high industrial value.

[Brief description of drawings]

FIG. 1 is a principle diagram of an optical wavelength converter according to an embodiment of the present invention, FIG. 2 is a principle diagram of an optical wavelength converter according to another embodiment of the present invention, and FIG. 3 is still another embodiment of the present invention. 4 is a view showing the principle of the optical wavelength converter in the embodiment of the present invention, FIG. 4 is an external view of the conventional optical wavelength converter, FIG. 5 is the same principle diagram, and FIG. 6 is a conventional optical wavelength converter. It is a relationship diagram of a beam shape and a waveguide cross-sectional shape. 1 ... Optical wavelength converter, 2 ... Lithium niobate single crystal,
3 ... Waveguide, 4 ... Semiconductor laser, 5 ... Lens system,
6 ... First end face, 7 ... Second harmonic wave, 8 ... Second end face, 14 ... First two-wavelength separating means, 15 ... Second two-wavelength separating means

Claims (6)

[Claims] 1. A fundamental wave is made incident on a buried type waveguide formed inside a lithium niobate single crystal from a first end face, and a second harmonic of the fundamental wave is radiated over the entire circumference of the waveguide. And an optical wavelength converter, wherein the second harmonic is obtained from the second end face. 2. The optical wavelength converter according to claim 1, wherein a buried type waveguide is constituted by joining a plurality of lithium niobate single crystals having a waveguide formed on the surface thereof. . 3. A buried waveguide is formed by joining a lithium niobate single crystal having a waveguide formed on its surface to another lithium niobate single crystal. The optical wavelength converter described. 4. A means for transmitting a fundamental wave and reflecting a second harmonic of the fundamental wave is provided on the first end face, and a means for reflecting the fundamental wave and transmitting the second harmonic is second. The optical wavelength converter according to claim 1, wherein the optical wavelength converter is provided on an end face of the. 5. The optical wavelength converter according to claim 1, wherein the buried waveguide has a circular cross-sectional shape. 6. The optical wavelength converter according to claim 1, wherein the second end face has a conical shape.