JPH01238630A - Waveguide type wavelength transducing element - Google Patents

Abstract

PURPOSE:To provide the waveguide type wavelength transducing element of the structure with which secondary higher harmonics are obtd. from the plane waveguide by providing a side wall onto the crystal plane of lithium niobate in the direction nearly orthogonal with the Z-axis thereof and providing a channel optical waveguide and the plane waveguide along the side wall. CONSTITUTION:A substrate 1 is the crystal plate of LiNbO3 and the side wall 2 progressing in the direction nearly orthogonal with the Z-axis is provided on this crystal plane. The channel light guide 3 is formed on the crystal plane along the side wall 2. The plane waveguide 4 is provided in combination on the same crystal plane on which the channel optical waveguide 3 is formed. The wave front propagation direction is rotated in the plane waveguide 4 when a basic wave of 0.83mum wavelength is injected to the channel optical waveguide 3 by using semiconductor laser 10 light as the basic wave. This light is then radiated from the crystal end face as the SHG light 6 of 0.415mum which is the secondary higher harmonics at about 16-17 deg. angle from the Y-axis by having the spreading angle one-dimensionally in the perpendicular direction of the waveguide and is transduced to a circularly collimated beam 8 by a cylindrical lens 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wavelength conversion element that makes it possible to realize a coherent short wavelength compact light source.

[Conventional technology]

Wavelength conversion elements, especially second harmonic generation (SHG) elements, are extremely important in industry as devices that obtain coherent short wavelength light that is difficult to obtain with excimer lasers or the like.

Semiconductor lasers are used as compact, high-power coherent laser light sources in various optical communication devices and optical information devices. Currently, the wavelength of light obtained from this semiconductor laser is 0.7
The wavelength is in the near-infrared region of 8 μm to 1.55 μm. In order to apply this semiconductor laser to a wider variety of devices such as displays, there is a need for light with shorter wavelengths such as red, green, and blue, but with current technology it is not possible to quickly realize this type of semiconductor laser. It's difficult. If a wavelength conversion element capable of efficiently converting wavelength even with the output of a semiconductor laser could be realized, the effect would be enormous.

In recent years, semiconductor laser manufacturing technology has developed, and it has become possible to obtain higher output characteristics than ever before. For this reason, by configuring an optical waveguide type SHG element, it is possible to avoid a decrease in energy density due to light diffraction, and it is possible to realize a wavelength conversion element with relatively high conversion efficiency even with a light intensity comparable to that of a semiconductor laser. An example of this is a method in which an optical waveguide is formed in a lithium niobate crystal, near-infrared light is transmitted through the optical waveguide, and the second harmonic is radiated (Cherenkov radiation) into the crystal substrate. There is an invention of SHG element (Japanese Patent Laid-Open No. 60-14222, Japanese Patent Laid-Open No. 61-940)
31). This type of SHG element has the advantage that it does not require precise temperature control because the phase matching condition between the fundamental wave and the SHG wave is automatically established.On the other hand, since the SHG output is substrate radiation, the wavefront is Light with a unique, severe aberration, and an intensity distribution similar to that of "thin eyebrows" emerges from the edge of the substrate. Therefore, converting this light into a normal, easy-to-use beam with a Gaussian intensity distribution requires a high-grade lens that corrects this aberration.

If the SHG output light is channel waveguided light like the output light of a semiconductor laser, or if it is plane waveguided light guided in at least one dimension, it can be easily parallelized using a circular or cylindrical lens. It can be converted into a beam, and such inconvenience does not occur.

[Problem to be solved by the invention]

An object of the present invention is to provide a waveguide type wavelength conversion element having a structure in which the SHG output light becomes planar waveguide light by eliminating the drawbacks of the above-mentioned conventional waveguide type SHG element.

[Means to solve the problem]

A channel optical waveguide provided with a side wall extending in a direction substantially perpendicular to the Z axis on an X-plate or Y-plate lithium niobate crystal plane, and formed on the lithium niobate crystal plane along the side wall, and the channel optical waveguide. A fundamental wave (frequency ω) is injected into the channel optical waveguide, and a second harmonic of the fundamental wave is obtained from the planar waveguide. By providing the channel and planar optical waveguides, a waveguide type wavelength conversion element in which the SHG output light has no wavefront aberration can be obtained.

〔Example〕

The present invention will be described in detail below based on embodiments and with reference to the drawings.

The figure is a diagram showing the structure of a waveguide type wavelength conversion element which is an embodiment of the present invention. 1 is a LiNbO3 crystal plate, and the substrate orientation is the X plate (that is, the normal line to the substrate is the X axis). A side wall 2 extending in a direction substantially perpendicular to the Z-axis is provided on this crystal plane, and a channel optical waveguide 3 is formed on the lithium niobate crystal plane along this side wall. A planar waveguide 4 is also provided on the same crystal plane on which the channel optical waveguide 3 is formed.

The above two optical waveguides have the following structures. The channel optical waveguide 3 that holds the fundamental wave 5 of the TE wave, which is incident light and has an electric field component parallel to the Z axis, on the X plane of the crystal substrate 1, is formed by using benzoic acid, pyrophosphoric acid, etc., which is a commonly used method. It is formed by proton (H+) exchange during heating and immersion, and its thickness is, for example, at a wavelength of 0.8 as the fundamental wave.
It is set so that it becomes a single mode waveguide when a 3 μm semiconductor laser (10) light is used. SMC light is emitted from this fundamental wave via a nonlinear optical constant d3s.

This SMC light is a guided light TE wave with the same polarization as the fundamental wave, and the planar waveguide 4 that outputs this SMC light as the planar waveguide light of the output light 6 is on the same crystal plane as the channel optical waveguide 3. It is formed by the above-mentioned proton (H+) exchange or Ti thermal diffusion method. This planar waveguide has a wavelength of 0, which is the second harmonic of the fundamental wave of 0.83 μm.
．． For light of 415 μm, it is a single mode waveguide, and for light of 0.83 μm, which is the fundamental wave, its thickness is set so as to provide a rough cutoff.

Phase matching between the fundamental wave and the SMC light is realized as follows. The equipolarized refractive index n(V'l
is about 2.34, and the equipolarized refractive index ntoll for the TE wave propagating in the same direction as the fundamental wave of the planar waveguide i4 for the wavelength 0.415 μm 5HG light (ie, the Y direction)
is about 2.32. Therefore, since there is a difference in the phase constants of the two waves, conversion from the fundamental wave to SHG light does not occur in the same propagation direction. When the wavefront propagation direction is rotated from the Y direction to the Z direction, the equipolar refractive index increases. 16-1 from Y axis
When deflected by about 7 degrees, the equipolarized refractive index nf21Ll) of the planar waveguide 4 for the TE wave becomes the same as that of the channel optical waveguide 3 described above.
is equal to the equipolarized refractive index for the fundamental wave propagating in the Y direction. SHG light 6 is emitted in this direction. This condition is that if there is no side wall of 2 and the planar structure is like -, then Y
The light exists in both +Z and -7 directions across the axis, and the conversion efficiency to SHG light is halved, but since the side wall 2 is provided as in this embodiment, conversion is efficiently achieved in one direction.

The planar waveguide SHG light 6 converted at an angle of about 16 to 17 degrees from the Y axis is emitted from the crystal end face with a one-dimensional spread angle in the direction perpendicular to the waveguide, and is converted into a circular collimated beam by the cylindrical lens 7. Converted to 8. If the Y-plane of the crystal in the figure were formed parallel, the circularly collimated SHG light 8 would travel in a direction deviated by about 8 degrees from the Y-axis, or if the Y-plane was If the SHG light 6 does not travel parallel to the axis, the end face from which the SHG light 6 is emitted may be formed as an oblique end face 9 with an angle of several degrees.

The planar waveguide 4 is formed by a single process such as an ion exchange method or a Ti thermal diffusion method, and the S emitted from the crystal end face is
If the intensity distribution of the HG light in the direction perpendicular to the waveguide is asymmetrical and the collimated light 8 exchanged by the cylindrical lens 7 differs in shape from the Gaussian circular beam, the planar waveguide 4
It is also possible to make the emitted light intensity distribution symmetrical by making it a buried structure. This is achieved by using a known technique of additionally diffusing atoms that lower the refractive index, such as magnesium, by thermal diffusion or the like after the above manufacturing process.

〔Effect of the invention〕

As described above, according to the present invention, a stable waveguide type wavelength conversion element in which the SHG output light has no wavefront aberration can be obtained.

The second feature of the present invention is that, unlike the conventional example described above, an X plate or a Y plate is used, and a Z plate is not used. As in the case of
There is no need to tilt it by 0 degrees, which is extremely convenient in terms of implementation.

[Brief explanation of the drawing]

The figure is a perspective view illustrating the structure of a waveguide type wavelength conversion element according to an embodiment of the present invention. 1...LiNbO3 crystal substrate, 2...side wall, 3...channel optical waveguide, 4...plane waveguide. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A channel optical waveguide provided with a side wall extending in a direction substantially perpendicular to the Z axis on an X-plate or Y-plate lithium niobate crystal plane, and formed on the lithium niobate crystal plane along the side wall, and the channel optical waveguide. A fundamental wave (frequency ω) is injected into the channel optical waveguide, and a second harmonic of the fundamental wave is obtained from the planar waveguide. A waveguide-type wavelength conversion element characterized in that it is provided with both the channel and planar optical waveguides.