JPH0212135A - Second harmonic wave generating element - Google Patents

Abstract

PURPOSE:To allow the generation of the second harmonic wave of semiconductor laser light by an LiNbO3 material by providing a waveguide layer consisting of LiNbO3 on a single crystal substrate layer consisting of LiTaO3. CONSTITUTION:The laser light having 0.82-0.84mum wavelength is determined as the light source wave of a basic wave. The LiNbO3 crystal waveguide layer 2 having 3.7-9.0mum film thickness is formed on the LiTaO3 single crystal substrate 1 and the incident angle of the laser light on the optical axis (Z axis) of the crystal is set at + or -0-+ or -35 deg.. The most preferable condition of the second harmonic wave generating element is the case in which the film thickness of the LiNbO3 crystal waveguide layer is 3.7-3.8mum and the incident angle of the laser light on the optical axis (Z axis) of the single crystal of the LiTaO3 is 0 deg.+ or -0.5 deg.. The generation of the second harmonic wave of the semiconductor laser light of 0.8mum band by the LiNbO3 is enabled in this way and the wide utilization of the element to optical disk memories and CD players, etc., is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a second harmonic generation (SHG) element used in optical disk memories, CD players, and the like.

(Prior Art) A second harmonic generation (SHG) element is an element that converts a laser beam of wavelength λ to a wavelength of 1/2λ by utilizing the nonlinear optical effect of an optical crystal material having a nonlinear optical effect. , the wavelength of the output light is halved, and the recording density can be quadrupled.
player, laser printer.

It is being applied to photolithography, etc.

Conventionally, a bulk single crystal of a nonlinear optical crystal has been used in an SHG element using a high-power laser as a light source.

However, in recent years, there has been a strong demand for miniaturization of entire devices such as optical disk devices and laser printers, and while gas lasers require an external transformer for optical modulation, semiconductor lasers can be directly modulated. For these reasons, and because semiconductor lasers are cheaper and easier to handle than gas lasers, semiconductor lasers have come to be mainly used as a light source instead of gas lasers.

When a semiconductor laser is used as a light source, an SHG element having a thin film waveguide structure is used because it is necessary to obtain high conversion efficiency with input light of several mW to several tens of mW. In other words, the generation of second harmonic light using a thin film waveguide has the following advantages: (1) it is possible to utilize the energy of light concentrated in the thin film, and (2) the light waves are confined within the thin film and do not spread, allowing interaction to occur over long distances. This is because it has the advantage of being able to achieve phase matching even in materials that cannot be phase matched in the bulk by utilizing mode dispersion in thin films (Miyama, Miyazaki;
Institute of Electronics and Communication Engineers Technical Research Report, 0QE75-6 (197
5), Miyazaki, Hoshino, Akao; Electromagnetic Field Theory Study Group Materials, EM
T-78-5 (1978)).

By the way, optical crystal materials with nonlinear optical effects include lithium niobate (LiNbOa), lithium tantalate (LiTaO,), KTiOPO4, KNbO,
, Ha, NaNb, 0. s, Ba, LiNb, 0.
However, in order to obtain a thin film waveguide structure as described above, it is necessary to form an optical waveguide. and,
LiNbO is a material that can form a high-quality optical waveguide.
3 is the most suitable.

However, using conventional LiNbO3 material, Ti diffusion,
When an optical waveguide is formed using methods such as proton exchange and external diffusion, the wavelength of the semiconductor laser light source (λ = 0.82 to 0.84 μ
(Yamada, Miyazaki; Institute of Electronics, Information and Communication Engineers Technical Research Report, MW87-113 (1988))
.

In other words, phase matching is to match the refractive index (effective refractive index) of the incident laser light in the waveguide with the effective refractive index of the second harmonic light, but the refractive index of a material generally varies depending on the wavelength. Therefore, by changing the wavelength of the incident laser light, the phase matching condition also changes, and LiNbO3
In the case of materials, phase matching becomes impossible at a semiconductor laser light source wavelength of 0.82 to 0.84 μm.

(Problems to be Solved) As a result of various studies using LiNbO3 material and a semiconductor laser light source to achieve phase matching between the fundamental wave light and the second harmonic light, the inventor found that LiTa0□ as a substrate.
was used to form a LiNbO3 thin film thereon.

It was discovered that phase matching was possible by providing a waveguide in this material, and the present invention was completed.The purpose of the present invention is to make it possible to generate the second harmonic of semiconductor laser light using LiNbO3 material. The goal is to provide a unique element.

(Means for Solving the Problem) The present invention uses a laser beam having a wavelength of 0.82 to 0.84 μm as a fundamental wave light source wavelength, and a LiNbO3 film with a thickness of 3.7 to 9.0 μm on a LiTaO3 single crystal substrate. This is a second harmonic generation element characterized in that a crystal waveguide layer is formed and the incident angle of laser light with respect to the optical axis (Z axis) of the crystal is set to ±35°.

That is, the layered structure of the second harmonic generation element of the present invention is shown in FIG. 1, in which a waveguide layer 2 made of LiNbO3 is provided on a single crystal substrate layer 1 made of LiTaO3, and A three-layer dielectric waveguide is constructed with an air upper layer 3 on the upper surface of the layer 2, and the refractive index of each layer is as shown in Table 1.

Table 1: Fundamental wave wavelength: 0.83 μm In the table, no and ne are the refractive indexes for ordinary rays and extraordinary rays, respectively. Further, V indicates a fundamental wave, and 2v indicates a second harmonic.

Note that the actual refractive index of the waveguide layer and the substrate layer varies somewhat depending on the method of creating the waveguide, so the values shown here are representative examples and are not absolute.

When the phase matching conditions for second harmonic generation were calculated using the refractive index values in Table 1, the range of the phase matching angle (the angle of incidence of the laser beam with respect to the optical axis of the crystal) was θ to 35°,
The thickness of the waveguide layer at that time is 3.7 to 9 μm.

The most preferable condition for the second harmonic generation element of the present invention is that the thickness of the LiNbO3 crystal waveguide layer is 3.7~
3.8 μm, optical axis (Z axis) of LiTaO3 single crystal
This is a case where the incident angle of the laser beam with respect to the laser beam is 0°±0.5°. In this case, the refractive index of each layer is preferably the value shown in Table 1.

In this case, the incident angle of the laser beam with respect to the optical axis (Z-axis) direction of the crystal of the single crystal substrate layer is approximately 0° (propagation in the optical axis direction).
Therefore, it has the advantage of widening the tolerance range of the incident angle.

Next, as a method for manufacturing the second harmonic generation element according to the present invention, a waveguide layer can be easily formed on a substrate layer by using a known thin film forming technique such as sputtering. Then, a method such as forming a Ti waveguide pattern on the waveguide layer by photolithography and RF sputtering and performing ion beam etching using this pattern as an etching mask can be used.

(Example) Hereinafter, a method for manufacturing a second harmonic generating element according to the present invention will be explained in detail with reference to FIGS. 2 and 3.

[Example 1] An X-cut LiTaO3 single crystal wafer with a thickness of 0.5 mm was cut with a wire cutter to obtain a substrate 1 with a size of 5 mm x 5 mm. At this time, the cutting direction was set along the Y axis and two axes of the single crystal. Approximately 4 μm thick sputtering was performed on this LiTaO3 substrate by RF (radio frequency) sputtering
A LiNbO3 single crystal thin film 2 having a thickness of . Furthermore,
Ion beam etching was performed to etch the LiNbO3 thin film to form a waveguide layer with a thickness of 3.7 μm.

In this way, LiTaO3 single crystal thin plate 1 and LiNb
A slab-type waveguide consisting of a 0° single crystal thin film 2 was formed.

When a semiconductor laser beam with a wavelength of 0.83 μm was made incident on this slab type waveguide, a second harmonic with a wavelength of 0.415 μm was generated. The conversion efficiency of the second harmonic generation at this time is 2 for a semiconductor laser light incident power of 20 mV.
It was X 10-'.

[Example 2] An X-cut LiTaO3 single crystal wafer with a thickness of 0.5+*+a was cut with a wire cutter to 5 mm x 5 m.
It was set as the substrate 1 of ta. At this time, the cutting direction was set along the Y axis and two axes of the single crystal. This LiTaO
A LiNbO3 single crystal thin film 2 having a thickness of approximately 4 μm was formed on the 3 substrates by RF (radio frequency) sputtering.

A pattern 3 made of a Ti thin film of approximately 4 μm and a width of 5 μm is formed on this LiNb0° single crystal thin film 2 by ordinary photolithography and RF (radio frequency) sputtering.
was formed. Ion beam etching is performed using this Ti pattern 3 as an etching mask, and LiNbO3
A channel type waveguide layer 4 with a width of 5 μm is formed by etching a thin film.
was formed.

Finally, the remaining Ti mask was removed to form a channel waveguide consisting of the LiTaO3 single crystal thin plate 1 and the LiNbO3 single crystal thin film 4.

When a semiconductor laser beam with a wavelength of 0.83 μm was incident on this channel type waveguide, the wavelength was 0.415 μm.
The second harmonic of m was generated. The conversion efficiency of the second harmonic generation at this time is the semiconductor laser light input power of 20+5w1C.
On the other hand, there was 4 x 10-'1'.

(Effect) As mentioned above, t, 1 on a LiTaO3 single crystal substrate
By providing a waveguide layer made of Nbo thin film, it is possible to generate the second harmonic of 0.8 μm band semiconductor laser light using LiNbO3 material, which was previously impossible, and it can be widely used in optical disk memories, CD players, etc. I can do it.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the waveguide structure of the second harmonic generation element according to the present invention, and FIGS. 2 and 3 are illustrations of the manufacturing process of the second harmonic generation element according to the present invention. It is a diagram. I LiTaO3 substrate 2 LJbOa thin film 3 Ti thin film 4 LxNbO, waveguide layer

Claims (1)

[Claims] 1. Laser light with a wavelength of 0.82 to 0.84 μm is used as the fundamental wave light source wavelength, and a film thickness of 3 μm is deposited on a LiTaO_3 single crystal substrate.
．． A second harmonic characterized in that a LiNbO_3 crystal waveguide layer with a thickness of 7 to 9.0 μm is formed, and the incident angle of the laser beam with respect to the optical axis (Z axis) of the crystal is set to ±0° to ±35°. Wave generating element. 2 LiNbO_3 crystal waveguide layer thickness 3.7-3.8μ
2. The second harmonic generating element according to claim 1, wherein the second harmonic generating element is m. 3. The second harmonic generating element according to claim 1, wherein the incident angle of the laser beam with respect to the optical axis (Z axis) of the LiTaO_3 single crystal is 0°±0.5°. 4 The refractive index of the LiNbO_3 waveguide layer and the LiTaO_3 single crystal substrate layer is as shown in Table 1, and the LiNbO_3
The thickness of the O_3 waveguide layer is 3.7 to 3.8 μm, LiTaO
_3 The second harmonic generating element according to claim 1, wherein the incident angle of the laser beam with respect to the optical axis (Z-axis) of the single crystal is 0°±0.5°.