JPH04116629A - Wavelength conversion element and production thereof - Google Patents

Abstract

PURPOSE:To obtain the second harmonic wave generating element having high conversion efficiency and the high reliability strong to a fluctuation in temp., etc., by forming this element in such a manner that the ordinary light refractive index at the frequency omegaof the incident light on a 2nd layer and a 3rd layer and the extraordinary light refractive index at frequency 2omega of the exit light satisfy a prescribed relation and satisfy the phase matching conditions for generating the second harmonic waves. CONSTITUTION:This element is made into the 3-layered structure laminated and formed with the waveguide phase consisting of a 2nd layer 3 consisting of an LiTayNb1-yO3 single crystal (O<=y<=1, and x<y) varying in the compsn. ratio and a 3rd layer 4 consisting of an LiTazNb1-zO3 single crystal (O<=z<=1, and z<y) on a 1st layer 2 consisting of an LiTaxNbrxO3 single crystal substrate (O<=x<=1) and is so formed that the 2nd layer 3 and the 3rd layer 4 satisfy the conditions of equation I when the ordinary light refractive index at the frequency omega of the incident light is designated as no<omega> and the extraordinary light refractive index at the frequency 2 omega of the exit light as ne<2omega>. The second harmonic wave generating element which allows easy produc tion, has the high conversion efficiency, is strong to a fluctuation in temp., etc., and has high reliability is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical wavelength conversion element used as a second harmonic generation element, a blue light emitting element, etc., and a method for manufacturing the same.

Conventional technology A second harmonic generation (SHG) element is a device that converts laser light with a wavelength of λ to a wavelength of λ/2 by using the nonlinear optical effect of an optical crystal material that has a nonlinear optical effect. This is an element that converts light into light. Therefore, the wavelength of the emitted light is 172 that of the incident light, and the recording density is 4.
Since it can be doubled, it is being applied to optical discs, CD players, laser printers, photolithography, etc.

In order to meet the demands for small size and direct modulation of such SHG elements, semiconductor lasers are becoming mainstream as input light sources. When such 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. L is generally used as an optical crystal material with a nonlinear optical effect that can form a high-quality optical waveguide.
iNbO3 is considered to be optimal. However, LiNb
In an O3 single crystal, at the semiconductor laser light source wavelength of 0.82 to 0.84 am, phase matching (phase matching refers to the incident
- It has been reported that the refractive index of the second harmonic light in the optical waveguide (meaning that the effective refractive index of the second harmonic light matches the effective refractive index of the second harmonic light) is impossible. In the case of LiNbO3, the ordinary refractive index n'' at the frequency ω of the incident light = 2.253, and the extraordinary refractive index n = 2.28 at the frequency 2ω of the incident light.
2, and the necessary condition for phase matching (n = n
) is not satisfied.

For this reason, for example, according to Japanese Unexamined Patent Application Publication No. 2-12135, using a laser beam with a wavelength of 0.82-0.84 (tm) as the fundamental light, LiTa0.
．． olIm LiNb0. There is a two-layer structure in which a waveguide layer is formed, and the SHG phase is matched by making the light incident at an angle of 0 to 35 degrees with respect to the crystal axis.

Also, the Institute of Electronics, Information and Communication Engineers Technical Research Report 9MW89-1
According to 44(7) Output characteristics of waveguide type SHG element using rLD light source, LiTa0. LiN on a single crystal substrate
b0. A three-layer structure is formed in which a thin film is formed, and an MgO-doped LiNb01 layer is further formed on the thin film, and the fundamental wavelength is 0.
A device in which 83 pm semiconductor laser light is converted to 5HGi is shown.

Problem to be Solved by the Invention According to the former publication method, LiNb0. By changing the thickness of the waveguide layer, the effective refractive index of the waveguide can be changed. When guiding light, a state exists in which the phase matching condition is satisfied by making the light incident at an angle that allows phase matching with respect to the Z axis (optical axis), and SHG is realized. However, it requires strict angular alignment accuracy and has the drawback of being vulnerable to changes in temperature, wavelength, etc.

On the other hand, in the case of the latter literature method, Mg○-doped LiN
The bO3 layer is a waveguide originally manufactured to satisfy phase matching conditions and has SHG characteristics. However, controlling the film thickness and its accuracy to satisfy the phase matching conditions is extremely difficult. Therefore, like the former case, it has the disadvantage of being vulnerable to changes in temperature, wavelength, etc.

Therefore, in the case of these conventional methods, the SHG conversion efficiency is greatly affected by various fluctuations, and in reality, the conversion efficiency is only a few percent, which is insufficient.

Means for Solving the Problems In an optical wavelength conversion element using an optical waveguide having a nonlinear optical effect, L 1TaxNb, -xO, single crystal substrate (
However, on the first layer with O≦x≦1), L I T a , N b +□○ with different composition ratios, single crystal (
2nd layer with 0≦y≦I and x<y) and L i T
A,Nbz-,0,single crystal (however, 0≦Z≦1 and z<y) has a three-layer structure in which a waveguide layer is laminated with a 73rd layer 2, and at the frequency ω of the incident light. When the ordinary light refractive index is n'' and the extraordinary light refractive index at the frequency 2ω of the emitted light is n2'', the second layer and the third layer are 0<(n'' - n'') (second layer )-(noω-n
2'') (third layer)≦o,01.

In this case, each of the first, second and third layers is doped with at least MgO, and the third layer is doped with Li, Be.
, Na, Ni, Ti, V, Nd.

Cr was doped with at least one of the elements Ca, Sr, Ce, and Ba.

As a manufacturing method of such an optical wavelength conversion element, at least a second layer and a third layer are formed on the first layer by a liquid phase growth method, and the third layer is formed by an ion implantation method, a sputtering method, or a diffusion method. The second layer and the third layer are doped with a desired element using a doping method such as a doping method or a laser ablation method so that the second layer and the third layer have a desired refractive index distribution relationship.

The composition ratio of the first layer made of Li'T'a, Nb-8○, and nail crystal matrix is varied, and the second layer made of iTa,\F)01 single crystal and LiT'a,\F , -703 In a three-layer structure in which a third layer is made of a single crystal and a waveguide layer is laminated, the ordinary refractive index of the second and third layers at the frequency ω of the incident light and the frequency 2ω of the output light are When the extraordinary light refractive index satisfies a predetermined relational expression, the phase matching condition for second harmonic generation is satisfied. Subtle control of the refractive index of the second and third layers so as to satisfy such conditions is easy using a doping method such as an ion implantation method as in the third aspect of the invention. Therefore, it is possible to realize a highly reliable second harmonic generation element that is easy to manufacture, has high conversion efficiency, and is resistant to fluctuations in temperature, etc., and can be used directly without the need for angle matching with a semiconductor laser with a wavelength of about 0.8 μm. It also becomes possible to generate second harmonics.

In particular, as claimed in claim 2, each layer is doped with MgO to reduce propagation loss, and the third layer is formed by doping with a predetermined element. It is easily realized that the refractive index distribution satisfies the phase matching condition for second harmonic generation.

Example An embodiment of the present invention will be described based on the drawings.

The optical wavelength conversion element 1 of this embodiment is basically as shown in FIG.
As shown in a), on the first layer 2 made of LITaXNbl-xO3 single crystal substrate (however, O≦x≦1), LiTa, Nb+-, O, single crystal with different composition ratios (however, 0≦y
≦1 and x<y) second layer 3 and L 1. T
a −N b + −! 03 single crystal (however, 0≦Z≦1
It has a three-layer structure in which a waveguide layer is laminated with a third layer 4 and a third layer 4 where z<y. When a fundamental wave of frequency ω is incident on such a thin film waveguide layer, the refractive index of ordinary light is n
'', when the refractive index of the extraordinary light with frequency 2ω produced by SHG is defined as rl 2'', in general, noω(n
2", the phase matching condition n"=nyO is not satisfied. Also, L i T a xN b L-XO,
In the case of delivery, even if the composition ratio X is changed, the above phase matching condition is not satisfied, and λ = 0.83
When using light such as a μm semiconductor laser, Si
-(G is not realizable.

Therefore, in this embodiment, the first to third layers 2 to 4 shown in FIG.
By changing the composition ratios X and 37°Z of n″ and n2″ of each layer,
In addition, by adding appropriate impurities (dopants), phase matching conditions can be satisfied over a wide range of temperature, wavelength, and film thickness.

First, in contrast to the first layer 2 of LiTaxNb+-xo, single crystal, the second layer 3 of LiTaxNb1-, ○, single crystal has its composition changed to LiTaO3 in order to lower the refractive index.
Move it in a direction that brings it closer to . For this purpose, the second layer 3 is formed under conditions such as X<y. Next, L i of the third layer 4
Ta, Nb,,0. Single crystals are made by introducing dopants that reverse the condition n"<02", and
〉n.

However, in order to satisfy stable phase matching conditions against changes in environmental temperature, semiconductor laser wavelength, waveguide layer thickness, etc., the second layer 3 and third layer 4 should be 0<(n2''-n''). (Second layer)"=(n"-n 2'
) (third layer)≦0. It is formed to satisfy the relational expression O1.

FIG. 2(a) shows a mode dispersion curve characteristic showing the state of phase matching when this condition is satisfied.

Incidentally, FIG. 6(b) shows the mode dispersion curve characteristics according to the conventional method. As can be seen from the figure, in the conventional method shown in Figure (b), the incident light TM" and 5) (G light TE
Which phase matching points intersect sharply, whereas according to FIG. It shows.

When looking at the entire three-layer structure, the refractive index distribution of each layer is the first
It is as shown in Figure (b). The second layer 3 is the first layer 2
By changing the composition ratio of Ta and Nb, niv,
The refractive index of n2" is made small. For the third layer 4, an element such that n" is larger than n, such as Na" is used.
, K”, Ca”, N i”T i”, Nd”,
Li+ or the like is doped as a dopant.

Methods for introducing these dopants include liquid phase epitaxial growth, sputtering, and recently, ion implantation to control n and n as desired. Furthermore, a laser ablation method may be used. Further, in order to alleviate propagation loss and the like, it is also necessary to dope MgO into each layer as a whole. In addition to the above-mentioned dopants, mainly alkaline dopants, for example, Be
, Ba, Ce, Sr, Cr, V, and other elements are promising.

Also, when looking at the third layer 4 as a waveguide layer, 00'', n2
It goes without saying that it is desirable that `` is larger than that of the second layer 3. Regarding the relationship between the crystal orientation and the mode of incident light, for X-cut and X-cut crystals, it is preferable that For C-axis cut), TE
Of course, the basic principle is incidence in mode.

By the way, practical SH based on such basic configuration'
The G element 1 may be configured as shown in FIG. 3, for example.

This has a ridge-type waveguide structure to improve light utilization efficiency. The basic structure or a specific manufacturing method of the SHG element as shown in FIG. 3 will be explained with reference to FIG. 4.

Specific example 1 First, as shown in FIG. 4(a), MgO-doped Li
Nb0. On the first layer 2 made of a single crystal substrate, LiTa, Nb1-yo, (where O≦y≦1
, here y=Q, 5) A single crystal thin film was epitaxially grown to form the second layer 3 to a thickness of 5 μm. moreover,
As the third layer 4, MgO-doped LiNb0. After growing the film to a thickness of 5 μm by liquid phase growth, as shown in FIG.
The dose amount was tl. At this time, the implantation was performed at two levels of energy, yOKeV and 60KeV, so that the ion implantation was uniform over the entire third layer 4 having a film thickness of 5 μm. As a result, the third layer 4 is formed as a doped layer.

Specific example 2 Mg0-doped L I T a XN b +-xo,
(However, OSX≦1, here x=0.1)
On the first layer 2 made of single crystal, a sputtering method is applied to form Ligo ayNb1-yo (with O≦y≦1,
In this case, a single crystal thin film with y=0.9) was formed to a thickness of 3 μm, and then annealing (600° C., 2 hours, in Ar inert gas) was performed to improve crystallinity. Thereafter, element ~' was deposited using an electron beam to form a film with a thickness of 100 nm, and the third layer 4 was formed by diffusion at 1000'C for 2 hours.

Concrete Example 3 In order to actually use the three-layer SHG element 1 formed in Concrete Example 1 (or Concrete Example 2) as a waveguide, the waveguide must be processed as shown in FIG. 4(c). administer. That is, a resist (○FPR) with a predetermined dimension, for example, W = 5 μm.
5 was formed on the third layer 4, and then etched by 2 μm using an ion beam etcher (Ar ions) to form a ridge-type waveguide as shown in FIG. The resist was removed by O and ashing for 30 minutes as shown in the same figure (d), and then annealing was performed (500°C for 130 minutes, O in O) to complete the S+-' G element l. Ta.

FIG. 3 shows an example of the structure of a blue light emitting device 7 formed by combining the S1-(G element f1 produced as shown in FIG. 2) with a semiconductor laser 6. 8 is a heatshisig.

According to such a specific example, the effective refractive index of the waveguide layer is S
λ = 0, which is the wavelength of the semiconductor that satisfies the HG condition.
．． Direct SHG is now possible for 83 μm, and a blue light-emitting element with a high efficiency of 10 to several tens of percent, which is unprecedented, has been realized.

Effects of the Invention As described above, the present invention provides L with different composition ratios for the first layer made of LiTa,...,Nb○, single crystal substrate.
In a three-layer structure in which a waveguide layer consisting of a second layer made of i Ta, N b +-, O Yu single crystal and a third layer made of LjTa, Nb, -, O, single crystal are laminated, the second layer and Third
The layer is formed so that the ordinary refractive index of the incident light at the frequency ω and the extraordinary refractive index of the output light at the frequency 2ω satisfy a predetermined relational expression and satisfy the phase matching condition for second harmonic generation. Therefore, as in the invention described in claim 3, it is possible to realize a highly reliable second harmonic generation element having a three-layer structure that is easy to manufacture, has high conversion efficiency, and is resistant to fluctuations in temperature, etc., and has a wavelength of 0°8.
It is also possible to directly generate second harmonics that do not require angle matching in a semiconductor laser of about μm, and in particular, according to the invention as claimed in claim 2, since each layer is doped with MgO, there is little propagation loss. In addition, since the third layer is doped with a predetermined element, the refractive index distribution in the thickness direction of the third layer satisfies the phase matching condition for second harmonic generation. This makes it possible to easily achieve delicate control.

FIG. 4 is a perspective view showing an example of the configuration of a color light emitting element, and FIG. 4 is a process diagram showing the manufacturing process.

Claims (1)

[Claims] 1. In an optical wavelength conversion element using an optical waveguide having a nonlinear optical effect, LiTa_xNb_1_-_xO_3
On a first layer made of a single crystal substrate (however, 0≦x≦1), a second layer made of LiTa_yNb_1_-_yO_3 single crystal (however, 0≦y≦1 and x<y) and LiTa_zNb_1_- with different composition ratios. ＿zO_3 single crystal (however, 0
≦z≦1) and a third layer with z<y), the optical refractive index at the frequency ω of the incident light is n_o^ω, and the frequency of the output light is 2ω. Let n_e^2^ω be the extraordinary refractive index at
An optical wavelength conversion element characterized in that it is formed to satisfy the following condition:_o^ω-n_e^2^ω)(third layer)≦0.01. 2. At least Mg in each of the first layer, second layer and third layer
In addition to doping with O, the third layer is doped with Li, Be, and Na.
, Ni, Ti, V, Nd, Cr, K, Ca, Sr, Ce
2. The optical wavelength conversion element according to claim 1, wherein the optical wavelength conversion element is doped with at least one of the following elements: , Ba. 3. Form at least a second layer and a third layer on the first layer by a liquid phase growth method, and dope the third layer by any of the ion implantation method, sputtering method, diffusion method, or laser ablation method. 1. A method for manufacturing an optical wavelength conversion element, characterized in that a desired element is doped into the second layer and the third layer to have a desired refractive index distribution relationship by a method.