JPH05210023A - Optical waveguide - Google Patents

Abstract

PURPOSE:To obtain the optical waveguide which can partially vary the refractive index of the optical waveguide layer of a sapphire-based substrate by adding Ga to part of the surface of the sapphire-based substrate and increasing the refractive index of the added part. CONSTITUTION:The optical waveguide has its optical waveguide layer formed of sapphire or sapphire containing an extremely small amount of added element and Ga is added to part of the surface of the sapphire-based substrate 4 to increase the refractive index of the added part. Namely, when this optical waveguide is applied to a waveguide type Ti:Al2O3 laser, a Ti:Al2O3 substrate 4 becomes a laser medium and a waveguide layer consisting of a Ga-added part 5 is provided at a nearly center part on the top surface of the substrate 4. Thus, Ga is added to the substrate 4 to increase the refractive index, and a three-dimensional optical waveguide can be constituted. High-reflectivity films 6 and 7 are adhered to both end surfaces to form a laser resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more particularly to improvement of a sapphire optical waveguide.

[0002]

2. Description of the Related Art An optical waveguide has a function of confining and propagating a light wave in a desired path, and is important as a constituent element of an optical resonator constituting a laser oscillator.

FIG. 5 is a structural diagram of a basic optical waveguide.
A waveguide layer 2 having a refractive index n _f is formed on the surface of a substrate 1 having a refractive index n _s, and a refractive index n _c is formed on the surface of the waveguide layer 2.
Is formed on the upper clad layer 3.

[0004] In this structure, the refractive index _{n f} of the waveguide layer 2 larger than the refractive index _{n c} of the refractive index _{n s} and the upper cladding layer 3 of the substrate 1 _{(n f>} n _{s, n} c) As a result, the light wave can be confined inside the waveguide layer 2.

FIG. 6 is an example of the refractive index characteristic of the structure of FIG. 5, where (a) is a step type and (b) is a graded type. As a typical example, the LiNbO ₃ waveguide realizes a waveguide structure by increasing the refractive index by diffusing Ti (titanium) in the portion to be the waveguide layer 2 or converting protons (H ⁺ ). .

[0006]

However, a method for forming a sapphire (Al ₂ O ₃ ) optical waveguide applicable to a variable wavelength laser, an ultrashort pulse laser, etc. has not been established.

It is considered that this is because no method has been found for easily changing the refractive index like LiNbO ₃ . The present invention has been made in view of such problems, and an object thereof is to provide an optical waveguide capable of partially changing the refractive index of a sapphire-based optical waveguide layer.

[0008]

SUMMARY OF THE INVENTION The present invention which solves such a problem is an optical waveguide in which an optical waveguide layer is formed of sapphire or sapphire containing a small amount of an additive element. It is characterized in that Ga is added to increase the refractive index of the added portion.

[0009]

The refractive index of the portion to which Ga is added is larger than that of the other portion of the substrate, and the optical waveguide layer is formed.

As a result, when a light wave is made incident from the end face of the Ga-added portion, the light wave propagates in the guided mode without spreading in the waveguide and is confined inside the waveguide layer.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.
I will explain in detail. Figure 1 shows Al_TwoO_ThreeGa_TwoO_ThreeAdded
Ga when_TwoO_ThreeIt is a characteristic view of concentration and refractive index change.
This property is due to Ga on an undoped sapphire substrate._TwoO_Three+ A
l_TwoO _ThreeTo form a mixture layer of_TwoAdd with laser
Sapphire substrate and recrystallization part of hot melt recrystallized sample
Relative refractive index difference and Ga of recrystallized part_TwoO_ThreeAnalyze concentration
It was obtained by doing. As is clear from the characteristics of Figure 1.
In addition, increasing the refractive index by adding Ga to sapphire
This substance (hereinafter referred to as Ga: Al_Two
O_ThreeIs transparent at least in the visible wavelength range.
Therefore, a good waveguide layer material can be obtained.

In addition, FIG. 2 shows Al_TwoO_ThreeGa_TwoO_ThreeWith
It is a state diagram when it is added. From the characteristic diagram of FIG. 1, for example,
To make the relative refractive index difference Δn 0.3%, Ga _TwoO
_ThreeOf 8 wt% (4.5 mol% in terms of mol) is added
It can be estimated that it can be obtained by And the state of FIG.
From the figure, αAl_TwoO_ThreeCan take the crystal form of (sapphire)
Ga_TwoO_ThreeThe addition limit amount of is 30 mol%.

FIG. 3 is a block diagram of an embodiment according to the present invention, which is applied to a waveguide type Ti: Al ₂ O ₃ laser. In the figure, 4 is a Ti: Al ₂ O ₃ substrate,
It becomes a laser medium. Reference numeral 5 denotes a waveguiding layer formed of a Ga-added portion, which is provided on the upper surface of the substrate 4 substantially in the center thereof.
By adding Ga5 to the substrate 4, the refractive index can be increased and a three-dimensional optical waveguide can be constructed. Reference numerals 6 and 7 are high-reflectance films, which are attached to both end faces to form a laser resonator.

In the structure of FIG. 3, when pumping light having a wavelength of about 500 nm is made incident from the end face of the Ga-doped portion 5, the pumping light propagates in the guided mode without spreading in the waveguide, so that the high optical power density in a long section. And a low laser oscillation threshold can be obtained. The oscillated light also oscillates as a guided mode in the Ga-doped optical waveguide.

FIG. 4 is a process diagram of Ga addition. (A) is the first step, for example, Ti: Al is formed by sputtering.
A mixture layer 8 of Ga ₂ O ₃ + Al ₂ O ₃ is formed on the surface of the ₂ O ₃ substrate 4.

(B) is a second step in which Ga5 is diffused into the substrate 4 to a desired depth by, for example, thermal diffusion.
Instead of thermal diffusion, the surface portion may be heated, melted and recrystallized by laser irradiation or the like.

Here, the mixture layer 8 is formed as shown in (a), for example.
By patterning the
The three-dimensional optical waveguide can be constructed. In the above-mentioned embodiment,
Ti: Al_TwoO_ThreeThe example of the laser is explained, but Cr: Al
_TwoO_ThreeThe same can be applied to a (ruby) laser.

[0018]

As described in detail above, according to the present invention, the following effects can be obtained. Since Ga can be relatively easily added to Al ₂ O ₃ ,
It becomes easy to form an Al ₂ O ₃ waveguide, which has been difficult until now.

The amount of Ga added and Ga ₂ O ₃ + Al ₂ O ₃
By controlling the patterning shape of the mixture layer of
The desired optical waveguide can be formed relatively freely.

[Brief description of drawings]

FIG. 1 shows the Ga when Ga ₂ O ₃ is added to Al ₂ O ₃ .
Characteristic diagram of ₂ O ₃ concentration and refractive index change

FIG. 2 is a state diagram when Ga ₂ O ₃ is added to Al ₂ O ₃ .

FIG. 3 is a block diagram of an embodiment according to the present invention.

FIG. 4 is a process diagram of Ga addition.

[Figure 5] Basic optical waveguide structure diagram

6 is a diagram showing an example of a refractive index characteristic of the structure shown in FIG.

[Explanation of symbols]

4 Ti: Al ₂ O ₃ Substrate 5 Ga Addition Part 6, 7 High Reflectivity Film 8 Mixture Layer (Ga ₂ O ₃ + Al ₂ O ₃ )

Claims (1)

[Claims] 1. In an optical waveguide in which an optical waveguide layer is formed of sapphire or sapphire containing a trace amount of an additive element, Ga is added to a part of the surface of a sapphire substrate to increase the refractive index of the added part. An optical waveguide characterized by the above.