JPS5810721B2 - Manufacturing method of thin film optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a thin film optical element mainly used for optical communications.

With the recent commercialization of optical communications, thin-film optical devices are being developed as functional units that can branch or filter optical communication beams for the same purposes as branch circuits and filter circuits in electrical circuits. has been developed, and has the advantage of having a planar configuration, smaller size, and lighter weight than conventional three-dimensional optical systems, and is gradually becoming more widely used.

FIG. 1 is a process diagram showing a conventional method for manufacturing such a thin film optical device, in which a glass substrate and air are used as cladding layers, and an optical waveguide layer as a core is formed on the glass substrate.

First, as shown in Figure A, a transparent optical waveguide layer 2 is formed on a transparent planar glass substrate 1 as a first cladding layer by means such as high frequency sputtering or vapor deposition, and then,
As shown in Figure B, a mask 3 is formed into a predetermined shape using a material that is resistant to etching, and then etched, unnecessary portions of the optical waveguide layer 2 are removed as shown in Figure C, and further, using a solvent or the like, etching is performed. When the mask 3 is removed, the optical waveguide layer 2 having a predetermined shape is covered with the glass substrate 1 as shown in the figure.
The refractive index of the glass substrate 1 as the first cladding layer at the wavelength of the light beam formed on the optical waveguide layer 2 and propagating in the optical waveguide layer 2 is n.
If the refractive index of the optical waveguide layer 2 is n2, and the refractive index of the air acting as the second cladding layer is n3, and the relationship n2>nl>n3 is maintained, the inside of the optical waveguide layer 2 can be operated on the same principle as glass fiber. The light ray propagates due to

However, as shown in the first diagram, the side surface 4 of the optical waveguide layer 2 becomes a non-smooth surface during etching, causing diffuse reflection of the light rays that should propagate there, which causes an increase in the propagation loss of the light ray. This requires advanced manufacturing technology, requires a large number of complex equipment and skilled workers, and has the drawback of high manufacturing costs.

Also, ``Method for manufacturing dielectric micro-optical circuits''
79655), there is a method in which an optical element is formed by using a material whose refractive index decreases when irradiated with light as a waveguide film and then irradiating light onto a desired part of the film. This can be applied to electro-optic crystals such as LiNbO3 and lithium oxate by visible light (wavelength 4
This method takes advantage of the fact that when irradiated with a large argon gas laser beam, etc., a photodamaged area is generated and the refractive index of this area decreases.
n is only 10-4 at most, and with this degree of refractive index change, the light confinement effect is weak, and even though it is possible to fabricate a straight waveguide, it is difficult to fabricate a curved waveguide. This results in disadvantages that make it impossible.

Furthermore, "Optical thin film element" (Japanese Patent Application Laid-Open No. 50-159626)
(No.), when the absorption edge of chalcogenide glass containing P (phosphorus) and Ge (germanium) is irradiated with short wavelength light, the refractive index of the irradiated part changes due to structural changes of the chalcogenide glass. However, in this case, chalcogenide glass is susceptible to alkali, which causes problems in terms of durability and weather resistance, and the manufacturing conditions have not yet been fully elucidated, making it difficult to create practical optical devices. However, there are disadvantages such as making it unsuitable for manufacturing.

The purpose of the present invention is to fundamentally solve the above-mentioned drawbacks of the conventional art, and to create a waveguide film having a film thickness equal to or greater than the cutoff thickness for the waveguide light using a substance that transmits the waveguide light onto a glass substrate and absorbs heat rays. is formed, and a predetermined portion of this waveguide film is heated with a hot wire to lower the refractive index of the predetermined portion by a desired amount,
The present invention provides a method for manufacturing a thin film optical device that can extremely easily manufacture a thin film optical device with high precision by forming an optical device in a waveguide film using this refractive index lowered portion.

Hereinafter, the present invention will be explained in detail with reference to FIG. 2 and subsequent figures showing embodiments.

FIG. 2 is a schematic diagram of the manufacturing method.
i02 (silicon dioxide), Ta203 (tantalum pentoxide), Ge02 (germanium dioxide), P2O5 (5
phosphorus oxide), B203 (boron oxide), Nb205 (niobium oxide), n203 (indium oxide), A12
A thin waveguide film 11 is formed by high frequency sputtering or vapor deposition using oxide glass whose main component is 03 (aluminum oxide), etc., and a laser beam 13 is emitted as a heat ray to a predetermined portion 12 of this waveguide film 11. When projected, the energy of the laser beam 13 is absorbed by the waveguide film 11 and the predetermined region 12 is heated.

That is, a laser oscillator 14 such as a carbon dioxide laser oscillator
After bending the laser beam 15 from the mirror 16, a lens 17 made of germanium, salt, zincated selenium, etc., which is transparent to the laser beam 15 and has excellent heat resistance,
The laser beam 15 is focused into a laser beam 13 and then projected onto the waveguide film 11, and the glass substrate 1 including the waveguide film 11 is moved in the X direction or the X direction shown by the arrow by a general feeding mechanism. By rotating or rotating in the θ direction, the projection area of the laser beam 13 onto the waveguide film 11 is moved, and the predetermined area 12 is heated into an arbitrary shape by the energy of the laser beam 13.

Note that the shutter 18 rotates freely in and out of the optical path of the laser beam 15, and is used to block the laser beam 15 when stopping the projection of the laser beam 13.

In addition, the glass substrate 1 is fixed, and the laser oscillator 14 is
The optical system of the lens 17 may be moved, and the same result can be obtained if the laser beam 13 and the waveguide film 11 are moved relative to each other.

As described above, when the waveguide film 11 is heated, the refractive index of the guided light in the oxide glass decreases depending on the amount of heating, and reflection or refraction of the guided light occurs at the portion where the refractive index decreases. An optical element is formed within the waveguide film 11 .

FIG. 3 is a diagram showing how the refractive index decreases due to the laser beam 13. As shown in FIG. 3A, the distance r from the center C of the laser beam 13 is , ω is the beam radius,)
If a Gaussian beam with a Gaussian distribution defined by is used, Y-
The refractive index n of the Y-direction cross section decreases as shown in FIG.

In the example shown in FIG. 3, a laser beam with a beam radius of about 450 μm, a total beam power of 221 W, and a wavelength of 10.6 μm is used, and a 5i02-Ta20 series with a refractive index of 1.987 is applied onto a glass substrate 1 made of Vycor glass. This is a case in which the waveguide film 11 is formed to have a thickness of 0.8 μm and is used, and the waveguide film 11 is moved in the X direction in FIG. 2 at a speed of 150 μm/SeC.

As is clear from FIG.
A reduction in the refractive index is observed, and the critical power density in the laser beam 13 for producing the necessary reduction in the refractive index is approximately 250 W/cm 2 .

In the experiment of the example shown in FIG. 3, no deformation or damage of the waveguide film 11 occurred at the predetermined region 12 onto which the laser beam 13 was projected and its surroundings.

In addition, the means shown in FIG. 4 can also be used to heat the predetermined region 12 and lower the refractive index by a desired amount.

That is, the region 21 onto which the laser beam 15 is projected, excluding the predetermined region 12, onto the waveguide film 11 is made of a metal containing any one of iron, cobalt, nickel, copper, chromium, aluminum titanium, gold, silver, platinum, etc. If the laser beam 15 is projected onto these areas 12 and 21 after being covered with a mask 22 such as a vapor-deposited film, the laser beam 15 will be reflected by the mask 22, so the waveguide film 11 directly below will not be heated, and the predetermined area will be 12
Only the area is heated, and an optical element is formed in this area.

It should be noted that while the reflectance of the metal vapor deposited film is 85% or more for carbon dioxide laser light, the waveguide film 11 made of the above-mentioned material is a good absorber of infrared rays, and therefore cannot completely achieve the purpose. I can do it.

Further, the waveguide film 11 is required to be transparent to the guided light, and for wavelengths of 0.4 μm to 1.6 μm, the above-mentioned SiO2, Ta205. GeO2, P2O5゜Al
Oxide glasses containing any of 2O3, B2O3, Nb2O6, In2O3, etc. are transparent, and when annealed in air at a temperature of 400°C or higher, the refractive index decreases.
The amount of the decrease is set at the melting temperature of the waveguide film 11 as an upper limit, and decreases as the heating temperature increases.

That is, as a specific example, 5i02. In the case of a waveguide film 11 with a film thickness of 1 μm using Ta205 and Corning product number #7059 glass, 5i02 is 2×10−3 and Ta205 is 4×10−2 by heating at about 800°C.
, #7059 obtained a refractive index reduction of 3X10-2 or more, and Ge02tP205. A120a, B203tNb2
05. In the case of the waveguide film 11 containing In2O3 etc., a reduction in refractive index of 10-3 to 10-2 can be obtained by heat annealing, and these materials can be used for infrared rays with a wavelength of 3 μm or more, and infrared rays with a wavelength of 10.6 μm.
It is extremely suitable because it absorbs heat rays such as carbon dioxide laser light with a wavelength of 2,000 A or less and excimer laser light with a wavelength of 2000 A or less.

Note that if the thickness W of the waveguide film 11 is equal to or greater than the cutoff thickness for the wavelength λ of the guided light, the guided light will propagate favorably, and this film thickness W is given by the following equation.

However, nl is the refractive index at wavelength λ of the glass substrate 1 which acts as the first cladding layer, B2 is the similar refractive index of the waveguide film 11, and B3 is present on the upper surface of the waveguide film 11 and acts as the second cladding layer. The waveguide film 11 has a similar refractive index to that of air, and in some cases, resin, glass, or the like is used as a second cladding layer by depositing it on the waveguide film 11.

FIG. 5 is a perspective view of an example in which the optical path deflector is formed as an optical element based on the present invention. After linearly heating a predetermined portion 12a with the laser beam 13, the shutter of FIG. 18 is temporarily closed, and the direction is further changed by an angle θ1 to linearly heat the predetermined region 12b.
As a result, the optical path of the guided light 32 is reflected by the predetermined portions 12a and 12b where the refractive index is lowered, and is deflected by an angle of 2θ1.

That is, when the amount of decrease in the refractive index is Δn, cos θ
〉(B2-Δn)/n2, (0〈θ〈π/2)
When the guided light 32 is incident at an incident angle θ that satisfies
2θ1-2θ+2θ=2θ with respect to the original incident path.
Deflect the optical path by 1.

However, the angle θ1 is cos(θ1-θ)>(n2-Δn
)/n2, (where 0<θ<π/2) must be satisfied, and the range thereof is shown by the following equation.

Note that any number of predetermined portions 12a and 12b may be selected depending on the deflection angle and direction (and at the same time, if the total power density of the laser beam 13 that projects the amount of decrease Δn in the refractive index is controlled, any value may be selected). is obtained.

In addition, the mask 22 shown in FIG.
The same effect can be obtained even if the shape is set as b and the laser beam 15 is projected.

FIG. 6 shows an example in which an optical splitter is formed as an optical element, in which a predetermined triangular region 41 is entirely heated by the means shown in FIG. When the amount of decrease is Δn, the angle θ2 of the same portion 420 is set to a value that satisfies the following equation.

Then, the guided light 3 that has entered the same part 42 from the direction of the line 43 that bisects the part 420 angle into which the guided light 32 is incident.
2 is totally reflected by both sides of the same portion 42, branched, and deflected in a direction at an angle 2θ2 with respect to the incident path, and branched into two directions.

FIG. 7A shows an example in which a thin film convex lens is formed in the same manner as described above, and one side 52 of a predetermined portion 51 is an arc centered on the 0 point, and since the refractive index of this portion is lower, parallel According to Snell's law, the angle α of the guided light 32 at 32b with the line connecting the 0 point in the circular arc and the angle β of the emitted light 53 a 53 b with the line connecting the circular arc and the 0 point holds the relationship α>β. and guided light 32a>32b
is focused at focal point F.

In addition, if one side 53 of the predetermined portion 51 is made to protrude in an arc shape as shown in FIG. If it is incident, it can be used as a thin film prism.

FIG. 8 shows an example in which a linear three-dimensional waveguide is formed, and as shown in FIG.
By the main laser beam 13at13b, or by the laser beam 13at13b,
A predetermined portion 61at is alternately
61b was linearly heated to obtain the result shown in FIG. 6B, which shows the refractive index n of the cross section in the XX direction in FIG.

The guided light 32 that has entered between the 6ib and the predetermined portion 61a.

Due to the decrease in the refractive index of 61b, total reflection is repeated between them,
It propagates within the waveguide 62 between the predetermined portions 61a and 6Ib.

However, the same effect can be obtained even if a linear mask 22 is used and heated by the laser beam 15 as shown in FIG.

In addition, in order to form a curved three-dimensional waveguide, FIG.
The predetermined portions 61a and 61b shown in FIG. 9 may be made into parallel curves, and the distance l between the two may be maintained constant during heating.

Note that a predetermined portion 61a with respect to the propagation direction of the guided light 32,
The amount of decrease in the refractive index of the waveguide 61b is extremely uniform and there is little change in the amount of reflection, so when compared to the conventional manufacturing method shown in FIG. A waveguide with propagation loss is obtained.

FIG. 10 is an example of forming a three-dimensional optical branching device by combining FIG. 6 and FIG.
As explained in the figure.

FIG. 11 shows an example in which a three-dimensional intersecting groove waveguide is formed by the means shown in FIG. 2, in which waveguides 62a and 62b similar to the waveguide 62 in FIG. Whereas the upper conductive pattern cannot be directly crossed, the guided light 32a.

The crossing of waveguide 62a>62b with respect to waveguide 32b does not cause interference between guided light beams 32a and 32b, and can be easily realized by the means shown in FIG.

That is, if we pay attention to the predetermined portion 61c within the intersection 71, the propagation loss for the guided light 32a is due to Fresnel reflection because the incident angle of the guided light 32a to the predetermined portion 61c is almost perpendicular, and is expressed by the following equation. .

However, the value is small, less than 10-4, and can be ignored.

Therefore, the loss to the guided light 32a at the predetermined portion 61d within the intersection portion 71 and the similar predetermined portion 61a,
The loss of the waveguide light 61b to the waveguide light 32b is also the same, and each waveguide light 32a, 32b suffers almost no loss and is independently connected to the waveguide 62a.

62b.

It should be noted that it is extremely difficult to manufacture such a cross-shaped groove wave path using the conventional method shown in FIG. 1, and it is only through the present invention that a cross-shaped groove wave path can be easily realized.

FIG. 12 shows the shapes of the masks 22a and 22b when forming the masks 22a and 22b shown in FIG. 11 by the method shown in FIG. A rectangular mask 22b is formed between the ends 81, facing each other and spaced apart from each other by a distance d.

Note that the interval d is the predetermined portion 61a, 61 in FIG.
b or the outer edge spacing of 61c and 61d.

FIG. 13 shows a perspective view of an example of forming a TEo mode filter. Since the propagation mode of the guided light 32 is different between TEo and TMo, the film thickness W that can be transmitted through the waveguide film 11 and the refractive index are different. A waveguide film 11 having a film thickness W shown in is formed.

Next, a predetermined region 71 defined in a direction perpendicular to the optical path of the guided light 32 is heated by the laser beam 13,
The refractive index of the predetermined portion 71 is decreased, and the amount of decrease Δn is set to a value that satisfies the following equation.

Then, the entrance prism 7 provided in close contact with the waveguide film 11
The light ray 73 incident on 2 becomes the waveguide light 32, and the light ray 73 enters the predetermined portion 7.
1, the TMo mode component is scattered out of the waveguide film 11 as a radiation mode, and only the TEo mode component passes through a predetermined portion 71 to become filtered waveguide light 74, which enters the incident prism 7.
The light is emitted as emitted light 76 through an emitting prism 75 similar to No. 2.

Note that a short wavelength optical filter is also formed in the same way, and in this case, the film thickness W1 of the waveguide film 11 and the refractive index determine the wavelength λ of the guided light 32 that can be transmitted, so first, the film thickness W1 shown in the following equation is determined. A waveguide film 11 is formed.

Then, the waveguide light 32 with a wavelength shorter than the wavelength λ1 passes through the waveguide film 11.
However, guided light 32 with longer wavelengths than the right wavelength cannot propagate, and a short wavelength optical filter is formed with wavelength λ1 as the cutoff wavelength.

7 However, the amount of decrease in the refractive index of the waveguide film 11 is Δn,
At the same time, if (n2-Δn)>nl, guided light 32 with a wavelength shorter than wavelength λ2 given by the following equation can be propagated.

Note that λ2 has a relationship of λ1>λ2.

Therefore, in FIG. 13, while making the light ray 73 of the mode or wavelength to be blocked enter the entrance pre-prism 72 and observing the exit light 76 from the exit prism 75, heating and cooling of the predetermined region 71 are repeated. When the heating temperature is gradually increased (and the refractive index reduction amount Δn reaches the condition of formula (7) or (8)), the emitted light 76 disappears, indicating that the desired filter has been formed. , a very accurate filter is obtained.

It goes without saying that the method shown in FIG. 4 also has the same effect.

In addition, in other optical devices, visible light is actually transmitted through the waveguide film 1.
1 while propagating into the predetermined portions 12° 12a, 12b.
, 41, 51, 61a to 61d, etc. are similarly heated,
Since it is easily indicated by the change in the path of visible light that the desired amount of refractive index reduction has been achieved, various optical elements can be reliably formed.

In addition, it goes without saying that various other optical devices can be manufactured by the present invention, and if the method shown in FIG. 2 or 4 is applied depending on the shape, accurate optical devices can be manufactured at low cost. can.

Further, as the heating wire, a carbon dioxide gas laser beam is suitable for absorbing energy in the waveguide film 11, but it is sufficient as long as it can heat only the intended part of the waveguide film 11, and various types can be applied as described above. The same is true for waveguide film 1
Various hot wires may be used depending on the characteristics of the material.

As is clear from the above description, according to the present invention, optical devices can be manufactured much more simply and easily than conventional etching methods, and special conditions such as gas atmosphere and vacuum are not required. Since the formation of the optical device can be performed under a normal working environment while actually observing changes in the propagation state of the guided light, the required optical device can be obtained with extreme accuracy.

In addition, the amount of decrease in the refractive index of the waveguide film due to heating is as large as about 10-2, making it possible to form a waveguide with a sufficient optical confinement function. properties and weather resistance.

Furthermore, the propagation loss due to diffuse reflection on the side of the waveguide is small, making it possible to realize high-performance optical devices, and the planar configuration provides high stability, making it possible to manufacture high-performance, high-stability, and high-precision optical devices at low cost. It will have a remarkable effect not only in optical communications, which will become more widespread in the future, but also in various optical application devices.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a conventional manufacturing method, FIG. 2 and subsequent figures show examples of the present invention, FIG. Fig. 4 is a perspective view when using a mask, Fig. 5 is a perspective view showing the optical deflector, Fig. 6 is a plan view showing the optical splitter, and Fig. 7 is a plan view showing the thin film convex lens, concave lens, and prism. 8A is a perspective view showing a linear waveguide, and FIG. 8B is a perspective view of a straight waveguide.
Figure 9 is a perspective view when a linear mask is used, Figure 10 is a plan view of a three-dimensional optical splitter, and Figure 11 is a three-dimensional intersecting groove waveguide. FIG. 12 is a plan view showing a mask for manufacturing the mask shown in FIG. 11, and FIG. 13 is a perspective view for manufacturing a filter. 1... Glass substrate, 11... Waveguide film, 12° 12a, 1
2b, 41, 51, 61a-61a. 71...Predetermined part, 13...Laser beam (heat ray), 1
4...shiichiza oscillator, 15...laser, beast heat ray), 16
...mirror, 17...lens, 21...part where heat rays are projected, 22y22a, 22b...mask, 32532
a, 32b... Waveguide light, Wm... Film thickness.

Claims (1)

[Scope of Claims] 1. A waveguide film that transmits guided light onto a glass substrate and has a thickness equal to or greater than the cutoff film thickness for the guided light is formed of oxide glass, and a predetermined portion of the waveguide film is By heating the oxide glass by irradiating it with heat rays having a wavelength that is absorbed by the oxide glass, the refractive index of a predetermined portion is lowered by a desired amount, and an optical element is formed in the waveguide film by the refractive index lowered portion. Characteristic method for manufacturing thin film optical devices. 2. A beam-shaped heat ray is used, the heat ray beam is projected onto a waveguide film, and the waveguide film and the heat ray beam are moved relative to each other to heat a predetermined portion of the waveguide film. A method for manufacturing a thin film optical device according to claim 1. 3. The method for manufacturing a thin film optical device according to claim 2, characterized in that a carbon dioxide laser beam is used as the beam-shaped heat ray. 4. Excluding a predetermined part of the waveguide film and covering the part to which the heat ray is projected with a substance that blocks heat rays, and then projecting the heat ray to the covered part and the predetermined part to cover the predetermined part of the waveguide film. 2. A method for manufacturing a thin film optical device according to claim 1, further comprising heating.