JPS60189709A - Photocoupler - Google Patents

Abstract

PURPOSE:To obtain a photocoupler with high precision and good efficiency by forming a light guide on which a grating is installed, and a buffer layer and a reflecting layer. CONSTITUTION:An LB film 31 having the plane type grating formed is adhered to a substrate 31. An LB film 33 is provided in recesses of the grating part of the LB film 31, and the LB film 31 and LB film 33 are in level with each other, thereby forming the phase difference type grating 36. Further, the LB films 31 and 33 have the same surface property. An LB film 34 is formed on the grating 36. The refractive index of the LB film 34 should be smaller than that of the LB film 31. The LB film 34 is made of the same material with the LB film 33 and functions as a buffer layer. The reflecting layer 35 is formed by vapor-depositing an Al film. Projection light beams 36-a and 36-b have a difference in optical path length and intensify each other when the optical path difference is an integral multiple of the wavelength. Consequently, the photocoupler with high precision and good efficiency is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical coupler, and more particularly to an optical coupler in which a grating is installed in a leading waveguide.

In recent years, with the development of optical integrated circuits, there has been a demand for highly accurate and efficient optical couplers.

However, conventionally, in order to obtain a coupler with desired precision, a high degree of microfabrication technology is required, which has resulted in a drawback that the yield is lowered and, therefore, the cost is increased.

Here, a conventional grating type optical coupler will be explained. FIG. 1 is a cross-sectional view of a conventional planar grating type optical coupler. In this figure, 2 is a substrate, and 1, for example,
glass, plastic or lithium niobate (LiNb)
A transparent substrate such as O3) or an opaque substrate such as silicon or ceramics is used. An optical waveguide 1 is arranged on the surface of a substrate 2. The optical waveguide l has a higher refractive index than the substrate 2. For example, when using lithium niobate as a substrate, titanium (Ti) is thermally diffused onto the surface of the lithium niobate. An optical waveguide 1 having a film thickness of about 100% can be obtained. Alternatively, if glass with a refractive index of 1.5 is used as a substrate, the surface of the glass has a refractive index of 1.55.
(wavelength 8328k) glass (for example, Corning Co., Ltd. product name C-70511) is sputtered to a film thickness of 0.
．． The optical waveguide 1 is obtained by forming a film to a thickness of about 5 to 5 μm.

6 is a grating, which usually has a pitch of 0.3 to 1 PL and a depth of 0.1 to 0.2 PL. When the incident light 3 enters the optical coupler configured in this way, the light 4 propagates through the waveguide by total internal reflection, is diffracted by the grating 6, and becomes the emitted light 5.
is taken out.

In this case, it is generally difficult to manufacture the grating. The planar type is more difficult than the relief type. In order to more effectively exhibit the function of the thinning 6, a completely rectangular grating is preferable, but it is generally not easy to obtain such a completely rectangular grating.

The present invention has been made in view of these points, and it is an object of the present invention to provide an optical coupler that is easy to manufacture and inexpensive.

A further object of the present invention is to provide a highly accurate and efficient optical coupler.

Furthermore, the present invention also includes other components (buffer layer) that are difficult to construct in the relief type grating 1- (described later).
An object of the present invention is to provide an optical coupler having a planar grating so that it can be easily constructed.

The present invention uses the single molecule accumulation method shown below to
The basic idea is to obtain a monomolecular stacked film, and further improvements have been made to enable a grating format.

Hereinafter, the single molecule accumulation method which is the basis of the present invention and the single molecule accumulation film formed thereby will be explained. The monomolecular accumulation method is a method in which a monomolecular film formed on the water surface is transferred to the surface of a substrate and layered one by one to form an ultra-thin film.It is also called the Langmuir-Blodget (LB) method after the inventor. .

Here, a monomolecular film refers to a uniform film with a thickness of one molecule,
A film in which this is accumulated is called a cumulative film.

The molecules constituting such a monomolecular film and a cumulative film must necessarily have at least a hydrophobic part and a woody part in the same chemical structure. The most typical hydrophobic moiety is a long-chain alkyl group, which generally has 5 carbon atoms.
Those having a carbon number of 10 to 25 are used, preferably 10 to 25. Furthermore, both straight-chain alkyl groups and branched alkyl groups are useful as long as the length of the alkyl chain is appropriate. Examples of groups constituting other hydrophobic moieties include olefinic hydrocarbon groups such as vinylene, vinylidene, and acetylene, condensed polycyclic phenyl groups such as phenyl, naphthyl, and anthranyl, and chain polycyclic groups such as biphenyl and terphenyl. There are phenyl groups, etc., and these may be used alone or in combination, or may be located at the end or in the middle of the alkyl group mentioned above. The most typical wood-philic moieties include, for example, carboxyl groups and their metal salts and amine salts, sulfonic acid groups and their metal salts and amine salts, sulfonamide groups, amide groups,
Amine group, imino group, hydroxyl group, quaternary amine group,
Examples include oximino group, oximino group, diazonium group, guanidine group, hydrazine group, phosphoric acid group, silicate group, aluminate group, and the like. However, a monomolecular film and a cumulative film may not always be formed with any combination of hydrophobic portions and lignophilic portions. In order to obtain a monomolecular film and a cumulative film by the monomolecular accumulation method, the following steps are required in the production process, as described below.
First, a monomolecular film must be formed on the water surface,
If hydrophilicity is stronger than hydrophobicity, the molecule dissolves in water and becomes an aqueous solution; conversely, if hydrophobicity is stronger, it separates into two phases. A monomolecular film is formed on the water surface when hydrophobicity and phyllophilicity are appropriately balanced. At this time, the molecules as a whole do not float or sink, but instead direct their woody parts toward the water phase and are adsorbed at the air-water interface, forming a monomolecular film. Therefore, the molecules constituting the monomolecular film and the cumulative film are required to have an appropriate balance of hydrophobic and hydrophilic parts.

Next, the LB film manufacturing apparatus and manufacturing method will be explained with reference to FIGS. 2(A) and 2(B). Here, the LB film refers to a monomolecular film and a cumulative film produced by a single-molecule accumulation method. The LB film manufacturing apparatus illustrated in FIGS. 2A and 2B was devised by Kuhn's research group based on the principle of the Langmuir-Blodgett method (LB method) described above. A polypropylene acid frame 15 is hung horizontally inside a shallow and wide rectangular water tank 14 to partition a water surface 23. The frame 15 functions as a two-dimensional cylinder as described below. A polypropylene acid float 16 is floated inside the frame 15. The width of the float 16 is made slightly narrower than the inside of the frame 15 so that it can move smoothly from side to side as a two-dimensional piston. A weight 17 is connected via a pulley 18 to pull the float 16 to the right. Generally, the repulsive force of a magnet is used to stop the float 1B or push it back to the left. For this purpose, a magnet 19 fixed to the float 16 and a pair of magnets 20 that can be moved left and right are provided. That is, when pushing back the float 16, if the counter magnet 20 is brought close to the magnet 19, a repulsive force acts and the float 16 is pushed back.

Instead of such weights and magnets 19, 20, it is also possible to directly move the float 16 from side to side using a rotary motor or pulley. The left and right suction nozzles 22 are connected to a suction pump (not shown) via suction pipes 21, respectively. In the monomolecular accumulation method, clean pure water is used to prevent impurities from entering the monomolecular film and the cumulative film.
A suction pump and a suction nozzle 22 (not shown) are used to clean the water surface 23 and quickly remove unnecessary monomolecular films. In that case, the water surface 23 is purified by sweeping up the unnecessary monomolecular layer and the like with the float 16 and quickly pushing it out with the suction nozzle 22.

In this way, the float 16 is brought to the left end of the purified water surface 23, and a few drops of a thin solution of the membrane constituent material dissolved in a volatile solvent such as benzene or chloroform at a concentration of ~5X 10-3 + mol/l are dropped onto the water surface. After the solvent evaporates, a monomolecular film is left on the water surface. This monomolecular film exhibits the behavior of a two-dimensional system at the water surface. When the areal density of molecules is low, it is called a gas film of a two-dimensional gas, and a two-dimensional ideal gas equation of state is established between the occupied area per molecule and the surface pressure. The occupied area and surface pressure are automatically and continuously measured by a measuring device (not shown). The occupied area and the amount of change thereof can be determined from the left and right movement of the float 16. The surface pressure measuring device uses a method to measure the surface pressure indirectly from the difference in surface tension between pure water and the water surface covered with a monomolecular film, and a float 16 floating to separate the pure water surface and the monomolecular film surface. There are methods that directly measure the two-dimensional pressure applied to the surface, and each has its own characteristics. From the state of a gas film, when the float 16 is gradually moved to the right to gradually reduce the expanse of the water surface on which the monomolecular film develops and increase the surface density, the intermolecular interaction becomes stronger and the liquid film of the two-dimensional liquid is formed. Then it turns into a two-dimensional solid film.

When it becomes a solid film, the molecular arrangement and height are perfectly aligned,
This results in the high degree of order and uniform ultra-thin film properties required for optical materials. Thus, it becomes possible to transfer the monomolecular film to the surface of a clean substrate 24 (for example, a substrate made of glass, ceramic, plastic, or metal is used) while maintaining the state of the solid film. It is also possible to accumulate any number of monolayers on top of the monolayer deposited on the substrate 24. Generally, the surface pressure of a monolayer suitable for cumulative operation is between 15 and 30 dyne/cm. Outside this range, the arrangement and orientation of molecules may be disturbed and the film may peel off, which is inappropriate. However, in special cases, for example, depending on the chemical structure of the membrane structure material, temperature conditions, etc., a suitable surface pressure value may fall outside the above range, so the above range is only a rough guide. A driving device (not shown) that drives the counter magnet 20 from side to side is controlled by a surface pressure control device (not shown) so that the monomolecular film can always maintain a constant surface pressure selected within the range of conditions suitable for cumulative operation. controlled. For example, in the cumulative operation process, when a monomolecular film is transferred to the substrate 24, the surface pressure naturally decreases, so the counter magnet 20 is moved, and therefore the float 16 is moved to compress the spread film area and surface the surface. An operation is automatically performed to correct the pressure drop and maintain a constant surface pressure. Monolayer 26
There are roughly two types of methods for transferring the water (see FIG. 3) from the water surface 23 to the substrate 24 surface. - is the vertical immersion method, and the others are the horizontal attachment method. The vertical immersion method involves transferring the monomolecular film 26 on the water surface 23 by moving the substrate 24 up and down in the direction across the film, that is, in the vertical direction, while applying a constant surface pressure suitable for cumulative operation to the monomolecular film 26 on the water surface 23. This is the way to take it.

Horizontal attachment method is to attach the substrate from above to the water surface 23 while keeping it horizontal.
Monolayer 2 from one end as close as possible to the monolayer at a slight angle.
This is the method of adhesion by touching 6. Each has its pros and cons. In the case of the vertical dipping method, three types of membrane structures can be formed as shown in FIG. 3 depending on the molecules constituting the membrane and the conditions for manufacturing the membrane. Figure 3 (A) shows an X type in which the film adheres only during immersion, Figure 3 (B) shows a Y type in which the film adheres both during immersion and pulling up, and Figure 3 (G) shows a film that adheres during pulling up. There is an X-type, in which only a film is attached.

Therefore, the X type is attached with the hydrophobic part facing the surface of the substrate 24 and the hydrophilic part facing outside. In the Z type, the hydrophilic portion Q is attached to the surface of the substrate 24, and the hydrophobic portion P is attached to the outside.

On the other hand, in the case of the horizontal deposition method, only an X-shaped cumulative film can be produced, but it is relatively easier to produce an X-shaped cumulative film with a superior cumulative ratio, which will be described later, than in the vertical dipping method. Furthermore, this horizontal deposition method is suitable for producing protein monolayers.

However, in either method, the substrate 24
The surface must be sufficiently clean from a surface chemical point of view. If the surface of the substrate 24 is insufficiently cleaned, the film will peel off, making it difficult to form a cumulative film.

For example, if a glass substrate is immersed in a chromic acid mixture, washed with distilled water, and then dried in a clean air stream, its surface becomes completely hydrophilic.

For example, molten iron stearate (II) is thoroughly applied to a cleaned solid surface, rubbed thoroughly with a clean cloth such as gauze, and then the parent wood is turned towards the solid surface. A monolayer of iron stearate (m) is formed,
The surface becomes completely hydrophobic.

In order to clarify the accumulation operation more specifically, the operation of producing a Y-shaped accumulation film by the vertical dipping method will be explained according to FIG. The illustrated example (FIG. 4) is a case where a hydrophilic substrate 24 is used. The first layer of the monomolecular film 26 attached to the hydrophilic substrate 24 is pulled as shown in FIG.
The actual procedure is to first immerse the substrate deeply in water, and then drop a dilute solution of the film constituent material. Then, the surface pressure is increased, and after reaching a surface pressure suitable for producing a cumulative film, the substrate 24 is pulled up. The pull-L pulling (lowering) speed suitable for producing a cumulative film is 0.1-10 cm/win. However, suitable conditions may exist outside this range depending on the film constituent materials and film manufacturing conditions.

In the first lifting process, the first calendar wheel molecular membrane is exposed to the hydrophilic portion Q.
is attached to the surface of the substrate 24, with the hydrophobic portion P facing outward.

In the next dipping (lowering) step (FIG. 4(B)), the second layer heavy molecular film is attached to the surface of the substrate 14 with the hydrophobic portion P facing outward and the hydrophilic portion Q facing outward. In addition, the first layer 26a
It has been found that the cumulative film does not peel off and the cumulative operation is more successful if the second layer 28b or more is applied after drying thoroughly in the air to remove moisture and other solvents. For the third layer 26c onwards, repeat the same operation (Fig. 4 (
C)), any number of cumulative films can be produced.

In the illustrated example, in the odd-numbered layers of the Y-type film, the hydrophilic portion Q always faces the surface of the substrate 24, and the hydrophobic portion P faces outward.

It has been confirmed through many experiments that the thickness of the cumulative film produced in this way is equal to the product of the length of the molecule (10 to 80 A) times the cumulative number of times (the number of monomolecular films). Other factors that affect the way the film adheres include (
1) Chemical structure of membrane constituents, (2) PH of the aqueous phase and type and concentration of salts contained.

(3) temperature, (4) type of substrate, etc. For example, it is easier to form a stable cumulative film with fatty acid salts than with pure straight-chain fatty acids, and salts of calcium, barium, cadmium, etc. are particularly good. In this case, the composition and deposition of the cumulative film differ depending on the pH of the aqueous phase. That is, in general, if the pH is 4 or lower, a pure fat film will be obtained, if the pH is 9 or higher, a metal salt film will be obtained, and if the pH is in the middle, a cumulative film containing these will be obtained. Note that an index called cumulative ratio is used to quantitatively display how the cumulative film is formed. The cumulative ratio refers to the ratio of the film area actually transferred from the water surface 23 to a predetermined area on the substrate. In addition, the membrane area transferred from the water surface is 1 float.
It can be determined by measuring the amount of movement of 6. For example, a cumulative ratio of 0 indicates that no film was attached at all, and a cumulative ratio of 1 indicates that the film was ideally transferred. Generally, the metal salt has a higher cumulative ratio than the free acid.

The substrate 24 used in the present invention may be any suitable substrate, and the dimensions of the substrate are not particularly limited. The thickness of the LB film in the present invention is determined by the above-mentioned repeated accumulation.
．． A material suitable for the grating-type optical coupler of the present invention in the range of 5 to 5 IL may be any material as long as it has appropriate optical properties and forms an LB film.

Particularly suitable, such as fatty acids, in particular straight-chain fatty acids containing 10 to 30 carbon atoms (stearic acid, araxic acid) and their salts (cadmium salts), the polymerizable L described below
This is a B film. The refractive index of these materials is easily controlled by appropriately selecting the length of the CH2 chain or by adding metal ions.

The formed LB film is patterned by known means. . Further, it is patterned into a desired shape by a novel patterning method related to another patent application (application number undetermined) filed by the present applicant. The patterned LB film functions as a waveguide.

Next, a method for forming a planar grating according to the present invention will be explained with reference to FIG. A photopolymerizable material is used as the LB film material. In this case, the LB film is assumed to be the aforementioned Y-type film.

First, the polymerizable LB film 7 is formed on the substrate 2 of glass, ceramics, plastics, silicon oxide, etc. by the single molecule accumulation method described above. Next, in order to obtain the desired shape of the optical coupler, after patterning with light or electrons (Fig. 3 (1)), the LB of the unexposed area is developed (developing solution: alcohol, chloroform, benzene, etc.). Remove the film (Fig. 5 (1), (2)). At this time, the polymerized portion is not eluted by the developer. (Figure 5 (2)).

Next, a polymerizable LB film 10 is formed on one of the polymerized LB films 9 by a single molecule accumulation method. The polymerizable LB film 10 is preferably of the same type as the polymerizable LB film 7, but may be of a different type as long as it satisfies the optical conditions.

In this case, if the surface of the polymerizable LB film 9 (the surface in contact with the polymerizable LB film 1O) is lignophilic, the surface of the polymerizable LB film 9 may be made hydrophobic, or the surface of the polymerizable LB film 9 may be hydrophobic. If the polymerizable LB film 10 is hydrophilic, it is necessary to adjust the thickness of the polymerizable LB film 10 so that the surface of the polymerizable LB film 10 becomes hydrophilic.

As is clear from the above-mentioned single molecule accumulation method, the surface of the LB film is necessarily either hydrophilic or hydrophobic, and the control thereof is extremely easy. The above-described patterning exposure is performed so that only the LB film laminated on the LBBaO surface of the desired shape remains. At that time, the grating pattern also
Expose at the same time or one after the other. After development, a relief pattern of the polymerized LB film 11 shown in FIG. 5(4) is obtained. At this time, the concave portion of the grating 11 is the polymerized LB.
Since this is the surface of the membrane 9 and the convex portion is the surface of O made of LB membrane, when one side is a wood-loving surface, the other side is a hydrophobic surface. Next, LBBi 12 and 13 are deposited on the polymerized LB film 11.
is formed by the single molecule accumulation method described above. At this time, if the four-part lower surface of polymerized LBIII is wood-loving, LBBi12
The first layer is attached so that the parent wood base faces the substrate side. Therefore, in the convex part, a hydrophobic group and a hydrophilic group (LBBi12 first
layer) will be facing each other. On the contrary, polymerized LB film 1
If the lower surface of the recess 1 is hydrophobic, the first layer of LBBi 12 is attached so that the hydrophobic side faces the substrate side. The thickness of the LBBi 12 is made to be the same as the depth of the grating (that is, the surface of the convex portion 11 and the surface of 13 are made to be on the same plane) (FIG. 5 (4)). The fact that the thickness of LBBi12 is extremely easy to control is clear from the characteristics of the single molecule accumulation method, which involves the step of repeatedly accumulating single molecules.

LBII112 and 1 stacked on polymerized L film II
3 is polymerizable or not, but the refractive index is polymerizable L.
B It is required to be smaller than that of B@.

Next, when the structure shown in Fig. 5 (4) is placed in an ultrasonic waterproof tank (not shown) and ultrasonic waves are generated under appropriate conditions, the bonding force is reduced because the hydrophobic group and the parent wood group are facing each other. Weak LBBi1
Peeling (removal) occurs at the contact surface of 212.

Since the hydrophilic groups (or hydrophobic groups) face each other at the contact surface between the LB membranes 1 and 13, the bonding force is relatively strong and no peeling occurs. Thus, by selective peeling (removal), a cross-sectional structure shown in FIG. 3(5) is formed.

The LBBi 1213 is formed on the same plane, thus constructing a planar type, that is, a phase difference type grating.

Such a phase difference coupler is advantageous when other components are built on top of the grating.

Next, one embodiment of the present invention will be explained with reference to FIG. 6. In this figure, a substrate 32 is provided with LBBa2O on which a planar grating is formed. LBll
LBBa2O in the concave part of the grating part 36 of 131.
The surface of the attached LBBa2O33 is on the same plane, forming a planar type, that is, a phase difference type grating 36. Furthermore, LBll131 and LBll33 have the same surface properties. That is, if the LBBa2O surface is lignophilic, the LBBa2O surface must also be made hydrophilic. Conversely, if the LBBa2O surface is hydrophobic, the LBBa2O surface must also be made hydrophobic.

A LBBa3O film is formed on the grating.

The condition is that the refractive index of LBBa3O is lower than the refractive index of LBBa2O. LBBa3OLBBa2O are preferably made of the same material or have the same refractive index. LBBa3
Functions as an O buffer layer. LB film (buffer layer) 3
A reflective layer 35 is attached to the upper surface of 4. The reflective layer 35 is A
1 film was deposited.

The film may be uniformly deposited on LBBa3OLBBa2OL, but it may be selectively deposited so that it is formed only on the grating as shown in FIG. At that time, in the case of a polymerizable LB layer, it is patterned into a desired shape by pattern exposure, and in the case of a non-polymerizable LB layer, it is patterned into a desired shape by a patterning method related to another patent application (application number undetermined) by the applicant. . The film thickness of the LBlli 34 is diffracted by the grating, and the light 36-b directly emitted to the substrate side 32 and the light 36-a reflected by the LBBa3O side emission reflection layer 35 and emitted to the substrate side 32 strengthen each other due to interference. It needs to be set as follows. In this case, the LB layer 34 functions as a buffer layer as described above.

Optimal film thickness conditions for the LBHIA 34 under which the emitted light beams 36-a and 38-b strengthen each other through interference can be easily derived from known optical laws. However, film thickness control below the wavelength of light is required. The emitted light beams 36-a and 36-b have different optical path lengths as shown in FIG. When this optical path difference is an integral multiple of the wavelength, they become stronger.

In this way, the optical coupler of the present invention, which includes a crating composed of the LB layer shown in FIG. 6, an optical waveguide, and a buffer layer provided with a reflective layer, can utilize the light emitted to the reflective side of the substrate 32. This has the effect of increasing injection efficiency. Furthermore, the present invention provides an inexpensive optical coupler,
An optical coupler having a planar grating in which 4777 layers can be easily constructed is provided.

<Example) ・Substrate ~ White plate glass, 10+w tray x 10m cabinet, 0.3
m (Si0281%, 820313%, Na2O4
%, Al2032%) Grating pitch 200 people Depth 0.1p Thickness of LB film 9 0.9#L 〃1O110,IIL // 12.13/I Q, IIL tt 14 // 0.2L・Incoming light ~ He-Me laser (8328A) Semiconductor laser (8300A) Olefin type (photopolymerizable) Polymerizes vinyl stearate by exposing it to gamma rays.

The exposed part at the end dissolves in alcohol.

-Polymerize totricosenic acid by exposing it to an electron beam (10-100KeV).

φ electron beam exposure device (JEOL TEBX-2B) ・Diacetylene derivatives are polymerized by ultraviolet light.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional optical coupler, and FIG. 2 (A). (B) is a perspective view and a cross-sectional view of the LB film production apparatus, Figures 3 (A), (B), and (C) are diagrams explaining three types of LB film configurations; Figures 4 (A), ( B), (C) is LB
Diagrams explaining the formation of the film, Figure 5, are (1), (2),
(3), (4). (5) is an explanatory diagram of the process of forming a planar grating of the present invention, and FIG. 6 is a sectional view of one embodiment of the present invention. 2--1 Substrate 7---Made of monomer L film 8-m-Exposed 9-m-polymerized LB film 10---Made of monomer L film 11-m-polymerized LB film 12, 13---Made of monomer L film 14--Aquarium 15-Frame 16--Float 18, 20--1 Magnet 23-m-Water surface 24-m-Substrate 2B--1 Monomolecular film 31--1 Optical waveguide 32-m-Substrate 33, 34---- LB film 35-m-Reflection layer Patent applicant Canon Corporation No. 1 To Fig. 3 Fig. 6 Fig. 2 (1m (a) Fig. 2 (1)) (A) Fig. 3 Fig. 114 Fig. 115

Claims (1)

[Claims] An optical waveguide with a grating installed, 4777 layers,
An optical coupler characterized by comprising a reflective layer.