JPS63218906A - Form refractive index bimodulation type waveguide lens and its manufacture - Google Patents

Abstract

PURPOSE:To enlarge an angle allowable degree and a wavelength allowable degree, and also, to improve the efficiency by manufacturing each of a recessed part and a projecting part of an uneven structure formed in a waveguide, by materials whose refractive indexes are different, and allowing the respective indexes to have a difference. CONSTITUTION:Each of binary grating elements consisting of a projecting part and a recessed part is constituted of materials whose refractive indexes are different, and these refractive indexes are allowed to have a difference. That is, in a cross section of the uneven structure, a code L denotes length of a waveguide lens, a code (d) denotes a step difference of the uneven structure, and the projecting part refractive index and the recessed part refractive index are denoted as na and nb, respectively. Accordingly, as for waveguide lenses 10, 20 of a Fresnel type and a Bragg grating type, even in case of the same step difference (d), the length L can be shortened. In such a way, an angle allowable degree and a wavelength allowable degree become larger, and the waveguide length having high efficiency can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide lens that controls guided light by phase control, and a method for manufacturing the same.

[Prior Art] A conventional technology will be described with reference to the perspective view of FIG. 1st
Figure (A) shows a Fresnel lens type waveguide lens 10,
The guided light is converged, diverged, and collimated within the waveguide 2 on the substrate l. Further, the Bragg grating type waveguide lens 20 shown in FIG. 2(B) also converges, diverges, and collimates the guided light within the waveguide 2 on the substrate l.

Such waveguide lenses have conventionally been produced by coating a substrate such as glass, plastic, semiconductor, or dielectric with a photoreactive organic compound using a method such as a spin code, and then irradiating it with ultraviolet light or the like through a photomask. After reacting, by removing the unreacted parts, the Fresnel lens 3 and the Bragg grating 4 with the uneven structure are attached to the substrate l.
It was manufactured by forming it inside the upper waveguide 2.

By the way, in such a method, there is no difference in refractive index between the materials of the exposed part and the light shielding part of the waveguide 2, or even if there is, it is small, at most 1% or less, and is caused by the uneven structure formed in the waveguide. Only the phase difference was controlled.

[Problems to be solved by the invention] In order to reduce the allowable manufacturing error in such a waveguide lens, it is necessary to improve the angular tolerance when there is a deviation in the incident angle, and the angular tolerance when there is a deviation in the wavelength. It is desired to increase the wavelength tolerance, which is the full width at half maximum.

Here, the angular tolerance means that if there is an error in the angle of the guided light incident on the waveguide lens from the designed value, the efficiency of the waveguide lens will decrease. The width of the angle that gives the efficiency or maximum value of 172 2
If Δθ is the angular tolerance, then the angular tolerance 2Δθ is C□Δ/L, where the period of the waveguide lens is Δ and the length is L.
becomes. Here, C8 is fm given by the size, focal length, etc. of the waveguide lens.

Further, the wavelength tolerance refers to the efficiency of the waveguide lens, which is similar to the angular tolerance described above, when the wavelength of the guided light incident on the waveguide lens has an error from the designed value. If the wavelength tolerance is the wavelength width 2Δ where the efficiency is 1/2 of the maximum value, then
The wavelength tolerance 2Δinput is c2 when the wavelength of the guided light is
Person Δ/L yells. Here, C2 is a value given by the size, focal length, etc. of the waveguide lens.

Therefore, if only the length of the waveguide lens is shortened, the angular tolerance and wavelength tolerance become large.

Furthermore, in order to control scattering loss and wavefront aberration of guided light, which are generally causes of decreased efficiency, the lens surface needs to have high flatness.

In the Fresnel type and black grating type waveguide lenses shown in Figure 1 (A) and (B), in order to increase the angle tolerance and wavelength tolerance,
), it is necessary to shorten the length of the Fresnel lens and Bragg grating shown in (B). However, if this length is shortened, the efficiency decreases, so in order to increase the efficiency, it is necessary to increase the height difference in the uneven structure. This requires ultra-precision processing technology, and it has been extremely difficult to produce Fresnel-type or black grating-type waveguide lenses that have large angular tolerances and wavelength tolerances, and are highly efficient.

This invention was made in view of these points, and the four parts and the convex parts of the uneven structure formed in the waveguide are each made of materials with different refractive indexes, so that the refractive indexes of each part are made different. Accordingly, it is an object of the present invention to provide a shape refractive index twin modulation type waveguide lens that has large angle tolerance and wavelength tolerance and is highly efficient, and a method for manufacturing the same.

Hereinafter, the configuration of the present invention will be explained in detail based on the drawings.

FIG. 2(A) is a cross-sectional view of the concavo-convex structure of a shape-modulating waveguide lens manufactured by conventional methods such as vacuum evaporation and electron beam, and FIG. FIG. 2 is a cross-sectional view of the concavo-convex structure of a form refractive index dual modulation type waveguide lens manufactured in FIG. In the figure, the reference numeral indicates the length of the waveguide lens, and d indicates the step of the concavo-convex structure. Also,
In Fig. 2(A), the refractive index of the convex part and the four parts is the same value n, and in Fig. 2(B), the refractive index of the convex part is na, and the refractive index of the concave part is n.
b.

Next, for the Fresnel type and Bragg grating type waveguide lenses shown in FIGS. 1(A) and 1(B), FIG. 3 shows the relationship between the step difference d and the length that maximizes the efficiency. When guided light with a wavelength is propagating through a waveguide, the equivalent refractive index of this waveguide is N, where the film thickness of the waveguide is T and the refractive index of the waveguide, substrate, and air is nr r ns +n0. is given by the following formula.

ky T= (m+1) π-tan-'
(kg/'fm)-jan-' (k
x/y. )---(1) Tatami, kg ==k
If we want to enter 0 = 2π/ in 27 pγ, =, vTTτ, 0 = 2π/ in vTTτ, the shape modulation type waveguide lens using the conventional method as shown in Fig. 2 (A) , by modulating the film thickness T, the equivalent refractive index N is modulated.
In the waveguide lens of the shape refraction double translation modulation type according to the method of the present invention as shown in Figure (B), the equivalent refractive index N is modulated by modulating the film thickness T and the refractive index n' of the waveguide. Therefore, the equivalent refractive index modulation ΔN is larger than that of the conventional one.In addition, in order to maximize the efficiency of the waveguide lens, the relationship between the equivalent refractive index modulation ΔN and the length is as follows.

In the case of a Fresnel type waveguide lens, L=in/4ΔN (2), and in the case of a Bragg grete ink type waveguide lens, L=πλ/4ΔN (3).

The wavelength of the guided light is, for example, 632.8 nm, the thickness of the waveguide is 1 lm, and the refractive index na of the convex portion in FIG. 2(B) is 1.525. When the refractive index nb of the recess is 1.520, calculate the relationship between the step d and the length L that maximizes the efficiency of the waveguide lens using equations (1), (2), and (3) above. The results are shown in FIG. 3, where the conventional shape modulation type waveguide lens is represented by a solid line, and the shape refraction double translation modulation type waveguide lens of the present invention is represented by a broken line.

As shown in this figure, the Fresnel type or Bragg grating type waveguide lens according to the present invention can be made shorter in length than the conventional shape modulation type waveguide lens for the same step difference d. Therefore, the angular tolerance and wavelength tolerance become larger, and a highly efficient waveguide lens can be formed.

The polymer having a photoreactive carbon-carbon double bond used in this invention is a polymer having a carbon-carbon double bond in the molecule that can undergo a reaction with an aldehyde or ketone, as shown in formula (4) below. Any polymer containing double bonds may be used. These polymers are obtained, for example, by reacting terpene-based alcohols having double bonds in the molecule, such as 2-butynol and geraniol, with acrylic acid-based polymers (polymer esterification reaction). It can also be obtained by polymerizing alone an ester consisting of an alcohol having a double bond and acrylic acid or methacrylic acid, or by copolymerizing it with another methacrylic ester.

Typical examples of other methacrylic acid esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, 1so-propyl methacrylate, etc., and there are no special restrictions on the molecular structure. However, cyclic compounds with π-electron systems, such as aromatics, have large molecular boundaries and a large number of π-electrons, and have the ability to increase both volume and refractive index. When increasing the film thickness and refractive index of the exposed portion by addition reaction, it is desirable that the methacrylic acid ester does not have a π-electron ring structure.

Esters consisting of alcohol and acrylic acid or methacrylic acid that have a double bond in the molecule include compounds with one double bond in the alcohol residue and non-conjugated carbon-carbon double bonds. It is broadly classified into compounds having two or more. Representative examples of the former include allyl methacrylate, crotyl methacrylate, 2-methyl-2-propenyl methacrylate, 3-methyl-3-propenyl methacrylate, 2-methyl-2-butenyl methacrylate, 1.1
-dimethyl-3-butenyl methacrylate, etc., and is suitable for producing a waveguide lens in which the step difference between the convex portion and the concave portion and the difference in refractive index are relatively small. Typical examples of the latter include geranyl methacrylate and geranylgeranyl methacrylate, which are suitable for producing a waveguide lens with a relatively large step difference and refractive index difference between the convex portion and the concave portion.

Aromatic ketones have the function of increasing both the step difference and the refractive index, and are broadly classified into compounds having a carbonyl group and compounds having two or more carbonyl groups. An example of the former is acetophenone.

Examples include benzophenone and benzaldehyde, which are suitable for producing waveguide lenses with relatively small steps and refractive index differences between convex and concave portions. Examples of the latter include 3-benzoylbenzophenone, 3,3°-dibenzoylbenzophenone, etc., which are suitable for producing a waveguide lens with a relatively large step and refractive index difference between the convex portion and the concave portion. Aromatic ketones with substituents such as alkyl groups and halogens on aromatic carbon also have the function of increasing the step difference and refractive index difference.

When a copolymer having a photoreactive carbon-carbon double bond and these aromatic ketones coexist, a wavelength of 300
When irradiated with ultraviolet light of ~400 nm, for example, formula (4)
Both of them form an oxetane ring and combine in the reaction pattern shown in .

Here, R1 and R2 are appropriate substituents, or R9 represents a copolymer skeleton. In order for this photoreaction to proceed selectively, the triplet energy of the aromatic ketone must be lower than the triplet energy of the carbon-carbon double bond on the copolymer, and vice versa. The photoexcitation energy is preferentially transferred from the aromatic ketone to the carbon-carbon double bond and is lost. From this point of view, conjugated carbon-carbon double bonds are not suitable, and the triplet energy is 65Kc.
Aromatic ketones in the range of a from 11 moles to 77 Kca to 11 moles are useful. Also.

In order to ease the development conditions by the reduced pressure heating method, it is desirable to use an aromatic ketone that easily sublimates.

The difference in level and refractive index between the exposed area and the light-blocking area not only depend on the type and concentration of the material, but also vary depending on the film thickness before UV irradiation, the output of the light source, the UV irradiation time, temperature, etc. By understanding in advance the characteristics of the control factors for the step difference and the refractive index difference, a desired form-refraction-translation modulation type waveguide lens can be created.

[Example] The following is a detailed explanation of the manufacturing method and optical characteristics of the shape refraction double translation modulation type waveguide lens according to the present invention by way of an example.

A copolymer of methyl methacrylate and crotyl methacrylate in a molar ratio of 1:1 was synthesized. A 4% by weight benzene solution prepared by adding 1 mol of benzophenone to 1 mol of this crotyl methacrylate component was spin-coated onto a 2 mm thick polymethyl methacrylate substrate to form a transparent thin film. Benzophenone was bonded to the crotyl methacrylate component by irradiating this thin film with ultraviolet rays for 20 minutes using an ultra-high pressure mercury lamp with an output of 250 W through a patterned photomask. By heating this sample under reduced pressure at 0.2 mmHg and 100°C for 1 hour to sublimate unreacted benzophenone,
Fresnel type and Bragg grating type waveguide lenses and grating lenses were fabricated. The measured value of the step d of the uneven structure using the stylus method was 0.14 m,
The equivalent refractive indexes of the convex and concave portions were measured using a He--Ne laser with a wavelength of 632.8 nm, and were found to be 1.510 and 1.500, respectively. As a result of examining the length that maximizes efficiency under these conditions, the optimal lengths for Fresnel type and Bragg grating type waveguide lenses are 654.
m and 50 Bm.

Example 2 In Example 1, 0.7 mole of 3-benzoylbenzophenone was added per mole of crotyl methacrylate component instead of benzophenone.

As a result of conducting a similar experiment, the level difference d of the uneven structure was 0.1
The equivalent refractive index of the convex and concave parts is 1.515g each.
and 1.500. Under these conditions, the optimal lengths of the Presnel type and Bragg grating type waveguide lenses were 42 ILm and 33 ILm, respectively.

[Effects of the Invention] According to the present invention, a waveguide lens that has greater angular tolerance and wavelength tolerance than conventional waveguide lenses and is highly efficient can be easily provided, and can be used to improve light concentration, divergence, and Useful for collimation and Fourier transform, etc.

Figure 1 (A) shows the Fresnel type, Figure 1 (B) shows the Bragg grating type, and Figures 2 (A) and (B) are enlarged views showing the uneven structure of the waveguide lens. In the cross-sectional views, FIG. 2(A) shows the conventional shape modulation type, and FIG. S2(B) shows the shape refraction double translation modulation type of the present invention.

FIG. 3 is a line section showing the relationship between the step height and the length at which the efficiency of the Fresnel type and Bragg grating type waveguide lenses is maximized.

l...Substrate 2... Waveguide 3... Fresnel type waveguide lens 4... Bragg grating type waveguide lens

Claims (3)

[Claims] (1) In a diffractive waveguide lens in which a diffraction grating is formed in an optical waveguide, each of the binary grating elements consisting of a convex portion and a concave portion is made of a material with a different refractive index, and the difference in the refractive index is A form refractive index dual modulation type waveguide lens characterized by: (2) The bimodulated refractive index type according to claim 1, characterized in that the refractive index of the material forming the convex portions of the binary grating element is higher than the refractive index of the material forming the concave portions. waveguide lens. (3) A) One or more compounds selected from (A) a polymer having a photoreactive carbon-carbon double bond, and (B) an aromatic aldehyde and an aromatic ketone that are unsubstituted or have a substituent. a step of forming a thin film from a composition containing two or more kinds; b) a step of irradiating the thin film with ultraviolet rays through a photomask in which a waveguide lens pattern is formed; c) removing unreacted compound (B). 3. A method for manufacturing a form refractive index dual modulation type waveguide lens according to claims 1 and 2, characterized in that the steps are performed sequentially.