JPS61162010A - Optical waveguide lens - Google Patents

Abstract

PURPOSE:To improve the resistance of optical damage by forming an optical waveguide lens from a Fresnel lens pattern or a grating lens pattern consisting of a part having a transmission constant lower than that of a optical waveguide. CONSTITUTION:The Fresnel lens pattern is formed by a part 9 which is not processed by proton replacement on a proton-replaced optical waveguide 6. Wave-guided light 4 is condensed into an I/O part through the pattern. To form the optical waveguide, Ti is diffused to the whole surface of a LiNbO3 substrate 1, the part 9 is covered with the mask of the Fresnel lens pattern and the whole part other than the part 9 is treated with the proton replacement processing. The change of an equivalent bending ratio can be adjusted by controlling the temperature and time of anneal processing after the proton replacement. Said processing can be also applied to a grating lens.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to an optical waveguide lens.

[Prior art]

Conventionally, a lens as shown in FIG. 8, for example, has been known as an optical waveguide lens (Zang Da YU''Wav
egniae optical planar Ien
@es iyn LiMbO, -Theory and
experiments, Opt, Oom, 47,
4 e 1) 1) 248-250 (1985)). Here, 1F-1 is a substrate made of lithium niobate (LiNO,), 6 is an optical waveguide formed by implanting ions into the surface of the substrate 1, and the optical waveguide 6 is also relatively This is a lens section with a lower propagation constant. The guided light 4 of the optical waveguide 6 is focused on the input/output section 5 by the lens section 7 . However, such lenses have the disadvantage that there is little freedom in lens design and the scope of application is limited. On the other hand, other optical waveguide lenses (11 geodesic lenses, (2) /I/Nebble lens, (5) 7 Renel lens, (4) grating lens, etc.
A Fresnel lens or a grating lens that utilizes a diffraction phenomenon is useful in terms of the degree of freedom in design parameters and the reproducibility of lens characteristics as described above. For example, as a Fresnel lens, a configuration as shown in FIG. 9 has been known.

In FIG. 9, LiNb0. An optical waveguide 2 in which T1 is diffused is formed on a substrate 1, and a Fresnel lens pattern 3 having a different propagation constant is formed on this optical waveguide 2. The guided light 4 is focused on the input/output portion 5 by the lens action of the pattern 3.

The allowable angle of incidence for Fresnel lenses and grating lenses increases in inverse proportion to the lens thickness α, so when using lenses over a wide range of incidence angles, the change in propagation constant should be made as large as possible. [Reducing Te is preferable in terms of improving lens characteristics. Therefore, the conventional Fresnel lens pattern 3Fi and T1 diffused optical waveguide 2iC were fabricated by partially diffusing protons. (
#Production of a waveguide Fresnel lens by proton exchange in the domain "LiNb0."" 1984 Autumn Conference of the Japan Society of Applied Physics 14a-L-6 (1984)).

However, in the above-mentioned optical waveguide lens, the optical waveguide portion outside the lens is composed of a small T1 diffused optical waveguide 2 that is resistant to optical damage, and has the disadvantage that large waveguide power cannot be detected by introducing it. In particular, the optical waveguide power density is extremely high at the input/output portion 5, which corresponds to the focal point of the lens.
There was a drawback that the waveguide characteristics deteriorated due to scattering, etc. [Summary of the Invention] The purpose of the present invention is to eliminate the drawbacks of the conventional example described above, and to provide a light guide with high resistance to optical damage and a wide acceptance angle. Our objective is to provide wave-path lenses.

The above object of the present invention is achieved by an optical waveguide lens in which a Fresnel lens pattern or a grating lens pattern consisting of a portion having a lower propagation constant than the optical waveguide is formed on an optical waveguide formed by implanting ions into the surface of the substrate. - [Example] Hereinafter, examples of the present invention will be explained with reference to the drawings. Fresnel lens amplitude transmission trill distribution t (Xi is approximately expressed by the following equation.

t (xl= to exp (+jβX”/2f) where X is a coordinate axis that is perpendicular to the central axis of the lens and lies within the waveguide plane, and the lens center is set to XmO. Also, j is the imaginary index and β index. The propagation constant of the wave light, f is the focal length of the lens, to
is a constant. A Fresnel lens may be used to provide a phase distribution φ(x) in consideration of a period of 2π as shown in FIG. 2.

The area for every 2π is divided by Xm given by the following equation.

Here, λ is the optical wavelength in vacuum, and N is the equivalent refractive index of the guided light, which is given by N=βλ/2π. The equivalent refractive index of the optical waveguide section is N, and the equivalent refractive index of the Fresnel lens section is N+ΔN. If the lens thickness distribution is D(Xi), the phase change t is given by 2π φ(xl=7ΔN−tortoise)+φ0.To realize the phase distribution φ(XI) shown in Fig. 2, K is When the propagation constant of the part is smaller than the propagation constant of the optical waveguide part (Δa<O), @s diagram (
It is sufficient to form a Fresnel lens pattern shown in al or (bl).

Corresponds to the phase change amount of maximum lens thickness d times 2π. Ku1=lλ/△N! is given by

T1 expansion LiNb0. When proton exchange is performed on the optical waveguide, the refractive index for extraordinary light increases, and when using a substrate with X and Y cuts, the equivalent refractive index of the TK fundamental mode is T1
It increases by ΔN~+0.1 compared to the diffusion waveguide section.

By locally annealing the proton exchange part, the distribution of protons in the depth direction is expanded, and the equivalent refractive index of the annealed part can be reduced by ΔN-0.01 to 0.1 compared to the non-annealed part, and the amount of reduction is depends on the annealing temperature and time.

In order to construct a waveguide lens that is resistant to optical damage, which is the main focus of the present invention, K may be treated by proton exchange on the main waveguide portion through which the guided light propagates. Examples of the structure of the optical waveguide lens of the present invention are shown below.

(1) On the optical waveguide 6 that has been proton-exchanged as shown in FIG. 1, a 7-Renel lens pattern shown in FIG. is focused on the input/output portion 5 by this pattern.For fabrication, T1 is first dispersed over the entire surface of the LiNb0.substrate 1, and then the aforementioned portion 9 is covered with a Fresnel lens pattern mask. Proton exchange processing is performed on the entire other portion to form a Yt waveguide.

The amount of change in the equal number of folds can be adjusted by controlling the temperature and time of annealing after proton exchange.
(As shown in FIG. 211E4, a 7-Renel lens pattern is formed by a locally annealed portion 9'. The other portions are the same as in FIG. 1, are given the same reference numerals, and detailed description thereof will be omitted.

Patterning of the lens by local annealing can be performed using an electron beam, a laser beam, or the like.

(As shown in Figure 51m5, the Fresnel lens pattern is formed by a part where the waveguide thickness is thinner than other parts?'. Other parts are the same as in Figure #ia1, are given the same reference numerals, and detailed explanations are omitted. The part 9' is formed by patterning with resist and etching using electron beam lithography or photolithography technology.As the waveguide layer becomes thinner, the number of folded layers decreases. ,the above(
It is possible to obtain optical waveguide lenses equivalent to those in 1) and (2).

Next, examples will be described to clarify the effects of the present invention.

<*Example 1> Figure 6 shows LiNb0. This is one of the embodiments in which the optical waveguide Fresnel lens of the present invention is used in a surface acoustic wave (hereinafter referred to as EIAV) yt (WA) device configuration using an optical waveguide formed on a substrate.

LiNb0. 200 μm of T1 was deposited on the substrate 21 by electron beam evaporation, and 965 μm of T1 was deposited.
℃ for 2.5 hours to form a T1 diffused optical waveguide layer on the entire surface. Next, the lens portions 23 and 24 where proton exchange was not performed were patterned by electron beam drawing or photolithography to form a metal mask. As a metal mask, it is sufficient to apply A/ or the like to about several hundred OA.

At this time, metal masks are also formed on regions 25 and 26 where 8AW excitation interdigitated electrodes (hereinafter abbreviated as iDT) are formed, thereby preventing deterioration of the piezoelectric effect that tends to occur during proton exchange processing. be able to.

After applying a metal mask, proton exchange was performed at 250°C for 60 minutes in benzoic acid to which lithium benzoate was added.
Completed the necessary buttering. In the region 56 where the SAW and the guided light interact, it is required that the electro-optic effect and piezoelectric effect are not lost and that the region is strong against optical damage, so this region is locally annealed with an electron beam or a laser beam. conduct. Alternatively, the entire waveguide can be annealed, and by using the latter method, it is possible to fold the entire waveguide in any number of layers. It is also possible to adjust the amount of change ΔN.

After removing the metal mask, tDTs 27 and 28 for SAW excitation were formed by photophosphorography in the curved regions 25 and 26 after proton exchange.

The manufactured original device can efficiently input and output guided light by polishing the end face of the optical waveguide, which is the focal plane of the optical waveguide lens.

A semiconductor laser 30 is installed at the focal point 35 of the input optical waveguide 7 Lenel lens 23.

The TK wave 51 emitted from the semiconductor laser 30 is efficiently collimated by the lens 25 and becomes a surface acoustic wave S.
After being diffracted by the light beam 2, the light is focused on the end face of the output optical waveguide 7 by the Renel lens 24. By connecting the source fiber to the focal point 54, it is possible to effectively take in the light that has been modified by surface acoustic waves.

Semiconductor laser coupling site 35 and output yIA surface coupling site 3
In No. 4 and No. 33, the nine waveguide lights are condensed by several μmK and combined, resulting in a significantly high b power density. However, the structure of the optical waveguide lens of the present invention makes it possible to realize an optical deflection device that is resistant to optical damage and stable and exhibits t operation. became.

<Example 2> In Example 1, a metal mask was used and nine selective proton exchange was used to form the lens portion, but in this example, the lens portion was formed by selective annealing after proton exchange. It is something.

As in Example 1, T is applied to the entire surface of the X-cut NOs substrate.
1. Perform diffusion to form an optical waveguide. 1DT for SAT excitation
Areas 25 and 26 are covered with a metal mask and proton exchange is performed in benzoic acid.

After the proton exchange, the lens portions 23 and 24 are scanned with an electron beam or a laser beam and subjected to local annealing to form portions with a low isolateral refractive index. Simultaneous KEI
The region 36 of interaction between the AW and the guided light is locally annealed. Alternatively, the entire waveguide may be annealed if there is a margin for the equipolarized refraction main change fK.

The device fabricated as described above, as in Example 1, was resistant to optical damage and exhibited stable operation.

In particular, in this embodiment, all the lens portions are formed by proton exchange treatment9, and this embodiment has a feature that it is even more resistant to optical damage than the first embodiment.

<Example 3> In Example 2, the lens portion was formed by selective annealing after proton exchange, but in this example, the lens portion was formed by etching.Similar to Example 2, After forming a T1 diffused optical waveguide on the entire surface of the X-cut-LiNbO3 substrate, apply a metal mask to regions 25 and 26 of the iDT for SAW excitation, and perform proton exchange in benzoic acid. After proton exchange, apply resist to the entire surface. Then, the lens portions 23 and 24 that require etching are etched with an electron beam, and then the photolithography technique is used to open the windows. Etching was performed by a dry process using an Ar ion beam. After etching, the resist was removed and then the metal mask at the iDT portion was removed.

Local annealing is performed on the region S6 where the 8AV and the guided light interact using the method shown in Example 1 above. Alternatively, the entire waveguide may be annealed. By using the latter method in combination, it is also possible to achieve a uniform refractive index change amount ΔN of w4.

There is no harm in performing the above annealing process before the etching process of the lens portion.

Finally, proton exchange is performed and the indentation part is 25°26 and 8
The patterning of the iDT for AV excitation is completed using photolithography technology.

The device fabricated as described above is described above! l! As in Example 1, it was shown that it was resistant to optical damage and exhibited stable operation. In this embodiment of IFFK, all the lens parts are formed by proton exchange treatment, and are characterized by being more resistant to optical damage than in the first embodiment.

The above is a description of the case of a Fresnel lens, but the present invention
It can also be used repeatedly for grating lenses. for example,
As shown in FIG. 7, a grating lens pattern is formed on the optical waveguide 6 formed by proton exchange on the LiN substrate 1 by a portion 19 having a lower propagation constant than the waist waveguide. can get. The guided light 4 is focused on the input/output section 5 by the grating lens pattern. Here, the grating is formed such that the inclination (corresponding to the Bragg angle) with respect to the guided light is small where the period is large, and the inclination is large where the period is small. Specifically, if the Bragg angle is θ, the grating period is human, the number of folded layers is N(β/k), and the wavelength of guided light in vacuum is λ, then the following is satisfied. The portion 19 with a low propagation constant has K, (11 selective proton exchange, (
It may be formed by either 2) selective annealing or (3) selective etching. In the case of this grating lens as well, exactly the same effect as the 7 renel lens can be obtained.

The present invention is not limited to the above examples, but can be applied in various ways.

For example, in the production of an optical waveguide, a method of implanting ions such as protons by a dry process technique such as proton exchange using benzoic acid or ion brush fusion may be used.As a substrate material, In addition to LjNb○, semiconductor materials such as GaAe and InP can also be used. [Effects of the Invention] As explained above, the Fresnel lens paroon or By forming the optical waveguide lens from the h grating lens pattern, it has the effect of increasing resistance to optical damage and allowing the device to operate with high efficiency and stability, especially for the high power density required in the end face coupling region. .

[Brief explanation of drawings]

Figure 1 is a perspective ellipse diagram showing an example of the configuration of the optical waveguide lens of the present invention, Figure 2 is a diagram showing the phase distribution of a Fresnel lens, and Figure 5 is a diagram showing a phase distribution of a Fresnel lens.
Figures (a) and (b) each show an example of a Fresnel lens pattern, and Figures 4, 5, 6, and 7 each show other configuration examples of the original 21-wavelength lens of the present invention. Perspective view, No. 8
9 and 9 are perspective views showing examples of conventional optical waveguide lenses, respectively. 1... LiNbO2 substrate 4... Waveguide light 5... Input/output portion 6... Optical waveguide 9, 9', 9'...7 Portion forming Renel lens pattern 2 ':, -2,...,゛2, -42'22 丙-j, procedure amendment form) % form% 2. Name of the invention Optical waveguide lens 3. Relationship with the person making the amendment Patent Applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (+00
) Canon Co., Ltd. Representative Yo Kaku 3 Department 4, Agent Address: 3-30-2 Shimomaruko, Ota-ku, Tokyo 146 Canon Co., Ltd. (758-2111), 6゜82
．． □+Eya, -Ujo Akira d, +”aiJk t?S 5, Date of amendment order (shipment date) April 30, 1985 6 Subject of amendment MTS and drawings 7 Contents of amendment

Claims (1)

[Claims] (1) An optical waveguide lens comprising an optical waveguide formed by implanting ions into the surface of a substrate, on which a Fresnel lens pattern or a grating lens pattern consisting of a portion having a lower propagation constant than the optical waveguide is formed.