JPS6060601A - Manufacture of plane lens - Google Patents

Abstract

PURPOSE:To reduce the scatter loss of light at the connection point of a waveguide and a lens by tapering a mask and slanting a substrate in the incidence direction of ions, and implanting ions while rotating the substrate. CONSTITUTION:The mask 5 which is tapered or bored internally is provided onto a photoconductive radio wave layer 3 having a higher refractive index than the substrate 1 and ions are implanted from above to form a part with a larger dose, manufacturing a plane lens 4. In this case, the mask 5 is tapered or bored internally to smooth variation in refractive index from the higher-dose part to a lower-dose part, and the substrate 1 is slanted in the incidence direction of the ions; and the ions are implanted while the substrate 1 is rotated to obtain the lens which has no astigmatism and small scatter loss.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a flat lens necessary for optical integrated circuits used in the fields of optical communications and optical information processing, particularly a flat lens with small astigmatism and low light scattering loss. This invention relates to a method for manufacturing lenses.

[Background of the invention]

In recent years, the practical application of optical communications has progressed rapidly, and research and development are actively being carried out to make optical components smaller and more reliable. A plane lens, which is a component of an optical product circuit, is manufactured using an ultrasonic processing method, a sputtering method, an ion exchange method, or the like. The ultrasonic processing method and the sputtering method are methods in which a part of a planar optical waveguide on a substrate is formed into a desired geometric shape so that the guided light acts as a convex lens or a concave lens. In the ion exchange method, for example, a substrate such as soda ash glass or borosilicate glass containing Na is immersed in a dissolved salt containing ions such as 'l't'', Ag'', K'', and Li+, and electrothermal diffusion is performed. Yoshi T
A planar optical waveguide is formed by introducing ions such as t'', Ag'', K'', Li+ into the substrate, and increasing the refractive index of that portion by several percent compared to the substrate. A plane lens can be obtained by providing a region in which the concentration of the above-mentioned ions is particularly high in a part of the wave path, and creating a region with a high refractive index so as to have a lens effect on the guided light.

Here, the drawbacks of the conventional method will be explained in detail with reference to the drawings regarding the ultrasonic processing method.

FIG. 1 shows a method of manufacturing a plane lens using an ultrasonic processing method. As shown in FIG. 1(a), a rod for transmitting ultrasonic waves (for example, a rod for transmitting ultrasonic waves whose tip has the same geometric shape as a lens) is attached to a substrate 1 (for example, GaAs: refractive index 3.44).
The substrate 1 is excavated by oscillating ultrasonic waves while dripping an abrasive material (for example, a liquid made by dissolving Carbon Random Na 600 in water) onto the contact area between the substrate 1 and the rod 2 (quenched and hardened iron). To go.

After the substrate is dug to a desired depth, a film 3 of a cylindrical optical material with a refractive index (for example, a 4 μm thick G a A
By attaching a high resistance film (refractive index=3.445), a desired lens 4 is formed on the substrate 1.

In conventional methods, the tip of the ultrasonic transmission rod that is in contact with the substrate also wears out during processing, making it difficult to carve the substrate into the desired geometric shape. For this reason, the lens did not have accurate rotational symmetry, and light entering the lens through the planar waveguide was not focused on the output side, resulting in large coupling losses when inserted into the optical quaino.

Furthermore, in the conventional method, it was difficult to connect the lens region and the waveguide connected thereto with a geometrically smooth curved surface, resulting in large light scattering loss at this connection point.

On the other hand, in the ion exchange method, Tt", Ag'".

Ions such as K+ and Ll+ are usually TlNO3°AgN
It is introduced into the substrate by electrolytic thermal diffusion in a dissolved salt of O3, KNO3, and LI2SOz. In this process, a positive electrode is placed in a dissolved salt, a negative electrode is attached to the back surface of the substrate glass, and an electric field is applied at high temperature to diffuse ions from the back surface of the substrate glass, causing an exchange reaction with Na+ in the substrate glass. cause to happen. This electrolytic thermal diffusion has the disadvantage that special care must be taken to ensure that the voltages applied to both sides of the substrate do not short through the molten salt or molten salt vapor.

Furthermore, since ion exchange utilizes the phenomenon of diffusion, it is extremely difficult to control the refractive index distribution to form a flat lens.

[Purpose of the invention]

The object of the present invention was to solve the above-mentioned problems, and it is an object of the present invention to precisely control the refractive index of the ophthalmic lens part, eliminate astigmatism, and eliminate light scattering loss at the connection point between the waveguide and the lens. The objective is to provide a method for manufacturing small lenses.

[Summary of the invention]

The structure of the present invention for achieving the above object is to provide a desired refractive index distribution on the blind plate by ion implantation. Since the present invention has the above-mentioned configuration, the flux of light incident on the lens through the waveguide is good, and the coupling efficiency of light between the waveguide and the lens is extremely good.

Ion implantation is widely applied to form a high-density layer of carriers on a substrate in the semiconductor integrated circuit manufacturing process. Examples of applying the ion implantation method to optical waveguide formation include E, GHrmire et al., Ap
pl, Phys, Lett, 21(3)87 (
1972). This is n-GaAS (100
) H+ is implanted into the surface of the substrate at a depth of 1015 cm-2 to compensate for the number of carriers in the surface layer to form a high refractive index layer and a planar optical waveguide.

In order to form a plane lens, it is necessary to precisely control the amount of ions implanted into the portion that will become the lens. In particular, in order to reduce the scattering loss of light incident on the lens and light emitted from the lens at the boundary between the plane lens and the plane optical waveguide, changes in the refractive index or the geometry of the substrate surface at this boundary are made smooth. There is a need.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail by way of examples.

Example 1 FIG. 2 schematically shows the manufacturing process of a flat lens according to the present invention. An n-type GaAs substrate (which becomes an optical integrated circuit board)
100) (Refractive index 3.4 for light with a wavelength of 1.15 μm
4. Carrier concentration 1018cm -3) 1 H+, acceleration voltage 150■, ion beam current 10μA 100
Vertical incidence was applied for 1 minute. H+ implanted into the surface of the substrate exhibited a concentration distribution with a maximum peak at a depth of 1.2 μm from the surface. The total dose of H+ is 1016 crn-2
Dechiru. The H+ particles reached a depth of about 2 μm from the substrate surface, and carriers were compensated on the substrate surface into which the H+ atoms were implanted, and a planar optical waveguide 3 of a high resistance layer was formed. 81025 was sputtered onto this substrate 1 to a thickness of DI-3μ.
Then, as shown in Figure 2 (a), the etched plate 8
I dug a bowl-shaped hole in 1025. The outer diameter of this hole is L
+=100 μmφ, and the inner diameter is R2=80 μmφ. Next, using this film 5 of 5102 as a mask, apply Hl to an accelerating voltage of 7
The ion beam was vertically incident at 5 kV with a current of 10 μA for 1000 seconds. After that, remove 5io25 and high resistance layer 3.
The refractive index distribution at a depth of 1.2 μm from the surface of the plane optical waveguide is N2 = 3.443, as shown in Figure 2(b).

Where the amount of Hl implanted was large, the refractive index changed smoothly at the boundary between the two refractive indexes Nl and N2 at Nt -3,450. This is because the opening of the mask 5 of 5i02 has a tapered shape, and the amount of H4' that passes through the thin SiO2 portion is large. When He-Ne laser beams with a wavelength of 1.15 μm are incident on this high-resistance layer 3 in parallel from three locations, the three beams that have passed through the high refractive index portion intersect at one point, and this high refractive index portion It was confirmed that the lens was a flat lens. Further, from the position where the three laser beams intersect, it was found that the focal length of this plane lens was 3.3 degrees from the center of the lens.

On the other hand, the hole in the mask 5 of 8102 in Fig. 2(a) was made into a cylindrical shape with a diameter of 90 μm instead of a tapered shape, and H+ was implanted under the same conditions as before to form a high refractive index layer that would become a lens part. It was found that the refractive index of the planar optical waveguide and the lens changes stepwise. When He--Ne laser light with a wavelength of 1.15 μm was incident on this planar optical waveguide layer, it was found that a portion of the laser light incident on the end of the lens was scattered. However, as shown in Figure 2(b), in a lens where the refractive index at the connection point between the planar optical waveguide and the lens changes gradually rather than in a step-like manner, the scattering of the laser light incident on the lens is The degree was very small.

Example 2 As in Example 1, an n-type GaAs substrate (100) (
The refractive index for light with a wavelength of 1.15 μm is 3.44, and the carrier concentration is 10" cm -3).
By vertically injecting the ion beam at 50 kV and an ion beam current of 10 μA for 100 minutes, a high resistance layer was formed on the substrate surface to serve as an optical waveguide layer having a high refractive index as well as the substrate. Next, as shown in Figure 3,
A metal W mask 5 was placed on the high resistance layer 3 so as to be in close contact with the substrate. This W mask 5 has a thickness Da=200 μm,
Diameter R3=2. A hole of Otranφ is provided, the diameter around this hole is R4-2, 4mmφ, depth D2=120
The inside has been ground down to a depth of μm. This board 1 is
While rotating the substrate 1 at 40 revolutions per minute at an angle of 10 degrees with respect to the incident direction of
I got pregnant with vertical incidence for 0 seconds. At this time, H+ is incident on the substrate 1 through the hole in the W mask 5 with an angular dispersion of θ=10 degrees, and the H+ dose distribution in the high resistance layer 3 is in the portion near the opening end of the W mask. Changes smoothly. The refractive index distribution in the cross section of the lens portion of the high resistance layer 3 changes smoothly at the refractive index difference portion, as shown in FIG. 2(b). When He-NeV-Boo light with a wavelength of 1.15 .mu.m was applied to this high resistance layer 3 in parallel from all three locations, the laser light that passed through the lens part stopped at a point 7 degrees away from the center of the lens. Next, this flat lens was heated at 450°C in an H2 atmosphere.
When annealing was performed for 30 minutes at
dB/crn. It was also found that the scattering loss at the connection point between the lens part and the optical waveguide layer connected thereto was further reduced.

This is because the damage done to the substrate surface during ion implantation was recovered by annealing.

Example 3 Imaya uses a fused silica substrate (wavelength 6328, refractive index 1.46 for human light) and deposits 30% Li+7 on the surface of the substrate.
iJJ implantation for 5 minutes at 0kv acceleration voltage, dose 10”
/ctl surface layer was formed. This has a wavelength of 632
When eight He-NeV-Boo lights were incident, the light was guided through the surface layer, and it was confirmed that a planar optical waveguide was formed on the substrate surface into which L L + 7 was implanted. Next, a tapered mask similar to that in Example 1 was formed using 5i02 on this substrate, and Li+7 was further applied at 300 kV.
A planar lens with a diameter of 200 μm was formed by implantation for 5 minutes at an accelerating voltage of . After that, the SiO2 mask was removed and He-NeV laser beams with a wavelength of 6328 people were made to enter the plane optical waveguide in parallel from three places. They intersected at a point 38 apart. Also, the transmission loss of the planar optical waveguide is 2.0 dB.
/cIn, but after annealing at 300C for 1 hour, it was reduced to 0.2 dB/cm or less.

Note that a similar planar lens could be fabricated by using a LiNbO3 substrate instead of the fused silica substrate and implanting rpj+4 ions. Furthermore, in this embodiment, a method was described in which the optical waveguide layer 3 was fabricated only by ion implantation, but after forming an optical waveguide layer with a higher refractive index than the substrate on the substrate by i'viQcVD method etc., ion implantation was performed. A flat lens may also be fabricated.

〔Effect of the invention〕

As shown in the above embodiments, according to the present invention, it is possible to produce a lens with small astigmatism and small light scattering loss at the boundary between the planar optical waveguide and the planar lens.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views showing part of the manufacturing process of a conventional plane lens, and Figure 2 (a) shows part of the manufacturing process used in an embodiment of the present invention. 8g3 is a cross-sectional view showing a part of the manufacturing process used in an embodiment of the present invention. FIG. 1...Substrate, 2...Ultrasonic transmission rod, 3...High refractive index film,

Claims (1)

[Claims] 1. A tapered mask or an inner mask is provided on the optical waveguide clay, which has a high refractive index as well as the substrate, and ions are injected from above to form a portion with a higher dose to form a flat surface. In the method of manufacturing lenses, the mask is tapered so that the change in refractive index from a region with a high ion dose to a region with a low ion dose is smooth. A method for manufacturing a flat lens, characterized by implanting ions while tilting the substrate with respect to the direction of ion incidence and rotating the substrate.