JPH0723922B2 - Flat micro lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a flat plate microlens in which a lens is integrally embedded in a transparent substrate by ion exchange or the like.

[Conventional technology]

[Prior Art] A flat microlens is an optical element in which a small lens portion having a refractive index gradient is embedded and formed in a transparent substrate having a flat surface. A lens in which a large number of minute lenses are arranged in a precise positional relationship Arrays are easy to fabricate, and because they have a flat plate shape, it is easy to assemble an optical system. Since they have many excellent characteristics compared to conventional spherical lenses, their applications are rapidly expanding.

When the above-mentioned flat plate microlens is manufactured using glass as a base material, the following method is generally used.

First, the glass substrate surface is covered with a metal coating mask for preventing ion permeation, and openings are formed in this mask with a predetermined lens shape and arrangement pattern, and ions for increasing the refractive index of the substrate glass are diffused into the substrate through the openings.

For example, a high temperature molten salt containing the above ions is brought into contact with the mask surface of the substrate, and the ions in the molten salt are diffused into the glass by utilizing the ion exchange between the ions in the molten salt and the ions in the glass. Let After this, if the mask is removed, a gradient index lens with a substantially semi-circular cross section having a distribution in which the refractive index is concentrically reduced toward the deepest and lateral sides at the maximum just below the mask opening is formed in the glass substrate. It is formed.

[Problems to be solved by the invention]

After removing the ion permeation preventive mask by the method described above, it is necessary to polish the substrate surface to adjust the focal length of the lens to a desired value, especially in the case of a micro-aperture lens with a diameter of about 200 μm or less. Polishing amount is several μm in the process
There is a problem in that precise initial focus control is extremely difficult because it must be controlled as follows.

[Means for solving problems]

It consists of a region on one surface of the glass substrate, the cross section of which is approximately semicircular by the ion exchange method, and the refractive index of which is maximum at the center of the semicircle and gradually decreases as the distance from the center increases. In a flat plate microlens having a lens part embedded therein, a light shielding tank is provided only on the substrate surface other than the lens part on the lens part formation surface side, and the lens is formed on the substrate surface on the lens part formation surface side. A transparent coating for adjusting the focal length of the lens and protecting the lens surface is provided in contact with the lens surface in the lens portion and laminated on the light shielding layer in the other portion, and the surface of the coating is smooth. To do.

[Work]

According to the above structure, the focal length of the lens embedded in the substrate can be finely adjusted by appropriately selecting the refractive index and the film thickness of the transparent coating.

Since the thickness of the above-mentioned coating can be precisely controlled by using a well-known thin film forming technique such as spin coating, vapor deposition, and sputtering, it is more accurate and stable as compared with the conventional case where the substrate surface is polished. Optical characteristics can be obtained. Further, the transparent film can protect the lens surface exposed on the substrate surface from deterioration or damage.

Further, since the surface of the substrate other than the lens portion is covered with the light-shielding layer, the light that does not contribute to the image formation that passes through the substrate part other than the lens portion is blocked, and a clear image with good contrast can be obtained.

〔Example〕

The present invention will be described below in detail based on the embodiments shown in the drawings.

In FIG. 1, a flat plate microlens 10 has a refractive index gradient lens 12 having a substantially semicircular cross section within the thickness of a transparent glass substrate 11.
A large number of ...... are embedded and formed at intervals.

The lens 12 has one lens surface 12A on the substrate surface 11A, and has a distribution in which the refractive index is maximum on the substrate surface and gradually decreases concentrically toward the deep portion. The surface of the substrate other than the lens surface 12A is covered with a light-shielding layer 13 for blocking transmitted light other than the lens portion, and the lens surface 12A exposed on the surface of the substrate is covered with a transparent film 14. . The transparent coating 14 is preferably excellent in weather resistance, and can be formed of a synthetic resin such as a silicone resin or a polyimide resin, or an inorganic material such as glass.

The transparent coating 14 corrects the shape when the lens surface 12A is not completely flat (for example, the bulging deformation associated with ion exchange) and refracts the incident light beam.
The focal length of the lens 12 changes depending on the refractive index of 14. Further, the coating film 14 can prevent the lens surface 12A from being deteriorated and scratched.

When the light-shielding layer 13 is provided around the lens portion as in the illustrated example, providing the transparent coating 14 on the light-shielding layer 13 also protects the light-shielding layer 13, and also only the lens portion is manufactured. It is easier than limited formation.

Next, the manufacturing method will be described with reference to FIGS.

First, as shown in FIG. 2, a borosilicate glass substrate 11 containing exchangeable ions such as Na ions and K ions is prepared, and the upper and lower surfaces of the substrate 11 are finished parallel and flat.

Next, as an example, Ti or Cr is formed with a film thickness of about 2 μm by a high frequency sputtering method on the surface of the substrate, and then an opening 16 is provided using a well-known photolithography technique to form an ion permeation preventive mask 15. The opening 16 has a shape similar to the planar shape of the lens to be obtained, such as a circle or a line, and is sufficiently smaller than the lens diameter.

Next, as shown in FIG. 3 and FIG. 4, the mask surface side of the substrate 11 is dipped in a molten salt 17 that is held at a high temperature and contains ions that increase the refractive index of the substrate glass, for example, Tl ions,
By natural diffusion (Fig. 3) or electric field application diffusion (Fig. 4) that applies an electric field between both sides of the substrate, the ions in the molten salt pass through the mask opening 16 and are exchanged with the ions in the glass to enter the substrate. Spread.

By the above ion diffusion treatment, a lens 12 having a substantially semicircular cross section having a refractive index gradient according to the concentration distribution of ions diffused and penetrated into the glass is formed in the substrate 11 as shown in FIG.

Next, the substrate 11 is taken out of the molten salt bath and washed, and the mask 15 is removed by etching. Then, the substrate surface other than the lens portion 12 is covered with the light shielding layer 13 by using a photolithography technique.
Cover with.

For example, 0.2μ of Cr or Ti by high frequency sputtering method
After adhering to the substrate surface with a film thickness of about m, the lens part 12 is aligned with a mask alignment device with high precision using the photolithography technique, and after exposure / phenomenon, it is almost the same as the lens part 12. An opening 17 having a size is provided and the rest is used as the light shielding layer 13.

Next, a portion of the light-shielding layer 13 is laminated on the light-shielding layer 13, and the lens portion 12 is covered with the transparent coating 14 in contact with the substrate surface. The transparent film 18 is formed by applying, for example, silicon resin by spin coating so that the film thickness is about 10 μm.

Specific numerical examples are shown below.

Example: The surface of a soda-lime glass substrate with a thickness of 5 mm is covered with a mask film with a circular opening with a diameter of 0.1 mm, and Tl ₂ SO ₄ : ZnSO ₄ = 6
When the mask is removed after immersion in 0:40 mol% mixed molten salt at 490 ° C for about 120 hours and ion exchange, the gradient index lens with a diameter of about 200 μm on the substrate surface Had been formed.

The focal length of the above lens was measured and found to be 310 μm.

Next, a commercially available silicone resin with a refractive index of 1.40 (KR112 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the lens surface on the substrate surface by spin coating at 2000 rpm for 60 seconds to form a transparent film with a thickness of 10 μm. After that, the focal length was measured to be 560 μm, which was largely different from the focal length before the resin film was provided of 310 μm, and it was confirmed that the desired lens focal length was almost satisfied.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIGS. 2 to 6 show an example of a method for manufacturing a flat plate microlens of the present invention, and FIG. 2 is a substrate on which an ion permeation preventive mask is formed. FIG. 3 is a sectional view showing an ion exchange treatment by natural diffusion, FIG. 4 is a sectional view showing an electric field application ion exchange treatment, and FIG. 5 is a refractive index gradient lens formed by the ion exchange treatment. FIG. 6 is a cross-sectional view showing the formed state, and FIG. 6 is a cross-sectional view showing the state in which a light shielding layer and a transparent coating are provided on the above substrate. 10 …… Flat microlens, 11 …… Substrate 12 …… Gradient index lens, 12A …… Lens surface 13 …… Light blocking layer, 14 …… Transparent coating 15 …… Mask, 16 …… Opening, 17 …… Melting salt

Claims (1)

[Claims] 1. A refractive index distribution in which the cross section is substantially semicircular on one surface of a glass substrate by an ion exchange method, and the refractive index is maximum at the center of the semicircle and gradually decreases as the distance from the center increases. The lens part consisting of the area with
In the embedded flat plate microlens, a light shielding tank is provided only on the substrate surface other than the lens portion on the lens portion forming surface side, and the focal length of the lens is further provided on the substrate surface on the lens portion forming surface side. A transparent coating for adjusting and protecting the lens surface is provided in contact with the lens surface in the lens portion and laminated on the light shielding layer in the other portion, and the surface of the coating is smooth. A flat plate micro lens.