JP4279598B2 - Manufacturing method of gradient index lens - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradient index lens used in optical communication, display devices, image reading devices such as scanners, information recording devices such as optical disks, and the like.
[0002]
[Prior art]
Lenses are used in various optical fields such as optical communication and display devices. Among them, the gradient index lens has a characteristic not found in a normal homogeneous lens in which lens characteristics are determined only by the outer shape of the lens.
[0003]
As shown in FIG. 13A, the gradient index lens has a refractive index distribution 16 concentrically from the central axis 70 of the cylindrical substrate 11 toward the outer periphery, and FIG. As shown in FIG. 13B, a lens having a hemispherical refractive index distribution 26 from the surface of the planar substrate 21 to the inside, or a spherical or aspherical lens 32 as shown in FIG. In which a refractive index profile 36 is introduced.
[0004]
Hereinafter, for the sake of simplicity, the lens as shown in FIG. 13A is simply referred to as a rod-type lens, the lens as shown in FIG. 13B is referred to as a flat lens, and the lens as shown in FIG. This is called a gradient index lens. These are collectively referred to as a gradient index lens. The rod-type lens has a cylindrical shape, and since the lens surface can be made flat, it can be easily held and positioned, and has good shape matching with the optical fiber, so that it is widely used particularly in the field of optical communication. The flat lens is suitable for producing a microlens array in which a plurality of microlenses are arranged, and is suitable for an optical system that processes light in parallel.
[0005]
In any of these lenses, it is required to reduce the reflectance on the lens surface. There are the following two purposes for keeping the reflectance on the lens surface low.
One is to keep the loss (insertion loss) due to the insertion of the lens as low as possible, and the other is that the reflected light from the lens surface returns to the incident side (reflected return light, especially in the field of optical communication). To keep the negative effects of
[0006]
In order to reduce the surface reflection of a gradient index lens, a method of coating a dielectric thin film consisting of a single layer or multiple layers on the lens surface is generally used (see, for example, Patent Document 1). It is a so-called non-reflective (AR) film or antireflection film, and is used not only for gradient index lenses but also for various parts such as ordinary homogeneous curved lenses.
[0007]
This method is intended to reduce insertion loss and reflected return light. However, when it is necessary to further suppress reflected return light, the lens surface 17 of the gradient index lens 13 is formed as shown in FIG. A method of polishing obliquely with respect to the optical axis 72 and shifting the reflected light 76 from the lens surface 17 from the direction of the incident light 74 is often used (see, for example, Patent Document 2).
[0008]
This method may be used together with the antireflection film 19 as shown in FIG. As shown in FIG. 16, in the flat lens 23, the lens surface of the substrate 27, not the lens surface, is polished obliquely, so that the lens surface is inclined with respect to the optical axis, thereby reducing reflected return light. .
The method as described above has already been applied to commercially available products, and a gradient index lens having a very low reflectance on the lens surface is widely used.
[0009]
[Patent Document 1]
JP 2001-235602 A
[Patent Document 2]
JP 2001-201657 A
[0010]
[Problems to be solved by the invention]
However, the above method has the following problems.
In the antireflection film, the reflectance varies depending on the refractive index of the material to be coated. In the gradient index lens, the refractive index is literally different between the lens center and the peripheral portion in any of FIGS. 13A, 13B, and 13C. Therefore, in order to obtain a good antireflection performance over the entire surface of the lens, it is necessary to have a film configuration that can maintain the antireflection performance according to the change in the refractive index from the center portion to the peripheral portion of the lens. .
[0011]
Such a high-performance antireflection film generally has a large number of layers, so that the film formation time becomes long, and as a result, the cost of the lens increases. In addition, when an anti-reflection film with a low number of layers is used, a certain amount of surface reflection remains due to the refractive index distribution of the lens itself as described above, which is applicable to the recent high demand for low reflection. Can not.
[0012]
The antireflection film also has the following problems.
As an example of using a gradient index lens, as shown in FIG. 15, two lenses 13a and 13b are faced to each other, an optical functional component 42 such as an optical filter is sandwiched between them, and the light emitted from the optical fiber 43a is reflected. A structure is known in which an action is exerted by the optical functional component 42 and then incident on the optical fiber 43b. Such a structure may be assembled by bonding the optical fibers 43a and 43b, the lenses 13a and 13b, and the optical functional component 42 with the adhesive 30 to each other.
[0013]
As described above, the performance of the antireflection film 19 varies depending on the refractive index of the base material. However, something other than air (in this case, the adhesive 30) is present on the surface on which the antireflection film 19 is formed as shown in FIG. When in contact, the performance of the antireflection film changes depending on the refractive index of the medium in contact. For example, since the refractive index of the lens base material and the adhesive varies depending on the temperature, the antireflection performance changes accordingly. Alternatively, even when the refractive index changes due to deterioration of the lens base material or the adhesive, the antireflection performance changes correspondingly. These antireflection performance changes are still a major issue in view of the recent high demand for low reflection.
[0014]
In the prior art, it has been described that the method of obliquely polishing the lens surface of the gradient index lens is used together. However, this oblique polishing has the following problems.
Not only is the process of obliquely polishing minute parts slanted, but also the lens surface is obliquely polished, so that the mechanical central axis of the lens and the optical central axis are shifted in order to obtain good light collecting performance. When the microlens is incorporated into the optical module, the configuration becomes complicated.
[0015]
Although it is possible to arrange the components almost linearly as in the configuration of FIG. 15, the center of the optical axis and the mechanical center are slightly deviated in the lens at this time, so that they are easily affected by aberrations. Become. This leads to an increase in the required value for the component position accuracy during assembly, and as a result, increases the product cost.
[0016]
The present invention has been made to solve such problems, and an object of the present invention is to provide a gradient index lens that has little insertion loss and reflected return light and whose characteristics do not change with temperature and time. .
[0024]
[Means for Solving the Problems]
In the present invention, the gradient index lens is manufactured by the following steps.
(1) A step of applying a photoresist to the surface of the lens forming the uneven structure,
(2) exposing the photoresist in a two-dimensional periodic pattern;
(3) developing a photoresist to obtain a photoresist pattern having a two-dimensional periodic structure;
(4) a step of etching the substrate using the photoresist pattern as a mask;
It is. Expose photoresist (2) In the step, the exposure is adjusted and the pattern is changed according to the refractive index distribution of the substrate. Further, a two-dimensional periodic pattern is obtained by performing multiple exposure by rotating a periodic light intensity distribution (interference pattern) formed by causing laser light to interfere with each other a plurality of times. This laser beam interference can be performed by either separating one laser beam and then superimposing it again, or using a phase grating.
[0025]
Further, the step (1) is a step of forming a metal film, a resin film, or an inorganic dielectric film on the surface of the base material on which the concavo-convex structure is formed, and applying a photoresist on the surface. 4) Using the photoresist pattern as a mask, the metal film, the resin film, or the inorganic dielectric film is etched to transfer the photoresist pattern, and the transferred metal film, resin film, or inorganic dielectric film It is also possible to use a method in which the substrate is etched using the above pattern as a mask.
[0028]
Moreover, it is preferable to apply a dry etching process in the step (4) of etching the substrate.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[Example 1]
FIG. 1 shows an example of an embodiment of a rod-type lens according to the present invention.
A minute concavo-convex structure in which the interval (period) of convex portions adjacent to the end surface 12 of the glass rod type lens 10 having a cylindrical shape of 1 mm in diameter and decreasing in refractive index toward the outer peripheral portion is 1 μm and the height is about 1 μm. 14 is formed.
[0030]
The rod type lens 10 as shown in FIG. 1 is manufactured by the following steps. The rod-type lens used here is manufactured by a so-called ion exchange method in which a homogeneous cylindrical glass is immersed in a molten salt to exchange ions in the glass and ions in the molten salt. The refractive index is distributed by gradually changing the ion concentration from the outer surface to the inside.
[0031]
A rod-type lens (hereinafter simply referred to as a lens) is cut to a predetermined length, and both end faces are optically polished. This lens was subjected to ultrasonic cleaning in an organic solvent to remove dirt and dust adhering to the end face. Next, a photoresist was applied to the end face of the lens by spin coating so as to have a thickness of about 1 μm. A positive resist THMR-iP3650 (manufactured by Tokyo Ohka) was used as the resist. After pre-baking in a thermostatic bath, patterning to the photoresist was performed by interference exposure.
[0032]
The interference optical system shown in FIG. 12 was used for the interference exposure. The light source 125 is a He-Cd laser (wavelength 325 nm, output about 20 mW). The light beam 222 emitted by the light source 125 is split by the beam splitter 134 so that the output ratio is 1: 1, and after passing through different optical paths, it is overlapped again. Match. The lens 110 coated with the resist is placed on a portion where the light beams overlap, and an interference pattern is formed on the end face. In order to form such an optical path, the direction of the light beam is changed using the mirrors 132, 136, and 138. Further, a filter 144 was inserted in the optical path before the division so that an appropriate exposure amount was obtained, and the exposure time was set by the shutter 142 and adjusted.
[0033]
The period Λ of the interference pattern is well known when the angle between the two beams is θ.
Λ = λ / 2sin (θ / 2)
It becomes. Where λ is the wavelength of the light source used (325 nm in this embodiment). Since the period to be manufactured is 1 μm, θ = 20.4 degrees was set. Of course, it is also possible to perform interference exposure with a different period, and by adjusting the wavelength λ or the beam angle θ of the laser light, an arbitrary period can be set within a range satisfying the above relational expression.
[0034]
As the light source, any laser having an output energy capable of exposing the photoresist, such as a gas laser such as an Ar laser or a solid laser such as a YAG laser, can be used.
[0035]
Further, in this embodiment, the photoresist is exposed by the interference optical system that separates one laser beam and then superimposes it again, but other than this, the method using the phase grating is the same as in this embodiment. Interference exposure can be performed. The phase grating is a kind of light transmission type diffraction grating, and is designed so that the 0th-order diffracted light becomes very small with respect to a specific wavelength. Thus, an interference pattern is formed immediately below the phase grating.
[0036]
The reason why the interference exposure is used here is that the structure is simple and the exposure is performed in a short period, but other than that, a reduction projection type exposure machine or the like can also be used for this purpose. Further, although it takes a long time to draw, an electron beam drawing apparatus can be used for the exposure for this purpose. Of course, it goes without saying that the type of photoresist changes depending on the type of exposure apparatus used.
[0037]
In the above-described interference exposure system, since exposure is performed only in a striped (one-dimensional) periodic pattern, in order to perform two-dimensional exposure, it is necessary to repeat this multiple times to perform multiple exposure. In the case of this example, after performing the first exposure, the lens was rotated 90 degrees, and the second exposure was performed to obtain an exposure pattern arranged in a square lattice pattern. Of course, multiple exposures can be performed three or more times. For example, in the case of triple exposure, if the substrate is rotated by 60 degrees for each exposure, a hexagonal densely exposed pattern can be obtained.
[0038]
After performing the exposure as described above, post-baking is performed, and further, the resist in the exposed portion is removed using NMD-3 developer (manufactured by Tokyo Ohka Kogyo Co., Ltd.), as shown in FIG. A photoresist pattern 15 was obtained.
[0039]
Next, using this photoresist pattern 15 as a mask, ICP (inductively coupled plasma) dry etching was performed to transfer the photoresist pattern onto the lens substrate surface 12. At this time, irregularities having various shapes can be formed by adjusting manufacturing conditions such as power, gas, and pressure to be supplied to the ICP device. FIG. 3 is a schematic view when the produced concavo-convex structure is observed with an electron microscope. By controlling the process conditions, the speed at which the etching proceeds perpendicularly to the lens surface and the speed at which the etching proceeds in the lateral direction were adjusted, and a conical convex structure 18 having a spherical top was obtained.
[0040]
If other process conditions are used, a cylindrical shape or a pointed cone-shaped structure can be formed. For the purpose of suppressing loss by reducing reflection at the lens end surface, which is an object of the present invention, it is necessary that the cross-sectional area of the shape of the minute protrusions decreases monotonously from the bottom surface toward the apex. A desirable form is a cone, but it may be any one of a cone, a polygonal pyramid, a truncated cone (cone whose apex is cut horizontally), a truncated pyramid, and the like. Furthermore, the hypotenuses of these cones may be curved or stepped, or the tops of the cones may be curved as shown in FIG.
[0041]
In this embodiment, ICP dry etching is used, but various other methods can be used for etching using a photoresist pattern as a mask. For example, other dry etching processes such as ECR plasma, and wet etching can be used depending on the type of lens substrate.
[0042]
In this embodiment, the method of etching the lens base material using the photoresist applied to the lens end face as a mask has been described, but other than that, a metal film such as Cr, a resin film, or an inorganic dielectric is used on the lens end face. After the body film is formed, a photoresist is applied thereon, a pattern is formed by interference exposure, the pattern is transferred to the film by etching, and then the substrate is etched using the film as a mask. In particular, when patterning a glass substrate by wet etching with an acid, it is generally performed by using a thin film made of Cr or a compound thereof as a mask. It can also be applied to the production of
[0043]
In addition, since the shape of the fine unevenness | corrugation formed of course changes with each etching method and process conditions, it is necessary to examine process conditions so that a desired uneven | corrugated shape can be obtained about each method.
[0044]
In this embodiment, the resist formed on the surface is also etched at the same time during ICP etching, so that the resist is not removed after fabrication. However, if there is a resist residue, cleaning with an organic solvent or oxygen plasma is performed. Residue residue can be removed by ashing. In the case where the etching process is performed using a metal film or the like as a mask, the residue of the mask is removed with an etching solution or the like after the etching process.
[0045]
FIG. 4 shows a schematic diagram of a reflection loss measuring apparatus for a gradient index lens manufactured by this method. The light source 120 is a laser diode having an emission wavelength of 1550 nm, and the length of the rod-type lens 110 is adjusted so that the light emitted from the single mode optical fiber 140 is emitted as almost parallel light 220 as shown in the figure. Has been. First, before attaching the lens, the light intensity is measured by the power meter 130 at the exit of the optical fiber (this is defined as Iin), and then the amount of light (Iout) transmitted through the lens is measured after the lens 110 is attached.
[0046]
The transmittance T of the lens is
T = Iout / Iin
Therefore, if the absorption loss and the scattering loss in the lens are small, the reflectance R at the lens end surface is combined with the incident side and the output side.
R = 1-T
It can ask for.
[0047]
With this apparatus, first, the reflectance of the end surface of the gradient index rod lens before the minute unevenness was formed on the end surface was measured and found to be about 7%. Note that the refractive index distribution type lens used here is not formed with an antireflection film made of a normal dielectric thin film.
[0048]
Next, when the refractive index distribution type rod lens of the present invention having the uneven structure described in this example formed on both surfaces of the lens (shown in FIG. 1) was attached and the reflectance was measured, it was 1%. The following values were obtained, and it was confirmed that reflection at the lens end face was clearly suppressed. This numerical value changes depending on the shape of the concavo-convex structure, and the reflectance can be further reduced by changing the process conditions and optimizing the shape.
[0049]
[Example 2]
Next, an example in which the present invention is applied to a gradient index lens formed on a flat substrate, that is, a flat lens will be described.
FIG. 5 shows a flat lens 20 of the present invention. Similar to the first embodiment, a minute concavo-convex structure 24 having a period of 1 μm and a height of about 1 μm is formed on the lens surface 22 on the surface of the substrate 28.
[0050]
For example, when a glass substrate is used, the flat lens 20 is formed by forming a metal mask having a minute opening on the substrate and diffusing ions in the salt from the opening by an ion exchange treatment. . Although the size of the refractive index distribution on the lens surface is smaller than that of the first embodiment, it is produced by the ion exchange method as described above, and therefore has a refractive index distribution on the lens surface.
[0051]
By the same method as in Example 1, a micro uneven structure having a period of 1 μm and a height of about 1 μm is periodically formed on the surface of the flat lens, and the reflectance of this lens is measured by the same measuring apparatus as in FIG. When measured, the reflectivity was about 3.5%. In this embodiment, since the surface 26 opposite to the surface on which the lens of the flat plate lens is formed is not subjected to the low reflection treatment, reflection loss occurs in that portion. Needless to say, the surface can be subjected to a low reflection treatment with a normal dielectric multilayer film, and in some cases, a micro uneven structure similar to the lens surface of the present invention is formed to make the low reflection treatment. You can also. In that case, since there is almost no reflection on the surface, a reflectance comparable to that of Example 1, that is, a reflectance of 1% or less can be easily realized.
[0052]
From Examples 1 and 2 described above, an excellent antireflection performance can be obtained by using a micro uneven structure having a spacing (period) of adjacent convex portions of 1 μm and a height of about 1 μm with respect to the use wavelength λ = 1550 nm. It became clear. The reflection performance varies depending on the period and height of the concavo-convex structure. If the period, that is, the interval between adjacent convex parts is larger than λ, and if the concavo-convex height is smaller than λ / 4 (0.25λ), The interaction of the concavo-convex structure is reduced, and sufficient antireflection performance cannot be obtained. In Examples 1 and 2, a structure having both a period and a height of about 0.64λ was used. However, a structure having a period, that is, an interval between adjacent convex portions of λ or less and a height of 0.25λ or more is desirable.
[0053]
In Example 1, the low reflection performance is slightly changed depending on the shape of the protrusions to be manufactured. Here, some examples of the shape of the concavo-convex structure manufactured by the present inventor will be further described. .
FIG. 6 is a schematic view of the cross-sectional shape of the concavo-convex structure produced by changing the dry etching conditions.
By adjusting the speed at which etching proceeds in the vertical direction and the speed at which etching proceeds in the horizontal direction, uneven structures having various cross-sectional shapes ((a) to (d)) are formed.
[0054]
FIG. 7 shows an example in which a concavo-convex structure is formed on the end face of a glass gradient index lens by wet etching. In this case, since the etching proceeds isotropically, the period of the two-dimensional structure cannot be reduced and the height of the protrusion cannot be increased. Therefore, it is difficult to obtain a sufficiently low reflection performance, but there is an advantage in that the manufacturing cost is low, and it can be applied to an application that does not require a high level of low reflection performance.
[0055]
The shape conditions for obtaining the low reflection performance are also described in, for example, Japanese Patent Laid-Open No. 2000-258607 and the literature included therein. It is desirable that the minute concavo-convex structure formed on the end face of the gradient index lens of the present invention also has a shape as described therein.
In particular, it is desirable that the shape of the concavo-convex structure is substantially dense in the vicinity of the substrate (that is, the concave portion has no flat portion when viewed from the upper surface of the surface on which the concavo-convex structure is formed).
[0056]
By the way, not only the shape of the concavo-convex structure changes depending on the etching conditions as described above, but the shape of the concavo-convex structure to be produced also changes depending on the photoresist pattern before etching. FIG. 8 is a schematic diagram of the fine structure of the lens surface after etching with the photoresist pattern and the same conditions obtained when the light intensity or exposure time during interference exposure is changed, that is, when the exposure amount is changed. The figure is shown.
[0057]
In the case of a positive type photoresist, when the exposure amount is small, the pattern is such that a circular opening 56 is opened in the photoresist film 55 as shown in FIG. As shown, a pattern is obtained in which the unexposed portion of the photoresist film 65 remains in a circular shape, and the rest of the photoresist film 65 has no photoresist film. When each is etched, in the case of (a), it becomes a lattice-like fine structure, and in the case of (b), it becomes a fine structure of a cone or frustoconical shape.
[0058]
When the above effect is used at the time of interference exposure, for example, a pattern whose shape changes toward the outer peripheral direction of the end surface of the rod-type lens 10 can be formed. FIG. 9 shows an irradiation optical system used at that time.
The lens is adjusted so that the light beams 78a and 78b of the interference optical system have light intensity distributions 80a and 80b in the cross section. When they are made to interfere with each other, a similar light intensity distribution 82 is formed. Where the light overlaps, each light is an ellipse, but a pattern whose shape changes isotropically from the center of the lens 10 toward the outer periphery is obtained.
[0059]
FIG. 10 shows another example of a method for producing such a pattern. In this example, after performing interference exposure by the same method as in the first embodiment, the third light beam 78c is irradiated almost from the front of the exposure surface, and the light intensity distribution 80c is provided in the beam, thereby exposing the exposure amount. Adjust.
[0060]
The above method can be used effectively when the etching rate of the gradient index lens changes depending on the refractive index (or ion concentration). In dry etching, it is generally known that the etching rate varies depending on the size of the opening of the mask. However, etching is performed after forming patterns with different opening sizes on the lens end face by the method described above. If the treatment is performed, irregularities having substantially the same shape can be formed in portions having different refractive indexes (that is, different etching rates). Alternatively, it is possible to adjust such that the height of the protrusion is increased at the central portion of the rod-type lens and is decreased at the peripheral portion.
[0061]
In applications where it is necessary that the wavefront after the light passes through the lens is not disturbed, shape control as described above is particularly important. The above shape control method is effectively applied in such a case.
[0062]
In the embodiments described so far, the antireflection performance in the case where the surface of the refractive index separating lens is in contact with air has been described. However, the lens of the present invention exhibits the same effect even in a medium other than air.
[0063]
As shown in FIG. 15, the rod-type lens may be used in a configuration in which two lenses 13a and 13b are combined and an optical functional component 42 such as a filter is inserted between them. Conventionally, as shown in FIG. 15, an antireflection film 19 made of a dielectric multilayer film is provided in this portion, and the refractive index of the adhesive 30 is matched to the lens material to reduce reflection loss. In this case, the problem is temperature characteristics or refractive index change with time.
[0064]
As shown in FIG. 17, an optical axis (Z-axis) with a refractive index n when antireflection films 19 a and 19 b are provided on the surfaces of two lenses 10 a and 10 b and a component 40 is sandwiched between them and adhered by an adhesive 30. This will be described using a direction profile. Immediately after the assembly, the refractive index of the lens and the refractive index of the adhesive can be matched exactly as shown by the solid line, so that the refractive index difference Δn ₀ By providing the antireflection films 19a and 19b between the lenses 10a and 10b and the adhesive 30, the reflection loss can be suppressed to a considerably small value.
[0065]
However, when the refractive index of the adhesive or the lens shifts as shown by the broken line due to temperature change or change with time, reflection occurs at the interface. The refractive index difference Δn between the lenses 10a, 10b and the adhesive 30 is also the initial Δn. ₀ Δn ₀ In some cases, the antireflection performance of the antireflection film designed for the difference in refractive index is lowered.
[0066]
In the refractive index separating lens of the present invention, as shown in FIG. 11, fine concavo-convex structures 14a and 14b are provided on the surfaces of two lenses 10a and 10b. Since a medium outside the lens (in this case, an adhesive) enters the gap of the concavo-convex structure, the refractive index is continuously connected between the lens and the medium macroscopically through the concavo-convex structure. In addition, low reflection performance is realized by the concave and convex structure using the same material as the material of each part of the lens surface, that is, the lens surface, so that the refractive index of the adhesive and the lens is shifted as in the conventional method described above. However, since the change between the lens and the adhesive is always kept continuous, there is no performance degradation.
[0067]
This is a function that can be realized by the characteristic that low reflection performance can be maintained regardless of the refractive index of the medium between the lenses, and is one of the major features of the gradient index lens of the present invention. According to this feature, when assembling a component as shown in FIG. 15, it is not necessary to strictly match the refractive index of the adhesive to that of the lens, so that there are significant industrial advantages such as labor saving in chemical solution management.
[0068]
【The invention's effect】
In the refractive index distribution type lens of the present invention, low reflection performance is realized by the micro uneven structure formed on the surface, so that the performance does not change due to the change of the refractive index of the substrate unlike the multilayer antireflection coating. As a result, good low reflection performance can be realized over the entire lens having a refractive index distribution.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a rod-type lens having an uneven surface according to the present invention formed on its end surface.
FIG. 2 is a view showing an example of a photoresist pattern used for producing the concavo-convex structure of the present invention.
FIG. 3 is a schematic diagram showing a concavo-convex structure formed on a lens end face in the present invention.
FIG. 4 is a diagram showing a configuration of an optical system for measuring reflectance from a lens end surface.
FIG. 5 is a schematic cross-sectional view of a flat lens in which the uneven structure of the present invention is formed on a light transmission surface.
FIG. 6 is a schematic cross-sectional view of various uneven structures.
FIG. 7 is a schematic cross-sectional view of another concavo-convex structure.
FIG. 8 is a schematic diagram of a photoresist pattern and a fine structure of a lens surface after processing.
FIG. 9 is a diagram showing an example of interference exposure applied to the present invention.
FIG. 10 is a diagram showing an example of another interference exposure applied to the present invention.
FIG. 11 is a schematic diagram showing a configuration and a refractive index distribution in the optical axis direction when the gradient index lenses of the present invention are opposed to each other.
FIG. 12 is a diagram showing a configuration of an optical system for two-beam interference exposure.
FIG. 13 is a schematic diagram showing a cross-sectional shape of a conventional gradient index lens.
FIG. 14 is a diagram showing an example of antireflection means for a rod-type lens by conventional oblique processing.
FIG. 15 is a schematic view showing an example of a conventional optical module using rod-type lenses facing each other.
FIG. 16 is a diagram showing an example of antireflection means for a flat lens by conventional oblique processing.
FIG. 17 is a schematic diagram showing a configuration of a conventional optical module using rod lenses facing each other and a refractive index distribution in the optical axis direction.
[Explanation of symbols]
10, 10a, 10b, 13, 13a, 13b, 110 Rod type lens
14, 14a, 14b, 24 Uneven structure
16, 26, 36 Refractive index distribution
19, 19a, 19b Antireflection film
20, 23 Flat lens
30 Adhesive
32 Axial gradient index lens
40, 42 Optical functional parts
43a, 43b Optical fiber
70, 72, 73 Optical axis

Claims (5)

In the manufacturing method of the gradient index lens, as a step of forming a minute uneven structure in the light transmission surface of the lens,
(1) applying a photoresist to the surface of the lens forming the concavo-convex structure;
(2) exposing the photoresist in a two-dimensional periodic pattern;
(3) developing a photoresist to obtain a photoresist pattern having a two-dimensional periodic structure;
(4) Etching the substrate using this photoresist pattern as a mask;
Including
In the step (2) of exposing the photoresist, the exposure amount is adjusted, and the pattern is changed according to the refractive index distribution of the base material. In the manufacturing method of the gradient index lens, as a step of forming a minute uneven structure in the light transmission surface of the lens,
(1) applying a photoresist to the surface of the lens forming the concavo-convex structure;
(2) exposing the photoresist in a two-dimensional periodic pattern;
(3) developing a photoresist to obtain a photoresist pattern having a two-dimensional periodic structure;
(4) Etching the substrate using this photoresist pattern as a mask;
Including
In the step of exposing the photoresist (2), a two-dimensional periodic patterns, and periodic light intensity distribution formed by the interference of the laser beam (interference pattern) is rotated a plurality of times, the multiple exposure A method for producing a gradient index lens, characterized by being obtained by performing the method.   3. The refractive index distribution type according to claim 2, wherein the interference of the laser beam is performed by any one of a method of superposing again after separating one laser beam, or a method of using a phase grating. Lens manufacturing method.   The step (1) is a step of forming a metal film, a resin film, or an inorganic dielectric film on the surface portion of the base material on which the concavo-convex structure is formed, and applying a photoresist to the surface. Etching the metal film, resin film, or inorganic dielectric film using the photoresist pattern as a mask to transfer the photoresist pattern, and masking the transferred metal film, resin film, or inorganic dielectric film pattern The method for producing a gradient index lens according to any one of claims 1 to 3, wherein a step of etching the substrate is used.   The method for manufacturing a gradient index lens according to claim 1, wherein a dry etching process is applied in the step (4) of etching the base material.

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