JP2002311212A - Working method for lens having distribution of refractive index in optical axis direction, lens having distribution of refractive index in optical axis direction produced by the method, and collimator using the lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a working method for a lens having distribution of refractive index in an optical axis direction, with which the dispersion of optical performance, especially, of spherical aberration is reduced, and to provide a collimator, with which satisfactory optical performance can be provided by reducing an insertion loss even when an inter-lens distance is changed over a wide range. SOLUTION: In a working method for a lens having distribution of refractive index in an optical axis direction, the lens having spherical surface of a curvature radius (r) on one end face side is formed from a substrate 11 (figure 1 (a)) having the distribution of refractive index different depending on depth positions in the direction of optical axis from one end face 11a, and the side of one end face 11a for each of samples 181 -185 produced from the substrate 11 is ground or polished so that each of stock removal ΔZ1 -ΔZ5 from one end face 11a can be different step by step. The surface refractive index of the end face of each sample produced by grinding is measured. On the basis of this measured result, the refractive index distribution of the substrate 11 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a refractive index distribution type lens in the optical axis direction used as a collimator lens in the field of optical communication and the like, and a collimator using a lens manufactured by the method.

[Detailed Description of the Invention]

[0003]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a refractive index distribution type lens in the optical axis direction used as a collimator lens in the field of optical communication and the like, and a collimator using a lens manufactured by the method.

[0004]

2. Description of the Related Art As a conventional collimator used in the field of optical communication, for example, light emitted from a single-mode optical fiber on the incident side is made parallel by a collimator lens, and this parallel light is collected by another collimator lens. A configuration in which light is coupled to a single-mode optical fiber or the like on the light receiving side is known. In such a collimator, an optical functional element (for example, an optical filter, an optical isolator, an optical switch, an optical modulator, etc.) is inserted between the two collimator lenses, so that the light propagating through the single-mode optical fiber on the incident side. After having a predetermined effect on the single mode optical fiber on the light receiving side.

As such a collimator lens (collimator lens), a uniform spherical lens or a uniform aspheric lens having a uniform refractive index, a radius having a refractive index distribution having a different refractive index depending on a radial position perpendicular to the optical axis. A directional refractive index distribution type rod lens and an optical axis direction refractive index distribution type lens having a refractive index distribution having a different refractive index depending on the position in the optical axis direction can be used.

[0006]

However, a collimator lens used in the field of optical communication and the like is required to have small spherical aberration and the like. Therefore, when each of the above lenses is used as a collimator lens in an optical communication field or the like, there are the following problems.

(1) In the above-mentioned homogeneous spherical lens, it is necessary to use a combination lens composed of a plurality of homogeneous spherical lenses in order to correct spherical aberration. In this case, the design and assembly of the combination lens become complicated.

(2) The above-mentioned homogeneous aspherical lens can be designed to minimize spherical aberration with a single lens. But,
Generally, since a homogeneous aspherical lens is manufactured by press molding, changing the shape of the lens requires a change in a mold, which increases the manufacturing cost.

(3) In the radial gradient index rod lens, the spherical aberration can be corrected to some extent by changing the refractive index distribution shape. In addition, since the rod lens has a cylindrical shape centered on the optical axis, it has good matching with an optical fiber or the like. However, when the end surface of the rod lens is a plane perpendicular to the optical axis, reflected return light to an optical fiber or the like is easily generated. If the end face is processed obliquely in order to reduce the reflected return light, the aberration will increase, the performance will decrease, and the manufacturing cost will increase.

(4) The refractive index distribution type lens in the optical axis direction has a spherical surface on at least one end surface side. In this lens, spherical aberration can be corrected even with a single lens by changing the refractive index distribution shape. The characteristics of the lens are determined by both the refractive index distribution formed by ion exchange and the like and the processing state of the spherical surface. However, this lens is made of a substrate having the above-mentioned refractive index distribution on one end surface side, but it is not known how far the substrate should be cut from the one end surface side to minimize the wavefront aberration. Therefore, as shown in FIG. 9, the dispersion of the optical performance, particularly the spherical aberration, becomes large.

The present invention has been made in view of such a conventional problem, and an object thereof is to provide a method of processing a refractive index distribution type lens in an optical axis direction with little variation in optical performance, particularly spherical aberration. It is in. Another object of the present invention is to provide a gradient index lens in the optical axis direction with little variation in optical performance, particularly spherical aberration. Still another object of the present invention is to provide a collimator which has a small insertion loss even when the distance between lenses is changed in a wide range, and which can obtain good optical performance.

[0012]

Means for Solving the Problems To solve the above problems, the invention according to claim 1 is based on a transparent substrate having a refractive index distribution having a different refractive index depending on a depth position from one end face in an optical axis direction. A method of processing an optical axis direction gradient index lens to produce at least one optical axis direction gradient index lens having at least one end surface having a spherical surface with a radius of curvature r, wherein the measured value of the refractive index distribution is measured. The gist is to process the lens based on.

According to this configuration, since the lens is processed based on the actually measured value of the refractive index distribution, it is possible to determine from the actually measured value how far the substrate should be cut from one end surface side to minimize the wavefront aberration. For this reason, it is possible to grind the one end surface side of the substrate with the aim of the shaving amount at which the wavefront aberration is minimized, and it is possible to manufacture a refractive index distribution type lens with small variations in optical performance, particularly spherical aberration.

According to a second aspect of the present invention, in the method of processing a refractive index distribution type lens in the optical axis direction according to the first aspect, based on the actually measured value of the refractive index distribution, the one end face where the wavefront aberration is minimized. Of optimal cutting amount ΔZm and optimal cutting amount ΔZ
Determine the surface refractive index n _t when shaving by m, based on this surface refractive index n _t , a preset numerical aperture NA, and a preset effective diameter De of the lens or the radius of curvature r, The gist is to determine the radius of curvature r or the effective diameter De.

According to this configuration, based on the actually measured value of the refractive index distribution, the optimum shaving amount Δ from one end face where the wavefront aberration is minimized.
Since Zm is obtained, it is possible to grind one end surface side of the substrate with the aim of the same shaving amount ΔZm. This makes it possible to manufacture a refractive index distribution type lens in the optical axis direction with a small variation in wavefront aberration from the substrate.

The radius of curvature is determined based on the surface refractive index n _t obtained by cutting by the optimum shaving amount ΔZm, the preset numerical aperture NA, and the preset effective diameter De of the lens or the radius of curvature r. r or the effective diameter De can be determined. Therefore, by giving the numerical aperture NA as a design parameter and the effective diameter De or the radius of curvature r of the lens, in addition to the optimum shaving amount ΔZm as a processing parameter,
The effective diameter De or the radius of curvature r is obtained. Thus, a refractive index distribution type lens in the optical axis direction having at least one spherical surface on one end surface side can be easily manufactured from the substrate.

According to a third aspect of the present invention, in the method of processing a refractive index distribution type lens in the optical axis direction according to the first or second aspect, the optimum shaving amount ΔZm in which the wavefront aberration is minimized.
Is the following polynomial n (Z) = n ₀ + n ₁ Z + n ₂ Z ² + · representing the refractive index n (Z) at each depth position Z in the optical axis direction having a different shaving amount ΔZ. .. (where n ₀
Is the refractive index at the position of ΔZ = 0, n ₁ is the distribution constant of the first-order term, and n ₂ is the distribution constant of the second-order term. ) To obtain the refractive index distribution and obtain the wavefront aberration based on the refractive index distribution as a function of the shaved amount ΔZ from the one end face.

According to this configuration, the refractive index distribution of the substrate can be accurately known by applying the measured value to the polynomial. At this time, the refractive index distribution of the substrate is ideally represented by a linear distribution (up to the first order term), but the refractive index distribution actually formed by the ion exchange method deviates from the linear distribution. It can be corrected by higher order terms.

Further, based on the refractive index distribution thus obtained, the wavefront aberration can be obtained as a function of the shaved amount ΔZ from the one end face. This calculation is performed using optical simulation software. Further, the shaving amount ΔZm that minimizes the wavefront aberration can be obtained from the function.

According to a fourth aspect of the present invention, in the method of processing a refractive index distribution type lens in the optical axis direction according to any one of the first to third aspects, one end surface of the substrate is moved from the one end surface. The point is that the actual measured value of the refractive index distribution is obtained by grinding or polishing while gradually changing the shaving amount ΔZ in the optical axis direction and measuring the surface refractive index of each end surface having the different depth position. And

According to this configuration, the one end surface of the substrate is ground or polished by gradually changing the shaving amount ΔZ in the optical axis direction, and the surface refractive index of each end surface having the different depth position is measured. Therefore, an accurate refractive index distribution of the substrate can be obtained based on the measurement result. This makes it possible to manufacture a refractive index distribution type lens with small variations in optical performance, particularly spherical aberration, in the optical axis direction.

According to a fifth aspect of the present invention, in the method of processing a refractive index distribution type lens in the optical axis direction according to the fourth aspect, when measuring the surface refractive index of each end face, the substrate is moved in the optical axis direction. Each end face side of a plurality of samples cut along
The gist is to grind or polish such that the shaving amount ΔZ from the same end face is different from each other, and to measure the surface refractive index of the end face of each of the cut samples.

According to this configuration, a plurality of samples are formed from the substrate, and one end surface of each sample is ground or polished so that the shaving amount ΔZ is different from each other, and the surface refraction of the end surface of each sample formed by the cutting is performed. Since the index is measured, an accurate refractive index distribution of the substrate can be obtained based on the measurement result. For this reason, the refractive index distribution of the substrate can be known using only one of the plurality of substrates each having the desired refractive index distribution formed in the same ion exchange lot.

According to a sixth aspect of the present invention, in the method of processing a refractive index distribution type lens in the optical axis direction according to the fifth aspect, each of the plurality of samples is ground such that the amount of shaving ΔZ is different from each other. Alternatively, at the time of polishing, each sample is placed on a plurality of mounting surfaces having different heights according to the shaved amount ΔZ of each sample, with one end surface thereof facing upward, and in this state, each of the plurality of samples is The gist is to grind or polish one end surface at the same height position.

According to this configuration, a jig having a plurality of mounting surfaces having different heights in accordance with the shaving amount ΔZ of each sample is prepared, and among these mounting surfaces, a mounting device having a low height is prepared. A plurality of samples are sequentially placed on the plurality of mounting surfaces such that a sample having a small shaving amount ΔZ is mounted on the mounting surface. In this state, by grinding or polishing each one end surface of the plurality of samples at the same height position, the shaving amount Δ from one end surface for the plurality of samples is obtained.
It can be easily cut by one processing so that Z is different. Thereby, the operation of grinding or polishing a plurality of samples to a desired length can be efficiently performed.

The invention according to claim 7 is the invention according to claims 1-6.
An optical axis direction gradient index lens manufactured by the method for processing an optical axis direction gradient index lens according to any one of the above items. According to this configuration, since it is manufactured by the above-described processing method, variation in optical performance, particularly, spherical aberration is reduced. In addition, since at least one end has a spherical surface, reflected return light is reduced.

The invention according to claim 8 is the invention according to claims 1 to 6.
A collimator using a lens manufactured by the method for processing an optical axis direction gradient index lens according to any one of the above, wherein the two optical axis direction gradient index lenses are used, and these two lenses are used. The gist is that the curved surfaces formed on the one end surface side are opposed to each other, and are arranged so that their optical axes coincide with each other.

According to this configuration, a collimator is formed by using two optical axis direction refractive index distribution type lenses having small variations in optical performance, particularly spherical aberration, manufactured by the above processing method. For this reason, the distance L between the lenses of the collimator
As is clear from FIG. 8 showing the relationship between the insertion loss and the insertion loss, for example, the insertion loss is reduced over a wide range where the distance L between lenses is from L = 0 to around L = 1000 mm, and good optical performance is obtained.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for processing a gradient index lens in the optical axis direction embodying the present invention, a gradient index lens in the optical axis direction produced by the method, and a collimator using the lens will be described. Embodiments will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description will be omitted.

[One Embodiment of Processing Method] FIGS.
FIG. 2F shows a method of processing an optical axis direction gradient index lens according to an embodiment, and FIG. 2A shows an optical axis direction gradient index lens manufactured by the same processing method. .

The processing method of this embodiment is a method for producing one or more refractive index distribution type lenses 12 in the optical axis direction shown in FIG. 2A from the transparent substrate 11 shown in FIG. is there. The substrate 11 shown in FIG. 1A is a glass substrate. The substrate 11 has a depth from one end surface 11a to a predetermined depth position A in the optical axis direction (width direction) according to the depth position in the same direction. Refractive index distributions having different refractive indices are formed by ion exchange. That is, the substrate 11 has a refractive index distribution region 1 extending from the one end face 11a having the refractive index distribution to a predetermined depth position A.
3 and the other end face 11b from the position A where the refractive index is uniform.
And a uniform refractive index region 14 up to Further, in the refractive index distribution region 13, the refractive index decreases substantially linearly according to the depth position from the one end face 11a in the optical axis direction (see FIG. 1B). FIG. 2B shows the substrate 1
1 shows a cross section of one sample cut into a column along the optical axis direction.

The optical axis direction refractive index distribution type lens 12
As shown in FIG. 2A, a flat surface 1 having a spherical surface 15 with a radius of curvature r on the one end surface 11a side, that is, the refractive index distribution region 13 side, and a vertical surface 1 perpendicular to the lens optical axis 16 on the other end surface 11b side.
7. That is, in the refractive index distribution type lens (hereinafter, simply referred to as a lens) 12 in the optical axis direction, the refractive index distribution region 13 in which the refractive index decreases substantially linearly from n ₀ by Δn according to the depth position has a spherical surface. 15 are formed (see FIG. 2B).

The processing method of the present embodiment includes the following steps (1) to (7). (Step 1) The substrate 11 shown in FIG. 1A is cut or cut out along the optical axis direction, and a sample 18 shown in FIG.
Are prepared. In this example, five samples 18 _{1-18 5} cut along the substrate 11 in the optical axis direction in a cylindrical shape (Fig. 1
(See (b) and (c)).

(Step 2) Each sample 18₁~ 18_FiveOne end face of
As shown in FIG. 1C, one end face 11a
From the surface (amount of grinding on the spherical surface side) ΔZ (ΔZ₁~ ΔZ_Five)But
Grind or polish differently in stages. Where each
Cutting amount ΔZ₁~ ΔZ_FiveIs ΔZ ₁<ΔZ_Two<ΔZ_Three<ΔZ_Four<
ΔZ_FiveIs in a relationship.

As described above, in order to grind or polish the one end surface 11a side of each of the samples 18 ₁ to 18 _{5 so} that the shaving amounts ΔZ _{1 to} ΔZ ₅ are different from each other, in this embodiment, the height from the bottom surface 19a is set. Jig 19 having _five different mounting surfaces 19 _{1 to} 19 ₅ is used. Five mounting surfaces 19 _{1 -1}
9 ₅ has a height towards the surface 19 ₅ side mounting from the mounting surface 19 ₁ side is increasingly high.

Each of the samples 18 ₁ to 18 ₅ is placed on each of the mounting surfaces 19 _{1 to} 19 _5.
18 ₅ Post posture to become the one end surface 11a on the side is.
At this time, a plurality of samples are sequentially placed on the plurality of mounting surfaces such that a sample having a small shaving amount ΔZ is mounted on a mounting surface having a low height among these mounting surfaces. In this state, the five respective end face 11a of the sample 18 _{1-18 5,} the bottom surface 1 of the jig 19
Grind or cut all at once at the same height H from 9a. Thus, one end surface 11a side is the respective samples 18 _{1-18 5,} scraped respectively by cutting the amount ΔZ ₁ ~ΔZ ₅ (Fig. 1
(C)).

[0037] (Step 3) the surface refractive index of the end faces of the sample 18 _{1-18 5} shaved can do in the above step (2), for example measured respectively Abbe's refractometer. With this measurement,
Each shaving amount ΔZ _{1 to} ΔZ ₅ and each sample 18 _{1 formed} by shaving
To 18 the refractive index of the _fifth end face of the (surface refractive index) nΔZ ₁ ~nΔZ
₅ relationship measurement result shown in FIG. 3 showing the between is obtained.

(Step 4) The refractive index distribution of the refractive index distribution region 13 of the substrate 11 is obtained based on the measurement result obtained in the above step (3). This refractive index distribution is obtained by converting the above measurement result shown in FIG. 3 into the following polynomial (1) n (Z) = refractive index n (Z) at each depth position Z in the optical axis direction with different shaving amount ΔZ. n ₀ + n ₁ Z + n ₂ Z ² + n ₃ Z ³ (1)

Here, n ₀ is the position of ΔZ = 0, that is, the refractive index at one end surface 11a of the substrate 11, n ₁ is the distribution constant of the first-order term, n ₂ is the distribution constant of the second-order term, and n ₃ is the third-order term. Is the distribution constant of

When calculating the refractive index distribution of the refractive index distribution region 13, higher order terms of the above polynomial (1) are added as necessary. That is, the refractive index distribution is ideally a linear distribution (up to the first order), but the refractive index distribution actually formed by the ion exchange method deviates from the linear distribution. Correct with.

For example, by adding up to the second order term in the above polynomial (1), the following distribution equation (2) is obtained as an example. n (Z) = 1.620 + (− 0.060) Z + (0.049) Z ² (2) That is, in the distribution formula (2), n ₀ = 1.620 and n ₁ = −0.06
0 and n ₂ = 0.049.

(Step 5) Based on the distribution equation obtained in the above step (4), for example, the refractive index distribution expressed by the above-mentioned distribution equation (2), the RMS (Root Mean Square) wavefront aberration (λ) is calculated on one end face 11a. As a function of the amount of shaving .DELTA.Z.

Here, the calculation of the wavefront aberration is performed by using optical simulation software (for example, Os by Sinclair Optics, USA).
lo Six etc.). RM obtained by such calculation
FIG. 4 shows the relationship between the S wavefront aberration (λ) and the shaving amount ΔZ (mm). From the figure, the optimum shaving amount ΔZmm from the one end face 11a at which the RMS wavefront aberration is minimized is ΔZm = 0.
It turns out that it is 08 mm.

(Step 6) The surface refractive index n _t (see FIG. 1 (d)) of the end face formed when the substrate 11 is cut by the optimum shaving amount ΔZm obtained in the above step (5) is obtained. The focal length f and the radius of curvature r of the lens 12 are obtained based on the obtained surface refractive index n _t and the numerical aperture NA and the effective diameter De (see FIG. 2A) of the lens 12 which are set in advance.

That is, the numerical aperture NA and the effective diameter De of the lens are preset and given in accordance with a request from the product specification, and the focal length f of the lens 12 is obtained by the following equation (3).

NA = De / 2f (3) Further, the focal length f obtained by the above equation (3) and the surface refractive index n _t , The radius of curvature r of the lens 12 is obtained by the following equation (4).

[0047] _{f = r / (n t -1} ) ················· (4) In addition, the lens thickness s of the lens 12, by the following equation (5) I get it. ^{s = r- (r 2 -De 2} /4) 1/2 ··········· (5) Thus, in processing parameters (the example for making the lens 12 from the substrate 11, optimal The shaving amount ΔZm, the radius of curvature r, and the lens thickness s) are obtained. These processing parameters are applicable to substrates of the same ion exchange lot.

(Step 7) The substrate 11 shown in FIG.
From the one end face 11a, the substrate is ground or polished by the optimum shaving amount ΔZm (the shaded portion in FIG.
e into a cylindrical lens preform 20 (see FIG. 1 (e)).
Cut out more than one piece. Further, one end surface side of the cut lens preform 20 is processed into a spherical surface having a radius of curvature r as shown in FIG. Finally, the lens preform 20 is cut or ground into a plane perpendicular to the lens axis 16 at a distance s from the top of the spherical surface.

Thus, the lens 12 shown in FIG. 2A having the spherical surface 15 on one end surface is completed. According to the processing method according to the embodiment configured as described above, the following operation and effect can be obtained.

(A) Five samples 18 ₁ shown in FIG.
The ~ 18 ₅ end face 11a side of shaving amount ΔZ ₁ ~ΔZ ₅ is ground or polished to different manner, one end face 11a
The surface refractive indices of the end faces of the respective samples having different depth positions in the optical axis direction from are measured. For this reason, the refractive index at each depth position where the depth in the optical axis direction from one end face differs from the one end surface by each of the shaving amounts ΔZ _{1 to} ΔZ ₅ can be obtained. Based on this measurement result, an accurate refractive index distribution (refractive index distribution represented by the above-mentioned distribution formula (2)) of the refractive index distribution region 13 of the substrate 11 can be obtained. This makes it possible to manufacture the lens 12 with small variations in optical performance, particularly RMS spherical aberration.

(B) Since a lens 12 with small variations in optical performance, particularly RMS spherical aberration, can be manufactured, the insertion loss can be reduced when a collimator is formed using two such lenses.

(C) Since the lens 12 is a plano-convex lens having a spherical surface 15 formed at least on one end side, reflected return light can be reduced. From the substrate 11 to produce a (D) lens 12, the sample for measuring the refractive index distribution five making, these five with the sample 18 _{1-18 5,} different from each other from one end surface 11a of the substrate 11 It is possible to know the refractive index at five positions at the depth position. For this reason, an accurate refractive index distribution of the substrate 11 can be obtained using only one of the plurality of substrates 11 each having a desired refractive index distribution formed in the same ion exchange lot.

(E) FIG. 3 shows the relationship between the shaved amounts ΔZ _{1 to} ΔZ ₅ and the refractive indices (surface refractive indexes) nΔZ _{1 to} nΔZ ₅ of the end faces of the samples 18 ₁ to 18 ₅ formed by shaving. Based on the measurement results as shown, the optimum shaving amount ΔZm from one end surface where the RMS wavefront aberration is minimized can be obtained. Therefore, the one end surface 11a side of the substrate 11 can be ground with the aim of the optimum shaving amount ΔZm. Thereby, RM
One or more lenses 12 with small variations in S wavefront aberration can be manufactured from the substrate 11.

For example, when the optimum shaving amount ΔZm is set to approximately 0.1 m
m, it is possible to grind the one end surface 11a side of the substrate 11 with the aim of the optimum shaving amount ΔZm. Therefore, as shown in FIG. It can be suppressed within a range of about 01λ.

(F) The numerical aperture NA and the effective diameter De of the lens are preset and given in accordance with a request from the product specification, and the focal length f of the lens 12 is determined by the above equation (3). Also, the focal length f obtained by the above equation (3) and
The radius of curvature r can be obtained by the above equation (4) from the surface refractive index n _t when the cutting is performed by the optimum shaving amount ΔZm.

For this reason, the substrate 11 is ground or polished from the one end face 11a by an optimum shaving amount ΔZm, and one or more cylindrical lens base materials 20 having an effective diameter De are cut out from the substrate 11 and one of the base materials 20 is cut out. By processing the end surface into a spherical surface having a radius of curvature r, the lens 12 having a small RMS wavefront aberration can be easily manufactured.

(G) By applying the measurement result as shown in FIG. 3 to the above polynomial (1), the refractive index distribution of the substrate 11 can be known accurately. (H) Based on the refractive index distribution thus obtained, the RMS wavefront aberration can be obtained as a function of the shaved amount ΔZ from the one end face 11a using optical simulation software. From the function thus obtained, the shaving amount ΔZm that minimizes the RMS wavefront aberration can be obtained.

(I) One end face 11a of each of the samples 18 ₁ to 18 ₅
In order to grind or polish the sides so that the shaving amounts ΔZ _{1 to} ΔZ ₅ are different from each other, a jig 1 for grinding has _five mounting surfaces 19 _{1 to} 19 ₅ having different heights from the bottom surface 19a.
9 is used. As a result, the five samples 18 ₁ to 18 ₅
Each end face 11a of the by grinding or cutting from the bottom 19a of the jig 19 at the position of the same height H, the end face 11a of the five samples 18 _{1-18 5,} one of the grinding or By the polishing process, it is possible to cut by the shaving amounts ΔZ _{1 to} ΔZ ₅ respectively. As a result, it is possible to efficiently perform the work of grinding or polishing a plurality of samples 18 _{1-18 5} to a desired length.

[One Embodiment of Collimator] Next, one embodiment of a collimator using the lens 12 manufactured by the processing method according to the one embodiment will be described with reference to FIGS. 7 and 8. FIG.

The collimator 30 shown in FIG. 7 uses two of the above lenses 12, and makes the two lenses 12, 12 face the respective curved surfaces 15, 15 formed on the one end surface side, and the lens light of each other. The shafts 16 are arranged so as to coincide with each other.

According to the collimator according to the embodiment having the above-described configuration, the following operation and effect can be obtained. (G) The collimator 30 is configured by using two lenses 12 with small variations in optical performance, particularly RMS spherical aberration. Therefore, as is apparent from FIG. 8 showing the relationship between the distance L between the lenses of the collimator 30 and the insertion loss (dB), the insertion loss can be reduced over a wide range from L = 0 to around L = 1000 mm. The size can be reduced, and good optical performance can be obtained. Therefore, even if the distance L between lenses is changed in a wide range, a high-performance collimator having small insertion loss and excellent optical performance can be obtained.

[Modification] The present invention can be embodied with the following modifications. · In the processing method of the embodiment, using 5 samples 18 _{1-18 5} produced from one substrate 11, but so as to obtain the refractive index distribution of the substrate 11, the number of sample 5 Any number other than the above may be used.

[0063] In the processing method of the above embodiment, but uses a plurality of sample 18 _{1-18 5} so as to obtain the refractive index distribution of the substrate 11, the present invention is not limited thereto. For example, the one end surface 11a side of the substrate 11 itself may be ground or polished by gradually changing the shaving amount ΔZ from the same end surface, or the surface refractive index of each cut end surface may be measured each time. .

In the processing method of the embodiment, the substrate 1
The surface refractive indices at different depth positions in the optical axis direction from one end face 11a of the substrate 1 are measured to obtain actual measured values of the refractive index distribution of the substrate 11, but the measured values of the refractive index distribution of the same substrate 11 are obtained. The measuring method is not limited to this.

In the processing method of the above embodiment, the jig 1
9 using although the one end face side of the sample 18 _{1-18 5} a plurality (five) to be ground or polished at a time in one process, or separately ground one end face of each sample Needless to say, polishing may be performed.

In the processing method of the above embodiment, the spherical surface 15 is formed only on one end surface of the lens 12, but the present invention is also applicable to the case where spherical surfaces are formed on both end surfaces of the lens 12. It is.

In the processing method according to the embodiment, when the refractive index distribution is represented by the distribution formula (2), the effective diameter De and the radius of curvature r of the lens are kept constant, and the shaving amount ΔZ is set to 0.02 mm. When the focal length f and the numerical aperture NA corresponding to each shaving amount ΔZ are calculated when the distance is changed from 0.0 to 0.20 mm at an interval of 0.02 mm, the NA becomes almost constant. FIG. 5 shows the relationship between the focal length f and the shaving amount ΔZ in this case. Here, De = 3.4 mm, r = 7.3 mm, s =
Calculated as 0.2 mm. As is clear from FIG. 5, the focal length f increases as ΔZ increases, but the NA is almost constant with changes in ΔZ.

From the above, if the numerical aperture NA and either the effective diameter De or the radius of curvature r are given as design parameters, the optimum shaving amount ΔZm is determined based on the refractive index distribution expressed by the above-mentioned distribution formula (2). At the same time, the radius of curvature r or the effective diameter De is determined. Thus, it can be seen that a refractive index distribution type lens in the optical axis direction having uniform characteristics with small variations in wavefront aberration can be manufactured.

Therefore, in the processing method of the embodiment, the numerical aperture NA of the lens 12 is used as a design parameter.
And the effective diameter De of the lens, the optimum shaving amount ΔZm and the radius of curvature r are determined as processing parameters, but the present invention is not limited to such a configuration. By providing the numerical aperture NA and the radius of curvature r as design parameters, the optimum cutting amount ΔZm and the effective diameter De may be obtained as the processing parameters.

In the processing method of the embodiment, the substrate 1
Although a glass substrate was used as 1, the substrate 11 is not limited to glass, and may be any material that can form a refractive index distribution in the optical axis direction.

[0071]

As described above, according to the first aspect of the present invention, it is possible to manufacture a refractive index distribution type lens in the optical axis direction with little variation in optical performance, particularly spherical aberration.

According to the seventh aspect of the present invention, it is possible to obtain a refractive index distribution type lens in the optical axis direction with small variations in optical performance, particularly spherical aberration. According to the invention according to claim 8, even if the distance between the lenses is changed in a wide range, a high-performance collimator having small insertion loss and excellent optical performance can be obtained.

[Brief description of the drawings]

FIGS. 1A to 1F are explanatory views showing a method of processing a gradient index lens in an optical axis direction according to an embodiment.

FIG. 2A is a side view showing a refractive index distribution type lens in an optical axis direction manufactured by the processing method, and FIG. 2B is an explanatory view showing a refractive index distribution of the lens.

FIG. 3 is a graph showing a relationship between a shaving amount and a refractive index.

FIG. 4 is a graph showing a relationship between a shaving amount and an RMS wavefront aberration.

FIG. 5 is a graph showing a relationship between a shaving amount and a focal length for explaining a modification of the embodiment.

FIG. 6 is a graph showing the relationship between the shaving amount ΔZ and the wavefront aberration when the optimum shaving amount ΔZm is set to approximately 0.1 mm by the working method according to one embodiment.

FIG. 7 is a schematic configuration diagram showing a collimator according to one embodiment.

FIG. 8 is a graph showing a relationship between an inter-lens distance and an insertion loss in the collimator.

FIG. 9 is a graph showing the relationship between the shaving amount and the wavefront aberration of a conventional gradient index lens in the optical axis direction.

[Explanation of symbols]

11: substrate, 11a: one end face, 12: optical axis direction refractive index distribution lens, 15: spherical surface, 16: lens axis (optical axis), 1
8 (18 _{1-18 5)} ... sample, 19 ... jig, 19 _{1-19 5}
... Mounting surface, 20. Lens base material, 30. Collimator.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA22 LA25 PA02 PA17 PB02 QA05 QA13 QA21 QA33 QA41 RA23

Claims (8)

[Claims] 1. A transparent substrate having a refractive index distribution having a different refractive index depending on a depth position in an optical axis direction from one end face, and at least one optical axis having at least one end face side as a spherical surface having a radius of curvature r. A method of processing an optical axis direction refractive index distribution lens for producing a directional refractive index distribution type lens, wherein the lens is processed based on an actually measured value of the refractive index distribution. How to process the lens. 2. An optimum shaving amount ΔZm from the one end face where a wavefront aberration is minimized based on a measured value of the refractive index distribution.
And the surface refractive index n when the cutting amount is the same as the optimum cutting amount ΔZm.
_t, and a curvature radius r or an effective diameter De based on the surface refractive index n _t , a preset numerical aperture NA, and a preset effective diameter De or the radius of curvature r of the lens. The method for processing a refractive index distribution type lens in the optical axis direction according to claim 1, wherein: 3. The optimum shaving amount ΔZm at which the wavefront aberration is minimized is obtained by converting the measured value to a refractive index n (Z) at each depth position Z in the optical axis direction where the shaving amount ΔZ differs. of the polynomial _{n (Z) = n 0 +} n 1 Z + n 2 Z 2 + ··· ( here, n ₀
Is the refractive index at the position of ΔZ = 0, n ₁ is the distribution constant of the first-order term, and n ₂ is the distribution constant of the second-order term. 3. The light according to claim 1 or 2, wherein the refractive index distribution is obtained by applying the formula (1), and the wavefront aberration is obtained as a function of a shaving amount ΔZ from the one end face based on the refractive index distribution. A method for processing an axial gradient index lens. 4. An end surface of the substrate is ground or polished by gradually changing a shaving amount ΔZ from the one end surface in an optical axis direction, and a surface refractive index of each end surface having a different depth position is determined. The method for processing a refractive index distribution type lens in the optical axis direction according to any one of claims 1 to 3, wherein an actual measurement value of the refractive index distribution is obtained by measuring the refractive index distribution. 5. When measuring the surface refractive index of each of the end faces, each of the one end faces of a plurality of samples obtained by cutting the substrate along the optical axis direction has the shaved amount ΔZ from the same end face. 5. The method of processing a refractive index distribution type lens in the optical axis direction according to claim 4, wherein each of the samples is ground or polished differently, and a surface refractive index of an end face of each sample formed by the grinding is measured. 6. When grinding or polishing each one end surface side of the plurality of samples so that the shaving amount ΔZ is different from each other,
The amount of shaving Δ of each sample, with one end face up,
Place them on a plurality of placement surfaces with different heights according to Z,
6. The method according to claim 5, wherein one end surface of each of the plurality of samples is ground or polished at the same height in this state. 7. An optical axis direction gradient index lens produced by the method for processing an optical axis direction gradient index lens according to any one of claims 1 to 6. 8. A collimator using a lens produced by the method for processing a gradient index lens in the optical axis direction according to any one of claims 1 to 6, wherein the gradient index lens in the optical axis direction is used. Using two lenses, these two
A collimator characterized in that two lenses are arranged such that their curved surfaces formed on the one end face face each other and their optical axes coincide with each other.