JP2002182009A - Collimator, collimator array, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a collimator or a collimator array in which the number of aligned core axes between index distribution type rod lenses is decreased, and to provide a method for manufacturing the collimator. SOLUTION: After the raw materials of long-length index distribution type rod lenses are arranged parallel to one another in a predetermined pitch on a substrate having flat end faces with the optical axes of the rod lens materials parallel to one end face of the substrate, the rod lens raw materials are divided by cutting together with the substrate at given intervals along the planes perpendicular to the optical axes. Then the divided raw materials of divided index distribution type rod lenses are adjusted to a specified lens length, and the cut end faces are opposed to each other to align the optical axes between opposing lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a collimator comprising a pair of refractive index distribution type rod lenses arranged to face each other, a collimator array having the collimators juxtaposed at a predetermined pitch, and a method of manufacturing the same. In particular, the present invention relates to a technique for simplifying the alignment process and obtaining a high-performance product.

[0002]

2. Description of the Related Art Conventionally, in optical information transmission, outgoing light, which is divergent light from one optical fiber, is converted into parallel light by a lens. Injection into an optical fiber has been performed. Such an optical system is called a “collimator”, and various optical modules are constructed by inserting various optical elements such as a filter, an element for an optical isolator, an optical switch, and an optical modulator between both lenses. be able to.

As the above lens, a convex lens is used, but a collimator using a gradient index rod lens is also used. This refractive index distribution type rod lens has a characteristic that the refractive index gradually changes in the radial direction around the axis, and by defining the lens length and the distance between the lens and the optical fiber in accordance with the wavelength, the incidence is increased. The collected light can be converted into parallel light or collected and emitted.

FIG. 7 is a perspective view showing a single-core collimator having a pair of refractive index distribution type rod lenses 1a opposed to each other. An optical fiber 4 is connected to each of the gradient index rod lenses 1a so that their optical axes coincide with the end surface opposite to the opposing surface, and the light from one optical fiber 4 is connected to the refractive index. The distributed rod lens 1a emits the light as parallel light, and the other refractive index distributed rod lens 1a condenses the parallel light and guides it to an optical fiber 4 connected thereto, thereby transmitting an optical signal. Therefore, in such a collimator using the gradient index rod lens 1a, in order to reduce the coupling loss, the optical axes of the opposite gradient index rod lenses 1a, 1a, and further, the gradient index rod lens. It is necessary to precisely match the optical axis of the optical fiber 1a with the optical axis of the optical fiber 4.

However, as shown in FIG. 8, when the refractive index distribution type rod lenses 1a, 1a are arranged to face each other, it is general that axial misalignments in various directions occur. FIG. 8A is a plan view of FIG. 7 as viewed from the gradient index rod lens 1a side, and FIG. 8B is a side view of the same. Also, as shown in FIG. 7, an ideal optical axis common to the gradient index rod lens 1a and the optical fiber 2a is denoted by a symbol C, and a direction parallel to the optical axis C is defined as a Z direction.
A direction orthogonal to the horizontal direction is defined as an X direction, and a direction orthogonal to the vertical direction is defined as a Y direction.

The possible axial misalignment between the opposing lenses includes displacement in the Y and X directions as shown in FIG. 8A, inclination θx in the X direction, and Y direction as shown in FIG. And a tilt θy in the Y direction occurs. Therefore, alignment over four axes is required to form a pair of collimators. Further, in the case of the collimator array, since the alignment of the lens array already fixed on one side is necessary, a rotation θz about the optical axis C as shown in FIG. 8A is added. That is, in the case of a collimator array,
It is necessary to repeat the alignment over five axes for each lens element.

[0007]

As described above, in the prior art, complicated and delicate alignment work in the multiaxial directions between the gradient index rod lenses 1a, 1a is required. However, the aligning operation has to be repeated a plurality of times, and the aligning step is extremely difficult.

The present invention has been made in view of the above circumstances, and provides a collimator or a collimator array having a reduced number of alignment axes between gradient index rod lenses, and a manufacturing method therefor. With the goal.

[0009]

In order to achieve the above object, the present invention provides the following collimator and collimator array, and a method of manufacturing the same. (1) In a collimator constituted by a pair of refractive index distribution type rod lenses facing each other, the refractive index distribution type rod lens is placed on a substrate having a flat end surface, and the optical axis of the refractive index distribution type rod lens is And one of the end faces is fixed to be parallel to each other, and the pair of substrates are opposed to each other while keeping the end faces parallel to each other. (2) Opposing refractive index distribution type rod In the lens pair,
The collimator according to the above (1), wherein the lens length of one of the gradient index rod lenses is longer than the lens length of the other gradient index rod lens by (1/2) pitch. In a collimator array configured by opposing a pair of rod lens arrays in which index distribution type rod lenses are juxtaposed at a predetermined pitch and facing each other, the refractive index distribution type rod lens is formed on a substrate having a flat end surface. The optical axis of the refractive index distribution type rod lens and one of the end faces are fixed at a predetermined pitch so as to be parallel, and a pair of the substrates are opposed to each other while keeping the end faces parallel to each other. (4) In the opposing gradient index rod lens pair,
The lens length of the gradient index rod lens forming one rod lens array is (1/1) of the lens length of the gradient index rod lens forming the other rod lens array.
2) The collimator array according to the above (3), wherein the collimator array is lengthened by the pitch. (5) In the method for manufacturing a collimator in which a pair of refractive index distribution type rod lenses are opposed to each other, a substrate having a flat end surface is provided. On top, a long gradient index rod material is fixed so that the optical axis of the gradient rod lens material and one of the end surfaces are parallel to each other, and then the refractive index is spaced at a predetermined interval. The distributed rod lens material is cut along the substrate perpendicular to the optical axis and divided into substrates, and then the individual refractive index distributed rod lens materials are adjusted to a specified lens length, and then the cut end surface is cut. A method of manufacturing a collimator, wherein the two substrates are opposed to each other, and the optical axes of both lenses are made to coincide with each other. (6) Both substrates after cutting are opposed to each other so that their end faces are parallel to each other. (7) The method of manufacturing the collimator according to the above (5), wherein the optical axes are aligned. (7) A pair of rod lens arrays, in which refractive index distribution type rod lenses are juxtaposed at a predetermined pitch, are opposed to each other. In the method for manufacturing a collimator array, a long gradient index rod lens raw material is placed on a substrate having a flat end surface, and the optical axis of the gradient index rod lens raw material is parallel to one of the end surfaces. After being arranged side by side at a predetermined pitch, the raw material of the gradient index rod lens is cut at a predetermined interval along with the substrate along a plane perpendicular to the optical axis and divided, and then the individual divided refractive index distribution type lenses are divided. A method of manufacturing a collimator array, comprising adjusting a rod lens material to a specified lens length, and then making the cut-side end surfaces face each other, and aligning the optical axis between the facing lenses. The two substrates, each of the end faces is made to face so as to maintain the parallel method of the collimator array of (7), wherein the match an optical axis between at least a pair of opposed lenses

[0010]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a procedure for manufacturing a collimator according to the present invention. First, as shown in FIG.
The raw material 1 having a long refractive index distribution type rod lens is placed on the side surface A (y
(A plane parallel to the -z plane) is fixed on a flat substrate 2 having a flat surface. The lens length (L) of the gradient index rod lens raw material 1 is at least twice the lens length of the gradient index rod lens 1a of the final product (hereinafter, referred to as a specified lens length). Further, upon fixing, the positioning is performed so that the optical axis C of the gradient index rod lens material 1 is parallel to the side surface A of the substrate 2.

FIG. 2 is a diagram showing a state in which light propagates meandering inside the gradient index rod lens and exits from the end face. This meandering period is called pitch, and is determined by the refractive index distribution of the lens. In the collimator, when the pitch is P, the lens length is specified to be P / 4 or shorter so that light is emitted from the end face of the refractive index distribution type rod lens with the maximum amplitude. Therefore, the lens length (L) of the refractive index distribution type rod lens raw material 1
Is at least twice as long as the specified lens length (for example, P / 4) plus a cutting margin (equivalent to the blade width) in a cutting step described later and a polishing margin for polishing and finishing the cut surface. I do. Hereinafter, for convenience of explanation, a case where the lens length (L) of the gradient index rod lens material 1 is set to twice the specified lens length will be exemplified.

Next, as shown in FIG. 1B, at a position which is just half the length of the gradient index rod material 1, the surface of the gradient index type rod lens is perpendicular to the optical axis C. The lens raw material 1 is cut together with the substrate 2 and halved.
As a cutting tool, a diamond cutter or the like can be used. However, as described above, when setting the lens length (L) of the gradient index rod lens material 1, the blade width of the cutting tool used is equivalent to the blade width. Add a minute (cut off).

After cutting, the cut surface of each of the half-divided gradient index rod lenses 1a, 1a is polished to adjust the lens length to a specified length and the end surface is made a smooth surface. Therefore, when setting the lens length (L) of the refractive index distribution type rod lens raw material 1, an amount corresponding to this polishing amount (polishing margin) is added.

As shown in FIG. 1B, a pair of refractive index distribution type rod lenses 1a, 1a facing each other as a collimator can be obtained at a time by this cutting and polishing. In the manufacture of a normal collimator, a long gradient index rod lens material 1 is cut into a predetermined lens length to produce a large number of gradient index rod lenses 1a. A pair is selected to form a lens pair.

On the other hand, in the method of the present invention, even if an angle shift occurs when the gradient index rod lens raw material 1 is cut, the two gradient index rod lenses 1a, 1 forming a pair.
The end faces of a are equally angularly displaced and this angular displacement remains up to the final product. As a result, the light passing through the gradient index rod lenses 1a, 1a only shifts in the propagation space in parallel to the X direction or the Y direction. Accordingly, the bottom surfaces B (planes parallel to the xz plane) of the two substrates 2a, 2a after cutting are kept parallel, and the side surfaces A (planes parallel to the yz plane) of both substrates 2a, 2a are parallel. It is only necessary to maintain the angle, and the angle alignment of θx and θy shown in FIG. 6 becomes unnecessary. In other words, the alignment which conventionally required five axes is reduced to three axes, and the alignment work is greatly simplified. When the optical fiber 4 is coupled to the rear end face of the gradient index rod lens 1a and light is incident, the rear end face of the gradient index rod lens 1a is obliquely processed to prevent reflection at the lens end face. There are cases. In this case, even if the incident light is parallel to the central axis of the gradient index rod lens 1a, the emitted light is no longer parallel to the central axis. Therefore, in such a case, the angle alignment of θx shown in FIG. 6 is necessary, but the alignment of θy is not required.

Then, as shown in FIG. 1C, the two refractive index distribution type rod lenses 1a, 1a have their cut-side end faces facing each other, and the other end faces have optical fibers 4, 4 with their respective optical axes. The collimator according to the present invention is completed by making the connections. The method of connecting the gradient index rod lens 1a to the optical fiber 4 is not particularly limited, and
For example, although not shown, the gradient index rod lens 1
The optical fiber 4 is inserted into a capillary having the same diameter as the optical fiber 4a, and the capillary is fixed on a substrate having the same thickness as the substrate 2a of the gradient index rod lens 1a. And the like can be adopted.

In the above, a substrate having a V-groove can be used. That is, as shown in FIG. 3, the substrate 2 on which the V-grooves 3 having a predetermined opening groove width and inclination angle are formed is used to accommodate the above-described refractive index distribution type rod lens material 1 in the V-grooves 3. The ridge line of the V groove 3 is formed parallel to the side surface A of the substrate 2, and the refractive index distribution type rod lens raw material 1 is
Simultaneously with the accommodation in the V-groove 3, the parallelism between the optical axis C and the side surface A of the substrate 2 is secured. Next, as shown in FIG.
At a position that is just half the length of the gradient index rod lens raw material 1, on a surface orthogonal to the optical axis C, the gradient index rod lens raw material 1 is cut together with the substrate 2 and halved. After cutting, the cut surface of each of the half-divided gradient index rod lenses 1a, 1a is polished to adjust the lens length to a specified length and the end surface is made smooth, and thereafter, as shown in FIG. The cut-side end faces of the refractive index distribution type rod lenses 1a, 1a are opposed to each other, and optical fibers 4, 4 are connected to the other end face so that their respective optical axes coincide with each other, thereby completing a collimator.

In the above description, the V-groove 3 is provided on the substrate 2 as a groove for accommodating the gradient index rod lens material 1. However, the present invention is not limited to this, and a groove having a semicircular cross section or a U-groove may be provided. Is also good.

Further, each of the above manufacturing methods can be applied to the production of a collimator array as shown in FIG. First, as shown in FIG. 4 (a), a plurality of long refractive index distribution type rod lens raw materials 1 (four in the example in the figure) are arranged at predetermined intervals, and a flat substrate having a side surface A that is a flat plate is formed. Fix it on 2. At this time, the positioning is performed so that each refractive index distribution type rod lens raw material 1 is parallel to the side surface A of the substrate 2. Then, FIG.
As shown in (b), a gradient index rod lens material 1
At a position just half the length of the above, on the surface orthogonal to the optical axis C, the refractive index distribution type rod lens raw material 1 is cut together with the substrate 2 and halved. After the cutting, the cut surface of each of the half-divided gradient index rod lenses 1a is polished to adjust the lens length to a specified length, and the end surface is made a smooth surface. This cutting,
By polishing, an array of a pair of refractive index distribution type rod lenses 1a facing each other when a collimator array is formed is obtained at a time. Then, as shown in FIG. 4C, the collimator array is completed by connecting the optical fiber 4 to each of the gradient index rod lenses 1a with the optical axis aligned.

According to this manufacturing method, a collimator array including a plurality of pairs of refractive index rod lenses and a plurality of optical fiber pairs having the same optical axis is obtained. And X-
Since the inclination (θx) in the Z plane and the inclination (θy) in the YZ plane do not substantially occur and the positional relationship between the lenses is fixed, the bottom surfaces of both substrates 2a, 2a B
Only need to be kept parallel, and the side surfaces A of both substrates 2a, 2a need only be kept parallel, so that X, Y, Z
Since only the three optical axes need to be matched, the alignment work is greatly simplified as compared with the related art.

The concept of preventing reflection by obliquely processing the end surfaces of the pair of collimators can be applied to a collimator array. Also, here, an example is shown in which two collimator lenses, that is, a pair of collimator lenses, are used from a long rod lens raw material, but a plurality of pairs of collimator lenses are made from a long rod lens raw material. It is also possible.

By the way, in the above collimator and collimator array, the gradient index rod lens pair, the lens length is made of the same ones. However, as described in detail below, when the optical fiber is aligned for some reason during the manufacturing process and the pair of gradient index rod lenses is displaced, the light receiving side gradient index rod lens is connected to the optical fiber. A large coupling loss occurs between the optical fiber and the optical fiber.

As shown in FIG. 5, optical fibers Fa1-F
The light from a3 is distributed to the gradient index rod lenses La1 to La.
3 (hereinafter, referred to as a “light-emitting side gradient index rod lens”), and opposing the gradient index rod lens L
It is assumed that a rod lens array has a configuration in which light beams are condensed by b1 to Lb3 (hereinafter referred to as "light-receiving side refractive index distribution type rod lens") and guided to optical fibers Fb1 to Fb3. Then, the light-emitting side gradient index rod lens La2 located in the middle of the drawing.
And the light-receiving-side gradient index rod lens Lb2 is shifted from the original axis, ie, the positions of the optical fibers Fa1 and Fb2, to the refractive index gradient rod lens pair La1 and Lb1 on both sides by Δx.
When the optical fiber Fa is displaced (according to the above method, the opposing gradient index rod lenses are displaced by the same amount in pairs), the optical fiber Fa
The light from No. 2 is incident on the light-emitting side gradient index rod lens La2 at a position shifted downward by Δx from the original optical axis, and travels upward in the drawing through the light-emitting side gradient index rod lens La2. The light then spreads as described above, and then travels straight as parallel light and enters the light-receiving-side gradient index rod lens Lb2. Therefore, the light-receiving side gradient index rod lens Lb2
, The parallel light is obliquely incident from below in the figure.

Thereafter, the parallel light is condensed while traveling through the light-receiving side gradient index rod lens Lb2. At this time, as shown in FIG. The light is condensed on the optical fiber Fb2 side end in contrast to the above. Therefore, the focal point f of the light-receiving side gradient index rod lens Lb2 is located at a position displaced upward (2 · Δx) from the optical axis of the optical fiber Fb2 which is the original optical axis.

As described above, the amount of displacement between the light-receiving side gradient index rod lens and the optical fiber connected to it is just 2 with respect to the amount of displacement of the gradient index rod lens pair.
Therefore, even if the amount of displacement of the refractive index distribution type rod lens pair is small, the optical coupling loss of the rod lens array becomes large and, in some cases, cannot be ignored in practical use.

Therefore, as shown in FIG. 6, the lens lengths of the light-emitting side gradient index rod lenses La′1 to La′3 are (3P / 4), and the light-receiving side gradient index rod lenses L ′
The lens lengths of b′1 to Lb′3 remain (P / 4).

In such a configuration, similarly to FIG. 5, the light-emitting side gradient index rod lens La located in the center of the figure is shown.
'2 and the light-receiving side gradient index rod lens Lb'2
Assuming that both the refractive index distribution type rod lenses La′1 and Lb′1 are displaced by Δx, the optical fiber Fa2
The light incident on the light-emitting side gradient index rod lens La'2 from the lens spreads inside the light-emitting side gradient index rod lens La'2 to a position of 1/3 of the lens length and 2/3 of the lens length. After being condensed at the position (point t), the light again spreads toward the end face, then becomes parallel light, travels straight, and enters the light-receiving side gradient index rod lens Lb′2. At that time, the incident light travels upward in the figure up to the point t, and travels downward in the figure after the point t. Also, t point located on the optical axis of the light exit side refractive index rod lens La'2, displacement with respect to the optical fiber Fa2, namely a △ x.

Therefore, the parallel light is incident on the light-receiving side gradient index rod lens Lb'2 from obliquely above in the drawing. Thereafter, the parallel light is collected while traveling through the light-receiving side gradient index rod lens Lb'2. At this time, as shown in the figure, the light emitting side gradient index rod lens La'2
Is focused on the end of the optical fiber Fb2 on the side of the optical fiber Fb2 in contrast to the traveling mode of the optical fiber Fb2.
The position coincides with the optical axis of b2.

As described above, the lens lengths of the light-emitting side gradient index rod lenses La′1 to La′3 are set to (3P / 4), and the light-receiving side gradient index rod lenses Lb′1 to Lb ′.
By setting the lens length of (3) to (P / 4), it becomes possible to suppress the light coupling loss of the rod lens array even if the refractive index distribution type rod lens pair is displaced.

In the above example, the case where the lens length of the refractive index distribution type rod lens on the light receiving side is (P / 4) has been exemplified.
/ 4) A collimator can be formed even by using a lens having a shorter lens length Z '. In this case, the lens length Z of the light-emitting side gradient index rod lens is (Z = Z ′ + P / 2).
Of course, the relationship between the lens lengths may be reversed such that the light-emitting side is Z 'and the light-receiving side is (Z' + P / 2).

[0032]

As is apparent from the above description, according to the present invention, there is no need for the angle alignment between the gradient index rod lenses, and the alignment operation is simplified, whereby the collimator having a small coupling loss is obtained. Alternatively, the collimator array can be obtained by a simple manufacturing process and without requiring any special device or operation.

Further, by defining the lens length of the gradient index rod lens pair, even if the gradient index rod lens pair is displaced, light coupling loss can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1C are perspective views showing a manufacturing procedure of a collimator according to the present invention.

FIG. 2 is an explanatory diagram showing a light propagation state inside a refractive index distribution type rod lens and at an end face.

FIGS. 3A to 3C are perspective views showing another example (using a V-groove substrate) of a manufacturing procedure of the collimator according to the present invention.

FIGS. 4A to 4C are perspective views showing a procedure for manufacturing a collimator array according to the present invention.

FIG. 5 shows that the lens length of the gradient index rod lens pair is (P
FIG. 14 is a top view for explaining a problem that occurs when the values are the same in (/ 4).

FIG. 6 shows that the lens length of the gradient index rod lens pair is (3
It is a top view which shows the structure changed to the combination of (P / 4) and (P / 4).

FIG. 7 is a perspective view showing a conventional collimator.

FIGS. 8A and 8B are a plan view and a side view, respectively, for explaining the axial displacement between the gradient index rod lenses of the collimator.

[Explanation of symbols]

 1: Raw material of refractive index distribution type rod lens 1, 1a: Distribution of refractive index type rod lens 2, 2a: Substrate 4: Optical fiber 5, 5a: Substrate La1 to La3: Outgoing side refractive index distribution type rod lens Lb1 to Lb3: Light-receiving-side refractive index distribution type rod lenses La′1 to La′3: Light-emitting-side refractive index distribution type rod lenses Lb′1 to Lb′3: Light-receiving side refractive index distribution type rod lenses Fa1 to Fa3: Optical fibers Fb1 to Fb3 : Optical fiber

Claims (8)

[Claims] 1. A collimator comprising a pair of gradient index rod lenses opposed to each other, wherein the gradient index rod lens is formed on a substrate having a flat end surface. A collimator characterized in that an optical axis and one of the end faces are respectively fixed so as to be parallel, and the pair of substrates are opposed to each other while the end faces are kept parallel to each other. 2. In a pair of opposed refractive index distribution type rod lenses, the lens length of one refractive index distribution type rod lens is made longer (（) pitch than the lens length of the other refractive index distribution type rod lens. The collimator according to claim 1, wherein: 3. A collimator array comprising a pair of rod lens arrays in which refractive index distribution type rod lenses are juxtaposed at a predetermined pitch and opposed to each other, wherein the refractive index distribution is formed on a substrate having a planar end face. The fixed rod lenses are fixed at a predetermined pitch so that the optical axis of the gradient index rod lens and one of the end faces are parallel to each other, and the pair of substrates are opposed to each other while the end faces are kept parallel to each other. A collimator array, wherein 4. In the pair of refractive index distributed rod lenses facing each other, the lens length of the refractive index distributed rod lens forming one rod lens array is set to the length of the refractive index distributed rod lens forming the other rod lens array. 4. The collimator array according to claim 3, wherein the length is increased by (1/2) pitch of the lens length. 5. A method of manufacturing a collimator comprising a pair of refractive index distribution type rod lenses opposed to each other, comprising: forming a long gradient index distribution type rod lens raw material on a substrate having a flat end surface; After fixing the optical axis of the refractive index distribution type rod lens raw material and one of the end faces to be parallel, the refractive index distribution type rod lens raw material is fixed at predetermined intervals on a surface orthogonal to the optical axis for each substrate. It cuts and divides, then adjusts each of the divided refractive index distribution type rod lens raw materials to a specified lens length, and then makes the cut-side end surfaces face each other and matches the optical axes of both lenses. Manufacturing method of a collimator. 6. The method for manufacturing a collimator according to claim 5, wherein the cut substrates are opposed to each other so that their end faces are parallel to each other so that the optical axes of both lenses coincide with each other. 7. A method of manufacturing a collimator array comprising a pair of rod lens arrays in which refractive index distribution type rod lenses are juxtaposed at a predetermined pitch and opposed to each other. The refractive index distribution type rod lens raw materials are arranged side by side at a predetermined pitch so that the optical axis of the refractive index distribution type rod lens raw material and one of the end faces are parallel to each other, and then the refractive index distribution is performed at predetermined intervals. Cut and split the rod material of the mold rod lens along with the substrate at a plane perpendicular to the optical axis, and then adjust each of the divided gradient index rod lens materials to the specified lens length. And a method of manufacturing a collimator array, wherein the optical axes of the opposed lenses are made to coincide with each other. 8. The substrate according to claim 7, wherein the cut substrates are opposed to each other so that their end faces are parallel to each other, and the optical axes of at least a pair of opposed lenses are aligned. Manufacturing method of collimator array.