JP2014211645A - Microlens array and optical transmission component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microlens array capable of maintaining high accuracy of positioning with an optical circuit such as a waveguide and facilitating connection work, and an optical transmission component including the microlens array.SOLUTION: A microlens array includes: plural microlenses 1 disposed in an array structure and having the same length as each other in the optical axis direction; alignment optical fibers 9 which are disposed on both ends of the array structure such that an optical axis is parallel to the optical axis of the microlenses, and whose length in the optical axis direction is the same as the length of the microlenses and whose waveguide mode diameter is smaller than an aperture of the microlenses; a V-shaped groove plate 2 in which V-shaped grooves are formed at fixed intervals in parallel with each other and the microlenses and the alignment optical fibers are placed in the respective V-shaped grooves; and an upper plate 3 for fixing the microlenses and the alignment optical fibers to the V-shaped groove plate.

Description

  The present invention relates to a microlens array for connecting between a planar lightwave circuit used in the field of optical communication and an optical semiconductor element array such as a photodiode, and an optical transmission component including the same.

  A refractive index distribution type (hereinafter referred to as GI) multimode optical fiber used in optical communication exhibits a square refractive index distribution with the refractive index of the core center as the maximum refractive index, and not only as an original optical transmission line. When used as a microlens, it exhibits a good lens function. Therefore, it is also used for optical coupling between an optical circuit and an optical semiconductor element such as a photodiode (hereinafter referred to as PD).

  FIG. 1 shows an example of a conventional microlens array used for such a purpose (see, for example, Patent Document 1). In FIG. 1, two arrays of microlenses 1 made of GI fiber and having an optical axis as the Z-axis direction are sandwiched between the V-groove plate 2 and the upper plate 3 so as to be arranged along the array axis parallel to the X-axis. It is fixed with an adhesive 4. The length of the microlens 1 in the Z direction varies depending on the desired condensing position and condensing diameter, but is usually about 0.3 to 1 mm.

JP 2008-04-0028 A

  Consider a case where the two-array microlens array shown in FIG. 1 is connected to the two branch side of the 1 × 2 branch optical circuit 5 as shown in FIG. The branch-side waveguide interval is the same as the array interval of the microlens array. Here, the optical circuit 5 includes an optical waveguide 7 composed of a core and a clad on a substrate, and a Yatoi plate for facilitating connection of fibers and other components at both ends. Connection and fixing of the microlens array is achieved by connecting an optical fiber or other component to the optical circuit end on one input side in advance and allowing the guided light to pass therethrough, while monitoring the output light from the microlens 1 with the monitor PD6. Fix in place of strength. There was the following problem here.

FIG. 3 is a diagram when the alignment state is viewed from the X direction. When the alignment is fixed, it is necessary to match the center of the waveguide mode field distribution propagating through the optical waveguide 7 with the center position of the microlens 1 in order to maximize the lens performance such as the light collecting ability. Normally, the waveguide mode diameter of the optical waveguide 7 is 10 μm or less, whereas the diameter of the microlens 1 is as large as 50 μm or more. Therefore, even if the lens center is shifted from the center of the waveguide mode, the emitted light from the microlens 1 Reaches the light receiving surface of the monitor PD 6 without attenuation or diffusion, and the amount of monitor light hardly changes in the radial direction from the optical axis as shown in FIGS. 3 (a) and 3 (b). That is, the position-monitor light intensity curve dually shown at the right end of FIG. 3B has a trapezoidal shape, and the lens center position coincident with the waveguide center cannot be obtained with sufficient accuracy. Here, the waveguide mode diameter is a diameter at which the light intensity becomes 1 / e ² from the peak in the waveguide mode field distribution curve shown in FIG.

  Therefore, as a method for solving this, as shown in FIG. 3C, a slit 8 having a hole diameter similar to the waveguide mode diameter of the optical waveguide 7 is placed in front of the monitor PD6. In this way, as shown in FIG. 3C, the position-monitor light intensity curve has a peak when the waveguide mode propagating through the optical waveguide 7 coincides with the center of the microlens 1 and can be aligned. It becomes.

  However, in the above method, the positional relationship between the slit 8 and the optical waveguide 7 is shown in the XY plane of the drawing so that the emitted light from the microlens 1 passes through the slit 8 when the center of the waveguide mode and the center of the microlens 1 coincide. In order to make them coincide with each other, it is necessary to set in advance with sufficient positional accuracy. For this reason, the above method has a problem that the lens mounting operation becomes complicated and the cost is difficult, for example, a dedicated device only for the optical circuit-lens connection step is required.

  Accordingly, in order to solve such problems, the present invention has an object to provide a microlens array that maintains high positional accuracy with an optical circuit such as a waveguide and that can be easily connected, and an optical transmission component including the microlens array. And

  In order to achieve the above object, a microlens array according to the present invention is characterized in that alignment optical fibers are arranged at both ends of a microlens arranged in an array.

  Specifically, the microlens array according to the present invention includes a plurality of microlenses arranged in an array structure and having the same length in the optical axis direction, and the optical axis is parallel to the optical axis of the microlens. It is arranged at both ends of the array structure, and the length in the optical axis direction is the same as the length of the microlens and the waveguide mode diameter is smaller than the diameter of the microlens and is aligned at a constant interval in parallel. A V-groove plate in which a V-groove is cut and the microlens and the alignment optical fiber are placed in each V-groove, and an upper plate that fixes the microlens and the alignment optical fiber to the V-groove plate And comprising.

  The intensity of light emitted from the alignment fiber is likely to change in the radial direction from the optical axis. For this reason, if a microlens and an alignment optical fiber are placed on the V-groove and fixed with the upper plate without using a slit having a hole diameter comparable to the waveguide mode diameter of the waveguide, the alignment fiber And the center of the waveguide mode of the waveguide such as an optical circuit can be made to coincide with each other with high accuracy. If an alignment waveguide is formed in parallel with the signal waveguide in the optical circuit connected to the microlens, the alignment waveguide and the alignment fiber of the microlens array are connected to each other. Positioning can be easily performed, and the microlens and the waveguide can be accurately connected.

  Therefore, the present invention can provide a microlens array that maintains high positional accuracy with an optical circuit such as a waveguide and that can be easily connected.

  The end surfaces of the microlens and the alignment optical fiber of the microlens array according to the present invention are flush with the end surfaces of the V-groove plate and the upper plate.

  In the microlens array according to the present invention, the microlens and the alignment optical fiber have the same cladding diameter.

  The microlens of the microlens array according to the present invention is a multimode gradient index optical fiber having a length in the optical axis direction of not less than 0.3 mm and not more than 1.0 mm. It is a one-mode optical fiber.

  The waveguide mode diameter of the optical fiber for alignment can be made sufficiently smaller than the aperture of the microlens, and the alignment accuracy can be improved.

  An optical transmission component according to the present invention includes an optical circuit including the microlens array, an optical waveguide optically connected to the microlens, and an alignment optical waveguide optically connected to a core of the alignment optical fiber; Have.

  In the optical circuit, an alignment waveguide is formed in parallel with the signal waveguide. Since the alignment waveguide and the alignment fiber of the microlens array can be easily aligned, the microlens and the waveguide of the optical circuit can be easily and accurately connected.

  Accordingly, the present invention can provide an optical transmission component that is easy to manufacture despite the high connection accuracy between an optical circuit such as a waveguide and a microlens array.

  Specifically, in the method for manufacturing a microlens array according to the present invention, a plurality of microlenses are provided in a V-groove cut in parallel at regular intervals of the V-groove plate, and the plurality of microlenses have outer diameters at both ends thereof. An alignment optical fiber having the same waveguide mode diameter smaller than the apertures of the plurality of microlenses is disposed, and the plurality of microlenses, the alignment optical fiber, and the upper plate are bonded to the V-groove plate with an adhesive. Fix and cut out the end face.

  The microlens and the alignment optical fiber can be aligned along the X axis, the Y axis, and the Z axis.

  According to the present invention, it is possible to provide a microlens array that maintains high positional accuracy with an optical circuit such as a waveguide and that can be easily connected, and an optical transmission component including the microlens array.

It is a perspective view of the conventional micro lens array. It is a perspective view which shows the connection operation | work of the conventional microlens array and an optical circuit. It is sectional drawing which shows the connection operation | work of the conventional microlens array and an optical circuit. (A) It is a figure when a waveguide and a lens optical axis have shifted | deviated. (B) It is a figure when a waveguide and a lens optical axis have shifted | deviated. (C) It is a figure explaining the operation | work which aligns a waveguide and a lens optical axis using a slit. It is sectional drawing which shows the connection operation | work of the microlens array which concerns on this invention, and an optical circuit. 1 is a perspective view of a microlens array according to the present invention. It is a perspective view which shows the connection operation | work of the microlens array which concerns on this invention, and an optical circuit. It is a comparative graph of the position-monitor light intensity curve of an optical waveguide and a micro lens. It is an expansion comparison graph near the optimal alignment position of the position-monitor intensity curve of an optical waveguide and a microlens.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments.

  In the configuration shown in FIG. 3, the microlens 1 is replaced with an alignment optical fiber 9 which is a single mode optical fiber having a waveguide mode diameter equivalent to that of the optical waveguide 7, and the configuration shown in FIG. 4 is considered. Then, the position-monitor light intensity curve received by the monitor PD 6 is high in the background light intensity because the alignment optical fiber 9 is as short as 1 mm or less, as schematically shown in the figure. When the waveguide mode center of the fiber 9 coincides with the waveguide mode center of the optical waveguide 7, the peak curve becomes maximum. In order to solve the above problem, the following may be performed.

  The microlens array of this embodiment is arranged in an array structure, and has a plurality of microlenses 1 having the same length in the optical axis direction, and both ends of the array structure so that the optical axis is parallel to the optical axis of the microlens 1. And an alignment optical fiber 9 having a length in the optical axis direction equal to the length of the microlens 1 and a waveguide mode diameter smaller than the aperture of the microlens 1.

  The microlens 1 is a multimode gradient index optical fiber, and the alignment optical fiber 9 is a single mode optical fiber.

  FIG. 5 shows a perspective view of the microlens array of the present embodiment. The microlens array is composed of two arrays of microlenses 1 made of GI fibers, and a single mode having a waveguide mode diameter equivalent to the waveguide mode diameter of the optical waveguide 7 on the both sides of the same cladding diameter as the GI fiber. And an alignment optical fiber 9 made of an optical fiber. The microlens array further includes a V-groove plate 2 and an upper plate 3 in which four parallel V-grooves having the same shape are formed in the Z-axis direction perpendicular to the straight line parallel to the X-axis. The micro lens 1 and the alignment optical fiber 9 are sandwiched between the V-groove plate 2 and the upper plate 3 and fixed with an adhesive 4.

  The interval between the microlenses 1 is matched with the waveguide interval of the optical circuit to be connected. The difference from the conventional type shown in FIG. 1 is that two alignment optical fibers 9 are provided on both sides of the array structure of the microlenses 1. Since the microlens 1 and the alignment optical fiber 9 have the same cladding diameter, the centers of the microlens 1 and the alignment optical fiber 9 are automatically aligned on a straight line.

  Another difference is that, as shown in FIG. 6 which is an application diagram of this microlens array, the optical circuit 5 and the alignment waveguide 10 and the optical waveguide 5 are aligned with the two alignment optical fibers 9. This is a point provided with a connected optical fiber 11.

  For alignment of the microlens array to the optical circuit 5, the monitor light from the alignment waveguide 10 is received by the monitor PD6. The position-monitor light intensity curve has a peak as shown in FIG. 4, and the optical circuit 5 is aligned by the alignment work of the alignment waveguides 10 and the alignment optical fibers 9 installed at both ends of the array structure. And the microlens array can be fixed in two axes.

  It is assumed that the clad diameters of the GI fiber used as the microlens 1 and the alignment optical fiber 9 are different. In that case, in the V-groove plate 2, the V-grooves corresponding to the microlens 1 and the alignment optical fiber 9 are set to different depths so that the centers of the microlens 1 and the alignment optical fiber 9 are aligned in a straight line. You can do it. Similarly, the upper plate 3 may be provided with a convex portion or a concave portion in addition to the V-groove plate so that the microlens 1 and the alignment optical fiber can be pressed and fixed.

Examples will be described below. In the embodiment, the operating wavelength is assumed to be 1.55 μm.
As the optical circuit 5, a quartz-based planar lightwave circuit having an NA of 0.21 and a waveguide mode diameter of 7 μm was used. For the microlens 1, a GI optical fiber having an NA of 0.28, a core diameter of 62.5 μm (that is, a lens aperture of 62.5 μm), and a cladding diameter of 125 μm was used. A single-mode optical fiber having an NA of 0.14, a waveguide mode diameter of 9.2 μm, and a cladding diameter of 125 μm was used as the alignment optical fiber 9 to be arranged on both sides. These fibers are made of Pyrex (registered trademark) glass and cut with a gap of 250 μm, a 60-degree V-groove plate 2, an adhesive 4, and an upper plate 3 made of a Pyrex (registered trademark) glass flat plate like the V-groove plate 2 A block was formed, and then cut into a length of 0.411 mm to form a microlens array with an interval of 250 μm.

  FIG. 7 and FIG. 8 show position-monitor light intensity curves at the time of the alignment operation to the optical circuit 5 of the microlens array with the alignment optical fiber. The light receiving diameter of the monitor PD 6 used here is 10 mmφ. In these figures, for comparison, a case where the microlens 1 (GIF in the figure), which is a conventional method, is aligned (without using the slit 8) and an optical fiber 9 for alignment according to the present invention (SMF in the figure). ) Are both shown. FIG. 7 is a position-monitor light intensity curve in a range of ± 50 μm with the point where the waveguide core of the optical circuit 5 and the center of the microlens 1 substantially coincide with each other. In the range of ± 10 μm or more, the position of the waveguide core and the alignment fiber 9 are greatly shifted. Therefore, the monitor PD 6 receives the light passing through the cladding of the alignment optical fiber 9 as background light and the background light intensity. Is stronger than that of the GI lens. On the other hand, in the range of ± 10 μm or less, it can be seen that a sharper peak than the GI lens transmitted light is shown. FIG. 8 is an enlarged graph of a range of ± 5 μm. As is apparent from the figure, in the GI lens, the position-monitor light intensity curve is constant in the region of ± 3 μm in the X direction and ± 2 μm in the Y direction, and the peak cannot be determined with higher accuracy. On the other hand, in the alignment using a single mode optical fiber as the alignment optical fiber 9, the peak was clear and the alignment optimum position could be determined with sub-μm accuracy.

  In this embodiment, the microlens array structure is described as two arrays, but the array structure is not limited to this. Further, the optical fiber for alignment is not limited to a single mode optical fiber but may be a multimode optical fiber. In any optical fiber, the waveguide mode diameter is required to be smaller than the aperture of the microlens. “Small” means that the waveguide mode diameter of the alignment optical fiber is larger than 0 and smaller than the aperture of the microlens. Regarding the alignment accuracy, the maximum accuracy is obtained when the waveguide mode diameter of the optical waveguide 7 and the waveguide mode diameter of the alignment optical fiber 9 coincide. In this case, the optical coupling between the optical waveguide 7 and the alignment optical fiber 9 is maximized, the background light is minimized, and the sharpest alignment peak curve is obtained, so that a peak with a low S / N can be identified. It is.

(Effect of embodiment)
As described above, according to the present embodiment, the following effects can be expected.
First, in this embodiment, the alignment optical fiber 9 is added to both sides of the array of the microlenses 1, and the optical fiber 11 corresponding to the input side of the optical circuit is added. However, the outer diameter accuracy of the optical fiber 11 is kept within ± 1 μm, and the unit price is low, and the fiber block fabrication technology using the V-groove is progressing in multi-array technology, which is technically difficult. There is no.

Further, it is necessary to add the alignment waveguide 10 to the optical circuit 5, but it is only used for alignment work, and there is no need to ask the quality of the waveguide itself, and it is added on the photomask at the design stage. Only.
Therefore, the effect on the cost increase by adopting this structure is negligible.

Next, further advantages of this embodiment will be described.
First of all, the biaxial alignment process may be the same process as a normal waveguide connection. By using sophisticated optical fiber array fabrication technology, the optical fiber for alignment can be substituted for the action of the slit 8 that requires high-precision positioning accuracy, and the conventional waveguide connection device remains as it is without any high functionality. It can be used.

  Second, the microlens array can be connected to a high-performance optical circuit using the electro-optic effect or the thermo-optic effect without operating those circuits. In the above-described high-function circuit, normally-off is often set. Conventionally, it has been necessary to drive the circuit during connection work in order to obtain monitor light. In the present embodiment, since a waveguide for alignment is used, such a driving device is also unnecessary.

  As described above, since the present invention can attach a microlens array to an optical circuit with high accuracy, 20 μm aimed at a band of 20 GHz or more which is expected to increase in demand as the capacity of optical communication increases in the future. It is effective for the connection between an optical circuit and an ultrahigh-speed photodiode with the following narrow light receiving diameter.

1: Micro lens 2: V groove plate 3: Upper plate 4: Adhesive 5: Optical circuit 6: Monitor PD
7: Optical waveguide 8: Slit 9: Alignment optical fiber 10: Alignment waveguide 11: Optical fiber

Claims (6)

A plurality of microlenses arranged in an array structure and having the same length in the optical axis direction;
The optical axis is arranged at both ends of the array structure so as to be parallel to the optical axis of the micro lens, the length in the optical axis direction is the same as the length of the micro lens, and the waveguide mode diameter is the micro lens. An optical fiber for alignment smaller than the diameter of
V-groove plates in which V-grooves are cut in parallel at regular intervals, and the microlenses and the alignment optical fibers are placed in the respective V-grooves;
An upper plate for fixing the microlens and the alignment optical fiber to the V-groove plate;
A microlens array comprising:   2. The microlens array according to claim 1, wherein end surfaces of the microlens and the alignment optical fiber are flush with end surfaces of the V-groove plate and the upper plate.   The microlens array according to claim 1 or 2, wherein the microlens and the alignment optical fiber have the same cladding diameter. The microlens is a multimode gradient index optical fiber having a length in the optical axis direction of 0.3 mm or more and 1.0 mm or less,
4. The microlens array according to claim 1, wherein the alignment optical fiber is a single mode optical fiber. The microlens array according to any one of claims 1 to 4,
An optical circuit comprising an optical waveguide optically connected to the microlens, and an alignment optical waveguide optically connected to a core of the alignment optical fiber;
An optical transmission component having.   A plurality of microlenses and outer diameters at both ends thereof are the same as those of the plurality of microlenses and the waveguide mode diameter is smaller than the diameters of the plurality of microlenses. A method of manufacturing a microlens array in which an alignment optical fiber is disposed, the plurality of microlenses, the alignment optical fiber, and an upper plate are fixed to the V-groove plate with an adhesive, and an end face is cut out.

Images