JP2004125899A - Optical waveguide with lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide in which good coupling efficiency with another optical element is easily obtained and a lens is provided. <P>SOLUTION: The optical waveguide consists of an under clad layer 21 formed on a substrate 10, a core 22 which is located on the layer 21 and is collectively patterned and integrally formed by photolithography using a same mask, a projected shape lens 26 which is projected from the end face of the core 22 along the parallel direction of the plate surface of the substrate 10 and an over clad layer 23 which is formed to cover the both side surfaces and the top surface of the core 22 without covering the lens 26. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical waveguide that can easily obtain good coupling efficiency when, for example, coupling light from a light emitting element to an optical waveguide in the field of optical communication and the like.
[0002]
[Prior art]
FIG. 3 shows an example of a conventional optical coupling structure between an optical waveguide and a light emitting element. An optical waveguide 20 is formed on one side of a substrate 10 and a laser diode is used as a light emitting element on the other side. (LD) 30 is mounted.
The optical waveguide 20 covers the under cladding layer 21 formed on the substrate 10, the core 22 formed on the under cladding layer 21 with a predetermined width and height, and both side surfaces and the upper surface of the core 22. The over cladding layer 23 is formed.
[0003]
The laser diode 30 is mounted on the electrode 11 formed on the substrate 10 with high accuracy using, for example, an alignment marker. In this example, the laser diode 30 and the optical waveguide 20 are directly coupled. ing.
The electrode 12 formed adjacent to the electrode 11 is connected to the upper surface electrode of the laser diode 30 by wire bonding, and the wires are not shown in this example. The electrodes 11 and 12 are made of, for example, gold (Au). In FIG. 3, reference numeral 13 denotes a solder layer, and reference numeral 31 denotes a laser beam emitted from the laser diode 30.
[0004]
Incidentally, in the structure in which the laser diode and the optical waveguide are directly coupled as shown in FIG. 3, a large coupling loss occurs due to a mode field diameter mismatch at the coupling portion between the laser diode and the optical waveguide. It has been difficult to produce an integrated laser / waveguide optical module with high output.
On the other hand, there is a method in which a lens is arranged between the laser diode and the optical waveguide, and the laser diode and the optical waveguide are coupled with high efficiency via the lens. Since the alignment accuracy is strict and active alignment is required, assembling man-hours are required at that point, and this has been a cause of high cost.
[0005]
On the other hand, FIG. 4 shows a conventionally proposed coupling structure between an optical waveguide and a light emitting element (laser diode), and portions corresponding to FIG. 3 are denoted by the same reference numerals.
In this example, a convex surface portion 24 protruding toward the laser diode 30 is formed on an end surface of the optical waveguide 20 formed on the substrate 10 facing the laser diode 30, thereby having a lens effect on the end surface of the core 22. (For example, see Patent Document 1).
FIG. 5 sequentially shows the steps of manufacturing the optical waveguide 20 having the convex surface portion 24 at the end face, and each step will be described below.
[0006]
(1) The under cladding layer 21 and the core layer are sequentially formed on the substrate 10 and the core layer is patterned to form the core 22.
(2) The over cladding layer 23 is formed so as to cover both side surfaces and the upper surface of the core 22.
(3) An etching mask 25 is formed on the upper surface of the over cladding layer 23. The etching mask 25 has a projection 25a formed on the edge thereof.
(4) The over cladding layer 23, the core 22, and the under cladding layer 21 are etched through the etching mask 25. As a result, a convex portion 24 is formed on the end surface of the optical waveguide 20.
Thereafter, by removing the etching mask 25, the optical waveguide 20 having the convex portion 24 at the end face shown in FIG. 4 is completed.
[0007]
[Patent Document 1]
JP-A-2000-39531 (FIG. 1-5)
[0008]
[Problems to be solved by the invention]
If a lens (lens structure) is integrally formed on the core as described above, active alignment that requires man-hours, unlike the case of disposing a lens as a discrete component, becomes unnecessary. Therefore, the optical waveguide is coupled to, for example, a laser diode. In this case, although the coupling efficiency can be increased at low cost, the conventional examples shown in FIGS. 4 and 5 have the following problems.
That is, in the conventional example, as shown in FIG. 5, after forming the core 22 and further forming the over cladding layer 23, etching is performed using the etching mask 25 to form the convex portion 24 on the end face of the optical waveguide 20. Since the projections 25a of the etching mask 25 must be positioned with high precision with respect to the fine core 22 embedded in the over cladding layer 23, it is difficult to determine the positioning accuracy. And, as a result, a situation in which good performance and coupling efficiency cannot be obtained due to the displacement of the etching mask 25 can occur.
[0009]
In view of this problem, an object of the present invention is to provide an optical waveguide with a lens having a lens integrally formed with a core, in which there is no deviation between the core and the lens, and thus a good coupling efficiency in coupling with an optical element such as a laser diode. Is to provide an optical waveguide with a lens that can easily (at low cost).
[0010]
[Means for Solving the Problems]
According to the present invention, an optical waveguide with a lens is an undercladding layer formed on a substrate, and a core located on the undercladding layer and integrally formed by collective patterning by photolithography using the same mask, A lens having a convex shape protruding in a direction parallel to the substrate plate surface from an end surface of the core, and an overcladding layer formed so as to cover both side surfaces and an upper surface of the core without covering the lens. Is done.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a coupling structure between an embodiment of an optical waveguide with a lens according to the present invention and a laser diode. Portions corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.
In this example, the core 22 and the lens 26, which is formed so as to protrude from the end surface of the core 22 in a direction parallel to the plate surface of the substrate 10 and has a convex shape, are collectively patterned by photolithography using the same mask and are integrally formed. It is assumed that it is.
[0012]
The over cladding layer 23 is formed without covering the lens 26, and the upper surface of the lens 26 is exposed to the outside together with its end surface.
FIG. 2 shows the manufacturing steps of the optical waveguide 20 with the lens 26 in the case where a photosensitive resin is used as the optical waveguide material, and each step will be described below with reference to FIG. In addition, as the photosensitive resin, an acrylic or epoxy UV curable resin can be used. The core 22, the under cladding layer 21, and the over cladding layer 23 have, for example, a relative refractive index difference Δn of about 0.3% to 2%.
[0013]
(1) The under cladding layer 21 is formed on the substrate 10 by spin coating and cured by exposure. For example, a silicon substrate is used as the substrate 10.
(2) A core layer 22 'is similarly formed on the under cladding layer 21 by spin coating.
(3) The core 22 and the lens 26 are collectively exposed / developed with the same mask and patterned. The core 22 is patterned with a width and a height of, for example, about 3 μm to 8 μm. The lens 26 is patterned in a semicircle in this example.
(4) The over cladding layer 23 is spin-coated thereon.
(5) The over cladding layer 23 is patterned by exposing / developing with a mask exposing the lens 26.
[0014]
Through the above steps, the optical waveguide 20 with the lens 26 is completed.
In the above, the reason why the over clad layer 23 is not covered on the upper surface of the lens 26 but is exposed is to increase the relative refractive index difference with the outside for the purpose of providing a lens effect. For example, the relative refractive index difference when the over clad layer 23 is covered here is about Δn = 0.3% to 2%, but becomes large as Δn = 30% when the outside is air.
In the above manufacturing process, the under cladding layer 21, the core layer 22 ', and the over cladding layer 23 are all applied and formed by spin coating. However, for example, a dip method can be used instead of spin coating.
[0015]
According to the optical waveguide 20 with the lens 26 configured as described above, since the lens 26 integrated with the core 22 is formed by patterning at the same time as patterning of the core 22, the position shift with respect to the core 22 is performed. Does not occur.
Therefore, when the laser diode 30 is coupled to the optical waveguide 20 with the lens 26 as shown in FIG. 1, good coupling efficiency between the optical waveguide 20 and the laser diode 30 is obtained, and The laser beam 31 emitted from the lens is collimated by the lens 26 and efficiently enters the core 22.
The lens 22 changes its radius R in the lateral direction of the light beam of the laser beam 31 (in the direction parallel to the plate surface of the substrate 10) so as to convert the mode field diameter of the optical waveguide 20 into the mode field diameter of the laser diode 30. Can be determined. That is, when the radius R is determined, the focal length f is determined. For these, there is an optimum value matching the lateral opening angle of the laser diode 30.
[0016]
On the other hand, in this example, since the lens effect is provided only in the horizontal direction, in the vertical direction, the field diameter of the optical waveguide 20 increases in proportion to the distance from the optical waveguide 20 according to the opening angle of the end face of the optical waveguide 20. It has become. Therefore, in the vertical direction, the optimum distance between the laser diode 30 and the optical waveguide 20 in the vertical direction in the conventional example not including the lens as shown in FIG. Since the optimum distance in the vertical direction and the optimum distance (f) in the horizontal direction generally do not coincide with each other, an advantageous distance and a lens radius R for the total light amount are appropriately selected from between the two.
[0017]
In the above-described embodiment, a UV-curable photosensitive resin is used as the optical waveguide material. However, the optical waveguide material is not limited to this, and an organic material such as polyimide can also be used.
In this case, the collective patterning of the core 22 and the lens 26 is performed by spin-coating a plasma-resistant resist on a core layer 22 ′ made of polyimide, and applying the resist using a mask having the shape of the core 22 and the lens 26. Exposure / development is performed, and the core layer 22 'is plasma-etched by reactive ion etching (RIE) using a resist as a mask.
[0018]
【The invention's effect】
As described above, according to the present invention, the core and the lens are collectively patterned by the same photolithography and are integrally formed, so that the coupling with the optical element such as a laser diode is the same as when a discrete lens is used. Troublesome positioning is not required, so that good coupling efficiency can be obtained at low cost.
Further, unlike the configuration of the conventional optical waveguide in which a convex portion is formed on the end face of the optical waveguide as shown in FIG. 4 and the lens face is provided with the lens effect, the position between the core and the lens does not shift. Therefore, in this regard, according to the present invention, the lens can be extremely easily and precisely arranged with respect to the core.
In addition, since a lens having an arbitrary shape can be easily manufactured by designing a mask, an optimal optical waveguide with a lens can be easily manufactured according to an application.
[Brief description of the drawings]
FIG. 1 is a diagram showing a coupling structure between an optical waveguide with a lens and a laser diode according to the present invention; FIG. 1A is a plan view;
FIG. 2 is a view for explaining a manufacturing process of the optical waveguide with a lens in FIG. 1;
FIG. 3 is a diagram showing a conventional coupling structure between an optical waveguide and a laser diode, where A is a plan view and B is a side view.
FIG. 4 is a perspective view showing a conventionally proposed coupling structure between an optical waveguide and a laser diode.
FIG. 5 is a view for explaining a manufacturing process of an optical waveguide having a convex portion on an end face in FIG. 4;

Claims (1)

An under cladding layer formed on the substrate,
A core that is located on the undercladding layer and is integrally formed by collective patterning by photolithography using the same mask, and a convex lens that protrudes from an end surface of the core in a direction parallel to the substrate plate surface. ,
An optical waveguide with a lens, comprising an over cladding layer formed so as to cover both side surfaces and an upper surface of the core without covering the lens.

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