JP2004271681A - Optical waveguide element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide element which enables a device including the optical waveguide element to be made small-sized as a whole by connecting an optical fiber for incidence and projection to the optical waveguide element in nearly 90° position relation. <P>SOLUTION: The optical waveguide element having a substrate 10 with electrooptic effect and an optical waveguide 11 formed on the substrate has a GRIN lens 20 for optically coupling the optical waveguide 11 and an optical fiber 22, and a flank of the GRIN lens is arranged opposite to a flank 2 of the substrate where an end of the optical waveguide is positioned and an end surface of the GRIN lens is arranged opposite to the optical fiber. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical waveguide device having an optical waveguide formed on a substrate having an electro-optic effect, and more particularly to an optical waveguide device having a feature in a connection structure between the substrate having an electro-optic effect and an optical fiber.
[0002]
[Prior art]
In response to the growing demand for high-speed, large-capacity information communication in recent years, the use of high-density wavelength multiplexing (DWDM) in optical communication has been progressing. Therefore, it is necessary to use a large number of optical waveguide elements such as optical modulators in combination, and in particular, to reduce the size of the optical waveguide element body and the state where the optical fiber is connected to the main body, thereby increasing the size of the entire device. And to make the whole compact.
[0003]
The conventional optical modulator module (in which the optical modulator main body and its associated parts are housed in a metal case and configured to be easy to handle) includes an optical waveguide in an optical waveguide element constituting the optical modulator, The input and output optical fibers to be connected are substantially on a straight line. Therefore, when the optical modulator module is housed in the device box, as shown in FIG. 1, the minimum bending length of the optical fiber 3 extending from the case (see FIG. Of the holding members 4 and 5 for holding the optical fiber extending from the case (strictly speaking, the space length obtained by adding the lengths l ₁ and l ₂ of the holding members 4 and 5).
[0004]
Therefore, in order to reduce the storage space of the optical modulator module, the angle between the input optical fiber and the output optical fiber extending from the optical modulator module is arbitrarily set as shown in FIG. It is necessary to reduce the space of the minimum bending length (R portion) of the optical fiber by bending to an angle.
1 and 2 denotes a terminal for inputting a microwave signal voltage, a terminal for outputting a detection signal from a light receiving element housed in the optical modulator module 1, and the like. . Further, in order to reduce the optical loss associated with the connection between the optical modulator and the optical fiber, a connection method having an inclination of about 2 ° as shown in FIGS. 1 and 2 is used.
[0005]
As shown in FIG. 2, in order to bend the optical fiber for input and output at 90 °, (1) a method of bending the optical fiber by 90 ° within the case of the optical modulator module 1 (Japanese Patent Laid-Open No. 7-294781), (2) A method has been proposed in which the optical axis is bent to 90 ° by using a reflecting member such as a prism for incident light or outgoing light from an optical waveguide element (Japanese Patent Application Laid-Open No. 2001-242338).
[0006]
However, in the case of the method (1), it is necessary to separately secure a space for accommodating a waveguide member such as an optical fiber bent at 90 ° inside the case. become longer. Moreover, in order to reduce the radius of curvature, it is necessary to use a high-refractive-index waveguide member to increase the confinement of the guided light. However, the mode pattern of the guided light is reduced, and the waveguide is formed in an external optical fiber. When this is combined, the junction loss of the guided light increases.
Also, in the case of the method (2), the length L ′ of the case itself is increased, the number of optical components is increased, and the optical position is increased. Manufacturing processes such as adjustment are complicated, and manufacturing is difficult. In addition, there is a drawback that the physical characteristic between the optical components is increased and the temperature characteristic is deteriorated.
[0007]
Further, Japanese Patent Application No. 2002-285721 filed by the present applicant (filing date: September 30, 2002) describes a method of forming a reflection means 12 on a side surface of a substrate of an optical waveguide element as shown in FIG. ing.
3, reference numeral 10 denotes a substrate having an electro-optical effect, 11 denotes an optical waveguide formed on the substrate, and 13 denotes an optical fiber. The light emitted from the optical waveguide propagates through the substrate as shown by 14 and enters the optical fiber 13.
[0008]
The folded structure of propagating light using the side surface of the substrate as shown in FIG. 3 has many advantages such as miniaturization of the entire device including the optical waveguide element. There is a problem that it largely depends on the processing accuracy of the formed substrate side surface.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and connect an input / output optical fiber to an optical waveguide element so as to have a positional relationship of approximately 90 °, thereby reducing the size of the entire device including the optical waveguide element. It is an object of the present invention to provide an optical waveguide device which enables the optical waveguide device.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, according to the invention according to claim 1, in an optical waveguide device having a substrate having an electro-optic effect and an optical waveguide formed on the substrate, the optical waveguide and the optical fiber are optically coupled. A GRIN lens for optically coupling, the side surface of the GRIN lens is arranged to face the side surface of the substrate where the end of the optical waveguide is located, and the end surface of the GRIN lens faces the optical fiber. It is characterized by being arranged.
[0011]
According to the first aspect of the invention, when the light emitted or incident from the optical waveguide of the optical waveguide element is bent at approximately 90 °, a GRIN lens having an optical characteristic such as a refractive index similar to that of an optical fiber is used. Therefore, it is possible to suppress the loss of the guided light in the connection with the optical fiber.
Further, since the GRIN lens is used, it can be in close contact with the substrate of the optical waveguide element or the optical fiber, and the temperature characteristics can be improved.
[0012]
Further, in the invention according to claim 2, in the optical waveguide device according to claim 1, the GRIN lens has a reflecting surface for reflecting light entering or exiting the optical waveguide in the optical axis direction of the GRIN lens. It is characterized by being formed.
[0013]
According to the second aspect of the present invention, the guided light is reflected by the reflection surface provided on the GRIN lens, and the guided light is made incident on the waveguide or the optical fiber of the optical waveguide element by utilizing the focusing function of the GRIN lens. As a result, propagation loss of guided light can be suppressed.
Moreover, by making the reflection surface mirror-like and totally reflecting the guided light, the propagation loss of the guided light can be further reduced.
[0014]
According to a third aspect of the present invention, in the optical waveguide device according to the second aspect, a reflection member is provided on the reflection surface.
[0015]
According to the third aspect of the invention, by providing a reflection member such as a reflection film, the reflection efficiency of guided light can be increased. Further, since the degree of freedom in setting the angle of the reflection surface with respect to the optical axis of the GRIN lens is increased, various device designs can be made.
[0016]
According to a fourth aspect of the present invention, in the optical waveguide device according to any one of the first to third aspects, a side surface of the GRIN lens is mirror-polished.
[0017]
According to the fourth aspect of the invention, since the side surface of the GRIN lens is mirror-polished, the optical coupling characteristics with the optical waveguide on the side surface of the substrate are improved, and the adhesion to the side surface of the substrate is also improved.
[0018]
According to a fifth aspect of the present invention, in the optical waveguide device according to any one of the first to fourth aspects, the side surface of the substrate where the end of the optical waveguide is located is a surface perpendicular to the optical axis of the optical waveguide. Characterized by being formed to be inclined with respect to.
[0019]
According to the fifth aspect of the present invention, since the side of the substrate at the end of the optical waveguide is inclined, the guided light emitted from the end of the optical waveguide is reflected at the side of the substrate at the junction between the substrate and the GRIN lens. However, it is possible to prevent returning to the optical waveguide direction. The inclination of the side surface of the substrate is caused by the difference in the refractive index between the substrate and the GRIN lens. Since guided light can always propagate on the optical axis of the lens, there is an effect of suppressing light loss as a result.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail using preferred examples.
In the following embodiments, an example using an optical modulator as an optical waveguide element will be described. However, the present invention is not limited to the optical modulator, and may be applied to an electric field sensor element for an optical electric field sensor system. Is possible. Further, in the optical modulator module, not only an optical waveguide element but also various optical components or electronic components such as a light source or a light receiving element such as a semiconductor laser can be modularized.
[0021]
As a substrate constituting the optical waveguide element, a material having an electro-optic effect, for example, lithium niobate (LiNbO ₃ ; hereinafter, referred to as LN), lithium tantalate (LiTaO ₃ ), PLZT (lead lanthanum zirconate titanate), In particular, LiNbO ₃ crystal, LiTaO ₃ crystal, or solid solution crystal composed of LiNbO ₃ and LiTaO ₃ is used because it is composed of a quartz-based material and is particularly easy to configure as an optical waveguide device and has large anisotropy. Is preferred. In this embodiment, an example using lithium niobate (LN) will be mainly described.
[0022]
As a method of manufacturing an optical waveguide device, an optical waveguide is formed by thermally diffusing Ti on an LN substrate, and then a dielectric SiO 2 is formed on the LN substrate to reduce the propagation loss of light in the optical waveguide. _Then, a modulation layer and a ground electrode having a height of several tens of μm are formed thereon by forming an electrode pattern of Ti / Au and gold plating. As a method of forming an electrode, a method of forming an electrode indirectly via a buffer layer as described above, or a method of forming an electrode directly on an LN substrate without providing a buffer layer over a part or the whole of a substrate There is a way.
Generally, a plurality of optical waveguide elements are formed on one LN wafer, and finally separated into individual optical waveguide element chips, whereby an optical waveguide element chip is manufactured.
[0023]
The optical waveguide element chip is usually used in the form of a module. Specifically, the optical waveguide element chip is accommodated in a metal case, and the input / output of light waves is performed from the optical waveguide element chip body to the outside of the metal case. And a conducting wire for energizing a signal electrode and the like are led out.
[0024]
FIG. 4 is a diagram showing a connection relationship between the optical waveguide element chip 10, the GRIN lens 20, and the optical fiber 22, which is a feature of the present invention.
An optical waveguide 11 is formed on the surface of the chip 10, and a GRIN lens 20 is arranged on a side surface of the chip substrate. An optical fiber 22 is connected to the end surface of the GRIN lens by using a capillary 21.
The GRIN lens is an abbreviation for a graded index lens, and is a name generally used in the art.
Since the GRIN lens has the same optical characteristics (refractive index, refractive index distribution, etc.) as the optical fiber, it is possible to suppress the optical loss at the time of coupling the two to, for example, about 0.2 dB.
[0025]
FIG. 5 shows a method of manufacturing the GRIN lens 20.
FIG. 5A shows a GRIN lens before processing, and FIG. 5B shows a GRIN lens after processing. Further, the right side of each drawing is the end face shape of the GRIN lens, and the left side is a side sectional view of the GRIN lens. Further, the solid line 26 in FIG. 5A indicates the course of the light wave traveling in the optical axis direction (dashed line) of the GRIN lens.
In the method for manufacturing a GRIN lens according to the present invention, a cylindrical GRIN lens 25 shown in FIG. 5A is manufactured by mirror-polishing the side surface and the end surface.
FIG. 5B shows a polished GRIN lens, 25 is a side surface formed by polishing in parallel to the optical axis of the GRIN lens, and 23 is a GRIN lens for entering or exiting the light from the side surface. This is a reflection surface for bending in the optical axis direction (dashed line) of the lens. The path of the bent light wave is shown by a solid line 24.
[0026]
The formation positions of the reflection surface 23 and the side surface 25 of the GRIN lens are set such that the focal points 27 and 28 of the light wave passing through the GRIN lens are located at the end surface and the side surface of the GRIN lens as shown in FIG. .
However, since the GRIN lens 20 and the optical fiber 22 are usually bonded to each other via the capillary 21 at a distance of about 20 μm, the focus of the above-described light wave is considered in advance in consideration of connection with the optical fiber and the optical waveguide element chip. It is also possible to set so that 27 and 28 are located at the end face of the optical fiber and at the end of the optical waveguide of the optical waveguide element chip, respectively.
[0027]
The angle of the reflection surface 23 is basically arbitrary, but is approximately 45 ° so that the mode pattern of the light wave at the focal point 27 on the end face and the mode pattern at the focal point 28 on the side surface are as uniform as possible. It is desirable that
Further, it is also desirable to set the angle of the reflection surface so that the reflection of the light wave by the reflection surface 23 is total reflection.
Further, in order to improve the reflection efficiency of the reflection surface, a multilayer reflection film or a metal film can be formed on the reflection surface 23.
[0028]
As shown in FIG. 4, the substrate side surface 2 of the optical waveguide element chip 10 is formed so as to be inclined by an angle of 5 ° from a plane perpendicular to the optical waveguide 11. The tilt angle is not limited to this value, but the light wave guided through the optical waveguide 11 on the substrate is reflected on the side surface of the substrate, and does not go backward in the optical waveguide 11. Due to the difference between the refractive index and the refractive index of the GRIN lens, even when the guided light bends at the joint surface between the two, the light on the optical waveguide of the substrate and the optical axis of the GRIN lens cooperate with the reflective surface of the GRIN lens. , So that guided light can always propagate.
For example, when the refractive index of the optical waveguide is 2.2 and the refractive index near the side surface of the GRIN lens is 1.6, the angle of the reflection surface 23 of the GRIN lens with respect to the lens optical axis is 5 ° when the inclination angle is 5 °. Is set to approximately 41 °.
[0029]
In joining the optical waveguide element chip 10 and the GRIN lens 20, it is desirable to use an adhesive having a high light transmission property such as an ultraviolet-curable adhesive to make close contact joining.
Further, in coupling the GRIN lens 20 and the optical fiber 22, the optical fiber is inserted into a capillary which is a joining reinforcing member, and an adhesive is applied to an end face of the capillary and the optical fiber or an end face of the GRIN lens. After positioning the and the GRIN lens, ultraviolet rays are applied to cure and join.
At the time of the above-described bonding, for example, the reference light that enters from the optical waveguide element chip side or the optical fiber side, passes through the optical waveguide, the GRIN lens, and the optical fiber, and exits from the other end face is separately separated. By detecting the light with the provided light receiving element, the optical components are positioned at a position where the detected light amount becomes the maximum value.
[0030]
The fixed angle between the optical waveguide element chip 10 and the GRIN lens 20 is not limited to the one fixed such that the optical axis of the GRIN lens 20 is parallel to the surface of the element chip as shown in FIG. For example, when the surface and the optical axis of the GRIN lens are perpendicular to each other, both can be fixed at an arbitrary angle.
This increases the degree of freedom with respect to the positional relationship between the optical waveguide element and the optical fiber, thereby making it easier to design a device including the optical waveguide element.
[0031]
When the optical loss in the optical waveguide device according to the present invention is roughly estimated, the coupling loss between the GRIN lens and the optical fiber is about 0.2 dB, the coupling loss due to the difference in the mode pattern between the optical waveguide and the optical fiber is about 1.1 dB, and the optical loss. The Fresnel reflection loss generated at the boundary between the wave path and the GRIN lens is about 0.2 dB, and the optical loss is about 1.5 dB as a whole.
It is needless to say that the present invention is not limited to the above description, and it is also possible to add a technique known in the technical field regarding the optical waveguide element.
[0032]
【The invention's effect】
As described above, the optical waveguide device of the present invention enables the input and output optical fibers to be connected to the optical waveguide device so as to have a positional relationship of about 90 °, so that the entire device including the optical waveguide device can be connected. The size can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing the structure of a conventional optical modulator module. FIG. 2 is a diagram showing the structure of an optical modulator module of the present invention. FIG. 3 is a diagram showing the connection between a conventional optical waveguide element chip and an optical fiber. FIG. 4 is a perspective view showing the connection between the optical waveguide element chip of the present invention and an optical fiber. FIG. 5 is a view for explaining a method of processing a GRIN lens.
DESCRIPTION OF SYMBOLS 1 Optical modulator module 2, 3, 13 Optical fiber 10 Optical waveguide element chip 20, 25 GRIN lens 21 Capillary 22 Optical fiber 23 Reflecting surface 25 Side surface

Claims (5)

In an optical waveguide element having a substrate having an electro-optical effect and an optical waveguide formed on the substrate,
Having a GRIN lens for optically coupling the optical waveguide and the optical fiber,
An optical waveguide device, wherein a side surface of the GRIN lens is arranged to face a side surface of a substrate where an end of the optical waveguide is located, and an end surface of the GRIN lens is arranged to face the optical fiber. 2. The optical waveguide device according to claim 1, wherein the GRIN lens has a reflection surface for reflecting light incident on or exiting the optical waveguide in the optical axis direction of the GRIN lens. Wave element. 3. The optical waveguide device according to claim 2, wherein a reflection member is provided on the reflection surface. 4. The optical waveguide device according to claim 1, wherein a side surface of the GRIN lens is mirror-polished. 5. The optical waveguide device according to claim 1, wherein a side surface of the substrate on which an end of the optical waveguide is located is formed to be inclined with respect to a plane perpendicular to an optical axis of the optical waveguide. An optical waveguide device characterized by the above-mentioned.

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