JP2001350046A - Integrated optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high density in an optical communication network by providing an integrated optical waveguide element, in which a connecting method of a new parallel type is adopted to plural optical waveguides. SOLUTION: A GRIN lens 26 is provided, so as to cover an output port 22A and an input port 23A of an output optical waveguide 22 and an input optical waveguide 23. A reflecting film 27 is provided in an end surface 26A of the GRIN lens 26. The central axis of the GRIN lens coincides with the center between the optical waveguides 22, 23 in a center line I. Also, the length of the GRIN lens 26 is set, so that a luminous flux exited from the output optical waveguide 22 becomes a parallel luminous flux at the end surface 26A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated optical waveguide device.

[0002]

2. Description of the Related Art In recent years, in the field of optical communication and the like, external modulators such as optical waveguide devices have been widely used for the purpose of enabling high-speed switching. Such an external modulator is formed by using lithium niobate (LiNbO ₃ ) having characteristics such as high-frequency characteristics, low insertion loss, and high extinction ratio as a substrate, and thermally diffusing Ti or the like into the substrate. A waveguide-type optical modulator including the above-described optical waveguide has been put to practical use.

FIG. 1 is a plan view showing an example of a conventional waveguide type optical modulator. The waveguide type optical modulator shown in FIG. 1 includes a substrate 1 made of a material having an electro-optic effect, and a Mach-Zehnder type optical waveguide 2. The Mach-Zehnder type optical waveguide 2 is composed of the first branch optical waveguide 2-1 and the second branch optical waveguide 2-1.
And a branched optical waveguide 2-2. The first branch optical waveguide 2-1 and the second branch optical waveguide 2-2 have 1
A pair of modulation electrodes 3-1 and 3-2 are provided.

A light wave incident on the Mach-Ender type optical waveguide 2 from the direction of the arrow by an optical fiber (not shown) is converted into a first branch optical waveguide 2-1 and a second branch optical waveguide 2 at a Y branch point 4. Branched to -2. When a predetermined electric signal is applied from the external power supply 10 between the modulation electrodes 3-1 and 3-2 to the light waves guided in these branch optical waveguides, the light waves change in phase. Receive. Then, the light waves having undergone the phase change are added together at the Y combining point 5, whereby the light intensities of the light waves are canceled in accordance with the phase difference between them, thereby switching the optical signal.

In configuring an actual optical communication network, recently, in addition to the light intensity modulator shown in FIG.
In many cases, functions such as a phase modulator and an attenuator are added. When the light intensity modulator is configured as a waveguide as described above, the phase modulator, the attenuator, and the like are also configured in another waveguide type module, and configured by connecting these separate modules in series. I was

On the other hand, an increase in demand for the Internet demands a high density of the entire optical communication network. For this reason, attempts have been made to pack various functions of the optical modulator in one package. Specifically, optical waveguides having a desired function are arranged on the same substrate in parallel to the width direction of the substrate, and each is connected by (1) a fiber.
(2) A connection is made with a semicircular waveguide on the same substrate, and (3) A connection is made with a connection waveguide utilizing reflection at the end face of the substrate.

FIG. 2 is a diagram for explaining the connection method (3). In the figure, for the sake of simplicity, only the configuration of the end of the substrate where the light wave is reflected is shown. The light wave guided through the output optical waveguide 12 formed on the substrate 11 reaches the substrate end face 16 via the bent optical waveguide 14.
Then, after being reflected on the substrate end face 16, the light reaches the input optical waveguide 13 via the bent optical waveguide 15. Therefore, by forming a plurality of optical waveguide structures as shown in FIG. 2 on the same substrate, a plurality of optical waveguides are connected using reflection of the end face of the substrate.

[0008]

However, (1)
In the method (1), a space for installing an optical fiber is required, and therefore, there has been a problem that a high density of an optical communication network by parallel connection cannot be sufficiently achieved. Also in the method (2), a semicircular optical waveguide is separately provided, and since the radius of the semicircle is very large, the substrate area is increased. As a result, the density of the optical communication network is increased. There is a problem that can not be achieved. Furthermore, the method (3) has a problem that the cutting position of the substrate end face 16 needs to be controlled with high precision, so that the productivity is reduced and the yield is reduced.

As a method similar to the connection method (3), Japanese Patent Application Laid-Open No. H11-237517 discloses a method of forming a substrate end face in the middle of a coupling portion of a zero-gap directional coupler. However, since the coupling length of the directional coupler depends on the wavelength, the degree of connection of each optical waveguide changes depending on the wavelength for high-density and high-modulation band applications such as the DWDM method. In some cases, it could not be used.

An object of the present invention is to provide an integrated optical waveguide device employing a new parallel connection method for a plurality of optical waveguides, thereby achieving high density in an optical communication network.

[0011]

In order to achieve the above object,
The integrated optical waveguide device of the present invention is an integrated optical waveguide comprising a substrate made of a material having an electro-optical effect, and an input optical waveguide and an output optical waveguide formed to be parallel in the width direction of the substrate. A waveguide element, wherein both ends of the input optical waveguide and the output optical waveguide are opened to both end surfaces of the substrate, and at least one end surface of the substrate covers open ends of the input optical waveguide and the output optical waveguide. Along with the center between the input optical waveguide and the output optical waveguide, the center axis coincides with the center axis, and has an end face orthogonal to the central axis on the side opposite to the substrate, and light emitted from the output optical waveguide is the center. A GRIN lens having a focal length such that a parallel light flux is formed at an end face perpendicular to the axis is provided. And wherein the digit.

FIG. 3 is a plan view showing an example of the configuration of the integrated optical waveguide device of the present invention. In the drawings, only the configuration of the end portion of the substrate is shown in order to briefly show the features of the present invention. The integrated optical waveguide device shown in FIG. 3 includes an output optical waveguide 22 and an input optical waveguide 23 on a substrate 21 having an electro-optic effect. Then, on the end face 21A of the substrate 21, the GRIN lens 26 is
Are provided so as to cover the output port 22A of the output optical waveguide 22 and the input port 23A of the input optical waveguide 23 via the.

The GRIN lens 26 is connected such that the center between the output optical waveguide 22 and the input optical waveguide 23 and the central axis of the GRIN lens 26 coincide with the center line I. In addition, the length is the output port 22A of the output optical waveguide 22.
From the end surface 26 of the GRIN lens 26
A is set to be parallel. The end face 26A is perpendicular to the central axis of the GRIN lens 26.
A reflective film 27 is provided on an end surface 26A of the GRIN lens 26 opposite to the substrate 21. In the present invention, the “center between waveguides” is a center connecting centers of respective optical modes propagating through the waveguide, and is not generally located on the substrate surface.

The light wave guided through the output optical waveguide 22 is:
When reaching the substrate end face 21A, a GRIN beam is output from the output port 22A as a Gaussian beam having the output port 22A as a waste.
Radiated into lens 26. The light wave emitted into the GRIN lens 26 propagates along the curve 28 as the speed of light having a spread as shown by hatching, and the GRIN lens 2
6 to the end surface 26A. After being reflected by the reflective film 27, the GRIN lens 2
6, the light propagates along the curve 29 in the GRIN lens 26 while gradually decreasing its spread, and reaches an end surface 26B opposite to the end surface 26A of the GRIN lens 26.

Since the center axis of the GRIN lens 26 and the center between the input optical waveguide and the output optical waveguide coincide with each other at the center line I, the light wave reaching the end face 26B is output from the output optical waveguide 22.
And a Gaussian beam having a waste at the center of the input port 23A of the input optical waveguide 23 existing at a position symmetrical with respect to the center line I. Thereafter, the light wave reaching the end face 26B is guided in the input optical waveguide 23 and undergoes a predetermined modulation.

By using an element configuration as shown in FIG. 3 on the same substrate, a plurality of optical waveguides formed in parallel on the same substrate can be connected in series. GR
Since the size of the IN lens is about 2 mm in diameter and about 5 mm in length, even if a large number of such GRIN lenses are used on the same substrate, little extra space is required. Therefore, it is possible to provide an optical waveguide device in which functions satisfying the demand for higher density required in an optical communication network or the like are connected to tandem.

Further, according to the integrated optical waveguide device of the present invention, it is not necessary to control the cutting position of the substrate end face or the like with high accuracy, so that productivity does not deteriorate. Further, since no directional coupler is used, the connection does not become insufficient depending on the wavelength of the light wave.

The GRIN lens is an abbreviation for a graded index lens, and is a name generally used by those skilled in the art.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. As described above, FIG. 3 is a plan view showing the configuration of an example of the integrated optical waveguide device of the present invention. The substrate 21 is made of a material having an electro-optical effect,
For example, lithium niobate, lithium tantalate, PL
It is made of ZT (lanthanum lead zirconate titanate) and a quartz-based material. Specifically, of these single crystal materials,
It is composed of an X-cut plate, a Y-cut plate, and a Z-cut plate. In particular, it is preferable to use lithium niobate because it can be easily configured as an optical waveguide device and has large anisotropy. The output optical waveguide 22 and the input optical waveguide 23 can be formed by a thermal diffusion method, a proton exchange method, or the like.

As the GRIN lens, a known lens such as a Selfoe Lens can be used. Also, GRIN lens 2
According to the present invention, the length of 6 needs to be set so that the light beam emitted from the output optical waveguide 22 at the end face 26A becomes a parallel light beam. Actually, GRIN lens 2
Although it is necessary to consider the thickness of an adhesive or the like for fixing the substrate 6 to the substrate 1, the length is generally set to about 4.8 mm.

In FIG. 3, the GRIN lens 26 is adhered and fixed to the substrate 21 by an adhesive 30. Thereby, the positional relationship between the two can be fixed, and the deviation between the center between the output optical waveguide 22 and the input optical waveguide 23 and the central axis of the GRIN lens 26 can be prevented. As a result, the end face 26 of the light wave emitted from the output optical waveguide 22
The shift of the focal position on B can be prevented, and it is possible to prevent light waves from being input to the input optical waveguide.

The material and configuration of the reflection film 27 are not limited as long as it has a high reflectivity to the light wave emitted from the output optical waveguide. Cr, Au, A
1 or a metal film made of a metal such as SiO ₂ and TiO
_For example, a dielectric multilayer film in which dielectrics such as ₂ are alternately laminated can be preferably used.

FIG. 4 is a plan view showing the configuration of another example of the integrated optical waveguide device of the present invention. Note that, similarly to FIG. 3, only the configuration of the end portion of the substrate is shown to clarify the features of the present invention. The integrated optical waveguide device of the present invention shown in FIG. 4 includes a substrate 31 made of a material having an electro-optical effect, an output optical waveguide 32, and an input optical waveguide 33. Further, the end face 31A of the substrate 31 is inclined by a predetermined angle α in the width direction from a direction X1 perpendicular to the length direction of the substrate.
Then, GRI is provided on the side of the inclined end surface 31A of the substrate 31.
The N lens 36 covers the output port 32A of the output optical waveguide 32 and the input port 33A of the input optical waveguide 33, and as shown by the center line II, the center between these optical waveguides and GRIN.
It is fixed so that the center axis of the lens is continuous.

The length of the GRIN lens 36 is set so that the light wave emitted from the output optical waveguide 32 is parallel at the end face 36 A opposite to the substrate 31. The end surface 36B of the GRIN lens 36 on the substrate side is inclined at a predetermined angle β in the width direction from a direction X2 perpendicular to the central axis. In addition, a reflective film 37 is provided on the end surface 36B of the GRIN lens 36.

As is clear from the drawing, the integrated optical waveguide device shown in FIG. 4 has end faces 31A and 36B in which the substrate 31 and the GRIN lens 36 are respectively inclined, and the light wave transmitted between these end faces is based on Snell's law. 3 differs from the integrated optical waveguide device shown in FIG. 3 in that the substrate 31 and the GRIN lens 36 are fixedly connected. According to the configuration shown in FIG. 4, the ratio of the light wave emitted from the output optical waveguide 32 reflected by the end surfaces 31A and 36B is reduced. Therefore, even when a plurality of GRIN lenses are provided, the propagation intensity of light waves does not deteriorate, and a high-density integrated optical waveguide element can be easily provided.

The specific values of the inclination angle α of the end face 31A and the inclination angle β of the end face 36B are not limited as long as the light wave transmitted between these end faces is guided according to Snell's law.

However, the inclination angle α is preferably about 5 degrees. Further, it is preferable that the inclination angle β is 7 to 7.5 degrees. Thus, the light wave to be guided can be made to follow the Snell's law accurately regardless of the type of the material constituting the substrate 31 and the type of the GRIN lens.

The substrate 31, the GRIN lens 36, etc.
A device similar to the integrated optical waveguide device shown in FIG. 3 can be used and formed in the same manner. In addition, the output optical waveguide 3
The light wave emitted from the light source 2 reaches the end face 36A along the curve 38 similarly to the case of the integrated optical waveguide element shown in FIG. And input to the input optical waveguide 33. The light wave emitted from the output optical waveguide 32 is input to the input optical waveguide 33 again, as in the case of the integrated optical waveguide element shown in FIG.
This is because the center axis of the lens is continuous as shown by the center line II.

FIG. 5 is a side view showing a modification of the integrated optical waveguide device of the present invention shown in FIG. In the integrated optical waveguide device shown in FIG. 5, the end face 41A of the substrate 41 is inclined in the thickness direction by an angle α from a direction Z1 perpendicular to the length direction. Similarly, the end surface 4 of the GRIN lens 46 on the substrate 41 side
6B is also inclined in the thickness direction by an angle β from a direction Z2 perpendicular to the length direction. The end of the upper surface 41C of the substrate 41 and the upper end of the end surface 46B of the GRIN lens 46 are connected and fixed by the reinforcing member 50. by this,
The fixation of the substrate and the GRIN lens becomes stronger, and it is possible to prevent a light wave propagation loss due to a defocus of the GRIN lens, which is caused by a deviation of the center axis of each other.

The integrated optical waveguide device shown in FIG. 5 can be formed by the same material and the same method as the optical waveguide device shown in FIGS. The propagation and reflection of light waves are also performed in the same manner as in the integrated optical waveguide device shown in FIG.

FIG. 6 is a plan view showing an example in which the integrated optical waveguide device of the present invention is applied to an integrated light intensity modulator. The integrated light intensity modulator shown in FIG. 6 includes Mach-Zehnder type optical waveguides 52 and 53 on a substrate 51 made of a material having an electro-optic effect. In FIG. 6, the former acts as an output optical waveguide, and the latter acts as an input optical waveguide.

The light wave incident on the output optical waveguide 52 according to the arrow is applied to the signal electrode 54 as described with reference to FIG.
After being intensity-modulated by applying an electric signal from the external power supply 60-1 between the −1 and the ground electrode 55, the light reaches the end face 52A, and the GRIN lens 56 reaches the reflection film 57 along the curve 58. Then, after being reflected by the reflection film 57, the light returns to the end face 52 </ b> A again along the curve 59 and is input to the input optical waveguide 53. After being subjected to the same intensity modulation by the external power supply 60-2 between the signal electrode 54-2 and the ground electrode 55, the light is emitted from the end face 51B of the substrate 51 according to the arrow.

FIG. 7 is a view schematically showing an optical waveguide device in which three sets of Mach-Zehnder type optical waveguides are formed and integrated on the same substrate. In the integrated optical waveguide device shown in FIG. 7, Mach-Zehnder optical waveguides 62 to 64 are formed on a substrate 61 made of a material having an electro-optical effect. Then, at both ends of the substrate 61, the GRIN lens 66 for the optical waveguides 62 and 63, and the optical waveguide 6
GRIN lenses 68 for 3 and 64 are provided.

The light wave incident on the optical waveguide 62 is
The light is reflected and guided by the GRIN lenses 66 and 68 in the direction of the arrow, guided through the optical waveguide 64 and taken out. Therefore, in this case, the optical waveguide 6
2 acts as an output optical waveguide, and the optical waveguide 64 acts as an input optical waveguide. The optical waveguide 63 is a GRI
It acts as an input optical waveguide for the N lens 66 and G
The RIN lens 68 functions as an output optical waveguide.

According to the configuration of the integrated type optical waveguide device shown in FIG. 7, a GRIN lens corresponding to the optical waveguide device is sequentially used, so that three or more sets of optical waveguides are integrated to increase the density of the optical waveguide device. Can be formed.

The present inventors formed an optical waveguide on a substrate made of lithium niobate by a Ti thermal diffusion method to produce an integrated light intensity modulator as shown in FIG.
A Selfoe Lens was used for the GRIN lens, and a dielectric multilayer film was used for the reflection film. As a result, it was confirmed that good light intensity modulation characteristics were obtained.

As described above, the present invention has been described in detail based on the embodiments of the present invention with reference to specific examples. However, the present invention is not limited to the above contents, and may be any form within the scope of the present invention. Deformation and modification are possible.

[0038]

As described above, according to the integrated optical waveguide device of the present invention, a plurality of optical waveguide devices formed on the same substrate are connected in series at a high density with extremely high reliability. It is possible. Therefore, it is possible to satisfy the demand for higher density of the optical communication network which is currently required.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a conventional waveguide type optical modulator.

FIG. 2 is a diagram illustrating an example of a conventional method of serial connection to an optical waveguide.

FIG. 3 is a plan view showing an example of the configuration of the integrated optical waveguide device of the present invention.

FIG. 4 is a plan view showing the configuration of another example of the integrated optical waveguide device of the present invention.

FIG. 5 is a side view showing a modification of the integrated optical waveguide device shown in FIG.

FIG. 6 is a plan view showing an example in which the integrated optical waveguide device of the present invention is applied to an integrated light intensity modulator.

FIG. 7 is a view schematically showing an optical waveguide device in which three sets of Mach-Zehnder type optical waveguides are formed and integrated on the same substrate.

[Explanation of symbols]

 1, 11, 21, 31, 41, 51, 61 Substrate 2, 12, 13 Optical waveguide 2-1 First branch optical waveguide 2-2 Second branch optical waveguide 3-1 3-2 Modulation electrode 4 Y branch point 5 Y combining point 10, 60-1, 60-2 External power source 14, 15 Bend optical waveguide 16 Substrate end face 22, 32, 52, 62, 63 Output optical waveguide 23, 33, 53, 63, 64 Input Optical waveguide 26, 36, 46, 56, 66, 68 GRIN lens 27, 37, 47, 57 Reflective film 30 Adhesive 50 Reinforcing member 54-1, 54-2 Signal electrode 55 Ground electrode α, β Tilt angle

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H047 KA15 KB03 KB09 LA09 MA03 NA02 RA08 TA01 2H079 AA02 AA12 BA01 BA03 CA05 DA03 EA05 EA21 EA28 GA01 KA03 KA14

Claims (7)

[Claims] 1. An integrated optical waveguide device comprising a substrate made of a material having an electro-optic effect, and an input optical waveguide and an output optical waveguide formed to be parallel in the width direction of the substrate. Both ends of the input optical waveguide and the output optical waveguide are open to both end surfaces of the substrate. At least one end surface of the substrate covers the open ends of the input optical waveguide and the output optical waveguide, and The center between the waveguide and the output optical waveguide coincides with the central axis, and has an end face orthogonal to the central axis on the side opposite to the substrate, and light emitted from the output optical waveguide is orthogonal to the central axis. A GRIN lens having a focal length such that a parallel light beam is formed at the end face is provided.
An integrated optical waveguide device, wherein a reflective film is provided on an end surface of the RIN lens that is orthogonal to the central axis. 2. An integrated optical waveguide device comprising a substrate made of a material having an electro-optical effect, and an input optical waveguide and an output optical waveguide formed to be parallel in the width direction of the substrate. Both ends of the input optical waveguide and the output optical waveguide are open to both end surfaces of the substrate, and at least one end surface of the substrate covers open ends of the input optical waveguide and the output optical waveguide, and The center between the optical waveguide and the output optical waveguide and the central axis are continuous at an angle satisfying Snell's law, have an end face orthogonal to the central axis on the side opposite to the substrate, and exit from the output optical waveguide. A GRIN lens having a focal length such that the divided light becomes a parallel light beam at an end face orthogonal to the central axis, and the GRIN lens is aligned with the central axis of the GRIN lens. An integrated optical waveguide device, wherein a reflection film is provided on an end face that intersects. 3. The substrate according to claim 2, wherein an end surface of the substrate on which the GRIN lens is provided is inclined.
3. The integrated optical waveguide device according to item 1. 4. The integrated optical waveguide device according to claim 2, wherein an end surface of the GRIN lens on the substrate side is inclined. 5. The method according to claim 1, wherein a center between the input optical waveguide and the output optical waveguide is a center between centers of respective optical modes propagating in these optical waveguides. An integrated optical waveguide device according to any one of the above. 6. The GRIN lens is adhered and fixed to at least one end surface of the substrate.
An integrated optical waveguide device according to claim 1. 7. The integrated optical waveguide device according to claim 1, wherein said reflection film is made of a metal film or a dielectric multilayer film.