JPH03100505A - Optical coupling structure of optical waveguide and light receiving device - Google Patents

Abstract

PURPOSE:To obtain the optical coupling structure of an optical waveguide and a light receiving device which is suitable for facilitating the assembling work by interposing a planar micro-lens in which many lens parts are formed like a plane between a waveguide substrate on which the optical waveguide is formed and a base provided with the light receiving device. CONSTITUTION:Between a waveguide substrate 4 on which an optical waveguide 2 is formed and a base 8 provided with the light receiving device 6, a plate micro-lens 12 in which many lens parts 10 are formed like a plane is interposed. In this state, a light beam emitted from the optical waveguide 2 is converged by one lens part of many lens parts 10 and made incident on the light receiving device 6. That is, by setting suitably the thickness of the planar micro-lens 12 to match a focal distance, optical coupling can be executed without executing a position adjustment in the optical axis direction of the waveguide substrate 4 and the base 8, when the planar micro-lens 12 is interposed between the waveguide substrate 4 on which the optical waveguide 2 is formed and the base 8 provided with the light receiving device. In such a manner, the assembling work of a device at the time of executing optical coupling of the optical waveguide 4 and the light receiving device 6 is facilitated.

Description

[Detailed Description of the Invention] Table of Contents Overview Industrial Field of Application Conventional Technology Means for Solving Problems to be Solved by the Invention (Figure 1) Function
(Figure 2) Example of implementation
(Figures 3 to 12) Outline of Effects of the Invention Regarding the optical coupling structure of an optical waveguide and a light receiver, a waveguide substrate on which an optical waveguide is formed and a light receiver are provided, mainly for the purpose of facilitating assembly work. A flat plate microlens having a plurality of lens parts formed in a plane is interposed between the base and the plurality of lens parts, and the light emitted from the optical waveguide is converged by one of the plurality of lens parts. The light beam is configured such that the light is incident on the light receiver.

Industrial applications The present invention relates to an optical coupling structure between an optical waveguide and a light receiver.

2. Description of the Related Art In recent years, with the progress of optical communication technology, various optical devices equipped with optical waveguides as optical propagation media have been provided as being suitable for miniaturization. When configuring this type of optical device, when attempting to optically couple an optical receiver that converts an optical signal into an electrical signal and an optical waveguide, the relative positional relationship between the optical waveguide and the optical receiver is directly determined. The use of a lens that affects the light receiving efficiency and has a converging effect in some cases is essential, and optimization of such an optical coupling structure is being sought.

Conventional technology When the light emitted from the end of an optical waveguide such as a diffused optical waveguide is made to enter the light receiving part of a light receiver such as a photodiode,
If you try to make the light emitted from the end of the optical waveguide according to its numerical aperture directly enter the light receiving part, especially if the optical waveguide is a single mode type, there will be tolerance (permission regarding relative positional relationship). capacity) is extremely small. For this reason, a lens having a convergence effect is interposed between the end of the optical waveguide and the light receiver to increase the above-mentioned tolerance.

An object of the invention is to provide an optical coupling structure for a light receiver.

On the other hand, when there are multiple optical waveguides close to each other, it becomes extremely difficult to interpose lenses between the multiple optical waveguides and the multiple light receivers corresponding to each optical waveguide during assembly work. There is a thing that happens.

Therefore, it is an object of the invention to provide an optical coupling structure between an optical waveguide and a light receiver, which can be easily assembled even when a plurality of optical waveguides are provided close to each other.

Problems to be Solved by the Invention However, when interposing a lens between an optical waveguide and a light receiver, the positioning accuracy of the lens is required to be almost the same as that of the optical waveguide and the light receiving section. This method requires extensive assembly work, which poses a problem in that the manufacturability of optical devices is poor.

Therefore, an optical waveguide suitable for facilitating assembly work and a means for solving the problem are shown in FIG. 1. FIG. 1 is a basic configuration diagram of the present invention. In this optical coupling structure between an optical waveguide and a light receiver, a large number of lens parts 10 are formed in a plane between a waveguide substrate 4 on which an optical waveguide 2 is formed and a base 8 on which a light receiver 6 is provided. A flat plate microlens 12 is interposed therebetween, and the light emitted from the optical waveguide 2 is converged by one of the plurality of lens sections 10 and is made to enter the light receiver 6. .

Since the working optical waveguide and the light receiver are optically coupled by the lens portion of the flat microlens, the following effects occur. In other words, the focal length of the lens part of a flat microlens is uniformly determined according to its shape, refractive index distribution, etc., so by appropriately setting and cleaning the thickness of the flat microlens according to this focal length, the optical waveguide can be When a flat plate microlens is interposed between a waveguide substrate on which is formed and a base provided with a light receiver, optical It is possible to make a physical combination.

A flat plate microlens having a plurality of lens parts formed in a plane is used, and the light emitted from the optical waveguide is converged by one of the plurality of lens parts and made to enter the light receiver. The effects caused by this are as follows. In FIG. 2, a flat plate microlens 12 on which a single lens portion 10 is formed is brought into close contact with the waveguide substrate 4, and the flat plate microlens 12 is slidably moved relative to the waveguide substrate 4 on a plane perpendicular to the plane of the paper. The current state is shown.

Generally, the width W of the optical waveguide 2 formed on the waveguide substrate 4 is 5 to 10 μm, and the diameter d of the lens portion 10 of the flat microlens 12 is 10 to 40 μm. When adjusting the position by sliding the flat microlens 12 with respect to the waveguide substrate 4, if the lens part 10 is single as shown in FIG. Since the positional relationship with respect to the end face cannot be easily known, assembly work is not easy. On the other hand, as in the basic configuration of the present invention shown in FIG.
In the case where there are a large number of lens sections 10 of 2, the function of the lens section is ensured no matter which lens section of the large number of lens sections 10 faces the optical waveguide 2, so the assembly work becomes easier. . In this case, the highly accurate adjustment of the relative positional relationship between the lens section 10 and the end surface of the optical waveguide 2 facing the optical waveguide 2 can be performed, for example, by adjusting the relative positional relationship such that light is emitted from the optical waveguide 2 via the lens section 10. Then, attach the flat microlens 1 so that its output beam axis coincides with the optical axis of the optical waveguide 2.
This can be done by slightly moving the waveguide substrate 2 relative to the waveguide substrate 4.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 3 is a block diagram of a receiving device for coherent optical communication to which the present invention can be applied. 14 is a signal light P;
and a waveguide type optical coupler that adds and distributes the local light (local oscillation light) Pt; 16 is a twin bin chip that performs optical detection by optically converting the light from the waveguide type optical coupler 14;
18 is a front end circuit for sending the detection signal from the twin bin chip 16 to the subsequent stage. The twin bin chip 16 has two photodetectors 5a and 5b made of PIN photodiodes with the same characteristics connected in series, and each photodetector (3a
, 5b is configured to extract a difference signal between the photocurrents generated in the photocurrents as a detection signal.

The light distributed by the waveguide type optical coupler 14 is transmitted to a light receiver (ia,
(When the light enters the light receiver 5a, the light enters the light receiver 5a.

Due to the square law detection characteristic of 6b, a detected signal having a frequency that is the difference between the frequency of the signal light and the frequency of the local light is obtained,
At this time, due to the asymmetric phase inversion effect in the waveguide type optical coupler 14 and the effect of the twin bin chip 16,
The detected signal based on the signal light is multiplied, and the detected signal based on the intensity noise component of the local light is canceled out, making it possible to receive the signal light with high reception sensitivity.

In order to effectively eliminate the influence of such intensity noise components of the local light, it is necessary to guide the light distributed 1:1 by the waveguide type optical coupler 14 to the light receivers [3a, (ib) with the same optical path length. and each receiver 6 with the same coupling efficiency.
It is desirable to optically couple to a and 6b. In other words, when optically coupling the waveguide type optical coupler 14 and the twin bin chip optical receivers 5a and ib, the optical path length connecting the functional part of the waveguide type optical coupler 14 and the optical receivers 6a and 6b is If there are variations, or if the coupling efficiency varies,
Improving reception sensitivity by using a twin pin nap becomes insufficient. Therefore, the present invention is applied to optical coupling between a waveguide type optical coupler and a twin-bin chip photoreceiver.

FIG. 4 shows the configuration of the waveguide type optical coupler 14.

For example, two optical waveguides 2a are formed on the surface or near the surface of a waveguide substrate 4 made of quartz glass by the thermal ion exchange method.
, 2b are formed such that midway portions of a predetermined length are arranged side by side at a predetermined interval, and the above-mentioned juxtaposed portions are provided with an optical doubler function.

Distance between end faces of optical waveguides 2a and 2b (distance between centers)
D is approximately 0.1 fight. Generally, when an optical waveguide is formed by the thermal ion exchange method, a masking made of metal or the like is applied on the waveguide substrate 4, but the dimensional accuracy of the mask pattern is extremely high, and on the other hand, the ion exchange depth is also extremely high due to process control. Since the settings can be made with high precision, the shapes of the optical waveguides 2a and 2b and the above-mentioned spacing are extremely precise.

In this way, the distance between the optical waveguides on the end face of the waveguide substrate is 0.
．． If it is as small as about one lens, it is extremely difficult to optically couple the optical waveguide and the light receiver using a normal lens such as a ball lens. Therefore, even if such circumstances are taken into consideration, the application of the present invention is effective.

FIG. 5 shows the configuration of the twin bin chip 16.

For example, Ga is placed on the base 8 made of InP substrate.
Two light receivers 6a, 6 each having a light receiving portion made of InAs.
b, and electrodes for wiring for each of the light receivers 6a and 6b are provided.

20 is a slit for electrically isolating the light receivers 5a and 5b. Light receiver 5a.

The spacing between the optical waveguides 6b is set to D, which is made to match the spacing between the end faces of the optical waveguides 2a and 2b. High dimensional accuracy can also be obtained with respect to the spacing between light receivers. In such a twin-bin chip, in order to improve high-speed operation, the optical receiver 5 is
It is necessary to make the receiving diameter of a and 5b several tens of micrometers or less, but in such a case, a flat plate microlens is used to converge the light from the waveguide type optical coupler and make it incident on each photoreceiver 5a and 5b. The structure of the present invention is effective.

FIG. 6 shows the configuration of a flat microlens in the first embodiment. The flat microlens 12 has a lower end 12a.
When the optical waveguide 2a is aligned with the bottom surface of the waveguide substrate 4, the optical waveguide 2a
, 2b, a large number of lens parts 10 are formed so as to be aligned on a straight line at equal intervals. The interval (distance between centers, that is, pitch) P between the lens parts 10 arranged at equal intervals is the same as the interval between the optical waveguides 2a and 2b and the light receiver 5.
a.

For a spacing of 6b, when n is an integer, D=n
Wipe to satisfy P. By satisfying such conditions, one of the lens parts 10 can be connected to the optical waveguide 2.
a or 2b, any of the lens parts other than the above-mentioned lens parts comes to face the other optical waveguide 2b.

As shown in FIG. 7, the flat plate microlens 12 is a lens portion having a uniform function by forming a roughly hemispherical high refractive index portion from one side of a flat glass plate by selective ion exchange. 10 was formed.

When using such a selective ion exchange method, the lens portion 1
By forming 0, the flatness of the glass plate can be improved (
Therefore, it is optimal when optically coupling the waveguide type optical coupler 14 and the twin bin chip 16. Note that if light having an appropriate beam diameter is made incident on the flat plate microlens 12 from the side where the lens portion 10 is formed, the light beam can be converged without causing large aberrations. If this light beam is made to enter the light receiver when it becomes sufficiently small, the light emitted from the optical waveguides 2a and 2b can be made to enter the light receivers 5a and 6b, which have relatively small receiving diameters, with high efficiency. can.

The assembly procedure of the device in the first embodiment will be explained with reference to FIG. First, the optical waveguide 2 in the waveguide type optical coupler 14
Optical fibers 20 are connected to the light inputs (12) of a and 2b, respectively.
．． 22 is connected, and the base 8 on which the light receivers 6a and 5b are formed is fixed to the end surface of the circuit board 28.
Electrical wiring for each light receiver (3a, 5b is performed using bonding wires 24 and 26. Next, the flat microlens 12 is adjusted in position and fixed to the end surface of the waveguide substrate 4 using, for example, optical adhesive. do.

The position adjustment of the flat plate microlens 12 is performed using an optical fiber 20.
．． 22 through the optical waveguides 2a and 2b, and the 91st! As shown in FIG. 1, the flat microlens 12 is moved in the left-right direction in the figure with the lower end of the flat microlens 12 aligned with the bottom surface of the waveguide substrate 4.
One of the optical waveguides 2a and 2b has a large number of lens sections 10.
All you have to do is make it relative to one of them. At this time, the height of each lens section 10 and the height of the optical waveguides 2a and 2b are set equal, and the height of the optical waveguide 2a.

Since the distance between the end surfaces of the optical waveguides 2b and 2b is set to be an integral multiple of the distance between the lens portions 2a and 2b, one of the optical waveguides 2b
When a or 2b faces the lens section 10, the other optical waveguide also faces the lens section 10. Therefore, adjustment work is simplified and assembly work is facilitated.

Once the flat microlens 12 is fixed to the waveguide substrate 4 in this way, the base 8 is attached to the flat microlens 12 using an optical adhesive, for example, so that the light receiving element (ia, 5b faces the corresponding lens part 10). In this case, since the spacing between the end faces of the optical waveguides 2a and 2b, the spacing between adjacent lens sections 100, and the spacing between the light receivers 6a and 13b are set accurately, the coupling at one optical coupling section is fixed. When the efficiency is maximized, the coupling efficiency in the other optical coupling section can also be easily maximized.

Also, the end faces of the optical waveguides 2a and 2b and the light receiver 6a.

The optical path length between the light receiving surface of 6b and the flat microlens 1 is
Since it is determined by the thickness of 2, optical path difference is unlikely to occur. Therefore, according to this embodiment, high reception sensitivity can be achieved in the assembled coherent optical communication receiver.

FIG. 10 shows the configuration of a flat microlens in the second embodiment. In this embodiment, as in the first embodiment, the interval P
A large number of lens parts 10 arranged at equal intervals on a straight line are
A plurality of rows are formed in the vertical direction in Figure 0. Although the interval B between each row is arbitrary, it is desirable that it be sufficiently small to the same extent as P. By forming the lens portions 10 in a lattice shape in this way, when adjusting the position of the flat microlens 12 with respect to the waveguide substrate 4, two lens portions 10 in an arbitrary row are placed opposite to the optical waveguides 2a and 2b. Therefore, the assembly work becomes easier than in the first embodiment.

The structure of the flat microlens according to the third embodiment will be explained with reference to FIG. In this example, a large number of lens parts 10 arranged at equal intervals on a straight line are formed in a plurality of rows on a flat plate microlens, and the distance between two adjacent lens parts in each row of the plurality of rows is P l + P2 + p, , p , so that they are different from each other. And optical waveguides 2a, 2b
distance and the light receiver 6a.

6b are set so that each interval is an integral multiple of a predetermined length. The above predetermined length is the distance between lens parts P1 to P4.
is set between the minimum and maximum spacing in . By doing this, variations in optical coupling efficiency caused by variations in processing dimensional accuracy, variations in lens focal length, etc. can be reduced.
Compensation can be achieved by selecting the optimum spacing between lens parts. As a result, it becomes possible to perform separate adjustment to always maximize the receiving sensitivity in a coherent optical communication receiving device configured by applying this flat microlens.

Modifications of the first to third embodiments will be explained with reference to FIG. 12. In this example, there are three optical waveguides (
2c, 2d, 2e) are formed on the waveguide substrate 4, and the distances D+ and D2 are respectively integer multiples of the distance P between the lens parts in the modified examples of the - and second embodiments. In a modification of the third embodiment, the length is an integral multiple of the predetermined length described above. Although not shown, each optical waveguide 2c, 2d,
2e is formed on the base. In this way, even if there are three or more pairs of optical waveguides and optical receivers to be optically coupled, the number of pairs of optical waveguides and optical receivers to be optically coupled is one or two.
The same effect as in the case of a pair can be obtained.

As described in detail, according to the present invention, the relative relationship between a waveguide substrate on which an optical waveguide is formed, a base provided with a light receiver, and a flat plate microlens on which a large number of lens parts are formed. Since the position adjustment becomes easy, it is possible to easily assemble the device when optically coupling the optical waveguide and the light receiver. Furthermore, when the present invention is applied to a receiver for coherent optical communication, the optical path length from the optical coupler to each twin-chip receiver can be set to be the same,
Moreover, since each light receiving efficiency can be made the same, there is an excellent effect of improving receiving sensitivity.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the present invention. FIG. 2 is a diagram for explaining the effect of the configuration of FIG. 1. FIG. 3 is a block diagram of a receiving device for coherent optical communication to which the present invention can be applied. , Fig. 4 is an explanatory diagram of a waveguide type optical coupler, Fig. 5 is an explanatory diagram of a twin chip, Fig. 6 is an explanatory diagram of a flat plate microlens in the first embodiment, and Fig. 7 is an explanatory diagram of a flat plate microlens. , Fig. 8 is an explanatory diagram of assembly of the first embodiment, Fig. 9 is an explanatory diagram of position adjustment of the flat plate microlens, Fig. 10 is an explanatory diagram of the flat plate microlens in the second embodiment, and Fig. 11 is an explanatory diagram of the third embodiment. FIG. 12 is an explanatory diagram of a modification of the first to third embodiments. 2... Optical waveguide, 4... Waveguide substrate, 6...
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Claims (4)

[Claims] (1) A large number of lens parts (10) are formed in a plane between a waveguide substrate (4) on which an optical waveguide (2) is formed and a base (8) on which a light receiver (6) is provided. The light emitted from the optical waveguide (2) is converged by any one of the plurality of lens parts (10) and sent to the light receiver (6). An optical coupling structure of an optical waveguide and a photoreceiver, characterized in that the light is incident on the optical waveguide. (2) The waveguide substrate (4) has a plurality of optical waveguides (2)
is formed, the base (8) is provided with a plurality of light receivers (6) corresponding to the plurality of optical waveguides (2), and the flat microlens (12) is provided with a number of lens parts ( 10) are formed so as to be arranged at equal intervals on a straight line, and the distance between any two optical waveguides in the plurality of optical waveguides (2) and the distance between any two optical receivers in the plurality of optical receivers (6) are The optical waveguide according to claim 1, wherein the distance is an integral multiple of the distance between two adjacent lens portions in the plurality of lens portions (10) arranged at equal intervals on the straight line. Optical coupling structure of photoreceiver. (3) A large number of lens parts arranged at equal intervals on the above straight line (
3. The optical coupling structure of an optical waveguide and a light receiver according to claim 2, wherein a plurality of rows of 10) are formed. (4) The waveguide substrate (4) has a plurality of optical waveguides (2)
The base (8) is provided with a plurality of light receivers (6) corresponding to the plurality of optical waveguides (2), and the flat microlenses (12) are provided with a plurality of light receivers (6) arranged at equal intervals on a straight line. A plurality of rows of a large number of lens portions (10) are formed, and the intervals between two adjacent lens portions in each row of the plurality of rows are different, and any two of the plurality of optical waveguides (2) are The optical waveguide and light receiving device according to claim 1, wherein the interval between two optical waveguides and the interval between any two optical receivers in the plurality of optical receivers 6 are each an integral multiple of a predetermined length. Optical coupling structure of the vessel.