JPH01183605A - Photodetecting device - Google Patents

Abstract

PURPOSE:To obtain the photodetecting device having a high optical coupling efficiency, and also, being miniature by sticking a condensing lens to the lower side face of a band-like core layer having an inclined end face which adheres closely and brought to optical coupling to the end face of an optical fiber and reflects the emitted light in the direction of the photodetecting surface of a photodetector. CONSTITUTION:On a circuit board 5 provided in parallel to an optical fiber 10 for transmitting an optical signal, a photodetector 1 whose photodetecting surface 3 has been turned upward is provided so as to photodetect the emitted light of the optical fiber 10. The end face of the optical fiber 10 adheres closely and brought to optical coupling to one end face of an optical waveguide body 20, and the other end face of the waveguide body 20 becomes an inclined end face 22-A. Also, a condensing lens 25 is stuck to the lower side face of a core layer 21 opposed to the inclined end face 22-A, therefore, the emitted light from the optical fiber 10 is reflected by the inclined end face 22-A, and thereafter, condensed to the photodetecting surface 3 by the condensing lens 25. Accordingly, even when the photodetecting surface 3 has been made narrow and small, the optical coupling degree is high, and the device can be miniaturized.

Description

[Detailed Description of the Invention] [Summary] Regarding a light receiving device that optically couples an optical fiber and a light receiving element, the purpose of the present invention is to provide a light receiving device that has high optical coupling efficiency and is small in size. and a light-receiving element mounted on a circuit board parallel to the optical fiber with its light-receiving surface facing upward in order to receive the light emitted from the optical fiber, wherein one end face is the end face of the optical fiber. a waveguide which is disposed above the light-receiving element in close contact with and optically coupled to the light-receiving element, and has a band-shaped core layer on the lower side surface with the other end face being inclined to reflect the emitted light toward the light-receiving surface; and a condenser lens attached to the lower surface of the core layer opposite to the oblique end surface. (1) A waveguide body having a belt-shaped core layer whose one end face is in close contact with the end face of the optical fiber and optically coupled, disposed above the light receiving element and transmits the optical signal on the lower face; Provided on the bottom surface of the desired location of the layer,
and a condensing grating coupler.

[Industrial application field]

The present invention relates to a light receiving device that optically couples an optical fiber and a light receiving element.

In recent years, light receiving devices have been provided in which an electric circuit such as a receiving circuit and a light receiving element are provided on the same circuit board.

At this time, if the optical transmission path and the electrical signal path are perpendicular to each other, there is a risk that the entire device will become larger. Therefore, it is desirable to have a so-called flat-mounted light-receiving device in which a circuit board provided with an electrical signal path and an optical transmission path are installed in parallel.

On the other hand, in order to improve frequency characteristics, the capacitance of the light receiving element is made as small as possible. As a result, the light-receiving surface of the light-receiving element becomes smaller, and the degree of optical coupling decreases.

Accordingly, there is a need for a light-receiving device in which an optical signal is efficiently incident on a light-receiving element.

[Conventional technology]

FIG. 6 is a side sectional view of a conventional example in which an optical fiber and a light receiving element are mounted in a plane-mounted manner. In FIG. 6, reference numeral 5 denotes a circuit board made of ceramic, plastic, etc., on which a desired electric circuit and a light-receiving element l such as a photodiode are mounted.
It is firmly fixed to the surface of the base 6.

The light-receiving element 1 is a chip-type element having a light-receiving surface 3 on the upper surface, and has an electrode provided on the entire back surface, and the electrode is closely connected to a pattern 4B provided on the surface of the circuit board 5. . Further, the other ring-shaped electrode 2A is provided on the periphery of the light receiving surface 3.
is provided, and the electrode 2^ is connected to the pattern 4A, which is another electrical signal path.
is connected to.

That is, the light receiving element 1 is mounted on the circuit board 5 with the light receiving surface 3 facing upward and parallel to the upper surface of the circuit board 5.

Reference numeral 10 denotes a single mode optical fiber, which is an optical transmission line through which an optical signal is input to the light receiving element 1.

The end face of the optical fiber 10 is not a plane perpendicular to the axial center, but is processed into an oblique end face 11 that is inclined at approximately 45 degrees with respect to the axial center.

7 is a fiber holding stand provided with, for example, a V-shaped groove so as to horizontally support the optical fiber 10, with the inclined end surface 11 of the optical fiber 10 facing upward, and the vicinity of the end of the optical fiber being placed in the groove. The optical fiber is inserted, and the outer peripheral surface of the optical fiber and the inner wall of the groove are bonded together using an adhesive or the like.

After adjusting the position of the fiber holder 7 so that the inclined end surface 11 of the optical fiber 10 faces the light-receiving surface 3 of the light-receiving element 1, the bottom surface of the fiber holder 7 is brought into close contact with the upper surface of the circuit board 5, and the fiber The holding stand 7 is fixed to the circuit board 5.

Therefore, the optical signal propagated through the optical fiber 10 is
The oblique end surface 11 is almost totally reflected in a downward direction substantially perpendicular to the axis, that is, toward the light receiving element 1, and the light is emitted from the outer circumferential surface of the cladding layer facing the oblique end surface 11, and is emitted from the light receiving surface. 3
incident on .

As mentioned above, conventional light-receiving devices are devices in which the end face of the optical fiber is inclined, and the axis of the optical fiber is mounted close to and parallel to the top surface of the circuit board. This has the advantage that the light-receiving device can be made more compact than when it is mounted perpendicularly to the surface of the circuit board.

[Problems to be Solved by the Invention] However, in recent years, the capacitance of light receiving elements has been reduced to improve frequency characteristics. That is, with the miniaturization of capacitance, the light-receiving surface of recent light-receiving elements has become narrower.

On the other hand, in the conventional light-receiving device described above, the end face of the optical fiber is an oblique end face, so the output beam reflected from the oblique end face is expanded into a conical shape with a major axis in the axial direction of the optical fiber. It is opened and projected onto the light receiving surface 3.

Therefore, the conventional light-receiving device has a problem in that the optical coupling efficiency becomes low as the light-receiving surface becomes narrower.

Furthermore, when adjusting the optical fiber in order to increase the optical coupling efficiency, there is a risk that the optical fiber will be brought too close to the light receiving element, causing the optical fiber to collide with the light receiving element, thereby destroying the light receiving element.

The present invention was created in view of the above points, and an object of the present invention is to provide a light-receiving device that has high optical coupling efficiency and is small in size.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an optical fiber 10 for transmitting an optical signal, and a circuit board 5 that is parallel to the optical fiber 10, with the light receiving surface 3 facing upward to receive the light emitted from the optical fiber 10. In a light-receiving device equipped with a light-receiving element 1 to be mounted, as illustrated in FIG. 20 is provided.

One end surface of the waveguide body 20 is made into a flat end surface, and is brought into close contact with the end surface of the optical fiber 10 for optical coupling. In addition, the waveguide body 2
The end face of the core layer 21 is configured to be an inclined end face 22-A, and the light emitted from the core layer 21 is reflected in the direction of the light receiving surface 3. The waveguide body 20 is held at a predetermined position above the circuit board 5 using the support stand 2OA.

A condensing lens 25 such as a convex lens or a Fresnel lens is attached to the lower surface of the core layer 21 facing the inclined end surface 22-A.

As another means, as illustrated in FIG.
A waveguide body 20 is provided.

One end face of the waveguide body 20 is made into a flat end face, and the waveguide body 20 is brought into close contact with the end face of the optical fiber 10 for optical coupling, and the waveguide body 20 is held at a predetermined position above the circuit board 5 using the support stand 20A.

A condensing grating coupler 35 is provided on the lower surface of the core layer 21 at a desired location so as to condense the light onto the light receiving surface 3.

[Effect]

According to the above item 1, the output side end face of the optical fiber is configured such that the inclined end face 22-A reflects the optical signal in the direction of the light receiving surface 3.
In addition, a condenser lens 25 is attached to the lower surface of the core layer 21 facing the oblique end surface 22-A.

Therefore, the light beam reflected so as to expand on the inclined end surface 22-8 is focused on the light receiving surface 3 by the condensing lens 25. Therefore, even when the light receiving surface 3 is made narrow, the degree of optical coupling is high.

According to item 2 above, since the semicircular condensing grating coupler 35 is provided on the lower surface of the desired portion of the core layer 21 through which the optical signal propagates, the light traveling through the core layer 21 is condensed. The light is refracted in the region of the optical grating coupler 35, projects from the core layer 21 toward the light receiving element 1, and is focused on the light receiving surface 3.

Therefore, even when the light receiving surface 3 is made narrow, the degree of optical coupling is high. Furthermore, since it has a light collecting function, there is a certain distance between the light receiving element and the light collecting grating coupler at a position where optical coupling is optimal. Therefore, there is no risk of damaging the light receiving element during adjustment.

〔Example〕

The present invention will be specifically described below with reference to the drawings. Note that the same reference numerals indicate the same objects throughout the figures.

Figure 1 is a sectional view of the embodiment described in item 1, Figure 2 is a sectional view of the example described in item 2, Figure 3 is a perspective view of another example described in item 1, and Figure 4 is a sectional view of the example described in item 2. Perspective views of other embodiments of Section 5, (al, (bl,
(C1 is a diagram showing the main part of the second term.

In FIG. 1, an electrical circuit such as a receiving circuit and a light receiving element 1 such as a photodiode are mounted on the surface of a circuit board 5 made of ceramics or the like, which is mounted in close contact with the surface of a base 6.
This is implemented.

The light-receiving element 1 that receives an optical signal is a chip-type element having a small capacitance and a narrow light-receiving surface 3 on the front side, and has an electrode (not shown) provided on the entire back surface in a pattern 4B.
Connect closely to surface glue.

The pufferfish-shaped electrode 2A is connected to the terminal of the pattern 4A provided on the surface of the circuit board 5 by wire bonding. That is, the light receiving element 1 is mounted on the circuit board 5 so that the light receiving surface 3 faces upward.

10 is, for example, a single mode optical fiber, and is an optical transmission line through which an optical signal is input to the light receiving element 1.

20 is a plate-shaped waveguide body made of lithium niobate or the like, and a belt-shaped core layer 21 is provided along the center line of the lower surface by diffusing titanium or the like to increase the refractive index.

The depth and width of the core layer 21 are the same as those of the optical fiber 10.
It is approximately equal to the diameter of the core of , which is about 10 μm.

One end surface of the waveguide body 20 is a vertical surface, and the other end surface is an inclined end surface 22-A in which the lower surface side of the core layer 21 is inclined at an acute angle, for example, at an angle of 45 degrees.

On the lower surface of the waveguide body 20 on the side that contacts the optical fiber 10,
A rectangular parallelepiped support stand 20 made of the same material as the waveguide body 20
Glue A on. This support stand 2OA shall be fixed so that the side wall of the support stand and the end face of the waveguide body 20 are on the same plane.

The tip of the optical fiber 10 is inserted into the center hole of a support plate 15 made of ruby or the like. Then, with the end surface of the optical fiber 10 in contact with the end surface of the core layer 21, the support plate 15 and the waveguide body 2 are
0 using an adhesive 16 to optically connect the optical fiber 10 and the core layer 21.

25 is a condensing lens such as a semi-hemispherical convex lens or a disc-shaped Fresnel lens, and its diameter is desirably larger than the width of the core layer 21. The flat surface of the condenser lens 25 is attached to the lower surface of the core layer 21 facing the oblique end surface 22-8 using an optical adhesive that transmits light.

Note that the condensing lens 25 is a lens having a desired focal length such that the light reflected by the inclined end surface 22-A is condensed onto the light receiving surface 3.

As described above, the waveguide body 20 equipped with the condensing lens 25 and the optical fiber 10 is placed on the condensing lens 25 of the support base 20A.
With the side wall of the example in contact with the side edge of the circuit board 5, the bottom surface of the support stand 20A is fixed to the base 6 using an adhesive. The height of the support base 20A is set to a desired height such that there is no possibility that the condenser lens 25 will collide with the light receiving element l.

Therefore, the light propagating through the optical fiber 10 travels through the core layer 21, reaches the inclined end surface 22-A, and reaches the inclined end surface j.
It is reflected in the direction of the light receiving element 2-a. The reflected light is focused by a condensing lens 25 and focused on the light receiving surface 3.

That is, even when the light-receiving surface 3 is made narrow, the optical coupling efficiency is high.

Note that since the axes of the optical fiber 10 and the waveguide body 20 are close to and parallel to the circuit board 5, the mounting speed is lower than when the axes of the optical fibers are mounted perpendicularly to the surface of the circuit board. The work is easy and the light receiving device is small.

The waveguide body 20 shown in FIG. 2 is completely the same as the waveguide body shown in FIG. 1' except that both end surfaces are vertical surfaces, and the optical fiber 10 is connected to one end surface. Also, with the core layer 21 facing downward, the circuit board 5 is placed through the support stand 20A.
It is also the same as shown in FIG.

A condensing grating cover 35 is formed on the lower surface of a desired portion of the core layer 21 by ion beam etching means so as to condense light onto the light receiving surface 3.

The condensing grating coupler 35 is provided as shown in detail in FIG.

FIG. 5(a) is a perspective view of the waveguide body 20 turned over, in which the end face of the optical fiber 10 is brought into contact with one end face of the core layer 21 provided on the waveguide body 20, and the optical fiber is 10
and the core layer 21 are optically connected.

Then, a large number of diffraction gratings each consisting of a substantially half-moon-shaped grating convex portion and grating grooves centered in the direction of the optical fiber 10 are provided on a desired surface of the core layer 21 to form a condensing grating coupler 35 .

Therefore, the light incident on the core 121 from the optical fiber 10 is in a single mode and is in the core J! 21 and reaches the condensing grating coupler 35. While passing through the condensing grating coupler 35, the light is refracted one after another and is directed from the core layer 21 toward the light receiving element (diagonally upward in FIG. 5).
The light jumps out and converges on the light receiving surface (point P in Fig. 5).

This condensing grating cover 35 has the following features as shown in FIG. 5(b).
There are two types of diffraction gratings: the blazed diffraction grating shown in Figure 5 (C1) and the rectangular uneven diffraction grating shown in Figure 5 (C1).Although any shape may be used, the blazed diffraction grating focuses light better. More light.

In FIG. 5(b), the core layer 2 provided in the waveguide body 20
A large number of blaze-like diffraction gratings each having a sawtooth cross section formed by grating protrusions 36-1 and grating grooves 36-2 are provided on the surface of the grating 1 in a semicircular shape.

The pinch of this grating convex portion 36-1 and its apex angle (blaze angle) are changed based on a certain law as the distance from the optical fiber (not shown) increases. Therefore, the light incident on the core layer 21 from the optical fiber travels through the core layer 21 in a single mode. When the light reaches the condensing grating lens 35, the light is refracted one after another at different angles and is focused diagonally upward at a point P shown in the figure.

FIG. 5 (In C1, the core layer 2 provided in the waveguide body 20
1, a large number of diffraction gratings each having a rectangular cross section formed by grating convex portions 37-1 and grating grooves 36-2 are provided in a semicircular shape.

The pitch and width of the grating protrusions 37-1 are changed based on a certain rule as the distance from the optical fiber (not shown) increases. Therefore, the core layer 2
The light incident on the core layer 1 travels through the core layer 21 in a single mode. When it reaches the condensing grating coupler 35, it is refracted one after another at different angles, and the point P shown diagonally upward three.
The light is focused on.

FIGS. 3 and 4 show examples in which an optical fiber array and a light receiving element array are optically coupled.

In FIG. 3, on the surface of the circuit board 5 mounted in close contact with the surface of the base 6, a plurality (three in the figure) of light-receiving elements l are arranged in close proximity at equal pitches to receive light. This is an element play.

Each light-receiving element 1 has a small capacitance (i.e., it is a chip type having a narrow light-receiving surface on the front side, and an electrode (not shown) provided on the entire back surface is closely connected to the pattern 4B. The ring-shaped electrode (not shown) on the surface is connected to the circuit board 5.
Each terminal of the pattern 4A provided in parallel above is connected by wire bonding.

Holes with an inner diameter equal to the outer diameter of the optical fiber 10 are formed at equal pitches (light-receiving elements The optical fibers 10 are arranged at a pitch equal to the arrangement pitch of , and the ends of the optical fibers 10 are fitted into each hole to form an optical fiber array 150.

The waveguide array 200 has a plate shape made of lithium niobate or the like. A plurality of belt-shaped core layers 21 are provided on the lower surface corresponding to the arrangement pitch of the optical fibers 10 of the optical fiber array 150.

One end surface of the waveguide array 200 is a vertical surface, and the other end surface is an inclined end surface 220-A in which the lower surface side of the core layer 21 is inclined at an acute angle, for example, at an angle of 45 degrees.

The lower surface of the waveguide array 200 on the side that contacts the optical fiber array 150 is made of the same material as the waveguide array 200.
A rectangular parallelepiped support stand 2008 is glued.

Then, with each end face of the optical fiber 10 in contact with the end face of the corresponding core layer 21 of the waveguide array 200, the optical fiber array 150 is bonded to the end face of the waveguide array 200 using an adhesive, each optical fiber 10
and each core layer 21 are optically connected.

A condenser lens 25 is attached to each lower surface of the core layer 21 facing the inclined end surface 220-A using an optical adhesive that transmits light.

As mentioned above, the condenser lens 25 and the optical fiber array 15
The bottom surface of the waveguide array 200 with the support base 200 attached thereto is fixed to the base 6 using an adhesive.

The arrangement pitch of the optical fibers of the optical fiber array 150 and the arrangement pitch of the core layer of the waveguide array 200 are as follows:
It is possible to arrange them with high precision using lithography means or the like.

Therefore, the light that has propagated through each optical fiber 10 travels through the corresponding core layer 21, reaches each inclined end surface 220-A, is reflected toward the light receiving element, and is focused by the condenser lens 25 to form the corresponding one. The light is focused on the light receiving surface 3 of the light receiving element.

In FIG. 4, a plurality of belt-shaped core layers 21 are provided on the lower side of the waveguide array 200 in correspondence with the arrangement pinches of the optical fibers of the optical fiber array 150.

Both end surfaces of the waveguide array 2000 are surfaces perpendicular to the core layer 21. Note that a rectangular parallelepiped support (not shown) made of the same material as the waveguide array 200 is bonded to the lower surface of the 150 optical fiber arrays of the waveguide array 200.

Then, on the lower surface of each core layer 21, at a position equidistant from the end surface on the optical fiber array 150 side, a converging grating coverr 35 having the same shape and approximately a half-moon shape is provided.

By using the waveguide array 200 in which the condensing grating coupler 35 is formed in this way, the light that propagates through each optical fiber of the optical fiber array 150 and enters the core layer 21 is transmitted by the condensing grating coupler 35. The light is focused on the light receiving surface of the light receiving element l.

〔Effect of the invention〕

As explained above, in the present invention, a condensing lens is attached to the core layer of a waveguide body or a waveguide array, or a semi-moon-shaped condensing grating cover is provided. Applied to a light receiving element and a light receiving element array,
It has excellent practical effects, such as high optical coupling efficiency between the optical fiber and the light-receiving element, easy mounting work, small size, and no risk of damaging the light-receiving element during assembly.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the embodiment described in item 1, Figure 2 is a sectional view of the example described in item 2, Figure 3 is a perspective view of another example described in item 1, and Figure 4 is a sectional view of the example described in item 2. Perspective views of other embodiments of Section 5, (a) and (b) of FIG.
(C) is a diagram showing the main parts of the invention of item 2, and FIG. 6 is a sectional view of a conventional example. In the figure, l is a light receiving element, 3 is a light receiving surface, 4A, 4B are patterns, 5 is a circuit board, 10 is an optical fiber, 11, 22-A, 220-A are oblique end faces, 15 is a support plate, 20 is a Waveguide body, 2OA, 200A are support base, 21 is core layer, 3°5 is condensing grating coupler, 150 is optical fiber array,] Shihaya 2 Dong's Shining Examples of Poetry Chains 2 P 2 Ro Rate I et al. CL) ('F)n

Claims (1)

[Claims] 1. An optical fiber (10) for transmitting an optical signal, and a light-receiving surface (3) facing upward and parallel to the optical fiber (10) in order to receive the light emitted from the optical fiber (10). circuit board (
5) A device comprising a light receiving element (1) mounted on the optical fiber (10), one end face of which is in close contact with the end face of the optical fiber (10) for optical coupling, and disposed above the light receiving element (1). a waveguide body (20) having a band-shaped core layer (21) on the lower surface thereof, the other end face of which is an inclined end surface to reflect the emitted light toward the light-receiving surface (3); A light-receiving device comprising: a condenser lens (25) attached to the lower surface of the core layer (21) facing the end surface. 2. An optical fiber (10) for transmitting an optical signal, and a circuit board (10) parallel to the optical fiber (10) with the light-receiving surface (3) facing upward in order to receive the light emitted from the optical fiber (10).
5) A device comprising a light receiving element (1) mounted on the optical fiber (10), one end face of which is in close contact with the end face of the optical fiber (10) for optical coupling, and disposed above the light receiving element (1). a waveguide body (20) having a strip-shaped core layer (21) on the lower surface for transmitting the optical signal; and a condensing grating coupler (35) provided on the lower surface at a desired location of the core layer (21). ) and a light-receiving device.