JP3096558B2 - Receiver / transmitter module for optical communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitting / receiving module for optical communication. More specifically, the present invention relates to a transmission / reception module suitable for time-division two-way communication among subscriber communication terminals using an optical fiber.

[0002]

2. Description of the Related Art As shown in FIG. 4 , a basic configuration of a transmission / reception module for optical communication is as follows: a light emitting element 21 such as a semiconductor laser for generating a transmission signal light;
A light receiving element 22 including a photodiode, a phototransistor, a photovoltaic cell, and the like, which receives light via the light source 23;
And a rod lens 25 for coupling the condensed light to a ferrule 26 of an optical transmission line.The rod lens 25 and the ferrule 26 are aligned so that the centers of the rod lens 25 and the fiber 27 at the center of the ferrule 26 match. Sleep split from 26
Held at 28. Rod lens 25 and ferrule
The 26 contact surfaces are each polished by a convex spherical surface so as to make physical contact. The ferrule 26 corresponds to the tip of the optical fiber. Here, the physical contact refers to a contact in which the contact surfaces are brought into close contact with each other by, for example, polishing the joint surfaces of the lens and ferrule end surfaces with a convex spherical surface to eliminate Fresnel reflection.

In this transmission / reception module, a transmission signal light and a reception signal light are separated by inserting a half mirror 23 into an optical path, and a light emitting element 21 and a light receiving element 22 are separately arranged. The signal light transmitted from the condenser lens
The light is condensed by 24 and converges on the physical contact portion between the rod lens 25 and the ferrule 26. The received signal light from the optical fiber is 50% at the half mirror 23
The light is reflected and received by the light receiving element 22. The end face of the light emitting element 21 and the light reflected by the end face of the light emitting element 21 when the received signal light reflected on the surface of the light receiving element 22 or transmitted through the half mirror 23 returns to the optical fiber and does not become a noise source. The light receiving surface of the light receiving element 22 is inclined with respect to the optical axis.

[0004]

As described above, the conventional transmission / reception module for optical communication transmits the received signal light to the optical transmission path such that the light receiving element forms an optical path different from the optical path from the light emitting element. Where they are separated by a half mirror. When the half mirror is placed in the convergent beam, astigmatism occurs and the spot is blurred, so that there is a problem that the coupling efficiency with the optical transmission line is reduced.

[0005] Further, since the end face of the light emitting element is inclined with respect to the optical axis of the transmission signal light, the coupling efficiency decreases.
Further, in the conventional module, the light receiving element protrudes from the optical axis connecting the light emitting element and the optical fiber in a direction perpendicular to the optical axis, and largely deviates from the axially symmetric shape. For this reason, there is a problem that the light receiving element has an adverse effect even when the optical system such as the light emitting element is floated by a spring to center the rod with a rod lens or a ferrule.

Further, since the half mirror is formed of a non-polarizing multilayer film, it is expensive, and the number of parts is increased, which leads to an increase in the number of assembling steps.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has a simple configuration of a transmission / reception module for optical communication which can separate transmission signal light and reception signal light without using a half mirror. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided a transmitting / receiving module for optical communication, comprising: a light emitting element for generating a transmission signal light; a condenser lens for coupling the transmission signal light from the light emitting element to an optical transmission path; An optical communication transceiver module comprising a light receiving element for receiving a signal light received from the optical transmission line,
A Foucault prism is provided on the optical path of the transmission signal light from the light emitting element, and the central portion of the light emitting portion and the light receiving portion is positioned with a surface formed by the dividing line of the Foucault prism and the traveling direction of the transmission signal light interposed therebetween. the light emitting element and the light receiving element is provided so as to, and the Foucault prism and the condenser
The optical lens is integrally formed .

Here, the Foucault prism has a shape in which two prisms having a small apex angle are aligned so that the slopes intersect with the bottom surface aligned, and light emitted from a point light source is separated by the two prisms. Refers to an element. The dividing line of the Foucault prism refers to a line formed by intersecting the slopes of the two prisms.

[0010]

The transmission signal light having passed through the Foucault prism and the condenser lens is incident on the other end of the rod lens having one end polished to a convex spherical surface, focuses on the convex spherical surface, and focuses on the convex spherical surface. It is preferable that the rod lens is provided so that the ferrule of the optical transmission line makes physical contact with the semiconductor laser so that reflected light at the end face of the optical fiber does not return to the semiconductor laser and generate noise.

The transmission signal light passing through the Foucault prism and the condenser lens is focused on a fiber portion provided at the center of the ferrule connected to the optical transmission line at the obliquely polished end of the ferrule. As described above, the oblique polishing ferrule may be provided.

Further, the light-emitting element and the light-receiving element are arranged so that at least a part of the light-receiving element receives light from a rear end face of the light-emitting element and the amount of light emitted from the light-emitting element can be monitored. This is preferable because the number of points can be reduced to reduce costs.

[0014]

According to the present invention, we have used a prism lenses integrally and Foucault prism and a condenser lens Runode, heart
Only one pull-out is required, and the assembly of the optical system is very easy.
Further, the Foucault prism divides the transmitted light into two to separate the transmitted and received light, and the received signal returned to the light emitting element does not return to the optical transmission path again. That is, half of the received signal light transmitted from an optical transmission line such as an optical fiber enters the light receiving element, and the other half separates and enters the light emitting element side, where the light reflected by the light emitting element is reflected. Of the two triangular prisms divided by the dividing line of the Foucault prism, returns to the optical transmission path side through a different prism from the prism that has passed before reflection, so returns to a position off the optical transmission path and returns to the optical transmission path. Does not enter. Therefore, since the end face of the light emitting element does not need to be inclined, the coupling efficiency between the transmission signal light transmitted from the light emitting element and the optical transmission path can be increased.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a transmitting / receiving module according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining the principle of the transmitting / receiving module of the present invention , and FIG. 2 is a transmitting / receiving module according to the present invention .
FIG. 3 is a diagram for explaining another embodiment of the module according to the present invention.

In one embodiment of the transmitting / receiving module of the present invention shown in FIG. 2 , a light emitting element 1 and a light receiving element 2 are arranged close to each other with their light emitting end faces and light receiving faces facing in the same direction. A prism lens 34 and a rod lens 5 are provided facing the end face and the light receiving surface, and the center of the convex spherical surface 5a of the rod lens 5 that makes physical contact with a ferrule 6 connected to an optical transmission path such as an optical fiber. The light-emitting element 1 and the prism lens 34 are arranged so as to converge light on the portion. The prism lens 34 condenses with the Foucault prism
The lens and the lens are integrally formed, as shown in FIG.
To separate the Foucault prism 3 and the condenser lens 4
It can be understood by referring to FIG.
I will explain it .

The light emitting element 1 is composed of, for example, a semiconductor laser in which a semiconductor laser chip 1a is provided on a silicon submount 1b, and generates a transmission signal light corresponding to an input signal such as voice. The light receiving element 2 is a photodiode,
It comprises a phototransistor, a photocell, and the like, and converts an optical signal, which is a received signal light sent from an optical transmission line, into an electric signal. The light-receiving element 2 can also use a part of the light-receiving element to receive light emitted from the rear surface of the light-emitting element 1 and also function as a monitoring light-receiving element for monitoring the light emission amount of the light-emitting element 1. Parts that can be shared
This is preferable because the number can be reduced. When the light receiving element 2 is also used as a monitoring light receiving element, normal transmission and reception are performed alternately in a time-division manner without forming a light receiving section separately for receiving the reception signal light. Are different in time, and it is possible to perform both reception of the reception signal light and reception of light for monitoring on the same light receiving surface.

As shown in FIGS. 1B and 1C, the Foucault prism 3 has two triangular prisms 31 and 32 having a small apex angle, as shown in a side view and a perspective view, respectively, in which the apex angle θ is exaggerated.
Has a structure synthesized by the dividing line 33, and the apex angle θ is 2 to 2.
Abrasion finishing is performed by injection molding of acrylic resin or press molding of glass so that the angle is about 3 °. In this case, since the change in refractive index of the acrylic resin due to heat is large, glass having a small change is preferable. The circular beam incident on the whole Foucault prism 3 separates into a semicircular portion incident on the upper prism 31 and a semicircular portion incident on the lower prism 32, and is condensed by the condenser lens 4. In the example shown in FIG. 1, light transmitted through the lower prism 32 is incident on the central portion A of the convex spherical surface 5a in FIG. The light transmitted through the upper prism 31 is split so as to converge at a point B in FIG. 1A, and the light converged at the point B does not enter the fiber 7 and is not used as transmission signal light. Therefore, less than half of the transmission signal light emitted from the light emitting element 1 is used. The above-mentioned Foucault prism has been described with a concave shape that is fitted when the slopes of the two prisms are lowered,
Even if the cross section to be combined is triangular due to the high slope, the light passing through the two prisms only intersects and converges to different points, and can be used similarly.

The condenser lens 4 is made of glass, acrylic resin, or the like, like the Foucault prism 3, and is a lens for converging light from the light emitting element 1, and has a known axial symmetry so that astigmatism does not occur. Formed as an aspheric lens. The rod lens 5 is for efficiently coupling the light condensed by the condensing lens 4 to the fiber 7 at the center of the ferrule 6. Light from the light emitting element 1 is converged on the center of the spherical surface 5 a without aberration, and is brought into physical contact with the ferrule 6 to enter the fiber 7 at the center of the ferrule 6. For this reason, the refractive index of the rod lens 5 is desirably the same as the refractive index of the fiber 7 of the ferrule 6 and desirably about 1.42 to 1.49. For example, glass such as FK3 (refractive index: 1.465) manufactured by SCHOTT of Germany is suitable, but other glass or sapphire can be used. Further, in order to make one end of the ferrule 7 be in physical contact with the end of the ferrule 7, the periphery of the rod lens 5 and the ferrule 6 is held by a slit sleeve 8, so that even if there is a center deviation of the center of the spherical surface, a physical conduct can be obtained reliably. It has been like that. 9 is a light emitting element 1
And a cover glass provided on the surface side of the light receiving element 2. T is a path of the transmission signal light, and R is a path of the reception signal light.

With this configuration, the dividing line of the Foucault prism 3
The light-emitting element 1 is arranged so that the center of the light-emitting portion is located at a position shifted by, for example, Δy on one side of a surface formed by 33 and the light traveling direction. The light receiving element 2 is arranged such that the center of the light receiving section is located at the position of Δy opposite to the surface formed by the step (1).

Assuming that the refractive index of the Foucault prism 3 is n and the apex angle is θ, the light transmitted through the Foucault prism 3 deviates from the incident light by (n−1) θ. Here, when the distance between the Foucault prism 3 and the light emitting portion of the light emitting element 1 is L, the deviation Δy of the light from the optical axis is Δy = LtanＬ (n−1) θ｝ (1) The light-emitting portion is arranged so as to be shifted from the surface formed by the above-mentioned division line by Δy obtained by the equation (1) (see FIG. 1D).

Further, the light receiving element 2 is directed in a direction slightly shifted from a plane perpendicular to the light traveling direction. This is to prevent the received signal light from being reflected on the light receiving surface of the light receiving element 2 and returning to the optical transmission path.

With this configuration, the light emitted from the light emitting element 1 enters the fiber 7 of the optical transmission line,
Even if the received signal light from the optical transmission line is received by the light receiving element 2 and the received signal light is reflected by the end face of the light emitting element 1 or the light receiving surface of the light receiving element 2, the light does not return to the optical transmission path, and the noise source Not be. The reason will be described below.

The transmission signal light emitted from the light emitting element 1 is
It is divided into two by Foucault prism 3, and as described above,
The light transmitted through the lower prism 32 in FIG. 1 is converged by the condenser lens 4 to the center point A of the convex spherical surface 5a of the rod lens 5,
Coupled with fiber 7. On the other hand, the light transmitted through the upper prism 31 converges to the point B in FIG. 1A and does not contribute to the transmission signal light. The light reflected on the surface of the fiber 7 follows the same optical path as indicated by R in FIG. 1 and does not return to the light emitting element 1 side, so that it has no influence on the light emitting element.

The received signal light transmitted from the optical transmission line is transmitted from the fiber 7 to the rod lens 5 from the point A of the convex spherical surface 5a.
After passing through the condenser lens 4 and the Foucault prism 3, the upper half of the light is split to the light receiving element 2 and the lower half of the light is split to the light emitting element 1 and converges. Most of the received signal light converged on the light receiving element 2 side is received by the light receiving element 2, and the light receiving element 2 is arranged such that a part of the light reflected from the light receiving surface is oblique to the light traveling direction. Therefore, the light is reflected in the horizontal direction and does not return to the optical transmission line. The light split into the light emitting element 1 is reflected by the end face of the light emitting element 1, but is reflected upward because the light is incident on the light emitting element 1 obliquely from below.
The light enters the upper prism 31. Therefore, the reflected light converges to the point B as described above, does not enter the fiber 7 of the ferrule, and does not return to the optical transmission line and become a noise source.

[0026]

The design method of the prism lens 34 is as follows. First, the light emitting element 1 is placed on the optical axis, and the aspherical surface is formed so as to have a predetermined focal length without astigmatism by a normal method without a Foucault prism. Design a condenser lens. Next, a Foucault prism having the same refractive index n as the condenser lens is arranged in contact with the condenser lens between the aspherical condenser lens and the light emitting element.

Next, the light emitting point of the light emitting element 1 is shifted from the optical axis by Δy obtained by the above equation (1) to correct the aspherical shape of the condenser lens. Next, the condenser lens is divided into two parts, and a Foucault lens is interposed therebetween to correct the surface shape of the condenser lens. Then, a mold is formed according to the shape, and glass is press-molded to produce a prism lens. The prism lens 34 can be made of glass or acrylic resin, but is preferably made of glass having a small difference in refractive index depending on temperature.

If the condensing lens and the Foucault prism are integrated into the prism lens 34 as described above, the centering is one.
It only takes a few turns and the assembly of the optical system becomes very easy.

FIG. 3 is an explanatory sectional view of another embodiment of the transmission / reception module according to the present invention. Portions corresponding to the embodiment of FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 3, reference numeral 10 denotes a ferrule whose end is obliquely polished, which may be in physical contact with the ferrule 6 of an optical fiber as an optical transmission line and a split sleeve 8, and the ferrule end face of an optical fiber such as a pigtail is obliquely polished. It may be done. The oblique polishing of the end of the ferrule is to prevent the received signal light traveling along the optical fiber from being reflected at the end face and returning to the inside of the fiber. Such ferrules can also be combined. In this embodiment, the distance between the light emitting element 1, the condenser lens 4, and the like is set so that the transmission / reception signal light converges on the end face 10a of the obliquely-polished ferrule 10.

[0031] In previous SL embodiment, as prism lens with an integrated Foucault blanking rhythm and aspheric lenses have been described Foucault prism lens in a manner sandwiched by the aspherical lens, the present invention is the heart not limited thereto It may be an integrated shape in which it contacts only with each other.

[0032]

According to the present invention, transmitted and received light can be separated without using a half mirror. As a result, since a half mirror is not used, expensive film formation such as a 50% reflection film is not required, cost can be reduced, astigmatism can be reduced, and coupling efficiency can be improved.

Further, since the light receiving element and the light emitting element are arranged in the same axial direction, the optical system becomes coaxial, the size can be reduced, the structure can be simplified, the assembly becomes easy, and the light emitting element and the condensing lens can be used. The optical system can be floated by a spring to provide free contact.

Further, since the Foucault prism shifts the optical path even if the end face of the light emitting element is not inclined with respect to the optical axis direction,
The reflected light of the received signal light does not enter the optical fiber, and the coupling efficiency of the transmitted signal light from the light emitting element is high.

[Brief description of the drawings]

FIG. 1 shows a prism lens of a transmission / reception module of the present invention.
Decomposed into Foucault prism and condenser lens, the principle
Is a diagram illustrating a.

FIG. 2 is an explanatory sectional view of one embodiment of the transmission / reception module according to the present invention.

FIG. 3 shows another embodiment of the transmission / reception module according to the present invention.
It is a diagram for explaining.

FIG. 4 is an explanatory diagram of a conventional transmitting / receiving module .

Claims (4)

(57) [Claims] A light emitting element for generating a transmission signal light; a condenser lens for coupling the transmission signal light from the light emitting element to an optical transmission path; and a light receiving element for receiving a reception signal light from the optical transmission path. An optical communication receiving and transmitting module comprising:
A Foucault prism is provided on the optical path of the transmission signal light from the light emitting element, and the central portion of the light emitting portion and the light receiving portion is positioned with a surface formed by the dividing line of the Foucault prism and the traveling direction of the transmission signal light interposed therebetween. the light emitting element and the light receiving element is provided so as to, and the Foucault prism and the condenser
Light passing credit transceiving module and an optical lens is integrally formed. 2. The transmission signal light having passed through the Foucault prism and the condenser lens is incident on the other end of a rod lens having one end polished to a convex spherical surface, focuses on the convex spherical surface, and focuses on the convex spherical surface. the rod lens is provided according to claim 1 Symbol mounting optical communication transceiving module as ferrule of the optical transmission line is physical contact spherical. 3. The transmission signal light having passed through the Foucault prism and the condenser lens is focused on a fiber portion provided at the center of the ferrule obliquely polished and connected to the optical transmission line. claim 1 Symbol mounting optical communication transceiving module the oblique polishing the ferrule is provided so as to connect. 4. The light-emitting element and the light-receiving element are arranged so that at least a part of the light-receiving element receives light from a rear end face of the light-emitting element and a light emission amount of the light-emitting element can be monitored. 4. The receiving / transmitting module for optical communication according to 1 , 2, or 3 .