JPH1164687A - Optical transmitting and receiving module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an S/N of a receiving signal by preventing a part of transmission light emitted from a light emitting element from being reflected by a demultiplexer and reaching a light receiving element after reflecting on a diagonally cut end face of an optical fiber. SOLUTION: To a case body block 20, an LD(laser diode) 6 emitting the transmission light of a 1st wavelength, a demultiplexer 5 transmitting the transmission light emitted from the LD 6 and a lens 13 collecting the light transmitting the demultiplexer 5 on a diagonally cut end face of an optical fiber are coaxially fitted and also, in parallel with this optical axis, a reflecting mirror 15 for light receiving and a PD(photodiode) 9 receiving the receiving light of a 2nd wavelength are coaxially fitted. In the case body block 20, an opening 35 communicating between the demultiplexer 5 and the reflecting mirror 15 is formed, the diameter ϕ of this opening 35 is set to ϕ<=0.3f (f is the focal length of the lens 13) and further, the center of the opening 35 is decentered by d=f.sinθ(where, θ is an emitting angle of the receiving light from the optical fiber 12) with respect to a straight line L perpendicular to the opening 35 passing through the intersection O of the axis of the lens 13 and the demultiplexer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission / reception module for coupling a light emitting element and a light receiving element to an optical fiber through which transmission light and reception light of a plurality of different wavelengths are transmitted.

[0002]

2. Description of the Related Art FIG. 4 is a cross-sectional view of a conventional optical transceiver module. As shown in FIG. 4, the housing of the optical transceiver module is roughly divided into a central block 1, an LD (laser diode) block 2, and a PD. (Photodiode) It is composed of four blocks, a block 3 and a fiber block 4, and a branching filter 5 is mounted in the central block 1. The LD block 2 is attached with an LD 6 as a light emitting element and a lens holder 8 supporting a lens 7, and the PD block 3 is attached with a PD 9 as a light receiving element and a lens holder 11 supporting a lens 10.
The fiber block 4 includes an optical fiber 12 and a lens 13.
Is mounted.

The transmission light of wavelength λ1 emitted from the LD 6 is collimated by the lens 7 on the LD block 2 side, passes through the demultiplexing filter 5 in the central block 1, and then passes through the lens 13 on the fiber block 4 side. And is incident on the end face of the optical fiber 12, and transmitted through the optical fiber 12. On the other hand, the received light of wavelength λ2 transmitted through the optical fiber 12 is diffused at the end face of the optical fiber 12, collimated by the lens 13 on the fiber block 4 side, and then separated by the splitter filter 5 in the central block 1. Then, the light is condensed by the lens 10 on the PD block 3 side and received by the PD 9.

[0004]

By the way, in the above-mentioned conventional optical transmitting and receiving module, in order to prevent the transmission light of the wavelength λ1 emitted from the LD 6 from being reflected by the tip end surface of the optical fiber 12 and returning to the LD 6. And optical fiber 1
2 is cut obliquely at a predetermined angle.

[0005] However, as shown by the broken line in FIG.
After a part of the transmission light of wavelength λ1 reflected by the obliquely cut end face of the optical fiber 12 is reflected by the demultiplexing filter 5 through the lens 13 on the fiber block 4 side, the PD
In some cases, the light may enter the light receiving surface of the PD 9 through the lens 10 on the block 3 side.
There is a problem that the / N ratio deteriorates.

[0006]

According to the present invention, there is provided an aperture which can limit transmitted light in an optical path of a receiving light emitted from an end face of an optical fiber, which is reflected by a demultiplexing filter and reaches a light receiving element. I do. When such an opening is provided, the received light of the second wavelength emitted from the end face of the optical fiber can enter the light receiving surface of the light receiving element through the opening, but can transmit the first wavelength emitted from the light emitting element. Even if a part of the light is reflected at the end face of the optical fiber and then reflected by the demultiplexing filter, this transmitted light does not reach the light receiving surface of the light receiving element through the aperture, so the transmitted light reaching the light receiving element is reduced. As a result, the S / N ratio of the received signal can be improved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an optical transceiver module according to the present invention, a light emitting element for emitting transmission light of a first wavelength, a demultiplexing filter for transmitting transmission light emitted from the light emitting element, and a demultiplexing filter are provided. A lens that collects light transmitted through the optical fiber at an obliquely cut end surface of the optical fiber, and a light receiving element that receives received light of a second wavelength emitted from the end surface of the optical fiber and collimated by the lens. In the optical transceiver module in which the received light is reflected by the demultiplexing filter and reaches the light receiving element through an opening having a diameter φ, the diameter φ of the opening is set to φ ≦ 0.3f (where f
Is the focal length of the lens) and the center of the aperture is d = f with respect to a straight line that passes through the intersection of the central axis of the lens and the demultiplexing filter and is perpendicular to the aperture.
The eccentricity was sin θ (where θ is the output angle of the received light from the optical fiber).

Further, in consideration of the level reduction of the incident efficiency from the optical fiber, the lower limit of the diameter φ of the opening is set to 0.1.
It was set in the range of 2f ≦ φ ≦ 0.3f.

[0009]

Embodiments will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an optical transceiver module according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a housing block provided in the optical transceiver module, and FIG. 3 is an explanatory diagram showing a main part of the optical transceiver module. In this case, components corresponding to those in FIG. 4 are denoted by the same reference numerals.

As shown in FIGS. 1 and 2, the optical transceiver module according to the present embodiment has one housing block 20,
The LD 6 described in the conventional example, the lens holder 8 supporting the lens 7, the demultiplexing filter 5, the lens holder 14 supporting the lens 13 on the transmission path side, and the front end surface are obliquely cut with respect to the housing block 20. Optical fiber 1
2 are mounted coaxially. In addition, the reflecting mirror 15 for receiving light is
And a lens holder 11 for supporting the lens 10 and a PD 9
And are mounted coaxially. Note that, instead of the reflection mirror 15, a branching filter that can reflect light of the wavelength λ2 may be used.

As shown in detail in FIG.
0, an opening 21 for disposing the lens holder 8;
An opening 22 for disposing the main body of the LD 6, a mounting hole 23 for mounting a flange of the LD 6, and an opening 24 for an optical path are formed continuously. The inner bottom surface 23a of the mounting hole 23 is a mounting reference surface of the LD 6, and the LD 6 is welded to the housing block 20 with its flange portion abutting against the inner bottom surface 23a of the mounting hole 23. Thereby, the entire flange portion of the LD 6 is fitted into the inside of the mounting hole 23, and only the lead portion is exposed from the side surface 31 of the housing block 20. A mounting surface 25 for mounting the demultiplexing filter 5 at an angle of 45 ° with respect to the optical axis, and the lens holder 14 are disposed coaxially with the openings 21, 22, and 24 on the light emitting side. The optical fiber 12 is attached to a side surface 28 of the housing block 20. In addition, in the housing block 20, in parallel with the openings 21, 22, 24 on the light emitting side,
An opening 29 for disposing the lens holder 11;
Opening 30 for disposing the main body of the
Mounting surface 32 for mounting at an angle of 45 ° with respect to the optical axis.
Are formed. Further, the housing block 20 includes
An opening 35 that connects the two mounting surfaces 25 and 32 is formed, and the opening 35 is orthogonal to the light-emitting-side openings 21, 22 and 24 and the light-receiving-side openings 29 and 30. The side surface 31 of the housing block 20 is a reference mounting surface of the PD 9, and the PD 9 is welded to the housing block 20 with its flange portion abutting against the side surface 31. Thereby, the PD 9 has a flange portion and a lead portion on the side surface 31.
The LD 6 is attached to the housing block 20 so that the LD 6 is exposed from the housing block 20.

The fronts perpendicular to the mounting surface 25 of the demultiplexing filter 5 and the mounting surface 32 of the reflection mirror 15 are largely open, and notches 25a, 3 corresponding to these open portions.
2 a is formed in the housing block 20. These notches 25a and 32a are covered by a pair of covers 40 attached to the housing block 20. The housing block 20 has a screw hole 33 and an engagement groove 34 formed therein.
The screw hole 33 is a hole for inserting a screw (not shown) for fixing the optical transceiver module to a chassis or a printed circuit board of the electronic device, and the engagement groove 34 is used to prevent rotation of the optical transceiver module when the screw is fixed. This is to prevent it.

In the optical transmitting / receiving module configured as described above, the transmission light of wavelength λ1 emitted from the LD 6 is:
After being collimated by the lens 7, the light is transmitted through the demultiplexing filter 5, condensed by the lens 13, enters the end face of the optical fiber 12, and transmitted through the optical fiber 12. on the other hand,
The received light of wavelength λ2 transmitted through the optical fiber 12 is diffused at the end face of the optical fiber 12, then collimated by the lens 13, reflected by the demultiplexing filter 5, and then reflected by the reflecting mirror 15 to be reflected by the lens. The light is condensed by 10 and received by PD 9. Here, the transmission light of the wavelength λ1 emitted from the LD 6 passes through the demultiplexing filter 5 and is condensed by the lens 13, but as shown by the broken line in FIG. After reflection
Since the light returns to the demultiplexing filter 5 through the lens 13, the position and size of the opening 35 are specified so that the transmission light does not enter the light receiving surface of the PD 9 to cause crosstalk.

That is, as shown in detail in FIG. 3, let O be the intersection of the central axis of the lens 13 and the demultiplexing filter 5, and let L be a straight line passing through this intersection O and perpendicular to the opening 35. The center of 35 is formed at a position decentered by d = f · sin θ with respect to the straight line L. In this equation, f is the focal length of the lens 13, θ is the emission angle of the received light emitted from the end face of the optical fiber 12, and the angle of the obliquely cut end face of the optical fiber 12 is θ _F , Assuming that the refractive index of the 12 cores is n, the emission angle θ is given by the following equation. θ = sin ⁻¹ (n · sin θ _F ) −θ _F ......
The light emitted from the (single-mode fiber) has a substantially Gaussian intensity distribution, the NA (numerical aperture) at which the intensity becomes 1 / e ² is about 0.08, and the angle θ _{F of the} light emitted from the optical fiber 12. Is expressed by the following equation. Light amount P contained in ^I = e -0.095θ ^{× θ} ............ angle theta _F is because it is ^{P = 1-e -0.095θ × θ} ............, from this equation, the light quantity P 99.9 % (10
0% is infinity) and θ = 8.627 °
And since NA = sin θ, NA = 0.1
It becomes 5. In other words, nearly 100% of the light enters the lens 13 at NA = 0.15. If the diameter of the opening 35 is φ, then φ = 2 × NA × f, so the upper limit of the diameter φ of the opening 35 is , Φ ≦ 0.3f... On the other hand, regarding the lower limit of the diameter φ of the opening 35, since the level reduction of the incident efficiency from the SMF, which does not pose a problem in practical use, is determined to be 95%, the light amount P becomes 95% from the above equation.
% Is obtained as θ = 5.74 °, and NA
= Sin θ, NA = 0.1. That is, in order for 95% of the light to enter, the lower limit of the diameter φ of the opening 35 needs to be 0.2f ≦ φ... It can be seen that it is sufficient to set the range of 2f ≦ φ ≦ 0.3f...

Therefore, the diameter φ of the opening 35 is set to a size that satisfies the above equation, and the center of the opening 35 is moved away from the optical fiber 12 by a deviation d with respect to the straight line L by the above equation. By eccentricity, L
Even if a part of the transmission light of the wavelength λ1 emitted from D6 is reflected by the end face of the optical fiber 12 and returns to the demultiplexing filter 5, this returning light is separated by the demultiplexing filter 5 as shown by the broken line in FIG. After being reflected, the light is blocked around the opening 35, so that the transmission light of the wavelength λ1 does not enter the light receiving surface of the PD 9 to generate crosstalk with the reception light of the wavelength λ2.

In the above embodiment, the case where the LD 6 and the PD 9 are arranged on the same side surface 31 of the housing block 20 has been described.
It is also possible to arrange the lens holder 11 and the PD 9 supporting the “0” on another side surface (the lower end surface in FIG. 1) of the housing block 20 orthogonal to the side surface 31.

[0017]

The present invention is embodied in the form described above and has the following effects.

A light emitting element for emitting transmission light of a first wavelength, a demultiplexing filter for transmitting transmission light emitted from the light emitting element, and an optical fiber in which the light transmitted through the demultiplexing filter is obliquely cut. A lens that converges light at an end face, and a light receiving element that receives light having a second wavelength emitted from the end face of the optical fiber and collimated by the lens, wherein the received light is reflected by the demultiplexing filter. In the optical transmitting and receiving module that reaches the light receiving element through the opening having the diameter φ, the diameter φ of the opening is set to φ ≦ 0.3f (where f is the focal length of the lens).
The center of the aperture is defined as d = f · sin θ (where θ is a distance from the optical fiber of the reception light) with respect to a straight line that passes through the intersection of the central axis of the lens and the demultiplexing filter and is perpendicular to the aperture. When the light is decentered by an amount corresponding to the output angle of the optical fiber, the received light of the second wavelength emitted from the end face of the optical fiber can enter the light receiving surface of the light receiving element through the opening, but the light of the first wavelength emitted from the light emitting element can be emitted. Even if a part of the transmitted light is reflected by the demultiplexing filter after being reflected by the end face of the optical fiber, the transmitted light does not reach the light receiving surface of the light receiving element through the aperture, so that the transmitted light reaching the light receiving element is Thus, the S / N ratio of the received signal can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical transceiver module according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a housing block provided in the optical transceiver module.

FIG. 3 is an explanatory diagram showing a main part of the optical transceiver module.

FIG. 4 is a sectional view showing a conventional optical transceiver module.

[Explanation of symbols]

 5 Demultiplexing filter 6 LD (laser diode) 9 PD (photodiode) 13 lens 12 optical fiber 20 housing block 35 opening

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kimihiro Kikuchi 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd.

Claims (2)

[Claims] 1. A light emitting element for emitting transmission light of a first wavelength, a demultiplexing filter for transmitting transmission light emitted from the light emitting element, and an oblique cut of an optical fiber for transmitting the light transmitted through the demultiplexing filter. A lens that condenses the light at the end face, and a light receiving element that receives the reception light of the second wavelength emitted from the end face of the optical fiber and collimated by the lens, wherein the reception light is filtered by the demultiplexing filter. In the optical transmitting / receiving module, which is reflected and reaches the light receiving element through the opening having the diameter φ, the diameter φ of the opening is set to φ ≦ 0.3f (where f is the focal length of the lens). The center of the aperture is defined as d = f · sin θ (where θ is the emission angle of the received light from the optical fiber) with respect to a straight line that passes through the intersection of the central axis and the branching filter and is perpendicular to the aperture. ) Optical transceiver module, characterized in that eccentrically. 2. The optical transceiver module according to claim 1, wherein the diameter φ of the opening is set to 0.2f ≦ φ ≦ 0.3f.