JPH09197177A - Bidrectional optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a compact and inexpensive bidirectional optical module capable of easily adjusting optical axis by providing the module with an wavelength multiplex transmission function between plural optical fibers and a bidirectional transmission function including light receiving/emitting elements and capable of receiving/emitting light by the same wavelength. SOLUTION: Light of 1st wavelength λ1 projected from the end part of a 1st optical fiber 1 is made incident on a 2nd optical fiber 2 through a 1st collimeter lens 3, an wavelength selecting filter 6 and a 2nd collimeter lens 4 to be transmitted. On the other hand, light of 2nd wavelength λ2 projected from the end part of the fiber 1 is reflected by the filter 6 and a part of the reflected light is passed through a half mirror 7 and received by a light receiving element 10 through a 3rd collimeter lens 5. Light of the 2nd wavelength λ2 projected from a semiconductor laser 8 is reflected by the half mirror 7 and the filter 6 through an NA conversion lens 9 and the lens 3 and made incident on the fiber 1 to be transmitted through the lens 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional optical module used for bidirectional optical fiber communication.

[0002]

2. Description of the Related Art As a conventional bidirectional optical module of this type, one having a structure shown in FIG. 6 and a light emitting element and a light receiving element integrated with each other is generally known. This bidirectional optical module includes an optical fiber 20, condenser lenses 21 and 22,
The light receiving element 23, the light emitting element 24, and the wavelength selection filter 25 are included.

In the above structure, first, the light emitting element 24 oscillates and emits light of wavelength λ ₁ and makes it enter the optical fiber 20 through the condenser lens 22 and the wavelength selection filter 25 for transmission.
On the other hand, the light of wavelength λ ₂ transmitted from the optical fiber 20 passes through the wavelength selection filter 25, is condensed by the condenser lens 21, and is incident on the light receiving element 23.

With this configuration, a bidirectional optical module having the same wavelength can be constructed by replacing the wavelength selection filter 25 with a half mirror.

[0005]

However, the bidirectional optical module having the above-mentioned conventional structure has only the bidirectional transmission function of the same wavelength or the wavelength multiplexing transmission function. When the wavelength multiplexing transmission function and the bidirectional transmission function with the same wavelength with built-in light receiving / light emitting elements are provided, problems such as an increase in the number of parts and an increase in the size of the module and difficulty in adjusting the optical axis occur. Become.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems, to suppress the increase in the number of parts as much as possible, and to provide an inexpensive bidirectional optical module in which the optical axis can be easily adjusted. .

[0007]

In order to achieve the above object, a bidirectional optical module of the present invention comprises: (1) transmitting light of a first wavelength in one direction and transmitting light of a second wavelength in both directions. A first optical fiber for transmission, a spherical first lens for converting the light of the first wavelength and the second wavelength emitted from the end of the first optical fiber into parallel light, and the parallel first wavelength A second lens for condensing light, a second optical fiber for transmitting the light of the first wavelength condensed by the second lens by entering the end portion, the first lens and the second lens A wavelength selection filter that is arranged between them and is inclined with respect to the optical axis and that transmits the light of the first wavelength but reflects the light of the second wavelength, and a part of the light of the second wavelength that is reflected by this wavelength selection filter. And a half mirror arranged so as to reflect the light and make it enter the center of the optical axis of the first lens again. A third lens that collects the light of the second wavelength that has passed through, a light receiving element that receives the light that is collected by the third lens, and a first lens that is located on the opposite side of the half mirror. And a second light output from the light emitting element that outputs the light of the second wavelength.
A fourth lens that converts the beam divergence angle of light of a wavelength and is incident on the first lens is provided.

According to this structure, the light of the first wavelength λ ₁ and the second wavelength λ ₂ emitted from the end portion of the first optical fiber is converted into parallel light by the spherical first lens, of which, The light of the first wavelength λ ₁ passes through the wavelength selection filter, is condensed by the second lens, and enters and is transmitted to the second optical fiber. Part of the light of the second wavelength λ ₂ reflected by the wavelength selection filter passes through the half mirror, is condensed by the third lens, and is received by the light receiving element. On the other hand, the second output from the light emitting element
The light of wavelength λ ₂ is converted by the fourth lens into the beam divergence angle and the parallel light by the first lens, and a part of the light is reflected by the half mirror and the wavelength selection filter. The light is condensed and is incident on the first optical fiber and transmitted.

(2) Further, the first lens, the wavelength selection filter and the half mirror of the above (1) are molded in a pentaprism shape with a light transmitting material.

According to this structure, since the first lens, the wavelength selection filter and the half mirror are integrated in a pentaprism shape, the mutual positional relationship is fixed, the optical axis adjustment becomes easy, and the small-sized mounting is possible. It will be possible.

(3) Further, the first optical fiber which transmits the light of the first wavelength in one direction and the light of the second wavelength in both directions, and is emitted from the end portion of the first optical fiber. A first lens for converting the light of the first wavelength and the second wavelength into parallel light, a second lens for collecting the parallel light of the first wavelength, and a first wavelength for the light collected by the second lens Is disposed between the first lens and the second lens and the second optical fiber for transmitting the light of the above to the end portion and is transmitted, and one ridge portion of the rectangular parallelepiped is formed on two surfaces forming the ridge portion. The light-transmitting optical block cut off at the surfaces intersecting each other at an angle of 45 degrees and the second-lens-side surface of this optical block are arranged, and the light of the first wavelength incident from the opposite surface is transmitted. The second wavelength light is reflected by the wavelength selection filter and is arranged on the cut surface of the optical block. A total reflection mirror that reflects the reflected light of the second wavelength, and a second wavelength that is arranged on a surface of the optical block that is orthogonal to the surface on which the wavelength selection filter is arranged and that is not adjacent to the cut surface and that is reflected by the total reflection mirror. Half mirror that reflects a part of the light and transmits the other part, a third lens that collects the light of the second wavelength that is reflected by the half mirror, and the light that is collected by the third lens A light-receiving element for receiving light, a light-emitting element that is arranged on the half mirror arrangement surface side of the optical block and outputs light of the second wavelength, and a beam divergence angle of the light of the second wavelength output from this light-emitting element is converted. And a fifth lens that converts the light of the second wavelength that has passed through the fourth lens into parallel light and makes the parallel light incident on the half mirror.

According to this structure, the light of the first wavelength λ ₁ and the second wavelength λ ₂ emitted from the end of the first optical fiber is
Each is converted into parallel light by the first lens and is incident on the optical block. The first wavelength lambda ₁ of the light incident at an angle theta ₁ to the wavelength selective filter in progress on a refraction angle theta _1, after passing through the wavelength selective filter, a second optical fiber is converged by the second lens It is incident and transmitted.

The light of the second wavelength λ ₂ is reflected by the wavelength selection filter through substantially the same optical path and is incident on the total reflection mirror arranged on the cut surface of the optical block at an angle θ ₂ .
The light reflected by the total reflection mirror is reflected by the half mirror at an angle θ ₁
Is incident on the reflecting surface of the optical block, a portion of which is reflected at an angle of θ ₃ . Further, the light reflected by the reflecting surface is incident on the exit surface of the optical block at an angle θ ₁ , and the light emitted from the exit surface is condensed by the third lens and received by the light receiving element.

On the other hand, the second wavelength λ output from the light emitting element
The light of No. ₂ has its divergence angle of No. 5
Is converted into parallel light by the lens and enters the half mirror. The light passing through the half mirror travels in the optical block at a refraction angle θ ₁ , is reflected by the total reflection mirror and the wavelength selection filter, is emitted from the optical block, and is condensed by the first lens to be the first light. It is incident on the fiber and transmitted.

(4) Further, a polarization beam splitter is arranged in place of the half mirror in the structure of (1). Here, the directions of the linear polarization plane of the light emitting element and the polarization plane reflected by the polarization beam splitter are matched.

According to this structure, since the linearly polarized light from the light emitting element is reflected by the polarization beam splitter, all the collimated light is incident on the first optical fiber.

(5) Further, in the above configuration (4), a depolarizer is provided in the optical path between the first optical fiber and the polarization beam splitter.

According to this structure, light having an arbitrary polarization component is converted into unpolarized light, and stable light enters the light receiving element regardless of the polarization state of the incident light.

[0019]

Embodiments of the present invention will be described below in detail. (Embodiment 1) FIG. 1 shows a configuration of a bidirectional optical module according to Embodiment 1 of the present invention.
A _first optical fiber that transmits light of wavelength λ ₁ in one direction and a second wavelength of light of wavelength λ ₂ in both directions, 2 is a second optical fiber that transmits light of first wavelength λ ₁ , 3 Is the first optical fiber 1
Spherical first collimator lens for converting the light of the first wavelength λ ₁ and the light of the second wavelength λ ₂ emitted from the end of the
Is a second optical fiber 2 that collects collimated light of the first wavelength λ ₁
A second collimator lens for inputting to the end of the, a wavelength selection filter 6 disposed between the first collimator lens 3 and the second collimator lens 4 inclining with respect to the optical axis,
The light of the first wavelength λ ₁ is transmitted, but the light of the second wavelength λ ₂ is reflected.

Reference numeral 7 denotes the second light reflected by the wavelength selection filter 6.
It is a half mirror that reflects part of the light of wavelength λ ₂ and allows other light to pass through. Here, the first collimator lens 3,
The positional relationship between the wavelength selection filter 6 and the half mirror 7 is
The light of the second wavelength λ ₂ emitted from the first optical fiber 1 and converted into parallel light by the first collimator lens 3 is reflected by the wavelength selection filter 6 and the half mirror 7, and again the first collimator lens 3 It is arranged so as to enter the center of the optical axis.

Reference numeral 5 denotes the second wavelength λ that has passed through the half mirror 7.
_A third collimator lens for condensing the light of No. ₂ , 10 is a light receiving element for receiving the light condensed by the third collimator lens 5, and 8 is opposite to the half mirror 7 with respect to the first collimator lens 3. A semiconductor laser as a light emitting element which is disposed on the side and outputs light of the second wavelength λ ₂ , and 9 is a first collimator for converting the beam divergence angle of the light of the second wavelength λ ₂ output from the semiconductor laser 8. It is an NA conversion lens as a fourth lens which enters the lens 3.

Next, the operation of the first embodiment will be described. First, the light of the first wavelength λ ₁ and the second wavelength λ ₂ emitted from the end portion of the first optical fiber 1 is converted into parallel light by the first collimator lens 3, and the first wavelength λ 1
The light of ₁ passes through the wavelength selection filter 6, is condensed by the second collimator lens 4, and enters the second optical fiber 2,
Transmitted. On the other hand, the light of the second wavelength λ ₂ reflected by the wavelength selection filter 6 partially passes through the half mirror 7, is condensed by the third collimator lens 5, and then is received by the light receiving element 10. .

Next, the second laser beam output from the semiconductor laser 8
The NA conversion lens 9 adjusts the divergence angle of the beam of the wavelength λ ₂ , and the first collimator lens 3 converts the beam into parallel light. The parallel light that has passed through the first collimator lens 3 is partially reflected by the half mirror 7, is further reflected by the wavelength selection filter 6 and is condensed by the first collimator lens 3, and then the first optical fiber 1 Is incident on and transmitted.

In FIG. 1, the ends of the first optical fiber 1 and the second optical fiber 2 are formed at right angles to the optical axis, but if they are formed obliquely, the return loss will be reduced. Needless to say, it is preferable to do so. Although the light receiving element 10 is arranged on the light passage side of the half mirror 7, the semiconductor laser 8 may be arranged at this position.

According to the bidirectional optical module of the first embodiment configured as described above, the first collimator lens 3 of the collimate coupling system for coupling with the first optical fiber 1 and the semiconductor laser 8 is shared. To reduce parts. Moreover, since the output light from the semiconductor laser 8 is once condensed by the NA conversion lens 9 and then converted into parallel light, the semiconductor laser 8 and the first optical fiber 1 can be coupled with high efficiency.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention, which is the first embodiment of the first embodiment.
The collimator lens 3, the wavelength selection filter 6 and the half mirror 7 are molded in a pentaprism shape with a light transmitting material. The first collimator lens 3 has a refractive index n
It is _one of a sphere, polymeric medium 11 having a refractive index n ₂ is used as a light-transmissive mold material. Polymer medium 11
Is formed in a pentaprism shape, and the wavelength selection filter 6 and the half mirror 7 are arranged on the slopes 11a and 11b, respectively.

Thus, the first collimator lens 3
By integrally molding the wavelength selection filter 6 and the half mirror 7 with each other, it is possible to save time and labor for position adjustment, and to realize compact mounting. Further, since the wavelength selection filter 6 and the half mirror 7 are integrally arranged on the slope of the pentaprism, there is no influence on the tilt of the optical axis due to the rotational displacement of the pentaprism.

(Third Embodiment) FIG. 3 shows the configuration of a bidirectional optical module according to a third embodiment of the present invention. 3, members having the same names as those in FIG. 1 are designated by the same reference numerals, 12 is an optical block, 13 is a total reflection mirror, and 14 is a fifth collimator lens.

The optical block 12 has a shape in which one ridge portion of a rectangular parallelepiped is cut off by a surface that intersects two surfaces forming the ridge portion at an angle of 45 degrees. Then, the wavelength selection filter 6 is arranged on the surface of the optical block 12 on the second collimator lens 4 side, and the total reflection mirror 13 is arranged on the cut surface, which is orthogonal to the surface on which the wavelength selection filter 6 is arranged and cut. The half mirror 7 is arranged on the surface not adjacent to the surface.

Next, the operation of the third embodiment will be described. The light of the first wavelength λ ₁ and the light of the second wavelength λ ₂ emitted from the end of the first optical fiber 1 are converted into parallel light by the first collimator lens 3 and enter the optical block 12. The first wavelength lambda ₁ of the light incident at an angle theta ₁ to the wavelength selective filter 6 in progress on a refraction angle theta _1, after passing through the wavelength selective filter 6, first is condensed by a second collimator lens 4 2
Is incident on and transmitted to the optical fiber 2. Here, since the entrance surface and the exit surface of the optical block 12 are parallel to each other, the entrance angle and the exit angle are the same.

Next, the light of the second wavelength λ ₂ is reflected by the wavelength selection filter 6 through almost the same optical path, and the optical block 12
The light is incident on the total reflection mirror 13 arranged on the cut surface of at an angle of θ ₂ . The light reflected by the total reflection mirror 13 is the half mirror 7.
The incident at an angle theta _1, part of which enters at an angle theta ₃ to the reflecting surface 12a of the reflected optically blocked. In addition, the reflective surface 12
The light reflected by a is incident on the emission surface of the optical block at an angle θ ₁ , and the light emitted from the emission surface is condensed by the third collimator lens 5 and received by the light receiving element 10.

On the other hand, the light of the second wavelength λ ₂ output from the light emitting element 8 is converted by the NA conversion lens 9 into a beam divergence angle, and converted into parallel light by the fifth collimator lens 14, and then is converted into a half mirror 7. Incident. The light passing through the half mirror 7 travels inside the optical block 12 at a refraction angle θ ₁ , is reflected by the total reflection mirror 13 and the wavelength selection filter 6, and is emitted from the optical block 12. The emitted light is condensed by the first collimator lens 3 and is incident on and transmitted to the first optical fiber 1.

Optical block 12 according to the third embodiment
The relationship between the incident angle and the reflection angle θ _{1 to} θ ₃ is (Equation 1)
It is as follows.

[0034]

[Number 1] _{θ 2 = 45 ° -θ 1,} θ 3 = 90 ° -θ 1 Thus, bidirectional optical module according to the third embodiment, the first light emitted from the optical fiber 1 is an optical block
Even if the light is incident on the incident surface 12 at an arbitrary angle (however, it is within an angle that does not cause total reflection), the angle emitted from the optical block 12 is the same as the incident angle.

That is, the optical axis directions of the first optical fiber 1 and the second optical fiber 2, the semiconductor laser 8 and the light receiving element 10.
It is shown that the relative angle with respect to the optical axis direction of is always 90 degrees. As a result, the angular deviation of the optical block 12 from the reference position during assembly affects only the optical axis deviation and does not affect the inclination of the optical axis.

(Embodiment 4) FIG. 4 shows the configuration of a bidirectional optical module according to Embodiment 4 of the present invention. The basic configuration is almost the same as that of the first embodiment, except that the half mirror 7 is replaced with a polarization beam splitter 15. Polarizing beam splitter
Reference numeral 15 transmits P-wave light and reflects S-wave light.

The operation of the fourth embodiment will be described below.
First, the first wavelength λ ₁ incident from the first optical fiber ₁
It is the same as in the first embodiment that the light of (1) is incident on the second optical fiber 2 and transmitted.

Next, the light emitted from the first optical fiber 1 having an arbitrary polarization component of the second wavelength λ ₂ passes through the first collimator lens 3 and the wavelength selection filter 6 and the polarization beam splitter 15 Incident on. Here, since the polarization beam splitter 15 passes the polarization component of the P wave and reflects the polarization component of the S wave, only the light of the polarization component of the P wave is incident on the light receiving element 10.

On the other hand, the second laser beam output from the semiconductor laser 8
The light of wavelength λ ₂ is converted into parallel light by the first collimator lens 3, is reflected by the polarization beam splitter 15, and is transmitted through the wavelength selection filter 6 and the first collimator lens 3 to the first optical fiber 1. Incident on and transmitted. Here, by using the polarization beam splitter 15, the semiconductor laser 8
All the light from will be incident on the first optical fiber 1.

(Fifth Embodiment) FIG. 5 shows the configuration of a bidirectional optical module according to a fifth embodiment of the present invention. Here, the difference from the fourth embodiment is that a depolarizer 16 is added to the end of the first optical fiber 1. The depolarizer 16 has, for example, optical fiber lengths of L and 2
Two L-length polarization-maintaining optical fibers are connected at an angle of 45 degrees.

Therefore, the light having an arbitrary polarization component of the second wavelength λ ₂ emitted from the first optical fiber 1 is converted into unpolarized light by the depolarizer 16 and collimated by the first collimator lens 3. After being converted into light, it is reflected by the wavelength selection filter 6, passes through only half by the polarization beam splitter 15, and enters the light receiving element 10.

As described above, by providing a means for converting unpolarized light into a part of the optical path, even if polarization fluctuation occurs, half of the light always enters the light receiving element 10 stably.

In the fifth embodiment, the depolarizer 16 has been described as an optical fiber type, but other depolarizers can be used as long as they convert circularly polarized light or unpolarized light into light of arbitrary polarization. You may use the thing of. Also, the installation position can be appropriately set in the optical path between the first optical fiber 1 and the polarization beam splitter 15.

[0044]

As described above, according to the first aspect of the present invention, since a part of the lens of the collimating coupling system is shared, the number of parts can be reduced and the light emitting element can be removed. Since the collimated coupling is performed after the emitted light is once condensed by the NA conversion lens, the light emitting element and the optical fiber can be coupled with high efficiency.

Further, according to the invention of claim 2, the lens of the collimating coupling system portion of the light emitting element and the optical fiber, the wavelength selection filter and the half mirror are integrally molded, so that the optical axis adjustment is easy. In addition, the module can be downsized.

Further, according to the invention of claim 3, by adopting a configuration in which a wavelength selection filter, a half mirror, and a total reflection mirror are respectively arranged in an optical block in which one edge portion of a rectangular parallelepiped is cut at 45 degrees, Since the optical axis relative angle between the light emitting element and the light receiving element and the two optical fibers can be set to 90 degrees, the housing can be easily designed. Further, the rotation deviation of the optical block from the reference position does not affect the inclination of the optical axis, and since the optical path is changed by one optical block, adjustment is easy, the number of parts is small, and the cost is low. be able to.

According to the fourth aspect of the present invention, the half mirror is replaced with a polarization beam splitter, and the polarization direction of the light emitting element and the polarization plane reflected by the polarization beam splitter are aligned, whereby the light emitting element and the optical fiber are combined. The binding can be improved.

Further, according to the invention of claim 5, in the optical path between the incident side optical fiber and the polarization beam splitter,
By disposing the depolarizer, light having an arbitrary polarization component can be made incident, and even if polarization fluctuation occurs, half of the incident light can be made to stably enter the light receiving element.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a bidirectional optical module according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an optical path dividing portion according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a bidirectional optical module according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a bidirectional optical module according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a bidirectional optical module according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a bidirectional optical module in a conventional example.

[Explanation of symbols]

1 ... 1st optical fiber, 2 ... 2nd optical fiber, 3
... 1st collimator lens, 4 ... 2nd collimator lens, 5 ... 3rd collimator lens, 6 ... Wavelength selection filter, 7 ... Half mirror, 8 ... Semiconductor laser,
9 ... NA conversion lens, 10 ... Light receiving element, 11 Polymer medium, 12 ... Optical block, 13 ... Total reflection mirror, 14
… Fifth collimator lens, 15… Polarizing beam splitter, 16… Depolarizer.

Claims (5)

[Claims] 1. A first optical fiber for transmitting light of a first wavelength in one direction and bidirectionally transmitting light of a second wavelength, and a first optical fiber emitted from an end of the first optical fiber. Wavelength and second
A spherical first lens that converts light of a wavelength into parallel light, a second lens that collects parallel light of a first wavelength, and an end of the light of the first wavelength that is collected by the second lens Is disposed between the first lens and the second lens to be incident on and transmitted to the first lens and the second lens so as to be inclined with respect to the optical axis, and the light of the first wavelength is transmitted, but the light of the second wavelength is transmitted. A reflecting wavelength selection filter, a half mirror arranged to reflect a part of the light of the second wavelength reflected by the wavelength selection filter and make the light incident again on the optical axis center of the first lens, and the half mirror. A third lens that collects the light of the second wavelength that has passed through the mirror;
A light receiving element for receiving the light condensed by the third lens,
A light emitting element, which is arranged on the opposite side of the half mirror with respect to the first lens and outputs the light of the second wavelength, and a beam divergence angle of the light of the second wavelength output from the light emitting element A fourth lens that enters the first lens, and transmits the light of the second wavelength that is output from the light emitting element and enters the first lens through the half mirror, the wavelength selection filter, and the first lens. A bidirectional optical module, characterized in that it is incident on the first optical fiber for transmission. 2. The bidirectional optical module according to claim 1, wherein the first lens, the wavelength selection filter and the half mirror are molded in a pentaprism shape with a light transmissive material. 3. A first optical fiber for transmitting light of a first wavelength in one direction and bidirectionally transmitting light of a second wavelength, and a first optical fiber emitted from an end of the first optical fiber. Wavelength and second
A first lens that converts light of a wavelength into parallel light, a second lens that collects parallel light of a first wavelength, and light of the first wavelength that is collected by the second lens is incident on the end portion. Second transmission
Which is arranged between the optical fiber and the first lens and the second lens, and cuts one ridge portion of a rectangular parallelepiped at a surface that intersects two surfaces forming the ridge portion at an angle of 45 degrees. A transparent optic block and the second of the optic block.
A wavelength selection filter which is disposed on the lens side surface of the optical block and transmits the first wavelength light incident from the opposite surface thereof but reflects the second wavelength light, and the wavelength selection filter is disposed on the ablation surface of the optical block. A total reflection mirror that reflects the light of the second wavelength reflected by the wavelength selection filter; and a total reflection mirror that is arranged on a surface of the optical block that is orthogonal to the surface on which the wavelength selection filter is arranged and that is not adjacent to the cut surface. A half mirror that reflects a part of the light of the second wavelength reflected by the mirror and transmits another part of the light, a third lens that collects the light of the second wavelength reflected by the half mirror, and a third lens The light receiving element that receives the light condensed by the lens No. 3, the light emitting element that is disposed on the side of the half mirror arrangement surface of the optical block and that outputs the light of the second wavelength, and the light emitting element that outputs the light of the second wavelength. Wide beam of two wavelength light Ri includes a fourth lens that converts an angular, and a fifth lens that enters the half mirror converts the light of the second wavelength passing through the fourth lens into a parallel light,
The light of the second wavelength output from the light emitting element and incident on the half mirror is subjected to the total reflection mirror, the wavelength selection filter,
A bidirectional optical module, characterized by being incident on the first optical fiber via a first lens for transmission. 4. A first optical fiber for transmitting light of a first wavelength in one direction and bidirectionally transmitting light of a second wavelength, and a first optical fiber emitted from an end of the first optical fiber. Wavelength and second
A spherical first lens that converts light of a wavelength into parallel light, a second lens that collects parallel light of a first wavelength, and an end of the light of the first wavelength that is collected by the second lens Is disposed between the first lens and the second lens to be incident on and transmitted to the first lens and the second lens so as to be inclined with respect to the optical axis, and the light of the first wavelength is transmitted, but the light of the second wavelength is transmitted. A reflecting wavelength selection filter, and a polarized light arranged to reflect a part of the light of the second wavelength reflected by this wavelength selection filter based on the polarization direction and to re-enter the center of the optical axis of the first lens. The beam splitter and the second beam that passed through this polarization beam splitter
A third lens that collects light of a wavelength, a light receiving element that receives the light collected by the third lens, and a polarization beam splitter that is disposed on the opposite side of the first lens, The light emitting element includes: a light emitting element that outputs light of a second wavelength; and a fourth lens that converts the beam divergence angle of the light of the second wavelength output from the light emitting element and enters the first lens. The light of the second wavelength that has been output from and has entered the first lens is incident on the first optical fiber via the polarization beam splitter, the wavelength selection filter, and the first lens, and is transmitted. Bidirectional optical module. 5. The bidirectional optical module according to claim 4, wherein a depolarizer is arranged in the optical path between the first optical fiber and the polarization beam splitter.