WO2005054922A1 - Wavelength division/multiplex optical module - Google Patents

Abstract

A wavelength division/multiplex optical module (100) includes: a first and a second optical fiber (103, 104); and a wavelength division/multiplex filter (105) sandwiched between a first end surface (1031) and a second end surface (1041) of the first and the second optical fiber (103, 104). The first end surface (1031) of the first optical fiber (103) is formed so as to have an angle in a range from 67.5 to 72.5 degrees with respect to the optical axis of the first optical fiber (103) while the second end surface (1041) of the second optical fiber (104) is arranged to be parallel to the first end surface (1031).

Description

 Specification

 Wavelength division multiplexing optical module

 Technical field

 The present invention relates to a wavelength division multiplexing optical module that divides or multiplexes an optical signal for transmission and reception.

 Background art

 [0002] With the spread of the Internet in recent years, optical communication services using optical fibers with a large amount of data transmission have attracted attention in subscriber systems. In a subscriber-based optical communication service, a single-core wavelength division multiplexing system that connects a single optical fiber to an optical terminator at each subscriber's home and transmits and receives downstream and upstream optical signals having different wavelengths is often used. RU

 [0003] In a subscriber-based optical communication service, an optical termination device installed in each subscriber's home is required to be reduced in size and cost. For this reason, it is essential to reduce the size and cost of the optical module used in the optical termination device.

 A conventional wavelength division multiplexing optical module is described in Patent Document 1. The wavelength division multiplexing optical module described in Patent Document 1 is used for an optical termination device of a single-core wavelength division multiplexing system. This conventional wavelength division multiplexing optical module is formed so that the angle of the end face of the first ferrule holding the optical fiber is about 60 degrees with respect to the optical axis of the optical fiber, and the end face of the first ferrule and the end face An optical filter for wavelength division multiplexing is sandwiched and fixed between the end face of the second ferrule and the end face of the second ferrule.

 [0005] In this conventional wavelength division multiplexing optical module, light of a specific wavelength among light propagating through an optical fiber is selectively reflected by an optical filter and incident on a light receiving element. On the other hand, of the light that has propagated through the optical fiber, the light outside the reflection wavelength range propagates through the optical filter and propagates in the optical fiber held by the opposing ferrule. As a result, the incident light is separated into optical signals of different wavelengths.

 Patent Document 1: JP 2003-215404 A

Disclosure of the invention Problems the invention is trying to solve

 [0006] However, in the conventional wavelength division multiplexing optical module, a terrestrial analog television signal or a cable television signal is combined with a data system downstream optical signal and a data system upstream signal to convert the terrestrial analog television signal or the cable television signal into a video system having a different wavelength from the data system optical signal. When applied to a three-wavelength division multiplexed video distribution system that distributes optical signals, the lower end of the wavelength of the video optical signal is close to 1550 nm, while the upper end of the wavelength of the downstream optical signal is 1500 nm. Therefore, there is a problem that it is difficult to separate an optical signal in the above-described conventional technology in which the light incident angle on the optical filter is large.

 [0007] In the conventional wavelength division multiplexing optical module, in order to ensure the degree of isolation of optical signals between adjacent wavelengths, that is, the amount of isolation, for example, when two optical filters are overlapped, the end face of a ferrule is required. Since the distance between them increases, there is a problem that the loss of light in the transmission band of the optical filter suddenly increases.

 [0008] In the conventional wavelength division multiplexing optical module, if the angle of the end face of the ferrule is made extremely small in order to secure the isolation amount, the space of light emitted from the optical fiber and selectively reflected by the optical filter is reduced. As a result, there is a problem that the light coupling efficiency with respect to the light receiving element and the high-frequency characteristics of the light receiving element decrease.

 An object of the present invention is to provide a small-sized, low-cost, high-isolation amount for an optical signal between adjacent wavelengths, and improved optical coupling efficiency to a light-receiving element and high-frequency characteristics of the light-receiving element. An object of the present invention is to provide a wavelength division multiplexing optical module.

 Means for solving the problem

[0010] A first aspect of the present invention includes an optical waveguide and a wavelength division multiplexing filter disposed on an end face of the optical waveguide, wherein the end face of the optical waveguide is arranged with respect to an optical axis of the optical waveguide.

Take a configuration that has an angle within the range of 67.5 degrees to 72.5 degrees

[0011] A second aspect of the present invention is directed to a wavelength division filter sandwiched between first and second optical waveguides and first and second end faces of the first and second optical waveguides. A multiplex filter, wherein the first optical waveguide has an angle in a range from 67.5 degrees to 72.5 degrees with respect to an optical axis of the first optical waveguide. And the second optical waveguide is formed as A configuration is adopted in which the second end face is arranged so as to be parallel to the first end face. The invention's effect

 According to the present invention, the optical coupling efficiency to the light receiving element, the high-frequency characteristics of the light receiving element, or the light coupling efficiency to the light emitting element are improved as the isolation amount of the optical signal between adjacent wavelengths increases. A small and inexpensive wavelength division multiplexing optical module can be realized.

 Brief Description of Drawings

FIG. 1 is a sectional view showing a wavelength division multiplexing optical module according to Embodiment 1 of the present invention.

 FIG. 2 illustrates a relationship between an angle of a first end face of the first optical fiber with respect to an optical axis of a first optical fiber according to Embodiment 1 of the present invention and an irradiation diameter at a light receiving section of a light receiving element. Figure to do

 FIG. 3 is a diagram for explaining transmission and reflection isolation amounts of the wavelength division multiplexing optical module according to Embodiment 1 of the present invention.

 FIG. 4 is a sectional view showing a wavelength division multiplexing optical module according to Embodiment 2 of the present invention.

 FIG. 5 is a perspective view showing a wavelength division multiplexing optical module according to Embodiment 3 of the present invention.

 FIG. 6 is a perspective view showing a wavelength division multiplexing optical module according to Embodiment 4 of the present invention.

 (Embodiment 1)

 Embodiment 1 of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a wavelength division multiplexing optical module according to Embodiment 1 of the present invention.

 As shown in FIG. 1, the wavelength division multiplexing optical module 100 according to Embodiment 1 of the present invention includes a first ferrule 101, a second ferrule 102, a first optical fiber (optical waveguide) 103, A second optical fiber 104, a wavelength division multiplexing filter 105, a light receiving element substrate 106, a light receiving element 107, and a light transmitting optical adhesive 108 are provided.

A first holding inner peripheral surface 1011 and a first inner peripheral surface 1012 are formed in the first ferrule 101. The second ferrule 102 has a second holding inner peripheral surface 1021 and a second inner peripheral surface 1022. The first holding inner peripheral surface 1011 and the second holding inner peripheral surface 1021 are used for inserting the first optical fiber 103 and the second optical fiber 104. A hole and a second holding hole are defined. The first optical fiber 103 and the second optical fiber 104 are inserted into the first holding hole and the second holding hole, and the first holding inner peripheral surface of the first ferrule 101 and the second ferrule 102. 1011 and the second holding inner peripheral surface 1021.

 [0017] The second inner peripheral surface 1022 is arranged to face the first inner peripheral surface 1012. The first inner peripheral surface 1012 and the second inner peripheral surface 1022 define a main space communicating with the first holding hole and the second holding hole.

 A light-receiving element substrate 106 is provided below the first ferrule 101 and the second ferrule 102. The light receiving element 107 is fixed on the central part of the light receiving element substrate 106 so as to be located in the main space of the first ferrule 101 and the second ferrule 102. An optical adhesive 108 is provided in the main space between the light receiving element substrate 106 and the light receiving element 107 and the first ferrule 101 and the second ferrule 102.

 The first optical fiber 103 is formed such that the first end face 1031 has an angle φ with respect to the optical axis of the first optical fiber 103 in a range from 67.5 degrees to 72.5 degrees. ing. The second optical fiber 104 is arranged such that the second end face 1041 is parallel to the first end face 1031 of the first optical fiber 103.

 [0020] The first ferrule 101 is formed such that the first end face 1013 has an angle φ within a range from 67.5 degrees to 72.5 degrees with respect to the optical axis of the first optical fiber 103. ing. The second ferrule 102 is arranged such that the second end face 1023 is parallel to the first end face 1013 of the first ferrule 101.

 The wavelength division multiplexing filter 105 is sandwiched between a first end face 1031 of the first optical fiber 103 and a second end face 1041 of the second optical fiber 104, and It is sandwiched between the first end face 1013 and the second end face 1023 of the second ferrule 102. The first end face 1013 of the first ferrule 101 and the second end face 1023 of the second ferrule 102 and the wavelength division multiplexing filter 105 are bonded by an optical adhesive. Therefore, the wavelength division multiplexing filter 105 is held between the first end face 1013 of the first ferrule 101 and the second end face 1023 of the second ferrule 102.

The wavelength division multiplexing filter 105 includes, for example, an optical signal having a wavelength of 1260 nm to 1360 nm and It consists of a thin film filter with a thickness of 20 μm to 40 μm consisting of a dielectric multilayer film that transmits optical signals with wavelengths of 1480 nm to 1500 nm and reflects optical signals with wavelengths of 1550 nm to 1560 nm.

 The light-receiving element 107 is a back-illuminated light-receiving element manufactured using an InP substrate. For example, the light-receiving element 107 has a thickness of 150 μm—300 μm and a light-receiving diameter of 35 μm— It is composed of 50 μm.

 A space between the light-receiving element substrate 106 and the first ferrule 101 and the second ferrule 102 is filled with a light-transmitting optical adhesive 108, and the light-receiving element substrate 106, the first ferrule 101, The second ferrule 102 is integrated with the optical adhesive 108.

 Next, the operation of the wavelength division multiplexing optical module 100 according to Embodiment 1 of the present invention will be described with reference to the drawings.

 An image-based optical signal having a wavelength of 1550 nm to 1560 nm that propagates through the first optical fiber 103 is reflected by the wavelength division multiplexing filter 105, propagates through the optically transparent optical adhesive 108, and Incident on.

 On the other hand, a downstream optical signal having a wavelength of 1480 nm to 1500 nm transmitted through the first optical fiber 103 transmits through the wavelength division multiplexing filter 105 and propagates through the opposing second optical fiber 104. go. In addition, a data-system upstream optical signal having a wavelength of 1260 nm-136 Onm propagating in the second optical fiber 104 passes through the wavelength division multiplexing filter 105 and propagates through the opposing first optical fiber 103. .

 The optical signal reflected by the wavelength division multiplexing filter 105 propagates as a Gaussian beam, and is an interface between the clad of the first optical fiber 103 and the optically transparent optical adhesive 108 and the optical adhesive 108 and the light receiving element 107. The light reaches the light receiving portion of the light receiving element 107 while being refracted at the interface. The irradiation pattern of the optical signal to the light receiving portion of the light receiving element 107 has an elliptical shape whose major axis is in the optical axis direction of the first and second optical fibers 103 and 104.

Here, FIG. 2 shows the relationship between the angle φ of the first end face 1031 of the first optical fiber 103 with respect to the optical axis of the first optical fiber 103 and the irradiation diameter at the light receiving section of the light receiving element 107. Has been. Figure 2 shows that the core diameter of the first optical fiber 103 is 9 m, the refractive index of the cladding of the first optical fiber 103 is 1.46, the cladding diameter of the first optical fiber 103 is 125 m, Permeable The refractive index of the optical adhesive 108 is 1.55, the thickness of the optical adhesive 108 is 50 m, the refractive index of the light receiving element 107 is 3.2, and the force of the first and second optical fibers 103 and 104 is also An example is shown in the case where the thickness up to the light receiving portion of the light receiving element 107 is calculated as 150 μm (solid line) or 300 μm (dashed line).

 In FIG. 2, the diameter in the short axis direction of the irradiation pattern in the light receiving portion of the light receiving element 107 is indicated by a circle, and the diameter in the long axis direction of the irradiation pattern is indicated by a triangle.

 As shown in FIG. 2, the light receiving diameter of the light receiving portion of the light receiving element 107 is 50 m, and the thickness from the first and second optical fibers 103 and 104 to the light receiving portion is 300 μm. In the case of the light receiving element 107, if the angle φ of the first end face 1031 of the first optical fiber 103 with respect to the optical axis of the first optical fiber 103 is 72.5 degrees or less, the irradiation diameter is within the light receiving diameter. Fits in. Similarly, in the case of the light receiving element 107 having a light receiving diameter of 35 m and a thickness of 150 μm from the first and second optical fibers 103 and 104 to the light receiving section, the first optical fiber 103 If the angle φ of the first end face of the first optical fiber 103 with respect to the optical axis is 67.5 degrees or more, the irradiation diameter falls within the light receiving diameter, and the light coupling efficiency to the light receiving element 107 and the light receiving element 107 High frequency characteristics are secured.

 On the other hand, the isolation characteristics of the wavelength division multiplexing filter 105 for optical signals between different wavelengths are improved because the smaller the light incidence angle of the wavelength division multiplexing filter 105 is, the more the polarization dependence is reduced. The tolerance of the error with respect to each film thickness of the dielectric multilayer film is reduced, so that the production of the wavelength division multiplexing filter 105 becomes easy. Therefore, the smaller the light incident angle on the wavelength division multiplexing filter 105, that is, the larger the angle φ between the first end face 1031 of the first optical fiber 103 and the second end face 1041 of the second optical fiber 104, the larger the angle φ. desirable.

Therefore, the optical coupling efficiency and high-frequency characteristics to the light receiving element 107 and the isolation characteristics of the wavelength division multiplexing filter 105 depend on the first optical fiber 103 with respect to the optical axis of the first optical fiber 103. There is a trade-off relationship with the angle φ of the end face 1031 of. As shown in FIGS. 2 and 3, when the angle φ is a value within the range of 67.5 degrees to 72.5 degrees, the light coupling efficiency to the light receiving element 107, the high-frequency characteristics of the light receiving element 107, and the wavelength This is preferable from the viewpoint of the isolation characteristics of the division multiplex filter 105. In this case, the light having a wavelength of 1550 nm with respect to the light having a wavelength of 1500 nm in the light transmitted through the wavelength division As shown by the curve A in FIG. 3, the transmission isolation amount can secure 30 dB or more. As shown by curve B in FIG. 3, 15 dB or more can be secured.

 As shown in FIGS. 2 and 3, when the angle φ is in the range from 69 degrees to 71 degrees, the optical coupling efficiency to the light receiving element 107, the high-frequency characteristics of the light receiving element 107, and the wavelength division multiplexing The balance with the isolation characteristics of Filter 105 is the best. Therefore, the optimal range of the angle φ is a range from 69 degrees to 71 degrees.

 As described above, according to the first embodiment of the present invention, the isolation amount for the optical signal between adjacent wavelengths is increased, and the optical coupling efficiency to the light receiving element and the high frequency characteristics of the light receiving element are improved. A small and inexpensive wavelength division multiplexing optical module is realized.

 (Embodiment 2)

 Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a sectional view showing a wavelength division multiplexing optical module according to Embodiment 2 of the present invention. In the second embodiment of the present invention, the same components as those in the first embodiment of the present invention are denoted by the same reference numerals, and description thereof will be omitted.

 As shown in FIG. 4, in the wavelength division multiplexing optical module 400 according to Embodiment 2 of the present invention, the first micro lens 401 and the second micro lens 402 in Embodiment 1 of the present invention are different from each other. I'm going to do it.

 That is, the wavelength division multiplexing optical module 400 according to Embodiment 2 of the present invention includes a first ferrule 101, a second ferrule 102, a first optical fiber (optical waveguide) 103, and a second optical fiber. 104, a wavelength division multiplexing filter 105, a light receiving element substrate 106, a light receiving element 107, a light transmitting optical adhesive 108, a first micro lens 401 and a second micro lens 402 are provided.

 The first micro lens 401 is formed at a joint between the first end face 1031 and the second end face 1041. The second micro lens 402 is formed on the light receiving element 107.

[0040] The first microlens 401 is made of, for example, a high-viscosity ultraviolet-curable optical adhesive in the first inner part. It is formed by dropping onto the joint between the peripheral surface 1012 and the second inner peripheral surface 1022, irradiating ultraviolet rays in a hemispherical state by surface tension, and curing.

Similarly, the second microlens 402 drops, for example, a high-viscosity ultraviolet-curable optical adhesive onto the light-receiving element 107 and irradiates ultraviolet rays in a hemispherical state due to surface tension.

, Formed by curing.

[0042] The material forming the first microlenses 401 and the second microlenses 402 has a refractive index higher than that of the transparent optical adhesive 108 in order to produce the effect of a spherical lens. Used.

 Next, the operation of the second embodiment of the present invention, which is different from the first embodiment of the present invention, will be described in detail with reference to FIG.

 The optical signal reflected by the wavelength division multiplexing filter 105 is collimated by the first minute lens 401, propagates through the light-transmitting optical adhesive 108, and further propagates through the second minute lens 401. The light 402 receives the light condensing action and is incident on the light receiving element 107. The distance between the first inner peripheral surface 1012 and the light receiving element 107 is reduced by the collimating action and the condensing action of the first minute lens 401 and the second minute lens 402, and the radius of the first and second ferrules 101 and 102 is increased. Even if it is larger, the irradiation diameter of the light signal reflected by the wavelength division multiplexing filter 105 at the light receiving element 107 becomes smaller than the light receiving diameter of the light receiving element 107, and the light coupling efficiency to the light receiving element 107 and the high-frequency characteristics of the light receiving element 107 are reduced. Secured.

 As described above, in the second embodiment of the present invention, by adding the first micro lens 401 and the second micro lens 402 in the first embodiment of the present invention, light between adjacent wavelengths can be obtained. A small, low-cost, wavelength-division multiplexed optical module that has a high signal isolation, improves the optical coupling efficiency to the light-receiving element 107, and improves the high-frequency characteristics of the light-receiving element 107! .

 Note that one of the first micro lens 401 and the second micro lens 402 may be deleted.

 (Embodiment 3)

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a perspective view showing a wavelength division multiplexing optical module according to Embodiment 3 of the present invention. In the third embodiment of the present invention, the same components as those in the first embodiment of the present invention have the same reference numerals. And description thereof is omitted.

 As shown in FIG. 5, a wavelength division multiplexing optical module 500 according to Embodiment 3 of the present invention includes a substrate 501, a first optical fiber (optical waveguide) 103, a second optical fiber 104, A multi-filter 105, a light receiving element 107 and a third optical fiber 502 are provided.

 [0049] The substrate 501 is formed of silicon. A V-groove 5011 is formed in the substrate 501. The first optical fiber 103, the second optical fiber 104, and the third optical fiber 502 are provided in a V-groove 5011 of the substrate 501.

 Further, a groove 5012 is formed in the substrate 501. The wavelength division multiplexing filter 105 is provided in the groove 5012 of the substrate 501. Light receiving element 107 is fixed on substrate 501. Third optical fiber 502 is arranged between wavelength division multiplexing filter 105 and light receiving element 107.

 Next, the operation of the third embodiment of the present invention, which is different from the first embodiment of the present invention, will be described in detail with reference to FIG.

The third embodiment of the present invention is different from the third embodiment of the present invention except that the optical signal reflected by the wavelength division multiplexing filter 105 is incident on the light receiving element 107 via the third optical fiber 502. It has the same effect as state 1. Embodiment 3 of the present invention has the same effect as Embodiment 1 of the present invention.

(Embodiment 4)

 Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a perspective view showing a wavelength division multiplexing optical module according to Embodiment 4 of the present invention. In the fourth embodiment of the present invention, the same components as those in the third embodiment of the present invention are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 6, a wavelength division multiplexing optical module 600 according to Embodiment 4 of the present invention

In Embodiment 3 of the present invention, instead of the first optical fiber 103, the second optical fiber 104, and the third optical fiber 502, a first optical waveguide 601, a second optical waveguide 602, and a second

Three optical waveguides 603 are provided.

An optical waveguide layer 604 is formed on the substrate 501. The optical waveguide layer 604 has a groove

6041. In the groove 6041 of the optical waveguide layer 604, a wavelength division multiplexing filter 105 is provided. Are arranged.

 [0056] The operation of the wavelength division multiplexing optical module 600 according to Embodiment 4 of the present invention is the same as that of Embodiment 3 of the present invention. Embodiment 4 of the present invention has the same effect as Embodiment 3 of the present invention.

 In Embodiments 14 of the present invention, the configuration in which the light receiving element 107 is used has been described. However, a light emitting element is used instead of the light receiving element 107, and light from the light emitting element is used. May be reflected by the wavelength division multiplexing filter 105 and coupled to the first optical fiber 103 to form a multiplexed wavelength division multiplexing optical module.

 [0058] A first aspect of the present invention includes an optical waveguide and a wavelength division multiplexing filter arranged on an end face of the optical waveguide, wherein the optical waveguide has an end face with respect to an optical axis of the optical waveguide. Take a configuration that has an angle within the range of 67.5 degrees to 72.5 degrees

[0059] According to this configuration, the isolation amount of the optical signal between adjacent wavelengths is high, and the efficiency of optical coupling to the light receiving element and the high frequency characteristics of the light receiving element can be improved. A wavelength division multiplexing optical module has been realized.

 [0060] A second aspect of the present invention is directed to a wavelength division filter sandwiched between first and second optical waveguides, and first and second end faces of the first and second optical waveguides. A multiplex filter, wherein the first optical waveguide has an angle in a range from 67.5 degrees to 72.5 degrees with respect to an optical axis of the first optical waveguide. And the second optical waveguide is arranged such that the second end face is parallel to the first end face.

 [0061] According to this configuration, the isolation amount for the optical signal between adjacent wavelengths is high, and the optical coupling efficiency to the light receiving element and the high frequency characteristics of the light receiving element can be improved. A wavelength division multiplexing optical module has been realized.

 [0062] In a third aspect of the present invention, in the second aspect of the present invention, the first and second optical waveguides are composed of first and second optical fibers, and the first and second optical waveguides are provided. A first and a second ferrule for holding the optical fiber, wherein the wavelength division multiplexing filter is sandwiched between a first end face and a second end face of the first and second ferrules. Take.

According to this configuration, in addition to the effect of the second aspect of the present invention, the first and second fuels The rule allows the wavelength division multiplexing filter to be reliably held.

 [0064] In a fourth aspect of the present invention, based on the third aspect of the present invention, the first and second ferrules define a main space through which a reflected light signal from the wavelength division multiplexing filter passes. A first inner peripheral surface and a second inner peripheral surface, and one of a light receiving element and a light emitting element disposed in the main space.

 [0065] According to this configuration, the isolation amount for the optical signal between adjacent wavelengths is increased, and the optical coupling efficiency to the light receiving element, the high frequency characteristics of the light receiving element, or the optical coupling efficiency to the light emitting element are improved. A compact and low-cost wavelength division multiplexing optical module that can be implemented is realized.

 [0066] In a fifth aspect of the present invention, in the fourth aspect of the present invention, a first microlens formed at a joint portion between the first and second ferrules, the light-receiving element or A configuration having at least one of a second microlens formed on the light emitting element is adopted.

 According to this configuration, in addition to the effect of the fourth aspect of the present invention, the light coupling efficiency to the light receiving element, the high frequency characteristics of the light receiving element, or the light coupling efficiency to the light emitting element can be further improved. Can be.

 [0068] This is based on Japanese Patent Application 2003-405978, which is filed by Honmei Itoda Parma, December 4, 2003. This content [well, I will include all here.

 Industrial applicability

The present invention is usefully applied to devices and systems that transmit or receive optical signals by dividing or multiplexing them.

Claims

The scope of the claims  [1] An optical waveguide, comprising: a wavelength division multiplexing filter disposed on an end face of the optical waveguide, wherein the end face of the optical waveguide is from 67.5 ° to 72.5 ° with respect to an optical axis of the optical waveguide. The wavelength division multiplexing optical module is formed to have an angle within the range described above.  [2] first and second optical waveguides, and a wavelength division multiplexing filter sandwiched between first and second end faces of the first and second optical waveguides, The first optical waveguide is formed such that the first end face has an angle in a range from 67.5 degrees to 72.5 degrees with respect to an optical axis of the first optical waveguide, and The wavelength division multiplexing optical module, wherein the optical waveguide is arranged such that the second end face is parallel to the first end face.  [3] The first and second optical waveguides are composed of first and second optical fibers, and have first and second ferrules for holding the first and second optical fibers, 3. The wavelength division multiplexing optical module according to claim 2, wherein the wavelength division multiplexing filter is sandwiched between a first end face and a second end face of the first and second ferrules.  [4] The first and second ferrules have a first inner peripheral surface and a second inner peripheral surface that define a main space through which a reflected light signal from the wavelength division multiplexing filter passes, 4. The wavelength division multiplexing optical module according to claim 3, further comprising one of a light receiving element and a light emitting element arranged in the main space.  [5] At least one of a first microlens formed at a junction of the first and second ferrules and a second microlens formed on the light receiving element or the light emitting element. 5. The wavelength division multiplexing optical module according to claim 4, comprising: