JP2004012801A - Filter module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter module satisfying the required insertion loss, of which the productivity is improved and the cost is reduced. <P>SOLUTION: The filter module 21 has a first lens 22 and second lens 23 which are the same lenses prefixed to be made nearly coaxial, a filter 24 arranged between the two lenses 22 and 23, optical fibers 25 and 26 arranged on the incident side of the first lens 22 and fixed to nearly parallel to the fiber axes, and an optical fiber 27 arranged on the exit side of the second lens 23. If the focal lengths of the lenses 22 and 23 are defined as f, the deviation value from the focal position of the first lens 22 of the filter 24 is set within ±25% of the focal lengths f. Such setting makes it possible to assemble the filter module having the insertion loss on the opposite side smaller than 0.2 dB without the θx and θy alignment of the optical fibers 25 to 27. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a filter module used for an optical communication system such as a dense wavelength division multiplexing (DWDM) transmission system.
[0002]
[Prior art]
In the above optical communication system, a multiplexing module for multiplexing (coupling) a plurality of optical signals having different wavelengths into one optical fiber and a wavelength division multiplexing signal transmitted through the optical fiber are demultiplexed (separated) for each wavelength. ) Is used. As a filter module configured as such a demultiplexing module, for example, an optical system as shown in FIG. 1 has been proposed by the present inventors. The filter module 11 includes a first lens 12 and a second lens 13 that are integrated beforehand such that their optical axes are substantially coaxial, a filter 14 disposed between the two lenses, and a first lens 12. It has two optical fibers 15 and 16 arranged on the incident side and one optical fiber 17 arranged on the exit side of the second lens 13. The two optical fibers 15 and 16 are fixed so that the fiber axes are substantially parallel. The optical fibers 15 and 16 are located at the same distance from the optical axis C on the opposite side. The optical fiber 17 is located at a position shifted from the optical axis C by the same distance on the same side as the optical fiber 16. Further, the same lens having a focal length f is used as the first lens 12 and the second lens 13, the distance between the lenses is set to 2f, and the filter 14 is arranged at the focal position of the first lens 12.
[0003]
When the filter module 11 causes the optical fiber 15 to emit light in the wavelength range that passes through the filter 14, the light is collimated by the first lens 12 and passes through the filter 14, and the transmitted light is passed through the second lens 12. The light is converged by 13 and enters the optical fiber 17. When the filter module 11 emits light in the wavelength range reflected by the filter 14 from the optical fiber 15, the light is collimated by the first lens 12 and reflected by the filter 14, and the reflected light is reflected by the first lens 12. And is incident on the optical fiber 16.
[0004]
The present inventors have proposed an optical system as shown in FIG. 2 equivalent to the optical system shown in FIG. 1 as the filter module. The filter module 21 includes a first lens 22 and a second lens 23 which are the same gradient index rod lens and are fixed in advance so that their optical axes are substantially coaxial. Further, the filter module 21 has a filter 24 disposed between the lenses 2 and 23, a two-core fiber chip 28 disposed on the incident side of the first lens 22, and disposed on the exit side of the second lens 23. And a single-core fiber chip 29. Each of the optical fibers 15 to 17 and 25 to 27 is a single mode optical fiber.
[0005]
[Problems to be solved by the invention]
Incidentally, the following alignment operations (a) to (d) are required for assembling the filter modules 11 and 21 shown in FIGS. 1 and 2. In the following description, a centering operation required for assembling the filter module 11 will be described. Note that the light propagating through the optical fiber is not completely confined in the core, and the skirt portion of the intensity distribution seeps into the cladding. In the case of a single mode optical fiber, the emitted light has a Gaussian beam having a Gaussian intensity distribution in a plane perpendicular to the fiber axis (a distribution in which the intensity is large at the center of the light beam and small at the periphery). It is. That is, the emitted light (Gaussian beam) from the optical fiber 15 is collimated by the first lens 12, but does not become parallel light between the two lenses 12 and 13, but has a beam waist in the middle. Further, the light converged by the second lens 13 does not converge on one point, and a beam waist is formed.
[0006]
(A) The light in the wavelength range reflected by the filter 14 is emitted from the optical fiber 15, the light reflected by the filter 14 is converged by the first lens 12, and the position of the beam waist of the light incident on the optical fiber 16 and the optical fiber Alignment work to match the end face of 17 In this alignment operation, the light in the wavelength range reflected by the filter 14 is emitted from the optical fiber 15, and while monitoring the reflected light emitted from the optical fiber 16 on the reflection port side, the amount of the reflected light is maximized. The optical fibers 15 and 16 are aligned in the X, Y, and Z directions so that the optical fibers 15 and 16 are aligned.
[0007]
Further, the light in the wavelength range that passes through the filter 14 is emitted from the optical fiber 15, and the light that has passed through the filter 14 is converged by the second lens 13 and the position of the beam waist of the light that enters the optical fiber 17 and the optical fiber 17. Alignment work to match the end face of In this alignment operation, light in a wavelength range that passes through the filter 14 is emitted from the optical fiber 15, and while monitoring the transmitted light emitted from the optical fiber 17, the light is adjusted so that the amount of the transmitted light is maximized. The fiber 17 is aligned in the X, Y, and Z directions.
[0008]
(B) Alignment work for matching the mode field diameter of each of the optical fibers 15 to 17 with the beam waist diameter. Here, the same lens is used as both lenses 12 and 13. Thereby, the position of the beam waist of the light emitted from the optical fiber 15 and the position of the beam waist of the light incident on the optical fiber 17 become symmetrical with respect to the optical axis, and the optical fibers 15 and The mode field diameter of 17 and the beam waist diameter respectively match. Further, the position of the beam waist of the light emitted from the optical fiber 15 and the position of the beam waist of the light incident on the optical fiber 16 are symmetrical with respect to the optical axis, and the respective optical fibers 15, The 16 mode field diameters and the beam waist diameters respectively match. Here, the “mode field diameter” is 1 / e of the peak value of the Gaussian intensity distribution. ² Refers to the diameter at which the strength becomes.
[0009]
(C) Alignment work for matching the principal ray of the beam with the fiber axis of each of the optical fibers 15 to 17. These alignment operations are performed by adjusting the inclination in the θx direction and the inclination in the θy direction with respect to the optical axis C for each of the optical fibers 15 to 17.
[0010]
(D) Alignment work to prevent beam jog on the way. This centering operation is performed by adjusting the inclination in the θx direction and the inclination in the θy direction with respect to the optical axis C for both lenses 12 and 13.
[0011]
In the filter modules 11 and 21, it takes time to perform all of the alignment operations (a) to (d) so that the required insertion loss is obtained, and it takes a long time to assemble the filter module. The productivity of the filter module that satisfies the required insertion loss is poor, and the cost increases.
[0012]
The present invention has been made in view of such conventional problems, and has as its object to provide a filter module that improves the productivity and reduces the cost of a filter module that satisfies the required insertion loss. Is to do.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is arranged between a first lens and a second lens, which are the same lens fixed in advance so that their optical axes are substantially coaxial, and between the two lenses. A filter, at least two optical fibers disposed on the incident side of the first lens, and fixed so that the fiber axes are substantially parallel, and at least one optical fiber disposed on the exit side of the second lens. In a filter module including an optical fiber, assuming that a focal length of the first lens and the second lens is f, a deviation amount of the filter from a focal position of the first lens is within ± 25% of the focal length f. The gist is to set to.
[0014]
According to this configuration, by setting the amount of deviation of the filter from the focal position of the first lens within ± 25% of the focal length f, the insertion loss on the reflection side can be suppressed to a maximum of about 0.2 dB. it can. Setting the assembly tolerance of the filter with respect to the first lens in this manner is to assemble a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the reflection side without aligning the optical fibers with θx and θy. This is a necessary condition. By satisfying such conditions, a filter module having an insertion loss smaller than a predetermined value can be assembled without aligning the optical fibers with θx and θy, thereby improving productivity and reducing manufacturing costs.
[0015]
Note that the “insertion loss on the reflection side” here means that light in a wavelength range reflected by a filter is emitted from one of at least two optical fibers disposed on the incident side of the first lens. The insertion loss when the reflected light collimated by the first lens and reflected by the filter is converged by the first lens and enters another one of the at least two optical fibers.
[0016]
According to a second aspect of the present invention, in the filter module according to the first aspect, the inclination of the optical fiber disposed on the incident side of the first lens in the θx direction and the inclination in the θy direction with respect to the optical axis of the first lens. Is set within 0.2 degrees.
[0017]
The “tilt in the θx direction” here refers to an angle around the X axis perpendicular to the optical axis. The term “inclination in the θy direction” refers to an angle around the Y axis perpendicular to the optical axis. According to this configuration, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the incident side of the first lens with respect to the optical axis of the first lens are each set within 0.2 degrees, The insertion loss on the reflection side can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the reflection side without aligning the optical fibers with θx and θy. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0018]
According to a third aspect of the present invention, in the filter module according to the first aspect, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side of the second lens with respect to the optical axis of the second lens. Is set within 0.2 degrees.
[0019]
According to this configuration, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side of the second lens with respect to the optical axis of the second lens are set within 0.2 degrees, respectively. The insertion loss on the transmission side can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the transmission side without aligning the optical fibers with θx and θy. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced. The “insertion loss on the transmission side” here means that when one of the optical fibers disposed on the incident side of the first lens emits light in the wavelength range that passes through the filter, It refers to the insertion loss when the collimated light that passes through the filter is converged by the second lens and enters the optical fiber disposed on the exit side of the second lens.
[0020]
According to a fourth aspect of the present invention, in the filter module according to the first aspect, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the incident side of the first lens with respect to the optical axis of the first lens. Are set within 0.2 degrees, and the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side of the second lens with respect to the optical axis of the second lens are respectively set to 0. The point is to set within two degrees.
[0021]
According to this configuration, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the incident side of the first lens and the optical fiber disposed on the exit side of the second lens are set within 0.2 degrees, respectively. By doing so, the insertion loss can be suppressed to a predetermined value or less. Such setting is necessary for assembling a filter module that satisfies both the required insertion loss on the reflection side and the transmission side (for example, 0.2 dB or less) without aligning the optical fibers with θx and θy. Condition. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0022]
According to a fifth aspect of the present invention, in the filter module according to the first aspect, a distance (WD) between the first lens and the second lens is set within a range of 2f ± 2f / 4. And
[0023]
According to this configuration, by setting the distance (WD) between the first lens and the second lens within the range of 2f ± 2f / 4, the insertion loss on the transmission side due to a shift in the distance between the lenses can be reduced. It can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the transmission side without aligning the optical fibers with θx and θy. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0024]
According to a sixth aspect of the present invention, in the filter module according to the first aspect, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the incident side of the first lens with respect to the optical axis of the first lens. Are set within 0.2 degrees, and the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side of the second lens with respect to the optical axis of the second lens are respectively set to 0. The gist is set to be within 2 degrees, and furthermore, the inter-lens distance (WD) between the first lens and the second lens is set within a range of 2f ± 2f / 4.
[0025]
According to this configuration, the insertion loss on the reflection side and the transmission side can be suppressed to a predetermined value or less, and the insertion loss on the transmission side due to a shift in the distance between the lenses can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the reflection side and the transmission side without aligning the optical fiber with θx and θy. It is. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0026]
According to a seventh aspect of the present invention, in the filter module according to the sixth aspect, a deviation between an optical axis of the first lens and an optical axis of the second lens is set within 2.5% of the focal length f. Is the gist.
[0027]
According to this configuration, the shift between the optical axis of the first lens and the optical axis of the second lens is set to be within 2.5% of the focal length f. Can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the transmission side without aligning the optical fibers with θx and θy. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0028]
According to an eighth aspect of the present invention, in the filter module according to the first aspect, the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the incident side of the first lens with respect to the optical axis of the first lens. Are set within 0.2 degrees, and the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side of the second lens with respect to the optical axis of the second lens are respectively set to 0. The gist is that the angle is set within 2 degrees, and the deviation between the optical axis of the first lens and the optical axis of the second lens is set within 2.5% of the focal length f.
[0029]
According to this configuration, the insertion loss on the transmission side can be suppressed to a predetermined value or less. Such setting is a necessary condition for assembling a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the transmission side without aligning the optical fibers with θx and θy. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0030]
According to a ninth aspect of the present invention, in the filter module according to any one of the first to seventh aspects, the first lens and the second lens are configured such that at least one of the light incident and exit surfaces is a flat surface with respect to the optical axis. The lens has a slanted surface that is inclined at an angle of 20 degrees or less.
[0031]
According to this configuration, by setting the deviation of the first lens and the second lens in the θz direction within 20 degrees, the insertion loss on the transmission side is suppressed to a predetermined value or less while preventing reflected return light. Can be. Such a setting is a necessary condition for reducing the insertion loss on the transmission side to a predetermined value, for example, 0.2 dB or less while preventing reflected return light.
[0032]
According to a tenth aspect of the present invention, in the filter module according to any one of the first to ninth aspects, the inclination of each of the first lens and the second lens with respect to the optical axis is set within 1.5 degrees. Is the gist.
[0033]
According to this configuration, the insertion loss on the transmission side can be further reduced. Further, in addition to the conditions described in claims 1, 6, 7 and 9, respectively, the inclinations of the first lens and the second lens with respect to the optical axis are set within 1.5 degrees, respectively, so that the above-mentioned four lenses are set. The necessary insertion loss can be obtained even if the alignment operations (c) and (d) are omitted from the alignment operations (a) to (d). As a result, the alignment time and the alignment work are reduced, so that the assembling time of the filter module is further reduced, and the manufacturing cost is further reduced.
[0034]
According to an eleventh aspect of the present invention, in the filter module according to the tenth aspect, a tilt error in a θx direction and a tilt error in a θy direction of each end face of the first lens and the second lens on the side facing each other are respectively defined by: The point is to set within 10 degrees.
[0035]
In this case, for example, when the respective end surfaces of the two lenses facing each other are flat surfaces perpendicular to the optical axis, the inclination of each end surface with respect to the optical axis is set within a range of 90 ° ± 10 °. Means to do. Further, when each of the end surfaces is an inclined surface inclined at a predetermined angle with respect to the optical axis, it means that the inclination of each end surface with respect to the optical axis is set within a range of a predetermined angle ± 10 degrees. According to this configuration, by setting the inclination error in the θx direction and the inclination error in the θy direction of each of the end surfaces of the first lens and the second lens facing each other within 10 degrees, a necessary insertion loss is obtained. (For example, 0.2 dB or less).
[0036]
According to a twelfth aspect of the present invention, in the filter module according to the eleventh aspect, the inclination error in the θx direction and the inclination error in the θy direction of the end surface of the first lens and the second lens on the side facing each optical fiber are determined. The gist is that each is set within 2.5 degrees.
[0037]
According to this configuration, the inclination error in the θx direction and the inclination error in the θy direction of the end surfaces of the first lens and the second lens on the side facing each optical fiber are set within 2.5 degrees, respectively. The required insertion loss (for example, 0.2 dB or less) can be obtained.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a filter module to which the present invention is applied will be described with reference to the drawings.
[0039]
The present invention is applied to the filter modules 11 and 21 shown in FIGS. 1 and 2 and the filter module 31 shown in FIG. First, the configurations of these filter modules will be described. The description of the filter module 11 shown in FIG. 1 is omitted.
[0040]
The filter module 21 illustrated in FIG. 2 includes the first lens 22 and the second lens 23, the filter 24, the two-core fiber chip 28, and the one-core fiber chip 29, as described above.
[0041]
Two optical fibers 25 and 26 are fixed to the two-core fiber chip 28 so that the fiber axes are parallel, and one optical fiber 27 is fixed to the single-core fiber chip 29. Further, the optical fibers 25 and 26 are located at positions opposite from the optical axis C by substantially the same distance. The same refractive index distribution type rod lens having a focal length f is used as the first lens 22 and the second lens 23, the distance between the lenses is set to 2f, and the filter 24 is connected to the lens side of the first lens 22. It is formed on the end face.
[0042]
Each of the first lens 22 and the second lens 23 is composed of a gradient index rod lens (flat lens) whose both end surfaces are flat surfaces perpendicular to the optical axis C.
The filter 24 is formed on an end surface (lens side end surface) of the first lens 22 on the side facing the second lens 23. The filter 24 is a wavelength selection film having a property of transmitting light in a certain wavelength range and reflecting light in a wavelength range different from the wavelength range.
[0043]
The two optical fibers 25 and 26 are arranged at symmetrical positions with respect to the optical axis C. That is, the optical fiber 25 is offset by a predetermined amount on the plus side (upward in FIG. 2) with respect to the optical axis C (fiber offset (+)), and the optical fiber 26 is on the minus side (FIG. Is offset by the same amount as the optical fiber 25 (fiber offset (−)). On the other hand, the optical fiber 27 is offset from the optical axis C on the same side as the optical fiber 26 and by the same amount. In the following description, the optical fiber 25 on the entrance port side is referred to as a first optical fiber 25, the optical fiber 26 on the reflection port side is referred to as a second optical fiber 26, and the optical fiber 27 on the transmission port side is referred to as a third optical fiber 27. . The “incident port side” refers to a channel on which light enters, the “reflection port side” refers to a channel on which reflected light from the filter 24 enters, and the “transmission port side” refers to the filter 24. The channel on the side where the transmitted light is incident.
[0044]
As described above, the same gradient index rod lens is used as the first lens 22 and the second lens 23. In this example, a gradient index rod lens having a lens diameter of 1.8 mm, a lens length of 0.23 pitch, and a focal length f of 1.95 mm is used as the two lenses 22 and 23.
[0045]
As each of the optical fibers 25 to 27, a normal single mode optical fiber having an outer diameter of 125 μm is used. Therefore, when the optical fibers 25 and 26 are held by the two-core fiber chip 28 at positions symmetrical with respect to the optical axis C and in contact with each other, the offset amount of the optical fiber 27 is about 60 μm or more.
[0046]
Then, when the filter module 21 emits light in the wavelength range that passes through the filter 24 from the first optical fiber 25, the light is collimated by the first lens 22 and passes through the filter 24, and the transmitted light passes through the second lens 22. The light is converged by the lens 23 and enters the third optical fiber 27. When the filter module 21 emits light in the wavelength range reflected by the filter 24 from the first optical fiber 25, the light is collimated by the first lens 22 and reflected by the filter 24. The light is converged by the lens 22 and enters the second optical fiber 26. As described above, the filter module 21 is a three-port (incident port, reflection port, and transmission port) demultiplexing module used in an optical communication system such as a wavelength division multiplexing (WDM) or high-density wavelength multiplexing (DWDM) transmission system. It is configured.
[0047]
Next, the filter module 31 shown in FIG. 3 will be described.
The filter module 31 includes a first lens 32 and a second lens 33, a filter 34, a two-core fiber chip 38, and a single-core fiber chip 39. The two-core fiber chip 38 holds two optical fibers 35 and 36, and the one-core fiber chip 39 holds one optical fiber 37.
[0048]
The first lens 32 has an end surface facing the second lens 33 (lens end surface) polished to a flat surface perpendicular to the optical axis C, and has an end surface facing the optical fibers 35 and 36 (optical fiber end surface). ) 32a is composed of a gradient index rod lens polished to an inclined surface inclined at a predetermined angle with respect to the optical axis C. A filter 34 is formed on the lens-side end surface. The filter 34 is a wavelength selection film similar to the filter 24 described above. Similarly to the first lens 32, the second lens 33 has a flat end surface (lens end surface) facing the second lens 33, and an optical fiber side end surface facing the optical fiber 37. Reference numeral 33a denotes a gradient index rod lens formed on an inclined surface inclined at a predetermined angle with respect to the optical axis C.
[0049]
The first lens 32 and the second lens 33 are inserted into a cylindrical glass tube 40, and are fixed to a predetermined position before being fixed to the glass tube 40.
The lens-side end surface 38 a of the two-core fiber chip 38 is formed on the same oblique surface as the optical fiber-side end surface 32 a of the first lens 32. The lens-side end surface 39 a of the single-core fiber chip 39 is also formed on the same oblique surface as the optical fiber-side end surface 33 a of the second lens 33.
[0050]
Further, in the filter module 31 of the present example, the two optical fibers 35 and 36 are arranged at substantially symmetrical positions with respect to the optical axis C, and the optical fiber 37 is connected to the optical axis of the second lens 33 from the optical axis. The optical fiber 36 is arranged so that the deviation is equal to the deviation of the optical fiber 36 from the optical axis of the first lens 32. In the following description, the optical fiber 35 on the incident port side is a first optical fiber 35, the optical fiber 36 on the reflective port side is a second optical fiber 36, and the optical fiber 37 on the transmission port side is a third optical fiber. It is called a fiber 37.
[0051]
[One embodiment]
Next, an embodiment of the present invention applied to the above-described filter modules 11, 21, 31 will be described.
[0052]
Here, among these filter modules 11, 21 and 31, the assembly tolerance (conditions 1 to 7) set mainly for manufacturing the filter module 21 will be described. These conditions are such that the absolute value of the allowable loss range of the filter module 21 is about 0.4 dB or less, that is, the loss due to lens aberration of 0.2 dB is considered, and the insertion loss on the reflection side and the transmission side is substantially zero. .2 dB or less.
[0053]
(Condition 1) Assuming that the focal length of the first lens 22 and the second lens 23 is f, the shift amount of the filter 24 from the focal position of the first lens 22 (the focal position of the first lens) is substantially equal to the focal length f. Set within ± 25%. In other words, the distance of the filter 24 from the first lens 22 is set substantially in the range of (ff / 4) to (f + f / 4).
[0054]
From the experimental results shown in FIG. 4, it was found that when the filter 24 was shifted from the focal position of the first lens 22 to the + side by approximately 0.5 mm (approximately 25% of the focal length f), the insertion loss increased by approximately 0.2 dB. . In FIG. 4, “0” on the horizontal axis representing the shift amount (movement amount in the Z-axis direction) of the filter 24 in the Z direction is the first lens 22 that is separated from the lens-side end surface of the first lens 22 by the focal length f. Is shown. The experimental results shown in FIG. 4 are data when the lens diameters of the first lens 22 and the second lens 23 are 1.8 mm, the lens length is 0.23 pitch, and the focal length f is 1.97 mm. The insertion loss indicated by the vertical axis in FIG. 4 refers to the above-mentioned “insertion loss on the reflection side”. That is, when the light in the wavelength range reflected by the filter 24 is emitted from the first optical fiber 25, the reflected light that is collimated by the first lens 22 and reflected by the filter 24 is converged by the first lens 22, This refers to the insertion loss when the light enters the optical fiber 26.
[0055]
(Condition 2) The inclination of the first, second, and third optical fibers 25, 26, and 27 with respect to the optical axis C of the first lens 22 in the θx direction and the inclination in the θy direction are each within 0.2 degrees. Set to.
[0056]
From the experimental results shown in FIG. 5, the rotation angles (°) of the optical fibers 25, 26, 27 in the θy direction with respect to an arbitrary position, that is, the inclination of the first lens 22 in the θy direction with respect to the optical axis C is 1. If the displacement is within 5 degrees, it can be estimated that there is no large insertion loss. If the inclination of the optical fibers 25, 26, and 27 in the θx direction is shifted within 1.5 degrees, it can be estimated that there is no large insertion loss. However, it has been found that it is necessary to set the inclinations of the optical fibers 25, 26, and 27 in the θx and θy directions within 0.2 degrees in consideration of the accumulation of other tolerances.
[0057]
(Condition 3) The distance (WD) between the first lens 22 and the second lens 23 is set within approximately 2f ± (25% of 2f), that is, approximately 2f ± 2f / 4.
[0058]
As described above, since the optical fiber diameter of each of the optical fibers 25 to 27 is usually 125 μm, the optical fibers 25 and 26 are held by the two-core fiber chip 28 at symmetrical positions with respect to the optical axis C and in contact with each other. In this case, the offset amount of the optical fiber 27 is about 60 μm (−60 μm in this example). In the case of such an offset amount, the experimental results shown in FIGS. 6 and 7 show that when the distance WD between the lenses is shifted by about 1 mm (about 25% of 2f), the insertion loss is increased by about 0.2 dB. In FIG. 7, the offset amount of the optical fiber 27 is shown for four cases of −60 μm, −70 μm, −80 μm, and −100 μm. However, the insertion loss in each case is shown by raising the level by about 0.10 dB. It is.
[0059]
(Condition 4) The deviation between the optical axis C of the first lens 22 and the optical axis C of the second lens 23 is set within 2.5% of the focal length f.
The insertion loss is estimated from the relationship between the deviation of the optical axes of the lenses 22 and 23 and the tilt of the beam, and the above-described experimental results shown in FIG. 5 regarding the tilts of the optical fibers 25 to 27 in the θx and θy directions. When the focal length f of the two lenses 22 and 23 was 1.95 mm, an estimated value that the deviation of the optical axis was set within 50 μm was obtained. That is, an estimated value that the deviation is set within 2.5% of the focal length f was obtained.
[0060]
(Condition 5) The deviation of the first lens 22 and the second lens 23 in the θz direction is set within 20 degrees.
Note that the condition 5 is such that, as in the filter module 31 shown in FIG. 3, as the first and second lenses 32 and 33, the refractive index distribution type in which the inclined surfaces 32a and 33a for preventing reflected return light are formed. Applicable only when using a rod lens. Therefore, it is not applied to the filter modules 11 and 21 shown in FIGS.
[0061]
(Condition 6) The inclination of each of the first lens 22 and the second lens 23 with respect to the optical axis C is set within 1.5 degrees.
The inclination and the insertion loss are estimated from the relationship between the inclination of the lens-side end surfaces of the two lenses 22 and 23 and the beam, and the above-described experimental results shown in FIG. 5 regarding the inclination of each of the optical fibers 25 to 27 in the θx and θy directions. Then, an estimated value that the inclination of each of the two lenses 22 and 23 with respect to the optical axis C is set within 1.5 degrees was obtained.
[0062]
(Condition 7) The inclination error in the θx direction and the inclination error in the θy direction with respect to the optical axis C of the respective lens-side end surfaces of the first lens 22 and the second lens 23 are set within 10 degrees (see FIG. 8). Further, the inclination error in the θx direction and the inclination error in the θy direction with respect to the optical axis C of the optical fiber side end surfaces of the first lens 22 and the second lens 23 are set within 2.5 degrees (see FIG. 8).
[0063]
The above conditions 1 to 7 are shown in FIG.
When the filter module 31 shown in FIG. 3 is manufactured, the above-described assembly tolerance (conditions 1 to 7) is set similarly to the case of manufacturing the filter module 21. Next, an assembling procedure of the filter module 31 satisfying the above conditions 1 to 7 will be described. The assembly includes the following steps 1 to 3. However, the two-core fiber chip 28 and the one-core fiber chip 29 are manufactured in advance.
[0064]
(Step 1) First lens 22 and second lens 23 are inserted into glass tube 40 and temporarily fixed.
(Step 2) The light in the wavelength range reflected by the filter 24 is emitted from the first optical fiber 25 on the incident port side, and the reflected light reflected by the filter 24 and incident on the second optical fiber 26 on the reflection port side is monitored. Meanwhile, the two-core fiber chip 38 is aligned in the X, Y, and Z directions so that the amount of the reflected light is maximized. After the alignment, the two-core fiber chip 38 is fixed to the first lens 32. Step 2 may be performed before step 1 described above.
[0065]
(Step 3) The light in the wavelength range that passes through the filter 24 is emitted from the first optical fiber 25, and the transmitted light that passes through the filter 24 and enters the third optical fiber 27 on the transmission port side is monitored while transmitting the light. The single-core fiber chip 39 is aligned in the X, Y, and Z directions so that the amount of light becomes maximum. After this alignment, the single-core fiber chip 39 is fixed to the second lens 23.
[0066]
Note that the alignment accuracy in the X, Y, and Z directions in the steps 2 and 3 needs to be 0.5 μm or less, but the accuracy can be sufficiently achieved by the current technology. Steps 2 and 3 correspond to the alignment operations (a) and (b) described above. In step 2, the mode field diameter of the optical fiber on the reflection side and the beam waist diameter are automatically matched. Similarly, in step 3, the mode field diameter on the transmission side coincides with the beam waist diameter automatically.
[0067]
Also, after the above steps 2 and 3, or together with these steps 2 and 3, a centering operation for matching the mode field diameter of each of the optical fibers 35 to 37 and the beam waist diameter is performed. That is, a centering operation similar to the above-described centering operation (b) is performed.
[0068]
The assembly of the filter module 31 is completed by the above steps 1 to 3, but since the filter module 31 satisfies all of the above conditions 1 to 7, the above four alignment operations (a) to ( In d), the necessary insertion loss can be obtained even if the alignment operations (c) and (d) are omitted. Further, the alignment work (b) is automatically performed when the alignment work (a) is performed.
[0069]
Next, examples and comparative examples will be described with reference to the table of FIG.
The data of Condition 1 (deviation from the focal point of the filter) in the table of FIG. 8 are obtained when a refractive index distribution rod lens having a refractive index distribution constant ΔA of 0.322 is used as each of the above lenses. It is.
[0070]
[Example 1]
As each of the lenses, a gradient index rod lens having a refractive index distribution constant √A of 0.322 and a lens length of 0.25 pitch (focal length f is 1.95 mm) is used. In addition, as shown in FIG. 3, the optical fiber side end face of each lens is polished to an oblique surface of 8 °. The permissible accuracy of the condition 1 (the deviation of the filter from the focal position) is set to less than 0.07 mm, that is, less than 3.5% of the focal length f. The allowable accuracy of the condition 3 (the deviation of the lens interval from 2 · f) is set to 0.5 mm, that is, the distance (WD) between the lenses 22 and 23 is set to 2f ± (13% of 2f). The other allowable accuracy is the same as in Example 2 described later.
[0071]
Then, in Example 1, the allowable accuracy of each condition was set as shown in the table of FIG. 8, and 15 filter modules were manufactured. For each of these filter modules, the reflection-side loss (the above-mentioned “insertion loss on the reflection side”) and the transmission-side loss (the above-mentioned “insertion loss on the transmission side”) were measured. Deviations and worst values were calculated. The data of each of these losses is shown in the table shown in FIG.
[0072]
[Example 2]
As each of the lenses, a gradient index rod lens having a refractive index distribution constant √A of 0.322 and a lens length of 0.23 pitch (focal length f is 1.97 mm) is used. Each of the lenses has an optical fiber side end face polished to an oblique surface of 8 °. In the second embodiment, the allowable accuracy of the condition 1 is set to 0.25 mm, that is, 13% of the focal length f. Further, the allowable accuracy of the condition 3 is set to 0 mm, that is, the inter-lens distance (WD) is set to 2f. The data of each loss described above for one filter module is shown in the lower column of the table shown in FIG.
[0073]
[Example 3]
As each of the lenses, a gradient index rod lens having a refractive index distribution constant √A of 0.322 and a lens length of 0.24 pitch (focal length f is 1.96 mm) is used. Each lens is a flat lens whose both end surfaces are polished to a flat surface perpendicular to the optical axis C as shown in FIG. The permissible accuracy of the condition 1 is set to 0.5 mm, that is, 25% of the focal length f. The allowable accuracy of the condition 3 is set to 1 mm, that is, the distance between lenses (WD) is set to 2f ± (25% of 2f). Further, since the flat lens is used, the permissible accuracy of condition 5 (θz shift of each lens) is set to zero. Other tolerances are the same as in the first and second embodiments. Then, the allowable accuracy of each condition was set as shown in the table of FIG. 8, and one filter module was manufactured. For this filter module, the data for each of the above losses is shown in the table shown in FIG.
[0074]
[Comparative Example 1]
As each of the lenses, a gradient index rod lens having a refractive index distribution constant √A of 0.322 and a lens length of 0.25 pitch (focal length f is 1.95 mm) is used. In addition, each lens is polished at an end surface on the lens side of 8 °. The permissible accuracy of the condition 1 is set to 0.07 mm, that is, 3.5% of the focal length f. The allowable accuracy of the condition 3 is set to 0.5 mm, that is, the distance between lenses (WD) is set to 2f ± (13% of 2f). Also, the allowable accuracy of the condition 2 (the inclinations θx and θy of the first and second optical fibers and the inclinations θx and θy of the third optical fiber) is set to 0.5 mm, which is larger than that of the first to third embodiments. I have. Other tolerances are the same as in the first and second embodiments.
[0075]
Then, in Comparative Example 1, the allowable accuracy under each condition was set as shown in the table in FIG. 8, and 13 filter modules were manufactured. For each of these filter modules, the reflection-side loss and the transmission-side loss were measured, and 13 average values, standard deviations, and worst values were calculated for each loss. The data of each of these losses is shown in the lower column of the table shown in FIG.
[0076]
[Comparative Example 2]
As each of the lenses, a gradient index rod lens having a refractive index distribution constant √A of 0.322 and a lens length of 0.24 pitch (focal length f is 1.96 mm) is used. Note that each lens uses the same flat lens as in the third embodiment. The permissible accuracy of the condition 1 is set to 0.16 mm, that is, 8% of the focal length f. The allowable accuracy of the condition 3 is set to 1.5 mm, that is, the distance between lenses (WD) is set to 2f ± (39% of 2f). Further, since a flat lens is used as in the third embodiment, the allowable accuracy of condition 5 (θz shift of each lens) is set to zero. Other tolerances are the same as in the first to third embodiments. Then, the allowable accuracy of each condition was set as shown in the table shown in FIG. 8, and one filter module was manufactured. For this filter module, data on each of the above losses is shown in the lower column of the table shown in FIG.
[0077]
Comparing the first embodiment with the second embodiment, since the allowable accuracy of the condition 1 is set more strictly in the first embodiment than in the second embodiment, the reflection-side loss is higher in the first embodiment than in the second embodiment. Also less. Further, since the allowable accuracy of the condition 3 is set more strictly in the second embodiment than in the first embodiment, the transmission-side loss is smaller in the second embodiment than in the first embodiment. Further, comparing the second embodiment and the third embodiment, the permissible accuracy of the conditions 1 and 3 is set more strictly in the second embodiment than in the third embodiment. Example 2 is less than Example 3.
[0078]
From these facts, it is understood that the permissible accuracy of the condition 1 greatly contributes to the improvement of the reflection-side loss, and the permissible accuracy of the condition 2 greatly contributes to the improvement of the transmission-side loss. This is also true when each of Examples 1 to 3 and Comparative Example 2 are compared.
[0079]
Further, when comparing Example 1 with Comparative Example 1, the allowable accuracy of Condition 2 is set more strictly in Example 1 than in Comparative Example 1, so that both the reflection-side loss and the transmission-side loss are equal to those of Example 1. 1 is much smaller than Comparative Example 1. In addition, the variation and the worst value of each loss are much better in Example 1 than in Comparative Example 1.
[0080]
According to the embodiment configured as described above, the following operational effects can be obtained.
The amount of deviation of the filter 24 from the focal position of the first lens 22 is set within ± 25% of the focal length f, that is, by satisfying the above condition 1, the insertion loss on the reflection side is at most about 0.2 dB. Can be suppressed. Setting the assembly tolerance of the filter 24 with respect to the first lens 22 (permissible accuracy of the condition 1) in this manner requires a filter module that satisfies the required insertion loss (for example, 0.2 dB or less) on the reflection side. This is a condition necessary for assembling without alignment of θx and θy. By satisfying such conditions, a filter module having an insertion loss smaller than a predetermined value can be assembled without aligning the optical fibers with θx and θy. Therefore, productivity can be improved and manufacturing costs can be reduced.
[0081]
By setting the inclination in the θx direction and the inclination in the θy direction of the optical fibers 25 and 26 disposed on the incident side of the first lens 22 with respect to the optical axis C of the first lens 22 within 0.2 degrees, respectively. The insertion loss on the reflection side can be suppressed to a predetermined value or less. Such setting is necessary for assembling the filter module 21 that satisfies the required insertion loss (for example, 0.2 dB or less) on the reflection side without aligning the optical fibers 25 and 26 with θx and θy. Condition. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0082]
The transmission of the optical fiber 27 arranged on the exit side of the second lens 23 by setting the inclination in the θx direction and the inclination in the θy direction with respect to the optical axis C of the second lens 23 within 0.2 degrees, respectively. Side insertion loss can be suppressed to a predetermined value or less. Such a setting is a necessary condition for assembling a filter module satisfying the required insertion loss (for example, 0.2 dB or less) on the transmission side without aligning the optical fiber 27 with θx and θy. . By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0083]
The inclination in the θx direction and the inclination in the θy direction of the optical fibers 25 and 26 disposed on the incident side of the first lens 22 and the optical fiber 27 disposed on the exit side of the second lens 23 are respectively within 0.2 degrees. By setting, the insertion loss can be suppressed to a predetermined value or less. Such setting makes it possible to assemble the filter module 21 that satisfies both the required insertion loss (for example, 0.2 dB or less) on the reflection side and the transmission side without aligning the optical fibers 25 to 27 with θx and θy. This is a necessary condition. By satisfying such conditions, productivity can be improved and manufacturing cost can be reduced.
[0084]
By setting the distance (WD) between the first lens 22 and the second lens 23 within 2f ± (25% of 2f), that is, satisfying the above condition 3, the transmission due to the deviation of the distance between the lenses. The increase in insertion loss on the side can be suppressed. As described above, setting the distance between lenses (WD) within 2f ± (25% of 2f) requires a filter module that satisfies the required insertion loss on the transmission side (for example, 0.2 dB or less). This is a necessary condition for assembling the optical fiber without alignment of θx and θy. Therefore, productivity can be improved and manufacturing costs can be reduced.
[0085]
By setting the deviation between the optical axis of the first lens 22 and the optical axis of the second lens 23 to within 2.5% of the focal length f, that is, by satisfying the above condition 4, the two lenses 22, 23 An increase in insertion loss on the transmission side due to displacement of the optical axis can be suppressed. Therefore, a filter module with a smaller insertion loss can be realized. Further, setting the deviation of the optical axes of the two lenses 22 and 23 within 2.5% of the focal length f as described above requires the required insertion loss on the transmission side (for example, 0.2 dB or less). This is a condition necessary for assembling a filter module satisfying the above condition without aligning the optical fibers with θx and θy. Therefore, productivity can be improved and manufacturing costs can be reduced.
[0086]
As described above, the condition 5 is such that, as in the filter module 31 shown in FIG. 3, the first lens and the second lens are oblique such that one of the light entrance and exit surfaces is flat and inclined with respect to the optical axis. Applied in the case of lenses having respective surfaces. In the case of the filter module 31, the optical fiber side end surface (incident surface) 32a of the first lens 32 and the optical fiber side end surface (outgoing surface) 33a of the second lens 33 are slanted surfaces. In this filter module 31, by setting the displacement of both lenses 32 and 33 in the θz direction, that is, the displacement of both optical fiber side end surfaces 32a and 33a in the θz direction within 20 degrees, it is possible to prevent reflected return light and transmit light. Side insertion loss can be reduced. As described above, in a filter module such as the filter module 31, setting the deviation of the two lenses 32 and 33 in the θz direction, that is, the deviation of the two optical fiber side end surfaces 32a and 33a in the θz direction within 20 degrees is a problem of the filter. This is a necessary condition for assembling the module without aligning the optical fibers with θx and θy. Therefore, productivity can be improved and manufacturing costs can be reduced.
[0087]
By satisfying the above conditions 1 to 7, a necessary insertion loss can be obtained even if the alignment operations (c) and (d) are omitted from the four alignment operations (a) to (d). . However, the condition 5 is applied to a case where the first lens and the second lens are each a lens having one of the light entrance and exit surfaces which is flat and has an inclined surface inclined with respect to the optical axis, as in the filter module 31. Is done. As a result, the number of alignment points and alignment operations are reduced, so that the assembling time of the filter module is reduced, and the manufacturing cost can be reduced. The alignment by the alignment operation (b) is automatically performed when the alignment operation (a) is performed.
[0088]
By setting the inclination error in the θx direction and the inclination error in the θy direction of the respective lens-side end surfaces of the first lens 22 and the second lens 23 within 10 degrees, the insertion loss can be suppressed to 0.2 dB or less. (See FIG. 8).
[0089]
By setting the inclination error in the θx direction and the inclination error in the θy direction of the optical fiber side end surfaces of the first lens 22 and the second lens 23 within 2.5 degrees, respectively, the insertion loss is reduced to 0.2 dB or less. Can be suppressed (see Fig. 8)
[Modification]
The present invention can be embodied with the following modifications.
[0090]
In the above embodiments, the filter modules 11, 21, and 31 are configured as demultiplexing modules, respectively. However, the present invention is also applied to a case where the filter modules 11, 21, and 31 are configured as multiplexing modules. You. In this case, light of different wavelengths sent from at least two optical fibers is configured to enter one optical fiber via the first lens and the second lens.
[0091]
In the above-described embodiment, of the filter modules 11, 21 and 31 shown in FIGS. 1, 2 and 3, respectively, an assembly tolerance (conditions 1 to 7) set mainly for manufacturing the filter modules 21 and 31 is set. ) Has been described, but these conditions can be similarly set when the filter module 11 is manufactured.
[0092]
The deviation in the θz direction in the above condition 5 is a parameter indicating the coincidence of the directions of the oblique surfaces of the rod lens, but this condition can be set for lenses other than the rod lens. For example, the conditions can be set when the flat side of a plano-convex spherical lens is polished to an oblique surface or when the end surface of a flat microlens is polished to an oblique surface.
[0093]
In the above-described embodiment, the three-port filter module has been described. However, three or more optical fibers are arranged on the entrance side of the first lens, and two or more optical fibers are arranged on the exit side of the second lens. The present invention is applicable to a filter module.
[0094]
【The invention's effect】
As described above, according to the first aspect of the present invention, by setting the amount of deviation of the filter from the focal position of the first lens within ± 25% of the focal length f, the insertion loss, particularly on the reflection side, is reduced. Can be suppressed to about 0.2 dB at the maximum. Setting the assembly tolerance of the filter with respect to the first lens in this manner requires a filter module that satisfies a required insertion loss, for example, a reflection-side insertion loss of approximately 0.2 dB or less, without aligning the optical fibers with θx and θy. This is a necessary condition for assembling. By satisfying such conditions, a filter module having an insertion loss smaller than a predetermined value can be assembled without aligning the optical fibers with θx and θy. Therefore, productivity can be improved and manufacturing costs can be reduced.
[0095]
According to the tenth aspect, the insertion loss on the transmission side can be further reduced. Further, in addition to the conditions described in claims 1, 6, 7 and 9, respectively, the inclinations of the first lens and the second lens with respect to the optical axis are set within 1.5 degrees, respectively, so that the above-mentioned four lenses are set. The necessary insertion loss can be obtained even if the alignment operations (c) and (d) are omitted from the alignment operations (a) to (d). As a result, since the number of alignment points and alignment operations are reduced, the assembling time of the filter module is further reduced, and the manufacturing cost can be further reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an optical system of a filter module using a spherical lens.
FIG. 2 is a configuration diagram showing an optical system of a filter module using a gradient index rod lens.
FIG. 3 is a configuration diagram showing an optical system of a filter module different from that of FIG. 2;
FIG. 4 is experimental data showing the relationship between the displacement of the filter and the insertion loss.
FIG. 5 is experimental data showing the relationship between the angular position of the optical fiber in the θy direction and the insertion loss.
FIG. 6 is experimental data showing a relationship between an offset amount of an optical fiber and an insertion loss.
FIG. 7 is experimental data showing the relationship between the amount of deviation of the distance WD between lenses and insertion loss.
FIG. 8 is a diagram showing a list of data of one embodiment, each example, and each comparative example of the present invention.
[Explanation of symbols]
C: optical axis, f: focal length, WD: distance between lenses 11, 21, 31 ... filter module, 12, 22, 32 ... first lens, 13, 23, 33 ... second lens, 14, 24, 34 ... Filters, 15-17, 25-27, 35-37 ... Optical fibers, 32a, 33a ... End faces.

Claims (12)

A first lens and a second lens, which are the same lens fixed in advance so that their optical axes are substantially coaxial, a filter disposed between the two lenses, and disposed on the incident side of the first lens; A filter module comprising: at least two optical fibers fixed so that fiber axes are substantially parallel; and at least one optical fiber disposed on the exit side of the second lens.
Assuming that a focal length of the first lens and the second lens is f, a shift amount of the filter from a focal position of the first lens is set within ± 25% of the focal length f. module. The inclination of the optical fiber disposed on the incident side of the first lens in the θx direction and the inclination in the θy direction with respect to the optical axis of the first lens is set within 0.2 degrees, respectively. 2. The filter module according to 1. The inclination of the optical fiber disposed on the emission side of the second lens in the θx direction and the inclination of the optical fiber in the θy direction with respect to the optical axis of the second lens is set within 0.2 degrees, respectively. 2. The filter module according to 1. The inclination of the optical fiber disposed on the incident side of the first lens in the θx direction and the inclination in the θy direction with respect to the optical axis of the first lens is set within 0.2 degrees, respectively. 2. The filter according to claim 1, wherein the inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side with respect to the optical axis of the second lens are each set within 0.2 degrees. module. 2. The filter module according to claim 1, wherein a distance (WD) between the first lens and the second lens is set within a range of 2f ± 2f / 4. 3. The inclination of the optical fiber disposed on the incident side of the first lens in the θx direction and the inclination in the θy direction with respect to the optical axis of the first lens is set within 0.2 degrees, respectively. The inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side with respect to the optical axis of the second lens are set within 0.2 degrees, respectively, and further, the first lens and the second lens 2. The filter module according to claim 1, wherein the lens-to-lens distance (WD) is set within a range of 2f ± 2f / 4. The filter module according to claim 6, wherein a deviation between an optical axis of the first lens and an optical axis of the second lens is set within 2.5% of the focal length f. The inclination of the optical fiber disposed on the incident side of the first lens in the θx direction and the inclination in the θy direction with respect to the optical axis of the first lens is set within 0.2 degrees, respectively. The inclination in the θx direction and the inclination in the θy direction of the optical fiber disposed on the emission side with respect to the optical axis of the second lens are set within 0.2 degrees, respectively. 2. The filter module according to claim 1, wherein the shift of the optical axis of the two lenses is set within 2.5% of the focal length f. The first lens and the second lens are each a lens having at least one of the light incident and exit surfaces which is flat and has an inclined surface inclined with respect to the optical axis. The filter module according to any one of claims 1 to 7, wherein the filter module is set within degrees. The filter module according to any one of claims 1 to 9, wherein an inclination of each of the first lens and the second lens with respect to an optical axis is set within 1.5 degrees. 11. The filter according to claim 10, wherein the inclination error in the θx direction and the inclination error in the θy direction of each of the end surfaces of the first lens and the second lens facing each other are set within 10 degrees. module. 12. The inclination error in the θx direction and the inclination error in the θy direction of the end surface of the first lens and the second lens on the side facing each optical fiber are set to be within 2.5 degrees, respectively. The filter module according to 1.

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