JP2001124960A - Light-receiving module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easily assemblable light-receiving module, capable of accurately adjusting optical axis of an optical fiber and a lens for converging signal light emitted from the end face of the optical fiber to the light-receiving part of a photodetector and keeping that state. SOLUTION: A fiber holder 2 and the lens 6 are formed in an equal outer diameter with each other, tightly inserted from both sides to a cylindrical ceramic sleeve 8 provided with an inner diameter equal to the outer diameter of both and integrated and held in a state of being abutted against each other. A BFP 7 is provided inside the ceramic sleeve 8 in the state of being clamped between the fiber holder 2 and the lens 6. The ceramic sleeve 8 is held by the holding member 9 of a double-cylinder structure fixed to a PD holder 4. The holding member 9 is composed by connecting an inner cylinder 9A, provided with a screw part 10a on an outer peripheral part and an outer cylinder 9B which is provided with a screw part 10b on an inner peripheral part, by screwing the screw parts 10a and 10b of each other, and the ceramic sleeve 8 is inserted and fixed to the inner cylinder 9A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a light receiving module used in a wavelength division multiplexing optical communication system or the like.

[0002]

2. Description of the Related Art FIG. 5 illustrates the structure of a conventional light receiving module 50 used in a wavelength division multiplexing optical communication system. In the figure, reference numeral 51 denotes an optical fiber which is an optical transmission line of a wavelength division multiplexing optical communication system, and reference numeral 52 denotes a photodiode (hereinafter referred to as PD) for detecting signal light transmitted through the optical fiber 51.
Reference numeral 53 denotes a spherical lens for converging the signal light emitted from the end face of the optical fiber 51 to the light receiving portion 52a of the PD 52. The lens 53 is held in a cylindrical lens holder 54. The PD 52 is held by an annular PD holder 56 fixed to one end 54 a of the lens holder 54. The optical fiber 51 is attached to a fiber holder 55 fixed to the other end 54 b of the lens holder 54 at its end 5.
1a is held. The fiber holder 55 includes a cylindrical holding portion 55a inserted into the lens holder 54 and a flange portion 55 fixed to the other end 54b of the lens holder 54.
b. An end face 55c of the holding portion 55a of the fiber holder 55 is slightly inclined with respect to the optical axis of the optical fiber 51, and a bandpass optical filter 57 is provided on the inclined end face 55a. The bandpass optical filter 57 is formed by forming an optical filter film 57b that transmits only light of a specific wavelength on one surface of a transparent substrate 57a. This light receiving module 50
Is assembled as follows. Optical fiber 51
End face 5 of holding portion 55a of fiber holder 55 holding
The bandpass optical filter film 57b is fixed to 5c with an adhesive. The holder 55a of the fiber holder 55 is inserted into the lens holder 54 holding the lens 53, and the lens 5
After adjusting the optical axis to 3, the flange 55b of the fiber holder 55 is welded to the lens holder 5 by YAG laser beam welding.
Fix to 4. Finally, after adjusting the optical axis of the PD holder 56 holding the PD 52 with the lens 53, the PD holder 56 is fixed to the lens holder 54 by YAG laser beam welding.

[0003]

As described above, the conventional light-receiving module 50 requires the optical fiber 5 during assembly.
The optical axis of the fiber holder 55 holding the lens holder 53, the lens holder 54 holding the lens 53, and the PD holder 56 holding the PD 52 are adjusted each time and welded with a YAG laser beam. Since the complicated work such as bonding the band-pass optical filter 57 to the filter must be performed, the production efficiency is low. In particular, since the diameter (core diameter) of the optical fiber 51 is extremely small, the operation of adjusting the optical axes of the fiber holder 55 and the lens holder 54 is very complicated, and this is the biggest factor that deteriorates the production efficiency. ing. Also, the light receiving module 50
When the ambient temperature changes, the distance between the optical fiber 51 and the PD 52 and the lens 53 changes due to expansion and contraction of the lens holder 54 and the like, so that light receiving loss due to defocus occurs. To avoid this, the optical fiber 51
The distance between the PD 52 and the lens 53 needs to be adjusted.
And the PD holder 56 are completely fixed by welding, and therefore cannot be adjusted after assembly. The present invention has been made in view of the above circumstances, and focuses an optical fiber, which is an optical transmission line of a wavelength division multiplexing optical communication system, and signal light emitted from an end face of the optical fiber on a light receiving portion of a light receiving element. It is an object of the present invention to provide a light receiving module that can accurately adjust the optical axis of a lens for performing the adjustment and maintain the state, and can easily assemble the light, and can optimally adjust the light receiving efficiency after the assembly.

[0004]

According to a first aspect of the present invention, there is provided a cylindrical fiber holder having an optical fiber constituting an optical transmission line, the end of which is held at the center, and the optical fiber. A light receiving element holder holding a light receiving element for detecting the signal light transmitted through the fiber, a lens for condensing the signal light emitted from the end face of the optical fiber to a light receiving portion of the light receiving element, and In a light receiving module including an optical filter that transmits only light of a specific wavelength out of the signal light, a cylindrical lens having the same outer diameter as the fiber holder is used as the lens, and the lens and the fiber holder are both used. Characterized by being inserted into and integrated with a cylindrical ceramic sleeve having an inner diameter equal to the outer diameter of. According to a second aspect of the present invention, there is provided a light receiving module according to the first aspect, wherein an inner cylinder having a thread portion on an outer peripheral portion and an outer cylinder having a thread portion on an inner peripheral portion are screwed together. A holding member having a cylindrical structure is provided, wherein the ceramic sleeve is inserted and fixed in the inner cylinder, and the light receiving element holder is fixed to an end of the outer cylinder. According to a third aspect of the present invention, in the light receiving module according to the first or second aspect, the optical filter is provided so as to be sandwiched between the fiber holder and the lens.
The invention according to claim 4 is the invention according to claim 1 or claim 2.
The light receiving module according to claim 1, wherein the optical filter includes an optical filter having a characteristic that a wavelength of transmitted light changes according to an incident angle of light, and the optical filter is disposed between the lens and the light receiving element. Characterized by being held by a movable member whose angle can be adjusted with respect to the optical axis. According to a fifth aspect of the present invention, in the light receiving module according to the first or second aspect, an optical filter having a characteristic that a wavelength of transmitted light changes according to a light incident position is used as the optical filter. A filter is disposed between the lens and the light receiving element and is held by a movable member whose position can be adjusted in a direction intersecting the optical axis of the lens.

According to the light receiving module of the present invention, a cylindrical lens having the same outer diameter as the fiber holder holding the optical fiber is used, and the lens and the fiber holder are connected to each other by the outer diameter. Since the optical fiber and the lens are inserted into and integrated with a cylindrical ceramic sleeve having the same inner diameter as that of the optical fiber, the optical axis can be easily and accurately adjusted to maintain the state. Further, according to the light receiving module of the second aspect, the inner cylinder of the holding member having the double cylindrical structure formed by screwing the inner cylinder having the screw portion on the outer peripheral portion and the outer cylinder having the screw portion on the inner peripheral portion to each other. By inserting and fixing a ceramic sleeve to the outer cylinder and fixing the light receiving element holder to the end face of the outer cylinder, the distance between the lens and the light receiving element can be easily adjusted by adjusting the relative position between the inner cylinder and the outer cylinder. be able to. This adjustment can be performed even after the light receiving module is assembled. According to the light receiving module of the third aspect, since the optical filter is provided in a state sandwiched between the fiber holder and the lens, the position and the angle of the optical filter with respect to the optical fiber and the lens due to a change in ambient temperature or the like. It can be prevented from changing. Since an optical filter generally has an angle dependence with respect to the optical axis, if its position or angle changes with respect to other optical elements, the transmission wavelength changes, and the wavelength of the optical signal focused on the light receiving element changes. However, such a problem can be prevented by keeping the position and the angle of the optical filter constant. According to the light receiving module of the fourth aspect, the optical filter is disposed between the lens and the light receiving element, and is held by the movable member whose angle can be adjusted with respect to the optical axis of the lens. By adjusting the wavelength, it is possible to easily adjust the transmission wavelength of the optical filter to a desired wavelength. According to the light receiving module of the fifth aspect, the optical filter having the characteristic that the wavelength of the passing light changes depending on the incident position of the light is arranged between the lens and the light receiving element, and the direction intersecting the optical axis of the lens. The transmission wavelength of the optical filter can be easily adjusted to a desired wavelength by adjusting the position of the movable member by holding the movable member whose position can be adjusted. Further, by using a band-pass optical filter made of a dielectric multilayer film having a small temperature dependence of a transmission wavelength as an optical filter, a change in a light receiving wavelength due to a change in an ambient temperature can be extremely small.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. [First Embodiment] FIG. 1 is a longitudinal sectional view showing a first embodiment of a light receiving module according to the present invention. The light receiving module 100 detects a signal light transmitted through the optical fiber 1 and a cylindrical fiber holder 2 holding an end 1a of the optical fiber 1 at the center, which is an optical transmission line of the wavelength division multiplexing optical communication system. PD3 which is a light receiving element
And a columnar refractive index distribution self-converging lens (hereinafter simply referred to as a lens) that focuses the signal light 5 emitted from the end face of the optical fiber 1 on the light receiving portion 3a of the PD 3. And a band-pass optical filter (hereinafter referred to as BPF) 7 that transmits only light of a specific wavelength band out of the incident light from the optical fiber 1. The fiber holder 2 and the lens 6 have the same outer diameter, and are inserted densely from both sides into a cylindrical ceramic sleeve 8 having an inner diameter equal to the outer diameter of both, and are integrated with each other in a state where they abut each other. Is held. BPF7
Is provided in the ceramic sleeve 8 while being sandwiched between the fiber holder 2 and the lens 6. The ceramic sleeve 8 is a precision integral molded product that is fired while strictly controlling the dimensional accuracy. The lens length of the lens 6 is 0.25 pitch or more and less than 0.5 pitch so that the signal light 5 diffused and emitted from the end face of the optical fiber 1 can be converged and focused on the light receiving portion 3a of the PD 3. Dimensioned precisely. In the refractive index distribution self-focusing rod lens, when the lens length is 0.25 pitch, the incident light becomes parallel light on the emission surface (6a), and when the lens length is 0.5 pitch, the light beam on the emission surface (6a) is formed. Has the same characteristics as the state on the incident surface (6b), and if it is out of this range, the signal light 5 will be emitted from the exit surface (6a).
This is because the light is emitted as diffused light and cannot be collected on the light receiving portion 3a of the PD 3.

The BPF 7 is formed by directly forming an optical filter film on one of the opposing surfaces of the fiber folder 2 and the lens 6 or by forming an optical filter film on the surface of a fluorinated polyimide film with the fiber folder 2 and the lens 6. 6 is provided. The end faces of the fiber holder 2 and the lens 6 are formed obliquely at the same angle as each other.
This prevents reflected light from returning from the end face of the lens 6 into the optical fiber 1. Further, since the BPF 7 is also disposed obliquely with respect to the optical path, the optical fiber 1
The return of the reflected light to is also prevented. The ceramic sleeve 8 is held by a holding member 9 having a double cylindrical structure fixed to the PD holder 4. The holding member 9 is formed by connecting an inner cylinder 9A having a screw portion 10a on an outer peripheral portion and an outer cylinder 9B having a screw portion 10b on an inner peripheral portion by screwing each other with the screw portions 10a and 10b. The ceramic sleeve 8 is inserted and fixed in the inner cylinder 9A. And outer cylinder 9
The PD holder 4 holding the PD 3 is joined to the end face of B,
It is fixed by YAG laser beam welding. Outer cylinder 9
In B, injection holes 12 for injecting an adhesive 11 for fixing the inner cylinder 9A and the outer cylinder 9B are formed at several places. The PD holder 4 has a through hole 4a at the center thereof.
It comprises a PD holder body 4A holding D3, and a holding plate 4B holding the PD 3 against the PD holder body 4A. The driving circuit 13 of the PD 3 is provided at the center of the holding plate 4B.
And a through-hole 4 for receiving the electrode pin 14
b is provided. PD holder body 4A and holding plate 4B
Are fixed with screws 15.

The light receiving module 100 is assembled by the following procedures. Fiber holder 2 holding optical fiber 1 and lens 6
Are inserted into the ceramic sleeve 8 from both sides so as to sandwich the BPF 7. As a result, the fiber holder 2 and the lens 6 are integrally held by the BPF 7 butted against each other. The ceramic sleeve 8 is inserted into the inner cylinder 9A of the holding member 9 and fixed. At this time, an adhesive 16 is applied to the outer surface of the ceramic sleeve 8 and the ceramic sleeve 8
And the inner cylinder 9A are firmly adhered and fixed. The inner cylinder 9A is screwed into the outer cylinder 9B. The holding member 9 and the PD holder 4 are temporarily assembled, and the position of the inner cylinder 9A with respect to the outer cylinder 9B is adjusted so that the amount of light entering the PD 3 from the optical fiber 1 through the lens 6 is maximized. After adjusting the optical axis of the holding member 9 and the PD holder 4 so that the amount of light received by the PD 3 becomes maximum, the PD of the PD holder 4 is attached to the outer cylinder 9B of the holding member 9 by YAG laser beam welding.
The holder body 4a is fixed. As described above, the cylindrical ceramic sleeve having the inner diameter equal to the outer diameter of both the lens 6 and the fiber holder 2 is used by using the columnar lens 6 having the same outer diameter as the fiber holder 2 holding the optical fiber 1. 8, the optical fiber 1 and the lens 6 can be easily and accurately adjusted in optical axis to maintain the state. Also, a screw portion 10 is provided on the outer peripheral portion.
a ceramic sleeve 8 is inserted and fixed in an inner cylinder 9A of a holding member 9 having a double cylindrical structure formed by screwing an inner cylinder 9A having an inner cylinder 9a and an outer cylinder 9B having a screw portion 10b on the inner periphery. Since the PD holder 4 was fixed to the end face of 9B,
By adjusting the screwing amount of the inner cylinder 9A into the outer cylinder 9B, the relative position between the inner cylinder 9A and the outer cylinder 9B is adjusted,
The distance between the lens 6 and the PD 3 can be easily adjusted. Further, since the BPF 7 is provided so as to be sandwiched between the fiber holder 2 and the lens 6, the BP for the optical fiber 1 and the lens 6 can be maintained even when the ambient temperature changes.
Since the position and angle of F7 do not change, BPF7
Is kept constant. Therefore, an optical signal in a specific wavelength band can be always detected by the PD 3 irrespective of a change in ambient temperature.

[Second Embodiment] FIG. 2 is a longitudinal sectional view showing a light receiving module according to a second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals as in FIG. 1, and description thereof is omitted. In the light receiving module 200 of this embodiment, the BPF 7 is
3 and is held by a movable member 17 whose angle with respect to the optical axis of the lens 6 can be adjusted. Therefore, since the fiber holder 2 and the lens 6 are directly joined, an antireflection film is formed on the joint surface of both. Also, since the movable member 17 needs to be accommodated, the PD holder body 4
A 'is larger than that of the first embodiment. The movable member 17 is formed integrally with a holding frame portion 17a holding the BPF 7 and a support portion 17b fixed to a rotating shaft 18 provided radially through the side wall of the PD holder main body 4A. A rotating lever (not shown) is provided at one end or both ends of the rotating shaft 18. By rotating the rotating lever, the movable member 17 is rotated in the direction of arrow A in the figure, and The angle can be adjusted. The BPF 7 is formed by forming a filter film 7b made of a dielectric multilayer film on the surface of a fluorinated polyimide film 7a. The filter film 7b is formed by an ion beam assisted vapor deposition method or an ion plating vapor deposition method.

The light receiving module 200 is assembled by the following procedures. Fiber holder 2 holding optical fiber 1 and lens 6
Are inserted into the ceramic sleeve 8 from both sides.
As a result, the fiber holder 2 and the lens 6 are integrally held in such a manner that they abut each other. The ceramic sleeve 8 is inserted into the inner cylinder 9A of the holding member 9 and fixed. At this time, an adhesive 16 is applied to the outer surface of the ceramic sleeve 8 and the ceramic sleeve 8
And the inner cylinder 9A are firmly adhered and fixed. The inner cylinder 9A is screwed into the outer cylinder 9B. The movable member 17 holding the BPF 7 is attached to the PD holder 4 '. The holding member 9 and the PD holder 4 'are temporarily assembled, and the position of the inner cylinder 9A with respect to the outer cylinder 9B is adjusted so that the amount of light entering the PD 3 from the optical fiber 1 through the lens 6 is maximized. After adjusting the optical axis of the holding member 9 and the PD holder 4 'so that the amount of light received by the PD 3 becomes maximum, the PD holder main body 4A' of the PD holder 4 'is attached to the outer cylinder 9B of the holding member 9 by YAG laser beam welding. Fix it. Light is introduced into the optical fiber 1 and the angle of the movable member 17 is adjusted while monitoring the output of the PD 3 with a spectrum analyzer so that the band of the transmission wavelength of the BPF 7 is adjusted to a predetermined band. According to this embodiment, the BPF
7 is disposed between the lens 6 and the PD 3 and is held by the movable member 17 whose angle can be adjusted with respect to the optical axis of the lens 6. Can be easily adjusted to the desired wavelength. Further, even after the assembly, the angle of the BPF 7 can be corrected by operating the rotating lever. The transmission wavelength of the filter film 7b is the longest wavelength side at the time of normal incidence, and the transmission band can be shifted to the short wavelength side by tilting the incident light. The transmission wavelength of about 3 nm can be adjusted by changing the angle by 6 degrees.

[Third Embodiment] FIG. 3 is a longitudinal sectional view showing a third embodiment of the light receiving module according to the present invention. The same components as those in the first or second embodiment are denoted by the same reference numerals as those in FIGS. 1 and 2, and description thereof is omitted. In the light receiving module 300 of this embodiment, a BPF 7 ′ having a characteristic of changing the wavelength of transmitted light depending on the incident position of light is disposed between the lens 6 and the PD 3, and obliquely intersects the optical axis of the lens 6. The movable member 17 ′ is position-adjustable in the direction (arrow B direction in the figure). The movable member 17 ′ includes a holding frame portion 17 a holding the BPF 7 ′ and a screw 1 on a side wall of the PD holder main body 4 A.
The support part 17b 'fixed at 9 is integrally formed.
The screw 19 is inserted into the elongated hole 20 of the support portion 17b '. By loosening the screw 19, the position of the movable member 17' can be adjusted by sliding the movable member 17 'within the allowable range of the elongated hole 20,
The screw 19 can be fixed at that position by tightening. The BPF 7 'is formed by forming a filter film 7b' made of a dielectric multilayer film having a characteristic that the wavelength of transmitted light changes according to the incident position (passing position) of light on the surface of the fluorinated polyimide film 7a. Filter film 7b '
Is formed by an ion beam assisted vapor deposition method or an ion plating vapor deposition method. During the vapor deposition, the film thickness is closer to the vapor deposition source by holding the fluorinated polyimide film at an angle to the vapor deposition source. Are made thicker and thinner as the distance increases, so as to have characteristics as shown in FIG. The horizontal axis of the graph shown in FIG. 4 is the length direction of the BPF 7 ', and the vertical axis is the center wavelength of the transmitted light. As can be seen from the characteristic diagram, the BPF 7 'has a characteristic that the center wavelength of the passing light changes linearly as the incident position of the light changes in the length direction of the BPF 7'. In the illustrated example, the BPF
The center wavelength of the transmitted light at the center position (0 mm) in the length direction of 7 ′ is 1550 nm, and ± 1 mm when shifted from that position by ± 2.5 mm.
The center wavelength of the transmitted light changes by 1 nm to 1551 nm and 15
It becomes 49 nm.

The light receiving module 300 is assembled by the following steps (1) to (4). Fiber holder 2 holding optical fiber 1 and lens 6
Are inserted into the ceramic sleeve 8 from both sides.
As a result, the fiber holder 2 and the lens 6 are integrally held in such a manner that they abut each other. The ceramic sleeve 8 is inserted into the inner cylinder 9A of the holding member 9 and fixed. At this time, an adhesive 16 is applied to the outer surface of the ceramic sleeve 8 and the ceramic sleeve 8
And the inner cylinder 9A are firmly adhered and fixed. Inner cylinder 9A to outer cylinder 9
Screw into B. The movable member 17 'holding the BPF 7' is attached to the PD holder 4 '. The holding member 9 and the PD holder 4 'are temporarily assembled, and the position of the inner cylinder 9A with respect to the outer cylinder 9B is adjusted so that the amount of light entering the PD 3 from the optical fiber 1 through the lens 6 is maximized. The optical axis of the holding member 9 and the PD holder 4 'is adjusted so that the amount of light received by the PD 3 is maximized, and the position of the movable member 17' is adjusted with respect to the optical axis so that the band of the transmission wavelength of the BPF 7 'is reduced. After adjusting to a predetermined band, the PD holder main body 4A 'of the PD holder 4' is fixed to the outer cylinder 9B of the holding member 9 by YAG laser beam welding. According to this embodiment, the BPF 7 ′ is disposed between the lens 6 and the PD 3, and is held by the movable member 17 ′ whose position can be adjusted in a direction intersecting the optical axis of the lens 6, so that the movable member 17 By adjusting the position of 'BPF7'
Can easily be adjusted to a desired wavelength. Note that the present invention is not limited to the embodiment described above. For example, in the first to third embodiments, instead of the ceramic sleeve 8 of the integrally molded product, a ceramic sleeve divided into a half structure may be used. Further, in the first and second embodiments, instead of forming an antireflection film on the joint surface between the fiber holder 2 and the lens 6, the joint surface between the two may be fixed with an adhesive. Further, in the third embodiment, the movable member 1
If the position of 7 ′ can be adjusted from the outside of the PD holder 4 ′, the transmission of the BPF 7 ′ can be performed even after the light receiving module 300 is assembled, that is, after the holding member 9 and the PD holder 4 ′ are welded by the YAG laser beam. The angle of the movable member 17 'can be adjusted so that the wavelength band becomes a predetermined band.

[0013]

As described above, the present invention has the following excellent effects. According to the first aspect of the present invention, a cylindrical ceramic having an inner diameter equal to the outer diameter of both the lens and the fiber holder is used by using a cylindrical lens having the same outer diameter as the fiber holder holding the optical fiber. By inserting the optical fiber and the lens into the sleeve and integrating them, the optical axis of the optical fiber and the lens can be adjusted easily and accurately, and the state can be maintained. According to the second aspect of the invention, in addition to the effect of the first aspect, a double cylinder formed by screwing together an inner cylinder having a screw portion on an outer peripheral portion and an outer cylinder having a screw portion on an inner peripheral portion. The ceramic sleeve is inserted and fixed in the inner cylinder of the cylindrical holding member, and the light receiving element holder is fixed to the end of the outer cylinder. By adjusting the relative position between the inner cylinder and the outer cylinder, the lens and the light receiving element are adjusted. The distance between them can be easily adjusted. According to the third aspect of the invention, in addition to the effects of the first and second aspects, the optical filter is provided so as to be sandwiched between the fiber holder and the lens, so that the optical fiber can be changed due to a change in ambient temperature or the like. Also, the position and angle of the optical filter with respect to the lens are prevented from changing, and the light receiving element can always detect an optical signal in a specific wavelength band. According to the fourth aspect of the present invention, in addition to the effects of the first and second aspects, the optical filter is disposed between the lens and the light receiving element, and the movable member can be adjusted in angle with respect to the optical axis of the lens. By holding, the transmission wavelength of the optical filter can be easily adjusted to a desired wavelength by adjusting the angle of the movable member. According to the fifth aspect of the invention, in addition to the effects of the first and second aspects, an optical filter having a characteristic that the wavelength of transmitted light changes depending on the incident position of light is disposed between the lens and the light receiving element. Then, by holding the movable member whose position can be adjusted in a direction intersecting the optical axis of the lens, the transmission wavelength of the optical filter can be easily adjusted to a desired wavelength by adjusting the position of the movable member. it can.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of a light receiving module according to the present invention.

FIG. 2 is a longitudinal sectional view showing a second embodiment of the light receiving module according to the present invention.

FIG. 3 is a longitudinal sectional view showing a third embodiment of the light receiving module according to the present invention.

FIG. 4 is a characteristic diagram showing a graph of a relationship between a light incident position (passing position) to the bandpass optical filter in FIG. 3 and a passing center wavelength.

FIG. 5 is a longitudinal sectional view illustrating the structure of a conventional light receiving module used in a wavelength division multiplexing optical communication system.

[Explanation of symbols]

 1: Optical fiber 1a: End portion 2: Fiber holder 3: PD (light receiving element) 3a: Light receiving section 4: PD holder (light receiving element holder) 5: Signal light 6: Refractive index distribution self-converging lens 7, 7 ': Band Pass light filter 7b, 7b ': filter film 8: ceramic sleeve 9: holding member 9A: inner tube 9B: outer tube 10a, 10b: screw portion 17, 17': movable member 17a: holding frame portion 17b, 17b ': support Part 18: Rotating shaft 19: Screw 20: Slot 100, 200, 300: Light receiving module

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference)

Claims (5)

[Claims] 1. A cylindrical fiber holder holding an end of an optical fiber constituting an optical transmission line, a light receiving element holder holding a light receiving element for detecting a signal light transmitted through the optical fiber, and the light A lens that focuses the signal light emitted from the end face of the fiber on a light receiving portion of the light receiving element,
In a light receiving module including an optical filter that transmits only light of a specific wavelength out of signal light from the optical fiber, a cylindrical lens having the same outer diameter as the fiber holder is used as the lens, and the lens and the fiber holder are used. A light-receiving module, wherein the light-receiving module is inserted into a cylindrical ceramic sleeve having an inner diameter equal to the outer diameter of the both to integrate them. 2. A holding member having a double cylindrical structure in which an inner cylinder having a screw portion on an outer peripheral portion and an outer cylinder having a thread portion on an inner peripheral portion are screwed together, and the ceramic sleeve is provided on the inner cylinder. 2. A light receiving element holder is fixed to an end of the outer cylinder while inserting and fixing the light receiving element holder.
The light receiving module as described. 3. The light-receiving module according to claim 1, wherein the optical filter is provided in a state sandwiched between the fiber holder and the lens. 4. An optical filter having a characteristic that a wavelength of transmitted light changes according to an incident angle of light as the optical filter, and the optical filter is disposed between the lens and the light receiving element. The light receiving module according to claim 1, wherein the light receiving module is held by a movable member that can adjust an angle with respect to the optical axis. 5. An optical filter having a characteristic that a wavelength of transmitted light changes according to a light incident position as the optical filter, and the optical filter is disposed between the lens and the light receiving element, and the optical filter is The light receiving module according to claim 1, wherein the light receiving module is held by a movable member whose position can be adjusted in a direction intersecting the optical axis.