Optical passive component for optical transmission and method for manufacturing optical passive component for optical transmission

Abstract

An optical passive component 1 for optical transmission is provided with an optical circuit to / from which an optical signal is input and output, the optical passive component 1 comprising a housing 2, an optical element d disposed inside the housing, and a plurality of terminals 10 for inputting / outputting an optical signal to / from the housing, the plurality of terminals including n first-type terminals 10a connected to an external device and second-type terminals 10b not connected to an external device, where n ≥ 2, the optical passive component 1 having a bypass optical path in which two second-type terminals as a pair are connected by an optical fiber 22 outside the housing, and the optical circuit being constituted from: an in-housing circuit part in which two first-type terminals spatially coupled to each other at both ends of one optical path (31-34) are used as input / output ends for an optical signal, the number of optical paths being m, where m ≥ n, and a detour optical path not being included; and a bypass circuit part including the bypass optical path in the middle of the optical path 34.

Description

Optical passive component for optical transmission and method for manufacturing optical passive component for optical transmission

[0001] The present invention relates to an optical passive component for optical transmission and a method for manufacturing the optical passive component for optical transmission.

[0002] Optical circuits, through which optical signals are input and output, are configured with optical elements arranged along an optical path from an input terminal where the optical signal is input to an output terminal where the optical signal is output. One type of optical circuit is called a free-space type. In a free-space type optical circuit, optical transmission between the input terminal and optical elements, between the optical elements and the output terminal, and between optical elements are performed in free space (free space) without using optical waveguides or optical fibers. Optical transmission components equipped with such free-space type optical circuits are configured by arranging multiple optical elements with optical functions within a housing. Optical transmission components include active optical components for optical transmission that include an optical circuit with active optical elements such as laser diodes, and passive optical components for optical transmission that include an optical circuit with only passive optical elements such as filters. In the case of passive optical components for optical transmission, an optical signal input into the housing via a terminal (input terminal) such as an optical fiber collimator travels along the optical path of the optical circuit and is emitted from a terminal (output terminal) to the outside of the housing.

[0003] Furthermore, optical passive components for optical transmission equipped with free-space optical circuits are characterized by low transmission loss because they do not use optical fibers for optical transmission in the internal optical circuits. Furthermore, free-space optical passive components for optical transmission can reduce manufacturing costs because they do not require the process of coupling optical elements within a housing with optical fibers. Furthermore, in the case of free-space optical passive components for optical transmission, the size of the light input / output surfaces of the optical elements within the housing theoretically only needs to be the size of the spot diameter of the laser light that forms the optical path, and no space is required for routing optical fibers between the optical elements. Therefore, free-space optical passive components for optical transmission are also suitable for miniaturization. Patent Document 1 listed below describes an optical amplifier and a light receiving device, which are optical transmission components with free-space optical circuits formed within a housing.

[0004] Japanese Patent Application Publication No. 7-335956

[0005] As described above, free-space type optical passive components for optical transmission do not use optical fibers for optical transmission in their internal optical circuits, and therefore most of the loss associated with optical transmission is coupling loss that occurs between the optical circuit and the terminal. Therefore, free-space type optical passive components for optical transmission can reduce the overall loss between the input and output terminals of the optical passive components for optical transmission by reducing the coupling loss between the terminal and the optical circuit.

[0006] However, in a free-space optical passive component for optical transmission in which optical circuits for realizing multiple functions are configured within a single housing, a pair of terminals is required for each function of the optical circuit. That is, for each function of the optical circuit, an optical signal is guided from the outside into the housing using one terminal as an input terminal for the optical signal, propagates along one optical path in the optical circuit, undergoes transmission and reflection by optical elements arranged along the optical path, and is finally coupled to one terminal that serves as an output terminal and output to the outside. Therefore, when multiple functions are realized with a single optical passive component for optical transmission, the optical circuit will have multiple pairs of terminals that serve as an input terminal and an output terminal. In addition, one of a pair of terminals for realizing a certain function may also serve as either an input terminal or an output terminal for another function. For example, in the four-port optical passive component 100 for optical transmission shown in FIG. 1, a total of four optical fiber collimators 10 are attached to two opposing surfaces 3 of a rectangular box-shaped housing 2, with the optical fiber collimators 10 serving as terminals, and a free-space optical circuit is formed within the housing 2 in which multiple optical elements d are arranged.

[0007] Here, the four optical fiber collimators 10 are identified as first to fourth optical fiber collimators (11 to 14), and the first and third optical fiber collimators (11, 13) are attached to one of the two mutually facing surfaces 3, and the second and fourth optical fiber collimators (12, 14) are attached to the other. A total of four optical paths are formed in the optical circuit: a first optical path 31 from the first optical fiber collimator 11 to the second optical fiber collimator 12, a second optical path 32 from the third optical fiber collimator 13 to the second optical fiber collimator 12, a third optical path 33 from the third optical fiber collimator 13 to the fourth optical fiber collimator 14, and a fourth optical path 34 from the fourth optical fiber collimator 14 to the second optical fiber collimator 12.

[0008] The assembly procedure for the optical passive component for optical transmission 100 illustrated in FIG. 1 may include, for example, first arranging the first to fifth filters (F1 to F5) and the first and second mirrors (M1, M2) as the multiple optical elements d included in the optical circuit within the housing 2. Once all of the optical elements d have been arranged within the housing 2, the first and second optical fiber collimators (11, 12) are aligned to form the first optical path 31. Next, the third optical fiber collimator 13, which is paired with the aligned second optical fiber collimator 12 in the second optical path 32, is aligned to form the second optical path 32. Similarly, the fourth optical fiber collimator 14, which is paired with the aligned third optical fiber collimator 13 in the third optical path 33, is aligned. At this point, the first to third optical paths (31 to 33) are formed.

[0009] However, at this point, the aligned second and fourth optical fiber collimators (12, 14) are not necessarily coupled with high precision to form the fourth optical path 34. In such cases, to ultimately achieve low-loss coupling in all optical paths (31-34), it may be necessary to fine-tune the angles of the first and second mirrors (M1, M2) associated with the already-placed fourth optical path 34, or to repeat the alignment process for the aligned second and fourth optical fiber collimators (12, 14) and for other optical fiber collimators (11, 13) coupled to these optical fiber collimators (12, 14) via other optical paths (31-33). It may also be necessary to readjust the positions of the filters (F1-F5) in addition to the mirrors (M1, M2). Of course, because the alignment range of the optical fiber collimator 10 is limited, it is also necessary to position the optical element d with extremely high precision in advance to enable alignment in all optical fiber collimators 10.

[0010] Therefore, it was difficult to reduce the overall loss of conventional free-space type passive optical components for optical transmission. In addition, the complicated alignment process made it difficult to provide passive optical components for optical transmission at low cost due to the high cost of the process.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical passive component for optical transmission that allows easy alignment during manufacture and has extremely low overall loss, and a method for manufacturing such an optical passive component.

[0012] One aspect of the present invention for achieving the above object is an optical passive component for optical transmission having an optical circuit for inputting and outputting optical signals, comprising: a housing; an optical element arranged inside the housing; and a plurality of terminals for inputting and outputting optical signals to and from the housing, wherein the plurality of terminals include n first type terminals connected to an external device and second type terminals not connected to an external device, where n≧2 (n is a natural number), and a detour optical path formed by a pair of the second type terminals being connected by an optical fiber outside the housing, wherein the optical circuit uses two of the first type terminals spatially coupled to each other at both ends of one optical path as input and output terminals for optical signals, the number of optical paths is m (m is a natural number), and the optical circuit is composed of an in-housing circuit section that does not include the detour optical path and a detour circuit section that includes the detour optical path midway through the optical path, where m≧n.

[0013] The circuit section within the housing may be an optical passive component for optical transmission having n-1 pairs of first-type terminals, each pair being both ends of one optical path.

[0014] The optical passive component for optical transmission according to claim 1 may have, as the terminal, a two-core optical fiber collimator incorporating an optical element that constitutes the optical circuit.

[0015] The optical passive component for optical transmission according to claim 1 may also be one having a two-core optical fiber collimator with a built-in optical element as the terminal, the two-core optical fiber collimator serving as both the first type terminal and the second type terminal, the optical element built in the two-core optical fiber collimator separating light directed from one of two optical fibers connected to the two-core optical fiber collimator toward the inside of the housing into light directed toward the inside of the housing and light incident on the other optical fiber, and the detour optical path being formed by the other optical fiber.

[0016] At least one of the terminals may be attached to the housing via an alignment mechanism.

[0017] The optical passive component for optical transmission may also have a second housing that houses the housing and the detour optical path, the detour optical path being housed within the second housing, and an optical fiber connected to an external device outside the second housing being guided to the outside of the second housing.

[0018] The scope of the present invention also includes a method for manufacturing an optical passive component for optical transmission, which includes: an optical element arranging step of arranging and fixing an optical element in a housing, in one detour optical path, where a second-type terminal that guides light from inside the housing to outside the housing is a first second-type terminal and a second-type terminal that guides light from outside the housing to inside the housing is a second second-type terminal; a terminal alignment and attachment step of aligning and attaching a plurality of terminals to the housing; and a detour optical path forming step of connecting the first second-type terminal and the second second-type terminal with an optical fiber to form the detour optical path.

[0019] According to the present invention, an optical passive component for optical transmission that allows easy alignment during manufacturing and has extremely low overall loss, and a method for manufacturing such an optical passive component, are provided. Other advantages will be made clear in the following description.

[0020] FIG. 1 is a diagram showing the configuration of an optical passive component for optical transmission according to a comparative example. FIG. 2 is a diagram showing the appearance of an optical passive component for optical transmission according to a first embodiment. FIG. 3 is a diagram showing the configuration of an optical passive component for optical transmission according to the first embodiment. FIG. 4 is a diagram showing a manufacturing method of an optical passive component for optical transmission according to the first embodiment. FIG. 5 is a diagram showing an alignment mechanism. FIG. 6 is a diagram showing an optical passive component for optical transmission according to the first embodiment housed in a second housing. FIG. 7 is a diagram showing the configuration of an optical passive component for optical transmission according to a second embodiment. FIG. 8 is a diagram showing the configuration of a two-core optical fiber collimator provided in the optical passive component for optical transmission according to the second embodiment. FIG. 9 is a diagram showing an optical passive component for optical transmission according to another embodiment, showing the mounting position on the housing of a second type optical fiber collimator provided in the optical passive component for optical transmission. FIG. 10 is a diagram showing an optical passive component for optical transmission according to another embodiment, showing the configuration of an optical circuit when all optical fiber collimators are arranged on the mounting surface of the housing without using mirrors. FIG. 11 is a diagram showing a state in which two optical passive components for optical transmission according to the first embodiment are connected. FIG. 10 is a diagram showing the configuration of an optical passive component for optical transmission according to another embodiment, and is a diagram showing the configuration of an optical passive component for optical transmission having two first-class optical fiber collimators.

[0021] Cross-Reference to Related Applications This application claims priority to Japanese Patent Application No. 2023-187072, filed October 31, 2023, and incorporates the contents thereof by reference. An embodiment of the present invention will be described below with reference to the accompanying drawings. Note that in the drawings used in the following description, identical or similar parts may be designated by the same reference numerals, and redundant description may be omitted. A part designated by a reference numeral in one drawing may not be designated by the reference numeral in other drawings if unnecessary. ===First Embodiment==== <Optical Circuit Configuration> Figure 2 is a diagram showing the appearance of an optical passive component for optical transmission 1 according to an embodiment of the present invention. The optical passive component for optical transmission 1 shown in Figure 2 has three optical fiber collimators (10a, 10b) attached as terminals to each of two parallel, facing surfaces (hereinafter sometimes referred to as "mounting surfaces 3") of a rectangular box-shaped housing 2. An optical fiber 21 or an optical fiber 22 (sometimes collectively referred to as optical fiber 20) is connected to these optical fiber collimators (10a, 10b). Of the six optical fiber collimators (10a, 10b), the optical fiber 21 connected to four of the optical fiber collimators (11-14) serves as an input or output terminal for an optical signal to an external device. However, two optical fiber collimators (15, 16) are not connected to an external device, but are connected to each other in a loop shape by a single optical fiber 22. A plurality of optical elements are arranged within the housing 2, and the optical circuit formed by these optical elements is of the free space type.

[0022] FIG. 3 shows an optical circuit of an optical passive component for optical transmission 1 according to an embodiment. FIG. 3 shows optical elements d arranged in a housing 2 and optical paths (31-34) of the optical circuit configured by these optical elements d. The optical circuit of the optical passive component for optical transmission 1 according to the embodiment shown in FIG. 3 has substantially the same function as the optical passive component for optical transmission 1 shown in FIG. 1 (hereinafter, sometimes referred to as "comparison example 100" or "optical passive component for optical transmission 100 according to a comparison example"). That is, the optical circuit has a first optical path 31 through which an optical signal propagates along a path that spatially couples first and second optical fiber collimators (11, 12), a second optical path 32 that spatially couples second and third optical fiber collimators (12, 13), a third optical path 33 that spatially couples third and fourth optical fiber collimators (13, 14), and a fourth optical path 34 that spatially couples fourth and second optical fiber collimators (14, 12). The optical element d includes first to fifth filters (F1 to F5) and first and second mirrors (M1, M2).

[0023] In the optical circuit of the optical passive component 1 for optical transmission according to the embodiment, the first to fifth filters (F1 to F5) are, for example, wavelength-selective filters that transmit light in a predetermined wavelength band and reflect light in other wavelength bands. Examples of wavelength-selective filters include interference filters in which a dielectric multilayer film is stacked on a transparent substrate. The first filter F1 transmits light in the wavelength band λ1 (i.e., light in a predetermined bandwidth centered on the peak wavelength λ1). The second and third filters (F2, F3) transmit light in the wavelength band λ2 (light in a predetermined bandwidth centered on the peak wavelength λ2). The fourth filter F4 transmits light in the wavelength band λ4 (light in a predetermined bandwidth centered on the peak wavelength λ4). The fifth filter F5 transmits light in the wavelength bands λ1 and λ3 (light in a predetermined bandwidth centered on the peak wavelength λ1 and light in a predetermined bandwidth centered on the peak wavelength λ3).

[0024] The first optical fiber collimator 11 is an optical port (hereinafter sometimes referred to as an "input port") for inputting an optical signal in the wavelength band λ1 transmitted from an external device via the optical fiber 20 into the first optical path 31 of the optical circuit. The second optical fiber collimator 12 is an optical port (hereinafter sometimes referred to as an "output port") for outputting an optical signal obtained by multiplexing the optical signal in the wavelength band λ1 propagated through the first optical path 31, the optical signal in the wavelength band λ3 propagated through the second optical path 32, and the optical signal in the wavelength band λ4 propagated through the fourth optical path 34. The third optical fiber collimator 13 is an input port for the second optical path 32 and the third optical path 33, and inputs an optical signal obtained by multiplexing the optical signal in the wavelength band λ2 and the optical signal in the wavelength band λ3 into the optical circuit. The fourth optical fiber collimator 14 is an output port for the second optical path 31 through which the optical signal in the wavelength band λ2 propagates, and is also an input port for inputting the optical signal in the wavelength band λ4 into the fourth optical path 34. In FIG. 3, light in wavelength band λ1 is indicated by a thick solid line, and light in wavelength band λ2 is indicated by a thin solid line. Light in wavelength band λ3 is indicated by a dashed line, and light in wavelength band λ4 is indicated by a dotted line. Thus, the optical passive component for optical transmission 1 according to the comparative example 100 and the example have the same combination of input and output ports for each of the optical paths 31 to 34 in the optical circuit. If the filters F1 to F5 are the same, the optical passive component for optical transmission 1 according to the example will have substantially the same function. However, the optical passive component for optical transmission 1 according to the example has a different path for the fourth optical path 34 than the optical passive component for optical transmission 1 according to the comparative example 100.

[0025] Specifically, the optical passive component for optical transmission 1 according to the embodiment includes an optical fiber collimator (hereinafter referred to as a "first-type optical fiber collimator 10a") that is connected to an external device and is involved in the input and output of optical signals, as well as an optical fiber collimator (hereinafter sometimes referred to as a "second-type optical fiber collimator 10b") that is not connected to an external device in order to form a fourth optical path 34.

[0026] The second type optical fiber collimators 10b are configured in pairs, and one pair of second type optical fiber collimators (15, 16) is connected by an optical fiber 22 that passes outside the housing 2. In the following, in the optical circuit, the path of the optical signal formed by the optical fiber 22 outside the housing 2 and the second type optical fiber collimators 10b connected to both ends of the optical fiber 22 will be referred to as a detour optical path.

[0027] The optical circuit of the optical passive component for optical transmission 1 according to the embodiment shown in Figure 3 includes four first-class optical fiber collimators 10a (hereinafter sometimes referred to as "first to fourth first-class optical fiber collimators 11 to 14") and two second-class optical fiber collimators 10b (15, 16). The optical circuit is composed of a circuit portion (hereinafter sometimes referred to as "in-housing circuit portion") that includes first to third optical paths (31 to 33) in which pairs of first-class optical fiber collimators 10a are spatially coupled to each other without passing through a detour optical path, and optical elements (F1 to F4) that are interposed along these optical paths (31 to 33), and a circuit portion (hereinafter sometimes referred to as "detour circuit portion") that includes a fourth optical path 34 in which pairs of first-class optical fiber collimators 10a are spatially coupled to each other via a detour optical path, and optical elements (F3, F4, M1, M2, F5) that are interposed along this optical path 34. That is, in the optical circuit provided in the optical passive component for optical transmission 1, the circuit section within the housing is a free-space type optical circuit composed only of optical paths (31 to 33) formed within the housing 2, and the detour circuit section is an optical circuit in which a detour optical path via the optical fiber 22 is added to the free-space type optical circuit. Note that the routes of the first to third optical paths (31 to 33) in the circuit section within the housing are the same as those in the comparative example 100.

[0028] On the other hand, in the fourth optical path 34 in the embodiment, first, the light of the wavelength band λ4 that enters the housing 2 from the fourth type 1 optical fiber collimator 14 travels backward along the third optical path 33 is reflected by the filter F3 and split, and at the end of the split, it is spatially coupled with one 15 of the two type 2 optical fiber collimators 10b that constitute the detour optical path, and is guided to the outside of the housing 2. Specifically, the light that is reflected and split by the filter F3 is reflected by the mirror M1 located at the end of the split in the direction of the mounting surface 3 on the right side of the paper in Figure 3, and the reflected light is coupled with one of the pair of type 2 optical fiber collimators 15, and is guided to the outside of the housing 2 by the optical fiber 22 that constitutes the detour optical path. The optical signal then enters the housing 2 again via the other of the pair of type-2 optical fiber collimators 16, is reflected downward in the plane of the drawing by mirror M2, and is then reflected to the right in the plane of the drawing by filter F5 interposed on the first optical path 31 of the circuit section within the housing, where it merges with the first optical path 31 and is coupled to the second type-1 optical fiber collimator 12. <Manufacturing Procedure for an Optical Passive Component for Optical Transmission> Next, a manufacturing method for an optical passive component for optical transmission 1 according to the embodiment will be described. An example of the manufacturing procedure for the optical passive component for optical transmission 1 is shown in (s1) to (s6) of Figure 4. First, an optical element d is placed and fixed in the housing 2. Six optical fiber collimators (11 to 16) are attached to the mounting surface 3 without being completely fixed (s1). That is, the optical fiber collimators (11 to 16) are attached so as to be alignable. Type-2 optical fiber collimators (15, 16) are connected to both ends of the optical fiber 22 constituting the bypass optical path, respectively.

[0029] Next, the first to third optical paths (31 to 33) constituting the circuit section inside the housing are formed in this order. Specifically, to form the first optical path 31, the mounting positions and mounting angles of the first and second type 1 optical fiber collimators (11, 12) on the mounting surface 3 are adjusted, and when the coupling loss is minimized, the first and second type 1 optical fiber collimators (11, 12) are fixed by adhesive, welding, or the like (s2). As is well known, the alignment work for the optical fiber collimator 10 is performed by irradiating a light beam from one of a pair of optical fiber collimators 10 spatially coupled at both ends of the optical path and measuring the intensity of the light beam output from the other optical fiber collimator 10. Then, the intensity of the output light beam is maximized.

[0030] Similarly, to form the second optical path 32, the third type 1 optical fiber collimator 13, which is spatially coupled to the aligned second type 1 optical fiber collimator 12 via the second optical path 32, is aligned and fixed (s3). The fourth type 1 optical fiber collimator 14, which is spatially coupled to the third type 1 optical fiber collimator 13 via the third optical path 33, is also aligned and fixed in the same manner (s4).

[0031] Next, a fourth optical path 34 constituting the detour circuit section is formed. Specifically, of the two type-2 optical fiber collimators (15, 16), if the type-2 optical fiber collimator 15 that guides an optical signal from inside the housing 2 to outside the housing 2 is designated as the first type-2 optical fiber collimator 15 and the other type-2 optical fiber collimator 16 connected to this type-2 optical fiber collimator 15 via an optical fiber 22 is designated as the second type-2 optical fiber collimator 16, the first type-2 optical fiber collimator 15 is aligned and fixed so that the coupling loss between the fourth type-1 optical fiber collimator 14 that serves as the input port of the fourth optical path 34 and the first type-2 optical fiber collimator 15 is minimized (s5). As a result, a path 34a from the fourth type-1 optical fiber collimator 14 to the first type-2 optical fiber collimator 15 is formed in the fourth optical path 34. Then, the second type-2 optical fiber collimator 16 is aligned and fixed so that the coupling loss between the second type-1 optical fiber collimator 12, which serves as the output port of the fourth optical path 34, and the second type-2 optical fiber collimator 16 is minimized (s6). In this way, the first to fourth optical paths (31 to 34) are formed, and the optical circuit of the optical passive component for optical transmission 1 is configured.

[0032] In the optical passive component for optical transmission 1 according to the first embodiment, the circuit unit within the housing has three optical paths (31 to 33) for the four first-class optical fiber collimators 10a. That is, the number of optical paths (31 to 33) is one less than the total number of the first-class optical fiber collimators 10a. In such a case, for the optical paths (31 to 33) in the circuit unit within the housing, there is no need to perform realignment on the first-class optical fiber collimators 10a that have already been aligned. However, if an attempt is made to form the same number of optical paths (31 to 34) as or more than the number of the first-class optical fiber collimators 10a in the circuit unit within the housing, as in the comparative example 100, there is a high possibility that realignment will be required on the already-aligned first-class optical fiber collimators 10a. Therefore, when the optical circuit has the same number of optical paths (31 to 34) as or more than the number of first-type optical fiber collimators 10a, by providing a detour optical path, it is possible to eliminate the need to perform re-alignment work on the first-type optical fiber collimators 10a that have already been aligned.

[0033] In other words, if the number m of optical paths to be provided in the optical circuit (m is a natural number) is equal to or greater than the number n of first-type optical fiber collimators 10a (n is a natural number), then the nth or more optical paths may be formed by the detour circuit section. That is, the basic configuration of the embodiment of the present invention, including the optical passive component for optical transmission 1 according to the first embodiment, includes an optical circuit having an internal circuit section within the housing that does not include a detour optical path and a detour circuit section that includes a detour optical path as part of the optical path, where m≧n. Furthermore, the alignment work for forming the fourth optical path 34 and the alignment work for forming the first to third optical paths (31-33) are independent of each other, and one alignment work does not affect the other alignment work. Therefore, there is no need to position the optical element d with extremely high positional accuracy from the beginning. That is, the optical passive component for optical transmission 1 according to the embodiment can reduce the cost of the alignment work as well as the process related to the placement of the optical element d. Furthermore, the optical passive component for optical transmission 1 according to the embodiment has a synergistic effect of low coupling loss between the optical fiber collimators 10 at both ends of each optical path (31-34), and the inherent low transmission loss of free-space optical circuits, resulting in extremely low overall loss. <Alignment Mechanism> The optical fiber collimators (10a, 10b) may be attached to the housing 2 via an alignment mechanism. FIG. 5 shows a schematic configuration of the optical fiber collimators (10a, 10b) attached via an alignment mechanism 50. The alignment mechanism 50 is incorporated into a holder 60 for attaching the optical fiber collimators (10a, 10b) to the housing 2. The alignment mechanism 50 is configured to align and detachably hold the optical fiber collimators (10a, 10b). The holder 60 comprises the alignment mechanism 50 and a base 53, which serves as a member for attaching the holder 60 to the housing 2. By fixing the base 53 to the housing 2, the optical fiber collimators (10a, 10b) are attached to the housing 2 in an alignable manner. Of course, the optical fiber collimators (10a, 10b) may be held in an undetachable manner by the holder 60. In other words, the optical fiber collimators (10a, 10b) themselves may be equipped with the alignment mechanism 50.

[0034] The alignment mechanism 50 is a mechanism that can move relatively to a base 53 fixed to the housing 2 while holding the optical fiber collimators (10a, 10b). The alignment mechanism 50 is configured, for example, similarly to a well-known xy stage, and includes a mechanism 51 for finely moving the optical fiber collimators (10a, 10b) in two directions (x direction and y direction) parallel to the mounting surface 3, and a mechanism 52 for finely adjusting the attitude of the optical fiber collimators (10a, 10b) in a rotation direction θ about an axis of a normal line 5 to the mounting surface 3 and in a direction φ tilted relative to the normal line 5, and configured similarly to a well-known rotation / tilt stage.

[0035] By attaching the optical fiber collimators (10a, 10b) to the housing 2 via the alignment mechanism 50, alignment can be performed, for example, during the manufacture of the optical passive component for optical transmission 1, without using a dedicated jig or the like specifically designed for alignment. If the alignment state of the optical fiber collimators 10 becomes misaligned for some reason after manufacture, they can be easily readjusted. It is not necessary for all of the optical fiber collimators (10a, 10b) to be attached to the housing 2 via the alignment mechanism 50. <Regarding the Housing> In the optical passive component for optical transmission 1 according to the embodiment, the second-type optical fiber collimators (15, 16) are not involved in transmitting and receiving optical signals with external devices. Therefore, the housing 2, the second-type optical fiber collimators (15, 16) constituting the bypass optical path, and the optical fiber 22 connected thereto may be housed in a separate housing, and the optical fiber 21 connected to the first-type optical fiber collimators (11-14) may be guided from that housing (hereinafter sometimes referred to as the "second housing") to the outside of the second housing.

[0036] FIG. 6 shows a schematic structure of an optical passive component for optical transmission 101 including a second housing 102. The housing 2 and the components (15, 16, 22) of the detour optical path are housed within the second housing 102. A hole is formed in the second housing 102 to connect the inside and outside of the housing. An optical fiber 21 connected to a first-class optical fiber collimator (11-14) is guided to the outside through the hole. Instead of directly guiding the optical fiber 21 connected to the first-class optical fiber collimator (11-14) outward through the hole, the optical fiber 21 may be separated into two fibers at the hole. In this case, a female optical connector is attached to the tip of the optical fiber 21 connected to the first-class optical fiber collimator (11-14) and fixed to the hole from the inside of the second housing 102. Another optical fiber 21 with a male optical connector is then connected to the optical connector from the outside of the second housing 102. Furthermore, a plurality of optical passive components for optical transmission 1 may be housed in the second housing 102. In any case, the second housing 102 only needs to be configured to house the housing 2 and the detour optical path, while guiding the optical fiber 21 connected to an external device outside itself to the outside. This prevents bending or damage to the optical fiber 22 of the detour optical path that is not involved in the connection with the external device when handling the optical passive component for optical transmission 101. ===Second Example=== In the optical passive component for optical transmission 1 according to the first example, the first type optical fiber collimator 10a and the second type optical fiber collimator 10b are all configured as individual optical fiber collimators (11 to 16). From here on, however, as an optical passive component for optical transmission according to the second example, an optical passive component for optical transmission will be described in which a two-core optical fiber collimator incorporating an optical element d is used to combine one first type optical fiber collimator 10a and one second type optical fiber collimator 10b.

[0037] Fig. 7 shows a schematic configuration of an optical passive component for optical transmission 201 according to the second embodiment. The function of the optical passive component for optical transmission 201 shown in Fig. 7 is the same as that of the first optical passive component for optical transmission 1, but the fourth type 1 optical fiber collimator 14 and the first type 2 optical fiber collimator 15 are replaced with a two-core optical fiber collimator 210 incorporating the filter F3 in the first embodiment. One 21 of the two optical fibers 20 connected to the two-core optical fiber collimator 210 is connected to an external device, and the other 22 is connected to the second type 2 optical fiber collimator 16.

[0038] Figure 8 shows the schematic structure of a two-core optical fiber collimator 210 incorporating a filter F3. As shown in Figure 8, a ferrule 212 that holds two optical fibers (21, 22) is attached to one end of a hollow cylindrical sleeve 211. The other end of the sleeve 211 is open. Inside the sleeve 211, a filter F3 and a collimating lens 213 are arranged in this order from the opening toward the ferrule 212.

[0039] In the optical passive component for optical transmission 201 according to the second embodiment, the dual-core optical fiber collimator 210 reflects light in the wavelength band λ4 propagating through one optical fiber 21 from an external device by a built-in filter F3, couples the light to the other optical fiber 22, and guides the light to the outside of the housing 2. As a result, the light propagating through the optical fiber 22 is guided into the housing 2 via the second type-2 optical fiber collimator 16, and couples with the second type-1 optical fiber collimator 12, which serves as the output port of the fourth optical path 34. An optical signal in the wavelength band λ2 propagating through the third optical path 33 from the third type-1 optical fiber collimator 13 is coupled to one 21 of the two optical fibers 20 while passing through the built-in filter F3 of the dual-core optical fiber collimator 210.

[0040] In the optical passive component for optical transmission 201 according to the second embodiment, the filter F3, which was disposed inside the housing 2 in the optical passive component for optical transmission 1 according to the first embodiment, is disposed inside the two-core optical fiber collimator 210, and accordingly the filter F4 is relocated between the second second-type optical fiber collimator 16 and the mirror M2 in the fourth optical path 34.

[0041] In this way, in the optical passive component for optical transmission 201 according to the second embodiment, one 15 of the pair of type-2 optical fiber collimators 10b is replaced with a two-core optical fiber collimator 210 that also serves as the type-1 optical fiber collimator 10a. This reduces the number of optical fiber collimators (10a, 10b) compared to the first embodiment, eliminating the need for alignment work for one 15 of the pair of type-2 optical fiber collimators 10b. Furthermore, since one mirror M1 can be omitted along with one type-2 optical fiber collimator 10b, the optical passive component for optical transmission 201 can be provided more inexpensively, and further miniaturization is expected. ===Other Embodiments=== The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit and scope of the present invention. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations. Furthermore, some of the configurations of the above-described embodiments may be added, deleted, or replaced with other configurations.

[0042] For example, in the optical passive component for optical transmission 1 according to the first embodiment, three optical fiber collimators (10a, 10b) are attached to each of the two mounting surfaces 3 of the housing 2, and the first-type optical fiber collimators (11-13, 12-14) and the second-type optical fiber collimators (15-16) are attached facing each other. However, the first and second optical fiber collimators (10a, 10b) may also face each other. Alternatively, the optical fiber collimators (10a, 10b) attached to each of the two mounting surfaces 3 do not have to face each other. For example, when viewed from the direction of the normal 5 of the mounting surfaces 3, the optical fiber collimators (10a, 10b) on the front and back mounting surfaces 3 may be arranged alternately. In any case, the attachment positions of the optical fiber collimators (10a, 10b) can be changed as appropriate depending on the arrangement of the optical elements d of the optical circuit and the paths of the optical paths (31-34).

[0043] Furthermore, in the optical passive component for optical transmission 1 according to the first embodiment, two surfaces of the housing 2 facing each other are used as mounting surfaces 3 for the optical fiber collimators 10. As a result, in the optical passive component for optical transmission 1 according to the first embodiment, all of the optical fiber collimators (11 to 16) protrude only in the direction of the normal 5 to the mounting surfaces 3, thereby reducing the overall installation area of ​​the optical passive component for optical transmission 1. Of course, the mounting surfaces 3 for the optical fiber collimators 10 do not have to be limited to the two surfaces facing each other. For example, in the optical passive component for optical transmission 301 shown in FIG. 9 , the two mirrors (M1, M2) constituting the bypass circuit section are omitted from the optical passive component for optical transmission 1 according to the first embodiment, and second-type optical fiber collimators (15, 16) are attached to the surface 4 of the housing 2 in the traveling direction of the optical signal reflected by the filter F3 on the fourth optical path 34. In this way, by using any surface of the housing 2 as the mounting surface (3, 4) of the optical fiber collimators (10a, 10b), it is possible to omit a part of the optical element d. This makes it possible to further reduce the size of the housing 2 and reduce component costs. Of course, each of the multiple first-class optical fiber collimators 10a may be mounted on an appropriate surface of the housing 2 depending on the situation regarding the installation of the optical passive component for optical transmission 1, such as the relative positional relationship between the external devices connected to each of the multiple first-class optical fiber collimators 10a and the optical passive component for optical transmission 1.

[0044] 10, a first-class optical fiber collimator 10a and a second-class optical fiber collimator 10b may be disposed opposite each other. This allows all of the optical fiber collimators 10 to be attached to the mounting surfaces 3 of the housing 2 that face each other, without using mirrors (M1, M2), while configuring an optical circuit that is substantially the same as the optical passive component for optical transmission 1 according to the first embodiment.

[0045] 10, the optical path 33 in the first embodiment is configured as a detour circuit portion. The alignment process in the manufacturing procedure for this optical passive component for optical transmission 401 is, for example, first aligning the first and second type-1 optical fiber collimators (11, 12) and spatially coupling them, then aligning the third type-1 optical fiber collimator 13 and spatially coupling it with the aligned second type-1 optical fiber collimator 12. Then, to form the optical path 33 that constitutes the detour circuit portion, aligning the first type-2 optical fiber collimator 16 and spatially coupling it with the aligned third type-1 optical fiber collimator 13, and then aligning the second type-2 optical fiber collimator 15 and the fourth type-1 optical fiber collimator 14 and spatially coupling them.

[0046] The manufacturing procedure for the optical passive component for optical transmission 1 according to the first embodiment described above includes a procedure for aligning the first-class optical fiber collimator 10a to form an in-housing circuit section, and then a procedure for aligning the second-class optical fiber collimator 10b to form a detour circuit section. However, this is intended to prevent the optical fiber collimator 10, which has been aligned to form a certain optical path, from being realigned when forming another optical path. Therefore, the optical passive component for optical transmission 1 according to the first embodiment may be manufactured by aligning the first-class optical fiber collimator 10a and the second-class optical fiber collimator 10b in an appropriate order, as in the manufacturing procedure for the optical passive component for optical transmission 401 shown in FIG. 10 above. Of course, the second-class optical fiber collimator 10b may be aligned first.

[0047] In any case, if the number of optical paths is m, where n≧2, and there are n first-type optical fiber collimators 10a, and the optical passive component for optical transmission (1, 301, 401) is m≧n, then, regardless of whether it is a first-type or second-type, appropriate optical fiber collimators 10 are sequentially aligned until the (n-1)th optical path is formed, and when forming the mth or higher optical path, the optical fiber collimators 10 that have never been aligned up to that point are aligned to complete the optical circuit.

[0048] Furthermore, the manufacturing procedure for the above-described optical passive component for optical transmission (1, 301, 401) may be a mode including a step of attaching all the optical fiber collimators 10 to the housing 2 in an alignable manner and a step of subsequently aligning each of the optical fiber collimators 10, or a mode in which each of the optical fiber collimators 10 is attached while being aligned sequentially. In either case, it is sufficient to align and attach the optical fiber collimators 10.

[0049] A plurality of optical passive components for optical transmission (1, 201) according to the first or second embodiment may be connected to each other via an optical fiber 20. FIG. 11 shows an example in which two optical passive components for optical transmission (1a, 1b) are connected to each other. As shown in FIG. 11, two optical passive components for optical transmission (1a, 1b) having a similar external configuration to the optical passive component for optical transmission 1 according to the first embodiment are connected to each other via an optical fiber 23. In the example shown in FIG. 11, the fourth first-class optical fiber collimator 14 in one optical passive component for optical transmission 1a and the second first-class optical fiber collimator 12 in the other optical passive component for optical transmission 1b are connected to each other via the optical fiber 23. The optical circuits of the optical passive components for optical transmission (1a, 1b) connected to each other may be the same or different.

[0050] In this way, by connecting the first-class optical fiber collimators 10 of the two optical passive components for optical transmission (1a, 1b) with the optical fiber 23, it is possible to distribute a large number of optical elements d among multiple housings 2. This makes it possible to construct an optical circuit with more functions. In other words, it is possible to realize a single multifunctional optical passive component for optical transmission having multiple housings 2. Of course, three or more optical passive components for optical transmission 1 may be connected. It is also possible to house multiple interconnected optical passive components for optical transmission 1 in a single second housing 102, and guide only the optical fiber 21 connected to an external device outside the second housing 102.

[0051] In the optical passive component for optical transmission 201 according to the second embodiment, the dual-core optical fiber collimator 210 serves both as the first-type optical fiber collimator 10a (14) and the second-type optical fiber collimator 10b (15). However, the dual-core optical fiber collimator 210 may also serve as two first-type optical fiber collimators 10a. Alternatively, the dual-core optical fiber collimator 210 may also serve as two second-type optical fiber collimators 10b. In this case, the optical passive component for optical transmission 201 can form a bypass circuit section having two or more optical paths. In either case, the use of each dual-core optical fiber collimator 210 incorporating the optical element d can reduce the number of optical elements d in the housing 2 by one, and can also reduce the space required to install one optical fiber collimator 10 in the housing 2. In other words, the use of the dual-core optical fiber collimator 210 incorporating the optical element d can reduce the size of the housing 2, thereby achieving a reduction in the overall size of the optical passive component for optical transmission 201.

[0052] The optical circuits of the optical passive component for optical transmission (1, 201) according to the first or second embodiment are merely examples for facilitating understanding of the present invention, and it goes without saying that the configuration of the optical circuit and the optical element d used in the optical circuit are not limited to those of the above-described embodiments. For example, in the first embodiment, the optical passive component for optical transmission 1 includes wavelength-selective filters (F1 to F5) as the optical elements d and functions as an optical multiplexer / demultiplexer. However, in reality, the characteristics of some wavelength-selective filters (F1 to F3, F5) become unstable (the characteristics vary more) as the inclination with respect to the optical axis increases. Therefore, in order to obtain more stable characteristics, optical elements d such as beam splitters or half mirrors are often placed in the positions of the wavelength-selective filters (F1 to F3, F5), and the wavelength-selective filters (F1 to F3, F5) are placed on the light transmitted or branched by these optical elements d in the same manner as the wavelength-selective filter F4 in FIG. 3 . That is, although the wavelength-selective filters (F1 to F3, F5) are slightly tilted to suppress returning light, they are arranged so that the light incident surface and the incident light are nearly perpendicular to each other. This increases the number of optical elements d that must be arranged in the housing 2, making it difficult to make the housing 2 smaller.

[0053] Therefore, it is conceivable to replace the wavelength-selective filters (F1-F5) with TAP filters, which can obtain stable characteristics even when used at a 45° angle with respect to the optical axis. Furthermore, by using a TAP filter, the propagation directions of the reflected light and transmitted light when light is incident on the optical element d are at a 90° angle with each other. Therefore, by attaching the optical fiber collimator 10 to the mounting surface 3 of the housing 2 and the surface 4 perpendicular thereto, the distance between the two opposing surfaces (3-3, 4-4) in the housing 2 can be shortened. In other words, if Figure 3 etc. is a diagram of the optical passive component for optical transmission (1, 301) viewed from above and below, the housing 2 can be made nearly square when viewed from above, making it possible to make the housing 2 more compact.

[0054] In any case, by appropriately selecting the types of optical elements that make up the optical circuit and by appropriately designing the optical path, it is possible to realize optical passive components for optical transmission with different functions, such as optical attenuators, optical isolators, optical switches, optical multiplexers, and optical demultiplexers, or to implement multiple functions in a single optical passive component for optical transmission.

[0055] The number of optical fiber collimators (10a, 10b) can be changed appropriately depending on the optical circuit configured inside the housing 2. For example, the number of pairs of second-type optical fiber collimators 10b is not limited to one, and in the optical passive component for optical transmission 1 according to the first embodiment, some of the optical paths (31 to 33) configuring the circuit section inside the housing may be replaced with detour optical paths.

[0056] Naturally, the number of the first type optical fiber collimators 10a is not limited to four, and the total number of the optical fiber collimators 10 is not limited to six. The optical circuit only needs to have one or more combinations of input and output ports. In other words, there only needs to be two or more first type optical fiber collimators 10a and one or more pairs of second type optical fiber collimators 10b.

[0057] FIG. 12 illustrates an example of an optical passive component for optical transmission 501 having two first-type optical fiber collimators 10a. The optical circuit included in this optical passive component for optical transmission 501 includes two optical paths (533, 534): one optical path 533, which constitutes the internal circuit section and through which an optical signal in the wavelength band λ2 propagates, and one optical path 534, which constitutes the detour circuit section and through which an optical signal in the wavelength band λ4 propagates. In the optical circuit of the optical passive component for optical transmission 501 shown in FIG. 12, the wavelength bands λ2 and λ4 of light traveling along each optical path (533, 534) are indicated by solid and dotted lines, respectively. Optical elements d having the same functions and operations as those of the optical element d shown in FIG. 3 are denoted by the same reference numerals. Specifically, the second filter F2 and the third filter F3 transmit light in the wavelength band λ2 and reflect light in other wavelength bands. The fourth filter F4 transmits light in the wavelength band λ4 and reflects light in other wavelength bands.

[0058] 12 , a function such as the removal of noise components is considered. For example, when a combined light L1 of light in wavelength band λ2 and light in wavelength band λ4, which contains light in unnecessary wavelength bands as noise components, is input from an external device, the light L1 is demultiplexed into light in wavelength band λ2 and light in wavelength band λ4 by filter F2. Then, the light in each wavelength band (λ2, λ4) passes through filters (F3, F4) arranged along the respective optical paths (533, 534), is combined by filter F3, and is coupled to the other type-1 optical fiber collimator 512. Then, each time the light passes through or is reflected by each filter (F2, F3, F4), noise components are removed from the light. Finally, light L2, which is a combined light of light in wavelength band λ2 and light in wavelength band λ4 with extremely low noise components, is output to the external device. In the optical passive component for optical transmission 501 shown in FIG. 12, one 534 of the two optical paths (533, 534) passes through a detour optical path.

[0059] 12, the combination of first-class optical fiber collimators (511, 512) spatially coupled at both ends of the optical path 533 of the circuit section inside the housing is the same as the combination of first-class optical fiber collimators (511, 512) spatially coupled at both ends of the optical path 534 of the detour circuit section. Of course, the optical elements d and their operations in the optical passive component for optical transmission 501 shown in FIG. 12 are not limited to those described above. In any case, the number of first-class optical fiber collimators 10 and the number of sets of second-class optical fiber collimators 10 can be set appropriately depending on the arrangement of the optical elements d in the housing 2, the configuration of the optical circuit, or the ease of alignment work during manufacturing.

[0060] In the above embodiment, the terminals include first and second type optical fiber collimators (10, 10a, 10b, 11-16, 511, 512), but it is also possible to have a terminal for discarding light that is not involved in input / output to external devices, such as stray light within the housing 2, outside the housing 2.

[0061] In the above-described embodiments, the optical fiber collimators (10, 10a, 10b, 11-16, 511, 512) are used as the terminals of the optical passive components for optical transmission 1, 201, 301, 401, and 501. However, the tip of the optical fiber 20 connected to the optical fiber collimators (10, 10a, 10b, 11-16, 511, and 512) may also be used as the terminal. In this case, the tip of the optical fiber 20 may be a terminal to which a known optical connector is attached, or may be the open end of the optical fiber 20. When the open end of the optical fiber 20 is used as the terminal, one detour optical path is formed by fusing the open ends of the optical fibers 22 connected to the pair of second-type optical fiber collimators 10b, respectively, or by connecting these open ends with another optical fiber 22. In any case, the optical passive components for optical transmission according to the embodiments have a detour optical path connected by the optical fiber 22 outside the housing.

[0062] External devices for the optical passive components for optical transmission according to the embodiments include optical signal transmitters and receivers, other optical transmission components, and optical amplifiers using erbium-doped optical fibers. Note that the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included within the scope of the present invention.

[0063] 1, 101, 201, 301, 401, 501 Optical passive component for optical transmission, 2 Housing, 3 Mounting surface, 5 Normal to mounting surface, 10, 10a, 10b, 11 to 16, 511, 512 Optical fiber collimator, 20, 21, 22, 23 Optical fiber, 31 to 34, 533, 534 Optical path, 50 Alignment mechanism, 102 Second housing, 210 Two-core optical fiber collimator, d Optical element, F1 to F5 Filter, M1, M2 Mirror

Claims

1. An optical passive component for optical transmission having an optical circuit for inputting and outputting optical signals, comprising: a housing; an optical element arranged inside the housing; and a plurality of terminals for inputting and outputting optical signals to and from said housing, wherein said plurality of terminals include n number of first type terminals connected to an external device, where n is greater than or equal to 2, and second type terminals not connected to an external device, and a detour optical path is provided in which a pair of said second type terminals are connected by an optical fiber outside said housing, said optical circuit has two first type terminals spatially coupled to each other at both ends of one optical path as input and output ends of optical signals, the number of optical paths is m, and said optical passive component for optical transmission is composed of an internal housing circuit section that does not include said detour optical path, and a detour circuit section that includes said detour optical path midway through the optical path, wherein m is greater than or equal to n.

2. An optical passive component for optical transmission according to claim 1, wherein said circuit section within said housing has n-1 pairs of first type terminals each forming both ends of a single optical path.

3. An optical passive component for optical transmission according to claim 1, comprising, as said terminal, a two-core optical fiber collimator incorporating an optical element constituting said optical circuit.

4. An optical passive component for optical transmission as claimed in claim 1, comprising as said terminal a two-core optical fiber collimator incorporating an optical element constituting said optical circuit, said two-core optical fiber collimator serving as both said first type terminal and said second type terminal, said optical element incorporated in said two-core optical fiber collimator separating light directed from one of two optical fibers connected to said two-core optical fiber collimator toward the inside of a housing into light directed toward the inside of the housing and light incident on the other optical fiber, and said detour optical path being formed by the other optical fiber.

5. An optical passive component for optical transmission according to claim 1, wherein at least one of said terminals is attached to said housing via an alignment mechanism.

6. An optical passive component for optical transmission according to any one of claims 1 to 5, further comprising a second housing that houses the housing and the bypass optical path, and an optical fiber connected to an external device outside the second housing is guided to the outside of the second housing.

7. A method for manufacturing an optical passive component for optical transmission as described in claim 1, comprising: an optical element arrangement step of arranging and fixing an optical element within a housing, wherein in one detour optical path, a second type terminal that guides light from inside the housing to outside the housing is a first second type terminal, and a second type terminal that guides light from outside the housing to inside the housing is a second second type terminal; a terminal alignment and installation step of aligning and installing a plurality of terminals on the housing; and a detour optical path formation step of connecting the first second type terminal and the second second type terminal with an optical fiber to form the detour optical path.

Images