JP2006171508A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem; it has been difficult to increase an optical coupling efficiency in an optical module which is constituted of 1st and 2nd optical fibers arranged with the end faces opposed to each other, an [MK2] optical device arranged obliquely to the axial center of the first optical fiber between these end faces, and a third optical fiber arranged so that at least a part of light-wave made to exit from the first optical fiber and reflected by the optical device is made to incident thereto, and in which a part of the light-wave passing through the first optical fiber passes through the optical device and is made to incident to the second optical fiber, and the other light-wave is reflected by the optical device and is made incident to the third optical fiber. <P>SOLUTION: Since the mode field diameters or the numerical apertures on the end faces of the first-third optical fibers 11, 12, 13 abutting on each other change compared with the other parts, optical coupling loss can be improved by suppressing the loss to the gap produced by positioning of the optical device 51 and presence of the shapes of the optical fibers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical module used in the field of optical communication and the like.

  In recent years, the Internet has spread to ordinary households, and ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Desk) are always connected, and mega-class high-speed and low-cost services have penetrated. And video chat are becoming popular.

  For such broadbandization, the B-PON (Broadband Passive Optical Network) system that can simultaneously provide high-speed data transmission of 100 Mbps peak time and multi-channel video distribution of up to 500 channels with a single optical fiber has been developed by ITU-T (Telecommunication Standardization sector of International Telecommunication Union). A configuration example of this system is shown in FIG.

  In FIG. 6, a communication station A is connected to a plurality of subscriber stations B via a communication optical fiber C. In the figure, B-ONU is a data home device, WDM is an optical coupler, V-ONU is a video home device, NE-OSS is a data system monitoring and control device, B-OLT is a data home device, and EMDX is an Ether demultiplexer. A device, V-OLT, indicates a video system in-house device.

  The major feature of this system is that it can simultaneously watch multi-channel video distribution by superimposing another optical wavelength in addition to the two wavelengths used for transmission and reception of high-speed data communication due to the new optical wavelength arrangement. is there. Usually, the high-speed data communication wavelength to be transmitted / received is 1.49 μm band (1.48 to 1.50 μm) for downlink and 1.31 μm band (1.26 to 1.36 μm) for uplink, and EDFA (Erbium Doped Fiber Amplifier) ) Is distributed in the 1.55 μm band (1.55 to 1.56 μm), which is an amplification band.

In the B-PON system, since optical signals of three types of wavelengths are transmitted using a single optical fiber C, each subscriber station B, as shown in FIG. Optical multiplexing / demultiplexing module D that demultiplexes and synthesizes light waves from 49μm band and 1.31μm band, optical coupler E that separates and mixes 1.49μm band and 1.31μm band, and the above that propagates in optical fiber An optical coupler / distributor (not shown) that distributes video signals with equal intensity is required.
In the present invention, the optical multiplexing / demultiplexing module D, the optical coupler E, the optical coupler / distributor and the like are collectively referred to as an optical module.

  Conventionally, various types of optical modules used for these have been proposed. Among them, the first and second optical fibers whose end faces are arranged to face each other and the first light between the end faces are proposed. An optical element having an optical transmission / reflection characteristic disposed obliquely with respect to the axis of the fiber and a position on an extension line where the light wave emitted from the first optical fiber is reflected by the optical element And a part of a light wave passing through the first optical fiber passes through the optical element and enters the other optical fiber, and passes through the first optical fiber. Various optical modules have been proposed in which the remaining light wave is reflected by the optical element and branched to the third optical fiber, or a part or all of the light wave flows in the opposite direction. (For example, see Patent Documents 1 to 4)

  FIG. 8 shows an optical module disclosed in Patent Document 1 and the like. 8, 11, 12 and 13 are optical fibers, 21 and 22 are ferrules, 31 and 32 are lenses, 35 and 36 are lens holders for holding the lenses 31 and 32, 51 is an optical element, and 55 is an optical element. An optical element holder 60 for holding the optical element 51 is a housing. End faces of the optical fiber 11 and the optical fiber 12 are held by the housing 60 so as to face each other through the lens 31, the optical element 51, and the lens 32.

  The optical element 51 has wavelength selection characteristics. That is, the light wave having a specific wavelength λ1 is transmitted and the other specific wavelength λ2 is reflected. The lenses 31 and 32 are installed so that the light incident and incident on the end faces of the optical fiber 11 and the optical fiber 12 are optically matched, and optically and efficiently couple both optical fibers. The light of wavelength λ2 reflected by the optical element 51 is optically coupled between the optical fiber 11 and the optical fiber 13 efficiently.

  Therefore, when light waves in the wavelength λ1 band and λ2 band are propagated through the optical fiber 11 and these light waves are emitted from the end portion 11 ′, the light wave in the wavelength λ1 band passes through the optical element 51 and enters the optical fiber 12. The light wave of the wavelength λ2 band is reflected by the optical element 51 and efficiently coupled to the optical fiber 13. Moreover, even if the propagation direction of all or part of these light waves is opposite to the above, it can be optically coupled efficiently.

  FIG. 9 shows another conventional example described in Patent Document 2 and the like. The end faces of the optical fibers 11 to 13 are processed obliquely with respect to the axis of the optical fiber, the end faces of the optical fiber 11 and the optical fiber 12 face each other in the ferrule 23 so as to face each other, and wavelength selection is performed between both end faces. An optical element 51 having characteristics is arranged. Further, the second optical element 51 is disposed on the end face of the optical fiber 13 and is disposed so as to be parallel to the optical fibers 11 and 12 in the ferrule 23. As a result, when light waves in the wavelength λ1 band and λ2 band are propagated through the optical fiber 11 and these light waves are emitted from the end 11 ′, the light wave in the wavelength λ1 band passes through the optical element 51 and enters the optical fiber 12. In addition, the light wave having the wavelength λ2 is reflected by the optical element 51, further reflected again by the second optical element 52, and coupled to the optical fiber 13. Further, even if the propagation directions of all or part of these light waves are opposite to the above, they can be optically coupled in the same manner.

  FIG. 10 shows another conventional example described in Patent Document 3 and the like. The optical fibers 11 to 14 are arranged so that the axes thereof are aligned with each other, one end face is cut obliquely by 45 degrees, and the cut faces are sequentially arranged so as to face the upper side of the drawing. The optical fibers 15 to 17 are arranged so that their end faces are located below the portion cut obliquely by 45 degrees and face the portion cut obliquely by 45 degrees. Furthermore, optical elements 531 to 533 having different transmission / reflection boundaries are arranged at the positions cut obliquely by 45 degrees. That is, the optical elements 531 to 533 are selected and arranged so that the transmission / reflection boundary wavelength is λ1 ′ <λ2 ′ <λ3 ′. For this reason, when light waves in the wavelength λ1 to λ4 band are incident on the optical fiber 11 and propagated to the obliquely cut side, the light waves of the wavelengths λ2 to λ4 are branched into the optical fibers 15 to 17, respectively. The light wave of λ1 passes through the respective optical elements 531 to 533 and is guided to the optical fiber 14.

FIG. 11 shows another conventional example described in Patent Document 3 and the like. The optical fiber 11 and the optical fiber 12 are arranged so that the axes thereof are aligned with each other, one end face is cut off obliquely, and the cut face is arranged so as to face the upper side of the drawing. The optical fiber 13 and the optical fiber 14, and the optical fiber 15 and the optical fiber 16 are also cut and arranged in the same relationship as described above.
In addition, optical elements 531 to 533 having different transmission / reflection boundaries are arranged on the cut surfaces of the optical fibers 11, 13, and 15. That is, the optical elements 531 to 533 are selected and arranged so that the transmission / reflection boundary wavelength is λ1 ′ <λ2 ′ <λ3 ′.

  Further, the optical fiber 13 is cut obliquely so that the end opposite to the cut side is at an angle parallel to or close to the cut surface, and the second optical element 521 is formed on the cut surface. The light wave propagated through the optical fiber 11 is reflected by the optical element 531 disposed on the end face of the optical fiber 11, further reflected by the second optical element 521 and incident on the optical fiber 13. A fiber 13 is arranged. That is, the light wave paths are arranged in a Z-shape.

  Further, the optical fiber 15 is cut obliquely so that the end opposite to the cut side has an angle parallel to or close to the cut surface, and the second optical element 522 is formed on the cut surface. The optical wave that is disposed and propagated through the optical fiber 13 is reflected by the optical element 532 disposed on the end face of the optical fiber 13, further reflected by the second optical element 522, and incident on the optical fiber 15. 15 is arranged. That is, the light wave paths are arranged in a Z-shape.

  Further, the optical fiber 17 is cut obliquely so as to be at an angle parallel to or close to the cut surface of the optical fiber 15, and the second optical element 523 is arranged on the cut surface, and the optical fiber 15 is The optical fiber 17 is arranged at a position where the propagated light wave is reflected by the optical element 533 arranged on the end face of the optical fiber 15 and then reflected by the second optical element 523 and enters the optical fiber 17. That is, the light wave paths are arranged in a Z-shape.

  For this reason, when a light wave having a wavelength λ1 to λ4 is incident on the optical fiber 11 and propagated to the obliquely cut side, the light wave in the λ1 band is transmitted through the optical element 531 and propagates to the optical fiber 12, and the rest Are reflected by the optical element 531 and further reflected by the second optical element 521 and enter the optical fiber 13. Of the light waves incident on the optical fiber 13 in this way, the light wave having the wavelength λ 2 passes through the optical element 532 and enters the optical fiber 14, and the light waves in the other wavelengths λ 3 and λ 4 are reflected by the optical element 532 and further. The light is reflected by the second optical element 522 and enters the optical fiber 15. In this way, among the light waves incident on the optical fiber 15, the light wave having the wavelength λ 3 is transmitted through the optical element 533 and incident on the optical fiber 16, and the light wave in the other wavelength λ 4 band is reflected by the optical element 533 and further reflected by the second light wave. It can be reflected by the optical element 523 and incident on the optical fiber 17.

JP 2002-267876 A Japanese Unexamined Patent Publication No. 01-231008 JP 59-210412 A JP 2002-196192 A

Among the above conventional optical modules, the optical module shown in FIG. 8 is a system in which the optical fibers 11 to 13 are optically coupled by the lens 31, so that the coupling efficiency can be increased, but the lens 31 is disposed. The product cannot be downsized because it requires a large space. In addition, the number of parts is large, and the process is complicated, so that there is a problem that it is expensive.
Further, the optical modules shown in FIGS. 9 to 11 have a characteristic that it can be made compact because no lens is used, but have a characteristic that it is difficult to increase the coupling efficiency. The light emitted from the optical fiber has a divergence angle corresponding to the numerical aperture. For example, when a general SMF is used, a loss of 1 dB occurs when the distance between the fiber end faces is 50 um, and 3 dB when the distance between the fibers is 100 um. Accordingly, when the distance of propagation of the beam by the optical element or the clad layer disposed between the fibers exceeds several tens of um, the coupling efficiency is deteriorated.

  The present invention has been made in view of the above points, and provides a structure that can easily increase the coupling efficiency with a simple configuration. The feature of the present invention is that the end faces are arranged to face each other. And the second optical fiber, an optical element having both transmission and reflection characteristics disposed obliquely with respect to the axis of the first optical fiber between the end faces, and emitted from the first optical fiber. And a third optical fiber disposed so as to receive a light wave reflected by the optical element, and a part of the light wave passing through the first optical fiber passes through the optical element and passes through the second light. Light that enters the fiber and passes through the first optical fiber is reflected by the optical element and branches to the third optical fiber, or a part or all of the light wave propagates in the opposite direction In the module, the first to third optical fibers The end of the bar is characterized in that the mode field diameter or the numerical aperture is changed as compared with other fiber portions.

  Further, another invention of the present application includes first to third optical fibers, and the first optical fiber has an end face formed obliquely, and the first optical fiber is formed with the obliquely formed end face and the second optical fiber. The optical fibers are arranged so as to face each other so that their axial centers coincide with each other, so that a part of the light wave emitted from the first optical fiber receives a light wave reflected by the obliquely formed surface. A third optical fiber is disposed on the first optical fiber, and a part of the light wave passing through the first optical fiber is reflected by the obliquely formed end face and is incident on the third optical fiber. In the optical module in which another light wave passing through the light passes through the obliquely formed end face and enters the second optical fiber, or a part or all of the light wave propagates in the reverse direction, The end of the optical fiber is in the mode compared to the other parts. The Dofield diameter or the numerical aperture is changed.

  Conventionally, as shown in FIG. 12, the first and second optical fibers 11 and 12 whose end faces are arranged to face each other, and the axis between the end faces is inclined with respect to the axis of the first optical fiber. And the light receiving element 19 at a position on the extension line where the light wave emitted from the first optical fiber 11 is reflected by the optical element 51, and further, the first and second light The idea of increasing the mode field diameter at the ends of the fibers 11 and 12 to increase the optical coupling between them is disclosed in Patent Document 4.

  However, such a product is for monitoring the light wave propagating through the optical fiber 11 with the light receiving element 19, and there is no third optical fiber as in the present invention. The light receiving characteristics of PD and optical fiber are completely different, and in the case of PD, light incident within the light receiving diameter of PD is almost received regardless of the shape and size of the beam. On the other hand, in the case of a single mode optical fiber, the mode field diameter of the beam incident on the optical fiber is equal to the mode field diameter of the optical fiber, and the loss is not required unless the beam waist position is close to the beam waist position of the optical fire bar. appear. Even in a multi-fiber, the incident beam must be incident on the core at a numerical aperture of the optical fiber or less.

  Therefore, not only the distance between the optical fibers but also the influence on the beam shape of the medium interface outside the core / cladding / fiber is related. In consideration of the above, the present invention has a configuration in which the third optical fiber having a changed mode field diameter or numerical aperture at the tip portion is disposed. Therefore, the above invention is completely different from the present invention. is there.

  In the above inventions of the present application, the end portions of the first to third optical fibers that are optically coupled to each other have a configuration in which no lens is used by changing the mode field diameter or numerical aperture as compared to other portions. Also has a feature that enables efficient optical coupling.

The present invention can employ the following various embodiments.
The optical element is characterized by having wavelength selectivity.
The optical element has a polarization dependent characteristic.
The optical element is formed of a dielectric multilayer film.
The optical element is composed of a photonic crystal.
The optical element is disposed by being attached to an end face of the first or second optical fiber formed obliquely.
The optical element is deposited and disposed on the end face of the first or second optical fiber formed obliquely.

Various functions can be realized by changing the type of the optical element. Optical element functions include wavelength selectivity, gain control, mirrors, polarizers, and phase shifters. By using these elements, filters such as wavelength multiplexer / demultiplexers, gain controllers, and optical multiplexer / demultiplexers are used. An optical module having functions such as a module, a polarization separation combiner, and a polarization controller can be produced. In the case of an optical module such as a polarization beam splitter / combiner or a polarization controller, the optical fiber is a polarization maintaining fiber according to the configuration. For example, in the polarization beam splitter / combiner, the first optical fiber is a single mode fiber, and the second and third optical fibers are polarization maintaining fibers, so that polarization can be combined or separated. Depending on the purpose of use, the first optical fiber may also be a polarization maintaining fiber.
Examples of the optical element having the above function include a dielectric multilayer film, a photonic crystal, a metal film, a polarizer, glass, a resin, and an optical crystal.

In addition, the optical element can be affixed to or inserted into the end face of the first or second optical fiber formed obliquely, thereby simplifying the configuration and allowing light to propagate outside the fiber. Therefore, it is advantageous for light coupling.
Furthermore, by directly depositing and forming on the end face of the optical fiber formed obliquely, it is possible to reduce the labor of parts and arrangement, and further reduce the space propagation distance, so that the optical coupling can be further reduced. It will be advantageous.

The end face of the third optical fiber is formed obliquely with respect to the axis of the optical fiber, and the second optical element is disposed on this end face.
The second optical element is disposed by being attached to the end face of the optical fiber.
The second optical element is disposed on the end face of the optical fiber by vapor deposition.
The second optical element has the same or similar characteristics as the optical element.

  Similarly to the first optical element, the configuration of the second optical element can be simplified by being attached to or inserted into the end face of the obliquely formed third optical fiber. Furthermore, by directly depositing or forming the end face of the optical fiber formed obliquely, it is possible to reduce the labor of parts and arrangement. If the optical fiber is directly attached to or formed on the end face of the optical fiber, the placement accuracy of each component is improved as compared with the case where the optical element and the optical fiber are separately placed, and the loss due to placement errors can be suppressed. The characteristics of the second optical element may be different from those of the first optical element. For example, the light reflected by the first optical element passes through the optical element 2 as in the optical fibers 15, 16, and 17 in FIG. If it is configured to be coupled to the third optical fiber, it may be 100% transmissive, or reflected by the second optical element and coupled to the third optical fiber as shown in FIG. If it is a structure, a total reflection mirror may be sufficient. Further, optical elements having different characteristics may be used.

  However, depending on the function of the optical element, it is possible to make an optical module with better characteristics by setting the characteristics of the second optical element to be the same as or similar to the characteristics of the first optical element. For example, in the reflection characteristic of a wavelength selection filter of a general dielectric multilayer film, isolation can be achieved only up to about 20 dB by design. However, in the configuration in which the reflected light from the first optical element of the present invention is reflected by the second optical element and coupled to the third optical fiber, the first optical element and the second optical element are the same. If the filter has a transmission characteristic, the characteristic on the reflection side is the characteristic when it passes through the filter twice, so that isolation of 20 dB with one filter can be increased to 40 dB. In addition, when the optical element has polarization dependency like a polarizer, the extinction ratio on the reflection side can be increased in the same manner. In such a configuration, since the first and second optical elements can be manufactured in the same process, there is a merit that cost and time are not required while having high functionality.

  When the optical element is arranged or formed directly on the end face of the optical fiber formed obliquely, the optical module characteristics should be improved by selecting the inclination angle of the fiber end face to an angle that matches the characteristics of the optical element. Can do. For example, a filter formed of a dielectric multilayer film generally exhibits better characteristics when the incident angle is shallower. Therefore, it is better that the polishing angle of the fiber end face is smaller. However, even in the case of a filter formed of the same dielectric multilayer film, for example, in the case of a polarization beam splitter (PBS Polarization Beam Splitter), it has a high polarization separation function near an incident angle of 45 °. ° Near. However, when the cutting angle of the fiber end face is shallow, the shallower the cutting angle, the longer the distance until the light reflected by the first optical element reaches the outer periphery of the optical fiber and the larger the incident angle. Therefore, it becomes a factor that generates a loss. For this reason, the angle of the fiber end face should be determined in consideration of the characteristics of the optical element and the outer shape of the optical fiber.

The end face of the third optical fiber is formed obliquely so as to have a Brewster angle.
An end face formed obliquely of the first optical fiber is set to a Brewster angle.
One of the first to third optical fibers has a polarization plane holding characteristic.
A refractive index adjusting material having a predetermined refractive index is interposed between the end faces of the first to third optical fibers.

In the present invention, even when one or both of the first and second optical elements are not provided, an optical module having several functions can be manufactured by using the optical fiber end face formed obliquely. . For example, the end face of the optical fiber has a reflectance corresponding to the refractive index, the refractive index of the outer medium, and the incident angle of light. If this is utilized, it can be set as a branch mirror.
Here, if the fiber end face has a total reflection angle, it can be used as a total reflection mirror.
Furthermore, by setting the end face angle of the optical fiber to the Brewster angle, a polarization beam combiner / separator can be configured without arranging a polarizer as an optical element.

  As described above, in the present invention, various fiber shapes and optical elements can be selected. However, when the first and second optical elements or the corresponding fiber end faces may have equivalent functions. The first to third optical fiber end face angles are the same, the third optical fiber is parallel to the first and second optical fibers, and the reflected light from the first optical element or the optical fiber end face is second. The arrangement of the optical element or the third optical fiber so that it is reflected by the end face of the third optical fiber and coupled to the third optical fiber has a small number of parts and the shape of the member that holds the fiber is simple and highly accurate. Is appropriate.

The refractive index adjusting material has a refractive index equivalent to that of the clad of the optical fiber. As a result, when the light reflected by the optical element enters and exits the end face of the third optical fiber, the light travels straight on the outer periphery of the first optical fiber or the third optical fiber without bending, and optical coupling is performed. Can be increased.
In the optical module of the present invention, when a refractive index adjusting material having an arbitrary refractive index is arranged between the optical fiber end face and the optical fiber constituting the optical module, it becomes possible to control light transmission / reflection characteristics and refraction. Effective for improving efficiency and optical characteristics.

  For example, when the end face of the first optical fiber is formed obliquely, the light emitted from the first optical fiber is Snell according to the refractive index of the first optical fiber and the medium through which the light emitted from the first optical fiber passes. Has a certain refraction angle θ with the central axis of the optical fiber. If the centers of the first and second optical fibers are arranged on the same line, the position of light incident on the second optical fiber is determined by the distance d between the first optical fiber and the second optical fiber. And x = d · tan θ, the incident position is shifted by x, resulting in loss. Here, when the refractive index of the medium approaches the refractive index of the core of the optical fiber, θ approaches 0 °, and the light travels straight and the incident position is not displaced, so no loss occurs. Even if the physical distance between the fibers is the same, the higher the refractive index, the shorter the optical path length. Therefore, there is an effect that the loss due to the distance between the fibers can be suppressed accordingly.

  Further, when a refractive index adjusting material having the same refractive index as that of the cladding, for example, is disposed between the first and third optical fibers, the incident angle of light passing across the cladding of the first optical fiber and the third optical fiber. Even when is large, the reflectivity can be reduced, and the influence of beam shape conversion due to the presence of the interface on the outer periphery of the fiber can be suppressed.

  Here, the refractive index shown here is the refractive index of the optical fiber or cladding so that the same effect can be obtained even if the refractive index at the fiber end is not the refractive index of the core but the refractive index of the cladding. Even if it is not exactly the same as the rate, it may be selected within a range where the effect can be appropriately obtained.

For example, when using the characteristics of the fiber end face formed obliquely instead of the optical element, the angle and transmission characteristics of the fiber end face can be changed by the refractive index of the refractive index matching material to be arranged. A refractive index adjusting material may be selected so as to match.
The same can be said for the medium in contact with the end face of the third optical fiber and the second optical element.
Here, examples of the refractive index adjusting material include air, glass, resin containing adhesive, matching oil, and other liquids such as water and organic solvents. Use of glass or adhesive is convenient because the fiber can be fixed simultaneously with the adjustment of the refractive index.

The end faces of the first to third optical fibers are held by a ferrule for storing multiple fibers.
The end faces of the first to third optical fibers are held by a multi-core housing groove.
Thereby, the optical fiber can be firmly held and fixed.
By holding the first to third optical fibers with a multi-core ferrule or a multi-core groove body such as a V-groove, the optical fibers can be arranged with high accuracy. Here, when the third optical fiber is arranged parallel to the first and second optical fibers, the same or parallel hole is formed in the case of a multi-core ferrule, and the parallel groove is formed in the case of a multi-core groove. Since the formed member can be used, the optical fiber can be arranged with higher accuracy.

  FIG. 1 illustrates an optical module that functions as a multiplexer / demultiplexer according to an embodiment of the present invention. In FIG. 1, 11, 12, 13, 23, 51 and 52 are respectively the same as in FIG. 9, the first optical fiber, the second optical fiber, the third optical fiber, the ferrule, the optical element, These are two optical elements, and each component operates in the same manner as shown in FIG. However, in the present embodiment, the mode field diameter at each butt end of the optical fibers 11 to 13 is enlarged as compared with the other parts, or the numerical aperture (NA) of the optical fiber is formed to be small. It is completely different from the case of. In this embodiment, the first to third optical fibers are single mode fibers having a mode field diameter of 10 umφ and an outer shape of 125 umφ which are generally used as communication optical fibers, and the mode field diameter is 30 umφ at the end of each optical fiber. The mode field is converted so that

Various methods of changing the mode field diameter at the end of the optical fiber and changing the aperture ratio (NA) of the optical fiber are already known. For example, an optical fiber used for communication is usually made of fused silica as a main component, and a dopant such as germanium is blended in the core 11a to increase the refractive index. When such an optical fiber is heated for a predetermined time at a predetermined temperature with a heater or the like from its side, the dopant diffuses in the direction from the core 11a to the cladding 11b according to the magnitude of the received thermal energy, and the mode field diameter Expands. Then, the optical fiber 11-13 shown to a figure can be manufactured easily by cut | disconnecting the expanded part and processing it diagonally.
Further, as another method, the optical fiber can be formed by shortening its length and enlarging the diameter while heating.

As yet another method, tension is applied to the optical fiber having a multi-clad structure while applying heat from its side, and stress is left in the optical fiber to change the refractive index. There is also a method of fusing mode fibers.
FIG. 2 is a cross-sectional view taken along the line PP and the line QQ in FIG. 1. In the cross-sectional view taken along the line PP, the mode field diameter at the ends of the optical fibers 11 and 13 is enlarged. Things are shown.

  The optical element 51 is disposed between the abutting surfaces of the optical fiber 11 and the optical fiber 12. At this time, the optical element 51 may be attached to or formed on the end surface of one of the optical fibers.

In this embodiment, the optical element 51 is an optical filter having wavelength selectivity, but is composed of a dielectric multilayer film, a photonic crystal, an etalon, or the like.
Even if the optical element 51 has the same configuration, its characteristics vary depending on the incident angle to the optical element. For example, assuming a wavelength selection filter composed of a dielectric multilayer film as the optical element 51, a film having a simple structure and a small PDL separation can be designed as the incident angle is smaller. However, as the incident angle is decreased, the distance between the first optical fiber and the third optical fiber increases, and the loss increases. At an incident angle of 0 °, light cannot be coupled to the third optical fiber. Therefore, it is advantageous for light coupling that the end face angle of the optical fiber is increased in a range where the characteristics of the optical element are good. Here, the end face angles of the first to third optical fibers are set to 6 to 10 °, and the end face angles To be the same.

  FIG. 3 shows the coupling loss with respect to the distance between the beam waists when the mode field diameter at the end of each single mode optical fiber is changed. Here, the distance between the beam waists corresponds to the distance between the cores of the end face of the optical fiber. The refractive index of the medium is calculated as 1.5. From this graph, in the case of a single mode fiber having a mode field diameter of 10 μm, which is commonly used, when the distance between the fiber end faces exceeds 0.1 mm, the loss deteriorates to several dB, whereas the mode field diameter is increased. As shown, the loss with respect to the distance between the beam waists rapidly decreases, and when the mode field diameter is 30 μm or more, the loss can be suppressed to about 0.5 dB or less even when the distance is 0.5 mm.

  The actual coupling loss is not determined only by the distance between the beam waists, but also includes the effect of beam conversion due to the existence of the interface between the core and the cladding, and the beam conversion due to the interface between the cladding and the optical fiber medium. Determined. In general, it is better that the mode field diameter is large and the numerical aperture is small, but it is determined in consideration of the above. Further, in actual manufacturing, there are errors such as the angle accuracy of the optical fiber end and the parallelism of the optical fiber, so if the mode field diameter is made too large, the tolerance for the angle accuracy becomes severe. Therefore, the mode field diameter is determined in consideration of theoretical coupling loss and machining accuracy.

For example, in this embodiment, when the refractive index of the medium around the fiber is the same as the refractive index of the cladding and the angle of the optical fiber end is 8 degrees, the distance between the physical end faces of the first optical fiber and the third optical fiber is The theoretical optical fiber loss is 2 dB at a mode filled diameter of 20 μm, 0.3 dB at 30 μm, and 0.1 dB at 40 μm at a wavelength of 1.55 μm. When the mode field diameter is 40 μm or more, the coupling loss becomes very small. However, considering the end face angle error of the optical fiber, it is appropriate to set the mode field diameter to about 30 μm.
In addition, when a thin fiber having an outer shape of 80 umφ or the like having a small fiber outer shape is used even in the same configuration, the propagation distance of the reflected light can be reduced, so that the loss can be further reduced.

  Here, when the incident angle to the optical element 51 is 8 degrees, the light reflected by the optical element 51 is totally reflected on the outer periphery of the optical fiber and does not efficiently pass outside the optical fiber. If a refractive index matching material is inserted between optical fibers, the transmittance to the outside of the optical fibers can be increased. If a refractive index matching material is inserted between the first and second optical fibers, even if the end face of the optical fiber is oblique, the angle at which the outgoing light deviates from the optical fiber axis is small, and the axial misalignment can be suppressed. Is suppressed.

In the above embodiment, an example of the optical element 51 having wavelength selection characteristics is shown. However, the present invention is not limited to these, and the transmission characteristics and the reflection characteristics may simply have a predetermined ratio. In addition, the transmission characteristics and the reflection characteristics may be wavelength-dependent. By changing the characteristics of the optical element 51 in this way, an optical module that functions as an optical multiplexer / demultiplexer or a gain controller can be produced.
Examples of these optical elements include a dielectric multilayer film, a photonic crystal, a combination of a polarizer and a retardation plate using an optical crystal, and the like.

For example, when performing wavelength selection, the second optical element 52 has characteristics similar to those of the first optical element 51, so that the characteristics can be passed twice. It can be improved or cut well, but it is not limited to this, and it may function as a total reflection mirror whose reflection characteristics are close to 100%, and other optical characteristics depending on the target characteristics An element having
Further, depending on the characteristics of the optical element, the fiber end face angle and the mode field diameter are not limited to the above. The optical fiber may not be a general single mode fiber.

  FIG. 4 shows another embodiment of the present invention. Compared to the embodiment shown in FIG. 1, the optical element 51 has a polarization-dependent characteristic, and a point that a part or all of the optical fiber is composed of a polarization-maintaining fiber having a polarization dependence. Different. Here, the optical fiber 11 is a normal single mode fiber, and the optical fibers 12 and 13 are polarization maintaining fibers. The light emitted from the optical fiber 11 is polarized and separated by the optical element 51 having a polarization separation function, and is coupled to the optical fibers 12 and 13. On the other hand, polarization combining can be performed by making the polarization suitable for the polarization transmission / reflection characteristics of the optical element 51 enter from the optical fibers 12 and 13, so that an optical module having a polarization separation / combination function can be made. Can do. Depending on the purpose of use, the optical fiber 11 may also be a polarization maintaining fiber.

The optical fiber 12 and the optical fiber 13 are respectively rotated along the central axis of the optical fiber, and the extinction is performed by aligning the direction of the main polarization of each polarization maintaining fiber with the polarization axis direction of the optical element 51 functioning as a polarizer. Although the ratio can be easily adjusted, in this embodiment, the polishing direction is set so that the normal line of the obliquely formed fiber end face exists in the same plane as one of the main polarizations of the polarization maintaining fiber. Thus, the extinction ratio can be maximized when the coupling efficiency is maximized.

  In the embodiment shown in FIG. 4, the optical element 51 having polarization dependent characteristics is formed of a dielectric multilayer film. Since the configuration is the same as that of a general PBS, unlike the case shown in FIG. 4, an incident angle of about 45 degrees is appropriate. The angle of inclination of the end face of each optical fiber is set to about 45 °, and the polishing direction is set so that the end face normal of the fiber exists in the same plane as one of the main polarizations of the polarization maintaining fiber as described above. When the optical element 51 is directly formed or arranged on the end face of the optical fiber 11 or 12, the polarization maintaining fiber can be obtained when the coupling efficiency between the fibers is maximized without considering the polarization axis direction of the optical element 51. And the polarization direction of the optical element 51 are also matched, and the extinction ratio can be made high. If the optical element 52 is an optical element similar to the optical element 51, the extinction ratio can be increased, and it can be manufactured in the same process, thereby reducing the number of man-hours and the price. However, a total reflection mirror or the like may be used.

  In this embodiment, since the optical element 51 is arranged so that the incident angle is about 45 °, the light reflected by the optical element 51 is in a direction of about 90 ° with respect to the central axis of the optical fiber. Propagate. For this reason, the propagation distance is smaller than that of the embodiment of FIG. 1 and can be substantially equal to the outer shape of the optical fiber.

In this embodiment, the case where the optical element 51 is formed of a dielectric multilayer film has been described as an example, but it may be formed of a photonic crystal. In that case, the tilt angle of the optical element is not limited to approximately 45 °. Further, the polarization dependence characteristic of the reflectance of a material having a large refractive index difference with a fiber such as silicon and having a good transmittance may be used. In this case, the tilt angle of the optical element is preferably in the vicinity of the Brewster angle. The same applies to the optical element 52.
Further, the configuration of the optical element makes it possible to extract polarized light with a high extinction ratio and extract partially polarized light.

  FIG. 5 shows still another embodiment of the present invention. Compared with the embodiment shown in FIGS. 1 and 4, the optical element 51 is not arranged, but instead the end face of the first optical fiber 11 has an optical Brewster angle. Yes. The types of optical fibers are the same as those described in the embodiment shown in FIG.

This Brewster angle is determined by the core refractive index of the optical fiber 11 and the refractive index of the medium in contact with the end face of the optical fiber 11. The core refractive index of the optical fiber 11 is θ _f and the medium in contact with the end face of the optical fiber 11 is used. When the refractive index is θ _m , the Brewster angle, that is, the end face cutting angle of the optical fiber 11 is θ _b = atan (θ _m / θ _f ).

Since the Brewster angle has a feature that the reflectance of the p-polarized light component is 0, polarized light can be cut out. The Brewster angle varies according to the refractive index of the optical fiber and the refractive index of the medium in contact with the end face as shown in the above formula, and the transmission / reflection characteristics of the s-polarized component can be adjusted by adjusting the refractive index of the medium in contact with the end face of the optical fiber. It is also possible to change. Increasing the refractive index difference between the core and the medium of the optical fiber can increase the reflectivity of the s-polarized component and increase the extinction ratio of the light coupled to the optical fiber 12.

  In this embodiment, the end face angle of each fiber is the same as the end face angle of the optical fiber 11. If the end faces of the optical fibers 11 and 12 are parallel, the transmittance of the s-polarized component can be lowered and the reflectance can be increased by utilizing the effect of interference. In addition, it is more preferable that the end face angle of the optical fiber 13 is set to the total reflection angle or the total reflection mirror is disposed or formed because loss of the s-polarized light component at the end face of the optical fiber 13 does not occur.

In this embodiment, the case where the fiber end face angle is the Brewster angle has been described as an example. However, the fiber end face angle may not be the Brewster angle. For example, if the total reflection angle is used, the total reflection mirror is used. Can be used as If the transmittance and reflectance at a certain angle are used, it can be used as a partial reflection mirror, and if the polarization dependency of the transmittance and reflectance is used, it can also be used as a polarization-dependent mirror. it can.
The type of the optical fiber may not be the same as that of the embodiment of FIG. 4, and may be configured by combining various optical elements and characteristics of the fiber end face as exemplified in this embodiment.

  In addition, each of the above embodiments describes a case where the end face of the optical fiber is polished at an angle with respect to its axis as an example of obliquely polishing the end face of the optical fiber. It may be processed.

  In addition, although all of the embodiments of the present invention are described using only the first to third optical fibers and the optical fibers are arranged in parallel, the present invention is within a range that satisfies the constituent elements of the present invention. However, the present invention can be applied in the same manner to the configurations shown in FIGS. 10 and 11, for example, using other numbers and arrangements of optical fibers.

The principal part longitudinal cross-sectional view which shows one Example of this invention. The principal part cross-sectional view shown in FIG. The characteristic view which shows the coupling loss with respect to the distance between beam waists in various mode field diameters. The principal part longitudinal cross-section clear figure which shows the other Example of this invention. The principal part longitudinal cross-sectional view which shows further another Example of this invention The schematic diagram which shows an example of a general optical communication system. FIG. 7 is a main part schematic diagram of the optical communication system shown in FIG. 6. The principal part longitudinal cross-sectional view which shows an example of the past. The principal part longitudinal cross-sectional view which shows the other example of the past. The principal part longitudinal cross-sectional view which shows other conventional examples. The principal part longitudinal cross-sectional view which shows other conventional examples. The principal part longitudinal cross-sectional view which shows other conventional examples.

Explanation of symbols

11 optical fiber 12 optical fiber 13 optical fiber 14 optical fiber 15 optical fiber 16 optical fiber 17 optical fiber 51 optical element 521 second optical element 522 second optical element 523 second optical element 531 optical element 532 optical element 533 optical element 60 housing body

Claims (25)

  The first and second optical fibers whose end faces are arranged to face each other, the [MK1] optical element arranged obliquely with respect to the axis of the first optical fiber between the end faces, and the first And a third optical fiber disposed so that at least a part of the light wave emitted from the optical fiber and reflected by the optical element is incident thereon, and a part of the light wave passing through the first optical fiber is the Another optical wave that passes through the optical element and enters the second optical fiber and passes through the first optical fiber is reflected by the optical element and enters the third optical fiber, or one of the optical waves In the optical module in which the part or all of the incident / outgoing directions are reversed, the mode field diameter or numerical aperture of the end portions of the first to third optical fibers is changed as compared with the other optical fiber portions. An optical module characterized by   2. The optical module according to claim 1, wherein the optical element has wavelength selectivity.   2. The optical module according to claim 1, wherein the optical element has polarization dependent characteristics.   4. The optical module according to claim 1, wherein the optical element is composed of a dielectric multilayer film.   5. The optical module according to claim 1, wherein the optical element is made of a photonic crystal.   The optical module according to any one of claims 1 to 5, wherein the optical element is disposed on an end face of the first or second optical fiber formed obliquely.   6. The optical module according to claim 1, wherein the optical element is disposed by being deposited or directly formed on an end face of the first or second optical fiber formed obliquely. .   The end face of the third optical fiber is formed obliquely with respect to the axis of the optical fiber, and the second optical element is disposed on the end face. The optical module as described in.   The optical module according to claim 8, wherein the second optical element is attached to the end face of the optical fiber.   9. The optical module according to claim 8, wherein the second optical element is disposed by vapor deposition or directly formed on an end face of the optical fiber.   The optical module according to claim 8, wherein the second optical element has the same or approximate characteristics as the optical element.   11. The optical module according to claim 8, wherein the second optical element has total reflection characteristics.   The optical module according to any one of claims 1 to 7, wherein an end face of the third optical fiber is formed obliquely so as to have a total reflection angle or a Brewster angle.   The first optical fiber includes first to third optical fibers, and the end surfaces of the first optical fibers are formed obliquely, and the obliquely formed end surfaces of the first optical fibers and the second optical fibers are axially aligned with each other. And the third optical fiber so that at least a part of the light wave that is reflected by the obliquely formed surface is incident on the other optical wave. Is disposed, and a part of the light wave that passes through the first optical fiber is reflected by the obliquely formed end face, enters the third optical fiber, and another light wave that passes through the first optical fiber. In the optical module in which the light wave passes through the obliquely formed end face and enters the second optical fiber, or a part or all of the light wave enters and exits in opposite directions. Compared with other optical fiber parts An optical module characterized in that the mode field diameter or the numerical aperture is changed.   The optical module according to claim 14, wherein the obliquely formed end face of the first optical fiber is set to a Brewster angle.   16. The light according to claim 14, wherein an end face of the third optical fiber is formed obliquely with respect to the axis of the optical fiber, and a second optical element is disposed on the end face. module.   The optical module according to claim 16, wherein the second optical element is disposed on the end face of the optical fiber.   The optical module according to claim 16, wherein the second optical element is disposed by vapor deposition or directly formed on an end face of the optical fiber.   19. The optical module according to claim 16, wherein the second optical element has total reflection characteristics.   The optical module according to any one of claims 1 to 19, wherein at least one of the first to third optical fibers has a polarization plane maintaining characteristic.   A refractive index adjusting material having a predetermined refractive index is interposed between the first fiber and the third fiber and any one of the end faces of the first to third optical fibers. Item 21. The optical module according to any one of Items 20.   The optical module according to claim 21, wherein the refractive index adjusting material is any one of air, glass, adhesive, matching oil, liquid resin, and solid resin.   The optical module according to claim 22, wherein the refractive index adjusting material is equivalent to a refractive index of a clad of an optical fiber.   The optical module according to any one of claims 1 to 23, wherein end faces of the first to third optical fibers are held by a ferrule for storing multiple fibers.   The optical module according to any one of claims 1 to 24, wherein end faces of the first to third optical fibers are held by a multi-core housing groove.

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