JP2009222893A - Single-core bidirectional optical module - Google Patents

Abstract

A low-cost single-core bidirectional optical module having good optical characteristics of an LD is provided.
A single-core bidirectional optical module 1 includes a semiconductor light-emitting element 11 that outputs transmission light incident on an optical fiber 21a, a semiconductor light-receiving element 12 that receives reception light emitted from the optical fiber 21a, and transmission light and A wavelength multiplexing / demultiplexing filter 13b is provided that transmits one of the received light, reflects the other, and transmits the transmitted light to the optical fiber 21a, and causes the semiconductor light receiving element 12 to receive the received light. Then, light formed by integrally forming a rotating element 40a that emits incident light by rotating its polarization direction and a wavelength band-dependent polarization characteristic film 40b that exhibits polarization characteristics with respect to a specific wavelength band. The isolator 40 is provided between the optical fiber 21a and the wavelength multiplexing / demultiplexing filter 13b.
[Selection] Figure 1

Description

  The present invention relates to a single-core bidirectional optical module that transmits and receives optical signals.

  In recent years, a PON (Passive Optical Network) system has become available for subscriber communications networks (access systems) represented by FTTH (Fiber to the Home), which enables high-speed, large-capacity immediate communications at a reasonable price. Progressing. In this PON system, the number of fibers is reduced by adopting the single-core bidirectional communication method, and the station side and the fiber transmission line are shared by multiple users (home side). Realize a good service. Note that the PON system uses a wavelength division multiplexing (WDM) system that transmits and receives digital signals in the 1.31 μm band and 1.49 μm band and / or analog signals in the 1.55 μm band using a single optical fiber. Adopted.

  In a single-core bidirectional module (Bi-D: Bi-Directional Module) used in such a PON system, transmission light emitted from a semiconductor light emitting element (LD) is optically coupled to an optical fiber and transmitted. On the other hand, the received light emitted from the optical fiber is optically coupled to a semiconductor light receiving element (PD: Photodiode) and received. Various types of Bi-D have been proposed.

One example is a two-package Bi-D (see, for example, Patent Documents 1 and 2). The two-package Bi-D includes a transmission optical module and a reception optical module in which an LD and a PD are separately stored in a so-called CAN package. In the optical path between these modules and the optical fiber, transmission light is transmitted. And a WDM filter for multiplexing and demultiplexing the received light. Note that the WDM filter can perform the multiplexing / demultiplexing by transmitting one of transmission light and reception light and reflecting the other according to the wavelength, for example. Further, on the transmission optical module side of the two package type Bi-D, the transmission light emitted from the LD passes through a lens (condensing lens, collimating lens, etc.) or a WDM filter and is optically coupled to an optical fiber. On the other hand, on the receiving optical module side, the received light emitted from the optical fiber passes through the WDM filter and the lens and is optically coupled to the PD.
Such a Bi-D structure is widely used in that an existing CAN package type optical module can be used and it can be relatively easily assembled.

  As another example of Bi-D, there is a so-called one-package Bi-D in which LD and PD are incorporated in one CAN package (see, for example, Patent Document 3). In this Bi-D, in addition to the LD and PD, a lens, a mirror (half mirror, total reflection mirror), a WDM filter, a diffraction element, and the like are housed in a package. In addition, the transmission light emitted from the LD is reflected by a WDM filter disposed between the LD and the lens, then passes through the lens, and is further coupled to the optical fiber. Also, the received light emitted from the optical fiber passes through the lens and the WDM filter and is coupled to the PD.

  When the two-package Bi-D or the one-package Bi-D is adapted to the optical communication standard of ONU (Optical Network Unit) or OLT (Optical Line Terminal), good optical characteristics are required. In this case, for example, a distributed feedback LD (DFB-LD) having excellent dispersion characteristics can be used as the LD. However, an LD such as a DFB-LD emits light when the emitted light (transmitted light) is reflected at the coupling end face of the optical fiber or other discontinuous interface and returns to the LD resonator. May become unstable.

  Therefore, in order to obtain good optical characteristics in Bi-D, conventionally, light from one direction (transmitted light) is transmitted without loss so as to prevent reflected return light from returning to the LD, but from the opposite direction. An optical isolator having a function of blocking and transmitting light (reflected return light), that is, a unidirectional transmission function of light, is disposed between the DFB-LD and the optical fiber.

  FIG. 11 is a diagram illustrating an example of an optical isolator. As shown in FIG. 11A, the optical isolator 100 is composed of a Faraday rotator 101 having a garnet as a material and rotating the polarization direction (polarization plane) of light by 45 degrees with respect to the arrow Z direction, and a predetermined polarization. The polarizers 102a and 102b transmit only light having a direction. The direction in which the transmission light from the LD travels is called the forward direction, and the direction in which the reflected return light of the transmission light travels is called the reverse direction.

  The Faraday rotator 101 is a nonreciprocal element that is disposed between the polarizer 102a and the polarizer 102b and rotates the polarization direction in the same direction in the forward direction and the reverse direction by the magneto-optic effect. The polarizer 102a is disposed so as to transmit only light whose polarization direction is 0 degrees with respect to the arrow Z. In addition, the polarizer 102b is disposed so as to transmit only light whose polarization direction is 45 degrees with respect to the polarizer 102a.

  In such an optical isolator, as shown in FIG. 11B, only light having a polarization direction of 0 degrees with respect to the arrow Z out of light incident from the forward direction (transmitted light) passes through the polarizer 102a. To Penetrate. Further, the light transmitted through the polarizer 102a is rotated by 45 degrees in the polarization direction by the Faraday rotator 101 and is transmitted through the polarizer 102b.

On the other hand, as shown in FIG. 11C, of the light incident from the opposite direction (reflected return light), only light having a polarization direction of 45 degrees with respect to the arrow Z is used for the polarizer 102b. To Penetrate. The light transmitted through the polarizer 102b is rotated by 45 degrees in the polarization direction by the Faraday rotator 101, and becomes linearly polarized light having a polarization direction of 90 degrees with respect to the arrow Z. For this reason, the light incident from the opposite direction cannot pass through the polarizer 102a, so that the reflected return light can be blocked. Such an optical isolator 100 is also called a polarization-dependent optical isolator.
JP 2006-126495 A JP 2000-180671 A JP 2004-271922 A

  However, the optical isolator used in the conventional Bi-D as shown in FIG. 11 is expensive, and depending on the form of the Bi-D, the geometric arrangement of the components in the Bi-D is limited. It may not be implemented because it exists.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low-cost single-core bidirectional optical module having good LD optical characteristics.

  In order to solve the above-described problems, a single-core bidirectional optical module of the present invention includes a semiconductor light-emitting element that outputs transmission light incident on an optical fiber, a semiconductor light-receiving element that receives reception light emitted from the optical fiber, and a transmission It is equipped with a wavelength multiplexing / demultiplexing filter that transmits one of the light and the received light, reflects the other, makes the transmitted light incident on the optical fiber, and receives the received light on the semiconductor light receiving element. An optical isolator, in which a rotating element that rotates the polarization direction and emits light, and a wavelength band-dependent polarization characteristic film that exhibits polarization characteristics with respect to a specific wavelength band, are integrally formed with an optical fiber and wavelength multiplexing / demultiplexing. It is provided between filters.

  The wavelength band-dependent polarization characteristic film of the optical isolator is preferably formed at least on the optical fiber side surface of the rotating element. The optical isolator is preferably bonded to the end face of the optical fiber.

  According to the present invention, an optical isolator having a wavelength band-dependent polarization characteristic film that can be formed at low cost is provided between an optical fiber and a wavelength multiplexing / demultiplexing filter, so that reflected return light affects the optical characteristics of the LD. Therefore, it is possible to provide a low-cost single-core bidirectional optical module with good LD optical characteristics.

  FIG. 1 is a diagram illustrating an outline of an example of a single-core bidirectional optical module according to an embodiment of the present invention. The single-core bidirectional optical module (Bi-D) 1 includes, for example, an optical device 10 in which a semiconductor light emitting element (LD) 11 and a semiconductor light receiving element (PD) 12 are incorporated in one package, and the LD 11 and PD 12 in the optical device 10. A sleeve portion 20 for forming an optical connection between the optical device 10 and the external optical transmission line, and a joint sleeve (J sleeve) 30 for connecting the optical device 10 and the sleeve portion 20 to each other. Bi-D1 is formed by coupling the sleeve portion 20 to the optical device 10 via the J sleeve 30, and is optically connected to the external transmission path via the optical connector when the optical connector is inserted into the sleeve portion 20. The optical signal can be transmitted and received.

  The optical device 10 includes, for example, an LD 11, a PD 12, a stem 13, and a lens cap 14. The LD 11 outputs transmission light (for example, wavelength 1310 nm) to an external transmission path. In this specification, a distributed feedback type LD that emits light having a polarization direction in a direction parallel to the active layer. Suppose that The PD 12 receives received light having a wavelength (for example, wavelength 1490 nm) different from the transmitted light.

  The stem 13 forms a CAN package having an element mounting space in cooperation with the lens cap 14. The LD 11 and the PD 12 are mounted on the stem 13, and lead pins 13 a for electrical connection to an external circuit are glass-sealed. ing. On the stem 13, a WDM filter (also referred to as a wavelength multiplexing / demultiplexing filter) 13b is inclined and mounted at a position where the optical path of the transmission light and the optical path of the reception light intersect to selectively transmit and receive the light. Are separated by reflection or transmission.

  The lens cap 14 functions as a cap that hermetically seals the LD 11 and the PD 12 in cooperation with the stem 13. A lens 14 a that condenses the transmission light from the LD 11 and the reception light to the PD 12 is arranged at the upper center. Glass is sealed in the opening 14b. The opening 14b (that is, the lens 14a) serves as a transmission light exit port and a reception light entrance port, and an inexpensive ball lens can be used as the lens 14a.

Next, the sleeve portion 20 will be described. The sleeve portion 20 receives an optical connector (not shown) for optical connection with an external optical transmission line, and includes a stub 21, a sleeve 22, a sleeve shell 23, and a bush 24.
The columnar stub 21 is for optically coupling the LD 11 and PD 12 in the optical device 10 and the optical connector with high optical coupling efficiency, and a single mode optical fiber 21a is inserted in the center thereof. The sleeve 22 is configured to allow the optical fiber in the ferrule and the optical fiber 21a in the stub 21 to abut each other when the ferrule of the optical connector is inserted. Hold together.

  The sleeve shell 23 receives the optical connector and houses and protects the sleeve 22. As will be described later, the bush 24 is used for alignment in the direction perpendicular to the axial direction, and a sleeve shell 23 for housing the sleeve 22 fitted with the stub 21 is mounted thereon. Note that the end face of the stub 21 on the optical device 10 side is polished obliquely together with the optical fiber 21a so as to suppress the reflection return of the signal light on the end face.

  Next, the J sleeve 30 will be described. The optical device 10 and the sleeve portion 20 described above are coupled via the following J sleeve 30. The J sleeve 30 has a flat upper end surface 30a and an opening 30b provided at the center of the upper portion. The signal light condensed by the lens 14a and the signal light directed to the lens 14a are provided in the opening 30b. Pass through.

  In addition, the J sleeve 30 is disposed between the opening 30b and the optical device 10 (that is, between the stub 21 and the lens 14a), and is a wavelength selective optical isolator 40 that is an optical isolator related to the features of the present invention (details will be described later). Have A magnet 30 c for the Faraday rotator 40 a constituting the isolator 40 is provided around the wavelength selective optical isolator 40. The magnet 30c is configured such that the Faraday rotator can rotate the vibration direction of light in a predetermined direction by the magnetic field.

  In Bi-D1, the alignment in the axial direction and the radial direction is performed via the J sleeve 30. The axial position between the optical device 10 and the sleeve portion 20 (condensing distance of incoming / outgoing light) is adjusted by the fitting length of the J sleeve 30 and the lens cap 14 in the axial direction. On the other hand, the radial position between the optical device 10 and the sleeve portion 20 (the position of incident / exit light) is adjusted by changing the relative position of the J sleeve 30 and the bush 24. After these adjustments, the J sleeve 30 is fixed to and integrated with the lens cap 14 and the bush 24 by bonding or welding.

  When Bi-D1 is aligned as described above, the transmitted light output from the LD 11 is reflected by the WDM filter 13b, collected by the lens 14a, transmitted through the wavelength selective optical isolator 40, and the J sleeve. The light enters the optical fiber 21a of the stub 21 through the 30 openings 30b. On the other hand, the signal light from the external transmission path is emitted from the optical fiber 21a of the stub 21, passes through the opening 30b of the J sleeve 30, passes through the wavelength selective optical isolator 40, and is collected by the lens 14a, and is collected by the WDM filter. The light is received by the PD 12 through 13b.

  Here, most of the signal light emitted and output by the LD 11 is incident on the optical fiber 21 a of the stub 21 and transmitted to the external transmission path. However, a part of the output signal light is, for example, that of the stub 21. It is reflected at the end face and returns to the optical device 10 side as reflected return light. In the present invention, the reflected return light is suppressed by providing the wavelength selective optical isolator 40 in the J sleeve 30.

  Next, an example of a wavelength selective optical isolator will be described with reference to FIG. This wavelength selective optical isolator 40 is formed by forming a wavelength band-dependent polarization characteristic film 40b on a Faraday rotator 40a that rotates the polarization direction of light by 45 degrees. The wavelength band-dependent polarization characteristic film 40b exhibits polarization characteristics (polarization characteristics) for light in a specific wavelength band and does not exhibit polarization characteristics for light in another wavelength band. The wavelength band-dependent polarization characteristic film 40b of the present example shows, for example, polarization characteristics with respect to light in the wavelength band 1310 nm, and only light in this band having a specific polarization direction (specific polarization only). , And other light (light in the wavelength band 1490 nm in this example) does not show polarization characteristics, and light in this band is transmitted regardless of the polarization direction. In addition, the wavelength band dependent polarization characteristic film 40b is formed on one surface (surface on the optical fiber side) of the Faraday rotator 40a in the example of the figure.

  The Faraday rotator 40a is formed by, for example, garnet, and the formation of the wavelength band dependent polarization characteristic film 40b on the Faraday rotator 40a is performed by, for example, a nanoimprint technique. Nanoimprint technology is a technology that is gaining interest as a technology that breaks the physical limits of machining and lithography. Resin material with unevenness of several tens to several hundreds of nanometers engraved in a mold applied to a substrate It is a technology to transfer the shape by pressing on. A periodic grating structure smaller than the wavelength of light can be formed on glass or the like. With nanoimprint technology, the transfer process can be completed in a few minutes, enabling mass production of parts with the same shape in a short amount of time, as well as integration of elements obtained by laminating lattices. A plurality of functions can be provided on the element.

  Next, in Bi-D1 of FIG. 1, the process in which the transmission light of the distributed feedback type LD 11 passes through the wavelength selective optical isolator 40 of the example of FIG. 2 and is coupled to the optical fiber 21a, and the reflection return of the transmission light A process in which light passes through the optical isolator 40 and a process in which received light passes through the optical isolator 40 will be described with reference to FIGS. In the wavelength selective optical isolator 40 shown in the figure, the Faraday rotator 40a rotates the polarization direction of light by −45 degrees with respect to the arrow Z. The wavelength band-dependent polarization characteristic film 40b is disposed so as to transmit light having a wavelength band of 1310 nm and having a polarization direction of 45 degrees with respect to the arrow Z in accordance with the polarization direction of the LD 11. The

  As shown in FIG. 3A, the transmission light (wavelength 1310 nm) of the LD 11 is reflected by the WDM filter 13b, collected by the lens 14a, transmitted through the wavelength selective isolator, and optically coupled to the optical fiber 21a. At this time, the transmission light from the LD 11 has a polarization direction of 90 degrees with respect to the arrow Z before entering the Faraday rotator 40 as shown in FIG. 3B, but the Faraday rotator 40a. Is rotated by −45 degrees and becomes light having a polarization direction of 45 degrees with respect to the arrow Z. Therefore, the light passes through (transmits) the wavelength band-dependent polarization characteristic film 40b and is coupled to the optical fiber 21a. .

  Further, as shown in FIG. 4A, the transmitted light that has passed through the wavelength band-dependent polarization characteristic film 40b is reflected by the end face of the optical fiber 21a, the transmission path, or the like, and again as the reflected return light, the wavelength selective optical isolator 40. Transparent. At this time, as shown in FIG. 4B, the reflected return light is blocked by the wavelength band-dependent polarization characteristic film 40b other than the polarized light in the specified direction (45 degrees with respect to the arrow Z). Further, the reflected return light in one polarization direction that has passed through the wavelength band-dependent polarization characteristic film 40b is rotated by −45 degrees by the Faraday rotator 40a, and the polarization direction is 0 degrees with respect to the arrow Z. The light returns to the LD 11. The light returning to the LD 11 is orthogonal to the polarization direction of the LD emitted light, that is, the LD 11 (in this example, light having a polarization direction in a direction parallel to the active layer is emitted. ) Has a polarization direction in the direction perpendicular to the active layer, and does not affect the LD characteristics.

  Also, the received light (wavelength 1490 nm) from the optical fiber 21a passes through the wavelength selective optical isolator 40, is condensed on the lens 14a, passes through the WDM filter 13b, and is received by the PD 12. At this time, when the received light is emitted from the optical fiber 21a, the wavelength band-dependent polarization characteristic film 40b does not exhibit polarization characteristics in the wavelength band of the received light, and thus passes through the film 40b as it is, and is received by the Faraday rotator 40a. The polarization direction is rotated by −45 degrees and collected on the PD 12. Therefore, the PD 12 can receive received light in the 1490 nm band. The light receiving characteristics of the light receiving surface of the PD 12 are not related to the polarization direction.

  As described above, in this Bi-D, when the reflected return light of the transmission light emitted from the distributed feedback type LD enters the LD through the wavelength selective optical isolator, the polarization direction of the incident light is output. Since it is orthogonal to the polarization direction of the incident light, the LD characteristics do not change, and the received light from the optical fiber can be condensed on the PD even through the wavelength selective optical isolator.

  Further, in Bi-D, if the optical isolator using the conventional polarizing element of FIG. 11 is arranged between the WDM filter and the lens, there is a possibility of blocking received light whose polarization direction is unknown. For this reason, it has been necessary to arrange between the LD and the filter. However, the space between the LD and the lens is an extremely narrow space in the one package type Bi-D, and it is virtually impossible to dispose a conventional optical isolator at this location. As an example, in one package type Bi-D, since there is a very limited geometric arrangement, using an optical isolator conventionally has a very limited geometric arrangement. It was virtually impossible to do.

  However, in the Bi-D of the present invention, the wavelength selective optical isolator transmits the reflected return light as light having a polarization direction orthogonal to the polarization direction of the light emitted from the LD, as described above, and substantially. Since the Bi-D is provided with an isolator function with respect to the transmission light and all of the reception light can be transmitted, it can be disposed (that is, mounted) between the lens and the optical fiber.

  FIG. 6 is a diagram showing another example of the wavelength selective optical isolator. In the wavelength selective optical isolator used in the Bi-D of the present invention, the wavelength band-dependent polarization characteristic film 40b is formed on the optical fiber side surface (one surface) of the Faraday rotator 40a. Not limited. In the wavelength selective optical isolator, for example, as shown in FIG. 6A, the wavelength band dependent polarization characteristic film 40b may be formed on both surfaces (optical fiber side and lens side surfaces) of the Faraday rotator 40a.

  In addition, as shown in FIG. 6B, the wavelength selective isolator is provided with a wavelength band-dependent polarization characteristic film 40b on the surface of the Faraday rotator 40a on the optical fiber side, and a polarizing element (wavelength band-dependent polarization characteristic film 40b is provided). 40c (which transmits only light having the same polarization direction as that of light having polarization characteristics and transmitted through the film 40b) may be provided on the lens side. Further, as shown in FIG. 6C, a wavelength band-dependent polarization characteristic film 40b may be provided on the lens side surface of the Faraday rotator 40a, and the polarizing element 40c may be provided on the optical fiber side. In this case, the received light emitted from the optical fiber is changed into polarized light (polarized light) by the polarizing element 40c and received by the PD. However, as described above, the light receiving characteristics of the light receiving surface of the PD 12 are biased. Since it does not depend on the wave direction, there is no significant effect on the light receiving characteristics.

When the isolator is configured as shown in FIGS. 6A to 6C, the isolation function of reflected return light can be further enhanced.
The optical isolator on which a wavelength-selective film (wavelength band-dependent polarization characteristic film) by nanoimprinting related to the present invention is formed is a conventional polarization-dependent optical isolator (polarizing elements provided on both sides of a Faraday rotation element). ), The polarizing element is not used or the number of polarizing elements is small, the cost can be reduced correspondingly, and the effect is great in Bi-D where a low price is required.

The present invention can also be applied to the arrangement of the Bi-D LDs and PDs of the present embodiment (except for the WDM that transmits light in the 1310 nm band and reflects light in the 1490 nm band). Filter).
The Bi-D in the above example is an ONU-use optical module that uses light having a wavelength of 1310 nm as transmission light and light having a wavelength of 1490 nm as reception light. However, in the present invention, light having a wavelength of 1490 nm is transmitted as light. The present invention can also be applied to an optical module for OLT applications that uses 1310 nm light as received light (in this case, it exhibits polarization characteristics for light in the 1490 nm band and does not exhibit polarization characteristics for light in the 1310 nm band). Wavelength selective optical isolator is used).

Further, the present invention is not limited to the above-described receptacle type but can also be applied to a pigtail type Bi-D.
In the Bi-D in the above example, the wavelength selective optical isolator is attached to the J sleeve constituting the optical connecting member for optically connecting the optical fiber and the optical device of the CAN package. The fiber stub can be bonded to an optical fiber or the like.

  Next, Bi-D according to another embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a cross-sectional view of an example of Bi-D according to the present embodiment, and FIG. 8 is a diagram illustrating an optical coupling relationship at Bi-D in FIG. In addition, about the part similar to the above-mentioned embodiment, the description is abbreviate | omitted suitably by attaching | subjecting the same reference number. As shown in FIG. 7, the Bi-D of the present embodiment is a two-package single-core Bi-D including a transmission optical device 50 and a reception optical device 60 in which the LD 11 and the PD 12 are separately housed in a CAN package. Diplexer). The Bi-D 2 includes a sleeve member 70 and a J sleeve 80 in addition to the transmission and reception optical devices 50 and 60.

  The LD 11 of the transmitting optical device 50 emits an optical signal having a first wavelength (wavelength 1310 nm), and the PD 12 of the receiving optical device 60 receives an optical signal having a second wavelength (wavelength 1490 nm). The sleeve member 70 holds the ferrule 71 at the end of the fiber cable. The transmitting optical device 50, the receiving optical device 60, and the sleeve member 70 are coupled via a J sleeve 80.

  In addition to the transmission optical device 50, the reception optical device 60, and the sleeve member 70 being attached to the J sleeve 80, a WDM filter 81 that transmits an optical signal having a wavelength of 1310 nm and reflects an optical signal having a wavelength of 1490 nm, and wavelength selective light. An isolator 40 is attached.

The WDM filter 81 is in the optical path between the optical fiber 71 a of the ferrule 71 of the sleeve member 70 and the LD 11 of the transmitting optical device 50 and in the optical path between the optical fiber 71 a and the PD 12 of the receiving optical device 60. Is provided.
The wavelength selective optical isolator 40 is provided between the WDM filter 81 and the optical fiber 71 a of the ferrule 71 of the sleeve member 70 in accordance with the polarization direction of the LD 11 of the transmission optical device 50. That is, in the wavelength selective optical isolator 40, the relationship between the LD 11 and the optical fiber 71a is the relationship between the LD 11 and the optical fiber 21a in FIGS. 3B, 4B, and 5B, and the PD 12 and the optical fiber. The relationship with respect to 71a is provided so as to be the relationship with respect to PD 12 and optical fiber 21a in FIG.

  In Bi-D2, the transmitting optical device 50 is adjusted in a direction parallel to the optical axis in the first through hole 82b opened in the first surface 82a of the J sleeve 80, and the sleeve member 70 is adjusted to the J sleeve 80. On the second surface 82c, by aligning in the direction perpendicular to the optical axis, so-called triaxial alignment is performed with respect to the LD 11, and each of them is fixed by YAG welding. Next, the receiving optical device 60 is aligned on the third surface 82d of the J sleeve 80 in a direction perpendicular to the optical axis, so-called biaxial alignment is performed with respect to the PD 12, and is fixed by YAG welding.

  When Bi-D2 is aligned as described above, the transmission light output from the LD 11 of the transmission optical device 50 is condensed by the lens 14a of the transmission optical device 50, as shown in FIG. The light passes through the WDM filter 81, passes through the wavelength selective optical isolator 40, and enters the optical fiber 71 a of the ferrule 71 of the sleeve member 70.

  At this time, the transmitted light in the 1310 nm band is rotated by the Faraday rotator 40a (the polarization direction is −45 degrees) in the same manner as in FIG. 3B, and the wavelength band-dependent polarization characteristic film 40b formed by the nanoimprint technology is used. pass. The transmitted light that has passed is reflected and returned by the end face of the optical fiber 71a, the transmission path, and the like. However, in the same manner as in FIG. Is cut off. The reflected return light in one polarization direction that has passed through the wavelength band-dependent polarization characteristic film 40b is rotated by the Faraday rotator 40a (the polarization direction is −45 degrees) and is polarized in a direction orthogonal to the polarization direction of the LD transmission light. Since the light has a wave direction, the LD is not affected.

  When Bi-D2 is aligned as described above, the signal light from the external transmission path is emitted from the optical fiber 71a of the ferrule 71 of the sleeve member 70 and passes through the wavelength selective optical isolator 40. , Reflected by the WDM filter 81, collected by the lens 14 a of the receiving optical device 60, and received by the PD 12. At this time, the received light in the 1490 nm band passes through the wavelength band-dependent polarization characteristic film 40b as it is regardless of the polarization direction.

  As described above, also in the Bi-D of the present embodiment, the reflected return light is converted into light having a polarization direction orthogonal to the polarization direction of the light emitted from the LD using a low-cost wavelength selective optical isolator. All of the received light can be transmitted and received by the PD while preventing the transmitted and reflected return light from adversely affecting the characteristics of the LD.

Further, in the two package type Bi-D, the optical isolator using the conventional polarizing element of FIG. 11 is arranged between the lens of the optical device for transmission and the WDM filter. Therefore, the planar size of the isolator becomes large (about 0.5 mm square). In FIG. 8, the mounting position when the conventional optical isolator of FIG. 11 is provided instead of the Bi-D wavelength selective optical isolator 40 of the present embodiment is indicated by a virtual line.
On the other hand, since the wavelength selective optical isolator used in the present invention can be arranged near the condensing point (position close to the fiber), the plane size can be reduced (in terms of chipping by cutting and handling), 0.2 mm. The cost can be reduced, and the effect is great in Bi-D where a low price is required.

  The present invention is also applicable to the Bi-D transmitting optical device and the receiving optical device in which the arrangement of the Bi-D according to the present embodiment is interchanged as in the Bi-D of the embodiment shown in FIG. Yes (however, it is necessary to configure the J sleeve 80 so that three-axis alignment can be performed with respect to the LD 11). Further, the present invention is similar to Bi-D in FIG. 1 except that Bi-D of this embodiment is an optical module for OLT applications in which light having a wavelength of 1490 nm is transmitted light and light having a wavelength of 1310 nm is received light. Can also be applied.

  Next, Bi-D according to still another embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG. 9 is a cross-sectional view of an example of Bi-D according to the present embodiment, and FIG. 10 is a diagram illustrating an optical coupling relationship at Bi-D in FIG. In addition, about the part similar to the above-mentioned embodiment, the description is abbreviate | omitted suitably by attaching | subjecting the same reference number. As shown in FIG. 9, the Bi-D of the present embodiment is similar to the CAN 91 in addition to the transmission optical device 50 and the reception optical device 60 in which the LD 11 and the PD 12 are separately housed in the CAN package. This is a 3-package single-core Bi-D (triplexer) including a receiving optical device 90 housed in a package.

  In Bi-D3, the LD 11 of the transmitting optical device 50 emits an optical signal having a first wavelength (wavelength 1310 nm), and the PD 12 of the receiving optical device 60 outputs an optical signal having a second wavelength (wavelength 1490 nm). The PD 91 of the receiving optical device 90 receives the optical signal having the third wavelength (wavelength 1550 nm). As shown in FIG. 9, the transmitting optical device 50, the receiving optical device 60, the receiving optical device 90, and the sleeve member 70 are coupled via a J sleeve 80 '.

  The transmitting optical device 50, the receiving optical device 60, the receiving optical device 90, and the sleeve member 70 are attached to the J sleeve 80 '. In addition, a WDM filter 81, a WDM filter 83 'that transmits an optical signal having a wavelength of 1310 nm and an optical signal having a wavelength of 1490 nm, and reflects an optical signal having a wavelength of 1490 nm, and a wavelength selective optical isolator 40 are attached. The wavelength selective optical isolator 40 exhibits, for example, polarization characteristics for light in the wavelength band 1310 nm, and polarization characteristics for other light (light in the wavelength bands 1490 nm and 1550 nm in this example). Is not shown.

  The WDM filter 83 ′ is in the optical path between the optical fiber 71 a of the ferrule 71 of the sleeve member 70 and the LD 11 of the transmitting optical device 50, and between the optical fiber 71 a and the PD 12 of the receiving optical device 60. It is provided in the optical path between the optical fiber 71a and the PD 91 of the receiving optical device 90. The wavelength selective optical isolator 40 is provided between the WDM filter 83 ′ and the optical fiber 71 a of the ferrule 71 of the sleeve member 70 according to the polarization direction of the LD 11 of the transmission optical device 50.

  In Bi-D3, the transmitting optical device 50 is adjusted in the direction parallel to the optical axis in the J sleeve 80 ′ in the same manner as in Bi-D2, and the sleeve member 70 is placed on the J sleeve 80 ′. By aligning in the direction perpendicular to the optical axis, so-called triaxial alignment is performed on the LD 11 and each is YAG welded and fixed. Next, the receiving optical device 60 is aligned in the direction perpendicular to the optical axis on the J sleeve 80 'in the same manner as in Bi-D2, and so-called biaxial alignment is performed on the PD, and YAG welding is performed. And fix. Then, the receiving optical device 90 is aligned on the fourth surface 82e 'of the J sleeve 80' in the direction perpendicular to the optical axis, so-called biaxial alignment is performed with respect to the PD 91, and YAG welding is performed.

  When Bi-D3 is aligned as described above, the transmission light output from the LD 11 of the transmission optical device 50 is condensed by the lens 14a of the transmission optical device 50, as shown in FIG. The light passes through the WDM filter 81 and the WDM filter 83 ′, passes through the wavelength selective optical isolator 40, and enters the optical fiber 71 a of the ferrule 71 of the sleeve member 70.

  At this time, the transmitted light in the 1310 nm band is rotated by the Faraday rotator 40a and passes through the wavelength band-dependent polarization characteristic film 40b formed by the nanoimprint technique, as in FIG. 3B. The transmitted light that has passed is reflected and returned by the end face of the optical fiber 71a, the transmission path, and the like. However, in the same manner as in FIG. Is cut off. The reflected return light in one polarization direction that has passed through the wavelength band-dependent polarization characteristic film 40b is rotated by the Faraday rotator 40a and becomes light having a polarization direction perpendicular to the polarization direction of the LD transmission light. Does not affect LD.

  When Bi-D3 is aligned as described above, the signal light emitted from the optical fiber 71a of the ferrule 71 of the sleeve member 70 is transmitted through the wavelength selective optical isolator 40 in the 1490 nm band. Then, the light passes through the WDM filter 83 ′, is reflected by the WDM filter 81, is collected by the lens 14 a of the receiving optical device 60, and is received by the PD 12. Of the signal light from the optical fiber 71a, the one in the 1550 nm band passes through the wavelength selective optical isolator 40, is reflected by the WDM filter 83 ', and is collected by the lens 14a of the optical device for reception 90, Light is received by PD91. At these times, the received light in the 1490 nm band and the 1550 nm band passes through the wavelength band-dependent polarization characteristic film 40 b as it is regardless of the polarization direction.

As described above, the Bi-D of the present embodiment also has a polarization direction in the direction orthogonal to the polarization direction of the outgoing light from the LD using the low-cost wavelength-selective optical isolator. All of the two types of received light can be transmitted and received by the corresponding PDs, while being transmitted as light and preventing the reflected return light from adversely affecting the characteristics of the LD.
Also in the Bi-D of the present embodiment, the wavelength selective optical isolator used in the present invention can be arranged in the vicinity of the condensing point (position close to the fiber), so that the cost can be reduced and the price is low. The effect is great in the required Bi-D.

  The present invention can also be applied to an arrangement in which the arrangement of the Bi-D optical devices of the present embodiment is exchanged (however, it is necessary to configure the J sleeve 80 'so that it can perform triaxial alignment with respect to the LD 11). Therefore, it is necessary to select the characteristics of the WDM filter as appropriate).

As described above, according to the present invention, the optical characteristics of the LD can be improved at low cost in Bi-D by using a low-cost optical isolator formed with a wavelength band-dependent polarization characteristic film by nanoimprinting. .
Further, the conventional polarization-dependent isolator (polarizing element + Faraday rotator (element) + polarizing element) has a thickness of each element constituting the optical isolator of about 0.2 to 0.3 mm. Is about 0.7 mm. The wavelength-selective optical isolator according to the present invention does not use a polarizing element or has a smaller size in the thickness direction because the number of polarizing elements is small, and an optical length (distance between a fiber and a lens or a WDM filter). Can be suitably used for Bi-D having a small value.

It is a figure explaining the outline of an example of a single core bidirectional optical module (Bi-D) concerning one embodiment of the present invention. It is a figure which shows an example of a wavelength selection type optical isolator. In Bi-D of FIG. 1, it is a figure explaining the process in which the transmission light of LD permeate | transmits the wavelength selection type optical isolator of FIG. In Bi-D of FIG. 1, it is a figure explaining the process in which the reflected return light of transmission light permeate | transmits the wavelength selection type optical isolator of FIG. FIG. 3 is a diagram illustrating a process in which received light passes through the wavelength selective optical isolator of FIG. 2 in Bi-D of FIG. 1. It is a figure which shows the other example of a wavelength selection type optical isolator. It is sectional drawing of an example of Bi-D which concerns on other embodiment of this invention. It is a figure which shows the optical coupling relationship in Bi-D of FIG. It is sectional drawing of an example of Bi-D which concerns on another embodiment of this invention. It is a figure which shows the optical coupling relationship in Bi-D of FIG. It is a figure explaining an example of the conventional optical isolator.

Explanation of symbols

1, 2, 3 ... single-core bidirectional optical module (Bi-D), 10 ... optical device, 11 ... LD, 12 ... PD, 13 ... stem, 13a ... lead pin, 13b ... WDM filter, 14 ... lens cap, 14a ... lens, 14b ... opening, 20 ... sleeve portion, 21 ... stub, 21a ... single mode optical fiber, 22 ... sleeve, 23 ... sleeve shell, 24 ... bushing, 30 ... J sleeve, 30a ... upper end surface, 30b ... opening, 30c ... Magnet, 40 ... Wavelength selective optical isolator, 40a ... Faraday rotator, 40b ... Wavelength band dependent polarization characteristic film, 50 ... Optical device for transmission, 60 ... Optical device for reception, 70 ... Sleeve member, 71 ... Ferrule, 71a: optical fiber, 80, 80 '... J sleeve, 81 ... WDM filter, 83' ... WDM filter, 90 ... reception The optical device, 91 ... PD.

Claims (3)

A semiconductor light-emitting element that outputs transmission light incident on an optical fiber, a semiconductor light-receiving element that receives reception light emitted by the optical fiber, and transmits one of the transmission light and the reception light and reflects the other, A single-core bidirectional optical module comprising a wavelength multiplexing / demultiplexing filter that causes transmission light to enter the optical fiber and receive the reception light by a semiconductor light receiving element,
An optical isolator comprising a rotating element that emits incident light by rotating its polarization direction and a wavelength band-dependent polarization characteristic film that exhibits polarization characteristics with respect to a specific wavelength band. A single-core bidirectional optical module provided between an optical fiber and the wavelength multiplexing / demultiplexing filter.   The single-core bidirectional optical module according to claim 1, wherein the wavelength band-dependent polarization characteristic film is formed at least on a surface of the rotating element on the optical fiber side.   The single-core bidirectional optical module according to claim 1, wherein the optical isolator is bonded to an end face of the optical fiber.

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