Abstract:
The present invention provides a bi-direction optical assembly with two optical transmitting channels by a small-sized package and relatively low cost. In the bi-directional optical assembly, the first transmitting optical subassembly (TOSA) and the receiving optical subassembly (ROSA) are optically coupled with the optical fiber via the inner housing. While the second transmitting optical subassembly is optically coupled with the optical fiber via the outer housing slidable to the inner housing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a bidirectional optical assembly, in particular, the invention relates to a bidirectional optical assembly having two ports for an optical transmitter.  
         [0003]     2. Related Prior Art  
         [0004]     A bidirectional optical assembly comprises an optical transmitting subassembly (hereinafter referred by TOSA) for a transmitting channel, an optical receiving subassembly (hereinafter referred by ROSA) for a receiving channel, an optical fiber and a housing. The housing forms a tubular shape, one end of which secures the TOSA that is arranged along an axis of the tube, while, the other end thereof secures the optical fiber to optically couple with the TOSA in precise. On the other hand, the ROSA is supported in the side of the tubular housing and coupled with the optical fiber via an optical filter. Refer to Japanese patent application published as JP-2003-524789A.  
         [0005]     It is known that one type of the bidirectional optical assembly with two channels for the transmission includes two TOSAs and one ROSA independent to each other. In this assembly, each of the optical transmitting subassembly and the optical receiving subassembly couple with the respective optical fibers, and respective optical fibers are attached with an optical filter to transmit signal light with preset wavelengths. Moreover, the optical fibers are coupled with the optical coupler. This type of the optical assembly is hard to miniaturize and is relatively cost un-effective because the assembly requires a number of optical element, for instance, the optical filter and the optical coupler.  
         [0006]     The present invention is to provide a bidirectional optical assembly having two transmitting channels with a miniaturized shape and a low-cost.  
       SUMMARY OF THE INVENTION  
       [0007]     One aspect of the present invention relates to an arrangement of a bi-directional optical subassembly. The bi-direction optical subassembly of the present invention comprises first and second transmitting optical subassemblies (TOSA), a receiving optical subassembly (ROSA), a sleeve assembly including an optical fiber that carries both transmitting and receiving optical signals, first and second wavelength division multiplex (WDM) filters, and a housing configured to install these filters and to secure two TOSAs, the ROSA, and the sleeve assembly. The first TOSA emits light with the first wavelength, the second TOSA emits light with the second wavelength, and the ROSA receives light with the third wavelength. These first to third wavelengths are different from each other. The first WDM filter, arranged between the first TOSA and the sleeve assembly, reflects the light with the first wavelength and transmits the light with the second wavelength. The second WDM filter, arranged between the sleeve assembly and the ROSA, transmits the light with first and second wavelengths and reflects the light with the third wavelength. Moreover, the housing includes an inner housing configured to secure the first TOSA, the ROSA and the sleeve assembly and an outer housing configured to receive the inner housing and to secure the second TOSA.  
         [0008]     The first TOSA and the ROSA are fixed to the inner housing as aligning along the optical axes thereof. On the other hand, the sleeve assembly is fixed as aligning the position thereof along two directions perpendicular to the optical axis. Moreover, the second TOSA is fixed to the outer housing as aligning the position thereof along the optical axis, while, the outer housing is fixed to the inner housing as aligning the position thereof along two directions perpendicular to the optical axis. Therefore, since the first and second TOSAs, and the ROSA may be independently aligned along three directions against the optical axis of the sleeve assembly, the fine optical coupling for respective assemblies may be independently obtained.  
         [0009]     The first TOSA and the ROSA are preferable to provide wavelength selective filters to selectively transmit light with first and third wavelengths, respectively, which enables to reduce the optical noise.  
         [0010]     Further, it is preferable to provide an isolator between the first and second WDM filters to transmit light propagating from the first WDM filter to the second WDM filter and to cut light propagating from the second WDM filter to the first WDM filter, which prevent light emitted from the optical fiber from returning the first and second TOSAs to become a noise source for the light-emitting devices installed within the first and second TOSAs.  
         [0011]     The inner housing preferably provides a flange in an end surface thereof. The sleeve assembly may slide on an outer surface of this flange along two directions perpendicular to the optical axis. While, by sliding an end surface of the outer housing on an inner surface of this flange, the outer housing may slide along two directions perpendicular to the optical axis. Thus, the first and second TOSAs may be independently aligned in their position.  
         [0012]     Another aspect of the present invention relates to a method for manufacturing the bi-directional optical assembly. In the present method, first of all, the first TOSA permanently fixes in the position thereof by the YAG laser welding after aligning with the sleeve assembly via the inner housing. The first TOSA optically aligns with the inner housing along the direction parallel to the optical axis, while, the sleeve assembly optically aligns with the inner housing along directions perpendicular to the optical axis. Next, the second TOSA optically aligns with the outer housing along the direction parallel to the optical axis, while, the outer housing optically aligns with the inner housing along directions perpendicular to the optical axis. Thus, the first and second TOSAs may be aligned independently and separately along three directions against the optical axis, which attains a superior optical coupling efficiency.  
         [0013]     The alignment between the ROSA and the sleeve assembly may be carried out after the optical alignment between the first TOSA and the sleeve assembly, or may be preformed after the optical alignment between the second TOSA and the sleeve assembly.  
         [0014]     Moreover, by securing the ROSA to the inner housing through the second alignment member, the ROSA may be aligned not only in two directions perpendicular to the optical axis but also in the direction parallel to the optical axis. Accordingly, the superior optical coupling efficiency may be attained for the ROSA. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1  is an exploded perspective view showing the bidirectional optical assembly according to the first embodiment of the invention;  
         [0016]      FIG. 2  is a cross sectional view of the bidirectional optical assembly according to the first embodiment of the invention;  
         [0017]      FIG. 3  is a cross sectional view of the bidirectional optical assembly according to the second embodiment of the invention;  
         [0018]      FIG. 4  shows the sleeve assembly according to a modified embodiment; and  
         [0019]      FIG. 5  shows the housing according to a modified embodiment. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]     Next, preferred embodiments of the present invention will be described as referring to accompanying drawings. In the drawings, same numerals and symbols will refer to the same elements or the elements equivalent to each other.  
       First Embodiment  
       [0021]      FIG. 1  is an exploded perspective view showing a bidirectional optical assembly according to the first embodiment of the present invention, which is partially broken.  FIG. 2  is a cross sectional view of the bidirectional optical assembly according to the first embodiment. The bidirectional optical assembly  10  shown in  FIGS. 1 and 2  comprises a first transmitting optical subassembly (TOSA)  12 , a second TOSA  14 , a receiving optical subassembly (ROSA)  16 , a sleeve assembly  18 , an inner housing  20  and an outer housing  22 .  
         [0022]     The first TOSA  12  comprises a package  12   a , a sub-mount  12   b , a light-emitting device  12   c , a condenser lens  12   d , and a sleeve  12   e . The package  12   a  includes a stem  12   f , a lens cap  12   g , and a lead terminal  12   h . The stem  12   f  provides a mounting surface  12   i . A plurality of lead terminals  12   h  extend from the stem  12   g  to a direction substantially perpendicular to the stem  12   f . On the mounting surface  12   i  is installed with the sub-mount  12   b , and on the sub-mount  12   b  is mounted with the light-emitting device  12   c . The light-emitting device  12   c  emits light with the first wavelength. The light-emitting device may be a laser diode for emitting light with the wavelength of 1350 nm as a center wavelength.  
         [0023]     On the mounting surface  12   i  is secured with the lens cap  12   g . The lens cap  12   g  is a tubular member to form, co-operated with the stem  12   f , a cavity where the sub-mount  12   b  and the light-emitting device  12   c  is installed therein. This cavity is air-tightly sealed from the outside. The lens cap  12   g  holds the lens  12   d  in one end, the ceiling thereof. The condenser lens  12   d , receiving the light emitted from the light-emitting device  12   c  by one surface thereof, outputs the light from the other surface thereof as focusing it. The lens cap  12   g  provides the sleeve  12   e  with a tubular shape in the periphery thereof. One end of the sleeve  12   e  is supported by the mounting surface  12   i . The sleeve  12   e  may be made of material able to be welded by the YAG laser, for instance, made of stainless steel.  
         [0024]     The second TOSA  14 , similar to the configuration of the first TOSA  12 , includes the package  14   a , the sub-mount  14   b , the light-emitting device  14   c , the condenser lens  14   d , and the sleeve  14   e . The package  14   a  includes the stem  14   f , the lens cap  14   g , and a plurality of lead terminals  14   h . The configuration of the second TOSA  14  is the same with those of the first TOSA  12  except that the light-emitting device  14   c  of the second TOSA  14  emits light with the second wavelength different from the first wavelength, for example, a center wavelength thereof being around 1570 nm.  
         [0025]     The ROSA  16  receives the light with the third wavelength, for example, a center wavelength of 1510 nm, from the optical fiber  18   f  that will be described later. The ROSA  16  includes the package  16   a , the chip carrier  16   b , the light-receiving device  16   c , and the condenser lens  16   d . The package  16   a  includes the stem  16   f , the lens cap  16   g , and a plurality of lead terminals  16   h . The stem  16   f  provides the mounting surface  16   i . The lead terminals  16   h  protrude from the stem  16   f  along a direction nearly perpendicular to the mounting surface  16   i . On the mounting surface  16   i  is installed with the light-receiving device  16   c  via the chip carrier  16   b . The light-receiving device  16   c  may be a photodiode.  
         [0026]     The mounting surface  16   i  mounts the lens cap  16   g  thereon. This lens cap  16   g , cooperating with the stem  16   f , forms a cavity where the light-receiving device  16   c  and the sub-mount  16   b  are enclosed therein. The cavity is hermetically sealed from the outside. The lens cap  16   g  is made of material able to be welded by the YAG laser, for instance, made of kovar. The end of the lens cap  16   g , namely, the ceiling thereof holds the condenser lens  16   d , which receives the light with the third wavelength in one surface thereof and focuses this light on the light-receiving device  16   c.    
         [0027]     The sleeve assembly  18  includes the stub  18   a , the bush  18   b , the cover  18   c , and the optical fiber  18   d . The stub  18   a  includes the ferrule  18   e  and the coupling fiber  18   f.    
         [0028]     The ferrule  18   e  secures the coupling fiber  18   f  in a center thereof. The bush  18   b  secures the stub  18   b  within the bore thereof. This bush  18   b  forms a flange in the end portion thereof, and this flange constitutes the end of the sleeve assembly  18 . The bush  18   b  is made of material able to be welded by the YAG laser, for instance, made of stainless steel, and is welded by the flange. A portion of the bush  18   b  and a portion of the optical fiber  18   d  continuous to the stub  18   f  are protected by the cover  18   c.    
         [0029]     The inner housing  20  extends along the axis X. The inner housing  20  is made of material able to be welded by the YAG laser, for instance, made of stainless steel. The inner housing  20  includes a first surface  20   a , which becomes one end surface thereof, and a second surface  20   b  opposite to the first surface. In the present embodiment, the inner housing  20  provides a body portion  20   i  and a flange  20   j  in this order along the axis X. The cross section of the flange  20   j  is greater than the cross section of the body portion  20   i . The end surface of the flange  20   j  forms the first surface  20   a , while a surface opposite to the first surface  20   a  becomes the second surface  20   b.    
         [0030]     In the body portion  20   i  of the inner housing  20  is formed with an opening  20   d  along a direction Y intersecting the axis X. Moreover, the body portion  20   i  forms another opening  20   e  along the direction Z also intersecting the axis X. The opening  20   d  includes a couple of openings, each having larger and smaller bores, sequentially formed heading to an inner bore  20   f  of the inner housing  20 . In a step between these larger and smaller bores is attached with the wavelength selective filter  24 . One surface  24   a  of the wavelength selective filter  24 , which faces the first TOSA  12 , optically couples with the condenser lens  12   d  within the first TOSA  12 , while, the other surface  24   b  of the wavelength selective filter  24  optically couples with one surface  28   a  of the wavelength division multiplex (WDM) filter that will be described later. This wavelength selective filter  24  transmits the light with the first wavelength, while, it reflects the light with other wavelengths. Therefore, this wavelength selective filter  24  prevents the light with the second wavelength emitted from the second TOSA  14  from entering the first TOSA  12 .  
         [0031]     The opening  20   e , similar to the opening  20   d , includes a couple of bores sequentially formed in this order along a direction for the inner bore  20   f  of the inner housing  20 , each having a larger diameter and a smaller diameter. In the step between two bores is installed with the wavelength selective filter  26 . One surface  26   b  of the wavelength selective filter  26  optically couples with the condenser lens  16   d , while, the other surface  26   b  of the filter optically couples with one surface  32   a  of the second WDM filter to be described later. The wavelength selective filter  26  transmits the light with the third wavelength, while, it reflects light with other wavelengths. Therefore, the filter prevents the light with wavelengths other than the third wavelength emitted from the coupling fiber  18   f  from entering the ROSA  16 .  
         [0032]     Within the inner bore  20   f  of the inner housing  20  is installed with the first WDM filter  28 , the optical isolator  30 , and the second WDM filter  32  in this order along the axis X. The first WDM filter  28  is placed on a surface intersecting both axes, X and Y. One surface  28   a  of the first WDM filter  28  optically couples with the other surface  24   b  of the first wavelength selective filter  24 , while, the other surface  28   b  thereof optically couples with the condenser lens  14   d  within the second TOSA  14 . The first WDM filter  28  reflects the light with the first wavelength that is incident from the first TOSA  12  transmitting through the first bore  20   d  to the direction along the axis X, while, it transmits the light with the second wavelength that is incident from the second TOSA  2  to the side of the sleeve assembly  18 .  
         [0033]     The isolator  30  is an optical device to permit light to transmit along only one direction. This isolator  30  prevents light from transmitting from the side of the sleeve assembly  18   f  to the second TOSA  14 . Therefore, the isolator may prevent the light with the third wavelength from the coupling fiber  18   f  from entering the first and second TOSAs,  12  and  14 .  
         [0034]     The second WDM filter  32  is arranged on a plane intersecting both axes, X and Z. One surface  32   a  of the second WDM filter  32  optically couples with the end of the coupling fiber  18   f  and the other surface  26   b  of the wavelength selective filter  26 . The other surface of the second WDM filter  32  optically couples with the surface  28   a  of the first WDM filter  28  through the isolator  30 . This second WDM filter  32  transmits the light with the first wavelength emitted from the first TOSA  12  and the light with the second wavelength emitted from the second TOSA  14  to the end of the coupling fiber  18   f , while, it reflects the light with the third wavelength emitted from the end of the coupling fiber  18   f  to the condenser lens  16   d.    
         [0035]     The inner housing  20  includes first and second alignment members,  20   k  and  20   m , respectively. The first alignment member  20   k , having a tubular shape, secures the first TOSA  12  and has an inner diameter nearly equal to an outer diameter of the sleeve  12   e  of the first TOSA  12 . This first alignment member  20   k  is installed within the inner housing  20  so as to align the axis thereof along the axis Y and welded by the YAG laser to the side of the body portion  20   i . The bore of the first alignment member  20   k  continues to the opening  20   d.    
         [0036]     The second alignment member  20   m , also having a tubular shape, secures the ROSA  16 . The inner diameter of the second alignment member  20   m  is nearly equal to an outer diameter of the lens cap  16   g  of the ROSA  16 . This second alignment member  20   m  is installed within the inner housing  20  so as to align the center thereof along the axis Z and welded by the YAG laser to the side of the body portion  20   i . The bore of the second alignment member  20   m  continues to the opening  20   e.    
         [0037]     The outer housing  22 , extending along the axis X, includes a support portion  22   a  and a cap portion  20   b  along the axis X in this order. The support portion  22   a , having a tubular shape, supports the second TOSA  14 . The inner diameter of the support portion  22   a  is nearly equal to an outer diameter of the sleeve  14   e . The cap portion  22   b  receives the body portion  20   i  of the inner housing  20 . The cross section of the cap portion  22   b  along directions intersecting the axis X is greater than the cross section of the body portion  20   i . This cap portion  22   b  provides, in the end portion thereof, a third surface  22   c  facing the second surface  20   b  of the inner housing  20 . The cap portion  22   b  includes an opening  22   d  along the axis Y, through which the first alignment member  20   k  passes. The inner diameter of the opening  22   d  is greater than the outer diameter of the first alignment member  22   k . Moreover, the cap portion  22   b  forms another opening  22   e  along the axis Z, thorough which the second alignment member  20   m  passes. The diameter of this opening  22   e  is greater than the outer diameter of the second alignment member  20   m.    
         [0038]     Next, a method for assembling the bi-direction optical assembly  10  will be described. First, the cap portion  22   b  of the outer housing  22  receives the body portion  20   i  of the inner housing  20 . Next, the first alignment member  20   k  is inserted into the opening  22   d  along the axis Y, while, the second alignment member  20   m  is inserted into the opening  22   e  along the axis Z. Subsequently, the first alignment member  20   k  and the second alignment member  20   m  are welded to the side of the body portion  20   i  by the YAG laser.  
         [0039]     Next, the first TOSA  12  is installed within the first alignment member  20   k , and the first TOSA  12 , in particular, the sleeve  12   e  thereof, is slid along the axis Y within the first alignment member  20   k  to align the condenser lens  18   d  with the light-emitting device  12   c  within the first TOSA  12 , and condenser lens  12   d  is optically aligned with the coupling fiber  18   f  by sliding the bush  18   b  on the first surface  20   a  of the inner housing  20 . Thus, the light-emitting device  12   c  may optically couple with the coupling fiber  18   f . Subsequently, the sleeve  12   e  is welded to the first alignment member  20   k , while, the bush  18   b  is welded to the inner housing  20  by the YAG laser.  
         [0040]     Next, inserting the ROSA  16  into the second alignment member  20   m , the lens cap  16   g  of the ROSA is welded to the second alignment member  20   m  by the YAG laser. Thus, the condenser lens  16   d  may be optically couple with the end of the coupling fiber  18   f.    
         [0041]     Next, inserting the second TOSA  14  into the support portion  22   a  of the outer housing  22 . The condenser lens  14   d  may be aligned with the coupling fiber  18   f  by sliding the second TOSA  14  along the axis X and by sliding the third surface  22   c  of the outer housing  22  on the second surface  20   b  of the inner housing  20 . This alignment process does not disarrange the optical coupling between the coupling fiber  18   f  and the first TOSA  12 , or between the coupling fiber  18   f  and the ROSA  16 . Then, the sleeve  14   e  of the second TOSA  14  is welded to the support portion  22   a , and the outer housing  22  is also welded to the inner housing  20 .  
         [0042]     According to the bi-directional optical assembly  10  of the present invention, the light-emitting device  12   c  may optically align with the coupling fiber  18   f  by sliding the first TOSA  12  along the axis X and the sleeve assembly  18  along two directions each intersecting the axis X. Accordingly, the end of the coupling fiber  18   f  may be precisely positioned on a focal point of the condenser lens  12   d.    
         [0043]     Moreover, the second light-emitting device  14   c  may optically align with the end of the coupling fiber  18   f  by sliding the second TOSA  14  along the axis X and by sliding the outer housing  22  on the inner housing  20 . Accordingly, the end of the coupling fiber  18   f  may be precisely positioned on a focal point of the condenser lens  14   d.    
         [0044]     In the bi-directional optical assembly  10 , the housing comprising two bodies of the inner and outer housings,  20  and  22 , respectively, assembles the first and second TOSAs,  12  and  14 , respectively, and the ROSA  16 . Moreover, the bi-directional optical assembly may optically couple the first and second TOSAs,  12  and  14 , and the ROSA  16  with the single coupling fiber  18   f  without providing a costly optical coupler.  
       Second Embodiment  
       [0045]      FIG. 3  is a cross sectional view of the second embodiment of the bi-directional optical assembly according to the present invention. Next, regarding the bi-directional optical assembly  10   b  shown in  FIG. 3 , configurations different from those of the bi-directional optical assembly  10  already described will be described.  
         [0046]     In the bi-directional optical assembly lO b , the ROSA  16  further provides the sleeve  16   j . This sleeve  16   h  has a tubular shape with one end thereof being secured by the mounting surface  16   i , while, the other end thereof facing the end of the second alignment member  20   m . The inner diameter of the second alignment member  20   m  is slightly greater than the outer diameter of the lens cap  16   g.    
         [0047]     According to this bi-directional optical assembly, the ROSA  16  may adjust the position along two directions each intersecting the axis Z by sliding the end surface of the sleeve  16   j  on the end surface of the second alignment member  20   m . Accordingly, the optical coupling between the ROSA  16  and the coupling fiber  18   f  may be further precisely carried out.  
         [0048]     The present invention is not restricted to those embodiments mentioned above and may have various modifications. For example, the bi-directional optical assembly mentioned above has a configuration what is called as the pig-tailed type. However, the bi-directional optical assembly may be what is called as the receptacle type.  
         [0049]     The bi-directional optical assembly with the receptacle type may provide a sleeve assembly  36  shown in  FIG. 4  instead of the sleeve assembly  18 .  FIG. 4  shows the sleeve assembly  36  in partially broken. This sleeve assembly  36  comprises a stub  36   a , a sleeve  36   b , a bush  36   c  and a sleeve cover  36   d.    
         [0050]     The stub  36   a  includes a ferrule  36   e  and a coupling fiber  36   f  provided in a center of the ferrule  36   e . The stub  36   a  is secured in a root portion of the sleeve  36   b . The sleeve  36   b  secures the optical fiber inserted into a tip portion thereof. The sleeve  36   b  may be a split sleeve with a slit along the axis thereof. The root portion of the sleeve  36   b  is secured by the bush  36   c . The bush  36   c  secures the stub  36   a  via the root portion of the sleeve  36   b  inserted into a bore thereof. The sleeve cover  36   d  is provides so as to cover the bush  36   c  and the sleeve  37   b.    
         [0051]     This sleeve assembly  36  is fixed to the inner housing  20  after aligning sleeve by sliding the end surface of the bush  36   c  on the first surface  20   a  of the inner housing  20 . The one end of the coupling fiber  36  within the sleeve assembly  36  optically couples with the condenser lenses,  12   d ,  14   d  and  16   d.    
         [0052]     Moreover, a modified housing  122   b  shown in  FIG. 5  may be applied instead of the outer housing  122 .  FIG. 5  is a perspective view of the modified housing  122   b . Next, structures of the modified housing  122   b  different from the outer housing  20  will be described. The modified housing  122   b  forms a first slit  22   m  instead of the opening  22   d , and a second slit  22   n  instead of the opening  22   e . These two slits,  22   m  and  22   n , extend along the axis X to the end, a side to where the sleeve assembly  18  is to be fixed thereto, of the modified housing  122   b.    
         [0053]     When this modified housing  122   b  is practically applied, the cap portion  22   b  of the modified housing  122   b  receives the inner housing  20  after the body portion  20   i  installs the first and second alignment members,  20   k  and  20   m.