Abstract:
The present invention discloses an optical-fiber-block assembly for minimizing stress concentration. The optical-fiber-block assembly is comprised of a fiber-alignment area mounted with a plurality of V-grooves at which optical fibers are disposed and a stress-relief-depth area extending from the fiber-alignment area and formed by etching the fiber-alignment area deeper by a predetermined amount, for relieving stress that is caused by the coating thickness of the fiber, wherein the fiber-alignment area further includes: (a) a first fiber-alignment area having a first V-grooves with a constant width for receiving the bare fibers, such that the first fiber-alignment area do not contact the external side of the bare fiber, and (b) a second fiber-alignment area having a second V-grooves with a constant width extending from the first V-grooves for receiving the bare fiber, wherein the width of the first V-grooves is substantially wider than the width of the second V-grooves.

Description:
CLAIM OF PRIORITY 
     This application makes reference to and claims all benefits accruing under 35 U.S.C. Section 119 from applications entitled, “Optical Fiber Block Assembly for Minimizing Stress Concentration and Contacting Device Therewith,” filed in the Korean Industrial Property Office on Nov. 1, 2001 and Dec. 27, 2001 and there duly assigned Ser. No. 2001-67761 and Ser. No. 2001-85796, respectively. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical-fiber-block assembly for connecting a planar-light circuit (PLC) to an optical fiber. In particular, the present invention relates to an optical-fiber-block assembly that includes an optical-fiber block and a glass cover for minimizing stress imposed on the optical fiber, and its related contacting device. 
     2. Description of the Related Art 
     In WDM (Wavelength Division Multiplexing) communication systems, optical signals with multiple N wavelengths are transmitted simultaneously through a single strand of optical fiber to accommodate a large volume of data traffic. To this end, a PLC (Planar Lightwave Circuit) is widely used for the optical-signal processing, such as the optical signal&#39;s bifurcation, modulation, switching, multiplexing, and so forth. To connect the PLC to an optical fiber, an optical-fiber block is typically employed. The optical-fiber block is also one of the optical components that are used as an input/output port of a Micro-Optic device. 
     FIG. 1 illustrates a connection state of a conventional Planar-Lightwave Circuit  10  (PLC) with an optical-fiber block  20  and  30 . As shown in the drawing, each of the optical blocks  20  and  30  is connected to the PLC  10  at its input/output side and also connected to each single fiber F 1  and a ribbon fiber F 2 . In operation, N wavelengths (N is a natural number) are inputted in the input port of the PLC  10  via the single fiber F 1 , then the inputted optical signals are multiplexed while passing through the PLC  10 . Each multiplexed optical signal is then outputted through the ribbon fiber F 2 , respectively. An adhesive B, such as epoxy resin, is used to fix the alignment of the input/output side of the optical fiber block  20  and  30 , each being connected to the input/output port of the PLC  10 . In addition, glass covers C 1  through C 4  are adhered to the input/out side of the PLC  10  as well as the input/output side of the optical fiber block  20  and  30 , respectively. The glass covers C 1  and C 2  are adhered to the input/output side of the PLC  10  for processing, and the glass covers C 3  and C 4  are adhered to the input/output side of the optical fiber block  20  and  30  to support each aligned optical fiber. In the drawing, the reference mark S indicates a silicon substrate on which the optical circuit is provided to process optical signals. 
     With reference to FIGS. 2 through 4, the components of an output side optical-fiber block  30  in accordance with the related art will be explained hereinafter. As depicted in the drawings, the conventional optical-fiber block  30  is divided into a fiber-alignment area  301  in which the bare fibers BF whose coatings are peel-off are aligned, and a stress-relief-depth area  302  for relieving the stress that is generated due to the coating thickness of the ribbon fiber. For the fiber-alignment area  301 , a plurality of V-grooves  310  is provided to receive the bare fibers BF. Note that the fiber-alignment area  301  and the stress-relief-depth area  302  are created in a very precise manner through a wet-etching process. 
     A vital function of the fiber block  30  is to support the bare fiber BF disposed in the V-groove  310 , to fixate or secure the alignment of each bare fiber BF, and to have the bare fibers BF positioned at a regular interval from each other. Accordingly, it is absolutely important to manufacture a precise V-groove  310  and a glass cover C 4  that is in contact with the fiber block  30 . Referring to FIG. 4, the cover C 4  is attached to the fiber-alignment area  301  for supporting the upper portion of the bare fibers BF aligned thereon. Then, the fiber block  30  and the cover C 4  undergo a polishing process to be etched in the form of dicing them to a designated degree (θ), thereby finalizing the alignment state of the fiber. 
     However, when the fiber block and the fiber are assembled in the manner shown in FIG. 2, that is, if the bare fibers BF are aligned in each V-groove  310 , and the glass cover C 4  is used to fixate the alignment state after injecting epoxy resin B, the following problems inevitably occur. 
     First, as shown in FIG. 3, the V-groove  310 , the bare fiber BF, and the glass fiber C 4  form a contact point at three different locations, P 1 , P 2 , and P 3 , respectively. Although these three contact points P 1 , P 1 , and P 3 , are necessary to maintain the precise alignment state of the bare fibers BF, they experience a considerable amount of stress due to the contraction and expansion of the adhesive B, which was injected to the contact points during the fabrication process. In the drawing, the stress intensity is indicated by the length variation of the arrow, and the direction of the arrow indicates the direction of the stress distribution. As evident in the stress distribution according to the arrow&#39;s direction, the stress is concentrated at the three contact points, and particularly, the stress is highest at the contact point P 3 , where the bare fiber comes in contact with the glass cover C 4 . In the long run, such stress eventually fatigues the adhesion at the contact point P 3 , thus causes delamination, a phenomenon where the boundary sides forming the contact point fall apart or become delaminated. This process eventually deteriorates the reliability of the optical components in general. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an optical-fiber-block assembly that includes an optical-fiber block with minimum stress concentration and a cover. 
     It is another object of the present invention to provide a contacting device therewith. 
     According to one aspect of the invention, there is provided an optical-fiber-block assembly, which includes an optical-fiber block for connecting a lightwave element to a fiber, and a cover that is in contact with the optical-fiber block for supporting the fiber disposed along at least one V-groove of the optical-fiber block, wherein the cover, for the purpose of minimizing stress concentration, includes: (a) a planar portion having a top surface and a bottom surface; (b) at least one ridge in a designated position of the bottom surface for supporting the fiber disposed in the V-grooves, and (c) a slot adjoined to the ridge gap receiving an adhesive material. 
     Another aspect of the present invention provides a contacting device using the cover described above which connects a planar-lightwave circuit to an optical fiber. The device includes: (a) an optical block on which at least one optical fiber is aligned along a V-groove; and (b) a cover in a spatial contact relationship with the optical-fiber block using an adhesive material. 
     Yet another aspect of the present invention provides an optical-fiber-block assembly for minimizing stress concentration using an optical-fiber block having a fiber-alignment area mounted with a plurality of V-grooves at which optical fibers are disposed and a stress-relief-depth area, which is an extended part formed by etching the fiber-alignment area, for relieving stress that is caused by the coating thickness of the fiber. The optical-fiber block further comprises: (a) a first fiber-alignment area having a width within a range that does not contact an external side of the aligned bare fiber, in which the first V-grooves with a constant width are uniformly aligned and extended therefrom; and (b) a second fiber-alignment area having a second V-grooves extending from the first V-grooves and in contact with the external side of the aligned bare fiber, wherein the width of the first V-grooves is substantially wider than the width of the second V-grooves. 
     The foregoing and other features and advantages of the invention will be apparent from the following, more detailed description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, the emphasis instead is placed upon illustrating the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a prospective view of an input-fiber block and an output-fiber block connected to a Planar-Lightwave Circuit (PLC) according to the related art; 
     FIG. 2 is a prospective view of the contact state of an optical fiber supported by an optical-fiber block and a cover according to the related art; 
     FIG. 3 is a front view showing a cross section of the optical fiber taken along the direction A in FIG. 2; 
     FIG. 4 is a side view of the optical fiber taken along the direction B in FIG. 2; 
     FIG. 5 is a prospective view of the magnified cover of an optical-fiber block assembly according to the first preferred embodiment of the present invention; 
     FIG. 6 is a prospective view of the magnified cover of an optical-fiber block assembly according to the second preferred embodiment of the present invention; 
     FIG. 7 is a prospective view of an optical fiber supported by a cover prior to an etching process according to the first preferred embodiment of the present invention; 
     FIG. 8 is a prospective view of an optical fiber supported by a cover after an etching process according to the first preferred embodiment of the present invention; 
     FIG. 9 is a front view showing a cross section of the optical fiber taken along the direction A in FIG. 8; 
     FIG. 10 is a side view of the optical fiber taken along the direction B in FIG. 8; 
     FIG. 11 is the prospective view of a magnified optical-fiber block of an optical-fiber-block assembly according to the third preferred embodiment of the present invention; 
     FIG. 12 is a prospective view reflecting the fixed state of a ribbon fiber by using an optical-fiber block of an optical-fiber-block assembly according to the third preferred embodiment of the present invention; and, 
     FIG. 13 is a cross-sectional view of the ribbon fiber taken along the section line X—X in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. It should be noted that an optical-fiber-block assembly mentioned in this disclosure indicates an optical-fiber block with a cover. 
     Now, the structure of the cover, which is a part of the optical-fiber block assembly, according to the first preferred embodiment of the present invention is explained hereinafter with reference to FIG.  5 . As shown in FIG. 5, the cover C 5  is planar and may be made of glass, quartz, or silicon material. The cover C 5  includes a top surface  501  and a bottom surface  502 . A pair of ridges  504  and  505  is provided to both ends of the bottom surface  502 , respectively. Each ridge  504  and  505  extends linearly, thereby forming a slot  506  therebetween. The slot comes in contact with the bottom surface  502 , such that at least one ridge  504  or  505  can be part of the cover C 5 . The ridge  504  and  505  is in contact with a bare fiber that is disposed in the V-groove of the fiber-alignment area. When the cover C 5  comes in contact with the optical-fiber block, the ridges  504  and  505  are placed in a perpendicular direction to the alignment of the bare fiber. 
     Referring to FIG. 6, the cover structure of the optical-fiber-block assembly according to the second embodiment of the present invention is explained hereinafter. As depicted in the drawing, the cover C 6  is planar and may be made of glass, quartz, or silicon material. The cover C 6  includes the top surface  601  and the bottom surface  602 . The ridges  604  through  606  are provided to both ends and the center of both ends of the bottom surface  602 , thereby forming two slots  607  and  608  between the ridges. Each of the slot  607  and  608  not only comes in contact with the bottom surface  602  but also adjoins the ridges  604 ,  605 , and  606 . Here, more than one ridge can be provided to the cover C 6 . In this case, three ridges  604 ,  605 , and  606  are provided. Note that the ridges are spaced apart at regular intervals. 
     With reference to FIGS. 7 through 10, a contacting structure of the optical-fiber block  30  using the cover C 5  depicted in FIG. 5 will be explained now. As shown in FIG. 7, the optical-fiber block  30  is vital to connect the Planar-Lightwave Circuit (PLC) and the fiber, and the cover C 5  is necessary to support the fiber that is placed on the V-groove  310  of the optical-fiber block  30 . The optical-fiber block  30  is divided into a fiber-alignment area  301  having a plurality of V-grooves  310  on which the bare-fiber BF is aligned, and a stress-relief-depth area  302  that is formed by etching the fiber-alignment area  301  more deeply. The bare-fiber BF or the uncoated ribbon fiber is disposed in the fiber-alignment area  301 , while the ribbon-fiber F 2  is disposed at the stress-relief-depth area  302 . Thusly contacted fiber then undergoes the dicing and the etching processes to finalize the fiber-alignment state. In FIG. 7, L 1  indicates a standard vertical line; L 2  indicates a line that is to be diced and etched; and, the angle θ indicates an etching angle. The complete fiber-alignment state after the dicing and the etching processes is shown in FIGS. 8 through 10. 
     As illustrated in the drawings, the ridge of the cover C 5  forms a contact point with the bare-fiber BF. Then, the diced and etched cover C 5  to a designated angle is eliminated later as the ridge on the front end is etched, shown in FIGS. 8 and 10. Here, the cover C 5  is fixated at a distant position from the bare-fiber BF, which is placed on the V-groom  310 . Thus, there exists a split between the bare-fiber BF and the bottom surface of the cover C 5 , to which the adhesive, epoxy-resin B, is filled in and hardened. 
     As shown in FIG. 9, if the fiber alignment is appropriately fixated by using the cover C 5  and the optical-fiber block  30 , one of the bare fibers BF forms two contact points P 1  and P 2  with the V-grooves  310 , but maintains a little bit of separation with the cover C 5 . Similar to FIG. 3, in FIG. 9, the arrow indicates the direction of stress, and the length of the arrow indicates the intensity of the stress. When comparing FIG. 3 with FIG. 9, it is found that by applying the cover of the present invention to the fiber-contacting structure, the intensity at the contact point was decreased and the number of the contact points was also decreased, even though the bare-fibers BF formed three contact points with the ridges  504  and  505 . The contacting structure using the cover of the present invention noticeably decreased the entire stress distribution compared to the prior art. Namely, the stress distribution existing between the cover and the bare fiber is decreased. Note that the separation between the cover and the bare fiber was merely several micrometers. 
     FIG. 11 is the prospective view of an optical-fiber block  40  of an optical-fiber-block assembly according to the third embodiment of the present invention. As shown in the drawing, the optical-fiber block  40  is divided into a fiber-alignment area  42  including a first and second fiber-alignment areas  421  and  422 , and a stress-relief-depth area  44 , which is an extended part from the fiber-alignment area  42 . The optical-fiber block  40  shown in FIG. 11 is employed to support the 4-core ribbon fiber. The first and the second fiber-alignment areas  421  and  422 , and the stress-relief-depth area  44  are prepared using a photo mask and wet-etching process on a silicon wafer. 
     The fiber-alignment area  42  includes the first fiber-alignment area  421  mounted with a first V-groove  421   a , and the second fiber-alignment area  422  mounted with a second V-groove  422   a . More specifically, the fiber-alignment area  42  includes 8 of the first V-grooves  421   a  and the second V-grooves  422   a , which are formed by extending the first V-grooves. Every first V-groove  421   a  has the same pitch P 1 , and every second V-groove  422   a  also has the same pitch P 2 . The stress-relief-depth area  44  is formed by etching technique known to one of averaged skilled in the art so that the coating part of the ribbon fiber can be disposed thereon. It is so because the bare fibers are aligned along the first and the second V-grooves  421   a  and  422   a , and the coated ribbon fiber is disposed at the stress-relief-depth area  44 . 
     The first V-grooves  421   a  has a designated width, which is wider than that of the second V-grooves  422   a . As such, the external side of the bare fiber touches the second V-grooves due to the higher displacement of the second V-grooves  422   a  that has a shorter width than the first V-grooves  421   a . At this time, the first V-grooves  421   a  are positioned at the front end. 
     As shown in FIGS. 12 and 13, if epoxy resin is applied to the bare fiber on the first and the second V-grooves  421   a  and  422   a , to which a glass cover  60  is used for fixating the bare fiber, the external side of the bare fiber maintains a certain separation from the first V-grooves  421   a , while being in contact with the glass cover  60 . On the other hand, the bare fiber is in contact with the second V-grooves  422   a  as well as with the glass cover  60 . In other words, the optical-fiber block  40  mounted with the first V-grooves according to the present invention successfully minimizes the stress concentration by keeping the external side of the bare fiber away from the first V-grooves  421   a , thus eliminating the contact points thereon. 
     While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. For example, in the optical-fiber block of the present invention, the first V-grooves do not have to be disposed at the front end of the fiber-alignment area. Similarly, the second V-grooves do not have to be disposed at the rear end of the fiber-alignment area only. Instead, the first V-grooves can be disposed at the rear end, that is, the stress-relief-depth area, while the second V-grooves can be disposed at the front end. Furthermore, like the first V-grooves, a plurality of V-grooves with a designated length can be aligned along the longitudinal direction thereof, given that the grooves do not contact the bare fiber disposed thereon. Therefore, the foregoing description is intended to embrace all such alternatives and variations falling with the spirit and broad scope of the appended claims.