Abstract:
The present invention provides a method for fabricating an optical fiber block capable of preventing degradations due to an outgassing effect provided from an epoxy material.  
     The inventive method includes the steps of: forming an adhesion layer and a solder on predetermined regions of a first substrate where a predetermined plurality of grooves are formed; arranging a number of optical fibers in the plurality of grooves; covering a second substrate to the first substrate; soldering the solder to bond the first and the second substrates together; and simultaneously fixing the optical fibers within the V-grooves.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an optical coupling technology in optical communications; and, more particularly, to a method for fabricating an optical fiber block.  
         DESCRIPTION OF RELATED ARTS  
         [0002]    Optical fiber block is an optical element for optical coupling between an optical fiber and optical devices. The optical fiber block is widely used in a planar lightwave circuit (PLC), a dense wave division multiplexer (DWDM), an optical switch, a splitter, an arrayed waveguide grating (AWG), a multiplexer, an inverse-multiplexer and so forth.  
           [0003]    The optical fiber block includes a V-shaped groove (hereinafter referred as to V-groove) for aligning and fixing optical fibers. Although a single type of the optical fiber block includes one V-groove, an array type of the optical fiber block including a number of V-grooves is mainly used due to a common usage of optical array elements in an optical coupling technology.  
           [0004]    Silicon, glass and plastic are main materials used for constructing a substrate of the optical fiber block. Among those materials, the silicon is, however, most commonly used for the substrate because it is advantageous of mass-production due to its characteristic wet etching in accordance with crystal surfaces.  
           [0005]    The optical fiber block as described above includes a lower substrate and an upper substrate. An optical fiber or an optical fiber array is aligned in a V-groove of the lower substrate, and the upper substrate subsequently covers the lower substrate. Afterwards, the lower and the upper substrates are adhered together. At this time, an epoxy is used for adhering the two substrates. Typically, a thermoset epoxy and an ultra violet epoxy are used.  
           [0006]    However, most of epoxies decrease their adhesion strengths when exposed to moisture. Also, the epoxy itself containing organic materials results in an outgassing problem in a sealed state. Therefore, this fact further results in degradations of the optical fiber and the optical device. Furthermore, a decrease in the alignment accuracy of the optical fiber occurs due to a relatively ease of deformation in a high temperature or a low temperature environment.  
           [0007]    Meanwhile, the epoxy in accordance with a prior art is also used for fixing the optical fiber. However, instead of using the epoxy, it has been attempted to use a solder because of the above-mentioned disadvantages of using the epoxy (referred to Mark W. Beranek et al., Passive Alignment Optical Subassemblies for Military/Aerospace Fiber-Optic Transmitter/Receiver Modules. IEEE Transactions on Advanced Packaging Vol. 23(3), August 2000).  
           [0008]    [0008]FIG. 1 is a diagram of a solder-bonded fiber within a V-groove. Referring to FIG. 1, an optical fiber  104  is inserted to a silicon substrate  100  in which a V-groove  102  is formed and a metal-coated portion  106  of the optical fiber  104  is fixed by a solder  108 . Although it is not shown in FIG. 1, metal layers are formed on a surface of the V-groove  102  where the solder is arranged.  
           [0009]    However, the above-mentioned optical fiber block has drawbacks that an alignment accuracy is decreased and a process time is prolonged since an individual soldering is required for each optical fiber in case of an array type fiber blocks using ribbon optical fiber.  
         SUMMARY OF THE INVENTION  
         [0010]    It is, therefore, an object of the present invention to provide a method for fabricating an optical fiber block capable of preventing an outgassing from an adhesion material and deformation of the adhesion material in a particular temperature. Also, it is another object of the present invention to provide a method for fabricating an optical fiber block capable of fixing an optical fiber easily and accurately within V-grooves.  
           [0011]    In accordance with an aspect of the present invention, there is provided a method for fabricating an optical fiber block, comprising the steps of: forming an adhesion layer and a solder on predetermined regions of a first substrate where a predetermined plurality of grooves are formed; arranging a number of optical fibers in the plurality of grooves; covering a second substrate to the first substrate; and heating the solder to bond the first and the second substrates together.  
           [0012]    In summary, the present invention provides a method for fabricating an optical fiber block capable of preventing an outgassing from an adhesion material and deformation of the adhesion material in a particular temperature. Therefore, the present invention uses a solder that has no problem of outgassing and deformation at a high temperature so as to adhere the optical fiber blocks. That is, the solder is placed on a contact region of a lower substrate and an upper substrate, and then heated to a melting temperature of the solder and rapid cooled down to room temperature as to adhere the two substrates of the optical fiber block. An adhesion layer is previously formed on either of the two substrates by taking an account of adhesion strength between the solder and the substrate. A lift-off technique is used to arrange the adhesion layer and the solder, and a halogen lamp is used for heating the solder.  
           [0013]    Also, the solder is used for directly fixing the metal-coated optical fiber and the substrate including V-grooves. In other words, the solder is deposited within the V-groove, and the metal-coated optical fiber is subsequently arranged. After the arrangement, the optical fiber is fixed and aligned within the V-groove through a heating and cooling process(hereinafter referred as to soldering process). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       [0014]    The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a diagram of the solder-bonded fiber within a V-groove;  
         [0016]    [0016]FIGS. 2A to  2 C are views illustrating a process for fabricating an optical fiber block in accordance with a preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 3 is a top view showing a lower silicon substrate wherein a solder illustrated in FIG. 2 is formed;  
         [0018]    [0018]FIG. 4 is a perspective view showing disassembled elements of an optical fiber fabricated in accordance with the preferred embodiment of the present invention;  
         [0019]    [0019]FIG. 5 is a cross-sectional view depicting an optical fiber block fabricated by using asymmetrical substrates; and  
         [0020]    [0020]FIG. 6 is a cross-sectional view for describing a process for fabricating an optical fiber block in accordance with another preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIGS. 2A to  2 C are views illustrating a process for fabricating an optical fiber block in accordance with a preferred embodiment of the present invention.  
         [0022]    Referring to FIG. 2A, V-grooves  11 A are formed on a lower silicon substrate  10  by performing a photolithography process and a wet etching process using potassium hydroxide (KOH) aqueous solutions. On the lower silicon substrate  10 , the V-groove  11 A is formed as the same number of optical fibers included in an optical fiber ribbon. Another groove  11 B is formed for inserting a portion of optical fiber coated with plastic overcoat. Herein, the groove  11 B is etched more deeply and widely than the V-groove  11 A to accommodate the overcoat.  
         [0023]    Referring to FIG. 2B, which shows the cross-sectional view according to the line A-A′ of FIG. 2A, the lower silicon substrate  10  is coated with a photoresist, and then, a surface of the lower silicon substrate  10  on which a solder  12  is set is exposed through an photolithography process. Thereafter, an adhesion layer  14  and a solder  12  are deposited on the exposed surface of the lower silicon substrate  10 . The adhesion layer  14  and the solder  12  are then remained individually at required regions by lifting the photoresist off. Herein, the adhesion layer  14  is used to reinforce an adhesion between the lower silicon substrate  10  and the solder  12 . It is preferable to use the multi layers of Ti/Ni/Au as the adhesion layer  14 . Also, it is allowable to substitute Ti with Crand to substitute Ni with Pt, Cu or the mixture of Pt and Cu. Although the solder  12  can have various constitutions, a pure Au or a mixture of Au and Sn is used. Herein, the ratio of Au/Sn is 80 wt % to 20 wt %. The thickness of the solder  12  ranges from several micro meters to tens of several micro meters. Various deposition techniques or an electro plating technique can be employed to form the solder  12 .  
         [0024]    [0024]FIG. 3 is a top view showing the lower silicon substrate after the solder  12  is formed.  
         [0025]    Referring to FIG. 2C, an uncovered part of an optical fiber  13 A is mounted in the V-groove  11 A. Subsequently, an upper silicon substrate  20  including the identical V-groove  21 B and the groove (not shown) as of the lower silicon substrate  10  is mounted on top of the lower silicon substrate  10 . After this arrangement, the solder  12  is heated at a temperature ranging from about 280° C. to about 360° C., preferably in a range of 320° C.±10° C., so as to adhere the upper silicon substrate  20  and the lower silicon substrate  10 . At this time, a halogen lamp is preferably employed for a rapid heating and cooling. In case of using the pure Au for the solder  12 , it is more preferable to employ an ultrasonic-assisted heating method.  
         [0026]    [0026]FIG. 4 is a perspective view showing disassembled parts of the optical fiber block fabricated in accordance with the preferred embodiment of the present invention.  
         [0027]    Although the process illustrated in FIGS. 2A to  2 C represents a case that the upper and the lower silicon substrates  20  and  10  are symmetrically structured, it is still possible to apply the process to an asymmetric structure of the upper and the lower silicon substrates  40  and  30  shown in FIG. 5.  
         [0028]    With reference to FIG. 5, V-grooves  31  is formed on a lower silicon substrate  30 . Compared to the V-grooves  11 A in FIG. 1A, the V-grooves  31  have a deeper depth. An upper silicon substrate  40  is different from the upper silicon substrate  20  depicted in FIG. 2C in an aspect that the upper silicon substrate  40  has a flat surface without any V-grooves formed therein. Therefore, unlike to the arrangement shown in FIG. 2B, a solder is not arranged on the lower silicon surface between the V-grooves  31 . Instead, the solder  32  is deposited merely in each edge region wherein the lower silicon substrate  30  and the upper silicon substrate  40  are contacted to each other. A reference numeral  33  represents an optical fiber, and detailed descriptions on the optical fiber  33  will be omitted. At this time, the solder adheres the lower silicon substrate  30  to the upper silicon substrate  40  through the use of adhesion layers  34  and  35 .  
         [0029]    In the preferred embodiment of the present invention, the optical fiber  33  is not directly adhered to the upper and the lower silicon substrates  40  and  30 . Indeed, a force provided from the upper silicon substrate  40  fixes the optical fiber  33 .  
         [0030]    On the other hand, another preferred embodiment of the present invention makes the solder within the V-groove, and then fixes the metal-coated optical fiber FIG. 6 is a cross-sectional view illustrating a process for fabricating an optical fiber block in accordance with another preferred embodiment of the present invention.  
         [0031]    Referring to FIG. 6, during the adhesion layer and solder formation process as shown in FIG. 2B, each predetermined thickness of an adhesion layer  52  and a solder  53  is set to be remained within each V-groove  51 . An optical fiber  54  is then arranged on the V-groove  51  of a lower silicon substrate  50 , being covered with an upper silicon substrate (not shown) thereafter. Once the solder  53  is undergone through a heating and cooling procedure, metals, e.g., Ni and Au, covering the optical fiber  54 , and the solder  53  are bonded through a strong adhesion force so that the optical fiber  54  is allowed to be fixed more firmly within the V-groove  51 . On the other hand, in the case of a symmetric structure wherein V-grooves are formed on an upper and a lower silicon substrates, it is preferable to form both the adhesion layer and the solder within the V-groove of the upper and the lower silicon substrates. In accordance with another preferred embodiment of the present invention, it is possible to fix a number of optical fibers simultaneously, and this effect results in a shortened process time and an improvement on align accuracy.  
         [0032]    Since the solder used in the present invention does not have an outgassing problem, which is usually observed in an adhesive material, epoxy, degradations of an optical fiber and an optical device can be reduced. Also, the solder is relatively insensitive to deformation in a high temperature or in a low temperature environment. As a result, the optical fiber block can be widely applicable. It is experimentally demonstrated that the solder does not causes any problem in the align accuracy of optical fiber in e a wide range of temperature environment ranging from about −40° C. to about 110° C. Furthermore, since the solder is less expensive than the epoxy, it is possible to reduce costs for fabricating the optical fiber block. In addition, the molten solder is solidified very rapidly.  
         [0033]    In summary, the present invention provides advantages as the following: an optical fiber to silicon substrate bonding is not degraded due to an outgassing; an optical fiber block has a wide applicability because of less deformations in a high temperature or in a low temperature environment; it is cost effective on the optical fiber block fabrication; a high adhesion strength between an upper and a lower silicon substrates is provided; a process duration time is shortened; and a process for fixing an optical fiber within a V-groove can be carried out accurately and rapidly.  
         [0034]    In the preferred embodiment of the present invention, there is described a case of using a silicon substrate. However, it is still possible to apply a glass substrate, a plastic substrate and so on.  
         [0035]    Also, although the preferred embodiment of the present invention demonstrates another case of constructing an array type of the V-grooves with the use of an optical fiber ribbon, the present invention can be applied to a single type of an optical fiber.  
         [0036]    While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.