Abstract:
Disclosed is an optical printed circuit board (PCB) having a multi-channel optical waveguide, which comprises: an optical waveguide having an optical path for transmitting light beams; a groove for penetrating the optical waveguide; and an optical interconnection block inserted in the groove and connected to the optical waveguide to transmit the light beams, wherein the optical interconnection block includes an optical fiber bundle bent by the angle of 90°. The optical interconnection block connects a plurality of multi-layered optical waveguides to transmit light beams to the optical waveguides. The optical fiber bundle is installed as a medium of the multi-channel optical waveguide in the optical PCB.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korea Patent Application No. 10-2004-67105 filed on Aug. 25, 2004 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to an optical printed circuit board (PCB) and an optical interconnection block using an optical fiber bundle. More specifically, the present invention relates to an optical printed circuit board with a built-in optical waveguide, and an optical interconnection block in optical PCB based optical interconnectors. 
     (b) Description of the Related Art 
     In general, a printed circuit board (PCB) represents a phenol-resin or epoxy-resin circuit board on which various components are mounted and paths for interconnecting the components are fixedly printed. As to a PCB manufacturing process, a thin film of copper is attached to one side of a phenol-resin insulation board or an epoxy-resin insulation board, the thin film is etched according to predetermined patterns to configure a desired circuit, and holes for mounting components are generated. 
     The PCB can be classified as a single layer substrate, a double layer substrate, and a multi-layered substrate, and the multi-layered substrates are used in high-precision products because the increased layers allows more installation capacity. A multi-layered PCB represents a printed circuit board having conductive patterns on at least three layers that are separated by insulation matter. 
     The copper film is patterned to form an inner layer and an outer layer on the PCB in the conventional PCB manufacturing process, but high polymers and glass fibers have been recently used to insert optical waveguides into the PCB, which is referred to as an electro-optical circuit board (EOCB). The EOCB has optical waveguides and glass substrates in addition to the copper circuit patterns and allows both electrical signals and optical signals so that the EOCB may interface very high-speed data communication executed on the same board by using optical signals and may convert the optical signals into electrical signals and store data or process signals. 
     Various coupling methods for connecting the optical signals on the multi-layered PCB have been proposed, and general multi-channel interconnection methods include the direct writing method, the beam reflection method, the reflection mirror using method, and the direct coupling method. 
       FIG. 1  shows a conventional optical PCB and an optical connection structure using an optical interconnection block. 
     Referring to  FIG. 1 , a via hole is generated in the optical PCB  1 , and an optical connection rod  4  having a reflection mirror with the angle of 45° on the top thereof is inserted into the via hole. In this instance, the reflection mirror is formed by coating silver (Ag) or aluminum (Al) on the optical connection rod  4 , or the same is configured by attaching an additional reflection mirror thereon. Light beams output by a light source of an optical transmitter are reflected by 90° on the mirror with the angle of 45° to be transmitted through an optical waveguide  2  to a mirror with the angle of 45° of the optical connection rod  4  at the side of an optical receiver, and the light beams, again reflected by 90° on the mirror, are transmitted to a photo-detector  6  of the optical receiver. 
     For example, when electrical signals are applied to the optical transmitter by a process board, the electrical signals are converted into optical signals by a laser diode  5 , the optical signals are transmitted through a lens to the left reflection mirror to be reflected, the reflected optical signals are provided through the optical waveguide to the right reflection mirror to be reflected again, and the reflected optical signals are transmitted through another lens to a photodiode  6  functioning as a photo-detector in the optical receiver. In this instance, the optical waveguide transmits the light beams through a multi-mode polymer waveguide core with low loss, and a waveguide clad is formed around the core. Therefore, the electrical signals provided by the left processor board are converted into optical signals and transmitted to the right processor board, and are then converted into electrical signals again. 
     In the prior art, when the vertical cavity surface emitting laser (VCSEL)  5  emits light, a micro-lens gathers the light and transmits the same to the optical waveguide through a PCB hole or an optical via hole  3 , and the light is transmitted to another layer through the hole. A silicon optical bench (SiOB) generally referred to as a silicon wafer is formed on the PCB  1 , and a polymer substrate can be used for the SiOB. The optical waveguide transmits the light provided by the VCSEL through the lens to another optical waveguide on another layer. 
     The VCSEL represents a light source for vertically outputting laser beams on a substrate and is used to transmit and amplify optical data. LEDs and edge emitting laser diodes (LDs) have been widely used as the light sources, although surface-emitting lasers (SELs), developed in the nineties, have recently come to be used instead of the LEDs and the edge emitting LDs. The VCSELs are used for optical fiber communication, interface, and parallel processing of large amounts of information. 
       FIGS. 2A and 2B  show conventional optical interconnection blocks configured by optical interconnectors for transmitting light beams of various channels in parallel. 
     Referring to  FIG. 2A , the optical interconnection block includes a plurality of optical connection rods  8  in parallel, each having a mirror  10  with the reflection angle of 45°. Vertical light beams  11  output from the light source of the transmitter or input to the photo-detector of the receiver are input to/output from the side  9  of the transmitter of the optical connection rod  8 , and the light beams are reflected on the mirror  10  by the angle of 90°, and are then horizontally transmitted through the optical waveguide  2  of the optical PCB  1  of  FIG. 1 . 
     Referring to  FIG. 2B , the optical interconnection block includes a plurality of parallel optical connection rods  8  bent by the angle of 90°. Vertical light beams  17  output from the light source of the transmitter or input to the photo-detector of the receiver are input to/output from the side  15  of the transmitter of an optical fiber  14 , and the light beams are horizontally transmitted through the optical fiber  14  and are transmitted through the optical waveguide  2  of the optical PCB  1  of  FIG. 1 . 
     However, it is difficult to accurately match the position of the optical fiber  8  or  14  in the optical interconnection block with the position of the optical waveguide  2  of the optical PCB  1  since the optical interconnection blocks are connected with a single optical fiber for each optical signal channel. That is, it is difficult to control an optical path when the optical paths, in the order of the light source  5  of the transmitter←→the optical fibers  8  and  14  in the optical interconnection block ←→the optical waveguide  2  in the optical PCB ←→the optical fibers  8  and  14  ←→the photo-detector  6  of the receiver, cross each other and the light beams are provided to an adjacent channel. 
     SUMMARY OF THE INVENTION 
     It is an advantage of the present invention to provide an optical PCB using an optical fiber bundle, and an optical interconnection block for increasing the tolerance of misalignment without using a single optical fiber for each channel. 
     It is another advantage of the present invention to provide an optical PCB using an optical fiber bundle, and an optical interconnection block for using an optical fiber bundle in a multi-layered optical PCB and an optical interconnection block to generate optical waveguides once, instead of individually generating the optical waveguides. 
     In one aspect of the present invention, an optical printed circuit board (PCB) having a multi-channel optical waveguide comprises: an optical waveguide having an optical path for transmitting light beams; a groove for penetrating the optical waveguide; and an optical interconnection block inserted in the groove and connected to the optical waveguide to transmit the light beams, wherein the optical interconnection block includes an optical fiber bundle bent by the angle of 90°. 
     The optical interconnection block connects a plurality of multi-layered optical waveguides to transmit light beams to the optical waveguides. 
     A diameter of a core of an optical fiber ranges from 0.5 to 20 μm. 
     A radius of inside curvature of the optical fiber bundle ranges from 0.1 to 10 mm within the thickness of the optical PCB. 
     The optical fiber bundle is installed as a medium of the multi-channel optical waveguide in the optical PCB. 
     In another aspect of the present invention, an optical interconnection block for transmitting light beams comprises: an optical fiber bundle having a plurality of optical fibers bent by the angle of 90°; and a filler for fixing the optical fiber bundle in the optical interconnection block. 
     The optical fiber includes a core and a clad, and a diameter of the core ranges from 0.5 to 20 μm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: 
         FIG. 1  shows a conventional optical PCB and an optical connection structure using optical interconnection blocks; 
         FIGS. 2A and 2B  show conventional optical interconnection blocks; 
         FIG. 3A  shows an optical interconnection block using an optical fiber bundle according to an exemplary embodiment of the present invention; 
         FIG. 3B  shows a cross-sectional view of an optical interconnection block using an optical fiber bundle according to an exemplary embodiment of the present invention; 
         FIG. 4  shows a process for assembling optical fiber bundles into grooves in an optical PCB according to an exemplary embodiment of the present invention; 
         FIG. 5A  shows an assembled structure of an optical interconnection block, an optical PCB, and an optical transmit/receive module according to an exemplary embodiment of the present invention; 
         FIG. 5B  shows a light beam propagation path according to an exemplary embodiment of the present invention; 
         FIG. 6  shows an assembled structure of optical interconnection blocks, a multi-layered optical PCB, and optical transmit/receive modules according to an exemplary embodiment of the present invention; 
         FIG. 7  shows a light beam propagation path in a multi-layered optical PCB according to an exemplary embodiment of the present invention; and 
         FIGS. 8A and 8B  respectively show a structure of an optical fiber bundle and a structure of an optical fiber bundle bent by the angle of 90° according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive. To clarify the present invention, parts which are not described in the specification are omitted, and parts for which same descriptions are provided have the same reference numerals. 
       FIG. 3A  shows an optical interconnection block using an optical fiber bundle bent by the angle of 90° according to an exemplary embodiment of the present invention, and  FIG. 3B  shows a cross-sectional view (a top surface  22  or a side surface  23 ) of an optical interconnection block using an optical fiber bundle according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 3A and 3B , the optical interconnection block  20  has an optical fiber bundle  21  in a filler, a diameter of the fiber is very much less than the diameter R of a light beam  24  for transmitting optical signals of each channel, and the optical fibers  21  are bent by the angle of 90° so as to transmit the light beams  24  in the vertical direction. 
     When the height h and the length L of the optical interconnection block  20  including the optical fibers  21  are established to be greater than the diameter R, the tolerance of misalignment is increased since the light beams  24  are connected when the light beams  24  are located at any area of the optical fiber bundle  21 . 
     Also, each optical fiber of the bundle is an independent optical waveguide, and no light beam  24  digresses from the optical fiber during transmission, and hence, the light beams are transmitted to the top surface  22  or the side surface  23  of the optical interconnection block  20  without changes of diameters of the light beams. 
       FIG. 4  shows a process for assembling optical fiber bundles into grooves in an optical PCB,  FIG. 5A  shows an assembled structure of an optical interconnection block, an optical PCB, and an optical transmit/receive module, and  FIG. 5B  shows a light beam propagation path. 
     Referring to  FIGS. 4 to 5B , optical waveguides  26  are provided in the optical PCB  25 , where the optical waveguide  26  includes a polymer optical waveguide and an optical fiber. 
     As shown in  FIG. 4 , 4-channel optical waveguides are provided in the optical PCB  25 , a groove  27 L on the transmitter side and another groove  27 R on the receiver side are generated in the optical PCB  25 , and optical interconnection blocks  20 L and  20 R are respectively inserted into the grooves. 
     When an optical transmit module  30 L and an optical receive module  30 R are installed on the optical interconnection blocks  20 L and  20 R, as shown in  FIG. 5A , after assembling the optical interconnection blocks  20 L and  20 R, the light beam  33  is transmitted in the order of a light source  31 L of the optical transmit module  30 L, a top surface  22 L of the optical interconnection block  20 L on the transmitter side, a side surface  23 L of the optical interconnection block  20 L, an optical waveguide surface  28 L on the transmitter side in the optical PCB  25 , an optical waveguide surface  28 R on the receiver side, a side surface  23 R of the optical interconnection block  20 R, a top surface  22 R of the optical interconnection block  20 R, and a photo-detector  31 R of the optical receive module  30 R. 
     The tolerance of misalignment is increased in the alignment in the side direction (the Y direction) and the depth direction (the Z direction) in the optical PCB by controlling the height h and the length L of the top surfaces  22 L and  22 R and the side surfaces  23 L and  23 R to be greater than the surfaces  28 L and  28 R of the optical waveguide in the assembling process for alignment between the optical interconnection blocks  20 L and  20 R and the optical waveguides  28 L and  28 R. 
     However, no tolerance of misalignment is increased in the alignment between the optical transmit and receive modules  30 L and  30 R and the optical interconnection blocks because it is needed to accurately align the light source  31 L and the photo-detector  31 R respectively on a predetermined position to which the light beam is input on the top surface  22 L and on another predetermined position from which the light beam is output on the top surface  22 R, since the positions are determined after the optical interconnection blocks  20 L and  20 R are assembled. 
     In this instance, the optical interconnection blocks using an optical fiber bundle are more applicable to an optical PCB into which multi-layered optical waveguides are installed, as shown in  FIG. 6 . An electrical connector  32  includes a solder for attaching the above-noted optical transmit and receive modules. 
       FIG. 6  shows an assembled structure of optical interconnection blocks, a multi-layered optical PCB, and optical transmit/receive modules according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , multi-layered optical waveguides  26   a  and  26   b  are connected to the optical interconnection blocks once when the height h of the optical interconnection blocks  20 L and  20 R is established to be higher than the height of the multi-layered optical waveguides. 
       FIG. 7  shows a light beam propagation path in a multi-layered optical PCB according to an exemplary embodiment of the present invention where the optical waveguide installed in the optical PCB is made of an optical fiber bundle. 
     Referring to  FIG. 7 , the optical fiber bundle is used as the optical waveguide  34  in the multi-layered optical PCB, and hence, the optical waveguide  34  is formed once without generating the individual optical waveguides at regular pitches, and is applicable to a multi-layered optical connection structure. 
     As shown, the optical interconnection structure between two layers is achieved by generating an N×M multi-channel optical connection (where N is a number of channels in the y direction and M is a number of channels (layers) in the z direction) without generating an inter-layer optical interconnection channel. That is, light beams  33   a  and  33   b  output by the light sources  31 La and  31 Lb are provided in the fine optical fibers and are transmitted therein, and hence, the light beams are transmitted to photo-detectors  31 Ra and  31 Rb through elements in the order of the optical interconnection block  20 L of the transmitter, the optical fiber bundle  34  in the optical PCB, and the optical interconnection block  20 R of the receiver without generation of crosstalk between layers or between channels. 
     The tolerance of misalignment is not increased in the alignment between the optical transmit and receive modules  30 L and  30 R and the optical interconnection blocks when the optical fiber bundle is used in the optical interconnection blocks but the same is not used in the optical waveguide, as shown in  FIG. 5 . Compared to this, the tolerance of misalignment of either the optical transmit module  30 L or the optical receive module  30 R is increased when the optical fiber bundle is also used in the optical waveguide. 
     For example, when the optical transmit module  30 L is provided at a random position of the top surface  21 L of the optical interconnection block with the optical fiber bundle, the light beam is transmitted to the top surface of the optical interconnection block of the receiver through the optical fibers. Hence, it is required to accurately align the optical receive module so that photo-detectors  31 Ra and  31 Rb of the optical receive module may be arranged on the positions of the light beams  33   a  and  33   b  of corresponding channels transmitted to the top surface of the optical interconnection block of the receiver. 
     In a like manner, when the optical receive module  30 R is arranged at a random position on the top surface  21 R of the optical interconnection block, it is needed to accurately align the optical transmit module  30 L so that the light beams  33   a  and  33   b  may be transmitted to the photo-detector  31  Ra and  31  Rb of the corresponding channels. 
     Therefore, it is only needed to accurately align one of the optical transmit module  30 L and the optical receive module  30 R, while it is allowed to roughly align the other one thereof, and thus the light beam is transmitted through the elements in the order of the optical interconnection block  20 L of the transmitter, the optical waveguide  34  in the optical PCB, and the optical interconnection block  20 R of the receiver, so that the light beam may not digress from the propagation path in the configuration in which the optical fiber bundles are used in the optical interconnection blocks and the optical waveguide of the optical PCB. 
       FIGS. 8A and 8B  respectively show a structure of an optical fiber bundle and a structure of an optical fiber bundle bent by the angle of 90° according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 8A , the optical interconnection block  20  and the optical fiber bundle used as an optical waveguide  33  in the optical PCB are illustrated. Fine optical fibers forming the optical fiber bundle respectively have a core  35  and a clad layer  36 . In a like manner of general optical fibers, the refractive index of the core is established to be lower than that of the clad layer so that the light beams may be transmitted following the core. 
     In this instance, the diameter D of the core  35  is established to be less than the diameter R of the light beam, and it is desirable to establish the diameter D of the core to be from 0.5 to 20 μm since the diameter of the light beams used for optical interconnection using the optical PCB is given to be. from 5 to 200 μm. 
     Further, the thickness of the clad layer  36  is to be determined in consideration of crosstalk between optical fibers, and an optical coupling loss. An evanescent wave is provided to a core of an adjacent optical fiber to generate crosstalk when the clad layer  36  is thin, and the optical coupling loss is increased when the clad layer  36  is thick. That is, most of the light beams are transmitted in the core  35 , the optical coupling loss is proportional to clad area/(core area+clad area), and hence, the optical coupling loss is further decreased as the clad layer  36  becomes thinner. 
     Referring to  FIG. 8B , the optical fiber bundle can be bent by the angle of 90° when the radius r of inside curvature of the optical fiber bundle is given to be less than the optical PCB in which the optical fiber bundle is installed. Hence, it is appropriate for the radius r to range from 0.1 to 10 mm since the thickness of the optical PCB ranges from 0.1 to 10 mm. 
     Further, it is appropriate for the height h of the optical fiber bundle to range from 50 μm to 10 mm since it is desirable for the height h thereof to be greater than the diameter R (from 5 to 200 μm) of the light beam  24  and be less than the thickness of the optical PCB. The length L of the optical interconnection block can be varied from more than 50 μm appropriate for a single channel to several tens of centimeters corresponding to the width of the optical PCB since the length L can be varied depending on the number of channels and channel pitches. 
     Therefore, the above-described exemplary embodiment applies optical fiber bundles to the optical PCB, into which optical waveguides are installed, and the optical interconnection blocks, to thus generate optical paths. The optical PCB and the optical interconnection blocks using optical fiber bundles increase the tolerance of misalignment of optical paths compared to the prior art using a single optical fiber, and easily realizes multi-layered optical connection. In this instance, the optical fiber bundles are made of plastic optical fibers (POFs) or silica optical fibers, and the optical interconnection block includes an optical fiber bundle bent by the angle of 90° and installed in a filler. 
     Therefore, when the optical interconnection block is arranged into a groove in the optical PCB, the light beams output by the light source provided on the optical PCB are horizontally transmitted in the optical waveguides, and are then transmitted to the photo-detector provided on the optical PCB. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.