Patent Abstract:
The present invention provides an optical bridge for interconnecting optical networking components and methods of making optical bridges that include a waveguide that are compatible with semiconductor processing steps. The optical bridge of the present invention has less optical losses and is less affected by misalignment that prior art interconnections. The waveguide is formed of a curable optical material that spans optically active areas of two components. In one embodiment of the present invention, one optical component is an optical circuit board and the connected optical component is an electro-optical integrated circuit package containing light emitting or light receiving elements. The method provides a curable optical liquid to the components, bringing the components together to form a continuous optical liquid between the components, and curing the optical liquid.

Full Description:
FIELD OF THE INVENTION 
   This invention is related to interconnecting optical devices. In particular, the present invention is directed to devices and methods for optically connecting electronic components and optical circuit boards. 
   BACKGROUND OF THE INVENTION 
   The growth of networks capable of handling high data-rate transfer of voice and data has created a demand for optical networks. While information can be transferred optically over large distances, there is also a need for interfacing the optical portion of an optical network with electrical and electro-optical components. Thus, for example, optical networks include amplifiers for strengthening optical beams, switches for routing signals, and conversions between electrical and optical signals at either end of the network. These functions are performed by devices that include optical, electro-optical and electrical components. 
   As with electronic devices, it is advantageous to arrange optical and electro-optical components in a chip-like configuration on a circuit board that allows for interconnection between devices. Numerous methods have been proposed for the interconnection of optical beams of integrated circuit chips. Each of these methods has problems in aligning or having losses in the transmission of the optical beam, or is expensive or difficult to produce or use. Other problems occur when attempting to scale the proposed methods to accommodate a large number of optical beams. 
   In one system, an electro-optical chip is positioned over a substrate with a ball grid array. An emitter of the chip is aligned with a waveguide on the substrate, and signals are transmitted between the chip and substrate without an intervening material, that is, the interconnection is through free space. Since there is nothing to guide the beam between the components, such a system is susceptible to losses mostly due to component misalignment and the light beam divergence. Lenses can be used to couple the beam between the transmitter and the waveguide as well as between the waveguide and receiver. However, the lenses need to be well aligned with the other components and also have back reflections that results in additional optical power losses. In another system, optoelectronic transmitters and receivers are coupled without wave guiding structures. The emitted light is collimated in beams of 0.5–1 mm size and the holographic optical elements (“HOEs”) or other coupling gratings are used to direct optical beams from optoelectronic transmitters directly into receivers located at a relatively large distance, usually more than 10 mm. This type of interconnect has the disadvantage of very difficult alignment procedures as well as of space required for the collimating lenses and thus reduced possibilities for compact integration. 
   Therefore, it would be desirable to have an optical interconnect and method that are compatible with existing interconnect technology, are relatively insensitive to slight misalignment between the components, have minimal or no optical loss, that prevent particles from interfering with light transmission, and that can be easily scaled to devices that transmit many optical beams. It is also desirable to have an optical connection and method that does not require extensive processing of the chips and that is reliable and relatively inexpensive. 
   SUMMARY OF THE INVENTION 
   The present invention provides optical interconnections and methods for providing optical interconnections between optical or electro-optical components and an optical circuit board. 
   It is one aspect of the present invention is to provide a device and method for optically connecting two components wherein the components are parallel and spaced apart, and separated by an optical polymer. 
   It is another aspect of the present invention to provide an optical bridge having a lower divergence angle than free-space interconnects. 
   It is yet another aspect of the present invention to provide an optical bridge that is self-correcting for slight misalignment or movement between components. 
   It is one aspect of the present invention to provide a waveguide between optically active areas of optical components. 
   It is another aspect of the present invention to provide an optical bridge that prevents particles from interfering with light transmission between optically active areas of optical components. 
   It is another aspect of the present invention to provide an optical bridge for communicating between optical components, where light is transmitted between pairs of optically active areas. Each pair of optically active areas includes a first optically active area on a first optical component and a second optically active area on a second optical component in opposed spaced apart relationship to the first optical component. The optical bridge includes one or more waveguides each extending between a corresponding pair of optically active areas and each having an outer surface between the corresponding pair of optically active areas with a concave cross-section. In one embodiment of the present invention, the optical bridge is formed from an optical liquid and comprises a wetting surface of the optical liquid on at least one optically active area of the corresponding pair of optically active areas, with a non-wetting surface surrounding the wetting surface. In another embodiment, the optical bridge further comprises a non-wetting surface of the optical liquid surrounding at least one optically active area of the corresponding pair of optically active areas. Additionally, the waveguide has a boundary at the optically active areas that is equal to or greater than the boundary of the optically active area. For optically active areas that transmit light from the optical component, the waveguide has approximately the same or a larger boundary than the optically active area, and for optically active areas that receive light into the optical component, the waveguide has a boundary approximately equal to the optically active area. 
   It is yet another aspect of the present invention to provide an apparatus for optically communicating through one or more optically active areas of an optical component to an optical circuit board. The apparatus includes an optical circuit board having a surface comprising at least one optically active area, and one or more optical bridges each including a waveguide. In one embodiment, the waveguide extends between a corresponding pair of optically active areas and has an outer surface between the corresponding pair of optically active areas having a concave cross-section. In another embodiment, the optical bridge is formed from an optical liquid and further comprises a wetting surface of said optical liquid on at least one optically active area of the corresponding pair of optically active areas. In yet another embodiment, the optical bridge further comprises a non-wetting surface surrounding at least one optically active area of the corresponding pair of optically active areas. Additionally, the waveguide has a boundary at the optically active areas that is equal to or greater than the boundary of the optically active area. If one of the optically active areas is a transmitting area, the waveguide has approximately the same or a larger boundary than the optically active area, and if the optically active area is a receiving area, the waveguide has a boundary approximately equal to the optically active area. 
   It is one aspect of the present invention to provide a method of forming an optical bridge. The method includes: depositing a curable optical liquid on either one or both of a pair of optically active areas including a first optically active area of a first optical component and a second optically active area of a second optical component opposing and spaced apart from the first optical component; aligning the first and second optical components with the pair of optically active areas in an opposing relationship and having a spacing therebetween; adjusting the spacing to where the optical liquid contacts each of the pair of optically active areas; and curing the optical liquid. In one embodiment, the optically active area includes a wetting surface, and the depositing deposits the curable optical liquid on the wetting surface. In another embodiment, one or both optical components include a non-wetting surface surrounding the corresponding optically active area. The method alternatively includes forming a spacing element on one or both of the first and second optical components, and the adjusting step includes contacting the spacing element and the optical components. In another alternative method, the first optical component is an optical waveguide having an embedded waveguide core, and the method includes providing an opening from the first optically active area to the waveguide core and depositing the optical liquid in the opening. 
   These features, together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the optical deflecting device, optical switching modules and method of the present invention, preferred embodiments thereof being shown with reference to the accompanying drawings, by way of example only. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The foregoing aspects and the attendant advantages of this invention will become more readily apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a top plan view of a circuit board having an integrated optical waveguide with optical components mounted thereon; 
       FIG. 2  is a sectional side view  2 — 2  of  FIG. 1  showing an embodiment of the present invention; 
       FIGS. 3A ,  3 B, and  3 C are sectional side views showing several embodiments of an optical bridge of the present invention, where  FIG. 3A  is a first embodiment of an optical bridge having a longitudinal concave shape with a waist between the two bridge ends,  FIG. 3B  is a second embodiment of an optical bridge having a longitudinal concave shape with a waist at one of the two bridge ends, and  FIG. 3C  is a third embodiment of an optical bridge having a convex shape; 
       FIG. 4A  is a detailed sectional side view of the first embodiment of an optical bridge of the present invention transmitting light from an optoelectronic integrated circuit (“OEIC”) to a circuit board; 
       FIG. 4B  is a detailed sectional side view of the first embodiment of an optical bridge of the present invention transmitting light from a circuit board to an OEIC; 
       FIGS. 5A and 5B  are sectional side views the optical bridge of  FIG. 4A  illustrating the inherent optical alignment of the optical bridge during two lateral displacements of the optical bridge; 
       FIGS. 6A ,  6 B,  6 C, and  6 D are sectional side views illustrating a method for manufacturing the first embodiment of the optical bridge of the present invention, where  FIG. 6A  shows a deposited optical liquid on a circuit board,  FIG. 6B  shows contact between the circuit board and component,  FIG. 6C  shows the circuit board and component being separated to form the optical bridge, and  FIG. 6D  shows the optical bridge after curing; 
       FIGS. 7A ,  7 B, and  7 C are sectional side views illustrating an alternative method for manufacturing the first embodiment of the optical bridge of the present invention, where  FIG. 7A  shows a deposited optical liquid on a circuit board and opposing component,  FIG. 7B  shows the circuit board and component contacting, and  FIG. 7C  shows the optical liquid being UV cured; and 
       FIGS. 8A ,  8 B,  8 C, and  8 D are sectional side views illustrating a method for manufacturing the second embodiment of the optical bridge of the present invention, where  FIG. 8A  shows a the preparation of the circuit board for depositing optical liquid,  FIG. 8B  shows the deposition of optical liquid on the circuit board,  FIG. 8C  shows the circuit board and component being contacted, and  FIG. 8D  shows the circuit board and component separated and cured to form the optical bridge. 
   

   Reference symbols are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein. 
   DETAILED DESCRIPTION 
   The present invention is directed to devices and methods for providing a waveguide to permit optical communications between optical components, for example between light emitting or light receiving elements and a waveguide of an optical circuit board. In particular, the invention is an “optical bridge” formed of a material positioned between the optical components and arranged to facilitate the exchange of optical signals across the optical bridge as a waveguide. In general, the optical bridges of the present invention include materials, such as optical polymers, which are shaped to facilitate the transmission of optical signals. The optical bridge may either be surrounded by free space, or alternatively may be surrounded by another material, such as an underfill material, that does not interfere with the transmission of light. 
   Several examples of optical bridges are presented herein as providing a waveguide between an optical component and an optical circuit board on which the component is mounted. This selection of optical components is illustrative and is not meant to limit the scope of the present invention. Optical circuit boards typically include both electrical wiring and embedded waveguide cores for optical communication. One example of an optical circuit board is described in U.S. Pat. No. 6,611,635 to Yoshimura, et al, which is assigned to the assignee of the present application and incorporated herein by reference. The optical bridge of the present invention is in contact with the waveguide core and a component mounted on the board that transmits light, such as light emitting diodes (LED) or vertical cavity surface emitting lasers (VCSEL), or that receives light, such as photodiodes (PD). Alternatively, the optical connection may be between two circuit boards, for example between an optical circuit board and an optical daughterboard, or between transmitting and receiving components. The optical bridges and methods of making optical bridges of the present invention are compatible with methods of forming electrical connections between components and circuit boards, and permits both optical and electrical connections between opposing sides of a component and circuit board, for example in a flip-chip configuration. 
   Referring now to the figures in combination with the description hereinafter presented, and wherein similar parts of the embodiment of the present invention are identified with like reference numbers,  FIG. 1  is a top view of a circuit  100  formed from an optical circuit board  101  on which is mounted integrated circuits including one or more optoelectronic integrated circuit (OEIC) chips  103 , and  FIG. 2  is a side sectional view  2 — 2  of  FIG. 1  showing optical bridges  200   a  and  200   b , or in general  200 . In general, optical circuit board  101  can be a multi-level substrate, such has a multi-layer printed circuit board having one or more electrical layers (not shown) and one or more waveguides  107 . In addition to OEICs  103  connected to electrical and optical layers, circuit  100  may also include one or more electronic integrated circuit chips that are connected to only the electrical layers of board  101 . 
   Circuit  100  includes OEICs  103   a ,  103   b ,  103   c , and  103   d , which are components that are mounted on and communicate with board  101  by a combination of optically and/or electrical signals. Thus, for example each OEIC  103  may include one or more light sources, such as an LED or VCSEL, and/or one or more light receivers, such as an LED. In general, circuit  100  includes electrical and optical signals, and optical bridge  200  forms an optical path for the light between each OEIC  103  and board  101 . For example, a light source, such as an LED or a VCSEL of one OEIC  103  sends an optical signal through optical bridge  200  into board  101 . The light signal is then directed to a light receiver, such as a PD, of another OEIC  103 . 
   In addition to the optical connection discussed herein, OEIC  103  is electrically attached to board  101 . Electrical connection methods are well known in the art and include, for example, the use of solder bumps, wire-bonding, and conductive adhesive. Thus, for example, board  101  and OEIC  103  may, as shown in  FIG. 2 , be electrically connected by conductors  209 , which can be solders ball, posts or similar structures to provide electrical connections between the board and OEIC, as are known in the art. An underfill or other mechanical support (not shown in  FIG. 2 ) can be provided between board  101  and OEIC  103  for bonding the component to the board. The underfill should have optical properties that do not interfere with optical waveguide  200 . In general that implies that the underfill should be optically transparent material, or at least not absorbing, and have a refractive index lower than the polymer used for optical bridge  200 . 
   Thus, for example, an OEIC containing an LED is mechanically attached to the board, is electrically connected to the board to provide power to the LED, and is optically connected to the board to allow light from the LED to pass into a waveguide of the optical circuit board. 
   The details of optical bridge  200  and the connection to board  101  and OEIC  103  are now presented with reference to  FIGS. 1 and 2 . Board  101  is a multilayer substrate having, for example, one or more conductors  109 , such as conductive layers and vias and the like, for transmitting electrical signals, and one or more optical waveguides  107  for transmitting optical signals. As shown in  FIG. 1 , components  103  are positioned on top of conductors  109  and waveguides  107  with connections made between the components and one or more of the conductors and waveguides, as necessary. In general, optical bridges  200  are positioned between a pair of optically active areas  207  consisting of an optically active area  113  of surface  111  and an optically active area  213  of surface  201 . The term “optically active area” refers to a surface area of a board or component through which light may propagate for optical communication with another board or component. 
   As is further illustrated in  FIG. 2 , waveguide  107  includes a first waveguide  107   a  within the plane of board  101  and a second waveguide  107   b  perpendicular to the first waveguide and out of the plane of the board. Waveguide  107  is preferably a multimode waveguide having cross-sectional dimensions of 10–100 μm, preferably from 20–50 μm. Each waveguide  107   a ,  107   b  is surrounded by a cladding  107   c  having a refractive index that differs from the waveguide refractive index. Each waveguide  107   a ,  107   b  also has a corresponding angled portion  115   a ,  115   b , preferably angled at 45°, for redirecting light between a direction within waveguide  107  and a direction perpendicular to surface  111  and towards optically active area  113   a ,  113   b . Component  103  includes a light emitting sub-component  203  that projects light through optically active area  213   a  of surface  201 , and a light receiving sub-component  205  that accepts light through optically active area  213   b  of surface  201 . The direction of light propagation during optical communication is indicated by the arrows in the corresponding light bridge  200 . Surfaces  111  and  201  may include pads  211  on and/or near optically active areas  113  and  213  to aid in forming the shape of the bridges, as described below. 
   Optical bridge  200  is formed from a material  303  having a surface  301  that acts as a waveguide between optically active areas  113  and  213 . As shown in  FIG. 2 , board  101  has a surface  111  that opposes a surface  201  of component  103 . Each surface  111  and  201  has optically active area that forms a pair of optically active areas for optical communication. As illustrated, surface  111  has optically active areas  113   a  and  113   b . As indicated by the arrows in  FIG. 2  within optical bridges  200 , area  113   a  receives optical signals and area  113   b  transmits optical signals. Surface  201  has optically active areas  213 , shown as areas  213   a  and  213   b , for light communication with optically active areas  113   a  and  113   b , respectively.  FIG. 2  thus shows two pairs of optically active areas: a first pair  207   a  comprising optically active areas  113   a  and  213   a  connected by first optical bridge  200   a , and a second pair  207   b  comprising optically active areas  113   b  and  213   b  that are connected by second optical bridge  200   b.    
   In the embodiment of  FIG. 2 , surfaces  101  and  201  are planar and parallel. Optically active pairs  207  are spaced a distance x apart. The present invention is useful for a wide range of spacing between surfaces  201  and  111 . The distance x can be from 10 μm (micron) to 1000 μm, preferably from 50 μm to 150 μm 
   Optical bridge  200  is formed from a material that is optically transparent at the wavelengths used between pairs of optically active areas  207 . In general, bridge  200  is formed from a material  303  that defines a surface  301  extending longitudinally between a first end  305  at surface  101  and a second end  307  at surface  201 . It is preferred that ends  305  and  307  have boundaries that have at least the same extent as the corresponding surfaces of active areas  113  and  213 , respectively. It is preferred that optical bridge is formed from a curable liquid polymer with a refractive index of between the refractive index of waveguide core material  107  and the RI of optically active areas  207  and is surrounded by a gas, such as air, or by another solid material having a lower refractive index than material  303 . As described subsequently, the propagation of light between the pair of optically active areas  207  is determined by the shape of surface  301 , the size and position of ends  305  and  307  with respect to optically active areas  113  and  213 , and the refractive index of bridge  300  and any material surrounding material  303 . 
   As an example of optical bridges of the present invention, several exemplary embodiments are illustrated in  FIGS. 3A–3C  as a first, second, and third optical bridge of the present invention,  200 ′,  200 ″, and  200 ′″, respectively. The exemplary embodiments illustrate the optical bridge of the present invention, and are not intended to limit the scope of the present invention. Optical bridge  200 ′ ( FIG. 3A ) has a surface  301 ′ between first end  305 ′ and second end  307 ′, with a waist  309 ′ midway between the ends. The longitudinal cross-sectional shape of surface  301 ′, as shown in  FIG. 3A  is concave with a minimum extent at waist  309 ′ and a maximum extent at ends  305 ′ and  307 ′, and the transverse cross-sectional shape (not shown) is approximately circular. The profile of  FIG. 3A  is a preferred embodiment of the present invention. Ideally, the preferred shape of the optical bridge comprises a cylinder with perfectly straight walls. As a practical matter, it is almost impossible to achieve this preferred shape and, therefore, the inward wall curvature of  FIG. 3A  is preferred. However, in order not to exclude the straight-walled shape of a cylinder, as used herein the term “concave” is defined to include a wall which has no curvature. 
   Optical bridge  200 ″ ( FIG. 3B ) has a surface  301 ″ between first end  305 ″ and a larger second end  307 ″. Surface  301  ″ is tapered from second end  307 ″ to a waist  309 ″ at first end  305 ″. The longitudinal cross-sectional shape of surface  301 ″ is thus concave and tapered from the larger second end  307 ″ to first end  305 ″. Optical bridge  200 ′″ ( FIG. 3C ) has a surface  301 ′″ between first end  305 ′″ and a larger second end  307 ′″. Surface  301 ′″ is convex between first end  305 ′ and second end  307 ′ with a maximum size at bulge  311 . The longitudinal cross-sectional shape of surface  301 ″ is thus convex. 
   Optical bridge  200 ′ is now described in more detail with reference to the detailed sectional side view of  FIG. 4A , showing optical bridge  200   a ′ which transmits light from OEIC  103  to circuit board  101 , and of  FIG. 4B , showing optical bridge  200   b ′, which transmits light from the circuit board to OEIC  103 . Optical bridges  200   a ′,  200   b ′ include a corresponding bottom pads  401   a ,  401   b  over active areas  113   a ,  113   b , top pads  403   a ,  403   b  over active areas  213   a ,  213   b , and optical material  303  between the respective top and bottom pads. Pads  401   a ,  401   b ,  403   a , and  403   b  are optically transparent, and help control the shape of optical material  303 , as described subsequently. As shown in  FIG. 4A , optical bridge  200 ′ can be surrounded by an underfill  407  in the space between OEIC  103  and circuit board  101 . It is important that the refractive index of underfill  407  is lower than that of optical material  303  and is not absorbing at the operating light wavelength to prevent light leakage and loss from optical bridge  200 ′. In an alternative embodiment, the shape of material  303  on active areas  113   a ,  113   b ,  213   a , or  213   b  can be controlled by placing barriers (not shown) outside of the active areas to prevent the spread of material  303 . 
   Active areas  113   a ,  113   b  are at an end of waveguides  107   a ,  107   b , and include a cladding  404  to contain light propagation through the waveguide. Active area  213  can be either the active area of a light transmitting component, such as the output aperture  203  of a VCSEL, or the active area of a light receiving component, such as active area  213   b  of a PD. Where there a bridge has a specific direction for light propagation, the bridge shape can be tailored to reduce optical losses. Specifically, the transmission of light through an optical bridge is in part determined by the relative size of the ends of the optical bridge and the corresponding optically active areas. For an optically active area that transmits light, the optical bridge end is preferably equal or larger than the optically active area so that all or nearly all of the transmitted light enters the optical bridge. For an optically active area that receives light, the optical bridge end is preferentially approximately equal to the optically active area or smaller so that all or nearly all of the light is received by the optically active area. Thus, for example, the end of the optical bridge that accepts light preferably covers an area equal to or larger than the active area from which light is accepted, and the end of the optical bridge transmitting light preferably has an area equal to or slightly larger than the active area which receives light. The preferred configurations are shown, for example, in  FIG. 4A , which shows OEIC  103  having a light transmitting component and having end  307   a ′ larger than active area  203  and end  305   a ′ slightly larger than active area  113   a , and in  FIG. 4B , which shows OEIC  103  having a light receiving component and having end  307   b ′ corresponding to the shape of active area  213   b  and end  305   b ′ slightly larger than active area  113   b.    
     FIGS. 5A and 5B  are sectional side views of the optical bridge with a displaced OEIC  103 . Specifically,  FIGS. 5A and 5B  shown the effect of laterally translating OEIC  103  from the aligned configuration of  FIG. 4A , as indicated by the horizontal arrows of  FIGS. 5A and 5B . The lateral translation of  FIGS. 5A and 5B  can represent a misalignment of OEIC  103  during manufacturing or the displacement as the result of a force to circuit  100 . Optical material  303  is preferably a polymeric material that can accommodate some lateral motion. In addition, the deformation of material  303  in response to lateral motion does not appreciably affect the optical performance of optical bridge  200  since the light is guided due to the total internal reflection in the bridge. 
   The optical bridge of the present invention has many advantages over prior art optical interconnects. Thus, for example, free-space transmission results in typical divergence angles of 10–40°. Due to this strong divergence, there can be large optical losses even across short distances, such as 50 μm to 150 μm. In contrast, optical bridge  200  confines light as it propagates between an OEIC and an optical circuit board, reducing coupling losses. In addition, optical bridge  200  prevents foreign particles from blocking the light path. Also, as shown in  FIGS. 5A and 5B  the shape of optical bridge  200  can adapt to lateral movements of the component and is self-focusing. Also, the optical bridge material reduces the backreflection losses since its refractive index better matches the refractive indexes of the optically active areas connected by the bridge. 
   Steps for manufacturing optical bridge  200 ′ from an optical liquid  601  that can be cured to form optical material  303  is shown in the sequence of sectional side views  FIGS. 6A–6D , where optically active area  113  is a light receiving surface and optically active area  213  is a light transmitting surface. Examples of optical liquid  601  include, but are not limited to heat-curable or UV light-curable polymers. Prior to the step illustrated in  FIG. 6A , pads are formed on board  101  and OEIC  103  to aid in the shaping of optical bridge  200 ′. Specifically, wetting pad  401  is formed substantially over the optically active area  113  of the light receiving surface, wetting pad  403  is formed over an area equal or larger than the optically active area  213  of the light transmitting surface, and stand-off pads  603  are formed on surface  111 . It is preferred that wetting pads  401  and  403  are formed from a material that allows optical liquid  601  to wet the pad, and that surfaces  111  and  201  surrounding the wetting pads are non-wetting surfaces, resulting in optical liquid  601  being confined to the surface of the wetting pads. For example, an optical liquid  601  of optical epoxy or gel wets an optical polymer(epoxy, polyimide etc.) surface and does not wet a metal or oxide dielectric surface. Forming wetting pads  401  and  403  of polymer with surfaces  111  and  201  of metal or oxide causes an epoxy optical liquid  601  to remain over the wetting pads. Alternatively, pads  401  or  403  can be surface finishes that provide appropriate wetting properties. 
   Thus, for example wetting pads  401  and  403  are optical polymers and are formed on surfaces  111  and  201  by spin coat and lithographic patterning. Stand-off pads  603  are mechanical stops that provide a stand-off height H of from 20 μm to 500 μm between board  101  and OEIC  103  during processing. Pads  603  are formed, for example, from standard polymers used in electronics packaging using the process of e.g., spin coating. 
   As shown in  FIG. 6A , a predetermined amount of optical liquid  601  is dispensed on wetting pad  401  of circuit board  101 , and a OEIC  103  having a wetting pad  403  is positioned over the circuit board. Optical liquid  601  is a liquid that, when cured, forms optical material  303 . It is important that optical liquid  601  has fluid properties that permit the liquid to wet pads  401  and  403 , and not spread onto the surface surrounding the pads. 
   Next, as shown in  FIG. 6B , OEIC  103  and circuit board  101  are moved into contact with pads  401  and  403  aligned. Stand-off pads  603  provide spacing, but allow liquid  601  to contact wetting pad  403 . At this point, liquid  601  may extend beyond wetting pads  401  and  403  without wetting the surrounding surfaces. In an alternative embodiment, pads  603  are incorporated onto the surface of OEIC  103 . 
     FIG. 6C  shows circuit board  101  and OEIC  103  being separated to a predetermined separation distance X. Liquid  601  remains wetted to pads  401  and  403  during the separation indicated in  FIG. 6C , resulting in a concave shape having a waist midway between pads  401  and  403 . In the best case the shape of the bridge has perfectly straight sidewalls. However, due to surface tension effects and lack of necessary precision, as a practical matter it is extremely difficult to achieve straight sidewall. Lastly, optical liquid  601  is cured, preferably by heating or UV light exposure, to form optical material  303  of optical bridge  200 ′ as shown in  FIG. 6D . The temperature at which optical liquid  601  cures depends on the fluid, and can range from room temperature to an elevated temperature of up to 200° C. maintained for several minutes to many hours. 
   The shape of optical bridge  200 ′ depends on the amount of optical liquid dispensed between board  101  and OEIC  103 , the size of pads  401  and  403 , the spacing X, and the change in volume of optical liquid  601  upon curing. An optical bridge  200  having a final bridge height of 100 μm, with top and bottom pads having a diameter of 50 μm, requires about 2×10 −4  mm 3  of optical fluid. To achieve this configuration, the height of the stand-off pad should be in the range of 30–80 μm, depending on the viscosity of the optical material. As noted previously, the transmission of light is increased by having an optical bridge that is larger than the optically active area of the transmitting side and that matches the optically active area of the receiving side. 
   Alternative steps for manufacturing optical bridge  200 ′ from an optical liquid  709  that can be cured to form optical material  303  are shown in  FIGS. 7A–7C . Optical liquid  709  is a UV-curable (or thermally curable), such as UV-curable epoxy or gel, which remains a viscous liquid until exposed to UV radiation, as described below. As shown in  FIG. 7A , board  101  has a pair of stand-off pads  701  and OEIC  103  has a pair of stand-off pads  703 . Pads  701  and  703  are formed by the methods previously described with reference to  FIGS. 6A–6D , and are positioned to oppose each other and cooperate to provide a combined stand-off height H. Before arranging board  101  and OEIC  103  in the opposing position shown in  FIG. 7A , the board and OEIC are faced with pads  401  and  403  facing upwards, and predetermined amounts of an optical liquids  705  and  707 , which are preferably the same type of liquid, is dispensed on wetting pad  401  and  403 , respectively. Board  101  and OEIC  103  are then faced in opposition, as shown in  FIG. 7A . The board  101  and OEIC  103  are the moved together as shown in  FIG. 7B , allowing optical liquids  705  and  707  to coalesce form a single mass of fluid  709  having a concave shape. Waveguide  107  is provided with UV radiation, indicated by the arrow in  FIG. 7C . Waveguide  107  directs the UV radiation upwards and through fluid  709  to cure the fluid and form optical bridge  200 ′. 
   Steps for manufacturing optical bridge  200 ″ from an optical liquid  601  that can be cured to form optical material  303  is shown in the sequence of sectional side views  FIGS. 8A–8D . Optical bridge  200 ″ extends from a point inside of an optical circuit board  101 ′ to a wetting pad  403  on OEIC  103 . Specifically, as shown in  FIG. 8A , optical circuit board  101 ′ has a waveguide  107  that terminates at angled portion  115  that has a finish that reflects light 45°, as described previously. As a first step, surface  111  is provided withstand-off pads  603  having height H and optional non-wetting pads  803  surrounding optically active area  113 , if necessary. It is preferred that non-wetting pads  803  are formed from a material that prevents optical liquid  601  from wetting the pads. Thus, for example non-wetting pads  803  are metal or oxide and are formed on surface  111  by e.g. sputtering. As a next step, an opening  801  is formed through optically active area  113 , into optical circuit board  101 ′ and to angled portion  115 . Opening  801  may be formed by etching, laser drilling, or other known techniques. 
   As shown in  FIG. 8B , optical liquid  601  is next dispensed into opening  801  to a height greater than H above surface  111 . Non-wetting pads  803  prevent fluid  601  from adhering to the surface beyond optically active area  113 . Next, as shown in  FIG. 8C , OEIC  103  and circuit board  101 ′ are moved towards one another until OEIC  103  touches stand-off pads  603 . The movement of OEIC  103  and circuit board  101 ′ to the point where the spacing is determined by stand-off pads  603  results in fluid  601  contacting wetting pad  403  without wetting the surfaces surrounding the wetting pads. Optionally, stand-off pads  603  are not needed if the motion of OEIC  103  and circuit board  101 ′ during the approach of these components are controlled accurately enough to achieve spacing H. 
     FIG. 8D  shows circuit board  101  and OEIC  103  being separated to a predetermined separation distance X. Fluid  601  extends from angled surface  115  to pad  403  during the separation indicated in  FIG. 8D , resulting in a concave shape having a waist near non-wetting pad  803 . Lastly, optical liquid  601  is cured to form optical material  303  of optical bridge  200 ″ as shown in  FIG. 8D . It is preferred that the refractive index of optical material  303  matches the refractive index of waveguide  107 . Optical bridge  200 ″ formed in this way confines the light passing between the light emitting or receiving component of OEIC  103  and waveguide  107  of optical circuit board  101 ′, substantially minimize the coupling loss of light through the optical bridge. 
   The processes described with reference to  FIGS. 6–8  are examples of processes that form one or more optical bridges between the optical components and the optical circuit board. These processes can be applied in parallel with other processes, including but not limited to mechanical attachment techniques such soldering or conductive epoxy bonding. 
   The present invention thus provides a device and method for connecting two optical components. The embodiments described above are illustrative of the present invention and are not intended to limit the scope of the invention to the particular embodiments described. Accordingly, while one or more embodiments of the invention have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit or essential characteristics thereof. For example, while the present invention describes the use of certain optical polymers, other polymers or combinations of polymers may be used. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Technology Classification (CPC): 6