Patent Publication Number: US-6905260-B2

Title: Method and apparatus for coupling optical elements to optoelectronic devices for manufacturing optical transceiver modules

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following co-pending applications, each assigned to the Assignee of the present invention. 
     application Ser. No. 09/749,279, filed Dec. 26, 2000, entitled “Apparatus for Holding an Optical Element”; 
     application Ser. No. 09/749,281, filed Dec. 26, 2000, entitled “An Apparatus and Method of Using Flexible Printed Circuit Board in Optical Transceiver Device (as amended)”; 
     Application Ser. No. 09/749,282, filed Dec. 26, 2000, entitled “Attenuator and Conditioner”; 
     Application Ser. No. 09/749,283, filed Dec. 26, 2000, entitled “Optoelectronic Mounting Structure”; 
     Application Ser. No. 09/749,284 filed Dec. 26, 2000, entitled “Optical Transmitter, Receiver or Transceiver Module”; 
     Application Ser. No. 09/749,285 filed Dec. 26, 2000, entitled “Housing and Mounting Structure”; and 
     Application Ser. No. 09/749,286, filed Dec. 26, 2000, entitled “Optical Power Control System”. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a process for coupling optical elements to optoelectronic devices, and the process may be used in conjunction with making an optical transmitter, receiver or transceiver module. 
     BACKGROUND OF THE INVENTION 
     Fiber optics are one of the most important new media for transmitting information. Fiber optics are capable of carrying enormous quantities of voice, data and video traffic on light impulses over hair-thin glass fibers. Fiber optics transmit more information and data over a shorter period of time than circuit-transmission media. For example, optical signals may be transmitted over fiber optics with losses of less than 0.1 dB/km. In sharp contrast, data generally is transmitted over a pair of twisted copper wires with losses of up to 50 dB/km. The capabilities of fiber optics have fundamentally changed communications. 
     The fiber optics industry has exploded as the Internet and telecommunication field have created a skyrocketing demand for broadband, high-speed pipe lines to carry data. Long-span fiber optic networks of 100 kilometers or more carry bandwidth ranging from 40 to 50 giga bites per second. Similarly, high-speed fiber optics are capable of connecting wide-area networks of approximately 200 kilometers. Also, fiber optics may connect metropolitan networks of 500 meters to 2 kilometers, such as connecting one building to another building. The largest growth area for high-speed fiber optics, however, is connecting distances of less than 300 meters. In this sub-300 meter or short-distance market, fiber optics are used for a wide variety of purposes, including connecting computers within a room and linking routers, switches and transport equipment. 
     While significant progress has been made in the area of fiber optics, more wide-spread use is dependent upon the availability of a low cost, easy-to-use and efficient (i.e., low loss of light) optical transmitter and receiver module to link fiber optics to various electronic devices and components such as computers and routers. A critical aspect of such a module is the accurate alignment and attachment of the individual optical fibers to the electronic devices that transmit and receive light streams to and from the optical fibers. These electronic devices, known as optoelectronic devices, use optical and electronic technology or optoelectronics to convert electrical signals into optical radiation or light and transmit the radiation into optical fibers. Other optoelectronic devices receive optical radiation from optical fibers and convert it into electrical signals for processing. Accurate alignment and attachment of the individual optical fibers to the optoelectronic devices is essential to achieving a good and efficient optical connection, one that produces a low loss of light at the interface between the optical fibers and the optoelectronic devices. 
     A known method for precisely coupling optical fibers to optoelectronic devices is active alignment. Specifically, a photo-detector is placed at one end of an optical fiber, and an optoelectronic device, such as a vertical cavity surface emitting laser, is placed near the other end of the optical fiber. After turning on the laser, the optical fiber is manipulated manually around the light-emitting surface of the laser until the photo-detector detects the maximum amount of optical radiation as indicated by an output electrical signal. Similarly, a photo-detector can be actively coupled to an optical fiber by transmitting laser light into one end of an optical fiber and manually adjusting the position of the other end of the optical fiber relative to the photo-detector until the detector receives the maximum amount of optical radiation. 
     Actively aligning an array of optical fibers to an array of optoelectronic devices is not practical because the dimensions of an optoelectronic device and the cross-section of an optical fiber are small and multiple dimensions of rotation and translation motion must be controlled. The active alignment process to connect even a single optical fiber strand to an optoelectronic device is usually time-consuming and requires knowledge, skill and expertise. The active alignment process is particularly laborious and time-intensive when a number of optical fibers must be individually aligned to an array of optoelectronic devices. This process requires a variety of relatively complex and costly components that significantly increase the fabrication costs to produce precisely aligned optical devices. Moreover, during the active alignment process, optoelectronic devices emit a significant amount of optical power and energy. The heat generated by the devices can produce thermal strain that may cause the optical fibers and the optoelectronic devices to be misaligned. 
     Various passive alignment techniques have been developed, such as the use of guide pins and holes, to attempt to provide fast, easy and simultaneous alignment and attachment of an array of optical fibers to optoelectronic devices. Passive alignment typically indicates a technique for aligning a laser and an optical fiber that does not require the laser to be turned on during the alignment process; whereas an “active” technique requires the laser to be turned on. However, these passive alignment techniques often do not provide a precision coupling of the optical fibers to optoelectronic devices. 
     Accordingly, there is a need in the art to provide a method and apparatus for precise, fast and easy alignment and attachment of optical fibers to optoelectronic devices, which may be mounted on a circuit board. In addition, there is a need in the art to provide an inexpensive method and apparatus for aligning and attaching optical fibers to optoelectronic devices so that the method and apparatus are suitable for mass production. Finally, there is a need in the art for a small apparatus coupling optical fibers to optoelectronic devices so that the apparatus can easily be mounted on a circuit board. 
     SUMMARY OF THE INVENTION 
     In view of the above-stated disadvantages of the prior art, an object of the present invention is to provide a process for coupling optical elements to optoelectronic devices, and the process may be used in conjunction with making an optical transmitter, receiver or transceiver module. 
     Another object of the present invention is to provide an apparatus and process for quickly, easily and precisely aligning and connecting at least one optical fiber to at least one optoelectronic device by using highly precise machinery and adhesive. 
     Another object of the present invention is to provide an apparatus and process for aligning and connecting at least one optical fiber to at least one optoelectronic device while maintaining a gap between at least one optical fiber and at least one optoelectronic device. 
     Another object of the present invention is to provide an apparatus and process for quickly, easily and precisely aligning and connecting at least one optical fiber to a wide variety of device(s) or object(s) by using highly precise machinery and adhesive. 
     Another object of the present invention is to provide an inexpensive method and apparatus for aligning and connecting at least one optical fiber to at least one optoelectronic device so that the method and apparatus are suitable for mass production. 
     Another object of the present invention is to provide an inexpensive method and apparatus for aligning and connecting at least one optical fiber to a wide variety of device(s) or object(s) so that the method and apparatus are suitable for mass production. 
     Another object of the present invention is to provide a small apparatus for coupling at least one optical fiber to at least one optoelectronic device so that the apparatus can easily be mounted on a circuit board. 
     In accordance with the first object of the present invention, a process is provided for aligning and connecting at least one optical fiber to at least one optoelectronic device so as to couple light between at least one optical fiber and at least one optoelectronic device. One embodiment of this process comprises the following steps: (1) holding at least one optical element close to at least one optoelectronic device, at least one optical element having at least a first end; (2) aligning at least one optical element with at least one optoelectronic device; (3) depositing a first non-opaque material on a first end of at least one optoelectronic device; and (4) bringing the first end of at least one optical element proximate to the first end of at least one optoelectronic device in such a manner that the first non-opaque material contacts the first end of at least one optoelectronic device and the first end of at least one optical element. The optical element may be an optical fiber, and the optoelectronic device may be a vertical cavity surface emitting laser. The first non-opaque material may be a UV optical adhesive that provides an optical path and mechanical stability. In another embodiment of the alignment process, the first end of at least one optical element is brought proximate to the first end of at least one optoelectronic device in such a manner that an interstitial space exists between the first end of at least one optoelectronic device and the first end of at least one optical element. 
     In accordance with other aspects of the present invention, an optical transmitter, receiver or transceiver module is provided that includes a flexible printed circuit board that is bent at an angle, forming a head region, buckle region and main body region. The flexible printed circuit board supports the electrical components and circuitry of the present invention. 
     An array of optoelectronic devices, a driver or amplifier chip, a photo-detector, conducting lines, and electronic components may be mounted on a first surface of the head region of the flexible printed circuit board. The optoelectronic devices send and or receive light to and from optical fibers. The optoelectronic devices may be mounted on top of a spacer that may be attached to the head region of the flexible printed circuit board. The spacer raises the height of the optoelectronic devices so that they may efficiently communicate with the optical fibers and other electrical components that are mounted on the head region of the flexible printed circuit board. Alternatively, the optoelectronic devices may be mounted on an optoelectronic mounting structure that is accessible through a window in the flexible printed circuit board. When the optoelectronic devices function as emitters for emitting optical signals into optical fibers, they may be oxide-confined vertical cavity surface emitting lasers; if the optoelectronic devices function as receivers for receiving optical signals from optical fibers, they may be photo-detectors formed on a semiconductor chip. The driver or amplifier chip modulates and drives the optoelectronic devices. An optical power control system may monitor, regulate and stabilize the temperature, power and wavelength of the optoelectronic devices. Additionally, an attenuator may improve the performance of the optoelectronic devices by attenuating the optical energy emitted from the devices. Similarly, a conditioner may improve the performance of the optical fibers by conditioning the launch of the optical energy into the fibers. 
     The remaining electrical components and circuitry of the optical module may be located on the main body region of the flexible printed circuit board. 
     The buckle region of the flexible printed circuit board, the region connecting the main body region and head region, absorbs any stress that may occur in connecting a fiber optic cable to the present invention and assists in providing alignment between the optical fibers and optoelectronic devices. 
     A first ferrule, packaging an array of optical fibers, is mounted on top of the array of optoelectronic devices on the first surface of the head region of the flexible printed circuit board. Highly precise machinery optically aligns aligns the array of optical fiber in the first ferrule to the array of optoelectronic devices. A gap or interstitial space is established between a second end of the first ferrule and a top surface of the optoelectronic devices. Optical adhesive is dispensed in the space or gap between the first ferrule and the optoelectronic devices so as to maintain the precise axial alignment of the array of optical fibers to the array of optoelectronic devices. The optical adhesive provides a optically transparent and stable medium between the optoelectronic devices and the fibers. 
     After the optical adhesive is cured, a dam may be formed on the first surface of the head region of the flexible printed circuit board. A second adhesive is dispensed inside the dam, and the second adhesive further mechanically stabilizes the first ferrule to the flexible printed circuit board. The second adhesive also protects the circuitry in the immediate vicinity of the optical fibers and optoelectronic devices. For airtight sealing of the optical module, the surface area of the second adhesive may be covered with a third layer, such as a gel silicon resin. 
     After the first ferrule is firmly attached to the head region of the flexible printed circuit board, the circuit board is wrapped around and attached to a circuit board mounting structure with an adhesive. 
     A housing snaps or otherwise mounts with screws, adhesives or other means onto a first end of the circuit board mounting structure, enclosing the head region of the flexible printed circuit board along with the first ferrule that is mounted on the head region. The first ferrule fits inside a longitudinal cavity extending from a first end of the housing to a second end of the housing. Ridges inside the longitudinal cavity grab and hold the first ferrule in place. 
     In operation, a fiber optic cable from an external system is brought in proximity to the housing to create an optical connection. A second ferrule is located at one end of the fiber optic cable, and the second ferrule is designed to mate with the second end of the housing. The second ferrule is inserted into the second end of the housing and ridges in the housing&#39;s longitudinal cavity engage and hold the second ferrule in place. Once inside the longitudinal cavity, the second ferrule mates with the first ferrule by engaging guide pins located on a front end of the first ferrule with guide holes located on a front end of the second ferrule. As a result, the array of optical fibers packaged in the two ferrules are axially aligned. Upon mating the ferrules together, light may be transmitted from the fiber optic cable through the two ferrules and to the optoelectronic devices that are adapted to the flexible printed circuit board. The optoelectronic devices convert the light into electrical signals for processing and vice versa. 
     A further significant aspect of the present invention involves a process by which the first ferrule is aligned and connected to the array of optoelectronic devices, according to a preferred embodiment of the invention. A process of aligning and connecting the first ferrule to the array of optoelectronic device comprises the following steps:
         1. Aligning the optical fiber(s) packaged in the first ferrule with the optoelectronic device(s) so that each optical fiber is optically aligned to a corresponding optoelectronic device(s);   2. Depositing optical adhesive on a top surface of the optoelectronic device(s);   3. Placing the first ferrule on top of the optical adhesive while maintaining the alignment of step 1;   4. Tacking and curing the optical adhesive; and   5. Forming a dam around the first ferrule that is mounted on the head region of the flexible printed circuit board, dispensing adhesive and curing the adhesive.       

     Although the above-stated process has been discussed in terms of accurately aligning and attaching the first ferrule to the array of optoelectronic devices, the same process may be used to accurately align and attach a single optical fiber or an array of optical fibers to a single optoelectronic devices or an array of optoelectronic devices. Similarly, the process may be used to accurately align and connect at least one optical element to a wide variety of devices and objects other than optoelectronic devices. The optical element may comprise a lenslet array, diffractive optic array or an optical fiber. For example, the process may be used to connect an optical element to a micro-electromechanical system (“MEMS”) or a biological or chemical sample held on a substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is perspective view of an embodiment of the invention. 
         FIG. 2  shows a perspective view of an embodiment of the invention mounted on the edge of a circuit board. 
         FIGS. 3   a - 3   b  are diagrams of cut-away-side views of the flexible printed circuit board, according to an embodiment of the invention. 
         FIG. 4  is a diagram of an embodiment of the optical power control system, according to an embodiment of the invention. 
         FIGS. 5   a - 5   d  are diagrams of different optical beam patterns on an aperture of a photo-detector, according to an embodiment of the invention. 
         FIGS. 6   a - 6   b  are diagrams of alternative embodiments of the optical power control system, according to an embodiment of the invention. 
         FIGS. 7   a - 7   b  are cut-away-side views showing embodiments of a head region of the flexible printed circuit board, according to embodiments of the invention. 
         FIG. 8  is side-view showing an alternative embodiment of a first ferrule and the head region of the flexible printed circuit board, according to an embodiment of the invention. 
         FIG. 9  is an exploded view of an embodiment of the housing, an embodiment of the first ferrule, an embodiment of a circuit board mounting structure and an embodiment of the flexible printed circuit board, according to an embodiment of the invention. 
         FIG. 10  is a three-dimensional view of an embodiment of the housing, according to an embodiment of the invention. 
         FIGS. 11   a - 11   c  are diagrams illustrating an apparatus for holding an optical element in accordance of an embodiment of the present invention. 
         FIGS. 12   a - 12   d  show views of images of optoelectronic devices and images of optical fibers under the high magnification of a split-field microscope. 
         FIG. 13  shows the display on a monitor of a video image measuring system. 
     
    
    
     DETAILED DESCRIPTION 
     I. Introduction 
     The following embodiments will be described in the context of an optical transceiver, receiver or transceiver module and a method of making the same. Those skilled in the art, however, will recognize that the disclosed methods and structures are adaptable for broader applications. If the same reference numeral is repeated with respect to different figures, it refers to the corresponding structure in each figure. 
     With reference to  FIG. 1 , an optical transmitter, receiver or transceiver module  100  is depicted, according to an embodiment of the invention. The optical module  100  comprises a flexible printed circuit board  102  that wraps around and attaches to a circuit board mounting structure  104 . The flexible printed circuit board  102  functions to support the electrical components of the optical module  100 , such as an array of optoelectronic devices  106 , a driver or amplifier chip  108 , and a photo-detector  110 . A first ferrule  112 , packaging an array of optical fibers  114 , is mounted on top of the array of optoelectronic devices  106  in such a manner that one or more of the optical fibers in the array is optically aligned to one or more of the optoelectronic devices. 
     Prior to mounting the first ferrule  112  on the array of optoelectronic devices  106 , a first adhesive  116  is dispensed on a top surface of the array of optoelectronic devices  106 . The first adhesive  116  functions to maintain the precise axial alignment between the array of optical fibers  114  and array of optoelectronic devices  106 . The first adhesive  116  also functions to produce a high, optical coupling efficiency between the optical fibers  114  and optoelectronic devices  106 . Additionally, the first adhesive  116  functions to mechanically stabilize the first ferrule  112  to the optoelectronic devices  106 . 
     To further mechanically stabilize the first ferrule  112  to the flexible printed circuit board  102 , a dam  120  may be formed on the flexible printed circuit board  102  and filled with a second adhesive  122 . An housing  124  is attached to the circuit board mounting structure  104 , surrounding and enclosing the first ferrule  112  that is connected to the flexible printed circuit board  102 . 
     In an illustrative embodiment, an optical transmitter or receiver module  100  is mounted on a second circuit board  202 , as depicted in FIG.  2 . The optical module, however, does not have to be mounted at the board&#39;s edge. The optical module may be mounted anywhere on the circuit board so long as there is room for connecting the optical module to the external environment. In operation, the optical module  100  is connected to the external environment by connecting a fiber optic cable  204  to the optical module  100 . This is accomplished by plugging a second ferrule  206  that is attached to one end of a fiber optic cable  204  into the optical module  100 . Once the second ferrule  206  is plugged into the optical module  100 , the module  100  is optically connected to the fiber optic cable  204 . Accordingly, if the optical module  100  functions as a transmitter, the optical module  100  receives electrical signals from the second circuit board  202 , converts the electrical signals into optical signals, and transmits the optical signals into the fiber optic cable  204 . On the other hand, if the optical module  100  functions as a receiver, the optical module  100  receives optical signals from the fiber optic cable  204 , converts the optical signals into electrical signals and transmits the electrical signals to the second circuit board  202 . 
     II. Flexible Printed Circuit Board 
     The flexible printed circuit board  102  is now described in further detail. Specifically,  FIG. 3   a  is a cut-away-side view of an embodiment of the flexible printed circuit board  102 . The flexible printed circuit board may be bent or folded in any direction, and another embodiment of the flexible printed circuit board is shown in  FIG. 3   b . The flexible printed circuit board  102  is thin, rectangular and flexible with various edge contours, and it is composed of flexible metal layers that are sandwiched between insulating layers. The entire flexible printed circuit board may be composed of this multi-layered structure. In addition to supporting the electrical components and circuitry of the optical module  100 , the flexible printed circuit board  102  also provides stress relief when connecting the optical module  100  to an external source and aids in maintaining the precise alignment of the optoelectronic devices  106  with an the optical fibers  114 . 
     The flexible printed circuit board  102  is bent in the “Y” direction to form a head region  302 , a buckle region  304  and a main body region  306 . The head region  302  may function to support the key electrical components and other elements of the optical module  100 , such as the optoelectronic devices  106  and driver or amplifier chip  108 . The main body region houses a plurality of electronic components  308  and a plurality of electronic circuitry of the optical module  100 . The buckle region  304  is that area of the flexible printed circuit board  102  that connects the head region  302  to the main body region  306 . 
     Each region of the flexible printed circuit board is described in detail below. 
     A. Head Region 
     The head region  302  of the flexible printed circuit board  102  is now described in detail, and it is shown in  FIG. 3   a  or  FIG. 3   b . The head region  302  is composed of the same multi-layered structure as the other regions of region  302  is orientated in the “Y” direction, and the head region  302  may be on a plane that is substantially perpendicular to the main body region  306  of the flexible printed circuit board  102 , as shown in  FIG. 3   a  or  FIG. 3   b.    
     The head region  302  is orientated in the “Y” direction so that the optical fibers  114  packaged in the first ferrule  112  are optically aligned with the optical fibers  114  packaged in the second ferrule  206 . As shown in  FIG. 3   a  or  FIG. 3   b , the head region  302  of the flexible printed circuit board  102  may function to support the key electrical components of the optical module  100  such as the driver or amplifier chip  108 . 
     The flexible printed circuit board performs the function of changing the plane on which the signals are received. Specifically, the signals are received by the flexible printed circuit board in the “X” direction from the first ferrule  112  that is optically connected to the optoelectronic devices  106 , which are adapted to the head region  302  of the flexible printed circuit board  102 . The signals then flow in substantially the “Y” direction in the head region  302  of the flexible printed circuit board  102 . The signals then change planes, as they pass from the head region  302  through the buckle region  304  and to the main body region  306  of the flexible printed circuit board  102 , as shown in  FIG. 3   a  or  FIG. 3   b . The signals flow in the “X” direction in the main body region. Advantageously, by changing the plane on which the signals travel, the flexible printed circuit board functions to efficiently communicate with both the fiber optical cable attached to the optical module and an external circuit board upon which the optical module is mounted. 
     1. Optoelectronic Devices 
     One board-level component of the head region  302  may be the array of optoelectronic devices  106 . The array of optoelectronic devices  106  may be adapted approximately in the center of a first surface  310  and/or the second surface  704  of the head region  302 , as shown in  FIG. 3   a  or  FIG. 3   b . The array of optoelectronic devices  106  may be a one-dimensional, two-dimensional or a multi-dimensional array of optoelectronic devices  106 . 
     The array of optoelectronic devices  106  may be various types of devices such as edge-emitting lasers, light-emitting diodes (“LEDs”), vertical cavity surface emitting lasers (VCSELs), other surface emitting devices or photo-detectors. The optoelectronic devices  106  may also be integrated devices combining one or more devices such as the combination of VCSELs and transistors or photo-detectors and transistors (or VCSELs, photo-detectors and transistors). The optoelectronic devices  106  may also be a heterogeneous array where some of the array elements are emitters and some are detectors. 
     If the optoelectronic devices  106  are VCSELs, the optical module  100  functions as a transmitter, sending optical signals into the array of optical fibers  114  that are packaged in the ferrule. 
     If the optoelectronic devices  106  are photo-detectors formed on a semiconductor chip, the optical module  100  functions as a receiver for receiving optical signals from the array of optical fibers  114  packaged in the first ferrule  112 . 
     In an embodiment, the optoelectronic devices  106  are oxide-confined VCSELs. Advantageously, oxide-confined VCSELs operate at higher speeds and have lower threshold currents than non-oxide VCSELs, such as ion-implant VCSELs. Additionally, oxide-confined VCSELs are stable VCSELs, exhibiting uniform power and wavelength performance over varying temperature ranges. This advantageously would allow the module to perform for longer a duration and high degree of accuracy. Moreover, it is contemplated that use of oxide VCSELs would obviate the need for a feedback loop, as hereafter described. Moreover, oxide-confined VCSELs allow the fabrication of highly uniform arrays, enabling multi-channel, parallel optic applications. 
     Lastly in another embodiment, a micro-electromechanical system (“MEMS”) array, a micro-pipette array or a biological or chemical sample held on a substrate may be used in place of the array of optoelectronic devices  106 . 
     2. Driver or Amplifier Chip 
     Another board-level component of the head region  302  of the flexible printed circuit board  102  may be the driver or amplifier chip  108 , as shown in  FIG. 3   a  or  FIG. 3   b . Specifically, a driver or amplifier chip  108  may be adapted next to the array of optoelectronic devices  106  on the first surface  310  and or the second surface  704  of the head region  302  of the flexible printed circuit board  102 , as shown in  FIG. 3   a  or  FIG. 3   b . In another embodiment, the driver or amplifier chip  108  may be adapted to the main body region of the flexible printed circuit board. 
     Where the optoelectronic devices  106  are VCSELs, a driver chip is used, and it functions to drive and modulate the VCSELs. Where the optoelectronic devices  106  are photo-detectors, then an amplifier chip is used, and it amplifies the electronic signals received from photo-detectors. Wire bonds  312  or any other suitable means such as plating, welding, tape-automated bonding or the use of flip-chip technology may be used to connect the driver or amplifier chip  108  to the optoelectronic devices  106 , as shown in  FIG. 3   a  or  FIG. 3   b . The driver or amplifier chip  108  may be monolithically formed on a semiconductor chip or integrated with the array of optoelectronic devices  106  as a hybrid circuit. 
     3. Optical Power Control System 
     Still another board-level component of the head region  302  of the flexible printed circuit board  102  may be an optical power control system. During operation, temperature changes across an array of VCSELs and other factors can cause the power and wavelength of the VCSEL array to change. The optical power control system functions to stabilize the performance of the array of VCSELs over changing conditions. Specifically, if the array of optoelectronic devices  106  are transmitters such as VCSELs, an optical power control system is adapted proximate to the array of optoelectronic devices  106  on the first surface  310  of the head region  302  of the flexible printed circuit board  102 . 
       FIG. 4  is an embodiment of the optical power control system. The optical power control system utilizes the photo-detector  110  (or alternatively a light-pipe) to measure the optical output power of a VCSEL in an array of VCSELs. In an embodiment of the invention, if the optoelectronic devices  106  are VCSELs, the optical power control system measures the power of a thirteenth VCSEL  404  in the array of VCSELs. However, the optical power may be measured by any other suitable VCSEL in the array of VCSELs. The photo-detector&#39;s measurement is used to adjust the electrical power input to each individual VCSEL. This is accomplished by a feedback loop between the photo-detector  110  and the driver chip  108 . The driver chip  108  adjusts the laser injection current in response to the feedback, and this results in a stable array of optoelectronic devices. 
       FIGS. 5   a - 5   d  are diagrams of different optical beam patterns on apertures of photo-detectors. A critical aspect of a robust optical power control system is the tracking ratio. The tracking ratio is the ability of the photo-detector  110  to track and capture the optical beam  408  so that the photo-detector  110  accurately measures the amount of power emitted by the VCSEL array. In the ideal situation, the optical beam  408  is fully captured by the photo-detector&#39;s aperture  502  as shown in  FIG. 5   a . This allows the photo-detector  110  to precisely measure the power of the beam. However, temperature changes, aging, and other factors during operation can cause the optical beam  408  to become misaligned, as shown in  FIG. 5   b . Since the photo-detector&#39;s aperture  502  captures less of the optical beam  408 , the photo-detector is unable to accurately measure the beam&#39;s power. This causes the optical power control system to improperly adjust the power of the VCSEL array. Similarly as shown in  FIG. 5   c , changes in laser injection current and other factors can create a diverged or enlarged optical beam  504 . Again, the photo-detector&#39;s aperture  502  detects less power, causing inaccurate adjustments to the power output of the VCSEL array. 
     Advantageously, the present invention improves the tracking ratio under changing conditions. The present invention accomplishes this task by adapting a reflector/scatterer  410  to a second end of the first ferrule  320 , as shown in FIG.  4 . An optical path may be created from the thirteenth VCSEL  404  to the reflector/scatterer  410  and onto the photo-detector  110 . The geometry and surface roughness of the reflector/scatterer  410  produces a beam pattern  506  that is highly uniform, scattered and larger than the photo-detector&#39;s aperture, as shown in  FIG. 5   d . This uniform and scattered beam pattern  506  has a high tolerance for alignment and divergence changes. Accordingly, it is less sensitive to temperature changes, aging and other issues. Advantageously, this allows the photo-detector  110  to accurately measure the power of the optical beam  408  under varying conditions and environmental circumstances. For example, temperature changes across the VCSEL array may change the optical beam&#39;s pattern, alignment and divergence, and this impacts the photo-detector&#39;s  110  ability to accurately measure power. However, the highly scattered and uniform beam pattern produced by the reflector/scatterer  410  is significantly less sensitive to temperature changes. This allows the photo-detector  110  to capture the optical beam  504  and accurately measure power. The novel beam pattern produced by the unique reflector/scatterer  410  allows the optical power control system to maintain constant power across the VCSEL array under changing conditions. Consequently, the optical power control system produces a stable and uniform VCSEL array. 
     In an embodiment, the reflector/scatterer  410  is a conical hole that is coated with a reflecting/scattering coating. The reflective/scattering coating may be gold, titanium, aluminum or other types materials that have the effect of both reflecting and scattering light. The reflector/scatterer  410  may also be an arbitrarily shaped rough surface, sphere, notch, prism or optical element. 
     An alternative embodiment of the optical power control system is show in  FIG. 6   a . A glob top of optical resin  602  is coated with a reflective scatterer and is dispensed on the top surface of the array of optoelectronic devices  106  and a top surface of the photo detector  606 . The glob top  602  scatters light in multiple directions, and a portion of the light is detected by the photo-detector  110 . The shape and coating of the glob top  602  may be engineered to provide varying amounts of scattering for more uniformity and reflection and thus higher energy transfer. As shown by dashed lines in  FIG. 6   a , a notch may be cut in the first ferrule  112  to allow room for the glob top of optical resign. 
     Another embodiment of the optical power control system is show in  FIG. 6   b . Here, a reflector  608  is formed separately and then adapted to the top surface of the array of optoelectronic devices  106  and to the top surface of the photo detector  606 . Similar to the glob top  602 , the reflector  608  scatters light in multiple directions, and a portion of the light is detected by the photo-detector  110 . The shape and coating of the reflector  608  may be engineered to provide varying amounts of scattering for more uniformity and reflecting and thus higher energy transfer. The reflector may be in the shape of an ellipsoid, three-dimensional conical hole or other shape. It also may be a geometrically-shaped object. In another embodiment, the reflector is adapted to the second end  320  of the first ferrule  112  rather than adapted to the top surface of array of optoelectronic devices  106  and photo detector  606 . As shown by dashed lines in  FIG. 6   a , a notch may be cut in the ferrule to allow room for the glob top of optical resign. 
     4. Spacer 
     An additional board-level component of the head region  302  of the flexible printed circuit board  102  may be a spacer  314 , as shown in  FIG. 3   a  or  FIG. 3   b . The spacer  314  may be shaped like a square and may be composed of silicon material. A bottom surface of the spacer  314  may be adapted approximately in the center of the head region  302 , as shown in  FIG. 3   a  or  FIG. 3   b . A top surface of the spacer  314  may serve as a mounting surface for the array of optoelectronic devices  106  when they function as receivers (e.g., photo-detectors). The spacer  314  is optional if the optoelectronic devices  106  function as emitters (e.g., VCSELs). The spacer also may function as a mounting surface for other components such as the first ferrule  112 . 
     The spacer  314  may function to raise the height of the array of optoelectronic devices  106  so as to maximize the optical coupling between the optoelectronic devices  106  and the optical fibers  114 , which are packaged in the first ferrule  112 . The spacer may function to adjust the length of the wire bonds or other electrical connection means between the array of optoelectronic devices  106  and other components such as the driver or amplifier chip  108 . The spacer also may be used to aid in creating a gap between the array of optoelectronic devices  106  and the array of optical fibers that are inside the first ferrule  114 . 
     The spacer  314  also may function to raise the height of the array of optoelectronic devices  106  so that a top surface of the array of optoelectronic devices  106  is approximately on the same plane as the other components, such as the driver or amplifier chip  108 , that are adapted on the head region  302 , as shown in  FIG. 3   a  or  FIG. 3   b . Advantageously, by maintaining the optoelectronic devices on the same plane as the other electrical components, the wire bonds  312  between the components on the head region  302  more robust and efficient. 
     The spacer  314  may be optional if the optoelectronic devices  102  have sufficient height so as to place the second end of the first ferrule  320  at an optimal position above the top surface of the driver or amplifier chip  108 . According to a preferred embodiment, a small interstitial space or gap is maintained between the second end of the first ferrule  320  and the top surface of the optoelectronic devices  102 . In alternative embodiments, this interstitial gap may be omitted. 
     In another embodiment, the spacer  314  also may function to create or form a gap between the array of optoelectronic devices  106  and the array of optical fibers. Specifically, the spacer  314  may be adjacent to the array of optoelectronic devices. The top surface of the spacer  314  may be higher than the top surface of the array of optoelectornic devices  106 . The top surface of the spacer may be in contact with the second end of the first ferrule  320 . Accordingly, this creates or forms a gap between the optoelectronic devices and array of optical fibers packaged in the first ferrule. 
     5. Optoelectronic Mounting Structure 
     The electrical components on the flexible printed circuit board  102  generate heat, and an optoelectronic mounting structure  702  may be used to transmit this heat to the circuit board mounting structure  104 , as explained below. 
       FIG. 7   a  is a cut-away-side view showing an alternative embodiment of the head region  302  of the flexible printed circuit board  102 , according to an embodiment of the invention. Specifically, the optoelectronic mounting structure  702  has a first surface  710  and a second surface  712 . The first surface  710  of the optoelectronic mounting structure  702  passes along a second surface  704  of the head region  302  of the flexible printed circuit board  102 . The second surface  712  of the optoelectronic mounting structure  702  is adapted to an upper surface  708  of the circuit board mounting structure  104  with a compliant adhesive. The optoelectronic mounting structure may be copper or a similar conductive material. The optoelectronic mounting structure may be coated with gold or other adhesion promotion layers such as nickel. An window  706  may be formed in the head region  302  of the flexible printed circuit board  102  so as to provide access to the optoelectronic mounting structure  702 . The array of optoelectronic devices  106  may be mounted in the window  706  directly on top of the optoelectronic mounting structure  702 . Accordingly, the optoelectronic mounting structure provides a thermal and an electrical contact area for the optoelectronic devices. Other electrical components, such as the driver or amplifier chip  108  also may be mounted in the window  706  directly on the optoelectronic mounting structure  702 . 
     The optoelectronc mounting structure advantageously  702  dissipates heat generated by the array of optoelectronic devices  106  and other electrical components by spreading the heat and efficiently transmitting it to the circuit board mounting structure  104 . The optoelectronic mounting structure  702  also provides an electrical contact path to the optoelectronic devices  106  since the back side of the optoelectronic devices  106  may be gold or copper plated and may be mounted directly to a copper optoelectronic mounting structure  702 . Moreover, since the optoelectronic mounting structure  702  may be a solid copper plane, it may acts to limit electromagnetic interference. Acting as a ground plane for the optoelectronic devices  106 , the optoelectronic mounting structure  702  provides electrical shielding by containing any electrical fields that may exist so that the electrical fields do not radiate and create cross talk. The optoelectronic mounting structure  702  additionally may provide a stable mounting surface for the optoelectronic devices  106 , and it may function to raise or change the height of the electrical components. The optoelectronic mounting structure  702  also provides mechanical rigidity to the head region  302  of the flexible printed circuit board  102 . This mechanical rigidity stiffens the head region  302  and advantageously aids in the assembly process. 
       FIG. 7   b  is a cut-away-side view showing an alternative embodiment of the head region  302  of the flexible printed circuit board  102 , according to an embodiment of the invention. Specifically, openings  714  in the head region  302  of the flexible printed circuit  102  board may function to dissipate heat to the optoelectronic mounting structure  702 . The openings  714  may be heat pipes, thermal vias or similar structures that transmit heat. The openings  714  may be formed in the head region  302  so as to provide access to the optoelectronic mounting structure  702 . Electrical components, such as the array of optoelectronic devices  106  and the driver or amplifier chip  108 , may be mounted on the first surface of the head region  302 . Heat generated by these electrical components may pass through the openings  714  and to the optoelectronic mounting structure  702 . The optoelectronic mounting structure  702  dissipates or spreads this heat to the circuit board mounting structure  104 . 
     6. Ferrule 
     The optical module  100  may include the first ferrule  112 , as shown in  FIG. 3   a  or  FIG. 3   b . The first ferrule is mounted on the head region  302  of the flexible printed circuit board  102 . More specifically, the second end of the first ferrule  320  is mounted on the top surface of the array of optoelectronic devices  106 . The first ferrule  112  is precisely aligned and attached directly above the active region of the array of optoelectronic devices  106  so that a high coupling efficiency (low loss of light) is achieved. In other words, each optical fiber  114  in the first ferrule  112  is accurately aligned to a corresponding individual optoelectronic device  106  so that the array of optical fibers  114  inside the first ferrule  112  is optically aligned with the array of optoelectronic devices  106 . The precise alignment and attachment of the first ferrule  112  to the array of optoelectronic devices  106  is accomplished by using highly precise machinery and adhesive, and this novel process is explained below. 
     The first ferrule  112  may comprise a rectangular ferrule. The first ferrule  112  packages an array of optical fibers  114 , extending from a first end  318  of the first ferrule  112  to a second end  320  of the first ferrule  112 . Two alignment pins  316  may be adapted to the first end  318  of the first ferrule  112 . The alignment pins function to mate the first ferrule  112  to a second ferrule  206 . Alternatively, two alignment pin holes may be adapted to the first end  318  of the first ferrule  112  in place of the two alignment pins  318 . The alignment pin holes function to mate the first ferrule  112  to a second ferrule  206 . 
       FIG. 8  is a side-view showing an alternative embodiment of the first ferrule  112  and the head region  302  of the flexible printed circuit board  102 , according to an embodiment of the invention. Costs are reduced by using a smaller optoelectronic device  106 , as shown in  FIG. 8. A  notch  802  exists at the second end of the first ferrule  320  so that there is sufficient room for wire bonding between the optoelectronic devices  106  and driver or amplifier chip  108 . Advantageously, the notch  802  allows positioning the driver chip or amplifier chip  108  in close proximity to the smaller optoelectronic devices  106 . Therefore, the notch  802  obviates the need for long wire bonds to connect the optoelectronic devices to the driver or amplifier chip. 
     In another embodiment, an array of optical elements may be used in place of the array of optical fibers  114 . The optical element may comprise a lenslet array, diffractive optic array, a lens, filter, pipette, capillary tube or optical fibers. Also, the optical element does not have to be optical as, for example, in embodiments of the present invention in which biological or chemical analysis is performed. The optical element array may be a one-dimensional, two-dimensional or multi-dimensional array of optical elements. 
     In contrast to a single optical element or fiber, an array of optical elements or fibers introduces engineering, design, assembly and packaging complexity. This complexity was taken into account in embodiments of the invention. For example, an array of optical elements generates more heat and electromagnetic interference that a single optical element, and this must be considered in all aspects of making and using the device. Also, unlike aligning a single optical element to an optoelectronic device, aligning an array of optical elements to an array of optoelectronic devices is considerably more difficult and complex. Moreover, an array of optical elements can more readily become effected by electrical or optical cross-talk since the optical elements are closely coupled. Therefore, the array is highly subject to signal degradation, and design limitations must be made to take these factors into account. Additionally, working with an array rather than a single optical fiber requires developing new tools and techniques for various manufacturing aspects such as precision alignment and eye-safety. Such tools and techniques were developed specifically for embodiments of this invention. In summary, for these and other reasons, an array of optical elements introduces engineering, design, assembly and packaging complexity that is simply not present with a signal optical element, and this added complexity was taken into account in embodiments of the invention. 
     7. First Adhesive 
     Prior to mounting the first ferrule  112  on top of the array of optoelectronic devices  106 , a first adhesive  116  is dispensed on the top surface of the array of optoelectronic devices  106 , as shown in  FIG. 3   a  or  FIG. 3   b . The first adhesive is preferably an optically clear adhesive or a gel that has a complementary index of refraction to the optical fibers  114 . 
     The first ferrule  112  is held suspended above the top surface of the array of optoelectronic devices  106  in the first adhesive  116 . The optical adhesive  116  may be cured with UV light, RF radiation, air, microwave radiation or thermal means, depending on the type of adhesive that is used. Once the optical adhesive  116  is cured, the space or gap between the second end of the first ferrule  320  and the top surface of the optoelectronic devices  118  is preserved or set; this space having been filled with the first adhesive  116 . In other words, a thin layer of first adhesive  116  exists at the interface between the second end of the first ferrule  320  and the top surface of the optoelectronic devices  118 . 
     The first adhesive  116  functions to stabilize and hold the first ferrule  112  to the array of optoelectronic devices  106 . The first adhesive  116  maintains the precise alignment of the array of optical fibers  114  packaged in the first ferrule  112  to the array of optoelectronic devices  106 . The first adhesive also functions to maintain the gap that exists between the first ferrule  112  and array of optoelectronic devices  106 . 
     Advantageously, the first adhesive  116  produces a high coupling efficiency between the array of optical fibers  114  packaged in the first ferrule  112  and the array of optoelectronic devices  106 . Specifically, the first adhesive  116  is an optically clear adhesive or gel and has almost the same refractive index as the optical fibers. Accordingly, by providing a refractive index match to the optical fibers, light passing from the array of optoelectronic devices  106  to the array of first fibers  114  (or vice versa) experiences minimal Fresnel reflection loss and optical divergence over the gap distance that exists between the array of optoelectronic devices  106  and the array of first fibers  114 . This produces a high-coupling efficiency at the interface between the top surface of the optoelectronic devices  106  and the optical fibers  114 . The first adhesive  116  also serves to prevent air from existing at the interface or space between the first ferrule  112  and the array of optoelectronic devices  106 . The elimination of air at the interface or gap is desirable because air has a lower refractive index than the optoelectronic devices  106 , the optical fibers  114  and the first adhesive  116 . The refractive index difference introduces reflection losses, and the lower reflective index results in greater beam divergence per unit propagation length. If air were present, light passing from the optoelectronic devices  106  to the optical fibers  114  (or vice versa) may experience greater divergence, thereby reducing the efficiency of the coupling. Furthermore, the first adhesive prevents a second adhesive  122  from inadvertently seeping or wicking into the gap or space between the bottom surface of the ferrule and the top surface of the optoelectronic devices. Consequently, the first adhesive  116  advantageously produces a high-coupling efficiency between the optoelectronic devices  106  and the optical fibers  114  that are packaged in the first ferrule  112 . 
     The first adhesive  116  not only enhances the coupling efficiency between the optical fibers  114  and optoelectronic devices  106  by providing a refractive index match to the optical radiation, but it also serves another important purpose. Specifically, the first adhesive  116  provides mechanical robustness by securing the first ferrule  112  to the array of optoelectronic devices  106 . As previously stated, the gap or space between the bottom surface of the first ferrule  112  and the top surface of the optoelectronic devices  118  is filled with the first adhesive. The first adhesive functions to mechanically stabilize the first ferrule  112  to the head region  302  of the flexible printed circuit board  102 . The first adhesive  116  provides support for any lateral, axial or rotational strain that may be created when a fiber optic cable is attached to the optical module. Furthermore, this allows proceeding to the dam and well-fill step, which is explained below, with minimal or no supporting structure to maintain the precision axial alignment of the array of optical fibers  114  packaged in the first ferrule  112  to the array of optoelectronic devices  106 . Accordingly, the first adhesive  116  advantageously reduces manufacturing time and costs by providing mechanical robustness in addition to providing high coupling efficiency. 
     8. Second Adhesive and Dam 
     As previously stated, the first adhesive mechanically stabilizes the first ferrule  112  to the head region  302  of the flexible printed circuit board  102 . In another embodiment, a second adhesive  122  may be adapted to the head region  302  to further mechanically stabilizes the first ferrule  112  to the head region  302  of the flexible printed circuit board  102 , as shown in  FIG. 3   a  or  FIG. 3   b . Similar to the first adhesive  116 , the second adhesive  122  may provide support for any lateral, axial or rotational strain that may be created when a fiber optic cable is attached to the optical module. No dam is necessary to form the first adhesive  116 . 
     To further mechanically stabilize the first ferrule  112  to the head region, a dam  120  may be formed on the head region  302  and filled with the second adhesive  122 , as shown in  FIG. 3   a  or  FIG. 3   b . The second adhesive, however, may be used without the dam. The dam may be constructed or dispensed, and the dam  120  may be dispensed and formed in a single or multi-layered path. The dam  120  may be in the shape of a square, diamond, oval or any other shape that effectively stabilizes and encloses the optoelectronic devices and possibly wire bonds and other die on the head region  302  of the flexible printed circuit board  102 . The dam  120  may furthermore surround and enclose all of the components on the head region  302  for extra protection. The dam  120  may be constructed and formed on the first surface  310  of the head region  302  of the flexible printed circuit board  102 . 
     The dam  120  may surround the first ferrule  112 , driver or amplifier chip  108  or other electrical components, as shown in  FIG. 3   a  or  FIG. 3   b . The dam  120  may be composed of adhesive or epoxy. The dam  120  may be formed or built by dispensing several layers of adhesive or epoxy on top of each other over time until the desired height and width of the dam  120  is achieved. The adhesive or epoxy may be any standard well-fill or potting epoxy. Alternatively, as previously stated, the dam may be dispensed and formed in a single path. 
     The area within the dam may be filled with the second adhesive  122 . The second adhesive  122  preferably covers the driver or amplifier chip  108 , array of optoelectronic devices  106 , and any other electrical components that are adapted to the head region  302 , as shown in  FIG. 3   a  or  FIG. 3   b . A sufficient amount of second adhesive  122  is poured inside the dam area so that the height of the second adhesive  122  may span from the first surface  310  of the head region  302  of the flexible printed circuit board  102  to somewhere below the first end  318  of the first ferrule  112 , as shown in  FIG. 3   a  or  FIG. 3   b . After the second adhesive  122  has been cured, the dam  120  and second adhesive  122  function to mechanically stabilize the first ferrule  112  to the first surface  310  of the head region  302  of the flexible printed circuit board  102 . 
     Advantageously, the dam  120  and second adhesive  122  may provide additional mechanical support to further stabilize the first ferrule  112  to the head region  302  of the flexible printed circuit board  102 . The dam  120  and second adhesive  122  may function to absorb stress and provide rigidity and strength that may be needed when connecting the optical module to an external environment such as a fiber optic cable. Also, the dam  120  and second adhesive  122  may prevent movement that may occur over temperature variances. Moreover, the dam  120  and second adhesive  122  may function to provide moisture blocking and protection to the electrical components and circuitry adapted to the first surface  310  of the head region  302  of the flexible printed circuit board  102 . 
     9. Third Layer 
     For airtight sealing of the optical module, the surface area of the second adhesive  122  may be covered with a third layer. The third layer may protect the optical module by blocking the permeation of moisture and providing electric shielding. The third layer may be a conductive and or moisture blocking adhesive such as gel silicon resin. It may also be a metallic, dielectric or other type of coating that provides necessary protection to the optical module. 
     10. Attenuator or Conditioner 
     In an embodiment of the invention, an attenuator may be used that functions to modify the performance of the array of optoelectronic devices. Specifically, superior performance of the array of optoelectronic devices typically is found if such devices are operated at the midpoint rather than low-point of their power range. However, operating the optoelectronic devices at the mid-point of their power range may not meet optical output requirements. One solution is to operate the optoelectronic devices at the mid-point of their power range but not transmit all of the power out of the end of the array of optical fibers. This may be accomplished through the use of the attenuator. The attenuator may function to reflect, absorb and or scatter the optical output of at least one optoelectronic device. Also, the attenuator advantageously may control optical cross-talk, reduce back-reflection and may eliminate feedback noise. 
     One embodiment of the attenuator may be a coating on the first or second end of the first ferrule or a coating on the first or second end of the array of optical elements that are packaged in the ferrule. It also may comprise a coating on the first end of the array of optoelectronic devices. The coating may be a metal, dialetric, organic or other material, and the coating may be patterned. Another embodiment of the attenuator may be a gel-like substance that is deposited in the gap that exists between the first end of the optoelectronic devices and the first end of the optical fibers. In this embodiment, the attenuator would function to absorb some of the light emitted by the optoelectronic devices. Other embodiments of the attenuator may be increasing the absorption of the first adhesive, introducing a controlled seeping or wicking of an absorbing second adhesive, changing the gap distance to reduce coupling, changing the refractive index to introduce Fresnel reflection and introduce divergence, changing the lateral alignment, or changing the surface finish of the optical fibers. Finally, other embodiments of the attenuator may include changing the optical transmission characteristics of the array of optical fibers so that they absorb, reflect and or scatter light. In this manner, the optical energy exiting the array of optical fibers will have its signal power reduced. This may be accomplished by changing the surface finish of the cores of the optical fibers (e.g., using frosted, wavy or rough surface glass) or by coating the inner surfaces of the fiber optic cores. 
     Finally, in another embodiment of the invention, a conditioner may be used to improve the performance of the array of optical fibers by changing the way the optical energy is launched into the optical fibers. For example, conditioning the launch of optical energy can improve the effective bandwidth of the optical fibers. The conditioner may function to change the phase distribution of the optical energy that is emitted by the optoelectronic devices. 
     Conditioning the launch of the optical energy flowing into the optical fibers from the optoelectronic devices may be accomplished as follows: (1) patterning a coating on the first end of the array of optoelectronic devices; (2) patterning a coating on the first or second end of the array of optical fibers; (3) depositing a gel-like substance between the first end of the optoelectronic devices and the first end of the optical fibers; (4) adapting a diffractive object on the input or output of the array of optical fibers so as to change the structure of the optical energy; (5) changing the lateral position of the array of optoelectronic devices relative to the array of optical fibers; (6) changing the optical transmission characteristics of the array of optical fibers; (7) tilting the array of optoelectronic devices relative to an optical path; and (8) changing the optical transmission characteristics of the array of optical fibers so that they absorb, reflect and or scatter light. These and other methods that are known in the art may be used to improve the performance of the array of optical fibers by changing the way the optical energy is launched into the optical fibers. 
     B. Buckle Region 
     In addition to the head region  302 , the flexible printed circuit board  102  also comprises a buckle region  304 , which will now be described with reference to  FIG. 3   a  or  FIG. 3   b . The buckle region  304  is that area of the flexible printed circuit board  102  connecting the head region  302  to the main body region  306  of the flexible printed circuit board  102 . The buckle region  304  is thin and composed of the same multi-layered structure as the other regions of the flexible printed circuit board  102 . A plurality of electrical circuitry may be adapted both to a first surface and a second surface of the buckle region  304 . The electrical circuitry functions to electrically connect the head region  302  to the main body region  306  of the flexible printed circuit board  102 . 
     The buckle region functions to absorb any stress and misalignment that may occur when the head region  302  and main body region  306  are connected to the circuit board mounting structure  104  during the assembly process. Specifically, after the head region  302  is attached to the circuit board mounting structure  104 , the flexible printed circuit board  102  is wrapped or folded around and attached to the circuit board mounting structure  104 , as explained in detail below. Alternatively, the main body region  306  may be first connected to the circuit board mounting structure  104  followed by folding the flexible printed circuit board and connecting its head region  302  to the circuit board mounting structure  104 . The housing  124  is then connected to the circuit board mounting structure  102 . The first ferrule  112 , which is adapted to and protrudes from the head region, is then aligned and housed in a longitudinal cavity  1006  of the housing  124 . However, stress or misalignment may occur when connecting the housing  124  to the circuit board mounting structure  104 . 
     The buckle region  304  functions to absorb any misalignment or stress that may occur during this assembly process. As shown in  FIG. 3   a  or  FIG. 3   b , the buckle region  304  bends in the “Y” direction. Bending the buckle region  304  provides the buckle region  304  with bending freedom in the x, y and z direction, as well as rotational freedom. This bending freedom allows the buckle region  304  to absorb any stress that may occur during the assembly process when aligning and attaching the housing  124  to the circuit board mounting structure  104 . 
     C. Main Body Region 
     In addition to a buckle region  304  and a head region  302 , the flexible printed circuit board  102  also comprises a main body region  306 . The main body region  306  will now be described with reference to  FIG. 3   a  or  FIG. 3   b . The main body region  306  is thin, rectangular shaped and flexible. The main body region  306  is composed of the same multi-layered structure as the other regions of the flexible printed circuit board. The main body region  306  functions to house the other electrical components and circuitry of the optical module  100 . The electrical components may serve a variety of functions, including connection of the optical module to the system to which it is located. Accordingly, a plurality of electrical components  308  and a plurality of electrical circuitry may be adapted to a first surface  324  and/or a second surface  326  of the main body region  306  of the flexible printed circuit board  102 , as shown in  FIG. 3   a  or  FIG. 3   b.    
     1. Electrical Connections 
     A series of electrical connections may be adapted to the first or second surface  324  of the main body region  324  of the flexible printed circuit board  102 . The electrical connections function to electrically connect the flexible printed circuit board to an external environment such as another circuit board. The electrical connections may comprise ball grid arrays, solder balls, wire leads, land-grid arrays with conductive interposers, or any other means to electrically connect the flexible printed circuit board to an external environment. 
     D. Summary 
     In summary, the flexible printed circuit board  102  supports the main electrical components and elements of the optical module, such as the aptoelectronic devices  106 , driver or amplifier chip  108  and first ferrule  112 , as well as providing bending freedom and stress relief to the optical module  100 . The flexible printed circuit board  102  is attached to, and partially enclosed by, a housing, which is described below. 
     II. Circuit Board Mounting Structure and Housing 
       FIG. 9  is an exploded view of the flexible printed circuit board  102 , first ferrule  112 , a circuit board mounting structure  104  and an housing  124 . 
     A. Circuit Board Mounting Structure 
     The circuit board mounting structure  104  functions in part as a mounting structure for the flexible printed circuit board and as a heat sink to dissipate heat generated by the circuit board  102 . Specifically, the flexible printed circuit board  102  is bent and wrapped around the circuit board mounting structure  104 . A second surface  904  of the flexible printed circuit board  102  is attached to a bottom surface  914  and a first end  910  of the circuit board mounting structure  104 , as shown in FIG.  9 . Alignment ridges, guide pins or guide pin holes may exist along the bottom surface  914  and first end  910  of the circuit board mounting structure, although they are not necessary. The alignment features assist in aligning and holding the flexible printed circuit  102  board to the circuit board mounting structure. A fourth adhesive is used to firmly attach the flexible printed circuit board  102  to the circuit board mounting structure  104 . The thermal expansion coefficient and compliance of the fourth adhesive advantageously assists in preventing expansion or contraction of the circuit board mounting structure from damaging the flexible printed circuit board  102 . The flexible printed circuit board  102  bends around the circuit board mounting structure  104  in such a manner that the head region  302  of the flexible printed circuit board  102  is housed inside the first end  910  of the circuit board mounting structure  104 , as shown in  FIG. 9. A  cavity  912  on the first end  910  of the circuit board mounting structure  104  functions to house the head region  302  of the flexible printed circuit board  102 . In another embodiment, there is no cavity  912 , as explained below. A series of heat sink ridges adapted to the circuit board mounting structure function to dissipate heat generated by the flexible printed circuit board. 
     In an embodiment as shown in  FIG. 7 , the second surface  704  of the head region  302  of the flexible printed circuit board  102  is attached to the first surface  710  of the optoelectronic mounting structure  702 . The second surface  712  of the optoelectronic mounting structure  702  is attached to the upper surface  708  of the circuit board mounting structure  104  with a compliant adhesive. The flexible printed circuit board  102  then wraps around the circuit board mounting structure  104  so that the remaining portion of the second surface  904  of the flexible printed circuit board is attached to the bottom surface  914  of the circuit board mounting structure  104 , as shown in FIG.  9 . 
     As shown in  FIG. 9 , the circuit board mounting structure has feet  916  for connecting the optical module  100  to an external environment such as a second circuit board  202 . The feet  916  have ridges that allow a portion of each foot  916  to drop into a hole on the second circuit board  202  and therefore attach and align the optical module  100  to the second circuit board  202 . The ridges on the feet also maintain the optical module  100  at a specified distance above the second circuit board  202 . 
     The circuit board mounting structure  104  has snap slots  906 , set screw holes and or alignment pin holes on the first end  910  for connecting the first end of the circuit board mounting structure to housing  124 , as discussed in detail below. 
     B. Housing 
     The housing  124  is connected to the circuit board mounting structure  104 , and the housing  124  will now be described in detail with reference to FIG.  10 . The housing  124  may be made of a non-conductive material. The housing  124  comprises a mating end  1002 , as shown in  FIG. 10   a , and a receiving end  1004 , as shown in  FIG. 10   b . A longitudinal cavity  1006  extends through the housing  124  from the mating end  1002  to the receiving end  1004 , as shown in  FIGS. 10   a - 10   b.    
     The mating end  1002  of the housing  124  has tabs  1008  and alignment pins  1010  for connecting the mating end  1002  to the first end  910  of the circuit board mounting structure  104 , as shown in  FIG. 10   a . The position of the tabs  1008  correspond to the position of the snap slots  906  located on the first end  910  of the circuit board mounting structure  104 . Similarly, the position of the alignment pins  1010  correspond to the position of the alignment pin holes on the first end  910  of the circuit board mounting structure  104 . (See  FIG. 9. ) Thus, by simply engaging the tabs  1008  and alignment pins  1010  on the housing  124  into the snap slots  906  and alignment pin holes on the circuit board mounting structure  104 , the housing  124  snaps on to the circuit board mounting structure  104  and is firmly attached. In the above-stated embodiment, the housing is snapped onto the circuit board mounting structure. In other embodiments, the housing may be connected by using other attachment methods such as glue, screws or through the use of other mechanical fixtures. Furthermore, inserts may be adapted to the mating end of the housing that function to hold the circuit board mounting structure to the housing. The inserts aid in applying a force to the tabs that maintain the tabs firmly in place. These inserts may be in the form of wedges, spring-clips, stakes or shims. 
     Additionally, alignment members on the mating and receiving ends of the housing function to hold and align the position of the first and second ferrules relative to the position of the housing. These alignment members may be inwardly sloping walls at an opening of the longitudinal cavity. The alignment members act independently or in concert with the alignment pins and tabs to align and connect the first ferrule and the circuit board mounting structure. 
     Once the housing  124  is snapped onto the circuit board mounting structure  104 , at least one elastomeric pressure ring  1012  that is in proximity to the housing  124  functions to secure the housing  124  and the head region  302  of the flexible printed circuit board  102  to the circuit board mounting structure  104 . Specifically, the elastomeric pressure ring  1012  may be in a variety of shapes and forms such as a circular, oval spaces or donuts, as shown in FIG.  9 . The elastomeric pressure ring  1012  has multiple purposes. First, upon connecting the housing  124  to the circuit board mounting structure  104 , the elastomeric pressure ring  1012  is compressed, and this compression creates an outward elastomeric force in the direction of the receiving end  1004  of the housing  124  that maintains the tabs  1008  and the snap slots  906  in a firmly locked position. With the compression force on the tabs  1008  and snap slots  906 , a high degree of manufacturing tolerances is achieved. Second, the pressure or force created by the compressed ring  1012  aids in bonding the optoelectronic mounting structure  702  to the circuit board mounting structure  104 . The optoelectronic mounting structure  702  is bonded to the circuit board mounting structure  104  with adhesive, and the pressure produced by the compressed ring  1012  holds the optoelectronic mounting structure  702  firmly against the circuit board mounting structure  104  while the adhesive is cured. Accordingly, the elastomeric pressure ring  1012  produces tighter bonding between the circuit board mounting structure  104  and the optoelectronic mounting structure  702 . Third, once the housing  124  is snapped onto the circuit board mounting structure  104 , the pressure or force created by the elastomeric pressure ring  1012  provides a more robust moisture seal between the housing  124  and the circuit board mounting structure  104 . 
     Upon attachment of the housing  124  to the circuit board mounting structure  104 , the first ferrule  112  is housed in the longitudinal cavity  1006  of the housing  124 , and alignment ridges inside the longitudinal cavity  1006  engage and hold the first ferrule  112  in place. 
     In the above-described embodiment as shown in  FIGS. 9-10 , the housing  124  slides into the circuit board mounting structure  104 , and the head region  302  of the flexible printed circuit board  102  is buried in the cavity  912  of the first end  910  of the circuit board mounting structure  104 . However, in another embodiment, the first end  910  of the circuit board mounting structure  104  may not have a cavity, and the head region  302  may exist on the outside of the first end  910  of the circuit board mounting structure  104 . In this embodiment, instead of having the housing  124  slide into the circuit board mounting structure  104 , the housing  124  may slide over the circuit board mounting structure  104 , and the head region  302  may be housed in a cavity inside the housing  124 . In still another embodiment, neither the housing  124  nor the circuit board mounting structure  104  may have a cavity, and the two parts simply may mate with each other. 
     Finally, in another embodiment of the housing, a metallic coating may be applied to at least a portion of the mating end  1002  of the housing  124 . The metallic coating functions to provide electromagnetic shielding. In yet another embodiment, the housing may be made out of multiple materials and at least one of those materials would function to provide electromagnetic shielding. 
     C. Attachment of Fiber Optic Cable 
     Finally, as shown in  FIG. 10   b , the receiving end  1004  of the housing  124  functions to connect the optical module  100  to an external system. The receiving end  1004  receives a second ferrule  206 , which is typically attached to one end of a fiber optic cable  204 . The second ferrule mates with the first ferrule, as described below. The second ferrule  206  may be a MT type connector, MU type connector, MPO type connector or other type connectors. 
     In operation, the second ferrule  206  is inserted into the receiving end  1004  of the housing  124 . Wings  1014 , snaps or beams on the receiving end  1004  align, grab and hold the second ferrule  206 , and the wings  1014  snap onto the second ferrule  206 . The wings  1014  function to provide alignment compliance when connecting the second ferrule  206  to the housing  124 . Moreover, the wings  1014  are flexible and may absorb any stress that may arise due to movement of the cable  204  that is attached to the second ferrule  206 . The wings  1014  further provide a holding force that aids in holding the second ferrule  206  to the first ferrule  112 . Alignment ridges inside the longitudinal cavity  1006  of the housing  124  further engage and hold the second ferrule  206  in place. 
     Once inside the longitudinal cavity  1006 , the second ferrule  206  mates with the first ferrule  112  that is also housed in the longitudinal cavity  1006  of the housing  124 . The second ferrule  206  mates with the first ferrule  112  by engaging the alignment pins  316  located on the first end  318  of the first ferrule  112  with alignment pin holes located on a mating end of the second ferrule  206 . The alignment pins  316  and alignment pin holes function to provide fine alignment between the mating arrays of optical fibers that are packaged within the mating ferrules. Alternatively, the first ferrule may have alignment holes and the second ferrule may have alignment pins, and the ferrules would accordingly mate in a similar fashion. 
     Once the ferrules are mated, the array of optical fibers that are packaged in the ferrules are axially aligned, and the ferrules are optically connected. For example, if the optical module  100  functions as a receiver, optical signals pass from the fiber optic cable  204 , through the optical fibers packaged in the ferrules  206  and  112  and to the optoelectronic devices  106 , which are mounted on the flexible printed circuit board  102 . The optical module  100  converts the optical signals into electrical signals and transmits these signals to an external environment, such as a printed circuit board, for processing. 
     III. Alignment and Attachment Process 
     A. Overview 
     An important aspect of an embodiment of the invention is the precise alignment and attachment of the first ferrule  112  to the array of optoelectronic devices  106  that are mounted on the flexible printed circuit board  102 . A process, according to an embodiment of the invention, for aligning and connecting the first ferrule  112  to the array of optoelectronic devices  106  comprises the following steps: 
     1. Holding the first ferrule  112  directly above the optoelectronic devices  106 ; 
     2. Aligning the array of optical fibers  114  packaged in the first ferrule  112  with the array of optoelectronic devices  106  so that each optical fiber is optically aligned to a corresponding individual optoelectronic device; 
     3. Depositing the first adhesive  116  on a top surface of the array of optoelectronic devices  106 ; 
     4. Placing the first ferrule  112  on top of the first adhesive  116 ; 
     5. Tacking and curing the first adhesive  116  as to mechanically stabilize the first ferrule  112 ; and 
     6. Forming a dam  120  around the first ferrule  112  on the flexible printed circuit board  102 , dispensing the second adhesive  122  inside the dam area, and curing the first adhesive  122 . 
     These precision alignment and attachment steps are discussed below. 
     FIG  11   a  illustrates an apparatus of a high-precision alignment machine  1150 , which may be used in combination with a series of other apparatuses to produce precise alignment and attachment of optical fibers to optoelectronic devices. These machines combine many critical technologies to perform alignment with a low-cost manufacturing environment. These technologies include: (1) a high-precision stage  1152  that is used to hold the flexible printed circuit board  102 ; (2) a high-precision alignment arm  1154  for accurately placing the first ferrule  112  on the optoelectronic devices  106  that are adapted to the flexible printed circuit board  102 ; (3) a top-down view camera  1156 ; (4) side-view camera  1158 ; (5) video monitors  1160 ; (6) split-field microscope  1162 ; and (7) an optical video machine vision system  1164  which function together with human vision  1166  to replace the labor-intensive active-alignment process. In one embodiment, a touch sensor  1168  is used to determine the position or space between the array of optical fibers and the optoelectronic devices. Alternatively, computers and software may function within the machine vision system  1164  to perform many of the above stated technologies in place of human vision  1166 . An example of one of the many processes that may be used with this equipment is explained in the following paragraphs. 
     B. An Apparatus For Holding an Optical Element 
     The first step in the precise alignment and attachment of the first ferrule  112  to the array of optoelectronic devices  106  is to hold the first ferrule  112  at the end of a high-precision stage  1152 . This is accomplished through the use of an apparatus for holding an optical element, as explained in this section. 
       FIGS. 11   b - 11   c  show views of an embodiment of the apparatus for holding an optical element. The apparatus for holding an optical element  1100  holds the first ferrule  112  through the use of pin-positioning holes  1102  and vacuum pressure. The apparatus for holding an optical element has a first end  1112  and a second end  1114 . The apparatus for holding an optical element  1100  may have two pin-positioning holes  1102  on a bottom surface  1104  of the second end  1114  for receiving the alignment pins  316  of the first ferrule  112 , as shown in  FIGS. 11   b - 11   c  As shown in  FIG. 11   c , an array of optical fibers  1106  may be packaged between the pin-positioning holes  1102 , and it is optically aligned with the array of optical fibers  114  that are packaged in the first ferrule  112 . The innermost optical fibers in the apparatus for holding an optical element  1100  are milled out, forming a longitudinal cavity  1108  running through the apparatus for holding an optical element  1100  from the first end  1112  to the second end  1114 , as shown  FIG. 11   c . A vacuum is placed at a top surface of the first end  1112  of the longitudinal cavity  1108 , and the longitudinal cavity  1108  functions as a vacuum slot. Accordingly, once the alignment pins  316  from the first ferrule  112  are mated with the pin-positioning holes  1102  on the apparatus for holding an optical element  1100 , the vacuum slot functions as a vacuum clamp, holding the first ferrule  112  in place. Alternatively, an electrostatic clamp may be used in place of the vacuum clamp. Also, another embodiment may comprise alignment pins in place of the pin-positioning holes  1102 , and the alignment pins would function to connect to pin-positioning holes in a ferrule. 
     The apparatus for holding an optical element  1100  has multiple advantages and uses. First, it permits holding and manipulating the first ferrule  112  in both the x, y, and z direction as well as rotational directions. This aids in achieving precise alignment and attachment of the first ferrule  112  to the optoelectronic devices  106 . Also, the apparatus for holding an optical element  1100  grasps the first ferrule  112  without interfering, obscuring or damaging the optical fibers  114  in the first ferrule  112 . Additionally, the apparatus for holding an optical element  1100  allows access to the optical fibers  114  in the first ferrule  112  so that optical coupling may be achieved. For example, a light may be mounted on top of the apparatus for holding an optical element  1100  so that the optical fibers  114  emit light while being held by the apparatus for holding an optical element  1100 . The light emitted from the fibers  114  may then be used to aid in optically coupling the first ferrule  112  to the optoelectronic devices  106 . Conversely, light from the optoelectronic devices may be used to aid in optically coupling the first ferrule  112  to the optoelectronic devices  106 . Additionally, the apparatus for holding an optical element  1100  provides a strain-less release mechanism through the use of the vacuum clamp. By simply turning off the vacuum pressure, the apparatus for holding an optical element  1100  gently releases the first ferrule  112 . 
     The apparatus for holding an optical element  1100  also may be used for a variety of different purposes other than holding a ferrule. For example, it may be used to align and attach a micro-pipette array to a biological sensor array or a lens array to a MEMS modulator array. It also may be used to attach a single or array of optical fibers to a variety of different objects or devices. Moreover, the optical element may be a MT type connector, ferrule, MT-like ferrule, lenslet array, a diffractive optical element or any other type of device that may be aligned with the device. Accordingly, the apparatus for holding an optical element  1100  has multiple advantages and uses. 
     C. Alignment Process—X, Y and Rotational Directions 
     Once the first ferrule  112  is held at the end of the high precision arm by the apparatus for holding an optical element  1100 , the next step is to align the optical fibers with the optoelectronic devices in the x, y and rotational directions. In this section, three different alignment process are described.
         1. Image Alignment Process       

     The first process for aligning the optical fibers with the optoelectronic devices in the x, y and rotational directions is an image alignment process. In this embodiment of the invention, a split-field microscope is used to align the optical fibers with the optoelectronic devices by super-imposing an image of at least one optical fiber with an image of at least one optoelctronic devices. Specifically, once the first ferrule  112  is held at the end of the high precision arm by the apparatus for holding an optical element  1100 , the array of optoelectronic devices, which are mounted on a flexible printed circuit board, are held on a high-precision stage. A top-down view camera may be mounted above the high-precision stage holding the optoelectronic devices. With the aid of a split-view microscope and a split-field optic video system, a top-down image of the flexible printed circuit board  102 , situated on the high precision stage, is displayed on a monitor. 
     The focus and zoom on the split-field microscope and or the stage holding the flexible printed circuit board are adjusted until the optoelectronic devices  106  that are adapted to the flexible printed circuit board  102  are in view on the video monitor. The top surface of the array of optoelectronic devices  106  appears as rings  1202  on the video monitor under the high magnification of the microscope, as shown in  FIG. 12   a . A split-field video system permits simultaneous viewing of two opposite corners  1204  or ends of the array of optoelectronic devices  106  with high magnification on the video monitor. The precision stage holding the flexible printed circuit board is adjusted until the first optoelectronic device  1206  and the twelfth optoelectronic device  1208  are displayed simultaneously on the video monitor, as shown in  FIG. 12   b.    
     A light is mounted above the high-precision arm, emitting optical radiation down into the optical fibers  114  that arm packaged in the first ferrule  112 . The light flowing down the optical fibers back-lights the fiber cores and this provides a well-resolved image of the fiber cores under the split-field microscope. The image of the cores  1210  then appear as an array of well-resolved spots under the split field microscope, as shown in  FIG. 12   c.    
     Once the split-field microscope has formed an image of the fiber cores and an image of the optoelectronic devices, these two images are then superimposed by the split-field microscope to perform the alignment process. Specifically, by adjusting the x and y position of the high-precision stage, the image of the illuminated fiber cores of the first optical fiber  1212  and twelfth optical fiber  1214  are aligned within the image of the rings of the first optoelectronic device  1206  and twelfth optoelectronic device  1208  via the split-field microscope so that the spots and rings form a bull&#39;s eye pattern, as shown in  FIG. 12   d . This process precisely aligns in the x, y and rotational direction the array of optical fibers  114  that are packaged in the first ferrule  112  with the array of optoelectronic devices  106  that are adapted to the flexible printed circuit board  102 . In another embodiment, images of the optical fibers and optoelectronic devices other than the images of the first and twelfth optical fibers and optoelectronic devices may be used to achieve the same result. 
     2. Optical Energy Alignment Process 
     A second process to align the optical fibers with the optoelectronic devices in the x, y and rotational directions is an optical energy alignment process. In this embodiment of the invention, the flexible printed circuit board is again held by a high-precision stage. A light is mounted above the high-precision arm that holds the first ferrule, and the light emits optical radiation down into the optical fibers  114  that are packaged in the first ferrule  112 . The light flowing out of the optical fibers  114  radiates down onto the flexible printed circuit board  102 , which is positioned on the high-precision alignment stage. Under the high magnification of a microscope, this light appears as a series of illuminating spots on the optoelectronic devices  106 . Each illuminating spot corresponds to an optical fiber in the array of optical fibers  114  that are packaged in the first ferrule  112 . By adjusting the x and y position of the high-precision stage, the spots may be visually aligned with the rings to form a bull&#39;s eye pattern under the high magnification of a microscope. (This alignment process may be performed by machine vision rather than by human vision.) The alignment process precisely aligns in the x, y and rotational direction the array of optical fibers  114  that are packaged in the first ferrule  112  with the array of optoelectronic devices  106  that are adapted to the flexible printed circuit board  102 . 
     3. Precision Placement Alignment System 
     A third process to align the optical fibers with the optoelectronic devices in the X, Y and rotational directions is a precision placement system. In this embodiment of the invention, a precision placement system is connected to a high-precision arm that holds the first ferrule, and the system also is connected to a high-precision stage that holds the optoelectronic devices. The precision placement system aligns the objects by first calculating their initial position in space by comparing their position to a known position in space. Based upon this information, the system calculates the relative distances that the objects are apart. Once the relative distances are determined, the precision placement system aligns the objects by sequentially moving the objects and re-calculating their relative distances until they are precisely aligned. 
     In one embodiment of the invention, the precision placement system may determine the initial position in space of the array of optical fibers and the optoelectronic devices by holding the objects within a field of view of a microscope. Since the position of the cross-hairs on the microscope is known, the precision placement system knows the position of the optical fibers and optoelectronic devices relative to the position of the cross-hairs. Based upon this information, the precision placement system then calculates the relative positions of the objects to each other. Knowing the relative distances, the precision placement sequentially and continually moves the position of the objects and re-calculates their relative positions to each other until the optical fibers and optoelectronic devices are precisely aligned. 
     In another embodiment of the invention, the precision placement system may determine the initial position in space of the array of optical fibers and the optoelectronic devices by moving the objects to a point in space whose position is already known by the system. For example, the system may move the objects to corner mark on a jig or a precision touch sensor. Once the objects are referenced to that point in space, the precision placement system can calculate their relative positions to each other. The precision placement system then sequentially moves the position of the objects while continually re-calculating their relative positions to each other until they are precisely aligned. 
     D. Alignment Process—Z Axis Direction 
     Once the optical fibers  114  and optoelectronic devices  106  are aligned the X, Y and rotational directions, the high-precision alignment arm is lowered until the first ferrule  112  is within a few microns from the optoelectronic devices  106 . This vertical or Z-axis alignment process is accomplished through the use of a video-image measuring system that functions in concert with the previously-described precision equipment. This z-axis alignment process is described below. 
     A video-image measuring system is connected between a monitor and a side-view camera that is mounted near the side of the high-precision stage. With the aid of the microscope, the side-view camera views the side of the optoelectronic devices  106  and first ferrule  112 , and this image is displayed on the monitor. 
       FIG. 13  is a view of the monitor when using the video-image measuring system. The video image measurement system generates positional measuring lines  1302  over the images on the monitor, and the lines  1302  allow a user to measure the vertical distance or Z-axis height between a bottom edge  1304  of the first ferrule  112  and a top edge  1306  of the optoelectronic devices  106 , as shown in FIG.  13 . By adjusting the z position of the high-precision arm and the high-precision stage, the distance between the bottom edge  1304  of the first ferrule  112  to the top edge  1306  of the optoelectronic devices  106  is adjusted until the objects are within a few microns (e.g., approximately  35  microns apart). Accordingly, a gap exists between the first ferrule  112  and the optoelectronic devices  106 . 
     In another embodiment of the process, the z-axis alignment process may be accomplished by using laser-triangulation, interference microscophy or a touch sensor. 
     E. Mechanical Stabilization Process 
     After the first ferrule  112  and optoelectronic devices  106  are precisely positioned in space, the high-precision placement arm is raised, moving the first ferrule  112  away from the optoelectronic devices  106  in the vertical or Z-axis direction. A small volume of first adhesive  116  is then dispensed on the top surface of the optoelectronic devices  106  by a high precision, motor-driven syringe. 
     The high-precision placement arm is again lowered in the vertical or Z-axis direction until the first ferrule  112  contacts the optical adhesive  116 , which has been dispensed on the top surface of the optoelectronic devices  106 . The first ferrule  112  is suspended above the top surface of the optoelectronic devices in the liquid optical adhesive  116 . The first adhesive  116  may be cured using a UV light curing system. 
     At this point, the first ferrule  112  is attached to the optoelectronic devices  106  with the first adhesive  116  and is held from above by the apparatus for holding an optical element  1100 . As previously stated, the first adhesive mechanically stabilizes the first ferrule  112  to the optoelectronic devices  106 . The first ferrule  112  is separated from the apparatus for holding an optical element  1100  releasing the vacuum clamp on the apparatus for holding an optical element  1100  and raising the high precision alignment arm. 
     To further mechanically stabilize the first ferrule  112  to the head region  302  of the flexible printed circuit board  102 , a dam  120  may be formed on the flexible printed circuit board  102  and filled with the second adhesive  122 . A software-controlled dam and dam fill dispensing machine may be used to apply the dam  120  on the first surface  310  of the head region  302  of the flexible printed circuit board  102 . Alternatively, the dam and filling process may be done manually. The dam  120  is formed on the first surface  310  of the head region  302  of the flexible printed circuit board  102  surrounding the first ferrule  112 , driver or amplifier chip  108  and any other electrical components. The dam  120  is composed of an adhesive. 
     Once the dam  120  is formed on the flexible printed circuit board  102 , the automated fluid dispensing machine may be used to fill the area within the dam  120  with the second adhesive  122 , as shown in  FIG. 3   a . The second adhesive  122  may be cured by placing the flexible printed circuit board  102  in an oven. After curing, the first ferrule  112  becomes further mechanically stabilized to the first surface of the head region  302  of the flexible printed circuit board  102 . 
     F. Automating the Alignment Process 
     The entire process of precisely aligning and attaching the first ferrule  112  to the optoelectronic devices  106  and mechanically stabilizing it to the flexible printed circuit board  102  may be done manually. Alternatively, this process may be done automatically through the use of a computer generated system that functions in concert with the above-described precision equipment. Accordingly, this process is compatible with a mass-production manufacturing process that is the type of technology that is necessary to lower the cost of any commercially-available high-volume product. 
     G. Other Applications 
     Although an embodiment of the invention has been discussed in terms of accurately aligning and attaching an array of optical fibers to an array of optoelectronic devices, the same methodology may be employed to accurately align and connect an array of optical fibers to a wide variety of devices or objects other than optoelectronic devices. This is because there is a trend to miniaturization in many fields of science and technology that require work pieces to be positioned to a few microns and many times to sub-microns. Such fields include optics, microscopy, semiconductor technology, micro-machining, the life sciences and others. Accordingly, an embodiment of the invention may be used, for example, to accurately align and connect optical fibers to a microscope slide so as to study fluorescence light emitted from a biological sample such as a gene or insect. The light may be collected by the optical fibers and transmitted to a spectrometer for study. In another example, an embodiment of the invention may be used to accurately align and connect an array of optical fibers to micro-electromechanical systems (“MEMS”). MEMS technology involves combining semiconductor and micro-machining processes to produce tiny devices that are capable of motion on a microscopic scale on a silicon substrate. These systems may utilize the technology contained in an embodiment of the invention to accurately align and connect an array of optical fibers to the tiny devices in the micro-electromechanical system for a wide variety of applications. Consequently, an embodiment of the invention may be used to couple an array of optical fibers to a wide variety of devices or objects. 
     Finally, although an embodiment of the invention has been discussed in terms of passive alignment, an embodiment of the invention allows for active alignment and attachment of the array of optical fibers to an array of optoelectronic devices. As explained earlier, this process involves manually manipulating and connecting the optical fibers to the optoelectronic devices. 
     While we have described our preferred embodiments of the present invention, it is understood that those skilled in the art, both now and in the future, may make various improvements and enhancements that fall within the scope of the claims that follow. These claims should be construed to maintain the proper protection for the invention first disclosed.