Abstract:
A method of aligning an optical fiber to a laser diode obtains first light from the laser at a point designated as the center of a planar geometric shape. Data points are taken at the vertices of the shape, whereby a scan measures alignment quality at each of the vertices and the center. The scan begins by obtaining data at the center and moves to a vertex and the remaining vertices in either a clockwise or counterclockwise fashion. Alignment qualities are compared and the location of highest alignment quality is designated as a new center. The scan repeats until the location of the new center remains unchanged, whereby the new center becomes the point of alignment. Alternately, the scan iteration may repeat with increased resolution by reducing the size of the geometric shape and/or increasing the power from the laser until a point of alignment is found at highest resolution.

Description:
TECHNICAL FIELD 
   The present invention relates generally to align and attach systems and, more particularly, to a method of aligning an optical fiber to an optical output port in a planar space. 
   BACKGROUND OF THE INVENTION 
   The importance of achieving accurate mutual alignment of individual components in any optical system is well known. The miniature dimensions of components used in modern optical communication systems render such alignment difficult both to achieve and to maintain. For example, one problem in the construction of laser transmitters is that of efficiently coupling the optical output from a laser diode into an optical fiber. To obtain efficient coupling, the fiber end is desirably precisely aligned with the emitting area of the laser. When such alignment is achieved, the fiber is then fixed in place, ideally by a method that ensures alignment is sustained throughout the device lifetime. 
   The current methods of obtaining an initial alignment between an optical fiber and a laser output port are primarily a raster scan or a spiral scan. An exemplary embodiment of a raster scan is shown in  FIG. 1A , and an exemplary embodiment of a spiral scan is shown in  FIG. 1B . The scans are characterized by their data points  1 – 16  and  100 – 119 , respectively, whereby the scan obtains a measure of alignment quality (i.e., coupled optical power) at each data point in the sequence indicated by the arrows. The optical fiber is initially fixed to an X-Y linear movement table and positioned in front of a stationary laser diode output port. The laser diode is activated, and the scan proceeds to activate the linear table, moving the optical fiber along the respective paths indicated in  FIGS. 1A–B  for raster and spiral scans. At each of the predefined positions  1 – 16  and  100 – 119 , data is collected about the alignment quality between the optical fiber and the laser output face. A determination is then made as to the location of the predefined position with the highest, or otherwise desirable, alignment quality. A position of final alignment may then be designated at the predefined position with the desired alignment quality. 
   Such scans are useful for characterizing the input and output ports (i.e., optical fiber face and laser output face), but are generally time consuming in a manufacturing process. For example, a raster scan may be characterized by a 6 micron square with 0.3 micron resolution for an initial low resolution scan, and a 1 micron square with 0.09 micron resolution for a final high resolution scan. Such a scan may require the gathering of 521 data points, whereby each data point may require 100 milliseconds to be processed. In a typical raster scan described above, therefore, approximately 52 seconds may be needed for the complete scan. 
   It can be seen, therefore, that the large number of data points used in the alignment process typically take an undesirable amount of time to collect and analyze. Furthermore, the final coupling efficiency that is achieved may not always be the highest coupling efficiency that is possible for a particular interface due to an undesirably large number of data points needed for a high resolution scan. 
   SUMMARY OF THE INVENTION 
   The present invention is embodied in a method of aligning an input port having a face to an output port having a face. The method includes designating a center data point on the face of the output port, designating at least three perimeter data points disposed around the center data point in a planar geometric configuration at respective predetermined distances from the center data point, obtaining a measure of alignment quality at the center data point and each of the perimeter data points by translating the face of the input port to the center data point each of the perimeter data points, and translating the face of the input port to the data point having a highest measure of alignment quality. 
   In an alternate embodiment, the method further comprises the steps of designating a new center data point at one of the center and perimeter data points having the highest measure of alignment quality; and iterating the method beginning from the designation of the at least three perimeter data points, where the at least three perimeter data points are now disposed around the new center data point. 
   In a further embodiment of the present invention, the predetermined distances of the at least three perimeter data points from the center data point are set according to a scan resolution having a current setting. The method is initialized with a scan resolution having a lowest setting, and setting the scan resolution to a higher setting if the new center data point is at the same location as the center data point and if the current setting of the scan resolution is not at a highest setting. In another embodiment, the scan resolution is also changed by setting the scan resolution to an intermediate setting if the current setting of the scan resolution is at the highest setting and if the alignment quality at the center data point falls within an intermediate threshold range; and by setting the scan resolution to the lowest setting if the current setting of the scan resolution is at the highest setting and if the alignment quality at the center data point falls below a lowest threshold. Alternately, there are a plurality of intermediate settings with a corresponding plurality of intermediate threshold ranges. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
       FIG. 1A  is a plan view of a typical raster scan as characterized by its data points, according to the prior art; 
       FIG. 1B  is a plan view of a typical spiral scan as characterized by its data points, according to the prior art; 
       FIG. 2A  is a plan view of an exemplary diamond 2D scan as characterized by its data points, according to the present invention; 
       FIG. 2B  is a plan view of an alternate exemplary diamond 2D scan as characterized by its data points, according to the present invention; 
       FIG. 2C  is a plan view of a hexagonal 2D scan as characterized by its data points, according to the present invention; 
       FIG. 3  is a front plan drawing of an exemplary laser diode output face, according to the prior art; 
       FIG. 4  is a flowchart illustrating an exemplary method of the scan procedure according to an embodiment of the present invention; 
       FIG. 5  is a flowchart illustrating a further exemplary method of the scan procedure, according to the present invention; 
       FIG. 6  is a state diagram illustrating resolution shifts in an exemplary method, according to the present invention; 
       FIG. 7A  is plan view of the low resolution alignment of an optical fiber to an optical output port by an exemplary method, according to the present invention; 
       FIG. 7B  is plan view of the medium resolution alignment of an optical fiber to an optical output port by an exemplary method, according to the present invention; 
       FIG. 7C  is plan view of the high resolution alignment of an optical fiber to an optical output port by an exemplary method, according to the present invention; and 
       FIG. 8  is a block diagram of an embodiment of the present invention aligning an optical fiber to an optical source, according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawing, in which like reference numbers refer to like elements throughout the various figures that comprise the drawing,  FIG. 2A  shows an exemplary scan pattern of the present invention. The scan pattern is characterized by five data points comprising a center data point  20 , and diamond vertex data points  21 – 24  disposed around the center data point  20 . The vertex data points  21 – 24  may be disposed at the same distance from center data point  20 , or from desirably varying distances from center data point  20  (not shown in  FIG. 2A ). As shown in prior art  FIG. 3 , for example, a laser diode output face  300  is characterized by light emitting region  301  having a height LH and a width LW, where the location of highest alignment quality is at center point  302 . For such an output port, it may be desirable for the diamond scan pattern of  FIG. 2A  to have horizontal vertex data points  21  and  23  disposed at a greater distance from center data point  20  than vertical vertex data points  22  and  24  so as to substantially match the elliptical shape of light emitting region  301 . Such an embodiment of the present invention is shown in  FIG. 2B , where center data point  25  has vertex data points  26 – 29 , and the distances from horizontal vertex data points  26  and  28  to center data point  25  are longer than the distances from vertical vertex data points  27  and  29  to center data point  25 . An arrangement such as the one shown in  FIG. 2B  favors the elliptical shape of light emitting region  301 —which is more sensitive in the vertical direction—and, therefore, may result in more efficient scanning of laser diode output face  300 . 
   Generally, a scan according to the present invention may obtain a measure of alignment quality at the center data point of the scan pattern and then proceed to take further measures at the vertex data points in either a clockwise or counterclockwise progression. The first vertex data point at which a measure of alignment quality is made may be substantially to the right of the center data point, as shown in  FIGS. 2A–C . Those skilled in the art will recognize, however, that the first vertex data point to be scanned may be selected according to many different schemes without departing from the invention. 
   Furthermore, those skilled in the art will recognize that a scan pattern of the present invention may generally be characterized by any planar geometric shape about the center data point. One alternate embodiment of the invention, for example, may comprise a hexagonal scan pattern as shown in  FIG. 2C , where center data point  210  is surrounded by hexagonal vertex data points  211 – 216 . 
   In the present invention, a method is presented for aligning an optical fiber to an optical output port having a face in order to achieve a desired alignment quality. Alignment quality may generally be expressed as a measure of optical coupling efficiency or an optical power reading. The optical output port may include any surface which may receive an optical signal or from which an optical signal may radiate, such as the output port of a single mode semiconductor laser, a multi-mode semiconductor laser, an optical mirror, a second optical fiber, a semiconductor optical amplifier, an optical concentrator, and a light-emitting diode. Further, the optical fiber may be one of a metallized or non-metallized wedge-lensed, ball, conical, and flat-cleaved fiber, or generally, any surface that may receive an optical signal. 
   One exemplary embodiment of the present invention is illustrated in the flowchart of  FIG. 4 . In this embodiment, step  402  designates a center data point on the face of the optical output port. Step  402  also designates vertex data points as being disposed around the center data point in a predetermined pattern, such as one of the patterns of  FIGS. 2A–C . In designating the location of a center data point, step  401  may be performed to find a first light signal on the face of the optical output port, whereby the location of the first light signal is designated as the location of the center data point in step  402 . Alternately, either a random location or a predetermined location on the face of the optical output port may be used as the location of the center data point. Once the data points have been designated, step  403  proceeds to obtain respective measures of alignment quality at each of the center and vertex data points. As described above, the scan obtains a measure of alignment quality at the center data point and then obtains further measures of alignment quality at each of the vertex data points. In final step  404 , the location of the data point having the highest alignment quality measured in step  403  is designated as the new center data point. The new center data point may then be used as a final point of alignment of the optical fiber to the optical output port. Alternately, the method may be iterated from step  402 , with the new vertex data points being disposed around the new center data point. 
   A further exemplary embodiment of the present invention, illustrated in  FIG. 5 , presents a method of aligning an optical input port to an optical output port to achieve substantially optimized initial coupling. The method begins at step  505  by designating a current center of the scan. The current center may be designated as the location of a first light signal found in step  503 , or may generally be any predetermined or randomly selected point on the face of the optical output port. 
   Step  507  then proceeds to designate vertex data points around the current center at distances determined by a current resolution setting and at locations according to a predetermined scan pattern (such as one of the patterns in  FIGS. 2A–C ). The current resolution setting may take on a lowest value, a highest value, and one or more intermediate values. A setting of the current resolution, therefore, designates the respective distances of vertex data points from the center data point, whereby higher resolution values designate vertex data points at distances closer to the center data point. The current resolution setting may be initialized in step  501  to a lowest setting. 
   Step  509  then obtains measures of alignment quality at the center data point and each of the vertex data points to obtain five respective measures of alignment quality. In obtaining the measures of alignment quality, step  509  first obtains a measure at the center data point followed by a measure at a vertex data point located substantially to the right of the center data point and further measures at the remaining vertex data points in a clockwise or counterclockwise progression. 
   Step  511  then specifies the location of highest alignment quality among the five respective measures of alignment quality, and determines whether that location is at the center data point. If the highest alignment quality is not located at the center data point, then step  513  assigns a new center data point as being located at the location of highest alignment quality determined in step  511 . The method then proceeds back to step  507 , where the vertex data points are now disposed around the new center data point assigned in step  513 . Step  509  then obtains a measure of alignment quality at the new center data point and then moves to the vertex data point that is in the same direction as the new center data point relative to the previous center data point. The scan generally proceeds in such an iterative fashion until step  511  determines the location of highest alignment quality among the five respective measures of alignment quality to be at the location of the center data point. 
   The method then proceeds to step  515 , which determines whether the current resolution setting is at a highest value or not. If it is determined that the current resolution setting is not at a highest value in step  515 , step  517  increases the current resolution setting from its present value to the next highest value. Steps  507 – 515  are then iterated until the current resolution setting is the highest resolution, whereby the method moves to step  519 . 
   Step  519  determines whether a resolution shift is required according to predetermined criteria. The predetermined criteria for shifting the resolution may be illustrated by the state diagram of  FIG. 6 . Starting at lowest resolution setting  601 , there are two transition paths that may be taken, non-transition  611  is taken if the new center C n  is not at the same location as the previous center C n-1 , as previously described. If the new center C n  is at the same location as the previous center C n-1 , low-to-mid 1  transition  613  is taken from lowest resolution setting  601  to a first intermediate resolution setting  603 . At first intermediate resolution setting  603 , there are two transition paths that may be taken, non-transition  633  is taken if the new center C n  is not at the same location as the previous center C n-1 , as previously described. If the new center C n  is at the same location as the previous center C n-1 , mid 1 -to-high transition  637  is taken from first intermediate resolution setting  603  to a highest resolution setting  607 . At highest resolution setting  607 , there are three transition paths that may be taken, according to predetermined alignment quality threshold settings. Non-transition  677  is taken if the highest alignment quality measured Q falls within a highest threshold range TR high ; high-to-mid 1  transition  673  is taken if the highest alignment quality measured Q falls within a first intermediate threshold range TR m1 ; and high-to-low transition  671  is taken if the highest alignment quality measured Q falls within a lowest threshold range TR low . Each threshold range generally corresponds to a respective resolution setting and is defined by an upper and lower threshold, where the upper threshold of a threshold range having a resolution setting coincides with the lower threshold of a threshold range having the next highest resolution setting. 
   It will be recognized by those skilled in the art that there may be any number of intermediate resolution settings. As shown in  FIG. 6 , for example, a second intermediate resolution setting  605  is shown in phantom. If second intermediate resolution setting  605  is implemented, then mid 1 -to-high transition  637  is removed. In such an alternate embodiment, mid 1 -to-mid 2  transition  635  is initiated from first intermediate resolution setting  603  to second intermediate resolution setting  605  if the new center C n  is not at the same location as the previous center C n-1 , as previously described. At the second intermediate resolution setting  605 , non-transition  655  is taken if the new center C n  is not at the same location as the previous center C n-1 , as previously described; and mid 1 -to-high transition  657  is taken if the new center C n  is at the same location as the previous center C n-1 . At highest resolution setting  607 , there are now four transition paths that may be taken, according to predetermined alignment quality threshold settings. Non-transition  677  is taken if the highest alignment quality measured Q falls within a highest threshold range TR high ; high-to-mid transition  675  is taken if the highest alignment quality measured Q falls within a second intermediate threshold range TR m2 ; high-to-mid 1  transition  673  is taken if the highest alignment quality measured Q falls within a first intermediate threshold range TR m1 ; and high-to-low transition  671  is taken if the highest alignment quality measured Q falls within a lowest threshold range TR low . In an alternate embodiment, there may be additional transition paths (not shown in  FIG. 6 ) from intermediate resolution settings, if the highest alignment quality measure at each of the intermediate resolution settings falls within a respective threshold range of a lower resolution setting. 
   In one embodiment of the present invention, a highest threshold range may be, for example, characterized by a coupled optical power measure that is greater than or equal to 95% of a maximum power value; a first intermediate threshold range may be, for example, characterized by a coupled optical power measure that is greater than or equal to 60% of the maximum power value; and a lowest threshold range may be, for example, characterized by a coupled optical power measure that is greater than about 5% of the maximum power value. The maximum power value may be a predetermined value, or the maximum value of optically coupled power that is measured in any iteration of the scan according to the method shown in  FIG. 5 . In a further embodiment, a lowest resolution setting may be characterized by 700–800 nm step size (i.e., the distance between the center data point and any vertex data point); a first intermediate resolution setting may be characterized by 350–450 nm step size; and a highest resolution setting may be characterized by 80–150 nm step size. Alternately, a lowest resolution setting may be characterized by 5–7 micron horizontal step size and 700–800 nm vertical step size; a first intermediate resolution setting may be characterized by 1.5–2.5 micron horizontal step size and 350–450 nm vertical step size; and a highest resolution setting may be characterized by 250–350 nm horizontal step size and 80–150 nm vertical step size. 
   If it is determined in step  519  that a resolution shift is needed, as described above, then step  523  changes the resolution accordingly and begins the scan iteration again from step  507 . If no resolution shift is needed, then a determination is made in step  521  whether to end the scan or to continue with further iterations from step  507 . If the decision is made to end the scan, step  525  stops the process. If the decision is made to continue the scan, then the process continues with further iterations from step  507 . In general, step  521  may set to “NO” until a manual input is provided indicating an end of the process. 
     FIGS. 7A–C  illustrate an exemplary scan performed according to one embodiment of the present invention.  FIG. 7A  illustrates respective center and vertex data points  700 – 707  for a scan being performed at a lowest resolution setting. The scan initially designates data point  700  as the first center alignment point in the scan, whereby a measure of alignment quality is obtained at data point  700 . The scan then proceeds to obtain further measures of alignment quality at data points  701 ,  702 ,  703 , and  704 , respectively. From the five respective measures of alignment quality, it is determined that data point  703  has the highest measure of alignment quality. Data point  703  is then designated as the new center alignment point, whereby a measure of alignment quality is obtained at data point  703 . The scan then proceeds to obtain further measures of alignment quality at data points  705 ,  706 ,  700 , and  707 , respectively. From the current five respective measures of alignment quality, it is determined that data point  703  still has the highest measure of alignment quality. The scan, therefore, increases the current setting of resolution from the lowest setting to a first intermediate setting. 
     FIG. 7B  illustrates respective center and vertex data points  708 – 715  for the continuation of the scan in  FIG. 7A  at the first intermediate resolution setting, with previous data points in phantom. The scan initially designates data point  708  as the first center alignment point in the scan, whereby a measure of alignment quality is obtained at data point  708 . The scan then proceeds to obtain further measures of alignment quality at data points  709 ,  710 ,  711 , and  712 , respectively. From the five respective measures of alignment quality, it is determined that data point  712  has the highest measure of alignment quality. Data point  712  is then designated as the new center alignment point, whereby a measure of alignment quality is obtained at data point  712 . The scan then proceeds to obtain further measures of alignment quality at data points  713 ,  714 ,  708 , and  715 , respectively. From the current five respective measures of alignment quality, it is determined that data point  712  still has the highest measure of alignment quality. The scan, therefore, increases the current setting of resolution from the lowest setting to a highest setting. 
     FIG. 7C  illustrates respective center and vertex data points  716 – 723  for the continuation of the scan in  FIG. 7B  at the highest resolution setting, with previous data points in phantom. The scan initially designates data point  716  as the first center alignment point in the scan, whereby a measure of alignment quality is obtained at data point  716 . The scan then proceeds to obtain further measures of alignment quality at data points  717 ,  718 ,  719 , and  720 , respectively. From the five respective measures of alignment quality, it is determined that data point  717  has the highest measure of alignment quality. Data point  717  is then designated as the new center alignment point, whereby a measure of alignment quality is obtained at data point  717 . The scan then proceeds to obtain further measures of alignment quality at data points  721 ,  722 ,  716 , and  723 , respectively. From the current five respective measures of alignment quality, it is determined that data point  717  still has the highest measure of alignment quality. The scan may then designate the location of data point  717  as the point of desirable alignment. 
   Alternately, the system may continuously scan around data point  717  to move to a new center data point and/or initiate a change in the resolution setting, if necessary in order to account for thermal drift. 
   It can be seen that certain data points in a scan may be located off of the face of the optical output port. In one embodiment of the invention, such data points may generally be omitted from the scan, or may have their location adjusted so that they are on the face of the optical output port. Alternately, such a circumstance may cause a shift to higher resolution. Further, there may be two or more data points in a single scan iteration that have the same value of highest alignment quality. In one embodiment of the invention, the data point located in the direction of highest alignment quality from a previous scan iteration may be chosen as the location of the new center data point. Alternately, a random selection may be made designating one of the data points as the location of the new center data point. 
   It can be seen that measures of alignment quality are obtained twice for data points  700  and  703  at the lowest resolution setting, data points  708  and  712  at the first intermediate resolution setting, and data points  716  and  717  at the highest resolution setting. Furthermore, it can be seen that same resolution data redundancy, described above, coupled with cross-resolution data redundancy (e.g., data points  703  and  708  may generally be at the same location and may therefore have the same measure of alignment quality) in the present embodiment may generate  9  redundant measures of alignment quality. In an alternate embodiment of the invention, it may be desirable to remove such data redundancy by using alignment quality data already stored in memory for the location of a particular data point. 
   Once a desirable alignment has been achieved, the optical fiber is attached to a mount pad region using a heat sensitive attachment means (e.g. solder). It may be desirable to perform further adjustments of the optical fiber relative to the optical output port upon application of the heat sensitive attachment means to correct for thermal drift and misalignments induced by the application of the heat sensitive attachment means. Furthermore, it will be recognized by those skilled in the art that the alignment algorithm of the present invention may be applied to the alignment of an output port that is moved with respect to an input port as well as the alignment of an input port that is moved with respect to an output port, without departing from the invention. 
     FIG. 8  is a block diagram of one embodiment of the system. It shows an apparatus for aligning an optical input port  87  of optical fiber  86  with respect to an optical output port  84  of optical source  82 . The apparatus comprises X-Y linear table  80  for movement of optical input port  87  with respect to optical output port  84  in the X- and Y-directions, or vice versa (not shown in  FIG. 8 ), where the other end  89  of optical fiber  86  is held in place facing optical power meter  88 , which obtains measures of alignment quality of optical input port  87  to optical output port  84  at one or more scan coordinates. The apparatus is further managed by controller  81 , which directs movement of X-Y linear  80  table to one or more scan coordinates, compares measures of alignment quality received from the optical power meter at the one or more scan coordinates, initializes and changes scan resolution settings, and designates and updates the one or more scan coordinates according to the scan resolution setting and comparison of the measures of alignment quality. In a further embodiment, the apparatus may further comprise means for collecting and displaying measures of alignment quality, the scan resolution setting, and the one or more scan coordinates, wherein the controller may be manually operated. In another embodiment, the apparatus may also include memory (not shown) for storing measures of alignment quality at the one or more scan coordinates. 
   Although illustrated and described above with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.