Abstract:
A system and method for facilitating passive alignment of an optical component in an optical bench. A groove is etched into the optical bench. The groove has two sections. The first section is configured to act as an optical guide. The second section is configured to receive the optical component. An optical component is inserted into the first section and moved into the second section. The optical component may be bonded to the optical bench.

Description:
BACKGROUND OF THE INVENTION 
     One of the primary technical challenges associated with the manufacture of optical systems is component alignment of optical devices. In the manufacturing Micro Electro-Mechanical Systems (MEMS) devices, sub-micrometer alignment tolerances are often required. 
     There are two general classes of alignment strategies for optical components: active and passive. In passive alignment, alignment features are fabricated directly on the components as well as on the substrate to which the components are to be mounted. The components are then mounted and bonded directly to the substrate using the alignment features. 
     In active alignment, an optical signal is transmitted through the components and detected, sometimes after an initial passive alignment of the components. The alignment is performed manually, based on checking and adjusting the optical components to achieve the desired performance of the system. Accordingly, the process of checking and adjusting optical components requires substantially higher labor costs than passive alignment. The difference in labor costs is further compounded in fabricating MEMS devices because MEMS devices can have hundreds of components that need to be aligned in order for the system to function properly. In such a system, the cost of active alignment could total thousands of times the cost of passive alignment. 
     Generally, optical system manufacturing seeks to improve the efficiency of which the optical systems can be configured. Passive alignment is essential to any large scale manufacturing of MEMS optical systems because it drastically reduces the necessary labor costs. The availability of passive aligning optical components greatly influences whether it is economically feasible to produce a particular MEMS optical device. 
     SUMMARY OF THE INVENTION 
     Using grooves to facilitate passive alignment of optical components in an optical bench. One or more grooves are etched into the optical bench. The grooves are configured to act as optical guides. An optical component is inserted into a first section of the groove and moved into the second section of the groove. The first section of the groove is tapered and is configured to guide the optical components into the second section. The second section is configured to receive the optical component. 
     In accordance with yet other aspects of the invention, the optical component is then bonded to the optical bench. 
     In accordance with still another aspect of the invention, a lid is attached to the optical bench to cover the etched grooves and optical components. 
     In accordance with still further aspects of the invention, the slot section of the etched groove intersects with a second etched groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  is a top view of the optical bench system formed in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of a portion of an optical bench system formed in accordance with an embodiment of the present invention; and 
         FIG. 3  is a perspective view of an inventive tapered recess etched into an optical bench. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an optical bench system  10  utilizing MEMS processes and materials. The optical bench system  10  includes an optical bench  12 , a laser light source  18 , and a coil  42 . The optical bench  12  includes a substrate, preferably made out of silicon. The optical bench  12  has a first surface  62  and a second surface  64 . In some embodiments, the first surface  62  and/or second surface  64  of the optical bench  12  could be closed with one or more lids to protect and/or attach optical components (not shown) to the optical bench  12 . 
       FIG. 2  shows a detailed view of the integration of an optical alignment system  90  into the optical bench  12 . A tapered recess  152  is etched into the first surface  62  the optical bench  12  to facilitate passive alignment of a mirror  132  while maintaining the desired tolerances. The etching is accomplished utilizing Deep Reactive Ion Etching (DRIE) techniques. The tapered recess  152  has three sections: a rear section  170 , a tapered section  168  and a slot section  172 . The rear section  170  has a width  162 , which is constant. The slot section  172  has a width  164 , which is constant. The tapered section  168  has a width that tapers, starts at equal to the width of the rear section  162  and ends with the width  164  of the slot section  172 . The tapered recess  152  has a floor  180  having a depth  178 . Throughout the tapered recess  152 , the depth  178  is constant. 
     The tapered recess  152  has a first slot end point  190  and a second slot end point  192 . The mirror  132  has to where most of the mirror  132  is located in the slot section  172 , with one end of the mirror  132  in contact with the second slot endpoint  192 . After the mirror  132  is received within the slot section  182 , the mirror  132  is exposed to a first etched groove  128  and a second etched groove  129  between the first slot end point  190  and the second slot end point  192 . An arrow  158  indicates the direction that the mirror  132  has been moved to effectuate passive alignment of the mirror  132  in the optical bench  12 . The mirror  132  has a width  102  that is smaller than the width  164  of the slot section  172 . The difference between the width  164  of the slot section  172  and the width  102  of the mirror  132  should be configured so that the mirror  132  may be passively aligned into its desired position. Proper insertion of the mirror  132  is crucial because it ensures the laser light will be split and steered to other optical components the optic circuit. Misplacement of the mirror  132  can cause gross misalignments. 
     Laser light enters this view of the system via a first optical fiber  122 , which is in a first etched groove  148 . Laser light travels below the surface of the optical bench  12  in a series of etched grooves. The first optical fiber  122  is located below the surface of the optical bench  12 . A first resilient clamp  120  holds the first optical fiber  122  in place in the first etched groove  148 . Laser light leaves the first optical fiber  122  and enters a second etched groove  126 . The second etched groove contains a first ball lens  124 . The first ball lens  124  columnates the laser light. The laser light leaves the first ball lens  124  and enters a third etched groove  128 . A mirror  132  is exposed to the laser light traveling along a first path  106  in the third etched groove  128  between the first slot end point  190  and the second slot end point  192 . The mirror  132  is configured to function as a beam splitter. The ratio of reflection versus transmission of laser light at the mirror  132  depends on the composition of the mirror  132  and the composition and thickness of material used to coat the mirror  132 . The mirror  132  is made of silicon and is coated with a dielectric. In other embodiments, the mirror  132  could reflect all light. Complete reflection is accomplished by coating the mirror  132  with a metal. 
     Some laser light is transmitted through the mirror  132  in the direction of a third path  100 , while some laser light is reflected off the mirror  132  along the direction of a second path  104  in a fourth etched groove  129 . The third etched groove  128  is oriented perpendicular to the fourth etched groove  129 . An angle  194  is formed between the mirror  132  and the fourth etched groove  129 . The angle between the mirror  132  resting within the slot section  172  and the fourth etched groove  129  is approximately 45 degrees. 
     After reflecting off the mirror  132  and entering the fourth etched groove  129 , the laser light enters a fifth etched groove  146 . The fifth etched groove  146  contains a second ball lens  146 . Laser light enters the second ball lens  144 . The second ball lens  144  columnates the laser light and directs it towards a second optical fiber  142  that is held in place by a second resilient clamp  108 . 
       FIG. 3  is a perspective view of the mirror insertion system  90 . In one embodiment, the tapered recess  152  is etched directly into the optical bench  12  so that the mirror  132  is located below the surface of the optical bench  12 . The tapered recess  152  has a depth  178  that is greater than the height of any optical component in the mirror insertion system  90 . In alternative embodiments, an optical component may have a height that is greater than the depth  178  of the tapered recess  152 . 
     The width of the rear section  162  is approximately three times larger than the width  102  of the mirror  132 . The tapered recess  152  has a floor  180  that is flat. The walls of the tapered recess  152  are oriented perpendicular to the floor  180 . The tapered recess  152  has a drop target  160 . The drop target  160  is where the mirror is placed when it initially enters the mirror insertion system  90 . In this embodiment, the tapered section  168  is convex with respect to substrate of the optical bench  12 . However, concave or straight transitions from the rear section  172  to slot section  168  could be utilized. 
     A method for inserting a mirror into the optical bench system  10  ensures that the mirror  132  is passively aligned into the slot section  170  while keeping within a very small tolerance with respect to the optical bench  12 . A first step of the method involves etching a tapered recess  152  into the optical bench  12 . Referring to  FIG. 3 , the tapered recess  152  is etched into the base using DRIE techniques. A second step is to manually or robotically drop the mirror  132  into the tapered recess  152  so that the mirror  132  rests initially on the drop target  160 . A third step is to move the mirror  132  in the direction of the arrow  158  into the slot section  172  until the end of the mirror  132  contacts the slot end point  138 . In the third step, the decreasing width of the tapered section  168  guides the optical component smoothly into the slot section  170 . The movement of the mirror  132  into the slot section  172  is done by hand with a vacuum pencil. Alternatively, robotic means or three-axis controller could be used to move the mirror  132  into the slot section  172 . Movement of the mirror  132  in the direction of the arrow  158  ceases when the mirror reaches the second slot endpoint  192  of the tapered recess  152 . The mirror  132  is then secured to the optical bench  12 . The mirror  132  could be secured to the optical bench  12  by bonding using a UV cured epoxy. Preferably, the epoxy is applied to both the mirror  132  and the optical bench  12  at the second slot endpoint  192 . Other types of glues or epoxies could be utilized. Alternatively, the mirror  132  could be secured to the optical bench  12  by wedging the mirror  132  into the slot section  172 . Also, the mirror  132  could be held in place by wedging silicon or some other material into the tapered recess  152  behind the inserted mirror  132 . Once the end of the mirror  132  is secured to the second slot endpoint  192 , no further alignment is necessary. An optional step is to attach a lid to the first surface  62  and/or second surface  64 . The lid may be attached to the optical bench  12  by fusing, soldering or forming eutectic bonds. The method saves time and money by passively aligning the mirrors in the optical bench  12 . 
     In alternative embodiments various optical components can be added or rearranged to split, merge, and/or measure laser light in order to build different optical systems known to those of ordinary skill in the art. Other etching techniques may be used that are capable of producing straight vertical or negatively sloped side walls. Also, light sources may be used that produce light other than laser light. Additionally, it is understood that more than one mirror could be aligned in the optical bench  12 . Moreover, optical components other than mirrors may be aligned using the principles of this invention. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.