Abstract:
A planar light circuit may be mounted in the housing a one-point mounting. The one-point mounting may reduce the tendency of thermal deformations in the housing to be transmitted to the planar light circuit.

Description:
BACKGROUND 
     This invention relates generally to planar light wave circuits. 
     Planar light wave circuits are optical circuits that may be formed using conventional integrated circuit techniques. 
     Optical components are generally mounted in aluminum housings that may be temperature tuned. Aluminum is light weight and has good mechanical properties. To reduce heater power ratings, plastic housings have been suggested. 
     However, deformation in plastic housings has been observed after machining. Mounting a planar light circuit on any non-flat surface of the housing may then become a problem. 
     Thus, there is a need for better ways to mount planar light circuits in housings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the present invention; and 
         FIG. 2  is a cross-sectional view taken generally along the line  2 - 2  in  FIG. 1  after the device has been placed in a housing in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a planar light circuit module  100  may include a planar light circuit  10 , a heat spreader  12 , a heater  14 , and a one-point heater support  16  in accordance with one embodiment of the present invention. The planar light circuit  10  is an optical circuit formed on a semiconductor substrate using integrated circuit fabrication techniques. The heater  14  is used to change optical characteristics of a component, such as a thermo-optic switch. The heater  14  may change the refractive index of a material. The heat spreader  12  spreads the heat from the heater  14  over a greater area of the circuit  10 . 
     The heater  14  may be coupled by metallizations  18  to a source of power. In some embodiments the heater  14  may be formed of a more resistive material and the metallizations may be formed of a less resistive material. Optical and electrical signals may be coupled to the planar light circuit  10  through couplers  20  and  22 . 
     The one-point heater support  16  may include an upper enlarged end  24   a , a lower enlarged end  24   b , and a reduced diameter intermediate portion  26 , which couples the enlarged ends  24   a  and  24   b . As shown in  FIG. 2 , the enlarged end  24   b  may be mounted on a lower support surface of a housing  30 . In one embodiment, the housing  30  may be a plastic housing. The intermediate portion  26  may be telescopically plugged into appropriate openings in the upper and lower enlarged portions  24   a  and  24   b . The portions  24  and the ends  24  may be tubular in one embodiment, having a round external surface. 
     Through the use of single point mounting, thermal deformation of the housing  30  may not distort the planar light circuit  10  in one embodiment. For example, in a multi-point mounting system, if the housing distorts between the two points of connection to a planar light circuit, the planar light circuit would be similarly distorted. Such distortions may modify characteristics of light signals associated with the circuit  10 . 
     In one embodiment of the present invention, the upper enlarged end  24   a  may be secured to the heater  14 , for example by glue. The end  24   a  may have a coefficient of thermal expansion similar to that of the circuit  10  in one embodiment. The lower enlarged end  24   b  may have a coefficient of thermal expansion similar to that of the housing  30  in one embodiment. 
     As a result of the matched coefficients of thermal expansion, thermal stress may be reduced between both attaching points represented by the enlarged ends  24   a  and  24   b . Relative motion may be possible between the ends  24  and the intermediate portion  26 . For example, the portion  26  may telescope into and out of the ends  24  in one embodiment. Thus, the joints between the ends  24  and the portion  26  may be stress relieving. The portion  26  may also be softer than the ends  24  in one embodiment. With a one-point mounting, stress transfer to the circuit  10  may be reduced even when the housing  30  is deformed, for example by heating. 
     In some embodiments, the environmental thermal load may be reduced through the use of a housing  30  that is made of plastic and one-point mounting. The thermal gradient of the planar light circuit  10  is accordingly smaller in some embodiments, thereby reducing the refractive index variation due to thermal stress. With reduced thermal stress on the planar light circuit  10 , the test failure rate can also be reduced in some cases. 
     In addition, deformation stress due to the housing  30  may be reduced with one-point mounting in some embodiments. The yield of the packaged planar light circuit devices may then be increased. Mechanical stress perturbations on the planar light circuit  10  may be reduced by reducing mechanical induced stress on the packaged module  100 . 
     In some embodiments, the mounting of the planar light circuit  10  may be simplified using the one-point mounting. By using round, telescoping components  24  and  26 , a socket mounting may be achieved in some embodiments. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.