Continuous base beneath optical sensor and optical homodyning system

A method for enclosing a cavity within an optical device for use on a surface, the method comprising:

• providing a light source for illuminating the surface;
• providing a sensor for receiving light scattered from the surface;
• enclosing a cavity containing the light source and sensor with a continuous base having no openings, the continuous base including a window which allows the light from the light source and the light scattered from the surface to pass through it, the continuous base preventing entry of foreign elements into the optical device;
• and
• preventing parasitic rays generated by the window from reaching the sensor.

A control device configured for use on a surface, the control device detecting optical displacement relative to the surface, the control device comprising:

• a housing;
• a light source located within the housing for illuminating a surface with an illumination beam;
• an illumination lens located within the housing to direct light from the illumination beam onto the surface;
• a sensor located within the housing to receive light scattered off the surface;
• a continuous bottom portion of the housing having no openings and including a window configured to allow light from the light source to be directed onto the surface and to allow reception of the scattered light on the sensor, wherein the window has active optical properties.