Phase-front-modulation sensor and method of fabrication

Abstract

A sensor and a method of fabrication are provided. The sensor includes at least one optical waveguide and an optical reflector. The optical reflector is optically coupled to the at least one optical waveguide and includes a first portion and a second portion. The first portion is configured to reflect a first portion of light back to the at least one optical waveguide. The second portion is configured to reflect a second portion of light back to the at least one optical waveguide. The reflected second portion of the light differs in phase from the reflected first portion of the light by a phase difference that is not substantially equal to an integer multiple of π when the second portion of the optical reflector is in an equilibrium position in absence of the perturbation.

What is claimed is: 
     
         1 . A sensor comprising:
 at least one optical waveguide configured to emit light in a direction; and   an optical reflector optically coupled to the at least one optical waveguide, the optical reflector configured to reflect at least a portion of the light, the optical reflector comprising:
 a first portion of the optical reflector configured to reflect a first portion of the light back to the at least one optical waveguide; and 
 a second portion of the optical reflector configured to reflect a second portion of the light back to the at least one optical waveguide, the second portion of the optical reflector responsive to a perturbation by moving relative to the first portion of the optical reflector, the reflected second portion of the light differing in phase from the reflected first portion of the light by a phase difference that is not substantially equal to an integer multiple of π when the second portion of the optical reflector is in an equilibrium position in absence of the perturbation. 
   
     
     
         2 . The sensor of  claim 1 , wherein the at least one optical waveguide comprises an optical fiber. 
     
     
         3 . The sensor of  claim 2 , wherein the at least one optical waveguide further comprises at least one lens configured to receive the light from the optical fiber and to transmit the light towards the optical reflector. 
     
     
         4 . The sensor of  claim 3 , wherein the at least one lens comprises a graded-index lens. 
     
     
         5 . The sensor of  claim 3 , wherein the at least one lens is configured to collimate the light emitted from the optical fiber and to return the reflected first portion of the light and the reflected second portion of the light to the optical fiber. 
     
     
         6 . The sensor of  claim 1 , further comprising a laser configured to generate the light, the light having at least one wavelength, the sensor further comprising an optical signal analyzer configured to receive the reflected first portion of the light and the reflected second portion of the light from the at least one optical waveguide. 
     
     
         7 . The sensor of  claim 1 , wherein the optical reflector comprises a wafer, the first portion of the optical reflector comprising a first surface of the wafer, the second portion of the optical reflector comprising a diaphragm offset from the first portion of the optical reflector along the direction, the diaphragm in a well surrounded by the first surface. 
     
     
         8 . The sensor of  claim 7 , wherein the diaphragm is thinner than portions of the wafer surrounding the diaphragm. 
     
     
         9 . The sensor of  claim 7 , wherein the diaphragm is elastically deformable in response to the perturbation. 
     
     
         10 . The sensor of  claim 7 , wherein the light has a wavelength and the well has a depth substantially equal to one-eighth of the wavelength. 
     
     
         11 . The sensor of  claim 7 , wherein the light has a width greater than a width of the well. 
     
     
         12 . The sensor of  claim 7 , wherein the light has a width less than or equal to a width of the well. 
     
     
         13 . The sensor of  claim 7 , wherein the optical reflector comprises a plurality of spring structures mechanically coupled to the first portion of the optical reflector and to the diaphragm, the plurality of spring structures configured to elastically stretch and move such that the diaphragm translates in a direction that is generally perpendicular to the diaphragm. 
     
     
         14 . The sensor of  claim 7 , wherein the diaphragm is mechanically coupled to the wafer along a perimeter of the diaphragm, and the diaphragm is configured to elastically bow back and forth in a direction that is generally perpendicular to the diaphragm. 
     
     
         15 . The sensor of  claim 1 , wherein the phase difference is substantially equal to an odd integer multiple of π/2. 
     
     
         16 . The sensor of  claim 1 , wherein the phase difference has a magnitude that is in at least one of the following ranges: substantially greater than zero and substantially less than π, substantially greater than π and substantially less than 2π, substantially greater than 2π and substantially less than 3π, substantially greater than zero and less than or equal to π/2, greater than or equal to π/2 and substantially less than π, substantially greater than π and less than or equal to 3π/2, greater than or equal to 3π/2 and substantially less than 2π, substantially greater than 2π and less than or equal to 5π/2, and greater than or equal to 5π/2 and substantially less than 3π. 
     
     
         17 . A method for fabricating a sensor, the method comprising:
 providing a first tube comprising a ferrule inside the first tube, the ferrule comprising an optical waveguide configured to emit a light beam;   inserting at least one lens into the first tube, a portion of the at least one lens extending outwardly past an end of the first tube, the at least one lens configured to receive the light beam emitted from the optical waveguide;   affixing a first end of a second tube to the portion of the at least one lens extending outwardly past the end of the first tube; and   affixing an optical reflector to a surface of a second end of the second tube.   
     
     
         18 . The method of  claim 17 , further comprising adjusting a distance between the optical waveguide of the ferrule and the at least one lens to modify a radius of a collimated light beam propagating from the at least one lens. 
     
     
         19 . The method of  claim 18 , further comprising bonding the ferrule and the at least one lens to the first tube. 
     
     
         20 . The method of  claim 17 , wherein the surface of the second end of the second tube is perpendicular to a longitudinal axis of the second tube within ±0.2 degree. 
     
     
         21 . The method of  claim 17 , further comprising forming at least one vent hole through a side of the second tube.