Interferometer using vertical-cavity surface-emitting lasers

Abstract

An interferometer which incorporates a single mode VCSEL to facilitate miniaturization through integration of parts. The interferometer includes a beam splitter for partially reflecting and transmitting light; a single mode vertical-cavity surface-emitting laser for generating a beam of light perpendicular to a wafer; a first mirror fixedly perpendicular to the first path to reflect the portion of light reflected from the beam splitter; a second mirror movably arranged along the second path to reflect the beam portion transmitted through the beam splitter. A photodetector arranged along the second path detects the beam portion reflected from the first mirror and transmitted again through the beam splitter and the beam portion reflected from the second mirror and reflected again from the beam splitter to locate the second mirror based on an interference fringe created by a difference in the paths between the two beam portions.

1 . An interferometer comprising:
 a beam splitter for partially reflecting and transmitting light;   a single mode vertical-cavity surface-emitting laser for generating a beam of light perpendicular to a wafer along a first path toward the beam splitter;   a first mirror fixedly arranged in a position along a second path, which is perpendicular to the first path to reflect the portion of light reflected from the beam splitter;   a second mirror movably arranged along the second path to reflect the beam portion transmitted through the beam splitter; and   a photodetector arranged along the second path, the photodetector detecting the beam portion reflected from the first mirror and transmitted again through the beam splitter and the beam portion reflected from the second mirror and reflected again from the beam splitter to locate the second mirror based on an interference fringe created by a difference in the paths between the two beam portions.   
   
   
       2 . The interferometer according to  claim 1 , wherein the vertical-cavity surface-emitting laser is flip-chip bonded to a transmission substrate with a micro lens arranged thereon. 
   
   
       3 . The interferometer according to  claim 1 , wherein the vertical-cavity surface-emitting laser comprises a micro lens arranged on a base substrate to emit the collimated beam through a rear portion of the vertical-cavity surface-emitting laser. 
   
   
       4 . The interferometer according to  claim 1 , wherein the beam splitter comprises a beam splitter cube with the first mirror arranged on a face thereof, the vertical-cavity surface-emitting laser is flip-chip bonded to an outer face of the beam splitter cube perpendicular to a surface where the first mirror is arranged, and the photodetector is flip-chip bonded to a face of the beam splitter cube opposing, on a same path, the face of the beam splitter cube where the first mirror is arranged. 
   
   
       5 . The interferometer according to  claim 4 , wherein the first mirror comprises a metal coat or a dielectric coat arranged on a face of the beam splitter cube. 
   
   
       6 . An interferometer comprising:
 a beam splitter for partially reflecting and transmitting light;   a single mode vertical-cavity surface-emitting laser for generating a beam of light perpendicular to a wafer along a first path toward the beam splitter;   a first mirror movably arranged in a position along a second path, which is perpendicular to the first path to reflect the portion of light reflected from the beam splitter;   a second mirror fixedly arranged along the second path to reflect the beam portion transmitted through the beam splitter; and   a photodetector arranged along the second path, the photodetector detecting the beam portion reflected from the first mirror and transmitted again through the beam splitter and the beam portion reflected from the second mirror and reflected again from the beam splitter to locate the first mirror based on an interference fringe created by a difference in the paths between the two beam portions.   
   
   
       7 . The interferometer according to  claim 6 , wherein the beam splitter comprises a cube mirror with the second mirror arranged in a face of thereof, the single mode vertical-cavity surface-emitting laser is flip-chip bonded to an outer face of the beam splitter cube opposite to the face where the second mirror is arranged, and the photodetector is flip-chip bonded to a face of the beam splitter cube along the second path. 
   
   
       8 . An interferometer comprising:
 a transparent substrate having a transmission grating and a reflection grating arranged on one side thereof, each of the transmission and reflection gratings adapted to form a zero order beam advancing straight and a first order beam diffracted at a predetermined angle;   a single mode vertical-cavity surface-emitting laser for generating a beam of light perpendicular to a wafer, the vertical-cavity surface-emitting laser surface-mounted on the other side of the transparent substrate so that a portion the beam passes through the transmission grating of the substrate;   a mirror cube movably arranged on a path of the beam portion to displace the zero order beam transmitted through the transmission grating to a predetermined length in parallel and reflect the replaced zero order beam toward the reflection grating; and   a photodetector arranged on paths of the first order beams from the transmission grating and from the reflection grating to detect the first order beam reflected from the mirror cube and diffracted by the diffraction grating of the substrate and the first order beam diffracted by the transmission grating thereby locating the mirror cube based on an interference fringe created by a difference in optical paths of the two first order beams.   
   
   
       9 . The interferometer according to  claim 8 , wherein the transmission grating and the reflection grating are arranged to have a same period so that the first beams directed toward the photodetector are set parallel with each other.