Method and apparatus for micromachining bulk transparent materials using localized heating by nonlinearly absorbed laser radiation, and devices fabricated thereby

Abstract

Thermal 3-D microstructuring of photonic structures is provided by depositing laser energy by non-linear absorption into a focal volume about each point of a substrate to be micromachined at a rate greater than the rate that it diffuses thereout to produce a point source of heat in a region of the bulk larger than the focal volume about each point that structurally alters the region of the bulk larger than the focal volume about each point, and by dragging the point source of heat thereby provided point-to-point along any linear and non-linear path to fabricate photonic structures in the bulk of the substrate. Exemplary optical waveguides and optical beamsplitters are thermally micromachined in 3-D in the bulk of a glass substrate. The total number of pulses incident to each point is controlled, either by varying the rate that the point source of heat is scanned point-to-point and/or by varying the repetition rate of the laser, to select the mode supported by the waveguide or beamsplitter to be micromachined. A wide range of passive and active optical and other devices may be thermally micromachined.

1 - 11 . (canceled) 
   
   
       12 . Apparatus for thermal 3-D micromachining of a photonic structure, comprising:
 a laser system including an oscillator producing a train of laser pulses;   a substrate holder adapted to receive a substrate having a bulk to be micromachined transparent to said laser pulses; and   means, coupled to said laser system and cooperative with the substrate holder, for directing said train of laser pulses in a focal volume about each of different points in the bulk of the substrate where said photonic structure is to be micromachined (1) with an intensity high enough to cause the bulk confined within the focal volume about each said point to non-linearly absorb energy from the laser pulses and (2) at a rate that delivers the energy of the laser pulses into the focal volume faster than it can diffuse out of the focal volume so as to produce a controlled source of heat in the focal volume about each said point to cause a predetermined alteration of a region of the bulk having a volume greater than the focal volume about each said point.   
   
   
       13 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said laser system including an oscillator producing a train of laser pulses is an unamplified laser system. 
   
   
       14 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said unamplified laser system includes a MHz laser oscillator producing a train of femtosecond pulses. 
   
   
       15 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said laser system including an oscillator producing a train of laser pulses is an amplified laser system. 
   
   
       16 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said directing means includes a controller coupled to said laser system operative to deposit the energy of multiple pulses within the focal volume at each point at a rate faster than it can thermally diffuse out of the focal volume about each point. 
   
   
       17 . The thermal 3-D micromachining apparatus of  claim 16 , wherein said controller is manually controlled. 
   
   
       18 . The thermal 3-D micromachining apparatus of  claim 16 , wherein said controller is computer-controlled. 
   
   
       19 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said substrate is glass, wherein said predetermined alteration produced by said controlled source of heat is refractive index change in the region of the bulk greater than the focal volume about each said point of said substrate, and said photonic structure is an optical interconnect. 
   
   
       20 . The thermal 3-D micromachining apparatus of  claim 19 , wherein said optical interconnect is one of a waveguide and a beamsplitter. 
   
   
       21 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said photonic structure is an optical interconnect, wherein said substrate is glass, and wherein said directing means is further operative to control the total number of pulses incident to each point to select the mode supported by said optical interconnect. 
   
   
       22 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said substrate holder includes a translation table. 
   
   
       23 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said directing means includes steerable beam direction control optics. 
   
   
       24 . The thermal 3-D micromachining apparatus of  claim 12 , wherein said directing means includes focusing optics. 
   
   
       25 . (canceled) 
   
   
       26 . Apparatus for 3-D thermal micromachining of a photonic structure, comprising:
 a substrate holder adapted to receive a substrate having a bulk to be micromachined;   means for depositing laser energy by non-linear absorption into a focal volume about each point of the bulk of the substrate to be micromachined at a rate greater than the rate that it diffuses thereout to produce a point source of heat in a region of the bulk larger than the focal volume about each point that structurally alters the region of the bulk larger than the focal volume about each point; and   means for dragging the point source of heat thereby provided point-to-point along any linear and non-linear path to fabricate said photonic structure in the bulk of the substrate.