Integrated Resonant Accelerometer Using Optical Strain Sensor

Abstract

An accelerometer may comprise a proof mass, a first tether mechanically coupled to the side of the proof mass and to an anchor, and a ring resonator integrated with the tether to form a sensing tether. The ring resonator and the tether may be configured such that a strain sustained by the sensing tether causes a change of a resonance condition of the ring resonator. The accelerometer may comprise a wavelength locking loop configured to adaptively maintain a center frequency of the light energy at a resonant frequency of the sensing element, and a scale factor calibrator configured to stabilize a scale factor associated with the accelerometer. The accelerometer may further include a detection processor configured to receive the detection signal and produce an acceleration signal therefrom. The acceleration signal may correspond to an amount of change of the resonance condition with respect to a reference resonance condition.

What is claimed is: 
     
         1 . A method of fabricating an accelerometer, comprising:
 defining at least one of a photonic waveguide and a photonic ring resonator on a silicon-on-insulator (SOI) substrate, the SOI substrate having an insulator layer and a silicon layer;   integrating one or more active components on the SOI substrate;   defining at least one sensing tether by etching partially through the insulator layer of the SOI substrate;   defining a proof mass associated with the at least one sensing tether by etching through the silicon layer of the SOI substrate;   releasing the at least one sensing tether by selectively etching the insulating layer of the SOI substrate.   
     
     
         2 . The method of  claim 1 , wherein the one or more active components comprises at least one of (i) a photodiode, (ii) a laser, (iii) a phase tuner, and (iv) a photonic ring resonator. 
     
     
         3 . The method of  claim 2 , wherein the one or more active components further comprises at least one of a scale factor calibrator and a wavelength locking loop. 
     
     
         4 . The method of  claim 1 , wherein defining at least one sensing tether further comprises forming the at least one sensing tether to have cross-sectional dimensions, W×L, of at least one of W<5μ and L<5μ. 
     
     
         5 . The method of  claim 1 , wherein integrating one or more active components on the SOI substrate further comprises forming a photonic ring resonator on a first tether of the at least one sensing tether to form a first sensing tether, such that the photonic ring resonator undergoes strain along with the first tether. 
     
     
         6 . The method of  claim 1 , further comprising coupling an excitation and detection system to the photonic ring resonator, the excitation and detection system configured to sense the resonance condition of the photonic ring resonator and to produce a detection signal corresponding to the resonance condition of the photonic ring resonator. 
     
     
         7 . The method of  claim 6 , further comprising integrating the excitation and detection system on the SOI substrate. 
     
     
         8 . The method of  claim 6 , further comprising integrating a scale factor calibrator on the SOI substrate, the scale factor calibrator configured to stabilize a scale factor associated with the accelerometer. 
     
     
         9 . The method of  claim 1 , wherein defining the proof mass further comprises fashioning the proof mass from a full thickness of a bulk silicon wafer upon which the accelerometer is fabricated. 
     
     
         10 . The method of  claim 1 , wherein defining the at least one sensing further comprises defining a first tether mechanically coupled to a first side of the proof mass and mechanically coupled to a first anchor site, and defining a second tether mechanically coupled to a second side of the proof mass and mechanically coupled to a second anchor site. 
     
     
         11 . The method of  claim 10 , wherein integrating one or more active components on the SOI substrate further comprises:
 (i) forming a first photonic ring resonator on a first tether of the at least one sensing tether to form a first sensing tether, such that the first photonic ring resonator undergoes strain along with the first tether, and   (ii) forming a second photonic ring resonator on a second tether of the at least one sensing tether to form a second sensing tether, such that the second photonic ring resonator undergoes strain along with the second tether.