Apparatus and method for operating a real time large diopter range sequential wavefront sensor
A sequential wavefront sensor includes a light source, a beam deflecting element, a position sensing detector configured to output a plurality of output signals and a plurality of composite transimpedance amplifiers each coupled to receive an output signal. The output of each composite transimpedance amplifier is phase-locked to a light source drive signal and a beam deflecting element drive signal.
1. A wavefront sensor comprising:
a light source configured to output a light beam to illuminate a subject eye;
a light source driver circuit coupled to the light source, configured to output a light source drive signal at a first pulsing frequency;
a position sensitive detector having a plurality of detector elements configured to output a plurality of detector output signals indicating signal strength of incident light on each detector element;
a beam deflecting element configured to intercept a wavefront beam returned from a subject eye when the subject eye is illuminated by the light source and configured to direct a portion of the wavefront beam from the subject eye through an aperture toward the detector, where the portion of the wavefront beam directed through the aperture forms a spot on the detector, where an amplitude of deflection of a centroid of the spot from a reference point on the detector is approximately indicated by a ratiometric combination of the signal strengths, and where the amplitude of the deflection indicates the degree of tilt or convergence or divergence of the portion of the wavefront from a plane wave;
a beam deflecting element driving circuit, coupled to the beam deflecting element, configured to output a beam deflecting element drive signal to scan the portion of the wavefront beam at a wavefront scanning frequency; and
a plurality of composite transimpedance amplifiers, each having an input coupled to receive one of the plurality of detector output signals and an output for providing an amplified detector output signal, with the output of each transimpedance amplifier phase-locked to the light source drive signal and the beam deflecting element drive signal.
2. The wavefront sensor of claim 1 with each composite transimpedance amplifier comprising a low pass filter to increase stability and reduce high frequency noise.
3. The wavefront sensor of claim 2 with the low pass filter comprising:
a first operational amplifier U 2 A having an input and output;
a first resistor R 3 ; and
a first capacitor C 3 with the first resistor and capacitor connected in series between the input and output of the first operational amplifier.
4. The wavefront sensor of claim 3 with the composite transimpedance amplifier further comprising:
a second operational amplifier U 1 A having an input and an output; and
a feedback resistor R 1 , having a feedback resistance value, coupling the output of the first operational amplifier to the input of the second operational amplifier where the amplitude of the amplified detector output signal is proportional to R 1 and the noise is proportional to the square root of R 1 .