Apparatus and methods for uniform frequency sample clocking

Abstract

A method and a system for Uniform Frequency Sample Clocking to directly sample the OCT signal with a temporally-non-linear sampling clock derived from a k-space wavemeter on the external sample clock input port of a digitizer.

1 - 20 . (canceled) 
     
     
         21 . A method for generating an optical coherence tomography (OCT) image, the method comprising:
 producing light from a swept laser source;   splitting the light into a first and a second portion, wherein the first portion is sent to an OCT interferometer to produce an OCT signal and the second portion is sent to a uniform frequency sample clock;   sending the OCT signal to a digitizer   processing the second portion into an external clock signal that is accepted by the digitizer;   sending the clock signal to the digitizer upon receipt of a signal from an optical trigger that is also sent to the digitizer; and   generating an OCT image from a combination of the OCT signal and the clock signal.   
     
     
         22 . The method of  claim 21 , wherein processing comprises the steps of characterizing the swept laser source, creating a digital representation of the clocking signal by the characterizing step, and generating the clock signal as an output to a digitizer. 
     
     
         23 . The method of  claim 22 , further comprising the step of outputting the clock signal for each laser sweep of the swept laser source triggered by an electrical synchronization pulse from the swept source laser output. 
     
     
         24 . The method of  claim 23 , further comprising the step of providing at least one waveform to an arbitrary waveform generator and generating the waveform during a triggering event. 
     
     
         25 . The method of  claim 21 , wherein processing comprises coupling an auxiliary wavemeter to the swept source laser and processing an output of the auxiliary wavemeter to generate the clocking signal. 
     
     
         26 . The method of  claim 25 , further comprising the step of outputting the clock signal for each laser sweep of the swept laser source triggered by an electrical synchronization pulse from the swept source laser output. 
     
     
         27 . The method of  claim 26 , wherein the processing step further comprises a digital processing step. 
     
     
         28 . The method of  claim 26 , further comprising the step of repeatedly outputting the digitally-processed signal by an arbitrary waveform generator. 
     
     
         29 . The method of  claim 28 , further comprising the step of collecting an intensity profile of the laser sweep with a sweep detector, shaping the intensity profile with a delay generator, and coupling the shaped intensity profile to a switching circuit. 
     
     
         30 . The method of  claim 29 , further comprising the step of coupling the auxiliary wavemeter output to the switching circuit and outputting the clock signal from the electronic switching circuit under a first condition. 
     
     
         31 . The method of  claim 25 , wherein the processing step is an analog processing step. 
     
     
         32 . The method of  claim 21 , further comprising the step of coupling the auxiliary wavemeter to a sampling circuit during the limited duty cycle of the swept laser source and deriving the clock signal from a pre-locked voltage controlled oscillator during the non-sweeping segment of each duty cycle. 
     
     
         33 . The method of  claim 25 , wherein the processing step further comprises an analog processing step further comprising coupling the analog processing output to a digitizer, coupling the digitizer output to digital to analog processor to generate the clock signal. 
     
     
         34 . The method of  claim 21 , wherein processing comprises the steps of coupling the swept source laser to a uniform frequency sample clock generator and generating the clocking signal. 
     
     
         35 . The method of  claim 24 , wherein the uniform frequency sample clock generator further comprises a gas cell providing a metric on the absolute lasing wavelength at digitized sampling times and an optical wavemeter coupled to a digitizer providing the relationship between the sampling time and lasing wavelength, further comprising determining the wavenumber bias of the swept laser source. 
     
     
         36 . The method of  claim 24 , wherein the uniform frequency sample clock generator further comprises a detector channel and a gas cell channel to generate a gas cell pulse, differentiating the gas cell pulse to replace the maximum absorption gas cell lines with a zero crossing voltage, producing a transistor-transistor logic pulse with rising edges corresponding to the central wavelength of the absorption gas cell lines, repeatedly outputting the shape of the laser source sweep, and producing a window pulse to select one of the gas cell pulses. 
     
     
         37 . A system for producing an optical coherence tomography (OCT) image, the system comprising:
 a swept laser source;   an OCT interferometer operatively coupled to the swept laser source;   a uniform frequency sample clock system operatively coupled to the swept laser source and configured to process light received from the swept laser source into an external clock signal; and   a digitizer having a first port coupled to the OCT interferometer to receive an OCT signal and a second port coupled to the uniform frequency sample clock system to receive the clock signal, which is sent to the digitizer upon receipt of a signal from an optical trigger that is also sent to the digitizer.