Optical coherence tomography laser with integrated clock
A frequency swept laser source for TEFD-OCT imaging includes an integrated clock subsystem on the optical bench with the laser source. The clock subsystem generates frequency clock signals as the optical signal is tuned over the scan band. Preferably the laser source further includes a cavity extender in its optical cavity between a tunable filter and gain medium to increase an optical distance between the tunable filter and the gain medium in order to control the location of laser intensity pattern noise. The laser also includes a fiber stub that allows for control over the cavity length while also controlling birefringence in the cavity.
1. A sampling clock system for an optical coherence analysis system including a swept source generating a tunable optical signal, an interferometer that receives the tunable optical signal from the swept source via an optical fiber and conveys the optical signal on a reference arm and a sample arm and combines the optical signal returning from the reference arm and the sample arm to generate a combined signal, a detector system that detects the combined signal, and a sampling system that samples an output of the detector system and receives an electronic clock, the sampling clock system comprising:
an optical detector for detecting an optical clock signal generated by optically filtering the tunable optical signal from the swept source to generate the electronic clock; and
an electronic time delay circuit for delaying the electronic clock by an amount corresponding to the propagation time of the light from the swept source in the optical coherence analysis system that includes the optical fiber, the interferometer arms and path to the detector system to improve delay matching between the electronic clock and the combined signal.
2. A system as claimed in claim 1 , wherein the electronic time delay circuit imparts a programmable delay to the electronic clock.
3. A system as claimed in claim 1 , further comprising a high pass filter for filtering the electronic clock from the optical detector.
4. A system as claimed in claim 1 , further comprising a frequency divider for decreasing a frequency of the electronic clock from the optical detector.
5. A system as claimed in claim 1 , further comprising a frequency multiplier for increasing a frequency of the electronic clock from the optical detector.
6. An optical coherence tomography system comprising:
a swept source that generates an optical signal that is tuned over a spectral scan band;
a clock subsystem that filters the optical signal and then detects the filtered optical signal with a clock detector that generates a dock signal;
an interferometer that receives the optical signal via an optical fiber and divides the optical signal between and combines the optical signal from a sample arm and a reference arm;
a detection system that detects the combined signal generated from the optical signal from the reference arm and the sample arm;
an analog to digital converter system that samples the combined signal and receives the clock signal; and
an electronic time delay circuit for delaying the clock signal that is received by the analog to digital converter system by an amount corresponding to the propagation time of the light from the swept source in the interferometer that includes the optical fiber, the interferometer arms and path to the detector system to improve delay matching between the electronic clock and the combined signal.
7. A system as claimed in claim 6 , wherein the electronic time delay circuit imparts a programmable delay to the clock.
8. A system as claimed in claim 6 , further comprising a high pass filter for filtering the clock signal from the clock detector.
9. A system as claimed in claim 6 , further comprising a frequency divider for decreasing a frequency of the clock signal from the clock detector.
10. A system as claimed in claim 6 , further comprising a frequency multiplier for increasing a frequency of the clock signal from the clock detector.
11. An optical coherence tomography method comprising:
generating an optical signal that is tuned over a spectral scan band;
filtering the optical signal;
detecting the filtered optical signal with a clock detector that generates a clock signal;
transmitting the optical signal to an interferometer;
dividing the optical signal between and combining the optical signal from a sample arm and a reference arm of the interferometer;
transmitting the combined signal to a detector system;
detecting the combined signal generated from the optical signal from the reference arm and the sample arm;
electronically delaying the clock signal by an amount corresponding to the propagation time of the light to the interferometer, in the sample arm and the reference arm and to the detector system; and
sampling the combined signal and receiving to the clock signal that was electronically delayed.
12. A method as claimed in claim 11 , further comprising electronically changing the amount of the delay of the clock signal.
13. A method as claimed in claim 11 , further comprising high pass filtering the clock signal from the clock detector.
14. A method as claimed in claim 11 , further comprising frequency dividing the clock signal from the clock detector.
15. A method as claimed in claim 11 , further comprising a frequency multiplying the frequency of the clock signal from the clock detector.