Coaxial time-of-flight optical fiber distance measurement

A laser tissue ablation system, comprising:

• an endoscope;
• a therapeutic laser light source spaced apart from the endoscope and configured to generate therapeutic laser light pulses at first times;
• a measurement light source spaced apart from the endoscope and configured to generate measurement light pulses at second times different from the first times;
• an optical fiber including a distal end extending from the endoscope, the optical fiber configured to:
• receive the therapeutic laser light pulses at the first times;
• receive the measurement light pulses at the second times;
• direct the therapeutic laser light pulses and the measurement light pulses along the optical fiber to emerge from the distal end of the optical fiber toward a target;
• collect, as collected light pulses, at least some of the measurement light pulses that are reflected from the target;
• and
• direct, as return light pulses, at least some of the collected light pulses along the optical fiber away from the distal end of the optical fiber;
• an optical detector configured to sense at least some of the return light pulses;
• and
• processor circuitry configured to:
• perform a time-of-flight analysis of the sensed return light pulses to determine a spacing between the distal end of the optical fiber and the target by, for an individual return light pulse, determining a time duration between the sensing of the return light pulse by the optical detector and an arrival at the processor circuitry of a corresponding reference signal;
• and
• generate a spacing data signal representing the determined spacing;
• wherein:
• the measurement light source includes a first light source configured to generate first measurement light pulses at a first wavelength and a second light source configured to generate second measurement light pulses at a second wavelength different from the first wavelength;
• the optical fiber includes a fiber material having non-zero dispersion such that the first measurement light pulses and the second measurement light pulses propagate along the optical fiber at different speeds;
• the first measurement light pulses form the return light pulses;
• and
• the second measurement light pulses are sensed by the optical detector to form the corresponding reference signals.