Swept source OCT system with multi spatial mode gain chip

A method of optical coherence tomography comprising:

• generating, with a swept optical source including a semiconductor gain chip configured to lase in a plurality of spatial modes comprising at least one higher-order spatial mode, a swept optical beam;
• delivering the swept beam to a free-space interferometer via coupling optics that preserve the plurality of spatial modes;
• dividing the beam into free-space sample and reference arms, combining light from the arms at a detector to produce interferometric signals;
• and
• reconstructing depth-resolved information from the interferometric signals.

A swept optical source comprising:

• a semiconductor gain chip configured during operation to lase in a plurality of spatial modes comprising at least one higher-order mode;
• an optical tuning element configured to vary output optical frequency over a sweep;
• and
• an output coupling arranged to deliver the output outside the laser cavity while preserving the plurality of spatial modes for free-space propagation or for injection into a multimode optical fiber;
• or
• An optical coupling apparatus configured to be arranged between a swept optical source and a free-space interferometer of an OCT system, the apparatus comprising:
• at least one of (i) a free-space relay with numerical-aperture stops selected to pass higher-order spatial content from the source and (ii) a multimode optical fiber having a length of at least 1 m, and in some examples at least 10 m, arranged so that the plurality of spatial modes from the source are preserved to the interferometer while lateral spatial coherence is reduced;
• or
• A full-field swept-source OCT system comprising:
• a free-space interferometer configured to illuminate an areal field on a sample and to combine sample-arm and reference-arm light on a two-dimensional camera;
• and a reference arm arranged to introduce at least one of (i) an off-axis tilt between reference and sample beams at the camera and (ii) phase-stepping via a driven reference mirror, whereby interferometric cross-terms are separable prior to k-space processing;
• or
• An OCT system comprising:
• a swept source;
• a free-space interferometer;
• and
• a homogenizer disposed in a collimated section between the source and the interferometer, the homogenizer having a small diffusion angle selected to spatially mix the multimode field and reduce lateral coherence while maintaining the spectral linewidth required for axial OCT ranging.