2kL method of the optical-path difference

additional optical path difference

angle multi-path optical system

automatic optical-path switching protection

coaxial optical path

coaxial symmetric optical path

Coherent optical path

difference in optical path

double optical path

double optical path-replacement method

double-optical path

endoscopic optical path

Equivalent Optical Path

extra difference of optical path

Infinite optical path

light path and optical path length control mirror

Measuring optical path

multi-optical path absorption

multiple-ring optical path