Metrology and calibration system of ophthalmic optical standard models based on time-domain OCT system

Ophthalmic optical equipment is a kind of clinical medical equipment based on optical principles, which can be used for ophthalmic examinations and diagnoses. Their imaging qualities and measurement accuracies are very important. Therefore, regular calibrations with ophthalmic optical standard models are needed. Aiming at the metrology of axial parameters of ophthalmic optical standard models, a time-domain OCT metrology system based on multi-spectrum is developed. It can measure and calibrate the optical path values or physical thicknesses (refractive indexes are known) of each layer inside the models at different wavebands. The developed metrology system has the advantages of high speed, non-contact, disassembly free, and application to complex structures. To meet the metrology needs of ophthalmic optical instruments in different working bands, three commonly used bands can be switched in this system by an optical switch, whose central wavelengths are 840nm, 1060nm, and 1310nm respectively, with a bandwidth of around 60nm. The reference arm of the system adopts a high-precision electronic control optical path matching device, and the sample arm can achieve a maximum detection depth of 80mm in air. Combining dispersion compensation mirror and algorithm, a clear interface edge and an axial resolution of 10μm are obtained. In addition, the axial length standard model recommended by ISO 22665 and the anterior segment standard model developed by the national institute of metrology were measured experimentally. In the experiment, refractive indexes of materials in each waveband are known, and the maximum error of measuring each layer’s thickness is less than 10μm. In a word, the developed system in this paper can effectively solve the axial parameters’ metrology and calibration problem of ophthalmic optical standard models, especially with large depth and complex internal structures.