Photonic integrated circuits for Optical Coherence Tomography (OCT)
Being transparent over a long wavelength range, silicon-nitride based TriPleXtm photonic integrated circuits are applied in many applications outside the communication band. In the medical market the application of Optical Coherence Tomography is gaining more and more interest. In ophthalmology OCT has become a standard tool nowadays. However the system is still large and photonic integration is well suited to lower the complexity and size of these systems enabling new application areas. More upcoming markets for OCT are dermatology and other (biomedical) industrial markets.
OCT is the optical analogue of ultrasound imaging and enables mm-scale morphological and functional imaging with a contactless technology. Where ultrasound typically generates large-area low-resolution pictures, OCT technology enables high resolution imaging of smaller samples.
Low loss waveguides around 850 or 1060 nm wavelengths, allow compact and complex structures like filters, combiners and phase control elements, all needed for swept-source or spectral domain OCT in these often used wavelength ranges. Integrating the laser by hybrid assembly, as well as the detector into a single module, stabilizes the complete system, while making it compact. LioniX International’s long time experience with packaging and assembly ensures a fixed integration of all parts of the system that needs no optical adjustments anymore and all moving parts are removed from the system. A plug and play module can be realized.
As prototype we have developed the first fully integrated common path OCT PIC solution for a spectral domain OCT around a wavelength of 850 nm. The chip contains a common path interferometer and the spectral analysis is done via an on-chip spectrometer resulting in a complete handheld OCT probe. A broadband SLED is used as the light-source and the spectrometer is realized by using a cascaded Arrayed Waveguide Grating (AWG) on chip resulting in a 512 channel spectrometer to which the readout CCD is integrated. Combining both the common path interferometer and the spectrum analyser on chip results in a stable system allowing fast OCT analysis.
Other wavelengths and ASIC
An additional advantage of using silicon-nitride for OCT applications is a broad scope of possible wavelengths. This means that also outside of the medical field and into the metrology markets, at visible light or infrared, such a system can be offered. By adding application specific functions onto the PIC it is possible to create customized specifications.