Photonics uses light rather than electrons to perform varieties of applications. Silicon photonics, in particular, has gained a lot of interest in the past few decades due to its unique ability to utilize standard complementary metal-oxide-semiconductor manufacturing processes and materials, resulting in high density, high yield, and the massive fabrication of optical devices at low cost. Although the field has its roots in the telecommunications industry, it has expanded to many new applications such as sensing, spectroscopy, nonlinear optics, quantum optics, optomechanics, and even neuroscience. Silicon nitride, one of the mature silicon family materials has been widely used in photonics research and development. It combines the beneficial properties of a wide transparency range covering visible to mid-IR, a moderately high nonlinear refractive index which is ten times higher than silica, and semiconductor mass manufacturing compatibility. Most importantly, silicon nitride can achieve ultra-low loss and high confinement simultaneously.
In optics, when a collection of nonlinear processes act together on a pump beam, the resulting spectral broadening of the original pump beam gives rise to a supercontinuum. Supercontinuum sources for optical coherence tomography are of great interest since they provide a broad bandwidth for high resolution and high-power imaging sensitivity. Commercial fiber-based supercontinuum systems use high pump powers to generate a broad bandwidth and customized optical filters to modulate the spectra.
In a report published in Science Advances, we introduced a supercontinuum platform based on a 1 mm silicon nitride photonic chip for optical coherence tomography (OCT). We directly pumped and efficiently generated a supercontinuum near 1300 nm and used the setup to image biological tissues and show the strong imaging performance of the device. The new chip will facilitate portable OCTs and integrated photonics during optical imaging studies.
Optical frequency combs can enable ultrafast processes in physics, biology, and chemistry, as well as improve communication and navigation, medical testing, and security. The Nobel Prize in Physics 2005 was awarded to the developers of laser-based precision spectroscopy, including the optical frequency comb technique, and microresonator combs have become an intense focus of research over the past decade.
In a letter published on Nature, we have demonstrated low-power chip unites lasers and frequency combs for the first time and can be powered by an AAA battery, opening the door to portable devices for a wide range of applications from spectroscopy to optical communications to LIDAR.
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