Wavelength references in the telecom spectrum have applications in communications and dimensional metrology. However, they typically consist of bulk optics and vapor cells. Photonic integration of these components may lead to low cost, portable devices.
Here we demonstrate the incorporation of a photonic Rb spectrometer with an AlN microresonator frequency doubler. Light at 1560 nm is coupled onto a chip containing the AlN microresonator frequency doubler. The resulting 780 nm light is sent to the photonic Rb spectrometer, which consists of an apodized grating beam expander and microfabricated MEMS vapor cell. We perform Doppler broadened spectroscopy of the D2 line and demonstrate preliminary laser stabilization to these features.
In the pursuit of developing a portable wavelength reference, a photonically integrated chip (PIC) was developed to perform high resolution spectroscopy in a small package. The PIC outcouples light from one grating into free space where it is reflected and directed into an adjacent grating that couples into a separate waveguide. These gratings are extreme-mode-converters which convert the confined mode with a characteristic mode size of less than a micron to a collimated 100 micron diameter beam in order to mitigate transit time broadening for high resolution spectroscopy as well as reduce the diffraction angle. A miniature atomic vapor cell is inserted in the path of the beam to complete the spectroscopic platform. Preliminary results demonstrate sub-Doppler features. Coupling into the chip is achieved using fiber arrays enabling the spectroscopic signal to be routed back through an optical fiber and monitored. A laser is then locked to these sub-Doppler features completing an integrated wavelength reference. Analysis of the atom-light interactions made available by this platform will be discussed with an emphasis on the application of such structures to portable wavelength metrology.
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