Photonic comb: a stabilized single-mode fiber etalon for wavelength calibration

We present a low-cost alternative to more complex laser metrology systems that uses a single-mode fiber Fabry-Perot etalon to generate an emission spectrum of evenly spaced lines with similar intensities, ideal for calibrating spectrographs (both in terms of wavelength and image quality). The system uses the hyperfine transition lines of ⁸⁷ R b near 780.24 nm as an absolute reference. By controlling the cavity dimensions by small changes in temperature, we can tune and thus stabilize the transmission spectrum. A 20 Hz PID loop controls the etalon temperature and locks it to the ⁸⁷ R b transitions. Through this method, we achieve a centroid error/precision of <1m/s (2.6 fm or 1.3 MHz) for 1 s integrations and 1 cm/s (0.026 fm or 13 kHz) for 30 min integrations of the reference line. We also show that a solution can be found to mathematically describe the spectrum. With the correct calibration and environmental controls in place, we show that this setup has the potential to be competitive with the best existing methods based on expensive and cumbersome laser combs.