Residual Phase Noise Measurement of Optical Second Harmonic Generation in PPLN Waveguides

TL;DR

This paper characterizes the residual phase noise and stability of fiber-coupled PPLN waveguides used for frequency doubling, demonstrating their suitability for ultra-stable optical clock applications.

Contribution

It introduces a novel noise measurement technique and provides detailed residual phase noise data for PPLN modules used in precision metrology.

Findings

Residual phase noise below -35 dBrad^2/Hz at 1 Hz

Doubling efficiency up to 117.5 %/W

External parameters do not limit stability

Abstract

We report on the characterization, including residual phase noise and fractional frequency instability, of fiber-coupled PPLN non-linear crystals. These components are devoted to frequency doubling 871 nm light from an extended-cavity diode laser to produce a 435.5 nm beam, corresponding to the ytterbium ion electric quadrupole clock transition. We measure doubling efficiencies of up to 117.5 %/W. Using a Mach-Zehnder interferometer and an original noise rejection technique, the residual phase noise of the doublers is estimated to be lower than ${\rm -35\, dBrad^2/Hz}$ at 1 Hz, making these modules compatible with up-to-date optical clocks and ultra-stable cavities. The influence of external parameters such as pump laser frequency and intensity is investigated, showing that they do not limit the stability of the frequency-doubled signal. Our results demonstrate that such compact, fiber-coupled modules are suitable for use in ultra-low phase noise metrological experiments, including transportable optical atomic clocks.