Quadrature amplitude modulation for electronic side and Pound-Drever-Hall locking

Published

September 13, 2024

Author(s)

Juntian Tu, Alessandro Restelli, Tsz-Chun Tsui, Kevin Weber, Ian Spielman, James(Trey) Porto, Steven Rolston, Sarthak Subhankar

Abstract

The Pound-Drever-Hall (PDH) technique is routinely used to stabilize the frequency of a free-running laser to an ultralow expansion (ULE) reference cavity. The electronic sideband (ESB) locking scheme—a variant of the standard PDH locking scheme—helps bridge the frequency difference between the quantized frequencies enforced by the cavity and the laser frequency of interest. Here we use quadrature amplitude modulation (QAM)—a technique routinely used in digital signal communication—to implement the ESB PDH locking scheme. We theoretically analyze the effects of I/Q impairments on the ESB PDH error signal. We develop two distinct, tunable, and compact system architectures for implementing QAM: one built from the ground up around an in-phase/quadrature-phase (I/Q) modulator, the other built upon the code base for a software defined radio (SDR) evaluation board intended for hobbyists, educators, and students. Using these system architectures, we engineer a high-quality phase-modulated radio-frequency (rf) signal with a large phase modulation index of 1.01 radians, a tunable carrier wave frequency in the range of 450 MHz to 4 GHz, and a maximum modulation frequency of 3 MHz. We strongly suppress residual amplitude modulation (RAM) in the phase-modulated rf signal by compensating for I/Q impairments. We use this rf signal to drive an electro-optic modulator (EOM) to optically generate the ESB PDH error signal, using a high-finesse ULE cavity as the absolute frequency reference.

Citation

Review of Scientific Instruments

Pub Type

Journals

Keywords

Laser stabilization, Electronic Sideband, Pound Drever Hall

Citation

Tu, J. , Restelli, A. , Tsui, T. , Weber, K. , Spielman, I. , Porto, J. , Rolston, S. and Subhankar, S. (2024), Quadrature amplitude modulation for electronic side and Pound-Drever-Hall locking, Review of Scientific Instruments (Accessed January 13, 2025)