Analog Stabilization of an Electro-Optic I/Q Modulator with an Auxiliary Modulation Tone

TL;DR

This paper introduces an all-analog phase bias locking method for electro-optic I/Q modulators using an auxiliary RF tone, enabling stable operation up to 10 GHz with suppressed carrier and sideband.

Contribution

The paper presents a novel analog phase locking scheme utilizing an auxiliary RF tone to stabilize I/Q modulators at high frequencies, improving their performance and stability.

Findings

Achieved stable operation of I/Q modulator up to 10 GHz.

Successfully suppressed carrier and sideband to below -27 dB.

Developed a simple analytical model for error signal calculation.

Abstract

Proper operation of electro-optic I/Q modulators rely on precise adjustment and control of the relative phase biases between the modulator's internal interferometer arms. We present an all-analog phase bias locking scheme where error signals are obtained from the beat between the optical carrier and optical tones generated by an auxiliary 2 MHz RF-tone to lock the phases of all three involved interferometers for operation up to 10 GHz. With the developed method, we demonstrate an I/Q modulator in carrier-suppressed single-sideband mode, where the suppressed carrier and sideband are locked at optical power levels $< -27 dB$ relative to the transmitted sideband. We describe a simple analytical model for calculating the error signals, and detail the implementation of the electronic circuitry for the implementation of the method.