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Journal of Optics

Control of electro-optic sideband spectrum using sequential modulators

Umakanth Dammalapati, Rachel Elvin, Paul F. Griffin, Erling Riis

Published Feb 20, 2025• 2 citations

Abstract

Abstract Electro-optic modulators are widely used for the generation of optical sidebands for various applications. Here, we report on a technique enabling control of the relative amplitudes of optical sidebands generated by electro-optic modulators. The technique makes use of a phase modulator and Mach–Zehnder amplitude modulator, connected in series to break the symmetry of the sideband amplitudes. The generated optical sideband spectrum can be controlled by the two radio frequency (RF) modulation amplitudes, the attenuation level of the amplitude modulator, and the relative RF phase of the two modulations. We demonstrate near-complete suppression of one first-order sideband and with simultaneously achieving equal amplitudes of the carrier and the other first-order sideband with > 94% purity. The technique can be utilised to produce a spectrum with effectively two frequency components. This enables application in atomic physics experiments such as the minimisation of off-resonant light shifts that can limit the performance of atomic clocks and interferometers. We demonstrate operation in the near-infrared, at 795 nm, using commercial-off-the-shelf components and circumventing the need for frequency doubling of lasers in the optical communications region.

DOI: 10.1088/2040-8986/adb860

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We demonstrate a simple method to obtain accurate optical waveforms with a gigahertz-level programmable modulation bandwidth and a watt-level output power for wideband optical control of free atoms and molecules.Arbitrary amplitude and phase modulations are transferred from microwave to light with a low-power fiber electro-optical modulator.The sub-milliwatt optical sideband is co-amplified with the optical carrier in a power-balanced fashion through a tapered semiconductor amplifier (TSA).By automatically keeping TSA near saturation in a quasi-continuous manner, typical noise channels associated with pulsed high-gain amplifications are efficiently suppressed.As an example application, we demonstrate interleaved cooling and trapping of two rubidium isotopes with coherent nanosecond pulses.

A compact and robust laser system is essential for mobile atom interferometers. Phase modulation can provide the two necessary phase-coherent frequencies without sophisticated phase-locking between two different lasers. However, the additional laser frequencies generated can perturb the atom interferometer. In this article, we report on a novel method to produce a single high-power laser beam composed of two phase-coherent sidebands without the perturbing carrier mode. Light from a diode laser is phase-modulated by using a fiber-coupled electro-optic modulator driven at 3.4 GHz and passes through a Fabry-Perot cavity with a 6.8 GHz free spectral range. The cavity filters the carrier mode to leave the two first-order sidebands for the two-photon Raman transition between the two hyperfine ground states of 87 Rb. The laser beam is then fed to a single tapered amplifier, and the two sidebands are both amplified without mode competition. The phase noise is lower than that of a state-of-the-art optically phase-locked external-cavity diode laser (−135 dBrad 2 /Hz at 10 kHz) at frequencies above 10 Hz. This technique can be used in all-fiber-based laser systems for future mobile atom interferometers.

We propose a novel scheme that uses only a single passive phase compensation device to achieve stable optical and radio frequency joint transfer. The phase noises of optical and radio frequency can be simultaneously compensated by passively embedding their phase information on the two optical carrier sidebands generated by an electro-optical modulator without using the phase discrimination and active servo controller. As a result, this scheme has many advantages, such as high spectral purity, short settling time and infinite compensation accuracy. We experimentally demonstrate the joint transfer of optical and 1 GHz RF over 120 km fiber spools. The optical frequency stability achieves 6.9 × 10 −17 at 1 s and 7.03 × 10 −19 at 10000 s, while the 1 GHz RF is 6.47 × 10 −13 at 1 s and 3.96 × 10 −16 at 10000 s.