Arbitrary Phase Access for Stable Fiber Interferometers

Abstract

Well-controlled yet practical systems that give access to interference effects are critical for established and new functionalities in ultrafast signal processing, quantum photonics, optical coherence characterization, etc. Optical fiber systems constitute a central platform for such technologies. However, harnessing optical interference in a versatile and stable manner remains technologically costly and challenging. Here, degrees of freedom native to optical fibers, i.e., polarization and frequency, are used to demonstrate an easily deployable technique for the retrieval and stabilization of the relative phase in fiber interferometric systems. The scheme gives access (without intricate device isolation) to <1.3 × 10 −3 rad error signal Allan deviation across 1 ms to 1.2 h integration times for all tested phases, ranging from 0 to 2 . More importantly, the phase-independence of this stability is shown across the full 2 range, granting access to arbitrary phase settings, central for, e.g., performing quantum projection measurements and coherent pulse recombination. Furthermore, the scheme is characterized with attenuated optical reference signals and single-photon detectors, and extended functionality is demonstrated through the use of pulsed reference signals (allowing time-multiplexing of both main and reference signals). Finally, the scheme is used to demonstrate radiofrequency-controlled interference of high-dimensional time-bin entangled states.

Phase-locking an interferometer with single-photon detections

“…Here, in order for ϕ 0 to be a stable locking point, ϵ and r ′ 0 need to have opposite signs. It is evident from equation (11) that in absence of external noise, the locking error scales with the square root of the chosen step size |ϵ|.…”

“…This drift error is proportional to 1/ϵ. Together with the locking error (11), it leads to a total phase error of…”

“…In contrast, QKD applications require signals on the level of single resolvable photons (femtowatts to picowatts), where an intense locking beam in the signal path is a huge disturbance. The issue is sometimes circumvented by using different wavelengths for the signal and locking [9][10][11][12], which can be separated after the MZI. Suppression of leakage from locking light into the signal path is however limited, and the signal phase becomes ambiguous after phase slips of the locking light.…”

Integral order photonic RF and microwave signal processors based on Kerr micro-combs

“…They offer a much higher number of wavelengths than typically is available through EO combs, together with a wide range of comb spacings (free spectral range (FSR)) including ultra-large FSRs, as well as greatly reduced footprint and complexity. Micro-combs have enabled many fundamental breakthroughs [50] including ultrahigh capacity communications [77][78][79], neural networks [80][81][82], complex quantum state generation [83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] and much more. In particular, microcombs have proven to be very powerful tools for a wide range of RF applications such as optical true time delays [31], transversal lters [34,38], signal processors [29,32], channelizers [37] and others [15, 18, 26-28, 36, 39-41].…”

Integral order RF and microwave photonic based signal processors using Kerr soliton crystal micro-combs

“…They offer a much higher number of wavelengths than typically is available through EO combs, together with a wide range of comb spacings (free spectral range (FSR)) including ultralarge FSRs, as well as greatly reduced footprint and complexity. Micro-combs have enabled many fundamental breakthroughs [50] including ultrahigh capacity communications [77][78][79], neural networks [80][81][82], complex quantum state generation [83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] and much more. In particular, micro-combs have proven to be very powerful tools for a wide range of RF applications such as optical true time delays [31], transversal filters [34,38], signal processors [29,32], channelizers [37] and others [15, 18, 26-28, 36, 39-41].…”