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Self-referenced nonlinear interferometry for chromatic dispersion sensing across multiple length scales

Romain Dalidet, Sébastien Tanzilli, Gregory Sauder, Laurent Labonté, Anthony Martin

TL;DR

This work addresses the challenge of measuring chromatic dispersion (CD) for short length–dispersion products, where traditional interferometers struggle with sensitivity and stability. It introduces a fully fiber-integrated, self-referenced nonlinear Sagnac interferometer that uses cascaded second-order processes (SHG followed by DFG) to generate a frequency-anticorrelated idler and exploit energy and phase conservation, causing odd-order dispersion terms to cancel. Consequently, the relative phase Φ depends primarily on the second-order dispersion term, with $Φ = β^{(2)} L Δω^2 + O(Δω^4)$, while zeroth-order terms cancel within the common loop. Readout is performed directly on a standard optical spectrum analyzer with dual-port normalization, yielding calibration-free, broadband spectra and high fringe visibility. The method is demonstrated across fiber lengths from 25 cm to 4 km, achieving high-precision CD values and enabling rapid, robust metrology at telecom wavelengths.

Abstract

Chromatic dispersion critically impacts the performance of numerous applications ranging from telecommunication links to ultrafast optics and nonlinear devices, yet fast and precise measurements are challenging, especially for short length-dispersion products. We present a fully fiber-integrated nonlinear Sagnac interferometer that exploits cascaded second-order processes to generate frequency-anticorrelated idler light and achieve odd-order dispersion cancellation without active stabilization. The measurement is intrinsically self-referenced, as the dispersion-induced phase is extracted from the interference between counter-propagating nonlinear processes within the same Sagnac loop, eliminating the need for an external reference arm or prior calibration. Operating entirely at telecom wavelengths and read out on a standard optical spectrum analyzer, the device produces instantaneous, high-visibility fringes and calibration-free spectra using dual-port normalization. We demonstrate chromatic dispersion measurements on fiber samples ranging from 25 cm to 4 km, spanning short fiber segments to long-haul links. This architecture combines self-stability, broadband compatibility, and rapid acquisition, offering a practical metrology tool for both research and industry.

Self-referenced nonlinear interferometry for chromatic dispersion sensing across multiple length scales

TL;DR

This work addresses the challenge of measuring chromatic dispersion (CD) for short length–dispersion products, where traditional interferometers struggle with sensitivity and stability. It introduces a fully fiber-integrated, self-referenced nonlinear Sagnac interferometer that uses cascaded second-order processes (SHG followed by DFG) to generate a frequency-anticorrelated idler and exploit energy and phase conservation, causing odd-order dispersion terms to cancel. Consequently, the relative phase Φ depends primarily on the second-order dispersion term, with , while zeroth-order terms cancel within the common loop. Readout is performed directly on a standard optical spectrum analyzer with dual-port normalization, yielding calibration-free, broadband spectra and high fringe visibility. The method is demonstrated across fiber lengths from 25 cm to 4 km, achieving high-precision CD values and enabling rapid, robust metrology at telecom wavelengths.

Abstract

Chromatic dispersion critically impacts the performance of numerous applications ranging from telecommunication links to ultrafast optics and nonlinear devices, yet fast and precise measurements are challenging, especially for short length-dispersion products. We present a fully fiber-integrated nonlinear Sagnac interferometer that exploits cascaded second-order processes to generate frequency-anticorrelated idler light and achieve odd-order dispersion cancellation without active stabilization. The measurement is intrinsically self-referenced, as the dispersion-induced phase is extracted from the interference between counter-propagating nonlinear processes within the same Sagnac loop, eliminating the need for an external reference arm or prior calibration. Operating entirely at telecom wavelengths and read out on a standard optical spectrum analyzer, the device produces instantaneous, high-visibility fringes and calibration-free spectra using dual-port normalization. We demonstrate chromatic dispersion measurements on fiber samples ranging from 25 cm to 4 km, spanning short fiber segments to long-haul links. This architecture combines self-stability, broadband compatibility, and rapid acquisition, offering a practical metrology tool for both research and industry.
Paper Structure (4 sections, 9 equations, 3 figures)

This paper contains 4 sections, 9 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Discussion
  4. Conclusion

Figures (3)

  • Figure 1: a) Experimental setup for CD measurement using a cascaded nonlinear Sagnac interferometer. A Superluminescent diode and pump laser generate a frequency-anticorrelated superposed state inside the loop via a nonlinear crystal. The CD of the FUT is retrieved by measuring the interference fringes on a standard OSA. b) Schematic of the cascaded nonlinear process. The pump is first converted into its second harmonic, which then interacts with the signal in the second step to generate an idler via difference-frequency generation. SDEL : superluminescent diode. WDM: Wavelength-division multiplexer. PC: Polarization controller. Circ: circulator. PBS: Polarizing beam splitter. FUT : fiber under test. SHG: Second-harmonic generation. DFG: difference-frequency generation. OSA: optical spectrum analyzer.
  • Figure 2: Raw spectra measured by the optical spectrum analyzer at the two output ports of the final PBS in the setup. The complementary spectral modulations in the idler part arise from the interference and confirm the high visibility and intrinsic stability of the Sagnac configuration.
  • Figure 3: Normalized interference patterns (experimental data, blue) and corresponding fits (red) using Eq. \ref{['eq: normalized proba']}. The results are shown for (a) a 1m long PM dispersion-compensating fiber, (b) a 25cm long PM fiber, (c) a dispersion-compensation fiber module of $L \approx 200~\mathrm{m}$, and (d) a $L \approx 4~\mathrm{km}$ coil of standard telecom single-mode fiber. These measurements illustrate the versatility of the method, covering dispersion–length products from sub-meter to multi-kilometer scale.