J. Eur. Opt. Society-Rapid Publ. 2025, 21, 25 Ó The Author( s), published by EDP Sciences, 2025 https:// doi. org / 10.1051 / jeos / 2025023 Available online at: https:// jeos. edpsciences. org
EOSAM 2024 Guest editors: Luca De Stefano and Raffaele Velotta
Journal of the European Optical Society-Rapid Publications REVIEW ARTICLE
Backward-wave optical parametric oscillators: principles, applications, and recent advancements
Fredrik Laurell * and Valdas Pasiskevicius Department of Applied Physics, Royal Institute of Technology, Hannes Alfvéns väg 12, 11419 Stockholm, Sweden
Received 5 February 2025 / Accepted 29 April 2025
Abstract. Backward-wave optical parametric oscillators( BWOPOs) represent a significant advancement in nonlinear optics, offering unique capabilities such as narrowband, highly stable outputs without the need for mirrors or coatings. Leveraging self-established distributed feedback, these devices exhibit exceptional spectral and spatial properties. This paper explores the principles behind BWOPOs, materials and techniques used, and their applications, particularly in mid-infrared lidar systems including CO 2 monitoring. Recent developments in cascaded systems and BWOPO waveguides are highlighted, demonstrating the potential of BWOPOs to revolutionize laser technology.
Keywords: Nonlinear optics, backward-wave optical parametric oscillation, Laser, Gas sensing.
1 Introduction
Optical parametric oscillators( OPOs) are versatile and widely used sources of tunable coherent light and constitutes a crucial part of nonlinear optics [ 1 ]. They rely on the process of optical parametric amplification( OPA), where a nonlinear crystal mediates the conversion of a high-energy photon from a pump beam into two lowerenergy photons, the signal and idler. Conventional OPOs consist of a nonlinear crystal, enclosed in a cavity for radiation buildup. They operate in a forward configuration, where the signal and idler waves are generated colinearly with the pump beam. For efficient energy transfer the phase-matching condition must be fulfilled as the signal and idler waves travel forward along with the pump beam throughout the nonlinear crystal. The parametric process conserves energy and momentum, and by tuning the latter output is possible across a wide range of wavelengths, from the ultraviolet to the mid-IR. Originally birefringent phasematching was exploited, where tuning was obtained either by adjusting the temperature of the sample, by rotating it, or by tuning the pump wavelength. Today quasi-phase matching( QPM) is the most commonly used technique to obtain tuning. Here a periodic modulation of the nonlinearity adds to the phasematching condition and allow flexibility in generation of desired wavelengths. OPOs play a significant role in spectroscopy, quantum optics, laser sources, and telecommunications due to their flexibility in
* Corresponding author: flaurell @ kth. se generating light at wavelengths not easily accessible by traditional lasers [ 2, 3 ].
The development of OPOs traces back to the early 1960s, shortly after the advent of the laser in 1960. The theoretical foundation for parametric processes in nonlinear optics was laid by Bloembergen and his colleagues [ 4 ], while the first experimental demonstration of an OPO came in 1965, when Giordmaine and Miller successfully generated tunable coherent light using a lithium niobate crystal pumped by a ruby laser [ 5 ]. The same year a Russian group led by Khokhlov also demonstrated an OPO [ 6 ]. These marked pivotal moments, showcasing the potential of nonlinear optics to generate wavelengths not readily accessible with conventional lasers. Over the years, OPOs became increasingly important due to the tunability of the phase matching condition within nonlinear crystals, enabling efficient conversion of pump photons into signal and idler photons.
The concept of backward-wave optical parametric oscillators( BWOPOs) emerged as an extension of OPO research and inspiration from backward microwave oscillators( carcinotrons) [ 7 ]. The backward-wave process, in which the signal and / or idler photon propagates in the opposite direction to the pump photon, was theoretical proposedin1966 [ 8 ]. However, it was not until the late 1990s and early 2000s that significant experimental and theoretical breakthroughs occurred [ 9, 10 ]. The backward interaction has a tough phase-matching condition which requires QPM and a very densely modulated v 2 nonlinearity. This configuration leads to distinct properties, such as enhanced spatial coherence and high beam quality. Additionally,
This is an Open Access article distributed under the terms of the Creative Commons Attribution License( https:// creativecommons. org / licenses / by / 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.