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Ultrafast Optics: Vector Cavity Lasers — Physics and Technology

Investigating the operation of fiber lasers where the vector nature of light propagation in the laser cavity is considered.

Fiber lasers have found widespread applications in industrial material processing, scientific research and military systems due to their advantages of easy maintenance, excellent stability, compact size and low cost. One characteristic of fiber lasers, compared to other types of lasers, is that strong light is confined to propagating a long distance in a fiber core that has a very small cross-sectional area. This has the consequence that the nonlinear light interaction with the matter has a very long length. This results in the strength of all nonlinear optical processes being strongly amplified. This means that a conventionally weak, nonlinear optical effect can become significant. Therefore, apart from the practical applications, fiber lasers also constitute an ideal platform for the exploration of various complex nonlinear dynamics.

A schematic diagram of the fiber laser experimental setup. PC: Polarization controller; EDF: Erbium doped fiber; WDM: Wavelength-division multiplexer; OC: Optical coupler; ISO: Isolator; OSA: Optical spectrum analyser.

Previous studies on the operation of fiber lasers have revealed many interesting nonlinear optical phenomena. Studying these nonlinear optical effects has not only led to a better understanding of the operation of fiber lasers, but also has driven the performance of the fiber lasers to the extreme through exploiting features of the nonlinear optical effects for better laser operation. However, previous studies of fiber lasers have mainly focused on the simple scalar cavity lasers, which ignore the vector nature of light propagation in fibers. For many practical cases, e.g. a fiber laser with a polarization sensitive component in the cavity, this is justified as the existence of the polarization sensitive component fixes the polarization of light in the laser cavity. However, for the comprehensive understanding of the features of fiber lasers, the vector nature of light propagation in the cavity fibers has to be considered. Theoretical studies have shown that the vector light propagation in single mode fibers involves the nonlinear coupling between the two orthogonal polarization components of light, which could introduce a number of new nonlinear dynamics, such as various types of vector soliton formation, polarization domains and domain walls, and black-white vector solitons. The aim of this research project is to investigate the operation of fiber lasers with a quasi-vector cavity both numerically and experimentally. It is expected that through this study, a deep and comprehensive understanding of the operation of fiber lasers could be gained, and fiber lasers with novel features could be further developed.

This research mainly focused on the study of two types of quasi-vector cavity fiber lasers. One is with a saturable absorber in the cavity where, due to the effect of the saturable absorber, the laser will be automatically mode locked. Mode locking generates a high peak power optical pulse in the laser cavity. Depending on the concrete laser operation conditions, the mode locked pulse would then be shaped into various forms of dissipative solitons through the nonlinear propagation in the laser cavity. Experimental studies based on the atomic layer graphene mode locked fiber lasers have revealed a number of interesting dissipative soliton operation features.

Another type is the case of the vector cavity fiber lasers without any saturable absorber in the cavity. For this type of fiber laser, it is shown that due to the cavity detuning, strong CW emission is intrinsically unstable as a result of the cavity induced modulation instability. It automatically becomes a periodic pulse train. Under strong pumping, the peak power of the pulses could become sufficiently strong that the nonlinear pulse shaping drives the pulses into dissipative solitons. As there is no saturable absorber in the cavity, the dynamics and features of the dissipative solitons are different from those with a saturable absorber in the cavity. Following convention, the dissipative solitons are called “temporal cavity solitons”.

This work was done by Dingyuan Tang of the Nanyang Technological University for the Air Force Research Laboratory.For more information, download the Technical Support Package (free white paper) here under the Photonics category. AFRL-0274

Topics:
Aerospace Defense Fiber Optics Fibers Lasers Lasers & Laser Systems Optical Components Optics Optics Photonics Research and development
This Brief includes a Technical Support Package (TSP).
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Ultrafast Optics: Vector Cavity Lasers — Physics and Technology

(reference AFRL-0274) is currently available for download from the TSP library.

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    Aerospace & Defense Technology Magazine

    This article first appeared in the September, 2019 issue of Aerospace & Defense Technology Magazine.

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    Overview

    The document titled "Ultrafast Optics - Vector Cavity Fiber Lasers: Physics and Technology" is a final report authored by A/Prof. Tang Dingyuan from Nanyang Technological University, covering research conducted from March 28, 2013, to March 28, 2016. Sponsored by the Air Force Office of Scientific Research (AFRL/AFOSR), the report focuses on the advancements in high power fiber lasers, particularly emphasizing the vector nature of light propagation within fiber laser cavities.

    Traditionally, studies on fiber lasers have concentrated on scalar field operations, which simplify the complexities of light behavior. However, this research highlights the significance of considering the nonlinear coupling between two orthogonal polarization components of light, leading to a deeper understanding of laser dynamics. The report introduces the concept of vector cavity fiber lasers, which account for these interactions and reveal a range of intriguing phenomena.

    Key findings from both experimental and numerical investigations include the formation of vector solitons, phase-locked vector solitons, induced solitons, and bright-dark pulse pairs. The report details how these phenomena arise from the nonlinear interactions in the fiber laser cavity, providing insights into their properties and behaviors. The experimental studies confirm the theoretical predictions, showcasing the rich dynamics that can occur in fiber lasers when the vector nature of light is taken into account.

    The report also discusses the implications of these findings for the development of advanced laser technologies, suggesting that understanding vector solitons and their interactions could lead to improved performance in applications such as telecommunications, material processing, and medical technologies.

    In summary, this document presents a comprehensive overview of the research on vector cavity fiber lasers, illustrating the importance of nonlinear optical effects and the potential for innovative applications in ultrafast optics. The findings contribute significantly to the field, paving the way for future studies and advancements in high power fiber laser technology. The report is publicly available, reflecting its contribution to the scientific community and its relevance to ongoing research in laser dynamics.

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