MOBILITY ENGINEERING Produced by SAE Media Group
MOBILITY ENGINEERING
Magazines
Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Stimulated Brillouin Scattering (SBS) Suppression and Long Delivery Fibers at the Multikilowatt Level with Chirped Seed Lasers

Using chirped seed amplification with a MEMS VCSEL seed to scale the output power of a ytterbium fiber amplifier.

One obstacle in the scaling of high-power fiber lasers arises because of nonlinear effects (e.g., stimulated Brillouin scattering [SBS]) due to the large intensity times length product. Efforts to raise the power threshold include:

  1. reducing the Brillouin gain by combining materials with positive and negative elasto-optic coefficients or tailoring the acoustic index to avoid guiding the acoustic wave,
  2. reducing the effective Brillouin gain by using a seed linewidth much wider than the Brillouin bandwidth,
  3. enlarging the Brillouin bandwidth relative to the seed linewidth,
  4. lowering the laser intensity by enlarging the fiber core, and
  5. minimizing the required active fiber length by pumping at the wavelength of maximum absorption and doping as heavily as possible.
Experimental setup with chirped diode laser (ChDL), distributed feedback Bragg (DFB) laser, electro-optic modulator (EOM), photodiodes (PDs), cladding mode stripper (CMS), and end cap

Conventional approaches to broadening the seed linewidth reduce the coherence length, making it difficult to coherently combine multiple fiber amplifiers. For example, a seed bandwidth of 40 GHz (coherence length in fiber = 5 mm) will require path-length matching of much less than 1 mm to maintain high coherence.

It has been shown that chirped seed amplification (CSA) in conjunction with acousto-optic frequency shifters and feedback circuitry can maintain coherence between 2 fiber amplifiers, despite path-length differences of 10–50 cm. The maximum path-length difference is limited to cΔv max/β n, where Δv max is the maximum available frequency shift, β is the chirp, and and c/n is the speed of light in the fiber. It is also limited by the intrinsic coherence length of the unchirped laser. The laser described in this report has an unchirped bandwidth of 40 MHz (full width at half maximum [FWHM]), therefore a coherence length of 5 m.

In a tiled geometry, this ability to control the phase electronically can be used to predistort an emitted wavefront to compensate for atmospheric turbulence. CSA also leads to an SBS threshold that is fiber length independent in the long fiber limit. This approach is compatible with the other techniques for suppressing SBS, except those that increase the Brillouin linewidth. The present work describes the use of CSA with a micro-electromechanical system (MEMS)-vertical-cavity, surface-emitting laser (VCSEL) seed to scale the output power of a ytterbium (Yb) fiber amplifier to 1.6 kW, while at the same time allowing a delivery fiber of 19 m. A numerical simulation of the experiment shows that the SBS threshold could be raised to 2 kW by optimizing the pump attenuation.

This work was done by by Jeffrey O. White, Sensors and Electron Devices Directorate, ARL; Mark Harfouche and Amnon Yariv, Department of Electrical Engineering, California Institute of Technology; John Edgecumbe, Nufern; Naresh Satyan and George Rakuljic, Telaris, Inc. for the Army Research Laboratory. ARL-0204

Topics:
Acoustics Aerodynamics Amplifiers Electronic equipment Fiber Optics Fibers Lasers Lasers & Laser Systems Microelectromechanical devices Optics Optimization Parts Photonics Pumps Research and development Research and development Sensors and actuators Turbulence
This Brief includes a Technical Support Package (TSP).
Document cover
Stimulated Brillouin Scattering (SBS) Suppression and Long Delivery Fibers at the Multikilowatt Level with Chirped Seed Lasers

(reference ARL-0204) is currently available for download from the TSP library.

Don't have an account?

More From SAE Media Group

    Magazine cover
    Aerospace & Defense Technology Magazine

    This article first appeared in the September, 2017 issue of Aerospace & Defense Technology Magazine.

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Stimulated Brillouin Scattering (SBS) Suppression and Long Delivery Fibers at the Multikilowatt Level with Chirped Seed Lasers" presents research focused on addressing challenges associated with high-power laser systems, particularly in the context of SBS, which can limit the efficiency and effectiveness of laser delivery systems.

    SBS is a nonlinear optical effect that occurs when intense laser light interacts with acoustic waves in a medium, leading to energy loss and distortion of the laser beam. This phenomenon is particularly problematic in long optical fibers used for delivering high-power laser beams, as it can significantly reduce the output power and degrade beam quality. The document outlines innovative strategies to suppress SBS, thereby enhancing the performance of laser systems.

    One of the key approaches discussed in the report is the use of chirped seed lasers. Chirped lasers emit light that varies in frequency over time, which can help mitigate the conditions that lead to SBS. By employing this technique, researchers aim to maintain high power levels while minimizing the adverse effects of SBS. The document details experimental setups, methodologies, and results that demonstrate the effectiveness of chirped seed lasers in suppressing SBS in long delivery fibers.

    Additionally, the report highlights the importance of optimizing fiber design and material properties to further reduce the susceptibility to SBS. The research findings indicate that specific fiber configurations and compositions can significantly enhance the performance of high-power laser systems.

    The implications of this research are substantial for various applications, including military, industrial, and medical fields where high-power lasers are utilized. By improving the reliability and efficiency of laser delivery systems, the advancements discussed in the document could lead to more effective laser-based technologies and applications.

    Overall, the document serves as a comprehensive resource for understanding the challenges posed by SBS in high-power laser systems and presents viable solutions through innovative laser technologies. The findings contribute to the ongoing efforts to enhance laser performance, making it a valuable reference for researchers and practitioners in the field of laser technology.

    Top Stories

    INSIDERDesign

    Feature Image Venus Aerospace’s Rotating Detonation Rocket Engine Completes First Flight...

    INSIDERDesign

    Feature Image Bombardier is Digitally Upgrading its Aircraft Design, Engineering and...

    INSIDERDefense

    Feature Image How the US Army is Advancing Research in Robotics, AI and Autonomy

    INSIDERManned Systems

    Feature Image New Copper Alloy Could Provide Breakthrough in Durability for Military Systems

    Original EquipmentManned Systems

    Feature Image ACT Expo 2025: Heavy-Duty EVs, H2 Trucks and Tariff Talk Dominate Day One

    Technology ReportPower

    Feature Image ICE and Hybrid-Electric Propulsion Show Staying Power

    Webcasts