The key challenge for high-power delivery through optical fibers is overcoming nonlinear effects. To keep a smooth output beam, most techniques mitigating nonlinearities are restricted to single-mode fibers. Moving out of the paradigm, we show experimentally that wavefront-shaping coherent input light highly multimode fiber can increase power threshold stimulated Brillouin scattering (SBS) by an order magnitude, whilst simultaneously controlling beam profile. SBS suppression results from...

Transverse Mode Instability (TMI) that results from dynamic nonlinear thermo-optical scattering is the primary limitation to power scaling in high-power fiber lasers and amplifiers. It has been proposed TMI can be suppressed by exciting multiple modes a highly multimode fiber. We derive semi-analytic frequency-domain theory of threshold for onset narrowband amplifiers under arbitrary input excitation general geometries. Our detailed model includes effect gain saturation, pump depletion,...

High-power fiber laser amplifiers have enabled an increasing range of applications in industry, science, and defense. The power scaling for is currently limited by transverse mode instability. Most techniques suppressing the instability are based on single- or few-mode fibers order to output a clean collimated beam. Here, we study theoretically using highly multimode amplifier with many-mode excitation efficient suppression thermo-optical nonlinearity We find that mismatch characteristic...

Stimulated Brillouin scattering (SBS) is often an unwanted loss mechanism in both active and passive fibers. Highly multimode excitation of fibers has been proposed as a novel route toward efficient SBS suppression. Here, we develop detailed, quantitative theory which confirms this proposal elucidates the physical mechanisms involved. Starting from vector optical scalar acoustic equations, derive appropriate nonlinear coupled mode equations for signal Stokes modal amplitudes analytical...

We outline a recently developed theory of impedance-matching, or reflectionless excitation arbitrary finite photonic structures in any dimension. It describes the necessary and sufficient conditions for perfectly to be possible, specifies how many physical parameters must tuned achieve this. In absence geometric symmetries tuning at least one structural parameter will excitation. The employs identified set complex-frequency solutions Maxwell equations as starting point, which are defined by...

Time-reversal symmetry enables shaping input waves to control output in many linear and nonlinear systems; however energy dissipation violates such symmetry. We consider a saturated multimode fiber amplifier which light generates heat flow suffers thermo-optical scattering, breaking time-reversal identify spacetime maps the target back an field. This mapping employs phase conjugation, gain absorption substitution but not time reversal, holds steady-state for slowly varying inputs. Our...

Monitoring the movement and vital signs of patients in hospitals other healthcare environments is a significant burden on staff. Early warning systems using smart bed sensors hold promise to relieve this improve patient outcomes. We propose scalable cost-effective optical fiber sensor array that can be embedded into mattress detect movement, both sensitively spatially.Proof-of-concept demonstration multimode (MMF) specklegram used image bed.Seven MMFs are attached upper surface such they...

Stimulated Brillouin Scattering (SBS) provides a major limitation on power scaling in high fiber lasers and amplifiers. Using wavefront shaping highly multimode fibers promising avenue to suppress SBS while maintaining good beam quality. We present here generalized theory for find the Stokes susceptibility terms of eigenmode expansions vector optical acoustic wave equations. An analytical form relevant gain matrix is obtained modal overlap integrals. will discuss strategies based properties matrix.

By coherently seeding a multimode fiber amplifier with tailored spatial wavefront, it is possible to generate the target output profile in presence of thermo-optical nonlinearity and gain saturation. We prove numerically that such wavefront exists modified phase-conjugation approach. An optical beam power launched from distal end proximal waveguide absorption, exiting phase-conjugated sent back loss switched equal magnitude. The obtained enhanced threshold for transverse mode instability due...

Wavefront shaping has become a powerful tool for manipulating light propagation in various complex media undergoing linear scattering. Controlling nonlinear optical interactions with spatial degrees of freedom is relatively recent but growing area research. A wavefront-shaping-based approach can be used to suppress stimulated Brillouin scattering (SBS) and transverse mode instability (TMI), which are the two main limitations power scaling high-power narrowband fiber amplifiers. Here we...

We demonstrate a single-frequency multimode-fiber amplifier free of stimulated Brillouin scattering up to 474 W. The optical efficiency is 89 % and spectral linewidth 19.8 kHz. focus the output beam using input wavefront shaping.

Multimode fibers provide a promising platform for realizing high-power laser amplifiers with suppressed nonlinearities and instabilities. The potential degradation of optical beam quality has been major concern highly multimode fiber amplifiers. We show numerically that the propagation factor M2 single-frequency amplifier can be reduced to nearly unity by shaping input or output profile spatial phase-masks. Our method works narrowband strong gain saturation, pump depletion, random mode...

High-power fiber laser amplifiers have enabled an increasing range of applications in industry, medicine and defense. The power scaling for narrow-band is currently limited by the transverse modal instability. Various techniques been developed to suppress instability a single or few-mode order output clean, collimated beam. Here we propose use highly multimode equal excitation thermo-optical nonlinearity Our numerical simulations theoretical analysis predict significant reduction dynamic...

Transverse Mode Instability (TMI) is one of several nonlinear effects that limit power scaling in high fiber lasers and amplifiers. We demonstrate TMI can be effectively suppressed by spreading multiple modes the fiber. show threshold scales linearly with number modes, upon equal excitation caused smearing thermally induced refractive index grating. The multimode focused to a diffraction limited spot, giving quality beam increased threshold. finally linear maintained inclusion gain saturation.

Stimulated Brillouin scattering (SBS) is an important nonlinear optical effect which can both enable and impede processes in guided wave systems. Highly multi-mode excitation of fibers has been proposed as a novel route towards efficient suppression SBS active passive fibers. To study the effects multimode generally, we develop theory for arbitrary input excitations, fiber cross section geometries refractive index profiles. We derive appropriate coupled mode equations signal Stokes modal...

The key challenge for high-power delivery through optical fibers is overcoming nonlinear effects. To keep a smooth output beam, most techniques mitigating nonlinearities are restricted to single-mode fibers. Moving out of the paradigm, we show experimentally that wavefront-shaping coherent input light incident on highly multimode fiber can increase power threshold stimulated Brillouin scattering (SBS) by an order magnitude, whilst simultaneously controlling beam profile. theory reveals...

For many applications of high-power delivery through optical fibers and fiber amplifiers, high average power beam quality are both needed but difficult to meet simultaneously. This is because operation requires a large core minimize nonlinear effects, usually supports modes — it general belief that output-beam single-mode operation. The scaling for narrowband amplifiers often limited by the stimulated Brillouin scattering (SBS), which introduces transmission loss can induce strong...