The theoretical fundamentals of fiber-based optical parametric amplifiers(OPA) are reviewed,and their applications are discussed in this paper.In the end the future research aspects are expected.

Fiber-based Optical Parametric Amplifiers and Their Applications

A laser is based on the electromagnetic modes of its resonator, which provides the feedback required for oscillation Enormous progress has been made toward controlling the interactions of longitudinal modes in lasers with a single transverse mode For example, the field of ultrafast science has been built on lasers that lock many longitudinal modes together to form ultrashort light pulses However, coherent superposition of longitudinal and transverse modes in a laser has received little attention We show that modal and chromatic dispersions in fiber lasers can be counteracted by strong spatial and spectral filtering This allows locking of multiple transverse and longitudinal modes to create ultrashort pulses with a variety of spatiotemporal profiles Multimode fiber lasers thus open new directions in studies of nonlinear wave propagation and capabilities for applications

Spatiotemporal mode-locking in multimode fiber lasers

We observe efficient supercontinuum generation that extends into the visible spectral range by pumping a low differential mode group delay graded index multimode fiber in the normal dispersion regime. For a 28.5 m long fiber, the generated spectrum spans more than two octaves, starting from below 450 nm and extending beyond 2400 nm. The main nonlinear mechanisms contributing to the visible spectrum generation are attributed to multipath four-wave mixing processes and periodic spatio-temporal breathing dynamics. Moreover, by exploiting the highly multimodal nature of this system, we demonstrate versatile generation of visible spectral peaks in shorter fiber spans by altering the launching conditions. A nonlinearly induced mode cleanup was also observed at the pump wavelength. Our results could pave the way for high brightness, high power, and compact, multi-octave continuum sources.

Visible supercontinuum generation in a graded index multimode fiber pumped at 1064 nm.

The ability to process optical signals without passing into the electrical domain has always attracted the attention of the research community. Processing photons by photons unfolds new scenarios, in principle allowing for unseen signal processing and computing capabilities. Optical computation can be seen as a large scientific field in which researchers operate, trying to find solutions to their specific needs by different approaches; although the challenges can be substantially different, they are typically addressed using knowledge and technological platforms that are shared across the whole field. This significant know-how can also benefit other scientific communities, providing lateral solutions to their problems, as well as leading to novel applications. The aim of this Roadmap is to provide a broad view of the state-of-the-art in this lively scientific research field and to discuss the advances required to tackle emerging challenges, thanks to contributions authored by experts affiliated to both academic institutions and high-tech industries. The Roadmap is organized so as to put side by side contributions on different aspects of optical processing, aiming to enhance the cross-contamination of ideas between scientists working in three different fields of photonics: optical gates and logical units, high bit-rate signal processing and optical quantum computing. The ultimate intent of this paper is to provide guidance for young scientists as well as providing research-funding institutions and stake holders with a comprehensive overview of perspectives and opportunities offered by this research field.

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Roadmap on all-optical processing

We provide a perspective overview of the emerging field of nonlinear optics in multimode optical fibers. These fibers enable new methods for the ultrafast light-activated control of temporal, spatial, and spectral degrees of freedom of intense, pulsed beams of light, for a range of different technological applications.

Multimode nonlinear fiber optics, a spatiotemporal avenue

Nonlinear frequency mixing as a means to coherently convert light to new frequencies is widely used in many branches of optics. This process requires momentum conservation through phase matching (PM). In free-space optics, PM is achieved through angle tuning the medium with respect to the incoming light—here we explore an in-fiber analogue: PM using spatial modes of the fiber. We demonstrate over two octaves (400–1700 nm) of coherent spectral translation generated by intermodal four-wave mixing between subsets of 11 different Bessel-like fiber modes. These interactions are facilitated by the unique mode-coupling resistance of this subset of azimuthally symmetric, zero orbital angular momentum fiber modes. Their stability allows overcoming previous limitations of multimode nonlinear-optical systems imposed by mode coupling, hence enabling long interaction lengths, large effective mode areas, and a highly multimode basis set with which a new degree of freedom for versatile PM can be obtained.

Intermodal nonlinear mixing with Bessel beams in optical fiber

Fiber-optic parametric wavelength conversion (PWC) below the zero-dispersion wavelength of silica is typically constrained by the requirement of a small, tightly confined mode with anomalous dispersion to achieve phase matching. This limits the ability to power scale PWC at arbitrary wavelengths. However, the constraint is lifted for higher-order modes. We demonstrate PWC in the 1 μm band via degenerate four-wave mixing pumped in a large effective area (>600  μm2) LP0,7 mode of a double-clad fiber. We obtain up to 25% conversion in to the Stokes line with 0.5 ns pump pulses, corresponding to ∼20  kW peak power at the converted wavelength.

Broadband parametric wavelength conversion at 1 μm with large mode area fibers

Optical fibers have long been used to impose spatial coherence to shape free-space optical beams. Recent work has shown that one can use higher order fiber modes to create more exotic beam profiles. We experimentally generate optical bottles from Talbot imaging in the coherent superposition of two fiber modes excited with long period gratings, and obtain a 28 μm × 6 μm bottle with controlled contrast up to 10.13 dB. Our geometry allows for phase tuning of one mode with respect to the other, which enables us to dynamically move the bottle in free space.

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Dynamically tunable optical bottles from an optical fiber

We propose exploiting intermodal four-wave mixing for energy-scalable tuneable fiber lasers, hitherto restricted to low powers, constrained by dispersion-tailoring limitations in PCFs. Conversion over an octave, at mJ-energy-levels, appears feasible.

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High-energy fiber lasers at non-traditional colours, via intermodal nonlinearities

We demonstrate, for the first time, four-wave mixing, in the 1-μm spectral regime, in an LMA silica fiber. Pumping a 618-μm2 LP07 mode (λZDW=1038.4 nm) with a 1064.6-nm Nd:YAG laser results in the generation of modulation instability, and multiple Stokes/anti-Stokes lines, opening up the prospect of high-energy parametric processes with fibers.

/pdf/high-energy-four-wave-mixing-with-large-mode-area-higher-1vqrgpt7ch.pdf

Y. Chen

Papers

Intermodal nonlinear mixing with Bessel beams in optical fiber

Broadband parametric wavelength conversion at 1 μm with large mode area fibers

Dynamically tunable optical bottles from an optical fiber

High-energy fiber lasers at non-traditional colours, via intermodal nonlinearities

High-energy four-wave mixing, with large-mode-area higher-order modes in optical fibres