The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

High power fiber lasers: current status and future perspectives [Invited]

The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

/pdf/optical-gas-sensing-a-review-4uaf589xiq.pdf

Optical gas sensing: a review

In this paper, we summarize the fundamental properties and review the latest developments in high power fiber lasers. The review is focused primarily on the most common fiber laser configurations and the associated cladding pumping issues. Special attention is placed on pump combination techniques and the parameters that affect the brightness enhancement observed in single-mode and multimode high power fiber lasers. The review includes the major limitations imposed by fiber nonlinearities and other parasitic effects, such as optical damage, transverse modal instabilities and photodarkening. Finally, the paper summarizes the power evolution in continuous-wave and pulsed ytterbium-doped fiber lasers and their impact on industrial applications.

High Power Fiber Lasers: A Review

In recent decades, rare earths have become vital to a wealth of advanced materials and technologies including catalysts, alloys, magnets, optics and lasers, rechargeable hydride batteries, electronics, economical lighting, wind- and solar-energy conversion, bio-analyses and imaging. In this perspective article we give a broad overview of rare earth resources and uses first and then of selected applications in dedicated fields such as telecommunications, lasers, photovoltaics (solar-energy conversion), lighting (fluorescent lamps and OLEDs), luminescent probes for bio-analyses and bio-imaging, as well as magnetism and magnetic refrigeration.

/pdf/rare-earths-jewels-for-functional-materials-of-the-future-1rcxl48wlx.pdf

Rare earths: jewels for functional materials of the future

We discuss fundamental aspects and future prospects of high power fiber lasers and amplifiers with particular attention to high control of cladding-pumped, rare-earth-doped fiber sources in a multitude of regimes.

/pdf/high-control-in-high-power-fiber-lasers-and-amplifiers-ie9ww54lbd.pdf

High control in high power fiber lasers and amplifiers

Lithium niobate is a versatile optical material with many applications that result from its wide range of electro-optic, nonlinear, photorefractive and piezoelectric properties. The ability to produce complex, yet controllable, aligned structures in lithium niobate without the need for photolithographic patterning, would allow the implementation of a range of applications such as Bragg and relief grating, periodically poled structures, and miniature electro-optic devices.

/pdf/sub-micron-filamentary-structures-formed-during-light-1zo3r8ypqf.pdf

Sub-micron filamentary structures formed during light induced frustrated etching of fe-doped lithium niobate: results and modelling

We report a novel beam deflection and switching method that occurs due to the electro-optic effect under applied field when a beam at grazing incidence is incident on an interface between anti-parallel domains in a sample of LiNbO3. We present data obtained for wavelengths of 0.543µm and 1.52µm and compare this with theoretical models. For deflection, improvements can be obtained for both range of angular deflection and transmission uniformity, by faceting the exit face of the device at an optimum angle. A theoretical analysis is presented for this configuration and compared with data obtained for a wavelength of 1.52µm. A practical geometry would permit a deflection of ~140mrad for an applied voltage of 1kV. For switching there are many attractive properties, as TIR is a 100% efficient process this leads to the possibility of high contrast ratios; current data shows contrast ratios greater than 100:1 (20dB). Other properties include relatively simple fabrication procedure, low drive voltages and a wavelength dependence that is less than other electro-optic devices such as Pockels cells.

Electro-optically controlled beam deflection and switching via total internal reflection at a domain-engineered interface in LiNbO3

Ferroelectric materials such as lithium niobate (LN) or lithium tantalate (LT) are examples of an extremely versatile class of optical crystals. In bulk single crystal, single domain format, these crystalline hosts find numerous applications in nonlinear optics, optical storage, photorefraction, surface acoustic wave devices, optical waveguides, piezoelectric and pyroelectric devices and electro-optic modulation. Single domain crystals can be subsequently engineered via spatially selective poling to yield domain structures whose size can lie in the region of a few tens of µm to sub-µm, for applications and device fabrication that are impossible to implement in single domain geometry. This paper discusses our progress to date in micro- and nanostructuring of such materials, for applications in nonlinear optics, switching and deflection, and 3-dimensional sculpting for possible MEMS use, The techniques and benefits are discussed of using both light-assisted and direct optical poling for achieving controllable domains that can be irregular or periodic, bulk or surface, at sizes that approach the 100 nm scale. For surface inversion, domain features can be produced that lack the otherwise characteristic crystal symmetry imposed hexagonal shapes observed in conventional electric field poling.

Progess in Ferroelectric Domain Engineering at the Micro/Nanoscale

We review and discuss the recent advances in high-power fibre lasers with a particular focus on novel fibre technology, which includes conventional double-clad, large-core fibres for continuous-wave generation, double-clad passive-core fibres for Raman conversion, microstructured fibres for four-wave mixing, all-solid photonic bandgap fibres for waveguide filtering, etc.

Alexander J. Boyland

Papers

High control in high power fiber lasers and amplifiers

Sub-micron filamentary structures formed during light induced frustrated etching of fe-doped lithium niobate: results and modelling

Electro-optically controlled beam deflection and switching via total internal reflection at a domain-engineered interface in LiNbO3

Progess in Ferroelectric Domain Engineering at the Micro/Nanoscale

Novel fibre technology for high-power lasers