The Analysis of Time Series: An Introduction, 4th edn. By C. Chatfield. ISBN 0 412 31820 2. Chapman and Hall, London, 1989. 242 pp. £13.50.

The Analysis of Time Series: An Introduction

In this paper, a review of fiber laser technology as relevant for applications in ultrafast optics is given. We discuss core enabling fiber technologies, such as fiber amplifiers, all-fiber dispersion control, and highly nonlinear and large-core fibers. We concentrate on systems built around passively mode-locked fiber lasers and fiber frequency combs, which are further amplified in large-core fiber amplifiers. Our review further encompasses coherent supercontinuum generation and techniques for absolute phase control of fiber lasers and amplifiers. Applications concerned with spectral generation in the range from the vacuum UV to the terahertz range are also described.

Ultrafast Fiber Laser Technology

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

This review focuses on the optical properties and device applications of deterministic aperiodic media generated by mathematical rules with spectral features that interpolate in a tunable fashion between periodic crystals and disordered random media. These structures are called Deterministic Aperiodic Nano Structures (DANS) and can be implemented in different materials (linear and nonlinear) and physical systems as diverse as dielectric multilayers, optical gratings, photonic waveguides and nanoparticle arrays. Among their distinctive optical properties are the formation of multi-fractal bandgaps and characteristic optical resonances, called critical modes, with unusual localization, scaling and transport properties. The goal of the paper is to provide a detailed review of the conceptual foundation and the physical mechanisms governing the complex optical response of DANS in relation to the engineering of novel devices and functionalities. The discussion will mostly focus on passive and active planar structures with enhanced light-matter coupling for photonics and plasmonics technologies.

Deterministic aperiodic nanostructures for photonics and plasmonics applications

A compact, low-noise, single-frequency fiber laser by using a newly developed Yb³⁺ heavily doped single-mode phosphate glass fiber has been demonstrated Over 400 mW stable continuous wave single transverse and longitudinal mode laser at 106 μm was achieved from a 08 cm long active fiber The measured slope efficiency and estimated quantum efficiency of laser emission are 727% and 93%, respectively The signal-to-noise ratio is higher than 72 dB, and the linewidth of the fiber laser is less than 7 kHz, while the measured relative intensity noise is less than -130 dB/Hz at frequencies of over 15 MHz

400 mW ultrashort cavity low-noise single-frequency Yb^3+-doped phosphate fiber laser

We report on the development of novel high-power light sources utilizing a Yb3+-doped phosphate fiber as the gain element This host presents several key benefits over silica, particularly much higher Yb2 O3 concentrations (up to 26 wt%), a 50% weaker stimulated Brillouin scattering (SBS) gain cross section, and the absence of observable photodarkening even at high population inversion These properties result in a greatly increased SBS threshold compared to silica fibers, and therefore, potentially much higher output powers out of either a multimode large mode area or a single-mode fiber, which means in the latter case a higher beam quality To quantify these predictions, we show through numerical simulations that double-clad phosphate fibers should produce as much as ~ 700 W of single-frequency output power in a step index, single-mode core As a step in this direction, we report a short phosphate fiber amplifier doped with 12 wt% Yb2 O3 that emits 16 W of single-frequency single-mode output We also describe a single-mode phosphate fiber laser with a maximum output power of 57 W The laser slope efficiency is currently limited by the fairly high fiber loss ( ~ 3 dB/m) Measurements indicate that 77% of this loss originates from impurity absorption, and the rest from scattering

High-Power $\hbox{Yb}^{{\bm 3}{\bm +}}$ -Doped Phosphate Fiber Amplifier

We have demonstrated what is to our knowledge the first successful achievement of multiwavelength conversion in an aperiodic optical superlattice (AOS) lithium niobate crystal with equalized gain. The two AOS devices in our experiment, numerically synthesized from 2857 crystal blocks with a unit block thickness of 3.5 µm, have fundamental wavelengths of 1540 and 1545 nm for double-wavelength second-harmonic generation (SHG) and of 1540, 1545, and 1553 nm for triple-wavelength SHG at 50 °C. Our experiment and simulation show that the output spectrum of an AOS wavelength converter is fairly insensitive to typical fabrication errors.

Nonlinear multiwavelength conversion based on an aperiodic optical superlattice in lithium niobate.

We report the demonstration of the first, to our knowledge, cladding-pumped continuous-wave Yb3+-doped phosphate-glass fiber laser. Phosphate hosts are of interest because they can be much more heavily doped than silica, and because of the possibility that they may have a higher photodarkening threshold. In an 84.6 cm double-clad fiber doped with 12 wt. % of Yb2O3 and laser-diode pumped at 940 nm, nearly 20 W of single-mode 1.07 μm output power was generated with 60.2 W of absorbed pump power. The measured dependence of the output power on pump power is in excellent agreement with simulations.

20 W single-mode Yb 3+ -doped phosphate fiber laser

The broadband parasitic amplification in a diode-seeded nanosecond ytterbium-doped fiber laser amplifier system is numerically and experimentally investigated. The amplification is originated from a weak and pulsed parasitic signal associated with the 1064-nm seed diode laser. Although the average power of the parasitic pulse is less than 5% of the total seed laser power, a significant transient spike is observed during the amplification. In agreement with the simulation, nonlinear effects caused by the transient spike limits the scaling of signal peak power in fiber preamplifiers. With the utilization of a narrow bandwidth filter to eliminate the parasitic pulse, the power and energy scalability of a multistage diode-seeded fiber amplifier laser system has been significantly improved. At 1064 nm, pulses with the peak power of 120 kW and energy of 1.2 mJ have been successfully generated in the multistage $\hbox{Yb}^{3+}$ -doped fiber amplifier with an energy gain of 63 dB and 56% conversion efficiency. In viewing of the parasitic pulse's 8.8-nm bandwidth, it has the potential to become a novel seed source for high-peak-power fiber amplifiers.

Parasitic Stimulated Amplification in High-Peak-Power and Diode-Seeded Nanosecond Fiber Amplifiers

The measurement of record-high photodarkening resistance in single- mode phosphate fibres doped with 12 and 6 wt.% Yb 2 O 3 is reported. After pumping for 10 000 min at a high population inversion (~47%), the fibre exhibited no photodarkening at 660 nm. Silica fibres pumped to the same inversion did show photodarkening, indicating that the phosphate fibre can be doped with at least six times as much Yb and still show no photodarkening.

Yin-Wen Lee

Papers

High-Power $\hbox{Yb}^{{\bm 3}{\bm +}}$ -Doped Phosphate Fiber Amplifier

Nonlinear multiwavelength conversion based on an aperiodic optical superlattice in lithium niobate.

20 W single-mode Yb 3+ -doped phosphate fiber laser

Parasitic Stimulated Amplification in High-Peak-Power and Diode-Seeded Nanosecond Fiber Amplifiers

Measurement of high photodarkening resistance in heavily Yb3+-doped phosphate fibres