73 nm wavelength tuning from a frequency-doubled quantum-dot laser in PPKTP waveguides

A compact all-room-temperature CW 73-nm tunable laser source in the visible spectral region (574nm-647nm) has been demonstrated by frequency-doubling of a broadly-tunable InAs/GaAs quantum dot external-cavity diode laser in periodically-poled potassium titanyl phosphate waveguides with a maximum output power in excess of 12mW and a maximum conversion efficiency exceeding 10%. Three waveguides with different cross-sectional areas (4×4μm2, 3×5μm2 and 2x6μm2) were investigated. Introduction - Development of compact broadly tunable laser sources in the visible spectral region is currently very attractive area of research with applications ranging from photomedicine and biophotonics to confocal fluorescence microscopy and laser projection displays. In this respect, semiconductor lasers with their small size, high efficiency, reliability and low cost are very promising for realization of such sources by frequency­doubling of the infrared light in nonlinear crystal waveguides. Furthermore, the wide tunability offered by quantum-dot (QD) external-cavity diode lasers (ECDL), due to the temperature insensibility and broad gain bandwidth [1,2], is very promising for the development of tunable visible laser sources [3,4]. In this work we show a compact green-to-red tunable all­room-temperature CW laser source using a frequency-doubled InAs/GaAs QD-ECDL in periodically-poled potassium titanyl phosphate (PPKTP) crystal waveguides. This laser source generates frequency-doubled light over the 574nm-647nm wavelength range utilizing the significant difference in the effective refractive indices of high-order and low-order modes in multimode waveguides [3]. Experimental results - Experimental setup used in this work was similar to that described in [3] and consisted of a QD gain chip in the quasi­Littrow configuration and a PPKTP waveguide. Coarse wavelength tuning of the QD-ECDL between 1140 nm and 1300 nm at 20°C was possible for pump current of 1.5 A. The laser output was coupled into the PPKTP waveguide using an AR-coated 40x aspheric lens (NA ~ 0.55). The PPKTP frequency-doubling crystal (not AR coated) used in our work was 18 mm in length and was periodically poled for SHG (with the poling period of ~ 11.574 11m). The crystal contained 3 different waveguides with cross-sectional areas of ~ 4x4 11m2, 3x5 11m2 and 2x6 11m2. Both the pump laser and the PPKTP crystal were operating at room temperature. The waveguides with cross-sectional areas of 4x411m2, 3x511m2 and 2x611m2 demonstrated the tunability in the wavelength ranges of 577nm - 647nm, 576nm -643nm and 574nm - 641nm, respectively, with a maximum output power of 12.04mW at 606 nm Conclusion - We demonstrated a compact all-room-temperature broadly­tunable laser source operating in the visible spectral region between 574nm and 647nm. This laser source is based on second harmonic generation in PPKTP waveguides with different cross-sectional areas using an InAs/GaAs QD-ECDL References [I] E.U. Rafailov, M.A. Cataluna, and W. Sibbett, Nat. Phot. 1,395 (2007). [2] K.A. Fedorova, M.A. Cataluna, I. Krestnikov, D. Livshits, and E.U. Rafailov, Opt. Express 18(18), 19438-19443 (2010). [3] K.A. Fedorova, G.S. Sokolovskii, P.R. Battle, D.A. Livshits, and E.U. Rafailov, Laser Phys. Lett. 9, 790-795 (2012). [4] K.A. Fedorova,G.S. Sokolovskii, D.T. Nikitichev, P.R. Battle, I.L. Krestnikov, D.A. Livshits, and E.U. Rafailov, Opt. Lett. 38(15), 2835-2837 (2013) © 2014 IEEE.

Control of the properties of micro-structured waveguides in lithium niobate crystal

We study numerically depressed-cladding, buried waveguides that can be formed in a lithium niobate crystal by femtosecond laser writing. We demonstrate that the guiding properties can be controlled by the waveguide structural characteristics.

Efficiency enhancement of components based on Talbot effect

Two ways to increase efficiency of components based on Talbot effect are considered: optimization of waveguide wall impedance and corrections of waveguide cross-section. It is shown that for many cases undesired scattering losses can be made several times less than that for usual cases of infinite of zero impedance and rectangular waveguide cross-section.

High sensitivity sensors utilising characteristics of dispersion-turning-point of long-period gratings in B/Ge co-doped fibre

Systematically investigated the waveguide dispersion characteristics of LPFGs. It has been revealed that the coupled cladding modes resonating in the dispersion-turning-point region are intrinsically sensitive to the external perturbation. Thus, LPFG-based application devices requiring good stability should avoid this region. On the other hand, this mode ultra-sensitive-zone can be explored to realise sensors and tuneable filters of high efficiency.

Transfer characteristics and propagation effects of a multi-resonance ring resonator-based optical device

We describe the linear and nonlinear optical transfer characteristics of a multi-resonance device consisting of two optical ring resonators coupled one to the other and to an optical waveguide. The propagation effects displayed by the device are compared with those of a sequence of fundamental ring resonators coupled to a waveguide.

Optimization of micro-structured waveguides in lithium niobate

We describe how the guiding properties of buried, micro-structured waveguides that can be formed in a lithium niobate crystal by direct femtosecond laser writing can be optimized for low-loss operation in the mid-infrared region beyond 3 μm.

A cloud-based farm management system:architecture and implementation

Recent technological advances have paved the way for developing and offering advanced services for the stakeholders in the agricultural sector. A paradigm shift is underway from proprietary and monolithic tools to Internet-based, cloud hosted, open systems that will enable more effective collaboration between stakeholders. This new paradigm includes the technological support of application developers to create specialized services that will seamlessly interoperate, thus creating a sophisticated and customisable working environment for the end users. We present the implementation of an open architecture that instantiates such an approach, based on a set of domain independent software tools called "generic enablers" that have been developed in the context of the FI-WARE project. The implementation is used to validate a number of innovative concepts for the agricultural sector such as the notion of a services' market place and the system's adaptation to network failures. During the design and implementation phase, the system has been evaluated by end users, offering us valuable feedback. The results of the evaluation process validate the acceptance of such a system and the need of farmers to have access to sophisticated services at affordable prices. A summary of this evaluation process is also presented in this paper. © 2013 Elsevier B.V.

574-647 nm wavelength tuning by second-harmonic generation from diode-pumped PPKTP waveguides

We present a compact, all-room-temperature continuous-wave laser source in the visible spectral region between 574 and 647 nm by frequency doubling of a broadly tunable InAs/GaAs quantum-dot external-cavity diode laser in a periodically poled potassium titanyl phosphate crystal containing three waveguides with different cross-sectional areas (4 × 4, 3 × 5, and 2 μm × 6 μm). The influence of a waveguide's design on tunability, output power, and mode distribution of second-harmonic generated light, as well as possibilities to increase the conversion efficiency via an optimization of a waveguide's cross-sectional area, was systematically investigated. A maximum output power of 12.04 mW with a conversion efficiency of 10.29% at 605.6 nm was demonstrated in the wider waveguide with the cross-sectional area of 4 μm × 4 μm.

On the use of the type I and II scheme for classifying ultrafast laser direct-write photonics

The use of the Type I and Type II scheme, first introduced and used by fiber Bragg grating researchers, has recently been adopted by the ultrafast laser direct-write photonics community to classify the physical geometry of waveguides written into glasses and crystals. This has created confusion between the fiber Bragg grating and direct-write photonics community. Here we propose a return to the original basis of the classification based on the characteristics of the material modification rather than the physical geometry of the waveguide.

Picosecond pulse amplification up to a peak power of 42 W by a quantum-dot tapered optical amplifier and a mode-locked laser emitting at 1.26 μm

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 μm without pulse compression, external cavity, gain-or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.

CROW bottles

A coupled resonator optical waveguide (CROW) bottle is a bottle-shaped nonuniform distribution of resonator and coupling parameters. This Letter solves the inverse problem for a CROW bottle, i.e., develops a simple analytical method that determines a CROW with the required group delay and dispersion characteristics. In particular, the parameters of CROWs exhibiting the group delay with zero dispersion (constant group delay) and constant dispersion (linear group delay) are found. © 2014 Optical Society of America.

Discrete solitons in coupled active lasing cavities

We examine the existence and stability of discrete spatial solitons in coupled nonlinear lasing cavities (waveguide resonators), addressing the case of active defocusing media, where the gain exceeds damping in the low-amplitude limit. A new family of stable localized structures is found: these are bright and gray cavity solitons representing the connections between homogeneous and inhomogeneous states. Solitons of this type can be controlled by discrete diffraction and are stable when the bistability of homogenous states is absent. © 2012 Optical Society of America.

Nonlinear semi-analytical model for simulation of few-mode fiber transmission

In this letter, a nonlinear semi-analytical model (NSAM) for simulation of few-mode fiber transmission is proposed. The NSAM considers the mode mixing arising from the Kerr effect and waveguide imperfections. An analytical explanation of the model is presented, as well as simulation results for the transmission over a two mode fiber (TMF) of 112 Gb/s using coherently detected polarization multiplexed quadrature phase-shift-keying modulation. The simulations show that by transmitting over only one of the two modes on TMFs, long-haul transmission can be realized without increase of receiver complexity. For a 6000-km transmission link, a small modal dispersion penalty is observed in the linear domain, while a significant increase of the nonlinear threshold is observed due to the large core of TMF. © 2006 IEEE.

Nonlinear propagation of an optical speckle field

We provide a theoretical explanation of the results on the intensity distributions and correlation functions obtained from a random-beam speckle field in nonlinear bulk waveguides reported in the recent publication by Bromberg et al. [Nat. Photonics 4, 721 (2010) ].. We study both the focusing and defocusing cases and in the limit of small speckle size (short-correlated disordered beam) provide analytical asymptotes for the intensity probability distributions at the output facet. Additionally we provide a simple relation between the speckle sizes at the input and output of a focusing nonlinear waveguide. The results are of practical significance for nonlinear Hanbury Brown and Twiss interferometry in both optical waveguides and Bose-Einstein condensates. © 2012 American Physical Society.

Micro-holographic methods for sub-micrometer grating fabrication in fused silica with UV femtosecond laser

The optical layouts incorporating binary phase diffractive grating and a standard micro-objective were used for femtosecond microfabrication of periodical structures in fused silica. Two beams, generated in Talbot type interferometer, interfered on a surface and in the bulk of the sample. The method suggested allows better control over the transverse size of the grating pitch, and thus control the reflection strength of the waveguide or fibre grating. We present the examples of direct inscription of the sub-micrometer periodical structures using a 267 nm femtosecond laser radiation.