The ultrafast laser inscription of photonic devices for integrated optical applications

A study of some key areas in which ultrafast laser inscription may usefully be employed is presented. The thesis includes waveguide inscription in a variety of substrates including passive glass, doped glass and a nonlinear crystal. The work contained can be split into three studies, with some overlap between them. Firstly fused silica glass is used, both in planar substrates and as flat fibre, for the inscription of two sensing elements. The planar substrate is used for a device similar in design to a side-polished fibre and the flat fibre is used for the fabrication of a Bragg grating waveguide array. In the second study, waveguides are inscribed in the nonlinear crystal monoclinic bismuth borate, and used for guided mode second harmonic generation. A novel waveguide design is employed to increase overlap between the pump and second harmonic waveguide modes. The remainder of the thesis investigates the applicability of ultrafast laser inscription to the fabrication of compact modelocked lasers. Lasing is demonstrated, both continuous wave and modelocked, using a laser inscribed erbium doped bismuthate glass waveguide as the gain element. A study is then undertaken into methods of integrating carbon nanotubes, used as saturable absorbers to modelock lasers, into laser inscribed waveguides

Direct ultrafast laser written C-band waveguide amplifier in Er-doped chalcogenide glass

This paper reports the fabrication and characterization of an ultrafast laser written Er-doped chalcogenide glass buried waveguide amplifier; Er-doped GeGaS glass has been synthesized by the vacuum sealed melt quenching technique. Waveguides have been fabricated inside the 4 mm long sample by direct ultrafast laser writing. The total passive fiber-to-fiber insertion loss is 2.58 +/- 0.02 dB at 1600 nm, including a propagation loss of 1.6 +/- 0.3 dB. Active characterization shows a relative gain of 2.524 +/- 0.002 dB/cm and 1.359 +/- 0.005 dB/cm at 1541 nm and 1550 nm respectively, for a pump power of 500 mW at a wavelength of 980 nm. (C) 2012 Optical Society of Americ

Evanescent-wave coupled right angled buried waveguide: Applications in carbon nanotube mode-locking

In this paper we present a simple but powerful subgraph sampling primitive that is applicable in a variety of computational models including dynamic graph streams (where the input graph is defined by a sequence of edge/hyperedge insertions and deletions) and distributed systems such as MapReduce. In the case of dynamic graph streams, we use this primitive to prove the following results: -- Matching: First, there exists an $\tilde{O}(k^2)$ space algorithm that returns an exact maximum matching on the assumption the cardinality is at most $k$. The best previous algorithm used $\tilde{O}(kn)$ space where $n$ is the number of vertices in the graph and we prove our result is optimal up to logarithmic factors. Our algorithm has $\tilde{O}(1)$ update time. Second, there exists an $\tilde{O}(n^2/\alpha^3)$ space algorithm that returns an $\alpha$-approximation for matchings of arbitrary size. (Assadi et al. (2015) showed that this was optimal and independently and concurrently established the same upper bound.) We generalize both results for weighted matching. Third, there exists an $\tilde{O}(n^{4/5})$ space algorithm that returns a constant approximation in graphs with bounded arboricity. -- Vertex Cover and Hitting Set: There exists an $\tilde{O}(k^d)$ space algorithm that solves the minimum hitting set problem where $d$ is the cardinality of the input sets and $k$ is an upper bound on the size of the minimum hitting set. We prove this is optimal up to logarithmic factors. Our algorithm has $\tilde{O}(1)$ update time. The case $d=2$ corresponds to minimum vertex cover. Finally, we consider a larger family of parameterized problems (including $b$-matching, disjoint paths, vertex coloring among others) for which our subgraph sampling primitive yields fast, small-space dynamic graph stream algorithms. We then show lower bounds for natural problems outside this family

An 11.5 W Yb:YAG planar waveguide laser fabricated via pulsed laser deposition

We present details of the homo-epitaxial growth of Yb:YAG onto a <100> oriented YAG substrate by pulsed laser deposition. Material characterization and initial laser experiments are also reported, including the demonstration of laser action from the 15 µm-thick planar waveguide generating 11.5 W of output power with a slope efficiency of 48%. This work indicates that under appropriate conditions, high-quality single-crystal Yb:YAG growth via pulsed laser deposition is achievable with characteristics comparable to those obtained via conventional crystal growth techniques

Registration of ‘Hallam’ Wheat

‘Hallam’ (Reg. no. CV-983, PI 638790) is a hard red winter wheat (Triticum aestivum L.) cultivar developed cooperatively by the Nebraska Agricultural Experiment Station and the USDA-ARS and released in 2005 by the developing institutions. Hallam was released primarily for its superior adaptation to rainfed wheat production systems in eastern Nebraska. The name Hallam was chosen to honor Hallam, NE, a town and its people rebuilding after a tornado. Hallam was selected from the cross ‘Brule’ (Schmidt et al., 1983)/‘Bennett’ (Schmidt et al., 1981)//‘Niobrara’ (Baenziger et al., 1996) that was made in 1992. The F1 generation was grown in the greenhouse and the F2 to F3 generations were advanced using the bulk breeding method in the field at Mead, NE. In 1995, single F3:4 rows were planted for selection. Hallam was selected in the F4 and there was no further selection thereafter. Hallam was evaluated as NE98471 in Nebraska yield nurseries starting in 1999, in the Northern Regional Performance Nursery in 2001 and 2002, and in Nebraska cultivar performance trials from 2002 to 2004. In the Nebraska cultivar performance trials, it was narrowly adapted and performs best in eastern Nebraska. The average Nebraska rainfed yield of Hallam of 4110 kg ha-1 (41 environments from 2002 to 2004) was greater than the yields of ‘Wahoo’ (4030 kg ha-1; Baenziger et al., 2002), ‘Alliance’ (3880 kg ha-1; Baenziger et al., 1995), and ‘Harry’ (4000 kg ha-1; Baenziger et al., 2004b), but was lower than ‘Millennium’ (4180 kg ha-1; Baenziger et al., 2001) and ‘Wesley’ (4210 kg ha-1; Peterson et al., 2001). In its primary area of adaptation (eastern Nebraska), Hallam has yielded 4540 kg ha-1 (five environments), which was greater than Wesley (4150 kg ha-1), Millennium (4250 kg ha-1), Wahoo (3940 kg ha-1), and Alliance (3900 kg ha21). In the Northern Regional Performance Nursery, Hallam ranked 14th of 30 in 2001 (12 environments) and fourth of 25 entries in 2002 (13 environments) and averaged 100 kg ha-1 more grain yield than ‘Nekota’ (Haley et al., 1996). Hallam is not recommended for use in irrigated production systems where other wheat cultivars with superior performance, especially with better straw strength (described below), would be recommended. Other measurements of performance from comparison trials show that Hallam is moderately early in maturity (142 d after January 1, five environments), about 2.5 d and 1.2 d earlier flowering than Millennium and Wesley, respectively. Hallam is a semidwarf wheat cultivar. Hallam has a medium short coleoptile (46 mm), as expected for a semidwarf wheat cultivar, and is shorter than ‘Goodstreak’ (61 mm; Baenziger et al., 2004a) and slightly longer than semidwarf wheat cultivars such as Harry (36 mm). The mature plant height of Hallam (86 cm) is 3 cm shorter than Millennium and 6 cm taller than Wesley (41 environments). Hallam has moderate straw strength (45% lodged), similar to Wahoo (46% lodged), but worse than Wesley (34% lodged) in those environments (3) where severe lodging was found. The winter hardiness of Hallamis good to very good, similar to ‘Abilene’ (PI 511307) and comparable to other winter wheat cultivars adapted and commonly grown in Nebraska

Registration of ‘Hallam’ Wheat

‘Hallam’ (Reg. no. CV-983, PI 638790) is a hard red winter wheat (Triticum aestivum L.) cultivar developed cooperatively by the Nebraska Agricultural Experiment Station and the USDA-ARS and released in 2005 by the developing institutions. Hallam was released primarily for its superior adaptation to rainfed wheat production systems in eastern Nebraska. The name Hallam was chosen to honor Hallam, NE, a town and its people rebuilding after a tornado. Hallam was selected from the cross ‘Brule’ (Schmidt et al., 1983)/‘Bennett’ (Schmidt et al., 1981)//‘Niobrara’ (Baenziger et al., 1996) that was made in 1992. The F1 generation was grown in the greenhouse and the F2 to F3 generations were advanced using the bulk breeding method in the field at Mead, NE. In 1995, single F3:4 rows were planted for selection. Hallam was selected in the F4 and there was no further selection thereafter. Hallam was evaluated as NE98471 in Nebraska yield nurseries starting in 1999, in the Northern Regional Performance Nursery in 2001 and 2002, and in Nebraska cultivar performance trials from 2002 to 2004. In the Nebraska cultivar performance trials, it was narrowly adapted and performs best in eastern Nebraska. The average Nebraska rainfed yield of Hallam of 4110 kg ha-1 (41 environments from 2002 to 2004) was greater than the yields of ‘Wahoo’ (4030 kg ha-1; Baenziger et al., 2002), ‘Alliance’ (3880 kg ha-1; Baenziger et al., 1995), and ‘Harry’ (4000 kg ha-1; Baenziger et al., 2004b), but was lower than ‘Millennium’ (4180 kg ha-1; Baenziger et al., 2001) and ‘Wesley’ (4210 kg ha-1; Peterson et al., 2001). In its primary area of adaptation (eastern Nebraska), Hallam has yielded 4540 kg ha-1 (five environments), which was greater than Wesley (4150 kg ha-1), Millennium (4250 kg ha-1), Wahoo (3940 kg ha-1), and Alliance (3900 kg ha21). In the Northern Regional Performance Nursery, Hallam ranked 14th of 30 in 2001 (12 environments) and fourth of 25 entries in 2002 (13 environments) and averaged 100 kg ha-1 more grain yield than ‘Nekota’ (Haley et al., 1996). Hallam is not recommended for use in irrigated production systems where other wheat cultivars with superior performance, especially with better straw strength (described below), would be recommended. Other measurements of performance from comparison trials show that Hallam is moderately early in maturity (142 d after January 1, five environments), about 2.5 d and 1.2 d earlier flowering than Millennium and Wesley, respectively. Hallam is a semidwarf wheat cultivar. Hallam has a medium short coleoptile (46 mm), as expected for a semidwarf wheat cultivar, and is shorter than ‘Goodstreak’ (61 mm; Baenziger et al., 2004a) and slightly longer than semidwarf wheat cultivars such as Harry (36 mm). The mature plant height of Hallam (86 cm) is 3 cm shorter than Millennium and 6 cm taller than Wesley (41 environments). Hallam has moderate straw strength (45% lodged), similar to Wahoo (46% lodged), but worse than Wesley (34% lodged) in those environments (3) where severe lodging was found. The winter hardiness of Hallamis good to very good, similar to ‘Abilene’ (PI 511307) and comparable to other winter wheat cultivars adapted and commonly grown in Nebraska