Analytical approximation for photonic array modes in two-dimensional photonic crystal lattices.

We presented here a comprehensive analytical approximation, describing array modes (both the modal fields and their associated propagation constants) in 2D photonic lattices (i.e., arrays of identical coupled waveguides/lasers). Our approximation is a vectorial approach, accounting for the TE and TM polarizations. It is applicable to both the low-contrast and high-contrast photonic devices. The model of standing waves of a membrane was used for analytical evaluation of envelopes of the array modes and the total modal fields. Combination of this model with the coupled-mode formalism for 2D infinite photonic lattices allowed for evaluation of propagation constants of the array modes. Both the computations required only a few seconds. Still, the results, acquired with the analytical approximation, are in close agreement with those acquired with well-established approaches. Moreover, for the first time, analytical expressions for the modal fields and propagation constants become available.

Analytical approximation for photonic array modes in 1D photonic crystal superlattices.

We present a comprehensive analytical approximation for array modes (both the modal fields and their associated propagation constants) for 1D photonic crystal superlattices (i.e., large periodic arrays of repeated sequences of different coupled waveguides/lasers). In this class, a regular periodicity of a photonic lattice is supplemented with the additional periodicity of a larger scale. Our approximation is a vectorial approach, accounting for the TE and TM polarizations. It can be applied to both the low- and high-contrast photonic devices. We used the model of standing waves for analytical evaluation of envelopes of array modes in a photonic superlattice. Combination of the model of standing waves with the coupled-mode formalism for infinite photonic superlattices allows evaluation of propagation constants of the array modes. Both the evaluations require only a fraction of a second for computation. Still, the results, acquired with the analytical approximation, are very close to those of well-established approaches. Furthermore, for the first time, analytical expressions for the modal fields and propagation constants become available.

Analytical approximation for photonic array modes in one-dimensional photonic crystal devices.

A new analytical approximation for photonic array modes is presented. We consider the specific class of one-dimensional (1D) photonic crystals (encompassing large arrays of coupled identical planar waveguides, large arrays of identical phase-locked lasers, etc.), in which light propagates along the optical axis of the device. Approximate analytical expressions for the array modes (both spatial distribution and propagation constants) become available. This approach allows a fast, simple, and accurate analytical evaluation of the electromagnetic field in 1D photonic crystal devices.

In vitro large diameter bowel anastomosis using a temperature controlled laser tissue soldering system and albumin stent.

BACKGROUND AND OBJECTIVE: In today's age of advancing surgical technology, there is a need for better and simpler methods of tissue bonding. The use of lasers for tissue welding or soldering is one of these sutureless methods. In 30 years of laser tissue bonding (LTB) research, published reports of cylindrical organ anastomosis were limited to small diameters. The tension resisted by the anastomosis, which is caused by the intraluminal pressure, is also proportional to the organ diameter. Therefore the anastomosis of large diameter organs requires significantly stronger mechanical strength. The aim of this study is to demonstrate such an anastomosis. MATERIALS AND METHODS: In vitro anastomosis of porcine small bowel was performed by either LTB or sutures. Anastomosis in the laser group (number of samples, n = 15) included two main stages of soldering. The bowel edges were approximated over a solid albumin stent and heated with a temperature controlled GaAs laser system to 75 degrees C. This was followed by spreading liquid albumin on the anastomotic line and heating by the same system again to 75 degrees C. The control group (n = 5) was sutured anastomosis. All anastomoses were assessed by burst pressure measurement. RESULTS: The burst pressure of the laser group attained 170+/-40 mmHg which was significantly higher than that of the sutured group 83+/-37 mmHg (P < 0.001). CONCLUSION: This report describes the in vitro LTB anastomosis of a large diameter cylindrical organ. The immediate bond strength, as estimated by burst pressure measurements, was double compared to sutured anastomosis.

Omnidirectional reflection in several frequency ranges of one-dimensional photonic crystals.

We investigate omnidirectional reflection from higher-order gaps in one-dimensional photonic crystals. Moreover, we present a designing criterion for omnidirectional reflection from several distinct gaps simultaneously, using only a single photonic crystal with a constant period. We show that for practical values of photonic crystals parameters, several relatively large omnidirectional gaps may be obtained. As an example, we demonstrate an omnidirectional reflector that exhibits two distinct wide omnidirectional ranges at near-infrared wavelengths. This omnidirectional reflector that operates in several ranges of wavelengths may have various potential applications.

Analysis of nonlinear gain-induced effects on short-pulse amplification in doped fibers by use of an extended power equation.

Optical pulse amplification in doped fibers is studied using an extended power transport equation for the coupled pulse spectral components. This equation includes the effects of gain saturation, gain dispersion, fiber dispersion, fiber nonlinearity, and amplified spontaneous emission. The new model is employed to study nonlinear gain-induced effects on the spectrotemporal characteristics of amplified subpicosecond pulses, in both the anomalous and the normal dispersion regimes.

Three-dimensional analysis of mode discrimination in vertical-cavity surface-emitting lasers.

Optical mode discrimination in vertical-cavity surface-emitting lasers that contain distributed Bragg reflectors (DBRs) and a spatially limited gain medium is analyzed numerically. It is assumed that the output field is linearly polarized owing to gain selectivity. The analysis employs a three-dimensional model and an angular spectrum of plane-wave decomposition with the proper polarizations. Two types of round aperture are considered, namely, a Gaussian aperture and a ring-peak aperture that represents gain saturation. Coupled with the DBRs, the former aperture yields nearly Laguerre-Gaussian modes, whereas the latter aperture significantly distorts the mode shapes. In both cases, narrowband DBRs provide the best mode discrimination.

Tight packaging of erbium-doped waveguide amplifiers.

A numerical model for erbium-doped waveguide amplifiers (EDWAs) containing bent waveguides was developed. The model uses rate-propagation equations and takes into account bend-induced losses in the waveguide with a varying radius of curvature. It is applied to the design of tightly packed erbium-doped waveguide amplifiers under two constraints: minimization of the area required to obtain a predetermined gain and maximization of the gain available from a given area. Numerical calculations based on realistic waveguide parameters demonstrate the possibility of fabricating high-gain, small-size EDWAs. Simple design rules, based on geometric formulas and consideration of bend losses, are given and compared with the results of numerical calculations.