Optical filtering enabled by cascaded parametric amplification.

A cascaded parametric amplifier consists of a first parametric amplifier, which amplifies an input signal and generates an idler, which is a copy of the signal, a signal processor, which controls the phases of the signal and idler, and a second parametric amplifier, which combines the signal and idler in a phase-sensitive manner. In this paper, cascaded parametric amplification is modeled and the conditions required to maximize the constructive-destructive extinction ratio are determined. The results show that a cascaded parametric amplifier can be operated as a filter: A desired signal-idler pair is amplified, whereas undesired signal-idler pairs are deamplified. For the desired signal and idler, the noise figures of the filtering process (input signal-to-noise ratio divided by the output ratios) are only slightly higher than those of the copying process: Signal-processing functionality can be achieved with only a minor degradation in signal quality.

Signal replication by multiple sum- or difference-frequency generation.

In this paper, the coupled-mode equations for sum-frequency generation (SFG) and difference-frequency generation (DFG) driven by multiple pumps are solved, and the noise figures of idler generation are determined. For SFG, the (common) noise figure is n, the number of pumps (and idlers), whereas for DFG, the (common) noise figure is 2, independent of n. Thus, DFG driven by multiple pumps enables the generation of multiple low-noise idlers.

Continuously active interferometer stabilization and control for time-bin entanglement distribution.

We describe a new method enabling continuous stabilization and fine-level phase control of time-bin entanglement interferometers. Using this technique we demonstrate entangled photon transmission through 50 km of standard single-mode fiber. This technique reuses the entangled-pair generation pump which is co-propagated with the transmitted entangled photons. The co-propagating pump adds minimal noise to the entangled photons which are characterized by measuring a two-photon interference fringe.

Phase discrimination and simultaneous frequency conversion of the orthogonal components of an optical signal by four-wave mixing in an SOA.

Simultaneous conversion of the two orthogonal phase components of an optical input to different output frequencies has been demonstrated by simulation and experiment. A single stage of four-wave mixing between the input signal and four pumps derived from a frequency comb was employed. The nonlinear device was a semiconductor optical amplifier, which provided overall signal gain and sufficient contrast for phase sensitive signal processing. The decomposition of a quadrature phase-shift keyed signal into a pair of binary phase-shift keyed outputs at different frequencies was also demonstrated by simulation.

Generation of 21.3 Gbaud 8PSK signal using an SOA-based all-optical phase modulator.

We describe a novel SOA-based all-optical pure-phase modulator, and show how deleterious cross-gain modulation from the SOAs can be suppressed by utilizing an integrated interferometer structure. We experimentally demonstrate the use of the optical gate as a π/4 phase modulator producing 21.3 Gbaud 8PSK from 21.3 Gbit/s OOK and 21.3 Gbaud QPSK inputs. The modulator produces 3 dB of gain and coherent detection-based bit error rate measurements indicate a 2.4 dB excess penalty.

All-optical technique for modulation format conversion from on-off-keying to alternate-mark-inversion.

We propose and numerically investigate for the first time a novel all-optical on-off-keying to alternate-mark-inversion modulation format converter operating at 40 Gbps employing a semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI). We demonstrate that this SOA-MZI operates as a pulse subtractor, and in the absence of patterning will produce perfectly phase inverted pulses regardless of the individual SOA phase excursions. We use a comprehensive computer model to illustrate the impact of patterning on the output phase modulation, which is quantified through the definition of the phase compression factor.

Pattern compensation in SOA-based gates.

We propose a novel scheme employing complementary data inputs to overcome the patterning normally associated with semiconductor optical amplifier based gates and demonstrate the scheme experimentally at 42.6Gb/s. The scheme not only avoids introducing patterning during switching, but also compensates for much of the patterning present on the input data. A novel gate was developed for the experiment to provide the complementary signals required for the scheme.

Differential diagnosis and treatment of heel pain.

Heel pain caused by heel spur syndrome is a common finding in the podiatric community. It can be baffling and frustrating to the podiatric physician when its rectification becomes conservatively prolonged. This article helps the podiatric physician realize that heel pain may be present whether there is a spur or not and helps give a basic understanding of the systemic disorders that can be involved with heel pain.

Preoperative examination and criteria for office-based surgery.

The most important part of any surgical procedure is the consideration of all the available criteria and findings in choosing the procedure that will yield the optimum result for that particular deformity. This article addresses the rationale of the preoperative examination and criteria for office-based surgical correction of a variety of deformities.

Preoperative work-up and criteria.

No matter what the underlying podiatric problem, if surgical correction is considered, a good preoperative work-up is essential. This article deals with the preoperative work-up and criteria for a variety of ambulatory surgical procedures.

The scaphoid compression staple: an effective form of fixation.

This paper involves an overview of bone healing with its relationship to tension and compression of osteotomy sites, followed by a presentation on the use of the Richards scaphoid compression staple as an effective form of fixation for closing abductory base wedge osteotomies.