High-efficiency ytterbium-free erbium-doped all-glass double cladding silicate glass fiber for resonantly-pumped fiber lasers.

A highly efficient ytterbium-free erbium-doped silicate glass fiber has been developed for high-power fiber laser applications at an eye-safe wavelength near 1.55 µm. Our preliminary experiments show that high laser efficiency can be obtained from a relatively short length of the gain fiber when resonantly pumped at 1535 nm in both core- and cladding-pumping configurations. With a core-pumping configuration as high as 75%, optical-to-optical efficiency and 4 W output power were obtained at 1560 nm from a 1 m long gain fiber. When using a cladding-pumping configuration, approximately 13 W output power with 67.7% slope efficiency was demonstrated from a piece of 2 m long fiber. The lengths of silicate-based gain fiber are much shorter than their silica-based counterparts used in other experiments, which is significantly important for high-power narrow-band and/or pulsed laser applications.

Coherence-multiplexed, label-free biomolecular interaction analysis.

This Letter describes an interferometric technique based on the principle of coherence multiplexing for multichannel, label-free biosensing applications. Multiple biosensors can be interrogated simultaneously with a single spectral-domain, phase-sensitive interferometer by coding the individual sensograms in coherence-multiplexed channels. The experimental results demonstrate the multiplexed quantitative biomolecular interaction of antibodies binding to antigen-coated functionalized biosensor chip surfaces. The described technique also applies to a variety of other distributed and multiplexed sensing applications besides biosensing.

Polarization-independent Fabry-Perot interferometer in a hole-type silicon photonic crystal.

We propose and numerically demonstrate a polarization-independent Fabry-Perot interferometer (PI-FPI) based on the self-collimation effect in a hole-type silicon photonic crystal (PhC). By use of the polarization peak matching method, a resonance frequency of the transverse-electric modes can equal that of the transverse-magnetic modes in the PI-FPI, although the transmission spectra are quite polarization dependent due to birefringence of the PhC. For the operating wavelength of 1550 nm, the PI free spectral range of the PI-FPI is up to 32.3 nm, which nearly covers the whole optical communication C-band window. With its small dimensions, simple structure, and silicon-based material, this PI-FPI may play an important role in photonic integrated circuits.

Photonic crystal ring resonators: characteristics and applications.

We review the characteristics and applications of photonic crystal ring resonators (PCRRs), which can potentially provide a good alternative to the traditional micro ring resonators, as one of the key contributors to the emerging low-power nanophotonic technology. Applying numerical analysis together with the theory of mode superposition, the properties of PCRRs have been comprehensively investigated. We will report PCRR key characteristics, including diameter (D)-dependent loss, quality factor (Q), and free spectral range (FSR). No size-dependent loss was found in PCRRs, unlike the approximately 1/D dependent loss in micro-strip resonators, making PCRRs a promising candidate for ultra-compact ring resonators.

Polarization-independent drop filters based on photonic crystal self-collimation ring resonators.

We report here a polarization-independent drop filter (PIDF) based on a photonic crystal self-collimation ring resonator (SCRR). Despite of the large birefringence associated with the polarization-dependent dispersion properties, we demonstrate a PIDF based on multiple-beam interference theory and polarization peak matching (PPM) technique. The PIDF performance was also investigated based on finite-difference time-domain (FDTD) technique, with excellent agreement between the theory and the simulation. For the designed drop wavelength of 1550 nm, the polarization-independent free spectral range is about 36.1 nm, which covers the whole optical communication C-band window. The proposed PIDFs are highly desirable for applications in photonic integrated circuits (PICs).

Photonic NOT and NOR gates based on a single compact photonic crystal ring resonator.

New all-optical NOT and NOR logic gates based on a single ultracompact photonic crystal ring resonator (PCRR) have been proposed. The PCRR was formed by removing the line defect along the GammaM direction instead of the conventional GammaX direction in a square-pattern cylindrical silicon-rod photonic crystal structure. The behavior of the proposed logic gates is qualitatively analyzed with the theory of beam interference and then numerically investigated by use of the two-dimensional finite-difference time-domain method. No nonlinear material is required with less than a 2.2 microm effective ring radius. The wavelengths of the input signal and the probe signal are the same. This new device can potentially be used in on-chip photonic logic-integrated circuits.

Polarization and angular dependent transmissions on transferred nanomembrane Fano filters.

We report angular and polarization dependent transmission properties of Fano resonance optical filters with transferred silicon nanomembrane on glass substrate. The transmission spectra of the filters can have either weak or strong polarization and angular dependence, depending on properties of individual Fano resonance modal dispersion. Measurement results agree very well with simulations based on a rigorous coupled-wave analysis for the transmission spectra, on planewave expansion wave-vector technique for the dispersion property analysis, and on a three-dimensional finite-difference time-domain technique for the propagating modal study. These results will provide importance guidance for the design of a new class of ultra-compact surface-normal frequency selective components with preferred polarization and angular properties. These components are highly desirable for silicon photonic integration.

Optical add-drop filters based on photonic crystal ring resonators.

We present here an optical add-drop filter (ADF) design based on ultra-compact photonic crystal ring resonators (PCRRs). The normalized transmission spectra for single-ring and dual-ring configurations have been investigated by using the two-dimensional finite-difference time-domain (FDTD) technique in a square lattice dielectric-rod photonic-crystal structure. With the introduction of four scatterers at the corners of quasisquare- ring PCRR, high wavelength selectivity and close to 100% drop efficiency can be obtained. Both backward- and forward-dropping were achieved by controlling the coupling efficiency between two PCRR rings for resonant modes with different symmetry. The resonant-mode quality factor Q and the wavelength tunability were also analyzed, opening opportunities for PCRRs as ultra-compact filters, optical add-drop multiplexers, electrooptical N x N switches and electrooptical modulators.

Far infrared photonic crystals operating in the Reststrahl region.

We report here far infrared photonic crystals comprised of a lattice-matched pair of semiconductor materials: GaP and Si, or GaAs and Ge, or AlAs and GaAs. The crystals operate in a wavelength range where the real refractive index of one material undergoes a major dispersion associated with the LO and TO phonon absorption peaks. Using electromagnetic theory, we investigated the photonic-bandgap response for both TE and TM polarizations. Propagation losses for two types of crystals are estimated in this paper. These structures offer promise for the integration of III-V materials (GaP, GaAs) on group IV (Si, or Ge) for practical, active, far infrared photonic devices, such as light sources, amplifiers, modulators, reconfigurable waveguides and switches.

A novel 3-stage structure for a low-noise, high-gain and gain-flattened L-band erbium doped fiber amplifier.

The configuration of the novel three-stage L-band erbium-doped fiber amplifier with very large and flat gain and very low noise figure presented in this paper uses the forward ASE (amplified spontaneous emission) from the first section of the EDF (erbium-doped fiber) and the backward ASE from the third section of the EDF (both serve as the secondary pump sources of energy) to pump the second EDF. To improve the pump efficiency, the power of the pump is split into two parts (with a ratio of e.g. 2:7). The characteristics of this L-band EDFA are studied on the basis of the Giles Model with ASE.