Experimental investigation on submicron rib waveguide microring/racetrack resonators in silicon-on-insulator

in experiment, characteristics of silicon microring/racetrack resonators in submicron rib waveguides have been systematically investigated. It is demonstrated that only a transverse-electric mode is guided for a ratio of slab height to rib height h/H = 0.5. Thus, these microring/racetrack resonators can only function for quasi-transverse-electric mode, while they get rid of transverse-magnetic polarization. Electron beam lithography and inductively coupled plasma etching were employed and improved to reduce side-wall roughness for low propagation loss and high performance resonators. Then, the effects of waveguide dimensions, coupling region design, waveguide roughness, and oxide cladding for the resonators have been considered and analyzed. (C) 2008 Elsevier B.V. All rights reserved.

Compact four-channel reconfigurable optical add-drop multiplexer using silicon photonic wire

We designed and fabricated a four-channel reconfigurable optical add-drop multiplexer based on silicon photonic wire waveguide, which is controlled through the thermo-optic effect. The effective footprint of the device is about 1000 x 500 mu m(2). The minimum insertion loss including the transmission loss and coupling loss is about 10.7 dB. The tuning bandwidth is about 17 nm, the average tuning efficiency about 6.11 mW/nm and the tuning speed about 24.5 kHz. (c) 2009 Elsevier B.V. All rights reserved.

Injection locked Fabry-Perot laser diodes for WDM passive optical network spare function

In this paper, a protection scheme for transmitters in wavelength-division-multiplexing passive optical network (WDM-PON) has been proposed and demonstrated. If any downstream transmitter encounters problems at the central office (CO), the interrupted communication can be restored immediately by injecting a Fabry-Perot laser diode (FP-LD) with the upstream lightwave corresponding to the failure transmitter. Compared with the conventional methods, this proposed architecture provides a cost-effective and reliable protection scheme employing a common FP-LD. In the experiment, a 1 36 protection capability was implemented with a 2.5 Gbit/s downstream transmission capability. (C) 2009 Elsevier B.V. All rights reserved.

Elimination of environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating sensor array

We present a novel reference compensation method for eliminating environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating (FBG) sensors. By employing a shielded wavelength-division-multiplexed reference FBG in the system the environmental noise is mea, sured from the reference channel, and then subtracted from the demodulation result of each sensor channel. An approximate 40 dB reduction of the environmental noise has been experimentally achieved over a frequency range from 20 Hz to 2 kHz. This method is also suitable for the elimination of broadband environmental noise. The corresponding FBG sensor array system proposed in this paper has shown a wave-length resolution of 7 x 10(-4) pm/root Hz. (c) 2009 Elsevier B.V. All rights reserved.

Wavelength conversion based on degenerate-four-wave-mixing with continuous-wave pumping in silicon nanowire waveguide

We present a comprehensive numerical study on the all-optical wavelength conversion based on the degenerate four-wave-mixing with continuous-wave pumping in the silicon nanowire waveguide. It is well known that the conversion efficiency and the 3-dB bandwidth can be greatly affected by the phase-matching condition. Through proper design of the waveguide cross-section, its dispersion property can be adjusted to satisfy the phase-matching condition and therefore effective wavelength conversion can be achieved in a large wavelength range. Generally, the group velocity dispersion plays a dominant role in the wavelength conversion. However, the fourth-order dispersion takes an important effect on the wavelength conversion when the group velocity dispersion is near the zero-point. Furthermore, the conversion efficiency and the 3-dB bandwidth can also be affected by the interactive length and the initial pump power. Through the numerical simulation, the optimal values for the interactive length and the initial pump power, which are functions of the propagation loss, are obtained to realize the maximum conversion efficiency. (C) 2008 Elsevier B.V. All rights reserved.

Thermal effects investigation and cavity design in passively mode-locked Nd:YVO4 laser with a SESAM

A diode-pumped passively mode-locked Nd YVO4 laser with a five-mirror folded cavity is presented by using a semiconductor saturable absorber mirror (SESAM). The temperature distribution and thermal lensing in laser medium are numerically analyzed to design a special cavity which can keep the power density on SESAM under its damage threshold. Both the Q-switched and continuous-wave mode-locked operation are experimentally realized. The maximum average output power of 8.94 W with a 9.3 ps pulse width at a repetition rate of 111 MHz is obtained under a pump power of 24 W, correspondingly the optical slope efficiency is 39.2%. (C) 2008 Elsevier B.V. All rights reserved.

All-optical continuously tunable delay with a high linear-chirp-rate fiber Bragg grating based on four-wave mixing in a highly-nonlinear photonic crystal fiber

A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10(-9) BER for a 10 Gb/s 2(31)-1 pseudo random bit sequence (PRBS) data. (c) 2009 Elsevier B.V. All rights reserved.

Wide-band polarization-insensitive high-output-power semiconductor optical amplifier based on thin tensile-strained bulk InGaAs

A polarization-insensitive semiconductor optical amplifier (SOA) with a very thin active tensile-strained InGaAs bulk has been fabricated. The polarization sensitivity of the amplifier gain is less than 1 dB over both the entire range of driving current and the 3 dB optical bandwidth of more than 80 nm. For optical signals of 1550 nm wavelength, the SOA exhibits a high saturation output power +7.6 dBm together with a low noise figure of 7.5 dB, fibre-to-fibre gain of 11.5 dB, and low polarization sensitivity of 0.5 dB. Additionally, at the gain peak 1520 nm, the fibre-to-fibre gain is measured to be 14.1 dB.

Structural and optical properties of InAs/In0.52Al0.48As self-assembled quantum wires on InP(001)

Six-stacked InAs/In0.52Al0.48As self-assembled quantum wires (QWRs) on InP(001) by molecular-beam epitaxy (MBE) have been studied by high-resolution transmission electron microscopy (HRTEM) and polarized PL measurements. We obtained the chemical lattice fringe (CLF) image of InAs self-assembled QWRs embedded in the In0.52Al0.48As matrix by the interference between the (002)-diffracted beam and the transmitted beam in the image plane of the objective lens. The results show that the InAs QWRs were bounded by (113), (001) and (114) facets. Both the size and strain distribution in QWRs were determined. It was found that with the growth of successive periods, the height and height fluctuation of InAs QWRs decreased from the bottom period to the upper one. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs. (c) 2005 Elsevier B.V. All rights reserved.

Influence of exotic Mn on magnetic properties of YCo5.0-xMnxGa7.0 (0.05 <= x <= 3.0)

The YCo5.0-xMnxGa7.0 compounds crystallize with the ScFe6Ga6-type structure. The lattice of YCo5.0-xMnxGa7.0 expands with the increase of the Mn content for 0.05 <= x <= 2.5, but the lattice of YCo2.0Mn3.0Ga7.0 shrinks compared with YCo2.5Mn2.5Ga7.0. The shrinkage of the lattice is attributed to the magnetostriction of YCo2.0Mn3.0Ga7.0. The substitution of Mn for Co forms magnetic clusters in the antiferromagnetic matrix. The magnetic frustration results in the spin-glass-like behavior for 0.8 <= x <= 1.5 and the difference between zero-field-cooling (ZFC) and field-cooling (FC) magnetizations for x = 2.0, 2.5, and 3.0. A stable long-range magnetic ordering appears among the Mn-centered magnetic clusters with the ordering temperature 110 K for x = 2.0. The hump in the thermomagnetization of YCo3.0Mn2.0Ga7.0 can be attributed to the competitive effects between the thermal fluctuation and the enhanced magnetic interaction. Both the hump and the bifurcation between the ZFC and the FC magnetizations of YCo3.0Mn2.0Ga7.0 occur at lower temperatures as the applied field increases. On the two-step magnetization curve of YCo3.0Mn2.0Ga7.0, the inflection point at 4000 Oe is due to the coercive field, and the magnetic moments in the clusters are tilted to the applied field above 4000 Oe. The magnetic ordering temperature is further increased to 210 K for x = 2.5 and to 282 K for x = 3.0. The spontaneous magnetization of YCo2.0Mn3.0Ga7.0 is 0.575 mu B/f.u. at 5 K with a canted magnetic structure.

Comparative study of InAs quantum dots grown on different GaAs substrates by MOCVD

We present a comparative study of InAs quantum dots grown on Si-doped GaAs (10 0) substrates, Si-doped GaAs (10 0) vicinal substrates, and semi-insulating GaAs (10 0) substrates. The density and size distribution of quantum dots varied greatly with the different substrates used. While dots on exact substrates showed only one dominant size, a clear bimodal size distribution of the InAs quantum dots was observed on GaAs vicinal substrates, which is attributed to the reduced surface diffusion due to the presence of multiatomic steps. The emission wavelength is blueshifted during the growth of GaAs cap layer with a significant narrowing of FWHM. We found that the blueshift is smaller for QDs grown on GaAs (10 0) vicinal substrates than that for dots on exact GaAs (100) substrates. This is attributed to the energy barrier formed at the multiatomic step kinks which prohibits the migration of In adatoms during the early stage of cap layer growth. (c) 2005 Elsevier B.V. All rights reserved.

The effect of In content on high-density InxGa1-xAs quantum dots

We have successfully grown self-assembled InxGa1-xAs (x = 0.44, 0.47, 0.50) quantum dots (QDs) with high density (> 10(11)/cm(2)) by MBE. The effect of In content on the high-density QD is investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectra. It is found that sample with In-mole-fraction of 0.5 shows small size fluctuation and high PL intensity. The influence of growth temperature on high-density QD is also investigated in our experiment. (c) 2005 Elsevier B.V. All rights reserved.

Optical and magnetic properties of ZnS nanoparticles doped with Mn2+

ZnS:Mn nanoparticles of the cubic zinc blende structure with the average sizes of about 3 nm were synthesized using a coprecipitation method and their optical and magnetic properties were investigated. Two emission bands were observed in doped nanoparitcles and attributed to the defect-related emission of ZnS and the Mn2+ emission, respectively. With the increase of Mn2+ concentration, the luminescence intensities of these two emission bands increased and the ZnS emission band shifted to lower energy. Based on the luminescence excitation spectra of Mn2+, the 3d(5) level structure of Mn2+ in ZnS nanoparticles is similar to that in bulk ZnS:Mn, regardless of Mn2+ concentration. Magnetic measurements showed that all the samples exhibit paramagnetic behavior and no antiferromagnetic interaction between Mn2+ ions exists, which are in contrast to bulk ZnS:Mn. (c) 2005 Elsevier B.V. All rights reserved.

Oil-immersion or solid-immersion power enhancement of very-small-aperture lasers

An analysis of the enhancement of light transmission through a sub-wavelength aperture by oil- or solid-immersion is presented in this letter. An output power enhancement phenomenon related to the oil-immersion or solid-immersion mechanism is realized experimentally and reported for a very small aperture laser, which is an agreement with simulation analysis. This phenomenon could be useful for future optical data storage, microscopy and lithography.

Post-growth and in situ annealing on GaInNAs(Sb) and their application in 1.55 mu m lasers

Rapid thermal annealing (RTA) has been demonstrated as an important way to improve the crystal quality of GaInNAs(Sb)/GaAs quantum wells. However little investigation has been made into their application in laser growth, especially at a wavelength of 1.55 mu m. When a GaAs-based laser is grown, AlGaAs is usually used for cladding layers. The growth of the p-cladding layer usually takes 30-45 min at a growth temperature higher than that of the GaInNAs(Sb) active region, which affects the material quality. To investigate this effect, various post-growth annealing processes were performed to simulate this process. Great enhancement of the PL intensity was obtained by a two-step process which consisted of annealing first at 700 degrees C for 60 s and then at 600 degrees C for 45 min. We transferred this post-growth annealing to in situ annealing. Finally, a GaInNAsSb laser was grown with a 700 degrees C in situ annealing process. Continuous operation at room temperature of a GaAs-based dilute nitride laser with a wavelength beyond 1.55 mu m was realized for the first time.