Electronic structure and optical gain saturation of InAs1-xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143025]

Ultra-compact silicon-on-insulator optical filter based on sidewall Bragg grating

Micro-cavity structure composed of silicon wire with 240nm square cross section and two symmetrical sidewall waveguide Bragg gratings is fabricated and studied for the operation under telecommunication wavelengths. Optical filter of quasi-TE mode was realized based on this cavity. In such micro-cavity, optical quality factor (Q) was measured up to 380 with a 4.8nm free spectral range (FSR) and 12dB fringe contrast (FC). The measured group index of silicon waveguide with only 240nm square cross section was between 3.80 and 5.43. It is the first time group delay of silicon wire waveguide with such small core dimension is studied. Larger group delay can be expected after optimizing the design parameters and the fabrication process.

Widely Frequency-Tunable Optical Microwave Source Based on Amplified Feedback Laser

A monolithic integrated amplified feedback semiconductor laser is demonstrated as an optical microwave source. The optical microwave frequency is continuously tunable in the range of 19.87-26.3 GHz with extinction ratio above 6 dB, 3-dB linewidth about 3MHz.

Experimental Demonstration on Structure-Parameter Dependence of Photonic Crystal Optical Spectrum

We present fabrication and experimental measurement of a series of photonic crystal waveguides and coupled structure of PC waveguide and PC micro-cavity. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-holes single-line-defect waveguide. We fabricated these devices on a silicon-on-insulator substrate and characterized them using tunable laser source. We've obtained high-efficiency light propagation and broad flat spectrum response of photonic-crystal waveguides. A sharp attenuation at photonic crystal waveguide mode edge was observed for most structures. The edge of guided band is shifted about 31 nm with the 10 nm increase of lattice constant. Mode resonance was observed in coupled structure. Our experimental results indicate that the optical spectra of photonic crystal are very sensitive to structure parameters.

Tandem electroabsorption modulators integrated with DFB laser by ultra-low-pressure selective-area-growth MOCVD for 10 GHz optical short pulse generation - art. no. 60200O

A novel device of tandem multiple quantum wells (MQWs) electroabsorption modulators (EAMs) monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 mbar) selective area guowth (SAG) MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mX output light power of 4.5 mW and over 20 dB extinction ratio when coupled into a single mode Fiber. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using I this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with a width of 13.7 ps without any compression elements is obtained.

Novel compact SOI-based reconfigurable optical add/drop multiplexer using microring resonators - art. no. 60190L

Novel compact design for 4-channel SOI-based reconfigurable optical add/drop multiplexer using microring resonators is presented and analyzed. Microring resonators have two important attributes as a key new technology for future optical communications, namely functionality and compactness. Functionality refers to the fact that a wide range of desirable filter characteristics can be synthesized by coupling multiple rings. Compactness refers the fact that ring resonators with radii about 30 mu m can lead to large scale integration of devices with densities on the order of 10(4) similar to 10(5) devices per square centimeter. A 4-channel reconfigurable optical add/drop multiplexer comprises a grid-like array of ridge waveguides which perpendicularly cross through each other. SOI-based resonators consisted of multiple rings at each of the cross-grid nodes serve as the wavelength selective switch, and they can switch an optical signal between two ports by means of tuning refractive index of one of the rings. The thermo-optic coefficient of silicon is 1.86x 10(-4) /K. Thus a temperature rise of 27K will increase the refractive index by 5 x 10(-3), which is enough to cause the switching of our designed microring resonators. The thermo-optic effect is used to suppress the resonator power transfer, rather than to promote loss. Thus, the input signal only suffers small attenuation and simultaneously low crosstalk can be achieved by using multiple rings.

A low power consumption thermo-optic variable optical attenuator based on SOI material

A SOI thenno-optic variable optical attenuator with U-grooves based on a multimode interference coupler principle is fabricated. The dynamic attenuation range is 0 to 29 dB; at the wavelength range between 1510 nm and 1610nm, and the maximum power consumption is only l30mW. Compared to the variable optical attenuator without U-groove, the maximum power consumption decreases more than 230mW

Electrical and Optical Phase Transition Properties of Nano Vanadium Dioxide Thin Films

Nano-vanadium dioxide thin films were prepared through thermal annealing vanadium oxide thin films deposited by dual ion beam sputtering. The nano-vanadium dioxide thin films changed its state from semiconductor phase to metal phase through heating by homemade system. Four point probe method and Fourier transform infrared spectrum technology were employed to measure and anaylze the electrical and optical semiconductor-to-metal phase transition properties of nano-vanadium dioxide thin films, respectively. The results show that there is an obvious discrepancy between the semiconductor-to-metal phase transition properties of electrical and optical phase transition. The nano-vanadium dioxide thin films' phase transiton temperature defined by electrical phase transiton property is 63 degrees C, higher than that defined by optical phase transiton property at 5 mu m, 60 degrees C; and the temperature width of electrical phase transition duration is also wider than that of optical phase transiton duration. The semiconductor-to-metal phase transiton temperature defined by optical properties increases with increasing wavelength in the region of infrared wave band, and the occuring temperature of phase transiton from semiconductor to metal also increases with wavelength increasing, but the duration temperature width of transition decreases with wavelength increasing. The phase transition properties of nano-vanadium dioxide thin film has obvious relationship with wavelength in infrared wave band. The phase transition properties can be tuned through wavelength in infrared wave band, and the semiconductor-to-metal phase transition properties of nano vanadiium dioxide thin films can be better characterized by electrical property.

Effects of Hydrogen Plasma Treatment on the Electrical and Optical Properties of ZnO Films: Identification of Hydrogen Donors in ZnO

Wurtzite ZnO has many potential applications in optoelectronic devices, and the hydrogenated ZnO exhibits excellent photoelectronic properties compared to undoped ZnO; however, the structure of H-related defects is still unclear. In this article, the effects of hydrogen-plasma treatment and subsequent annealing on the electrical and optical properties of ZnO films were investigated by a combination of Hall measurement, Raman scattering, and photoluminescence. It is found that two types of hydrogen-related defects, namely, the interstitial hydrogen located at the bond-centered (H-BC) and the hydrogen trapped at a O vacancy (H-O), are responsible for the n-type background conductivity of ZnO films. Besides introducing two hydrogen-related donor states, the incorporated hydrogen passivates defects at grain boundaries. With increasing annealing temperatures, the unstable H-BC atoms gradually diffuse out of the ZnO films and part of them are converted into H-O, which gives rise to two anomalous Raman peaks at 275 and 510 cm(-1). These results help to clarify the relationship between the hydrogen-related defects in ZnO described in various studies and the free carriers that are produced by the introduction of hydrogen.

Experimental and theoretical analysis of nondegenerate ultrabroadband chirped pulse optical parametric amplification

Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 muJ at pump intensity 3 GW/cm(2), the corresponding parametric gain reached 3.6 x 10(3), the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.

Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb(3+)-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 x 10(7) at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse. (C) 2009 Elsevier B.V. All rights reserved.

Efficient Mode-locked and Q-switched Nd∶YVO_4 Laser with Semiconductor Saturable Absorber Mirror

We reported an efficient diode pumped Nd ! YVO, 1 064 nm laser passively mode-locked and Q-switched by a semiconductor saturable absorber mirror(SESAM). At the incident pump power of 7. 5 W, 2. 81 W average output power was obtained during stable CW mode locking with a repetition rate of 111 MHz. The optical conversion efficiency was 37. 5% , and the slope efficiency was 39%. So far as we know, this is the highest optical-optical conversion efficiency with a SESAM at home.

Optical analysis of AlGaInP laser diodes with real refractive index guided self-aligned structure

Optical modes of AlGaInP laser diodes with real refractive index guided self-aligned (RISA) structure were analyzed theoretically on the basis of two-dimension semivectorial finite-difference methods (SV-FDMs) and the computed simulation results were presented. The eigenvalue and eigenfunction of this two-dimension waveguide were obtained and the dependence of the confinement factor and beam divergence angles in the direction of parallel and perpendicular to the pn junction on the structure parameters such as the number of quantum wells, the Al composition of the cladding layers, the ridge width, the waveguide thickness and the residual thickness of the upper P-cladding layer were investigated. The results can provide optimized structure parameters and help us design and fabricate high performance AlGaInP laser diodes with a low beam aspect ratio required for optical storage applications.

Structural and optical changes in GaAs/InAs/GaAs structure induced by thermal annealing

Self-organized InAs quantum; dots sheets are grown on GaAs(100) substrate and tapped by 80nm GaAs layer with molecular beam epitaxy. Samples were annealed and characterized with Raman spectra, transmission electron microscopy (TEM) and photolumincscence (PL). The Raman spectra indicates arsenic clusters in the GaAs capping layer. The TEM analysis revealed the relaxation of strain in some InAs islands with the introduction of the network of 90 dislocations. In addition, the structural changes also lead to the changes of the PL spectra from me InAs islands. Their correlation was discussed, Our results suggest:est that annealing may be used to intentionally modify me properties of self-organized InAs islands on GaAs.

Surface morphology and optical property of 1.3 mu m In0.5Ga0.5As/GaAs self-organized quantum dots grown by MBE

Surface morphology and optical properties of 1.3 mum self-organized InGaAs/GaAs quantum dots structure grown by molecular beam epitaxy have been investigated by atomic force microscopy and photoluminescence measurements. It has been shown that the surface morphology evolution and emission wavelengths of InGaAs/GaAs QDs can be controlled effectively via cycled monolayer deposition methods due to the reduction of the surface strain. Our results provide important information for optimizing the epitaxial parameters for obtaining 1.3 mum long wavelength emission quantum dots structures. (C) 2002 Elsevier Science B.V. All rights reserved.