Fourier series expansion method for gain measurement from amplified spontaneous emission spectra of Fabry-Perot semiconductor lasers

A gain measurement technique, based on Fourier series expansion of periodically extended single fringe of the amplified spontaneous emission spectrum, is proposed for Fabry-Perot semiconductor lasers. The underestimation of gain due to the limited resolution of the measurement system is corrected by a factor related to the system response function. The standard deviations of the gain-reflectivity product under low noise conditions are analyzed for the Fourier series expansion method and compared with those of the Hakki-Paoli method and Cassidy's method. The results show that the Fourier series expansion method is the least sensitive to noise among the three methods. The experiment results obtained by the three methods are also presented and compared.

Stabilized and tunable single-frequency erbium-doped fiber ring laser employing external injection locking

A stabilized and tunable single-longitudinal-mode erbium-doped fiber ring laser has been proposed and experimentally demonstrated. The laser is structured by combining the compound cavity with a fiber Fabry-Perot tunable filter. An injection-locking technique has been used to stabilize the wavelength and output power of the laser. One of the longitudinal modes is stimulated by the injected continuous wave so that this mode is able to win the competition to stabilize the system. A minimum output power of 0.6 dBm and a signal-to-noise ratio of over 43 dB within the tuning range of 1527-1562 nm can be achieved with the proposed technique. A wavelength variation of less than 0.01 nm, a power fluctuation of less than 0.02 dB, and a short-term linewidth of about 1.4 kHz have also been obtained.

A bidirectionall diode-pumped, passively mode-locked Nd : YVO4 ring laser with a low-temperature-grown semiconductor saturable absorber mirror

We report the operation of a bidirectional picosecond pulsed ring Nd:YVO4 laser based on a low-temperature-grown semiconductor saturable absorber mirror. Except for the laser crystal, the six-mirror ring laser cavity has no intra-cavity elements such as focusing lens or mirror. The bidirectional mode locked pluses are obtained at the repetition rate of 117.5 MHz, pulse duration of 81 ps, power of 2 x 200 mW.

Novel hybrid voltage controlled ring oscillators using single electron and MOS transistors

This paper proposes two kinds of novel hybrid voltage controlled ring oscillators (VCO) using a single electron transistor (SET) and metal-oxide-semiconductor (MOS) transistor. The novel SET/MOS hybrid VCO circuits possess the merits of both the SET circuit and the MOS circuit. The novel VCO circuits have several advantages: wide frequency tuning range, low power dissipation, and large load capability. We use the SPICE compact macro model to describe the SET and simulate the performances of the SET/MOS hybrid VCO circuits by HSPICE simulator. Simulation results demonstrate that the hybrid circuits can operate well as a VCO at room temperature. The oscillation frequency of the VCO circuits could be as high as 1 GHz, with a -71 dBc/Hz phase noise at 1 MHz offset frequency. The power dissipations are lower than 2 uW. We studied the effect of fabrication tolerance, background charge, and operating temperature on the performances of the circuits.

Complex quantum ring structures formed by droplet epitaxy

Well-defined complex quantum ring structures formed by droplet epitaxy are demonstrated. By varying the temperature of the crystallizing Ga droplets and changing the As flux, GaAs/AlGaAs quantum single rings and concentric quantum double rings are fabricated, and double-ring complexes are observed. The growth mechanism of these quantum ring complexes is addressed. (c) 2006 American Institute of Physics.

A new beam propagation method based on least-squares expansion approximating

A new finite difference wide-angle beam propagation method is developed by introducing the least-squares expansion approximant in the propagator expansion. In this new method it is not necessary to select the reference index point because of the whole region approaching the lease-square expansion. This method avoids the problems induced by error selection of the reference index in the old methods based on Taylor or Pade expansion. Several typical structures are simulated by the new method and the results prove the validity of it.

Coherent transport through a quantum dot embedded in a double-slit-like Aharonov-Bohm ring

Coherent transport through a quantum dot embedded in one arm of a double-slit-like Aharonov-Bohm (AB) ring is studied using the Green's function approach. We obtain experimental observations such as continuous phase shift along a single resonance peak and sharp inter-resonance phase drop. The AB oscillations of the differential conductance of the whole device are calculated by using the nonequilibrium Keldysh formalism. It is shown that the oscillating conductance has a continuous bias-voltage-dependent phase shift and is asymmetric in both linear and nonlinear response regimes.

Valence band structures of the InAs/GaAs quantum ring

In the framework of effective-mass envelope function theory, the valence energy subbands and optical transitions of the InAs/GaAs quantum ring are calculated by using a four-band valence band model. Our model can be used to calculate the hole states of quantum wells, quantum wires, and quantum dots. The effect of finite offset and valence band mixing are taken into account. The energy levels of the hole are calculated in the different shapes of rings. Our calculations show that the effect of the difference between effective masses of holes in different materials on the valence subband structures is significant. Our theoretical results are consistent with the conclusion of the recent experimental measurements and should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 American Institute of Physics.

Electronic states of InAs/GaAs quantum ring

In the framework of effective mass envelope function theory, the electronic states of the InAs/GaAs quantum ring are studied. Our model can be used to calculate the electronic states of quantum wells, quantum wires, and quantum dots. In calculations, the effects due to the different effective masses of electrons in rings and out rings are included. The energy levels of the electron are calculated in the different shapes of rings. The results indicate that the inner radius of rings sensitively changes the electronic states. The energy levels of the electron are not sensitively dependent on the outer radius for large rings. If decreasing the inner and outer radii simultaneously, one may increase the energy spacing between energy levels and keep the ground state energy level unchanged. If changing one of two radii (inner or outer radius), the ground state energy level and the energy spacing will change simultaneously. These results are useful for designing and fabricating the double colors detector by intraband and interband translations. The single electron states are useful for studying the electron correlations and the effects of magnetic fields in quantum rings. Our calculated results are consistent with the recent experimental data of nanoscopic semiconductor rings. (C) 2001 American Institute of Physics.

Energy spectrum and persistent currents in finite-width mesoscopic ring with radial potential barrier threading a magnetic flux through its hole

The energy spectrum and the persistent currents are calculated for a finite-width mesoscopic annulus with radial potential barrier, threading a magnetic flux through the hole of the ring. Owing to the presence of tunneling barrier, the coupling effect leads to the splitting of each radial energy subband of individual concentrical rings into two one. Thus, total currents and currents carried by single high-lying eigenstate as a function of magnetic flux exhibit complicated patterns. However, periodicity and antisymmetry of current curves in the flux still preserve.

Polarization-Independent Micro-Ring Resonator on Silicon-on-Insulator

Polarization-independent laterally-coupled micro-ring resonator has been designed and demonstrated. The origin of the polarization-sensitivity of the photonic wire waveguide (PWW) was analyzed. A polarization-insensitive PWW structure was designed and a polarization-insensitive MRR based on this PWW structure was designed by finite difference time-domain method and was fabricated on an 8-inch silicon-on-insulator wafer. The offset between the resonant wavelengths of the quasi-TE mode and the quasi-TM mode is smaller than 0.15 nm. The FSR is about 17 nm, extinction ratio about 10 dB and Q about 620.

The whispering gallery mode in photonic crystal ring cavity - art. no. 698438

Whispering gallery modes (WGMs) in microcavities possess ultra-high cavity Q factor. Such microcavity are easy to be fabricated, so WGMs have attracted much attention in the area of photonics and integrated photonic circuits. It is well known that the effect of total internal reflection restricts the size of this mirocavity. Such drawback goes against the integration of photon. However, the photonic crystal microcavities (PCMC) make a breakthrough recently. The WGMs in the PCMC are possible to gain both ultra-high Q and ultra-small mode volume. In this paper, the property of the mode in photonic crystal ring cavity is analyzed by FDTD and PWE. By modifying the airholes in the corners of the ring cavity, we can obtain the WGM. Also the Q factor of WGM in photonic crystal ring cavity is calculated. This favors the design of the photonic crystal microcavity components.

Phase-locked ring-defect photonic crystal vertical-cavity surface-emitting laser

Phase-locked oxide-confined ring-defect photonic crystal vertical-cavity surface-emitting laser is presented. The coupled-mode theory is employed to illustrate the two supermodes of the device, in-phase and out-of-phase supermode. Experimental results verify the two supermodes by the characteristics of the spectra and the far field patterns. At the lower current, only the out-of-phase supermode is excited, whereas under the higher current, the in-phase supermode also appears at the shorter wavelength range. In addition, the measured spectral separation between the two supermodes agrees well with the theoretical result.

12 W high efficiency single frequency ring laser

Single-frequency output power of 12 W at 1064 nm is demonstrated. Pumped by a fiber-coupled diode laser, the Nd:YVO4 produces 58.6% of the slope efficiency with respect to absorbed pump power, and 52.7% of the optical-optical efficiency and nearly diffraction-limited output with a beam quality parameter of M-2 approximate to 1.11. To the best of our knowledge, this is the highest slope efficiency and optical-optical efficiency in single-frequency Nd:YVO4 ring laser. The slope efficiency of the single frequency laser is close to the limit of the efficiency. [GRAPHICS] output spectrum of the single-frequency Nd:YVO4 ring laser

Kondo effect in a triangular triple quantum dots ring with three terminals

For a triangular triple quantum dots (TTQDs) ring with three terminals, when lowering one of the dot-lead coupling to realize the left-right (L-R) reflection symmetry coupling, the internal C-upsilon of the TTQDs is well preserved in the absence of many-body effect for the symmetric distribution of the dot-lead coupling on the molecular orbits. In the presence of Kondo effect, the decrement of one of the dot-lead couplings suppresses the inter-dot hopping. This happens especially for the coupled quantum dot (QD), which decouples with the other two ones gradually to form a localized state near the Fermi level As a result, the internal dynamic symmetry of the TTQDs ring is reduced to L-R reflection symmetry, and simultaneously, the linear conductance is lifted for the new forming molecular orbit near the Fermi level