IEEE Journal of Quantum Electronics

Hybrid organic light-emitting devices (HOLEDs) were fabricated with the active molecularly doped polyimide (AMDPI) thin film as a hole-injecting-transporting layer through the mixed vapor deposition polymerization (VDP) process. As a comparison, the polyimide thin film as a hole-injecting-transporting layer was also prepared for a HOLED via VDP. Both the AMDPI and polyimide thin films were almost optically transparent over the entire visible range because the bandgap energy was /spl sim/2.9 eV. HOLEDs with the AMDPI thin film showed a higher luminance and efficiency than that with the polyimide thin film. In particular, the application of a lithium-aluminum cathode significantly enhanced the luminance and the efficiency of HOLEDs with the AMDPI thin film.

1.3-/spl mu/m InGaAsP multiple-quantum-well (MQW) capped mesa buried heterostructure (CMBH) lasers with mesa widths ranging from 1 /spl mu/m (standard single mode) to 100 /spl mu/m (wide area) were fabricated on one wafer with identical current blocking layers at the sides. The single-mode devices had three times larger nominal threshold current density than the wide-area devices. Measurement of gain and loss in the devices showed the single-mode devices to have 6-8 cm/sup -1/ higher loss and 40% lower optical confinement than the wide-area devices. Beyond these differences, the measurements show that up to 30% of the threshold current in the single-mode CMBH lasers does not contribute to the pumping of the MQW active region. Injection efficiency is measured to be close to unity for both single-mode and wide mesa devices. Scenarios to explain this parasitic current are discussed, including the potential role for nonradiative recombination centers at the regrown epitaxial interface, which can be consistent with all of the experimental results.

A novel method was proposed to glue an AlGaInP-GaAs light-emitting diode (LED) onto a transparent sapphire substrate. The absorbing GaAs was subsequently removed by selective wet etching. It was found that the emission efficiency could reach 401 m/W under 20-mA current injection for the 622-nm glue bonded (GB) AlGaInP-sapphire LED. It was also found that these GB LEDs are highly reliable, with small variations in operation voltage and luminescence intensity during the life test.

Relative intensity noise (RIN) and the frequency/phase noise spectrum (FNS) equivalent circuit of a multimode semiconductor laser diode are derived from multimode rate equations with the inclusion of noise Langevin sources. FNS is an important parameter in optical communication systems, and its circuit model is presented, for the first time, in this paper. Both circuit models for RIN and FNS are integrated in one circuit. RIN and FNS are calculated as functions of frequency, output power, and mode number. It is shown that the RIN of the main mode is increased in the multimode lasers with higher mode numbers. Furthermore, we show that RIN and FNS are enhanced for higher output power. The dependency of a multimode laser diode linewidth on output power is also analyzed using the model.

We theoretically and experimentally studied the dispersion effects in an actively mode-locked inhomogeneously broadened laser. In the positive group velocity dispersion (GVD) region, the laser generates incoherent pulses. Self-phase modulation and resonant dispersion impede reduction of the pulse duration when the GVD is small or near zero. A single, stable, soliton-like pulse can be generated only when the GVD is within a certain range of negative values. When the negative GVD is too small, the laser generates only multiple soliton-like pulses because of excess gain filtering. When the negative GVD is too large, the soliton pulse-shaping process fails, and the laser generates only incoherent pulses due to insufficient gain filtering. In the experiment, we characterized an actively mode-locked inhomogeneously broadened Nd:silicate glass laser and confirmed this GVD dependence. The laser generated self-sustaining, soliton-like pulses as short as 77 fs.

Spectacular improvements in both resolution and signal-to-noise ratio of two-photon Ramsey fringes obtained at 30 THz have been achieved by implementing a new detection scheme. A molecular beam of SF/sub 6/, after passing through the Ramsey regions, is interrogated by a separate laser beam which makes optimal use of the entire Doppler profile by generating a comb of frequencies within a compensated high-finesse cavity. Resulting molecular spectra have the highest resolution ever obtained with CO/sub 2/ lasers and, as a standard, the system will soon outperform the best currently available.

Using scanning reflection electron microscopy and a high-temperature scanning tunneling microscopy (STM), we study the growth processes of Si and Ge nanostructures on Si substrates covered with ultrathin SiO/sub 2/ films. Si windows are formed in the ultrathin SiO/sub 2/ films by irradiating focused electron beams used for SREM or field emission electron beams from STM tips before or during heating samples. Ge nanoislands are grown only at the Si window positions by depositing Ge on the samples and by subsequent annealing of them. Moreover, Ge nanoislands about 7 nm in size and ultrahigh density (>10/sup 12//cm/sup 2/) are grown on the ultrathin SiO/sub 2/ films. These nanoislands can be manipulated by STM when they are separated from Si substrates by the ultrathin SiO/sub 2/ films. Si, Ge, Ge/Si and Si/Ge/Si nanoislands can also be grown on the Si windows by selective growth using Si/sub 2/H/sub 6/ and GeH/sub 4/ gases. These nanoislands are found to be stable on the Si windows during high-temperature annealing. These results indicate that ultrathin SiO/sub 2/ technology is useful for growing Si and Ge nanostructures on given areas.

A calculation procedure for evaluation of the coupling length of two parallel coupled channel waveguides in a planar photonic crystal is proposed. The first step of the calculation is evaluation of the band structure of a photonic crystal containing two coupled linear defects. The eigenvalue corresponding to eigenstates localized in the linear defect (the waveguide) is split due to the coupling. This splitting is treated within the coupled-mode theory that yields a simple relation between the splitting and the coupling length. The MIT photonic bands code is used to evaluate the coupling between channel waveguides in silicon./sup 1/ These calculations show that in contrast to the finite-difference time-domain approach, the method is effective for three-dimensional light propagation.

A numerically stable method to calculate the quantum states of carriers based on the variational principle is proposed. It is especially effective for the carriers confined in the quantum wells under the influence of self-interaction of the carriers. In this treatment, a wave function is defined as a set of scalar numbers based on the finite-difference approach. An action defined as the expectation value of a Hamiltonian becomes a multivariate function of the wave function. Application of numerical multidimensional minimization procedures to the action can achieve stable convergence even under the conditions where the conventional self-consistent approach to Schrodinger and Poisson equations fails to give solutions. Application to the calculations of ground states in modulation-doped single quantum wells is demonstrated, and quantitative comparison to the conventional method is also presented. This method has implications not only for numerical procedures, but also for the numerical realization of the variational principle, a fundamental concept in physics.