Xiaopeng Zhu

Performance analysis of very-small-aperture lasers

The fabrication of very-small-aperture lasers is demonstrated, and their performance is analyzed. Because of strong optical feedback caused by a gold film on the front facet of the laser, its behavior changes: The threshold current decreases, the density of light inside the laser diode and the redshift effect of the spectra are enhanced, and the laser diodes lifetime is shorter than that of common laser diodes with large driving current.

Eye-safe single-frequency single-mode polarized all-fiber pulsed laser with peak power of 361 W

An all-fiber, single-frequency, single-mode linearly polarized, high peak power pulsed laser at 1540 nm for coherent Doppler wind lidar is demonstrated. A narrow-linewidth seed laser is pulse modulated by an acousto-optic modulator and then amplified by two-stage cascade amplifiers. An 0.8 m long erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber of a power amplifier, and longitudinally varied strains are applied on the gain fiber to realize approximately 3.4 times enhancement of the stimulated Brillouin scattering threshold. Peak power of 361 W pulse width of 200 ns at 10 kHz repetition rate is achieved with transform-limited linewidth and diffraction-limited beam quality. To the best of our knowledge, it is the highest peak power of an eye-safe, single-mode narrow-linewidth pulsed fiber laser based on 10 μm core diameter silica fiber.

All fiber pulsed coherent lidar development for wind profiles measurements in boundary layers

An all fiber pulsed coherent Doppler lidar (CDL) system at 1.54 ?m wavelength is developed for wind profiles measurements. This lidar affords 43.0-?J pulse energy at 10-kHz pulse repetition frequency with 500-ns pulse width. The lidar is operated in monostatic mode with 50-mm diameter telescope. The heterodyne mixing signals are acquired with 500 M/s analog to digital converter and 2048 points fast Fourier transform (FFT) is implemented. Line of sight wind speeds are measured with more than 3.0-km range in a horizontal direction and about 1.9 km in the vertical direction with 75-m range resolution. Systematic error of speed measurement of 0.2 m/s is validated.

Development of All-fiber Coherent Doppler Lidar to Measure Atmosphere Wind Speed

An all-fiber pulsed coherent Doppler lidar (CDL) prototype is developed to measure wind profiles in the lower atmosphere layer. The all-fiber single frequency pulsed laser is operated with pulse energy of 50μJ, pulse width of 500ns and pulse repetition rate of 10kHz. The AOM heterodyne frequency is about 55MHz. The diameter of the telescope is 100mm. The heterodyne mixing signal is acquired with 500M/s AD card. Several experiments are implemented to validate the performance of the system. With 3000 pulses accumulated, the maximum horizontal measurement range of wind speed is about 4.2km in clear day, and the maximum vertical range is near 2km. The speed measurement accuracy of the lidar in hard target experiment is shown to be about 0.2m/s. An engineering prototype is being developed to measure wind speed in 5000m range, which will be used in the airport to measure atmosphere windshear.

Development of a coherent Doppler lidar to measure atmosphere windshear

A pulsed coherent Doppler lidar prototype at wavelength of 1064nm was developed to measure windshear in the lower troposphere layer. The laser transmitter was an injection-seeded pulsed Nd:YAG laser with pulse energy of 0.5mJ, pulse duration of 80ns and pulse repetion rate of 200Hz. Hard-target speed calibration expriments were carried out to demonstrate speed measurement accuracy of 0.23m/s for the lidar. Then line-of sight atmosphre wind velocity measurement in 500m range with 40m range resolution was implemented. The lidar is being optimized to measure windshear at 2km range away.

Calculation of valence subband structures for strained GaInP/AlGaInP quantum wells without axial approximation

Usually in the calculation of valence subband structure for III-V direct bandgap material, axial approximation had been used in the Luttinger-Kohn model to simplify the computational efforts. In this letter, the valence subband structure for the GaInP/AlGaInP strained and lattice-matched quantum wells was calculated without axial approximation, on the basis of 6×6 Luttinger-Kohn Hamiltonian including strain and spin-orbit splitting effects. The numerical simulation results were presented with help of the finite-difference methods. The calculation results with/without axial approximation were compared and the effect of axial approximation on the valence subband structure was discussed in detail. The results indicated that there was a strong warping in the GaInP valence band, and axial approximation can lead to an error when k was not equal to zero, especially for compressively strained and lattice-matched GaInP/AlGaInP quantum wells.

Theoretical analysis of the bandgap for the intermixed Gainp/AlgaInP quantum wells

Compositional distribution of the quantum well and barrier after quantum well intermixing for GaInP/AlGaInP system was theoretically analyzed on the basis of atom diffusion law. With the compositional distribution result, the valence subband structure of the intermixed quantum well was calculated on the basis of 6×6 Luttinger-Kohn Hamiltonian, including spin-orbit splitting effects. To get more accurate results in the calculation, a full 6-band problem was solved without axial approximation, which had been widely used in the Luttinger-Kohn model to simplify the computational efforts, since there was a strong warping in the GaInP valence band. At last, the bandgap energy of the intermixed quantum well was obtained and the calculation result is of much importance in the analysis of quantum well intermixing experiments.

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.