Chongyang Liu

Low transparency current density and high temperature operation from ten-layer p-doped 1.3μm InAs∕InGaAs∕GaAs quantum dot lasers

High temperature photoluminescence up to 100°C was demonstrated from the p-doped ten-layer InAs∕InGaAs quantum dot (QD) laser structure. 1.3μm InAs QD lasers were fabricated using pulsed anodic oxidation from this structure. High output power of 882mW and low transparency current density of 5.9A∕cm2∕QD layer were obtained. Ground state (GS) lasing could be maintained from a QD laser with short cavity length of 611μm, corresponding to the maximum modal gain of 23.1cm−1 from this laser system. GS continuous wave operation up to 100°C was also demonstrated from an InAs QD laser (50×2500μm2).

Optimization of ridge height for the fabrication of high performance InGaAsN ridge waveguide lasers with pulsed anodic oxidation

The dependence of the ridge height on the performance of the ridge waveguide (RWG) lasers has been systematically studied. It was found that the optimum ridge height corresponds to an etching depth where all the p-doped layers above the active region were removed. InGaAsN triple-quantum-well RWG lasers with optimized ridge height were fabricated with pulsed anodic oxidation. The lowest threshold current density (Jth) of 711A∕cm2 was obtained from a 10×1300μm2 InGaAsN RWG laser. The corresponding transparency current density (Jtr) of the fabricated InGaAsN RWG lasers was 438A∕cm2 (equivalent to 146A∕cm2 per well).

Effects of rapid thermal annealing on optical properties of p-doped and undoped InAs/InGaAs dots-in-a-well structures

Postgrowth rapid thermal annealing was used to investigate the intermixing and structural changes in p-doped and undoped InAs/In0.1Ga0.9As dots-in-a-well (DWELL) structures grown by molecular beam epitaxy. Interdiffusion of In and Ga atoms caused by thermal annealing was proven from photoluminescence (PL) measurements, where blueshifts of the energy peaks were observed. The results show that p-doped quantum dot (QD) structures are more resistant to intermixing with higher thermal energy onset, and the reason is explained as the suppressed Ga diffusion resulted from the Be dopant. Rapid quenching of the integrated PL intensity at high temperature was observed in both undoped and p-doped DWELL QDs. Good agreement was obtained by fitting the integrated PL profile using two nonradiative recombination mechanisms, resulting in two activation energies that correspond to loss of carriers to nonradiative centers.

High-power 1.3‐μm InGaAsN strain-compensated lasers fabricated with pulsed anodic oxidation

Ridge waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal-organic chemical vapor deposition were fabricated with pulsed anodic oxidation. Laser output power reached 962mW in cw mode at room temperature from 100‐μm stripe lasers with a wavelength of 1297nm. The threshold-current density was 256A∕cm2. The characteristic temperature of the lasers was 138K in the linear region (20–80°C).

Rate equation model of the negative characteristic temperature of InAs∕GaAs quantum dot lasers

The negative characteristic temperature of InAs∕GaAs quantum dot lasers is studied using a rate equation model. It is found that the decrease in the total contribution to lasing following a decrease in temperature is the reason for the occurrence of negative characteristic temperature in these lasers. The temperature corresponding to the occurrence of negative characteristic temperature is determined by the carrier escape rate from the quantum dots to the wetting layer or cap layer, carrier recombination lifetime, and rate of carrier loss due to deviation from (quasi-) Fermi equilibrium. The negative characteristic temperature in InAs∕GaAs quantum dot lasers does not occur under conditions of low carrier recombination lifetime and high quantum dot energy level occupation.

Investigation of the optical properties of InGaAsN∕GaAs∕GaAsP multiple-quantum-well laser with 8-band and 10-band k·p model

We have used both 10-band and 8-band k·p Hamiltonian to investigate the maximum TE-mode optical gain for the triple quantum wells with In0.35Ga0.65As0.985N0.015 as the active layers and barriers comprised of two unstrained GaAs layers and one tensile-strained GaAs0.82P0.18 layer. The results were compared to a similar structure without the GaAsP layer and were discovered that the presence of the GaAsP barrier reduced the carrier density at threshold condition. However, the characteristics of the optical gain versus radiative current density for both structures are very similar. We also found the conduction band energy dispersion curves calculated by the 8-band model are flatter than the 10-band model due to the larger InGaAsN effective mass used. The transparent carrier density of the 10-band model is smaller than that of the 8-band model. The radiative recombination coefficient B calculated by the two models varies from 3.5×10−11cm3∕s for the 8-band model to 8.0×10−11cm3∕s for the 10-band model. Using Jt...

Conversion between EIT and Fano spectra in a microring-Bragg grating coupled-resonator system

A conversion between the electromagnetically induced transparency (EIT) transmission and Fano transmission is theoretically and experimentally demonstrated in an all-pass microring-Bragg grating (APMR-BG) coupled-resonator system. In this work, the coupling between the two resonators (the microring resonator and the Fabry-Perot resonator formed by two Bragg gratings) gives rise to the EIT and Fano transmissions. The resonant status strongly depends on the round-trip attenuation of the microring and the coupling strength. By tuning the coupling strength, the EIT and Fano transmissions can be controlled and converted. The device performance has been theoretically calculated and analyzed with a specially developed numerical model based on the transfer matrix method. The APMR-BG coupled-resonator systems with different gap widths were designed, fabricated, and characterized on a silicon-on-insulator (SOI) platform. The conversion of resonance was experimentally observed and verified. In addition, this on-chip...

Effects of Thermal Annealing on the Dynamic Characteristics of InAs/GaAs Quantum Dot Lasers

We investigated the effects of rapid thermal annealing (RTA) on the dynamic characteristics of the InAs/GaAs ten-layer quantum dot (QD) laser. Improvements in the temperature stability of bandwidth have been demonstrated upon annealing. We attribute the improvements to the following factors: 1) increase in internal quantum efficiency and 2) reduction in temperature dependency of differential gain. The increase in bandwidth at high temperature from the annealed QDs could be due to a reduction in the relaxation time on the order of 0.1 ps. More importantly, the RTA process resulted in better temperature stability in the differential gain and gain compression. This is beneficial for the development of uncooled high-speed QD lasers.

Design and Analysis of 2-μm InGaSb/GaSb Quantum Well Lasers Integrated Onto Silicon-on-Insulator (SOI) Waveguide Circuits Through an Al 2 O 3 Bonding Layer

GaSb-based quantum well (QW) laser diode, with emission wavelength ~2 μm, integrated onto a silicon-on-insulator (SOI) waveguide circuit through a high-thermal-conductivity Al2O3 bonding layer has been designed and analyzed. Prior to bonding, the fabricated Fabry-Perot GaSb QW laser worked under continuous wave operation at room temperature, with a low threshold current of 37 mA at the emission wavelength of 2019 nm, demonstrating high material quality. A tapered structure has been used for evanescent coupling of light from the GaSb laser to the underlying Si waveguide. Instead of using SiO2 for direct bonding or Benzocyclobutene for adhesive bonding, the use of Al2O3 to directly bond GaSb lasers onto SOI wafers is proposed. The optical mode distribution simulations by a beam propagation method software show that light can be coupled efficiently to the underlying Si waveguide through the tapered structure without compromise in optical coupling efficiency. Furthermore, there is a significant reduction (~70%) in the total thermal resistance compared with the same structure using a SiO2 bonding layer. Our results suggest that the Al2O3 bonding layer could be a promising candidate for III-V lasers integrated on SOI circuits, where thermal dissipation is very critical.

Electromagnetically induced transparency-like effect in microring-Bragg gratings based coupling resonant system.

An all-pass microring-Bragg gratings (APMR-BG) based coupling resonant system is proposed and experimentally demonstrated to generate electromagnetically induced transparency (EIT)-like transmission for the first time. The coupling between two light path ways in the micro-ring resonator and the Fabry-Pérot (F-P) resonator formed by two sections of Bragg gratings gives rise to the EIT-like spectrum. This system has the advantage of a small footprint consisting of only one microring resonator and one bus waveguide with Bragg gratings. It also has a large fabrication tolerance as the overlap requirement between the resonance wavelengths of the microring and the F-P resonator is more relaxed. The two most important properties of the EIT-like transmission namely the insertion loss (IL) and the full-width-at-half-maximum (FWHM) have been analytically investigated by utilizing the specially developed model based on the transfer matrix method. The APMR-BG based coupling resonant system was fabricated on a silicon-on-insulator (SOI) platform. The EIT-like transmission with an extinction ratio (ER) of 12 dB, a FWHM of 0.077 nm and a quality factor (Q factor) of 20200 was achieved, which agree well with the simulated results based on our numerical model. A slow light with a group delay of 38 ps was also obtained.