Quantum frequency down-conversion of single photons at 1552 nm from single InAs quantum dot

Near-infrared single photon sources in telecommunication bands, especially at 1550 nm, are required for long-distance quantum communication. Here a down-conversion quantum interface is implemented, where the single photons emitted from single In As quantum dot at 864 nm is down converted to 1552 nm by using a fiber-coupled periodically poled lithium niobate(PPLN) waveguide and a 1.95 μmm pump laser, and the frequency conversion efficiency is ~40%. The singlephoton purity of quantum dot emission is preserved during the down-conversion process, i.e., g~((2))(0), only 0.22 at 1552 nm.This present technique advances the Ⅲ-Ⅴ semiconductor quantum dots as a promising platform for long-distance quantum communication.     

Optimization of wide band mesa-type enhanced terahertz photoconductive antenna at 1550 nm

A mesa-type enhanced InGaAs/InAlAs multilayer heterostructure(MLHS) terahertz photoconductive antenna(PCA)at 1550 nm is demonstrated on an InP substrate. The InGaAs/InAlAs superlattice multilayer heterostructures are grown and studied with different temperatures and thickness ratios of InGaAs/InAlAs. The PCAs with different gap sizes and pad sizes are fabricated and characterized. The PCAs are evaluated as THz emitters in a THz time domain spectrometer and we measure the optimized THz bandwidth in excess of 2 THz.     

2-μm single longitudinal mode GaSb-based laterally coupled distributed feedback laser with regrowth-free shallow-etched gratings by interference lithography

We report a type-I Ga Sb-based laterally coupled distributed-feedback(LC-DFB) laser with shallow-etched gratings operating a continuous wave at room temperature without re-growth process. Second-order Bragg gratings are fabricated alongside the ridge waveguide by interference lithography. Index-coupled LC-DFB laser with a cavity of 1500 μm achieves single longitudinal mode continuous-wave operation at 20℃ with side mode suppression ratio(SMSR) as high as 24 dB.The maximum single mode continuous-wave output power is about 10 mW at room temperature(uncoated facet). A low threshold current density of 230 A/cm~2 is achieved with differential quantum efficiency estimated to be 93 mW/A. The laser shows a good wavelength stability against drive current and working temperature.     

Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots

The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots(SQDs) to raise the growth repeatability.Here,through many growth tests on rotating substrates,we develop a proper In deposition amount(θ) for SQD growth,according to the measured critical θ for test QD nucleation(θ_c).The proper ratio θ/θ_c,with a large tolerance of the variation of the real substrate temperature(T_(sub)),is 0.964-0.971 at the edge and 0.989 but 0.996 in the center of a 1/4-piece semi-insulating wafer,and around 0.9709 but 0.9714 in the center of a 1/4-piece N~+ wafer as shown in the evolution of QD size and density as θ/θ_c varies.Bright SQDs with spectral lines at 905 nm-935 nm nucleate at the edge and correlate with individual 7 nm-8 nm-height QDs in atomic force microscopy,among dense 1 nm-5 nm-height small QDs with a strong spectral profile around 860 nm-880 nm.The higher T_(sub) in the center forms diluter,taller and uniform QDs,and very dilute SQDs for a proper θ/θ_c:only one 7-nm-height SQD in25 μm~2.On a 2-inch(1 inch = 2.54 cm) semi-insulating wafer,by using θ/θ_c = 0.961,SQDs nucleate in a circle in 22%of the whole area.More SQDs will form in the broad high-T_(sub) region in the center by using a proper θ/θ_c.     

Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

In this paper we focused on the mask technology of inductively coupled plasma(ICP) etching for the mesa fabrication of infrared focal plane arrays(FPA).By using the SiO_2 mask,the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls.Comparing the IV characterization of detectors by using two different masks,the detector using the SiO_2 hard mask has the R_0A of 9.7×10~6 Ω·cm~2,while the detector using the photoresist mask has the R_0A of3.2 × 10~2 Ω·cm~2 in 77 K.After that we focused on the method of removing the remaining SiO_2 after mesa etching.The dry ICP etching and chemical buffer oxide etcher(BOE) based on HF and NH4 F are used in this part.Detectors using BOE only have closer R_0A to that using the combining method,but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE.We finally choose the combining method and fabricated the 640×512 FPA.The FPA with cutoff wavelength of 4.8 μm has the average R_0A of 6.13 × 10~9 Ω·cm~2 and the average detectivity of 4.51 × 10~9 cm·Hz~(1/2).W~(-1)at 77 K.The FPA has good uniformity with the bad dots rate of 1.21%and the noise equivalent temperature difference(NEDT) of 22.9 mK operating at 77 K.     

Spectral dynamical behavior in two-section,quantum well,mode-locked laser at 1.064 μm

In this study, two-section mode-locked semiconductor lasers with different numbers of quantum wells and different types of waveguide structures are made. Their ultrashort pulse features are presented. The spectral dynamical behaviors in these lasers are studied in detail. In the simulation part, a two-band compressive-strained quantum well(QW) model is used to study thermally induced band-edge detuning in the amplifier and saturable absorber(SA). A sudden blue shift in laser spectrum is expected by calculating the peak of the net gain. In the experiment part, the sudden blue shift in the emission spectrum is observed in triple QW samples under certain operating conditions but remains absent in single QW samples.Experimental results reveal that blue shift phenomenon is connected with the difference between currents in two sections.Additionally, a threshold current ratio for blue-shift is also demonstrated.