Triple-mesa avalanche photodiodes with very low surface dark current.

The dark current of a photodetector is a key parameter for high-sensitivity optical receivers. We report low-dark-current, triple-mesa avalanche photodiodes that have ~50 times lower dark current than conventional single-mesa devices, and suppress surface leakage. The tolerances of triple-mesa avalanche photodiode parameters are presented.

High-power continuous-wave interband cascade lasers with 10 active stages.

We report the pulsed and continuous wave (cw) performance of 10-stage interband cascade lasers (ICLs) emitting at both λ ≈3.2 µm and λ ≈3.45 µm. The slope efficiency is higher while the external differential quantum efficiency per stage remains about the same when comparison is made to earlier results for 7-stage ICLs with similar carrier-rebalanced designs. At T = 25°C, an 18-µm-wide ridge with 4.5 mm cavity length and high-reflection/anti-reflection coatings emits up to 464 mW of cw output power with beam quality factor M(2) = 1.9, for higher brightness than has ever been reported previously for an ICL. When the cavity length is reduced to 1 mm, both the 10-stage and 7-stage devices reach 18% cw wallplug efficiency at T = 25°C.

Pulsed and CW performance of 7-stage interband cascade lasers.

We report a narrow-ridge interband cascade laser emitting at λ ≈3.5 µm that produces up to 592 mW of cw power with a wallplug efficiency of 10.1% and beam quality factor of M(2) = 3.7 at T = 25 °C. A pulsed cavity length study of broad-area lasers from the same wafer confirms that the 7-stage structure with thicker separate confinement layers has a reduced internal loss of ≈3 cm(-1). More generally, devices from a large number of wafers with similar 7-stage designs and wavelengths spanning 2.95-4.7 µm exhibit consistently higher pulsed external differential quantum efficiencies than earlier state-of-the-art ICLs.

Continuous-wave interband cascade lasers operating above room temperature at λ = 4.7-5.6 µm.

We have substantially improved the performance of interband cascade lasers emitting at λ = 4.7 and 5.6 µm, by applying the recently-pioneered approach of heavily doping the injector regions to rebalance the electron and hole concentrations in the active quantum wells. Ridges of ≈10 µm width, 4 mm length, and high-reflectivity back facets achieve maximum continuous wave operating temperatures of 60°C and 48°C, respectively. The threshold power density of ≈1 kW/cm2 at T = 25°C is over an order of magnitude lower than for state-of-the-art quantum cascade lasers emitting in this spectral range.

High-power room-temperature continuous-wave mid-infrared interband cascade lasers.

We demonstrate cw output powers >290 mW into a nearly diffraction-limited (M² ≈2.2) output beam from an interband cascade laser operating at λ = 3.6-3.7 µm at room temperature. The interband cascade laser was designed for nearly equal electron and hole populations in the active region with heavy electron-injector doping, and was processed into narrow ridges mounted epitaxial side down on a copper heat sink. A 15.7-µm-wide, 4-mm-long ridge with the back facet coated for high reflection (HR) and an anti-reflection-coated front facet produced 253 mW of cw output power at T = 25°C into a beam with M² ≈2.7. Furthermore, corrugating the sidewalls of the ridge leads to a 20% improvement in the brightness. A 15.7-µm-wide, 0.5-mm-long ridge with an HR-coated back facet and an uncoated front facet exhibited a maximum cw wall-plug efficiency of nearly 15% at room temperature.

Development and applications of tethered bis(8-quinolinolato) metal complexes (TBOxM).

The tethered bis(8-quinolinolato) metal (TBOxM) complexes have found practical use in many asymmetric reactions. The development of highly enantioselective reactions using TBOxM is surveyed. General reaction schemes and examples using these highly active and selective catalysts are given and discussed in this tutorial review.

Performance characteristics of a continuous-wave compact widely tunable external cavity interband cascade lasers.

We present the design and performance of a novel broadly tunable continuous-wave external-cavity interband cascade laser (ECicL). The ICL die growth and fabrication, as well as the external cavity geometry are described. Tuning across the 3.2-3.35 microm wavelength range, limited by the gain width of the ICL active medium, is achieved at a maximum power level of 4 mW.

Dual-activation asymmetric strecker reaction of aldimines and ketimines catalyzed by a tethered bis(8-quinolinolato) aluminum complex.

An aluminum complex was found to be high yielding and enantioselective for the addition of cyanide to aldimines and ketimines. Although catalytic asymmetric addition of cyanide to imines to generate alpha-amino-protected nitriles (the Strecker reaction) has been extensively studied in the past, alternative, easier-to-handle reagents for this process are required for modern organic synthesis. To date, there are a limited number of reports utilizing alternative sources of cyanide other than KCN/HCN or TMSCN for this important reaction. The present catalyst provides uniformly high enantioselectivity for aromatic, heteroaromatic, and aliphatic aldimines and ketimines using ethyl cyanoformate as the cyanide source.

Catalytic enantioselective Pudovik reaction of aldehydes and aldimines with tethered bis(8-quinolinato) (TBOx) aluminum complex.

New chiral tethered bis(8-quinolinolato) (TBOx) aluminum(III) complexes effectively catalyze the addition of phosphites to aldehydes and aldimines to give enantioenriched alpha-hydroxy and alpha-amino phosphonates in high yields and enantioselectivities with unprecedented reactivity (TON =100 as high as 200). The catalyst is optimized with the low catalyst loading of 0.5 - 1.0 mol %. The modular synthesis of the catalyst allows for potential to tune the reaction for maximum catalytic activity. To date there are few examples with broad substrate scopes that can catalyze both aldehydes and aldimines with such high selectivity and no reports utilizing such low catalyst loading.