Two HSCT Mach 1.7 low sonic boom designs

The objective of this study was to provide low sonic boom concepts, geometry, and analysis to support wind tunnel model designs. Within guidelines provided by NASA, two High Speed Civil Transport (HSCT) configurations were defined with reduced sonic boom that have low drag, high payload, and good performance. To provide information for assessing the feasibility of reduced sonic boom operation, the two designs were analyzed in terms of their sonic boom characteristics, as well as aerodynamics, weight and balance, and performance characteristics. Low drag and high payload were achieved, but both of the blended arrow-wing configurations have deficiencies in high lift capability, fuel volume, wing loading, balance, and takeoff gross weight. Further refinement of the designs is needed to better determine the commercial viability of low boom operation. To help in assessing low boom design technology, the two configurations were defined as wind tunnel models with altered aft-bodies for the wind tunnel sting mounting system

High-Speed VCSELs with Strong Confinement of Optical Fields and Carriers

We present the design, fabrication, and performance of our latest generation high-speed oxide-confined 850-nm verticalcavity surface-emitting lasers. Excellent high-speed properties are obtained by strong confinement of optical fields and carriers. Highspeed modulation is facilitated by using the shortest possible cavity length of one half wavelength and placing oxide apertures close to the active region to efficiently confine charge carriers. The resulting strong current confinement boosts internal quantum efficiency, leading to low threshold currents, high wall-plug efficiency, and state-of-the-art high-speed properties at low bias currents. The temperature dependent static and dynamic performance is analyzed by current-power-voltage and small-signal modulation measurements

High Speed VCSELs and VCSEL Arrays for Single and Multicore Fiber Interconnects

Our recent work on high speed 850 nm VCSELs and VCSEL arrays is reviewed. With a modulation bandwidth approaching 30 GHz, our VCSELs have enabled transmitters and links operating at data rates in excess of 70 Gbps (at IBM) and transmission over onboard polymer waveguides at 40 Gbps ( at University of Cambridge). VCSELs with an integrated mode filter for single mode emission have enabled transmission at 25 Gbps over > 1 km of multimode fiber and a speed-distance product of 40 Gbps . km. Dense VCSEL arrays for multicore fiber interconnects have demonstrated 240 Gbps aggregate capacity with excellent uniformity and low crosstalk between the 40 Gbps channels

25 Gbit/s transmission over 500 m multimode fibre using 850 nm VCSEL with integrated mode filter

An integrated mode filter in the form of a shallow surface relief was used to reduce the spectral width of a high-speed 850 nm vertical-cavity surface-emitting laser (VCSEL). The mode filter reduced the RMS spectral width from 0.9 to 0.3 nm for a VCSEL with an oxide aperture as large as 5 mu m. Because of reduced effects of chromatic and modal fibre dispersion, the mode filter significantly increases the maximum error-free (bit error rate < 10(-12)) transmission distance, enabling transmission at 25 Gbit/s over 500 m of multimode OM3+ fibre

High-speed 850 nm VCSELs operating error free up to 57 Gbit/s

Error-free transmission is demonstrated at bit rates up to 57 Gbit/s back-to-back, up to 55 Gbit/s over 50 m fibre and up to 43 Gbit/s over 100 m fibre using an oxide-confined 850 nm high-speed vertical cavity surface-emitting laser with a photon lifetime optimised for high-speed data transmission

Silicon-Integrated Hybrid-Cavity 850-nm VCSELs by Adhesive Bonding: Impact of Bonding Interface Thickness on Laser Performance

The impact of bonding interface thickness on the performance of 850-nm silicon-integrated hybrid-cavity vertical-cavity surface-emitting lasers (HC-VCSELs) is investigated. The HC-VCSEL is constructed by attaching a III–V “half-VCSEL” to a dielectric distributed Bragg reflector on a Si substrate using ultrathin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding. The thickness of the bonding interface, defined by the DVS-BCB layer together with a thin SiO2 layer on the “half-VCSEL,” can be used to tailor the performance, for e.g., maximum output power or modulation speed at a certain temperature, or temperature-stable performance. Here, we demonstrate an optical output power of 2.3 and 0.9 mW, a modulation bandwidth of 10.0 and 6.4 GHz, and error-free data transmission up to 25 and 10 Gb/s at an ambient temperature of 25 and 85 °C, respectively. The thermal impedance is found to be unaffected by the bonding interface thickness

Impact of Damping on Large Signal VCSEL Dynamics

The dependence of large signal VCSEL dynamics on damping is studied through time-domain measurements of turn-on transients and timing jitter for VCSELs having K-factors from 0.1 to 0.4 ns

Quasisymmetric Schur functions

We introduce a new basis for quasisymmetric functions, which arise from a specialization of nonsymmetric Macdonald polynomials to standard bases, also known as Demazure atoms. Our new basis is called the basis of quasisymmetric Schur functions, since the basis elements refine Schur functions in a natural way. We derive expansions for quasisymmetric Schur functions in terms of monomial and fundamental quasisymmetric functions, which give rise to quasisymmetric refinements of Kostka numbers and standard (reverse) tableaux. From here we derive a Pieri rule for quasisymmetric Schur functions that naturally refines the Pieri rule for Schur functions. After surveying combinatorial formulas for Macdonald polynomials, including an expansion of Macdonald polynomials into fundamental quasisymmetric functions, we show how some of our results can be extended to include the $t$ parameter from Hall-Littlewood theory.Comment: 30 pages; references added; new subsections on transition matrices, how to include the $t$ parameter from Hall-Littlewood theory and further avenues; new survey of combinatorial formulas for Macdonald polynomials, including an expansion of Macdonald polynomials into fundamental quasisymmetric function