GHz modulation of carbon nanotube cathodes for microwave amplifiers

Cold cathodes based on carbon nanotubes (CNs) allow to produce a pulsed/directly modulated electron beam. Using an array of vertically aligned CNs that exhibit an aspect ratio of around 200, we demonstrated the modulation of a 1.5 A/cm2 beam at 1.5 GHz frequency. Such CN cathodes are very promising for their use in a new generation of compact and low cost microwave amplifiers that operates between 30 and 100 GHz. ©2005 IEEE.

35 GHz passive mode-locking of InGaAs/GaAs quantum dot lasers at 1.3 μm with Fourier-limited pulses

We report 35 GHz passive mode-locking and 20 GHz hybrid mode-locking of quantum dot (QD) lasers at 1.3 μm. Our investigations show ultrafast absorber recovery times and for the first time transform-limited mode-locked pulses. © 2003 Optical Society of America.

Monolithic electro-optically modulated VCSEL suitable for radio over fibre applications to 20 GHz

An integrated EOM VCSELs is shown to offer high linearity (92dB/Hz 2/3 at 6GHz) and by extrapolation ∼90dB/Hz2/3 up to 20GHz. Successful modulation with IEEE 802.11g signals is demonstrated at 6GHz with a 12dB dynamic range. © 2011 Optical Society of America.

Subcarrier modulation for transmission of 1-Gbit/s channels over 500 m of 62.5-μm multimode fiber

The use of two different subcarriers at frequencies up to 5.5 GHz each transmitting 1 Gbit/s over 500 m of multimode fiber (MMF) is demonstrated. By transmitting the two subcarrier channels simultaneously alongside the baseband signal, an aggregate bit rate of 2.8 Gbit/s is possible.

Unsteady shock motion on a NACA0012 aerofoil at low reduced frequencies

Using transonic blowdown windtunnel experiments, the 2D unsteady shock motion on a NACA0012 aerofoil is examined at various frequencies typical for helicopter blades in forward flight. The aerofoil is subjected to freestream velocities oscillating periodically between M = 0.66 and M = 0.77. Unsteady pressure traces and schlieren images are analyzed over a range of low reduced frequencies to provide information on shock location and strength throughout the cycle. Unsteady effects were noticeable even at very low reduced frequencies (down to O(0.01). However, through the range of frequencies investigated, and within experimental error, the unsteady shock location showed no discernible lag compared to the quasi-steady behaviour. On the other hand, significant variations were observed in shock strengths with the upstream running part of the cycle (decreasing Mach number) displaying considerably stronger shocks than during the accelerating part of the cycle. It could be shown that this variation in shock strength is primarily caused by the shock motion modifying the relative shock Mach number. As a result is was possible to use the quasi-steady results to predict the unsteady shock behaviour at the frequencies investigated here (below 0(0.1)).

Unsteady shock motion on a NACA0012 aerofoil at low reduced frequencies

Using transonic blowdown windtunnel experiments, the 2D unsteady shock motion on a NACA0012 aerofoil is examined at various frequencies typical for helicopter blades in forward flight. The aerofoil is subjected to freestream velocities oscillating periodically between M = 0.66 and M = 0.77. Unsteady pressure traces and schlieren images are analyzed over a range of low reduced frequencies to provide information on shock location and strength throughout the cycle. Unsteady effects were noticeable even at very low reduced frequencies (down to O(0.01). However, through the range of frequencies investigated, and within experimental error, the unsteady shock location showed no discernible lag compared to the quasi-steady behaviour. On the other hand, significant variations were observed in shock strengths with the upstream running part of the cycle (decreasing Mach number) displaying considerably stronger shocks than during the accelerating part of the cycle. It could be shown that this variation in shock strength is primarily caused by the shock motion modifying the relative shock Mach number. As a result is was possible to use the quasi-steady results to predict the unsteady shock behaviour at the frequencies investigated here (below 0(0.1)).