Follow the links to read the full papers in the IET Digital Library.
Long and intense
Four-intensity level pulse amplitude modulation (4PAM) is an attractive modulation format for large capacity optical light sources, and researchers in Japan have achieved 25-Gbaud/s 4-PAM modulation with 1.3-μm DML and 10-km transmission over single-mode fibre for the first time.Their device will be employed as a light source in an optical transmitter for optical network systems.
Terahertz frequency radiation has many potential applications, ranging from imaging and chemical sensing through to telecommunications. However, one of the principal challenges is to develop compact, low-cost, efficient THz sources. To address this, researchers in the UK have developed high-power THz quantum cascade lasers operating in pulsed mode. Their devices deliver peak output power of up to 1.01 W from a single facet at 10 K.
Researchers in the US have presented a wide band GaN HEMT mixer which has very low loss and high dynamic range. Since resistive mixers are a commonly used component in military or satellite communication systems, their reduction of typical in-band resonance means they may contribute to the improvement of microwave communication systems.
The first investigation of the total phase noise and frequency stability of the signals using independent cryogenic sapphire oscillators has been demonstrated by researchers in Australia. They have shown that the phase noise and frequency stability results were not estimated from residual noise measurements of the synthesis chain, as was the previous state-of-the-art.
A novel switching architecture for exponential function generation in CMOS technology has been demonstrated by researchers in the US. Their CMOS quadratic function generator circuit – removing the necessity for a squarer/multiplier circuit – means non-idealities in sub-micron technology can introduce a technique to extend dynamic range.