technology photodiodes
Figure 4.(a) Conceptual diagrams of a broadside patch antenna and an end-fire tapered slot antenna for rectangular waveguide (WR) excitations; and (b) conceptual cross-sectional view of UTC-PD based photomixers with integrated patch antenna and tapered slot antenna for WR-10 and WR-08 waveguide excitations,respectively
.(re-printed by permission from A.Ueda,et al.,IEEE Trans.Microwave Theory Tech.,
vol.51,
pp.1455-1459.May,2003 © 2003 IEEE and A.Hirata,et al.,IEEE Trans.Microwave Theory Tech.,vol.52, pp.1843-1850,Aug.2004 © 2004 IEEE)
MMW power. The high speeds and powers of UTC-PDs and NBUTC-PDs enable the construction of photo- transmitters that can produce a range of radiation patterns, operate at 0.1 to 1 THz, and deliver output powers that are typically 20 dB higher than those associated with photo-transmitters based on conventional photodiodes. By pairing the UTC-PD based photo-transmitter with an end-fire taper slot antenna or a broadside patch antenna, researchers have shown that it is possible to excite WR-10, WR-08, and WR-03 rectangular waveguide-based horn antenna (see Figure 4). This has enabled the demonstration of 10 Gbit/s and 16 Gbit/s line-of-sight data transmission using centre frequencies of 120 GHz and 300 GHz by use of the WR-08 and WR-03 waveguides based photonic transmitter, respectively.
Our NBUTC-PD based photo-transmitters have a unique advantage over UTC-PD based photo-transmitters: An ultra-fast switching speed. This means that the photo- generated MMW power from the NBUTC-PD can be shut ‘on’ and ‘off’ very fast with a high extinction ratio,
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www.compoundsemiconductor.net March 2012
simply by switching the bias point. To realise this, we incorporate an additional input port, an intermediate- frequency input, into our device. We use this for injecting high-speed electrical data and for also modulating both the bias point and photo-generated MMW power of our novel photo-diode.
Our device can do more than just convert the incoming optical MMW envelope into electrical data: It can also up-convert incoming electrical data to the MMW regime. The entire device functions as an MMW mixer called the photonic-transmitter-mixer (see Figure 5). The superior modulation speed of our device stems from a combination of bias modulation in only the reverse bias regime, and a high extinction ratio MMW envelope, which predominantly originates from variations in electron drift-velocity in the collector layer under different reverse bias voltages.
However, in order to quench the photo-generated MMW power from the UTC-PD, it is necessary to push the device into near forward bias operation. This induces a
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