Publication: Millimeter-wave and terahertz optical heterodyne photonic integrated circuits for high data rate wireless communications
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2016-03
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2016-05-09
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Abstract
The data rate of wireless communications systems has been increasing because of the new applications that today’s society are applying. The prospective data rate for wireless communications in the marketplace will be 100 Gbps within 10 years. Therefore, to enable such data rates the use of millimetre and terahertz (THz) waves, whose frequencies range from 100 GHz to 1 THz, for broadband wireless communications is very suitable and efficient. At frequencies above 100 GHz, GaAs and InP based devices and integrated circuits (ICs) have been key players in THz communications research, because of high cut-off and maximum frequencies of transistors.
In fact, the photonics-based transmitter has become more effective to achieve higher data rates of over 20 Gbps. This could be realized thanks to the availability of telecom-based high-frequency components such as lasers, modulators and photodiodes (O-E converters). The use of optical fiber cables enables us to distribute high-frequency RF signals over long distances, and makes the size of transmitter frontends compact and light. Regarding the photonics-based receiver, photodiode is the photonic component best suited to be a signal downconverter. It is used an enveloped detector, so an easy modulation format such as on-off keying shifting (OOK) can be used to recover the transmitted data.
Most common optical continuous wave (CW) signal generator is based on an optical heterodyning, using a dual-wavelength optical source. In this technique, two optical wavelengths λ1 and λ2 are mixed on a photodiode or a photoconductor to generate an electrical beat note with its frequency being determined by the difference of the two optical wavelengths. There are different solutions to implement the dual wavelength source. The most straightforward source involves combining the light from two independent different single-frequency semiconductor lasers.
The most straightforward approach to implement these signal generation schemes is to assemble the required discrete components. However, the optical fiber connections that are required introduce many problems, including path length variations due to thermal variations. A novel approach, that is becoming readily available nowadays, is to use photonic integration techniques. Photonic integration allows placing all of the required components onto a single chip. This has several advantages, starting from eliminating fiber coupling losses among the different components. Besides, a reduced size of the components gives a result a cost-effective solution.
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Wireless communications, Optical communications, Optoelectronics