What does photonic mean

Microwave phototonics

Microwave photonics is an interdisciplinary area investigating the interaction between microwave signals and optical signals. Important points are the generation, the distribution and the processing of millimeter wave signals by means of photonics. The advantages of fiber (high bandwidth and low attenuation) are combined with those of electronic modules creating innovative solutions.
In communications, microwave photonics can be implemented in various applications from the antenna unit to the in house or distribution network: For example in Radio-over-Fiber systems and attached photonic steerable antennas that emit millimeter wave signals.

Radio over fiber
Radio-over-fiber systems are fiber optical solutions in the access network distributing radio signals. To lower capital expenditures (CAPEX) and operational expenditures (OPEX) cost-intensive equipment is shared in the central office (CO) for different base stations (BS). In the most simple case, they are implemented as remote antenna units (RAU) emitting just the radio signals generated in the CO and sending the received signals back there.
With increasing bandwidth demand the requirements to the fiber as transmission medium increase as well. Impairments such as nonlinearities and distortions like chromatic dispersion or polarization mode dispersion can no longer be ignored especially in the metro network and have to be equalized.
Synergies are used by the joint development of radio-over-fiber and radio front ends. Trend-setting system concepts can be realized.

Photonic steerable antennas
Photonic steerable antennas feature the optical feeding of the antenna elements and the opto-electrical conversion directly before emitting. The use of optical waveguides increases the electromagnetic compatibility of the feeding network. At the same time, the generation of the signals can be delocalized from the place of radiation because of the low attenuation of optical transmission.
One advantage of optical feeding networks is the practicability of extremely broadband phase shifters. Only in optics, true time delay techniques are easily available.

RF generation
The efficient generation of RF carriers up to the THz range is one base technology for various applications: Modern radio systems in the 60 GHz badn, radio-over-fiber access networks, RADAR and THz techologies demand stable low noise RF signals.
The generation of such RF carriers with frequencies of more than 10 GHz is a technological challenge. Different approaches may be followed: The use of electronic oscillators with and without frequency multiplication is one possibility. This direct generation of the frequency has to be performed at its place of operation and requires special cost-intensive circuits. For semiconductors, the power dissipation increases with the frequency reducing the energy efficiency of this approach.
Optical RF generation with lower electrical reference frequencies if required increases the electromagnetic compatibility (EMC) of the frequency generating circuit. The possibilities in the system design are expanded by using optical interconnects and delocalizing the frequency generator and the radio signal emission. The opto-electric conversion is performed by a photodiode that limits the maximum frequency in the system.

Electro magnetic modeling and characterization of photonic structures
Photonic structures (wave guides, couplers, gratings etc.) can be used for information transmission and processing. For example, microwave photonic systems can be integrated. Another possibility is the analysis of the transfer function depending on the environmental conditions for sensor applications. Here, bio sensors evaluating the change of the refractive index of the surrounding medium are focused.
The modeling is performed using analytical methods as well as numerical FDTD approaches.

Future topics
Further applications can be found in THz techniques and in innovative RADAR concepts using optical as well as electrical signals.