Silicon photonic (SiPho) platforms hold vast potential for providing multi-functional processing capabilities, such as filtering, mode-handling, modulation, etc. Structures for polarization manipulation have become essential elements to enhance channel capacity and to facilitate polarization multiplexing functions. Therefore, 1x2 polarization beam splitters (PBS) are introduced as polarization-division key building blocks based on a silicon-on-insulator (SOI) platform for separating/combining the fundamental modes. By cascading three bent directional couplers (DC), high-performance coupling characteristics can be obtained similar to those of asymmetric ones. A first-ever integration of this kind of PBS has been achieved utilizing Tower Semiconductor's PH18MA silicon photonics platform, which offers 180 nm SOI process technology. In this work, both output ports of the proposed PBS are being tested for polarization filtering across a polarization sweep. The advanced features of this integration process pave the way for next-generation coherent transceivers and aim to meet future optical interconnecting requirements. Furthermore, Synopsys OptoCompiler and the Photonic IC Design Flow, featured in Tower’s process design kit (PDK), were used to design the devices.
This paper evaluates experimentally a centralized radio access network (C-RAN) based on multi-core fiber (MCF) for the transmission of high-bandwidth signals in the sub-THz band. We compare the system performance when the data and carrier wavelengths to be mixed at the receiver for optical heterodyning are transmitted over the same or over different cores of a MCF link. Full-duplex transmission on MCF is evaluated using the same received wireless signal downconverted and transmitted back as uplink over the same carrier wavelength. The performance with different digital signal processing (DSP) configurations and with higher-power interference in the other cores are also analyzed in this work. Successful provision of 12.5 GBd 16QAM signals is achieved after 1-km of 7-core MCF transmission including a short wireless link at 182 GHz, obtained with optical heterodyning. C-RAN implementation with MCF simplifies the remote nodes as all the lasers can be located in the central office, while minimizing the number of lasers needed at the central office thanks to wavelength re-use. It also provides more flexibility to the system, as it enables using the same LO for different purposes (i.e. THz generation of other data or optical modulation for uplink transmission).
In this paper we present two different techniques for photonic generation of millimeter and THz waves. Each of them tackles the phase noise problem associated with optical sources in a different way. The first one relays on the heterodyne down-conversion of two phase noise correlated optical tones. The correlation is achieved by generation of an optical frequency comb. To select one of the optical lines we use an optical phase lock loop, which besides enabling a frequency offset between output and input, can provide optical gain and is highly selective. The second one relays on the envelope detection of a single sideband-with carrier signal. In this approach the photonic remote antenna unit is implemented as monolithically integrated photonic chip.
KEYWORDS: Terahertz radiation, Wireless communications, Heterodyning, Digital signal processing, Modulation, Receivers, Signal processing, Antennas, Optical amplifiers, Signal generators
Terahertz wireless communication is receiving great interest from researchers and industries, thanks to the new spectral windows between 0.1 and 1 THz offering opportunities for ultra-high-data-rate wireless transmission. Wavelength division multiplexing for wireless-over-fiber is foreseen as an enabling technique to support connection between base stations and a central station. This paper reviews architectures for photonic distribution and generation of multiband signals for sub- THz wireless communications, giving rates up to 100 Gb/s (20 Gb/s per band) using the full spectrum between 220 GHz and 280 GHz for downlink wireless transmission, and 10 Gb/s for uplink using on-off keying.
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