Spoof Surface Plasmon Polariton Based THz Circuitry

Terahertz, abbreviated as THz, is defined as the frequency band spanning from 300 GHz to 10 THz, which is located between the microwave from the electronic side of the electromagnetic (EM) spectrum to mid-Infra-Red on the photonic side of the EM spectrum. As accelerated research and innovations over the past seven decades have resulted in widespread commercialization of both electronic and photonic components, THz band has remained underdeveloped, underexploited, and mostly unallocated by the Federal Communications Commission (FCC). Though certain definitive merits of EM waves at THz have evoked interests of physicists, chemists, biologists and material scientists to deploy THz in Time-Domain Spectroscopy (TDS), bio-sensing, and classical imaging applications, the field of THz circuits (also known as THz electronics) has continued to remain in embryonic stage due to the speed limitations of conventional Silicon and compound semiconductor devices like Field Effect Transistors (FETs), Hetero-junction Bipolar Transistors (HBTs), and Hot Electron Mobility Transistors (HEMTs). On the other hand, conventional photonic devices cannot be readily adopted to design new THz circuits and systems. Our research vision in THz circuits and systems is to study the meta-material properties of THz in various forms of sub-wavelength structures and exploit those unique properties to invent the designs of large THz systems like the THz switch, Analog-to-Digital Converter (ADC), etc. The potential large bandwidth and high propagation speed helps photonic circuitry to be proposed against the above-mentioned challenges faced by its electronic counterpart. Optical-assisted as well as all-optical systems in various forms have been reported to realize different data-processing functionalities. For example, analog-to-digital converters (ADC) with the potential of high speed operation have been demonstrated by optical-assisted or all-optical approaches. Photonic logic has also been reported in numerous works by coding the Boolean information in the amplitude, phase or wavelength of the optical signals. Despite these efforts, however, the key element to address the fundamental deficiencies of CMOS circuit remained missing. The use of optical frequencies in these works brought about common shortcomings including dimension mismatch, lack of coherent detection, inflexibility, susceptibility to mechanical and environmental variations, and the presence of bulky optical elements (i.e., mirrors, beam splitters, lenses, etc.). More seriously, these works inherited sequential circuit designs directly from CMOS. It indicates that the cumulative delay still dominated the speed performance, which prevented further decrease of the circuit latency. In light of these problems, we foresee the implementation of THz circuitry as the next reasonable step to take in designing high-speed analog as well as digital circuits. Spoofed Surface Plasmon Polariton (SSPP) is known as a pseudo-surface mode in THz frequencies that mimics the slow wave nature and localized E-M field distribution of the plasmon mode typically observed in optical domain. By introducing periodic corrugations on the surfaces of a metal-dielectric-metal structure, SSPP mode is realized for propagating THz signal, and its mode dispersion is strongly dependent on the geometric dimensions as well as the material properties of the architecture. Recently propagation of THz wave utilizing Spoof surface plasmon polariton (SSPP) earned a great deal of attention due to the ability of SSPP modes to guide THz waves at very low dispersion. In this research, we exploit and investigate the SSPP modes in different periodic structure and utilizing them in different structure to introduce new THz devices, such as, polarization rotator, THz switch, ADC, etc.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144105/1/mahdia_1.pd

Fully-photonic digital radio over fibre for future super-broadband access network applications

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityIn this thesis a Fully-Photonic DRoF (FP-DRoF) system is proposed for deploying of future super-broadband access networks. Digital Radio over Fibre (DRoF) is more independent of the fibre network impairments and the length of fibre than the ARoF link. In order for fully optical deployment of the signal conversion techniques in the FP-DRoF architecture, two key components an Analogue-to-Digital Converter (ADC) and a Digital-to-Analogue Converter (DAC)) for data conversion are designed and their performance are investigated whereas the physical functionality is evaluated. The system simulation results of the proposed pipelined Photonic ADC (PADC) show that the PADC has 10 GHz bandwidth around 60 GHz of sampling rate. Furthermore, by changing the bandwidth of the optical bandpass filter, switching to another band of sampling frequency provides optimised performance condition of the PADC. The PADC has low changes on the Effective Number of Bit (ENOB) response versus analogue RF input from 1 GHz up to 22 GHz for 60 GHz sampling frequency. The proposed 8-Bit pipelined PADC performance in terms of ENOB is evaluated at 60 Gigasample/s which is about 4.1. Recently, different methods have been reported by researchers to implement Photonic DACs (PDACs), but their aim was to convert digital electrical signals to the corresponding analogue signal by assisting the optical techniques. In this thesis, a Binary Weighted PDAC (BW-PDAC) is proposed. In this BW-PDAC, optical digital signals are fully optically converted to an analogue signal. The spurious free dynamic range at the output of the PDAC in a back-to-back deployment of the PADC and the PDAC was 26.6 dBc. For further improvement in the system performance, a 3R (Retiming, Reshaping and Reamplifying) regeneration system is proposed in this thesis. Simulation results show that for an ultrashort RZ pulse with a 5% duty cycle at 65 Gbit/s using the proposed 3R regeneration system on a link reduces rms timing jitter by 90% while the regenerated pulse eye opening height is improved by 65%. Finally, in this thesis the proposed FP-DRoF functionality is evaluated whereas its performance is investigated through a dedicated and shared fibre links. The simulation results show (in the case of low level signal to noise ratio, in comparison with ARoF through a dedicated fibre link) that the FP-DRoF has better BER performance than the ARoF in the order of 10-20. Furthermore, in order to realize a BER about 10-25 for the ARoF, the power penalty is about 4 dBm higher than the FP-DRoF link. The simulation results demonstrate that by considering 0.2 dB/km attenuation of a standard single mode fibre, the dedicated fibre length for the FP-DRoF link can be increased to about 20 km more than the ARoF link. Moreover, for performance assessment of the proposed FP-DRoF in a shared fibre link, the BER of the FP-DRoF link is about 10-10 magnitude less than the ARoF link for -19 dBm launched power into the fibre and the power penalty of the ARoF system is 10 dBm more than the FP-DRoF link. It is significant to increase the fibre link’s length of the FP-DRoF access network using common infrastructure. In addition, the simulation results are demonstrated that the FP-DRoF with non-uniform Wavelength Division Multiplexing (WDM) is more robust against four wave mixing impairment than the conventional WDM technique with uniform wavelength allocation and has better performance in terms of BER. It is clearly verified that the lunched power penalty at CS for DRoF link with uniform WDM techniques is about 2 dB higher than non-uniform WDM technique. Furthermore, uniform WDM method requires more bandwidth than non-uniform scheme which depends on the total number of channels and channels spacing

Terahertz (THz) Waveguiding Architecture Featuring Doubly-Corrugated Spoofed Surface Plasmon Polariton (DC-SSPP): Theory and Applications in Micro-Electronics and Sensing

Terahertz (10^12 Hz) has long been considered a missing link between microwave and optical IR spectra. This frequency range has attracted enormous research attentions in recent years, with ever-growing anticipation for its applications in remote sensing, molecular spectroscopy, signal processing and next-generation high-speed electronics. However, its development has been seriously hindered by the lack of waveguiding and manipulating architectures that could support the propagation of THz radiations without excessive signal distortion and power loss. Facing this challenge, this work exploits the spoofed surface plasmon polariton (SSPP) mode of the THz oscillation and introduces the doubly corrugated SSPP (DC-SSPP) architecture to support sub-wavelength, low-dispersion THz transmission. DC-SSPP displays unique bandgap structure, which can be effectively modulated via structural and material variables. These unequaled properties make DC-SSPP the ideal solution to support not only signal transmission but also THz sensing and THz-electronics applications. In this thesis, theoretical analysis is carried out to thoroughly characterize the THz propagation, field distribution and transmission band structures in the novel architecture. Via numerical approximation and finite element simulations, design variations of the DC-SSPP are further studied and optimized to fulfill application-specific requirements. We demonstrate effective DNA sensing by adopting the Mach-Zehnder interferometer (MZI) or waveguide-cavity-waveguide insertions, which showed detectability with minuscule sample size even in the aqueous environment. We manifest high-speed analog-to-digital conversion via a combination of MZI DC-SSPP with nonlinear, partial-coupling detector arrays. Full characterization of the proposed ADC is carried out where high operation speed, small signal distortion, and great output linearity is shown. Also included in this work is a detailed review of the THz emitters and detectors, which are indispensable constituents of the THz system discussed herein. The future of the DC-SSPP in building THz bio-computing and THz digital circuits, considered as the next step of this research work, is also explored and demonstrated with the novel concept of directed logic network.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137130/1/xuzhao_1.pd