Graphene is an ideal 2D material system bridging electronic and photonic devices. It also breaks the fundamental speed and size limits by electronics and photonics, respectively. Graphene offers multiple functions of signal transmission, emission, modulation, and detection in a broad band, high speed, compact size, and low loss. Here, we have a brief view of graphene based functional devices at microwave, terahertz, and optical frequencies. Their fundamental physics and computational models were discussed as well.

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Graphene based functional devices: A short review

In this paper, we have presented the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz. THz electromagnetic wave can permit more densely packed communication links with increased security of communication transmission. The simulated results such as gain, radiation efficiency and 10 dB impedance bandwidth of rectangular microstrip patch antenna at THz frequencies without shorting post configuration are 3.497 dB, 55.71% and 17.76%, respectively, whereas with shorting post configuration, corresponding parameters are 3.502 dB, 55.88% and 17.27%. The simulation has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the method of finite difference time domain technique.

Rectangular Microstirp Patch Antenna Design at THz Frequency for Short Distance Wireless Communication Systems

Exceptional advancement has been made in the development of graphene optical nanoantennas. They are incorporated with optoelectronic devices for plasmonics application and have been an active research area across the globe. The interest in graphene plasmonic devices is driven by the different applications they have empowered, such as ultrafast nanodevices, photodetection, energy harvesting, biosensing, biomedical imaging and high-speed terahertz communications. In this article, the aim is to provide a detailed review of the essential explanation behind graphene nanoantennas experimental proofs for the developments of graphene-based plasmonics antennas, achieving enhanced light-matter interaction by exploiting graphene material conductivity and optical properties. First, the fundamental graphene nanoantennas and their tunable resonant behavior over THz frequencies are summarized. Furthermore, incorporating graphene-metal hybrid antennas with optoelectronic devices can prompt the acknowledgment of multi-platforms for photonics. More interestingly, various technical methods are critically studied for frequency tuning and active modulation of optical characteristics, through in situ modulations by applying an external electric field. Second, the various methods for radiation beam scanning and beam reconfigurability are discussed through reflectarray and leaky-wave graphene antennas. In particular, numerous graphene antenna photodetectors and graphene rectennas for energy harvesting are studied by giving a critical evaluation of antenna performances, enhanced photodetection, energy conversion efficiency and the significant problems that remain to be addressed. Finally, the potential developments in the synthesis of graphene material and technological methods involved in the fabrication of graphene-metal nanoantennas are discussed.

A Review on the Development of Tunable Graphene Nanoantennas for Terahertz Optoelectronic and Plasmonic Applications

The concept of dual-band reconfigurable terahertz patch antenna using a graphene-stack-defined backing cavity is presented. The proposed antenna employs patch resonance based on backing cavity defined by interleaved graphene/Al 2O3 stacks, which can be dynamically dual-resonance frequency-tuned on large range about 1 THz via electrostatic gating on the graphene stack. The performance is analyzed in terms of its directivity, sidelobe suppression, return loss, and bandwidth for different chemical potential. By applying different voltages on graphene stack, the direction of the antenna main beam can be steered with appreciable variation range.

Dual-Band Reconfigurable Terahertz Patch Antenna With Graphene-Stack-Based Backing Cavity

This paper proposes the novel concept of an optically invisible antenna built using photolithography that can be integrated in active display panels such as organic light emitting diodes and liquid crystal displays. Represented as antenna-on-display (AoD), this proposed approach is exemplified for future millimeter-wave (mmWave) 5G cellular devices. Empirical examinations confirm that the devised diamond-grid-shaped 2000 A-thick Ag-alloy electrodes on a glass substrate feature electrical loss characteristics of approximately 0.4 dB/mm at 28 GHz amid 88% optical transparency. Using the aforementioned material, a transparent diamond-grid antenna element is formulated and verified. Complete optical invisibility is achieved by implementing identical dummy grids around the antenna region. A multilayer schematic is designed in order to expand the antenna element into a phased-array configuration. The designed and fabricated $1 \times 8$ optically invisible AoD exhibits 6.66 dBi boresight gain at 28 GHz while maintaining 88% optical transparency. This gain includes 1.5 dB feedline loss and approximately 4 dB anisotropic conductive film (ACF) bonding loss. Current challenges include the immaturity of the ACF bonding process and the gain degradation caused by the dummy grids, and these need to be addressed to further improve the presented AoD concept. Nonetheless, this paper aims to serve as a foremost example for future optically invisible AoD.

An Optically Invisible Antenna-on-Display Concept for Millimeter-Wave 5G Cellular Devices

With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.

Analysis of graphene based optically transparent patch antenna for terahertz communications

Recent years, the design of photonic crystal (PC) based optical devices is receiving keen interest in research and scientific community In this paper, two dimensional (2D) PC based eight channel demultiplexer is proposed and designed and the functional characteristics of demultiplexer namely resonant wavelength, transmission efficiency, quality factor, spectral width, channel spacing and crosstalk are investigated The demultiplexer is designed to drop the wavelength centred at 15376 nm, 15385 nm, 15394 nm, 15404 nm, 15412 nm, 15419 nm, 15426 nm and 15431 nm The proposed demultiplexer is primarily composed of bus waveguide, drop waveguide and quasi square ring resonator The quasi square ring resonator and square ring micro cavity (inner rods) are playing a vital role for a desired channel selection The operating range of the devices is identified through a photonic band gap (PBG) which is obtained using a plane wave expansion (PWE) method The functional characteristics of the proposed demultiplexer are attained using a 2D finite difference time domain (FDTD) method The proposed device offers low crosstalk and high transmission efficiency with ultra-compact size, hence, it is highly desirable for DWDM applications

Performance analysis of an eight channel demultiplexer using a 2D-photonic crystal quasi square ring resonator

An indium-doped tin oxide (ITO) and a fluorine-doped tin oxide (FTO)-based optically transparent U-shaped patch antennas are designed to resonate at 750 GHz and their performances are analyzed. Impedance bandwidth, radiation efficiency, directivity and gain of the proposed antennas are investigated. The proposed transparent antenna׳s characteristics are compared with the copper-based non-transparent U-shaped patch antenna, which is also designed to resonate at 750 GHz. Terahertz antennas are essential for inter-satellite communications systems to enable the adequate spatial resolution, broad bandwidth, higher data rates and highly directional beam with secured data transfer. The proposed ITO- and FTO-based transparent antennas have yielded impedance bandwidth of 9.54% and 11.49%, respectively, in the band 719–791 GHz and 714–801 GHz, respectively. The peak gain for ITO and FTO based transparent antennas is 3.35 dB and 2.26 dB at 732 GHz and 801 GHz, respectively. The proposed antennas are designed and simulated by using a finite element method based electromagnetic solver, Ansys - HFSS.

Performance analysis and comparison of ITO- and FTO-based optically transparent terahertz U-shaped patch antennas

In this attempt, Two Dimensional Photonic Crystal (2DPC) Quasi Square Ring Resonator (QSRR) based four channel demultiplexer is proposed and designed for Wavelength Division Multiplexing systems. The performance parameters of the demultiplexer such as transmission efficiency, passband width, line spacing, Q factor and crosstalk are investigated. The proposed demultiplexer is composed of bus waveguide, drop waveguide and QSRR. In the proposed demultiplexer, the output ports are arranged separately in odd and even number, where an odd number of ports are located on the right side and even number of ports are located on the left side of the bus waveguide that are used to reduce the channel interference or crosstalk. Further, the refractive index of rods around the center rod is increased linearly one to another in order to improve the signal quality. The resonant wavelengths of the proposed demultiplexer are of 1521.1 nm, 1522.0 nm, 1523.2 nm and 1524.3 nm, respectively. The footprint of the device is of 180.96 μm2. Then, a four channel point to point network is designed and the proposed four channel demultiplexer is implemented by replacing a conventional demultiplexer. Finally, functional parameters of the network, namely, BER, receiver sensitivity and Q factor are estimated by varying the link distance. This attempt could create new dimensions of research in the domain of photonic networks.

Investigation of 2D-photonic crystal resonant cavity based WDM demultiplexer

A nano periodic two dimensional photonic crystal (2DPC) structure is proposed to design Ring Resonator based eight channels demultiplexer for wavelength division multiplexing applications. The proposed demultiplexer is composed of linear bus waveguide, modified quasi square ring resonator and L bend waveguide. The channel selection is done by altering the size of the ring resonator. The finite difference time domain and plane wave expansion methods are utilized to calculate the normalized transmission and photonic band gap of the structure. The proposed demultiplexer is dropped eight channels that are centred at 1606.8, 1608.8, 1610.4, 1612.4, 1613.9, 1615.9, 1617.7 and 1619.3 nm. The average transmission efficiency, Q factor, and line spacing are 90 %, 1960 and 1.8 nm, respectively. The miniaturized size of this device could be implemented effectively for photonic integrated circuits for dense wavelength division multiplexing applications.

Sriram Kumar Dhamodharan

Papers

Analysis of graphene based optically transparent patch antenna for terahertz communications

Performance analysis of an eight channel demultiplexer using a 2D-photonic crystal quasi square ring resonator

Performance analysis and comparison of ITO- and FTO-based optically transparent terahertz U-shaped patch antennas

Investigation of 2D-photonic crystal resonant cavity based WDM demultiplexer

Investigation on modified quasi-square PCRR based demultiplexer for WDM applications