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Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Organic terahertz (THz) crystals consist of polar molecules with various functional substituents, resulting in numerous molecular phonon vibrations in the THz frequency range. However, the effect of incorporating substituents into organic THz crystals on the resulting THz absorption is rather an unexplored area. In this work, by choosing an appropriate model system consisting of two benchmark organic nonlinear optical crystals, exhibiting an identical type of phenolic cation–anion assembly but different substituents, their ultra‐broadband THz wave generation characteristics are demonstrated and investigated. Compared to the unsubstituted crystals, the substituted crystals possess one more methoxy substituent on highly polar cationic chromophores. Their vibrational modes and THz absorption characteristics are investigated theoretically by periodic density functional theory and experimentally by ultra‐broadband THz spectroscopy up to 12 THz. In phenolic parallel‐type cation–anion assembled organic THz crystals, the existence of a methoxy substituent differently influences the molecular vibrations in low and high THz frequency ranges. In the lower THz frequency range, the unsubstituted crystals exhibit additional strong entire molecular vibrations, the so‐called cation‐on‐cation slipping vibrations, which do not exist in the substituted crystals. In contrast, the methoxy substituent leads to additional strong intramolecular vibrations in the higher THz frequency range. [ABSTRACT FROM AUTHOR]

In organic π‐conjugated crystals, enhancing molecular optical nonlinearity of chromophores (e.g., first hyperpolarizability β ≥ 300 × 10−30 esu) in most cases unfortunately results in zero macroscopic optical nonlinearity, which is a bottleneck in organic nonlinear optics. In this study, a new class of nonlinear optical organic crystals introducing a chromophore possessing an extremely large first hyperpolarizability is reported. With newly designed 4‐(4‐(4‐(hydroxymethyl)piperidin‐1‐yl)styryl)‐1‐(pyrimidin‐2‐yl)pyridin‐1‐ium (PMPR) chromophore, incorporating a head‐to‐tail cation‐anion OH⋯O hydrogen‐bonding synthon and an optimal selection of molecular anion into crystals results in extremely large macroscopic optical nonlinearity with effective first hyperpolarizability βiiieff$\beta _{{\rm{iii}}}^{{\rm{eff}}}$ of 335 × 10−30 esu. This is in sharp contrast to zero βiiieff$\beta _{{\rm{iii}}}^{{\rm{eff}}}$ value for previously reported analogous crystals. An ultrathin PMPR crystal with a thickness of ≈10 µm exhibits excellent terahertz (THz) wave generation performance. Both i) broadband THz wave generation with a wide flat‐spectral‐band in the range of 0.7–3.4 THz defined at −3 dB and high upper cut‐off generation frequency of > 7 THz as well as ii) high‐generation efficiency (5 times higher THz amplitude than ZnTe crystal with a mm‐scale thickness) are simultaneously achieved. Therefore, new PMPR crystals are highly promising materials for diverse applications in nonlinear optics and THz photonics. [ABSTRACT FROM AUTHOR]

Ultrafast nonlinear dynamics driven by high-peak-power ultrashort mid-infrared (mid-IR) pulses gives rise to ultrabroadband radiation whose spectrum spans over multiple decades, stretching from the terahertz (THz) to the microwave range. We show that, despite its enormous, multidecade bandwidth, an accurate spectral and spatial-mode characterization of this radiation is possible via a suitable combination of mutually complementary signal-analysis methods borrowed from ultrafast optics, radioelectronics, THz photonics, and microwave engineering. This analysis reveals intense subgigahertz radiation emitted as a part of mid-IR-driven supercontinuum generation and shows that microwave-to-THz field waveforms can almost reach the diffraction limit in their beam focusability, yielding field strengths above 3 MV/cm. [ABSTRACT FROM AUTHOR]

Newly designed halogenated organic quinolinium crystals proposed in this work provide fully optimized molecular ordering for maximizing the optical nonlinearity and high‐performance broadband terahertz (THz) wave generation. The ultralarge diagonal optical nonlinearity (almost 300 × 10−30 esu) of the new halogenated crystals is approximately two times larger than that of state‐of‐the‐art pyridinium‐based crystals. In contrast, nonhalogenated analogous crystals exhibit very low (or vanishing) diagonal optical nonlinearity. This is attributed to halogen‐induced unique interionic interactions and fine‐tuning of the space‐filling characteristics. In addition, the halogenated crystals show a good ability for bulk crystal growth of few millimeters lateral size with plate‐like morphology and high thermal stability that are finally required for real‐world applications. The new halogenated quinolinium crystals exhibit excellent THz wave generation characteristics, significantly surpassing the limit of conversion efficiency and spectral bandwidth of inorganic benchmark crystals. A 0.16 mm thick chlorinated crystal generates a 29‐times larger THz field than 1.0 mm thick inorganic ZnTe crystals at 1500 nm pump wavelength with a flat and broadband spectrum extending up to ≈8 THz. Therefore, introducing halogen substituents is a potential design strategy for designing new organic crystals showing ultralarge macroscopic hyperpolarizability and high‐performance THz wave generation. [ABSTRACT FROM AUTHOR]

Organic nonlinear optical salt crystals are widely used as efficient broadband THz generators. Although solid state molecular motions of organic crystals can greatly influence THz generation characteristics, their origin and effects on THz photonics are not clearly identified. In this work, the origin of solid‐state molecular motions of the state‐of‐the‐art nonlinear optical organic salt crystals and their effects on THz generation characteristics are theoretically investigated. A model crystal, HMQ‐TMS (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 2,4,6‐trimethylbenzenesulfonate) with large macroscopic optical nonlinearity, which is very attractive for intense broadband and narrowband THz wave generation, is chosen. The solid‐state molecular vibrations of HMQ‐TMS crystals can be classified in three frequency regions: phonon mode region, intramolecular motion region, and their mixing region. For the first time for ionic organic crystalline THz generators, the contributions of cationic chromophores and anionic matchmakers on each of vibrational modes are quantitatively separated. In addition, the influence of solid‐state molecular vibrations of HMQ‐TMS crystals on the generated THz spectra is investigated. These results provide an essential information for design of new organic nonlinear optical salt crystals for THz generators as well as detectors and for optimization of THz generation performance. [ABSTRACT FROM AUTHOR]

A microwave photonic system based on a silicon add‐drop microring resonator is proposed and analyzed in simulation environment. It is observed that when a pulsed laser source (PLS) of repetition rate of 100 Gbps is fed to input port of MRR and a PLS with repetition rate of 50 Gbps is fed at the add port of the MRR, THz signals in the frequency band of 0.1‐1.5 THz are generated with a spacing of 0.05 THz. The power of the highest frequency component (1.5 THz) is ‐65.1 dBm when the pulse width of PLS is 0.1 ps. This generation of THz signals is a result of interference between two optical signals of different repetition rates which are evanescently coupled into the ring cavity at the input ports of MRR. It is found that power of THz signal is higher when the pulse width of PLS is smaller. [ABSTRACT FROM AUTHOR]

In this letter, we propose and experimentally demonstrate photonic generation and de-chirp processing of terahertz (THz) linear-frequency-modulated (LFM) signals using coherent photonic super-heterodyne based on frequency quadrupling and photo mixing. In the experiment, a 340–380-GHz LFM signal with 40-GHz bandwidth is successfully generated with a temporal period of $1\,\,\mu \text{s}$. As a result, a range resolution of 5 mm is successfully enabled, which is close to the theoretical limit. Benefited from photonic de-chirp processing, the requirements of receiving instantaneous bandwidth and sampling rate are reduced. Moreover, the proposed scheme features high stability, and the measured performance of the system has not deteriorated within 2 hours in the experiment. Therefore, our proposed system has a great potential in THz ranging and imaging applications. [ABSTRACT FROM AUTHOR]

In this letter, we propose and experimentally demonstrate an ultrahigh resolution terahertz (THz) range sensing system by digitally synthesizing multiple-band linear frequency-modulated (LFM) pulses. In the experiment, two-band LFM pulses with 20-GHz bandwidth in the THz band are photonically generated based on frequency-to-time mapping, resulting in a synthetic LFM signal with 40-GHz bandwidth operating within the 315–360 GHz. As a benefit, a range resolution as high as 3.9 mm over more than 2 m is successfully achieved in multi-target ranging. The proposed technology not only releases the requirements for instantaneous bandwidth and sampling rate but also breaks the bandwidth limitation of THz receiver in enabling ultrahigh resolution in the THz region. [ABSTRACT FROM AUTHOR]

Multifunctional convergence is one of the key physical features in future generation networks and Internet of things architectures. In this paper, we propose and experimentally demonstrate a unified terahertz (THz) system operating in the 300 GHz band, with a potential of simultaneously enabling high-speed communication and high-resolution ranging over a common optical infrastructure. Both THz communication and THz sensing signals are generated based on THz photonics and cutting-edge terahertz transceiver technologies. In the experiment, 16-quadrature amplitude modulation modulated THz signal is generated by photo-mixing two free running lasers for the communication, and linear frequency modulated (LFM) THz pulses are generated based on optical interferometer-based frequency-to-time mapping (FTM) for sensing. The experimental results show that up to 56 Gbit/s net rate is successfully transmitted over a 2 m free-space line-of-sight link, and the THz LFM pulses with a time-bandwidth product of up to 207 are successfully generated, which is potentially able to enable a cm-scale range resolution. We also investigate the frequency multiplexing schemes for two signals by changing the channel gap at the transmitter side. To the best of our knowledge, such a system represents the first demonstration of integrated generation system in the THz region above 300 GHz, which has great potential in prospective applications of future converged networks. [ABSTRACT FROM AUTHOR]

In this letter, we experimentally demonstrate terahertz (THz) photonic wireless transmission of high-speed quadrature-phase-shift-keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) signals in the 350-GHz band, with an effort to extend the wireless reach of ultrafast 100 Gbit/s. In the experiment, a narrowband unitraveling-carrier photodiode (UTC-PD) is used for heterodyne generation of THz communication signals, which is transparent to optical modulation formats. Experimental results show that 30 GBd/s QPSK (60 Gbit/s) and 25 GBd/s 16-QAM signals (100 Gbit/s) are successfully transmitted over a 350-GHz wireless link with an extended distance of 2 m. This enhancement is enabled by combining the techniques of employing cutting-edge narrowband UTC-PD as the photomixing THz emitter, spectrally efficient modulation format and advanced digital signal processing algorithms. The achievement makes 100 Gbit/s THz wireless communication systems promising for future smart wireless services. [ABSTRACT FROM AUTHOR]

A photonic multi-channel terahertz (THz) wireless transmission system in the 350–475 GHz band is experimentally demonstrated. The employment of six THz carriers modulated with 10 Gbaud Nyquist quadrature phase-shift keying baseband signal per carrier results in an overall capacity of up to 120 Gb/s. The THz carriers with high-frequency stability and low phase noise are generated based on photonic photomixing of 25-GHz spaced six optical tones and a single optical local oscillator derived from a same optical frequency comb in an ultra-broadband uni-travelling carrier photodiode. The bit-error-rate performance below the hard decision forward error correction threshold of 3.8\times 10^\mathrm \mathbf -3 for all the channels is successfully achieved after wireless delivery. Furthermore, we also investigate the influence of the harmonic spurs in a THz receiver on the performance of transmission system, and the experimental results suggest more than 30 dB spur suppression ratio in downconverted intermediate frequency signals for obtaining less than 1 dB interference. [ABSTRACT FROM PUBLISHER]

With the mass development of mobile data transfers, wireless communications have recently entered a new area: the carrier frequency is now entering the THz region. After a brief overview of context and key features of THz communication, focus is given on photonic-based THz emitters based on quasi-optic UTC-PDs. A special design of wideband photomixer is presented and its applications for narrow bandwidth THz generation. Using this photomixer, communication links at 200, 400 and 600 GHz are presented. [ABSTRACT FROM AUTHOR]

This paper introduces a novel family of devices for ultra-fast, ultra-sensitive and ultra-low-noise optoelectronics, namely superconductive traveling-wave photodetectors (STWPDs). STWPDs can be optimized for ultra-wideband/ultra-sensitive photodetection, photomixing and microwave/THz waveform generation. An STWPD is a distributed device, both electrically and optically, which consists of a superconductive thin film kinetic-inductive photodetector integrated with a microwave/THz transmission line and an optical waveguide. We will present the principles of operation of STWPDs, a framework to calculate the input-output relation and the effects of the modal characteristics of the optical propagation on the device performance. Moreover, we will elaborate on how one can design an STWPD for each of the aforementioned applications. Different strategies for the design of the optical waveguide as well as some important design rules will also be discussed. We will report the current status of STWPDs and point out some key issues that should be met in the future for further development. [ABSTRACT FROM AUTHOR]

A 2-D photonic crystal waveguide with strong passbands in the THz frequency range is demonstrated. The 2-D metallic photonic crystal waveguide structure is bounded by parallel metal plates in the vertical direction and by a square lattice of metallized cylinders on the horizontal axis. The attenuation of the photonic crystal waveguide is experimentally determined and compared to the fundamental mode of a comparably sized rectangular waveguide. The measured dispersion characteristics of the waveguide are discussed, and the output is compared to a finite-difference time-domain simulation. [ABSTRACT FROM PUBLISHER]