Considerable
luminescence dissymmetry factor (g
lum)
is vital for application implementation of circularly
polarized luminescence (CPL) materials. Moreover, a dual CPL switch
has promising prospects in high-security encryption and sensor devices.
Herein, we designed and synthesized an emissive chiral nematic liquid
crystal (N*-LC) by doping a luminescent chiral additive (NO2-CS-C6-Chol) into a nematic liquid crystal (5CB). The
helical assembly structure produced by inducing the formation of N*-LC
endows the prepared emissive N*-LC with a larger g
lum value. With the increase of the doping concentration
from 1 to 10 wt %, the helical pitch (P) of N*-LC
gradually decreases from 25.48 to 3.92 μm. The corresponding g
lum value increases first, reaches the maximum
value (−0.38) at 6 wt %, and then decreases slightly. Further,
the prepared emissive N*-LC doped with 6 wt % NO2-CS-C6-Chol is injected into an indium-tin oxide (ITO)-coated LC
cell, to which a direct current (DC) electric field is applied. The g
lum value can be repeatedly shuttled between
the “on” and “off” state by adjusting
the applied voltage. Meanwhile, owing to the inherent thermal dependence
of the liquid crystal phase structure, the g
lum value can also be switched between the on and off state
by regulating the temperature. Therefore, an electrically controlled
and thermocontrolled dual CPL switching device is successfully constructed.
How to improve the performance of circularly polarized luminescence (CPL) materials in film state is a significant subject to realize its further application. Herein, we synthesized the side-chain chiral fluorescent...
Triple stimuli-responsive circularly polarized luminescent materials with large glum values and high fluorescence quantum yields were successfully prepared.
For mobile THz applications, integrated beam steering THz transmitters are essential. Beam steering approaches using leaky-wave antennas (LWAs) are attractive in that regard since they do not require complex feeding control circuits and beam steering is simply accomplished by sweeping the operating frequency. To date, only a few THz LWAs have been reported. These LWAs are based on polymer or graphene substrates and thus it is quite impossible to monolithically integrate these antennas with state-of-the-art indium phosphide (InP) based photonic or electronic THz sources and receivers. Therefore, in this paper, we report on an InP-based THz LWA for the first time. The developed and fabricated THz LWA consists of a periodic leaking microstrip line integrated with a grounded coplanar waveguide to microstrip line (GCPW-MSL) transition for future integration with InP-based photodiodes. For fabrication, a substrate-transfer process using silicon as carrier substrate for a 50 µm thin InP THz antenna chip has been established. By changing the operating frequency from 230 GHz to 330 GHz, the fabricated antenna allows to sweep the beam direction quasilinearly from-46° to 42°, i.e. the total scanning angle is 88°. The measured average realized gain and 3 dB beam width of a 1.5 mm wide InP LWA are ~11 dBi and 10°. This paper furthermore discusses the use of the fabricated LWA for THz interconnects. Index Terms-Beam steering, indium phosphide, leaky wave antenna, monolithic integrated circuits, wafer bonding. I. INTRODUCTION ERAHERTZ (THZ) waves feature distinct advantages compared to its neighboring spectra, making this frequency spectrum (0.1-10 THz) very attractive for several applications. THz waves are far less energetic than X-rays, i.e. they are nonionizing for biological tissues and, consequently, are promising for several medical applications [1-4]. Benefiting from the shorter wavelength in contrast to microwaves, THz waves offer a much higher spatial resolution which makes them quite intriguing for high-resolution imaging applications [5, 6]. Beyond the high spatial resolution, most dry dielectric materials are transparent for THz waves, whereas materials with high
THz communications is envisaged for wide bandwidth mobile communications eventually reaching data capacities exceeding 100 Gbit/s. The technology enabling compact chip-integrated transceivers with highly directive, steerable antennas is the key challenge at THz frequencies to overcome the very high free-space path losses and to support user mobility. In this article, we report on mobile and multi-user THz communications using a photonic THz transmitter chip featuring 1D beam steering for the first time. In the proposed approach, 1D THz beam steering is achieved by using a photodiode excited leaky-wave antenna (LWA) in the transmitter chip. The on-chip LWA allows to steer the directive THz beam from 6° to 39° within the upper WR3-band (0.28-0.33 THz). The antenna’s directivity is 14 dBi which is further increased to 23 dBi using an additional hemicylindrical Teflon lens. The 3-dB beam width and coherence bandwidth of the fabricated THz transmitter chips with lens are 9° and 12 GHz, respectively. The proposed approach allows steering the THz beam via the beat frequency of an optical heterodyne system at a speed up to 28°/s. Without using a THz amplifier in the transmitter chip, a data rate of 24 Gbit/s is achieved for a single user for all beam directions and at short wireless distances up to 6 cm. The wireless distance is successfully increased to 32 cm for a lower data rate of 4 Gbit/s, still without using a transmitter amplifier. Also, multi-user THz communications and the overall capacity of the developed THz transmitter chip is studied revealing that up to 12 users could be supported together with a total wireless data capacity of 48 Gbit/s. Fully integrated 2D transmitter chips are expected to reach wireless distances of several meters without additional amplifiers.
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