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Historical perspective of free space optical communications: from the early dates to today's developments
摘要： This survey article discusses the revolutions of wireless communication technologies right from the prehistoric man's fire signals to today's space optical communications. A brief description of evaluations of communication technologies from the ancient Greece to today's mature telecommunication fields is discussed in this review paper. Principle, significance, demonstration and development of free space optical (FSO) communication technology over different decades are discussed. Major FSO channel limitations, temporal and spatial challenges of FSO communication system and their state-of-art mitigation techniques are presented. Classical quantitative analysis of reliability of FSO communication, developments on radio over FSO (RoFSO) and hybrid FSO/RF systems are also explained. Advanced developments of FSO communication techniques such as optical free space wavelength division multiplexing (WDM), sub-carrier multiplexing (SCM), worldwide interoperability for microwave access (WiMAX), visible light communications (VLC) and vehicular visible light communications (VVLC) are reported. Deep space optical communication systems and next generation FSO wireless terrestrial/global network architecture are summarised. Research challenges of FSO systems for internet of things/everything (IoT/IoE), 5G communication, mobile-network, terahertz spectrum, quantum communication and underwater optical applications are presented. Based on the review, we outlined the challenges that need to be addressed in near-future researches to realize full potential FSO communication systems.
关键词： quantum communication,RoFSO,SCM,FSO,IoT/IoE,5G,WDM,underwater optical applications,VVLC,free space optical communications,VLC,WiMAX
更新于2025-09-19 17:13:59
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Composite GaN-C-Ga (‘GaCN’) Layers with Tuneable Refractive Index
摘要： This article describes novel composite thin films consisting of GaN, C and Ga (referred to as ‘GaCN’, as an analogue to BCN and other carbonitrides) as a prospective material for future optical applications. This is due to their tuneable refractive index that depends on the carbon content. The composites are prepared by introducing alternating pulses of trimethylgallium (TMG) and ammonia (NH3) on silicon substrates to mimic an atomic layer deposition process. Since the GaCN material is hardly reported to the best of our knowledge, a comprehensive characterization is performed to investigate into its chemical nature, primarily to determine whether or not it exists as a single-phase material. It is revealed that GaCN is a composite, consisting of phase-segregated, nano-scale clusters of wurtzitic GaN polycrystals, in addition to inclusions of carbon, nitrogen and gallium, which are chemically bonded into several forms, but not belonging to the GaN crystals itself. By varying the deposition temperature between 400 and 600 oC, and the NH3 partial pressure between 0.7×10-3 and 7.25 mbar, layers with a wide compositional range of Ga, C and N are prepared.
关键词： composite thin films,atomic layer deposition,optical applications,GaCN,tuneable refractive index
更新于2025-09-09 09:28:46
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Epitaxial ferroelectric oxide thin films for optical applications
摘要： Ferroelectrics are non-centrosymmetric crystalline materials that possess a spontaneous polarization that can be switched by an electric field. The electric-field-dependent optical response of these materials makes them important for optical devices, such as modulators or beam deflectors. In the inexorable drive to miniaturization, the concept of integrated thin film optical devices has led to the incorporation of ferroelectric thin films on single-crystal substrates. These structures have appealing electro-optic modulation characteristics, interesting strain-dependent bandgaps and refractive index, as well as promising possibilities for solar harvesting. Here, we review the work on epitaxial ferroelectric (FE) films for optical applications. We first show that FE thin film materials are attractive for integrated electro-optic modulators and then show that epitaxial strain can be used to enhance the FE and optical functionality of films. Next, we describe some of the photovoltaic functionality of FE thin film materials’ systems and conclude the review by highlighting some thin-film devices that exploit the aforementioned optical effects.
关键词： epitaxial strain,electro-optic modulators,thin films,photovoltaic,optical applications,ferroelectric
更新于2025-09-09 09:28:46
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Tunable Direct Semiconductor Gap and High Carrier Mobility of Mo <sub/>6</sub> Br <sub/>6</sub> S <sub/>3</sub> Monolayer
摘要： Two-dimensional materials with direct semiconductor gaps and high mobilities can play an important role in future electronic and optical applications. Here we propose that Mo6Br6S3 monolayer as a new two-dimensional material is stable and can be exfoliated from corresponding layered bulk. Our first-principles results show that the monolayer has a direct semiconductor gap beyond 1 eV (between PBE and HSE values) and a very high electron mobility (6880 cm2V?1s?1), and these can be tuned through in-plane strain by applying uniaxial stress. Furthermore, we show that the Mo6Br6S3/graphene heterostructure makes a p-type Schottky barrier and the amplitude of band bending (0.03 eV) is extremely low compared to other similar junctions because the Mo6Br6S3 monolayer has a close work function to graphene. With all these useful properties and functions, the Mo6Br6S3 monolayer can be very promising for nanoelectronic and optical applications.
关键词： Mo6Br6S3 monolayer,p-type Schottky barrier,optical applications,Two-dimensional materials,electron mobility,high mobilities,first-principles,direct semiconductor gaps,nanoelectronic
更新于2025-09-04 15:30:14