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ABSTRACT The next generation of communication networks is envisioned to be driven by high‐altitude platform (HAP)‐to‐satellite systems. License‐free narrow beam free space optics (FSO) can provide uninterrupted connectivity in satellite‐enabled Internet of Things scenarios. This work proposes a HAP‐to‐satellite hybrid mode division multiplexing–optical code division multiple access (MDM‐OCDMA) scheme employing zero cross‐correlation (ZCC) and multidiagonal (MD) codes. In high‐speed satellite communications, a 12 × 10‐Gbps hybrid MDM‐OCDMA scheme carrying four donut modes (0, 1, 2, and 3) enables high channel capacity, sufficient spectral efficiency, and data security under severe link conditions. Based on simulations, the hybrid MDM‐OCDMA scheme using the ZCC code achieves a greater FSO link distance of 420 m compared with when using the MD code at a 10e‐9 error correction limit under clear air and weak turbulent scenario. The reliable transmission distance of 250 m is achievable with the 120‐Gbps proposed system, assuming pointing errors of 2 mrad, 1‐dB receiver, and 2.5‐dB transmitter losses. The results also show that the system can sustain an additional loss of 1.5–2 dB over 250 m for all donut modes. Additionally, the system using ZCC code contributes to low power consumption over MD and variable weight ZCC code and thus requires a minimum received power of −4.02 dBm. It also offers high optical signal to noise of 42–52 dB, −11.58 to −22.20 dB of gain, 11.58–22.20 dB of noise figure, and −48.11 to −58.73 dBm of signal power at output over 200–700 m range up to 2 dB of additional loss. Comparative analysis indicates that the proposed system is more efficient, less complex, adequately distance‐friendly (=420 m), and capable of higher data rates (=120 Gbps) compared with other works. This makes it a promising solution for future high‐speed satellite communications considering the impact of link losses and atmospheric conditions. [ABSTRACT FROM AUTHOR]

We demonstrate in-fiber polarization-dependent optical filter by nanopatterning an asymmetric metallic metasurface array on the end-facet of polarization-maintaining photonic-crystal fibers. The asymmetric cross-typed nanoslit metasurface arrays are fabricated on the core of the optical fiber using the focused ion beam milling technique. Highly polarization- and wavelength-dependent transmission with transmission efficiency of ∼70% in the telecommunication wavelength was observed by launching two orthogonal linear-polarization states of light into the fiber. Full-wave electromagnetic simulations are in good agreement with the experimental results. These advanced meta-structured optical fibers can potentially be used as novel ultracompact in-fiber filters, splitters, and polarization converters.

Recently, there has been an increase in interest in using optical wireless communication (OWC) links on high-altitude platforms (HAPs) for satellite applications. We implement an orbital angular momentum (OAM) multiplexed orthogonal frequency division multiplexing (OFDM) system using an OWC link. A space-to-air scenario is considered in which transmission pointing errors, geometric loss, turbulence, and additional link losses are taken into account to extend the transmission range, system capacity, and throughput. At 200 Gbps per channel data rate, four different OAM modes are implemented with higher order Laguerre–Gaussian (LG) modes of [0,0], [0,13], [0,40], and [0,80]. An aggregate 800 Gbps data rate can deliver a maximum OWC range of 3300–5000 km for all channels. The maximum received power over the 1000 km range is −19.34 to −32.59 dBm with an additional gain of 0–2.5 dB. It is also possible to obtain a better performance over large distances of 500–3500 km with an error vector magnitude of 2.98–17.5%. Furthermore, a high gain of −40.80 dB, a signal-to-noise ratio (SNR) of 55.21 dB, and an optical SNR of 67.25 dB can be achieved for varied transmitter pointing errors of 0.1 rad. As compared to other literature, this system exhibits a superior performance. [ABSTRACT FROM AUTHOR]