In this paper, recent progress in millimeter-wave (MMW) photonic gigabit wireless communication is reviewed. This technique is attractive partly because the MMW signal can be easily distributed from central to base stations through the use of a low-loss optical fiber. This radio-over-fiber approach facilitates the transmission of MMW signals. An MMW photonic transmitter, comprised of high-power photodiodes with integrated antennas for MMW signal broadcasting, is needed for signal generation only over the last mile. The development of several different low-noise optical MMW sources and high-power photonic transmitters and photodiodes for optical MMW wireless links is summarized. The performance of photonic wireless links with extremely high data rates (>10 Gbit s−1) developed based on these key components and using different modulation schemes is also reviewed. Finally, some advanced commercially available products and the prospects of a future gigabit wireless communication era are discussed.

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Millimeter-wave photonic wireless links for very high data rate communication

Aluminium/gallium co-doped ZnO (AGZO), indium/gallium co-doped ZnO (IGZO), and aluminium/indium co-doped ZnO (AIZO) thin films were synthesised on glass substrates via aerosol assisted chemical vapour deposition (AACVD). The films were fully characterised by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The optoelectronic properties of the films were determined using UV/vis spectroscopy and Hall effect measurements. The AGZO film displayed the lowest resistivity (1.3 × 10−2 Ω cm) and highest carrier mobility (7.9 cm2 V−1 s−1), due the relatively low amount of disorder in the structure. The incorporation of In3+ resulted in the most disorder in the structure due to its large radius, which led to an increase in optical absorption, and a decrease in resistivity.

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Aluminium/gallium, indium/gallium, and aluminium/indium co-doped ZnO thin films deposited via aerosol assisted CVD

We demonstrate a novel scheme for photonic generation of chirped millimeter-wave (MMW) pulse with ultrahigh time-bandwidth product (TBP). By using a fast wavelength-sweeping laser with a narrow instantaneous linewidth, wideband/high-power photonic transmitter-mixers, and heterodyne-beating technique, continuously tunable chirped MMW waveforms at the W-band are generated and detected through wireless transmission. Compared with the reported optical grating-based wavelength-to-time mapping techniques for chirped pulse generation, our approach eliminates the problem in limited frequency resolution of grating, which seriously limits the continuity, tunability, and TBP of the generated waveform. Furthermore, by changing the alternating current (AC) waveform of the driving signal to the sweeping laser, linearly or nonlinearly continuously chirped MMW pulse can be easily generated and switched. Using our scheme, linearly and nonlinearly chirped pulses with record-high TBPs (89-103 GHz/ 50 μs/7 × 105) are experimentally achieved.

Photonic Generation and Wireless Transmission of Linearly/Nonlinearly Continuously Tunable Chirped Millimeter-Wave Waveforms With High Time-Bandwidth Product at W-Band

We demonstrate a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD) with a scaled-down epi-layer structure designed for high-power performance in the sub-THz frequency regime. Compared with UTC-PDs, NBUTC-PDs offer a higher optimum bias voltage for the near-ballistic transport of electrons, which leads to improvement in the output power performance. Furthermore, a small load resistance ( <; 50nΩ), which would sacrifice the output power for minimizing the output ac voltage swing on dc bias point, is not necessary. By scaling down the collector layer thickness and active area of the NBUTC-PDs, we achieve a large optical-to-electrical bandwidth (250 GHz) and a high saturation current (17 mA), which is close to the theoretical maximum, under a 50-Ω load and -2-V bias.

Design and Analysis of Ultra-High-Speed Near-Ballistic Uni-Traveling-Carrier Photodiodes Under a 50- $\Omega$ Load for High-Power Performance

We demonstrate a remotely up-converted and distributed 20-Gbit/s wireless on-off-keying (OOK) data transmission link at the W-band that uses a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD)-based photonic transmitter-mixer. This device consists of an active NBUTC-PD integrated with a planar passive circuit for feeding the intermediate-frequency (IF) modulation input and extracting the up-converted optical-to-electrical (O-E) output signals. An equivalent-circuit model is developed, which allows for the O-E and IF responses to be independently optimized. Accordingly, we can achieve both an ultra-wide O-E bandwidth (67-118 GHz) and IF modulation bandwidth (>;15 GHz) with a very-low coupling loss (<; 2 dB) from the NBUTC-PD to the WR-10 waveguide. We adopted a remotely distributed 1-ps optical pulse train source with a repetition rate at 93 GHz to serve as a high-performance photonic carrier, which is generated by a spectral line-by-line shaper utilizing the repetition-rate multiplication (RRM) technique. In contrast to lossy amplitude filtering, our RRM is based on applying periodic loss-less spectral phase filtering onto the 31-GHz comb lines. In comparison with the conventional 93-GHz sinusoidal carrier, the photogenerated millimeter-wave (MMW) power of this kind of carrier is 4 dB higher than that of PD under the same output photocurrent. In contrast to the traditional mode-locked laser, the fiber dispersion can be totally precompensated without additional dispersion compensation components. By use of such device and optical MMW source, we successfully demonstrate remotely distributed and up-converted 20-Gbit/s error-free OOK wireless data transmission link over a 25-km standard single-mode fiber.

Remotely Up-Converted 20-Gbit/s Error-Free Wireless On–Off-Keying Data Transmission at W-Band Using an Ultra-Wideband Photonic Transmitter-Mixer

In this study, we demonstrate near-ballistic uni-traveling carrier photodiodes (NBUTC-PDs) with an optimized flip-chip bonding structure, wide 3-dB optical-to-electrical (O-E) bandwidth (> 110 GHz), and extremely high saturation current-bandwidth product performance (37 mA, > 110 GHz, > 4070 mAmiddot GHz). NBUTC-PDs with different active areas (28-144 mum2) are fabricated and flip-chip bonded with coplanar waveguides onto an AlN-based pedestal. The overshoot drift velocity of the electrons in the collector layer of the NBUTC-PD means that both the thicknesses of the collector layer and active areas of our device can be increased to reduce the density of the output photocurrent, compared to that of the traditional UTC-PD. This improves the high power performance without seriously sacrificing the speed performance. According to the measured O-E frequency responses, devices with even a large active area (144 mum2 ) can still have a flat O-E frequency response, from near dc to 110 GHz. A three-port equivalent circuit model for accurately extracting the 3-dB bandwidth of the devices is established. The extracted 3-dB O-E bandwidth of a device with a small active area (28 mum2) can be as high as 280 GHz under a load of 25 Omega . In addition, the saturation current measurement results indicate that after inserting a center bonding pad on the pedestal (located below the p-metal of the NBUTC-PD for good heat sinking), the saturation current performance of the device becomes much higher than that of the control device (without the center bonding pad), especially for the device with a small active area (28 mum2 ). The measurement and modeling results indicate that a device with a 144 mum2 active area and optimized flip-chip bonding pedestal can achieve an extremely high saturation current-bandwidth product (6660 mA-GHz, 37 mA, 180 GHz).

Extremely High Saturation Current-Bandwidth Product Performance of a Near-Ballistic Uni-Traveling-Carrier Photodiode With a Flip-Chip Bonding Structure

This study explores the effects of both Oxygen and temperature on the carrier dynamics of isoelectronic ZnSe1−xOx (x=0027 and 0053) semiconductors using photoluminescence (PL) and time-resolved PL spectroscopy We find that the Kohlrausch law is highly consistent with the complex decay traces induced by isoelectronic O traps, and the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature Complex recombination processes are clarified using the relaxation model based on various decay channels These findings are consistent with the initial fall in the stretching exponent β followed by its monotonic increase with increasing temperature

Carrier dynamics in isoelectronic ZnSe1−xOx semiconductors

Optical and electrical properties of ZnSeO alloys grown by plasma-assisted molecular beam epitaxy

Undoped and Ga-doped ZnO films are grown on GaN templates by plasma-assisted molecular beam epitaxy for systematic investigation of the influence of native defects on their electrical properties. The distinct electrical properties of the undoped and Ga-doped ZnO films are observed after thermal treatment in a nitrogen and an oxygen ambient. It is found that the undoped ZnO films show improved characteristics when annealed in an oxygen ambient, and the Ga-doped ZnO films exhibit stable characteristics when annealed in a nitrogen ambient. The variation in electrical properties revealed by the photoluminescence measurements can be attributed to the generation and annihilation of native defects, which are dependent on the ambient of treatments. The properties of the annealed undoped ZnO films grown in an O-rich environment are affected mainly by the oxygen vacancies, antisite oxygen and oxygen interstitials, while the annealed Ga-doped ZnO films are dominated by oxygen interstitials. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

http://jss.ecsdl.org/content/5/9/Q222.full.pdf

Influence of Point Defects on the Properties of Undoped and Ga-Doped ZnO Films Grown by Plasma-Assisted Molecular Beam Epitaxy in an O-Rich Environment

Cheng Yu Chen

Papers

Extremely High Saturation Current-Bandwidth Product Performance of a Near-Ballistic Uni-Traveling-Carrier Photodiode With a Flip-Chip Bonding Structure

Carrier dynamics in isoelectronic ZnSe1−xOx semiconductors

Optical and electrical properties of ZnSeO alloys grown by plasma-assisted molecular beam epitaxy

Influence of Point Defects on the Properties of Undoped and Ga-Doped ZnO Films Grown by Plasma-Assisted Molecular Beam Epitaxy in an O-Rich Environment

Low resistivity and low compensation ratio Ga-doped ZnO films grown by plasma-assisted molecular beam epitaxy