Radio-frequency communication systems have long used bulk- and surface-acoustic-wave devices supporting ultrasonic mechanical waves to manipulate and sense signals. These devices have greatly improved our ability to process microwaves by interfacing them to orders-of-magnitude slower and lower-loss mechanical fields. In parallel, long-distance communications have been dominated by low-loss infrared optical photons. As electrical signal processing and transmission approach physical limits imposed by energy dissipation, optical links are now being actively considered for mobile and cloud technologies. Thus there is a strong driver for wavelength-scale mechanical wave or “phononic” circuitry fabricated by scalable semiconductor processes. With the advent of these circuits, new micro- and nanostructures that combine electrical, optical, and mechanical elements have emerged. In these devices, such as optomechanical waveguides and resonators, optical photons and gigahertz phonons are ideally matched to one another, as both have wavelengths on the order of micrometers. The development of phononic circuits has thus emerged as a vibrant field of research pursued for optical signal processing and sensing applications as well as emerging quantum technologies. In this review, we discuss the key physics and figures of merit underpinning this field. We also summarize the state of the art in nanoscale electro- and optomechanical systems with a focus on scalable platforms such as silicon. Finally, we give perspectives on what these new systems may bring and what challenges they face in the coming years. In particular, we believe hybrid electro- and optomechanical devices incorporating highly coherent and compact mechanical elements on a chip have significant untapped potential for electro-optic modulation, quantum microwave-to-optical photon conversion, sensing, and microwave signal processing.

https://biblio.ugent.be/publication/8626734/file/8626737.pdf

Controlling phonons and photons at the wavelength scale: integrated photonics meets integrated phononics

Free space optical (FSO) communication technology, also known as optical wireless communications, has regained a great interest over the last few years. In some cases, FSO is seen as an alternative to existing technologies, such as radio frequency. In other cases, FSO is considered as a strong candidate to complement and integrate with next-generation technologies, such as 5G wireless networks. Accordingly, FSO technology is being widely deployed in various indoor (e.g., data centers), terrestrial (e.g., mobile networks), space (e.g., inter-satellite and deep space communication), and underwater systems (e.g., underwater sensing). As the application portfolio of FSO technology grows, so does the need for a clear classification for FSO link configurations. Most existing surveys and classifications are single-level classifications, and thus not inclusive enough to accommodate recent and emerging changes and developments of different FSO link configurations and systems. In this paper, we propose a multi-level classification framework to classify existing and future indoor, terrestrial, space, underwater, and heterogenous FSO links and systems using common and simple unified notation. We use the proposed classification to review and summarize major experimental work and systems in the area until 2017. Using the proposed classification and survey, we aim to give researchers a jump-start to tap into the growing and expanding realm of the FSO technology in different environments. The proposed classification can also help organize and systematically present the progress in the research on FSO technology. This makes the identification of the market needs for standards an easier task. Moreover, different entities involved in the standardization process including academic, industry, and regulatory organizations can use the proposed classification as a unified language to communicate during the early stages of standard development which require ambiguity-free discussions and exchange of ideas between different standardization entities. We use the proposed classification to review existing standards and recommendations in the field of FSO. It is also envisioned that the proposed classification can be used as a unified framework to define different FSO channel models for simulation tools.

Classification Framework for Free Space Optical Communication Links and Systems

Microwave signal filtering is a fundamental and central functionality in radio-frequency (RF) systems. Underpinned by advanced integrated photonics technologies, emerging integrated microwave photonic (IMWP) filter platforms enable reconfigurable and widely tunable RF signal filtering functionalities that were unattainable using conventional electronics while also exhibiting superior features in terms of compactness, light weight, stability, low power consumption, and low latency. This paper presents a comprehensive review of the principles, architectures, and performance of IMWP filters. We highlight recent advances of IMWP filters enabled by on-chip nonlinear optics, RF-interference technology and emerging integration platforms, with an emphasis on the RF performance which is critical for their usability in real-world applications. We conclude with a perspective on future research challenges and new possibilities for IMWP filters.

Integrated microwave photonic filters

A wavelength-division-multiplexing (WDM) free-space optical (FSO) communication system of a high-speed hybrid signal is proposed and demonstrated in this study. This study is the first to transmit a high-speed hybrid signal mixed with four wavelengths that are modulated with different signals, namely 10, 25, 28, and 32 Gb/s, using a single beam. Favourable bit error rate (BER) and clear eye maps are achieved by adopting parameters after investigating the bandwidth of tuneable optical bandpass filter, channel spacing, and number of mixed light channel effects on system performance. The WDM-FSO communication system of a high-speed hybrid signal has a simple configuration, low cost, and low BER.

WDM Free-Space Optical Communication System of High-Speed Hybrid Signals

Optical wireless communication (OWC) covering an ultra-wide range of unlicensed spectrum has emerged as an extent efficient solution to mitigate conventional RF spectrum scarcity ranging from communication distances from nm to several kilometers. Free space optical (FSO) systems operating near IR (NIR) band in OWC links has received substantial attention for enormous data transmission between fixed transceivers covering few kilometers path distance due to high optical bandwidth and higher bit rate as well. Despite the potential benefits of FSO technology, its widespread link reliability suffers especially in the long-range deployment due to atmospheric turbulence, cloud induced fading, some other environmental factors such as fog, aerosol, temperature variations, storms, heavy rain, cloud, pointing error, and scintillation. FSO has the potential to offloading massive traffic demands from RF networks, consequently the combined application of FSO/RF and radio over FSO (RoFSO) systems is regarded as an excellent solution to support 5G and beyond for improving the limitations of an individual system. This survey presents the overview of several key technologies and implications of state-of-the-art criteria in terms of spectrum reuse, classification, architecture and applications are described for understanding FSO. This paper provides principle, significance, demonstration, and recent technological development of FSO technology among different appealing optical wireless technologies. The opportunities in the near future, the potential challenges that need to be addressed to realize the successful deployment of FSO schemes are outlined.

A Contemporary Survey on Free Space Optical Communication: Potential, Technical Challenges, Recent Advances and Research Direction.

An all-optical forwarding relay (AOFR) system is proposed to provide an arbitrary forward with multiple channels and demonstrated by incorporating multiple acquisition, tracking, and pointing (ATP) systems and an arbitrary optical forwarding system (AOFS) with eight channels carrying passive loads. The insertion loss and arbitrary switching time of the AOFS are tested to be $Q$ factor are evaluated with three modulation formats, 997 Mb/s 16-QAM, 27 Gb/s BPSK, and 54 Gb/s QPSK. The results indicate that the connection time of the optical communication is reduced to a few milliseconds by using the rapid arbitrary channel switching and the pre-point of ATP systems. In addition, the AOFR system is fully transparent to the channel wavelengths, forwarding ports, data rates, and modulation formats. To the best of our knowledge, the proposed AOFR system demonstrates the first arbitrary channel forwarding solution for large-capacity passive load among satellites, which will be an enabling solution for future interstellar optical communication networks.

All-Optical Transparent Forwarding Relay System for Interstellar Optical Communication Networks

A wide-spectrum, ultra-stable optical frequency comb (OFC) module with 100 GHz frequency intervals based on a quantum dot mode locked (QDML) laser is fabricated by our lab, and a scheme with 12.5 Gb/s multi-channel broadcasting transmission for free-space optical (FSO) communication is proposed based on the OFC module. The output power of the OFC is very stable, with the specially designed circuit and the flatness of the frequency comb over the span of 6 nm, which can be limited to 1.5 dB. Four channel wavelengths are chosen to demonstrate one-to-many channels for FSO communication, like optical wireless broadcast. The outdoor experiment is established to test the bit error rate (BER) and eye diagrams with 12.5 Gb/s on-off keying (OOK). The indoor experiment is used to test the highest traffic rate, which is up to 21 Gb/s for one-hop FSO communication. To the best of our knowledge, this scheme is the first to propose the realization of one-to-many broadcasting transmission for FSO communication based on the OFC module. The advantages of integration, miniaturization, channelization, low power consumption, and unlimited bandwidth of one-to-many broadcasting communication scheme, shows promising results on constructing the future space-air-ground-ocean (SAGO) FSO communication networks.

12.5 Gb/s multi-channel broadcasting transmission for free-space optical communication based on the optical frequency comb module.

A 300 kbps wide-angle non-line-of-sight ultraviolet communication system with voice transmission function is designed here. Based on Poisson distribution theory, we design the symbol detecting method for the receiving discrete photon signals. Using 272 nm LED array as the light source and PMT as the detector, the voice transceiver is integrated into the carriable size of 200 × 90 × 65 mm3. An outfield test shows the system obtains the BER of 0.88% under 200 m. Under 10° wide-angle deviation of the transmitter, a BER below 1.33% is achieved.

The realization of a wide-angle voice transmission non-line-of-sight ultraviolet communication system

In this paper, an efficient photonics time-delayed mixer (PTDM) is proposed and demonstrated. It mainly consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and a dispersion medium (DM). To eliminate the carrier component, the carrier-suppressed dual-sideband (CS-DSB) modulation is implemented without optical filters. Besides, the CS-DSB modulation is also the key to make the phase response is proportional to the converted frequency. Thanks to the controllable DC bias of the modulator, the power response of this PTDM is also tunable. Thus, this property also endows the PTDM able to resist the dispersion-induced power fading (DIPF) when considering the use of large dispersion medium. Experimental results verify the ability of wideband frequency up- and down-conversion. Moreover, a converted signal with linear phase-frequency response is also achieved, which implies the time delay capability. Time delay tuning is realized by altering the wavelength of the carrier with a stable power response. This structure is very compact and thus compresses the signal processing system volume, which is qualified to be integrated into a receiver/transmitter.

Microwave Photonics Time-Delayed Mixer

A novel approach to simultaneous radiofrequency self-interference cancellation (SIC) and frequency down-conversion in a unified system is proposed and demonstrated experimentally based on cascade Mach–Zehnder modulators (MZM). The local oscillator signal is injected into the MZM1, whereas the received RF signal and the reference signal are fed into MZM2 and MZM3. After photoelectrical conversion by a balanced photodetector, the desired intermediate frequency signal with SIC is obtained. The cancellation depth for the single frequency SIC with frequency down-conversion is around 38 dB, and that for a wideband signal is around 19 dB. No electrical delay and attenuation are used in the proposed system, so it can potentially reach a wider frequency band and a higher cancellation depth.

/pdf/optical-self-interference-cancellation-with-frequency-down-46qowkkbpl.pdf

Yuehui Wang

Papers

All-Optical Transparent Forwarding Relay System for Interstellar Optical Communication Networks

12.5 Gb/s multi-channel broadcasting transmission for free-space optical communication based on the optical frequency comb module.

The realization of a wide-angle voice transmission non-line-of-sight ultraviolet communication system

Microwave Photonics Time-Delayed Mixer

Optical Self-Interference Cancellation With Frequency Down-Conversion Based on Cascade Modulator