C.W. Oh

Advanced Integration Techniques on Broadband Millimeter-Wave Beam Steering for 5G Wireless Networks and Beyond

Recently, the desired very high throughput of 5G wireless networks drives millimeter-wave (mm-wave) communication into practical applications. A phased array technique is required to increase the effective antenna aperture at mm-wave frequency. Integrated solutions of beamforming/beam steering are extremely attractive for practical implementations. After a discussion on the basic principles of radio beam steering, we review and explore the recent advanced integration techniques of silicon-based electronic integrated circuits (EICs), photonic integrated circuits (PICs), and antenna-on-chip (AoC). For EIC, the latest advanced designs of on-chip true time delay (TTD) are explored. Even with such advances, the fundamental loss of a silicon-based EIC still exists, which can be solved by advanced PIC solutions with ultra-broad bandwidth and low loss. Advanced PIC designs for mm-wave beam steering are then reviewed with emphasis on an optical TTD. Different from the mature silicon-based EIC, the photonic integration technology for PIC is still under development. In this paper, we review and explore the potential photonic integration platforms and discuss how a monolithic integration based on photonic membranes fits the photonic mm-wave beam steering application, especially for the ease of EIC and PIC integration on a single chip. To combine EIC, for its accurate and mature fabrication techniques, with PIC, for its ultra-broad bandwidth and low loss, a hierarchical mm-wave beam steering chip with large-array delays realized in PIC and sub-array delays realized in EIC can be a future-proof solution. Moreover, the antenna units can be further integrated on such a chip using AoC techniques. Among the mentioned techniques, the integration trends on device and system levels are discussed extensively.

Steerable pencil beams for multi-Gbps indoor optical wireless communication.

We report a novel optical wireless communication (OWC) system solution that supports multi-Gbps (Gigabit-per-second) capacity for indoors. Narrow beams, termed as pencil beams, are directed to wireless users using a tunable laser and a passive diffractive optical element. This enables a wide coverage of ultra-high-capacity communication links to serve multiple network users simultaneously. Experimental results demonstrating data rates of up to 10 Gbps, with on-off keying modulation format, over a distance of more than 2.5 m, are reported. Error-free links beam-steered over a total wavelength range of 130 nm, with steering angle of 17.16°, have been achieved. This system is proposed for short-range OWC and is promising for seamless integration in in-building optical networks.

Free-space transmission with passive 2D beam steering for multi-gigabit-per-second per-beam indoor optical wireless networks.

In order to circumvent radio spectrum congestion, we propose an innovative system which can provide multiple infrared optical wireless beams simultaneously where each beam supports multi-gigabit-per-second communication. Scalable two-dimensional beam steering by means of wavelength tuning is proposed. A passive beam-steering module constructed with cascaded reflection gratings is designed for simultaneous multi-user coverage. We experimentally characterized the beam-steered system and thoroughly evaluated the performance of steered channels using the spectrally efficient and robust discrete multitone modulation in a bandwidth-limited system deploying 10 GHz telecom transceivers. This study reports the achievement of at least 37 Gbps free-space transmission per beam over a distance of up to 2 m over 5.61° × 12.66° scanning angles.

Toward multi-Gbps indoor optical wireless multicasting system employing passive diffractive optics

This Letter presents the evaluation and demonstration of an optical free-space (FS) multicasting system for multi-Gigabits-per-second (multi-Gbps) indoor transmission. These simultaneous line-of-sight links are formed by infrared beams and are beam-steered using a passive diffraction grating. The experiment has resulted in error-free links (bit error rate <10(-9) at 2.5 Gbps on-off keying) and is scalable to support higher data rates. This system is proposed for short-range optical wireless communication and can be seamlessly integrated in in-building fiber networks.

61.3-Gbps Hybrid Fiber-Wireless In-Home Network Enabled by Optical Heterodyne and Polarization Multiplexing

A hybrid fiber-wireless in-home network is proposed to support high-speed multiple input and multiple output (MIMO) orthogonal frequency division multiplexing systems operating at millimeter wave (mm-wave) band by employing optical heterodyne (OH) and polarization multiplexing (PolMux). OH enables the optical generation of mm-wave signals without the intrinsic frequency limitation of electrical local oscillators. Moreover, the frequency agility can be provided by tuning the optical wavelength in an OH system. PolMux explores two orthogonal polarizations at the same optical wavelength to satisfy the wireless MIMO service with low additional cost. Enabled by these techniques, the fiber transmission (1 km) and wireless delivery (1 m) of 61.3-Gbps data at 40-GHz mm-wave are successfully demonstrated. To the best of our knowledge, a record spectral efficiency of 6.82 bit/s/Hz is achieved in such kind of systems.

42.8 Gbit/s indoor optical wireless communication with 2-dimensional optical beam-steering

To combat the imminent radio frequency spectrum crunch, we propose an infrared optical wireless communication solution for in-home networks, with remotely controlled 2-dimensional passive optical beam-steering, which exhibited 42.8 Gbit/s over 2.5 m free-space transmission.

Spatial Filtering in a Broadband In-Home OFDM Radio-Over-Fiber Network

The spatial filtering in an orthogonal frequency division multiplexing (OFDM) radio-over-fiber network is proposed to boost its capacity using broadband optical true time delay enabled microwave beam steering. The observed suppression ratio of the spatial filtering is 19.4 dB. The optical delivery and directional wireless transmission of 3.975 Gb/s OFDM data on a 19-GHz microwave carrier is studied. The observed beam directing-induced bit error ratio improvement is more than four orders of magnitude.

Optical wireless data transfer enabled by a cascaded acceptance optical receiver fabricated in an InP membrane platform

Utilizing an InP membrane based cascaded acceptance optical receiver (CAO-Rx), we demonstrate 17.4Gbps optical wireless transmission in C-band. By separating light collection and opto-electrical conversion, CAO-Rx provides better optical efficiency and electrical bandwidth simultaneously.

36.7 Gbps spectrum-efficient indoor optical wireless system with beam-steering

We propose a novel spectrum-efficient indoor optical wireless solution providing multi-Gigabits-per-second with passive diffractive beam-steering technique and discrete multitone modulation. Diffracted link performance of 36.7 Gbps over more than 2.5 m is reported.

Low-Crosstalk Full-Duplex All-Optical Indoor Wireless Transmission With Carrier Recovery

We propose and demonstrate a novel bi-directional free-space (FS) optical wireless communication system for indoor wireless networks. A 2-D infrared beam-steered system supporting full-duplex communication of at least 10 Gb/s capacity per wireless terminal with simple NRZ-OOK modulation format is experimentally demonstrated. The uplink (UL) is implemented using the optical carrier recovery technique, in which the downlink (DL) OOK modulation is erased by means of two cascaded SOAs operating in the saturation region. We experimentally demonstrate the system with asymmetric speeds (10 Gb/s DL/2.5 Gb/s UL) and symmetric speeds (10 Gb/s) duplex communication over an FS transmission distance of 3 m. We also report the crosstalk in such a system.