Optical integrated reconfigurable mode generator-multiplexer for radio-frequency orbital angular momentum.

Radio-frequency orbital angular momentum (RF-OAM) mode multiplexing has received increasing attention in next-generation (6G) wireless communication as a new spatial multiplexing dimension to further extend data capacity. In particular, the circular antenna array (CAA) based RF-OAM generation using photonic methods is a promising approach due to its flexible reconfigurability, low propagation loss, high operating bandwidth, and high pattern quality. However, most current reports focus either on the bulk optics-based implementations or on band-limited delay line-based approaches.

Digital-filter-aided crosstalk-mitigation for a high spatial resolution AWGR-based 2D IR beam-steered indoor optical wireless communication system.

The growing demand for wireless connectivity is attracting interest in optical wireless communication (OWC) technique. In this paper, a filter-aided crosstalk mitigation scheme, employing digital Nyquist filters, is proposed to eliminate the trade-off between the spatial resolution and the channel capacity for the AWGR-based 2D infrared beam-steered indoor OWC system. By shaping the transmitted signal for narrow spectral occupancy, the inter-channel crosstalk resulting from the imperfect AWGR filtering can be avoided, which enables a denser AWGR grid.

Real-time transmission of geometrically-shaped signals using a software-defined GPU-based optical receiver.

A software-defined optical receiver is implemented on an off-the-shelf commercial graphics processing unit (GPU). The receiver provides real-time signal processing functionality to process 1 GBaud minimum phase (MP) 4-, 8-, 16-, 32-, 64-, 128-ary quadrature amplitude modulation (QAM) as well as geometrically shaped (GS) 8- and 128-QAM signals using Kramers-Kronig (KK) coherent detection. Experimental validation of this receiver over a 91 km field-deployed optical fiber link between two Tokyo locations is shown with detailed optical signal-to-noise ratio (OSNR) investigations.

Monolithic integrated two-stage cascaded SOA-PIN receiver for high-speed optical wireless communication.

Monolithic integrated receivers are highly desired due to the potential of mass production and the reduction of device size and cost. In this Letter, a monolithic integrated optical wireless communication (OWC) receiver with optical preamplifiers is designed, fabricated, and investigated to achieve high sensitivity based on photonic integration technology. The proposed receiver consists of one waveguide PIN photodetector integrated with two semiconductor optical amplifiers (SOAs).

Ultra-high-capacity wireless communication by means of steered narrow optical beams.

The optical spectrum offers great opportunities to resolve the congestion in radio-based communication, aggravated by the booming demand for wireless connectivity. High-speed infrared optical components in the 1500 nm window have reached high levels of sophistication and are extensively used already in fibre-optic networks. Moreover, infrared light beyond 1400 nm is eye-safe and is not noticeable by the users.

Cost-efficient half-duplex 10 Gbit/s all-optical indoor optical wireless communication enabled by a low-cost Fabry-Perot laser/photodetector.

To develop an indoor optical wireless communication (OWC) system, both the system complexity/cost and data rate need to be taken into consideration. In this Letter, a cost-efficient half-duplex OWC system for photonic home area network applications is proposed and experimentally demonstrated. A low-cost Fabry-Perot laser diode is proposed to be employed as both the downlink receiver (Rx) and uplink transmitter at the user side.

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.

Characterization of Rayleigh backscattering arising in various two-mode fibers.

We experimentally characterize the mode dependent characteristics of Rayleigh backscattering (RB) arising in various two-mode fibers (TMFs). With the help of an all-fiber photonic lantern, we are able to measure the RB power at individual modes. Consequently, mode dependent power distribution of RB light caused by arbitrary forward propagation mode superposition can be obtained.

Mode-dependent characterization of photonic lanterns.

We propose and experimentally demonstrate a simple method for characterizing the power transfer matrix of photonic lanterns (PLs) used for mode division multiplexing (MDM) transmission. Due to the optical reflection arising at output facet of the few-mode fiber (FMF), we are able to detect the power at the individual single-mode fiber (SMF) input port and exploit a series of equations based on the theory of energy conservation to obtain mode-dependent characteristics of the PL, including the property of mode selectivity, insertion loss (IL), and channel-dependent loss (CDL). The proposed method is experimentally verified for both the mode selective and the nonmode selective photonic lanterns.

Advanced coding techniques for few mode transmission systems.

We experimentally verify the advantage of employing advanced coding schemes such as space-time coding and 4 dimensional modulation formats to enhance the transmission performance of a 3-mode transmission system. The performance gain of space-time block codes for extending the optical signal-to-noise ratio tolerance in multiple-input multiple-output optical coherent spatial division multiplexing transmission systems with respect to single-mode transmission performance are evaluated. By exploiting the spatial diversity that few-mode-fibers offer, with respect to single mode fiber back-to-back performance, significant OSNR gains of 3.

Compact spatial multiplexers for mode division multiplexing.

Spatial multiplexer (SMUX) for mode division multiplexing (MDM) has evolved from mode-selective excitation, multiple-spot and photonic-lantern based solutions in order to minimize both mode-dependent loss (MDL) and coupler insertion loss (CIL). This paper discusses the implementation of all the three solutions by compact components in a small footprint. Moreover, the compact SMUX can be manufactured in mass production and packaged to assure high reliability.

Interleaved and partial transmission interleaved optical coherent orthogonal frequency division multiplexing.

A novel group of interleaved orthogonal frequency division multiplexing (IL-OFDM) and partial transmission IL-OFDM (PT-IL-OFDM) schemes are proposed for optical coherent detection. In the interleaved operation, the odd (or even) subcarriers of an OFDM symbol are reserved (closed). Such an interleaved arrangement can gain the tolerance toward phase noise induced interchannel interference (PN-ICI).

In-home networks integrating high-capacity DMT data and DVB-T over large-core GI-POF.

The low-cost in-home distribution of full-standard digital TV jointly with high-bitrate data using 50 m long 1 mm core diameter graded-index plastic optical fiber (GI-POF) is proposed and experimentally demonstrated. Discrete multitone (DMT) modulation is demonstrated to provide an adaptive bitrate which can spectrally coexist with digital video broadcasting-terrestrial (DVB-T) signals in 470-862 MHz. A 3 Gb/s DMT signal and two DVB-T channels are generated, transmitted and received exhibiting excellent performance.

TDM-PON with 30 Gb/s D8PSK downstream and 10 Gb/s OOK upstream based on a digital incoherent receiver.

In this paper, we propose the use of multilevel modulation formats with differential detection to enable Next-Generation Time-Division Multiplexing Passive Optical Networks (TDM-PONs). Bidirectional transmission of 30 Gb/s Differential 8 Phase-Shift Keying (D8PSK), on the downstream, and 10 Gb/s On-Off Keying (OOK), on the upstream, over a TDM-PON has been demonstrated experimentally. Furthermore, some of the functionalities that can be implemented in Digital Signal Processing (DSP) in the receiver, namely wavelength misalignment compensation, IQ imbalance mitigation and data-aided multiple symbol phase estimation, are explored.

Introduction: ECOC 2012 in Amsterdam.

We introduce the Optics Express special issue from the 38th European Conference on Optical Communication and Exhibition (ECOC). A total of 134 expanded papers from ECOC 2012 are included in this special issue.

In-band 16-QAM and multi-carrier SCM modulation to label DPSK payload signals for IP packet routing.

We present an experimental demonstration of the feasibility of in-band subcarrier multiplexing (SCM) for labeling of differential phase shift keying (DPSK) payload signals. We show that by proper selection of the value of the subcarrier frequency the effect of the superimposed SCM label on the performance of the DPSK signal is minimized. Furthermore, we show experimentally the advantages of using alternative modulation formats such as 16-QAM and multi-carrier SCM for optical labeling of a 10 Gb/s DPSK payload signal.