Integrated remotely tunable optical delay line for millimeter-wave beam steering fabricated in an InP generic foundry.

A compact and fabrication-tolerant integrated remotely tunable optical delay line is proposed for millimeter-wave beam steering and is fabricated in an InP generic foundry. The proposed delay line is based on a spectrally cyclic-arrayed waveguide grating feedback loop. Its major features include the tolerant architecture with reduced chip size, and bi-directional operation with simplified remote tuning. Moreover, its cyclic feature guarantees further cascaded operations either for 2D radio beam steering or for high-resolution delay generation. The experimental results show less than 6.5-dB insertion loss of the integrated delay line. Five different delays from 0 to 71.6 ps are generated with less than 0.67-ps delay errors.

Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis.

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.

Phase modulation parallel optical delay detector for microwave angle-of-arrival measurement with accuracy monitored.

A novel phase modulation parallel optical delay detector is proposed for microwave angle-of-arrival measurement with accuracy monitored by using only one dual-electrode Mach-Zehnder modulator. A theoretical model is built up to analyze the proposed system including measurement accuracy monitoring. The spatial delay measurement is translated into the phase shift between two replicas of a microwave signal. Thanks to the accuracy monitoring, the phase shifts from 5° to 165° are measured with less than 3.1° measurement error.

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.

Synchronized signaling delivery for broadband 60 GHz in-building optical wireless network based on digital frequency division multiplexing and digital Nyquist shaping.

A simple and low-cost synchronized signaling delivery scheme has been proposed for a 60 GHz in-building optical wireless network with 12.7Gbps throughput based on digital frequency division multiplexing and digital Nyquist shaping.

Power-efficient impulse radio ultrawideband pulse generator based on the linear sum of modified doublet pulses.

We propose a new and power-efficient impulse radio ultawideband (IR-UWB) pulse design concept. The proposed concept is based on a linear sum of modified doublet pulses. The proposed concept is both simulated and experimentally demonstrated. The experimental demonstration employs a photonic scheme that generates the designed pulse using two main steps, mainly optical shaping and differential detection. The optical shaping is performed using a single electro-optic modulator biased in the nonlinear portion of its transfer function, and the differential detection is performed using a balanced photodetector. The generated IR-UWB pulse is fully Federal Communications Commission compliant, even in the highly power-restricted global positioning system band. The proposed optical scheme has potential to be integrated on a compact optical chip and thus suitable for reliable, low-cost, high-speed, short-range UWB wireless access, such as in-building networks.

Cost optimization of optical in-building networks.

Optical fiber-based in-building network solutions can outperform in the near future copper- and radio-based solutions both regarding performance and costs. POF solutions are maturing, and can already today be cheaper than Cat-5e solutions when ducts are shared with electricity power cabling. We compare the CapEx and OpEx of in-building networks for fiber and Cat-5E solutions. For residential homes, our analysis shows that total network costs during economic lifetime are lowest for a point-to-point duplex POF topology.

10-Gb/s transmission over 20-km single fiber link using 1-GHz RSOA by discrete multitone with multiple access.

We demonstrate a novel 10.5-Gbit/s transmission scheme over 20-km single fiber link by using a remotely fed 1-GHz reflective semiconductor optical amplifier (RSOA). Discrete multitone (DMT) modulation with adaptive bit-/power-loading is applied to overcome the bandwidth limitation of the RSOA. Transmission performance of the proposed scheme is analyzed in terms of various system parameters, such as the nonlinearity of the RSOA, optical signal-to-noise ratio of the optical seed carrier, the overhead size impact on dispersion, the number of DMT subcarriers, and the reflection noise from the single fiber link. We also report flexible-bandwidth-allocated multiple access operation based on the proposed scheme. The throughput for all cases is approximately 10 Gbit/s with BER < 10(-3).

Record high-speed short-range transmission over 1 mm core diameter POF employing DMT modulation.

We report multigigabit/second transmission capacity in 1 mm core diameter graded index plastic optical fiber (POF) exploiting off-the-shelf low-cost components and discrete multitone (DMT) modulation. Transmission capacities of 10.1 Gbits/s x 15 m and 12.7 Gbits/s x 3 m are achieved for average bit-error rates less than 10(-3).

All-optical demultiplexing of 640 to 40 Gbits/s using filtered chirp of a semiconductor optical amplifier.

We present a high-capacity ultrafast all-optical time demultiplexer that can be employed to retrieve 40 gigabits/second (Gb/s) base-rate channels from a 640 Gb/s single-polarized signal. The demultiplexer utilizes ultrafast effects of filtered chirp of a semiconductor optical amplifier. Excellent demultiplexing performance is shown at very low switching powers: +8 dBm (640 Gb/s data) and -14 dBm (40 GHz clock). The demultiplexer has a simple structure and, in principle, allows monolithic integration.

40 Gb/s all-optical packet clock recovery with ultrafast lock-in time and low inter-packet guardbands.

We demonstrate a 40 Gb/s self-synchronizing, all-optical packet clock recovery circuit designed for efficient packet-mode traffic. The circuit locks instantaneously and enables sub-nanosecond packet spacing due to thelow clock persistence time. A low-Q Fabry-Perot filter is used as a passive resonator tuned to the line-rate that generates a retimed clock-resembling signal. As a reshaping element, an optical power-limiting gate is incorporated to perform bitwise pulse equalization. Using two preamble bits, the clock is captured instantly and persists for the duration of the data packet increased by 16 bits. The performance of the circuit suggests its suitability for future all-optical packet-switched networks with reduced transmission overhead and fine network granularity.

SOA-based all-optical switch with subpicosecond full recovery.

We investigate all-optical switching in a multi-quantum-well semiconductor optical amplifier-based nonlinear polarization switch using optical pulses with duration of 200 fs at a central wavelength of 1520 nm. We show full recovery of the switch within 600 fs, in both the gain and absorption regime. We discuss the switching and recovery mechanisms using numerical simulations that are in qualitatively good agreement with our experimental data.

Sub-picosecond pulse generation employing an SOA-based nonlinear polarization switch in a ring cavity.

We demonstrate the generation of sub-picosecond optical pulses using a semiconductor optical amplifier (SOA) and a linear polarizer placed in a ring-laser configuration. Nonlinear polarization rotation in the SOA serves as the passive mode-locking mechanism. The ring cavity generates pulses with duration below 800 fs (FWHM) at a repetition rate of 14 MHz. The time -bandwidth product is 0.48. Simulation results in good agreement with the experimental results are presented.

Carrier recovery time in semiconductor optical amplifiers that employ holding beams.

An analytical expression for the carrier recovery time in semiconductor optical amplifiers (SOAs) that employ holding beams is presented. The amplifier model from which the expression is derived assumes a uniform carrier density along the SOA's length and that the signal and the holding beams both receive amplification. Simulations and experiments show that the expression predicts the recovery time well over a wide range of amplifier gains, holding beam powers, and configurations.