Vahid R. Arbab

Theoretical and Experimental Investigations of Direct-Detected RF-Tone-Assisted Optical OFDM Systems

In this paper, we propose and experimentally demonstrate a radio frequency (RF)-tone-assisted optical orthogonal frequency-division multiplexing (OFDM) transmission. By inserting an RF tone at the edge of the signal band and biasing the Mach-Zehnder modulator (MZM) at the null point, the proposed system has a better sensitivity and chromatic dispersion (CD) tolerance compared to the previous intensity-modulated single-sideband OFDM (SSB-OFDM). We show analytically that the majority of the linear channel impairments, such as the transmitter, CD, optical filtering, and receiver, can be compensated for by a simple zero-forcing equalizer. Besides, the optimum value of the important parameter, carrier-to-signal-power ratio (CSPR), is analytically obtained and supported via the experimental results. We also observe that the relatively worse sensitivity of the previous SSB-OFDM can be attributed to the limited CSPR. We experimentally demonstrate a 10-Gb/s, 8 quadrature-amplitude modulation (QAM) RF-tone-assisted OFDM transmission, and show that our system has a ~ 5-dB better sensitivity compared to the previous intensity-modulated SSB-OFDM and exhibits a negligible transmission penalty after 260-km uncompensated standard single-mode fiber (SSMF).

Spectrally efficient direct-detected OFDM transmission employing an iterative estimation and cancellation technique.

We demonstrate a linearly field-modulated, direct-detected virtual SSB-OFDM (VSSB-OFDM) transmission with an RF tone placed at the edge of the signal band. By employing the iterative estimation and cancellation technique for the signal-signal beat interference (SSBI) at the receiver, our approach alleviates the need of the frequency gap, which is typically reserved for isolating the SSBI, and saves half the electrical bandwidth, thus being very spectrally efficient. We derive the theoretical model for the VSSB-OFDM system and detail the signal processing for the iterative approach conducted at the receiver. Possible limitations for this iterative approach are also given and discussed. We successfully transmit a 10 Gbps, 4-quadrature-amplitude-modulation (QAM) VSSB-OFDM signal through 340 km of uncompensated standard single mode fiber (SSMF) with almost no penalty. In addition, the simulated results show that the proposed scheme has an approximately 2 dB optical-signal-to-noise-ratio (OSNR) gain and has a better chromatic dispersion (CD) tolerance compared with the previous intensity-modulated SSB-OFDM system.

Experimental Demonstration of a Coherently Modulated and Directly Detected Optical OFDM System Using an RF-Tone Insertion

We experimentally demonstrate an RF-tone assisted OFDM transmission. Our system has a 5-dB better sensitivity compared to the conventional baseband SSB-OFDM and exhibits a negligible penally transmission after 260 km of SSMF.

Experimental Demonstration of 340 km SSMF Transmission Using a Virtual Single Sideband OFDM Signal that Employs Carrier Suppressed and Iterative Detection Techniques

We propose and demonstrate a virtual SSB-OFDM with direct detection that uses half the electrical bandwidth by employing an RF tone at the edge of the signal. We transmit 10 Gbps data with a 4-QAM over 340 km of SSMF with no penalty.

Tunable optical wavelength conversion of OFDM signal using a periodically-poled lithium niobate waveguide

We experimentally demonstrate tunable optical wavelength conversion of a 10-Gb/s radio frequency (RF)-tone assisted orthogonal-frequency-division-multiplexing (OFDM) signal with approximately-5 dB (approximately 30%) efficiency over approximately 30 nm bandwidth using a periodically-poled lithium-niobate (PPLN) waveguide. A penalty of < 3 dB is obtained after wavelength conversion. Quadrature amplitude modulation (QAM) size and subcarrier number are varied to further evaluate the performance of the wavelength converter.

Advanced Techniques to Increase the Number of Users and Bit Rate in OCDMA Networks

Optical code-division multiple-access (OCDMA) systems have recently become a topic of interest for their potential application in access points and optical LANs. In this paper, we review OCDMA systems and their limitations, as well as various experimental techniques to increase the number of users and/or bit rate in a system or a network. These techniques include incorporating M-ary modulation formats, hard-limiting receiver, variable thresholding, and orthogonal polarizations as the third dimension. We also discuss some network limitations such as congestion collapse and near-far effect, and we investigate two techniques to overcome them: interference avoidance and missing chip detection.

Experimental Demonstration of an Interference-Avoidance-Based Protocol for O-CDMA Networks

We demonstrate the transmission scheduling algorithm in an O-CDMA network to avoid congestion collapse in an O-CDMA network. Our result shows that transmission scheduling increases the performance of the system by orders of magnitude.

Increasing the bit rate in OCDMA systems using pulse position modulation techniques

We have experimentally demonstrated two novel pulse position modulation techniques, namely Double Pulse Position Modulation (2-PPM) and Differential Pulse Position Modulation (DPPM) in Time-Wavelength OCDMA systems that will operate at a higher bit rate compared to traditional OOK-OCDMA systems with the same bandwidth. With 2-PPM technique, the number of active users will be more than DPPM while their bit rate is almost the same. Both techniques provide variable quality of service in OCDMA networks.

Effects of fiber impairments on constellation diagrams of optical phase modulated signals

The effects of chromatic dispersion (CD) and first order polarization mode dispersion (PMD) on constellation diagrams of phase modulated signals are investigated via simulation and different methods to visualize these effects are presented. It is shown that constellation diagrams of (D)QPSK signals sampled by an asynchronous receiver can be used to simultaneously monitor CD and first order PMD. The amount of accumulated impairments can be estimated by quantifying certain deformations in patterns of constellation diagrams.

Experimental demonstration of multicarrier-CDMA for passive optical networks

Optical multicarrier-CDMA is experimentally demonstrated for the first time. The system supports up to 256 users at a total bit rate of 15-Gb/s with almost no penalty after 70-Km transmission.