A.B. Sahin

Doubling of bandwidth utilization using two orthogonal polarizations and power unbalancing in a polarization-division-multiplexing scheme

We propose and experimentally implement a method of demultiplexing two data channels, which were multiplexed using orthogonal polarizations on the same wavelength in a power ratio of 1:2 in order to double the bandwidth utilization in the fiber. Our technique facilitates the straightforward decoding of the two data channels and does not require the demultiplexing of the two orthogonal polarizations at the receiver. The two polarization channels each at 2.2 Gb/s are recovered after 100 km of fiber transmission with <1.0-dB power penalty.

All-optical address recognition for optically-assisted routing in next-generation optical networks

Optical fiber communication technology enabled high-speed, long-distance capacity in todays networks. The packet switching functions such as address recognition and routing are performed in the electrical domain after optical-to-electrical conversion. As more real-time applications come online, demand for bandwidth increases, and electronic processing may potentially become a bottleneck at the intermediate nodes along the network. We introduce some optical address recognition schemes for optically-assisted routing that may decrease the processing delay at these nodes.

Performance optimization of RZ data format in WDM systems using tunable pulse-width management at the transmitter

Tunable pulse-width management is one of the efficient methods to enhance the robustness of return-to-zero (RZ) data formats for long-haul transmission systems. We demonstrate both single channel and 4 /spl times/ 10-Gb/s wavelength-division-multiplexed performance optimization using tunable pulse-width management. Pure RZ single with tunable pulse-width is generated by changing the driving voltages on a phase modulator and the dispersion values of a tunable dispersion element simultaneously according to our simulation results. Varying the pulse width from 50 to 10 ps at the transmitter can almost double the transmission distance with 4% variation in the residual link dispersion.

First-order PMD monitoring for NRZ data using RF clock regeneration techniques

We propose and demonstrate two novel techniques for 10 Gb/s polarization-mode-dispersion (PMD) monitoring for NRZ signals that use a regenerated RF clock tone as a monitoring signal. Our techniques regenerate the RF clock tone that is usually absent after square-law detection in the electrical NRZ data spectrum (in the absence of dispersion). Our first technique uses a dispersive element in the monitoring tap-line to put the beat terms between the optical clock sidebands and the carrier in phase and thus regenerates the RF clock tone after detection. Our second technique involves the use of an optical filter that is centered at the bit rate frequency on either the upper or lower sideband of the optical spectrum, removing one of the sidebands and thus preventing the beating that normally cancels the RF clock tone. We show (theoretically, via simulation, and experimentally) the effect that PMD has on these regenerated RF clock tones. We also demonstrate PMD compensation at 10 Gb/s using these techniques for monitoring and show a 6-dB improvement in the 1% power penalty tail. Our techniques are simple, do not require modification at the transmitter, and can be applied to WDM systems via the use of a multichannel dispersive element or a tunable filter swept across all channels.

PMD monitoring by tracking the chromatic-dispersion-insensitive RF power of the vestigial sideband

We demonstrate a simple technique for polarization-mode-dispersion (PMD) monitoring that is insensitive to chromatic dispersion (CD). By monitoring the extracted radio-frequency clock power from the vestigial sideband, a CD-insensitive PMD feedback signal is realized. For a 10-Gb/s return-to-zero (RZ) system, experimental results show that the fluctuation of the feedback clock power due to CD is reduced from /spl sim/20 to /spl sim/3 dB. In the presence of all-order PMD, the distribution of the clock power is essentially unchanged as the inline CD varies. Simulation results for a 40-Gb/s RZ system are also presented.

All-optical wavelength and time 2-D code converter for dynamically-reconfigurable O-CDMA networks using a PPLN waveguide

We demonstrate all-optical wavelength and time code conversion for O-CDMA networks at 2.5-Gbit/s with 10-Gchip/s. Difference-frequency generation provides wavelength-shifting and fiber-Bragg gratings introduce cyclic time-shifts to the incoming code, generating a new time/wavelength code with less than 0.7-dB power penalty.

Multiwavelength-channel header recognition for reconfigurable WDM networks using optical correlators based on sampled fiber Bragg gratings

We demonstrate a tunable, multiwavelength optical correlator that uses an array of sampled fiber Bragg gratings (FBGs) as the correlating element. The incoming wavelength-division-multiplexing (WDM) data streams are tapped off and the packet headers on each 10-Gb/s channel are simultaneously recognized and correlated to a reconfigurable header code. The correlation output for each channel is compared to a threshold level, and simple decision electronics are used to drive a set of switches to route the individual WDM packets accordingly. Using this technique, we recognize two WDM 10-Gb/s packet headers simultaneously, with a negligible power penalty when switching packets to the appropriate output port. Moreover, we tune the gratings for reconfigurable routing.

Spectrum-Aware Underwater Networks: Cognitive Acoustic Communications

In this article, CAC to empower SUN inspiring from CR paradigm in wireless terrestrial communications is proposed. Spectrum scarcity in UAC due to the uniquely challenging underwater acoustic spectrum is discussed, and the need for spectrum-aware communication techniques is pointed out. We explore the capacity gain that can be achieved via CAC in SUN by simulation experiments and investigate the advantages and limitations of SUN along with its tradeoffs for DSA and OSA separately. Clearly, SUN can reach higher capacities than traditional fixed-spectrum approaches with the help of CAC capability. We expect that this article will provide better recognition for the capabilities of SUN and actuate further research efforts to explore this favorable area.

Statistics of PMD-induced power fading for intensity-modulated double-sideband and single-sideband microwave and millimeter-wave signals

Polarization-mode dispersion (PMD) can severely degrade the performance of millimeter-wave fiber-optic links by inducing a power fading penalty of the received signal that is dependent on the subcarrier frequency and accumulated PMD along the fiber. We experimentally investigate the statistics of PMD-induced power fading as a function of the differential group delay (DGD) for intensity-modulated double- and single-sideband subcarrier-multiplexed signals in the absence of chromatic dispersion. We find a similar susceptibility to PMD-induced power fading for both modulation formats with a subcarrier frequency of 7 GHz using a PMD emulator with a Maxwellian distribution of DGD (average DGD /spl sim/40 ps). A significant improvement in the worst case power fading penalty (/spl sim/20 dB) is achieved by using an electronically controlled polarization controller in combination with a single section of polarization maintaining fiber in a dynamic first-order PMD compensator. Furthermore, the results of numerical Monte Carlo simulations support the measured data and show the scalability of PMD-induced power fading for subcarrier-multiplexed signals in the microwave and millimeter-wave region.

Distance-independent microwave and millimeter-wave power fading compensation using a phase diversity configuration

We use a nonlinearly chirped fiber Bragg grating in a phase diversity configuration to achieve distance-independent microwave and millimeter-wave dispersion-induced power fading compensation for double-sideband subcarrier-multiplexed systems. We demonstrate compensation for power fading over 150 km at 8 and 12 GHz, with received subcarrier power in all cases uniform to within 1 dB.