L. L. Buhl

Spectrally Efficient Long-Haul Optical Networking Using 112-Gb/s Polarization-Multiplexed 16-QAM

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 112-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 14 Gbaud and spectral efficiencies beyond 4 b/s/Hz. We describe the (off-line) digital signal processing and blind filter adaptation algorithms used in our intradyne receiver and characterize its performance using both simulated and measured 16-QAM waveforms. We measure a required optical signal-to-noise ratio of 20.2 dB (0.1-nm reference bandwidth; 10-3 bit-error ratio), 3.2-dB off the theoretical limit. We study the effects of finite analog-to-digital converter resolution, laser frequency offset, laser phase noise, and narrowband optical filtering. Our experiments on a 25-GHz WDM grid (4.1-b/s/Hz spectral efficiency) reveal a 1-dB penalty after 7 passes though reconfigurable optical add/drop multiplexers (ROADMs) and an achievable transmission reach of 1022 km of uncompensated standard single-mode fiber. At a spectral efficiency of 6.2 b/s/Hz (16.67-GHz WDM channel spacing) a transmission reach of 630 km is attained.

Narrowband grating resonator filters in InGaAsP/InP waveguides

We report the first demonstration of efficient narrowband optical wavelength filters using InGaAsP/InP passive waveguide grating resonators. Filter bandwidths as narrow as 1 A, centered about λ=1.55 μm with excess resonator loss as low as 1 dB, have been achieved.

8-Gbit/s transmission experiment over 68 km of optical fiber using a Ti:LiNbO 3 external modulator

We report a single-channel optical fiber data link with the largest bit-rate<tex>x</tex>repeater spacing product achieved to date- ∼ 0.5 Tb . km/s. The multi-gigabit per second system is the first to incorporate a Ti:LiNbO<inf>3</inf>external modulator as the data encoder.

OSNR Monitoring Method for OOK and DPSK Based on Optical Delay Interferometer

We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift-keying (DPSK) signals by using an optical delay interferometer (ODI) having a sinusoidal and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit ODI and a 40-Gb/s DPSK signal by using a partial-bit ODI with the OSNR ranging from 5 to 25 dB.

Mode size and method for estimating the propagation constant of single-mode Ti:LiNbO 3 strip waveguides

We have formulated a model to calculate the mode size and propagation constant of single-mode titanium-lithium niobate diffused strip waveguides directly from controllable fabrication parameters and basic constants. The model is compared to measurements of the lateral and vertical mode width of Ti:LiNbO 3 waveguides for a variety of diffusion conditions. We show that the model accurately predicts the geometrical mean mode size of the two-dimensional waveguide. The model provides a simplified method for estimating the mode size and propagation constant of the guide, and is useful in designing waveguide devices having low fiber/waveguide coupling and bending losses.

Packaged Monolithic Silicon 112-Gb/s Coherent Receiver

Using a Si photonic integrated circuit and separate SiGe transimpedance amplifiers, we created a high-performance dual-polarization, dual-quadrature coherent receiver. It requires only 16.3-dB optical signal-to-noise ratio to receive a 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying signal at a 10-3 bit-error rate.

Efficient single-mode fiber to titanium diffused lithium niobate waveguide coupling for &#955; = 1.32 &#181;m

We report detailed results on the achievement of very high optical throughput for titanium diffused lithium niobate waveguides coupled between input and output single-mode fibers. By determining appropriate diffusion parameters to obtain excellent dimensional match between the fiber and waveguide modes and simultaneously low propagation loss, we have achieved total measured fiber-waveguide-fiber insertion loss as low as 1 dB for a 1 cm long waveguide at \lambda = 1.32 \mu m. The relative contributions of coupling and propagation loss are determined. Very good correlation is found between the coupling loss and the match between the fiber and waveguide mode dimensions. Design data for diffusion parameters to obtain good mode match for arbitrary fiber dimension are presented.

Fully connectorized high-speed Ti:LiNbO 3 switch/modulator for time-division multiplexing and data encoding

We demonstrate a fully connectorized and packaged, 2×1 high-speed Ti:LiNbO 3 directional coupler switch suitable for both optical time-division multiplexing/demultiplexing and modulation at a 1.3- μm wavelength. The device has an intrinsic switching time of 60 ps and a small-signal 50-percent optical modulation depth bandwidth of 6 GHz. We have actively multiplexed two optical pulse streams with output non-return-to-zero (NRZ) center-to-center bit spacings of less than 100 ps, while incurring an average optical power penalty of only 0.5 dB. In addition, we have used this switch as a modulator to encode a pseudo-random data stream at 2-Gbit/s NRZ without degradation of the eye pattern or the semiconductor laser source spectrum.

An automatic 40-wavelength channelized equalizer

We demonstrate a wavelength equalizer in planar silica waveguides that can automatically control individual channel powers in a 40-channel 100-GHz-channel-spacing wavelength-division multiplexed system, yet gives no distortion to channels that already have the same power as their neighbors. It has <6.8 dB insertion loss over 32-nm, 9-13-dB attenuation range, and <0.18 dB polarization/time-dependent loss.

All-optical XOR and XNOR operations at 86.4 Gb/s using a pair of semiconductor optical amplifier Mach-Zehnder interferometers

We propose a method for increased-speed all-optical XOR operation using semiconductor optical amplifiers. We demonstrate XOR and XNOR operations at 86.4 Gb/s using a pair of photonic-integrated semiconductor optical amplifier Mach-Zehnder interferometers.