Rod C. Alferness

Polarization rotation in asymmetric periodic loaded rib waveguides

A new mechanism for polarization rotation in rib waveguides is suggested and demonstrated in InP waveguides. The polarization rotation is achieved by loading a rib waveguide in a periodic asymmetric way. Complete TE↔TM conversion, with only 2–3 dB excess loss, is obtained in a 3.7‐mm‐long InP loaded waveguide. Strong polarization rotation (80%), in shorter devices (0.3 mm long), is also demonstrated.

Broadly tunable InGaAsP/InP laser based on a vertical coupler filter with 57‐nm tuning range

We have integrated a broadly tunable grating‐assisted vertical coupler as an intracavity filter to demonstrate a novel monolithic multiple‐quantum‐well InGaAsP/InP laser. The narrow, bandpass intracavity filter results in an extended cavity laser with a measured electrical tuning range of 57 nm with single‐frequency operation over most of that range.

Grating-assisted InGaAsP/InP vertical codirectional coupler filter

We report a novel wavelength selective coupler based upon grating‐assisted forward coupling between two, nonidentical, vertically stacked InGaAsP/InP waveguides. Using a 14.4 μm period to provide phase matching between the asynchronous waveguides, we achieve a filter bandwidth (full width at half maximum) of 65 A and coupling efficiency of ∼65% with a device length of only 1.0 mm.

Dispersion compensation by active predistorted signal synthesis

Techniques for the synthesis of an optical signal predistorted to compensate for fiber dispersion are discussed theoretically. A scheme for very high bit rate (>10 Gbit/s) time-division-multiplexed transmission is proposed which neither requires extremely short pulse sources nor suffers from their inherent dispersion limitations. The rudimentary aspects of the techniques have been verified experimentally by demonstrating both enhanced and degraded transmission of a 4-GHz modulated signal at 1.55 μm over 10-30 km of optical fiber.

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.

Broadly Tunable InGaAsP/Inp Buried Rib Waveguide Vertical Coupler Filter

We report the first demonstration of broadly electrically tunable (215 A), narrow‐band (∼20 A full width at half maximum), wavelength selective, grating‐assisted coupling between vertically stacked buried rib InGaAsP/InP channel waveguides. This current injection tuned device is suitable for integration in a variety of photonic devices and integrated circuits including broadly tunable extended cavity lasers, amplifier/filter, and demultiplexer/detector circuits.

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.

The evolution of optical systems: Optics everywhere

With the explosion of capacity demands driven by the Internet, optical networking systems are experiencing tremendous growth and are providing increasingly high transmission capacities. As importantly, with the advent of the optical amplifier and wavelength division multiplexing (WDM), optics is playing a larger role in networking and is extending further to the edge of the network. Once limited to long-haul point-to-point systems, Lucent Technologies is now commercializing multipoint metro WDM ring systems that include software-controlled optical wavelength add/drop multiplexers and soon will offer large optical cross connects. These optical network elements, together with network management software, will enable rapid provisioning of wavelength services, as well as rapid network restoration. In addition, as the cost of optics is driven down and the demand for bandwidth to businesses and residential customers continues to grow, optical systems are extending out from the network core and metro to access applications. The confluence of a proliferation of broadband service applications and rapidly maturing optical technology are literally driving optical systems into all segments. Increasingly, optics is literally everywhere.

Time- and frequency-domain response of directional-coupler traveling-wave optical modulators

We analyze the time- and frequency-domain response of directional-coupler traveling-wave optical modulators (DCTWOM) in which the optical and electrical velocities are not matched. We demonstrate for traveling-wave modulators that a directional-coupler device is intrinsically faster, by nearly a factor of \sqrt{3} for the same drive, than an interferometric device of the same length. We also show, that because of nonlinearities in the directional-coupler response, the switching speed inferred through a numerical analysis in the frequency domain underestimates the impulse response derived directly in the time domain. For a directional-coupler traveling-wave modulator based in LiNbO 3 , the Fourier transformation of the impulse response (33 ps/cm FWHM) indicates a characteristic length-bandwidth product of 15 GHz. cm when microwave loss is neglected. When realistic frequency-dependent losses are included in the frequency-domain calculations, we conclude that a 1-cm-long directional coupler in LiNbO 3 has a large signal 3-dB bandwidth in excess of 10 GHz. We determine the optical response to closely spaced electrical pulses, in order to evaluate the signal encoding bit rate capabilities of the device and its relation to the frequency bandwidth.

Vertically coupled InGaAsP/InP buried rib waveguide filter

We report the first demonstration of narrowband (<17 A full width at half maximum) wavelength selective grating‐assisted coupling between vertically stacked buried rib InGaAsP/InP channel waveguides. These vertically coupled channel waveguides form the basis both of integrable filters essential to photonic circuits such as amplifier/filter and demultiplexer/detector circuits as well as a general approach to vertical integration of photonic circuits.