Mark Wegmuller

Experimental study of polarization properties of highly birefringent photonic crystal fibers.

We analyze experimentally the polarization properties of highly nonlinear small-core photonic crystal fibers (PCFs) with no intentional birefringence. The properties of recently emerged polarization maintaining PANDA PCFs are also investigated. The wavelength and temperature dependence of phase and group delay of these fibers are examined in the telecommunications wavelength range. Compared to a standard PANDA fiber, the polarization characteristics and temperature dependence are found to be qualitatively different for both types of fibers.

Photon counting at telecom wavelengths with commercial InGaAs/InP avalanche photodiodes: current performance

Abstract InGaAs/InP avalanche photodiodes operated in the so-called Geiger mode currently represent the best solution to detect single-photon beyond 900nm. They cover the 1100–1650nm wavelength interval, which includes in particular the two windows used for optical communications (1310 and 1550nm). A detection efficiency at 1550nm of 10% with a dark count probability of 10−5 ns−1 is common, although significant variations can be encountered. At this efficiency, a FWHM temporal response of 300 ps can be achieved. Afterpulses caused by charges trapped by defects in the high field region of the junction constitute the main performance impairment phenomenon. They enhance the dark count probability and reduce out-of-gate detector blindness. These photon counting detectors can be used in optical time-domain reflectometry to improve the spatial resolution and reduce dead-zone effects. Quantum key distribution over metropolitan area networks also constitutes an important application.

High-speed (11 Gbit/s) data transmission using perfluorinated graded-index polymer optical fibers for short interconnects (<100 m)

Perfluorinated graded-index polymer optical fibers (GI-POFs) have been developed that offer low losses (<50 dB/km) and high bandwidth (>0.3 GHz km) at data communication wavelengths (0.85 and 1.3 /spl mu/m). Here we demonstrate that such fibers can support data rates up to 11 Gbit/s for 100 m with low-power penalty and large-power margins. Although a restricted launch was used, differential mode delay measurements show that, in a large central region of the fiber core (50% of the core diameter), very large bandwidths can be obtained with modest alignment requirements. These improved transmission characteristics (obtained using inexpensive, uncooled, unisolated 1.3-/spl mu/m Fabry-Perot sources and pin detectors) together with potential low-cost connectorization and a small fiber bend-radius make perfluorinated GI-POFs a candidate for premise networks and short-reach telecom and computer interconnections.

Photon-counting OTDR for local birefringence and fault analysis in the metro environment

Optical time domain reflectometery (OTDR) is one of the most used measurement techniques in the characterization of optical fiber links. In this paper, we present a thorough investigation of an OTDR using a Peltier cooled photon-counting detector at 1.55 um. Due to its superior spatial resolution and the absence of classical dead-zones, it is well suited for detailed, high resolution analysis of problem zones. We give a detailed analysis of its performance, and also demonstrate that a polarization-sensitive photon-counting OTDR can be used to extract local birefringences too large to be measured with standard P-OTDRs.

Investigation of the ratio between phase and Group birefringence in optical single-mode fibers

A measurement technique for the phase and group birefringence of an optical fiber is thoroughly investigated. It is based on differential group delay measurements of twisted fibers and is capable of giving in a simple and elegant way the intrinsic birefringence values in the absence of twist. Analyzing various fibers with this method, we find that phase and group birefringence can be quite different for certain fiber types. Consequently, the commonly used assumption that in an optical fiber, phase and group birefringence are equal-and the resulting carelessness in distinguishing between these two a priori separate physical effects-is to be employed cautiously.

Experimental investigation of the polarization properties of a hollow core photonic bandgap fiber for 1550 nm.

The properties of a hollow core photonic bandgap fiber designed for 1.55 um transmission are investigated with special emphasis on polarization issues. Large and strongly wavelength dependent phase and group delays are found. At the same time the principle states of polarization move strongly and erratically as a function of wavelength, leading to strong mode coupling. Wavelength regions with high polarization dependent loss coincide with depolarization due to a polarization dependent coupling to surface modes at these wavelengths.

Distributed gain measurements in Er-doped fibers with high resolution and accuracy using an optical frequency domain reflectometer

For critical erbium-doped fiber amplifier (EDFA) design, e.g., gain tilt optimization in WDM booster amplifiers, knowledge of the gain distribution within the active fiber can present a valuable information. Among the different techniques to evaluate the distributed gain in active fibers, the technique of optical frequency domain reflectometry seems most promising as it is a non-destructive measurement method well matched to the task due to its dynamic range, resolution, and range. Moreover, background light from ASE or residual pump light is strongly rejected due to the coherent detection scheme employed. Using different erbium-doped fibers with strongly varying doping levels and confinements, we demonstrate the excellent accuracy and reproducibility of the technique.

Emulator of first- and second-order polarization-mode dispersion

Contrary to approaches which try to mimic a standard fiber as closely as possible, the emulator presented here gives constant (but user adjustable) values for differential group delay (DGD) and ratio of first- to second-order polarization-mode dispersion (PMD). Once it is set, the ratio is conserved while the DGD can be easily varied within a range of 0-300 ps. This allows to investigate the low-probability events of large DGD and second-order PMD important for system outage.

Long-distance OTDR using photon counting and large detection gates at telecom wavelength

Photon-counting OTDRs are typically used in a mode with spatial resolutions in the centimeter range. Here we demonstrate that their sensitivity and dynamic range can be enlarged using lower resolutions. A 44-dB dynamic range was experimentally obtained at a wavelength of 1550 nm. This represents a 4-dB increase compared to state-of-the-art long-haul classical OTDRs having the same spatial resolution, and could even be extended to 6.5 dB when using a source with +13-dBm peak power. Furthermore we demonstrate an original solution to suppress perturbing dead-zones.

Measurements of the nonlinear coefficient of standard, SMF, DSF, and DCF fibers using a self-aligned interferometer and a Faraday mirror

Using a method based on the detection of the Kerr phase shift by a self-aligned interferometer, we present measurements of the nonlinear coefficient n/sub 2//A/sub eff/ for standard single-mode fiber (SMF), dispersion-shifted fibers, and dispersion compensating fibers. The presence of a Faraday mirror in the interferometer makes the setup very robust, and different test fibers can be measured without any further readjustments. Interlaboratory comparisons show that the values found with our method are in good agreement with the other ones. Further, analysis of a SMF fiber with large chromatic dispersion shows a good reproducibility of the n/sub 2//A/sub eff/ measurements as a function of fiber length.