Michel A. Duguay

An optical frequency scale in exact multiples of 100 GHz for standardization of multifrequency communications

Absolute laser frequency assignment in projected dense wavelength division multiplexing (DWDM) networks has become a very important issue for standardization purposes. Recently, a proposal was made to the International Telecommunication Union suggesting a set of standard wavelengths in the 1550 mn communications band. It recommended the use of a krypton line at 193.68625 THz as an absolute frequency reference and a set of 32 wavelengths evenly spaced by 100 GHz around that value. In this paper, we propose the use of an optical frequency scale with markers at exact multiples of 100 GHz for standardization. Our proposed scale is independent of the atomic or molecular species used for calibration (and thus accessible to any user), and moreover is uniformly applicable to all spectral regions. We show one way of implementing such a scale in the 1550 nm band through the use of an absolutely calibrated Fabry-Perot resonator set with a free spectral range of 100 GHz.

Remotely switched hollow-core antiresonant reflecting optical waveguide.

We describe a hollow-core antiresonant reflecting optical waveguide whose transmission can be remotely modulated by the motion of a glass substrate placed at a distance from the light-guiding core that ranges from tens to hundreds of micrometers. A maximum on-off ratio of 17 dB was observed. An analytical mathematical formalism developed to fit the data predicts the possibility of achieving on-off ratios of 30 dB.

Use of a sampled Bragg grating as an in-fiber optical resonator for the realization of a referencing optical frequency scale for WDM communications

Standardization for absolute laser frequency assignment in projected dense wavelength-division multiplexing (DWDM) networks has become a very important issue. Recently, we have proposed a referencing scale of standard optical frequencies that are exact multiples of 100 GHz. Such a scale is independent of the atomic or molecular reference used to set the absolute value and is uniformly applicable to all spectral ranges. Here, we propose the use of sampled Bragg gratings to realize the optical resonator. This resonator is adaptable, robust, potentially cost efficient and readily compatible with the fiber network.

Numerical analysis of the optimal length and profile of a linearly chirped fiber Bragg grating for dispersion compensation.

We propose a theoretical investigation of the length and coupling profile of a linearly chirped fiber Bragg grating for maximum dispersion compensation in a repeaterless optical communication system. The system consists of 100 km of standard optical fiber in which a 1550-nm signal, directly modulated at 2.5 Gbits/s, is launched. We discuss the results obtained with 6-, 4.33-, and 1-cm-long linearly chirped fiber Bragg gratings having Gaussian and uniform coupling profiles. We numerically show that a 4.33-cm-long chirped fiber Bragg grating having a uniform coupling profile is capable of compensating efficiently for the dispersion of our optical communication system.

Antiresonant waveguide add/drop filter using Fabry-Pérot interference

Abstract We describe planar waveguide structures that accomplish the Fabry-Perot filtering functionality by using the wavelength selective coupling between antiresonant optical waveguides. By using different cladding layer thicknesses wavelength selectivity is achieved despite the fact that the coupled waveguides have equal core thicknesses, in contrast with filters based on conventional waveguides. For the polymer-based configuration investigated here a resolution of 1.2 nm was obtained with a free spectral range of 12 nm. We also describe a dual output filter which could drop or add two different wavelengths at once in a wavelength division multiplexing (WDM) system.

Interferometric time measurements of intermodal dispersion in optical fibers by using a CCD photodetector array

An interferometric time measurement of the intermodal dispersion in a 40-m telecommunication fiber at 560 nm is reported. Six modes are identified as LP modes by their spatial interference pattern and are clearly time resolved. To overcome laser noise and low interference contrast, a new interferometric time measurement technique has been developed. The image of the interference fringe pattern is analyzed by a CCD photodetector array. Interference fringes produce a modulation at the CCDs output that can be filtered and averaged to retrieve accurate time information.

Time-resolved identification of modes and measurement of intermodal dispersion in optical fibers

Picosecond pulses from a tunable mode-locked visible dye laser are injected into a 603-m few-mode optical fiber. Measurements of the output power temporal profile with 35-ps resolution show six clearly resolved modes. Time-profile measurements over a two-dimensional array of points in the fiber output far field yield a picture of each mode that identifies it. Measurements as a function of wavelength and fitting to waveguide dispersion calculations are used to model the fiber core refractive-index profile. As a result for the nominal step-index fiber used in this work, the presence of an index dip at the center of the core was detected.

High finesse wavelength selective coupler based on ARROWs

We describe the design of an add/drop filter for wavelength division multiplexing applications that has a periodic Fabry-Perot functionality with a finesse of 100. The filter is based on a directional coupler comprising antiresonant reflecting waveguides (ARROWs) that are deliberately designed to be slightly asymmetric in order to increase the finesse. The insertion loss due to filtering is 3 dB for the selected (added/dropped) wavelengths, while the cross-talk of unselected ones is -25 dB.

Frequency-stabilized lasers for multifrequency optical communications: work done at Universite Laval

We have undertaken a research directed to the realization of frequency-stabilized lasers for multifrequency optical communications in the 375 THz, 229 THz, and 193 THz (0.8, 1.3, and 1.55 micrometers ) bands. In this paper, we present an overview of our latest results in the 1.55 micrometers band. We compare the performance of optical frequency references based on lasers frequency-locked to acetylene molecules and rubidium atoms. The absolute vales and the frequency stability improvements are discussed. We also present techniques to transfer those performance to multiple frequencies for multifrequency communication systems. We study the use of an absolutely calibrated multimode Fabry-Perot optical resonator with transmission peals set at exact multiples of 100 GHz. We also study the use of a calibrated wavemeter based on a sum-frequency surface emitting multilayered nonlinear crystal to allow the precise tuning at any frequency in the vicinity of an absolute optical frequency standard.

Wavelength division multiplexing based on mode-selective coupling

We propose devices for wavelength-division muliplexing based on coupling between different modes in optical fiber. A mode-selective directional coupler (MSDC) couples the LP01 mode of one fiber to the LP02 mode of a second fiber with a bandwidth. -length products of about 4 nmcm an improvement of a factor of 10 over LP01 + LP01 coupling. Refractive index gratings written with UV light can also couple light from the LP01 to the LP02 mode either in a counterpropagating way (Bragg grating) or a codirectional way. Combined with the MSDC they can make efficient channel-drop filters.