Etienne Rochat

Experimental demonstration of cascaded AWG access network featuring bi-directional transmission and polarization multiplexing

We present the first experimental demonstration of a bidirectional cascaded arrayed-waveguide grating (AWG) access network combining one NxN AWG in the central office with multiple 1xN AWGs at the distribution points, such as to individually address N(2) users with only N wavelengths. Downstream and upstream data share the same optical path. BER curves were measured using 2.5Gb/s data stream in each direction, and error free transmission achieved for downstream and upstream, with only 0.3dB power penalty for simultaneous transmission. The addition of two orthogonal polarization-multiplexed channels per wavelength doubled the number of possible end users. Error free transmission was achieved with simultaneous upstream and downstream transmission of a composite signal featuring eight 2.5Gb/s channels (2 polarizations x 4 wavelengths).

Polarimetric fiber laser sensor for hydrostatic pressure

A polarimetric Fabry-Perot fiber laser sensor for fluid pressure up to 100 MPa is investigated. The fluid acts on one of two elliptical-core fiber sections in the laser cavity, producing a shift in the differential phase of the two orthogonal polarization modes and thus a variation in the beat frequencies of the corresponding longitudinal laser modes. The second fiber section, with a 90 degrees offset in the core orientation, compensates for temperature-induced phase shifts. The dispersion in the birefringent fiber Bragg grating reflectors is employed to remove the near degeneracy of the polarization mode beat frequencies of a given order and to improve substantially the resolution of the sensor to a few parts in 10(6) of the free spectral range. Further investigations address the effect of the fluid on the integrity of the fiber, the influence of various fiber coatings on the sensor response, and the intrinsic stability of erbium-doped and undoped sensing fibers under fluid pressure.

Fiber amplifiers for coherent space communication

We report on the application of double-clad doped fiber amplifiers for coherent space communication systems using a master oscillator power amplifier (MOPA) design at 1.06 /spl mu/m. The master oscillator is either a single-frequency Nd:YAG solid-state laser or a distributed-feedback fiber laser. The power amplifier is a diode-laser-pumped double-clad Nd doped fiber with polarization control, 20 dB gain, and about 1.3 W output power. A dual stage configuration using a solid-state Nd:YAG amplifier as second stage is presented as well, increasing the output power to 3.5 W with 28 dB gain. We also report on the possibility to integrate a single-frequency fiber laser, an all-fiber phase modulator, and a fiber amplifier to build an all-fiber phase-modulated MOPA. Up to 1 W continuous-wave output phase-modulated with a bandwidth of 196 MHz has been achieved.

High-power Nd-doped fiber amplifier for coherent intersatellite links

Intersatellite optical communication links require laser beams of at least 1 W of power modulated at gigahertz frequencies. They can be delivered by a master oscillator power amplifier system which consists of a stable single-frequency Nd:YAG laser, a high-speed phase modulator, and an optical amplifier. To allow coherent detection, the polarization state must be stable and controllable at the amplifier output and the phase noise must be kept low. We report here the design and the experimental results of a diode laser-pumped double clad Nd-doped fiber amplifier with polarization control, 30-dB gain, and about 1.3 W of output power.

Polarisation and wavelength division multiplexing at 1.55μm for bandwidth enhancement of multimode fibre based access networks

We demonstrate how a combination of polarisation-division multiplexing (PDM) and wavelength-division multiplexing (WDM) applied to graded index 50 mum multimode fibres (MMF) at 1.55 mum can be used to greatly increase the available optical bandwidth. A proof of principle experiment demonstrated error-free data transmission over 3km of MMF, using two 100GHz-spaced wavelengths, each carrying two 2.5Gb/s orthogonal PDM multiplexed channels, resulting in a 10Gb/s data rate. Polarisation and wavelength demultiplexing were simultaneously achieved by use of a grating based monochromator. We also practically implemented this transmission scheme in an all-fibre experiment, replacing the monochromator by a more convenient polarisation-insensitive, 200GHz ITU grid spacing 62.5 mum MMF pigtailed WDM demultiplexer. Using two polarizations each on four wavelengths (2P x 4lambda), we repeatedly achieved error-free data transmission for both circularly and linearly polarisation-wavelength-division-multiplexed channels over a MMF span of 300m, featuring a 20Gb/s data rate. Overall, we have demonstrated a major increase in the MMF bandwidth-distance product up to 30GHz-km.

Polarization dependent loss and temperature fluctuations effect on degree of orthogonality in polarization multiplexed arrayed waveguide grating based distribution networks

We analyze the effect of arrayed-waveguide grating (AWG) polarization dependent loss (PDL) on the orthogonality between polarization multiplexed channels in a cascaded AWG-based access network topology. For a single AWG, with 0.5-dB PDL, we find an experimental degradation in polarization multiplexing orthogonality to be a maximum of 0.9/spl deg/, in good agreement with theory. In addition, experimental, and numerically simulated maps of orthogonality degradation versus input states of polarization (SOP) are investigated and found to agree well. Consequently, we analyze the effect of cascaded AWGs and again find that the experimental result of maximum 2.9/spl deg/ degradation in polarization multiplexing orthogonality closely matches theoretical predictions. Thermal variations are also found to have similar effects for all SOPs, with a measured degradation in orthogonality of up to 2.5/spl deg/ for a temperature range between 20/spl deg/C and 55/spl deg/C. Overall, this indicates the robustness of polarization multiplexing, making it applicable for appropriate deployment in bandwidth/user-enhanced access networks based on cascaded AWGs.

C-band polarisation orthogonality preservation in 5Gb/s, 50µm multimode fibre links up to 3km

We have investigated the polarisation-maintenance capability of 50microm graded-index multimode fibres (MMF) in the Cband. Using both circularly, and linearly polarisation-multiplexed signals centre-launched into the MMF, we found that orthogonality is sufficiently maintained in both cases to yield typically 10dB optical isolation between the channels.Using orthogonally circular polarisationmultiplexed signals, we show experimentally that two 3 and 5Gb/s data channels may be transmitted error free over 50microm multimode fibre spans up to 3km in length.

All-order PMD compensation using filter theory interpretation of Poincare sphere trajectories

We have shown how polarization trajectories on the Poincare Sphere due to PMD effects can be modelled using optical lattice filter theory. Our theory shows that variation of polarisation ellipticity /spl delta/ with angular frequency /spl omega/, is the cause of differential PMD degradation, whereas variation in polarisation orientation /spl chi/ with /spl omega/ is analogous to basic group delay and conventional chromatic dispersion. This new approach is scaleable and allows all PMD orders to be mitigated. Dynamic control of filter parameters depends on the characteristics of a global multiple loop feedback system.

All-fiber phase-modulated master oscillator power amplifier for coherent communication

An all-fiber phase-modulated master oscillator power amplifier for free-space coherent communication is presented. A distributed-feedback fiber laser at 1.06 /spl mu/m is used as master oscillator. A novel phase modulator based on a ZnO-coated single-mode fiber modulates the single frequency communication signal. The modulated signal is then amplified in a double-clad doped fiber power amplifier. Up to 1 W cw single-frequency output power, phase modulated at 196 MHz, has been obtained.

High-gain solid-state and fiber amplifier-chain for high-power coherent communication

We report on the experimental results of a dual-stage amplifier combining a Nd-doped double-clad fiber and a Nd-doped YAG crystal. We obtained up to 3.5-W single-mode single-frequency output power with 28-dB gain. This is, to the best of our knowledge, the first demonstration of a dual-stage amplifier combining doped fibers and solid-state amplifiers.