Ernst Brinkmeyer

High-resolution OCDR for testing integrated-optical waveguides: dispersion-corrupted experimental data corrected by a numerical algorithm

A numerical algorithm is presented and applied to dispersion-corrupted experimental data taken by coherence domain reflectometric (OCDR) measurements. It results in a retrieval of micrometer resolution and an enhanced dynamic range. High-resolution OCDR measurements may be seriously impaired by dispersion effects in the waveguides under test and rugged source spectra. In the investigation (Ti:LiNbO/sub 3/ single-mode waveguide, 16 mm long; superluminescent diode source at lambda /sub 0/=820 nm) the spatial resolution progressively deteriorates along the waveguide by about one order of magnitude (from 6 to 60 mu m). The algorithm was applied to the experimental data and successfully removed the dispersive broadening of the signatures. >

Analysis of Raman lasing characteristics in silicon-on-insulator waveguides.

Numerical analysis predicts that continuous-wave Raman lasing is possible in silicon-on-insulator (SOI) waveguides, in spite of the detrimental presence of two-photon absorption and free-carrier absorption. We discuss in particular the dependence of the lasing characteristics of SOI Raman lasers on the effective lifetime of the free carriers generated by two-photon absorption. It is shown that the pump-power-dependent cavity losses lead to a rollover of the output-power characteristics at a certain pump-power level and that there exists an upper shutdown threshold at which the laser operation breaks down.

Pulse generation in fiber lasers with frequency shifted feedback

Lasers with frequency shifted feedback may spontaneously generate periodic trains of short optical pulses. Frequency shifts as small as several kilohertz per roundtrip are shown to sustain pulsing at the cavity fundamental frequency in Er/sup 3+/- and Nd/sup 3+/-fiber lasers with intracavity acousto-optic frequency shifters. A numerical model based on the split step Fourier method suggests that this pulse mode of operation may be attributed to the Kerr-type nonlinearity of the optical fiber. >

Comment on "Nonreciprocal light propagation in a silicon photonic circuit".

We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.

Simple algorithm for reconstructing fiber gratings from reflectometric data.

A simple, fast, and accurate algorithm is presented that is suitable for retrieving spatial grating structures in single-mode waveguides from reflectometric data. In particular, it is tailored to coherence-domain reflectometric measurements. Since the scheme uses a physical/experimental line of reasoning and the standard mathematics of communication theory, it is easy to survey and may also yield a simplified access to generalized problems not covered by the common coupled-mode equations.

Automatic PMD compensator in a 160-Gb/s OTDM transmission over deployed fiber using RZ-DPSK modulation format

We report on a magneto- and electrooptically tuned dynamic polarization-mode dispersion (PMD) compensator that enabled error-free single-channel 160-Gb/s RZ-DPSK transmission over a 75-km SMF link with a mean differential group delay (DGD) of more than 30% of the bit period. Polarization scrambling and DOP measurements were utilized to automatically adapt the compensator. We present bit error rate (BER) measurements and describe the operation of the compensator in detail.

Feedforward approach for automatic PMD-compensation at 80 Gbit/s over 45 km installed single mode fiber

We report 80 Gbit/s transmission over 45 km installed fiber employing automatic PMD-compensation. A feedforward controller adjusts the DGD (differential group delay) of the PMD (polarization mode dispersion) compensator in a single step, avoiding the need for dithering.

Gain Enhancement in Cladding-Pumped Silicon Raman Amplifiers

Core-pumped silicon Raman amplifiers reported so far have exhibited gains of 4 dB or less in continuous-wave operation, limited by free-carrier absorption. Here we propose a device design that mitigates the problem of free-carrier absorption and leads to significantly higher gain values. In the new design, we surround the silicon waveguide with an additional rib-shaped passive cladding with a refractive index between that of silicon and the silica buffer. By injecting the pump power into the cladding, instead of directly into the silicon core, the overlap of the pump power with the silicon core is reduced and thus the effect of free-carrier absorption on the pump is weakened. The amplifier may therefore be made much longer, and higher total gains be achieved than in conventional core-pumped amplifiers. We present a detailed analysis of a design where a total gain as high as 18 and 34 dB may be achieved with pump powers of 300 mW and 1 W, respectively. We describe the model we have developed to design and optimize cladding-pumped silicon Raman amplifiers. Explicit expressions are formulated for the nonlinear effective areas for stimulated Raman scattering and two-photon absorption in silicon waveguides, taking into account the differing tensorial structures of these nonlinearities.

UV-induced absorption, scattering and transition losses in UV side-written fibers

We demonstrate that UV-illumination of hydrogen-loaded photosensitive fiber leads to considerable loss. The three contributing loss mechanisms of absorption, scattering, and losses are quantified and discussed.

Numerical optimization of multi-wavelength and cascaded Raman fiber lasers

We present a model for the simulation and optimization of Raman fiber lasers. Applications include cascaded Raman lasers as well as lasers running on several wavelengths within one Stokes band. The model takes into account forward and backward propagating waves as well as Raman induced interactions between all pump and Stokes lines. Example calculations for both the simulation of a laser and the optimization of the mirror reflectivities for maximum overall output power and equalized laser lines are performed.