Polarization-multiplexed LDPC-coded QAM robust to I-Q imbalance and polarization offset is proposed. Efficient
mitigation of I-Q imbalance and polarization offset is demonstrated with LDPC-coded turbo equalization by
simultaneous MAP detection of symbols transmitted over two orthogonal polarizations. The proposed scheme is much
more efficient in I-Q imbalance and polarization offset compensation than conventional approaches.
In recent years LDPC codes have gained significant interest in the area of optical communication systems due to their
capacity-approaching performance, high coding gain and low decoding-complexity. We describe the construction
principles of high-rate, high-girth, quasi-cyclic LDPC codes and present an LDPC-coded turbo equalization scheme
suitable for simultaneous mitigation of multiple transmission impairments. The equalization scheme is based on the
maximum a posteriori probability detection, based on Bahl Cocke Jelinek Raviv (BCJR) algorithm that employs the
conditional density probability functions of the channel to calculate the initial log-likelihood ratios for the LDPC
decoder. To optimize the code performance extrinsic information transfer charts are used.
We then investigate and evaluate the performance of the proposed scheme in the presence of polarization mode
dispersion (PMD), fiber nonlinearities and chromatic dispersion for 10 Giga symbols/s transmission system and various
modulation formats including NRZ and polarization-multiplexed BPSK with both direct and coherent detection. LDPC
codes of rates 0.8, 0.9 and 0.95 are evaluated. Experiments with and without chromatic dispersion compensation are
This paper describes the development of a miniature assembly cell for microsystems. The cell utilizes a transparent electrostatic gripper allowing the use of computer vision for part alignment with respect to the gripper. Part to assembly alignment is achieved via optical triangulation using a fiber-coupled laser and a position sensitive detector (PSD). The system layout, principle of operation and design are described along with the visual and optical control algorithms and their implementation. Experimental measurements of the performance of the stage indicate normal and tangential gripping forces in the range of 0.03-2.5 mN and 1.-9. mN respectively. The visual search algorithm limits the feature tracking speed to 111ms /search. The alignment accuracy of the visual and optical proportional position feedback controls were determined to be ±7 μm and ±10 μm respectively.