In this paper, we propose a multi-level non-binary quasi-cyclic low density parity check (NB-QC-LDPC) coded modulation (CM) scheme to reduce the decoding complexity while maintaining and/or exceeding the super BER performance of the traditional NB-QC-LDPC CM scheme. Firstly, local optimal searching combined with the classical superposition construction is proposed to construct the required NB-QC-LDPC codes with possibly enlarged girth and less number of the shortest cycles. Secondly, by analyzing the changing trend of the BER performance and decoding complexity of the NB-QC-LDPC code defined over 𝐺𝐹(𝑄) incident to 𝑄. We find that the decoding complexity increases proportionally with the increase of 𝑄, but the best BER performance usually corresponds to a smaller 𝑄. Finally, by replacing the high-order NB-QC-LDPC code based CM scheme to the multi-level low-order NB-QC-LDPC code based CM scheme, the decoding complexity can be effectively reduced. Simulation results show that the designed two-level 𝐺𝐹(4)/𝐺𝐹(8) QC-LDPC code based 16QAM/64QAM CM system can perform almost the same or even better BER performance with/than the corresponding traditional 𝐺𝐹(16) / 𝐺𝐹(64) QC-LDPC code based 16QAM/64QAM CM system.
To reduce the diode laser bar’s smile effect induced by packaging, a method based on a chip mounter is presented. When the bare bar is picked up by the pick-up tool (PUT) of the chip mounter, the curve direction and volume of the bar can be measured by scanning the P side surface of the bar with a laser rangefinder, and they can be controlled through adjusting the setting up of the PUT. By controlling the curve direction and volume at an appropriate state to compensate the packaging induced strain, the obtaining smile effect is restricted within 0.5μm steadily.
To improve the heat management of high-power diode lasers, a microchannel heat sink is obtained, whose structure is optimized in method of numerical simulation. Following such a design, the microchannel heat sink is fabricated by nickel-based doping rare earth materials by laser three-dimensional (3-D) printing procedure. Since the noncorrosion property of such material has been preliminarily demonstrated by salt spray test, there is no necessity to plate the interior of the laser 3-D printing microchannel heat sink with gold. The coefficient of thermal expansion of such material is 11 ppm/K. The diode laser array (LDA) with 80-W cw output power, 2-mm cavity length, 100-μm emitter width, and 20% fill-factors is mounted on it for the thermal resistance test, and the result is 0.40 K/W. Moreover, the smile effect of the mounted LDA is merely 0.8 μm.