Optoelectronic optimization of mode selective converter based on liquid crystal on silicon

• The LCOS-based mode converter for mode multiplexing is investigated systematically.
• The modulation depth and quantization error of ADC are studied quantitatively.
• The influence of the utilized free-space optical components is also explored.
• The tolerance is acceptable considering insertion loss and mode extinction ratio.

We carry out comprehensive optoelectronic optimization of mode selective converter used for the mode division multiplexing, based on liquid crystal on silicon (LCOS) in binary mode. The conversion error of digital-to-analog (DAC) is investigated quantitatively for the purpose of driving the LCOS in the application of mode selective conversion. Results indicate the DAC must have a resolution of 8-bit, in order to achieve high mode extinction ratio (MER) of 28 dB. On the other hand, both the fast axis position error of half-wave-plate (HWP) and rotation angle error of Faraday rotator (FR) have negative influence on the performance of mode selective conversion. However, the commercial products provide enough angle error tolerance for the LCOS-based mode selective converter, taking both of insertion loss (IL) and MER into account.