The computation capacity of conventional FPGAs is directly proportional to the size and expressive power of Look Up Table (LUT) resources. Individual LUT performance is limited by transistor switching time and power dissipation, defined by the CMOS fabrication process. In this paper we propose OLUT, an optical core implementation of LUT, which has the potential for low latency and low power computation. In addition, the use of Wavelength Division Multiplexing (WDM) allows parallel computation, which can further increase computation capacity. Preliminary experimental results demonstrate the potential for optically assisted on-chip computation.