We propose and demonstrate a method that can demultiplex an optical OFDM signal with various capacity based on time lens-based optical Fourier transform. The proposed tunable optical OFDM signal demultiplexer is composed of a phase modulator and a tunable chromatic dispersion emulator. The spectrum of the variable capacity OFDM signal is transformed into Nyquist time-division multiplexing pulses with the optical Fourier transform, and the OFDM sub-carrier channels are dumultiplexed in the time-domain. We also propose a simple method for approximating and generating quadratic waveform to drive the phase modulator. After explaining the operating principle of the method and the design of some parameters in detail, we show successful demultiplexing of 4×8 and 4×10 Gbit/s optical OFDM signals with our proposed method as the preliminary investigation results.