We propose to utilize the digital optical phase conjugation (D-OPC) technique for the compensation of mode crosstalk in the mode-division-multiplexed (MDM) transmission system. To realize the D-OPC technique, we send the CW light from the receiver side, measure its wavefront at the transmitter side, and then, transmit the phase-conjugated signal to the receiver. By using this technique, we demonstrate the transmission of four LP modes, each carrying 10-Gb/s ON-OFF keying signals, over a 100-m long few-mode fiber link. These signals are detected by using direct-detection receivers with no electrical equalizer. The results show that, by applying the proposed D-OPC technique, we can achieve the bit-error rate of < 10(-3) for all four modes.