A small silicon mode (de)multiplexer with cascaded asymmetrical directional couplers is demonstrated experimentally. As an example, a four channel mode (de)multiplexer is designed and realized for TM polarization. The fabricated mode (de)multiplexer has a low excess loss (<1 dB) as well as low crosstalk (≤23 dB) over a broad wavelength range (~20 nm). More channels can be achieved with two sets of orthogonal-polarization modes (e.g., 2N=8) multiplexed when desired.