Arbitrary TE$_0$/TE$_1$/TE$_2$/TE$_3$ Mode Converter Using 1 × 4 Y-Junction and 4 × 4 MMI Couplers

We propose a compact silicon-on-insulator based device which is capable of arbitrarily converting optical modes TE
₄
to TE
¹
(i, j = 0, 1, 2, 3). The device consists of two symmetric 1 × 4 V-junction couplers connected back-to-back with a 4 × 4 multimode interference coupler (MMI). While the two 1 × 4 V-junction couplers are designed to divide and combine modes at the input and output of the device, the 4 × 4 MMI coupler is used to direct signals from its inputs to suitable outputs. The conversion of a pair of modes is decided by four phase shifters located at the input and output of the MMI coupler. Through beam propagation method (BPM) with effective index method (EIM) simulations, we show that by setting the phase shifters to 0° or 180°, 16 different conversion pairs of input-output modes (TEi-TEj) are successfully realized with a mode conversion efficiency larger than 98% and a crosstalk smaller than -30 dB within a wide wavelength range from 1530 nm to 1565 nm.