A universal principle to achieve different optical hybrids is summarized based on general nonoverlapping-image MMI couplers. An optical 72 • hybrid is proposed and demonstrated which is achieved by a 2 × 5 multimode interference (MMI) coupler with length of 89.5 μm and width of 8.0 μm. The device is fabricated in silicon-on-insulator (SOI) with 220 nm thick top silicon layer and the buried oxide layer is 3 μm thick. The proposed device exhibits an extinction ratio larger than 20 dB from 1470.8

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... 20 dB from 1470.8 nm to 1581.2 nm. The excess loss of optical hybrid is about 1.4 dB and a phase deviation less than ±6.0 • is obtained with the bandwidth of 51.5 nm.