InGaAsP/InP optical digital-to-analogue converter for 40 Gbit/s, 3-bit operation

A 40 Gbit/s, 3-bit operation of a semiconductor optical digital-to-analogue converter, consisting of inputand output-side 1 ?? 3 MMI couplers and 1and 2-bit optical delay lines based on InGaAsP/InP materials, is presented. Splitting the ratio of an input-side 1 ?? 3 MMI coupler is designed to have almost equal signal quality in each output level under the extinction ratio of the input signal of 23 dB. Moreover, the difference of two adjacent delay lines is intentionally different to obtain an arbitrary combination of optical phase difference. An output signal with 7-level amplitude under the same phase bias condition is achieved successfully for the first time.