Phase modulator for optical signal using multimode interference couplers

摘要

The invention provides an optical system and method for outputting a phase modulated signal using a multimode interference (MMI) device. The MMI device, MMI2, has at least two inputs and at least one output, with the relative phase between the two inputs being fixed at a given phase difference. The phase difference is fixed such that the output signal can be phase modulated by modulating the input power of at least one of the inputs. The given phase difference between the inputs may be set by a second MMI device, MMI1, or by coupling the MMI device within a resonator. If two MMI devices are present they may be coupled together using waveguides of similar length to generate a binary phase shift keying signal (BPSK). Alternatively the MMI devices may be coupled together using two connecting arms that are biased so that the gain in the arms changes the output of the MMI device with the output of the MMI device being input back into the second MMI device so that a BPSK or Quadrature phase shift keying signal (QPSK) is produced (see Figure 4).