Method of achieving phase delay with wide optical bandwidth in multimode interference devices

A completely passive method of achieving phase delays inside multimode interference devices is presented. The desired relative phase is obtained by adjustment of the width of the waveguides in conjunction with the tapers to avoid interference inside the multimode section. One can generally apply the delay lines to avoid the use of active elements, and they are less sensitive to changes in wavelength than the traditional method with bends. Using this method, we have designed and analyzed a zero-to-one mode converter. The converter exhibits minimum excess loss of 0.100 and 0.102 for TE and TM polarization, respectively. A very large 1-dB bandwidth exceeding 350 nm is achieved.