Comparison of characteristic of two and three couplers Mach-Zehnder interferometers

Mach-Zehnder Interferometer (MZI) is used to measure the phase shift (Δφ) between two light beams related to relative length difference (ΔL) of MZI's two arms. The phase shift of the interferometer output is represented by output Free Spectral Range (FSR). Thus the FSR can be configured by setting its length difference of the two arms, to vary the phase shift. In this paper, the FSR of two couplers MZI are compared with three couplers MZI with two configurations based on the two couplers MZI's length difference. Length difference of the two couplers MZI is utilized for both of the length differences for the first configuration of three couplers MZI. As for the second configuration, each of the three couplers MZI length differences is half of the two couplers MZI length difference. The two couplers MZI are designed to have FSR at 10 nm, which can be obtained by using 0.166 mm as the length difference. 3 dB couplers are used for all of the configurations. Only one input port is utilized and the outputs are simulated in a normalized graph form. The MZIs simulation shows that the FSR of three couplers MZI first configuration is 5 nm, half of the FSR of two couplers MZI, while the FSR of three couplers MZI second configuration is 10 nm, the same as the FSR of two couplers MZI.