Mach-Zehnder interferometer MZI

Based on the way the interferometer is configured, CCMI sensors can be categorized into two groups, namely the Mach-Zehnder interferometer (MZI) type and the Michelson interferometer (MI) type. The MZI sensor works in transmission mode, i.e., the transmitted interference signal is detected. The MI sensor works in reflection mode, where the light passes the interferometer twice and the reflected interference signal is detected. 

Fig. 9.13 Mach Zehnder interferometer (MZI) sensor interrogation circuit using (a) conventional linear waveguide geometry and (b) folded spiral waveguide geometry. The dashed line in (b) indicates the sensor window boundaries in this infra red camera image...

Fig. 9.14 (a) The measured variation of the Mach Zehnder interferometer (MZI) output intensity as a monolayer of streptavidin is bound to the surface, and (b) the optical phase change calculated from this intensity data... 

One of the main advantages of the optical-based sensors is their high resolution. Integrated optical sensors16, especially the interferometric ones that have been developed in recent years, such as the Mach-Zehnder interferometer (MZI)17 and the Young interferometer 18-21, show an extremely high refractive index resolution in the range of 10 1—10 8 RIU (refractive index units)17,21, which is equivalent to... 

In a Mach-Zehnder interferometer (MZI) device the light from a laser beam is divided into two identical beams that travel the MZI arms (sensor and reference areas) and are recombined again into a monomode channel waveguide giving a signal which is dependent on the phase difference... 

Figure 16.23 (a) Quasi-static strain measured with the tunable Fabry—Perot filter (TFPF)-demodulated FBG sensor signal (b) strain wave signals measured with the Mach-Zehnder interferometer (MZI)-demodulated FBG sensor compared with that measured by the PZT sensor [47]. 

Figure 9. Mach-Zehnder interferometer configuration scheme and its working principle (left) 3-D view of the MZI structure (right).

An attractive aspect of this device is the possibility of using long interaction lengths, in this way increasing the sensitivity of the device. An MZI offering a phase resolution of 0.002ir, which corresponds to a refractive-index resolution of 10 has been described [51]. A theoretical study shows that the Mach-Zehnder interferometer sensor seems to be one of the more promising concepts [15] for detection of low concentrations of small molectdes without labels (10 M or even lower). 

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