A Core-Offset Mach Zehnder Interferometer Based on A Non-Zero Dispersion-Shifted Fiber and Its Torsion Sensing Application

Abstract

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) based on a non-zero dispersion-shifted fiber (NZ-DSF) is presented. The MZI was implemented by core-offset fusion splicing one section of a NZ-DSF fiber between two pieces of single mode fibers (SMFs). Here, the NZ-DSF core and cladding were used as the arms of the MZI, while the core-offset sections acted as optical fiber couplers. Thus, a MZI interference spectrum with a fringe contrast (FC) of about 20 dB was observed. Moreover, its response spectrum was experimentally characterized to the torsion parameter and a sensitivity of 0.070 nm/° was achieved. Finally, these MZIs can be implemented in a compact size and low cost.

Fiber-Optic Sensors for Measurements of Torsion, Twist and Rotation: A Review

“…When two or more modes with different field confinements and, consequently, different effective index dependences on the fiber twist rate, are coupled locally at two spatially dislocated points along the sensing fiber, an in-fiber Mach-Zehnder interferometer is formed that is sensitive to the fiber’s twist/torsion [67,68,69,70,71,72,73,74]. A basic example of modal interferometer for twist/torsion sensing is shown in Figure 12, which consists of two spatially-dislocated mode-coupling events that couple two (or more) modes with different field confinements.…”

“…Other methods are also possible, like core offsets [72], abrupt tapers [75], LPFBG or similar. Michelson interferometer configuration is also possible by replacing one coupling event by a mirror [68], which allows for design of a compact sensor system that utilizes a single lead-in fiber.…”

“…Modal interferometers can utilize coupling among guided modes [67], guided and cladding modes [68,70,71,72] or a combination of both approaches [69]. While solid core fibers can be used to build torsion sensitive fiber modal interferometers [72], most solutions utilize PCF, mainly to achieve low temperature sensitivity [67,68,69,70,71].…”

“…While solid core fibers can be used to build torsion sensitive fiber modal interferometers [72], most solutions utilize PCF, mainly to achieve low temperature sensitivity [67,68,69,70,71]. A rather special case of modal interferometer is the solution presented in [73], where a large square core fiber is applied as a multimode interferometer for twist/rotation sensing.…”

Theoretical study of the dispersion effects occurring at optical fiber connections

“…The fact that rate of signal propagation in a medium depends on the medium refractive index (more precisely, on the group refractive index) should be taken into consideration. Then, it is easy to assume that the connection points can cause effects of signal distortion similar to dispersion [15,16].…”