Research On Design And Application Of Devices Based On Two-mode Microfiber

Microfiber is prepared from a standard optical fiber by means of fusion.In comparison with traditional optical fibers,the diameter of microfiber is close to or less than the wavelength of light,typically in the order of micrometers or nanometers.And the refractive index difference between the core and the cladding is larger.Microfiber has the advantages of strong light field confinement,strong evanescent field,and small mass.These advantages make microfibers have broad application prospects in optical communications,optical fiber sensing,fiber lasers,optical amplification and optical modulation.Two-mode fiber supports the transmission of LP₀₁ mode and LP₁₁ mode in the fiber.The interference between the two kinds of modes will arouse energy exchange and mode coupling.Two-mode fiber can transmit larger data streams through mode division multiplexing,to increase communication capacity.At the same time,since there are fewer modes,the process of mode change can be explored more clearly.This paper combines microfiber and two-mode fiber to study the design and application of structure based on tapered two-mode fiber(TTMF).Starting from the fabrication of the TTMF,the sensing characteristics of the TTMF structure are analyzed.Combining it with an erbium-doped fiber laser,a wavelength-switchable mode-locked fiber laser is proposed.The main research results are as follows:1.Real-time analysis of TTMF mode field based on spatial and spectral(S²)resolution technology.The fabrication method of the TTMF structure and the operation steps of S² resolution technology are introduced.Afterward the real-time analysis of its mode field is carried out.The transmission mode of the TTMF structure is resolved,and it proved that as the diameter of the TTMF gradually decreases during the process of tapering,the original core almost disappears,and the cladding becomes a new core.The LP₀₁ and LP₁₁ modes are excited and become waveguide cladding mode.The two kinds of modes are combined to obtain a smooth interference spectrum.2.High-sensitivity temperature sensor based on cascaded TTMF structure.The temperature sensitivity of a single TTMF structure is considered.By changing the free spectral range(FSR)of TTMF,it can be seen that with the narrowing of FSR,the absolute value of sensitivity increases exponentially.Subsequently,the two TTMF structures are connected in series to form a new temperature sensor.Benefiting from the Vernier effect,the temperature sensor possesses sensitivity of-3.348 nm/?in temperature measurement range from 25?to 60?,11.3 times sensitivity enhancement in comparison with single TTMF.3.Wavelength switchable mode-locked fiber laser with TTMF.It proved from both simulation and experiment that the larger the diameter of taper waist,the wider the FSR of the TTMF based filter.Exploiting the filtering function of TTMF structure,the intracavity wavelength is filtered and selected.When the FSR of the TTMF based filter is 8.5 nm,the laser can switch the central wavelength between two different wavelengths(1560.0 nm and 1568.5 nm)to achieve mode-locking status at the same time.When the FSR of the TTMF based filter is 3.1 nm,the laser can switch the central wavelength between three different wavelengths(1531.8 nm,1564.9 nm and1568.0 nm)to achieve mode-locking status simultaneously.