Fabrication Of Linear Waveguides In Fiber Using Femtosecond Laser And Study On The Coupling Characteristics

For the direction of high-speed, large capacity and wide bandwidth with opticalcommunication, it requires high integration of optoelectronic devices, which isbased on miniaturization of optoelectronic devices. Therefore, the micromachiningof optoelectronic devices remains a frontier and an active topic of research inphoto-communication field. In recent years, compared to traditional optoelectronicstechnology, femtosecond laser micromachining has become a new generation oftechnologies for the manufacture of optoelectronic devices. In particular,femtosecond laser micromachined waveguides attracted the interest of researchersincreasingly.First we introduced the foreign and domestic research on optical waveguide byfemtosecond laser direct writing in a variety of transparent medium. Then wededuced the eigenvalue equation of the transmission mode in fiber core and thetransverse coupling theory of the waveguides. And the impact of coupling efficiencyon the difference in propagation constants of the coupler was discussed. Then thewaveguide design software OptiBPM used in the simulation of this paper and itsalgorithm--BPM (Beam Propagation Method) were described.The optical waveguides in single mode fiber cladding were successfully writtenby transverse writing using the femtosecond laser pulses with a repetition rate of1KHz and a pulse duration of120fs at a central wavelength of800nm inexperiments. And the influence of machined good waveguides on the pulse power,the numerical aperture of objective and the scanning speed of the stage has beendiscussed. Moreover, how to focus in fiber with femtosecond laser pulse preciselywas also studied.Here we report, for the fist time to our knowledge, the fabrication of the coupleddevice, which is composed of fiber core and femtosecond laser machinedwaveguides that are adjacent to the fiber core by single scan or multiscan. Themultiscan written waveguide has a rectangular core. Compared to the waveguides bysingle scan, the coupling efficiency of the coupled device by multiscan is better. Andthe coupling characteristics of the device by multiscan with respect to the waveguidelength in two communication windows (1310nm and1550nm) and with respect to afraction of C-band around1550nm have been studied, respectively. Then weimproved the structure of the waveguide by using software from cross-section andthe refractive index in theory. With the formation of the waveguides in fiber, theoptical intensity modulator, optical splitter, optical switch, micro-ring resonator,optical attenuating probe, directional couplers and Mach-Zehnder interferometers based on waveguides in fiber could be produced with the incorporation of the fibercore. Thus, these basic components could constitute three dimension all-fiber opticalcircuits, which would open new prospects for manufacturing compact and functionaloptical microsystems for Telecom, sensing and lab-on-a-fiber applications.