A cylindrical microresonator based on standard silica optical fibers is a promising platform for nonlinear devices such as low-repetition rate frequency comb generators. Though, enlarged mode volumes lead to higher pump powers and third-order nonlinearity level together with the stricter requirements on low propagation losses in order to achieve effective four-wave nonlinear interactions. We consider sputter deposition of thin films with higher nonlinear refractive index made of silicon and silicon nitride layers to enhance the nonlinearity within the microcavity. We inspect the variations of the cylinder radius that arise during the deposition and determine the quality factors achievable.
An output dielectric mirror is deposited on the central part (~15 μm diameter) at the end face of a 1-km graded-index fiber and tested as output mirror of multimode Raman laser with highly-multimode (M2~34) 940-nm LD pumping. In the cavity with highly-reflective input FBG, Raman lasing of Stokes wave at 976 nm starts at the threshold pump power of ~80 W. The output beam quality factor measured near the threshold (~1W at 976 nm) M2~2 confirms mode selective properties of such output mirror. The power scaling capabilities at increased pump power together with a more detailed characterization of the output beam (spatial profile, spectrum and its stability) are performed and the obtained characteristics are compared with those for output coupling based on Fresnel reflection from the mirror-free fiber end face.
We investigate possibilities of using a multicore fiber containing fiber Bragg grating (FBG) in sensing applications. We use the advantages of the femtosecond point-by-point technique to inscribe FBGs in the selected cores of polyimidecoated 7-core fiber. Besides the results on 3D shape sensing we present new approaches for acoustic wave detection and environment refractive index sensing. In particular, we show that spatial division multiplexing with a multicore fiber allows one to create multipoint acoustic sensor based on a single laser source. In addition, to detect the change in environment refractive index by using point-by-point FBG, there is no need in fiber coating removal. Thus, durability of the fiber along with the FBG inscription approach is of great potential for fabrication of next generation multiple parameter sensors.
Experimental investigation of thermochemical laser-induced periodic surface structures (TLIPSS) formation on metal films (Ti, Cr, Ni, NiCr) at different processing conditions is presented. The hypothesis that the TLIPSS formation depends significantly on parabolic rate constant for oxide thin film growth is discussed. Evidently, low value of this parameter for Ni is the reason of TLIPSS absence on Ni and NiCr film with low Cr content. The effect of simultaneous ablative (with period ≈λ) and thermochemical (with period ≈λ) LIPSS formation was observed. The formation of structures after TLIPSS selective etching was demonstrated.
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