Twin-core optical fiber with large core ellipticity

Multiple hollow-core anti-resonant fiber as a supermodal fiber interferometer

Hollow-core anti-resonant fiber technology has made a rapid progress in low loss broadband transmission, enabled by its much reduced light-material overlap. This unique characteristic has driven emerging of new applications spanning from extreme wavelength generation to beam delivery. The successful demonstrations appear to suggest progression of the technology toward device level development and all-fiberized systems. We investigate this opportunity and report an in-fiber interferometer built in a dual hollow-core anti-resonant fiber. By placing multiple air cores in a single fiber, coherently interacting transverse modes are excited, which becomes a basis of an interferometer. We use this hollow core based inherent supermodal interaction to demonstrate highly sensitive in-fiber interferometer. Unique combination of the air guidance and the supermodal interaction offers robust, simple yet highly sensitive interferometer with suppressed temperature cross-talk that has been an enduring problem in fiber strain sensing applications. The in-fiber interferometer is further investigated as a sensing element for pressure measurement based on an interferometric phase change upon external strain. The interferometer features 39.3 nm/MPa of ultrahigh sensitivity with 0.14 KPa/°C of negligible gas pressure temperature crosstalk. The performance, which is much improved from prior fiber sensors, testifies advances of hollow core fiber technology toward a device level.

Enhanced power transfer and mode coupling in spun twin-core optical fibers

In a twin-core optical fiber a propagating light pulse periodically transfers power between its two cores. Experiments by Tjugiarto et al. [Opt. Lett. 17, 1058 (1992)] have demonstrated that this coupling length is considerably reduced when the fiber is also spun. A coupled-mode analysis reveals a pitch resonance that couples a cladding mode with the circularly polarized core mode whose handedness matches that of the helical twist of the cores. This resonance mechanism explains the observation of enhanced coupling and claddingmode cross coupling.

Accurate elasto-optic probe method for measurement of coupling length in twin-core optical fiber

The theoretical principle and experimental procedure of a new method of measuring the coupling length of a twin-core fiber are presented. This method is simple, nondestructive, and gives direct results without extensive data processing. It is based on the elasto-optic technique and had a very good spatial resolution so that coupling lengths of the order of a few millimeters can be measured. We show how this method can be applied to the measurement of the polarization coupling of birefringent noncircular twin-core fibers.

Soliton propagation in twin-core fiber rocking filters

We investigate nonlinear pulse propagation in a twin-core fiber whose birefhingent axes have been periodically rocked at the beat length of the cores. We find that the four coupled-mode equations that describe this system can be reduced to a pair of coupled nonlinear Schrödinger equations under suitable conditions. Consequently we find two new types of compound soliton: one that propagates down both cores of the fiber simultaneously and another that couples completely between the cores of this structure without degradation. These solitons typically have a peak power of ~1 W and a length of ~10 ps.

Dual-core fiber as a tunable directional coupler

The bending-induced birefringence in a fiber loop is used to restore locally perfect coupling conditions between the two slightly detuned cores of a dual-core fiber. It is also shown that varying the angle between the birefringence and the core's axis allows one to obtain perfect control (0-100%) of the coupling ratio.

Couplings in spun twin-core optical fibers

A new effect of spun twin-core fiber is observed in which the coupling between the two cores is increased with the spin rate. In addition, the cladding-mode attenuation is also increased. These effects can find many useful applications in fiber devices for optical communication, sensing, or signal processing.