A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

We demonstrate for the first time, to the best of our knowledge, an all-fiber orbital angular momentum (OAM) multiplexer that multiplexes both OAM modes of −l and +l up to the second order by using a mode-selective photonic lantern and a mode polarization controller. The experimentally obtained mode profiles are close to the theoretical results, and the mode purities are higher than 89% for all the OAM modes at 1550 nm. The losses for all mode generations are less than 3.8 dB in the C-band.

All-fiber orbital angular momentum mode multiplexer based on a mode-selective photonic lantern and a mode polarization controller.

We propose spatial-mode filters based on embedding graphene films in optical waveguides. To demonstrate the effectiveness and the flexibility of this approach, we design and fabricate several mode filters where graphene films of different widths and lengths are placed in different locations of polymer waveguides. Our mode filters are easy to make and can provide high mode extinction ratios that are insensitive to the operation wavelength. Such mode filters could find applications in broadband mode-division-multiplexing transmission systems and other areas that involve mode selection or stripping.

Ultra-broadband mode filters based on graphene-embedded waveguides

We propose an effective approach to generate tunable orbital angular momentum (OAM) beam based on all-fiber fused coupler consisting of a single mode fiber (SMF) and a two-mode fiber. The fundamental mode in the SMF is directly coupled to the LP11 mode group (TE0,1, $\text {HE}^{\text {even,odd}}_{2,1}$ , TM0,1) by appropriately phase matching the modes in the fiber coupler. The experimental results demonstrate that the OAM beam is produced by combining $\text {HE}^{\text {even}}_{2,1}$ and TE0,1 (or $\text{HE}^{\text {odd}}_{2,1}$ and TM0,1) with a $\pi $ /2 phase shift and the OAM topological charge could be tuned from $l = -1$ to $l =+1$ by adjusting a polarizer set at the output end of fiber.

Tunable Orbital Angular Momentum Generation Using All-Fiber Fused Coupler

An optical fiber twist sensor based on surface plasmon resonance (SPR) excitation and able to operate in both gaseous and liquid media is proposed and demonstrated. The use of a gold-coated 37.5° tilted fiber Bragg grating allows one to generate two windows of cladding mode resonances, providing surrounding refractive index sensitivity in two different external media. The relative optical power of the SPR mode in each case exhibits a linear response to the twist angle of the fiber from 0° to 90°, as well as from 90° to 180°, as a consequence of the polarization dependency of these sensors. The results show sensitivities of 1.15%/° and 1.22%/° with the sensor working in air and liquids, respectively, being suitable for deformation measurement and structural health monitoring applications.

Twist sensor based on surface plasmon resonance excitation using two spectral combs in one tilted fiber Bragg grating

We presented a simple method for measuring the mode purity of linearly polarized orbital angular momentum (OAM) modes in optical fibers. The method is based on the analysis of OAM beam projections filtered by a polarizer. The amplitude spectrum and phase spectrum of a data ring derived from the beam pattern are obtained by Fourier transform. Then the coefficients of the mixed electric field expression can be determined and the mode purity can be obtained. The proposed method is validated and it is experimentally demonstrated in a two-mode fiber.

Linearly polarized orbital angular momentum mode purity measurement in optical fibers.

Core-cladding mode coupling of tilted long period fiber gratings in dual-mode fibers

We present a strain-independent torsion and displacement fiber sensor using acoustically-induced fiber grating (AIFG) in dual-mode fiber (DMF). By tuning the radio frequency of driving signal, LP01 and LP11 modes generated by the AIFG can be exploited to measure the dynamic displacement and torsion variations, respectively. Both the twist angle and the twist direction can be monitored via image detection facility at the end of DMF. Between torsion angles of −80° and 80°, the highest twist sensitivity reaches 15 pixel/°. The average displacement sensitivity is 5 pixel/µm within the recorded two-dimensional movement of 100um × 80um. The stable property of sensor is verified when the strain is varied from 100 μe to 1500 μe.

Yu Liu

Papers

Linearly polarized orbital angular momentum mode purity measurement in optical fibers.

Core-cladding mode coupling of tilted long period fiber gratings in dual-mode fibers

Strain-independent fiber torsion and displacement sensor based on acoustically-induced fiber grating

Vector mode conversion based on tilted fiber Bragg grating in ring-core fibers

Dual-pumped flat optical frequency comb based on normal dispersion AlGaAs on insulator waveguide: Numerical investigation