High Sensitivity Temperature Sensor Based on Harmonic Vernier Effect

A high-sensitivity temperature sensor based on the harmonic Vernier effect is proposed and verified by experiments.The main component of the sensor is a Sagnac interferometer consisting of two sections of polarization maintaining fibers(PMFs)spliced with an intersection angle of 45o between their fast axes.The harmonic Vernier effect is achieved by setting the length of one of the PMFs an integral multiple(i-times)of the length of the other plus a detuning factor.Compared with the Sagnac interferometer based on the fundamental Vernier effect,the temperature sensitivity of the harmonic Vernier effect is higher,reaching i+1 times of that of the fundamental Vernier effect(i is the order of the harmonic).

Cylindrical vector beam fiber laser with a symmetric two-mode fiber coupler

We demonstrate a passively mode-locked all-fiber laser generating cylindrical vector beams(CVBs)only using a symmetric two-mode fiber optical coupler(TMF-OC)for both high-order mode excitation and splitting.Theoretical analyses show that for a symmetric TMF-OC with appropriate taper diameter,the second-order mode can be excited and coupled into output tap with high purity due to the effective index difference of different modes.Based on the fabricated TMF-OC,the passively mode-locked fiber laser delivers pulsed CVBs at a center wavelength of 1564.4 nm with 3 d B linewidth of 11.2 nm,pulse duration of 2.552 ps,and repetition rate of3.96 MHz.The purity of both radially and azimuthally polarized beams is estimated to be over 91%.Due to simple fabrication method of the TMF-OC and high purity of the generated CVBs,this mode-locked CVB fiber laser with all-fiber configuration has potential applications in optical trapping,optical communications,material processing,etc.

Ultralarge Rabi splitting and broadband strong coupling in a spherical hyperbolic metamaterial cavity

Strong coupling(SC) between two resonant plasmon modes can result in the formation of new hybrid modes exhibiting Rabi splitting with strong energy exchange at the nanoscale. However, normal Rabi splitting is often limited to ~50–320 me V due to the short lifetime of the plasmon mode. Here, we theoretically demonstrate a record Rabi splitting energy as large as 805 me V arising from the SC between the high-Q plasmonic whispering gallery mode and high-Q cavity plasmon resonance supported by a spherical hyperbolic metamaterial cavity,which consists of a dielectric nanosphere core wrapped in 7 alternating layers of silver/dielectric materials.In addition, the new hybrid modes formed by the SC are shown to exhibit an extralong lifetime of up to 71.9–81.6 fs, with the large electric field intensity enhancement at both the dielectric core and the dielectric layers. More importantly, the spectral ranges of SC can be tuned across an ultrabroad range from the visible to the near-IR by simply changing the dielectric core size. These findings may have potential applications in bright single-photon sources.

Mode field switching in narrow linewidth mode-locked fiber laser

Acousto-optic interaction can be used for ultrafast optical field control in passively mode-locked fiber lasers.Here,we propose the use of an intracavity acousto-optic mode converter (AOMC) with combination of a few-mode fiber Bragg gratings (FM-FBG) to achieve narrow linewidth mode-locked pulse output with switchable transverse mode and wavelength in a ring fiber laser.Due to the selectivity of the FM-FBG to the input mode,the output mode and wavelength can be adjusted in the mode-locked fiber laser based on a semiconductor saturable absorption mirror.In experiments,by adjusting the acoustic frequency imposed in the AOMC,the wavelength of mode-locked pulses was switched from 1551.52 nm to 1550.21 nm,retaining the repetition rate of 12.68 MHz.At the same time,the mode conversion from the LP;to the LP;mode in the FM-FBG transmission port was achieved.This laser may find application in mode-division multiplexing systems.

Mode-locked pulse generation from an all-FMF ring laser cavity

Experimental generation of stable mode-locked pulses and cylindrical vector beams(CVBs),from an all fewmode fiber(FMF)ring laser is first reported,to the best of our knowledge.In this laser,a section of few-mode erbium-doped fiber(FM-EDF)is used as the gain medium.The FM-EDF is pumped by 976nm laser with LP11 mode,which is simultaneously converted and multiplexed through a homemade hybrid device,i.e.,wavelength division multiplexing-mode selection coupler(WDM-MSC).All the components in our experiment are connected using FMF.The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 m W.Moreover,both azimuthally and radially polarized CVBs were achieved with a high purity of>95%.This mode-locked CVB fiber laser with an all FMF configuration opens the way to manipulate the transverse mode in mode-locked fiber lasers.

Improvement on refractive index sensing by exploiting the tapered two-mode fibers

The spectral characteristics and sensitivities of a tapered two-mode fiber sandwiched between two single-mode fibers are systematically investigated. Theoretical calculations reveal that a dispersion turning point(DTP)appears when the group effective refractive index(RI) difference between the fundamental mode and the higher-order mode equals zero;as a result, ultrahigh RI sensitivities can be achieved. Furthermore, the location of the DTP is strongly dependent on the tapering condition. Then, we experimentally demonstrate high sensitivities of the RI sensor with the waist diameter of 4 μm by means of immersing it in a flow cell filled with glycerol solution. In further tracking of the resonant wavelength shift around the DTP, it is found that the proposed RI sensor exhibits a sensitivity of 1.81 × 104 nm/RIU and a limit of detection down up to 3.29 × 10-5 RIU in a liquid glycerol solution.