Polarization and magneto-optical characteristics of Tb:YAG crystal-derived silica fiber via laser-heating drawing technique

Fiber quarter-wave plates and magneto-optical fibers are important components that greatly affect the sensitivity of fiberoptic current sensors.A Tb:YAG crystal-derived silica fiber(TYDSF)was fabricated using a CO_(2) laser-heating drawing technique.The linear birefringence of TYDSF was measured as 6.661×10^(-6)by a microscope birefringence measurement instrument.A fiber quarter-wave plate was fabricated by TYDSF at 1310 nm,which produced circularly polarized light with a polarization extinction ratio of 0.34 d B.Additionally,the linear birefringence of TYDSF was decreased by 22%by annealing at 750℃ for 7 h,and the Verdet constants of annealed TYDSF were measured to be 9.83,6.67,and 3.48 rad/(T·m)at 808,980,and 1310 nm,respectively.

High-order mode lasing in all-FMF laser cavities

We experimentally demonstrate two kinds of all few-mode fiber(FMF) ring lasers with high-order mode(HOM)oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams(OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams(CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.

Over 255 mW single-frequency fiber laser with high slope efficiency and power stability based on an ultrashort Yb-doped crystal-derived silica fiber

A single-frequency distributed Bragg reflector (DBR) fiber laser at 1030 nm has been demonstrated using a 0.7 cm long homemade Yb:YAG crystal-derived silica fiber (YCDSF).The absorption and emission cross sections of the YCDSF are 4.93×10^(-20)cm^(2) at 980 nm and 1.1×10^(-20)cm^(2)at 1030 nm.Using this gain fiber,an over 255 m W continuous-wave lasing in the constructed laser has been obtained at single transverse and longitudinal mode operation.The slope efficiency and the pump threshold of the fiber laser were up to ~35%and as low as 25 m W,respectively.The fiber laser also demonstrated an optical signal-to-noise ratio of 79 dB and a beam quality factor of 1.016 in two orthogonal directions.Its power fluctuation at 210.5 m W was less than 0.85%of the average power within 13 h.Moreover,the relative intensity noise and linewidth of the laser are also investigated at the different pump powers.The results indicate that the single-frequency DBR fiber laser has potential applications in high-quality seed sources and high-precision optical sensing.

Development of Bi/Er co-doped optical fibers for ultra-broadband photonic applications

Targeting the huge unused bandwidth（BW）of modem telecommunication networks,Bi/Er co-doped silica optical fibers（BEDFs）have been proposed and developed for ultra-broadband,high-gain optical amplifiers covering the 1150-1700 nm wavelength range.Ultrabroadband luminescence has been demonstrated in both BEDFs and bismuth/erbium/ytterbium co-doped optical fibers（BEYDFs）fabricated with the modified chemical vapor deposition（MCVD）and in situ doping techniques.Several novel and sophisticated techniques have been developed for the fabrication and characterization of the new active fibers.For controlling the performance of the active fibers,post-treatment processes using high temperature,γ-radiation,and laser light have been introduced.Although many fundamental scientific and technological issues and challenges still remain,several photonic applications,such as fiber sensing,fiber gratings,fiber amplification,fiber lasers,etc.,have already been demonstrated.

All-fiber linear polarization and orbital angular momentum modes amplifier based on few-mode erbium-doped fiber and long period fiber grating

A few-mode erbium-doped fiber（FM-EDF） is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,respectively. The refractive index difference is 0.98%, numerical aperture（NA） is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating（LPFG） is fabricated, which can convert LP〈01 mode to LP11 mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum（OAM） is also generated by combining the LPFG and polarization controller（PC）. Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP11 mode and first-order OAM beams, is built up. Its on-off gain of the LP11 mode beam is 37.2 d B at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP11 mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme,which can be used in the optical communication fields.

Highly efficient excitation of LP01 mode in ring-core fibers by tapering for optimizing OAM generation

We have demonstrated the highly efficient excitation of the linearly polarized mode(LP01)in ring-core fibers(RCFs)by tapering the spliced point between the RCF and the standard single-mode fiber(SMF)to optimize all-fiber orbital angular momentum(OAM)generation.The tapering technique has been investigated theoretically and experimentally.Before tapering,only 50%of light can be coupled from SMFs to RCFs.The modal interference spectrum with an extinction ratio(ER)of～9 dB is observed,showing that higher-order modes are excited in RCF.By tapering the spliced point,90%of light is coupled,and the ER is minimized to be～2 dB,indicating that the higher-order modes are effectively suppressed by tapering.Such tapered spliced points of RCF–SMF are further applied for all-fiber OAM generation.The efficiencies of OAM+1 and OAM?1 generation are found to be enhanced by approximately 11.66%and 12.41%,respectively,showing that the tapered spliced point of the RCF–SMF is a feasible way to optimize OAM generation.

High signal-to-noise ratio fiber laser at 1596 nm based on a Bi/Er/La co-doped silica fiber

We fabricate a high-performance Bi/Er/La co-doped silica fiber with a fluorescence intensity of-33.8 dBm and a gain coefficient of 1.9 dB/m.With the utilization of the fiber as a gain medium,a linear-cavity fiber laser has been constructed,which exhibits a signal-to-noise ratio of 74.9 dB at 1596 nm.It has been demonstrated that the fiber laser has a maximum output power of 107.4 mW,a slope efficiency of up to 17.0%,and a linewidth of less than 0.02 nm.Moreover,an all-fiber single-stage optical amplifier is built up for laser amplification,by which the amplified laser power is up to 410.0 mW with pump efficiency of 33.8%.The results indicate that the laser is capable of high signal-to-noise ratio and narrow linewidth,with potential applications for optical fiber sensing,biomedicine,precision measurement,and the pump source of the mid-infrared fiber lasers.