Effects of Post Treatments on Bismuth-Doped and Bismuth/ Erbium Co-doped Optical Fibres

Bismuth-doped and bismuth/erbium co-doped optical fibres have attracted much attention for their great potential in the photonic applications at ultrawide O, E, S, C and L bands. The effects of post treatments, including various heating, high energy ray radiation, laser radiation and H2 loading processes, on these fibres’ performance, functionality and stability have been experimentally studied. Experimental results demonstrate that these post treatments could allow us to get insights regarding the formation and the structure of bismuth active centre (BAC) and be used to control and regulate the formation of BAC

Experimental observation of wave localization at the Dirac frequency in a two-dimensional photonic crystal microcavity

Trapping light within cavities or waveguides in photonic crystals is an effective technology in modern integrated optics. Traditionally, cavities rely on total internal reflection or a photonic bandgap to achieve field confinement. Recent investigations have examined new localized modes that occur at a Dirac frequency that is beyond any complete photonic bandgap. We design Al2O3 dielectric cylinders placed on a triangular lattice in air, and change the central rod size to form a photonic crystal microcavity. It is predicted that waves can be localized at the Dirac frequency in this device without photonic bandgaps or total internal reflections. We perform a theoretical analysis of this new wave localization and verify it experimentally. This work paves the way for exploring localized defect modes at the Dirac point in the visible and infrared bands, with potential applicability to new optical devices

Orbital-angular-momentum fluorescence emission based on photon–electron interaction in a vortex field of an active optical fiber

We develop a model of interaction between photons and electrons in an active vortex field, which can generate a fluorescence spectrum with the characteristics of orbital angular momentum (OAM). In an active optical fiber, our findings generalize the notion of photon–electron interaction and point to a new kind of OAM-mode broad-spectrum light source, which could be interpreted in two processes: one microscopically is the excitation of OAM-carrying photons based on the photon–electron interaction; the other macroscopically is the emission and transmission of a donut-shaped fluorescence in a vortex field with a spiral phase wavefront in a ring-core active fiber. Here we present a straightforward experimental method that the emission of broad-spectrum fluorescence with an OAM feature is actualized and validated in a ring-core erbium-doped fiber. The spectrum has a broad spectral width up to 50 nm. Furthermore, four wavelengths are extracted from the fluorescence spectrum and superimposed with their corresponding Gaussian beams, from which the spiral-shaped interferograms of OAM modes in a broad spectrum are identified with high purity. The application of the OAM-based fluorescence light source may range from classical to quantum information technologies, and enable high-capacity communication, high-sensitivity sensing, high-resolution fluorescence imaging, etc

Over 100 mW stable low-noise single-frequency ring-cavity fiber laser based on a saturable absorber of Bi/Er/Yb co-doped silica fiber

Two kinds of Yb-doped fibers were fabricated, namely, Yb: YAG crystal-derived silica fibers (YCDSFs) with a gain coefficient of 6.0 dB/cm, and Bi/Er/Yb co-doped silica fibers having a Yb concentration of 0.1310^26 ion/m^3. Based on these fibers, a ring-cavity single-frequency fiber laser (SFFL) has been constructed, in which the YCDSF was used as a gain medium and the Bi/Er/Yb co-doped fiber acted as a saturable absorber. It has been demonstrated that the SFFL had an over 100 mW output at 1030 nm, slope-efficiency of up to 18.3%, and an optical signal-to-noise ratio of over 63 dB. The fluctuation of the output power of the laser was less than 0.65% of 103.5 mW within 10 hrs and no mode-hopping was observed for 5 hrs. The SFFL had a linewidth <7.5 kHz at the maximum output power, and the measured relative intensity noise was lower than 142 dB/Hz at a frequency above 1.0 MHz. The results indicate that the ring-cavity SFFL built could be used as a laser source for applications in a high-power fiber laser, and high-precision optical fiber sensing and detection

BAC Photobleaching in Bismuth-Doped and Bismuth/Erbium Co-Doped Optical Fibers

Bismuth-doped optical fiber (BDF) and bismuth/erbium co-doped optical fiber (BEDF) have attracted much attention due to their ultra-broadband luminescence in the near-infrared (NIR) region. The photobleaching effect on bismuth active centers (BACs) related to the NIR luminescence has been systematically investigated and summarized, in terms of irradiation intensity, irradiation wavelength, and temperature. All these findings not only give the deep insights into the fundamental structure of BACs but also provide an effective way to control the BACs. They play an important role for the development of BDF- and BEDF-based devices with high performance and stability under laser exposure in future

Broadband high-gain Yb : YAG crystal-derived silica fiber for low noise tunable single-frequency fiber laser

An over 75 nm broadband spectrum with a gain per unit length of >2 dB/cm was obtained from a homemade Yb: YAG crystal-derived silica fiber (YCDSF) with Yb-doping concertation of 6.57 wt.%. Using a 13-cm-long YCDSF, a low-noise wavelength-tunable single-frequency fiber laser has been constructed, enabling a single longitudinal mode oscillation from 1009 to 1070 nm. In particular, in the 1023-1056 nm waveband, the laser operating at any wavelength exhibited a maximum output power over 37 mW with power fluctuations below 0.38%, a slope efficiency >8%, and an optical signal-to-noise ratio higher than 60 dB. A linewidth of less than 2.8 kHz was also observed at the maximum pump powers, and relative intensity noise was as low as -155 dB/Hz at frequencies above 1.0 MHz. These results indicate that the YCDSFs with broadband high-gain characteristics are promising for wavelength-tunable fiber lasers in applications such as optical coherence tomography, precision metrology, nonlinear frequency conversion, and so on

Low-noise-figure and high-purity 10 vortex modes amplifier based on configurable pump modes

We have explored an orbital angular momentum (OAM) amplifier of 10 vortex modes under different-order OAM pump modes, i.e. OAM0, OAM1, and OAM2. The all-fiber amplification system consists of an active few-mode erbium-doped fiber (FM-EDF), a mode selective pump (MSP), and a mode selective signal (MSS). These mode selective components are based on fused-taper mode selective couplers (MSC) under different wavelengths fabricated by a passive ring-core fiber (RCF). Under different-order mode pumps, the OAM amplifier experimentally exhibits mode gains (MGs) above 15 dB for 10 vortex modes with the mode purities only 89%, essentially in line with the simulation results. Especially when the signal-mode profiles are better matched to the pump-mode profiles, i.e. the OAM pumps with the same order as signals, the obtained MGs are all over 20.2 dB and the amplified OAM mode purity is up to 97%; the acquired noise figures (NFs) are <4.9 dB and even the minimum NF is 3.2 dB. The results reveal that the OAM amplifier shows low-NF and high-purity characteristics under configurable pump modes in C-band. The amplified high-order OAM mode could be promising for uses in the long-distance mode division multiplexing (MDM) and in mitigation of the upcoming capacity crunch in optical fiber communication

Radiation Effect on Optical Properties of Bi-Related Materials Co-Doped Silica Optical Fibers

Three kinds of Bi-related materials co-doped silica optical fibers (BRDFs), including Bi/Al, Bi/Pb, and Bi/Er co-doped fibers, were fabricated using atomic layer deposition (ALD) and modified chemical vapor deposition (MCVD). Then, the effect of irradiation on the optical properties of BRDFs was investigated. The experimental results showed that the fluorescence intensity, the fluorescence lifetime of BRDFs at the 1150 nm band, increased significantly with low-dose treatment, whereas it decreased with a further increase in the radiation dose. In addition, the merit Mα values of the BRDFs, a ratio of useful pump absorption to total pump absorption, decreased with an increase of the radiation doses. The Verdet constants of different doped fibers increased up to saturation level with increases in the radiation dose. However, for a Bi-doped fiber, its Verdet constant decreased and the direction of Faraday’s rotation changed under low-dose radiation treatment. In addition, the Verdet constant increase of the Bi-doped silica fiber was much faster than that of other single mode fiber (SMF) and Pb-doped silica fibers treated with high-dose radiation. All of these findings are of great significance for the study of the optical properties of BRDFs