A relatively simple design of a terahertz (THz) polarization splitter based on an asymmetric dual-suspended-core fiber is proposed. One core is formed by two intersecting rectangular dielectric strips with dissimilar thickness, whereas the other is a round solid core suspended by crossed dielectric strips with the same thickness. The distance between the cores can be adjusted to ensure a short splitting length and low transmission loss. A THz polarization splitter with a length of 1.27 cm is realized with a low transmission loss of 0.53 and 0.67 dB for the x- and y-polarization modes, respectively. An extinction ratio of about −20 dB and a broad bandwidth of 0.046 THz are demonstrated.
Single-mode operation with low-bending loss based on few-mode optical fiber is investigated. The fiber is designed with a group of ring modes in the cladding. The higher-order modes in the fiber can be eliminated by splicing with the single-mode optical fiber and bending the fiber to induce a strong coupling between the ring modes and the higher-order modes. Experimental results show that the bending losses of the LP01 mode can be lower than 0.001 dB/turn for a low-bending radius of 7.5 mm. The low-bending loss and the low splicing loss characteristics are also demonstrated. The proposed fiber can be bent multiple turns with a small bending radius which is preferable for fiber-to-the-home-related applications.
A few-mode microstructured optical fiber is designed for low bending loss applications. Low-index rods and air-holes are applied to lower the splicing loss with the standard single-mode optical fiber (SMF) and to achieve ultra-low bending loss. Numerical results show that the proposed fiber can realize low bending loss of 0.004 dB/turn at the bending radius of 5 mm and low splicing of 0.04 dB with the standard SMF.
In this paper, a novel double-pass bidirectional pump broadband L-band erbium-doped superfluorescent fiber source
(SFS) is demonstrated for the first time. In this fiber source, the EDF is divided into two segments, one of which (EDF2)
is bidirectional pumped by a 980nm laser diode through two wavelength division multiplexers (WDM), and the other one
(EDF1) is arranged between the reflector and the first WDM. EDF1 is unpumped. The fiber length ratio of the EDF1
length to the total length is defined as R<sub>L</sub>=L<sub>EDF1</sub>/(L<sub>EDF1</sub>+ L<sub>EDF2</sub>). The pump power ratio of forward to total pump power
of EDF2 is defined as K=P<sub>forward</sub>/P<sub>total</sub>. The effects of the fiber length and pump power arrangement on the output
characteristics of the L-band fiber source are simulated. With an appropriate pump power ratio K and an optimal fiber
length ratio R<sub>L</sub>, broadband L-band erbium-doped SFS with flat output spectrum can be obtained. Additionally, the
optimal fiber length ratio R<sub>L</sub> is also depended on the pump power ratio K. When K>0.4, the optimal R<sub>L</sub> tends to be
changeless. When K=0.1, the optimal R<sub>L</sub> is 0 and widest flat spectrum is achieved with a 3-dB bandwidth of 63 nm
A 1.16-W superfluorescent fiber source (SFS) centered at 1561 nm with a 3-dB bandwidth of 8 nm has been achieved, under the pumping of a 3.56-W 976-nm laser diode array. The optical conversion efficiency reaches 32%. The source is constructed in a dual-stage configuration. The first stage is an ASE seed source with output power about 30 mW in the C band. The second stage is a backward-pumped high-power erbium-ytterbium-codoped double-clad fiber amplifier. An interesting phenomenon has been observed: low-power ASE seed source causes laser oscillation in the SFS, yet a relatively high-power ASE seed source prevents the SFS from lasing. The Rayleigh backscattering and the saturation effect of the amplifier are considered to explain the phenomenon.
The cavity configurations of erbium-ytterbium co-doped fiber ring lasers (EYDFL) have been experimentally investigated. Additional attention has been paid to the mode competition effect of the laser. It is demonstrated that even in a traveling wave cavity, mode competition occurs when the cavity configuration or the output splitting ratio are incorrectly chosen. By employing the proper cavity configuration and an optimal output splitting ratio, an extremely stable ring cavity EYDFL with fine-shaped laser spectrum is obtained at 1565.8nm. Output power of 1.07 W is achieved under 3.5W 976nm pump power, with an optical conversion efficiency of 30.6%.