dB For Fibers Research Articles

The design of large mode-area, single mode Yb:KYW rib loaded waveguide for high performance waveguide laser applications

Direct fiber-laser diode pumping is intriguing for waveguide laser operation, for robustness and high laser efficiency. However, the huge mismatch between waveguide and fiber modes limits the further improvement of waveguide laser performance. Here we design and take numerical study on the large-mode-area, single-mode Yb:KYW loaded-rib waveguide structure with tilt side walls, which is easy to fabricate using existing techniques. It is demonstrated that the waveguide structure guarantees direct butt coupling with insertion loss <3 dB for fibers with core diameter ranging from 11.0 to 55.5 μm. The effect of alignment mismatch is also studied, showing good alignment tolerance. The overlap ratio of modes between pumping and laser emission wavelength is as high as 99.84%, with extreme small laser divergence angle. These features make the waveguide promising candidate for high power waveguide laser applications.

Ultra reliable infrared absorption water vapor detection through the all-electronic feedback stabilization

Single-beam balanced radiometric detection (BRD) system with all-electronic feedback stabilization has been proposed for high reliability water vapor detection under rough environmental conditions, which is insensitive to the fluctuation of transmission loss of light. The majority of photocurrent attenuation caused by the optical loss can be effectively compensated by automatically adjusting the splitting ratio of probe photocurrent. Based on the Ebers–Moll model, we present a theoretical analysis which can be suppressed the photocurrent attenuation caused by optical loss from 0.5552dB to 0.0004dB by using the all-electronic feedback stabilization. The deviation of the single-beam BRD system is below 0.29% with the bending loss of 0.31dB in fiber, which is obviously lower than the dual-beam BRD system (5.96%) and subtraction system (11.3%). After averaging and filtering, the absorption sensitivity of water vapor at 1368.597nm has been demonstrated, which is 7.368×10−6.

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.

Fusion splices for single-mode optical fibers

A practical low loss splicing method based on the discharge fusion for single-mode fibers was developed. Average splice losses of 0.4, 0.2, and 0.1 dB for fibers with 5.2, 7, and 10 μm core diameters, respectively, are obtained by a simple apparatus utilizing the self-alignment effect due to the surface tension of melted fiber ends. The surface tension effect is analyzed both experimentally and theoretically. Experimental splice losses, both after and during heating, coincide with the theoretical estimated values. It was found that the optimum heating temperature for low loss splices is near 2000°C at 8.5 W electric discharge power. Splicing loss causes are examined. The main cause of the practical splice loss is the residual core axis misalignment caused by an insufficient surface tension effect and core eccentricity with respect to cladding.