Ruifeng Zhao

All-fiber low-loss connector for accessing both close cores of twin-core fiber.

A novel all-fiber connector is proposed for connecting each core of a twin-core fiber (TCF) to a single-core fiber (SCF) core simultaneously and accessing independently the both close cores of the TCF. The connector is mainly composed of two cascaded pieces of collinear four-core fiber (CFCF). The two close optical fields launched from the TCF are separated into two far apart optical fields, so that each optical field could be butt-coupled into one of the cores of one gemini fiber segment, which has two single-mode SCF pigtails. For the simulated example, the center distance of the two optical fields is increased from 16 μm to more than 90 μm, the cross-talk is -37 dB, and the power loss is 0.056 dB. The feasibility of the strategy is partially demonstrated experimentally by fabricating a CFCF by groove & stack & draw method and one gemini fiber segment with pigtails by flame-brushing technology.

Experimental research of temperature sensor based on twin-core fiber

A low-cost, compact, and lossless temperature sensor based on a twin-core fiber (TCF) is demonstrated and manufactured by splicing two single-mode fibers to the ends of a TCF. The extinction ratio of the comb transmission spectrum is bigger than 15 dB, and the temperature sensitivity of the coupling angle is -0.02 rad/(oC.m) at -30-90 oC and -0.032 rad/(oC.m) at 90-175 oC. Finite element method is used to calculate the supermodes of the TCF, and the result agrees well with the experiment.

Low Loss Splicing Method to Join Silica and Fluoride Fibers

By decreasing the arc power and choosing the optimal arc time, we use the FSM-20PM ARC Fusion Splicer for joining fluoride(ZBLAN) and silica fibers. The best results of the splice loss is 1.58dB, and the results can be improved if the Fusion Splicer with more stable arc power. Then glue connection is used to fix the splicing point, and the minimal loss we measured is 0.14dB. The above results show that it is possible to connect the fluoride and silica fibers by using Fusion Splicer with appropriate arc power and arc time, which will make the fabrication of these splices simpler and easier to be handled.

Influences on the bandwidth at the drop port of the add/drop filter using a fiber grating coupler by uniform and linearly chirped fiber Bragg grating

Writing a fiber Bragg grating (FBG) in an optical fiber coupler is a very effective way to implement an optical add/drop filter (OADF). In order to analyze the influences on the bandwidth at the drop port of the OADF using fiber grating-assisted mismatched coupler, a uniform FBG and a linearly chirped FBG were written on the coupler, and two different OADFs were fabricated. The fiber grating is written in a 2×2 mismatched coupler, which is fused and tapered with a standard single mode fiber (SMF) and a high germanium doped photosensitive fiber, by using a 248 nm ultraviolet laser. For the OADF using the uniform FBG, the 3 dB and 20 dB bandwidths are 0.1 nm and 0.3 nm, respectively; for the OADF using the linear chirped FBG, the 3 dB and 20 dB bandwidths are 0.8 nm and 2 nm, respectively. The experimental results meet the theoretical analysis well. The bandwidth at the drop port of the device can be adjusted by adjusting the chirped coefficient of the linearly chirped FBG.

Comb-Filter Based on In-Fiber Mach-Zehnder Interferometer Using a Twin-Core Fiber

A comb-filter based on in-fiber Mach-Zehnder interferometer (MZI) is experimentally fabricated by splicing a section of single mode noncircular twin-core fiber (TCF) between two single mode fibers (SMFs). The wavelength spacing between the adjacent transmission peaks was numerically and experimentally analyzed, and it is associated with the effective index difference of the two cores and the length of the TCF. The wavelength spacing between the adjacent transmission peaks can be narrowed by increasing the length of the TCF or the effective index difference of the two cores. This device is compact and easy to be fabricated.

All-fiber optical attenuator based on eccentric core single-mode fiber

All-fiber optical attenuators based on an eccentric core single-mode fiber, whose core is away from the axis of the fiber, are demonstrated. By controlling the distance between the core and the axis of the fiber, attenuators with different attenuation can be made. The device is simple, reliable, and economical.

Precise method for modifying birefringence of stress-induced high-birefringence fiber

A precise method for modifying the birefringence of stress-induced high-birefringence (Hi-Bi) fiber is demonstrated by side polishing a Panda-type fiber with a maximum polished length of at least 14 cm. The polishing depth is controlled with an accuracy of 0.1 microm by piezoelectric ceramic microdisplacement. The accuracy of the birefringence is of the order of 10(-6). This method allows high-quality Hi-Bi fiber segments to be conveniently implemented with low loss at any desired birefringence between 3.17 x 10(-4) and 7.5 x 10(-5) in our experiment from one stress-induced Hi-Bi fiber and without changing the directions of the stress axes. The finite-element method is used to simulate the procedure, and the numerical results agree with the experiment.

A novel complex long-period-grating-assisted coupler

The coupled-mode equations corresponding to a novel complex long-period-grating-assisted coupler (LPGAC), which consists of both the periodic refractive index modulation and gain/loss perturbation, is introduced and the close-form analytical solution is obtained, for the first time to our knowledge. And a unique unidirectional and nonreversible filtering characteristic is achieved by adjusting the gain/loss to match with the refractive index modulation. In addition, the impact of deviations in the grating profile is also evaluated, and the results show that the required device performance can be realized by controlling the amplitude and phase deviation <5%.