Transmission networks are facing explosive growth in data traffic owing to the rapid developments in data centers and cloud computing services. Optical networks with high speeds, large capacities, and high-cost performances are now in urgent demand. Telecom operators and equipment manufacturers are actively promoting the application and deployment of 400G technologies. To further develop and utilize the transmission capacity of a single fiber and approach the limit of Shannon’s theorem, the next research direction of optical transmission is prioritizing further improvements in the capacity of a single channel, compressing the transmission channel interval, and increasing the number of channels. However, increasing the number of multiplexed channels leads to a serious nonlinear effect, which is inversely proportional to the effective area of the fiber. Therefore, the transmission bandwidth and nonlinear effect of the fiber can be improved and reduced, respectively, by increasing the effective area of the fiber. Consequently, the development of next-generation G.655 and G.656 fibers, particularly for broadband transmission DWDM systems, has important practical application value.
In this experiment, outside vapor deposition (OVD) was used to fabricate a non-zero dispersion-shifted fiber (Fig. 3). According to the transmission principle of optical fibers, G.655 must increase the refractive index difference (RID) of the 1st core layer Δn1 to increase the waveguide dispersion and shift the zero dispersion wavelength to 1500 nm, but the increase in Δn1 leads to a decrease in the fiber core radius. However, a core radius that is extremely small results in an increase in the dispersion and nonlinear effects caused by high power density. Therefore, the profile structure selected in this experiment is a triangular core and ring structure with a central depression (Fig. 2). First, by decreasing the RID and gradually increasing the thickness of the 2nd/3rd core radii, the mold field diameter (MFD), zero-dispersion wavelength, and other parameters of the optical fiber were measured and analyzed based on this structure (Table 1). Second, in Table 3, by increasing the 1st core radius alone, the influences of the 1st core radius on the optical fiber parameters were investigated.
This study investigates optical fibers’ optical properties, geometric parameters, and dispersion performance by varying the refractive index profile structure and core radius (Fig. 4). The refractive index profile structure can significantly affect the cutoff wavelength, effective area, and dispersion values. In the optimized profile-type study, when the core radius of R1, R2, and R3 are approximately 2.3, 5.6, and 8.2 μm and the RID of each layer is 0.52%, 0.04%, and 0.14%, respectively, the MFD can reach 9.6 μm, and the dispersion value ranges from 1.6 to 9.5 ps/(nm·km) in the C+ L band. Furthermore, the results indicate that the core radius of the fiber has an important influence on the MFD and zero-dispersion wavelength (Table 3). The decrease in the 1st core radius is proven beneficial for enlarging the MFD, shortening the cutoff wavelength, extending the zero-dispersion wavelength, increasing the zero-dispersion slope, and lowering the dispersion (Fig. 5). The spectral loss diagram, dispersion curve, and macrobending loss diagram of the designed optical fibers were comprehensively evaluated (Fig. 6). The test results indicate that the attenuation values are 0.296 dB/km, 0.195 dB/km, and 0.203 dB/km at 1383, 1550, and 1625 nm, respectively, and the dispersion is within the standard of the G.655.D fiber. The macrobending losses at 1550 and 1625 nm are lower than 0.027 dB and 0.045 dB, respectively, demonstrating a good bending resistance.
In this study, a non-zero dispersion-shifted fiber with a triangular core and annular structure was designed and fabricated using OVD. Based on this structure, the fiber exhibited a shorter cutoff wavelength, lower attenuation, larger MFD, and lower dispersion at 1550 nm. The results show that the MFD is 72 μm2, and the dispersion value is 1.6-9.5 ps/(nm·km) in 1530-1625 nm. The attenuation at 1550, 1383, and 1625 nm excelled that of the ITU-T G.655.D standard. Overall, the proposed profile structure realizes a translation of the zero-dispersion wavelength, low macrobending loss, and large effective area, which is suitable for DWDM applications in the C+ L band. In long-distance optical fiber communication, nonlinear effects, such as FWM and XPM, can be suppressed well, and the cost of dispersion management can be reduced, which has important practical application value.
