The previous papers of the research group have already found that the excitation of a 1310 nm endogenous pump by signal feedback combined with a single fiber Bragg grating (FBG) under the condition of 1240 nm pumping can significantly enhance the gain effect of bismuth-doped fiber amplifiers (BDFA) at long wavelengths. In order to further clarify the effect of the endogenous pump generation mode and the different feedback mechanisms on the broadening effect, we have used a tunable dual grating combined with a controllable pump/signal feedback amplifier structure, and compare in detail the broadening characteristics under the different conditions mentioned above. The experimental results show that any form of endogenous pumping can result in amplification bandwidth expansion, but there is a difference in the behavior of the broadening due to the dual grating line cavity versus the grating-signal reflector line cavity, as well as in the degree to which the broadening is affected by the pump feedback. The effective utilization of this property can provide positive assistance in enhancing the gain-bandwidth performance of BDFA as well as in improving the transmission capacity of communication systems.
Metasurfaces are two-dimensional planar structures composed of artificial atoms with special electromagnetic properties in a certain arrangement, which can flexibly control the amplitude, phase, and polarization of incident light, and have strong light field manipulation capabilities, so they have attracted extensive attention. In this work, a WDM based on all- dielectric metasurface is proposed to realize the beam combination function of ultra-wideband signal and narrowband pumping. The WDM can realize the low-loss and high-efficiency wavelength division multiplexing function of one ultra- wideband signal and one or two narrowband pumps by punching holes in the fused silica thin layer, with a signal passing bandwidth of more than 400nm, almost no energy loss on the signal wavelength, a pump loss of less than 1dB, and a pump occupied bandwidth of less than 3nm. It can well solve the problem of serious limitation of signal bandwidth of the current wavelength division multiplexer and provide important support for the key components and equipment of ultra-high bandwidth optical communication such as ultra-high bandwidth optical fiber amplifiers.
The photonic neural processing unit (PNPU) demonstrates ultrahigh inference speed with low energy consumption, and it has become a promising hardware artificial intelligence (AI) accelerator. However, the nonidealities of the photonic device and the peripheral circuit make the practical application much more complex. Rather than optimizing the photonic device, the architecture, and the algorithm individually, a joint device-architecture-algorithm codesign method is proposed to improve the accuracy, efficiency and robustness of the PNPU. First, a full-flow simulator for the PNPU is developed from the back end simulator to the high-level training framework; Second, the full system architecture and the complete photonic chip design enable the simulator to closely model the real system; Third, the nonidealities of the photonic chip are evaluated for the PNPU design. The average test accuracy exceeds 98%, and the computing power exceeds 100TOPS.
A novel square-assisted ring-core fiber characterized by a square region of low refractive index in the core was proposed. This fiber structure allows for spatial mode modulation. When the subscript m of the LPmn modes supported by the fiber is an even number, the spatial modes of the LPmn modes are degenerately separated. This fiber supports 15 modes over the entire C-band. The effective refractive index difference (Δneff) between spatial modes at 1550nm is greater than 1.18×10-4. At the same time, the Δneff between all adjacent modes is in the range of (1.13~13.52)×10-4. The polarization separation level of each mode is below 7.12×10-6, which is two orders of magnitude lower than the level of degenerate separation of spatial modes. Numerical simulations show that the dispersion values range from -16 ps/nm/km to 15 ps/nm/km for 15 modes over the entire C-band. This fiber has a good tolerance for process error, the optical fiber processing requirements can be met by using the existing optical fiber preparation technology.
Polarization beam splitter is an important part of integrated optical system to overcome the strong polarization dependence of silicon nanodevices, and has broad application prospects in optical fiber communication and polarization imaging. In this paper, a polarization beam splitter of metalens based on the fiber end face is designed. Through the planar light field control ability of metalens and the coordinated regulation of the geometric phase and propagation phase, the device adjusts the medium duty cycle in the meta-unit and the rotation angle of the nanoantenna to realize the polarization beam splitting and focusing simultaneously. In order to simplify the manufacturing process and achieve high focusing efficiency even further, Si with high transmittance in the near infrared band is selected as the nanoantenna, and SiO2 is used as the substrate. Since the substrate used the same material with fiber cladding, compared with the traditional polarization beam splitter, the structure can directly etch the nanofins periodically on the fiber end face, which is convenient for optical system integration. Theoretical design and numerical simulation results show that any polarized light in fiber cladding can realize polarization focusing through fiber end face.
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