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Fiber bend is a major challenge of multimode fiber (MMF) imaging. More robustness against fiber bend is demonstrated in compressive MMF imaging using mean speckle patterns captured at multiple potential bending configurations beforehand, rather than sticking to single patterns at initial configuration. Experiments demonstrate an overall quality improvement on recovered images than previous work, which is important for robust endoscopic application.

In this letter, the scheme of a tapered mode-selective coupler based on photonic crystal fiber (PCF) is proposed. Three typical mode converters, such as LP 01 to LP 11a , LP 01 to LP 11b , and LP 01 to LP 21 , are described and simulated in detail. The coupling loss and bandwidth is calculated to evaluate those mode converters. The results demonstrate that those mode converters are broadband and low-loss devices. In addition, those mode converters are insensitive to the orthogonal polarizations. They can be fabricated using PCF postprocessing technique and are useful for future mode-division multiplexing optical fiber communication systems.Index Terms-Mode-division multiplexing, mode converter, tapered mode-selective coupler, photonic crystal fiber.