Imaging through a multimode fiber (MMF) is a promising strategy for in vivo endoscopy due to its nature of simultaneously realizing high spatial resolution and minimal invasiveness. In MMF-based speckle imaging systems, a spatial light modulator (SLM) with a large number of pixels is commonly employed to enable independent controls of all the linearly polarized (LP) modes inside the MMF. Here, instead, we show that such an SLM can be replaced by a compact optical phased array (OPA) with a much smaller number of phase shifters without causing any penalty in resolution or sensitivity. Due to the nonlinear process inherent in field-to-intensity conversion, an OPA with $N$ phase shifters is capable of generating ${\sim}{N^2}$ independent illumination patterns. Since the resolution limit imposed by an MMF with $M$ LP modes per polarization is approximated as ${4}M$, we show that only $\sqrt {4M}$ phase shifters are essentially required to utilize the full spatial capacity of MMF. We can therefore enjoy the unique benefits of a low-cost, compact, and high-speed OPA that does not require thousands of phase shifters to achieve high-resolution imaging through an MMF.

中文翻译：

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使用多模光纤和相控阵的单像素散斑成像的分辨率极限

通过多模光纤（MMF）成像是体内内窥镜检查的一种有前途的策略，因为它具有同时实现高空间分辨率和微创的特性。在基于MMF的散斑成像系统中，通常使用具有大量像素的空间光调制器（SLM）来实现对MMF内部所有线性偏振（LP）模式的独立控制。在这里，相反，我们表明，这种SLM可以由紧凑的光学相控阵（OPA）代替，该光学相控阵具有很少数量的移相器，而不会造成分辨率或灵敏度的损失。由于场-强度转换固有的非线性过程，带有$ N $相移器的OPA能够生成$ {\ sim} {N ^ 2} $独立的照明模式。由于具有每个极化$ M $ LP模式的MMF施加的分辨率极限近似为$ {4} M $，因此我们证明，仅需要$ \ sqrt {4M} $个移相器即可利用MMF的全部空间容量。因此，我们可以享受低成本，紧凑且高速的OPA的独特优势，该优势不需要数千个移相器就可以通过MMF实现高分辨率成像。