![]() Here we demonstrate a low-cost, scalable spectrometer that has a picometer resolution and sub-millimeter footprint. The sharp angle of the taper makes it less susceptible to environmental disturbance compared with adiabatic fiber tapers. But, by engineering the drawing conditions, we can maximize the leaky modes generation within a 1 mm taper region and make use of the leaked random interference speckles. The latter process will generate leaky modes that normally being undesired for microfiber applications . If a microfiber taper is drawn under non-adiabatic condition, the fiber geometry will force the guiding modes to evolve from single-mode to multimode and then couple to single-mode/few-mode again in a short distance. But experiments usually use microfibers for confining light inside the fiber to propagate as long as possible. On the other hand, microfibers are ideal tools for manipulating light field for its tailorable dispersion and small footprint. Above all, a flexible low-cost tiny spectrometer with stable high performance is still elusive. The rest design requires structures with fancy characteristics that are difficult or expensive to fabricate . Long photonics crystal fibers or multimode fibers are vulnerable to environmental fluctuations thus weakening the stability of spectrometers based on them . Usually, optical fibers can generate random speckles, but the length of the fiber used are on the scale of meters. However, most spectrometer designs based on it rely on random medium such as rough surface , multimode fiber , integrating sphere , photonic crystals , etc., which usually require the companion of bulky or expensive equipment, such as a high-performance camera or even a microscope, to complete the measurement . Multimode interferences could generate random speckles which are associated with spectra information . On-chip spectrometers relying on nanofabrication usually have very low coupling efficiency for wideband operation . Filters (including narrowband and reconstructive types) based designs suffer from power loss caused by either absorption or reflection as well as limited resolution and bandwidth due to limited channel numbers . Generally, spectrometers with dispersive elements require extra spatial separations tend to leave a large footprint . But the existence of an inherent tradeoff between the above aspects are constraining this long-term theme of miniaturization from advancing. Researchers have been engineering spectrometers for lower cost, higher flexibilities, smaller size, better stabilities, and performances for quite some time. The miniaturization of traditionally bulky spectrometers has been strongly motivated by the vast applications, including biomedical sensing , material analysis , optical communication and light source characterization . The precision and elegance of obtaining abundant light-matter-interact information with a snapshot measurement makes optical spectroscopy indispensable elements for modern industries and scientific research . ![]()
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