Microstructured optical fiber-based sensors (MOF) have been widely developed finding numerous applications in various fields of photonics, biotechnology, and medicine. High sensitivity to the refractive index variation, arising from the strong interaction between a guided mode and an analyte in the test, makes MOF-based sensors ideal candidates for chemical and biochemical analysis of solutions with small volume and low concentration. Here, we review the modern techniques used for the modification of the fiber’s structure, which leads to an enhanced detection sensitivity, as well as the surface functionalization processes used for selective adsorption of target molecules. Novel functionalized MOF-based devices possessing these unique properties, emphasize the potential applications for fiber optics in the field of modern biophotonics, such as remote sensing, thermography, refractometric measurements of biological liquids, detection of cancer proteins, and concentration analysis. In this work, we discuss the approaches used for the functionalization of MOFs, with a focus on potential applications of the produced structures.

In the present paper, a unique semiconductor doped glass photonic crystal fiber has been designed which is suitable for soliton propagation at femto-Joule energy. The fiber promises to yield low and uniform anomalous dispersion profile and very large optical nonlinearities 25211 W $^{(-1)}$ km $^{(-1)}$ at telecommunication wavelength, thus facilitating soliton formation at ultralow energy. The observed magnitude of nonlinearity is the highest reported ever till date in AlGaAs doped glass. The soliton dynamics has been investigated taking into account of higher-order dispersions and nonlinearities. Propagating solitons breadth and experience large frequency shift, this decrease with the increase in the initial pulse width and increase with the increase in pulse energy. Temporal width of solitons oscillates, the frequency and amplitude of oscillations increase with the increase in the value of pulse energy.

Fiber delivery of ultrashort pulses is important for multiphoton endoscopy. A chirped photonic crystal fiber (CPCF) is first characterized for its transmission bandwidth, propagation loss, and dispersion properties. Its extremely low dispersion ($~150f{s}^2/m$) enables the delivery of sub-30 fs pulses through a ~1 m-long CPCF. The CPCF is then incorporated into a multiphoton imaging system and its performance is demonstrated by imaging various biological samples including yew leaf, mouse tendon, and human skin. The imaging quality is further compared with images acquired by a multiphoton imaging system with free-space or hollow-core photonic band-gap fiber (PBF) delivery of pulses. Compared with free-space system, the CPCF delivered system maintains the same ultrashort pulsewidth and the image qualities are comparable. Compared with the PBF delivery, CPCF provides a 35 times shorter pulsewidth at the sample location, which results in a ~12 and 50 times improvement in two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) signals respectively. Our results show that CPCF has great potential for fiber delivery of ultrashort pulses for multiphoton endoscopy.