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Stimulus-responsive optical polymers, especially gels, are enabling new-concept energy-transducing "smart" optics. Full exploitation of their molecule-derived tuning and integration with traditional micro/nano-optics/optoelectronics rely on the implementation of devices by advanced "intelligent" micro/nano-manufacturing technologies, especially photolithographies with wide compatibility. In light of the increasing need for an organic combination of smart optical materials and digital micro/nano-manufacturing, novel "smart" optical micro-switches, namely, stimulus-actuated Mach–Zehnder interferometers as a proof-of-concept demonstration, were prototyped with protein-based hydrogels via aqueous multiphoton femtosecond laser direct writing (FsLDW). Protein-based Mach–Zehnder-interferometric smart optical devices here display a morphological quality sufficient for optical applications (average surface roughness ≤ ∼20 nm), nano-precision three-dimensional (3D) geometry of these millimeter-scale devices and purposely structured distribution of photo-crosslinking degree. Moreover, the device configuration was customized with unbalanced branches in which meticulous stimulus-responsive ability can be realized by simply tuning the surrounding chemical stimuli (i.e., Na2SO4 concentration here). The "heterogeneous" configuration with unbalanced branches (i.e., different optical and stimulus-responsive features) exhibits as-designed "smart" switching of propagated near-infrared light (∼808 nm). These capabilities, along with total biodegradation, indicate the application promise of this gel-based optic construction strategy towards novel "intelligent", bio/eco-friendly, self-tuning or sensing photonic integrated systems like optofluidics. [ABSTRACT FROM AUTHOR]

Optical microcavities have been paid enormous attentions as a basic integrated element in photonic devices including micromodulators, microfilters, and microsensors. In particular, the microcavities that can produce unidirectional and single-mode lasing emissions are greatly demanded to meet the challenge of integrating high-efficiency and high-sensitivity optical functional systems. Herein, a three-dimensional polymer microlaser composed of stacked circular-ring-shaped and spiral-ring-shaped microcavities is fabricated directly on a narrow bandpass filter substrate by the femtosecond laser processing technique. The on-chip polymer microlaser provides a room-temperature, low-threshold, unidirectional, and single-mode laser output, resulting from the coupling between the two stacked microcavities. The fabrication of the on-chip low-threshold polymer microlaser opens up a possibility toward the integration of a variety of polymer microcavities for organic optoelectronic devices. [ABSTRACT FROM PUBLISHER]

Stimuli-Responsive Materials: Smart Compound Eyes Enable Tunable Imaging (Adv. Funct. Keywords: compound eyes; femtosecond laser; smart materials; tunable optical components; variable-focus imaging Compound eyes, femtosecond laser, smart materials, tunable optical components, variable-focus imaging. [Extracted from the article]

Compound eyes are natural multiaperture optical imaging systems and have substantial potential in the field of modern optics. However, both natural and artificial compound eyes are composed of ommatidia with fixed focal lengths, and thus incapable of variable‐focus imaging. In this study, inspired by the tunable crystalline lens of human eyes, smart stimuli‐responsive compound eyes based on the bovine serum album (BSA) protein are fabricated via femtosecond laser direct writing. Due to the swelling and shrinking effect of BSA under different pH conditions, a tunable field of view (FOV, 35°–80°) and variable focal length of ommatidia are achieved. In addition to the direct prototyping of an entire protein‐based compound eye, the ability to flexibly integrate the smart protein ommatidia with a conventional optical lens (an SU‐8 lens in this study) to form a composite compound eye is shown. The composite compound eye achieves nearly 400% of focal length tuning at a fixed FOV. It is anticipated that femtosecond laser fabrication and the integration of smart protein‐based compound eyes may emerge as an enabler for fabricating miniature tunable imaging systems. [ABSTRACT FROM AUTHOR]

On‐chip polarization manipulation is proposed via a waveguide that is adiabatically twisted along its longitudinal axis, which can be fundamental building blocks for polarization‐encoded optical communication and information processing. With the help of femtosecond direct laser writing, the polarization rotators for both telecom and visible wavelengths are fabricated, which show polarization conversion efficiencies of >90% at 1550 nm and ≈80% at 646 nm, respectively. Furthermore, a polarization router consisting of multiple waveguides with different twisting angles is demonstrated. With the polarization router, photons with different polarizations are directed to different paths. Based on such platform, the path entanglement between the photons can be transformed to polarization entanglement, which will extend the quantum information technology to higher‐dimensional Hilbert space. [ABSTRACT FROM AUTHOR]

For the first time, proteins, a promising biocompatible and functionality-designable biomacromolecule material, acted as the host material to construct three-dimensional (3D) whispering-gallery-mode (WGM) microlasers by multiphoton femtosecond laser direct writing (FsLDW). Protein/Rhodamine B (RhB) composite biopolymer was used as optical gain medium innovatively. By adopting high-viscosity aqueous protein ink and optimized scanning mode, protein-based WGM microlasers were customized with exquisite true 3D geometry and smooth morphology. Comparable to previously reported artificial polymers, protein-based WGM microlasers here were endowed with valuable performances including steady operation in air and even in aqueous environments, and a higher quality value (Q) of several thousands (without annealing). Due to the 'smart' feature of protein hydrogel, lasing spectrum was responsively adjusted by step of ~0.4 nm blueshift per 0.83-mmol/L Na2SO4 concentration change (0 ~ 5-mmol/L in total leading to ~2.59-nm blueshift). Importantly, other performances including Q, FWHM, FSR, peak intensities, exhibited good stability during adjustments. So, these protein-based 3D WGM microlasers might have potential in applications like optical biosensing and tunable 'smart' biolasers, useful in novel photonic biosystems and bioengineering. [ABSTRACT FROM AUTHOR]