Volume: 2 Issue 6
8 Article(s)

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Multifunctional integration on optical fiber tips: challenges and opportunities
Yifeng Xiong, and Fei Xu
The flat endface of an optical fiber tip is an emerging light-coupled microscopic platform that combines fiber optics with planar micro- and nanotechnologies. Since different materials and structures are integrated onto the endfaces, optical fiber tip devices have miniature sizes, diverse integrated functions, and low insertion losses, making them suitable for all-optical networks. In recent decades, the increasing demand for multifunctional optical fibers has created opportunities to develop various structures on fiber tips. Meanwhile, the unconventional shape of optical fibers presents challenges involving the adaptation of standard planar micro- and nanostructure preparation strategies for fiber tips. In this context, researchers are committed to exploring and optimizing fiber tip manufacturing techniques, thereby paving the way for future integrated all-fiber devices with multifunctional applications. First, we present a broad overview of current fabrication technologies, classified as “top-down,” “bottom-up,” and “material transfer” methods, for patterning optical fiber tips. Next, we review typical structures integrated on fiber tips and their known and potential applications, categorized with respect to functional structure configurations, including “optical functionalization” and “electrical integration.” Finally, we discuss the prospects for future opportunities involving multifunctional integrated fiber tips.
Advanced Photonics
  • Publication Date: Nov. 06, 2020
  • Vol.2 Issue, 6 064001 (2020)
Plasma-grating-induced breakdown spectroscopy
Mengyun Hu, Junsong Peng, Sheng Niu, and Heping Zeng
Laser-induced breakdown spectroscopy (LIBS) is a useful tool for determination of elements in solids, liquids, and gases. For nanosecond LIBS (ns-LIBS), the plasma shielding effect limits its reproducibility, repeatability, and signal-to-noise ratios. Although femtosecond laser filament induced breakdown spectroscopy (FIBS) has no plasma shielding effects, the power density clamping inside the filaments limits the measurement sensitivity. We propose and demonstrate plasma-grating-induced breakdown spectroscopy (GIBS). The technique relies on a plasma excitation source—a plasma grating generated by the interference of two noncollinear femtosecond filaments. We demonstrate that GIBS can overcome the limitations of standard techniques such as ns-LIBS and FIBS. Signal intensity enhancement with GIBS is observed to be greater than 3 times that of FIBS. The matrix effect is also significantly reduced with GIBS, by virtue of the high power and electron density of the plasma grating, demonstrating great potential for analyzing samples with complex matrix.
Advanced Photonics
  • Publication Date: Oct. 22, 2020
  • Vol.2 Issue, 6 065001 (2020)
High spatial and temporal resolution synthetic aperture phase microscopy
Cheng Zheng, Di Jin, Yanping He, Hongtao Lin, Juejun Hu, Zahid Yaqoob, Peter T. C. So, and Renjie Zhou
A new optical microscopy technique, termed high spatial and temporal resolution synthetic aperture phase microscopy (HISTR-SAPM), is proposed to improve the lateral resolution of wide-field coherent imaging. Under plane wave illumination, the resolution is increased by twofold to around 260 nm, while achieving millisecond-level temporal resolution. In HISTR-SAPM, digital micromirror devices are used to actively change the sample illumination beam angle at high speed with high stability. An off-axis interferometer is used to measure the sample scattered complex fields, which are then processed to reconstruct high-resolution phase images. Using HISTR-SAPM, we are able to map the height profiles of subwavelength photonic structures and resolve the period structures that have 198 nm linewidth and 132 nm gap (i.e., a full pitch of 330 nm). As the reconstruction averages out laser speckle noise while maintaining high temporal resolution, HISTR-SAPM further enables imaging and quantification of nanoscale dynamics of live cells, such as red blood cell membrane fluctuations and subcellular structure dynamics within nucleated cells. We envision that HISTR-SAPM will broadly benefit research in material science and biology.
Advanced Photonics
  • Publication Date: Nov. 30, 2020
  • Vol.2 Issue, 6 065002 (2020)
Research Articles
Extreme events in quantum cascade lasers
Olivier Spitz, Jiagui Wu, Andreas Herdt, Grégory Maisons, Mathieu Carras, Wolfgang Elsäßer, Chee-Wei Wong, and Frédéric Grillot
Advanced Photonics
  • Publication Date: Oct. 23, 2020
  • Vol.2 Issue, 6 066001 (2020)
Dynamic photonic barcodes for molecular detection based on cavity-enhanced energy transfer | On the Cover
Yunke Zhou, Zhiyi Yuan, Xuerui Gong, Muhammad D. Birowosuto, Cuong Dang, and Yu-Cheng Chen
Optical barcodes have demonstrated a great potential in multiplexed bioassays and cell tracking for their distinctive spectral fingerprints. The vast majority of optical barcodes were designed to identify a specific target by fluorescence emission spectra, without being able to characterize dynamic changes in response to analytes through time. To overcome these limitations, the concept of the bioresponsive dynamic photonic barcode was proposed by exploiting interfacial energy transfer between a microdroplet cavity and binding molecules. Whispering-gallery modes resulting from cavity-enhanced energy transfer were therefore converted into photonic barcodes to identify binding activities, in which more than trillions of distinctive barcodes could be generated by a single droplet. Dynamic spectral barcoding was achieved by a significant improvement in terms of signal-to-noise ratio upon binding to target molecules. Theoretical studies and experiments were conducted to elucidate the effect of different cavity sizes and analyte concentrations. Time-resolved fluorescence lifetime was implemented to investigate the role of radiative and non-radiative energy transfer. Finally, microdroplet photonic barcodes were employed in biodetection to exhibit great potential in fulfilling biomedical applications.
Advanced Photonics
  • Publication Date: Oct. 30, 2020
  • Vol.2 Issue, 6 066002 (2020)
Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3
Haihui Zhao, Xinhou Chen, Chen Ouyang, Hangtian Wang, Deyin Kong, Peidi Yang, Baolong Zhang, Chun Wang, Gaoshuai Wei, Tianxiao Nie, Weisheng Zhao, Jungang Miao, Yutong Li, Li Wang, and Xiaojun Wu
Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications, such as imaging, information encryption, and all-optical coherent control of terahertz nonlinear phenomena. Topological insulators featuring unique spin-momentum–locked surface state have already exhibited very promising prospects in terahertz emission, detection, and modulation, which may lay a foundation for future on-chip topological insulator-based terahertz systems. However, polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored. We systematically investigated the terahertz radiation from topological insulator Bi2Te3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality, ellipticity, and principal axis. The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect (PGE)-induced photocurrent, while the linearly polarized terahertz waves originated from linear PGE-induced shift currents. Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.
Advanced Photonics
  • Publication Date: Oct. 30, 2020
  • Vol.2 Issue, 6 066003 (2020)
Metalens-integrated compact imaging devices for wide-field microscopy
Beibei Xu, Hanmeng Li, Shenglun Gao, Xia Hua, Cheng Yang, Chen Chen, Feng Yan, Shining Zhu, and Tao Li
Metasurfaces have demonstrated unprecedented capabilities in manipulating light with ultrathin and flat architectures. Although great progress has been made in the metasurface designs and function demonstrations, most metalenses still only work as a substitution of conventional lenses in optical settings, whose integration advantage is rarely manifested. We propose a highly integrated imaging device with silicon metalenses directly mounted on a complementary metal oxide semiconductor image sensor, whose working distance is in hundreds of micrometers. The imaging performances including resolution, signal-to-noise ratio, and field of view (FOV) are investigated. Moreover, we develop a metalens array with polarization-multiplexed dual-phase design for a wide-field microscopic imaging. This approach remarkably expands the FOV without reducing the resolution, which promises a non-limited space-bandwidth product imaging for wide-field microscopy. As a result, we demonstrate a centimeter-scale prototype for microscopic imaging, showing uniqueness of meta-design for compact integration.
Advanced Photonics
  • Publication Date: Nov. 13, 2020
  • Vol.2 Issue, 6 066004 (2020)
Cascading optofluidic phase modulators for performance enhancement in refractive adaptive optics
Pouya Rajaeipour, Kaustubh Banerjee, Alex Dorn, Hans Zappe, and Çağlar Ataman
We discuss the implementation and performance of an adaptive optics (AO) system that uses two cascaded deformable phase plates (DPPs), which are transparent optofluidic phase modulators, mimicking the common woofer/tweeter-type astronomical AO systems. One of the DPPs has 25 electrodes forming a keystone pattern best suited for the correction of low-order and radially symmetric modes; the second device has 37 hexagonally packed electrodes better suited for high-order correction. We also present simulation results and experimental validation for a new open-loop control strategy enabling simultaneous control of both DPPs, which ensures optimum correction for both large-amplitude low-order, and complex combinations of low- and high-order aberrations. The resulting system can reproduce Zernike modes up to the sixth radial order with stroke and fidelity up to twice better than what is attainable with either of the DPPs individually. The performance of the new AO configuration is also verified in a custom-developed fluorescence microscope with sensorless aberration correction.
Advanced Photonics
  • Publication Date: Nov. 19, 2020
  • Vol.2 Issue, 6 066005 (2020)

About the Cover

The image on the cover for Advanced Photonics Volume 2 Issue 6 illustrates the concept of optical encoding with microdroplets controlled by energy transfer at the biointerface. The figure shows a dynamic evolution of energy transfer when biomolecules binds on the droplet interface. Here the microdroplet serves as the active optical resonator, while the biomolecules serve as the gain material. The radiative energy from a single microdroplet is transferred to binding biomolecules, converting dynamic biological information into more than trillions of distinctive photonic barcodes. This research illuminates a beacon for real-time intermolecular interaction, paving a new road for photonic encryption and biosensing.