PHB2 Alleviates Neurotoxicity of Prion Peptide PrP106-126 via PINK1/Parkin-Dependent Mitophagy.

Prion diseases are a group of neurodegenerative diseases characterized by mitochondrial dysfunction and neuronal death. Mitophagy is a selective form of macroautophagy that clears injured mitochondria. Prohibitin 2 (PHB2) has been identified as a novel inner membrane mitophagy receptor that mediates mitophagy. However, the role of PHB2 in prion diseases remains unclear. In this study, we isolated primary cortical neurons from rats and used the neurotoxic prion peptide PrP106-126 as a cell model for prion diseases. We examined the role of PHB2 in PrP106-126-induced mitophagy using Western blotting and immunofluorescence microscopy and assessed the function of PHB2 in PrP106-126-induced neuronal death using the cell viability assay and the TUNEL assay. The results showed that PrP106-126 induced mitochondrial morphological abnormalities and mitophagy in primary cortical neurons. PHB2 was found to be indispensable for PrP106-126-induced mitophagy and was involved in the accumulation of PINK1 and recruitment of Parkin to mitochondria in primary neurons. Additionally, PHB2 depletion exacerbated neuronal cell death induced by PrP106-126, whereas the overexpression of PHB2 alleviated PrP106-126 neuronal toxicity. Taken together, this study demonstrated that PHB2 is indispensable for PINK1/Parkin-mediated mitophagy in PrP106-126-treated neurons and protects neurons against the neurotoxicity of the prion peptide.

Highly sensitive torsion sensor based on a coupled optoelectronic oscillator incorporating nonlinear polarization rotation.

We propose and demonstrate a new, to the best of our knowledge, technique to implement a high-speed and highly sensitive torsion sensor based on a coupled optoelectronic oscillator (COEO) incorporating nonlinear polarization rotation (NPR). The COEO consists of a mode-locked laser loop and an OEO loop. In the laser loop, the NPR effect effectively induces intensity- and wavelength-dependent loss, which acts as a Lyot birefringent fiber filter. When twisting the polarization-maintaining fiber (PMF), the transmission of the filter varies as well as the laser output wavelength. In the OEO loop, the optical source is provided by the output signal of the mode-locked laser. The variation in the optical carrier wavelength changes the time delay and the oscillation frequency of the OEO loop. The oscillation frequency shift is a linear function of the twist angle. Sensitivities of -60.006 Hz/deg over 360° for a 48 cm PMF and -180.996 Hz/deg over 92° for a 22 cm PMF are achieved.

Optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator.

We have proposed and experimentally demonstrated an optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator (COEO). The COEO is a combination of an OEO and a mode-locked laser, sharing one optoelectronic modulator. The feedback between the two active loops makes the oscillation frequency equal to the mode spacing of the laser. It is equivalent to a multiple of the natural mode spacing of the laser, which is affected by the applied axial strain to the cavity. Therefore, we can evaluate the strain by measuring the oscillation frequency shift. Higher sensitivity can be obtained by adopting higher frequency order harmonics owing to the accumulative effect. We carry out a proof-to-concept experiment. The dynamic range can reach 10000 µ ε. Sensitivities of 6.5 Hz/µ ε for 960 MHz and 13.8 Hz/µ ε for 2700 MHz are obtained. The maximum frequency drifts of the COEO in 90 mins are within ±148.03 Hz for 960 MHz and ±303.907 Hz for 2700 MHz, which correspond to measurement errors of ±22 µ ε and ±20 µ ε. The proposed scheme has the advantages of high precision and high speed. The COEO can generate an optical pulse whose pulse period is influenced by the strain. Therefore, the proposed scheme has potential applications in dynamic strain measurement.

Enhancing spatial resolution of BOTDR sensors using image deconvolution.

We propose to employ the image deconvolution technique for Brillouin optical time domain reflectometry (BOTDR) systems to achieve a flexible and enhanced spatial resolution with pump pulses longer than phonon lifetime. By taking the measured Brillouin gain spectrum (BGS) distribution as an image blurred by a point spread function (PSF), the image deconvolution algorithm based on the two-dimensional Wiener filtering can mitigate the ambiguity effect on the Brillouin response. The deconvoluted BGS distribution reveals detailed sensing information within shorter fiber segments, improving the inferior spatial resolution and simultaneously maintaining other sensing performance parameters. Thanks to the proposed technique, a typical BOTDR sensor with 40 ns pump pulses reaches a submetric spatial resolution as high as 10 cm. Compared to the differential-spectrum-based BOTDR retrieving the same spatial resolution, the image deconvolution technique shows advantages in system complexity and measurement uncertainty. Moreover, the proposed technique is promising to improve the spatial resolution of other distributed optical fiber sensing (DOFS) techniques such as BOTDR systems with complex pump modulation methods.

Enhanced sensitivity of optical fiber vibration sensor based on radio-frequency Michelson interferometer.

We propose and demonstrate a new scheme for enhancing the sensitivity of an optical fiber vibration sensor based on microwave interferometry, which is realized by an incoherent optical Michelson interferometer (MI). The sensing arm of the MI is sensitive to environmental vibration; this will cause changes in the phase of the reflection spectra in the microwave domain. The phase sensitivity can be improved by adjusting the power ratio of the two beams in the interferometer and the driving frequency of the modulator. The system can overcome the problem of interference fading so that it is immune to environmental disturbance. The proposed scheme has merits of simplicity and compact configuration, and may provide a new type of high-precision fiber sensor for measuring vibration, temperature, strain, and so on.

Trace copper detection using in-line optical fiber Mach-Zehnder interferometer combined with an optoelectronic oscillator.

We experimentally demonstrate a novel optical fiber chemosensor for trace Cu2+ ions detection that is implemented by using an in-line optical fiber Mach-Zehnder interferometer (MZI) in conjunction with an optoelectronic oscillator (OEO). The MZI is fabricated by lateral offset splicing a section of D-shaped fiber between two single-mode fibers. It splices the broadband optical source into a sinusoidal-shaped light, which can form a single passband microwave photonic filter (MPF) by combining the Mach-Zehnder modulator, a segment of fiber and a photodetector. The center frequency of the MPF, determined by the free spectra range of MZI, is affected by the solution concentration. Incorporating the MPF in the OEO sensor, the oscillation frequency is determined by the solution concentration. Therefore, we can estimate the solution concentration by measuring the microwave frequency change. We carry out a proof to concept experiment. High sensitivity Cu2+ ions concentration sensing with sensitivity of 13 Hz/(µM/L) is achieved. The maximum measurement error of concentration obtained is within 1.38 µM/L. The proposed sensor has merits of high interrogation speed, simple operation, high sensitivity and accuracy, offering the potentials in a wide range of biological application scenarios.

High-precision strain-insensitive temperature sensor based on an optoelectronic oscillator.

We have proposed and experimentally demonstrated a high-precision and strain-insensitive temperature sensor based on an optoelectronic oscillator (OEO). The oscillation frequency of the OEO is determined by the single passband microwave photonic filter (MPF) by using stimulated Brillouin scattering (SBS). The sensing fiber, which acts as the SBS gain medium, is exposed to temperature variations. The Brillouin frequency shift (BFS) changes along with the temperature. Since the central frequency of the MPF is a function of the BFS, the oscillation frequency of the OEO is varied. Besides, due to the mode competition in the OEO, the influence of the strain is eliminated. Thus, the temperature variations can be estimated through measuring the oscillation frequency. We carry out a proof-to-concept experiment. Temperature sensing with a high sensitivity of 1.00745 MHz/°C is achieved. The maximum measurement error of temperature obtained is within ± 0.5 °C. The proposed scheme has merits of simplicity and compact configuration. In addition, the proposed temperature sensor can realize quasi-distributed measurement by utilizing wavelength division multiplexing (WDM).

Polarization-insensitive colorful meta-holography employing anisotropic nanostructures.

Benefiting from advances in nanofabrication technology, emerging metasurfaces are promising for compact and wearable multicolor meta-holograms with large fields of view. However, due to the inherent electromagnetic properties of the structures that are used, current multicolor meta-holograms are often sensitive to the incident light polarization, which greatly restricts the application of meta-holography. Here, we took advantage of the amplitude properties of metasurfaces and the off-axis illumination method to carry out experiments involving polarization-insensitive colorful meta-holography with anisotropic nanostructures. With red, green and blue lasers illuminating the meta-hologram along different angles, a polarization-insensitive colorful holographic image was achieved and the disturbance from zero-order diffraction light was essentially eliminated. To the best of our knowledge, the current work was the first time that a polarization-insensitive colorful meta-hologram with anisotropic nanostructures was experimentally demonstrated. We expect our approach to provide promising prospects for the use of metasurfaces in applications such as flat meta-lenses, data storage and virtual/augmented reality.

Distributed vibration measurement based on a coherent multi-slope-assisted BOTDA with a large dynamic range.

We propose a novel technique to enhance the dynamic range of a coherent slope-assisted Brillouin optical time domain analysis. A multi-tone probe and a reference wave are launched into the fiber under test (FUT); after interacting with the pump pulse, the Brillouin gain, as well as the Brillouin phase shift of each tone, can be demodulated simultaneously. In light of this, the strain information can be determined by the Brillouin phase-gain ratio of each tone. In the experiment, a three-tone probe with a 60 MHz interval is used; effective measurement frequency span larger than 180 MHz is verified in a ∼2 km single-mode fiber with 2.5 m spatial resolution and 1.5 kHz sampling rate to strain. A vibration signal with 41 Hz frequency and 2546 µÎµ amplitude is successfully demodulated.

Coherent optical modulation of graphene based on coherent population oscillation.

The optical modulation of graphene circumvents the "electrical bottleneck" in electrical field tuning of the Fermi level and motivates diverse graphene-based controllable photonic devices with extraordinary performances. Unfortunately, pervious optical modulation schemes are incoherent, and the Fermi-Dirac distribution formed from a strong pump laser prevents the absorption of a weak probe laser due to the Pauli blocking, making the modulation inconvenient and low in efficiency. Here we demonstrate the coherent optical modulation of graphene based on coherent population oscillation, where ground state population oscillates with a beat frequency equal to the pump and probe frequency difference. To distinguish it from the coexisting incoherent modulation in graphene, a phase-sensitive pump-probe system is constructed with a fiber-based Mach-Zehnder interferometer. Clear resonance within the burning hole of a pump laser is observed in the interference spectrum of a coherent probe laser. The discovery of highly coherent ground state population oscillation in graphene offers new possibilities for manipulating and controlling the phase response of graphene-based photonics with high efficiency.

Simultaneous measurement of strain and temperature based on hybrid EDF/Brillouin laser.

Simultaneous temperature and strain sensing is experimentally demonstrated based on erbium-doped fiber laser (EDFL) and Brillouin erbium fiber laser (BEFL) incorporated in a single ring laser cavity. The EDFL can be switched to BEFL by injecting the Brillouin pump into the laser cavity. Longitudinal modes beat frequency and Brillouin frequency shift are monitored to discriminate strain and temperature. The longitudinal modes beat frequency is measured by observing the self-beating signals of the EDFL, while the Brillouin frequency shift is measured by monitoring the heterodyning signal of the BEFL. The simultaneous measurement errors of strain and temperature are within ± 25.8µÎµ and ± 0.8°C. The sensor is of simple structure and compact size.

Optical single sideband modulation based on a high-order birefringent filter using cascaded Solc-Sagnac and Lyot-Sagnac loops.

We propose and experimentally demonstrate a simple and flexible photonic approach to implementing single sideband (SSB) modulation based on optical spectral filtering. The high-order birefringent filter is realized through the cascaded Solc-Sagnac and Lyot-Sagnac loops. By adjusting the rotation angle of the polarization controller (PC), the notch position to remove undesired sidebands changes. The frequency for SSB modulation varies accordingly. The periodical response of the filter spectrum allows both the carrier wavelength and the optical carrier to sideband ratio (OCSR) to be tunable. SSB modulation over a frequency range from 5 to 40 GHz and tunable OCSR ranging from -9.174 to 34.408 dB are obtained. The significant merits of the proposed approach are the simple structure, easy operation, large frequency range, tunable OCSR, and wavelength independence. The approach has potential applications in optimizing the transmission performance of photonic microwave signal processing systems.

Photonic approach for microwave frequency measurement with adjustable measurement range and resolution using birefringence effect in highly non-linear fiber.

We experimentally demonstrate a novel approach for microwave frequency measurement utilizing birefringence effect in the highly non-linear fiber (HNLF). A detailed theoretical analysis is presented to implement the adjustable measurement range and resolution. By stimulating a complementary polarization-domain interferometer pair in the HNLF, a mathematical expression that relates the microwave frequency and amplitude comparison function is developed. We carry out a proof-to-concept experiment. A frequency measurement range of 2.5-30 GHz with a measurement error within 0.5 GHz is achieved except 16-17.5 GHz. This method is all-optical and requires no high-speed electronic components.

Simultaneous generation of a frequency-multiplied and phase-shifted microwave signal with large tunability.

We demonstrate a photonic approach to simultaneously realize a frequency-multiplied and phase-shifted microwave signal based on the birefringence effects in the high nonlinear fiber. The phase shift caused by asymmetric variations in refractive indexes of fiber between two orthogonal polarization states is introduced into two coherent harmonic of the modulated signals. By beating the phase-modulated sidebands, a frequency-multiplied microwave signal is generated and its phase can be adjusted by simply controlling the pump power. A microwave signal at doubled- or quadrupled-frequency with a full 2π phase shift is obtained over a frequency range from 10 GHz to 30 GHz. The proposed approach has the potential applications in the system with larger-broadband, higher-frequency and -data-rate system, even to handle a multi-wavelength operation.

Mode conversion based on forward stimulated Brillouin scattering in a hybrid phononic-photonic waveguide.

We propose a scheme for on-chip all optical mode conversion based on forward stimulated Brillouin scattering in a hybrid phononic-photonic waveguide. To describe the mode conversion the theoretical model of the FSBS is established by taking into account the radiation pressure and the electrostriction force simultaneously. The numerical simulation is carried out for the mode conversion from the fundamental mode E11x to the higher-order mode E21x. The results indicate that the mode conversion efficiency is affected by the waveguide length and the input pump light power, and the highest efficiency can reach upto 88% by considering the influence of optical and acoustic absorption losses in the hybrid waveguide. Additionally, the conversion bandwidth with approximate 12.5 THz can be achieved in 1550nm communication band. This mode converter on-chip is a promising device in the integrated optical systems, which can effectively increase the capacity of silicon data busses for on-chip optical interconnections.

Dual-wavelength laser speckle imaging to simultaneously access blood flow, blood volume, and oxygenation using a color CCD camera.

We developed a dual-wavelength laser speckle imaging system using a single industrial-grade color CCD camera with Bayer filters to simultaneously image changes in blood flow, blood volume, and oxygenation. One frame of a color image recorded with dual-wavelength laser illumination provides not only the intensity fluctuation of the speckle pattern, but also the dual-wavelength optical reflectance signal. The method was validated using a tissue phantom and cuff ischemia experiments in the human arm. This system achieves complete time synchronization, unlike conventional time-sharing systems. Compared with a multicamera system, it also avoids the problem of image registration and can be less expensive.