A surface plasmon resonance (SPR) sensor based on dual-layered air hole shaped photonic crystal fiber (PCF) is proposed to realize the simultaneous measurement of refractive index (RI). The plasma ...materials silver (Ag) and titanium dioxide (TiO
2
) were sequentially coated on the outer surface of PCF to obtain enhanced sensing properties. By carefully adjusting the geometrical parameters, the simulation results show a maximum wavelength sensitivity of 72,000 nm/RIU for analyte refractive indices ranging from 1.26 to 1.365, which realizes the high-sensitivity sensing in the visible to near-infrared optical band. Moreover, the sensor attains a maximum figure of merit (FOM) of 229 and RI resolution of 1.29 × 10
− 6
. This work shows great potential for real-time, affordable, and accurate measurement in biomedical, biological and organic chemical domains.
A fiber-optic sensor that simultaneously measures relative humidity (RH) and temperature (T) based on a microfiber Sagnac loop (MSL) and MoS 2 nanosheets is proposed. The MSL is made from a ...microfiber coupler fabricated by hydrogen-oxygen flame heating technology. The sensor responses to RH and T are investigated by theoretical and experimental analyses. In our experiments, the RH sensitivities achieved are 176.6 pm/%RH for the wavelength shift and −0.017 dB/%RH for the intensity in the range from 60.6 to 78.6%RH, and the T sensitivities are −123.5 pm/°C and −0.079 dB/°C. The proposed sensor has potential applications in the simultaneous measurement of RH and T.
We propose a large detection range surface plasmon resonance (SPR) sensor based on hollow-core photonic crystal fiber in this paper. The sensor consists of an analyte channel in the core hole and a ...silver nanowire in the cladding holes. We investigate the resonance properties between the core modes and the surface plasmon polariton (SPP) modes excited on the nanowire surface in a large refractive index (RI) range from 1.33 to 1.5. Numerical results show that the resonance between the core mode and the higher order SPP modes can occur at particular wavelengths, thus exciting resonance peaks that shift to short wavelengths as RI increases. By tracking most sensitive peak, which is formed by the resonance combination of the x-polarized core mode and the second-order SPP mode, our sensor can measure large RI ranges of the analyte either higher or lower than that of the fiber material.
We propose a surface plasmon resonance (SPR) sensor based on the exposed-core microstructured optical fiber (EC-MOF) placed with a silver wire. The exposed section of the EC-MOF as a microfluidic ...channel is placed with the silver wire to avoid the metal coating and is then deposited with the analyte to avert the analyte filling. The proposed SPR sensor can support two polarized resonance peaks (x-polarized and y-polarized) caused by the silver wire. We theoretically investigate the sensitivities of the two polarized peaks both in the wavelength and amplitude interrogation methods and analyze the influences of the silver wire location on the sensing performances. The results show that the sensitivities of the two polarized peaks are similar and relatively stable for random locations of the silver wire. Moreover, the x-polarized peak provides a higher resolution for wavelength sensitivity and needs a shorter silver wire for the maximum amplitude sensitivity. This paper demonstrates that using the EC-MOF placed with the silver wire can simultaneously solve the metal coating and analyte filling problems in the other SPR sensors with no sacrifice in sensitivity.
Chiral metasurfaces can achieve giant chiral optical responses and have been expanded from the optical band to other electromagnetic bands. Here, we propose a new method for dynamic terahertz ...circular dichroism (CD) manipulation in metasurfaces. By introducing a patterned and electrically doped graphene into the metamirror consists of double layer C-shaped split ring resonators (SRRs), efficient terahertz CD modulation is observed. Since the electrical doping of graphene changes the absorption loss of the metasuface cavity, the structure shows switching between a chiral metasurface and an ordinary metal mirror, which can be seen as "on" and "off" states. The calculation results show an efficient modulation of the terahertz CD in a large dynamic range. In addition, we also use the new method to design two metasurfaces for dynamic terahertz wavefront modulation and near-field digital imaging, both of which show a high-performance electrical switching. This method provides a new way for the design of active terahertz devices based on metasurfaces, and also promotes the applications of terahertz chiral metasurfaces in high-speed wireless communication and dynamic imaging.
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If a metalens integrates the circular polarization (CP) conversion function, the focusing lens together with circular-polariz-ing lens (CPL) in traditional cameras may be replaced by a metalens. ...However, in terahertz (THz) band, the reported metalenses still do not obtain the perfect and strict single-handed CP, because they were constructed via Pancharatnam-Berry phase so that CP conversion contained both left-handed CP (LCP) and right-handed CP (RCP) components. In this paper, a silicon based THz metalens is constructed using dynamic phase to obtain single-handed CP conversion. Also, we can rotate the whole metalens at a certain angle to control the conversion of multi-polarization states, which can simply manipulate the focusing for incident linear polarization (LP) THz wave in three polarization conversion states, in-cluding LP without conversion, LCP and RCP. Moreover, the polarization conversion behavior is reversible, that is, the THz metalens can convert not only the LP into arbitrary single-handed CP, but also the LCP and RCP into two perpen-dicular LP, respectively. The metalens is expected to be used in advanced THz camera, as a great candidate for tradi-tional CPL and focusing lens group, and also shows potential application in polarization imaging with discriminating LCP and RCP.
We present a simple iterative pre-distortion algorithm for achieving a rapid linear frequency sweep of semiconductor lasers. The algorithm achieves the desired frequency swept linearity with only ...four iterations. We derive a general formula for iterative pre-distortion by establishing the relationship between the laser output frequency and the drive current. The linear frequency-swept laser source obtained by this algorithm can be used in FMCW LiDAR systems. Experimentally, we investigated the algorithm using a 1550 nm distributed feedback (DFB) laser, achieving frequency swept excursion of 30.26 GHz, and frequency swept slope of 504 THz/s. We analyzed the linearity of the frequency swept results for the fourth iteration, achieving less than 5 MHz root mean square (RMS) value of frequency swept nonlinearity.
We present numerical investigation on interference bands and the embedded fine interference fringes in the photoelectron momentum distributions (PMDs) induced from hydrogen ionization by intense ...spatiotemporal optical vortex (STOV) pulse. The simulation results show that the momentum bands in the coordinate-resolved PMDs are oppositely tilted for opposite topological charges of a STOV pulse, with the band separation in energy in approximately accordance with the multiphoton ionization nature. The fine fringes embedded in the momentum bands are deciphered with the governing role of the classical action phase accumulated for the STOV pulse spanning the singularity along the temporal direction. In addition, we propose an intuitive picture of double multi-slits interference for understanding the interference characteristics of the PMDs initiated by the STOV pulse.
Graphical abstract
Real-time, accurate, and portable detection of wireless signal is a crucial part of mobile communication. A highly sensitive detector with quickly response is the indispensable component for ...obtaining optical signal. Organic/inorganic hybrid perovskite (CH
3
NH
3
PbI
3
) has been fabricated to photodetectors with a rapid response time and high responsivity by optimizing the quality of photosensitive layer with appropriate transport layer. The devices show high responsivity of 436 mA W
−1
at 753 nm, fast response time of 1.7 μs, large linear dynamic range of 106 dB, as well as 75 kHz bandwidth, all under zero bias. Attributing to these prominent characteristics, this perovskite photodetector was integrated into an optical communication system, serving as a light sensor in receiver terminal. With it, the string, text and data files are transmitted by coded light successfully, accurately and rapidly. These results show the great potential of applications in visible light detection for organic/inorganic hybrid perovskite junction photodetectors.
We propose a temperature sensor design based on surface plasmon resonances (SPRs) supported by filling the holes of a six-hole photonic crystal fiber (PCF) with a silver nanowire. A liquid mixture ...(ethanol and chloroform) with a large thermo-optic coefficient is filled into the PCF holes as sensing medium. The filled silver nanowires can support resonance peaks and the peak will shift when temperature variations induce changes in the refractive indices of the mixture. By measuring the peak shift, the temperature change can be detected. The resonance peak is extremely sensitive to temperature because the refractive index of the filled mixture is close to that of the PCF material. Our numerical results indicate that a temperature sensitivity as high as 4 nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform. Moreover, the maximal sensitivity is relatively stable with random filled nanowires, which will be very convenient for the sensor fabrication.
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