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In this study, we report a new type of InGaAs/InP photodetector (PD) with nickel oxide (NiO) transparent p-region and electrode. By applying the NiO film, the device does not require the highly doped p-contact layer and the opaque p-contact metal electrode such as the traditional p-i-n PD. The epitaxial layer of the PD is simplified. Meanwhile, the optical power loss caused by the additional absorption in the highly doped p-contact layer can be avoided. With the fully covered transparent p-contact electrode, the PD can be illuminated from the p-side at the same time. The numerical simulation results show that the new structure can improve the 3-dB bandwidth and the RF output power of the PD. [ABSTRACT FROM AUTHOR]

Optical microfiber-based refractometer, which relies on modal interference operating near the dispersion turning point (DTP), has attracted a high level of research interest. The ultrahigh sensitivity can be achieved by mitigating the group effective refractive index difference between the modes in the coupling. Through modifying the microfiber diameter, the group effective refractive index difference can be modified to zero which is defined as DTP. However, all the DTP-based sensors report low fabrication tolerance and narrow operation bandwidth of probing wavelength for the high-sensitivity region where the refractive index (RI) sensitivities higher than 104 nm/RIU can be achieved, which extremely limits the practical applications. To address the challenge, we manipulate and optimize the mode dispersion by using a tapered specially-designed single stress-applying fiber (SSAF). By introducing the stress-applying part (SAP) into the cladding, the wavelength sensitivity of the group effective RI difference can be significantly reduced through the flexibly engineerable control over the material index. In this way, the operation bandwidth is dramatically broadened for 500 nm in comparison with that of conventional microfiber with the same diameter based on DTP, indicating a broad range of optional probing wavelength and high fabrication tolerance. We experimentally verify the ultrahigh sensitivity and broadband operation around the DTP using an SSAF-based microfiber with a waist diameter of about 2.3 μm. The maximum RI sensitivity of 30563 nm/RIU is obtained. [ABSTRACT FROM AUTHOR]

We propose a compact assemble-easy cost-effective vector bending sensor consisting of a short section of single stress-applying fiber (SSAF) spliced between two standard single-mode fibers (SMFs). The SSAF is specially designed by introducing a stress-applying part (SAP) into the cladding to achieve the asymmetrical geometry. Because of the mode field mismatch between the SMF and the SSAF, the cladding mode is effectively excited, which is sensitive to the bending and has orientation-dependence. Due to the large effective refractive index difference between the core and cladding mode, a compact dual-mode interferometer can be achieved with a thousands-micron-long structure. When the fiber is bent, the mode fields and the effective refractive indices will be modified, and accordingly, the direction-dependent interference spectral shift is observed. Owing to the well-designed SSAF structure, the cost-effective vector bending sensor can be easily realized by a simple sandwich structure without extra complex alignment procedures or fiber grating inscription. We experimentally verify the vector bending property. The maximum sensitivity of 2.04 nm/m−1 is obtained, and the experimental results match well with the simulations. Our proposed device is compact, easy to assemble, and cost-effective, which is promising in the field of vector bending measurement. [ABSTRACT FROM AUTHOR]

We report the phase shift of two types of photodetectors for a variation of bias voltage and optical power. One type is PIN-PD and the other is a modified uni-traveling carrier photodetector (MUTC-PD). In PIN-PD, the phase change shows a photocurrent-dependent variation of about 15 degrees at 3 GHz. It exhibits good stability over a wide bandwidth as the bias voltage changes. By comparison, the phase shift of the MUTC-PD is more sensitive to the bias voltage and the photocurrent. The continuous tunable range of phase shift in MUTC-PD reaches 50 degrees at 10 GHz. It is demonstrated that the adjustable phase shift mainly results from the transit time and the impedance dynamic effects in response to the optical power and bias voltage. [ABSTRACT FROM AUTHOR]

A novel Microstructure PIN photodiode (MPIN-PD) using the ray-optic theory of light trapping effect is presented and analyzed numerically. The MPIN-PD is proposed from an ordinary large-diameter PIN-PD by introducing an obconical shape surrounded by a V-groove trench. The photon-material interaction is increased by using the microstructure in the PIN-PD. It can control light and cause syntony in the absorption layer, reducing the junction capacitance of the PD, and suppressing the tradeoff between the efficiency and bandwidth. Thus, both 3-dB bandwidth and quantum efficiency can be improved simultaneously. The parameters of the MPIN-PD, including the depth and apex angles of the micro-structure, the distance between the cone and V-groove trench are carefully studied to estimate their positive effects of the performance of the MPIN-PD. The transmission line model is exploited for the specific structure to design the electrodes’ distribution. [ABSTRACT FROM AUTHOR]

A compact broadband polarization beam splitter is designed and experimentally demonstrated based on a silicon-nitride-assisted three-waveguide coupler. With the help of coving a layer of silicon nitride on the center bridged silicon waveguide, the phase matching is met for the TM mode but not for the TE mode. The final optimized device length is only $7~\mu \text{m}$ , and the polarization beam splitter has the high extinction ratios of more than 30 dB for the TE mode and that of more than 20 dB for the TM mode in the wavelength ranging from $1.5~\mu \text{m}$ to $1.6~\mu \text{m}$. And the corresponding insertion losses are less than 0.06 dB and 0.35 dB, respectively. The experimental measurement results also show the polarization beam splitter has good performances. [ABSTRACT FROM AUTHOR]

In this study, we have designed and fabricated a flexible and low-cost data glove and then successfully realized the accurate gesture recognition. By sewing the reduced graphene oxide (RGO)-coated fiber that is prepared in a simple method onto a textile glove, we have manufactured a data glove that has been used to monitor the motion of ten finger joints from one hand. In particular, we accurately realize the static and dynamic gesture recognition via the data glove, respectively. Experimental results on the classification of ten static gestures representing digits from “0” to “9” show the good stability and repeatability of the data glove, in which the recognition accuracy achieves 98.5% in 2000 test samples. In addition, the recognition of nine Chinese Sign Language (CSL) words is successfully implemented, and the recognition accuracy reaches 98.3% in 180 test samples, which demonstrates the good real-time monitoring ability and applicability of the dynamic gesture scenarios of the as-prepared data glove. [ABSTRACT FROM AUTHOR]

In this letter, we have conducted experiments on a traditional uni-traveling carrier photodiode (UTC-PD) and a previously modified UTC-PD under the zero-bias operational condition and make a comparison between them. The experimental results demonstrate that the modified UTC-PD is benefit to high speed, and the 3-dB bandwidth can achieve 40 GHz even when the active diameter of ${14}~{\mu }\text{m}$ under the zero-bias operation. Besides, based on the modified UTC-PD structure, we make some improvements in the collector to restrain the trend in which the bandwidth attenuated by the increase of photocurrent under the zero bias operation. [ABSTRACT FROM AUTHOR]