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This work presents a gas-liquid sensor based on chalcogenide etched-tapered fiber (ETF) functionalized with graphene oxide film. Unlike the preparation of conventional tapered fiber sensors, the core diameter of the optical fiber of this gas-liquid sensor was kept constant, and part of its cladding was removed via the chemical corrosion method that the fiber optic modes were the invariant. The energy distribution of transmission mode in the original fiber and tapered fiber is simulated respectively, and obtained the conclusion that the tapered fiber structure has higher sensing sensitivity. The sensors could detect VOCs such as formaldehyde (HCOH) and butane (C4H10) in the mid-infrared band. Results showed that the ETF sensor had a high detection sensitivity of both HCOH solution (2.6731 a.u./mg·mL−1) and C4H10 gas (0.2773 a.u./vol.%). A layer of graphene oxide (GO) film was coated on the ETF to further improve the sensitivity of the sensor. The GO coated etched-tapered fiber (GO-ETF) sensor’ sensitivity was substantially improved owing to the strong hydrophilicity and biocompatibility of GO which can absorb bioactive molecules. The high detection sensitivity of both solution and gas were 4.5091 a.u./mg·mL−1 and 0.4812 a.u./vol.%, respectively, which were 1.69 and 1.74 times higher than that of the sensor without a coating of GO film. The results further showed that the sensor had a rapid response speed, low detection limit, good repeatability, and stability. [ABSTRACT FROM AUTHOR]

Chalcogenide glass (ChG) optical fibers have excellent transmission performance in the mid-infrared range, and microstructured devices prepared on ChG fibers play an important role in the field of infrared sensing and optical integration. In this study, high-quality chalcogenide optical fibers were prepared, and grating structures were produced on their end surfaces. An easy-to-use FC cable was first prepared and polished to high flatness with the surface roughness of less than 0.08 μm. 1- and 2-D diffraction gratings were then prepared on the end surfaces of the chalcogenide fibers via femtosecond laser line-by-line direct writing technology. The ChG fiber end surface gratings prepared with optimized femtosecond laser parameters exhibited high diffraction efficiency and clear diffraction pattern, indicating that they had excellent optical performance. The performance of the grating was tested by using a laser source with wavelengths covering the visible to the near-infrared regions. This measurement showed that the first-order diffraction efficiency of the grating on the end face could reach close to 50% at 1550 nm. [ABSTRACT FROM AUTHOR]

We show that an optical modulator that consists of an integrated dual parallel Mach–Zehnder modulator (dMZM) can be used for obtaining not only optical single-side band modulation but also tunability of optical carrier to sideband ratio (OCSR) simultaneously. Such a modulator will be vital for optimizing the performance of radio over fiber links by improving modulation efficiency and receiver sensitivity and by removing fiber chromatic dispersion induced RF power fading. It is shown that a wide range of OCSR tunability can be obtained by altering bias voltage of dMZM, and optimum OCSR, to maximize the output RF power, depends on RF modulation index and extinction ratio of the integrated dMZM. Good agreement between theory, simulation, and experiment is obtained. For typical extinction ratio and low modulation index, it is found that an OCSR of 0 dB is optimum to maximize RF carrier power. However, for multiband orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) radio, the best error vector magnitude (EVM) of -21.8 dB is obtained experimentally at an OCSR of \sim5.4 dB due to avoidance of clipping induced nonlinear distortion. [ABSTRACT FROM PUBLISHER]

This paper presents investigation of the impact of electro-absorption modulator integrated laser (EML) on performance of multiband-orthogonal frequency-division-multiplexing (MB-OFDM) ultra wideband (UWB) signal over single-mode fiber transmission by theoretical and experimental analysis, considering various parameters, such as fiber length, bias voltage, modulation power, bias current, and temperature of EML. The effect of the EML modulation nonlinearities on the OFDM subcarriers in MB-OFDM UWB over fiber system is investigated considering intermodulation distortion (IMD) and adjacent channel power ratio. It is shown that MB-OFDM UWB over fiber is limited by SNR for small modulation power and EML modulation nonlinearities induced IMD for high modulation power. Fiber transmission length is mainly degraded by EML phase noise converted relative intensity noise and power fading. The developed theory is verified by experiments. [ABSTRACT FROM PUBLISHER]

We experimentally investigate and theoretically analyze the performance of a multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) wireless signal over fiber system considering the impact of laser relative intensity noise (RIN). Two types of RIN are considered: laser intrinsic RIN and laser phase-noise-converted RIN due to fiber dispersion. To reduce the impact of intrinsic RIN, laser output power of 2 dBm and beyond should be used. With the increase of fiber length and/or laser linewidth, UWB wireless signal over fiber is more degraded due to the converted RIN. For a given 0.6 dB degradation of error vector magnitude (EVM), the allowed laser linewidth is 30 MHz for 20 km of standard single-mode fiber for the first three bands. However, the converted RIN has much greater impact on higher-frequency UWB channels, depending on fiber length. A laser with a linewidth of less than 1 MHz will ensure that the EVM penalty due to the converted RIN is less than 1 dB for all 14 bands of MB-OFDM UWB. [ABSTRACT FROM PUBLISHER]