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Showing papers in "IEEE Photonics Technology Letters in 2017"


Journal ArticleDOI
TL;DR: An intelligent eye-diagram analyzer is proposed to implement both modulation format recognition (MFR) and optical signal-to-noise rate (OSNR) estimation by using a convolution neural network (CNN)-based deep learning technique.
Abstract: An intelligent eye-diagram analyzer is proposed to implement both modulation format recognition (MFR) and optical signal-to-noise rate (OSNR) estimation by using a convolution neural network (CNN)-based deep learning technique. With the ability of feature extraction and self-learning, CNN can process eye diagram in its raw form (pixel values of an image) from the perspective of image processing, without knowing other eye-diagram parameters or original bit information. The eye diagram images of four commonly-used modulation formats over a wide OSNR range (10~25 dB) are obtained from an eye-diagram generation module in oscilloscope combined with the simulation system. Compared with four other machine learning algorithms (decision tress, k-nearest neighbors, back-propagation artificial neural network, and support vector machine), CNN obtains the higher accuracies. The accuracies of OSNR estimation and MFR both attain 100%. The proposed technique has the potential to be embedded in the test instrument to perform intelligent signal analysis or applied for optical performance monitoring.

193 citations


Journal ArticleDOI
TL;DR: Numerical results demonstrate that multi-hop transmission, by alleviating channel impairments, can significantly improve the system performance and extend the viable end-to-end communication distance.
Abstract: In this letter, we analytically evaluate the end-to-end bit error rate (BER) of point-to-point multi-hop underwater wireless optical communication (UWOC) systems with respect to all degrading effects of the UWOC channel, namely absorption, scattering, and turbulence-induced fading. To do so, we first derive the BER expression of a single-hop UWOC link as the building block for end-to-end BER evaluation. We also apply Gauss–Hermite quadrature formula to obtain the closed-form solution for the system BER in the case of lognormal underwater fading channel. Numerical results demonstrate that multi-hop transmission, by alleviating channel impairments, can significantly improve the system performance and extend the viable end-to-end communication distance.

125 citations


Journal ArticleDOI
TL;DR: It is shown that with pseudorandom bit sequences, a large artificial gain can be obtained, which comes from pattern prediction rather than predicting or compensating the studied channel/phenomena.
Abstract: We investigate the risk of overestimating the performance gain when applying neural network-based receivers in systems with pseudorandom bit sequences or with limited memory depths, resulting in repeated short patterns. We show that with such sequences, a large artificial gain can be obtained, which comes from pattern prediction rather than predicting or compensating the studied channel/phenomena.

114 citations


Journal ArticleDOI
TL;DR: In this paper, the spectral properties of a nanostructured hyperbolic metamaterial (HMM)-based absorber are investigated and the effect of altering the slant angle and thickness of gold nanostrips in the HMM structure is reported.
Abstract: The spectral characteristics of nanostructured hyperbolic metamaterial (HMM)-based absorber is investigated. The HMM structure is comprised of periodically arranged assembly of gold nanostrips. The results indicate nearly perfect absorption by the structure in the entire ultraviolet (UV) regime of the electromagnetic spectrum under certain configuration – the feature which would be useful for UV-shield related applications. The absorptivity of the structure can be tailored by altering the slant angle and thickness of gold nanostrips (in the HMM structure). The effect of altering the incidence angle of light is also reported.

106 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate an indoor visible light positioning system based on optical camera communications, in which the transmitted coordinate data are spatially separated and demodulated by a camera and the receiver's position is calculated based on the coordinates of light-emitting diodes in the real word and in the image.
Abstract: We experimentally demonstrate an indoor visible light positioning system based on optical camera communications, in which the transmitted coordinate data are spatially separated and demodulated by a camera. The receiver’s position is calculated based on the coordinates of light-emitting diodes in the real word and in the image. The experimental results show that the proposed system with under-sampled phase shift keying modulation offers an error free data transmission and mean positioning errors of 5.0 and 6.6 cm for $h$ of 120 and 180 cm, respectively.

103 citations


Journal ArticleDOI
TL;DR: In this article, the fabrication and characterization of a polycarbonate (PC) microstructured polymer optical fiber (mPOF) Bragg grating (FBG) humidity sensor that can operate beyond 100°C was reported.
Abstract: We report the fabrication and characterization of a polycarbonate (PC) microstructured polymer optical fiber (mPOF) Bragg grating (FBG) humidity sensor that can operate beyond 100°C. The PC preform, from which the fiber was drawn, was produced using an improved casting approach to reduce the attenuation of the fiber. The fiber loss was found reduced by a factor of two compared to the latest reported PC mPOF [20] , holding the low loss record in PC based fibers. PC mPOFBG was characterized to humidity and temperature, and a relative humidity (RH) sensitivity of 7.31± 0.13 pm/% RH in the range 10–90% RH at 100°C and a temperature sensitivity of 25.86±0.63 pm/°C in the range 20–100 °C at 90% RH were measured.

100 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate theoretically and experimentally a chiral-selective plasmonic absorber by utilizing n-shaped-resonators in the visible frequencies.
Abstract: We demonstrate theoretically and experimentally a chiral-selective plasmonic absorber by utilizing n-shaped-resonators in the visible frequencies. Our metasurface design enables chiral-selective absorption bands, in which absorption peaks for left-handed circularly polarized and right-handed circularly polarized occur at different resonance wavelengths resulting in significant circular dichroism (CD). Both simulated and measured absorption spectra exhibit maximum absorptions exceeding 80% associated with a CD value of ~0.5. Such a chiral plasmonic metasurface absorber with high performance could find applications in optical filters, non-linear optics, thermal emitters, and hot-electron collection devices.

98 citations


Journal ArticleDOI
Laurens Breyne1, Guy Torfs1, Xin Yin1, Piet Demeester1, Johan Bauwelinck1 
TL;DR: In this paper, a comparison between ARoF and sigma delta modulated signal over fiber (SDoF) is presented, which quantifies the improvement in linearity and error vector magnitude (EVM) of SDoF over AROF.
Abstract: With the continuously increasing demand of cost effective, broadband wireless access, radio-over-fiber (RoF) starts to gain more and more momentum. Various techniques already exist, using analog (ARoF) or digitized (DRoF) radio signals over fiber; each with their own advantages and disadvantages. By transmitting a sigma delta modulated signal over fiber (SDoF), a similar immunity to impairments as DRoF can be obtained while maintaining the low complexity of ARoF. This letter describes a detailed experimental comparison between ARoF and SDoF that quantifies the improvement in linearity and error vector magnitude (EVM) of SDoF over ARoF. The experiments were carried out using a 16-QAM constellation with a baudrate from 20 to 125 MBd modulated on a central carrier frequency of 1 GHz. The sigma delta modulator runs at 8 or 13.5 Gbps. A high-speed vertical-cavity surface-emitting laser (VCSEL) operating at 850 nm is used to transmit the signal over 200-m multimode fiber. The receiver amplifies the electrical signals and subsequently filters to recover the original RF signal. Compared with ARoF, improvements exceeding 40 dB were measured on the third order intermodulation products when SDoF was employed, the EVM improves between 2.4 and 7.1 dB.

78 citations


Journal ArticleDOI
TL;DR: An adaptive demodulator based on machine learning for light beams carrying orbital angular momentums (OAMs) over free-space turbulence channels is proposed and demonstrated and shows that the demodulating error rate (DER) of CNN outperforms KNN, NBC, and BP-ANN, especially under stronger turbulence and longer distance.
Abstract: An $m$ -ary adaptive demodulator based on machine learning for light beams carrying orbital angular momentums (OAMs) over free-space turbulence channels is proposed and demonstrated. Benefiting from natural advantages in the image recognition, convolutional neural network (CNN) is selected to construct the adaptive demodulator. Without extra space light modulators and digital signal processing at the reception, the adaptive demodulator transforms the sequence of intensity patterns of received Laguerre–Gaussian beams carrying different OAM modes into initial signals efficiently. As comparison, K-nearest neighbor (KNN), naive Bayes classifier (NBC), and back-propagation artificial neural network (BP-ANN) are also studied. Furthermore, the demodulating accuracy of 4-, 8-, and 16-ary OAM is investigated with the comprehensive consideration of the atmospheric turbulence, OAM mode spacing, and transmission distance. The simulation results show that the demodulating error rate (DER) of CNN outperforms KNN, NBC, and BP-ANN, especially under stronger turbulence and longer distance. The DER of CNN is ~0.86% for the 1000-m 8-OAM system under strong turbulence, ~30 % less than those of KNN, NBC, and BP-ANN.

67 citations


Journal ArticleDOI
TL;DR: In this paper, a photonic approach based on optical frequency quadrupling and polarization multiplexing is proposed to generate dual-band linear frequency modulation (LFM) signal. But the proposed scheme has a very simple and compact structure, and the central frequency, bandwidth and temporal duration of the generated LFM signals can be easily adjusted.
Abstract: A photonic approach to generating dual-band linear frequency modulation (LFM) signal is proposed based on optical frequency quadrupling and polarization multiplexing. This is achieved by using an integrated polarization multiplexing dual-parallel Mach-Zehnder modulator to perform frequency quadrupling in two orthogonal polarizations independently. After optical-to-electrical conversion, two LFM signals in different frequency bands can be generated simultaneously. The proposed scheme has a very simple and compact structure. Thanks to the frequency quadrupling technique, high-frequency, and wideband LFM signals can be generated with low speed electrical devices. The central frequency, bandwidth, and temporal duration of the generated LFM signals can be easily adjusted. In the experiment, the generation of dual-band LFM signals in K-band and Ka-band (centered at 20 and 30 GHz, respectively) is demonstrated. Tunability of the central frequency, bandwidth, and time duration is also verified. The proposed signal generator is a promising candidate in dual-band multi-function radar applications.

62 citations


Journal ArticleDOI
TL;DR: In this paper, a pixelated VLC backscatter is proposed and implemented to overcome the channel capacity limitation, which enables the usage of advanced modulation schemes such as ON-OFF keying (OOK).
Abstract: Visible light communication (VLC) backscatter has been proposed as a wireless access option for Internet of Things. However, the throughput of the state-of-the-art VLC backscatter is limited by simple single-carrier pulsed modulation scheme, such as ON-OFF keying (OOK). In this letter, a novel pixelated VLC backscatter is proposed and implemented to overcome the channel capacity limitation. In particular, multiple smaller VLC backscatters are integrated to generate multi-level signals, which enables the usage of advanced modulation schemes. Based on experimental results, rate adaptation at different communication distances can be employed to enhance the achievable data rate. Compared with OOK, the data rate can be tripled, when 8-pulse amplitude modulation is used at 2 m. In general, $n$ -fold throughput enhancement is realized by utilizing $n$ smaller VLC backscatters, while incurring negligible additional energy using the same device space as that of a single large backscatter.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate high-speed nonpolar InGaN/GaN LEDs with a peak emission wavelength between 455 and 465 nm on free-standing non-polar GaN substrates.
Abstract: Free-standing nonpolar GaN substrates provide an excellent platform for the fabrication of high-speed blue and green light-emitting diodes (LEDs), which are attractive for visible-light communication, plastic optical fiber communication, and short-range under water optical communication. Nonpolar LEDs on free-standing GaN exhibit a large electron-hole wave function overlap, low extended defect density, and favorable thermal properties. Here, we demonstrate high-speed nonpolar InGaN/GaN LEDs with a peak emission wavelength between 455 and 465 nm on free-standing nonpolar GaN substrates. A large frequency modulation bandwidth of 524 MHz is demonstrated at a current density of 10 kA/cm 2 .

Journal ArticleDOI
Yuxiao Xu1, Tao Jin1, Hao Chi1, Shilie Zheng1, Xiaofeng Jin1, Xianmin Zhang1 
TL;DR: In this paper, a photonic method for the generation of dual-chirp signals was proposed, where a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator.
Abstract: We present a photonic method for the generation of dual-chirp signals. In this approach, a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator. Square-law detection in a photodiode then generates a dual-chirp signal whose center frequency and time-bandwidth product (TBWP) are fourfold increased. The dual-chirping and the improved TBWP can improve the range resolution of the radar system and help avoid the range measurement error caused by the range-Doppler coupling effect. The generation of bandwidth-quadrupled S-band dual-chirp waveforms is demonstrated experimentally. The processing of the dual-chirp signal is also discussed, in order to show its advantages over single-chirp signals. We believe that the proposed approach is a potential solution for the generation of dual-chirp signals with high center frequency and large bandwidth in modern radar systems.

Journal ArticleDOI
TL;DR: In this article, a chirped fiber Bragg grating photo-inscribed in undoped PMMA polymer optical fiber (POF) was reported for the first time, and the reflection amplitude spectrum evolution of a CPOFG was investigated as a function of the applied strain, temperature, and pressure.
Abstract: In this letter, we report for the first time, a chirped fiber Bragg grating photo-inscribed in undoped PMMA polymer optical fibre (POF). The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm and a 25-mm long chirped phase mask customized for 1550-nm grating inscription. The used laser pulsing frequency was 1 Hz with an energy of 5 mJ per exposure and only few shots for each grating inscription were employed. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain, temperature, and pressure. These results can potentiate further developments in different sensing fields, such as liquid level monitoring, splits, and transverse cracks in structural health monitoring by local pressure analysis or even biomedical field. Furthermore, CPOFBGs could present some critical advantages preferably replacing their silica counterparts as well as the uniform polymer FBGs.

Journal ArticleDOI
Chuanbowen Sun1, Sung Hyun Bae1, Hoon Kim1
TL;DR: In this paper, the authors explore the possibility of utilizing 1.55- $\mu \text{m}$ directly modulated lasers (DMLs) for optical access networks operating at 28 Gb/s per wavelength.
Abstract: We explore the possibility of utilizing 1.55- $\mu \text{m}$ directly modulated lasers (DMLs) for optical access networks operating at 28 Gb/s per wavelength. For this purpose, we attempt to maximize the power budgets of 28-Gb/s duobinary and four-level pulse amplitude modulation (PAM-4) signals generated from a DML without using optical amplifiers or optical dispersion compensation modules. For experimental investigation, we set the bias current of the DML far above the threshold current, optimize the extinction ratio of the signals, and utilize the electrical equalization at the receiver. The experimental results show that we can secure power margins of 9.6 and 10 dB after transmission over 40-km long standard single-mode fiber for the duobinary and PAM-4 signals, respectively.

Journal ArticleDOI
TL;DR: Experimental results verify that the proposed hybrid symbol substitution and interleaving technique is promising for physical-layer security-enhanced CO-OFDM-based access network systems.
Abstract: This letter proposes a hybrid symbol substitution and interleaving technique based on Brownian motion for security improvement in the coherent optical orthogonal frequency division multiplexed (CO-OFDM) passive optical network systems. The parameters of Brownian motion are generated by using the chaotic maps. Brownian motion-based hybrid symbol substitution and symbol interleaving are used to encrypt the OFDM signals. In our demonstration, 36.67-Gb/s encrypted OFDM signals are experimentally transmitted over a 100-km single mode fiber. Experimental results verify that the proposed technique is promising for physical-layer security-enhanced CO-OFDM-based access network systems.

Journal ArticleDOI
TL;DR: Two digital processing techniques are finally proposed to halve the guard time between NFDM symbol bursts and reduce the size of the processing window at the receiver, increasing spectral efficiency and reducing computational complexity.
Abstract: The performance of optical fiber systems based on nonlinear frequency-division multiplexing (NFDM) or on more conventional transmission techniques is compared through numerical simulations. Some critical issues affecting NFDM systems—namely, the strict requirements needed to avoid burst interaction due to signal dispersion and the unfavorable dependence of performance on burst length—are investigated, highlighting their potentially disruptive effect in terms of spectral efficiency. Two digital processing techniques are finally proposed to halve the guard time between NFDM symbol bursts and reduce the size of the processing window at the receiver, increasing spectral efficiency and reducing computational complexity.

Journal ArticleDOI
Xiaoyong Chen1, Jian Xu1, Xuejun Zhang1, Tuan Guo1, Bai-Ou Guan1 
TL;DR: In this paper, a multi-angle tilted fiber Bragg grating (TFBG) was proposed for dynamic refractive index (RI) measurement over a wide range (1.15-1.45).
Abstract: The conventional single-angle tilted fiber Bragg grating (TFBG) can only excite a certain range of cladding modes, limiting it for refractive index (RI) measurement in a wide range. In this letter, we fabricate and demonstrate a multi-angle TFBG, in which five individual TFBGs with tilt angles ranging from 5° to 25° are sequentially inscribed along the core of a single mode fiber within a length of 20 mm. The multi-angle TFBG excites a continuous spectral comb of narrowband-cladding modes over a much wider wavelength range (>170 nm) than a single-angle TFBG, making it suitable for dynamic RI measurement over a wide range (1.15–1.45). We have experimentally measured aqueous solutions with RI ranging from 1.30 to 1.45 using the uncoated (by monitoring the cut-off mode) and gold-coated (by monitoring the surface Plasmon resonance) multi-angle TFBGs, and both methods show linear responses, with RI sensitivities about 500 nm/RIU.

Journal ArticleDOI
TL;DR: In this article, the authors proposed and experimentally demonstrated an approach to jointly enhance the physical layer security and improve an optical orthogonal frequency division multiplexing (O-OFDM) transmission in passive optical network.
Abstract: This letter proposes and experimentally demonstrates an approach to jointly enhance the physical layer security and improve an optical orthogonal frequency division multiplexing (O-OFDM) transmission in passive optical network. It is proven that the Walsh–Hadamard Transform (WHT) matrix can effectively reduce the peak-to-average power ratio (PAPR) of OFDM signals after independent row/column permutations. A hyper digital chaos is adopted to generate the chaotic permutated WHT matrix for OFDM data encryption, which provides a total key space of $\sim 10^{178}$ to enhance the physical layer confidentiality. An 8.9-Gb/s encrypted 16-QAM O-OFDM signal transmission is successfully demonstrated over 20-km standard single-mode fiber, where the receiver sensitivity is improved by $\sim 1$ dB (BER@ $10^{\mathrm {-3}}$ ) due to the PAPR reduction through the chaotic WHT precoding. Moreover, the scheme does not require any additional sideband information and provides low computational complexity.

Journal ArticleDOI
TL;DR: In this paper, a micro-current source using the drive electron mobility model is proposed by using the non-linear micro-ring resonator, which consists of a nonlinear microring resonator known as Panda ring resonator made of InGaAsP/InP.
Abstract: A micro-current source using the drive electron mobility model is proposed by using the non-linear micro-ring resonator. The system consists of a nonlinear microring resonator known as Panda ring resonator made of InGaAsP/InP. The stacked waveguide (plasmonic island) of silicon-graphene-gold is formed at the center of the Panda ring, through which the whispering gallery mode (WGM) of light can be controlled and generated by the central ring it allows the driven electron mobility within the gold layer that can increase WGM beam acceleration and device current density with respect to the input optical power and ring parameters. The simulation results are obtained using the Opti-wave and MATLAB software programs. Results have shown that the relationship between the input of optical power and driven output current density can be obtained.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the hydrostatic pressure dependence of the Bragg wavelength of a fiber Bragg grating inscribed in a perfluorinated graded-index (PFGI-) polymer optical fiber (POF) at 1550 nm.
Abstract: We investigate the hydrostatic pressure dependence of the Bragg wavelength of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index (PFGI-) polymer optical fiber (POF) at 1550 nm. At 0.5 MPa, the Bragg wavelength increased with time and became almost constant ~150 min later. Such a long time constant probably originates from the unique structure of the PFGI-POF, which has a thick overcladding around its core and cladding. The pressure-dependence coefficient without considering the time constant was estimated to be 1.3 nm/MPa; this is over five times the values of other types of POF-FBGs. This indicates that by removing the overcladding of the PFGI-POF, fast-response high-sensitivity pressure sensing will be feasible. Once the Bragg wavelength became constant at 0.5 MPa, the pressure-dependence coefficient of the Bragg wavelength was measured to be −0.13 nm/MPa, the absolute value of which was comparable with those of other POF-FBGs, but with an opposite sign.

Journal ArticleDOI
TL;DR: In this article, a micro-tapered long-period fiber grating (MTLPFG) is fabricated successfully by periodically tapering a standard single-mode fiber with CO2 laser heating source.
Abstract: A microtapered long-period fiber grating (MTLPFG) is fabricated successfully by periodically tapering a standard single-mode fiber with CO2 laser heating source. This can be done by taking advantage of that the effective index difference between the core mode and the cladding modes is changed periodically during microtapering. High fabrication reproducibility and MTLPFGs quality can be achieved by this CO2 laser-heater-based fabrication scheme. In addition, the strain, bending, and liquid-level sensing characteristics of the MTLPFGs are investigated experimentally. Compared with the conventional long-period fiber gratings, it is found that the strain and bending sensitivities of fabricated MTLPFGs are improved by factors of about 10 and 5, respectively. Considering the simple and flexible fabrication process as well as the high quality and sensitivity of fabricated MTLPFGs, we believe that this may offer a simpler and alternative choice to current filters or sensing applications.

Journal ArticleDOI
TL;DR: In this paper, a robust graphene-coated in-fiber Mach-Zehnder interferometer (MZI) formed with a pair of 3-dB long-period fiber gratings is proposed and demonstrated for ammonia (NH3) gas sensing.
Abstract: A robust graphene-coated in-fiber Mach-Zehnder interferometer (MZI) formed with a pair of 3-dB long-period fiber gratings is proposed and demonstrated for ammonia (NH3) gas sensing. The sensor operates on the principle of changing the phase of the cladding mode of a fiber through changing the conductivity of the graphene coating by adsorbed NH3 molecules, which gives rise to a shift in the interference spectrum with an amount that depends on the gas concentration. Our experimental sensor shows a sensitivity of ~3 pm/ppm for a gas concentration from ~10 to ~180 ppm. The proposed in-fiber MZI can serve as a generic platform for the development of fiber sensors and devices that incorporate two-dimensional materials.

Journal ArticleDOI
TL;DR: Simulation results verify that the proposed scheme can also achieve performance improvement compared with both spatial modulation and conventional GSM under the line-of-sight channel condition, particularly for higher values of spectral efficiency.
Abstract: In this letter, we propose an active-space, collaborative constellation-based generalized spatial modulation (GSM) multiple-input multiple-output encoding that can enhance the power efficiency of indoor visible-light communication compared with the conventional optical GSM. Simulation results verify that the proposed scheme can also achieve performance improvement compared with both spatial modulation and conventional GSM under the line-of-sight channel condition, particularly for higher values of spectral efficiency.

Journal ArticleDOI
TL;DR: In this paper, a photonic multi-channel terahertz (THz) wireless transmission system in the 350-475 GHz band is experimentally demonstrated, where six THz carriers modulated with 10 Gbaud Nyquist quadrature phase-shift keying baseband signal per carrier results in an overall capacity of up to 120 Gb/s.
Abstract: A photonic multi-channel terahertz (THz) wireless transmission system in the 350-475 GHz band is experimentally demonstrated. The employment of six THz carriers modulated with 10 Gbaud Nyquist quadrature phase-shift keying baseband signal per carrier results in an overall capacity of up to 120 Gb/s. The THz carriers with high-frequency stability and low phase noise are generated based on photonic photomixing of 25-GHz spaced six optical tones and a single optical local oscillator derived from a same optical frequency comb in an ultrabroadband uni-travelling carrier photodiode. The bit-error-rate performance below the hard decision forward error correction threshold of 3.8×10 -3 for all the channels is successfully achieved after wireless delivery. Furthermore, we also investigate the influence of the harmonic spurs in a THz receiver on the performance of transmission system, and the experimental results suggest more than 30 dB spur suppression ratio in downconverted intermediate frequency signals for obtaining less than 1 dB interference.

Journal ArticleDOI
TL;DR: In this paper, an arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers was demonstrated.
Abstract: We experimentally demonstrate an automatic arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers. The proposed technology has been developed by implementing an embedded program in a commercial fusion splicer, which employs an ultraprecision motorized translation stage while the tensioning mass required by conventional inscribing technology is eliminated. More significantly, the arc-induced H-LPFGs have been reported to have potential usage as sensors in temperature, refractive index, twist stress, and strain.

Journal ArticleDOI
TL;DR: In this article, a dual-sideband (DSB) chirped lidar for simultaneous real-time ranging and velocimetry is proposed and demonstrated, in which a Mach-Zehnder modulator (MZM) is applied to generate the required optical DSB frequency-modulated continuous-wave (FMCW) signal.
Abstract: A dual-sideband (DSB) chirped lidar for simultaneous real-time ranging and velocimetry is proposed and demonstrated, in which a Mach–Zehnder modulator (MZM) is applied to generate the required optical DSB frequency-modulated continuous-wave (FMCW) signal. The inherent opposite frequency chirp and contrary wavelength offset to the optical carrier of the two generated sidebands make it possible to measure the distance and velocity by frequency mixing without complex post digital signal processing, meanwhile, make the measurement of velocity immune to the nonlinearity of the FMCW optical signals. An experiment is carried out, in which an 8–18 GHz saw-tooth FMCW signal is used to drive an MZM, generating a wideband optical DSB FMCW signal. The distance and the velocity are simultaneously derived from the real-time frequency spectra. Accurate velocimetry with a nonlinear FMCW signal is also investigated.

Journal ArticleDOI
TL;DR: In this article, an extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a novel mechanical design for nano-scale strain measurement is proposed.
Abstract: We propose an extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a novel mechanical design for nano-scale strain measurement. In our proposed sensor, a designed mechanical structure consists of a cylinder and a square column attached to a stainless steel substrate. This simple and compact structure along with a fiber ceramic ferrule and a gold-coated reflective mirror as a packaged EFPI sensor can resolve nano-scale strain with temperature self-compensation. In comparison with the existing nanostrain sensing methods, no reference sensors and complicated configurations are needed. The strain measured by our proposed sensor ranges from 0 to 677 ne with a measurement accuracy of ±5 ne. This robust and easy-to-build geometry-based nano-scale strain sensor has great potential in nanotechnology, geophysical research, seismic monitoring, and other practical applications.

Journal ArticleDOI
TL;DR: An approach to implementation of see-through head-mounted displays using hologram lenses, which are categorized by holographic optical elements, is introduced and the astigmatism of hologram lens is analyzed and its compensation method is proposed and verified.
Abstract: We introduce an approach to implementation of see-through head-mounted displays using hologram lenses, which are categorized by holographic optical elements. The hologram lenses magnify displayed images and superimpose the magnified images on the real-world simultaneously, which allows system configuration to be compact. Here, we investigate imaging properties and optical issues of hologram lenses using the spectral analysis of light field. Also, the astigmatism of hologram lenses is analyzed and its compensation method is proposed and verified. We conclude by describing display results and a practical application of the proposed method.

Journal ArticleDOI
TL;DR: In this article, a novel fiber Bragg grating displacement sensor with a sub-micrometer resolution was proposed, where a wedge-shaped sliding block and a T-shaped cantilever beam formed a conversion mechanism to transfer the horizontal measured displacement into the transverse movement of the optical fiber midpoint.
Abstract: This letter has proposed a novel fiber Bragg grating (FBG) displacement sensor with a sub-micrometer resolution through the use of the transverse property of a suspended optical fiber with a pre-tension force. A wedge-shaped sliding block and a T-shaped cantilever beam formed a conversion mechanism to transfer the horizontal measured-displacement into the transverse movement of the optical fiber midpoint. Compared with existing FBG displacement sensors, this design does not only avoid the FBG-pasting process and its associated issues, such as the chirping failure and low repeatability, but also achieves a high resolution. The sensing principle has been presented, and the corresponding theoretical model has been derived and validated. Experiments show that this design has an excellent sensitivity of 2086.27 pm/mm and a high resolution of $0.48~\mu \text{m}$ within a range of 1.0~2.0 mm. The displacement results from the proposed sensor closely agree with the values detected from the commercial laser displacement sensor, validating its effectiveness. Therefore, the proposed sensor can be directly utilized to measure the sub-micrometer displacement, and also support multi-point distributed detection.