KEYWORDS: Fiber Bragg gratings, Sensors, Bragg wavelengths, Education and training, Demodulation, Sensor networks, Signal detection, Data modeling, Optical engineering, Signal to noise ratio
Fiber Bragg grating (FBG) sensor arrays employ overlapped spectra in sensor channels to maximize bandwidth, often resulting in multiple local wavelength peaks that complicate accurate peak detection. Existing multiplexing methods encounter challenges due to crosstalk between adjacent sensors or high computational complexity. We propose a two-stage methodology to discern distinct wavelengths within highly overlapped FBG sensors. The method leverages a deep learning (DL) model in the initial stage to predict individual peak wavelengths. Subsequently, a peak optimization module is applied to refine these predictions by reconstructing the FBG spectrum based on the forecasts of the DL model. To validate the effectiveness of our approach, a comprehensive series of experiments was conducted. The experimental results demonstrate the superior performance of our proposed FBG demodulation scheme, achieving a remarkable 50.1% and 62.6% improvement in prediction accuracy for cases involving two and three overlapped FBG signals, respectively, in comparison to scenarios without the optimization module. The proposed method offers the potential to enhance the capacity of FBG sensors within a network, paving the way for notable advancements in signal demodulation within intricate sensor configurations.
A method to detect delamination in a composite material, using a surface mounted fiber Bragg grating (FBG) sensor, is proposed in this paper. In this method, the static strain is measured to accurately detect the delamination area. Experiments are carried out and results show the relation between the wavelength shift and the distance between the FBG center and the delaminated area. The sensitivity of this method is also discussed. Results show the feasibility of this technique for structural health monitoring applications.
We propose in this letter a simple and cost-effective method for a bandwidth enhancement of multimode fiber (MMF) using periodic mode scrambling. Simulations and experiments were carried out to verify the feasibility of this method, and results show that the bandwidth of multimode fiber is increased by about two times. This scheme can be used to support future large-bandwidth applications by upgrading existing MMF links.
We evaluate the performance of the externally modulated optical minimum shift keying (MSK) signal. The tolerance against fiber dispersion, linear crosstalk, self phase modulation (SPM), and stimulated Brillouin scattering (SBS) threshold for MSK is studied and compared with that of 50% duty cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty cycle RZ on-off-keying (RZ-OOK), via both experiment and simulation. Simulation results show that the MSK signal has the widest tolerance against SPM and the smallest linear crosstalk among these formats. Experimental results agree with the simulation on negative penalty against SPM tolerance and show widest tolerance against dispersion tolerance for MSK. The measured SBS threshold of both MSK and RZ-DPSK is more than 10 dB higher than that of an RZ-OOK system.
An optical bandpass filter with two ultranarrow transmission bands, based on fiber Bragg grating (FBG), is presented. The wavelength spacing can be easily changed through controlling the separate distance between two introduced π phase shifts. When it is served in a fiber ring laser, the stable dual-wavelength lasing with ultranarrow wavelength spacing is achieved. This novel device will find potential applications in the generation of various high-frequency microwave signals, fiber sensing, etc.
In today's high-bit-rate WDM systems, it is essential to monitor the residual chromatic dispersion (CD) to ensure that it does not exceed the designed tolerance. Among the schemes for CD monitoring reported so far, inband subcarrier tone method is relatively simple and effective for CD monitoring. However, this technique may be influenced by both polarization mode dispersion (PMD) and the chirp fluctuation of the external modulator. In this paper, we investigate the effect of PMD and chirp on CD monitoring and show that the presence of PMD and chirp induces significant CD monitoring errors. To tackle this problem, we propose a CD monitoring technique to
suppress the influence caused by PMD and chirp fluctuation. In the proposed CD monitoring scheme, two RF tones are added at the transmitter. The light is coupled into an apriori known dispersion offset and then split into two branches in the monitoring module. A fiber Bragg grating filter which can remove one sideband is inserted before the photodetector of one branch. The PMD effect is eliminated by optically sideband filtering and RF power ratio detection, and the monitoring error induced by the small chirp fluctuation can be suppressed using two RF tones and a dispersion offset. The operational principle is analyzed and the experimental investigation is presented. Experimental results show that this technique can accurately monitor the accumulated CD without being affected by the PMD and small chirp fluctuation.
We report our theoretical analysis on polarization mode dispersion (PMD) tolerance of the return-to-zero transmission system under error-free [bit error rate (BER) 10–12] conditions. The results show that the tolerable PMD cannot be further enhanced by increasing the receiver power margin when forward error correction is used. The investigation also reveals that optimal receiver bandwidth for minimum BER should be increased accordingly when the accumulated PMD is increased. By designing the receiving filter with adaptive bandwidth, the acceptable average differential group delay can be improved by up to 2% of the bit interval.
KEYWORDS: Switches, Microelectromechanical systems, Control systems, Optical switching, Packaging, Reflectivity, Optical fibers, Optical components, Control systems design, Computing systems
A digital control system implemented to operate the Microelectromechanical system (MEMS) optical switch is described. This MEMS switch is based on a voltage-controlled moving-mirror structure to control the optical path connections and optical power levels. The tiny MEMS devices may replace bulk optical-mechanical devices in lightwave equipment, and enable new functions not available from conventional devises. Here, by use of the proportional integral (PI) control system, each switch module functions either as a reflective optical switch or a variable attenuator. Moreover, this control system promises to improve the performance of the device, as well as make possible the monolithic integration packaging of MEMS with driving, controlling and signal processing electronics. One more attraction of this control system is its programmability. The rest of the paper describes the control system and experimental results for this MEMS optical switch.
All optical gain clamping technique of Raman fiber amplifier was experimentally investigated, and a better gain-clamping is achieved when clamping wavelength is in relatively low gain regime and multiwavelengths clamping technique is adopted. This dynamic gain control method is also suitable for the Raman amplifiers with multi-wavelength pump.
Ethernet is being groomed as the ISP WAN media protocol of the future, both for home users and the corporate market. The need to develop a standard for Ethernet in the first mile (EFM) was given enthusiastic endorsement by main access equipment providers. Ethernet solutions in the first mile enable designers of hardware systems to use the installed base of 300 million Ethernet ports and merchant industry of chipsets and optics. Standardization efforts for this emerging technology are already underway. This paper describes the media access control (MAC) design for the tree-topology Ethernet Passive Optical Network (EPON) system.
A flexible crosstalk analysis method based on scattering matrix for optical cross connect(OXC) with various topology is proposed. In this method, all components in the OXC are treated as multiple ports sub-networks represented using scattering parameters (S parameters). The crosstalk can be precisely computed using measured S parameters of every components. As an example, a 4 + 4 fiber bragg grating and optical circulator (FBG-OC) based reconfigurable nonblocking OXC is studied using the method.
Fiber Bragg grating (FBG) based wavelength division multiplexer (WDM) optical cross connect (OXC) is of great importance, which has the advantages of good performance and potential low cost. Optical crosstalk plays a major role in limiting practical implementations of an OXC. Crosstalk analyses presented so far generally focus on the traditional multiplexer/demultiplexer and optical switch based OXC architecture. In this paper, optical crosstalk in multiwavelength reconfigureable nonblocking OXCs using tunable FBGs and optical circulators (OCs) is discussed. Two crosstalk mechanisms, intraband and interband, are identified and analytical models are presented. Both first-order and second-order crosstalk contributions have been studied. For the intraband crosstalk, results show that the worst case coherent crosstalk is the dominant crosstalk, which is ~ 23 - 25 dB higher than the incoherent crosstalk, depending on the switching states of the 2 x 2 OXCs. For the interband crosstalk, results show that it is nonaccumulative and becomes very small with the increase of the number of fibers or the cascaded stages of 2 x 2 OXCs. However it deteriorates with the increase of the number of wavelengths per fiber.
Aberration of the coherent wavefront are analyzed using a phase Zernike filter. Developed iterative methods allow us to design a filter that decomposes the analyzed light field into a set of diffraction orders with amplitudes proportional to the circular Zernike polynomials. Operation of a 25-channel filter is simulated.
Multiple beam forming is widely used in modern RADAR system, and it can be accomplished at radar radio frequency by using integrated opto-electronics device and optical fiber distribution and time delay network. This paper describes a receiving system of multiple beams by using integrated opto- electronics device, optical fiber distribution network and optical fiber time delay line. When the opto-electronics switch with controllable extinction ratio and optical microwave phase shifter which can make a good control of phase shifting are applied in this system, the complex weight coefficient can be effectively adjusted, and the adaptive multiple beam forming networks can be established. With the optically controlled multiple beam forming technology, the weight and volume of the system can be reduced and the anti- interference ability and stability of temperature be increased. In addition, the channel numbers can also be increased, which is especially beneficial to large phased arrays system.
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