Zexin Kang

Multimode Synchronization of Chaotic Semiconductor Ring Laser and its Potential in Chaos Communication

We investigate numerically the synchronization of two multimode semiconductor ring lasers (SRLs) and demonstrate its potential in chaos-based communication. The extent of the SRLs chaos regime under external optical feedback is evaluated in terms of bifurcation diagram and the optimal feedback strength range for reliable chaotic communication is discussed as well. Under proper conditions, the receiver SRL can be satisfactorily synchronized with the transmitter SRL due to the injection-locking effect. The message encoding and decoding using chaos shift keying technique have been analyzed from the point of view of the total lasing output. The possibility of recovering the message using unidirectional output (clockwise output or counterclockwise output) is also examined and compared with that of the total output. The tolerance of the proposed scheme to the SRLs fabrication limitation and parameter mismatch are studied. In view of these results, chaos-based synchronization and communication over fiber optical link, with or without the amplified spontaneous emission noise induced by amplification, are demonstrated. We also check the negative influence of fiber nonlinearity on the system transmission performance.

Liquid level measurement by applying the Mach–Zehnder interferometer based on up-tapers

A novel scheme for liquid level detection using an all-fiber Mach-Zehnder interferometer, based on two up-tapers, is proposed and experimentally investigated. The effective refractive indices of the axisymmetric modes LP(0n) are analyzed while it is partly immersed in liquid. The sensitivity of the sensor is greatly dependent on the fiber length between the two up-tapers, as well as the order of the cladding modes through the calculation. The experimental results show that the sensitivity of the Mach-Zehnder interferometer reaches a 22.5 nm wavelength shift per meter of level change with the middle fiber length of 14.3 cm. The proposal might be attractive since the up-tapered liquid level sensor could easily be fabricated and used for a large measuring range.

Highly sensitive curvature sensor based on a multicladding fiber sandwiched dual no-core fibers structure

In this paper, we present a simple, compact, and highly sensitive optical fiber curvature sensor. It consists of dual no-core fibers for coupling energy from the lead-in single-mode fiber (SMF), and recoupling the energy into the lead-out SMF. The sensing section is constituted by multicladding fiber with a length of 5 cm. In the experiment, the spectrum shows a blueshift, and the energy corresponding to the resonant wavelength shows a cosine series with a bending of the sensing segment. The curvature sensitivity around the wavelength of 1550 nm shows -39.02 nm/m(-1) within the curvature range from 0.3 to 2.14 m(-1). The temperature sensitivity is 78.2 pm/°C in the temperature range of 10 °C-60 °C. It implies the possibility of temperature measurement.

Twin-Core Fiber-Based Erbium-Doped Fiber Laser Sensor for Decoupling Measurement of Temperature and Strain

In this paper, a novel all-fiber laser sensing configuration for decoupling measurement of strain and temperature based on the twin-core fiber (TCF) with an in-line embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated. An erbium doped fiber ring laser is built, with an optical signal-to-noise ratio higher than 40 dB and a power instability of 6.75 μW in 1 h. Due to the different spectrum responses of the TCF and FBG to the uniform variation of strain and temperature, the decoupling measurement for these two measurands could be achieved by real-time monitoring both the center wavelength shift and the peak power variation.

Novel bending-resistant design of two-layer low-index trench fiber with parabolic-profile core

A novel design, two-layer low-index trench fiber with parabolic-profile core, is proposed and investigated numerically in this paper. Based on scalar FD-BPM algorithm, the excellent performance over other types of structures and great potential in mode area enlargement are demonstrated. The effective mode area of our design (D = 100μm) is approximately 890 μm2. Both the high order mode (HOM) suppression and bending resistance of our design are better than that of Multi-Trench Fiber (MTF). The mode loss ratio and effective mode area are independent on the bending radius. Due to the circular symmetry of our proposed configuration design, the bending property is not varied with the changing of bending directions.

Spectra analysis of nonuniform FBG-based acousto-optic modulator by using Fourier mode coupling theory

Fourier mode coupling theory was first employed in the spectral analysis of several nonuniform fiber Bragg grating (FBG)-based acousto-optic modulators (NU-FBG-AOMs) with the effects of Gaussian-apodization (GA), phase shift (PS), and linear chirp (LC). Because of the accuracy and simplicity of the algorithm applied in this model, the modulation performances of these modulators can be acquired effectively and efficiently. Based on the model, the reflected spectra of these modulators were simulated under various acoustic frequencies and acoustically induced strains. The simulation results of the GA-FBG-AOM and PS-FBG-AOM showed that the wavelength spacing between the primary reflection peak and the secondary reflection peak is proportional to the acoustic frequency, and the reflectivity of reflection peaks depends on the acoustically induced strains. But for the LC-FBG-AOM, the wavelength spacing between the neighboring reflection peaks increased linearly and inversely with the acoustic frequency, and the extinction ratio of each peak relates to the acoustically induced strain. These numerical analysis results, which were effectively used in the designs and fabrications of these NU-FBG-AOMs, can broaden the AOM-based application scope and shed light on the performance optimization of optical wavelength-division multiplex system.

A Modified Bend-Resistant Multitrench Fiber With Two Gaps

We propose and investigate a modified multitrench fiber (MTF) design with two gaps numerically through the scalar FD-BPM algorithm. Excellent potential in mode area scaling, suppression of high-order modes (HOMs), and resistance to bending is demonstrated. Loss ratio between HOMs and the fundamental mode is more than 50 possibly over a wide range of high-index-ring thickness, gap width, bending radius, and bending orientation. Therefore, the required fabrication accuracy decreases. At 1050-nm wavelength and 20-cm bend radius, large effective mode area (920 μm2 ) is achievable with high loss ratio (>100). The fabricating technologies, carving grooves in the ordinary MTF and inserting rods in these grooves, can be possibly used to fabricate our modified two-gap-MTF.

Multi-trench fiber with four gaps for improved bend performance.

A modified multi-trench fiber (MTF) design with gaps to create leakage channels is proposed and investigated numerically using the scalar finite-difference beam-propagation method algorithm. Great potential in single-mode operation, mode area enlargement, and resistance to bending is demonstrated. A high loss ratio (>50) between high-order modes and the fundamental mode is possible over a wide range of high-index ring thickness, gap width, and bending orientation. This reduces the required fabrication accuracy. We obtain an effective area of 920  μm2 at a wavelength of 1050 nm and a 20 cm bend radius with a high loss ratio (>100). Our modified gap MTF can possibly be fabricated by drilling holes in an ordinary MTF and inserting rods into the holes.

Tunable and switchable fiber laser based on modal interference

A tunable and switchable erbium-doped fiber (EDF) laser based on modal interference has been proposed and experimentally demonstrated in this paper. Here a core-offset structure has been used to excite the cladding modes and a segment of polarization maintaining fiber inserted in a Sagnac loop interferometer has been used as wavelength selective component. By adjusting the statement of polarization controller (PC) and the bending of the core-offset structure, a tunable and switchable fiber laser with the signal-to-noise ratio (SNR) of more than 50 dB has been achieved in this paper.

High-Sensitive Microdisplacement Sensor Based on Fiber Mach–Zehnder Interferometer

A fiber-optic sensor based on Mach-Zehnder interferometer, which is composed of two cascaded fiber directional couplers, is investigated and applied for high-sensitive microdisplacement detecting. The free spectrum range of the transmission spectrum varies with the gap sizes in the sensing arm, which is used to sense displacement for the first time to the best of our knowledge. The experimental result is well agreed with the numerical simulation, and shows the maximum displacement sensitivity of 66 nm/μm which is at least forty times higher than that of the previous displacement fiber-optic sensors. Furthermore, the proposed sensor has the potential for higher sensitivity by enlarging the wavelength range of both optical source and signal detector.