Yanhui Qi

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.

All-Fiber Strain and Curvature Sensor Based on No-Core Fiber

A fiber-optic strain and curvature sensor based on no-core fiber has been proposed and demonstrated. The sensor is fabricated using a multimode fiber without cladding, known as the no-core fiber with a thinner diameter. The jointing point between the no-core fiber and single-mode fiber is a taper, which will improve the sensitivity of the sensor. The peak wavelength shift of the sensor exhibits an excellent response for strain and curvature changes.

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.

Tunable dual-wavelength fiber laser based on an MMI filter in a cascaded Sagnac loop interferometer

A widely tunable dual-wavelength erbium-doped fiber laser based on a cascaded Sagnac loop interferometer incorporating a multimode interference filter is proposed and experimentally demonstrated in this paper. The mode selection is implemented by using the cascaded Sagnac loop interferometer with two segments of polarization maintaining fibers, and the wavelength tuning was achieved by using the refractive index characteristic of multimode interference effects. The tunable dual-wavelength fiber laser has a wavelength tuning of about 40 nm with a signal-to-noise ratio of more than 50 dB.

Simultaneous measurement of pressure and temperature based on processed capillary tube and fiber Bragg grating

A hybrid optical fiber structure sensor for simultaneous measurement of temperature and low pressure based on Fabry–Perot (FP) interference and fiber Bragg grating (FBG) is proposed. The FP cavity is fabricated with a capillary pure silica tube, whose one end is surface processed to result in an open FP cavity. The measurement of refractive index change of different pressures has been achieved by monitoring the wavelength shift of the interference pattern in the reflection spectrum. The FP cavity is integrated with the FBG to obtain temperature measurement simultaneously.

Highly Sensitive Temperature and Pressure Sensor Based on Fabry–Perot Interference

In this letter, we propose and experimentally demonstrate an optical fiber structure sensor using Fabry-Perot interference for temperature and pressure measurement. The sensor head consists of an incident single-mode fiber, a section of capillary pure silica tube, and refractive index matching fluid. The measurement of cavity length change with different pressure and temperature has been achieved by monitoring the wavelength shift of the interference pattern in the reflection spectra. For the change in a small scale, the measurement sensitivity of temperature is 6.95 nm/°C and the estimated sensitivity of pressure is 0.15 nm/Pa. The sensor has the advantages of high sensitivity, low cost, compact size, and flexibility.

RI Ring Laser Sensor Based on Concatenating CLF and SMF With One Core-Offset Joint

In this letter, a novel all-fiber ring laser refractive index (RI) sensor is proposed and experimentally demonstrated. Such sensor is obtained by inserting a segment of cladding-less fiber between two sections of single-mode fiber with one core-offset joint, which is designed to enlarge the extinction ratio. With the help of ring laser sensing system, a 3-dB bandwidth below 0.2 nm and an optical signal-to-noise ratio near 30 dB can be achieved. Meanwhile, the high output power and the side-mode suppression ratio of the sensor are presented. Experimental results show that the RI sensitivity is 52.3 nm/RIU in the RI range of 1.334-1.370. The sensor also has the advantages of simple structure and low cost, preforming potentials in large-scale productions.

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.

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.

Low-threshold dual-wavelength erbium-doped fiber laser based on ring core fiber with core-offset structure

A low-threshold dual-wavelength erbium-doped fiber laser is proposed and tested in an experiment. The filter is based on a ring-core fiber with a core-offset structure. The threshold of the laser is as low as 16 mW. The operating wavelengths are 1560.02 and 1564.75 nm, respectively. Meanwhile, both of the side-mode suppression ratios of the operation wavelengths are higher than 50 dB when the pump power is 100 mW. In addition, the strain sensitivities are 0.7574 and 0.6676 pm μe −1, respectively.