Jiulin Gan

Narrow linewidth single frequency microfiber laser

A compact 2 kHz linewidth single frequency microfiber ring laser is demonstrated. Microfiber, with a diameter of 1.88 μm, which is drawn from an Er(3+)/Yb(3+) co-doped phosphate glass fiber, serves as the gain medium. By using this microfiber, a double-knot resonator with a total length of 1.75 mm is constructed. Based on this resonator, a narrow linewidth single frequency laser with output power higher than 0.95 μW is obtained at the wavelength of 1536.1 nm. The linewidth of this microfiber laser is as narrow as 2 kHz, and the side-mode-suppression ratio is higher than 38 dB.

Optical fiber design with orbital angular momentum light purity higher than 99.9

The purity of the synthesized orbital-angular-momentum (OAM) light in the fiber is inversely proportional to channel crosstalk level in the OAM optical fiber communication system. Here the relationship between the fiber structure and the purity is firstly demonstrated in theory. The graded-index optical fiber is proposed and designed for the OAM light propagation with the purity higher than 99.9%. 16 fiber modes (10 OAM modes) have been supported by a specific designed graded-index optical fiber with dispersion less than 35 ps/(km∙nm). Such fiber design has suppressed the intrinsic crosstalk to be lower than -30 dB, and can be potentially used for the long distance OAM optical communication system.

High Spatial Resolution BOTDR Based on Differential Brillouin Spectrum Technique

A novel differential-technique Brillouin optical time domain reflectometry with sub-meter spatial resolution is proposed and demonstrated. By analyzing the time-space related property of the pulse excited backward spontaneous Brillouin scattering light, a weighting factor distribution of the Brillouin spectrum along the fiber is obtained. Based on this distribution, a two-step-subtraction technique is proposed. A pulse pair with slightly width difference is employed as the probe pulse. At each corresponding location, for each pulse of the pulse pair a Brillouin-spectrum pair is extracted with two different time sequence length. By performing a two-step subtraction on these two Brillouin-spectrum pairs, the differential Brillouin spectrum is theoretically and experimentally proved to be spatially related with the width difference of the pulse pair. A spatial resolution of 0.4 m utilizing 60/56 ns pulse pair is experimentally achieved over 7.8-km sensing length with 4.1-MHz Brillouin frequency accuracy.

Slow/fast light using a very short Er 3+ /Yb 3+ co-doped fiber

A slow/fast light device with a sealed size of 130 mm×30 mm×3 mm has been demonstrated. Ultraslow propagation and superluminal propagation with group velocity values from 8.4 to -14.7 m/s are observed in a 3.86 cm long Er3+/Yb3+ co-doped single-mode phosphate glass fiber. The dependence of pump power, modulation frequency, and wavelength on the slow/fast light effect in this fiber is investigated in detail. These results suggest that this compact slow/fast device is more suitable for all-fiber applications than those made by traditional methods.

Temperature sensing based on a Brillouin fiber microwave generator

We propose and demonstrate a novel dual-frequency Brillouin fiber laser used for microwave generation. Based on this configuration, temperature sensing has been realized. The dual-frequency Brillouin lasing is generated independently from two pieces of fiber cascaded within one ring resonator. Microwave generation is acquired as the beat signal of the dual-frequency Brillouin fiber laser, with the beat frequency being linearly proportional to the temperature difference of the two fiber sections. In the experiment, the temperature coefficient of frequency shift is 1.015 ± 0.001 MHz °C−1. The temperature can be precisely measured by acquiring the frequency of the microwave generator, and this new configuration provides a promising application for temperature sensing.

Significant intensity noise suppression of single-frequency fiber laser via cascading semiconductor optical amplifier

Significant suppression of the intensity noise of single-frequency fiber laser is demonstrated with a cascading semiconductor optical amplifier (SOA). Based on the nonlinear amplification dynamics of the SOA, intensity noise reduction would take place in every transmission of the laser signal. By cascading two SOAs, a maximum noise suppression of 30 dB at around the resonant relaxation oscillation (RRO) frequency as well as a suppression bandwidth of up to 50 MHz is realized. Moreover, the RRO peak is restricted to a significant narrow frequency band, outside of which the laser noise approaches the noise floor of the measurement. The remarkable amplified spontaneous emission (ASE) introduced by the SOA is entirely filtered out with a fiber Bragg grating (FBG). Furthermore, no noticeable degradation of laser frequency noise has been observed.

High spatial resolution distributed fiber strain sensor based on phase-OFDR

A novel method to realize high spatial resolution distributed strain measurement is proposed based on phase demodulation scheme of optical frequency domain reflectometry (OFDR). Strain information can be demodulated directly by analyzing the phase change of Rayleigh backscattered light. Strain location can be obtained with high spatial resolution by cross-correlation method using a wide scanning range of tunable laser source. Based on the above scheme, breakpoint detection with 0.1 mm spatial resolution has been demonstrated, static and dynamic strain up to 100 Hz could be distributedly measured with 10 cm spatial resolution over 200 m sensing fiber, and the minimum measurable strain is about 1 με.

High-Speed Frequency Modulated Low-Noise Single-Frequency Fiber Laser

A novel high-speed frequency modulating scheme based on the self-injection locked single-frequency fiber laser is demonstrated. The laser frequency noise reaches -5 dB re Hz/Hz1/2 at ~25 kHz, while the linewidth is estimated to be ~800 Hz. By modulating the length of external cavity to which the laser is locked, a stable frequency modulated laser with a modulation speed up to 160 kHz, and modulation amplitude >145 MHz at a modulation speed of 60 kHz are realized. The intensity noise spectrum of the frequency modulated fiber laser is found to be the same with that of the laser before modulation, except a series of gradually weakened harmonic peaks at the modulating frequency.

Compact frequency-modulation Q-switched single-frequency fiber laser at 1083 nm

A compact frequency-modulation Q-switched single-frequency fiber laser is demonstrated at 1083 nm. The short linear resonant cavity consists of a 12 mm long homemade Yb3+-doped phosphate fiber and a pair of fiber Bragg gratings (FBGs) in which the Q-switching and the frequency excursion is achieved by a tensile-induced period modulation. Over 375 MHz frequency-tuning range is achieved with a modulation frequency varying from tens to hundreds of kilohertz. The highest peak power of the output pulse reaching 6.93 W at the repetition rate of 10 kHz is obtained.

Single-Frequency Microfiber Single-Knot Laser

A compact single-frequency microfiber laser was demonstrated in a single-knot Er3+/Yb3+ co-doped phosphate glass fiber ring with a diameter of 397.5 µm. The lasing wavelength is 1534.25 nm and the side-mode suppression ratio (SMSR) is higher than 27 dB. The linewidth is measured to be about 5 kHz and the relative intensity noise (RIN) is around -110 dB/Hz at frequencies over 50 kHz.