Frequency noise of distributed Bragg reflector single-frequency fiber laser.

We investigated the frequency noise in the distributed Bragg reflector single-frequency fiber laser (DBR-SFFL) theoretically and experimentally. A complete theoretical analysis is demonstrated by considering the energy-transfer upconversion (ETU) process and establishing linkages between the frequency noise and the relative intensity noise (RIN) of the DBR-SFFL. The experimental results of the diverse DBR-SFFLs in different working conditions are in good agreement with the theoretical analyses. These investigations are beneficial to optimizing frequency noise property to promote the wide application of the DBR-SFFLs. The proposed results can be generally applicable to the short-linear-cavity SFFL with centimeters order of the cavity length.

Self-injection locked and semiconductor amplified ultrashort cavity single-frequency Yb3+-doped phosphate fiber laser at 978 nm.

Based on a self-injection locking scheme and the nonlinear amplification effect of a semiconductor optical amplifier, a low intensity noise amplified ultrashort cavity single-frequency fiber laser at 978 nm is demonstrated with a final output power of > 230 mW and a broad temperature range of > 15 °C for single-longitudinal-mode operation. The effective cavity length of the fiber oscillator is less than 6 mm, comprising a 3.5-mm-long highly Yb3+-doped phosphate fiber and a pair of fiber Bragg gratings. For the frequency range from 1.8 to 10 MHz, the relative intensity noise close to -150 dB/Hz is achieved. The signal-to-noise ratio of > 68 dB and the laser linewidth of < 10 kHz are obtained. Such narrow linewidth low noise 978 nm laser is promising, as the high-performance pump source or the efficient blue and UV light sources after nonlinear frequency conversion.

Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser.

An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated. By the use of a tunable narrow-band fiber Fabry-Perot interferometer, the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of < 700 Hz. The laser frequency noise is less than 40 dB re Hz/Hz1/2 at low frequencies (< 100 Hz) and reaches -5 dB re Hz/Hz1/2 at around 25 kHz. The measured relative intensity noise (RIN) is less than -130 dB/Hz with regard to frequencies of over 3 MHz, while the obtained linear polarization extinction ratio (LPER) is higher than 28 dB. This ultra-narrow linewidth low-noise tunable single-frequency linear-polarization fiber laser provides a promising candidate for high-order quadrature amplitude modulation (QAM) optical communication system.

Linewidth suppression mechanism of self-injection locked single-frequency fiber laser.

Linewidth suppression mechanism of the self-injection locked single-frequency fiber laser (SFFL) is investigated theoretically and experimentally. An analytical model based on the semi-phenomenological approach is built up to characterize the optical feedback in SFFL. According to the theoretical prediction, the linewidth tends to be reduced with longer external cavity photon lifetime. Experimentally, a 200-Hz linewidth self-injection locked SFFL is achieved with 101 m long delay fiber, which agrees well with the theoretical simulation. The model provides a new perspective to understand the mechanism of linewidth reduction of self-injection locked SFFL.

Short all Tm-doped germanate glass fiber MOPA single-frequency laser at 1.95 µm.

Based on heavily Tm-doped germanate glass fibers (TGFs), a short all-TGF MOPA laser system with uniform core parameters in each stage was demonstrated. An 11.7 W stable single-frequency laser at 1.95 µm with an optical-to-optical conversion efficiency of 20.4% is obtained from a homemade 31-cm-long double-cladding single-mode TGF. The estimated stimulated Brillouin scattering (SBS) threshold of 980 W and the measured relative intensity noise of < -130 dB/Hz for frequencies above 2 MHz are achieved in this MOPA system. Furthermore, the prospect for further power-scaling of such short MOPA laser is considered.

Dual-wavelength passively q-switched single-frequency fiber laser.

We propose a compact dual-wavelength Q-switched single-frequency fiber laser based on a 17-mm-long home-made highly Er3+/Yb3+ co-doped phosphate fiber (EYDPF) and a semiconductor saturable absorber mirror (SESAM). The short cavity length and a polarization-maintaining fiber Bragg grating (PM-FBG) ensure that only one longitudinal mode is supported by each reflection peak. The maximum pulse energy of more than 34.5 nJ was realized with the shortest pulse duration of 110.5 ns and the Q-switched fiber laser has a repetition rate reaching over 700 kHz with a temporal synchronization of pulses at two wavelengths. Besides, the optical signal-to-noise ratio (OSNR) of larger than 64.5 dB was achieved.

Broad-bandwidth near-shot-noise-limited intensity noise suppression of a single-frequency fiber laser.

A significant broad-bandwidth near-shot-noise-limited intensity noise suppression of a single-frequency fiber laser is demonstrated based on a semiconductor optical amplifier (SOA) with optoelectronic feedback. By exploiting the gain saturation effect of the SOA and the intensity feedback loop, a maximum noise suppression of over 50 dB around the relaxation oscillation frequencies and a suppression bandwidth of up to 50 MHz are obtained. The relative intensity noise of -150 dB/Hz in the frequency range from 0.8 kHz to 50 MHz is achieved, which approaches the shot-noise limit. The obtained optical signal-to-noise ratio is more than 70 dB. This near-shot-noise-limited laser source shows important implications for the advanced fields of high-precision frequency stabilization, quantum key distribution, and gravitational wave detection.

Linearly frequency-modulated pulsed single-frequency fiber laser at 1083 nm.

A linearly frequency-modulated, actively Q-switched, single-frequency ring fiber laser based on injection seeding from an ultra-short cavity is demonstrated at 1083 nm. A piezoelectric transducer is employed to obtain linearly frequency-modulating performance and over 1.05 GHz frequency-tuning range is achieved with a modulating frequency reaching tens of kilohertz. A maximum peak power of the stable output pulse is over 3.83 W during frequency-modulating process. This type of pulsed fiber laser provides a promising candidate for coherent LIDAR in the measurement of thermosphere.