We demonstrate an effective approach of mode suppression by simply using a tungsten probe to destroy the external neck surface of polymer microbottle resonators. The higher-order bottle modes with large axial orders, spatially located around the neck surface of the microresonator, will suffer large optical losses. Thus, excitation just with an ordinary free-space light beam will ensure direct generation of single fundamental bottle mode lasers. This method is with very low cost and convenient and can obtain high side-mode suppression factors. Our work demonstrated here may have promising applications such as in lasing and sensing devices.

A microcavity laser based on evanescent-wave-coupled gain is formed using a silica fiber with a diameter of 125 μm in a rhodamine 6G ethanol solution. When the fiber is sticking to the cuvette wall by capillary force, using the excitation of a 532 nm nanosecond pulsed laser, single-mode laser emission is observed. While increasing the distance between the fiber and the cuvette wall, the typical multi-peak whispering-gallery-mode (WGM) laser emission can also be demonstrated. On the other hand, while increasing the refractive index of the solution by mixing ethanol and ethylene glycol with different ratios as a solvent, the single-mode emission would evolve to multi-peak WGM laser emission controllably.

A noise-sidebands-free and ultra-low relative intensity noise (RIN) 1.5 μm single-frequency fiber laser is demonstrated for the first time to our best knowledge. Utilizing a self-injection locking framework and a booster optical amplifier, the noise sidebands with relative amplitudes as high as 20 dB are completely suppressed. The RIN is remarkably reduced by more than 64 dB at the relaxation oscillation peak to retain below 150 dB/Hz in a frequency range from 75 kHz to 50 MHz, while the quantum noise limit is 152.9 dB/Hz. Furthermore, a laser linewidth narrower than 600 Hz, a polarization-extinction ratio of more than 23 dB, and an optical signal-to-noise ratio of more than 73 dB are acquired simultaneously. This noise-sidebands-free and ultra-low-RIN single-frequency fiber laser is highly competitive in advanced coherent light detection fields including coherent Doppler wind lidar, high-speed coherent optical communication, and precise absolute distance coherent measurement.

A multi-wavelength sampled Bragg grating (SBG) quantum cascade laser array operating between 7.32 and 7.85 μm is reported. The sampling grating structure, which can be analyzed as a conventional grating multiplied by a sampling function, is fabricated by holographic exposure combined with optical photolithography. The sampling grating period was varied from 8 to 32 μm, and different sampling order ( 1st, 2nd, and 3rd order) modes were achieved. We propose that higher-order modes with optimized duty cycles can be used to take full advantage of the gain curve and improve the wavelength coverage of the SBG array, which will be beneficial to many applications.

We propose a high-Q photonic-electronic hybrid cavity for single-longitudinal-mode narrow-linewidth oscillation, where part of the cavity is in the radio frequency (RF) domain by a pair of frequency conversions. In the RF part, we can easily achieve MHz filtering and a large delay by inserting an electronic filter. In mathematics, we prove that the frequency conversion pair and electronic filter in between can be equivalent to a high-Q optical filter cascaded low-noise optical amplifier as a whole. Finally, the 20-dB bandwidth of oscillation is 1/20 of that of an optical local oscillator, and the maximum phase noise suppression can reach 65 dB.

A scheme for measuring the intra-cavity round-trip loss of an all-solid-state single-frequency laser by inserting a type-I noncritical phase-matching nonlinear crystal introducing nonlinear loss into the resonator is presented. The intra-cavity round-trip loss is theoretically deduced by analyzing the dependence of the fundamental-wave (FW) and second-harmonic-wave (SHW) powers on the pump factor and the nonlinear conversion factor of the single-frequency laser and experimentally measuring them by recording different FW and SHW powers, which are decided by the temperature of the nonlinear crystal. The measured intra-cavity round-trip loss and pump factor are 4.84% and 6.91% W 1, respectively. The standard deviations of the measured intra-cavity round-trip loss and the pump factor are 0.26% and 0.07%, respectively. This scheme is very suitable for measuring the intra-cavity round-trip loss of a high-gain solid-state single-frequency laser.

We demonstrate a single-longitudinal-mode Ho3+:YVO4 unidirectional ring laser based on the acousto-optic effect, utilizing the features of the acousto-optical Q switch and half-wave plate to achieve unidirectional operation. The maximum power achieved in the single-longitudinal-mode at 2053.9 nm is 941 mW when the absorbed power is set as 4.4 W, yielding a nearly 50% slope efficiency. The M2 factor is 1.1. The results show that such a technique offers a potentially promising new method for achieving a high power and narrow linewidth 2 μm single-longitudinal-mode laser.

Based on a single-channel laser self-mixing interferometer, we present a new simultaneous measurement of the vibration amplitude and the rotation angle of objects that both affect the power spectrum containing two peaks of the interferometer signals. The fitted results indicate that the curve of the peak frequency versus the vibration amplitude follows a linear distribution, and the curve of the difference of the two-peak power values versus the angle follows a Gaussian distribution. A vibration amplitude with an error less than 3.0% and a rotation angle with an error less than 11.7% are calculated from the fitted results.

In this Letter, a single-frequency fiber laser using a molybdenum disulfide (MoS2) thin film as a saturable absorber is demonstrated. We use a short length of highly Yb-doped fiber as the gain medium and a fiber ferrule with MoS2 film adhered to it by index matching gel (IMG) that acts as the saturable absorber. The saturable absorber can be used to discriminate and select the single longitudinal modes. The maximum output power of the single-frequency fiber laser is 15.3 mW at a pump power of 130 mW and the slope efficiency is 15.3%. The optical signal-to-noise ratio and the laser linewidths are ～60 dB and 5.89 kHz, respectively.

Based on the modified ramp and fire technique, a novel injection seeding approach with real-time resonance tracking is successfully demonstrated in a single-frequency Nd:YAG pulsed laser. Appling a high-frequency sinusoidal modulation voltage to one piezo actuator and an adjustable DC voltage to another piezo actuator for active feedback, single-mode laser output with high-frequency stability is obtained, and the effect of the piezo hysteresis on the frequency stability can be eliminated for a laser diode pumped Q-switched Nd:YAG laser at a repetition rate of 400 Hz.