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We propose and theoretically study a two-section high-power distributed feedback (DFB) laser with three equivalent phase shifts (3EPSs). A tapered waveguide with a chirped sampled grating is introduced to amplify the output power and keep a stable single-mode operation. The simulation exhibits the maximum output power and side mode suppression ratio of a 1200 µm length two-section DFB laser as high as 306.5 mW and 40 dB, respectively. Compared with traditional DFB lasers, the proposed laser has a higher output power, which may benefit wavelength division multiplexing transmission systems, gas sensors, and large-scale silicon photonics.

Based on the randomness of spontaneous emission, the statistical characteristics of phase noise are discussed. A theoretical analysis model, focusing on the amplitude randomness of spontaneous emission, is established to calculate laser phase noise. Then, the coherence of a laser before and after phase-locked control is calculated when an ideal laser and nonideal laser are used as a reference light in an optical phase-locked loop (OPLL). The effects of the amplitude randomness of spontaneous emission on phase-locked laser coherence are analyzed in detail. The results show that phase noise randomness increases with the increase of the expectation or variance of spontaneous emission amplitude, which represents amplitude randomness. When an ideal light is used as reference light, if the expectation and the variance of spontaneous emission amplitude are about 10 and 100, respectively, the time constant of an OPLL should be set as 1 ns, while a favorable noise suppression result can be achieved. However, to achieve a favorable noise suppression result, the time constant of an OPLL should be set as 0.1 ns when a nonideal laser is used as reference light.

We demonstrate particle counting based on high-order Fano resonance (FR) in an optofluidic microcavity. The high-order FR excited by a thin fiber taper can penetrate the liquid core of a microcapillary. An optical pulse is generated due to the resonant spectrum shift when a particle crosses the microcavity. Analogous to other methods, such a pulse can be used for particle counting. The sampled particles of PS microspheres and super-absorbent polymer broken beads are used for particle-counting experiments. All results confirm the feasibility of such a counting method.

In this paper we demonstrate a high-sensitivity temperature sensor based on high-order Fano resonance (FR) in an optofluidic microcapillary resonator. High-order FR modes ( Q ∼ 3000 ) are excited in an ethanol-filled optofluidic microcapillary resonator for temperature sensing. Due to the high thermo-optic coefficient of ethanol and a large energy fraction of high-order modes in the core liquid, the sensitivity as high as − 0.402 n m / ∘ C and the detection limit of 0.026°C can be achieved. Also the sensitivity and free spectral range of different order radial modes are calculated theoretically. The experimental results agree well with the theoretical results. Through the comparison between the theoretical and experimental results, the radial order number of the mode used for temperature sensing is estimated to be 10.

Ray tracing is performed to investigate the optical distortions in the end-pumped, zigzag slab. Optical path differences caused by temperature, slab deformation, and stress birefringence are calculated under uniform pumping; the results show a steep edge in the width dimension and a thermal lens with an effective focal length as short as several meters in the thickness dimension. Dependence of depolarization on total internal reflection phase retardance as well as the slab's cut angle is studied by the Jones matrix technique; results show that although at the pumping power of 10 kW, the mean depolarization of the 2.5 mm×30 mm×150.2 mm Nd:YAG slab is generally below 3%, and it increases rapidly with pumping power. Besides, for the 0°- or 60°-cut slab, an optimal phase retardance range of 5° to 13° exists, in which the depolarization loss can be lower than 0.5%. Finally, experiments on temperature and depolarization measurements verify the numerical results.

For the first time femtosecond-laser writing has inscribed low-loss optical waveguides in Schott BK7 glass, a commercially important type of borosilicate widely used in optical applications. The use of a variable repetition rate laser enabled the identification of a narrow processing window at 1 MHz repetition rate with optimal waveguides exhibiting propagation losses of 0.3 dB/cm and efficient mode matching to standard optical fibers at a 1550 nm wavelength. The waveguides were characterized by complementary phase contrast and optical transmission microscopy, identifying a micrometer-sized guiding region within a larger complex structure of both positive and negative refractive index variations.

Surface-relief gratings with submicrometer modulation periods were ablated by F2-laser radiation in thin metal-oxide films to produce resonant grating waveguide structures. For 150 nm films of Nb2O5, grating amplitudes in the range of 5-50 nm could be reproducibly excised with a controlled exposure of a laser energy density and a number of pulses within a narrow processing window. Resonant coupling of 800 nm ultrashort pulsed laser light into the resulting grating waveguide structure is verified with reflection and transmission spectra and satisfactorily modeled by coupled-mode theory. The laser-fabricated grating waveguides are attractive for high damage threshold reflectors and biosensor applications.