Silicon nitride is widely used in photonic integrated circuits process flow, it’s an important component of the integrated silicon-based optical device. The fabrication of a low-loss waveguide is important in silicon nitride microresonator, which is generally composed of silica cladding and silicon nitride waveguide. This paper mainly optimizes the process flow of silicon nitride and silicon oxide film to obtain a low-loss waveguide. A critical thickness of the light leakage from the silicon nitride waveguide to the silicon substrate is obtained by simulation, and the process flow of dry oxidation, wet oxidation, and annealing are combined to fabricate silica film with high uniformity, compactness, and confinement. This process flow traps the light leakage from silica to silicon and reduces the surface roughness, providing a good environment for the growth of silicon nitride. Thin silicon nitride film is fabricated after the thick silicon nitride film is grown by two-step process flow, a long-time annealing after growing the thin film greatly reduced the loss of waveguide. In this paper, the scattering loss is reduced by optimizing the process flow of the silica layer, and the fabrication optimization of the silicon nitride layer leads to low absorption loss, providing superior performance optimization for high Q silicon nitride microresonators of photonic integrated circuits.
Frequency stabilized optical frequency combs has been crucial for applications of high-precision measurements, optical clocks, and parallel communications, et al. The most effective way of frequency stabilization of combs is stabilizing the repetition rate and carrier-envelope offset frequency of a generated comb, which requires octave-spanning spectrum generation. However, the spectrum bandwidth of microcavity comb is greatly limited in the existing microresonator-waveguides due to the interaction of dispersion and phase modulation. In this paper, we mainly study the generation of supercontinuum in Si3N4 waveguides of different sizes. Supercontinuum generation refers to the phenomenon that the frequency spectrum of the ultrashort pulse is greatly broadened after the linear and nonlinear effects, which has been the mainly mechanism of spectrum broadening in Si3N4 nonlinear medium. In this paper, the dispersion of different size of Si3N4 waveguides has been studied. Different structure of waveguides has been built of which the effective index, propagation constant and dispersion parameter has been simulated and calculated through mode analysis. The electric field mode of waveguide cross section is simulated, and light is well confined in the waveguide with height of 0.8 μm and width of 1.6 μm. Based on this structure, we can access the effective index neff, based of which we calculate the group velocity dispersion of waveguide. We can get flatter dispersion curve through dispersion-engineered waveguide and more broaden spectrum through dispersive wave with zero-dispersion.
Doppler broadening thermometry (DBT) takes advantage of the high resolution characteristic of laser absorption spectroscopy to obtain thermodynamic temperature by measuring optical frequency. It is one of the research hotspots in the field of thermodynamic temperature measurement after the Kelvin redefinition in 2018. In this paper, the direct absorption spectroscopy based on Cesium (133Cs) D1 (6S1/2→6P1/2) line was measured, and the thermodynamic temperature of atomic gas in thermal equilibrium state was obtained by extracting Doppler width of absorption line. The experimental results showed that average relative error of thermodynamic temperature was 0.01% and the standard deviation was 0.14% after 50 rounds of testing at 303.15 K. These research results prove the feasibility of Doppler broadening temperature measurement, and provide research support for the realization and transfer of thermodynamic temperature.
The self-injection locking based on the microcavity can be generated when the microcavity is directly pumped by the laser diode, and the linewidth can be narrowed. In this work, we used a DFB laser to pump a silicon nitride (Si3N4) micro ring resonator (MRR) with a 5e5 quality (Q) factor. Tapered fiber was used for the chip waveguide end face coupling. The transmission spectrum and wavelength locking region were obtained by scanning the drive current of laser diode. 0.09 nm width locking region was achieved at 1552.6 nm. Finally, the linewidth of the output laser was measured using path modulation non-zero frequency self-heterodyne interference method. Linewidth narrowing was found by comparing free running state and self-injection locking state of the laser diode. The experiment results show five times linewidth narrowing. The self-injection locking laser based on Si3N4 MRR is realized through fiber coupling, which is simple and compact in structure and significantly reduces the difficulty of optical alignment. At the same time, it can obtain extremely narrow linewidth, which has broad application prospects in precision metrology, optical fiber sensing, optical communication.
Si3N4 microresonator have been recently widely used in various applications. Key factor of OFC generation is high Qfactor microresonator device and the precisely dispersion control of waveguides. In this paper, low-propagation-loss structure with precisely engineered dispersion properties has been illustrated to realize microresonator-based optical frequency combs operating in the dissipative Kerr soliton regime. We designed a ring with 100 GHz free spectrum range (FSR) with the size of the chip about 5 mm×5 mm. The improvement included that we adopted high temperature annealing to reduce absorption loss, we used metal as hard mask layer before ICP etching of the Si3N4 layer and we etched the Si3N4 layer after deposition of the SiO2 layer to expose the waveguide section. The high Q-factor device need low optical pump power, such as on-chip diode laser and thus realized integrated on-chip microresonator optical frequency comb which was compatible with CMOS and be successfully used in chip-based optical clock and other applications.
As a thermal reference source, plane blackbody radiation source is widely used in infrared instrument calibration. In practical application, it is required that the normal spectral emittance of the plane blackbody radiation source should be greater than 0.95. However, the plane blackbody radiation source made by traditional sand blasting process cannot meet the requirement. Here we demonstrate a new manufacturing process for the plane blackbody radiation source. We selected aluminum material with a thickness of 10mm as the substrate, and then we roughed the substrate surface by femtosecond laser micromachining. Next, we sprayed on the prepared surface with heat resistant coatings and finished the manufacturing process. In comparison, we also made the plane blackbody radiation source by the sand blasting process with the same substrate and heat resistant coatings. Compared with the samples treated by sand blasting, we find that the samples treated by femtosecond laser show much smoother spectral emittance curves and higher spectral emissivity, and the average spectral emissivity is higher than 0.95 from 8μm to 18μm at the temperature of 500°C. Our results suggest that femtosecond laser micromachining is an effective way to obtain high quality plane blackbody radiation source.
We demonstrate an enhancing near-infrared photoresponse in sulfur-supersaturated silicon photodiodes. We obtain microstructured silicon doped with supersaturated sulfur by femtosecond laser ablation in SF6 atmosphere. Next, we introduce annealing process to activate the dopants and improve the material quality. Then we fabricate n+ n photodiodes using the microstructured silicon. We find that the spectral response of the photodiodes exhibits gain from 400 nm to 1200 nm under the reverse bias, and under the condition of 10 V reverse bias, the photoresponse can be up to 3.69 A/W and 2.45 A/W at the wavelength of 965 nm and 1064 nm, respectively. While for the ordinary silicon photodiode, the spectral response has no gain under the reverse bias, and the photoresponse is less than 0.7 A/W and 0.35 A/W at 965 nm and 1064 nm, respectively. Our results suggest that the sulfur-supersaturated silicon diode has the great potential to improve the performance of silicon detectors in the infrared range.
InGaN epitaxial layer has been studied by means of temperature dependent time-integrated photoluminescence (PL) and time-resolved photoluminescence (TRPL). The PL peak energy was fitted by a thermal activation and thermal transfer model, a fast carriers transfer time was obtained. A small redshift with increasing time was observed at low temperature in the TRPL spectra, and the redshift was enhancing with increasing temperature. These behaviors are caused by a change in the carrier dynamics with increasing temperature due to the carriers transferring in the localized states in InGaN eplayer.
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