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.
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