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Highlights • Thermal effect of the biphotons generated from M TiO X O 4 is thoroughly investigated. • The thermal effect is the key to precisely control the quantum state. • The maximal spectral purity of biphotons is insensitive to temperature shift. • The HOM interference patterns are very sensitive to temperature shift. • The research results are useful for quantum interference and spectroscopy. Abstract We theoretically and numerically investigate the temperature-dependent properties of the biphotons generated from four isomorphs of periodically poled KTiOPO 4 (PPKTP): i.e., PPRTP, PPKTA, PPRTA and PPCTA. It is discovered that the first type of group-velocity-matched (GVM) wavelength is decreased by 6.4, 1.2, 8.9, 25.6 and 6.3 nm, while the phase-matched wavelength is decreased by 4.4, −0.4, −1.2, 29.1 and 59.5 nm for PPKTP, PPRTP, PPKTA, PPRTA and PPCTA, respectively, when the temperature is increased from 20 °C to 120 °C. Although the maximal spectral purity of the heralded single photons is not changed at different temperature, the Hong-Ou-Mandel (HOM) interference shows different patterns due to a shift of the joint spectral amplitude. These thermal effects are very important for precise control of the quantum state for the future applications in quantum information processing, for example, in quantum interference or spectroscopy. [ABSTRACT FROM AUTHOR]

Highlights • Our fiber curvature sensor has merits of inline compact, low cost and sensitive. • Highly sensitivity −15.33 dB/m−1 in the range 3.63–4.69 m−1 is experimentally demonstrated. • Low cross sensitivity 0.018 m−1/°C implies it is insensitive to environmental temperature change. Abstract An inline fiber structure formed by a silica tube spliced between single-mode fibers has been developed and tested for curvature measurement based on anti-resonant reflecting waveguide. A Fabry-Perot resonator with leaky modes of guided light in the silica tube is formed based on anti-resonant effect in the resonant wavelengths, which results in lossy dips in the transmission spectrum. Since the transmission power of the resonant dips is sensitive to structure bending, an inline curvature sensor can be realized. Experimental results reveal a high sensitivity up to −15.33 dB/m−1 in the wide curvature range of 3.63–4.69 m−1. The proposed sensor also demonstrates a low temperature sensitivity 0.27 dB/°C implying a small temperature cross sensitivity 0.018 m−1/°C. Our sensor has its merits of compact, low cost and high sensitivity. [ABSTRACT FROM AUTHOR]

A modified Hong–Ou–Mandel (HOM) interference reveals that the two-photon interference phenomenon can be explained only by the concept of a two-photon wave packet rather than a single-photon one. However, the temporal interferogram in the modified HOM interferometer becomes flat in some cases so that no useful information can be extracted from time-domain measurement. Here, we theoretically explore such temporal interferogram from the frequency domain and obtain the spectrally resolved interference with high visibility. The result represents a modulation of the joint spectral intensity along both the frequency sum and the frequency difference directions. This is quite different from the cases of the spectrally resolved HOM interference and N00N state interference where the modulations happened only in one direction. Moreover, we have shown that such modulations have a potential application in the generation and characterization of high-dimensional frequency entanglement. • Spectrally resolved interference with high visibility in the modified HOM interferometer can be obtained even if the temporal visibility is zero. • Joint spectral intensity can be modulated by the time delay along both the frequency sum and the frequency difference directions. • High-dimensional frequency entanglement can be generated by adjusting the time delay and can be characterized directly using the two-side dips appeared in temporal interferogram. • The research results could facilitate further development of spectrally resolved multi-photon interference and its applications in quantum information science. [ABSTRACT FROM AUTHOR]

• Low-cost fiber MI temperature sensor is formed by filling SCF with polymer-UV glue. • High sensitivity is obtained due to the great thermal properties of UV glue. • Our sensor shows advantages of robust, small size, and low cost. • The reflective tip structure enable for remote sensing in practical applications. A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications. [ABSTRACT FROM AUTHOR]