Purpose: As measurement results of optical gas sensors are constantly affected by the pressure of a target gas, approaches must be taken to modify the results. The purpose of this paper is to compare the traditional measurement method with the new measurement system. At the same time, measurement results of the two systems under different pressures are presented for comparison of the detection performance. Design/methodology/approach: A theoretical model of line shape function and its impact on the measured results is presented, which is based on direct absorption and wavelength modulation spectroscopy (WMS) for gas concentration detection under different pressures. Methods of linear fitting and result modification have been illustrated and compared. A new testing system with the result modification method used for water vapor concentration detection under different pressures between 1 and 7 atm is applied. With an additional pressure sensor placed in the gas cell and calibration performed, relationships between the amplitude of the second harmonic and concentration of the target gas under different pressures can be obtained. Findings: Amplitude detection can be used for concentration detection regardless of the change in pressure for the method of direct absorption. Although, WMS with second harmonic detection is not enough. Two methods are presented and compared with WMS under different pressures. Moreover, the result modification method shows better performance as computation is significantly reduced. Originality/value: The comparison between linear fitting and the result modification method with WMS under different pressures is firstly presented. At the same time, a new testing system with better performance for water vapor concentration detection under different pressures is presented as well.

Tm³⁺/Yb³⁺ codoped tellurite glass has been prepared. Density, refractive index, optical absorption, Judd-Ofelt parameters and spontaneous transition probabilities of Tm³⁺ have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and S-band (1470 nm) fluorescence were investigated under the excitation of a 980 nm diode laser at room temperature. Judd-Ofelt parameters, strong blue three-photon upcoversion emission of Tm³⁺ in glass indicate that Tm³+/Yb³⁺ codoped tellurite glass is a promising blue color upconversion optical and laser material. In addition, experiment results showed the 980 nm laser was more efficient than 808 nm laser when pumping Tm³⁺/Yb³⁺ codoped tellurite glass, Tm³⁺/Yb³⁺ codoped tellurite glass also could be a promising material for S-band amplification.

In this paper, we verify the feasibility of our proposed design scheme for customizable optical pressure sensor based on the photo-elastic effect of SiO2 waveguide in asymmetric Mach-Zehnder interferometer (a-MZI) structure. The curve lengths and minimum radii of curvature of several common types of a-MZI arm curves are calculated theoretically. By analyzing the relationship between the radius of curvature of the long arm curve, the length of the long arm curve and the arm length difference of the a-MZI sensor under different types of arm curves, the design scheme for an a-MZI pressure sensor with a specific arm length difference is obtained. By selecting a rationalized arm design scheme, customization of the sensing range can be achieved. No special processing (such as etching) is required for the waveguide, which improves the pressure tolerance of the sensor. When using the SiO2 waveguide with a refractive index difference of 2%, the a-MZI pressure sensor based on sine type arm with arm length difference of 5 mm has a sensing range of 4.83 MPa and a sensitivity of 1.24 mW/MPa. The a-MZI pressure sensor with the ease of fabrication can be used to monitor various scenarios, such as marine and building monitoring.