In situ temperature near the chips in a multiple-chip power semiconductor module is important information for thermal design validation, condition monitoring, and overheat protection. Due to the compact packaging structure and clamping force, online detection of the temperature is challenging for a press-pack module. This study attempts to achieve measurement by integrating optical fiber Bragg grating (FBG) sensors into the device. Different integration schemes are examined using experiments and theoretical analysis to show the effects on the transient performance. It is shown that FBG sensors with plate housing can effectively indicate the transient temperature ripple in normal converter operation, owing to the fast dynamic response of a small size sensor. The package integration has only minimal effects on the original distributions of electrical, thermal, and mechanical quantities within the power module.

The performance and reliability of the high-power light-emitting diodes (HP LEDs) are closely related to the quality of the die attach adhesive (DAA) layer, because voids or delaminations in the layer may cause higher junction temperature, and even result in the break of the chip. In this paper, a dynamic compact thermal model is constructed for an independent HP LED without being attached on a cold plate. The time-constant spectrum method based on the thermal model is applied to characterize the transient thermal behavior of the DAA layer and other layers along the heat flow path. Thermal transient experiments are carried on HP LED samples with different DAA dosages. The theoretical and experimental results demonstrate that the time-constant spectrum for LEDs tested without cold plate can reflect the thermal characteristics of the DAA layer as well as that with cold plate. Differences in the HP LED samples with different DAA layers can be obviously distinguished in the time-constant spectrums as well. Compared with the traditional testing method with cold plate, direct test in air for HP LEDs has the advantages of easy operation, time saving, and no pollution to samples.

A fast real-time demodulation method based on the coarsely sampled spectrum is proposed for transient signals of fiber optic extrinsic Fabry-Perot interferometers (EFPI) sensors. The feasibility of phase demodulation using a coarse spectrum is theoretically analyzed. Based on the coarse spectrum, fast Fourier transform (FFT) algorithm is used to roughly estimate the cavity length. According to the rough estimation, the maximum likelihood estimation (MLE) algorithm is applied to calculate the cavity length accurately. The dense wavelength division multiplexer (DWDM) is used to split the broadband spectrum into the coarse spectrum, and the high-speed synchronous ADC collects the spectrum. The experimental results show that the system can achieve a real-time dynamic demodulation speed of 50 kHz, a static measurement root mean square error (RMSE) of 0.184 nm, and a maximum absolute and relative error distribution of 15 nm and 0.005% of the measurement cavity length compared with optical spectrum analyzers (OSA).

Most of the lighting designs are based on the far-field characteristics of light sources. It is important to know whether the measurement distance is far enough to simulate the light source as a point source. In this paper, we deduce the far-field conditions for surface light sources with continuous luminous area. The relative far-field distance for several typical flat and curved surface light sources, such as the round, rectangular, annular, hemispherical, and semi-cylindrical sources are calculated. Results show that the classical five times rule is not applicable to surface light sources with hemispherical, arc-shaped semi-cylindrical, and narrow annular luminous areas.

The light distributions in different tunnel zones have different requirements in order to meet the driver’s visual system. In this paper, the light intensity distributions of tunnel lamps in different zones of a long tunnel are optimized separately. A common nonlinear optimization approach is proposed to minimize the consuming power as well as satisfy the luminance and glare requirements both on the road surface and on the wall set by International Commission on Illumination (CIE). Compared with that of the reported linear optimization method, the optimization model can save energy from 11% to 57.6% under the same installation conditions.

The optical path length (OPL) of the Fabry-Perot cavity may change during the spectrum acquisition; it introduces demodulationerror or even causes demodulation failure based on traditional algorithms. To address this problem, the relationship between the dynamic OPL and instantaneous frequency is investigated. Demodulation of the dynamic OPL based on instantaneous frequency analysis is proposed. By combining spectrogram (SP) and Wigner-Ville Distribution (WVD), an effective time-frequency (TF) analysis method is investigated to calculate the dynamic OPL at each sampling point in a period of a sweeping laser. Experimental results show that the demodulation speed is 4.8 MHz at a 2 KHz sweeping rate, the max deviation of a sinusoidal variation of OPL is around 0.14 μm, and the max deviation of a triangular variation of OPL is around 0.13 μm.