1310nm long-wavelength vertical-cavity surface-emitting lasers (VCSELs) have a wide application prospect in optical data transmission over long distances, in particular for hybrid integration with silicon photonics. With the wide application of 1310nm VCSEL, the reliability requirement is becoming more and more high. In this paper, the degradation mechanism of 1310nm VCSEL is studied by accelerated stress aging experiment. The device accelerates aging for 4000 hours at 8 mA, the maximum output power decreases by 0.04 mW, and the power saturation current and V-I curve remain basically unchanged. Leakage current of the device increases and reverse bias breakdown voltage decreases. Current noise power spectral density of the device is an order of magnitude higher than before aging. In addition, the device with degraded performance is characterized by optical emission microscopy. When the device is forward biased, dark spot defect is found on the edge of the light-emitting hole of the device after burnin. The internal topography of the device is characterized by FIB-SEM, and the oxide layer warpage is found. This is due to the increase of heat inside the device and the increase of stress in oxide layer, resulting in degradation of device’s performance.
The electromigration problem in flip chip becomes one of the focuses of the microelectronic device durability. Temperature is a key parameter for the electromigration life evaluation, due to the occurrence of material structure defect will be accelerated with the rise of temperature. But it is difficult to measure the temperature inside the flip chip packaging structure of large-scale integrated circuits directly with traditional test means. In this paper, a distributed temperature profile test method in interconnect solder joints flip chip has been present, which is measured by the optical-frequency-domain reflectometry (OFDR) with telecom single model fiber. The most distinguishing feature of this method is that the thin flexible optical fiber can directly penetrate into the flip chip from the position of the interconnection solder joint to realize the distributed sensing of the temperature field of the solder joint inside the chip. The modulated linear sweep light directly injected into optical fiber and transmitted forward, and a certain interference pattern formed by back Rayleigh scattering is generated. When the temperature environment of the optical fiber changed, the interference pattern formed by back Rayleigh scattering will change accordingly, which will cause the wavelength shift of the interference pattern, that is similar to the fiber grating effect. Thus, the distributed temperature change can be demodulated from the wavelength shift. The experimental results show that this method can realize the distributed measurement of the internal temperature of flip chip directly, and provides a novel solution for more accurate evaluation of electromigration effect.
Tapered semiconductor lasers are widely used in space communication due to their high output power and high beam quality. The tapered semiconductor laser structure mainly consists of ridge region, absorption region and tapered region. The tapered semiconductor laser is analyzed by characterization methods such as EMMI, EDS and FIB-SEM in this paper. It is found that the waveguide damage in the ridge region is caused by the enhancement of the local optical power density in the ridge waveguide, and there are failure points inside the waveguide and the sidewall of the device, resulting in photon leakage. The closer to the optical cavity surface, the more holes between the solder and the electrodes, and the presence of oxygen elements near the optical cavity surface, indicating that the interface holes existing in the optical cavity surface would lead to the migration of oxygen elements. The research results reveal that the enhancement of local power density in the ridge waveguide is caused by the optical feedback process. The main failure mechanisms of the device contain the solder holes and the enhancement of local power density, which provide an important reference for the process optimization of high-power tapered semiconductor lasers.
The electrostatic discharge (ESD) effect and damage mechanism of Charge Coupled Device (CCD) is investigated. Transmission line pulsing (TLP) tests have been experimented to identify the instantaneous I-V characteristics of CCD detectors under ESD stress. The TLP I-V curves of the ports with or without ESD protection show different characteristics, which indicate that the electrostatic discharge is a capacitor charging process for the ports without protection. The ports with smaller capacitance such as the transfer clock and readout clocks are the weakness against ESD events. The electrostatic damage site is further analyzed using emission microscopy (EMMI) and Focused Ion beam technology (FIB), revealing that the electrostatic damage mechanism of CCD.
Cryogenic Infrared Rays Focal Plane Array (IRFPA) detectors have been widely used in industry, transportation, security monitoring, meteorology and medicine because of the high sensitivity and temperature resolution. For HgCdTe IRFPA detectors, the typical working temperature is about 80 K. To make the IRFPA detector works at low temperatures, the detector should be integrated on a Dewar cold platform, whose refrigeration power would be higher than the heat load of the IRFPA. In general, the IRFPA detector and the Dewar cold platform would be integrated together to form a Dewar assembly at room temperature. In addition, the materials in IRFPA have different thermal expand coefficients, it means the thermal mismatch in the IRFPA would be an unavoidable issue in work. The thermal strain has a significant effect on the solder joints in switching cycle, which could lead to the creep strain and thermal fatigue crack. With the increase of the switch cyclic number, the creep strain and thermal fatigue crack under the thermal stress would lead to the failure of solder joints. Therefore, the low temperature thermal strain in switching cycle can affect the reliability of IRFPA detectors. So, the low temperature thermal strain and the creep lifetime of solder joints has been researched.
Fiber-optic hydrophone is a new type of sensor which can detect acoustic signal in harsh seawater environment. For some application, the fiber-optic hydrophones should be serving for years or even decades, due to the high cost of placement. Because of multiple fiber-optic hydrophones are made into a hydrophone array by multiplexing generally, thus realize signal detection as a whole. To ensure the detection effect, sufficient number of elements in the array must be working order, otherwise the array may lose efficacy. Slow degradation of fiber-optic hydrophone is inevitable as time goes on. So, it is particularly important to control early failures. In this paper, a research on early failure mechanism of fiber-optic hydrophone has been present. In details, the actual service environment of fiber-optic hydrophone is analyzed firstly, and the weak links of fiber-optic hydrophone which may degrade rapidly are discussed and the early failure mechanisms are also analyzed. Further, the verification test was designed for the possible failure mechanism, and the failure analysis of the samples was carried out by using the advanced failure analysis instrument such as the scanning electron microscope (SEM) and the Fourier transform infrared spectrometry (FTIR). Results show that the bonding process defects is one of main reason for early failure of the fiber-optic hydrophone and the strength of package may degrade rapidly in seawater environment until the early failure occurs. This research will help to improve the process reliability of fiber-optic hydrophones and control the occurrence of early.
Optical-path difference (OPD) is a key parameter for the fiber-optic interferometer, especially for the large-scale multiplexing of fiber-optic interferometric sensors (FOIS) array. Due to the OPD directly affects the background noise of the system and the performance consistency among different array elements. Most of the time, the latter is very critical for the FOIS array. Several methods have been adopted for the OPD measurement of the fiber-optic interferometer, including the white-light interferometry, the optical-time-domain reflectometry (OTDR), the optical-frequency-domain reflectometry (OFDR). Unfortunately, none of the methods mentioned above can directly realize OPD on-line measurement of FOIS, which is multiplexed with the time division multiplexing (TDM) and the wavelength division multiplexing (WDM). In this paper, an OPD measurement method for multiplexing FOIS using TDM and WDM based on the improved OFDR has been present. The most distinguishing feature of this method is that it transformed the FOIS array under tested into a part of the OFDR system. The modulated linear sweep light directly injected into the FOIS array under tested and traversed every array element through array network. Thus every interferometer of FOIS became the interferometric structure of the improved OFDR, and the OPD measurement of complexity multiplexing FOIS array has been vastly simplified into the fiber length measurement of interferometer in proper order. Results show that the measurement accuracy of this approach can achieve millimeter level and the measurement range up to hundred meters for FOIS using TDM and WDM through a single measurement.
The phase-generated-carrier (PGC) algorithm is the most widely used signal demodulation method for fiber-optic interferometer sensors (FOIS), due to its distinct advantages of high resolution, wide dynamic range, good linearity and multi-channels demodulation capability. Even though significant progress has been made in PGC algorithm, the influence of phase modulation amplitude variation for PGC-differential-cross-multiplying approach (PGC-DCM) and PGC-Arctangent approach (PGC-Arc) still remains, especially on large-scale FOIS array. In this paper, a novel ameliorated digital PGC algorithm based on three-channel mixing signals has been present to mitigate this effect, which called PGC-differential-cross-dividing approach (PGC-DCD). The most distinguishing feature of this method is that it directly picks up the phase modulation amplitude from the interference signal by series of mathematical calculation and synchronically used in subsequent demodulation processing. So, the variation of phase modulation amplitude, induced by the internal or external disturbances, can be directly detected and synchronically updated in demodulation. The theoretical derivation and simulation experiment show that this approach is robust to the variation of phase modulation amplitude, and is a potential demodulation algorithm for FOIS, especially for large-scale FOIS array.
Aerosol light absorption plays an important role in the earth’s atmosphere direct and semi-direct radiate forcing, simultaneously, it also has a huge influence on the visibility impairment and laser engineering application. Although various methods have been developed for measuring aerosol light absorption, huge challenge still remains in precision, accuracy and temporal resolution. The main reason is that, as a part of aerosol light extinction, aerosol light absorption always generates synchronously with aerosol light scattering, and unfortunately aerosol light scattering is much stronger in most cases. Here, a novel photo-thermal interferometry is proposed only for aerosol absorption measurement without disturbance from aerosol scattering. The photo-thermal interferometry consists of a sinusoidal phase-modulating single mode fiber-optic interferometer. The thermal dissipation, caused by aerosol energy from photo-thermal conversion when irritated by pump laser through interferometer, is detected. This approach is completely insensitive to aerosol scattering, and the single mode fiber-optic interferometer is compact, low-cost and insensitive to the polarization shading. The theory of this technique is illustrated, followed by the basic structure of the sinusoidal phase-modulating fiber-optic interferometer and demodulation algorithms. Qualitative and quantitative analysis results show that the new photo-thermal interference is a potential approach for aerosol absorption detection and environmental pollution detection.
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