The effective pixel rate is a key performance parameter of infrared focal plane detectors and is also a key parameter for assessing the reliability degradation trend of the device. The application scenario of InGaAs short wavelength infrared focal plane detectors for interstellar alignment is different from that of conventional imaging detectors, where the signal values of each pixel of the focal plane are mainly used to determine the position of the laser bright spot, rather than the gray values used to generate the image. From the point of view of blind element evaluation, for the low-orbit satellite communications application scenario, the rate of change of the response values of the image elements in each local region of the InGaAs short-wave infrared focal plane detector for interplanetary alignment with optical flux has a greater impact on the performance of the device than the absolute response values of the image elements. In order to adapt to this evaluation requirement, this work designs a sliding window blind element determination method based on the rate of change of the dark signal voltage for the intrinsic characteristics of the detector, which utilizes the principle of equivalence of the effects of luminous flux and integration time on the detector signal voltage value, which is more adaptable to the practical application scenarios of interstellar-aligned shortwave infrared focal plane detectors, and the entire focal plane is divided into a number of localized regions, and the sliding detection window is used for blind element determination, which avoids the fully aligned shortwave infrared focal plane detector. Blind meta-judgment, which avoids the phenomenon of misjudgment that often occurs in global judgment. This blind judgment method is also of great importance for the reliability evaluation of InGaAs shortwave infrared focal plane detectors with high effective pixel rate for interstellar alignment.
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 HgCdTe Photodiode is the most basic and important unit of HgCdTe IRFPA (Infra-red focal plane array) detectors, which have been widely used in the fields of security, fire protection, remote sensing and deep space detection. For HgCdTe IRFPA, the trapped charges of the HgCdTe material and the ionic charges introduced during the preparation process are the factors, other than environmental stress, that have the greatest impact on IRFPA performance. The trapped charges come from the trap energy level in the HgCdTe material, which exist during the crystal growth process and can be improved by adjusting the growth conditions, but it cannot be completely avoided. The ionic charges introduced during the process are generally concentrated at the interface and surface of the HgCdTe material, which can be reduced by process improvement, but cannot be completely avoided. In order to analyze the mechanism of multiple charges affecting the HgCdTe detector performance, a type of n+ -on-p HgCdTe Photodiode is selected as the object of this work, and the effects of the concentration and distribution of charges on the carrier distribution and energy band structure of the n+ -on-p HgCdTe are analyzed in detail. The introduction of additional net charge relative to an ideal n+ -on-p HgCdTe Photodiode leads to the aggregation or scavenging of local carriers and affects the energy band structure near the charge, creating additional potential barriers or potential wells, which is likely to cause device degradation. On this basis, the optoelectronic properties of the HgCdTe Photodiode have been investigated under infrared radiation at a wavelength of 9.5 μm, as the light I–V characteristics, the dynamic resistance–voltage characteristics, band structure and carrier density distribution. According to the results of this work, the quasi-fixed charges introduced by defects or contamination will directly affect the generation rate of photogenerated carriers and affect the I–V and R–V characteristics of the HgCdTe Photodiode, leading to phenomena such as rising dark currents, decreasing spectral response, and decreasing quantum efficiency.
The waveguide branch plays an important role in integrated photonic circuits by dividing input light into two or more output lights, thereby facilitating optical power distribution and mode selection. Ordinary optical waveguides used in waveguide branches suffer from excessive optical loss and narrow branch angles, limiting their effectiveness in mode selection among other problems. Photonic crystals are constructed by arranging macroscopically homogeneous dielectric (or metallic) materials into periodic arrays, with carefully designed internal defects that provide them with frequency-selective and spatial properties. In this study, a silicon-based wide-angle waveguide branch composed of two-dimensional photonic crystals has been successfully created. The branch is capable of separating two wavelengths of light, namely 850 nm and 950 nm, by adjusting the positions of silicon cylinders in the two-dimensional photonic crystal with the purpose of optimizing optical power at different wavelengths. The silicon-based wide-angle waveguide branch is expected to be employed in multimode optical communication systems. Its utilization will contribute towards the reduction in size and complexity of integrated optical communication systems, while enhancing system reliability.
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.
HgCdTe infrared focal plane array imaging detectors have been widely used in a variety of fields such as night vision surveillance, remote sensing mapping and astronomical observation. In recent years, with the development of semiconductor manufacturing processes, the array size of HgCdTe IR focal plane array imaging detectors has gradually increased, and the preparation process has become increasingly complex. During the preparation process, impurity ions can enter the HgCdTe material and cause degradation of device performance or even device failure. This work investigates the distribution of impurity elements in HgCdTe IR focal plane array detectors prepared by both processes and the mechanism by which impurity elements cause device failure.
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.
Reliability is an important index to ensure the application of infrared focal plane arrays (IRFPAs) in complex environment, and it becomes a major bottleneck problem of IRFPAs’ development. Because of the characteristics such as type, nature, quantity, location and distribution et al, bad pixel which contains initial bad pixel and used bad pixel has outstanding advantage for failure analysis and reliability evaluation of IRFPAs. In this paper, the structure of IRPFAs has been introduced in detail, and the damage mechanisms of used bad pixel also have been analyzed deeply. At the same time, the feasibility to study IRPFAs' damage stress, failure position, damage mechanism has been discussed all around. The research of bad pixel can be used to optimize the structure and process, meanwhile it also can improve the accuracy of bad pixel identification and replacements.
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