The DC And Noise Characteristics Of High Power Laser Diodes

Laser diodes are widely used in military, industry, medicine and optical fiber communication. Their performances and reliability are very important in practical applications, especially in high reliability fields such as space flight, military et al.. Accelerated testing is a traditional method for predicting the lifetime of laser diodes, but it is destructive, expensive and time consuming, and it is limited by the quantity of aging equipment when the laser diodes are multiple. There is a requirement therefore for fast, cheap, simple and nondestructive tests. According to above purpose, the DC and noise characteristics are investigated in this paper, also, the mechanism of these characteristics and the relations between these characterisrics and the reliability of laser diodes are investigated. These investigations are guiding to estimate the reliability of laser diode.Voltage-current (V-I) characteristic is a general indicator to estimate the reliability nondestructively, but it is too insensitive to some microscopic processes. Some references have reported that electrical derivative (IdV/dI-I) is more sensitive than V-I. This method can be used to estimate the reliability of laser diodes by extrating the derivative parameter shch as ideality factor m, equivalent series resistance before threshold Rs1, equivalent series resistance after threshold Rs2, after threshold intercept b and dip hight h from derivative curve. The fluctuation of the V-I curve can easily be seen in the IdV/dI-I curve, and the IdV/dI-I method is more sensitive than the V-I method to defects of laser siodes. Moreover, IdV/dI-I method has quantitive parameters, and they can be used as a criterion to estimate reliability of laser diodes. So it is more scientific and effective than the V-I method. The electrical derivative method has been existed for 30 years after 1970's. More investigations are studied in low power laser diodes, and the investigations in high power laser diodes are very small. We report here the first use of electrical derivarive to predict the reliability of laser arrays. The one of primary contents in this paper is that the equivalent circuit model of laser array is established, and simulation processes are exploited on the model by using PSpice software. The simulation and experimental results indicate that the ideality factor of the laser array is equal to their elememts. This conclusion can be used to detect the extrinsic ideality factor of laser array element, and can also be used to study reliability of laser arrays. The reliability questions such as current leakage and the ideality facter increase can both result in the increase of the extrinsic ideality factor of laser array. This study can be used to further investigate the reliability of laser array and high power laser diode.For the first time, we obtain the analytic equation of before threshold electrical derivative of single laser diode by using equivalent electrical model. The quantitive relation of extrinsic ideality factor is proposed, and this study is more important in investigating the electrical derivative of laser array. The results in this paper indicate that the significant current leakage can results in the high initial peak in IdV/dI-I curve, and linear resistance in nonlinear leakage path (R2) is more insensitive than linear resistance in linear leakage path (R3 ) in predicting defects in laser diode. Aging test are executed on high power laser diodes, and we find that the parameters of ideality factor (m), equivalent resistances (Rs1, Rs2) increase significant after aging 350 hours, while the parameter b is invariable. This indicates that b is insensitive in reliability of high power laser diodes.Ideality factor is closely correlated with the reliability of laser diode (LD). The measured ideality factor of narrow-strip LD (2³) is larger than that of wide-strip LD (1²). Consideration of the structural difference between the wide-strip and the narrow-strip LDs, the simulation based on PSpice is exploited on the two types of LDs. The simulated and experimental results indicate that the current expansion is an important factor in affecting measured ideality factor. The higher the ability to limit current in active region is, the lower the measured ideality factor is.The fluctuation of the IdV/dI-I and the dP/dI-I is the second primary problem to investigate in this paper. Different devices have different fluctuations in the IdV/dI-I and dP/dI-I curves, and the further investigation is usful to obtain a new accurate reliability method. Theoretical investigation is discussed in this paper, and the correlations between the IdV/dI-I curve and the dP/dI-I curve are concluded, and the correlations between the IdV/dI-I, dP/dI-I curves and the reliability of laser diodes are also concluded. However, more experiments are expected in the further investigation. We conclude in this paper that the existence of peaks with opposite-direction and same-direction in dPopt/dI-I curve and IdV/dI-I curve are all correclated with the reliability of laser diode.Noise method as a new method to estimate the reliability of laser diodes has been widely investigated, and many references shown that there is correlation between the low frequency noise (LFN) and the reliability of laser diode. LFN is sensitive to the degradation and defect of the devices, and can be used as an usful method to estimate reliability. Moreover, noise investigation is also important for low noise investigation. The third primary problem, the 1/f noise characteristics and there relation to reliability are investigated, in this paper. The 1/f noise peak is measured and investigated, and the relations to reliability are also investigated. All these above can be used as a reference to study the 1/f noise under very low current bias.The amplitudes (BV) of low frequency 1/f noise at low bias currents (10-6A¹0-3A) are investigated on 42 high power InGaAsP/GaAs QW laser diodes. It is found that the intact 1/f noise peak (BV peak) can be observed if the injection current is low enough. Theoretical and experimental results indicate that the BV peak is an indicator of nonlinearity of laser diodes, and it is correlated with the parallel linear current leakage in laser diodes, and the current leakage can result in the right-shifted BV peak. We also concluded that the 1/f noise on the right side of the BV peak is correlated with the active region, and the 1/f noise on the left side of the BV peak is correlated with the parallel current leakage region around active region. This study proposed a reference for the noise diagnosis of current leakage.The DC characteristics (V-I and IdV/dI) and the LFN characteristics are indicaters of reliability of laser diodes. The correlations between these characteristics are the last problem to investigate in this paper. It is well known that methods with the correlation can only reflect the same defect in laser diode, while the methods with the noncorrelation can reflect different defect. So it is very important to investigate the correlations between the different methods. In this paper, the correlations between the DC and the LFN methods are investigated. The DC property and the 1/f noise property at low bias current (about 1mA) and low frequency (1.25Hz¹kHz) are investigated on the high power InGaAsP/GaAs QW laser diodes. By using DC test we found that V-I and IdV/dI-I are indicators of current leakage. By using low frequency noise (LFN) test we found that voltage noise amplitude BV∝I^β_V. Theoretical analysis and aging tests indicate that current indexβ_V is correlated with the carrier transport and current leakage mechanisms. The small |β_V| indicates that the lasers are unreliability devices with serious current leakage and non-radiative recombination. The DC characteristics (V-I and IdV/dI) and the LFN characteristics are correlated with ieality factor and derivative resistance.