Giulia Marcello

The role of the optical trans-characteristics in laser diode analysis

Abstract Current and/or photon crowding are indicted as a risk factor for high modulation speed laser diodes. A prompting field failure case is complemented with detailed the analysis of the DC measurements, highlighting the role of the transcharacteristics, and EBIC mapping.

Extended Modal Gain Measurement in DFB Laser Diodes

A practical method is proposed for complete gain measurement in distributed feedback (DFB) laser diodes. It is non-destructive and does not require any reference device. It includes the whole range of continuous gain values, from its minimum to threshold, passing through the transparency condition. The method requires a single absolute gain measurement for calibration. An example is reported for a DFB preserving Fabry–Perot multi-modes in the sub-threshold regime.

Side-Mode Excitation in Single-Mode Laser Diodes

A double-peaked spectrum in some distributed feedback laser diodes is demonstrated to relate to axially confined catastrophic optical damage (COD), followed by the excitation of a transversal optical mode. The melting-regrowth kinetics of CODs also reveal another possibility of COD-induced side optical modes in a fiber distributed Bragg reflector pump laser diode. A third case completely reverses the cause-effect relationship between CODs and lateral optical harmonics.

Proton Irradiation Effects on Commercial Laser Diodes

Time evolving alterations have been observed in DFB and VCSEL laser diodes after 3MeV proton irradiation. Kinetics are consistent with a diffusion process. The calculated and measured turning point for the alterations in the VCSEL allows to estimate the diffusion coefficient for the moving species. It results close to the known diffusion coefficient for H atoms in semiconductor crystals.

Clamp voltage and ideality factor in laser diodes

Abstract A recent model for laser diodes was applied to the decomposition of the experimental characteristics of several laser diodes into their fundamental components. This pointed out a problem involving the ideality factor and the clamp voltage. The two quantities indicate largely different values of the internal voltage, not explained or predicted by any theory. The solution of the puzzle requires going back to points as fundamental as the meaning of locality of band-to-band transitions in quantum or bulk active regions

Seed laser diodes in pulsed operation: limitations and reliability

Using InGaAs/AlGaAs 1060nm commercial Laser Diodes (LDs) and Laser Diode Modules (LDMs) under high current (> 2A) and nanosecond pulsed conditions offers a large flexibility for fiber Laser seeding applications. Nevertheless, the behavior and long term reliability of these LDs under such conditions is not well established. Our work focuses on determining the reliability of 1060nm seed LDs under such conditions by the extraction of Electro-Optical (EO) characteristics and the monitoring of their evolution during pulsed ageing tests. In this context, two segments of parasitic oscillations (“A” and “B” type) were observed in the optical response of LDs and LDMs driven under such conditions, with their associated threshold current (IthA and IthB) on three batches of Laser diodes, with different packaging. We observed a strong part-to-part variation in the value of IthA and a package dependency for IthB. We conducted a near-field and a time spectral analysis of the LDs optical responses. A near field widening, associated with A-type oscillations, and a temporal spectral broadening, associated with A-type and B-type oscillations, were highlighted. Step-stress ageing tests were then carried out on two batches of three LDMs each, with different values of IthA (3.9A, 7A and 11.2A for the first batch, 2.8A, 7.4A and 9.3A for the second). The modules with the lowest IthA values were the first to fail suggesting this IthA threshold as a key parameter for early failure detection. One module exhibited a gradual drop of the measured optical power. No variation of the optical power or of the IthA and IthB value were observed on the other modules, which were able to withstand the chosen ageing conditions without any noticeable decrease of their performances.

Practical optical gain by an extended Hakki-Paoli method

Abstract The revision of the classic Hakki-Paoli method shows that the a priori knowledge of facet reflectivity and confinement factor is not required for measuring optical gain in semiconductor laser and LED emitters. Moreover, a recently proposed new formula for gain as a function of the applied voltage, combined with that method, allows for calculating the relevant parameters of the gain function by the sole sub-threshold spectral data. This avoids the known critical problems issued by instrument resolution on spectral data from the above-threshold domain. Moreover, this last chance allows for complete gain measurement also in degraded devices, when they do no more display any laser threshold, and then for including optical gain among the relevant parameters for monitoring device degradation.

ESD tests on 850 nm GaAs-based VCSELs

Abstract Forward and reverse HBM, MM, CDM ESD tests have been performed on 850-nm VCSELs, together with EOS and overpower test. The physical analysis of the tested devices showed a variety of damages not easily correlated to the measured electro-optical degradations. The solution requires the detailed interpretation of the observed physical mechanism, by means of electron microscopy and device modelling.