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.
New phenomena are observed in the optical response of InGaAs/AlGaAs 1060nm Laser Diodes (LDs) and Laser Diode Modules (LDMs) driven under high peak current condition: two segments of parasitic oscillations appear in the optical response of every tested LD and LDM, when increasing the current above two respective thresholds. In order to understand their origins and to discuss their influence over the operation range and reliability of seed LDs, we designed a test bench, based on an Electro-Optical Modulator, devoted to the time-spectral analysis of LD optical responses under such conditions. A correlation was found between the presence of the first segment of oscillations on the optical response and a temporal broadening of the LD spectrum. The presence of the second segment of oscillations is associated with a red-shift of the LD spectrum, but not with a significant spectral broadening, suggesting different causes for these phenomena. Step-stress ageing tests have then been carried out, in order to estimate the evolution of those parasitic oscillations over the lifetime of these LDs for reliability investigations.
Cathodoluminescence (CL) analysis of high power laser diodes permits to reveal the main defects issued from the catastrophic optical degradation (COD). These defects are revealed as discontinuous dark lines along the ridge. The different levels of damage are analysed, and a thermomechanical model taking account of the thermal and mechanical properties of the laser structure is settled up. In this model the COD is described as a local temperature enhancement, which generates thermal stresses leading to the generation of dislocations, which are responsible for the degradation of the thermal conductivity of the of the active zone of the laser.
In this study, we report on a methodology based on reverse and forward current-voltage curves (I-V) and on Degree of Polarization (DoP) of electroluminescence measurements on 980 nm laser diodes chip-on-submount (CoS) for the improvement of screening tests. Current-voltage curves are performed at reverse bias up to breakdown voltage (VBR) using both a high current accuracy (< 1 pA) and high voltage resolution (< 10 mV) at different submount-temperatures (20-50°C). The DoP of luminescence of such devices, related to strains in materials and effect of shear strain on the birefringence, is calculated from the simultaneous measurement of TE (LTE) and TM (LTM) polarized light emissions. We observe that application of high reverse voltages occasionally produces significant micro-plasma (MP) pre-breakdown on reverse I-V characteristics as recently observed in InGaN/GaN LEDs and assumed to be a response of electrically active defects. Comparisons between breakdown voltages and number of MP, and changes of leakage current at low forward voltage (< 0.1 V) are considered. DoP measurements are also analyzed versus temperature. Finally the usefulness of these measurements for effective screening of devices is discussed.
High power 14xx laser pumps are more and more required for eye safe industrial, medical, safety and defense
applications as well as for increased telecom network capability (e.g. for 100 Gb Ethernet). However, this need of high
power requires to control the overall power consumption in a range in line with systems requirements. In this respect, 3S
PHOTONICS has developed a 14xx nm single mode laser diode with record internal losses of 1.5 cm-1 compared to the
2.7 cm-1 reported up to now. These lasers are based on p/nBH technology and use the asymmetric waveguide concept to
reduce internal losses. The record loss value, coupled to an internal efficiency higher than 0.8, allows realization lasers of
3 mm length with external efficiency higher than 0.5 W.A-1 at 25°C in AR/HR coating configuration. Modules using
direct coupling technology were realized. High coupling efficiency is obtained thanks to the 8° x 14° far field pattern of
the diode. Output power of 550 mW at 1.8 A is thus obtained, with or without FBG stabilization, with maximum output
power above 700mW. Thanks to the lasers' length, voltage at this current level is below 1.9 V, which gives a reduced
thermal load. Thus, the overall modules electrical consumption remains lower than 10 W at case temperatures ranging
from 0°C to 75°C. The 3 mm length also guaranties high reliability of these laser diodes.
Bonding-induced mechanical stress in GaAs-based laser diodes is studied by numerical and experimental techniques.
This stress, induced by the soldering processes, appears when cooling down the assembly because of Coefficient of
Thermal Expansion (CTE) mismatch, and dimensional disparities. Detailed mechanisms taking place are not fully
understood. Residual stress is also known to influence device reliability. Composite submounts studied are composed of
a CuW heat spreader on an AlN bottom plate in standard and optimized designs to lower mechanical stress levels. CuW
shows a high thermal conductivity and a matched CTE with GaAs. Plain AlN submounts are studied as a reference. The
numerical technique is a Finite Element Method calculation to compute the stress tensor induced in GaAs-based laser
diodes during the soldering process on submounts with 80-20 AuSn eutectic solder pads. Starting with 31 MPa on the
plain AlN submount, the standard composite submount gives 23.5 MPa while the optimized version is as low as 12 MPa.
The experimental technique consists of Degree of Polarization (DoP) measurements of the photoluminescence emitted
by a planarized diode bonded to a submount. From the DoP, relative stress variations induced by the submount are
estimated. Starting with DoP referenced at 100% on plain AlN submounts, the standard composite submount gives 46%
DoP reduction while the optimized version is expected to exhibit a reduction larger than 65%. Composite submounts
with reduced mechanical stress and preserved thermal properties were studied experimentally and theoretically. An
optimized design allows reducing the mechanical stress by a factor 2.5 at least.
Most Pulsed Fiber Lasers (FLs) are built on a Master Oscillator - Power Amplifier (MOPA) architecture, as this
configuration has the advantage, among others, of exploiting direct modulation of the diode laser seed (the MO) to reach
high repetition rates and high peak-power pulsed operation. To enhance the FL global performance and reliability, high
power single-lateral-mode 1064 nm diodes with outstanding long-term behavior are needed. The reliability of these
devices at high power has been a challenge for years, due to the high built-in strain in the Quantum Well (QW). In this
paper, we present excellent reliability results obtained, in both cw and pulsed conditions, on the latest generation of 1064
nm single-lateral-mode diodes developed at 3S PHOTONICS. Aging tests in cw conditions prove the intrinsic robustness
of the diode even at very high junction temperatures, while specific tests in pulsed operation at 45 °C heat-sink
temperature, and high repetition rates of several hundred kHz, confirm the stability of the devices in accelerated
conditions directly derived from real applications. Both free-running and wavelength stabilized (by means of a Fiber
Bragg Grating (FBG)) packaged devices show very stable performances under pulsed conditions. Reliable operation at
higher average power than currently commercially available diode lasers seeds is demonstrated.
Low levels of intensity noise in semiconductor lasers is a key feature for numerous applications such as high resolution
spectroscopy, fiber-optic sensors, signal distribution in broadband analog communications as CATV, and more generally
for microwave photonics systems. In particular, a DFB laser with very low relative intensity noise (RIN) levels from 0.1
to 20 GHz is a key component as it correspond to the whole frequency bandwidth of interest for radars. Several
approaches have been reported but most suffer from the compromise between RIN level and power out level and
stability, with RIN level in the range -150 dB.Hz-1 to -155 dB.Hz-1 in this frequency range [1,2]. We report here results
from a new AlGaInAs DFB laser developed at 3S PHOTONICS. Excellent device performance is observed across an
operating range from the laser threshold up to the thermal roll-over. Pure longitudinal single mode at 1545 nm is
obtained over the whole current operating range with side mode suppression ratio higher than 50dB. The maximum
output power reaches up to 130 mW. In these conditions, RIN levels below -160 dB.Hz-1 is obtained in up to 20 GHz.
These are the best results to our knowledge combining such high single mode output power with such low RIN level in
the frequency range 0.4-20 GHz.
M. Bettiati, V. Cargemel, P. Pagnod, C. Hervo, P. Garabedian, P. Issert, L. Raymond, L. Ragot, J.-C. Bertreux, J.-N. Reygrobellet, C. Crusson, F. Laruelle
Single-mode 980 nm pump lasers are mature products needed in an increasing range of applications and their power
level has been constantly raised in the last fifteen years from a few tens of mW for the first generations of devices up to
the current maximum level of 750 mW fiber-coupled output power. As the fiber output power increases, new
applications provide positive feed-back to continue the development of these devices, although severe constraints are
imposed both by reliability and the need for wavelength stabilization, which is generally built on the utilization of Fiber
Bragg Gratings (FBGs). We have developed in 2005 a record saturation power device (Psat=2.35W @ 25 °C, for 3.9
mm cavity lengths) whose fiber-coupled power has reached 750 mW for 25 °C cooled applications, limited mainly by
reliability as wavelength stabilization was already demonstrated up to levels above 1 Watt. 3S PHOTONICS has now
developed a new generation of powerful and reliable devices that allow foreseeing operation at or close to 1W for cooled
applications. We have further optimized the vertical structure to reduce the internal losses, and to reduce the junction
temperature for increased reliability. High kink-currents around 2.5 A have been measured on the best devices. The gain
bandwidth has been engineered to allow maintaining the wavelength stabilization even on very long laser cavities.
Encouraging preliminary reliability results have also been obtained.
We demonstrate very high reliability level on 980-1060nm high-power single-mode lasers through multi-cell tests. First,
we show how our chip design and technology enables high reliability levels. Then, we aged 758 devices during 9500
hours among 6 cells with high current (0.8A-1.2A) and high submount temperature (65°C-105°C) for the reliability
demonstration. Sudden catastrophic failure is the main degradation mechanism observed. A statistical failure rate model
gives an Arrhenius thermal activation energy of 0.51eV and a power law forward current acceleration factor of 5.9. For
high-power submarine applications (360mW pump module output optical power), this model exhibits a failure rate as
low as 9 FIT at 13°C, while ultra-high power terrestrial modules (600mW) lie below 220 FIT at 25°C. Wear-out
phenomena is observed only for very high current level without any reliability impact under 1.1A.
For the 1060nm chip, step-stress tests were performed and a set of devices were aged during more than 2000 hours in
different stress conditions. First results are in accordance with 980nm product with more than 100khours estimated
MTTF. These reliability and performance features of 980-1060nm laser diodes will make high-power single-mode
emitters the best choice for a number of telecommunication and industrial applications in the next few years.
We report on the development of a new generation of very high power 980 nm single lateral mode ridge-waveguide quantum-well lasers. An asymmetric-waveguides vertical structure has been optimized for very low internal losses while keeping the vertical mode-size large, thus allowing a low vertical far-field beam angle of less than 19°. Careful optimization of the doping profiles, and epitaxial interfaces optimization for reduced scattering, allowed to obtain internal losses as low as 0.6-0.7 cm-1. Such low losses are necessary to keep the external efficiency high in very long cavities, together with a high internal quantum efficiency. We thus reached our goal of keeping the external efficiency above 70% even for cavity lengths of 4.5 mm. The flared ridge waveguide has been designed to strongly filter higher order lateral modes, and kink-free operation has been obtained up to over 1.5 W output power, with very stable vertical and horizontal beam patterns. High saturation powers above 2 W have also been demonstrated at 25°C, and over 1.5 W at 75°C. Wavelength stabilized chips, by means of a fiber Bragg grating, reached linear fiber powers above 1.0 W with strong suppression of gain-peak lasing at all currents and good power stability.
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