Spaceborne lidar (light detection and ranging) systems have a large potential to become powerful instruments in the field of atmospheric research. Obviously, they have to be in operation for about three years without any maintenance like readjusting. Furthermore, they have to withstand strong temperature cycles typically in the range of -30 to +50 °C as well as mechanical shocks and vibrations, especially during launch. Additionally, the avoidance of any organic material inside the laser box is required, particularly in UV lasers. For atmospheric research pulses of about several 10 mJ at repetition rates of several 10 Hz are required in many cases. Those parameters are typically addressed by DPSSL that comprise components like: laser crystals, nonlinear crystals in pockels cells, faraday isolators and frequency converters, passive fibers, diode lasers and of course a lot of mirrors and lenses. In particular, some components have strong requirements regarding their tilt stability that is often in the 10 μrad range. In most of the cases components and packages that are used for industrial lasers do not fulfil all those requirements. Thus, the packaging of all these key components has been developed to meet those specifications only making use of metal and ceramics beside the optical component itself. All joints between the optical component and the laser baseplate are soldered or screwed. No clamps or adhesives are used. Most of the critical properties like tilting after temperature cycling have been proven in several tests. Currently, these components are used to build up first prototypes for spaceborne systems.
In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock
resistant mounting technique by soldering of optical components. Based on this technique a new generation of laser
sources for aerospace applications is designed. In these laser systems solder technique replaces the glued and bolted
connections between optical component, mount and base plate. Alignment precision in the arc second range and
realization of long term stability of every single part in the laser system is the main challenge.
At the Fraunhofer Institute for Laser Technology ILT a soldering and mounting technique has been developed for high
precision packaging. The specified environmental boundary conditions (e.g. a temperature range of -40 °C to +50 °C)
and the required degrees of freedom for the alignment of the components have been taken into account for this technique.
In general the advantage of soldering compared to gluing is that there is no outgassing. In addition no flux is needed in
our special process. The joining process allows multiple alignments by remelting the solder. The alignment is done in the
liquid phase of the solder by a 6 axis manipulator with a step width in the nm range and a tilt in the arc second range. In a
next step the optical components have to pass the environmental tests. The total misalignment of the component to its
adapter after the thermal cycle tests is less than 10 arc seconds. The mechanical stability tests regarding shear, vibration
and shock behavior are well within the requirements.
Laser diodes and diode laser bars are key components in high power semiconductor lasers and solid state laser systems.
During manufacture, the assembly of the fast axis collimation (FAC) lens is a crucial step. The goal of our activities is to
design an automated assembly system for high volume production. In this paper the results of an intermediate milestone
will be reported: a demonstration system was designed, realized and tested to prove the feasibility of all of the system
components and process features. The demonstration system consists of a high precision handling system, metrology for
process feedback, a powerful digital image processing system and tooling for glue dispensing, UV curing and laser
operation. The system components as well as their interaction with each other were tested in an experimental system in
order to glean design knowledge for the fully automated assembly system. The adjustment of the FAC lens is performed
by a series of predefined steps monitored by two cameras concurrently imaging the far field and the near field intensity
distributions. Feedback from these cameras processed by a powerful and efficient image processing algorithm control a
five axis precision motion system to optimize the fast axis collimation of the laser beam. Automated cementing of the
FAC to the diode bar completes the process. The presentation will show the system concept, the algorithm of the
adjustment as well as experimental results. A critical discussion of the results will close the talk.
System integrators are driven by the demands of hybrid module manufacturers to provide machines with a higher
degree of system integration while maintaining full process automation at max. throughput and yield. The full automated packaging process involves Pick&Place of several components like photo diode, laser sub-mount, integrated optical chip and PCB. Whereby some components are placed passively supported by vision inspection and some are aligned actively by closing a control loop on nano-scale precision. The system applies adhesive bonding for
fixation of the components.
The presentation shows how various assembly steps are combined in one machine concept for assembling and qualifying complex hybrid modules. Therefore modern assembly machines relay to special hardware designs i.e. for trays, chucks, motion concepts and calibration systems as well as for software features as data base interfaces, recipe
controlled processes and flexible process editor. However beside hardware and software feasibility also necessary device
characterisation is an important feature in assembly machines.
In optoelectronics diode lasers and especially diode laser bars are playing an important role for applications in high
power diode lasers as well as diode laser pumped solid state lasers. Inside the manufacturing process of laser bar systems
the electro optical test of laser bars is essential to sort out the good parts which fulfil the quality specified.
An electro optical test station was developed and integrated which performs the so called LIV test. The voltage vs.
current, the intensity vs. current and spectral distribution of each of the emitters can be measured and logged. The results
will be evaluated and according to flexible parameter management the decision about acceptable quality is supplied
automatically. The data will be processed by data base capabilities, hence this the system can be integrated into the
general manufacturing data management.
Due to the modular design of the test station it is capable to be integrated in a fully automated visual inspection and test
system suitable for mass production as well as in a semi automated system which fits more the demands of R&D
applications. The design of the test station, test results and a critical discussion of advantages will be presented.