John Himmelreich

Reverse-proton-exchanged waveguide frequency doublers for green light generation

We describe reverse-proton exchanged (RPE) waveguides in MgO-doped lithium niobate capable of stable secondharmonic generation (SHG) of over 100 mW of CW green light with conversion efficiency exceeding 200%/Wcm2. Substantially higher green power would require careful thermal management to limit the phase mismatch due to heating produced by optical absorption. RPE waveguides show ability to support high-power generation of green light superior to anneal-proton exchanged (APE) waveguides containing a higher-index layer. We also demonstrate devices with multipeak spectral response for speckle-reduced green laser by using phase-modulated, quasi-periodic ferroelectric domain structure.

Design of athermalized proximity coupled (APC) synthetic green laser opto-electronic package for microprojector displays: Numerical modeling and experiments

Micro-projector based displays are proposed for information display for a number of consumer devices. These displays would provide larger images than existing fixed Liquid crystal displays. The two major components of micro-projector technology are the Light source and the Imaging technology. Three primary colors, red, blue and green are required to create full color images. The light sources in the projection technology would be semiconductor devices that emit these colors. These devices could be either light emitting diodes (LEDs) or lasers. To enable the laser based projection technology, red and blue lasers are commerically available. Native semiconductor green lasers are still in development. As an alternative, synthetic green light can be produced by passing 1060nm infra-red light emitted from a GaAs based semiconductor laser diode (LD) through second harmonic generation (SHG) crystal, thereby emitting the green light at 530 nm. The current research work proposes bringing the SHG structure in close proximity to the LD, thereby eliminating the use of any optics in between. The proximity coupling approach promises to reduce the number of package components and process cost significantly. This paper presents the mechanical package design, coefficient of thermal expansion based displacement estimates, thermal analysis wherein the thermal impedance is predicted and measured, thermo-mechanical analysis wherein the thermo-mechanical stresses and strains are predicted. Shock modeling has been done to understand the displacements of the waveguides during the shock event. Optical modeling is performed to estimate the coupling efficiency change as a function of lateral and longitudinal offset between the LD and SHG waveguides. Finally, an assembled package that generated green light using this design is presented.

A Novel Precision Die Attach Technique for Opto-Electronics Packaging

Semiconductor Laser diodes that emit visible light have various interesting applications such as sensing, high density optical storage and projection displays. In any opto-electronic package, the laser diode chips are typically attached or soldered to metal or ceramic substrates that have good thermal conductivity and are well-matched in coefficient of thermal expansion using solder. Some applications require a critical alignment of the front facet of the laser diode to the front edge of the substrate onto which the laser diode chip is attached to. Depending on the application, the alignment precision could be varying from 20 μm to being as stringent as 0.5 to 1 μm. In many of these applications, the cost of packaging is also a very important factor. In such applications, it is essential to develop a laser diode chip bonding process that can meet such stringent die alignments along with a low cost manufacturing process. Therefore, the objective of this research work is to provide a low cost alternative solution for die attach process that can guarantee alignment precision of 0.5 to 1 microns and can be easily adapted to high volume manufacturing. The novel technique proposed in this work uses primarily gravity force for the facet alignments between the two components. In this passive-gravity assisted precision (P-GAP) assembly process, the laser diode (LD) chip is placed on the substrate using a traditional pick and place machine and later the substrate and the chip are tilted such that the chip slides on the substrate due to the gravity and touches a mechanical stop in-front of them. This does not involve any active alignment. In addition, we have provided few ideas to improve the sliding when gravity is used. This technique has been implemented on several samples and the feasibility of achieving the alignment precision to within a micron was demonstrated.Copyright