Laser Diode Arrays an overview of functionality and operation Jason Tang ECE 355 12 3 2001 Laser Diode Arrays LDA z z z z z z Primary Use in Research and Industry Technical Aspects and Implementations Output Performance How They Work Future Areas of Application Summary Primary use Diode Pumping of Solid State Laser z z z Spatially incoherent arrays are efficient pumps for solid state lasers Monolithic Diode Arrays fabricated from GaxAl1 xAs emit wavelengths in a 700nm 800 nm range This range coincides with strong absorption bands of solid state laser ions such as Nd Ho Er and Pm Diode Pumped Laser System z Typically the diode arrays are stacked and their output is coupled into a Nd YAG rod Typical Technical Specifications z z z z 100 um wide diode laser array for end pumping of Nd YAG Gain guided high reflection rear facet coating effective length of 500 um Ith 50 mA maximum peak overall electrical to optical efficiency tops off at 54 ohmic losses in crystal increase as the square of the current Thermal Effects z z z z Wavelength shift due to temperature increase typically around 0 3 nm K Efficiency is reduced by the ohmic electrical losses in the crystal and contacts Solutions include incorporation of a low conductivity heat spreader between the LDA and mount plate Design rules allow for varying of thickness of mounting plates to account for waste heat removal Efficiency output power Wavelength Chirp Coupling into Solid State Laser z End pumped z Side Pumped z Advantage large absorption path and efficient utilization of overlapping light Advantage large area available for illumination Disadvantage exhibits inferior mode matching and short absorption length Fiber Coupled Advantage Physical separation lowers effective thermal resistance and relaxes demand for heat transfer Disadvantage Optical brightness is attenuated significantly after propagating through length of fiber and at interfaces Array Lifetime z z End of life is defined as time interval at which the current increases by 50 in order to sustain constant output power Results of limited testing show that wavelength shifts are not significant Output Power of various LDA s Coupling Mechanism Evanescent in phase out of phase Diffraction Leaky Wave cw pulsed Maximum Power Diffraction Limited Narrow Beam 0 05W 0 05W 0 2W 3 DL 0 3W 1 5 DL 0 1W 3 DL 0 5W 2 1W 1W 1 7 DL 32W 2 3 DL Leaky Mode LDA s z z The antiguide core has index n lower than the index of the cladding Quantum mechanically this is equivalent to a quasibound state above a potential barrier Radiation is only partially reflected at the boundaries thus providing outwardly leaking radiation Ray Optics Representation z z Since the high index interelement regions had no gain only leaky array modes could lase This allowed for phase locking of multiple quantum wells High Power Arrays Past and Present Applications z z z z z z Free space optical communications Parallel optical signal processing Optical Interconnects Multi channel Optical Recording Materials Processing Medical Applications Free Space Optical Communications Metropolitan Data Transport Optical Signal Processing Optical Interconnects z z Free space optical interconnections within VLSI circuitry are used to create new computing and networking architectures with high I O rates in excess of 1 terabit second They eliminate the on chip I O bottleneck by creating dense optical off chip connections 30 000 cm2 that operate at on chip clock rates Optical Interconnects within VLSI z Four stage system that performs parallel pipelined cellular logic processing Green lines electronic control signals to each stage Red lines 2 D optical interconnect channels between stages Materials Processing z High power LDA s used for Welding Stripping Cladding Heat Treating Medical Applications z z z z 10 W of output power wavelength 808 nm Cutting Coagulating and Closing of wounds NASA and Air Force field tested units Summary z z Laser Diode Arrays have been developed for various applications the most prevalent being pumping of solid state lasers Future areas of research will find new uses for the high power output of LDA s