Spectral region beyond 1.7 μm is particularly interesting for biomedical spectroscopic sensing applications due to the presence of strong and molecule-specific ro-vibrational overtone and combination absorption bands for a number of important analytes such as glucose, lactate, urea, human serum albumin among others. However, this spectral region has been largely unexplored for applications targeting wearable device technology due to the absence of commercially available semiconductor light source technology. In this work we report on recent progress in developing beyond-stateof-the-art GaSb-based swept-wavelength laser technology as a key building-block of the proposed spectroscopic sensor concept. To demonstrate the capability of the technology, we provide experimental data of in vitro sensing concentrations down to the normal physiological range and beyond for glucose, lactates, urea and bovine serum albumin. Furthermore, we provide initial experimental evidence of non-invasive in vivo sensing experiment with extracted absorbance signature of human serum albumin collected from the wrist and demonstrate a clear path towards sensing other analytes. Finally, to demonstrate the full potential of the spectroscopic sensor technology for the wearable device market, we present results of our initial effort to realize a complete spectroscopic sensor system-on-a-chip based on hybrid GaSb/Si material platform and manufactured using conventional 200 mm silicon-on-insulator CMOS technology process in a commercial high-volume foundry.
The proliferation of man-portable air-defense systems (MANPADS) is extremely wide. MANPADS are responsible for over 60% of total aircraft casualties since 1960’s. It is estimated that over 500,000 of these systems are deployed worldwide with a large number being out of governmental control. Directional infrared countermeasure (DIRCM) systems have been deployed in order to counter the threat. Laser based DIRCM system requires laser sources which can operate in bands I, II and IV. Up to day bands II and IV are covered by compact and lightweight quantum cascade lasers (QCLs), but for wavelength generation in band I, bulky and expensive solid-state or fiber laser solutions are used. Recent development of GaSb laser diode technology at Brolis Semiconductors greatly improved optical output powers and efficiency of laser diodes working in 1900 - 2450 nm range (band I). In this work we present a laser diode module which is based on incoherent beam combining of two high-power GaSb laser diode emitters working in 2.1-2.3 μm spectral band. This laser module is capable of providing directional beam with radiant intensity value of more than 30 kW/str. Module is extremely compact and lightweight (<50 g). E-O efficiency of the module is 15% and it can be operated in CW or pulsed operation modes replicating any waveform required for DIRCM application.
Continuous advances in low-cost MANPAD heat-seeking missile technology over the past 50 years remains the number one hostile threat to airborne platforms globally responsible for over 60 % of casualties. Laser based directional countermeasure (DIRCM) technology have been deployed to counter the threat. Ideally, a laser based DIRCM system must involve a number of lasers emitting at different spectral bands mimicking the spectral signature of the airborne platform. Up to now, near and mid infrared spectral bands have been covered with semiconductor laser technology and only SWIR band remained with bulky fiber laser technology. Recent technology developments on direct-diode GaSb laser technology at Brolis Semiconductors offer a replacement for the fiber laser source leading to significant improvements by few orders of magnitude in weight, footprint, efficiency and cost. We demonstrate that with careful engineering, several multimode emitters can be combined to provide a directional laser beam with radiant intensity from 10 kW/sr to 60 kW/sr in an ultra-compact hermetic package with weight < 30 g and overall efficiency of 15 % in the 2.1- 2.3 micron spectral band offering 150 times improvement in efficiency and reduction in footprint. We will discuss present results, challenges and future developments for such next-generation integrated direct diode DIRCM modules for SWIR band.
Compact high-power 2100 nm laser diode module for next-generation directional infrared countermeasure (DIRCM) systems is presented. Next-generation DIRCM systems require compact, light-weight and robust laser modules which could provide intense IR light emission capable of disrupting the tracking sensor of heat-seeking missile. Currently used solid-state and fiber laser solutions for mid-IR band are bulky and heavy making them difficult to implement in smaller form-factor DIRCM systems. Recent development of GaSb laser diode technology greatly improved optical output powers and efficiencies of laser diodes working in 1900 - 2450 nm band  while also maintaining very attractive size, weight, power consumption and cost characteristics.<p> </p> 2100 nm laser diode module presented in this work performance is based on high-efficiency broad emitting area GaSb laser diode technology. Each laser diode emitter is able to provide 1 W of CW output optical power with working point efficiency up to 20% at temperature of 20 °C. For output beam collimation custom designed fast-axis collimator and slow-axis collimator lenses were used. These lenses were actively aligned and attached using UV epoxy curing. Total 2 emitters stacked vertically were used in 2100 nm laser diode module. Final optical output power of the module goes up to 2 W at temperature of 20 °C. Total dimensions of the laser diode module are 35 x 25 x 16 mm (L x W x H) with a weight of ~28 grams. Finally output beam is bore-sighted to mechanical axes of the module housing allowing for easy integration into next-generation DIRCM systems.
In this work we present latest achievements on gain chips as sources for single-frequency tunable laser absorption spectroscopy and sensing. External cavity lasers based on Brolis Semiconductors (2.05 – 2.45) μm wavelengths GaSb gain chips exhibited single mode laser emission with linewidths <100 kHz and output powers of <5 mW in the entire tuning range of <100 nm per chip. Continuous current tuning of 60 GHz and mode-hop free piezo tuning of 26 GHz were demonstrated. Additionally, we report on extended wavelengths range by demonstrating low spectral modulation 850 nm GaAs-based gain chips. Finally, experimental results on GaSb-based gain chip integration with silicon photonics are presented.