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.
III-V/silicon photonic integrated circuits (ICs) promise to enable low cost and miniature optical sensors for trace-gas detection, bio-sensing and environmental monitoring. A lot of these applications can benefit from the availability of photonic ICs beyond the telecommunication wavelength range. The 2 μm wavelength range is of interest for spectroscopic detection of many important gases and blood constituents. In this contribution we will present 2 μmwavelength-range III-V/silicon photonic ICs consisting of tunable laser sources, photodetectors and silicon waveguide circuits. Silicon waveguides with a loss of ~0.5 dB/cm are obtained in a well-established silicon photonics platform. Based on the waveguides, low insertion loss (2-3 dB) and low crosstalk (25-30 dB) arrayed waveguide gratings (AWGs) are realized for the 2.3 μm wavelength range. Active opto-electronic components are integrated on the photonic IC by the heterogeneous integration of an InP-based type-II epitaxial layer stack on silicon. III-V-on-silicon 2.3 μm range distributed feedback (DFB) lasers can operate up to 25 °C in continuous-wave regime and shows an output power of 3 mW. By varying the silicon grating pitch, a DFB laser array with broad wavelength coverage from 2.28 μm to 2.43 μm is achieved. III-V-on-silicon photodetectors with the same epitaxial layer stack exhibit a responsivity of 1.6 A/W near 2.35 μm. In addition, we also report a 2 μm range GaSb/silicon hybrid external cavity laser using a silicon photonic IC for wavelength selective feedback. A wavelength tuning over 58 nm and side mode suppression ratio better than 60 dB is demonstrated.
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 [1] while also maintaining very attractive size, weight, power consumption and cost characteristics.
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.
One of the most important factor of success in battlefield is the ability to remain undetected by the opposing forces while also having an ability to detect all possible threats. Illumination and pointing systems working in NIR and SWIR bands are presented. Wavelengths up to 1100 nm can be registered by newest generation image intensifier tubes, CCD and EMCCD sensors. Image intensifier tubes of generation III or older are only limited up to wavelength of ~900 nm [1]. Longer wavelengths of 1550 nm and 1625 nm are designed to be used with SWIR electro-optical systems and they cannot be detected by any standard night vision system. Long range SWIR illuminators and pointers have beam divergences down to 1 mrad and optical powers up to 1.5 W. Due to lower atmospheric scattering SWIR illuminators and pointers can be used at extremely long distances up to 10s of km and even further during heavy weather conditions. Longer wavelengths of 2100 nm and 2450 nm are also presented, this spectrum band is of great interest for direct infrared countermeasure (DIRCM) applications.
State-of-the-art SWIR and LWIR electro-optical systems are presented. Sensitive InGaAs sensors coupled with “fast" (low F/#) optical lenses can provide complete night vision, detection of all NIR and SWIR laser lines, penetration through smoke, dust and fog. Finally beyond-state-of-the-art uncooled micro-bolometer LWIR systems are presented featuring ultra-high sensor sensitivities of 20 mK.
In this work we present latest results on mid-infrared GaSb gain chips as high-output power narrow-linewidth continuouswave single-frequency laser sources for ultra-widely tunable spectroscopy and sensing applications. More than 30 mW CW output power with over 100 nm / chip tuning and < 1 MHz linewidth performance is demonstrated in the entire band from 1900 nm – 2450 nm covering most essential absorption features from CO, CO2, NH3, CH4 and N2O for environmental and medical applications. Finally, we report on complete single-frequency laser system with integrated gain-chip for highresolution spectroscopy and sensor applications.
Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of
numerous enabling applications in the field of gas sensing, medical, and defense applications. Gas sensing in this spectral
region is attractive due to the presence of numerous absorption lines for such gases as methane, ethane, ozone, carbon
dioxide, carbon monoxide, etc. Sensing of the mentioned gas species is of particular importance for applications such as
atmospheric LIDAR, petrochemical industry, greenhouse gas monitoring, etc. Defense applications benefit from the
presence of covert atmospheric transmission window in the 2.1-2.3 micron band which is more eye-safe and offers less
Rayleigh scattering than the conventional atmospheric windows in the near-infrared. Major requirement to enable these
application is the availability of high-performance, continuous-wave laser sources in this window. Type-I GaSb-based
laser diodes are ideal candidates for these applications as they offer direct emission possibility, high-gain and continuous
wave operation. Moreover, due to the nature of type-I transition, these devices have a characteristic low operation
voltage, which results in very low input powers and high wall-plug efficiency.
In this work, we present recent results of 2 μm – 3.0 μm wavelength room-temperature CW light sources based
on type-I GaSb developed at Brolis Semiconductors. We discuss performance of defense oriented high-power multimode
laser diodes with < 1 W CW power output with over 30 % WPE as well as ~ 100 mW single TE00 Fabry-Perot chips. In
addition, recent development efforts on sensing oriented broad gain superluminescent gain chips will be presented.
Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of numerous enabling applications in the field of gas sensing, medical, environmental and defense applications. Major requirement for these applications is the availability of laser sources in the atmospheric transmission window free of water vapor absorption, such as the 2-2.3 μm spectral window. Type-I GaSb-based laser diodes are ideal candidates for these applications being compact, electrically pumped, power efficient and able to operate at room temperature in continuous-wave. Moreover, due to the nature of type-I transition these devices have characteristic low operation voltage, typically below 1 V, resulting in low power consumption, and high-temperature of operation. In this work, we present recent progress of 2.1 μm wavelength single-spatial mode GaSb type-I laser diode development at Brolis Semiconductors. Experimental device structures were grown by solid-source multi-wafer MBE, consisting of an active region with 2 compressively strained (~1.3 %) GaInAsSb quantum wells. Epi-wafers were processed into a ridge-waveguide devices and mounted on Cu or CuW heatsink. Presented devices feature state-of-the art performance in CW mode with < 1.2 W and 30 % WPE for single emitter device as well as 9 W and 28 % WPE for a laser diode bar.
Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of numerous enabling applications in the field of gas sensing, medical, environmental and defense applications. Major requirement for these applications is the availability of laser sources in this spectral window. Type-I GaSb-based laser diodes are ideal candidates for these applications being compact, electrically pumped, power efficient and able to operate at room temperature in continuous-wave. Moreover, due to the nature of type-I transition; these devices have a characteristic low operation voltage, typically below 1 V, resulting in low power consumption, and high-temperature of operation. In this work, we present recent progress of 2.7 μm – 3.0 μm wavelength single-spatial mode GaSb type-I laser diode development at Brolis Semiconductors. Experimental device structures were grown by solid-source multi-wafer MBE, consisting of an active region with 2 compressively strained (~1.3 %-1.5 %) GaInAsSb quantum wells with GaSb barriers for 2.7 μm devices and quinternary AlGaInAsSb barriers for 3.0 μm devices. Epi-wafers were processed into a narrow-ridge (2-4 μm) devices and mounted p-side up on CuW heatsink. Devices exhibited very low CW threshold powers of < 100 mW, and single spatial mode (TE00) operation with room-temperature output powers up to 40 mW in CW mode. Operating voltage was as low as 1.2 V at 1.2 A. As-cleaved devices worked CW up to 50 deg C.
Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of
numerous enabling applications in the field of gas sensing, medical, environmental and defense applications. Major
requirement for these applications is the availability of laser sources in this spectral window. Type-I GaSb-based laser
diodes are ideal candidates for these applications being compact, electrically pumped, power efficient and able to operate
at room temperature in continuous-wave. Moreover, due to the nature of type-I transition these devices have
characteristic low operation voltage, typically below 1 V, resulting in low power consumption, and high-temperature of
operation.
In this work, we present recent progress of 2.1 μm wavelength single-spatial mode GaSb type-I laser diode
development at Brolis Semiconductors. Experimental device structures were grown by solid-source multi-wafer MBE,
consisting of an active region with 2 compressively strained (~1.3 %) GaInAsSb quantum wells. Epi-wafers were
processed into a narrow-ridge (3-5 μm) devices and mounted p-side up on CuW heatsink. Devices exhibited very low
CW threshold powers of < 30 mW, and single spatial mode (TE00) operation with room-temperature output powers up
to 200 mW in CW mode with a far-field fast axis divergence angle of ~ 57 degrees.
High temperature operation of terahertz (THz) sources based on quantum cascade lasers (QCLs) is discussed. THz QCLs are compact, powerful sources but can only operate at cryogenic temperatures. State-of-the art THz QCLs are made with GaAs/AlGaAs heterostructures and use a single composition of AlGaAs for the barrier material. It was recently shown that multi-composition barriers in the band structure can result in gain > loss at temperature as high as ~240K. We demonstrate early experimental results that yield QCLs that operate up to 184K – similar to QCLs based on single composition barrier designs. An alternative method of producing room-temperature THz is based on intra-cavity difference-frequency generation (DFG) in mid-infrared (mid-IR) QCLs. Here we report devices with record conversion efficiency. THz DFG QCLs reported previously are highly inefficient since THz radiation produced more than ~100 μm away from the exit facet is fully absorbed due to high THz losses in the QCL waveguide. Our lasers use a non-collinear Cherenkov DFG scheme to extract THz radiation from the active region. Dual-color mid-IR quantum cascade lasers with integrated giant optical nonlinearity are grown on semi-insulating (S.I.) InP substrates. THz radiation is emitted at an angle into the substrate with respect to the mid-infrared pumps. Since S.I. InP is virtually lossless to THz radiation, this scheme allows for efficient extraction of THz radiation along the whole waveguide length. As a result, our sources demonstrate large mid-infrared-to-THz conversion efficiency. Devices tested at room-temperature produced 18μW peakpower and 75μW/W2 conversion efficiency.
GaInAs/AlInAs/InP quantum cascade lasers (QCLs) have established themselves as reliable and versatile semiconductor
laser sources in the mid-infrared wavelength region. Due to the presence of unique molecular absorption lines, in
combination of water-free atmospheric transmission windows, this spectral range is of particular importance for sensing,
medical, material processing and homeland security applications. Being compact electrically pumped and able to operate
at room-temperature, QCLs are ideal choice for wavelengths between 3.5 - 12 microns. However, wavelengths above
and below are more challenging to obtain.
In our work, we use intracavity nonlinear frequency mixing in mid-infrared QCLs to extend the spectral coverage for
GaInAs/AlInAs/InP devices. We demonstrate that passive nonlinear structures, consisting of coupled quantum wells can
be grown on top of the mid-IR QCL active region. Such nonlinear structures can be designed to possess a resonant
nonlinear response for the pump frequency. Such concept, in combination with quasi-phase-matching technique can be
used for efficient short-wavelength lasing by second-harmonic generations. We demonstrated room-temperature lasing
down to 2.6 micrometer. For long-wavelengths, particularly THz frequencies, a novel waveguide concept was
introduced. Here, we used a leaky THz waveguide concept, for a difference-frequency generation device. Phase
matching was achieved by Cherenkov phase-matching scheme. This concept led to ultra-broadband THz emission at
room-temperature (1.2-4.5 THz) with pulsed output powers as high as 14 μW.
Room-temperature terahertz (THz) quantum cascade laser (QCL) sources based on intra-cavity difference-frequency
generation (DFG) with record THz conversion efficiencies is reported. THz DFG QCLs reported previously are highly
inefficient since THz radiation produced more than ~100 μm away from the exit facet is fully absorbed due to high THz
losses in the QCL waveguide. Our lasers use a non-collinear Čerenkov DFG scheme to extract THz radiation from the
active region. Dual-color mid-infrared quantum cascade lasers with integrated giant optical nonlinearity are grown on
semi-insulating (S.I.) InP substrates. A lateral current extraction scheme is used. THz radiation is emitted at an angle into
the substrate with respect to the mid-infrared pumps. Since S.I. InP is virtually lossless to THz radiation, this scheme
allows for efficient extraction of THz radiation along the whole waveguide length. As a result, our sources demonstrate
large mid-infrared-to-THz conversion efficiency and directional THz output. Experimentally, proof-of-principle devices
demonstrate a conversion efficiency up to 70 μW/W2 and provide output across a 1.2 - 4.5 THz spectral range.
GaInAs/AlInAs/InP quantum cascade lasers have established themselves as reliable laser sources in the mid-infrared region (3.8-10) μm, where they operate at room-temperature in continuous-wave with Watt-level output powers. However, wavelengths above this wavelength region are difficult to generate. At long wavelengths, devices suffer from increased free-carrier absorption and poor population inversion due to the short upper laser state lifetime, thus limiting their operation to cryogenic temperatures. An alternative way to generate new frequencies is the by means of nonlinear frequency mixing. For long-wavelengths, the process of difference frequency mixing is of particular interest, as it is possible to utilize the good performance of the mid-infrared QCLs, acting as pump sources, together with the giant nonlinear properties that can be realized in the intersubband transitions of the quantum wells. Moreover, the giant nonlinearity can be monolithically integrated with the pump sources, leading to a compact, electrically pumped room-temperature semiconductor laser source, emitting at terahertz frequencies. In our work, we present several different concepts of monolithic nonlinear quantum cascade laser sources, designed to emit in the THz range: devices with passive giant nonlinearities, active nonlinearities and, finally, devices with active nonlinearities, combined with novel THz waveguiding techniques. We will demonstrate how application of novel THz waveguiding techniques avoids the efficiency suppression the large free-carrier absorption at THz frequencies in the doped semiconductor layers enabling room-temperature operation up to 1.2 THz.
GaSb-based type-I quantum-well lasers, emitting in the spectral range from 2 to 4 μm are promising light sources for
various trace gas sensing systems by means of tunable diode laser absorption spectroscopy (TDLAS). Excellent device
performance has been achieved so far in the spectral range from 2 to 3 μm, however, room-temperature operation above
3 μm is much more difficult to achieve. In this work we demonstrate the extension of room-temperature operation
wavelength of GaSb-based type-I lasers up to 3.73 μm by implementation of high-quality quinternary AlGaInAsSb
heterostructures.
In this paper we describe the design and performance of nonlinear quantum cascade laser sources for near-infrared and
terahertz applications. Our devices are based on monolithically integrated mid-infrared quantum cascade lasers and
passive nonlinear structures which provide a giant nonlinear response for the pumping frequency. Such design concept
can be applied for both short-wavelength and long-wavelength generation. In our work, short-wavelength devices were
based on the concept of second-harmonic generation whereas long-wavelength devices utilized difference-frequency
generation. With this approach we demonstrate room-temperature operation down to 2.7 μm for near-infrared devices
and up to 70 μm at 210 K for terahertz devices. The performance of our nonlinear devices is very sensitive to the
resonance condition for the pump and nonlinearity. We demonstrate that, once resonant, nonlinear powers in the mW
range are available.
We discuss the design and performance of quantum cascade laser sources based on intra-cavity second harmonic
generation operating in at wavelengths shorter than 3.7μm. A passive heterostructure tailored for giant optical
nonlinearity is integrated on top of an active region and patterned for quasi-phasematching. We demonstrate operation of
λ≈3.6μm, λ≈3.0μm, and λ≈2.6m devices based on lattice-matched and strain-compensated InGaAs/AlInAs/InP
materials. Threshold current densities of typical devices with nonlinear sections are only 10-20% higher than that of the
reference lasers without the nonlinear section. Our best devices have threshold current density of 2.2kA/cm2 and provide
approximately 35μW of second-harmonic output at 2.95μm at room temperature. The second-harmonic conversion
efficiency is approximately 100μW/W2. Up to two orders of magnitude higher conversion efficiencies are expected in
fully-optimized devices.
Injectorless quantum cascade lasers are lately getting more and more into focus of research,
as they promise lower threshold current densities and higher output powers and efficiencies. Although
the research on them started seven years later in 2001 and was less intensive, they have achieved
much lower threshold current densities with 0.45 kA/cm2 at 300 K compared to injectorbased devices.
Additionally injectorless devices reached efficiencies and output powers in the important wavelength
range between 8 and 12 μm comparable to best performing injectorbased devices. With 2 W per facet
and an overall efficiency of 7 % around 9 μm, they show a strong potential regarding possible
applications.
The gain spectra of a continuous wave operating injectorless quantum cascade lasers are presented. These are extracted by the Hakki-Paoli method from electroluminescence measurements. The device operates around 7.4 µm and has threshold current densities in pulsed and continuous wave operation at room temperature that measure 1.1 and 1.76 kA/cm2, respectively. The differential gain coefficients around 100 cm/kA at liquid nitrogen temperature and 44 cm/kA around room temperature are determined. The gain measurement values are compared with the 1/L threshold behavior versus temperature, indicating a nonlinear gain current dependence of injectorless devices.
A detailed study of photosensitivity and noise characteristics of ultrafast InGaAsP/InP avalanche photodiodes with
separate absorption, grading, charge and multiplication regions was carried out. Carrier multiplication and noise factors
were evaluated. Noise origin in investigated APDs is 1/f, generation-recombination and shot noises. Different quality
samples have been investigated and it is shown that noise characteristics well reflect APD quality problems. It is shown
that low-frequency noise and excess shot noise characteristics are very sensitive to the APD quality problems and clear
up physical processes in device structure. Noise characteristic analyses can be used for the APD quality problems
revealing and optimal design development.
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