We have developed a proprietary Triple Junction laser diode at eye-safe 1550nm based on AlInGaAs/InP material systems for LiDAR and laser range finding applications. Three monolithic laser structures with tunnel junction layers are designed to reduce mechanical stress with superior heat dissipation. It achieves 3x output power and 2x wall plug efficiency of a single junction with low operating voltage and high slope efficiency at 1W/A. A 1550nmTriple Junction laser diode allows a LiDAR or laser rangefinder to achieve the longest detection range compared to a single junction or 905nm laser diode. Here we demonstrate the high reliability of Triple Junction high power laser diodes at 1550nm for adoption in various applications. The life test was performed on Triple Junction samples with 95μm aperture and 2.5mm cavity length in a TO9 package. They were driven at average power of 700mW in pulse width of 100 μsec and 10% duty cycle at 60°C. Such stressed electrical and thermal condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated over 1000 hours of life test on 17 devices. Based on Arrhenius conditions the estimated MTTF (mean time to failure) is 75k hours at 20°C and 17k hours at 50°C operating temperature, which is respectively 9.3x and 2.5x more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C and it shows no sign of COD (catastrophic optical damage). Under a high stress CW operating condition at 5W, Triple Junction laser diodes exhibit thermal rollover but return to normal performance under pulsed operation.
KEYWORDS: Semiconductor lasers, LIDAR, Reliability, Fiber lasers, Industry, Current confinement, High power lasers, Failure analysis, Diodes, Design and modelling
We have developed the world-leading Triple Junction laser diode based on AlInGaAs/InP material systems for LiDAR applications. The monolithic laser structure with tunnel junction layers is designed to reduce the stress and improve the heat dissipation. It has 3x the output power and 2x the wall plug efficiency of a single junction laser due to its low operating voltage and high slope efficiency at 1W/A. A single Triple Junction laser diode at eye-safe 1550nm allows a LiDAR to achieve over 200m detection range in all-weather conditions. It can drastically improve and simplify the LiDAR design compared to other laser choices such as 905nm or fiber lasers. For mass adoption by the automotive industry here we demonstrate the high reliability required for Triple Junction high power laser diodes at 1550nm. The life test was performed on 95um aperture Triple Junction with 2.5mm cavity length in a TO9 package. They were driven at an average power of 700mW with the pulse width of 100 micro-seconds and 10% duty cycle at 90°C. Such stressed electrical and temperature condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated for more than 1000 hours of life test on 30 devices. Based on Chi squared distribution analysis and Arrhenius equation the estimated MTTF (mean time to failure) is 248k hours at 20°C and 57k hours at 50°C operating temperature, which is respectively 31x and 7 more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C without performance degradation and without COD (catastrophic optical damage).
An echelle spectrograph can provide high resolving power (wavelength/FWHM) across a broad spectral range. These optical instruments are commonly used in spectroscopy for atomic and molecular identification in astronomical observations and laboratory analysis. The wavelength range of an echelle spectrograph is ultimately limited by the capabilities of the detector used to acquire the spectral data. Silicon based CCD, EMCCD and CMOS sensors typically enable measurements from 200nm to 1100nm. Infrared Laboratories and Catalina Scientific Instruments (CSI) have collaborated to demonstrate an application that combines IR Lab’s TRIWAVE camera with CSI’s EMU120/65 echelle spectrograph. The TRIWAVE camera covers a spectral range of 300nm to 1600nm, greatly increasing the wavelength range for applications using the EMU-120/65 spectrograph. With this increased capability, an opportunity exists for measuring the dielectric coating thickness of thin film by extracting and analyzing interference fringes from the spectral data. Methods and results of this measurement will be presented.
Visible-band cameras using silicon imagers
provide excellent video under daylight
conditions, but become blind at night. The
night sky provides illumination from 1-2 μm
which cannot be detected with a silicon sensor.
Adding short-wave infrared detectors to a
CMOS imager would enable a camera which
can be used day or night.
A germanium-enhanced CMOS imager
(TriWave®) has been developed with
broadband sensitivity from 0.4 μm to 1.6 μm.
A 744 x 576 format imager with 10 μm pixel
pitch provides a large field of view without
incurring a size and weight penalty in the
optics. The small pixel size is achieved by
integrating a germanium photodetector into a
mainstream CMOS process. A sensitive
analog signal chain provides a noise floor of 5
electrons. The imagers are hermetically
packaged with a thermo-electric cooler in a
windowed metal package 5 cm3 in volume. A
compact (<650 cm3) camera core has been
designed around the imager. Camera
functions implemented include correlated
double sampling, dark frame subtraction and
non-uniformity corrections.
In field tests, videos recorded with different
filters in daylight show useful fog and haze
penetration over long distances. Under clear
moonless conditions, short-wave infrared
(SWIR) images recorded with TriWave make
visible individuals that cannot be seen in
videos recorded simultaneously using an
EMCCD. Band-filtered videos confirm that
the night-sky illumination is dominated by
wavelengths above 1200 nm.
Recently, a number of research groups around the world have developed ophthalmic instruments capable of in vivo diffraction limited imaging of the human retina. Adaptive optics was used in these systems to compensate for the optical aberrations of the eye and provide high contrast, high resolution images. Such compensation uses a wavefront sensor and a wavefront corrector (usually a deformable mirror) coordinated in a closed- loop control system that continuously works
to counteract aberrations. While those experiments produced promising results, the deformable mirrors have had insufficient range of motion to permit full correction of the large amplitude aberrations of the eye expected in a normal population of human subjects. Other retinal imaging systems developed to date with MEMS (micro-electromechanical
systems) DMs suffer similar limitations.
This paper describes the design, manufacture and testing of a 6um stroke polysilicon surface micromachined deformable mirror that, coupled with an new optical method to double the effective stroke of the MEMS-DM, will permit diffraction-limited retinal imaging through dilated pupils in at least 90% of the human population. A novel optical design using spherical mirrors provides a double pass of the wavefront over the deformable mirror such that a 6um mirror
displacement results in 12um of wavefront compensation which could correct for 24um of wavefront error. Details of this design are discussed. Testing of the effective wavefront modification was performed using a commercial wavefront sensor. Results are presented demonstrating improvement in the amplitude of wavefront control using an existing high degree of freedom MEMS deformable mirror.
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