Dense array slab-coupled optical waveguide lasers (DASCOWLs) consist of several hundred single-mode SCOWL
lasers on a monolithic bar. Near diffraction-limited output of the SCOWLs is preserved with spacing down to 40μm.
Greater than 200W CW operation of a 4% FF, 100-element, 100μm-pitch, centimeter wide DASCOWL bar has
been demonstrated, corresponding to <2W/emitter in array format. We have also demonstrated near 500W
continuous wave (CW) operation from a 10% fill factor (FF) 1-cm wide, 1cm long DASCOWL bar which contains
250 emitters, with a 40μm pitch. The goal of 2W/emitter, 500W/bar represents a 5X increase above the conventional
10-emitter, 10% FF broad area laser diode bar that operates at 10W/100μm-emitter. Some of the reported
DASCOWL performance benefits from SRL’s low thermal resistance EPIC heat sinks.
Slab-coupled optical waveguide lasers (SCOWLs) and amplifiers (SCOWAs) are inherently low-confinement structures
with large nearly-circular modes that are easily coupled to optical fibers or collimated for free-space applications.
Recently SCOWL powers have increased to 3 W by increasing the cavity length to 1 cm and improving the heat
removal. SCOWAs are coherently combined using active phase control to achieve a very high-brightness source. Our
coherent beam combining system consists of single-pass amplifiers with angled-facet SCOWAs that suppress feedback.
Single-pass, 5-mm long, SCOWAs have now been demonstrated with 1.5 W CW output with only 50 mW seed power.
Arrays of 47 SCOWAs have demonstrated a raw power of 57 W with 50 mW of seed power per element. A coherent
beam combining demonstration is currently being assembled.
Arrays as large as 256 x 64 of single-photon counting avalanche photodiodes have been developed for defense
applications in free-space communication and laser radar. Focal plane arrays (FPAs) sensitive to both 1.06 and 1.55 μm
wavelength have been fabricated for these applications. At 240 K and 4 V overbias, the dark count rate (DCR) of 15 μm
diameter devices is typically 250 Hz for 1.06 μm sensitive APDs and 1 kHz for 1.55 μm APDs. Photon detection
efficiencies (PDE) at 4 V overbias are about 45% for both types of APDs. Accounting for microlens losses, the full FPA
has a PDE of 30%. The reset time needed for a pixel to avoid afterpulsing at 240 K is about 3-4 μsec. These devices
have been used by system groups at Lincoln Laboratory and other defense contractors for building operational systems.
For these fielded systems the device reliability is a strong concern. Individual APDs as well as full arrays have been run
for over 1000 hrs of accelerated testing to verify their stability. The reliability of these GM-APDs is shown to be under
10 FITs at operating temperatures of 250 K, which also corresponds to an MTTF of 17,100 yrs.
Avalanche Photodiode (APD) photon counting arrays are finding an increasing role in defense applications in laser radar
and optical communications. As these system concepts mature, the need for reliable screening, test, assembly and
packaging of these novel devices has become increasingly critical. MIT Lincoln Laboratory has put significant effort
into the screening, reliability testing, and packaging of these components. To provide rapid test and measurement of the
APD devices under development, several custom parallel measurement and Geiger-mode (Gm) aging systems have been
Another challenge is the accurate attachment of the microlens arrays with the APD arrays to maximize the photon
detection efficiency. We have developed an active alignment process with single μm precision in all six degrees of freespace
alignment. This is suitable for the alignment of arrays with active areas as small as 5 μm. Finally, we will discuss a
focal plane array (FPA) packaging qualification effort, to verify that single photon counting FPAs can survive in future
Arrays of InP-based avalanche photodiodes operating at 1.06-μm wavelength in the Geiger mode have been
fabricated in the 128x32 format. The arrays have been hermetically packaged with precision-aligned lenslet arrays,
bump-bonded read-out integrated circuits, and thermoelectric coolers. With the array cooled to -20C and voltage biased
so that optical cross-talk is small, the median photon detection efficiency is 23-25% and the median dark count rate is 2
kHz. With slightly higher voltage overbias, optical cross-talk increases but the photon detection efficiency increases to
almost 30%. These values of photon detection efficiency include the optical coupling losses of the microlens array and
We have developed and demonstrated a high-duty-cycle asynchronous InGaAsP-based photon counting detector system with near-ideal Poisson response, room-temperature operation, and nanosecond timing resolution for near-infrared applications. The detector is based on an array of Geiger-mode avalanche photodiodes coupled to a custom integrated circuit that provides for lossless readout via an asynchronous, nongated architecture. We present results showing Poisson response for incident photon flux rates up to 10 million photons per second and multiple photons per 3-ns timing bin.