Photonic integrated circuits require the ability to integrate both lasers and waveguides with low absorption and coupling loss. This technology is being developed at LLNL for digital logic gates for optical key generation circuits to facilitate secure communications. Here, we demonstrate an approach of integrating InGaAs DQW edge emitting lasers (EEL) with electron beam evaporated dielectric waveguides. The EELs are defined by electron cyclotron resonance etching (ECR). This approach results in highly anisotropic etched mirrors with smooth etched features (sidewall rms roughness = 28 Å, surface rms roughness = 10 Å). The mirror is etched to form both the laser cavity and define the waveguide mesa, which accommodates a dielectric stack, where the core is aligned with the active region of the laser to achieve maximum vertical mode overlapping. The waveguides are based on SiO2/Ta2O5/SiO2 which yields a high index contrast of 0.6, resulting in low loss guides (~2-3dB/cm). The design of the interface has taken into account the waveguide transmission loss, air gap spacing and tilt between the laser and waveguide. The critical feature for this deposition technique is its required high directionality or minimal sidewall deposition and corner effects. In the butt coupled EEL/waveguide system we have measured a slope efficiency to be as high as 0.45 W/A. We have in conclusion demonstrated a technology that allows direct coupling of a dielectric optical interconnect to a semiconductor laser monolithically fabricated on the semiconductor substrate.
Sputter deposition at long-throw distances (15-30 in.) and low pressures (<1 mTorr) were developed mainly for the semiconductor industry to deposit metals and dielectrics into trenches or vias on silicon and gallium arsenide wafers. Scientists found that sputter depositions performed at pressures below 1 mTorr (0.13 Pa) results in a virtually collision-free trajectory of the sputtered atoms from the target to the substrate. If the throw distance (source to substrate) is increased at these low pressures, the activated (ionized) gas and target atoms maintain their energy. We used this methodology along with dc-pulsed sputtering to deliver additional energy at the substrate. This allowed us to coat large optics (>21-in. diameter) in a standard box coater using smaller-diameter sputter cathodes. This paper will discuss the process used to successfully coat a 22-in.-diameter optic for the Keck Telescope in Hawaii with a new Wide-Band Durable Silver Mirror. The process uses smaller-diameter sputter cathodes in a 4-ft.-x-4-ft.-x-5-ft. box coater. We will also discuss how the process can be scaled to 36-in. or larger optics for use on terrestrial or space-based platforms.
Silver has the highest reflectance of all of the materials, but it tarnishes in the presence of sulfides, chlorides, and oxides in the atmosphere. Also, the silver reflectance is very low at wavelengths below 400 nm making aluminum more desirable mirror coating for the UV region. We have found a way to prevent silver tarnishing by sandwiching the silver layer between two thin layers of NiCrNx, and to extend the metal's high reflectance down to 200 nm by depositing the (thin) Ag layer on top of Al. Thus, the uv is transmitted through the thin Ag layer below 400 nm wavelength, and is reflected from the Al layer underneath. This UV-shifted durable coating provides a valuable alternative to the aluminum coating for telescope mirror coatings where high throughput and durability are important considerations. The throughput for a telescope with, say, six reflections from silver coatings is (0.97)6 equals 83% compared to (0.92)6 equals 60% for aluminum coatings, or 28% less. The use of silver coatings allows more photons to be collected by primary mirror. Aluminum also has a reflectance dip at 850 nm caused by inter-band transitions which is eliminated by placing the thin Ag layer on top. This paper describes a non-tarnishing silver coating having high reflectance down into the UV region. The average specular reflectance is 70% - 97% in the near-UV, 95% - 99% in the visible region, and >= 99% in the infrared region covering the total wavelength range 200 nm to 10,000 nm.
A durable protected silver coating was designed and fabricated for possible use on flashlamp reflectors in the National Ignition Facility to avoid tarnishing under corrosive conditions and intense visible light. This coating provides a valuable alternative for mirror coatings where high reflectance and durability are important requirements. This paper describes a protected silver coating having high reflectance from 400 nm to 10,000 nm. The specular reflectance is between 95 percent and 98 percent in the visible region and 98 percent or better in the IR region.
A durable protected silver coating was designed and fabricated for possible use on flashlamp reflectors in the National Ignition Facility to avoid tarnishing under corrosive conditions and intense visible light . This coating provides a valuable alternative for mirror coatings where high reflectance and durability are important requirements. This paper describes a protected silver coating having high reflectance from 400 nm to 10,000 nm. The specular reflectance is between 95 percent and 98 percent in the visible region and 98 percent or better in the IR region.
A durable protected silver coating was designed and fabricated for use on flashlamp reflectors in the National Ignition Facility to avoid tarnishing under corrosive conditions and intense visible light. This coating provides a valuable alternative for telescope mirror coatings where high reflectance and durability are important requirements. This paper describes a protected silver coating having high reflectance from 400 mm to 10,000 nm. An alternate coating design extends the high reflectance down to 300 nm while maintaining high reflectance out to 10,000 nm. The specular reflectance is between 95% and 97% in the visible region and 98% or better in the infrared region.
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