Integrated Photonics

Lincoln Laboratory has a history of more than 50 years in the research and development of advanced electro-optical materials and devices, optoelectronic components, and integrated photonic subsystems. The Laboratory was one of the "Original 4" research organizations that independently and nearly simultaneously reported the first demonstrations of the semiconductor diode laser in fall 1962. Since that time, scientists and engineers at the Laboratory have worked to develop new optoelectronic materials and material-growth techniques, fabricate and characterize novel components (e.g., lasers, detectors, modulators, waveguides, filters), and insert these components into subsystems of importance to the government.

Lincoln Laboratory was an early pioneer in the development of lithium-niobate
(LiNbO3) modulators and signal processing subsystems, such as optically sampled analog-to-digital converters (ADCs) and microwave photonic (MWP) links. This LiNbO3 modulator technology was transferred to industry and is now a key element in high-speed fiber-optic telecommunication networks. The Laboratory also pioneered the epitaxial growth of the indium gallium arsenide phosphide (InGaAsP) semiconductor material system and used it to implement the first room-temperature continuous-wave (CW) diode laser and early optical modulators.

For the past 15 years, Lincoln Laboratory has been working to mature and exploit its high-power, low-noise semiconductor slab-coupled optical waveguide (SCOW) emitter technology. This work has led to the demonstration of watt-class semiconductor optical amplifiers (SOAs), actively mode-locked lasers having femtosecond timing jitter, and single-frequency external-cavity lasers (ECLs) having high power (0.35 W) and narrow linewidth (~ 30 kHz). The SCOW concept has also been used to realize waveguide photodiodes having high external quantum efficiency (>90%), high saturation current (>30 mA), and wide bandwidth (>10 GHz). These components have been used to improve the performance of MWP links and optoelectronic oscillators.

Integrated Photonics Figure 1. Images of integrated photonic devices and circuits implemented using monolithic compound-semiconductor and silicon technologies, and hybrid integration techniques. (Click on image to see larger version.)

 

Currently, the Laboratory is working to develop photonic integrated circuits (PICs) using both monolithic and hybrid integration approaches (Figure 1) and to use these PICs to realize novel system applications. The Laboratory has expertise and capabilities in a number of optoelectronic materials, including InP, GaAs, GaSb, GaN, Si, and SiNx,* which enable the manipulation of optical signals having wavelengths ranging from less than 0.4 mm to greater than 10 mm. Examples of some of the areas being developed include

  1. Monolithic Compound-Semiconductor PICs
    This activity involves the integration of multiple active and passive components onto a compound semiconductor substrate such as InP or GaAs. Monolithic integration techniques that have been developed at the Laboratory include quantum-well intermixing (QWI), patterning of waveguide gratings using electron-beam lithography, and epitaxial material regrowth. These techniques have been used to fabricate and integrate SOAs, distributed Bragg reflector (DBR) lasers, electroabsorption modulators (EAMs), phase modulators, photodetectors, and saturable absorbers. Work is ongoing to integrate these conventional components with Lincoln Laboratory's SCOW platform.

  2. Monolithic Silicon PICs
    The Laboratory has developed a silicon PIC toolbox utilizing the 90-nm fabrication capability available in its Microelectronics Laboratory. Components available in this toolbox include low-loss waveguides, optical modulators, narrowband optical filters, wavelength division multiplexers (WDMs), and waveguide-to-fiber couplers. Components from the toolbox have been used to implement photonic ADCs, RF filters, and low-loss delay lines.

  3. Hybrid PICs
    Hybrid integration involves the heterogeneous integration of compound semiconductor materials and devices with silicon photonics and low-loss dielectric waveguides. Both wafer-bonded and pick-and-place hybrid integration approaches are being developed. The Laboratory is also actively pursuing electronic-photonic integration to reduce the size, weight, and power (SWaP) and improve the performance of optical transmitters, receivers, and signal processing subsystems. Electronic-photonic integration techniques that have been developed include wire bonding of side-by-side chips, flip-chip bonding, and wafer-scale oxide-bonded three-dimensional integration.

  4. Microwave Photonic Subsystems
    Microwave photonics (MWP) involves interactions between the RF/microwave/millimeter-wave and optical portions of the electromagnetic spectrum. Photonics is utilized for the generation, transmission, detection, processing, and control of microwave signals with direct applicability to antenna systems (e.g., wireless and array), sensing, and instrumentation. The Laboratory is working to develop MWP techniques and subsystems for radar, electronic warfare, and communications applications. It is anticipated that electronic-photonic integration will be needed to achieve the performance and SWaP required for these applications.

 

*indium phosphide (InP), gallium arsenide (GaAs), gallium antimonide (GaSb), gallium nitride (GaN), silicon (Si), and silicon nitride (SiNx)

 

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