NASA is working with US industry and academia to develop Photonic Integrated Circuits (PICs) for: (1) Sensors (2) Analog RF applications (3) Computing and free space communications. The PICs provide reduced size, weight, and power that is critical for space-based systems. We describe recent breakthrough 3D monolithic integration of photonic structures, particularly high-speed graphene-silicon devices on CMOS electronics to create CMOS-compatible highbandwidth transceivers for ultra-low power Terabit-scale optical communications. An integrated graphene electro-optic modulator has been demonstrated with a bandwidth of 30 GHz. Graphene microring modulators are especially attractive for dense wavelength division multiplexed (DWDM) systems. For space-based optical communication and ranging we have demonstrated generating a variable number of channels from a single laser using breadboard components, using a single-sideband carrier-suppressed (SSBCS) modulator driven by an externally-supplied RF tone (arbitrary RF frequency), a tunable optical bandpass filter, and an optical amplifier which are placed in a loop. We developed a Return--to-Zero (RZ) Differential Phase Shift Keying (DPSK) laser transmitter PIC using an InP technology platform that includes a tunable laser, a Semiconductor Optical Amplifier (SOA), high-speed Mach-Zehnder Modulator (MZM), and an electroabsorption (EAM) modulator. A Silicon Nitride (SiN) platform integrated photonic circuit suitable for a spectrally pure chip-scale tunable opto-electronic RF oscillator (OEO) that can operate as a flywheel in high precision optical clock modules, as well as radio astronomy, spectroscopy, and local oscillator in radar and communications systems is needed. We have demonstrated a low noise optical frequency combs generation from a small OEO prototypes containing very low loss (~1 dB) waveguide couplers of various shapes and sizes integrated with an ultrahigh-Q MgF2 resonators. An innovative miniaturized lab-on-a-chip device is being developed to directly monitor astronaut health during missions using ~3 drops of body fluid sample like blood, urine, and potentially other body fluids like saliva, sweat or tears. The first-generation system comprises a miniaturized biosensor based on PICs (including Vertical Cavity Surface Emitting Laser – VCSEL, photodetector and optical filters and biochemical assay that generates a fluorescent optical signal change in response to the target analyte.
Photon pairs and heralded single photons are a useful resource in quantum communication, computation, and measurement. Room-temperature microchip-scale integrated devices could enable scalability, robustness and low-cost deployment in practical applications. Silicon is an attractive integration platform, since pair generation by spontaneous four-wave mixing at 1.2 - 1.6 micron wavelengths requires optical power levels that can be delivered by compact electrically-driven laser diodes. However, silicon photonics lacks a native laser device, and the propagation losses are not especially low, although they are somewhat lower than III-V integrated optics, which does have an integrated laser. Nevertheless, silicon photonics can be expected to become a widely-adopted platform for photonics – both classical and quantum – because of the ability to leverage the mature fabrication processes using large-area silicon wafers inherited from the development of microelectronics. Moreover, scalable quantum optics requires electronics for control, drivers and readout circuits, which silicon microelectronic technology can supply. Our research is improving the performance of silicon photonics components for quantum optical communications, and is increasing the level of integration in the quantum silicon photonics toolkit, using microelectronic components and electrically-driven hybrid silicon lasers.
Silicon photonics has drawn a lot of attention over the last decades, mainly in telecom-related application fields where the nonlinear optical properties of silicon are ignored or minimized. However, silicon’s high χ(3) Kerr optical nonlinearity in sub-micron-scale high-confinement waveguides can enable significant improvements in traditional nonlinear devices, such as for wavelength conversion, and also enable some device applications in quantum optics or for quantum key distribution. In order to establish the viability of silicon photonics in practical applications, some big challenges are to improve the optical performance (e.g., optimize nonlinearity or minimize loss) and integration of optics with microelectronics. In this context, we discuss how electronic PIN diodes improve the performance of wavelength conversion in a microring resonator based four-wave mixing device, which achieves a continuous-wave four-wave mixing conversion efficiency of −21.3 dB at 100 mW pump power, with enough bandwidth for the wavelength conversion of a 10 Gbps signal. In the regime of quantum optics, we describe a coupled microring device that can serve as a tunable source of entangled photon pairs at telecommunications wavelengths, operating at room temperature with a low pump power requirement. By controlling either the optical pump wavelength, or the chip temperature, we show that the output bi-photon spectrum can be varied, with implications on the degree of frequency correlation of the generated quantum state.
The very high nonlinearity of silicon nanophotonic waveguides motivates research into chip-scale nonlinear optics
e.g., wavelength conversion via four-wave mixing (FWM). We demonstrate FWM in silicon coupled microrings
with a slow light enhanced effective nonlinear parameter γeff ~ 3700 (Wm)-1 at a pump wavelength of 1570
nm. Impairments on the wavelength conversion efficiency of these structures, such as linear and nonlinear
loss, waveguide and coupler dispersion as well as fabrication imperfections are discussed. Evaluation of the
performance of optimized waveguide designs shows coupled resonator waveguides to be a promising platform for
highly efficient wavelength converters.
Recently, we have demonstrated slow light propagation in coupled-resonator optical waveguides consisting of upto 235
directly-coupled silicon microrings. High resolution spectral measurements of light transmission and the scaling of
transport statistics with increasing length reveal that resonator excitations are mutually correlated, as expected from
theory. Successful light transmission through coherently-coupled resonator chains that are several hundreds of resonators
long is promising for future large-scale silicon photonic circuitry.
Structural imperfections in fabricated microring resonators make post-fabrication tuning of rings useful in order to obtain
desired transmission, phase and delay characteristics. Optical trimming of polymer microrings has been demonstrated
using photobleaching. Here we investigate post-fabrication tuning of silicon-on-insulator microrings and microring
based devices, including aligning the resonant frequencies of rings, and tuning the coupling coefficients.
An optical waveguide consisting of coupled identical resonators in a linear array can slow down the propagation
of light and act as a delay line. However, such a slow-wave structure offers only a modest improvement in delay
per unit length over a spool of optical fiber, as its performance rapidly degrades if the resonators or their spacing
are not exactly identical. Here we show that the same degree of functionality can be achieved in a more compact
and disorder-immune structure, formed by nesting one resonator inside another, and thereby folding the light
path back onto itself.
We describe the waveguiding principles of optical slow-wave structures that lead to the tight-binding form of
the dispersion relation. In the presence of the optical Kerr effect, we show that soliton-like non-propagating
envelopes ("frozen light") can be expected, but the presence of disorder e.g., in the coupling coefficients between
neighboring unit cells, creates a band-tail at the edges of the dispersion relation and causes non-zero propagation
velocity of such pulses.
Current optical networks are migrating towards WDM-based transport between traditional electronic multiplexers/demultiplexers, routers and switches. The ONRAMP Program addresses technologies, architectures and designs of future high performance data networks. This paper focuses on WDM aware IP networks with emphasis on access networks. The access network can be divided into the feeder network and the distribution network. Generally bandwidths of fiber closer to the end user is less precious. Thus in the distribution network, we propose the use of all passive optical components and remotely pumped amplifiers trading bandwidth assignment efficiencies for lower costs. We will examine the design of the distribution network from the view of services to be supported by the network and its desirable properties. Generic physical topologies will be considered and implementation optics presented.