The growing demand for bandwidth makes photonic systems a leading candidate for future telecommunication and radar technologies. Integrated photonic systems offer ultra-wideband performance within a small footprint, which can naturally interface with fiber-optic networks for signal transmission. However, it remains challenging to realize narrowband (∼MHz) filters needed for high-performance communications systems using integrated photonics. In this paper, we demonstrate all-silicon microwave-photonic notch filters with 50× higher spectral resolution than previously realized in silicon photonics. This enhanced performance is achieved by utilizing optomechanical interactions to access long-lived phonons, greatly extending available coherence times in silicon. We use a multi-port Brillouin-based optomechanical system to demonstrate ultra-narrowband (2.7 MHz) notch filters with high rejection (57 dB) and frequency tunability over a wide spectral band (6 GHz) within a microwave-photonic link. We accomplish this with an all-silicon waveguide system, using CMOS-compatible fabrication techniques.
The canonical beam splitter - a fundamental building block of quantum optical systems - is a reciprocal element. It operates on forward- and backward-propagating modes in the same way, regardless of direction. The concept of nonreciprocal quantum photonic operations, by contrast, could be used to transform quantum states in a momentum- and direction-selective fashion. Here we demonstrate the basis for such a nonreciprocal transformation in the frequency domain through intermodal Bragg scattering four-wave mixing (BSFWM). Since the total number of idler and signal photons is conserved, the process can preserve coherence of quantum optical states, functioning as a nonreciprocal frequency beam splitter. We explore the origin of this nonreciprocity and find that the phase-matching requirements of intermodal BSFWM produce an enormous asymmetry (76×) in the conversion bandwidths for forward and backward configurations, yielding ∼25 dB of nonreciprocal contrast over several hundred GHz. We also outline how the demonstrated efficiencies (∼10-4) may be scaled to near-unity values with readily accessible powers and pumping configurations for applications in integrated quantum photonics.
We demonstrate an optical waveguide device, capable of supporting the high, invacuum, optical power necessary for trapping a single atom or a cold atom ensemble with evanescent fields. Our photonic integrated platform, with suspended membrane waveguides, successfully manages optical powers of 6 mW (500 μm span) to nearly 30 mW (125 μm span) over an un-tethered waveguide span. This platform is compatible with laser cooling and magnetooptical traps (MOTs) in the vicinity of the suspended waveguide, called the membrane MOT and the needle MOT, a key ingredient for efficient trap loading. We evaluate two novel designs that explore critical thermal management features that enable this large power handling. This work represents a significant step toward an integrated platform for coupling neutral atom quantum systems to photonic and electronic integrated circuits on silicon.
We present narrowband RF-photonic filters in an integrated silicon platform. Using Brillouin interactions, the filters yield narrowband (∼MHZ) filter bandwidths with high signal rejection, and demonstrate tunability over a wide (∼GHz) frequency range.
Passive silicon photonic waveguides are exposed to gamma radiation to understand how the performance of silicon photonic integrated circuits is affected in harsh environments such as space or high energy physics experiments. The propagation loss and group index of the mode guided by these waveguides is characterized by implementing a phase sensitive swept-wavelength interferometric method. We find that the propagation loss associated with each waveguide geometry explored in this study slightly increases at absorbed doses of up to 100 krad (Si). The measured change in group index associated with the same waveguide geometries is negligibly changed after exposure. Additionally, we show that the post-exposure degradation of these waveguides can be improved through heat treatment.
As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser's frequency and phase can be controlled by an injected signal. Because of its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection-locking dynamics remain relatively untapped - despite significant potential for technological and scientific impact. Here, we demonstrate injection locking in a silicon photonic Brillouin laser. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the Brillouin gain bandwidth. Harnessing these dynamics, we demonstrate amplification of small signals by more than 23 dB. Moreover, we demonstrate that the injection-locking dynamics of this system are inherently nonreciprocal, yielding unidirectional control and backscatter immunity in an all-silicon system. This device physics opens the door to strategies for phase-noise reduction, low-noise amplification, and backscatter immunity in silicon photonics.
Moderate-temperature thermal sources (100° to 400°C) that radiate waste heat are often the by-product of mechanical work, chemical or nuclear reactions, or information processing. We demonstrate conversion of thermal radiation into electrical power using a bipolar grating-coupled complementary metal-oxide-silicon (CMOS) tunnel diode. A two-step photon-assisted tunneling charge pumping mechanism results in separation of charge carriers in pn-junction wells leading to a large open-circuit voltage developed across a load. Electrical power generation from a broadband blackbody thermal source has been experimentally demonstrated with converted power densities of 27 to 61 microwatts per square centimeter for thermal sources between 250° and 400°C. Scalable, efficient conversion of radiated waste heat into electrical power can be used to reduce energy consumption or to power electronics and sensors.
Silicon photonics is a platform that enables densely integrated photonic components and systems and integration with electronic circuits. Depletion mode modulators designed on this platform suffer from a fundamental frequency response limit due to the mobility of carriers in silicon. Lithium niobate-based modulators have demonstrated high performance, but the material is difficult to process and cannot be easily integrated with other photonic components and electronics. In this manuscript, we simultaneously take advantage of the benefits of silicon photonics and the Pockels effect in lithium niobate by heterogeneously integrating silicon photonic-integrated circuits with thin-film lithium niobate samples. We demonstrate the most CMOS-compatible thin-film lithium niobate modulator to date, which has electro-optic 3 dB bandwidths of 30.6 GHz and half-wave voltages of 6.7 V×cm. These modulators are fabricated entirely in CMOS facilities, with the exception of the bonding of a thin-film lithium niobate sample post fabrication, and require no etching of lithium niobate.
We present a 30 GHz heterogeneously integrated silicon photonic/lithium niobate Mach-Zehnder modulator simultaneously utilizing the strong Pockels effect in LiNbO3 while also taking advantage of the ability for photonic/electronic integration and mass production associated with silicon photonics. Aside from the final step of bonding the LiNbO3, this modulator can be entirely fabricated using CMOS facilities.
Phase errors in large optical phased arrays degrade beam quality and must be actively corrected. Using a novel, low-power electro-optic design with matched pathlengths, we demonstrate simplified optimization and reduced sensitivity to wavelength and temperature.
We demonstrate the ultrahigh extinction operation of a silicon photonic (SiP) amplitude modulator (AM) employing a cascaded Mach-Zehnder interferometer. By carrying out optimization sweeps without significantly degrading the extinction, the SiP AM is robust to environment changes and maintained >52 dB extinction for >6 hrs.
Measurement uncertainties in the techniques used to characterize loss in photonic waveguides becomes a significant issue as waveguide loss is reduced through improved fabrication technology. Typical loss measurement techniques involve environmentally unknown parameters such as facet reflectivity or varying coupling efficiencies, which directly contribute to the uncertainty of the measurement. We present a loss measurement technique, which takes advantage of the differential loss between multiple paths in an arrayed waveguide structure, in which we are able to gather statistics on propagation loss from several waveguides in a single measurement. This arrayed waveguide structure is characterized using a swept-wavelength interferometer, enabling the analysis of the arrayed waveguide transmission as a function of group delay between waveguides. Loss extraction is only dependent on the differential path length between arrayed waveguides and is therefore extracted independently from on and off-chip coupling efficiencies, which proves to be an accurate and reliable method of loss characterization. This method is applied to characterize the loss of the silicon photonic platform at Sandia Labs with an uncertainty of less than 0.06 dB/cm.
Electrical power generation from a moderate-temperature thermal source by means of direct conversion of infrared radiation is important and highly desirable for energy harvesting from waste heat and micropower applications. Here, we demonstrate direct rectified power generation from an unbiased large-area nanoantenna-coupled tunnel diode rectifier called a rectenna. Using a vacuum radiometric measurement technique with irradiation from a temperature-stabilized thermal source, a generated power density of 8 nW/cm2 is observed at a source temperature of 450 °C for the unbiased rectenna across an optimized load resistance. The optimized load resistance for the peak power generation for each temperature coincides with the tunnel diode resistance at zero bias and corresponds to the impedance matching condition for a rectifying antenna. Current-voltage measurements of a thermally illuminated large-area rectenna show current zero crossing shifts into the second quadrant indicating rectification. Photon-assisted tunneling in the unbiased rectenna is modeled as the mechanism for the large short-circuit photocurrents observed where the photon energy serves as an effective bias across the tunnel junction. The measured current and voltage across the load resistor as a function of the thermal source temperature represents direct current electrical power generation.
We present a quantitative analysis of the correlation of resonant wavelength variation with process variables, and find that 50% of the resonant wavelength variation for microrings is due to systematic process conditions. We also discuss the improvement of device uniformity by mitigating these systematic variations.