Shayan Shahnia

Integrated spatial multiplexing of heralded single-photon sources

The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the heralded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon interference, required at the core of optical quantum computing and quantum communication protocols.

Tailoring of the Brillouin gain for on-chip widely tunable and reconfigurable broadband microwave photonic filters

An unprecedented Brillouin gain of 44 dB in a photonic chip enables the realization of broadly tunable and reconfigurable integrated microwave photonic filters. More than a decade bandwidth reconfigurability from 30 up to 440 MHz, with a passband ripple <1.9  dB is achieved by tailoring the Brillouin pump. The filter central frequency is continuously tuned up to 30 GHz with no degradation of the passband response, which is a major improvement over electronic filters. Furthermore, we demonstrate pump tailoring to realize multiple bandpass filters with different bandwidths and central frequencies, paving the way for multiple on-chip microwave filters and channelizers.

High-efficiency frequency conversion in the single-photon regime

In this Letter we demonstrate frequency conversion in the single-photon regime through Bragg-scattering four-wave mixing with near-unit efficiency in a 750 m long commercially available dispersion-engineered highly nonlinear fiber, where all photons and pump laser frequencies are in the low-loss telecommunications band. We achieve 99.1%±4.9% downconversion and 98.0%±5.0% upconversion of photons by 12 nm using a weak coherent state with an average input of 0.27 photons per detection gate window.

Advanced Integrated Microwave Signal Processing With Giant On-Chip Brillouin Gain

Processing of microwave signals using photonics has several key advantages for applications in wireless communications. However, to bring photonic-based microwave signal processing to the mainstream requires a reduction of the form factor. Integration is a route for achieving high-performance, low-cost, and small-footprint microwave photonic devices. A high on-chip stimulated Brillouin scattering (SBS) gain is essential for synthesizing several key functionalities for advanced integrated microwave signal processing. We have optimized our on-chip SBS platform to achieve a record on-chip gain of 52 dB. In this paper, we discuss the implications of this giant gain from the viewpoint of new enabled technologies. The giant gain can be distributed over wide frequencies, which can be exploited for the realization of reconfigurable microwave bandpass, bandstop, and multiband filters. High gain also enables the demonstration of low-threshold on-chip lasers, which can be of relevance for a low-noise radio-frequency signal generation. These wide ranges of functionalities are made possible by the breakthrough on-chip gain makes Brillouin-based microwave photonic signal processing a promising approach for real-world implementation in the near future.

Signal interference RF photonic bandstop filter.

In the microwave domain, signal interference bandstop filters with high extinction and wide stopbands are achieved through destructive interference of two signals. Implementation of this filtering concept using RF photonics will lead to unique filters with high performance, enhanced tuning range and reconfigurability. Here we demonstrate an RF photonic signal interference filter, achieved through the combination of precise synthesis of stimulated Brillouin scattering (SBS) loss with advanced phase and amplitude tailoring of RF modulation sidebands. We achieve a square-shaped, 20-dB extinction RF photonic filter over a tunable bandwidth of up to 1 GHz with a central frequency tuning range of 16 GHz using a low SBS loss of ~3 dB. Wideband destructive interference in this novel filter leads to the decoupling of the filter suppression from its bandwidth and shape factor. This allows the creation of a filter with all-optimized qualities.

Chip scale humidity sensing based on a microfluidic infiltrated photonic crystal

This work presents an optical on-a-chip humidity sensor based on the hydroscopic behavior of an infiltrated liquid into the sub-micron holes of a silicon photonic crystal. Direct measurements of the liquid refractive index in combination with numerical simulations show that the sensitivity of the device is due to changes of both the liquids refractive index and volume. We report humidity sensing with a response time of 0.1 ms and study the stability and reversibility of the sensor. This demonstration highlights the sensitivity offered by optofluidics in photonic crystal circuits and the potential for realizing ultra-compact integrated humidity sensing components.

Broadband photon-counting Raman spectroscopy in short optical waveguides

We present a method of directly measuring the spontaneous Raman scattering in optical waveguides in an alignment-free setup. Using a pulsed laser, liquid-crystal-on-silicon spatial light modulator and single-photon detector, we create a broadband photon-counting Raman spectrometer. The temperature and polarization dependence are characterized in an As2S3 amorphous glass fiber for a Stokes detuning range of 1 to 9 THz from the pump frequency. We fit our experimental data with a theoretical model and extract the Raman-gain spectrum and compare to free-space measurements of bulk As2S3. The sensitivity of the method in principle allows direct characterization of chip-scale nanophotonic devices.

On-chip stimulated Brillouin scattering for microwave photonic signal processing

This paper gives an overview of the applications of on-chip stimulated Brillouin scattering (SBS) in RF photonic signal processing, including for high extinction notch filtering, tunable phase shifter, instantaneous frequency measurement, and bandwidth-reconfigurable signal processing.

Independent manipulation of the phase and amplitude of optical sidebands in a highly-stable RF photonic filter.

Microwave photonic cancellation notch filters have been shown capable of achieving ultra-high suppressions independently from the strength of optical resonant filter they use, making them an attractive candidate for on-chip signal processing. Their operation, based on destructive interference in the electrical domain, requires precise control of the phase and amplitude of the optical modulation sidebands. To date, this was attainable only through the use of dual-parallel Mach-Zehnder modulators which suffer from bias drifts that prevent stable filter operation. Here we propose a new cancellation filter topology with ease of control and enhanced stability using a bias-free phase modulator and a reconfigurable optical processor as the modulation sidebands spectral shaper. We experimentally verify the long term stability of the novel filter topology through continuous real-time monitoring of the filter peak suppression over 24 hours.

Spatial multiplexing of monolithic Silicon heralded single photon sources

Here we present the first experimental demonstration of spatial multiplexing of two integrated heralded single photon sources so as to enhance the heralded photon rate for a given single waveguide output power.