Chi Xiong

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.

Demonstration of a High Extinction Ratio Monolithic CMOS Integrated Nanophotonic Transmitter and 16 Gb/s Optical Link

We present a 16-Gb/s transmitter composed of a stacked voltage-mode CMOS driver and periodic-loaded reverse biased pn junction Mach-Zehnder modulator. The transmitter shows 9-dB extinction ratio and 10.3-pJ/bit power consumption and operates with 1.3 μm light. Penalties as low as 0.5 dB were seen as compared to a 25-Gb/s LiNbO3 transmitter with both a monolithic metal-semiconductor-metal receiver and a reference receiver at 16-Gb/s operation. We also present an analytic expression for relative transmitter penalty (RTP), which allows one to quickly assess the system impact of design parameters such as peak-to-peak modulator drive voltage, modulator figure of merit, and transmitter extinction ratio to determine the circumstances under which a stacked CMOS cascode driver is desirable.

A monolithic 56 Gb/s CMOS integrated nanophotonic PAM-4 transmitter

We report a demonstration of four-level pulse amplitude modulation (PAM-4) using a segmented traveling-wave silicon photonic Mach-Zehnder modulator with monolithically integrated CMOS drivers. The PAM-4 transmitter shows clear eye openings up to 28 Gbaud.

A monolithic 56 Gb/s silicon photonic pulse-amplitude modulation transmitter

Silicon photonics promises to address the challenges for next-generation short-reach optical interconnects. Growing bandwidth demand in hyper-scale data centers and high-performance computing motivates the development of faster and more efficient silicon photonics links. While it is challenging to raise the serial line rate, further scaling of the data rate can be realized by, for example, increasing the number of parallel fibers, increasing the number of wavelengths per fiber, and using multilevel pulse-amplitude modulation (PAM). Among these approaches, PAM has a unique advantage because it does not require extra lasers or a costly overhaul of optical fiber cablings within the existing infrastructure. Here, we demonstrate, to our knowledge, the first fully monolithically integrated silicon photonic four-level PAM (PAM-4) transmitter operating at 56xa0Gb/s and demonstrate error-free transmission (bit-error rate <10−12) up to 50xa0Gb/s without forward-error correction. The superior PAM-4 waveform is enabled by co-design and co-optimization of the silicon traveling-wave modulators with the monolithic CMOS driver circuits. Our results show that monolithic silicon photonics technology is a promising platform for future ultrahigh data rate optical interconnects.

Demonstration of Error-Free 32-Gb/s Operation From Monolithic CMOS Nanophotonic Transmitters

We present a monolithic CMOS-integrated nanophotonic transmitter with a link sensitivity comparable with a 25-Gb/s commercial reference transmitter. Our CMOS transmitter shows error-free operation up to 32 Gb/s, and exhibits a 4.8-dB extinction ratio and 4.9-dB insertion loss at 25 Gb/s.

An integrated silicon photonics technology for O-band datacom

A manufacturable platform of CMOS, RF and opto-electronic devices fully PDK enabled to demonstrate a 4×25 Gb/s reference design is presented. With self-aligned fiber attach, this technology enables low-cost O-band data-com transceivers. In addition, this technology can offer enhanced performance and yield in hybrid-assembly for applications at 25 Gbaud and beyond.

Effect of low-Raman window position on correlated photon-pair generation in a chalcogenide Ge11.5As24Se64.5 nanowire

We investigated correlated photon-pair generation via spontaneous four-wave mixing in an integrated chalcogenide Ge11.5As24Se64.5 photonic nanowire. The coincidence to accidental ratio, a key measurement for the quality of correlated photon-pair sources, was measured to be only 0.4 when the photon pairs were generated at 1.9 THz detuning from the pump frequency due to high spontaneous Raman noise in this regime. However, the existence of a characteristic low-Raman window at around 5.1u2009THz in this materials Raman spectrum and dispersion engineering of the nanowire allowed us to generate photon pairs with a coincidence to accidental ratio of 4.5, more than 10 times higher than the 1.9 THz case. Through comparing the results with those achieved in chalcogenide As2S3 waveguides which also exhibit a low Raman-window but at a larger detuning of 7.4 THz, we find that the position of the characteristic low-Raman window plays an important role on reducing spontaneous Raman noise because the phonon population is h...

Monolithic Travelling-Wave Mach-Zehnder Transmitter with High-Swing Stacked CMOS Driver

We present a 20 Gb/s monolithically integrated transmitter with stacked CMOS driver and periodic-loaded PN-junction Mach-Zehnder modulator fabricated in IBMs sub-100nm technology node. Transmitter extinction ratios of 10 dB at 20 Gb/s are demonstrated.

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.

Distributed electrode Mach-Zehnder modulator with double-pass phase shifters and integrated inductors.

A novel high-speed Mach-Zehnder modulator (MZM) fully integrated into a 90 nm CMOS process is presented. The MZM features `double-pass optical phase shifter segments, and the first use of integrated inductors in a `velocity-matched distributed-electrode configuration.