All-silicon microring avalanche photodiodes with a >65 A/W response.

We report an all-Si microring (MRR) avalanche photodiode (APD) with an ultrahigh responsivity (R) of 65 A/W, dark current of 6.5 µA, and record gain-bandwidth product (GBP) of 798 GHz at -7.36 V. The mechanisms for the high responsivity have been modelled and investigated. Furthermore, open eye diagrams up to 20 Gb/s are supported at 1310 nm at -7.36 V. The device is the first, to the best of our knowledge, low cost all-Si APD that has potential to compete with current commercial Ge- and III-V-based photodetectors (PDs). This shows the potential to make the all-Si APD a standard "black-box" component in Si photonics CMOS foundry platform component libraries.

32 Gbps heterogeneously integrated quantum dot waveguide avalanche photodiodes on silicon.

We report a heterogeneous GaAs-based quantum dot (QD) avalanche photodiode (APD) on silicon with an ultralow dark current of 10 pA at -1V, 3 dB bandwidth of 20 GHz and record gain-bandwidth product (GBP) of 585 GHz. Furthermore, open eye diagrams up to 32 Gb/s are demonstrated at 1310 nm. The k-factor has been measured for these devices to be as low as 0.14. A polarization dependence on gain and bandwidth has been observed and investigated. This shows the potential to integrate a high-speed receiver in a wavelength division multiplexing (WDM) system on a QD-based silicon photonics platform.

Frequency comb dynamics of a 1.3µm hybrid-silicon quantum dot semiconductor laser with optical injection: erratum.

In Opt. Lett.45, 5755 (2019)OPLEDP0146-959210.1364/OL.44.005755, a factor is missing in the result of Eq. (1). Thus, the width of the comb spectrum $ \Delta \nu $Δν becomes $ \Delta \nu = 2{\sqrt 3} \Gamma {\alpha _e} $Δν=23Γαe.

Frequency comb dynamics of a 1.3 µm hybrid-silicon quantum dot semiconductor laser with optical injection.

This work reports on the influence of bias voltage applied on a saturable absorber (SA) on a subthreshold linewidth enhancement factor (LEF) in hybrid-silicon quantum dot optical frequency comb lasers. Results show that the reverse bias voltage on SA contributes to enlarge the LEF and improve the comb dynamics. Optical injection is also found to be able to improve the comb spectrum in terms of 3 dB bandwidth and its flatness. Such novel findings are promising for the development of high-speed dense wavelength-division multiplexing photonic integrated circuits in optical interconnects and datacom applications.

A multi-directional backlight for a wide-angle, glasses-free three-dimensional display.

Multiview three-dimensional (3D) displays can project the correct perspectives of a 3D image in many spatial directions simultaneously. They provide a 3D stereoscopic experience to many viewers at the same time with full motion parallax and do not require special glasses or eye tracking. None of the leading multiview 3D solutions is particularly well suited to mobile devices (watches, mobile phones or tablets), which require the combination of a thin, portable form factor, a high spatial resolution and a wide full-parallax view zone (for short viewing distance from potentially steep angles). Here we introduce a multi-directional diffractive backlight technology that permits the rendering of high-resolution, full-parallax 3D images in a very wide view zone (up to 180 degrees in principle) at an observation distance of up to a metre. The key to our design is a guided-wave illumination technique based on light-emitting diodes that produces wide-angle multiview images in colour from a thin planar transparent lightguide. Pixels associated with different views or colours are spatially multiplexed and can be independently addressed and modulated at video rate using an external shutter plane. To illustrate the capabilities of this technology, we use simple ink masks or a high-resolution commercial liquid-crystal display unit to demonstrate passive and active (30 frames per second) modulation of a 64-view backlight, producing 3D images with a spatial resolution of 88 pixels per inch and full-motion parallax in an unprecedented view zone of 90 degrees. We also present several transparent hand-held prototypes showing animated sequences of up to six different 200-view images at a resolution of 127 pixels per inch.

Robust hybrid quantum dot laser for integrated silicon photonics.

We demonstrate the first quantum dot (QD) laser on a silicon substrate with efficient coupling of light to a silicon waveguide under the QD gain region. Continuous wave operation up to 100 °C and multiwavelength operation are demonstrated, paving the way towards highly efficient CMOS-compatible, uncooled, WDM sources.

Crosstalk analysis of ring resonator switches for all-optical routing.

Optical switches based on ring resonator cavities were fabricated by a silicon photonics foundry process and analyzed for optical crosstalk at various data rates and channel spacings. These devices were compared to commercial bandpass filters and at 20Gb/s, 0.5dB power penalty is observed due to spectral filtering for bit error ratio threshold of 1 × 10-9. Concurrent modulation at 20Gb/s with a channel spacing as narrow as 40GHz shows error-free transmission with 1dB power penalty as compared to wider channel spacing for the ring-based switch.

Carrier dynamics in GaAs photonic crystal cavities near the material band edge.

We measure fast carrier decay rates (6 ps) in GaAs photonic crystal cavities with resonances near the GaAs bandgap energy at room temperature using a pump-probe measurement. Carriers generated via photoexcitation using an above-band femtosecond pulse cause a substantial blue-shift of three time the cavity linewidth for the cavity peak. The experimental results are compared to theoretical models based on free carrier effects near the GaAs band edge. The probe transmission is modified by nearly 30% for an estimated above-band pump energy of 4.2 fJ absorbed in the GaAs slab.

Compact models for carrier-injection silicon microring modulators.

We propose compact DC and small-signal models for carrier-injection microring modulators that accurately describe the DC characteristics (resonance wavelength, quality factor, and extinction ratio) and the high frequency performance. The proposed theoretical models provide physical insights of the carrier-injection microring modulators with a variety of designs. The DC and small-signal models are implemented in Verilog-A for SPICE-compatible simulations.

A comb laser-driven DWDM silicon photonic transmitter based on microring modulators.

We demonstrate concurrent multi-channel transmission at 10 Gbps per channel of a DWDM silicon photonic transmitter. The DWDM transmitter is based on a single quantum dot comb laser and an array of microring resonator-based modulators. The resonant wavelengths of microrings are thermally tuned to align with the wavelengths provided by the comb laser. No obvious crosstalk is observed at 240 GHz channel spacing.

Sensitivity analysis and optimization of sub-wavelength optical gratings using adjoints.

Numerical optimization of photonic devices is often limited by a large design space the finite-differences gradient method requires as many electric field computations as there are design parameters. Adjoint-based optimization can deliver the same gradients with only two electric field computations. Here, we derive the relevant adjoint formalism and illustrate its application for a waveguide slab, and for the design of optical sub-wavelength gratings.

Picosecond all-optical switching in hydrogenated amorphous silicon microring resonators.

We utilize cross-phase modulation to observe all-optical switching in microring resonators fabricated with hydrogenated amorphous silicon (a-Si:H). Using 2.7-ps pulses from a mode-locked fiber laser in the telecom C-band, we observe optical switching of a cw telecom-band probe with full-width at half-maximum switching times of 14.8 ps, using approximately 720 fJ of energy deposited in the microring. In comparison with telecom-band optical switching in undoped crystalline silicon microrings, a-Si:H exhibits substantially higher switching speeds due to reduced impact of free-carrier processes.

High-speed and energy-efficient non-volatile silicon photonic memory based on heterogeneously integrated memresonator.

Recently, interest in programmable photonics integrated circuits has grown as a potential hardware framework for deep neural networks, quantum computing, and field programmable arrays (FPGAs). However, these circuits are constrained by the limited tuning speed and large power consumption of the phase shifters used. In this paper, we introduce the memresonator, a metal-oxide memristor heterogeneously integrated with a microring resonator, as a non-volatile silicon photonic phase shifter. These devices are capable of retention times of 12 hours, switching voltages lower than 5 V, and an endurance of 1000 switching cycles. Also, these memresonators have been switched using 300 ps long voltage pulses with a record low switching energy of 0.15 pJ. Furthermore, these memresonators are fabricated on a heterogeneous III-V-on-Si platform capable of integrating a rich family of active and passive optoelectronic devices directly on-chip to enable in-memory photonic computing and further advance the scalability of integrated photonic processors.

A 5 × 200 Gbps microring modulator silicon chip empowered by two-segment Z-shape junctions.

Optical interconnects have been recognized as the most promising solution to accelerate data transmission in the artificial intelligence era. Benefiting from their cost-effectiveness, compact dimensions, and wavelength multiplexing capability, silicon microring resonator modulators emerge as a compelling and scalable means for optical modulation. However, the inherent trade-off between bandwidth and modulation efficiency hinders the device performance. Here we demonstrate a dense wavelength division multiplexing microring modulator array on a silicon chip with a full data rate of 1 Tb/s. By harnessing the two individual p-n junctions with an optimized Z-shape doping profile, the inherent trade-off of silicon depletion-mode modulators is greatly mitigated, allowing for higher-speed modulation with energy consumption of sub-ten fJ/bit. This state-of-the-art demonstration shows that all-silicon modulators can practically enable future 200 Gb/s/lane optical interconnects.

Power enhancement and phase regimes in embedded microring resonators in analogy with electromagnetically induced transparency.

Coupled microresonators exhibit great potential for nonlinear applications. In the present work, we explore the nonlinear performance of an embedded ring resonator analogous to an electromagnetically induced transparency (EIT) medium, also known as coupled resonator induced transparency (CRIT). Interestingly, an EIT-like amplitude response can have a remarkably different power enhancement factor that varies by more than one order of magnitude, which is attributed to the different phase regimes of the embedded micro-ring resonators. In addition to the non-monotonic phase profile reported in atomic EIT systems, the phase responses featuring 2 π and 4 π monotonic transitions are identified and analyzed. We also present an interesting phenomenon, in which the power enhancement changes greatly, even with the same transfer function (both intensity and phase responses). This reveals that wisely choosing the operating regime is critical to optimize nonlinear performance of the embedded double resonator system, without adding to design or fabrication difficulty.

High-sensitivity magnetometry based on quantum beats in diamond nitrogen-vacancy centers.

We demonstrate an absolute magnetometer based on quantum beats in the ground state of nitrogen-vacancy centers in diamond. We show that, by eliminating the dependence of spin evolution on the zero-field splitting D, the magnetometer is immune to temperature fluctuation and strain inhomogeneity. We apply this technique to measure low-frequency magnetic field noise by using a single nitrogen-vacancy center located within 500 nm of the surface of an isotopically pure (99.99% 12C) diamond. The photon-shot-noise limited sensitivity achieves 38 nT/sqrt[Hz] for 4.45 s acquisition time, a factor of sqrt[2] better than the implementation which uses only two spin levels. For long acquisition times (>10 s), we realize up to a factor of 15 improvement in magnetic sensitivity, which demonstrates the robustness of our technique against thermal drifts. Applying our technique to nitrogen-vacancy center ensembles, we eliminate dephasing from longitudinal strain inhomogeneity, resulting in a factor of 2.3 improvement in sensitivity.

Optical and spin coherence properties of nitrogen-vacancy centers placed in a 100 nm thick isotopically purified diamond layer.

We have studied optical and spin properties of near-surface nitrogen-vacancy (NV) centers incorporated during chemical vapor phase growth of isotopically purified (12)C single-crystal diamond layers. The spectral diffusion-limited line width of zero-phonon luminescence from the NV centers is 1.2 ± 0.5 GHz, a considerable improvement over that of NV centers formed by ion implantation and annealing. Enhanced spin dephasing times (T(2)* ≈ 90 µs, T(2) ≈ 1.7 ms) due to the reduction of (13)C nuclear spins persist even for NV centers placed within 100 nm of the surface.

Silicon waveguide with four zero-dispersion wavelengths and its application in on-chip octave-spanning supercontinuum generation.

We propose a novel silicon waveguide that exhibits four zero-dispersion wavelengths for the first time, to the best of our knowledge, with a flattened dispersion over a 670-nm bandwidth. This holds a great potential for exploration of new nonlinear effects and achievement of ultra-broadband signal processing on a silicon chip. As an example, we show that an octave-spanning supercontinuum assisted by dispersive wave generation can be obtained in silicon, over a wavelength range from 1217 to 2451 nm, almost from bandgap wavelength to half-bandgap wavelength. Input pulse is greatly compressed to 10 fs.

Coupling of nitrogen-vacancy centers to photonic crystal cavities in monocrystalline diamond.

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.

Analysis and engineering of chromatic dispersion in silicon waveguide bends and ring resonators.

We analyze chromatic dispersion in tightly curved silicon strip and slot waveguides with high index contrast. It is found that the dispersion profile is changed dramatically at both polarization states, when bending radius is reduced to a few microns. Zero-dispersion wavelength may shift by more than 220 nm, which raises a critical issue in design and optimization of micro-resonator-based devices for nonlinear applications. We propose a slot structure to tailor in-cavity dispersion and obtain spectral lines with the standard deviation of frequency-dependent free spectral range of the slot-waveguide resonator made 460 times smaller than that of a strip-waveguide resonator, making it suitable for on-chip octave-spanning frequency comb generation in mid-infrared wavelength range.