Extending the spectrum of fully integrated photonics to submicrometre wavelengths.

Integrated photonics has profoundly affected a wide range of technologies underpinning modern society1-4. The ability to fabricate a complete optical system on a chip offers unrivalled scalability, weight, cost and power efficiency5,6. Over the last decade, the progression from pure III-V materials platforms to silicon photonics has significantly broadened the scope of integrated photonics, by combining integrated lasers with the high-volume, advanced fabrication capabilities of the commercial electronics industry7,8. Yet, despite remarkable manufacturing advantages, reliance on silicon-based waveguides currently limits the spectral window available to photonic integrated circuits (PICs). Here, we present a new generation of integrated photonics by directly uniting III-V materials with silicon nitride waveguides on Si wafers. Using this technology, we present a fully integrated PIC at photon energies greater than the bandgap of silicon, demonstrating essential photonic building blocks, including lasers, amplifiers, photodetectors, modulators and passives, all operating at submicrometre wavelengths. Using this platform, we achieve unprecedented coherence and tunability in an integrated laser at short wavelength. Furthermore, by making use of this higher photon energy, we demonstrate superb high-temperature performance and kHz-level fundamental linewidths at elevated temperatures. Given the many potential applications at short wavelengths, the success of this integration strategy unlocks a broad range of new integrated photonics applications.

Performance improvement in silicon arrayed waveguide grating by suppression of scattering near the boundary of a star coupler.

We investigate the reduction of transition loss across the star coupler boundary in a silicon arrayed waveguide grating (AWG) by suppressing multimode generation and scattering near the boundary of a star coupler. Eight-channel silicon AWGs were designed with optimal conditions based on enhanced field matching in combination with ultrashallow etched structures. The fabricated AWG demonstrates an insertion loss down to 0.63 dB with a cross talk of -23 to -25.3 dB, exhibiting ~0.8 dB improvement of insertion loss and ~4 dB improvement of cross talk compared to the Si AWG fabricated with a conventional double-etch technique.

A fiber-to-chip coupler based on Si/SiON cascaded tapers for Si photonic chips.

This paper reports a fiber-to-chip coupler consisting of a silicon inverted taper and a silicon oxynitride (SiON) double stage taper, where the cascaded taper structure enables adiabatic mode transfer between a submicron silicon waveguide and a single mode fiber. The coupler, fabricated by a simplified process, demonstrates an average coupling loss of 3.6 and 4.2 dB for TM and TE polarizations, respectively, with a misalignment tolerance of ± 2.2 µm for 1 dB loss penalty.

An integrated recirculating optical buffer.

This paper reports an integrated optical buffer consisting of a low loss silicon waveguide delay line and a silicon evanescent gate matrix switch. The integrated device demonstrates an error free operation at 40 Gb/s data rate with a packet delay of 1.1 ns. This demonstration also highlights the silicon evanescent device platform to realize new types of photonic integrated devices by combining the low loss silicon passive components with the silicon evanescent photonic active devices.

A racetrack mode-locked silicon evanescent laser.

By utilizing a racetrack resonator topography, an on-chip mode locked silicon evanescent laser (ML-SEL) is realized that is independent of facet polishing. This enables integration with other devices on silicon and precise control of the ML-SEL's repetition rate through lithographic definition of the cavity length. Both passive and hybrid mode-locking have been achieved with transform limited, 7 ps pulses emitted at a repetition rate of 30 GHz. Jitter and locking range are measured under hybrid mode locking with a minimum absolute jitter and maximum locking range of 364 fs, and 50 MHz, respectively.

Integrated AlGaInAs-silicon evanescent race track laser and photodetector.

Here we report a racetrack resonator laser integrated with two photo-detectors on the hybrid AlGaInAs-silicon evanescent device platform. Unlike previous demonstrations of hybrid AlGaInAs-silicon evanescent lasers, we demonstrate an on-chip racetrack resonator laser that does not rely on facet polishing and dicing in order to define the laser cavity. The laser runs continuous-wave (c.w.) at 1590 nm with a threshold of 175 mA, has a maximum total output power of 29 mW and a maximum operating temperature of 60 C. The output of this laser light is directly coupled into a pair of on chip hybrid AlGaInAs-silicon evanescent photodetectors used to measure the laser output.

A hybrid AlGaInAs-silicon evanescent preamplifier and photodetector.

We report the integration of a hybrid silicon evanescent waveguide photodetector with a hybrid silicon evanescent optical amplifier. The device operates at 1550 nm with a responsivity of 5.7 A/W and a receiver sensitivity of -17.5 dBm at 2.5 Gb/s. The transition between the passive silicon waveguide and the hybrid waveguide of the amplifier is tapered to increase coupling efficiency and to minimize reflections.

A hybrid AlGaInAs-silicon evanescent waveguide photodetector.

We report a waveguide photodetector utilizing a hybrid waveguide structure consisting of AlGaInAs quantum wells bonded to a silicon waveguide. The light in the hybrid waveguide is absorbed by the AlGaInAs quantum wells under reverse bias. The photodetector has a fiber coupled responsivity of 0.31 A/W with an internal quantum efficiency of 90 % over the 1.5 mum wavelength range. This photodetector structure can be integrated with silicon evanescent lasers for power monitors or integrated with silicon evanescent amplifiers for preamplified receivers.

1310nm silicon evanescent laser.

We report the first 1310 nm hybrid laser on a silicon substrate. This laser operates continuous wave (C.W.) up to 105 degrees C. The room temperature threshold current of this laser is 30 mA, and the maximum single sided fiber-coupled output power is 5.5 mW.

Experimental and theoretical thermal analysis of a Hybrid Silicon Evanescent Laser.

In this work we present both experimental and theoretical thermal analysis of an electrically pumped hybrid silicon evanescent laser. Measurements of an 850 mum long Fabry-Perot structure show an overall characteristic temperature of 51 oC, an above threshold characteristic temperature of 100 oC, and a thermal impedance of 41.8 oC/W. Finite element analysis of the laser structure predicts a thermal impedance of 43.5 oC/W, which is within 5% of the experimental results. Using the overall characteristic temperature, above threshold characteristic temperature, and the measured thermal impedance, the continuous wave output power vs. current from the laser is simulated and is in good agreement with experiment.

Electrically pumped hybrid AlGaInAs-silicon evanescent laser.

An electrically pumped light source on silicon is a key element needed for photonic integrated circuits on silicon. Here we report an electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding. This laser runs continuous-wave (c.w.) with a threshold of 65 mA, a maximum output power of 1.8 mW with a differential quantum efficiency of 12.7 % and a maximum operating temperature of 40 degrees C. This approach allows for 100's of lasers to be fabricated in one bonding step, making it suitable for high volume, low-cost, integration. By varying the silicon waveguide dimensions and the composition of the III-V layer, this architecture can be extended to fabricate other active devices on silicon such as optical amplifiers, modulators and photo-detectors.

Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum wells.

A novel laser that utilizes a silicon waveguide bonded to AlGaInAs quantum wells is demonstrated. This wafer scale fabrication approach allows the optical waveguide to be defined by CMOS-compatible silicon processing while optical gain is provided by III-V materials. The AlGaInAs quantum well structure is bonded to the silicon wafer using low temperature oxygen plasma-assisted wafer bonding. The optically pumped 1538 nm laser has a pulsed threshold of 30 mW and an output power of 1.4 mW.

Single-chip photonic transceiver based on bulk-silicon, as a chip-level photonic I/O platform for optical interconnects.

When silicon photonic integrated circuits (PICs), defined for transmitting and receiving optical data, are successfully monolithic-integrated into major silicon electronic chips as chip-level optical I/Os (inputs/outputs), it will bring innovative changes in data computing and communications. Here, we propose new photonic integration scheme, a single-chip optical transceiver based on a monolithic-integrated vertical photonic I/O device set including light source on bulk-silicon. This scheme can solve the major issues which impede practical implementation of silicon-based chip-level optical interconnects. We demonstrated a prototype of a single-chip photonic transceiver with monolithic-integrated vertical-illumination type Ge-on-Si photodetectors and VCSELs-on-Si on the same bulk-silicon substrate operating up to 50 Gb/s and 20 Gb/s, respectively. The prototype realized 20 Gb/s low-power chip-level optical interconnects for λ ~ 850 nm between fabricated chips. This approach can have a significant impact on practical electronic-photonic integration in high performance computers (HPC), cpu-memory interface, hybrid memory cube, and LAN, SAN, data center and network applications.