Silicon source of frequency-bin entangled photons.

New machine learning algorithms such as deep neural networks and the availability of large datasets have created a large drive towards new types of hardware capable of executing these algorithms with higher energy-efficiency. Recently, silicon photonics has emerged as a promising hardware platform for neuromorphic computing due to its inherent capability to process linear and non-linear operations and transmit a high bandwidth of data in parallel. At Hewlett Packard Labs, an energy-efficient dense-wavelength division multiplexing (DWDM) silicon photonics platform has been developed as the underlying foundation for innovative neuromorphic computing architectures. The latest research on our silicon photonic neuromorphic platform will be presented and discussed.

A compact three-laser source for optical sensing is presented. It is based on a low-noise implementation of the Pound-Drever-Hall method and comprises high-bandwidth optical phase-locked loops. The outputs from three semiconductor distributed feedback lasers, mounted on thermo-electric coolers (TEC), are coupled with micro-lenses into a silicon photonics (SiP) chip that performs beat note detection and several other functions. The chip comprises phase modulators, variable optical attenuators, multi-mode-interference couplers, variable ratio tap couplers, integrated photodiodes and optical fiber butt-couplers. Electrical connections between a metallized ceramic and the TECs, lasers and SiP chip are achieved by wirebonds. All these components stand within a 35 mm by 35 mm package which is interfaced with 90 electrical pins and two fiber pigtails. One pigtail carries the signals from a master and slave lasers, while another carries that from a second slave laser. The pins are soldered to a printed circuit board featuring a micro-processor that controls and monitors the system to ensure stable operation over fluctuating environmental conditions. This highly adaptable multi-laser source can address various sensing applications requiring the tracking of up to three narrow spectral features with a high bandwidth. It is used to sense a fiber-based ring resonator emulating a resonant fiber optics gyroscope. The master laser is locked to the resonator with a loop bandwidth greater than 1 MHz. The slave lasers are offset frequency locked to the master laser with loop bandwidths greater than 100 MHz. This high performance source is compact, automated, robust, and remains locked for days.

Light-emitting diodes (LEDs) based on III-V/II-VI materials have delivered a compelling performance in the mid-infrared (mid-IR) region, which enabled wide-ranging applications in sensing, including environmental monitoring, defense, and medical diagnostics. Continued efforts are underway to realize on-chip sensors via heterogeneous integration of mid-IR emitters on a silicon photonic chip, but the uptake of such an approach is limited by the high costs and interfacial strains, associated with the processes of heterogeneous integrations. Here, the black phosphorus (BP)-based van der Waals (vdW) heterostructures are exploited as room-temperature LEDs. The demonstrated devices emit linearly polarized light, and the spectra cover the technologically important mid-IR atmospheric window. Additionally, the BP LEDs exhibit fast modulation speed and exceptional operation stability. The measured peak extrinsic quantum efficiency is comparable to the III-V/II-VI mid-IR LEDs. By leveraging the integrability of vdW heterostructures, we further demonstrate a silicon photonic waveguide-integrated BP LED.

We present a flip-chip integration process in which the vertical alignment is guaranteed by a mechanical contact between pedestals defined in a recess etched into a silicon photonics chip and a laser or semiconductor optical amplifier. By selectively etching up to the active region of the III-V materials, we can make the accuracy of vertical alignment independent on the process control applied to layer thicknesses during silicon photonics or III-V chip fabrication, enabling alignment tolerances below ±10 nm in the vertical (Z-)direction.

We investigate the effect of tunable optical feedback on a commercial DFB laser edge coupled to a Silicon Photonics planar integrated circuit in which a tunable reflector has been implemented by means of a ring resonator based add-drop multiplexer. Controlled optical feedback allows for fine-tuning of the laser oscillation frequency. Under certain conditions it also allows suppression of bifurcation modes triggered by reflections occurring elsewhere on the chip. A semi-analytical model describing laser dynamics under combined optical feedback from the input facet of the edge coupler and from the tunable on-chip reflector fits the measurements. Compensation of detrimental effects from reflections induced elsewhere on a transceiver chip may allow moving isolators downstream in future communications systems, facilitating direct hybrid laser integration in Silicon Photonics chips, provided a suitable feedback signal for a control system can be identified. Moreover, the optical frequency tuning at lower feedback levels can be used to form a rapidly tunable optical oscillator as part of an optical phase locked loop, circumventing the problem of the thermal to free carrier effect crossover in the FM response of injection current controlled semiconductor laser diodes.

The knowledge of the exact frequency of an optical source has always been one of the ultimate goals in optics. Since the discovery of the laser, complex systems have been developed to address this challenge. That effort reached a significant milestone with the advent of the femtosecond laser frequency comb that reduced the system size from an entire lab down to the bench‐top. That spurred interest in the development of integrated optical frequency synthesizers that can generate precisely different optical frequencies on demand and can be deployed widely. In this work, such an optical frequency synthesizer using supercontinuum waveguide and second harmonic generator on silicon photonics platform is demonstrated. Integrated silicon photonics based tunable continuous wave laser is phase‐locked to a microwave reference, to synthesize absolute optical frequencies in the telecom band. A relative frequency instability of 1 × 10−12 at 1 s level is achieved by utilizing an integrated self‐referencing scheme that exploits the strong 3rd order and electric‐field‐induced 2nd order nonlinearities of silicon waveguides. With this work, an all on‐chip silicon photonics based frequency synthesizer seems promising for mass production of next generation broad‐band coherent optical communication systems, spectroscopic, detection, and ranging systems and future integrated quantum systems with Hz‐level precision.

Photonic integrated circuits (PICs), implementing optical functions such as light generation, modulation, routing and detection on a single chip, are emerging as a powerful platform to realize miniaturized optical systems. These chips find applications in various fields, ranging from high-speed optical transceivers to disposable biosensors, LiDARs for detection and ranging, spectroscopic analytical sensors, etc. Silicon photonics is the field that is using silicon fabrication technologies, developed over the last decades for advanced electronic integrated circuits, to realize PI Cs. Using this approach advanced PICs can be realized on 200 mm or 300 mm wafers in high volume and at low cost. On the silicon photonics platform many device structures are readily available: Si or SiN waveguides, micro-heaters for tuning/switching, Si or Ge based modulators and photodetectors. However, other optical functions such as light generation require the integration of III-V semiconductors on the silicon wafers. This can be realized using different approaches ranging from hybrid assembly over die-towafer bonding to monolithic integration. Every approach has its advantages and disadvantages. An interesting approach that we are developing is the use of microtransfer- printing technology for the integration of III-V semiconductor devices on a silicon photonic wafer, which is a scalable and minimally-invasive approach.

In this paper we describe our work on heterogeneously integrated laser diodes on a silicon photonics platform. Different types of laser diodes are presented, different both in terms of wavelength / material platform (850 nm, 1550nm, 2000nm, 2300nm) as well as laser geometry. The integration of the III-V semiconductor materials on the silicon photonic integrated circuits is realized through adhesive die-to-wafer bonding. We will report on the realization of hybrid 850 nm VCSELs and high-speed directly and externally modulated lasers, mode-locked lasers and tunable lasers in the C-band. We also discuss our work on single wavelength laser arrays and tunable lasers in the 2um wavelength range. These integrated laser sources complete the toolkit for silicon photonics enabling highly integrated solutions for optical communication and sensing applications.

We demonstrate an ultra-broadband silicon photonic interleaver capable of interleaving and de-interleaving frequency comb lines over a 125 nm bandwidth in the extended C- and L-bands. We use a ring-assisted asymmetric Mach Zehnder interferometer to achieve a flat-top passband response while maintaining a compact device footprint. The device has a 400 GHz free spectral range to divide an optical frequency comb with 200 GHz channel spacing into two output groups, each with a channel spacing of 400 GHz, yielding a potential capacity of 78 total wavelength-division multiplexed channels between 1525 nm and 1650 nm. This device represents an important step towards realizing highly parallel integrated optical links with broadband frequency comb sources within the silicon photonics platform.

Silicon photonics is advancing rapidly in performance and capability with multiple fabrication facilities and foundries having advanced passive and active devices, including modulators, photodetectors, and lasers. Integration of photonics with electronics has been key to increasing the speed and aggregate bandwidth of silicon photonics based assemblies, with multiple approaches to achieving transceivers with capacities of 1.6 Tbps and higher. Progress in electronics has been rapid as well, with state-of-the-art chips including switches having many tens of billions of transistors. However, the electronic system performance is often limited by the input/output (I/O) and the power required to drive connections at a speed of tens of Gbps. Fortunately, the convergence of progress in silicon photonics and electronics means that co-packaged silicon photonics and electronics enable the continued progress of both fields and propel further innovation in both.

We have proposed and demonstrated a method for the fabrication of a SOI platform with custom-design device layer thickness ( 1 μm, operating at λ ~ 1550 nm. The input/output waveguides can be pigtailed with standard single-mode fiber with lensed tip ensuring modal overlap of >70% (coupling loss <1.5 dB). Such a multi-input multi-output SOI platform will facilitate for CMOS silicon photonics based on-chip applications with an additional usage freedom of device layer thickness. Moreover, it can be potentially used to design SOI based stand-alone devices which can be useful at transmitters/repeaters for short-haul/long-haul optical communication.

We present a strictly nonblocking 4 × 4 electrooptic silicon photonic switch fabric with on-chip gain. The switch integrates 12 Mach-Zehnder cells in a 3-stage topology equipped with fast electrooptic phase shifters, and thermooptic phase trimmers. To compensate for the losses of the fabric, a 4-channel GaInAsP/InP semiconductor optical amplifier array is flip-chip attached into an etched cavity in the silicon photonic chip with butt-coupled waveguide interfaces. The chip is wirebonded to a CMOS driver that provides push-pull drive to each elementary Mach-Zehnder cell. We demonstrate an optical switch assembly with net neutral insertion loss in the C-band together with nanosecond-scale reconfiguration time.

We demonstrate on-chip non-invasive monitoring of orthogonal modes transmitted in a silicon photonic waveguide. The proposed technique exploits a recently developed ContactLess Integrated Photonic Probe (CLIPP) realizing a fully transparent integrated light detector. The optical intensity of the modes propagating in the waveguide is tracked in time by the CLIPP, with no signal quality degradation induced by monitoring operations. We exploit this concept for the simultaneous monitoring of two intensity modulated 10 Gbit/s data channels transmitted at the same wavelength and multiplexed on the fundamental transverse electric and magnetic modes of the silicon waveguide. By labeling each signal with a weakly modulated pilot tone, the CLIPP can discriminate at the same time the two channels, the monitoring of one signal not affecting the readout of the other one. The scalability of the presented technique to several modes on arbitrary polarization states, along with the fabrication simplicity and CMOS compatibility of the CLIPP detector, makes this approach promising for the monitoring and control of integrated components for mode-division multiplexing systems.

We propose a new opto-mechanical ultrasound sensor (OMUS) enabled by an innovative silicon photonics waveguide. We present experimental results up to 30 MHz, a 10-sensor array proof-of-concept and our latest findings.

We demonstrate an alignment tolerant through-substrate coupling interface by combining an optimized downward-directionality grating on a silicon photonic chip with a hybrid integrated polymer lens, generating a collimated beam at λ=1310nm for more than 600µm.