Monolithic integration of broadband optical isolators for polarization-diverse silicon photonics

Integrated optical isolators have been a longstanding challenge for photonic integrated circuits (PIC). An ideal integrated optical isolator for PIC should be made by a monolithic process, have a small footprint, exhibit broadband and polarization-diverse operation, and be compatible with multiple materials platforms. Despite significant progress, the optical isolators reported so far do not meet all these requirements. In this article we present monolithically integrated broadband magneto-optical isolators on silicon and silicon nitride (SiN) platforms operating for both TE and TM modes with record high performances, fulfilling all the essential characteristics for PIC applications. In particular, we demonstrate fully-TE broadband isolators by depositing high quality magneto-optical garnet thin films on the sidewalls of Si and SiN waveguides, a critical result for applications in TE-polarized on-chip lasers and amplifiers. This work demonstrates monolithic integration of high performance optical isolators on chip for polarization-diverse silicon photonic systems, enabling new pathways to impart nonreciprocal photonic functionality to a variety of integrated photonic devices

1.3 μm submilliamp threshold quantum dot micro-lasers on Si

As a promising integration platform, silicon photonics need on-chip laser sources that dramatically improve capability, while trimming size and power dissipation in a cost-effective way for volume manufacturability. Currently, direct heteroepitaxial growth of III–V laser structures on Si using quantum dots as the active region is a vibrant field of research, with the potential to demonstrate low-cost, high-yield, long-lifetime, and high-temperature devices. Ongoing work is being conducted to reduce the power consumption, maximize the operating temperature, and switch from miscut Si substrates toward the so-called exact (001) Si substrates that are standard in microelectronics fabrication. Here, we demonstrate record-small electrically pumped micro-lasers epitaxially grown on industry standard (001) silicon substrates. Continuous-wave lasing up to 100°C was demonstrated at 1.3 μm communication wavelength. A submilliamp threshold of 0.6 mA was achieved for a micro-laser with a radius of 5 μm. The thresholds and footprints are orders of magnitude smaller than those previously reported lasers epitaxially grown on Si

Integrated Optical Isolators and Circulators for Heterogeneous Silicon Photonics

Integrated optical isolators are nonreciprocal optical components that allow light to pass in one direction only. They are useful in conjunction with lasers, as they block undesired reflections from entering the laser cavity, where it might destabilize the device. Optical circulators are extensions of isolators, as they reroute the backwards propagating light into another direction. Thus, they can be used to separate counterpropagating signals. Both devices have many uses in photonic integrated circuits, but are challenging to implement, due to the reciprocal nature of most semiconductor and dielectric materials.Magnetic materials such as garnets can break the symmetry and are well suited for optical isolators and circulators. However, they are difficult to integrate with silicon, III-V, and other commonly used optical materials. Heterogeneous integration through wafer bonding can overcome this obstacle and is used successfully in this work to achieve integrated optical isolators and circulators on silicon with record performance. This is done through waveguide optimization, careful process development, and a novel idea to integrate the source of magnetic fields, an electromagnet, directly onto the chip. This not only shrinks the footprint of the devices, but also provides flexibility in design as well as wavelength tunability, which is critical if the device is to be used in a circuit.Two flavors of the isolator and circulator are presented. One is a resonant device using a microring that can achieve up to 32dB of isolation. Slight modifications to the design can result in a microring optical circulator as well, a first to the best of our knowledge. The other device architecture is a nonresonant device using a Mach-Zehnder interferometer. While these devices have larger footprint, they can achieve optical isolation over 20dB over a wide wavelength range of 18nm. This is extremely useful in applications such as data transmission, where backwards propagating light may be spread over several nanometers. Of course, the isolator should be paired with a laser to realize its true potential. Several design and fabrication challenges stand in the way of this, which are addressed in this work. Polarization rotators are implemented to match the operating polarization between the laser and the isolator, and fabrication is carefully tailored such that both devices can be integrated on the same chip. Preliminary results show that the laser and isolator integration can happen in the near future. Such a demonstration would open up new opportunities in photonic integrated circuits, and would be of great interest in optical communications, sensing, RF photonics, as well as new, unexplored fields

Electro-luminescent cooling: light emitting diodes above unity efficiency

Experimental demonstration of net electro-luminescent cooling in a diode, or equivalently electroluminescence with wall-plug efficiency greater than unity, had eluded direct observation for more than five decades. We review experiments demonstrating light emission from a light-emitting diode in which the electron population is pumped by a combination of electrical work and heat

A Sub-Picojoule per Bit Integrated Magneto-Optic Modulator on Silicon: Modeling and Experimental Demonstration

Integrated magneto-optic (MO) modulators are an attractive but not fully explored alternative to electro-optic (EO) modulators. They are current driven, structurally simple, and could potentially achieve high efficiency in cryogenic and room temperature environments where fJ bit−1 optical interfaces are needed. In this paper, the performance and energy efficiency of a novel MO modulator at room temperature are for the first time assessed. First, a model of the micro-ring-based modulator is implemented to investigate the design parameters and their influence on the performance. Then, a fabricated device is experimentally characterized to assess its performance in terms of bit rate and energy efficiency. The model shows efficient operation at 1.2 Gbps using a 16 mA drive current, consuming only 155 fJ bit−1. The experimental results show that the MO effect is suitable for modulation, achieving error-free operation above 16 mA with a power consumption of 258 fJ bit−1 at a transient limited data rate of 1.2 Gbps

Ultra-Low-Loss Silicon Waveguides for Heterogeneously Integrated Silicon/III-V Photonics

Integrated ultra-low-loss waveguides are highly desired for integrated photonics to enable applications that require long delay lines, high-Q resonators, narrow filters, etc. Here, we present an ultra-low-loss silicon waveguide on 500 nm thick Silicon-On-Insulator (SOI) platform. Meter-scale delay lines, million-Q resonators and tens of picometer bandwidth grating filters are experimentally demonstrated. We design a low-loss low-reflection taper to seamlessly integrate the ultra-low-loss waveguide with standard heterogeneous Si/III-V integrated photonics platform to allow realization of high-performance photonic devices such as ultra-low-noise lasers and optical gyroscopes