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Microwave photonics uses light to carry and process microwave signals over a photonic link. However, light can instead be used as a stimulus to microwave devices that directly control microwave signals. Such optically controlled amplitude and phase-shift switches are investigated for use in reconfigurable microwave systems, but they suffer from large footprint, high optical power level required for switching, lack of scalability and complex integration requirements, restricting their implementation in practical microwave systems. Here, we report Monolithic Optically Reconfigurable Integrated Microwave Switches (MORIMSs) built on a CMOS compatible silicon photonic chip that addresses all of the stringent requirements. Our scalable micrometer-scale switches provide higher switching efficiency and require optical power orders of magnitude lower than the state-of-the-art. Also, it opens a new research direction on silicon photonic platforms integrating microwave circuitry. This work has important implications in reconfigurable microwave and millimeter wave devices for future communication networks.

 

Abstract The past two decades have seen widespread efforts being directed toward the development of nanoscale lasers. A plethora of studies on single such emitters have helped demonstrate their advantageous characteristics such as ultrasmall footprints, low power consumption, and room-temperature operation. Leveraging knowledge about single nanolasers, the next phase of nanolaser technology will be geared toward scaling up design to form arrays for important applications. In this review, we discuss recent progress on the development of such array architectures of nanolasers. We focus on valuable attributes and phenomena realized due to unique array designs that may help enable real-world, practical applications. Arrays consisting of exactly two nanolasers are first introduced since they can serve as a building block toward comprehending the behavior of larger lattices. These larger-sized lattices can be distinguished depending on whether or not their constituent elements are coupled to one another in some form. While uncoupled arrays are suitable for applications such as imaging, biosensing, and even cryptography, coupling in arrays allows control over many aspects of the emission behavior such as beam directionality, mode switching, and orbital angular momentum. We conclude by discussing some important future directions involving nanolaser arrays. 

To realize ubiquitously used photonic integrated circuits, on-chip nanoscale sources are essential components. Subwavelength nanolasers, especially those based on a metal-clad design, already possess many desirable attributes for an on-chip source such as low thresholds, room-temperature operation and ultra-small footprints accompanied by electromagnetic isolation at pitch sizes down to ∼50 nm. Another valuable characteristic for a source would be control over its emission wavelength and intensity in real-time. Most efforts on tuning/modulation thus far report static changes based on irreversible techniques not suited for high-speed operation. In this study, we demonstratein-situdynamical tuning of the emission wavelength of a metallo-dielectric nanolaser at room temperature by applying an external DC electric field. Using an AC electric field, we show that it is also possible to modulate the output intensity of the nanolaser at high speeds. The nanolaser’s emission wavelength in the telecom band can be altered by as much as 8.35 nm with a tuning sensitivity of ∼1.01 nm/V. Additionally, the output intensity can be attenuated by up to 89%, a contrast sufficient for digital data communication purposes. Finally, we achieve an intensity modulation speed up to 400 MHz, limited only by the photodetector bandwidth used in this study, which underlines the capability of high-speed operation via this method. This is the first demonstration of a telecom band nanolaser source with dynamic spectral tuning and intensity modulation based on an external E-field to the best of our knowledge.

 

We experimentally demonstrate a silicon photonic chip-scale 16-channel wavelength division multiplexer (WDM) operating in the O-band. The silicon photonic chip consists of a common-input bus waveguide integrated with a sequence of 16 spectral add-drop filters implemented by 4-port contra-directional Bragg couplers and resonant cladding modulated perturbations. The combination of these features reduces the spectral bandwidth of the filters and improves the crosstalk. An apodization of the cladding modulated perturbations between the bus and the add/drop waveguides is used to optimize the strength of the coupling coefficient in the propagation direction to reduce the intra-channel crosstalk on adjacent channels. The fabricated chip was validated experimentally with a measured intra-channel crosstalk of ∼−18.9 dB for a channel spacing of 2.6 nm. The multiplexer/demultiplexer chip was also experimentally tested with a 10 Gbps data waveform. The resulting eye-pattern indicates that this approach is suitable for datacenter WDM-based interconnects in the O-band with large aggregate bandwidths.

 

We present an experimental demonstration of notch filters with arbitrary center wavelengths capable of tunable analog output power values varying between full extinction of 15 and 0 dB. Each filter is composed of highly modular apodized four-port Bragg add/drop filters to reduce the crosstalk between concatenated devices. The constructed photonic integrated circuit experimentally demonstrates spectra shaping using four independent notch filters. Each notch filter supports a bandwidth of$\sim 2\mathrm{nm}$and is shown to be suitable for realization of programmable photonic integrated circuits.

 

We demonstrate a laser tunable in intensity with gigahertz tuning speed based on a III/V reflective semiconductor optical amplifier (RSOA) coupled to a silicon photonic chip. The silicon chip contains a Bragg-based Fabry–Perot resonator to form a passive bandpass filter within its stopband to enable single-mode operation of the laser. We observe a side mode suppression ratio of 43 dB, linewidth of 790 kHz, and an optical output power of 1.65 mW around 1530 nm. We also investigate using a micro-ball lens as an alternative coupling method between the RSOA and the silicon chip.

 

We report an advanced Fourier transform spectrometer (FTS) on silicon with significant improvement compared with our previous demonstration in [Nat. Commun.9,665(2018)2041-1723]. We retrieve a broadband spectrum (7 THz around 193 THz) with 0.11 THz or sub nm resolution, more than 3 times higher than previously demonstrated [Nat. Commun.9,665(2018)2041-1723]. Moreover, it effectively solves the issue of fabrication variation in waveguide width, which is a common issue in silicon photonics. The structure is a balanced Mach–Zehnder interferometer with 10 cm long serpentine waveguides. Quasi-continuous optical path difference between the two arms is induced by changing the effective index of one arm using an integrated heater. The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at the bending sections to keep the footprint compact and avoid modal crosstalk. The reduction of propagation loss leads to higher spectral efficiency, larger dynamic range, and better signal-to-noise ratio. Also, for the first time to our knowledge, we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance. Additionally, we demonstrate that using wide waveguides efficiently leads to a fabrication-tolerant device. This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth (over 60 nm) and high resolution suitable for integration with various mobile platforms.

 

Current silicon waveguide Bragg gratings typically introduce perturbation to the optical mode in the form of modulation of the waveguide width or cladding. However, since such a perturbation approach is limited to weak perturbations to avoid intolerable scattering loss and higher-order modal coupling, it is difficult to produce ultra-wide stopbands. In this Letter, we report an ultra-compact Bragg grating device with strong perturbations by etching nanoholes in the waveguide core to enable an ultra-large stopband with apodization achieved by proper location of the nanoholes. With this approach, a 15 µm long device can generate a stopband as wide as 110 nm that covers the entire$\mathrm{C}+\mathrm{L}$band with a 40 dB extinction ratio and over a 10 dB sidelobe suppression ratio (SSR). Similar structures can be further optimized to achieve higher SSR of$><\#comment/>17\mathrm{d}\mathrm{B}$for a stopband of about 80 nm.