Fast optical switches have been proposed as a promising alternative to enable continual scaling of data centers with increasing size and data rates. Silicon photonics is a compelling platform for large-scale integrated photonic switches, leveraging advanced manufacturing foundries for electronic integrated circuits. In the past decade, the port counts of silicon photonic switches have increased steadily to $128\times 128$. Further scaling of the switch is constrained by the maximum reticle size (2–3 cm) of lithography tools. Here, we propose to use wafer-scale integration to overcome the die size limit. As a proof of concept demonstration, we fabricated a $240\times 240$ switch by lithographically stitching a $3\times 3$ array of identical $80\times 80$ switch blocks across reticle boundaries. Stitching loss is substantially reduced (0.004 dB) by tapering the waveguide width to 10 μm. The fabricated switch on a $4\mathrm{cm}\times 4\mathrm{cm}$ chip exhibits a maximum on-chip loss of 9.8 dB, an ON/OFF ratio of 70 dB, and switching times of less than 400 ns. To our knowledge, this is the largest integrated photonic switch ever reported. The loss-to-port count ratio (0.04 dB/port) is also the lowest.

Passive radiative cooling functions by reflecting the solar spectrum and emitting infrared waves in broadband or selectively. However, cooling enclosed spaces that trap heat by greenhouse effect remains a challenge. We present a Janus emitter (JET) consisting of an Ag–polydimethylsiloxane layer on micropatterned quartz substrate. The induced spoof surface plasmon polariton helps overcome inherent emissivity loss of the polymer and creates near-ideal selective and broadband emission on the separate sides. This design results in not only remarkable surface cooling when the JET is attached with either side facing outwards but also space cooling when used as an enclosure wall. Thus, the JET can passively mitigate the greenhouse effect in enclosures while offering surface cooling performance comparable to conventional radiative coolers.

We report on 50x50 silicon photonic MEMS switches with reduced polarization dependence. The switches make use of two-level waveguide crossbars and MEMS-actuated adiabatic couplers. Simulations indicate that by eliminating all polarization-dependent elements (e.g., waveguide crossings), low polarization-dependent losses (<1 dB) can be realized. An experimental prototype switch was fabricated by bonding two silicon-on-insulator (SOI) wafers. A polarization-dependent loss of 8.5 dB and a polarization-dependent delay of 44 ps were measured. The extinction ratios are greater than 40 dB for both polarizations. With improved fabrication, total on-chip loss < 2 dB can potentially be achieved for both polarizations.

We present a design for an analog phase shifter based on Silicon Photonic MEMS technology. The operation principle is based on a two-step parallel plate electrostatic actuation mechanism to bring a vertically movable suspended tapered waveguide in a first step into proximity of the bus waveguide and to tune the phase of the propagating coupled mode in a second step by actuation of the suspended waveguide to tune the vertical gap. In the coupled state, the effective index of the optical supermode and the total accumulated phase delay can be varied by changing the vertical separation between the adiabatically tapered suspended and the fixed bus waveguides. Simulations predict that π phase shift can be achieved with an actuation voltage of 19 V, corresponding to a displacement of 19 nm. With an adiabatic coupler geometry, the optical signal can be coupled between the moving waveguide and the bus waveguide with low loss in a wide wavelength range from 1.5 μm to 1.6 μm keeping the average insertion loss below 0.3 dB.

We report on monolithically integrated wavelength cross-connects (WXCs) on an enhanced silicon photonic platform with integrated micro-electro-mechanical-system (MEMS) actuators. An 8 × 8 WXC with 8 wavelength channels comprising 16 echelle gratings and 512 silicon photonic MEMS switches is integrated on a 9.7 mm × 6.7 mm silicon chip. The WXC inherits the fundamental advantages of silicon photonic MEMS space switches, including low loss, broad optical bandwidth, large fabrication tolerance, and simple digital control. The WXC exhibits a low crosstalk of −30 dB, a submicrosecond switching time of 0.7 µs, and on-chip optical insertion losses varying from 8.8 dB to 16.4 dB. To our knowledge, it is the largest channel capacity (64 channels = 8 ports × 8 wavelengths) integrated WXC ever reported.

Artificial intelligence and machine learning workloads are changing all aspects of the compute infrastructure—from data centers and cloud hyperscalers to high-performance computers (HPC).¹ Data centers are being enhanced with specialized HPC-like hardware to handle machine learning workloads. Hyperscale cloud infrastructure is enhanced with rack-scale and distributed solutions. Optical switching solutions have been proposed to improve the utilization of the computer resources as well as reducing latency and energy consumption.^{2 – 6} Silicon photonic switches are particularly attractive for such applications, and several research groups have developed silicon photonics switches based on cascaded Mach–Zehnder interferometers.^{7 – 14} However, their optical losses increase rapidly with port count, limiting the scalability of these switches.