Generating optical combs in a small form factor is of utmost importance for a wide range of applications such as datacom, LIDAR, and spectroscopy. Electrically powered mode-locked diode lasers provide combs with a high conversion efficiency, while simultaneously allowing for a dense spectrum of lines. In recent years, a number of integrated chip scale mode-locked lasers have been demonstrated. However, thus far these devices suffer from significant linear and nonlinear losses in the passive cavity, limiting the attainable cavity size and noise performance, eventually inhibiting their application scope. Here, we leverage the ultra-low losses of silicon-nitride waveguides to demonstrate a heterogeneously integrated III-V-on-silicon-nitride passively mode-locked laser with a narrow 755 MHz line spacing, a radio frequency linewidth of 1 Hz and an optical linewidth below 200 kHz. Moreover, these comb sources are fabricated with wafer scale technology, hence enabling low-cost and high volume manufacturable devices.
A novel hybrid integration strategy for compact, broadband and highly efficient mmWave on-chip antennas is demonstrated by realizing a hybrid on-chip antenna, operating in the [27.5-29.5] GHz band. A cavity-backed stacked patch antenna is implemented on a 600 µm-thick silicon substrate by using airfilled substrate-integrated-waveguide technology. A hybrid onchip approach is adopted in which the antenna feed and an air-filled cavity are integrated on chip and the stacked patch configuration is implemented on a high frequency PCB laminate that supports the chip. A prototype of the hybrid on-chip antenna is validated, demonstrating an impedance bandwidth of 3.7 GHz. In free-space conditions, a boresight gain of 7.3 dBi and a front-to-back ratio of 20.3 dB at 28.5 GHz are achieved. Moreover, the antenna is fabricated using standard silicon fabrication techniques and features a total antenna efficiency above 90 % in the targeted frequency band of operation. The high performance, in combination with the compact antenna footprint of 0.49 λmin × 0.49 λmin, makes it an ideal building block to construct broadband antenna arrays with a broad steering range.
Successful micro-transfer printing of lithium niobate on a silicon nitride platform is demonstrated. A proof of concept electro-optical modulator is fabricated using this hybrid integration method which shows a half-wave voltage-length product V π L π = 5.5 Vcm and insertion losses of 7 dB.
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