Gallium phosphide (GaP) is an indirect bandgap semiconductor used widely in solid-state lighting. Despite numerous intriguing optical properties-including large χ (2) and χ (3) coefficients, a high refractive index (> 3), and transparency from visible to long-infrared wavelengths (0.55 − 11 µm)its application as an integrated photonics material has been little studied. Here we introduce GaPon-insulator as a platform for nonlinear photonics, exploiting a direct wafer bonding approach to realize integrated waveguides with 1.2 dB/cm loss in the telecommunications C-band (on par with Si-on-insulator). High quality (Q > 10 5 ), grating-coupled ring resonators are fabricated and studied. Employing a modulation transfer approach, we obtain a direct experimental estimate of the nonlinear index of GaP at telecommunication wavelengths: n2 = 1.2(5) × 10 −17 m 2 /W. We also observe Kerr frequency comb generation in resonators with engineered dispersion. Parametric threshold powers as low as 3 mW are realized, followed by broadband (> 100 nm) frequency combs with sub-THz spacing, frequency-doubled combs and, in a separate device, efficient Raman lasing. These results signal the emergence of GaP-on-insulator as a novel platform for integrated nonlinear photonics.

Direct epitaxial growth of III-Vs on silicon for optical emitters and detectors is an elusive goal. Nanowires enable the local integration of high-quality III-V material, but advanced devices are hampered by their high-aspect ratio vertical geometry. Here, we demonstrate the in-plane monolithic integration of an InGaAs nanostructure p-i-n photodetector on Si. Using free space coupling, photodetectors demonstrate a spectral response from 1200-1700 nm. The 60 nm thin devices, with footprints as low as ~0.06 μm2, provide an ultra-low capacitance which is key for high-speed operation. We demonstrate high-speed optical data reception with a nanostructure photodetector at 32 Gb s−1, enabled by a 3 dB bandwidth exceeding ~25 GHz. When operated as light emitting diode, the p-i-n devices emit around 1600 nm, paving the way for future fully integrated optical links.

The development of integrated photonic circuits utilizing gallium phosphide requires a robust, scalable process for fabrication of GaP-on-insulator devices. Here, we present the first GaP photonic devices on SiO 2 . The process exploits direct wafer bonding of a GaP/Al x Ga 1 −x P/GaP heterostructure onto a SiO 2 -on-Si wafer followed by the removal of the GaP substrate and the Al x Ga 1 −x P stop layer. Photonic devices such as grating couplers, waveguides, and ring resonators are patterned by inductively coupled-plasma reactive-ion etching in the top GaP device layer. The peak coupling efficiency of the fabricated grating couplers is as high as −4.8 dB. Optical quality factors of 20 000 as well as second-and third-harmonic generation are observed with the ring resonators. Because the large bandgap of GaP provides for low two-photon absorption at telecommunication wavelengths, the high-yield fabrication of GaP-on-insulator photonic devices enabled by this work is especially interesting for applications in nanophotonics, where high quality factors or low mode volumes can produce high electric field intensities. The large bandgap also enables integrated photonic devices operating at visible wavelengths.

Gallium phosphide offers an attractive combination of a high refractive index ( > for vacuum wavelengths up to 4 µm) and a wide electronic bandgap (2.26 eV), enabling optical cavities with small mode volumes and low twophoton absorption at telecommunication wavelengths. Heating due to strongly confined light fields is therefore greatly reduced. Here, we investigate the benefits of these properties for cavity optomechanics. Utilizing a recently developed fabrication scheme based on direct wafer bonding, we realize integrated one-dimensional photonic crystal cavities made of gallium phosphide with optical quality factors as high as 1.1 × 10 5 . We optimize their design to couple the optical eigenmode at ~200 THz via radiation pressure to a co-localized mechanical mode with a frequency of 3 GHz, yielding sideband-resolved devices. The high vacuum optomechanical coupling rate ( = × kHz) permits amplification of the mechanical mode into the so-called mechanical lasing regime with input power as low as ~20 μW. The observation of mechanical lasing implies a multiphoton cooperativity of C > 1, an important threshold for the realization of quantum state transfer protocols. Because of the reduced thermo-optic resonance shift, optomechanically induced transparency can be detected at room temperature in addition to the normally observed optomechanically induced absorption.

On-chip optical light sources are key components in photonic integrated circuits and optical communication. In this paper, we use a novel integration technique called template-assisted selective epitaxy (TASE) to monolithically integrate InP microdisk lasers on silicon. TASE offers several advantages for new device concepts such as lateral doping, dense co-integration of different III-V materials, and in-plane integration with silicon electronics and passive components. Here, we demonstrate roomtemperature lasing from InP hexagonal microdisks integrated via TASE. In order to assess and evaluate the viability of TASE, a second InP hexagonal microdisk sample is prepared for comparison using the highly developed and mature direct wafer bonding technique. The lasing performance of the TASE monolithic devices and the bonded microdisk devices is investigated under pulsed optical pumping as a function of temperature and compared. The lasing threshold as well as the light-in light-out curves of our TASE structures compare favorably with the bonded InP hexagonal microdisks. This demonstrates that our TASE approach is a promising technique for the monolithic integration of optical devices on Si.