Monolithic Integration of Al₂O₃ and Si₃N₄ Toward Double-Layer Active–Passive Platform

Abstract

Low-cost, high-performance integration technologies are instrumental for active-passive integrated photonics devices. The monolithic integration of Al 2 O 3 and Si 3 N 4 is studied, enabling to combine the promising optical features of Si 3 N 4 with the excellent optical gain characteristics of rare-earth-ion doped Al 2 O 3 . The Al 2 O 3 and Si 3 N 4 layers are separated by a thin SiO 2 film and coupled by adiabatically width-tapered Al 2 O 3 and thickness-tapered Si 3 N 4 waveguides. In this paper, a detailed characterization of the couplers, as well as a study of the influence of the different design parameters and fabrication tolerances on the final device performance is presented. Test structures are characterized under transverse electric (TE) polarization. Measured loss per coupler is as low as 0.26 ± 0.03 dB at the wavelength of 1030 nm, and below 0.24 dB in the spectral window of 1460-1635 nm. Lateral misalignment of ±1 µm results in less than 0.6 dB increase of the coupler loss at 1030 nm, and the tolerance of misalignment goes up to 1.7 µm at the investigated longest wavelength of 1635 nm without introducing extra coupler losses. The reported integration technology paves the way toward a double-layer platform monolithically integrating Si 3 N 4 and rare-earth-ion doped Al 2 O 3 for active-passive photonic functionalities.

High-gain waveguide amplifiers in Si3N4 technology via double-layer monolithic integration

“…In this work, we present an integrated high total gain (i.e., from passive waveguide to passive waveguide) optical amplifier in Al 2 O 3 :Er 3 monolithically integrated onto the Si 3 N 4 platform via a double-layer platform [38]. Different from previous integration methodologies in which the Al 2 O 3 :RE 3 material was directly deposited onto Si 3 N 4 elements [20,21,23,31] or sputtered into SiO 2 trenches within the Si 3 N 4 platform [19,22], in our approach the Al 2 O 3 :RE 3 and the Si 3 N 4 waveguides are located in two individual layers separated by a thin SiO 2 film.…”

Rare-earth ion doped Al2O3 for active integrated photonics

“…For straight devices, such as distributed feedback lasers (DFB) and distributed Bragg reflector (DBR) lasers, the doped Al 2 O 3 layer can be simply deposited on top of the Si 3 N 4 waveguides both multi- [8,35,36,45] or single-striped [33,40,41] ( Figure 5 view schematics of the couplers as well as the cross-sections at different positions along the length of the coupler. Transition losses below 0.2 dB/ coupler were experimentally demonstrated [77,78]. The couplers exhibited very high tolerance to lateral misalignment (~±2 µm for 1 dB penalty for wavelengths in the C-band) during the lithography step of the top photonic layer.…”

“…Very recently, Mu et al proposed a smaller waveguide cross-section (i.e., a channel waveguide of 1 µm x 0.8 µm), with an erbium concentration of 1.7 × 10 20 cm −3 . Such waveguide amplifier was integrated onto the Si 3 N 4 integrated photonic platform via double-layer monolithic integration technology using adiabatic vertical tapers [77]. A net Si 3 N 4 -Si 3 N 4 peak gain of 18 dB was achieved with a 10 cm long spiral amplifier at 1532 nm with a bidirectional pumping scheme with total incident pump power of 50 mW (estimated coupling losses ~12 dB for 976 nm wavelength) and incident signal power of -20 dBm [108].…”

“…Benefiting from all the developments discussed above in this review paper, namely the development of low-loss Al 2 O 3 deposited at low temperature [37], integration with Si 3 N 4 using a trench configuration [12,39,44], DFB laser design [35,36,116] and adiabatic transitions from the hybrid active gain region to the passive Si 3 N 4 waveguides [39,77,78], complex systems can be built. An impressive demonstration of such system for LIDAR application was recently presented by Notaros et al [76].…”

Al2O3:Yb3+ integrated microdisk laser label-free biosensor

“…When doped with rare-Earth ions, it provides optical gain that has been used to demonstrate on-chip amplifiers [15] and lasers [16,17]. Recent reports have shown its monolithic integration with passive photonic functions [18][19][20]. These features make this material very interesting for the realization of active optical sensors.…”