Self-phase modulation (SPM) is an important third-order nonlinear optical process that has been widely used in many applications, such as broadband optical sources, optical diodes, optical spectroscopy, pulse compression, and many others. The ability to realize SPM based on-chip integrated photonic devices will reap attractive benefits of compact footprint, high stability, high scalability, and low-cost mass production. Here, we experimentally investigate enhanced SPM in silicon nitride (Si3N4) waveguides by integrating with 2D graphene oxide (GO) films. The on-chip integration of GO films is achieved on Si3N4 waveguides through a solution-based, transfer-free, layer-by-layer coating method with precise control of the film thickness. We use both picosecond and femtosecond optical pulses to perform detailed SPM measurements. Owing to the high Kerr nonlinearity of GO, the GO-coated waveguides show significantly improved spectral broadening for both the picosecond and femtosecond optical pulses compared to the uncoated waveguide, achieving a broadening factor of up to ~3.4 for a device with 2 layers of GO. Based on the experimental results which show good agreement with theory, we obtain an improvement in the waveguide nonlinear parameter by a factor of up to 18.4 and a Kerr coefficient (n2) of GO that is about 5 orders of magnitude higher than Si3N4. These results reveal the effectiveness of 2D GO films to improve the nonlinear performance of Si3N4 waveguides.
The power-sensitive photo-thermal tuning (PTT) of two-dimensional (2D) graphene oxide (GO) integrated on the top surface of silicon nitride (SiN) waveguides is experimentally investigated. For SiN waveguide coating with monolayer GO, the light power thresholds for reversible and permanent GO reduction are measured. There are three reduction stages identified based on the presence of reversible versus permanent reduction. We also compared the PTT induced by a continuous-wave laser and a pulsed laser with the same average power, confirming that the PTT is primarily determined by the average input power.
Silicon photonics based on CMOS technology is a very attractive platform to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of quantum key distribution protocols. We show record low propagation losses below 0.5 dB/cm and below 0.05 dB/cm for silicon and silicon nitride waveguides respectively. We will present our results on integrated components such as hybrid III-V on silicon lasers for weak coherent pulse generation, high-quality microresonators for entangled photon pair generation and we will show our recent developments on high crystalline quality NbN thin films with improved critical temperature for waveguide-integrated superconducting single photon detectors.
We experimentally demonstrate the feasibility of the use of integrated linearly uncoupled resonators, which are coupled solely through the nonlinear interaction, to selectively enhance or suppress nonlinear processes. This is exploited to selectively enhance dual-pump spontaneous four-wave mixing while suppressing the parasitic noise associated with single pump spontaneous four-wave mixing processes. A signal-to-noise ratio characterizing the generation of identical photon pairs of more than four orders of magnitude is reported, opening the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.
In this communication, we report on the design, fabrication, and testing of silicon-on-insulator (SOI) and silicon-nitrideon- insulator (SiNOI) photonic circuits for nonlinear and quantum optics applications. As recently demonstrated, the generation of correlated photons on Si platforms can be used for quantum cryptography and quantum computing. Concerning SiNOI waveguides, Kerr frequency combs have been proposed in many applications, such as atomic clocks, on-chip spectroscopy, and terabit coherent communications. Silicon is an attractive platforms for correlated photons sources because of its high nonlinearity, they can have several modes in telecom band with sharp line widths (tens of μeV) and its inherent complementary metal-oxide-semiconductor (CMOS) compatibility. Moreover, the SiNOI is an attractive platform for Kerr comb generation due to their large bandgap and consequently the low two-photon absorption in the telecommunication band. Furthermore, in all the previous SiNOI-based frequency combs, the silicon nitride film undergoes long and high-temperature annealing to reduce the absorption in the telecommunication band caused by the dangling N-H bonds, thus making such annealed Si3N4 films non-CMOS compatible. However, both in the case of correlated photons pairs generation and Kerr frequency combs, the source efficiency is related to the quality factor (Q), so that a high-Q resonator is required to get highly-efficient sources. Authors report here about the fabrication and the characterization of annealing-free CMOS-compatible SiNOI- and hydrogen-annealed silicon-based waveguides and microresonators featuring ultra-low losses (e.g., 0.6 dB/cm for single-mode Si waveguides) that can be used, respectively, as efficient sources for Kerr combs and correlated photon pairs sources.
In this communication, we report on the design, fabrication and testing of silicon-nitride-in-insulator (SiNOI) nonlinear photonic circuits for comb generation in silicon photonics and optoelectronics. The low two-photon absorption when compared with crystalline silicon makes the SiNOI an attractive platform for frequency comb generation. Kerr combs have been recently used in terabit per second coherent communications demos. Such devices can overcome the intrinsic limitations of nowadays silicon photonics notably concerning the heterogenous integration of III-V on SOI lasers for both datacom and telecom applications. By using monolithically-integrated SiN-based Kerr frequency combs, the generation of tens or even hundreds of new optical frequencies can be obtained in dispersion tailored waveguides and resonators, thus providing an all-optical alternative to the heterointegration of hundreds of standalone III-V on Si lasers. However, in all the previous SiNOI-based frequency combs, the silicon nitride film is annealed under long and high temperature which made the cointegration with silicon based optoelectronics elusive. The annealing steps used in common SiN fabrication processes are not only incompatible with the front-end of line complementary metal-oxidesemiconductor processes, but also costly and long and thus an important cost factor in non-CMOS compatible processes. In our work, we present the fabrication and testing of an annealing-free and crack-free SiNOI. Notably, a 800-nmspanning (1300-2100 nm) frequency comb is generated using 740-nm-thick silicon nitride featuring full compatibility with silicon photonics integrated circuits. This work constitutes a new, decisive step toward time-stable power-efficient Kerr-based broadband sources featuring full process compatibility with Si photonic integrated circuits (Si-PICs) on CMOS-lines.
Wavelength multiplexing (WMUX) channel transmission bandwidth should be sufficiently large to compensate for thermal drifts of the emitters at the transmitter side of the link all over their functional windows in terms of driving currents and operational temperature of the environment. As well as that, a nearly absolute thermal insensitiveness of the WMUX device performance itself has to be ensured across the link over the widest possible temperature range. In other terms, devices have to exhibit the smallest thermo-optic coefficient, in order to fulfill system specifications under any thermal condition applied to the optical link. In this paper, we present coarse wavelength division multiplexing (CWDM), echelle grating (EG) WMUX to operate in the O-band (1310 nm) designed accordingly to 4 x 20-nm-spaced standard and fabricated on 200-mm Silicon Nitride-on-Insulator (SiNOI). Taking advantage of PECVD SiN low thermooptic coefficient compared to crystalline silicon, thermally-insensitive demultiplexers can be obtained. The device show insertion losses as low as 1 dB, interchannel crosstalk averaging -25 dB, non-uniformity of 1.3 dB and a -1 dB and -3 dB bandwidths of nearly 10 nm and 13 nm, respectively. Such wide channel bandwidths allow the compensation of wavelength drifts due to the different thermal environments between the transmitter and the receiver as well as the detuning of emitters at the transmitter side of the link. The EG shows a quasi-absolute thermal insensitiveness in the temperature operation range from 20 °C up to 80 °C, highlighting the thermal robustness of such SiNOI EG devices. A thermally-dependent chromatic dispersion averaging less than 13 pm/K over different channels has been estimated, thus 6x times less than similar devices when realized on standard SOI.
In this communication, we report on the design, fabrication, and testing of Silicon Nitride on Insulator (SiNOI) and Aluminum-Gallium-Arsenide (AlGaAs) on silicon-on-insulator (SOI) nonlinear photonic circuits for continuum generation in Silicon (Si) photonics. As recently demonstrated, the generation of frequency continua and supercontinua can be used to overcome the intrinsic limitations of nowadays silicon photonics notably concerning the heterogeneous integration of III-V on SOI lasers for datacom and telecom applications. By using the Kerr nonlinearity of monolithic silicon nitride and heterointegrated GaAs-based alloys on SOI, the generation of tens or even hundreds of new optical frequencies can be obtained in dispersion tailored waveguides, thus providing an all-optical alternative to the heterointegration of hundreds of standalone III-V on Si lasers. In our work, we present paths to energy-efficient continua generation on silicon photonics circuits. Notably, we demonstrate spectral broadening covering the full C-band via Kerrbased self-phase modulation in SiNOI nanowires featuring full process compatibility with Si photonic devices. Moreover, AlGaAs waveguides are heterointegrated on SOI in order to dramatically reduce (x1/10) thresholds in optical parametric oscillation and in the power required for supercontinuum generation under pulsed pumping. The manufacturing techniques allowing the monolithic co-integration of nonlinear functionalities on existing CMOS-compatible Si photonics for both active and passive components will be shown. Experimental evidence based on self-phase modulation show SiNOI and AlGaAs nanowires capable of generating wide-spanning frequency continua in the C-Band. This will pave the way for low-threshold power-efficient Kerr-based comb- and continuum- sources featuring compatibility with Si photonic integrated circuits (Si-PICs).
In this communication, authors report for the first time on the fabrication and testing of Si3N4 non-linear photonic circuits for CMOS-compatible monolithic co-integration with silicon-based optoelectronics. In particular, a novel process has been developed to fabricate low-loss crack-free Si3N4 750-nm-thick films for Kerr-based nonlinear functions featuring full thermal budget compatibility with existing Silicon photonics and front-end Si optoelectronics. Briefly, differently from previous and state-of-the-art works, our nonlinear nitride-based platform has been realized without resorting to commonly-used high-temperature annealing (~1200°C) of the film and its silica upper-cladding used to break N-H bonds otherwise causing absorption in the C-band and destroying its nonlinear functionality. Furthermore, no complex and fabrication-intolerant Damascene process - as recently reported earlier this year - aimed at controlling cracks generated in thick tensile-strained Si3N4 films has been used as well. Instead, a tailored Si3N4 multiple-step film deposition in 200-mm LPCVD-based reactor and subsequent low-temperature (400°C) PECVD oxide encapsulation have been used to fabricate the nonlinear micro-resonant circuits aiming at generating optical frequency combs via optical parametric oscillators (OPOs), thus allowing the monolithic co-integration of such nonlinear functions on existing CMOS-compatible optoelectronics, for both active and passive components such as, for instance, silicon modulators and wavelength (de-)multiplexers. Experimental evidence based on wafer-level statistics show nitride-based 112-μm-radius ring resonators using such low-temperature crack-free nitride film exhibiting quality factors exceeding Q >3 x 105, thus paving the way to low-threshold power-efficient Kerr-based comb sources and dissipative temporal solitons in the C-band featuring full thermal processing compatibility with Si photonic integrated circuits (Si-PICs).
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