Demonstration of the DC-Kerr effect in silicon-rich nitride

We demonstrate the DC-Kerr effect in plasma enhanced chemical vapor deposition (PECVD) silicon-rich nitride (SRN) and use it to demonstrate a third order nonlinear susceptibility,$χ<#comment/>(3)$, as high as$(6±<#comment/>0.58)×<#comment/>10−<#comment/>19m2/V2$. We employ spectral shift versus applied voltage measurements in a racetrack resonator as a tool to characterize the nonlinear susceptibilities of these films. In doing so, we demonstrate a$χ<#comment/>(3)$larger than that of silicon and argue that PECVD SRN can provide a versatile platform for employing optical phase shifters while maintaining a low thermal budget using a deposition technique readily available in CMOS process flows.

Authors:
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Award ID(s):
Publication Date:
NSF-PAR ID:
10289632
Journal Name:
Optics Letters
Volume:
46
Issue:
17
Page Range or eLocation-ID:
Article No. 4236
ISSN:
0146-9592; OPLEDP
Publisher:
Optical Society of America
1. Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter,$χ<#comment/>p(π<#comment/>)$, which relates the particulate volume scattering function (VSF) at 180° ($β<#comment/>p(π<#comment/>)$) that a lidar measures to the particulate backscattering coefficient ($bbp$). However,$χ<#comment/>p(π<#comment/>)$has been seldom studied due to challenges in accurately measuring$β<#comment/>p(π<#comment/>)$and$bbp$concurrently in the field. In this study,$χ<#comment/>p(π<#comment/>)$, as well as its spectral dependence, was re-examined using the VSFs measuredin situat high angular resolution in a wide range of waters.$β<#comment/>p(π<#comment/>)$, while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference$<<#comment/>5%<#comment/>$at scattering angles$<<#comment/>170∘<#comment/>$. At angles immediately near or equal to 180°, the reconstructeddepends strongly on the inversion kernel.$χ<#comment/>p(π<#comment/>)$derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent with$χ<#comment/>p(π<#comment/>)$estimated directly from high-spectral-resolution lidar andin situbackscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles.$χ<#comment/>p(π<#comment/>)$derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests that$χ<#comment/>p(π<#comment/>)$is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value of$χ<#comment/>p(π<#comment/>)$is to be used to interpret lidar signal collected in different waters. On the other hand,$χ<#comment/>p(π<#comment/>)$showed little spectral dependence.
2. Materials with strong second-order ($χ<#comment/>(2)$) optical nonlinearity, especially lithium niobate, play a critical role in building optical parametric oscillators (OPOs). However, chip-scale integration of low-loss$χ<#comment/>(2)$materials remains challenging and limits the threshold power of on-chip$χ<#comment/>(2)$OPO. Here we report an on-chip lithium niobate optical parametric oscillator at the telecom wavelengths using a quasi-phase-matched, high-quality microring resonator, whose threshold power ($∼<#comment/>30µ<#comment/>W$) is 400 times lower than that in previous$χ<#comment/>(2)$integrated photonics platforms. An on-chip power conversion efficiency of 11% is obtained from pump to signal and idler fields at a pump power of 93 µW. The OPO wavelength tuning is achieved by varying the pump frequency and chip temperature. With the lowest power threshold among all on-chip OPOs demonstrated so far, as well as advantages including high conversion efficiency, flexibility in quasi-phase-matching, and device scalability, the thin-film lithium niobate OPO opens new opportunities for chip-based tunable classical and quantum light sources and provides a potential platform for realizing photonic neural networks.
3. The design, fabrication, and characterization of low-loss ultra-compact bends in high-index ($n=3.1$at$λ<#comment/>=1550nm$) plasma-enhanced chemical vapor deposition silicon-rich silicon nitride (SRN) were demonstrated and utilized to realize efficient, small footprint thermo-optic phase shifter. Compact bends were structured into a folded waveguide geometry to form a rectangular spiral within an area of$65×<#comment/>65µ<#comment/>m2$, having a total active waveguide length of 1.2 mm. The device featured a phase-shifting efficiency of$8mW/π<#comment/>$and a 3 dB switching bandwidth of 15 KHz. We propose SRN as a promising thermo-optic platform that combines the properties of silicon and stoichiometric silicon nitride.
4. We report on spectroscopic measurements on the$4f76s28S7/2∘<#comment/>→<#comment/>4f7(8S∘<#comment/>)6s6p(1P∘<#comment/>)8P9/2$transition in neutral europium-151 and europium-153 at 459.4 nm. The center of gravity frequencies for the 151 and 153 isotopes, reported for the first time in this paper, to our knowledge, were found to be 652,389,757.16(34) MHz and 652,386,593.2(5) MHz, respectively. The hyperfine coefficients for the$6s6p(1P∘<#comment/>)8P9/2$state were found to be$A(151)=−<#comment/>228.84(2)MHz$,$B(151)=226.9(5)MHz$and$A(153)=−<#comment/>101.87(6)MHz$,$B(153)=575.4(1.5)MHz$, which all agree with previously published results except for A(153), which shows a small discrepancy. The isotope shift is found to be 3163.8(6) MHz, which also has a discrepancy with previously published results.
5. Here, we report$χ<#comment/>(3)$-based optical parametric oscillation (OPO) with widely separated signal–idler frequencies from crystalline aluminum nitride microrings pumped at$2µ<#comment/>m$. By tailoring the width of the microring, OPO reaching toward the telecom and mid-infrared bands with a frequency separation of 64.2 THz is achieved. While dispersion engineering through changing the microring width is capable of shifting the OPO sideband by$><#comment/>9THz$, the OPO frequency can also be agilely tuned in the ranges of 1 and 0.1 THz, respectively, by shifting the pump wavelength and controlling the chip’s temperature. At high pump powers, the OPO sidebands further evolve into localized frequency comb lines. Such large-frequency-shift OPO with flexible wavelength tunability will lead to enhanced chip-scale light sources.