skip to main content


Title: Impact of the precursor gas ratio on dispersion engineering of broadband silicon nitride microresonator frequency combs

Microresonator frequency combs, or microcombs, have gained wide appeal for their rich nonlinear physics and wide range of applications. Stoichiometric silicon nitride films grown via low-pressure chemical vapor deposition (LPCVD), in particular, are widely used in chip-integrated Kerr microcombs. Critical to such devices is the ability to control the microresonator dispersion, which has contributions from both material refractive index dispersion and geometric confinement. Here, we show that modifications to the ratio of the gaseous precursors in LPCVD growth have a significant impact on material dispersion and hence the overall microresonator dispersion. In contrast to the many efforts focused on comparisons between Si-rich films and stoichiometric (Si3N4) films, here, we focus on films whose precursor gas ratios should nominally place them in the stoichiometric regime. We further show that microresonator geometric dispersion can be tuned to compensate for changes in the material dispersion.

 
more » « less
NSF-PAR ID:
10303519
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
Optical Society of America
Date Published:
Journal Name:
Optics Letters
Volume:
46
Issue:
23
ISSN:
0146-9592; OPLEDP
Format(s):
Medium: X Size: Article No. 5970
Size(s):
Article No. 5970
Sponsoring Org:
National Science Foundation
More Like this
  1. Amorphous tantala (Ta2O5) thin films were deposited by reactive ion beam sputtering with simultaneous low energy assistAr+orAr+/O2+bombardment. Under the conditions of the experiment, the as-deposited thin films are amorphous and stoichiometric. The refractive index and optical band gap of thin films remain unchanged by ion bombardment. Around 20% improvement in room temperature mechanical loss and 60% decrease in absorption loss are found in samples bombarded with 100-eVAr+. A detrimental influence from low energyO2+bombardment on absorption loss and mechanical loss is observed. Low energyAr+bombardment removes excess oxygen point defects, whileO2+bombardment introduces defects into the tantala films.

     
    more » « less
  2. We present the optical and structural characterization of films ofTa2O5,Sc2O3, andSc2O3dopedTa2O5with a cation ratio around 0.1 grown by reactive sputtering. The addition ofSc2O3as a dopant induces the formation of tantalum suboxide due to the “oxygen getter” property of scandium. The presence of tantalum suboxide greatly affects the optical properties of the coating, resulting in higher absorption loss atλ<#comment/>=1064nm. The refractive index and optical band gap of the mixed film do not correspond to those of a mixture ofTa2O5andSc2O3, given the profound structural modifications induced by the dopant.

     
    more » « less
  3. The mid-IR spectroscopic properties ofEr3+doped low-phononCsCdCl3andCsPbCl3crystals grown by the Bridgman technique have been investigated. Using optical excitations at∼<#comment/>800nmand∼<#comment/>660nm, both crystals exhibited IR emissions at∼<#comment/>1.55,∼<#comment/>2.75,∼<#comment/>3.5, and∼<#comment/>4.5µ<#comment/>mat room temperature. The mid-IR emission at 4.5 µm, originating from the4I9/2→<#comment/>4I11/2transition, showed a long emission lifetime of∼<#comment/>11.6msforEr3+dopedCsCdCl3, whereasEr3+dopedCsPbCl3exhibited a shorter lifetime of∼<#comment/>1.8ms. The measured emission lifetimes of the4I9/2state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for the4I9/2→<#comment/>4I11/2transition inEr3+dopedCsCdCl3andCsPbCl3were determined to be∼<#comment/>0.14×<#comment/>10−<#comment/>20cm2and∼<#comment/>0.41×<#comment/>10−<#comment/>20cm2, respectively. The results of Judd–Ofelt analysis are presented and discussed.

     
    more » « less
  4. Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings ofSiO2(silica) andTiO2:Ta2O5(titania-doped tantala) and post-deposition annealing to 500°C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the sensitivity of the detectors. This paper describes optical scattering measurements for single-layer, ion-beam-sputtered thin films on fused silica substrates: two samples ofTa2O5and two ofTiO2:Ta2O5. Using an imaging scatterometer at a fixed scattering angle of 12.8°, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500°C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25–30% for tantala and up to 74% for titania-doped tantala, while the scatter from the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggest some improvement in three of the four samples. These results demonstrate that post-deposition, high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter.

     
    more » « less
  5. We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside theLP11group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside theLP11group. We employ two output OAM modesl=+1andl=−<#comment/>1as resultant linear combinations of degenerateLP11aandLP11bmodes inside theLP11group of a∼<#comment/>0.6-kmGI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis withinLP11group, which is a subset of the full LP TM of the FMF-based system. An inverse TM is subsequently implemented before the receiver by a spatial light modulator to mitigate the intra-modal-group power coupling. With AO mitigation, the experimental results forl=+1andl=−<#comment/>1modes show, respectively, that (i) intra-modal-group crosstalk is reduced by><#comment/>5.8dBand><#comment/>5.6dBand (ii) near-error-free bit-error-rate performance is achieved with a penalty of∼<#comment/>0.6dBand∼<#comment/>3.8dB, respectively.

     
    more » « less