We present a methodology to distinguish between absorptive and scattering losses in SiN optical waveguide resonators by measuring the thermo-optic redshift in resonant wavelength and deducing absorption losses using thermal properties determined through the differential 3ω method. This information offers researchers valuable insights for improving device performance and optimizing fabrication processes. We demonstrate results on the effect of a 650oC thermal anneal on R=120um whispering-gallery mode microring resonators fabricated using N-rich PECVD SiN with n=1.92 at 800nm, which reduced total losses from 1.4dB/cm to 0.64dB/cm at 780nm and yielded an intrinsic-Q of 1.1 million, due primarily to decreased absorption losses.
We report on the design and performance of single-frequency VCSELs that are electro-optically tunable in the 852nm wavelength range. Electro-optic tuning of the index of refraction is achieved by changing the reverse-bias electric field in a secondary p-i-n junction that contains coupled quantum wells. The electro-optic tuning is enhanced by putting the index-tuning region in a secondary cavity of a dual-cavity VCSEL. Electro-optic tuning can achieve 1nm of wavelength tuning without changing laser power and can operate at modulation frequencies up to 1GHz.
Electric fields in a surface acoustic wave in a piezoelectric substrate can pattern charge in an adjacent graphene film via the acousto-electric effect and thus reconfigure the optical transmission in an unpatterned graphene metasurface
We report on the use of etching and regrowth to shift the longitudinal resonance wavelength of adjacent VCSELs by -4nm from 980nm. The etched VCSEL exhibited less than 5% change in threshold (from 0.36mA) and slope efficiency relative to neighboring un-etched VCSELs. This etch and regrowth technique can be applied to produce wavelength-division multiplexed (WDM) VCSEL arrays with close spacing (<100microns). We will also discuss applications to 2-dimensional index engineering of novel VCSEL devices, since wavelength shifting is equivalent to effective index tuning.
We have fabricated 3D printed micro-optics to feedback light into an 850-nm VCSEL with reduced top-mirror reflectivity and control its transverse modes. Our goal is to create a single-frequency VCSEL with output power on the order of 10 mW for use in atomic and quantum physics. Feedback of 50% can reduce threshold current 5-fold and preferentially select the fundamental transverse mode. We will compare theory and experiment for micro-optic length scales near 100 microns, yielding Gaussian mode diameters near 10 microns.
Controlling the permittivity of materials enables control over the amplitude, phase and polarization of light interacting with them. Tailorable and tunable transparent conducting oxides have applications in optical switching, beam steering, imaging, sensing, and spectroscopy.
In this work, we experimentally demonstrate wide tailoring and tuning of the optical properties of oxides to achieve fast switching with large modulation depths. In cadmium oxide, the permittivity and the epsilon-near-zero points can be tailored via yttrium doping to achieve large, ENZ-enhanced mid-IR reflectance modulation. In zinc oxide, the permittivity is tuned by interband pumping, achieving large reflectance modulation in the telecom regime. With aluminum-doped zinc oxide, we demonstrate tailorable Berreman-type absorbers that can achieve ultrafast switching in the telecom frequencies. Our work will pave the way to practical optical switching spanning the telecom to the mid-infrared wavelength regimes.
All-optical switching of metasurfaces enables dynamic control of the amplitude, phase and the polarization of light at picosecond timescales. The large free-carrier induced permittivity changes in transparent conducting oxides enable all-optical switching at femtosecond to picosecond timescales in planar, unpatterned films, without the need for lithography.
In this work, we experimentally demonstrate the wide-tuning of the optical properties of three materials to achieve fast optical switching with large modulation depth. Lithography-free designs such as Fabry-Perot cavities, metal-dielectric mirrors, and Berreman-type metasurfaces are demonstrated to showcase optical switching at powers on the order of 1 mJ/cm2. The switching speeds can vary from 50 ps in cadmium oxide, 20 ps in ZnO to 2 ps in aluminum-doped zinc oxides. Our work will pave the way to practical optical switching spanning the telecom to the mid-infrared wavelength regimes.
We experimentally investigate how the static and dynamic optical properties of cadmium oxide evolve with yttrium doping, for the design of optical and plasmonic devices spanning the near-infrared to the mid-infrared wavelengths. The metallicity is seen to increase and the epsilon-near-zero point blue-shifts with increasing yttrium-concentrations. We demonstrate broadband, optical-pump-induced reflection and transmission modulation ((up to 135% near ENZ), with picosecond response-times controlled by doping-concentration.
We report on the design and characterization of multi-mirror vertical-cavity surface-emitting lasers (VCSELs) that achieve linewidths less than 2 MHz. We have fabricated all-semiconductor multi-mirror VCSELs at 850 nm that operate in a single mode and are suitable for high-resolution spectroscopy. Cold-cavity linewidth measurements confirm increased quality factors relative to standard VCSEL resonators. Frequency noise power spectral density measurements exhibit 1/f noise and white-noise floors consistent with Lorentzian linewidths less than 2 MHz.
We report on mode selection and tuning properties of vertical-external-cavity surface-emitting lasers (VECSELs) containing coupled semiconductor and external cavities of total length less than 1 mm. Our goal is to create narrowlinewidth (<1MHz) single-frequency VECSELs that operate near 850 nm on a single longitudinal cavity resonance and tune versus temperature without mode hops. We have designed, fabricated, and measured VECSELs with external-cavity lengths ranging from 25 to 800 μm. We compare simulated and measured coupled-cavity mode frequencies and discuss criteria for single mode selection.
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