On-chip optical isolators constitute an essential building block for photonic integrated circuits. Monolithic magnetooptical isolators on silicon, while featuring unique benefits such as scalable integration and processing, fully passive operation, large dynamic range, and simple device architecture, had been limited by their far inferior performances compared to their bulk counterparts. Here we discuss our recent work combining garnet material development and isolator device design innovation, which leads to a monolithic optical isolator with an unprecedented low insertion loss of 3 dB and an isolation ratio up to 40 dB. To further overcome the bandwidth and polarization limitations, we demonstrated broadband optical isolators capable of operating for both TM and TE modes. These results open up exciting opportunities for scalable integration of nonreciprocal optical devices with chip-scale photonic circuits.
Mid-infrared (MIR, 2-6 μm wavelength) transparent metal oxides are attractive materials for planar integrated photonic devices for sensing applications. In this study, we present reactive sputtering deposited ZrO2-TiO2 (ZTO) thin films as a new material candidate for integrated MIR photonics. We demonstrate that amorphous ZTO thin films can be achieved with Ti concentration of 40 at.%. With increasing Ti concentration, the optical band gap decreases monotonically from 4.34 eV to 4.11 eV, while the index of refraction increases from 2.14 to 2.24 at 1 μm wavelength. MIR micro-disk resonators on MgO substrates are demonstrated using Ge23/Sb7S70/Zr0.6Ti0.4O2 strip-loaded waveguides with a loaded quality factor of ~11,000 at 5.2 μm wavelength. By comparing with a reference device of Ge23Sb7S70 resonator on MgO and simulating the optical confinement factors, the ZTO thin film loss is estimated to be below 10 dB/cm. Single mode shallow ridge waveguides with a ridge height of 400 nm and a slab height of 1.7 μm are also demonstrated using ZrO2 thin films on MgO substrates. The low loss, relatively high index of refraction, superior stability and proven CMOS compatibility of ZTO thin films make them highly attractive for MIR integrated photonics.
We report a theoretical study of the enhancement of Goos-Hänchen (GH) effect in a prism-waveguide coupling system
with magneto-optic materials, including dielectric waveguide (Prism/Air/Ce:YIG/SiO2) and plasmonic waveguide
(Prism/Au/Ce:YIG/SiO2) structures. Giant GH shift is observed in both waveguides. By applying opposite magnetic field across the CeYIG layer, a variation of the GH shift, namely MOGH (magneto-optical Goos-Hänchen effect) is observed.
Compared to the reflectivity and Goos-Hänchen effects of the structures, the MOGH effect shows higher sensitivity for
index variations, therefore is very promising for chemical or biomedical index sensors. The device performance as a
function of layer dimension, material refractive index and magneto-optical properties are simulated and discussed in
detail. It is observed that coupling layer, MO layer thickness and prism index plays an important role in the plasmonic
waveguide to control MOGH effect.
We report monolithic integration of chalcogenide glass(ChG)/iron garnet waveguides and racetrack resonators on silicon
for on-chip nonreciprocal photonic devices applications. Using a two step growth strategy, we successfully integrated
phase pure Bi0.8Y2.2Fe5O12 (Bi0.8YIG), Bi1.8Y1.2Fe5O12 (Bi1.8YIG) and Ce1Y2Fe5O12 (CeYIG) polycrystalline thin films
on silicon with low fabrication thermal budgets. Strip-loaded ChG/Iron garnet waveguides and racetrack resonators were
fabricated by thermal evaporation and lift off. The waveguide loss was systematically characterized by cutback and
paperclip methods. For the first time, the optical transmission loss of polycrystalline Bi or Ce doped garnets were
evaluated at communication wavelengths in waveguides. Polycrystalline CeYIG films show a saturation Faraday rotation
of -830deg/cm and transmission loss of ~40dB/cm at 1550nm, which is promising for on-chip nonreciprocal photonic
device applications. Such waveguide structures were successfully incorporated in GeS2/Bi0.8YIG racetrack resonators
which show well defined resonance spectrum at near infrared wavelength. The nonreciprocal phase shift (NRPS) and
device figure of merit of the ChG/Garnet waveguides were simulated by numerical methods. Possible improvements and
applications of such devices for integrated optical isolator applications are analyzed and discussed.
We report two novel strategies to integrate magneto-optical oxides on oxidized silicon and SOI platforms based on
strip-loaded waveguide structures. By using conventional waveguide fabrication and thin film deposition techniques,
strip-loaded waveguides for magneto-optical non-reciprocal phase shift (NRPS) applications can be integrated on a
silicon platform. As a demonstration, two structures, i.e. As2S3/Y3Fe5O12 (YIG) and YIG/SOI waveguides are fabricated.
Using pulsed-laser deposition followed by rapid thermal annealing, yttrium iron oxide films in which more than 95
vol.% had crystallized into the YIG phase were achieved on both substrates. The optical loss of the As2S3/Y3Fe5O12
waveguide was characterized by a cut-back method to be ~10 dB/cm at 1550 nm, while the optical loss of a 450nm wide
YIG/SOI waveguide was determined to be 41 dB/cm at 1550 nm by measuring the quality factor Q of a pulley-type ring
resonator consisting of such waveguides. The propagation loss of polycrystalline YIG on a SiO2/Si substrate was around
50 dB/cm at 1550 nm wavelength. The NRPS and figure of merit of both waveguides were simulated. It is suggested that
a Bi:YIG or Ce:YIG layer may be integrated in these waveguide structures to achieve a higher NRPS and figure of merit
for optical isolator applications. These waveguide fabrication techniques offer a compact, low cost and etch-free route for
integrating magneto-optical materials on a silicon platform, which may be useful for making future integrated optical
isolators and other magneto-optical components.
Sr(Ti0.6Fe0.4)O3 (STF) and Sr(Ti0.7Co0.3)O3 (STC) room-temperature ferromagnetic oxides were grown epitaxially on
LaAlO3(001), (LaSr)(AlTa)O3 (001) and Si (001) substrates. Both materials were demonstrated to be magneto-optically
active, and more optically transparent at 1550nm wavelength compared with other non-garnet ferromagnetic materials.
As2S3/STF and As2S3/STC strip-loaded waveguides were fabricated on epitaxial STF or STC films grown on LSAT (001)
substrates using thermal evaporation and lift-off processing. The absorption of STF at 1550 nm was measured by
ellipsometry and by optical transmission spectrum measurements of the As2S3/STF waveguides, which gave similar
results. A novel design for a Non-Reciprocal Phase Shift (NRPS) strip-loaded waveguide using chalcogenide glass (ChG)
as the guiding layer is proposed. The NRPS and figure of merit of these waveguides are simulated. The ChG strip-loaded
waveguide structure shows advantages both in fabrication and device performance according to the simulation results.
Our study suggests the possibility of magneto-optical magneto-optical isolators monolithically integrated on a silicon
platform.
The Atmospheric Infrared Sounder (AIRS) (Chahine et al., 2006) was launched in 2002 on AQUA, the second
of the EOS polar-orbiting satellites. The AIRS was the first of a new generation of meteorological advanced
sounders able to provide hyperspectral (sometimes referred to as ultraspectral) data for operational and research
use. The improved spectral resolution it provided compared to earlier passive infrared sounders, led to a
significant increase in vertical resolution and accuracy in determining thermal and moisture fields, increased
accuracy in the determination of the concentrations of absorbers such as ozone and improved numerical weather
prediction (NWP), (Le Marshall et al. 2006). It was also shown that expanded use of the information content of
infrared hyperspectral radiance data resulted in an increase in the benefit of these data to NWP. Experiments
which have shown the benefit of improved spatial coverage, spectral coverage and the use of moisture channel
data, are summarised in this paper. In addition, an experiment which has recorded the benefit of using
hyperspectral radiance data from fields of view containing clouds is also described. Again it is demonstrated that
a more complete use of the information content in the observations available from hyperspectral sounders has
resulted in improved benefits to numerical weather prediction. This conclusion is also supported by early
experiments reporting the benefits from using IASI data. Overall, the results indicate the significant benefits to
be derived from hyperspectral data assimilation and the benefits to be gained from an enhanced use of the
information content contained in hyperspectral radiance observations.
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