We demonstrate photonic crystal waveguide true-time-delay lines fabricated on a large area (>2cm × 2cm) silicon nanomembrane transferred onto a glass substrate. The photonic crystal waveguides are designed to provide large time delay values within a short length. 17.1 μm × 10 μm subwavelength grating (SWG) couplers are employed in order to enable efficient light coupling from and to a fiber. Photonic crystal tapers are implemented at the stripphotonic crystal waveguide interfaces to minimize loss and provide larger time delay values. A large group index of ~28.5 is calculated from the measurement data, thus indicating achievability of time delay larger than 58ps per millimeter length of the delay line within a tuning range of 20nm.
We report a four-channel on-chip true-time-delay (TTD) module based on a photonic crystal waveguide (PCW) array.
By minimizing the coupling loss with a photonic crystal taper (PC taper), the delay lines with 1–3mm long PCWs can
operate up to a group index ng~23 without significant loss. The large group velocity dispersion enables continuous and
wavelength-tunable time delays. Measurements show a highly linear phase-frequency relation, highest time delay up to
216.7 ps, and large tuning ranges of 58.28 ps, 115.74 ps, and 194.16 ps for 1–3mm delay lines, respectively. The
chip-scale TTD module can provide ±44.38° steering for an X-band phased array antenna (PAA), but occupies only 0.18 mm2 area.
Polymer based electro-optic modulators have shown great potentials in high frequency analog optical links. Existing
commercial LiNibO3 Mach-Zehnder modulators have intrinsic drawbacks in linearity to provide high fidelity
communication. In this paper, we present the design, fabrication and characterization of a traveling wave directional
coupler modulator based on electro-optic polymer, which is able to provide high linearity, high speed, and low optical
insertion loss. A silver ground electrode is used to reduce waveguide sidewall roughness due to the scattering of UV
light in photolithography process in addition to suppressing the RF loss. A 1x2 multi-mode interference 3dB-splitter, a
photobleached refractive index taper and a quasi-vertical taper are used to reduce the optical insertion loss of the device.
The symmetric waveguide structure of the MMI-fed directional coupler is intrinsically bias-free, and the modulation is
obtained at the 3-dB point regardless of the ambient temperature. By achieving low RF loss, characteristic impedance
matching with 50Ω load, and excellent velocity matching between the RF wave and the optical wave, a travelling wave
electrode is designed to function up to 62.5GHz. Domain-inversion poling with push-pull configuration is applied using
alternating pulses on a 2-section directional-coupler to achieve a spurious free dynamic range of 110dB/Hz2/3. The 3-dB
electrical bandwidth of device is measured to be 10GHz.
In this paper, we present the design and experimental demonstration of a high dynamic range electric field sensor based
on electro-optic (EO) polymer directional coupler waveguides that offers the strong and ultra-fast EO response of EO
polymer. As compared to conventional photonic electric field sensors, our directional coupler waveguide design offers
several advantages such as bias-free operation, highly linear measurement response up to 70dB, and a wide electric field
detection range from 16.7V/m to 750kV/m at a frequency of 1GHz.
We experimentally demonstrate two devices on the photonic crystal platform for chip-integrated optical absorption
spectroscopy and chip-integrated biomolecular microarray assays. Infrared optical absorption spectroscopy and
biomolecular assays based on conjugate-specific binding principles represent two dominant sensing mechanisms for a
wide spectrum of applications in environmental pollution sensing in air and water, chem-bio agents and explosives
detection for national security, microbial contamination sensing in food and beverages to name a few. The easy
scalability of photonic crystal devices to any wavelength ensures that the sensing principles hold across a wide
electromagnetic spectrum. Silicon, the workhorse of the electronics industry, is an ideal platform for the above optical
sensing applications.
We present preliminary designs and experimental results for creating a microarray nanoplatform based on twodimensional
photonic crystal devices in silicon. Multiple photonic crystal microcavities are coupled along the length of a
single photonic crystal waveguide that undergo resonance wavelength shifts when an antibody-antibody binding event
occurs in the immediate vicinity of the corresponding photonic crystal microcavity. The microarray nanoplatform
enables high throughput measurements of multiple antibody-antibody interactions via a single optical waveguide
transmission measurement.
We experimentally demonstrate a 300μm long silicon photonic crystal slot waveguide for on-chip near-infrared
absorption spectroscopy. Based on the Beer-Lambert absorption law, our device combines slow light in photonic crystal
waveguide with high electric field intensity in low-index 75nm wide slot, which effectively increases the optical
absorption path length of the analyte. We demonstrate near-infrared absorption spectroscopy of xylene in water,
independent of near-infrared absorption signatures of water, with a hydrophobic PDMS sensing phase that extracts
xylene from water. Xylene concentrations up to 100ppb (parts per billion) (86μg/L) in water were measured.
Slow light in photonic crystal waveguide can significantly enhance the light-matter interaction, which is a promising
approach toward building ultra-compact photonic devices. However, optical coupling from strip waveguide to slow light
photonic crystal waveguide is challenging due to the group velocity mismatch between these waveguides. This issue can
be addressed by designing a photonic crystal taper that allows the defect guided mode in photonic crystal waveguide to
slow down gradually when it enters the photonic crystal waveguide from strip waveguide, thereby minimizing the group
velocity mismatch. By using the photonic crystal taper design, experimental results show coupling efficiency can be
enhanced by more than 20dB in normal group velocity region with 5dB less fluctuation as compared to the control
group, which does not have photonic crystal taper. Enhancement right before photonic bandgap cutoff can be up to
28dB. Measurement results show excellent agreement with two-dimensional (2D) finite-difference time domain (FDTD)
simulation.
Defect engineered photonic crystals, with sub-micron dimensions have demonstrated high sensitivity to trace volumes of
analytes; however exact identification of analyte through spectroscopic signatures had not been demonstrated. We
demonstrate a 300micron long photonic crystal slot waveguide device which combines slow light phenomenon in
photonic crystal waveguides with large optical field intensity in a low index narrow slot at the center of the photonic
crystal waveguide for highly sensitive spectroscopic detection of methane on-chip at 100 parts per million (ppm) or
0.2% permissible exposure limit. Photonic crystal slot waveguide provides a factor of 1000 reduction in interaction
length compared to free-space infrared spectroscopy leading to enhanced optical absorption by analytes in the optical
path. By measuring absorption differences in presence and absence of methane, near-infrared absorption spectrum of
methane is determined.
In this paper, we present the results of the design and fabrication of a 12 channel nano-membrane-based optical phased
array that allows for large angle beam steering operating at wavelength=1.55μm. Our device is fabricated on silicon-oninsulator
using standard CMOS process. By implementing unequally spaced waveguide array elements, we can relax the
half-wavelength spacing requirement for large angle beam steering, thereby avoiding the optical coupling between
adjacent waveguides and reducing the side-lobe-level of the array radiation pattern. 1D beam steering of tranverseelectric
polarized single mode light is designed to be achieved thermo-optically through the use of thin film metal phase
shifters.
We experimentally demonstrate a Mach-Zehnder modulator based on electro-optic (EO) polymer (AJ-CKL1/PMMA)
infiltrated photonic crystal slot waveguide. The modulator design combines the advantage of excellent optical
confinement in silicon slot waveguide, slow light enhancement in photonic crystal waveguide, and strong electro-optical
response in EO polymer. This design allows us to achieve electro-optic modulation in active region only 352μm long.
Matching the mode profile and group velocity between strip and photonic crystal slot waveguide enables coupling into
slow light regime. The modulator shows a 22V switching voltage and an improved in-device EO coefficient of 51pm/V
as compared to recently reported value.
A Y-branch directional coupler modulator based on electro-optic (EO) polymer with domain-inversion is designed,
fabricated, and characterized. The functional core material is LPD-80 chromophore in amorphour-polycarbonate (APC)
host polymer which is cladded between UV15-LV and UFC-170A. The switching voltage of 4.4V and the electro-optic
coefficient (r33) of 90pm/V are measured from 4-domain directional coupler modulator and Mach-Zehnder modulator,
respectively. A two-tone test of domain-inversed directional coupler modulator demonstrates the spurious-free dynamic
range (SFDR) of 119dB/Hz2/3, which is enhanced by 11dB compared with the conventional Mach-Zehnder modulator.
The SFDR of Mach-Zehnder modulator shows good agreement with simulation result but the directional coupler
modulator shows approximately 10dB lower value than simulation result, which is mainly due to the high sensitivity of
directional coupler structure to the fabrication error. Further improvement can be achieved with completion of
fabrication precision.
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