In this paper, we provide a new type of subwavelength grating waveguides (SWGs) with a guiding mechanism from 1.5μm to 6μm on a silicon-on-insulator (SOI) platform. Two different SWGs with the same period but different height, corresponds to different effective subwavelength refractive indices, are designed and served as the core and cladding respectively. The biggest hindrance for transmission bandwidth, the buried oxide, is then removed to build up a suspended SWGs, contributing to bandwidth enlargement. In the meantime, the results also show light-matter interaction enhancement that ~34% propagating energy locates in the air can fully interact with testing analytes, leading to higher sensitivity. The broadband and high light-matter integral signatures would address the demands for ideal absorption spectroscopy based lab-on-chip.
In this paper, we propose a new type of subwavelength grating (SWG) racetrack resonator with engineered coupling condition and waveguide nanostructure. Highly dispersive coupling condition between bus waveguide and SWG ring is achieved, which has a V-shape envelope of resonance spectrum, through adjusting the SWG unit shape, dimension and the length of directional coupling region. When top cladding refractive index changes, instead of indicated in single resonant wavelength shift, which is the case for conventional SWG ring resonator, the movement of the spectrum envelope peak actually represents the sensitivity of our device. SWG racetrack resonators with two different widths are investigated, showing much bigger spectrum shift compared with the conventional one. The results may provide a new approach for further improve device sensitivity and hold great promise for potential applications in integrated optical sensor.
We proposed and demonstrated a deep learning assisted on-chip Fourier transform spectroscopy (FTS), using an artificial neural networks (ANN) to analyze the output stationary interferogram. It is found that, compared with the conventional FTS, the resolution could be improved without increasing the maximum path length difference and the number of MZIs, thus reducing the burden of adding more power budget. This new concept of enhancing spectral resolution may hold great promise for potential applications in integrated FTS.
We investigate a fourth-order PT symmetric optical sensor and analyze its eigenfrequency phase diagram. The four eigenfrequencies of our optical sensor simultaneously collapse at the high-order exceptional point in parameter space, providing a quarter root relation between the frequency splitting amount and the perturbation. A clear sensitivity boost is observed when comparing the frequency splitting with other optical sensors under small perturbation condition.
Phased-array antenna (PAA) technology plays a significant role in modern day radar and communication networks. Truetime- delay (TTD) enabled beam steering networks provide several advantages over their electronic counterparts, including squint-free beam steering, low RF loss, immunity to electromagnetic interference (EMI), and large bandwidth control of PAAs. Chip-scale and integrated TTD modules promise a miniaturized, light-weight system; however, the modules are still rigid and they require complex packaging solutions. Moreover, the total achievable time delay is still restricted by the wafer size. In this work, we propose a light-weight and large-area, true-time-delay beamforming network that can be fabricated on light-weight and flexible/rigid surfaces utilizing low-cost “printing” techniques. In order to prove the feasibility of the approach, a 2-bit thermo-optic polymer TTD network is developed using a combination of imprinting and ink-jet printing. RF beam steering of a 1×4 X-band PAA up to 60° is demonstrated. The development of such active components on large area, light-weight, and low-cost substrates promises significant improvement in size, weight, and power (SWaP) requirements over the state-of-the-art.
Ultracompact thermooptically tuned photonic crystal waveguide (PCW) based Mach–Zehnder interferometers (MZIs) working in silicon-on-sapphire in mid-infrared regime have been proposed and demonstrated. We designed and fabricated a PCW based silicon thermo-optic (TO) switch operating at 3.43 μm. Both steady-state and transient thermal analyses were performed to evaluate the thermal performance of the TO MZIs. The required π phase shift between the two arms of the MZI has been successfully achieved within an 80 μm interaction distance. The maximum modulation depth of 74% was demonstrated for switching power of 170 mW.
We experimentally demonstrate applications of photonic crystal waveguide based devices for on-chip optical absorption spectroscopy for the detection of chemical warfare simulant, triethylphosphate as well as applications with photonic crystal microcavity devices in the detection of biomarkers for pancreatic cancer in patient serum and cadmium metal ions in heavy metal pollution sensing. At mid-infrared wavelengths, we experimentally demonstrate the higher sensitivity of photonic crystal based structures compared to other nanophotonic devices such as strip and slot waveguides with detection down to 10ppm triethylphosphate. We also detected 5ppb (parts per billion) of cadmium metal ions in water at near-infrared wavelengths using established techniques for the detection of specific probe-target biomarker conjugation chemistries.
Typical L-type photonic crystal (PC) microcavities have a dynamic range of approximately 3-4 orders of magnitude in biosensing. We experimentally demonstrated that multiplexing of PC sensors with different geometry can achieve a wide dynamic range covering 6 orders of magnitude with potential for 8 or more orders with suitable optimization.
Previously, we introduced a novel and an etch-free solution based procedure utilizing a combination of imprinting and inkjet printing for developing polymer photonic devices to overcome the limitations of conventional polymer photonic device fabrication techniques, such as RIE or direct pattern writing. In this work, we demonstrate the feasibility of developing very large-area photonic systems on both rigid and flexible substrates. Specifically, a complete reconfigurable 4-bit true-time-delay module, comprising of an array of five interconnected TO switches and polymer delay lines, with a dimension of 25 mm × 18 mm is developed. Because of the roll-to-roll (R2R) compatibility of the employed solution processing techniques, photonic system development over large areas at high-throughput on rigid or flexible substrates is possible, which will lead to tremendous cost savings. Moreover, these devices can be integrated with other printed photonic and electronic components, such as light sources, modulators, antennas, etc., on the same substrate, thus enabling integrated systems that can be conformably integrated on any platform.
Quasi-Vertical tapers are designed to enable high coupling efficiency from a conventional single mode fiber into a single mode polymer rib waveguide. A triangular region fabricated under the single mode waveguide is adopted to adiabatically transform the fiber mode into the polymer rib waveguide mode. This structure works as an optical mode transformer. Because the trenches are deeper at the facets than at the active regions of the waveguide, the waveguide mode size in vertical direction becomes larger at the facets and can better match the input and output fiber mode. A coupling efficiency of 82.95% is achievable with a tip width of 1 μm.
Integrating photonic waveguide sensors with microfluidics is promising in achieving high-sensitivity and
cost-effective biological and chemical sensing applications. One challenge in the integration is that an air gap would
exist between the microfluidic channel and the photonic waveguide when the micro-channel and the waveguide
intersect. The air gap creates a path for the fluid to leak out of the micro-channel. Potential solutions, such as oxide
deposition followed by surface planarization, would introduce additional fabrication steps and thus are ineffective in
cost. Here we propose a reliable and efficient approach for achieving closed microfluidic channels on a waveguide
sensing chip. The core of the employed technique is to add waveguide crossings, i.e., perpendicularly
intersecting waveguides, to block the etched trenches and prevent the fluid from leaking through the air gap. The
waveguide crossings offer a smooth interface for microfluidic channel bonding while bring negligible additional
propagation loss (0.024 dB/crossing based on simulation). They are also efficient in fabrication, which are patterned and
fabricated in the same step with waveguides. We experimentally integrated microfluidic channels with photonic crystal
(PC) microcavity sensor chips on silicon-on-insulator substrate and demonstrated leak-free sensing measurement with
waveguide crossings. The microfluidic channel was made from polydimethylsiloxane (PDMS) and pressure bonded to
the silicon chip. The tested flow rates can be varied from 0.2 μL/min to 200 μL/min. Strong resonances from the PC
cavity were observed from the transmission spectra. The spectra also show that the waveguide crossings did not induce
any significant additional loss or alter the resonances.
We experimentally demonstrate transmission characteristics of a W1 photonic crystal waveguide in silicon on sapphire
at mid infrared wavelength of 3.43 m. Devices are studied as a function of lattice constant to tune the photonic stop
band across the single wavelength of the source laser. The shift in the transmission profile as a function of temperature
and refractive index is experimentally demonstrated. In addition to zero transmission in the stop gap, high transmission
was observe for the characteristic of the waveguiding behavior of photonic crystal line defect modes.
We compared different on-chip silicon waveguide based absorption sensors for the detection of xylene in water in nearinfrared with detection limit down to 1ppb. Strip waveguide, slot waveguide and PC-based chip integrated optical absorption spectroscopy devices are compared in near-infrared. PCW utilizes slow light effect to enhance absorbance and is most sensitive while slot waveguide strengthens light-matter interaction in a narrow low index slot by a factor up to 10 and performs better than a strip waveguide. The results provide a route for enhanced sensitivity via absorption spectroscopy while retaining device miniaturization.
A chip integrated infrared spectrometer for in situ sensing and spectroscopic identification of VOCs in water probing large absorption cross sections of VOCs in the mid-infrared is desired. Preliminary strip and slot waveguide devices fabricated in silicon-on-sapphire for operation at 3.4μm wavelength experimentally demonstrated propagation loss of 2.1dB/cm for strip waveguides and 11dB/cm for slot waveguide. VOC are extracted from water using PDMS for solid phase micro-extraction and enables absorbance measurements independent from the strong absorbance of water. Absorbance of xylene as a typical VOC is determined on chip from the difference in transmitted intensity in the presence and absence of xylene.
A platform for multiplexed detection of several biomolecular events, simultaneously at the same instant of time, is highly desirable in biomolecular diagnostics. Silicon Photonics is ideally suited for the above requirement. Our biosensor comprises a PC microcavity coupled to a PC waveguide. High sensitivities were achieved by slow light engineering which reduced the radiation loss and increased the stored energy in the photonic crystal microcavity resonance mode. Resonances with high quality factor Q~26,760 coupled with larger optical mode volumes allowed enhanced interaction with the analyte biomolecules which resulted in sensitivities down to 3.35pg/ml. We have multiplexed up to 64 PC microcavities in series and parallel for high throughput multiplexing using silicon integrated photonic components such as multimode interference power splitters combined with advanced group index engineering.
We present the design of a compact and highly sensitive electric field sensor based on a bowtie antenna-coupled slot photonic crystal waveguide (PCW). An electro-optic (EO) polymer with a large EO coefficient, r33=100pm/V, is used to refill the PCW slot and air holes. Bowtie-shaped electrodes are used as both poling electrodes and as receiving antenna. The slow-light effect in the PCW is used to increase the effective in-device r33>1000pm/V. The slot PCW is designed for low-dispersion slow light propagation, maximum poling efficiency as well as optical mode confinement inside the EO polymer. The antenna is designed for operation at 10GHz.
We demonstrate a device which can do multiplexed detection of two different chemicals on one chip by using infrared absorption spectroscopy. The signature of Trichloroethylene(TCE) and xylene in water enable multiplexed detection on one chip. We use the slow light effect in the photonic crystal design which enhances the absorption of the analytes by a factor of 30 as demonstrated by our previous works. In order to match the absorption peaks of these two analytes, photonic crystal slow light regions are designed at 1644nm and 1674nm with a SU8 cladding on top. Multiplexed detection is enabled by using a multimode interference (MMI) optical power splitter at the input, which divides optical power into two arms, and Y combiner at the output. Consequently, the absorption of these two chemicals can be enhanced by the slow light effect. The MMI structure and Y combiner also enable the multiplexed detection of two analytes on one chip.
We experimentally demonstrated a silicon photonic crystal (PC) microcavity biosensor with 50 femto-molar detection limit. Our devices have demonstrated sensitivities higher than than competing optical platforms at concentration of 0.1μg/ml across a range of dissociation constants KD 1 micro-molar to 1 femto-molar. High sensitivities were achieved by slow light engineering which reduced the radiation loss and increased the stored energy in the PC microcavity resonance mode which contributed to high Q as well as enhanced optical mode overlap with the analyte. By integrating subwavelength grating coupler, we showed that not only coupling efficiency increased but also the working device yield significantly improved
Detection of biomolecules on microarrays based on label-free on-chip optical biosensors is very attractive since this format avoids complex chemistries caused by steric hindrance of labels. Application areas include the detection of cancers and allergens, and food-borne pathogens to name a few. We have demonstrated photonic crystal microcavity biosensors with high sensitivity down to 1pM concentrations (67pg/ml). High sensitivities were achieved by slow light engineering which reduced the radiation loss and increased the stored energy in the photonic crystal microcavity resonance mode. Resonances with high quality factor Q~26,760 in liquid ambient, coupled with larger optical mode volumes allowed enhanced interaction with the analyte biomolecules which resulted in sensitivities down to 10 cells per micro-liter to lung cancer cell lysates. The specificity of detection was ensured by multiplexed detections from multiple photonic crystal microcavities arrayed on the arms of a multimode interference power splitter. Specific binding interactions and control experiments were performed simultaneously at the same instant of time with the same 60 microliter sample volume. Specificity is further ensured by sandwich assay methods in the multiplexed experiment. Sandwich assay based amplification increased the sensitivity further resulting in the detection of lung cancer cell lysates down to concentrations of 2 cells per micro-liter. The miniaturization enabled by photonic crystal biosensors coupled with waveguide interconnected layout thus offers the potential of high throughput proteomics with high sensitivity and specificity.
Lab-on-chip integrated infrared spectroscopy and sensing with hybrid polymer and silicon photonic crystal slot
waveguides is demonstrated for the specific and selective identification of volatile organic compounds, xylene and
toluene, in water. A 300 micron long photonic crystal slot waveguide was demonstrated that enabled the detection of
100ppb xylene in water by near-infrared absorption signatures, with five times higher sensitivity on an order of
magnitude smaller length scale. The on-chip absorption spectroscopy, determined by Beer-Lambert absorption law, is
enabled by the combined effects of slow light and high electric field intensity enhancement in photonic crystal slot
waveguides.
While Q ~ 1million has been demonstrated in freely suspended photonic crystal (PC) membranes, the reduced refractive
index contrast when PC microcavities are immersed in phosphate buffered saline (PBS), a typical ambient for
biomolecules, reduces Q by more than 2 orders of magnitude. We experimentally demonstrate photonic crystal
microcavity based resonant sensors coupled to photonic crystal waveguides in silicon on insulator for chemical and bio-sensing.
Linear L-type microcavities are considered. In contrast to cavities with small modes volumes but low quality
factors for bio-sensing, we show that increasing the length of the microcavity enhances the quality factor of the
resonance by an order of magnitude and also increases the resonance wavelength shift while still retaining compact
device characteristics. Q~26,760 and sensitivity down to 7.5ng/ml and ~9pg/mm2 in bio-sensing was experimentally
demonstrated in SOI devices for goat anti-rabbit IgG antibodies with Kd~10-6M. The increase in cavity length follows
from fundamental engineering limitations in ink-jet printing or microfluidic channels when unique receptor biomolecules
are coated on separate adjacent sensors in a microarray.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.