high-efficiency silicon strip waveguide to plasmonic slot waveguide converter based on the hybrid silicon-gold taper
is proposed and optimized. Through investigating the mode matching, the effective index matching, and the metallic
absorption loss considerations, the hybrid silicon-gold taper with an overall length of 1.7 μm having a very high
conversion efficiency of 93.3% at 1550nm is achieved. Besides, the configuration limitations for restricting this mode
converter to achieve a 100 % conversion efficiency are also studied in this paper. Such a high efficiency converter will
be an essential component in ultra-compact integrated circuits.
Silicon-organic hybrid integrated devices have emerging applications ranging from high-speed optical interconnects to photonic electromagnetic-field sensors. Silicon slot photonic crystal waveguides (PCWs) filled with electro-optic (EO) polymers combine the slow-light effect in PCWs with the high polarizability of EO polymers, which promises the realization of high-performance optical modulators. In this paper, a broadband, power-efficient, low-dispersion, and compact optical modulator based on an EO polymer filled silicon slot PCW is presented. A small voltage-length product of Vπ×L=0.282V×mm is achieved, corresponding to an unprecedented record-high effective in-device EO coefficient (r33) of 1230pm/V. Assisted by a backside gate voltage, the modulation response up to 50GHz is observed, with a 3-dB bandwidth of 15GHz, and the estimated energy consumption is 94.4fJ/bit at 10Gbit/s. Furthermore, lattice-shifted PCWs are utilized to enhance the optical bandwidth by a factor of ~10X over other modulators based on non-band-engineered PCWs and ring-resonators.
In on-chip optical interconnect, dielectric waveguide arrays are usually designed with pitches of a few wavelengths to
avoid crosstalk, which greatly limits the integration density. In this paper, we for the first time propose to use multipleinput
multiple-output (MIMO), a well-known technique in wireless communication, to recover the data from entangled
signals and reduce the waveguide pitch to subwavelength range. In the proposed on-chip MIMO system, there is
significant coupling among the adjacent waveguides in the high density waveguide region. In order to recover signals,
the N×N transmission matrix of N high-density waveguides is calculated to describe the relation between each input
ports and output ports. In the receiving part, homodyne coherent receivers are used to receive the transmitted signals, and
obtain the signal in phase and /2 out of phase with local oscillator. In the electrical signal processing, the inverse
transmission matrix is utilized to recover the signals in the electronic domain. To verify the proposed on-chip MIMO, we
used the INTERCONNECT package in Lumerical software to simulate a 10x10 MIMO system. The cross section of
each waveguide is 500 nm x 220 nm. The spacing is 250 nm. The simulation verifies the possibility of recovering 10
Gbps data from the heavily coupled 10 waveguides with a BER better than 10−12. The minimum input optical power for
a BER of 10−12 is greater than -18.1 dBm, and the maximum phase shift between input laser and local oscillator can
reach to 73.5˚.
The detection and measurement of electromagnetic fields have attracted significant amounts of attention in recent years. Traditional electronic electromagnetic field sensors use large active conductive probes which perturb the field to be measured and also make the devices bulky. In order to address these problems, integrated photonic electromagnetic field sensors have been developed, in which an optical signal is modulated by an RF signal collected by a miniaturized antenna. In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300μm, and the bowtie antenna has an area smaller than 1cm2. The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m2 at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz-1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electrooptic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.
We design, fabricate and experimentally demonstrate a highly efficient adiabatic mode converter for coupling light into a silicon slot waveguide with a slot width as large as 320nm. This strip-to-slot mode converter is optimized to provide a measured insertion loss as low as 0.08dB. Our mode converter provides 0.1dB lower loss compared to a conventional V-shape mode converter. This mode converter is used to couple light into and out of a 320nm slot photonic crystal waveguide, and it is experimentally shown to improve the coupling efficiency up to 3.5dB compared to the V-shape mode converter, over the slow-light wavelength region.
We design and demonstrate a compact, low-power, low-dispersion and broadband optical modulator based on electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW). The EO polymer is engineered for large EO activity and near-infrared transparency. The half-wave switching-voltage is measured to be Vπ=0.97±0.02V over optical spectrum range of 8nm, corresponding to a record-high effective in-device r33 of 1190pm/V and Vπ×L of 0.291±0.006V×mm in a push-pull configuration. Excluding the slow-light effect, we estimate the EO polymer is poled with an ultra-high efficiency of 89pm/V in the slot. In addition, to achieve high-speed modulation, silicon PCW is selectively doped to reduce RC time delay. The 3-dB RF bandwidth of the modulator is measured to be 11GHz, and a modulation response up to 40GHz is observed.
We design and demonstrate a compact and low-power band-engineered electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW) modulator. The EO polymer is engineered for large EO activity and nearinfrared transparency. A PCW step coupler is used for optimum coupling to the slow-light mode of the bandengineered PCW. The half-wave switching-voltage is measured to be Vπ=0.97±0.02V over optical spectrum range of 8nm, corresponding to the effective in-device r33 of 1190pm/V and Vπ×L of 0.291±0.006V×mm in a push-pull configuration. Excluding the slow-light effect, we estimate the EO polymer is poled with an efficiency of 89pm/V in the slot.
We investigate the loss mechanism in 3-moded multimode-interference couplers that are the building blocks of a compact and low-loss waveguide crossing structure. Broadband silicon waveguide crossing arrays with <0.01dB insertion loss per crossing are proposed using cascaded multimode interference couplers, where lateral subwavelength nanostructures are used to reduce the insertions loss. We design and fabricate a 101×101 waveguide crossing array with a pitch of 3.08μm. Insertion loss of ~0.02dB per crossing and crosstalk <-40dB at 1550nm operating wavelength and broad transmission spectrum ranging from 1520 to 1610nm are experimentally demonstrated.
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.
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 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.
Silicon microelectronics on unconventional substrates has led to numerous unprecedented applications. Inspired by the great success, it is a natural desire to integrate silicon photonic circuitry on unconventional substrates in the hope of extending the applicability range of silicon photonics to a multitude of novel hybrid silicon photonic devices. However, photonic devices usually have larger dimensions and more complicated morphologies. The transfer method used in electronics cannot be applied directly to transfer photonic devices. Here, we propose a low temperature transfer technique based on adhesive bonding and deep reactive ion etching. A defect-free transfer of 2 cm × 2 cm, 250 nm thick silicon nanomembrane onto a glass slide has been demonstrated. Single mode waveguides and splitters fabricated on the transferred SiNM exhibit comparable results to those fabricated on silicon-on-insulator. With a low process temperature, this method can be easily applied to transfer silicon nanomembranes onto various types of substrates.
We demonstrate board-to-board optical communication utilizing 45 degree mirrors and print-on-demand micro-lenses as
surface-normal coupler. The presented system which includes polymer waveguides, embedded 45 degree mirrors and
micro-lenses, realizes back-to-back optical interconnects between two boards. The waveguide and mirrors are fabricated
using molding method using a low-cost electroplated nickel mold. Micro-lenses (80 μm in diameter) are fabricated using
a material inkjet-printer, on top of the 45 degree mirrors. Experimental results show that each 45 degree mirror
contributes about 1.88 dB loss (65% coupling efficiency) to the total optical loss. When propagating in free space
without a lens, a 2 mm separation between boards results in a 9.9 dB loss, which is reduced to 7.5 dB when a micro-lens
is inserted in the path. High speed data transmission test is performed at various separations. At a separation of 1mm, the
system can provide 10Gbps error free transmission. At 2mm separation, the maximum error free data rate was measured
to be 3.5Gbps and 7.5Gbps, with and without the micro-lens, respectively. Printing the micro-lenses on both the input 45
degree mirror and the photodiode or the receiving 45 degree mirror in a confocal setup will significantly reduce the freespace
propagation loss. To the best of our knowledge, this is the first report of free-space coupling between waveguides
on separate boards.
We have investigated the feasibility of multimode polysilicon waveguides to demonstrate the suitability of polysilicon as
a candidate for multilayer photonic applications. Solid Phase Crystallization (SPC) with a maximum temperature of
1000°C is used to create polysilicon on thermally grown SiO2. We then measure the propagation losses for various
waveguide widths on both polysilicon and crystalline silicon platforms. We find that as the width increases for
polysilicon waveguides, the propagation loss decreases similar to crystalline silicon waveguides. The difference in loss
between the two platforms for a given waveguide width is due to the scattering from the polysilicon grain boundaries,
which excites higher order modes. Depending on the waveguide width, these modes either propagate as higher order
modes or are lost as radiation modes. Due to their different propagation constants, the presence of higher order modes is
confirmed using sub-wavelength grating couplers. At a waveguide width of 10μm, polysilicon and crystalline silicon
waveguides have propagation losses of 0.56dB/cm and 0.31dB/cm, respectively, indicating there is little bulk absorption
from the polysilicon. This propagation loss is the lowest for polysilicon demonstrated to date. Modal conversion in
multimode waveguides by polysilicon grain boundary scattering are investigated using a sub-wavelength grating coupler
and discussed. These results vindicate the use of polysilicon waveguides of varying widths in photonic integrated circuits.
In this paper we demonstrate a three-dimensional (3D) photonic integration scheme based on crystalline silicon. We
develop a process using SU-8 based adhesive bonding to fabricate vertically stacked, double-layer silicon
nanomembranes. A single-layer silicon photonic integrated circuit fabricated on a silicon-on-insulator (SOI) chip and a
bare SOI chip are bonded together, followed by removal of the bare SOI chip’s silicon substrate and buried oxide layer,
to form a silicon nanomembrane as a platform for additional photonic layer. We designed and fabricated subwavelength
nanostructure based fiber-to-chip grating coupler on the bonded silicon nanomembrane, and also inter-layer grating
coupler for coupling between two silicon nanomembranes. The fiber-to-chip grating coupler has a peak efficiency of -3.9
dB at 1545 nm operating wavelength with transverse-electric (TE) polarization. The inter-layer grating coupler has a
peak efficiency of -6.8 dB at 1533 nm operating wavelength with TE polarization. The demonstrated approach serves as
a potential solution for 3D photonic integration and novel 3D photonic devices.
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 demonstrate the practicality of using silicon nanomembranes for use in high performance flexible
photonic interconnects and devices. Using two silicon nanomembrane transfer schemes, we demonstrate successful
transfer of several photonic building blocks including large aspect ratio (>4000) and long (>5cm) strip waveguides,
band engineered slow light (ng > 30) photonic crystal waveguides, 1xN (1x2 and 1x6) multimode interference
couplers etc, on a flexible Kapton polyimide substrate. A two-step cleaving method is also developed and
implemented to facilitate testing of the transferred flexible photonic components for the first time. Upon cleaving,
the propagation loss in transferred ultralong strip waveguide (~5.7cm) is found to be 1.1dB/cm, which is comparable
to that of waveguides on SOI.
In this paper, we report the transfer and characterization of in-plane silicon nanomembrane based photonic devices on a
Kapton polyimide flexible substrate. Compared with electronic devices and surface normal optical devices, in-plane
photonic devices have stringent requirements on transfer precision because any shift in the position or breakage can
affect the performance of devices. Therefore, a supporting layer consisting of a photoresist is exploited to protect the
device during the transfer process. A modified stamp-assisted transfer technique is employed in order to transfer
nanomembrane devices onto the flexible film and the transfer of large aspect ratio (up to 4000) waveguides and 1x6
multimode interference (MMI) couplers on a flexible Kapton substrate is demonstrated. A two-step cleaving method is
developed in order to prepare the facets of the transferred waveguides and in-plane light coupling into a 60μm wide,
8mm long flexible waveguide from a lensed fiber is demonstrated. This demonstration opens limitless possibilities for a
whole new area of high performance flexible photonic components using silicon nanomembrane technology.
In this paper, we present a highly compact silicon nano-membrane based optical phased array fabricated using
conventional CMOS processing on silicon-on-insulator that provides for over 10 degrees of beam steering in a silicon
slab at λ=1.55μm using transverse-electrical polarized light. A low loss 1-to-12 multi-mode interference (MMI) optical
beam splitter with high uniformity is used to provide inputs to the optical phased array. Using an unequally spaced
waveguide array permits us to 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. S-bend waveguides convert the equally spaced MMI output to the unequally spaced wave guide array, while
passively equalizing the phases of each array element to compensate for the MMI output phase profile. Independently
controllable thin film metal heaters are used to achieve phase shifting using the strong thermo-optic response of silicon.
Heat-insulating air grooves minimize thermal crosstalk, while also achieving and low power consumption.
In this paper, we investigate the criteria for far-field approximation in a 2D problem, including the phase criterion.
Using a silicon-lab as the platform, we will also compare these criteria with those of a 3D scattering problem for
both sub-wavelength and large objects. The convergence of the exact solution, based on Hankel functions, and the
far-field approximation are presented.
The need for antennas with improved characteristics for communication and radar applications has resulted in an ever-increasing
demand for research in the field of high impedance surfaces, which can work as an artificial magnetic
conductor. One method in fabrication of these surfaces is formation of a metamaterial by patterning a metallic surface in
the shape of space filling curves (e.g. Hilbert or Peanu Curves). In this paper, we present a novel semi-analytical solution
to the problem of plasmonic propagation on these surfaces. The method is based on a previously presented Green's
function formalism, which has been reported in an earlier paper of ours. We have modified and improved the method for
analysis of periodic structures with a large number of spatial harmonics, and used different methods to get the necessary
stabilization. Here propagating modes of different structures and their corresponding frequencies are calculated, and the
possibility of frequency gap formation and stability of the method are investigated.
We present a design methodology for silicon-on-insulator photonic crystal waveguides to achieve wideband lowdispersion
slow light with only tuning the position of the first three inner rows. We aim to maximize the group index -
bandwidth product or the slowdown factor. Our design achieves a constant group index of 39.3 over 12 nm bandwidth
around 1550 nm, corresponding to a slow down factor of 0.3.
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 derive analytical formulations for the output phase profile of symmetrically excited one-to-N multimode interference
couplers. We show that the output phase increases quadratically from the middle of the MMI waveguide, which needs to
be taken into account for phase-dependent applications such as optical phased arrays.
We present a new approach to wide angle optical beam steering based on nano-membrane-based phased array structures with unequally spaced elements. In our approach, the array elements are positioned in such way that grating lobes associated with different sub-arrays do not overlap. Therefore, we reduce the side-lobe-level of the array radiation pattern and at the same time we can avoid the optical coupling between adjacent waveguides by relaxing the half-wavelength spacing requirement for large angle beam steering. By optimizing the optical waveguide structure for the maximum full-width at half-maximum of the single radiator's radiation pattern we discuss the optimum performance achievable using the Unequally-spaced Waveguide Arrays.
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