In this paper, we present novel designs for all optical analog-to-digital converters simulated and realized in
photonic crystal platforms. The designs presented were implemented on both photonic bandgap based
structures as well as self collimation based structures. Numerical simulation results as well as fabrication results
are also included. Characterization results validate the designs presented for a functional all optical two bit
analog to digital converters in photonic crystals. The design presented can be further scaled to higher resolution
conversion as well as to no optical frequencies if necessary.
We design and characterize a photonic crystal (PhC) based silicon electro-optic modulator. The device is composed of a
planar photonic crystal with associated input and output dielectric waveguides and a p-i-n diode to inject free carriers for
index modulation. The photonic crystal, which confines light using the self-collimation phenomenon, has two regions of
varying air hole diameters forming a defect area in a host self-collimation lattice. At the interface of the defect with the
host lattice, an impedance mismatch is formed which is modulated using free carrier injection. With sufficient index
modulation the impedance mismatch is large enough to decrease the transmission through the defect region, thus,
modulation the overall transmission of the device. Our analysis shows that with a doping concentration in the range of
1020/cm3, the injected free carrier concentration can exceed 2.5*1019 with a drive voltage of 2.6 V. This free carrier
concentration is sufficient to modulate the refractive index, Δn, greater than .05, which in turn produces a modulation
depth greater than 75%. A fabricated device produces a modulation depth of 80% with a drive current of 4mA.
We present a reconfigurable, compact, low loss, optical switch in silicon. The device utilizes the self-collimation
properties of photonic crystal structures and provides a technique for efficiently switching an electromagnetic wave
guided through a pre-engineered dispersion based photonic crystal self-guiding structure. The electromagnetic wave can
be either in the microwave or optical regime based on the constituent materials and dimensions of the photonic crystal
host. We propose that the "loss tangent" of dielectric material in the switching region can be modified by external
"commands" to control the direction of propagation of the self-collimated signal and hence attain switching, thereby redirecting
the light. Based on the geometrical orientation and position of the applied electric field, electromagnetic waves
can be completely redirected (switched), or partially routed towards any arbitrary direction on a Manhattan grid or
network. We have found that the induced loss does not significantly attenuate the waves switched in any direction. The
structure presented can be generalized to an arbitrary N by M interconnected switching network or fabric, where the
switching topology can be dynamically modulated by the application of external fields. To attain switching, the free-carrier
absorption loss of Si is controlled by carrier injection from forward-biased PN junction. The concept device is
designed and analyzed using the FastFDTDTM accelerated hardware based FDTD technology.
We demonstrate methods to enhance electro-optical effect in silicon. In the first method, a tunable PhC device is
proposed to consist of the self-guiding region and the tunable region. The tunable lattice is designed such that it has a
band gap and the self-guiding frequency is located at its bottom band edge of the conduction band. Therefore, the device
output can be tuned by injecting free carriers into the tunable region to slightly reduce its effective index to pull up the
band gap. In the second method we design a self-guiding PhC cavity. Using this cavity, we could switch output light on
and off with an extinction ratio of 17.5 dB by changing only 1e-3 of the effective refractive index of the silicon
background. The third method utilizes a 12-fold symmetric quasi- photonic crytal cavity to enhance electro-optical
effect in silicon. The designed cavity supports whispering gallery modes and one of such modes is found to have Q
value of 2.3e4.
In this paper, we present novel designs for all optical analog-to-digital converters simulated and realized in
photonic crystal platforms. The designs presented were implemented on both photonic bandgap based
structures as well as self collimation based structures. Numerical simulation results as well as fabrication results
are also included. Characterization results validate the designs presented for a functional all optical two bit
analog to digital converters in photonic crystals. The design presented can be further scaled to higher resolution
conversion as well as to no optical frequencies if necessary.
In this paper, we present novel designs for all optical analog-to-digital converters simulated and realized in photonic crystal platforms. The designs presented were implemented on both photonic bandgap based structures as well as self collimation based structures. Numerical simulation results as well as fabrication results are also included. Characterization results validate the designs presented for a functional all optical two bit analog to digital converters in photonic crystals. The design presented can be further scaled to higher resolution conversion as well as to no optical frequencies if necessary.
Photonic crystals have many potential applications due to their unique abilities to control the propagation of electromagnetic waves. If their bandgap and dispersive properties are modulated by external means, more exciting applications emerge. In this work, we present novel applications and devices created by tuning the bandgap and dispersive properties of periodic photonic crystal structures. We present our designs in both high- and low-refractive index materials. Many tunability alternatives exist including thermal, optical, electrical, microfluidic, and liquid crystals-based. In this paper, we will utilize these methods to implement various photonic crystal-based devices and applications.
In this paper, we present the design, fabrication, and characterization of large-diameter semiconductor ring lasers with a single out coupling waveguide using AlGaAs/GaAs multiquantum well wafer. We also investigate the influence of the coupling between the ring cavity and the straight waveguide on the threshold current. It was found that the threshold current reduces with the decrease of the coupling between the ring cavity and the waveguide due to the widening of the coupling gap. By optimizing the coupling gap, we achieve a device with the threshold current of as low as 49mA.
In this paper we presented the modeling, design of a millimeter wave (MMW) photonic modulator operating at high Giga-Hertz frequency, i.e. 94GHz. Our approach combines high quality factors (Qs) photonic microdisks with nonlinear properties of electro-optic (EO) material at the present of applied millimeter wave to achieve optical modulation. The high Q values and strong field densities associated with WGMs in microdisk resonators result in the enhancement of the nonlinear interaction of optical fields with a material that exhibits coherent attributes, even with weak millimeter waves. The coupled mode theory (CMT) is applied to incorporate the nonlinearity of EO material in the optical analysis. In the simulations, two EO materials, LiNBO3 and GaAs, are considered and designed to realize the MMW photonic modulation. In addition, carefully design and analysis is taken by using rigorous electromagnetic (EM) algorithm to accurately determine EM field in the MMW resonator, which will provide maximum modulation.
We demonstrate fabrication of silicon microring resonators with narrow coupling gaps using electron-beam lithography followed by lift-off process. Microring resonators of different diameters and 58 nm coupling gaps are fabricated in a silicon-on-insulator water. These devices are then characterized using a tunable laser source. For the microring resonator with a diameter of 7.5 µm, the measured maximum transmission is 88%, the free spectra range is 25 nm, the finesse is 28, and the Q factor is 1715.
We have developed a new approach for the fabrication of three-dimensional photonic crystals based on multi-layer photolithography. This method, which uses commercially available photoresist, allows parallel fabrication of three-dimensional photonic crystals, and possesses the flexibility to create a variety of different lattice arrangements and the freedom of arbitrary defect introduction. We describe in this work how this method is derived from mature two-dimensional photolithography and demonstrate it with the fabrication of multi-layer woodpile structures with and without defects as well as other unique three-dimensional microstructures.
In this paper, we review the confinement mechanism of self-collimation in planar photonic crystals. In this mechanism, an approximately flat equi-frequency contour (EFC) below the light cone of the planar photonic crystal can be used to laterally confine the light and total internal reflection (TIR) provides vertical confinement. To this end, self-collimation in both low-index and high-index planar photonic crystals are investigated using the three-dimensional (3D) finite-difference time-domain (FDTD) method and the 3D iterative plane wave method (PWM). It is found that low-loss self-guiding is achievable in both the valence and conduction bands for high-index planar photonic crystals. However, for low-index planar photonic crystals, low-loss self-guiding can be only observed in the valence band. Experimental results show a propagation loss of as low as 1.1 dB/mm for the self-guiding in a high-index planar photonic crystals.
In this paper we present a novel fabrication method for the realization of complex 3D multi-layer structures with commercially available photoresists. This method is based on the observation that during an image-reversal process, the post exposure bake (PEB) that is used to reverse the contrast of the exposed pattern reduces the sensitivity of the unexposed photoresist at the same time. In multi-layer lithography, this phenomenon, along with non-uniformly distributed dose can be exploited to eliminate the re-patterning effect of the subsequent exposures and thus makes suspended 3D structures possible. In this presentation we demonstrate this observation experimentally, and fabricate “woodpile” structures (≥ 3 layers) using the proposed method.
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