Waveguide based sensors allow independent control over sensitivity and dynamic range, which is not possible in
resonance based sensors. In this paper, we present a refractive index sensor based on using photonic crystal waveguides
(PCWs) in an unbalanced Mach-Zehnder interferometer configuration. In this configuration the dynamic range of the
sensor is determined by the path difference between the two arms and the sensitivity is controlled by the length of the
PCW. We show that by using PCWs we can get a factor of 8 improvement in sensitivity over a ridge-waveguide based
sensor. This enhanced sensitivity is achieved due to reduced group velocity in a PCW. By reducing the loss at low
group velocities the sensitivity can be further improved.
We identify factors affecting transmission and dispersive properties of photonic crystal waveguide (PCW) bends and
show how they can be varied in a systematic manner to achieve wide bandwidth bends with high transmission and low
dispersion. Our experiments show around 12 nm of bandwidth increase as compared to simple bends in a PCW at low
group velocities. The bandwidth increase at high group velocities is more than 30 nm.
Infiltration of planar 2D silicon photonic crystals with nanocomposites using a
simple melt processing technique is presented. The nanocomposites that were developed by
evenly dispersing functionalized TiO2 nanoparticles into a photoconducting polymer exhibit
high optical quality and tunable refractive index. The infiltrated photonic crystals show
tuning of the photonic band-gap that is controllable by the adjustment of the nanoparticle
loading level. These results may be useful in the development of tunable photonic devices,
hybrid light emitting diodes and photovoltaics.
We present methods for systematic design of couplers for efficient coupling of light into the slow group velocity modes
of photonic crystal waveguides (PCW).
The opportunity to manipulate optical properties of materials through fabrication is the unique capability offered by
photonic crystals. Among different directions to exploit the possibilities in this field, there have been recent research
activities to engineer the dispersive properties of photonic crystals to change the propagation properties of waves
passing through these periodic structures. To provide an efficient way to implement such devices, an approximate
modeling technique will be used to simplify the analysis and design process for dispersive photonic crystal devices.
Furthermore, the issue of efficient coupling to dispersive photonic crystal modes which is crucial for practical
implementation of these devices will be addressed. Here, in particular, we will focus on employing the dispersive
properties of photonic crystals to realize compact optical spectrometers and wavelength demultiplexers. We will show
that by combining multiple dispersive properties (i.e., negative diffraction and the superprism effect) it is possible to
enhance the performance of devices targeted for such applications. The potentials of these photonic crystal devices to
meet the requirements of current and future applications in optical information processing and integrated optical sensing
will be discussed.
We present a method for systematic design of Photonic Crystal Waveguide (PCW) bends to achieve high transmission and low dispersion over large bandwidths by identifying factors and studying their effects on transmission and dispersive properties of bends.
We show that femtosecond optical pulses at optical communication wavelengths can be used for real time dispersion measurement of photonic crystal waveguides. Spectral resolutions on the order of one nanometer and bandwidths as large as tens of nanometers are demonstrated in real time measurements. Preliminary results are shown and discussed.
Compact on-chip wavelength demultiplexers and spectrometers are essential components for a variety of applications
including integrated optical information processing devices, optical communications, and integrated optical sensing.
Implementation of such devices requires strong dispersion in the optical materials, which can be realized using unique
dispersive properties of photonic crystals (PCs). Possibility of integration, compactness, and compatibility with different
host materials are the main advantages of PC based demultiplexers and spectrometers compared to other techniques.
Here, we show an implementation of superprism-based photonic crystal devices (using a diffraction compensation
scheme) that improves the performance of these devices compared to the conventional implementation. Structures
obtained through optimization have been fabricated in SOI wafers using e-beam writing and ICP etching, and spatial
separation of channels (with good isolation) in these superprism devices is experimentally demonstrated. The
performance of these superprism devices as general-purpose spectrometers and for locating spectral features in a
sensing platform will be also demonstrated and discussed. Further steps for improvement of these devices are
considered and the related implementation issues are investigated.
Wavelength demultiplexing is one of the major applications of unique dispersion properties of photonic crystals (PCs). Possibility of integration and compactness are two main advantages of PC based demultiplexers compared to other demultiplexing techniques for applications including compact spectrometers (for sensory applications) and WDM demultiplexers. Here, we show that resolution and size limitations of conventional superprism-based photonic crystal
demultiplexers are caused by the choice of configuration. We suggest an alternative implementation (combining superprism effect and focusing) that improves the performance compared to the conventional implementation in terms of being more compact and relaxing the requirement for divergence angle of the incident beam. We use effective index model to describe the beam behavior inside the photonic crystal region. Using this model, effective indices (second
order and third order) are calculated directly from the band structure and are used to find the optimal operation parameters for the demultiplexing device. Detailed calculations show that the required size of preconditioned superprism photonic crystal demultiplexers scales up as N5/2 (N being the number of channels which is proportional to the resolution of the device) which shows significant advantage over N4 dependence in conventional superprism-based devices, especially for high resolutions required in practical DWDM systems or spectroscopic applications. Structures obtained through optimization have been fabricated in SOI wafers using e-beam writing and ICP etching, and spatial separation of channels (with good isolation) in focusing superprism devices is experimentally demonstrated.
We show that simultaneous perturbation of periodicity and radius of air holes next to the guiding region in a photonic
crystal waveguide results in low loss and large bandwidth waveguides that are also single mode. We also show the
results of a single shot spectral phase measurement that can be used for real time dispersion measurement of photonic
crystal waveguides.
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