The potentials of a nanophotonic platform, including compactness, low power consumption, integrability with other functionalities, and high sensitivity make them a suitable candidate for sensing applications. Strong light-matter interaction in such a platform enables a variety of sensing mechanisms, including refractive index change, fluorescence emission, and Raman scattering. Recent advances in nanophotonic devices include the demonstration of silicon and silicon-nitride microdisk resonators with high intrinsic Q values (0.5-2×106) for strong field enhancement and the realization of compact photonic crystal spectrometers (high spectral resolution at 100-µm length scales) for on-chip spectral analysis. These two basic building blocks, when combined with integrated fluidic channels for sample delivery, provide an efficient platform to implement different sensing mechanisms and architectures.
The potentials of integrated optical systems for implementing compact and low power consumption yet highly sensitive
sensing systems have made them a viable candidate for integrated chemical and biological sensing applications. In these
integrated optical sensing systems, spectrometers have a significant role as a building block that enables on-chip
spectral analysis. Monitoring the spectral features of the signal using an on-chip spectrometer brings about a variety of
new sensing mechanisms and architectures in an integrated platform. Monitoring absorption spectra, measuring Raman
emission features, and tracking changes in spectral signatures as a result of environmental changes are some of the
schemes made possible by such spectral analysis. In this work, we implement superprism-based photonic crystal devices
in planar platforms as on-chip spectrometers. We use planar silicon platform in a silicon-on-insulator (SOI) wafers for
the infrared wavelength range. A silicon-nitride (SiN) planar platform is used for the near infrared and visible
wavelength ranges. In both SOI and SiN implementations, superprism-based spectrometers are experimentally
demonstrated and compared with grating spectrometers made in the same platform. The potentials of the demonstrated
spectrometers to meet the requirements of current and future applications in integrated optical sensing are briefly
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.
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.
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.
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
By adding a point defect to a photonic crystal structure, a microcavity can be made to trap electromagnetic energy with wavelength inside the photonic bandgap (PBG). This property together with other unique properties of photonic crystals enables us to control the propagation and spectrum of transmitted wave inside the photonic crystal waveguiding structures and to design and implement microscale optical filters. In this paper we focus on the design of notch filters in photonic crystal waveguides based on the coupling of waveguide and cavity. We discuss about the properties of a single cavity and its necessary modifications to achieve efficient coupling between cavity and waveguide and eventually obtain desired notch filters at the frequency range of interest. We also discuss the coupling of multi-cavities to a waveguide and the possibility of attaining filters with better performances is presented, and the spectrum and lineshapes of the resulting filters are characterized.