Slow light propagated through a photonic crystal with a nematic liquid crystal-filled cavity has been simulated and presented. Both slow and fast modes propagate in the waveguide. Design efforts were made to adjust the group velocities of the propagating modes. Numerical studies show that the nematic liquid crystal provides designers an additional degree of freedom to tune the device by using external perturbations such as applying heat or electric field. Comparative studies have also been done to see the performance of the devices built in two different material platforms (silicon and InP). The device can be used as an economic and efficient functional materials system for building robust integrated photonic devices that have the ability to slow, store, and process light pulses.
An innovative technique to tune the slow light propagated through photonic crystal cavity filled with E7 type
nematic crystal has been simulated and presented. Observed propagating modes in the previously fabricated photonic
crystal indicate that both slow and fast modes propagate in the waveguide. Design efforts were made to adjust the
propagating modes as well as their group velocities. Numerical studies show that by inserting nematic liquid crystal,
designer can achieve additional degree of freedom to tune the device by using external perturbation such as applying heat
or electric field. Comparative studies have also been done to see the performance of the devices fabricated in two
deferent material platforms (silicon and InP) with an objective to develop economic and efficient functional material
systems for building robust integrated photonic devices that have the ability to slow, store, and process light pulses.
Optical fields that are periodic in the transverse plane self-image periodically as they propagate along the optical axis: a
phenomenon known as the Talbot effect. A transfer matrix may be defined that relates the amplitude and phase of point
sources placed on a particular grid at the input to their respective multiple images at an image plane. The free-space
Talbot effect may be mapped to the waveguide Talbot effect. Applying this mapping to the transfer matrix enables the
prediction of the phase and amplitude relations between the ports of a Multimode Interference (MMI) coupler– a planar
waveguide device. The transfer matrix approach has not previously been applied to the free-space case and its mapping
to the waveguide case provides greater clarity and physical insight into the phase relationships than previous treatments.
The paper first introduces the underlying physics of the Talbot effect in free space with emphasis on the positions along
the optical axis at which images occur; their multiplicity; and their relative phase relations determined by the Gauss
Quadratic Sum of number theory. The analysis is then adapted to predict the phase relationships between the ports of an
MMI. These phase relationships are critical to planar light circuit (PLC) applications such as 90° optical hybrids for
coherent optical receiver front-ends, external optical I-Q modulators for coherent optical transmitters; and optical phased
array switches. These applications are illustrated by results obtained from devices that have been fabricated and tested by
the PTLab in Si micro-photonic integration platforms.
Silicon-on-insulator (SOI) photonic integrated circuits have recently become a research topic of great interest due to their
compact confinements and compatibility with the modern micro-electronics. As the dominant issues of the integration
density of planar lightwave circuits on a single SOI chip, low-loss SOI curved waveguides and corner turning mirror
(CTM) structures are attracting attention. This work aims at the performance comparison between the SOI curved
waveguides and CTM structures. For this goal we have designed both SOI curved waveguides and SOI CTM structures
and then fabricated them. The performance of these two devices, such as the propagation loss and polarization dependent
loss, is measured and compared.
For the SOI-waveguide directional coupler (WDC), optical access loss (OAL) and polarization dependence (PD) are two
critical performance specifications which seriously affect the adoptability and deployment of a device, including optical
on-chip loss (OCL), polarization dependent loss (PDL) and extinction ratio of a 3dB-coupler based device. In this work,
using a commercial software tool - FIMMPROP, the performance of an SOI-WDC is simulated. Simulations find that the
curved waveguides for the turning sections of a 3dB WDC not only enlarge the footprint size, but also seriously
deteriorate the device performance. For instance, the two curved waveguide sections of a WDC induce an unpredictably
large change in the 3dB-coupling length, increase an OAL of 0.4-0.9dB, and seriously deteriorate the PD, and these
performance changes radically depend on rib size. After a corner-turning mirror (CTM) structure is introduced to a 3dB
SOI-WDC, the experiments show both the footprint length and 3dB-coupling length are unchanged, the OAL of the 3dB
coupler is only 0.5dB which is close to the simulation value. Therefore, for a 3dB-coupler based Mach-Zehnder
interference (MZI) structure, the OCL will be controlled to be <1.0dB in device design and will not depend on rib size.
Mach-Zehnder interference (MZI) construction is broadly exploited to implement optical switches and modulators in the field of integrated optical/photonic technology. Silicon-on-insulator (SOI) waveguides have been increasingly developed to implement highly integrated photonic devices and systems. In this work, for the SOI-waveguide MZI-type electro-optic (EO) modulated devices with free-carrier dispersion (FCD) effect, the FCD-induced extra optical absorption (EOA) loss and its negative impact upon the device performance are studied. An intrinsic limitation to this type of device is found to be the tension between the EOA loss and the interaction length for a half-wave modulation. The numerical calculation and professional software simulation show the EOA loss of <1.0dB determines an interaction length of 4-mm. The performance decay processes of both EO switch and modulator due to the modulation-induced EOA loss are modeled. The numerical calculation shows the optical on-chip (OC) loss is 1.0dB and the isolation between two outputs is 21dB for the EO switch, while for the EO modulator the OC loss is 1.0dB and 2.5dB at the off- and on-state, respectively, and the extinction ratio only approaches 20dB. The negative influence of this intrinsic limitation to the bandwidth of EO modulator is also analyzed.
This paper introduces a compact 90º optical hybrid, built on small size SOI waveguide technology .This optical hybrid
is a critical component of a potentially low-cost coherent optical receiver design developed within the frame of our
Optical Coherent Transmission for Access Network Extensions (OCTANE) project. In previous recent work, 90º
optical hybrids were realized in SOI rib waveguide technology with 4 μm top silicon and a rib height of approximately
2 μm. In this paper, we introduce a compact 90º optical hybrid, built on small size SOI waveguide technology (1.5 μm
SOI -based rib waveguide, with 0.8μm rib height). The proposed device consists of multimode interferometers (MMIs)
connected in such a way that four different vector additions of a reference signal (local oscillator) and the signal to be
detected are obtained. At the outputs, the hybrid provides four linear combination of the signal with the reference
which differs by a relative phase shift of the reference of 90º. The four output signals are detected by a pair of
balanced receivers to provide in-phase and quadrature (I&Q) channels. The phase differences arise naturally from the
self imaging property of a MMI.
The key elements of the 90º optical hybrid, including a 2×2 MMI, a 4×4 MMI, and polarization diversity
configuration have been designed and simulated, using the numerical mode solving tool FIMMPROB. The 2×2 and
4×4 MMI had overall lengths of 701μm and 3712.5μm lengths respectively. Tapers are used to couple adiabatically
single mode waveguides to the entrance and exit ports of the MMI to assure correct operation by avoiding coupling to
the higher order transverse modes allowed at the entrance and exit ports of the MMI. The simulation results at 1550nm
show polarization independence and phase errors between the ports of less than 0.03 degrees. Currently the design is
in fabrication at the Canadian Photonics Fabrication Center with the support of CMC Microsystems and experimental
results will be subject to a further report.
In this paper we introduce a multi gas sensor system based on refractive index changes in a 2D slab photonic crystal. The
sensor is formed by a L3 resonant cavity sandwiched between two W1.06 waveguides in the photonic crystal. The sensor
configuration is similar to an Add-Drop filter structure. The transmission spectrums of the sensor with different ambient
refractive indices ranging from n = 1.0 to n = 1.1 are calculated. The simulation results show that a change in ambient RI
of Δn = 0.0008 is apparent with a corresponding change in output wavelength of the sensor of 2.4 nm. The properties of
the sensor are simulated using the 3D finite-difference time-domain (FDTD) method. The Q-factor of the sensor is also
optimized, with highest values reaching over 30,000. The sensor system is hybrid integrated with a wireless RF chip
which processes the sensor data and transmits them in effect turning the entire system into a wireless sensor mote.