322 research outputs found
Compact Brillouin devices through hybrid integration on Silicon
A range of unique capabilities in optical and microwave signal processing
have been demonstrated using stimulated Brillouin scattering. The desire to
harness Brillouin scattering in mass manufacturable integrated circuits has led
to a focus on silicon-based material platforms. Remarkable progress in
silicon-based Brillouin waveguides has been made, but results have been
hindered by nonlinear losses present at telecommunications wavelengths. Here,
we report a new approach to surpass this issue through the integration of a
high Brillouin gain material, As2S3, onto a silicon chip. We fabricated a
compact spiral device, within a silicon circuit, achieving an order of
magnitude improvement in Brillouin amplification. To establish the flexibility
of this approach, we fabricated a ring resonator with free spectral range
precisely matched to the Brillouin shift, enabling the first demonstration of
Brillouin lasing in a silicon integrated circuit. Combining active photonic
components with the SBS devices shown here will enable the creation of compact,
mass manufacturable optical circuits with enhanced functionality
Technologies for single chip integrated optical gyroscopes
Optical gyroscopes are being employed for navigational purposes for decades now and have achieved comparable or better reliability and performance than rotor-based
gyroscopes. Mechanical gyros are however generally bulky, heavy and consume more power which make them unsuitable for miniaturized applications such as cube satellites
and drones etc. Therefore, much effort is being expended worldwide to fabricate optical gyros having tactical grade robustness and reliability, small size, weight, cost and power consumption with minimal sacrifice of sensitivity. Integrated optics is an obvious approach to achieving this. This work comprises detailed comparative analysis of different types and structures of integrated optical gyroscopes to find out the suitable option for applications which require a resolution of <10 o/h. Based on the numerical analysis, Add-drop ring resonator-based gyro is found to be a suitable structure for integration which has a predicted shot noise limited resolution of 27 o/h and 2.71 o/h for propagation losses of 0.1 dB/cm and 0.01 dB/cm respectively. An integrated gyro is composed of several optical components which include a laser, 3dB couplers, phase/frequency modulators, sensing cavity and photodetectors. This requires hybrid integration of multiple materials technologies and so choices about
which component should be implemented in which technology. This project also undertakes theoretical optimization of few of the above-mentioned optical components in materials systems that might offer the most convenient/tolerant option, this including 3dB coupler, thermo-optic phase modulator and sensing cavity (resonator and waveguide loop). In particular, the sensing element requires very low propagation loss waveguides which can best be realised from Si3N4 or Ta2O5. The optimised Si3N4 or Ta2O5 waveguides however are not optimal for other functions and this is shown and alternatives explored where the Si3N4 or Ta2O5 can easily be co-integrated. The fabrication process of low loss Si3N4 and Ta2O5 waveguides are also reported in this
thesis. Si3N4 films were grown by using low pressure chemical vapor deposition (LPCVD) technique. Dry etching of Si3N4 films have been optimized to produce smooth
and vertical sidewalls. Experimental results predicted that the propagation loss of 0.009 dB/cm is achievable by using optimum waveguide dimensions and silica cladding with the relatively standard processes available within the Laser Physics Centre at the Australian National University. A CMOS back end of line compatible method was developed to deposit good quality Ta2O5 films and silica claddings through ion beam sputtering (IBS) method. Plasma etching of Ta2O5 waveguides has been demonstrated by using a gas combination of CHF3/SF6/Ar/O2. Oxygen was introduced into the chamber to produce non-vertical sidewalls, so the waveguides could be cladded without voids with IBS silica. Average propagation losses of 0.17 dB/cm were achieved from Ta2O5 waveguides which appeared after extensive investigation to be limited by the spatial inhomogeneity of the processing. Lastly, a detailed theoretical and experimental analysis was performed to find out the possible causes of the higher average propagation loss in Ta2O5 waveguides, some sections being observed with 0.02 dB/cm or lower losses
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Ultrafast all-optical ALU operation using a soliton control within the cascaded InGaAsP/InP microring circuits
A dark-bright soliton conversion is used to perform the two arithmetic logic unit operations namely adder and subtractor operations. The advantage of the system such as power stability, non-dispersion and the dark-bright soliton phase conversion control can be obtained. The input source into the circuit is the bright soliton pulse, with the pulse width of 35 ps, the peak power at 1.55 µm is 1 mW. By using the dark-bright soliton conversion pair, the generated logic bits can be controlled, and the secure bits can be achieved. The simulation results show the output signal with a minimum loss of only 0.1% with respect to a low input power of 1 mW, and ultra-fast response time of about 1 ps can be achieved. It gives the ultra-high bandwidth of more than 40 Gbits−1. The circuit composes six microring resonators made of InGaAsP/InP material with smaller ring radii of 1.5 µm, and the total physical scale of the circuit less than 100 µm2
High-responsivity graphene photodetectors integrated on silicon microring resonators.
Graphene integrated photonics provides several advantages over conventional Si photonics. Single layer graphene (SLG) enables fast, broadband, and energy-efficient electro-optic modulators, optical switches and photodetectors (GPDs), and is compatible with any optical waveguide. The last major barrier to SLG-based optical receivers lies in the current GPDs' low responsivity when compared to conventional PDs. Here we overcome this by integrating a photo-thermoelectric GPD with a Si microring resonator. Under critical coupling, we achieve >90% light absorption in a ~6 μm SLG channel along a Si waveguide. Cavity-enhanced light-matter interactions cause carriers in SLG to reach ~400 K for an input power ~0.6 mW, resulting in a voltage responsivity ~90 V/W, with a receiver sensitivity enabling our GPDs to operate at a 10-9 bit-error rate, on par with mature semiconductor technology, but with a natural generation of a voltage, rather than a current, thus removing the need for transimpedance amplification, with a reduction of energy-per-bit, cost, and foot-print
Micro ring resonators in silicon-on-insulator
Silicon as a platform for photonics has recently seen a very large increase in interest
because of its potential to overcome the bandwidth limitations of microprocessor
interconnects and the low manufacturing cost given by the high compatibility
with the already established micro-electronics industry. There has therefore been
a signicant push in silicon photonics research to develop all silicon based optical
components for telecoms applications. The work reported in this Thesis is con-
cerned with the design, fabrication and characterisation of coupled ring resonators
on silicon-on-insulator (SOI) material. The nal objective of this work is to pro-
vide a robust and reliable technology for the demonstration of optical buers and
delay-lines operating at signal bandwidths up to 100 GHz and in the wavelength
region around 1550 nm. The core of the activity focused on the optimisation
of the fabrication technology and device geometry to ensure the required device
performance for the fabrication of long chains of ring resonators. The nal pro-
cess has been optimised to obtain both intra-chip and chip-to-chip reproducibility
with a variability of the process controlled at the nanometre scale. This was made
possible by careful control of all the variables involved in the fabrication process,
reduction of the fabrication complexity, close feature-size repeatability, line-edge
roughness reduction, nearly vertical sidewall proles and high uniformity in the
ebeam patterning. The best optical propagation losses of the realized waveguides
reduced down to 1 dB=cm for 480 220 nm2 rectangular cross-section photonic
wires and were consistently kept at typical values of around 1.5 dB=cm. Control
of the coupling coecients between resonators had a standard deviation of less
than 4 % for dierent realizations and resonance dispersion between resonators
was below 50 GHz. All these gures represent the state-of-the-art in SOI photon-
ics technology. Considerable eort has also been devoted to the development of
ecient thermal electrodes (52 W=GHz) to obtain a recongurable behaviour of
the structure and polymer inverse tapers to improve the o-chip coupling (inser-
tion losses < 2 dB). Phase-preserving and error-free transmission up to 100 Gbit=s
with continuously tunable optical delay up to 200 ps has been demonstrated on the
nal integrated systems, proving the compatibility of these devices with advanced
modulation formats and high bit-rate transmission systems
Numerical modelling of optical micro-cavity ring resonators for WDM networks
Augmenting the level of integration for a lower cost and enhancing the performance of the
optical devices have turned out to be the focus of many research studies in the last few
decades. Many distinct approaches have been proposed in a significant number of researches
in order to meet these demands. Optical planar waveguides stand as one of vital employed
approach in many studies. Although, their low propagation loss, and low dispersion, they
suffers from high power losses at sharp bends. For this reason, large radius of curvature is
required in order to achieve high efficiency and compromise the high level of integration. For
the purpose of this research, in this thesis different ways to improve the performance of
optical microcavity ring resonators (MRRs) have been thoroughly investigated and new
configurations have been proposed.
The Multiresolution Time Domain (MRTD) technique was further developed and employed throughout this thesis as the main numerical modelling technique. The MRTD algorithm is
used as a computer code. This code is developed and enhanced using self built Compaq
Visual Fortran code. Creating the structure and Post-processing the obtained data is carried
out using self built MATLAB code. The truncating layers used to surround the computational
domain were Uniaxial Perfectly Matched Layers (UPML). The accuracy of this approach is
demonstrated via the excellent agreement between the results obtained in literature using
FDTD method and the results of MRTD.
This thesis has focused on showing numerical efficiency of MRTD where the mesh size
allowed or the total number of computed points is about half that used with FDTD.
Furthermore, the MRR geometry parameters such as coupling gap size, microring radius of curvature, and waveguide width have been thoroughly studied in order to predict and
optimise the device performance.
This thesis also presents the model analysis results of a parallel-cascaded double-microcavity
ring resonator (PDMRR). The analysis is mainly focus on the extraction of the resonant
modes where the effect of different parameters of the structure on transmitted and coupled
power is investigated.
Also, accurate analysis of 2D coupled microcavity ring resonator based on slotted
waveguides (SMRR) has been thoroughly carried out for the purpose of designing optical
waveguide delay lines based on slotted ring resonator (SCROW).
The SCROW presented in this thesis are newly designed to function according to the
variation of the resonance coupling efficiency of a slotted ring resonators embedded between two parallel waveguides.
The slot of the structures is filled with SiO2 and Air that cause the coupling efficiency to vary
which in turn control both the group velocity and delay time of SCROW structures results
from the changing the properties of the bent slotted waveguide modes which strongly
depends on the slot’s position.
Significant improvements on the quality factor and greater delay time have been achieved by
introducing sub-wavelength-low-index slot into conventional waveguide
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