We propose and demonstrate compact optical mode and polarization filtering devices on a lithium niobate on insulator (LNOI) platform. The subwavelength grating-based high-order mode pass filter and TM-pass polarizer are designed and experimentally demonstrated successfully. The measured insertion losses and extinction ratio at 1550 nm are lower than 1.9 dB and larger than 30 dB, respectively, while the device lengths are only about 50 μm.
We experimentally demonstrate bandwidth-tunable RF photonic Hilbert transformer based on an integrated Kerr microcomb source. The micro-comb is generated by an integrated micro-ring resonator with a free spectral range of 48.9 GHz, yielding 75 micro-comb lines in the telecom C-band. By programming and shaping the generated comb lines according to calculated tap weights, we demonstrate high-speed Hilbert transform functions with tunable bandwidths ranging from 1.2 GHz to 15.3 GHz, switchable center frequencies from baseband to 9.5 GHz, and arbitrary fractional orders. The experimental results show good agreement with theory and confirm the effectiveness of our approach.
We report ultrahigh bandwidth applications of Kerr microcombs to optical neural networks and to optical data transmission, at data rates from 44 Terabits/s (Tb/s) to approaching 100 Tb/s. Convolutional neural networks (CNNs) are a powerful category of artificial neural networks that can extract the hierarchical features of raw data to greatly reduce the network complexity and enhance the accuracy for machine learning tasks such as computer vision, speech recognition, playing board games and medical diagnosis [1-7]. Optical neural networks can dramatically accelerate the computing speed to overcome the inherent bandwidth bottleneck of electronics. We use a new and powerful class of micro-comb called soliton crystals that exhibit robust operation and stable generation as well as a high intrinsic efficiency with an extremely low spacing of 48.9 GHz. We demonstrate a universal optical vector convolutional accelerator operating at 11 Tera-OPS/s (TOPS) on 250,000 pixel images for 10 kernels simultaneously — enough for facial image recognition. We use the same hardware to sequentially form a deep optical CNN with ten output neurons, achieving successful recognition of full 10 digits with 900 pixel handwritten digit images. We also report world record high data transmission over standard optical fiber from a single optical source, at 44.2 Terabits/s over the C-band, with a spectral efficiency of 10.4 bits/s/Hz, with a coherent data modulation format of 64 QAM. We achieve error free transmission across 75 km of standard optical fiber in the lab and over a field trial with a metropolitan optical fiber network. Our work demonstrates the ability of optical soliton crystal micro-combs to exceed other approaches in performance for the most demanding practical optical communications applications.
We report a photonic RF arbitrary waveform generator and phase encoded signal generator using a soliton crystal micro-comb source with a free spectral range (FSR) of 48.9 GHz, that provides 80 wavelengths. We achieve arbitrary waveform shapes including square waveforms with a tunable duty ratio from 10% to 90%, sawtooth waveforms with a slope ratio of 0.2 to 1, and a symmetric concave quadratic chirp waveform with an instantaneous frequency of sub GHz. The phase encoded signal generator achieves a high pulse compression ratio of 30 and phase encoding rates from 2 to 6 Gb/s This work verifies the effectiveness of using microcombs for high-performance, broad bandwidth, nearly user-defined RF waveform generation.
We review recent work on broadband RF channelizers based on integrated optical frequency Kerr microcombs combined with passive micro-ring resonator filters, with microcombs having channel spacings of 200GHz and 49GHz. This approach to realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.
We report world record high data transmission over standard optical fiber from a single optical source. We achieve a line rate of 44.2 Terabits per second (Tb/s) employing only the C-band at 1550nm, resulting in a spectral efficiency of 10.4 bits/s/Hz. We use a new and powerful class of micro-comb called soliton crystals that exhibit robust operation and stable generation as well as a high intrinsic efficiency that, together with an extremely low spacing of 48.9 GHz enables a very high coherent data modulation format of 64 QAM. We achieve error free transmission across 75 km of standard optical fiber in the lab and over a field trial with a metropolitan optical fiber network. This work demonstrates the ability of optical micro-combs to exceed other approaches in performance for the most demanding practical optical communications applications.
Optical artificial neural networks (ONNs) have significant potential for ultra-high computing speed and energy efficiency. We report a novel approach to ONNs that uses integrated Kerr optical micro-combs. This approach is programmable and scalable and is capable of reaching ultra-high speeds. We demonstrate the basic building block ONNs — a single neuron perceptron — by mapping synapses onto 49 wavelengths to achieve an operating speed of 11.9 x 109 operations per second, or Giga-OPS, at 8 bits per operation, which equates to 95.2 gigabits/s (Gbps). We test the perceptron on handwritten-digit recognition and cancer-cell detection — achieving over 90% and 85% accuracy, respectively. By scaling the perceptron to a deep learning network using off-the-shelf telecom technology we can achieve high throughput operation for matrix multiplication for real-time massive data processing.
Photonic chip based Kerr frequency combs are transforming diverse applications including spectroscopy, telecommunication, signal processing and metrology among others. Integrated silicon nitride (SiN) waveguides with anomalous dispersion have the potential to bring practical nonlinear optics to mainstream photonic integrated circuits; however, high stress and high processing temperatures for SiN deposited by low pressure chemical vapour deposition (LPCVD) remain an obstacle to mass adoption. We successfully demonstrate fully CMOS-compatible high confinement SiN microring resonators based on reactive sputtering thin-films at a maximum processing temperature of 400°C. We deposit 0.85 μm thick SiN thin-films with a low stress value of 41.5 MPa and bulk material losses of 0.3 dB/cm. Linear waveguides losses of 0.7 dB/cm (Qint= 4.9 × 105) and 0.5 dB/cm (Qint= 6.6 × 105) have been achieved at 1560 nm and 1580 nm, respectively. We characterised the nonlinear properties of the waveguides and measured a nonlinear coefficient of Υ = 2.1 W-1 m-1 and a nonlinear refractive index n2 of 5.6 × 10-19 m2 W-1. Modulation-instability (MI) optical frequency combs are observed by pumping a 120 μm radius microring resonator at 1560 nm with an estimated on-chip pump power of 850 mW, showing a native FSR spaced frequency comb covering a >250 nm wide spectral range.
We propose and demonstrate a reconfigurable microwave signal processor for fractional and regular Hilbert transform with 17 GHz bandwidth based on an integrated Kerr optical frequency comb source. Transmission responses and temporal characterization are experimentally demonstrated.
We demonstrate broadband radio frequency (RF) channelization based on a CMOS-compatible integrated optical micro-comb source, which provides a large number of wavelength channels as well as an RF operation bandwidth of ~90 GHz. We experimentally verify the RF channelization performance from ~1.7 GHz to ~19 GHz with a high spectral slice resolution of ~1.04 GHz.
A microwave photonic true time delay line based on an integrated Kerr comb source with 49 GHz free spectral range was proposed and demonstrated. We theoretically analyze the performance of a phased array antenna and show that this large channel count results in a high angular resolution and wide beam-steering tunable range.
Coupling light between optical components with different waveguide geometries on photonic integrated circuits have become an imperative function for many applications. Herein, we propose an algorithm for the design of low-reflection adiabatic optical components using a constant coupling approach. Low reflectivity is important for optical components that are in close proximity to semiconductor optical amplifiers, where a reflectivity of less than -50 dB is required. We apply the algorithm to a polarization mode converter on the silicon-on-insulator platform, where we reduce the back reflection from -41 dB to -58 dB. We also show the tradeoff between the reduction in the reflected power and the resulting device length.
A broadband microwave mixer is demonstrated based on an integrated optical micro-comb source, with an operation bandwidth up to over 60 GHz, a conversion efficiency of −6.8 dB and a spurious suppression ratio of over 43.5 dB, and experimentally verify the RF performance up to 40 GHz. This approach to realizing microwave mixers offers reduced complexity, size, and potential cost for a wide range of applications to microwave systems.
We demonstrate an orthogonally polarized optical single sideband (OP-OSSB) generator based on dual cascaded micro-ring resonators (MRRs). We achieve a large tuning range of the optical carrier to sideband ratio of up to 57.3 dB. The operation RF frequency of the OP-OSSB generator can also be continuously tuned with a 21.4 GHz range via independent thermal control of the two MRRs.
We demonstrate a high-Q RF transversal filter based on a 49GHz-FSR integrated microcomb source that provides 80 taps across the C-band. By employing an on-chip micro-ring resonator, we generate a broadband Kerr comb with a large number of comb lines and use it as a high-quality multi-wavelength source. A Q factor of 73.7, an out-of-band rejection of 48.9 dB, and a wide tunable range are demonstrated. The experimental results verify the feasibility of our approach as a solution towards implementing highly reconfigurable MPFs with a large tap number and reduced system complexity.
In this contribution, we show how the stability and ease-of-use of an integrated interferometric photonic biosensor platform can be enhanced using optical frequency combs, without any necessary changes to the sensor chip design. We show that if the comb line spacing of the optical frequency comb is adjusted to be at 120° intervals of the periodic spectral response of the used Mach-Zehnder interferometer and the transmission power values of the three comb lines are recorded over time, it is possible to extract the interferometer phase linearly and continuously for every sample point. This measurement approach provides an accurate phase measurement and is independent of the interferometer bias. Furthermore, it is robust against intensity fluctuations which are common to all three used comb lines. Our demonstration uses a simple silicon photonic interferometric refractive index sensor, and we show that the benefits of our approach can be achieved without degrading the lower limit of detection of 3.70×10-7 RIU of our sensor platform. Our technique can be applied to any interferometric sensor and only requires a single input and single output and does not need any special couplers. This technique offers a drop-in replacement to the commonly used single wavelength phase measurement.
We demonstrate an 80-tap radio frequency (RF) transversal filter based on a 49GHz-spacing integrated micro-comb source. By employing a record 80 micro-comb lines, or taps, for the transversal filter, we achieve very high performance including a QRF factor more than four times higher than previous results. Our experimental results match well with theory, showing that our transversal filter is a competitive solution to implement advanced adaptive RF filters with high frequency selectivity and reconfigurability, and with potentially lower cost and footprint. This approach is promising for applications in modern radar and satellite communications systems.
Microwave photonic true time delay lines (TTDLs), which can introduce multiple progressive time delays, are one of the basic building blocks of microwave photonic systems. Offering intrinsically low loss, ultra-wide operation bandwidth, and strong immunity to electromagnetic interference, photonic TTDLs have wide applications for phased array antennas (PAAs), microwave photonic filters, analog-to digital or digital-to-analog conversion, and arbitrary waveform generation. Here, we demonstrate significantly improved performance of a microwave photonic TTDL based on optical micro-comb generated by an integrated microring resonator with a free spectral range (FSR) of ~49 GHz, which performs as a highquality multi-wavelength source for the TTDL. The broadband (>100 nm) optical micro-comb achieved with a record low FSR of 49 GHz results in an unprecedented record high channel number (81 over the C band) the highest number of channels for an integrated comb source used for microwave photonic processing. As compared with conventional TTDLs implemented by discrete laser arrays, the system cost, size, and complexity of our TTDL can be significantly reduced. We investigate the performance of a phased array antenna based on our TTDL and show that the large channel count leads to a high angular resolution and wide tuning range of the beam steering angle. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.
In this paper, we first employ CMOS-compatible integrated optical combs to demonstrate a broadband RF channelizer. By using an on-chip nonlinear micro-ring resonator, a broadband 200GHz-spacing Kerr comb with a large number of comb lines are generated, providing a record large number of wavelength channels (over 60 in the C- and L- band) as well as over 100GHz potential RF operation bandwidth for RF channelizers with greatly reduced size, potential cost, and complexity. Record-high spectral slice resolution of 124.94 MHz is achieved through an on-chip MRR featuring a high Q factor up to 1.549×106. As a result, broadband channelization of RF frequencies ranging from 1.7 GHz to 19 GHz is experimentally demonstrated, verifying our approach’s feasibility and effectiveness towards the realization of broadband RF channelizer with large channel number and high resolution, as well as reduced cost and footprint.
A reconfigurable microwave photonic filter (MPF) based on an integrated Kerr comb source was proposed and
demonstrated. By employing an on-chip micro-ring resonator (MRR), a broadband Kerr comb with a large number of
comb lines was generated and used as a high-quality multi-wavelength source for the MPF, which greatly reduced the size
and cost. The enhanced performance of the MPF was theoretically analysed and systematically characterized. Due to the
large channel number and high reconfigurability of the scheme, the MPF features an improved Q factor and wideband
tunability. The experimental results matches well with theory, verifying the feasibility of our approach as a solution towards
implementing highly reconfigurable MPFs with reduced system complexity.
An arbitrary-order intensity differentiator for high-order microwave signal differentiation is proposed and experimentally demonstrated on a versatile transversal microwave photonic signal processing platform based on integrated Kerr combs. With a CMOS-compatible nonlinear micro-ring resonator, high quality Kerr combs with broad bandwidth and large frequency spacings are generated, enabling a larger number of taps and an increased Nyquist zone. By programming and shaping individual comb lines’ power, calculated tap weights are realized, thus achieving a versatile microwave photonic signal processing platform. Arbitrary-order intensity differentiation is demonstrated on the platform. The RF responses are experimentally characterized, and systems demonstrations for Gaussian input signals are also performed.
Photonic integrated circuits that exploit nonlinear optics in order to generate and process signals all-optically have achieved performance far superior to that possible electronically - particularly with respect to speed. We review the recent achievements based in new CMOS-compatible platforms that are better suited than SOI for nonlinear optics, focusing on radio frequency (RF) and microwave based applications that exploit micro-resonator based frequency combs. We highlight their potential as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement. We review recent work on a photonic RF Hilbert transformer for broadband microwave in-phase and quadrature-phase generation based on an integrated frequency optical comb. The comb is generated using a nonlinear microring resonator based on a CMOS compatible, high-index contrast, doped-silica glass platform. The high quality and large frequency spacing of the comb enables filters with up to 20 taps, allowing us to demonstrate a quadrature filter with more than a 5-octave (3 dB) bandwidth and an almost uniform phase response.
We present a new approach to planar photonic interconnects based on spatial adiabatic passage between thin ridge silicon waveguides. Our approach provides robust coupling between arbitrary pairs of well-separated waveguides across a single chip, potentially bypassing intermediate waveguides and structures. This new technique presents opportunities for waveguide routing and device topologies that cannot be achieved using traditional evanescent coupling, while remaining compatible with conventional CMOS fabrication techniques.
This paper demonstrates the structural optimization using Evolutionary Algorithms in a chalcogenide glass
waveguide. Four features are taken into consideration while optimizing the waveguide structure, they include:
single-mode, low dispersion, high nonlinearity and low loss. A set of waveguide structures which meet the
design criteria are shown in the paper. The best structure enhances the nonlinear coefficient to 26000 /W/km
at telecom wavelength. In this work, we demonstrate the methodology used to optimize waveguide as well as
the procedure of conducting the experiment.
We report on the design and simulation of a novel Silicon-On-Insulator waveguide structures which when excited with
TM guided light, emit TE polarized radiation with controlled radiation characteristics[1]. The structures utilize parallel
leaky waveguides of specific separations. The structures are simulated using a full-vector mode-matching approach
which allows visualisation of the evolution of the propagating and radiating fields over the length of the waveguide
structure. It is shown that radiation can be resonantly enhanced or suppressed in different directions depending on the
choice of the phase of the excitation of the waveguide components. Steps toward practical demonstration are identified.
This paper reports on the conceptual design and simulation of a new hybrid coupled plasmon/dielectric waveguide
device which may present opportunities for biosensing. The operation of the device is based on the phase matching
of wave propagation in the dielectric waveguide with that of the surface plasmons. Finite element method (FEM)
and eigenmode expansion (EME) methods have been utilised to analyse the characteristics of propagation of
these waves. A suitable periodic grating structure has been implemented to provide wavelength dependent phase
matching between the dielectric and plasmon modes. The selectivity of plasmon coupling makes it an ideal
technology to be utilised for sensing. Such a device may be fabricated as a low cost, highly sensitive, integratable
sensor allowing the detection of finite environmental changes including the presence of single layers of molecules.
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