Photonics for Dynamic and Ultrawideband Microwave Systems

Microwave Photonics

Description

Bringing together the worlds of radiofrequency and optics engineering, the interdisciplinary field of Microwave Photonics (MWP) pursues the generation, processing, and distribution of microwave and millimeter-wave signals by photonic means. Our research focuses on dynamic and flexible processing of RF signals.

Latest Microwave Photonics Projects

Microwave Photonic Spectral Shaper

We take advantages of photonics and demonstrate a highly-reconfigurable RF spectral shaper that can manipulate an RF spectrum of tens of GHz wide. The proposed scheme is based on a microwave photonic filter architecture with multiple tunable, reconfigurable and switchable passbands. By manipulating the shape, bandwidth, and frequency of the passbands, highly reconfigurable wideband frequency responses for spectral equalization are experimentally achieved, covering the entire 0 to 10 GHz frequency range with adjustable attenuation up to 40 dB. Various RF equalization functions including tunable positive/negative slope, non/inverted parabolic, and multi-point spectral control with tunable floor are experimentally demonstrated using the proposed system. Several of the demonstrated RF functions have also been applied to arbitrary pulse shaping. The RF spectral shaper can be tuned to adapt to different scenarios dynamically.

Microwave Photonic Spectral Shaper

We take advantages of photonics and demonstrate a highly-reconfigurable RF spectral shaper that can manipulate an RF spectrum of tens of GHz wide. The proposed scheme is based on a microwave photonic filter architecture with multiple tunable, reconfigurable and switchable passbands. By manipulating the shape, bandwidth, and frequency of the passbands, highly reconfigurable wideband frequency responses for spectral equalization are experimentally achieved, covering the entire 0 to 10 GHz frequency range with adjustable attenuation up to 40 dB. Various RF equalization functions including tunable positive/negative slope, non/inverted parabolic, and multi-point spectral control with tunable floor are experimentally demonstrated using the proposed system. Several of the demonstrated RF functions have also been applied to arbitrary pulse shaping. The RF spectral shaper can be tuned to adapt to different scenarios dynamically.

Tunable and Reconfigurable Multiband MWP Filter

A photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach–Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.

Self-Interference Cancellation

A wideband co-site co-channel interference cancellation system (ICS), based on hybrid electrical and optical techniques, is proposed and is experimentally demonstrated. The demonstrated cancellation system subtracts the in-band wideband interfering signal from the received signal, such that the weak signal of interest (SOI) can be recovered. Our system utilizes a broadband radio frequency (RF) Balun transformer to invert the phase of the interfering signal, while electro-absorption modulated lasers are used for converting the RF signals into the optical domain to enable fine adjustment with the hybrid ICS. We experimentally achieve 45 dB of cancellation over a 220 MHz bandwidth, and over 57 dB of cancellation for a 10 MHz bandwidth, at a center frequency of 900 MHz. The proposed system also experimentally shows good cancellation (30 dB) over an enormously wide bandwidth of 5.5 GHz. To the best of our knowledge, this is the first demonstration of such a wide bandwidth cancellation with good cancellation depth. This property is extremely useful when there are multiple interference signals at various frequency bands. The approach also works well for various frequency bands that are within the bandwidth of the Balun transformer and electro-absorption modulated lasers.

Mimic Unique Neural Algorithm with Photonics

Neuromorphic Photonics

Description

Bringing together the worlds of neuroscience and photonics, the interdisciplinary field of Neuromorphic and Photonics offers orders of magnitude improvements in both speed and energy efficiency over digital electronics. In neuromorphic photonics, the analog representation of information eliminates the need of sampling and digitization as in its digital counterpart, therefore, avoids the associated speed reduction and signal distortion as in digital systems.

Latest Neuromorphic Photonics Projects

Jamming Avoidance Response

Biomimetic photonics extract the good design of nature and mimic it with photonics. The weakly electric fish genus, Eigenmannia, has a unique neural algorithm – jamming avoidance response, to facilitate their survival in the deep dark ocean, by automatically adjusts the local transmitter carrier frequency to move away from the jamming frequency when it is within the jamming spectral range. Examining our own wireless microwave systems, the situation of inadvertent jamming is very similar as that in Eigenmannia. In this article, a biomimetic photonic approach inspired by the jamming avoidance response in a weakly electric fish genus, Eigenmannia, is naturally adopted to experimentally tackle signal jamming in wireless systems. Mimicking the system with photonics enables the proposed scheme to work for frequencies from hundreds of MHz to tens of GHz.

Spike Timing Dependent Plasticity

Through implementing this type of pulse processing with photonics, ultrafast decision-making and adaptability can be recognized at rates nearly billions of times faster than the speeds of the biological counterpart. In recent years, several photonic-neuron circuits have been developed, including a complete neuron, a crayfish tail-flip escape response, and a supervised learning circuit [2,5]. Adaptive feedback systems utilizing optical STDP offer an experimental representation of the efficiency of learning in cognitive computing and information-theoretic algorithms. In this paper, we designed and experimentally demonstrated the photonic implementation of STDP characteristics through the use of nonlinear polarization rotation (NPR) and cross gain modulation (XGM) within a single semiconductor optical amplifier (SOA), improving upon photonic STDP circuits that require multiple electro-optic devices.

STDP Based Localization

A photonic system exemplifying the neurobiological learning algorithm, spike timing dependent plasticity (STDP), is experimentally demonstrated using the cooperative effects of cross gain modulation and nonlinear polarization rotation within an SOA. Furthermore, an STDP-based photonic approach towards the measurement of the angle of arrival (AOA) of a microwave signal is developed, and a three-dimensional AOA localization scheme is explored. Measurement accuracies on the order of tens of centimeters, rivaling that of complex positioning systems that utilize a large distribution of measuring units, are achieved for larger distances and with a simpler setup using just three STDP-based AOA units.

Cray-fish Tailflip Escape Response

We developed a hybrid analog/digital lightwave neuromorphic processing device that effectively performs signal feature recognition. The approach, which mimics the neurons in a crayfish responsible for the escape response mechanism, provides a fast and accurate reaction to its inputs. The analog processing portion of the device uses the integration characteristic of an electro-absorption modulator, while the digital processing portion employ optical thresholding in a highly Ge-doped nonlinear loop mirror. The device can be configured to respond to different sets of input patterns by simply varying the weights and delays of the inputs. We experimentally demonstrated the use of the proposed lightwave neuromorphic signal processing device for recognizing specific input patterns.

Fiber Optic Sensors for Soft Robotics and biomedical Applications

Fiber Optics Sensing

Description

Fiber optic sensors have shown unique advantages over electronic sensor, such as small size, flexibility, and immunity to electromagnetic interference, optical fiber shows a very limited deformability– making it not suitable as a stretchable sensor that fits to a flexible object with significant deformations.We focus our research on using fiber optic sensors on bendable and deformable applications, including medical catheter and soft robotics.

Latest Fiber Optics Sensing Projects

Stretchable Fiber Optic Sensors for Soft Robotics

Soft robotics is an emerging field since they offer distinct opportunities in areas where conventional rigid robots are not a feasible solution. However, due to the complex motions of soft robots and the stretchable nature of the soft building materials, conventional electronic and fiber optic sensors cannot be used in soft robots, hindering its ability to sense and respond to its surroundings. Fiber Bragg grating (FBG) based sensor is a very popular fiber optic sensor but its stiff nature makes it challenging to be used in soft robotics. In this letter, a soft robotic gripper with sinusoidally embedded stretchable FBG-based fiber optic sensor is demonstrated. Unlike a straight FBG embedding configuration, this unique sinusoidal configuration prevents sensor dislocation, supports stretchability, improves sensitivity, and facilitates the detection of various movements and events occurring at the soft robotic gripper, such as actuating/ deactuating, holding/wiggling an object.

Stretchable Multi-function Fiber Sensors

We proposed a soft stretchable multifunction sensor based on the use of a fiber Bragg grating (FBG), embedded as a sinusoidal structure in a silicone sheet at an off-center position. This unique sinusoidal structure and the flexibility of silicone sheet make the sensor highly stretchable, while embedding the FBG at an off-center position enables the sensing of bi-directional bending and torsion directions during twisting. Unlike most proposed sensors that can only detect a single type of deformations, the proposed stretchable sensor can achieve accurate measurement for tension, torsion direction, and bending. The unique stretching capability, flexibility, and compact structure of the demonstrated fiber optic sensor are highly desired in biomedical applications and soft robotics. The material is potentially compatible with human body and can be mounted onto a flexible object that has large movement or deformation during measurement.

3D Shape Sensor

A compact soft 3D shape sensor utilizing a dual-layer orthogonal FBG mesh is demonstrated. The sensor consists of 18 standard FBGs, which are embedded inside a thin and flexible silicone rubber. The 18 FBGs are aligned orthogonally in a dual-layer mesh structure with 9 FBGs in each direction. Embedding the FBGs in two layers enable the sensing of both convex and concave object surfaces. While the FBGs are embedded and protected by the soft silicone rubber, the FBGs can bend along the bending curvature of the measured object due to the flexible property of silicone material. Unlike most of the optical fiber based shape sensor that can only measure the curvature change along the fiber, the proposed approach can measure the complete 3D shape of an object surface. The measured results are plotted out with a 3D visual figure, which provides good intuition of the measurement and 3D shape of the object. The compact and soft silicon rubber is highly compatible with human body, making the proposed sensor a promising design for human body monitoring and soft robotic applications.

Fiber Optic Sensors for Steerable Catheter

Bi-directional catheters are commonly used in electrophysiology mapping and ablation procedures. We have designed and demonstrated a temperature-insensitive contact force sensor for bi-directional catheters with variable curve diameter during deflection. The compact force sensor is based on a fiber Bragg grating (FBG) pair, where both FBGs have the same center wavelength and are fixed at two opposite deflection arcs of the bi-directional catheter. When the catheter is deflected or when contact force is applied to the catheter, bifurcation of the FBG pair spectrum is observed. The amount of spectral bifurcation and the applied contact force has a linear relationship. Contact force measurement, therefore, is accomplished by measuring the change in the spectral bifurcation of the FBG pair, i.e., the change in the Bragg wavelength difference between the two FBGs. Since the approach relies solely on the amount of spectral bifurcation of the FBG pair instead of the Bragg wavelength shift of one single FBG, the proposed contact force sensor is temperature insensitive.