Data augmentation using a generative adversarial network for a high-precision instantaneous microwave frequency measurement system.

In this Letter, an unsupervised-learning platform-generative adversarial network (GAN)-is proposed for experimental data augmentation in a deep-learning assisted photonic-based instantaneous microwave frequency measurement (IFM) system. Only 75 sets of experimental data are required and the GAN can augment the small amount of data into 5000 sets of data for training the deep learning model. Furthermore, frequency measurement error of the estimated frequency has improved by an order of magnitude from 50 MHz to 5 MHz.

Bio-inspired photonics - marine hatchetfish camouflage strategies for RF steganography.

Camouflage is a strategy that animals utilize for concealment in their habitat, making themselves invisible to their predators and preys. In RF systems, steganography or stealth transmission is the camouflage of information - a technology of hiding and transmitting secret messages in public media. Steganography conceals the secret message in publicly available media such that the eavesdropper or attacker will not be able to tell if there is a secret message to look for.

Hybrid wideband multipath self-interference cancellation with an LMS pre-adaptive filter for in-band full-duplex OFDM signal transmission.

A wideband multipath self-interference cancellation (SIC) system employing both dual-drive Mach-Zehnder modulator-based analog SIC and least mean square (LMS) algorithm-based pre-adaptive filter digital SIC is proposed and demonstrated for the cancellation of multipath self-interference (SI) and facilitation of in-band full-duplex (IBFD) orthogonal frequency-division multiplexing (OFDM) signal transmission. The multipath effect is an unavoidable challenge in SIC due to the dynamic and unpredictable properties in each path, as well as the need for separate matching components for compensating for each path. In this Letter, an LMS algorithm-based adaptive filter is used as a pre-equalizer to adapt and generate the matching signal to the closest approximate of the multipath SI signal.

Twining plant inspired pneumatic soft robotic spiral gripper with a fiber optic twisting sensor.

The field of soft robotics has been significantly advanced with the recent developments of pneumatic techniques, soft materials, and high-precision motion control. While comprehensive motions can be achieved by sophisticated soft robots, multiple coordinated pneumatic controls are usually required to achieve even the simplest motions. Furthermore, most soft robotics are lacking the ability to sense the environment and provide feedback to the pneumatic control system.

Adaptive photonic RF spectral shaper.

The radio frequency spectral shaper is an essential component in emerging multi-service mobile communications, multiband satellite and radar systems, and future 5G/6G radio frequency systems for equalizing spectral unevenness, removing out-of-band noise and interference, and manipulating multi-band signal simultaneously. While it is easy to achieve simple spectral functions using either conventional microwave photonic filters or the optical spectrum to microwave spectra mapping techniques, it is challenging to enable complex spectral shaping functions over tens of GHz bandwidth as well as to achieve point-by-point shaping capability to fulfill the needs in dynamic wireless communications. In this paper, we proposed and demonstrated a novel spectral shaping system, which utilizes a two-section algorithm to automatically decompose the target RF response into a series of Gaussian functions and to reconstruct the desired RF response by microwave photonic techniques.

Movement Detection in Soft Robotic Gripper using Sinusoidally Embedded Fiber Optic Sensor.

Soft robotics is an emerging field, since it offers 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 soft building materials, conventional electronic and fiber optic sensors cannot be used in soft robots, thus, hindering the soft robots' ability to sense and respond to their surroundings. Fiber Bragg grating (FBG)-based sensors are very popular among various fiber optic sensors, but their stiff nature makes it challenging to be used in soft robotics.

Adaptive over-the-air RF self-interference cancellation using a signal-of-interest driven regular triangle algorithm.

An optically-enabled radio frquency (RF) self-interference cancellation system is demonstrated for over-the-air in-band full duplex transmission, based on a signal-of-interest (SOI) driven regular triangle algorithm. Since the goal of a self-interference cancellation system is to retrieve the SOI that is masked by the in-band interference signal, using the SOI quality as the driven parameter for optimizing the self-interference cancellation performance is a natural and effective way to allow the system to adapt to changes and obtain the best cancellation performance. Since regular triangle algorithm has short iteration time, bursts of pseudo-random binary sequence would be used between real data transmission for optimizing the self-interference cancellation performance.

Microwave photonic multiband filter with independently tunable passband spectral properties.

Multiband RF filters with independently controllable passbands are an essential component in dynamic multiband RF communications. Unfortunately, even a fixed multiband RF filter without the capability to adjust the passband properties individually is very difficult to achieve using either RF electronics or microwave photonic technologies. In microwave photonic approaches, the critical limitation is the close relationship between passbands-the tuning of one passband leads to a change in another, hindering the ability to independently control each passband.

Stretchable fiber-Bragg-grating-based sensor.

A fiber-Bragg-grating-(FBG)-based sensor is a very popular fiber optic sensor due to its simplicity, mature fabrication technology, and sensitivity to a number of physical stimuli. However, due to the stiff nature of optical fiber, it is impossible to heavily stretch a FBG sensor. A stretchable sensor is highly desired in soft robotics, human motion detection, and biomedical applications, which could involve motions like tension, bending, and twisting.

Biomimetic photonics: jamming avoidance system in Eigenmannia.

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.

Dual-layer orthogonal fiber Bragg grating mesh based soft sensor for 3-dimensional shape sensing.

A soft shape sensor for 3-dimensional object shape measurement is demonstrated. The proposed sensor is based on dual-layer fiber Bragg grating arrays with an orthogonal mesh structure, which enables multi-point bi-directional shape sensing. The 3D shape reconstruction is based on a bi-directional curvature measurement at each sensing point, which is achieved through measuring the direction and amount of wavelength shift of each off-center embedded FBG.

A Two-Phase Coverage-Enhancing Algorithm for Hybrid Wireless Sensor Networks.

Providing field coverage is a key task in many sensor network applications. In certain scenarios, the sensor field may have coverage holes due to random initial deployment of sensors; thus, the desired level of coverage cannot be achieved. A hybrid wireless sensor network is a cost-effective solution to this problem, which is achieved by repositioning a portion of the mobile sensors in the network to meet the network coverage requirement.

Gigabit Ethernet signal transmission using asynchronous optical code division multiple access.

We propose and experimentally demonstrate a novel architecture for interfacing and transmitting a Gigabit Ethernet (GbE) signal using asynchronous incoherent optical code division multiple access (OCDMA). This is the first such asynchronous incoherent OCDMA system carrying GbE data being demonstrated to be working among multi-users where each user is operating with an independent clock/data rate and is granted random access to the network. Three major components, the GbE interface, the OCDMA transmitter, and the OCDMA receiver are discussed in detail.

Ultra High-Speed Radio Frequency Switch Based on Photonics.

Microwave switches, or Radio Frequency (RF) switches have been intensively used in microwave systems for signal routing. Compared with the fast development of microwave and wireless systems, RF switches have been underdeveloped particularly in terms of switching speed and operating bandwidth. In this paper, we propose a photonics based RF switch that is capable of switching at tens of picoseconds speed, which is hundreds of times faster than any existing RF switch technologies.

Passband switchable microwave photonic multiband filter.

A reconfigurable microwave photonic (MWP) multiband filter with selectable and switchable passbands is proposed and experimentally demonstrated, with a maximum of 12 simultaneous passbands evenly distributed from 0 to 10 GHz. The scheme is based on the generation of tunable optical comb lines using a two-stage Lyot loop filter, such that various filter tap spacings and spectral combinations are obtained for the configuration of the MWP filter. Through polarization state adjustment inside the Lyot loop filter, an optical frequency comb with 12 different comb spacings is achieved, which corresponds to a MWP filter with 12 selectable passbands.

Bit rate transparent interferometric noise mitigation utilizing the nonlinear modulation curve of electro-absorption modulator.

we propose a bit-rate transparent interferometric noise mitigation scheme utilizing the nonlinear modulation curve of electro-absorption modulator (EAM). Both the zero-slope region and the linear modulation region of the nonlinear modulation curve are utilized to suppress interferometric noise and enlarge noise margin of degraded eye diagrams. Using amplitude suppression effect of the zero-slope region, interferometric noise at low frequency range is suppressed successfully.

Photonic implementation of a neuronal algorithm applicable towards angle of arrival detection and 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.

High-speed tunable microwave photonic notch filter based on phase modulator incorporated Lyot filter.

A high-speed tunable microwave photonic notch filter with ultrahigh rejection ratio is presented, which is achieved by semiconductor optical amplifier (SOA)-based single-sideband modulation and optical spectral filtering with a phase modulator-incorporated Lyot (PM-Lyot) filter. By varying the birefringence of the phase modulator through electro-optic effect, electrically tuning of the microwave photonic notch filter is experimentally achieved at tens of gigahertz speed. The use of SOA-polarizer based single-sideband modulation scheme provides good sideband suppression over a wide frequency range, resulting in an ultrahigh rejection ratio of the microwave photonic notch filter.

Wideband co-site interference cancellation based on hybrid electrical and optical techniques.

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.

Rayleigh backscattering noise suppression based on real-time heterodyne receiver for loop-back WDM-PON.

In this paper, we propose a Rayleigh backscattering (RB) noise mitigation scheme based on the use of real-time heterodyne receiver for loop-back wavelength division multiplexing passive optical network (WDM-PON). Heterodyne detection has been utilized to increase the upstream receiver sensitivity, while an electro-absorption modulator (EAM) is used to simultaneously turn heterodyning bipolar signal into single polar signal and mitigate accumulated carrier RB noise. With the help of the nonlinear negative-slope transfer function of EAM, low frequency interference noise is suppressed successfully.

High-speed wavelength tunable DPSK demodulation using a phase modulator based loop mirror filter.

A high-speed wavelength tunable differential phase-shift-keying (DPSK) signal demodulator is presented using a phase modulator (PM) based fiber loop mirror filter. By controlling the birefringence of the PM inside the loop through electro-optic effect, wavelength tuning speed of tens of GHz and tuning range of over two free spectral ranges are achieved. Stable filter spectra with extinction ratio over 30 dB are obtained through the tuning process.

Spiral-structured fiber Bragg grating for contact force sensing through direct power measurement.

A high-sensitivity fiber Bragg grating (FBG) force sensor based on direct optical power measurement is presented. The approach utilizes a novel structure where the FBG is mounted on a thin tube-like fixture spirally. Contact force measurement is achieved through direct measurement of the FBG reflection power at a single wavelength using a power meter.

Suppression of Rayleigh backscattering noise using cascaded-SOA and microwave photonic filter for 10 Gb/s loop-back WDM-PON.

In this paper, we present a novel Rayleigh backscattering (RB) noise mitigation scheme based on central carrier suppression for 10 Gb/s loop-back wavelength division multiplexing passive optical network (WDM-PON). Microwave modulated multi-subcarrier optical signal is used as downstream seeding light, while cascaded semiconductor optical amplifier (SOA) are used in the optical network unit (ONU) for suppressing the central carrier of the multi-subcarrier upstream signal. With central carrier suppression, interference generated by carrier RB noise at low frequency region is eliminated successfully.

Compact and low-latency instantaneous frequency measurement using 38 cm bismuth-oxide fiber and fiber Bragg gratings.

We demonstrated a compact and low-latency photonic approach for broadband RF signal frequency measurement. The photonic approach does not require high-speed electronics for gigahertz RF signal measurement. Frequency-to-intensity mapping is achieved based on a two-tap finite-impulse-response filter architecture, where the time delay between signals is provided by fiber Bragg grating array.

A single source microwave photonic filter using a novel single-mode fiber to multimode fiber coupling technique.

In this paper we present a fully tunable and reconfigurable single-laser multi-tap microwave photonic FIR filter that utilizes a special SM-to-MM combiner to sum the taps. The filter requires only a single laser source for all the taps and a passive component, a SM-to-MM combiner, for incoherent summing of signal. The SM-to-MM combiner does not produce optical interference during signal merging and is phase-insensitive.