Research Areas

Lightwave Neuromorphic Signal Processing


Neuromorphic engineering provides a wide range of practical signal processing tools by exploiting the biophysics of neuronal computation algorithms. Implementing the function of a neuron using photonics allow the operation speed to be a billion time faster than its biological counterpart.

Microwave Photonics


The marriage of photonics and microwave solves fundamental challenges of wireless, and overcome computational and bandwidth limitations in wireless communications. Adopting the signal processing algorithms in neuromorphic processes, then implementing them using photonics and simplifying them with photonics building blocks solve the problem elegantly.

Fiber Optics Sensing


Fiber optics sensing has a wide range of applications including biomedical, civil, and ocean engineering. Due to the unique properties of fiber optics, is has been a great candidate for sensing in EM sensitive (MRI) and harsh environments.

Photonic Signal Processing


Instantaneous response of fiber optics provides real-time, EM immune, and low latency means to process optical, RF signals, and biomedical signals for communications, security/defense, and sensing applications.

Project Details

Lightwave Neuromorphic Signal Processing

The Photonic Neuron

Using photonics components to mimic neuro-biological architectures present in the nervous system and perform complex processing of broadband data using bio-inspired circuits. To meet the requirements of real-time signal processing, lightwave neuromorphic signal processing is utilized to provide the high-speed and low-latency performance that is characteristic of photonic technology. Lightwave neuromorphic signal processing incorporates hybrid analog and digital processing techniques that take advantage of both the bandwidth-efficiency of analog processing and the low noise characteristics of digital processing. We have successfully mimic a biologic LIF neuron with photonics devices, which have the same behaviors as the biological counterparts.


A Leaky-integrate-and-fire neuron


Experimental Setup of a bench-top photonic neuron


The Cray Fish

Crayfish escape from danger by means of a rapid escape response behavior. The corresponding neural circuit is configured to respond to appropriately sudden stimuli. Since this corresponds to a life-or-death decision for the crayfish, it must be executed quickly and accurately. A potential application of the escape response circuit based on lightwave neuromorphic signal processing could be for pilot ejection from military aircraft. Our device, which mimics the crayfish circuit using photonic technology, is sufficiently fast to be applied to defense applications in which critical decisions need to be made quickly while minimizing the probability of false alarm. With just two neuron, we demonstrate the escape response and apply it for pattern recognition.


Source: http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/



Schematic illustration of the crayfish


Spike Timing Dependent Plasticity

Neurons have the ability to learn and adapt their processing based on experience, through a change in the strength of synaptic connections in response to spiking activity. This mechanism is called “Spike Timing Dependent Plasticity” or “STDP.” Functionally, STDP constitutes a mechanism in which strengths of connections between neurons are based on the timing and order between pre-synaptic spike and post-synaptic spikes, essentially forming a pulse lead/lag timing detector that is useful in feedback control and adaptation. Here we report for the first time the demonstration of optical STDP that is useful in pulse lead/lag timing detection, and apply it to automatic-gain control of a photonic pulse processor.


Measured Biological spike timing dependent plasticity



Illustration of STDP and the reassembled Spike timing dependent plasticity using photonics


Microwave Photonics

Spectral Mining

In many current RF applications, such as dynamic spectrum access or electronic warfare, rapidly obtaining the spectral information associated with an environment, or with a short-lived communication signal, is extremely important as it would allow for the rapid detection of opportunities for communication using vacant spectrum, or for detecting ephemeral enemy communications. Unfortunately, the underlying signals of interest are often not known in advance. Further, when the bandwidth of interest is broad (hundreds of MHz), performing digital signal processing becomes impossible due to the sheer volume of data generated from the A/D conversion. The major obstacle here is the bandwidth of electronics and speed limitation of A/D convertors. Optical systems are generally not limited in terms of the signal bandwidth that they can process or the speeds at which underlying computational problems can be performed. For example, a typical optical carrier for communication is at 193 THz, while an optical fiber generally has a flat frequency response over a bandwidth of 3 THz. Signal processing in optical communication systems has been done all-optically at 640 G-bit/second. Translate problems from the RF domain into the optical domain. A problem involving scanning of hundreds of MHz in the RF domain can be dealt with more efficiently in the optical domain.


United States Frequency Allocations - The Radio Spectrum


Co-site Interference Cancellation and Uncoordinate Spectral Access

The broadcast nature of the wireless medium has facilitated a wide array of communication applications, including pervasive systems and remote sensing for cyberphysical systems. Although the broadcast nature of the wireless medium facilitates the vision of ubiquitous access to networks, the nature of the medium also makes such systems particularly susceptible to radio interference or jamming. Although the advantages of sharing the spectrum among different devices are obvious, mitigating interference in a wireless environment that consists of various types of devices and systems is difficult. Licensing personal devices would help cut down on interference; however, it would also dramatically reduce flexibility and scalability.

We aim to mitigate co-site interference using photonics while avoiding complicated changes in existing communication protocols. Moreover, the implementation of optical processing in the physical layer would not rely on a computing bottleneck or protocol synchronization, and would respond effectively in real time in finding the spectral hole.


Interference cancellation system with 30-dB cancellation over 5.5GHz bandwidth
and 45-dB cancellation over 200 bandwidth.


Widely Tunable Microwave Photonics Filter

RF filter has been a very useful devices in the field of microwave for removing out of band signal (single passband filter), or removing band limited signal (notch filter). In a dynamic communication system where the frequency and the bandwidth of the signal change dramatically, there is a critical need to design a tunable microwave filter to enable fast reconfiguration. Unfortunately, microwave filters are limited in tunability due to the fact that they are basically capacitor and inductor circuits.

We focus on using microwave photonics techniques to demonstrate a widely tunable microwave photonic filter (MPF). This filter allows reconfiguration of filter bandwidth and filter frequency; in addition, it can be tuned to have single or multiple filter bands. Notch filter can also be achieved with photonics techniques. Moreover, due to the low loss, broadband, and fast-tuning nature of photonics, the proposed effort can achieve a MPF with fast tuning speed, loss attenuation at the passband, and wideband operation.

Fiber Optics Sensing

We have invented a novel spiral structure for FBG sensor that has very high sensitivity and simple measuring system. Contact force measurement is achieved through direct measurement of the FBG reflection power at a single wavelength using a power meter. The measuring system in our approach is simple and does not require processing of massive amount of spectral data, enabling real-time contact force monitoring. An average sensitivity of 11.16 dB/N is experimentally achieved. This design significantly reduces system complexity and improves data processing speed. We have tested the sensor as an electromagnetic immune magnetic resonance imaging (MRI)-conditional contact force catheter sensor in electrophysiological (EP) therapy.


(a) Experimental setup for the wavelength determination of FBG; (b) Implementation of FBG on the catheter; (c) The catheter deflected until causing perforation on atrium wall of ex-vivo pig heart.

Currently, we are looking into serval sensing system:
(i) Multi-sensor system for MRI application
(ii) High resolution fiber sensor for Ocean Engineering
(iii) Fiber optics sensor for Agricultural Engineering

Photonic Signal Processing

Interferometric Noise Reduction

Interferometric noise reduction Interferometric noise resulting from beating between two optical signals at nominally the same wavelength is an undesirable phenomenon that severely affects the performance of systems in which optical interference may be either an intended or unintended consequence. Interferometric noise can strongly degrade the performance of optical networks and limit the scalability of microwave photonic filters. Mediating interferometric noise by assigning different wavelengths to interfering signals can substantially increase the complexity of optical processing. Unlike typical additive, independent Gaussian noise, the impact of interferometric noise on system performance is especially severe because the resultant noise amplitude exhibits square-law behavior. To avoid beat noise before signals are combined together, a single-mode to multimode (SM–MM) combiner is used such that the entire signal is launched to the output. By employing distinct spatial launching positions, the input signals are coupled into the multimode fiber in different modes with minimal or no coherent interaction.


Left: Using fused SM-SM coupler - sever beating. Right: Using SM-MM coupling - No beating.


Nonlinear Optical Signal Processing

We studies nonlinear processing of optical signals using semiconductor devices and speciality fiber, e.g.highly nonlinear bismuth oxide fiber (Bi-NLF). Our findings are based on self-phase modulation, cross-phase modulation, and four-wave mixing in the Bi-NLF. Applications of the nonlinear techniques in physical layer security, optical signal regeneration, tunable optical delay, stabilization of multiwavelength laser source, tunable optical pulse generation, microwave photonic carrier frequency multiplication, wavelength aware receiver, and all-optical wavelength conversion are demonstrated.


Autocorrelation peak extraction (Wavelength aware receiver) for optical CDMA signal using four wave mixing. Eye diagrams of the decoded optical CDMA signal detected using 30 GHz photodetector (a) in asynchronized system with PM/PA=0 dB, (b) in asynchronized system with PM/PA=0 dB after MAI removal, (c) in synchronized system with PM/PA=4 dB, and (d) in synchronized system with PM/PA=4 dB after MAI removal.


Eye diagrams of the optical CDMA signal detected using 1.25 Gbits/s receiver. (a) Without wavelength-aware receiver and PM/PA=0 dB, (b) without wavelength-aware receiver and PM/PA=−4 dB, (c) with wavelength-aware receiver for MAI removal and PM/PA =0 dB, (d) with wavelength-aware receiver for MAI removal and PM/PA=−4 dB. Inset, after the CDR system.