Microwave photonics has been extensively used for 5G mobile communications, radio-over-fiber communication, beamforming, satellite communication, military communication system, RADAR, and others. In this topic, we are mainly focused on secure, robust, and high-resolution RADAR and imaging systems which are obtained through the following approaches:

(i) Generation of robust microwave waveforms with the capability of reconfigurability

(ii) Object detection and imaging techniques for a better resolution and

(iii) Developing interference Agile system for a multi-radar environment

(iv) Implementing AI techniques for improving the detection with the highest probability and highest image resolution  

                                                                      Table I: Comparison of Different Sensing Technologies showing the Benefits of RADAR                         Table II: Comparison of Different waveform-based Photonics RADAR

RF signal and waveform generation are essential in microwave photonics systems, such as 5G, military communication with higher security, jamming-free communication, and a RADAR system. We used a specially designed single mode Fabry-Perot laser diode (SMFP-LD) and Distributed Feedback Laser (DFB) with external beam injection for generating multiple RF signals (from several GHz to tens of THz), switching, hoping, random wave generation (Sawtooth, linear frequency modulated signal) in high frequency with high bandwidth and different chirp. These signals help detect multiple moving objects. Rather than MIMO, we develop reconfigurable multi-chirp signals in a single system and implement them in radar imaging. The preliminary result of generating multi-chirp and detecting objects has been successfully demonstrated. Further, we are also working on implementing AI for increasing the resolution of imaging through our developed reconfigurable multi-chirp different IEEE band RADAR system.

Fig.1. Scenario of Multi-RADAR environments and problems associated with it

With the increase in the applications and users of Radar technology, security, the robustness of the detection under different target environments, and resolution become prime challenges in all applications such as defense, autonomous vehicles, weather monitoring, and consumer markets. Photonics-based RADAR has become one of the suitable solutions due to its inherent advantages of broad bandwidth, high signal-to-noise ratio, wavelength division multiplexing, and an all-weather system. However, with an increasing number of applications of RADAR systems, interference, spoofing, and jamming becomes critical issues as they affect the overall performance of the RADAR by decreasing the signal-to-noise ratio and increasing false detection, and reducing the resolution of the image. Consequently, it creates security threats, range ambiguity, and low-resolution imaging, which cannot be solved with the widely used linear frequency modulated (LFM) RADAR. Only a few research works have been done on addressing the interference in RADAR, which includes intraband, interband, and transient in mutual interferences. Besides the mutual interferences, safety and security problems by jamming and spoofing (intruders) are critical in communication, defense, and automobile applications.

Presently, most photonics-based RADAR research focuses on operating in isolated environments and fails to identify and analyze the issues that may occur while working in multi-radar scenarios where multiple RADARs are employed in the same frequency band. Hence, in this proposal, we focus on analyzing the interferences and intrusions in the multi-RADAR environment and investigate their effects on the secure operation of RADAR detection and imaging system. The analysis is followed by proposing a technique to mitigate the interference and intrusion, providing a robust RADAR system to operate in the multi-RADAR environment with high detection and ranging accuracy. Furthermore, band-fusion, filtering, and imaging techniques are implemented to obtain high-range and high-resolution imaging. Our goal of realizing a secure, robust, and high-resolution imaging photonics-based RADAR for a multi-RADAR environment in the presence of interference and intrusion is achieved through the following steps:

(1) identifying and analyzing the disturbances that are interband, intraband, transient, and spoofing by interferers and intruders, and their effects on LFM-based RADAR detection and imaging capability

(2) developing complementary chirp dual-band randomly hopped LFM-based RADAR to mitigate the interference and spoofing and

(3) integrating band fusion, filtering, and model-aware back projection imaging techniques to obtain a high probability of detection with high range resolution and high-resolution imaging.

The photonics-based complementary chirp dual-band randomly hopped LFM RADAR will be tested and verified in the presence of multiple interference and intrusions. The concept of this work will be extended to numerous applications in the future with international collaboration and academic exchange.   

Fig.2. Approach to address the Secure, Robustness and Resolution Challenges

Also, silicon photonics has been in consideration for the fabrication of the proposed scheme. 

Fig.1 Proposition of Optical ALU and research development map

This research topic focused on developing different optical components and sub-systems required for optical communication and Digital Photonics. We demonstrated all-optical logic gates, switches, wavelength converters, latches, and other digital blocks using SMFP-LDs with a data rate of 10 Gbps per channel. Our proposed techniques’ main advantage is a simple configuration, high speed, low cost, and effective power system.

Fig.2 Processor and memory gap and technology trends of their development

 In this project, we are currently working on reducing the performance gap between the processor speed and the memory accessing speed. We addressed the issue by introducing the wavelength division multiplexing in memory accessing, which integrates address decoding and read-write memory technique. This research’s primary goal is to reduce the processor-memory performance gap by increasing the bandwidth and reducing the access time from memory to processor. Using this technique, we hope the gap will be reduced at least by 25%. This research’s main objective is to develop a photonics chip that provides faster computation and memory access. Following main three tasks will be carried out in this project:

●       Experimental demonstration of read function at 10Gb/s using SMFP-LD

●       Experimental demonstration of read/write operation at 40Gb/s using SMFP-LD

●       Chip-level photonic integrated circuit design, integration and fabrication

Fig.3 Block diagram for memory accessing techniques

Silicon photonics has been developed as one of the most promising techniques for integrated photonics due to its unique advantages of high integration density, low loss and compatibility with the CMOS process, and cost and power effectiveness. Waveguides and Ring resonators are the main elements for integrated silicon photonics. This research topic mainly focuses on designing ring resonators for add-drop filters, logic and combination circuits, and memory units. Basic logic gates, and flip-flops have been demonstrated. With the development of various components, we focus on implementing in microwave photonics and reconfigurable computing units. Programmable photonics is emerging as a new paradigm that aims to design a common integrated optical hardware configuration. Hence, we also focused on realizing the programmable optical filter with a wideband, flat top, which can be used for CWDM. The switching function and the narrow bandwidth filters are also under development for microwave photonics and sensing units. The programmable integrated photonics gives the flexibility to get multiple functions by suitable programming. Hence, we target developing a high-speed optical computing unit with basic logic and arithmetic functions in silicon photonics. 

Fig.1 Ultra-compact wideband double modulated filter