Microwave photonic multiband filter with independently tunable passband spectral properties

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. Marine hatchetfish have two effective camouflage skills to help them hide from their predators - silvering and counterillumination. Silvering in marine hatchetfish uses its microstructured skin on its sides to achieve destructive interference at colors that could indicate the presence of the fish, while they also emit light at their bottom part to match its color and intensity to its surrounding, making it invisible from below, referred to as counterillumination. In this work, we borrow the two underwater camouflage strategies from marine hatchetfish, mimic them with photonic phenomena, and apply the camouflage strategies for physical stealth transmission of a 200 MBaud/s 16QAM OFDM secret signal at 5 GHz over a 25-km of optical fiber. The proposed bio-inspired steganography strategies successfully hid the secret signal in plain sight in temporal, RF spectral, and optical spectral domains, by blending in using counterillumination and turning invisible using silvering techniques. The stealth signal can only be retrieved with the precise and correct parameter for constructive interference at the secret signal frequency to unmask the silvering.

Ultrafast and Wideband Microwave Photonic Frequency-Hopping Systems: A Review

The increasing demands to enhance information security in data transmission, providing countermeasures against jamming in military applications, as well as boosting data capacity in mobile and satellite communication, have led to a critical need for high-speed frequency-hopping systems. Conventional electronics-based frequency-hopping systems suffer from low data rate, low hopping speed, and narrow hopping-frequency bandwidth. Unfortunately, those are important aspects to facilitate frequency-hopping in emerging microwave systems. The recent advancement of microwave photonics—the use of light to process microwave signals—provides promising solutions to tackle the challenges faced by electronic frequency-hopping systems. In this paper, the challenges of achieving real-time frequency-hopping systems are examined. The operation principles and results of various microwave photonics-enabled frequency-hopping systems are comprehensively discussed, which have wide hopping-frequency bandwidth and frequency-hopping speed from nanoseconds to tens of picoseconds. Lastly, a bio-inspired jamming-avoidance system that could potentially be used for adaptive frequency-hopping is also introduced.

Discretely programmable microwave photonic filter based on temporal Talbot effects

We propose and experimentally demonstrate a reconfigurable microwave photonic filter based on temporal Talbot effects. The microwave signal is first uniformly sampled by a train of optical pulses through electro-optic intensity modulation. The sampled optical pulses are then directed to a Talbot-based optical signal processor, consisting of an electro-optic temporal phase modulator and a chromatic dispersion line. The Talbot-based microwave photonic filter (TMPF) exploits the inherent properties of the Talbot self-imaging effect for mitigating pulse-to-pulse intensity fluctuations of optical pulses to transmit some fluctuation frequencies and mitigate or entirely block other microwave spectral components. The output microwave signal is finally reconstructed from the processed optical pulses and the resultant RF response is measured by a network analyzer. The TMPF exhibits an RF response with periodic, symmetric-profile passbands whose center frequency and free spectral range (FSR) are defined by the sampling rate and the dispersion value. The filter passbands can be reconfigured electrically, in discrete steps, by adjusting the modulation function of the phase modulator, i.e., without the need for manual adjustment of the optical components. This enables the capability of selection of specific passbands among the primary passbands. The phase modulation function is provided using an arbitrary waveform generator, with the potential for fast tuning of the filter's spectral response. The bandwidth of the filter passband can also be easily customized by adjusting the sampling pulse's temporal width using an optical bandpass filter. Examples of filter performance in various passband configurations are also presented in the time domain to further validate the operation of the filter.