[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Photonic signal processing offers the advantages of large time-bandwidth capabilities to overcome inherent electronic limitations. In-fibre signal processors are inherently compatible with fibre optic microwave systems that can integrate with wireless antennas, and can provide connectivity with in-built signal conditioning and electromagnetic interference immunity. Recent methods in wideband and adaptive signal processing, which address the challenge of realising programmable microwave photonic phase shifters and true-time delay elements for phased array beamforming; ultra-wideband Hilbert transformers; single passband, widely tunable, and switchable microwave photonic filters; and ultra-wideband microwave photonic mixers, are described. In addition, a new microwave photonic mixer structure is presented, which is based on using the inherent frequency selectivity of the stimulated Brillouin scattering loss spectrum to suppress the carrier of a dual-phase modulated optical signal. Results for the new microwave photonic mixer demonstrate an extremely wide bandwidth operation of 0.2 to 20 GHz and a large conversion efficiency improvement compared to the conventional microwave photonic mixer.

Microwave photonic signal processing.

As the only method for all-weather, all-time and long-distance target detection and recognition, radar has been intensively studied since it was invented, and is considered as an essential sensor for future intelligent society. In the past few decades, great efforts were devoted to improving radar's functionality, precision, and response time, of which the key is to generate, control and process a wideband signal with high speed. Thanks to the broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, ultrafast analog signal processing and electromagnetic interference immunity provided by modern photonics, implementation of the radar in the optical domain can achieve better performance in terms of resolution, coverage, and speed which would be difficult (if not impossible) to implement using traditional, even state-of-the-art electronics. In this tutorial, we overview the distinct features of microwave photonics and some key microwave photonic technologies that are currently known to be attractive for radars. System architectures and their performance that may interest the radar society are emphasized. Emerging technologies in this area and possible future research directions are discussed.

/pdf/microwave-photonic-radars-1mv4ppmi12.pdf

Microwave Photonic Radars

Microresonators with a high Kerr nonlinearity show great potential to generate optical frequency combs with ultrabroad spectra, high repetition rate, and high coherence between comb lines. The compact size and possibility of chip-level integration make the Kerr combs attractive for many applications, especially including photonic radiofrequency (RF) filters. In this paper we report the first demonstration of a programmable photonic RF filter based on the Kerr comb from a silicon nitride microring. A novel scheme enabled by the large frequency spacing of the Kerr comb is introduced in order to suppress unwanted RF passbands including the image and periodic passbands. As a result, a single passband is achieved. To the best of our knowledge, this is the first demonstration of a single-bandpass photonic RF filter employing a discrete-wavelength comb source.

/pdf/programmable-single-bandpass-photonic-rf-filter-based-on-svm7l7yzzj.pdf

Programmable Single-Bandpass Photonic RF Filter Based on Kerr Comb from a Microring

Microwave photonic techniques are attractive for processing high bandwidth signals, overcoming inherent electronic limitations. These processors provide new capabilities for realizing adaptive processing over extremely wide microwave frequency ranges, ultra-wideband operation, and electromagnetic interference immunity. In-fiber signal processors are inherently compatible with fiber-wireless systems, and can provide connectivity with in-built signal conditioning. Recent new methods in wideband microwave photonic processing are presented, including ultra-wideband phase shifters and true time delays for phased array beamforming, widely tunable single passband filters, switchable microwave photonic filters, wideband photonic mixers, high-resolution multiple frequency microwave photonic measurement systems, and photonic RF memory structures.

Ultra-Wideband and Adaptive Photonic Signal Processing of Microwave Signals

A new and simple structure for a single passband microwave photonic filter is presented. It is based on using an electro-optical phase modulator and a tunable optical filter and only requires a single wavelength source and a single photodetector. Experimental results are presented that demonstrate a single passband, flat-top radio-frequency filter response without free spectral range limitations, along with the capability of tuning the center frequency and filter bandwidth independently.

Single passband microwave photonic filter with wideband tunability and adjustable bandwidth

An integrated photonic sensor based on an optoelectronic oscillator with an on-chip sensing probe that is capable of realizing highly sensitive and high-resolution optical sensing is presented. The key component is an integrated silicon-on-insulator based microring resonator which is used to implement a microwave photonic bandpass filter (MPBF) to effectively suppress the side modes of the optoelectronic oscillator (OEO) by more than 30 dB, thus generating a peak RF signal that maps the detected optical change into a resulting shift in the oscillating frequency. As an application example, the proposed optical sensor system is employed to detect small changes in temperature, and experimental results demonstrate a highly sensitive optical temperature sensor with an achieved sensitivity of 7.7 GHz/°C. Moreover, the proposed sensing system revealed a 0.02 °C measurement resolution, which is a tenfold improvement to the modest resolution of 0.23 °C of the conventional MPBF system without the OEO loop, rendering it highly suitable for diverse high-resolution sensing applications.

Optoelectronic Oscillator Based Sensor Using an On-Chip Sensing Probe

A new technique to realize an array of multiple true-time-delay elements, which can be independently and continuously tuned, is reported. It is based on a WDM parallel signal processing approach in conjunction with a diffraction-based Fourier-domain optical signal processor. Programmable linear optical phase transfer functions are realized to obtain different electrical true-time delays. The technique can scale to a large number of wideband true-time-delay lines, with continuously tunable programmable delay. Results demonstrate multiple true-time-delay elements with independent tuning control and verify the concept by tuning the free spectral range of a microwave photonic notch filter. To our best knowledge, this is the first demonstration of multiple independently controllable true-time-delay lines for microwave photonic systems.

Programmable multiple true-time-delay elements based on a Fourier-domain optical processor

A new optical single-sideband (OSSB) modulation technique for wideband microwave photonic applications is presented. It is based on an integrated silicon-on-insulator dual-ring structure that exhibits weak electromagnetically induced transparency-like notch filter characteristics. Experimental results demonstrate optical sideband suppression of more than 29 dB for signals over 17–35 GHz with an achievable suppression as high as 40 dB. The OSSB structure is highly effective in suppressing dispersion penalties in microwave fiber transmission, with results showing a reduction in the electrical power ripple to less than ±1.5 dB for RF frequencies up to 30 GHz. The OSSB structure also enables new applications in optical vector network analyzers for optical component characterization, demonstrating the ability to measure both the amplitude and phase responses of a high-resolution ultranarrow filter based on stimulated Brillouin scattering, and also to perform wideband measurements over 10–30 GHz, offering an integrated approach for OSSB modulation that is compatible with silicon-based on-chip microwave photonic signal processing systems.

Silicon-on-Insulator Dual-Ring Notch Filter for Optical Sideband Suppression and Spectral Characterization

Owing to its attractive optical and electronic properties, silicon carbide is an emerging platform for integrated photonics. However an integral component of the platform is missing-an electro-optic modulator, a device which encodes electrical signals onto light. As a non-centrosymmetric crystal, silicon carbide exhibits the Pockels effect, yet a modulator has not been realized since the discovery of this effect more than three decades ago. Here we design, fabricate, and demonstrate a Pockels modulator in silicon carbide. Specifically, we realize a waveguide-integrated, small form-factor, gigahertz-bandwidth modulator that operates using complementary metal-oxide-semiconductor (CMOS)-level voltages on a thin film of silicon carbide on insulator. Our device is fabricated using a CMOS foundry compatible fabrication process and features no signal degradation, no presence of photorefractive effects, and stable operation at high optical intensities (913 kW/mm2), allowing for high optical signal-to-noise ratios for modern communications. Our work unites Pockels electro-optics with a CMOS foundry compatible platform in silicon carbide. 

https://www.nature.com/articles/s41467-022-29448-5.pdf

Liwei Li

Papers

Single passband microwave photonic filter with wideband tunability and adjustable bandwidth

Optoelectronic Oscillator Based Sensor Using an On-Chip Sensing Probe

Programmable multiple true-time-delay elements based on a Fourier-domain optical processor

Silicon-on-Insulator Dual-Ring Notch Filter for Optical Sideband Suppression and Spectral Characterization

Integrated silicon carbide electro-optic modulator