Tunable Multiband Microwave Photonic Filters

Mable Fok, Jia Ge
2017 Photonics  
The increasing demand for multifunctional devices, the use of cognitive wireless technology to solve the frequency resource shortage problem, as well as the capabilities and operational flexibility necessary to meet ever-changing environment result in an urgent need of multiband wireless communications. Spectral filter is an essential part of any communication systems, and in the case of multiband wireless communications, tunable multiband RF filters are required for channel selection,
more » ... erference removal, and RF signal processing. Unfortunately, it is difficult for RF electronics to achieve both tunable and multiband spectral filtering. Recent advancements of microwave photonics have proven itself to be a promising candidate to solve various challenges in RF electronics including spectral filtering, however, the development of multiband microwave photonic filtering still faces lots of difficulties, due to the limited scalability and tunability of existing microwave photonic schemes. In this review paper, we first discuss the challenges that were facing by multiband microwave photonic filter, then we review recent techniques that have been developed to tackle the challenge and lead to promising developments of tunable microwave photonic multiband filters. The successful design and implementation of tunable microwave photonic multiband filter facilitate the vision of dynamic multiband wireless communications and radio frequency signal processing for commercial, defense, and civilian applications. Photonics 2017, 4, 45 2 of 20 and immunity to electromagnetic interference. Furthermore, due to the rapid development of radio-over-fiber systems, radar and beamsteering of phased-arrayed antennas, microwave photonic filter naturally fits in nicely which enables the processing of RF signal without the need of high-performance analog-to-digital converters for down conversion. Single passband microwave photonic filters can be implemented using various techniques, including chip-based stimulated Brillouin scattering [10, 11] , optical comb based filter [12] [13] [14] , and programmable photonic signal processor chip [10, 11, 15, 16] . Some of the approaches are integratable [17, 18] and some are bench-top demonstrations. While development of microwave photonic filter has been a great success, and most of the schemes have been intensively summarized in a number of review papers [5, 19, 20] , there are still room for investigations including integration, tuning speed, noise, and power consumption. Although microwave photonic techniques for implementing single passband filter are well developed, there are very few successful examples where a multiband microwave photonic filter can be achieved. Most existing microwave photonic filter approaches either lack of the ability to support multiband operations, or the resultant passbands are periodic over a very wide frequency range, limiting its ability to isolate unwanted frequencies within a certain frequency range. By examining the principle of obtaining multiple passbands, the facts that hinder microwave photonic technologies to support multiband filtering capability are the special requirements in the optical source: (i) the optical comb carrier needs to simultaneously consist of multiple interleaving combs with different comb spacings [21] , or (ii) the optical comb carrier has to be sampled spectrally [22] , or (iii) large number of optical branches (light source or delay elements) are needed [23] . Optical combs are highly periodic in nature, thus, the above optical comb requirements are extremely hard to achieve-which is limited by the scalability, selectivity, and uniformity of most existing microwave photonic filter schemes. Due to these limitations, it is hard to achieve a microwave photonic multiband filter with a large passband number, high selectivity, and good passband uniformity. Needless to say, it is even more challenging to achieve a multiband filter with tuning and reconfiguring capabilities. Table 1 shows a list of multiband RF filter examples with two or more passbands based on various RF electronic and microwave photonic techniques.
doi:10.3390/photonics4040045 fatcat:nihctid6ujdbvooamcnhrsa4qa