Recently, a research team led by Prof. Dr. ZHANG Wenfu from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) proposed a new integrated optical filter based on cascaded Mach-Zehnder interferometers (MZIs). The new-type scheme shows a great potential in more compact footprint than that of conventional design based on directional form. The result was published in IEEE PHOTONICS JOURNAL. ( DOI: 10.1109/JPHOT.2019.2940564)
Wavelength-Division-Multiplexed (WDM) system plays an important role in optical communications, and filter components are basic elements in WDM system, such as a MZI or cascaded MZIs, which select individual wavelength channels from signal stream. One MZI is realized by connecting directional couplers (DCs) with an optical delay line.
While the MZIs circuits are popular for wavelength-selective operation with relatively weak sensitivity to fabrication errors, the sensitivity of DCs to fabrication errors and footprint of the cascaded circuit are in sore need of further reduction for compact integrated optical interconnects.
In order to enlarge target applications of cascaded MZIs filter, and at least get rid of the limitation associated with device length in the direction of light propagation. They tended to ingeniously address phase delay by difference between inner radius and outer radius of parallel spiral waveguides. In this way, when the number of stages and phase delay augment, more circles can bring enough phase delay and allow many stages at a lower footprint cost.
Despite of slight increase of footprint on width, it is notable that the cost has an exchange for considerable reduction of device length. Therefore, the scheme provides a feasible solution when device length is seriously limited and a significant guidance for compact MZIs filter with many stages in optical communication.
Schematic of the proposed structure. (Image by XIOPM)
（Original research article " IEEE Photonics Journal (2019) https://doi.org/10.1109/JPHOT.2019.2940564 "）
