High Performance Programmable Integrated Microwave Photonic Filters
Okky Daulay is a PhD student in the department Laser Physics & Nonlinear Optics. Supervisor is prof.dr.ir. D.A.I. Marpaung from the faculty of Science & Technology.
The increased demand for next-generation advanced communication systems requires a new paradigm of radio frequency (RF) front end designs that can push the field towards multiple bands, higher frequencies, and broader bandwidths. Although standard electronic devices can handle these challenges, demands cannot be fully met because of limited losses, tunability, and speed. These limitations can be solved by introducing photonic elements into the system. Microwave photonics (MWP) is an interdisciplinary research field that develops technologies to generate, process, and distribute RF/microwave signals using optical components. The advantages of having MWP in the system include higher speed, lower loss, wider bandwidths, and immunity from electromagnetic interference (EMI). Integrated MWP circuits offer these benefits with a reduced footprint and with better area and power consumption. To be usable in real RF applications, these circuits need to show advanced reconfigurability and high RF performance in terms of loss, noise figure, and dynamic range.
In the past decades, a number of integrated MWP functions, such as filter, phase shifter, delay line, and beamforming, have been developed. These functions were achieved using application-specific photonic integrated circuits (ASPICs). However, these circuits lack flexibility because of their design approach. New approaches to building a programmable integrated photonic (PIP) circuit using mesh network have been reported. PIP circuits can synthesize many functionalities through programming of custom-made software. Although these circuits are versatile, they have a significantly lower functional performance than that of ASPICs. This thesis addresses the limitations of ASPIC and PIP circuits to fully exploit and develop a programmable integrated MWP circuit that has a high integration density, versatile reconfigurability, and high RF performance.
In this thesis, the integrated MWP system is introduced, and the key components of the system are then discussed. These components include the modulation spectrum, signal processing elements, and photodetection. Three modulation spectrums (phase modulation, intensity modulation, and complex modulation) are introduced. Then, the all-pass and add-drop ring resonator is discussed. After this, the RF performance (link gain, noise figure, and dynamic range) is presented together with examples to better understand how these metrics influence the system performance. Two techniques for enhancing RF performance (optical carrier suppression and low-biasing Mach Zehnder modulator) are also introduced.
Two programmable MWP filtering functions in phase modulation-based systems are reported. These filters were synthesized using cascaded all-pass ring resonators. This involved three key operation procedures: modulation transformation, filter functionalities, and improved RF performance through optical carrier suppression. Though the circuit was programmable, the design was based on the ASPIC design, which limited the versatility.
A novel programmable photonic circuit built from a versatile modulation transformer (MT) and equally versatile double-injection ring resonator (DIRR) was introduced to overcome the versatility limitation. The MT can independently tailor the phase and amplitude of any input optical modulation spectrum and can convert the spectrum into different output optical modulations. The DIRR can synthesize six different responses from a single output, which made it an interesting option for the optical signal processing element in the circuit. Four different proof-of-concept scenarios are presented using the new circuit in an intensity modulation-based system. The circuit with combined MT and DIRR synthesized MWP bandstop-bandpass reconfigurable filters with high RF performance. The MWP bandstop/notch filter had 58 dB rejection with 10 dB of RF gain and 15 dB of NF. With proper tuning, the filter could be reconfigured into an MWP bandpass filter with 20 dB of rejection, 1.2 dB of RF gain, and 21.8 dB of noise figure. These results showed that the new circuit has versatile filtering functions and high RF performance. However, despite these achievements, the filter bandwidths of the new circuit were still in the order of hundreds of MHz, which is not sufficient for some RF applications.
To overcome this challenge and create an MWP filter with a narrow bandwidth, a nonlinear optical effect—stimulated Brillouin scattering (SBS)—was introduced to the system. SBS is a third-order nonlinear property in the optic that was created from the interaction of optic and acoustic waves in a waveguide. In the next circuit design, a spiral waveguide capable of induced SBS was added to the system. Together with MT and DIRR, this new circuit aimed to create a programmable MWP Brillouin filter with a reconfigurable narrow bandwidth and high RF performance.
