A novel tunable microwave optical notch filter

A widely tunable microwave photonic notch filter with adjustable bandwidth based on multi-wavelength fiber laser is proposed and demonstrated. The multi-wavelength fiber laser generates the multi-taps of the microwave photonic filter (MPF). In order to obtain notch frequency response, a Fourier-domain optical processor (FD-OP) is introduced to control the amplitude and phase of the optical carrier and phase modulation sidebands. By adjusting the polarization controller (PC), different numbers of taps are got, such as 6, 8, 10 and 12. And the wavelength spacing of the multi-wavelength laser is 0.4 nm. The bandwidth of the notch filter is changed by adjusting the number of taps and the corresponding bandwidths are 4.41 GHz, 3.30 GHz, 2.64 GHz and 2.19 GHz, respectively. With the additional phase shift introduced by FD-OP, the notch position is continuously tuned in the whole free spectral range (FSR) of 27.94 GHz. The center frequency of the notch filter can be continuously tuned from 13.97 GHz to 41.91 GHz.

A continuously tunable microwave photonic notch filter with complex coefficient based on phase modulation is proposed and demonstrated. The complex coefficient is generated using a Fourier-domain optical processor (FD-OP) to control the amplitude and phase of the optical carrier and radio-frequency (RF) phase modulation sidebands. By controlling the FD-OP, the frequency response of the filter can be tuned in the full free spectral range (FSR) without changing the shape and the FSR of the frequency response. The results show that the center frequency of the notch filter can be continuously tuned from 17.582 GHz to 29.311 GHz with FSR of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.

A continuously tunable microwave photonic notch filter at around 30 GHz is experimentally demonstrated and 100% fractional tuning over 360deg range is achieved without changing the shape of the spectral response. The tuning mechanism is based on the use of slow and fast light effects in semiconductor optical amplifiers assisted by optical filtering.

A coherent interference‐free tunable microwave photonic notch filter with a pair of negative and positive coefficients generated by employing polarisation multiplexing and cross gain modulation in a semiconductor optical amplifier is proposed and demonstrated through simulation results. The negative and positive coefficients of the notch filter are realised through two orthogonal polarisation states of a single continuous wave laser diode. The free spectral range of microwave photonic filter is tuned by varying the differential group delay of a birefringent single‐mode fibre. The proposed filter shows good tunability, easy implementation and is cost‐effective.

A widely tunable microwave photonic (MWP) notch filter with high linearity based on a dual-parallel Mach—Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. The motivation of this work lies in the fact that the MWP notch filter previously reported has nonlinear distortions generally induced by the nonlinear property of electro-optic devices. In this scheme, even-order modulated sidebands at the DPMZM output are effectively suppressed by properly adjusting bias voltages of the DPMZM, which are the dominant factor to induce the nonlinear distortions into the MWP notch filter. The proposed scheme is theoretically analyzed and experimentally verified.

We review the theory of slow and fast light effects due to coherent population oscillations in semiconductor waveguides, and potential applications of these effects in microwave photonic systems as RF phase shifters. In order to satisfy the application requirement of 360° RF phase shift at different microwave or millimeter-wave frequency bands, we present several schemes to increase the achievable RF phase shift by enhancing light slow-down or speed-up. These schemes include integrating gain and absorption sections, optical filtering and the exploitation of the initial chirp effects. As a real application in microwave photonics, a widely tunable microwave photonic notch filter with 100% fractional tuning range is also proposed and demonstrated.

A new all-optical microwave photonic notch filter (MPNF) is presented. It is based on controlling the amplitude and phase of the optical carriers and RF phase modulation sidebands via a diffraction-based Fourier-domain optical processor. It has the ability of realizing a flat-passband, narrow-notch, and large-free-spectral-range amplitude response and a group delay response with very few ripples. The carrier and sideband optical phase controls enable a continuous notch frequency tuning operation to be realized without altering the response shape. The filter has a simple structure and a wide bandwidth as it only involves optical components. Experimental results demonstrate an MPNF that exhibits a flat passband with <; 1 dB ripples, a deep notch of > 35 dB, and low group delay ripples of <; ±25 ps, together with the continuous notch frequency tunability and excellent long-term stability and repeatability.

Tunable single notch microwave photonic filter based on delay lines

We propose and experimentally demonstrate a simple photonic approach to achieving tunable and reconfigurable bandpass microwave photonic filters (MPFs) based on cascaded microring resonators (CMRRs). The optical spectrum of the silicon CMRRs could offer two bandpass responses to separately filter the optical carrier and one of the sidebands generated by the phase modulation. Thus we could achieve a bandpass MPF. Moreover, as the central frequencies and bandwidths of the two bandpass responses can be tuned by simply adjusting the voltages applied on one MRR, tunable and reconfigurable MPFs could be successfully achieved. A proof-of-concept experiment illustrates a central frequency tuning range from 19 GHz to 40 GHz, and a wide bandwidth tuning range from 5.5 GHz to 17.5 GHz.

A novel photonic microwave notch filter with capability of frequency tuning is proposed and experimentally demonstrated. The scheme is based on a fiber Bragg grating (FBG)-based, single longitudinal mode, wavelength-spacing tunable dual-wavelength fiber laser and a dispersive fiber delay line. By using a symmetrical S-bending technique along the FBGs, the wavelength spacing of the laser can be tuned, which enables the microwave notch frequency tuning. Experimental results show that the notch rejection of more than 30 dB and the flexible tunability of notch frequency can be readily achieved in the range of 1.2 approximately 6.7 GHz.

Through a combination of multiplexing and pipelining it is possible to implement in FPGAs a high-order tunable IIR notch filter using a new digital heterodyne technique. The notch center frequency can be tuned from DC to the Nyquist frequency and the characteristics of the IIR generated notch filter can be reprogrammed for specific applications. A specific implementation of a notch filter suitable for processing digital audio has a sampling frequency of 48 kHz and a maximum clock frequency of 192 kHz, well within the operating range of modern FPGA's. The whole system can be easily retargeted for an ASIC process such as that available through MOSIS.

We introduce a novel scheme based on slow and fast light effects in semiconductor optical amplifiers, to implement a microwave photonic notch filter with ~100% fractional tuning range at a microwave frequency of 30 GHz.

We propose and experimentally demonstrate a silicon photonic independently tunable dual-passband microwave photonic filter (MPF) based on cascaded high-Q silicon micro-disk resonators (MDRs). The MPF integrates a micro-ring resonator modulator (MRM), two thermally tunable MDRs, and a Mach-Zehnder interferometer (MZI) on a single chip. The MRM and MDRs are placed in one arm of the MZI to map the spectral response via single-sideband modulation and carrier beating. Independent tunability of dual-passband center frequencies is achieved through voltage-controlled thermal actuation of micro-heaters monolithically integrated atop the MDRs. Experimental results demonstrate that the proposed MPF chip has dual passbands with bandwidths of 325 MHz and 425 MHz, extinction ratios of 23 dB and 25 dB, and a continuously tunable center frequency spanning 3-31 GHz. Featuring narrow passband, high extinction ratio, flexible frequency tunability and high integration degree, the proposed dual-passband MPF is suitable for multi-functional photonic-assisted microwave processing systems.

Two single-chip designs implement in FPGA's a high-order tunable IIR notch filter using a new digital heterodyne technique. The notch center frequency can be tuned from DC to the Nyquist frequency and the characteristics of the IIR generated notch filter can be re-programmed for specific applications. The first chip is a single-chip version of a filter previously designed using three Xilinx FPGA's. Through Multiplexing and Pipelining it is possible to implement all three chips on one FPGA. The second chip makes use of a reduction in the sin-cos look-up tables to reduce the hardware even more. Both chips offer very flexible adaptive notch filters with the ability to design, a very complex notch without complicating the tuning process. These new single-chip versions offer considerable power and cost advantages over the earlier three-chip version.

We propose a continuously tunable high notch rejection microwave photonic filter which is based on a nonlinearly chirped fibre Bragg grating (NLCFBG). The filter response is caused by the dispersion induced by the NLCFBG and tunability is realized through changing the operating optical wavelength. Measured results demonstrating notch frequency tuning of 4.7 GHz with more than 45 dB notch rejection are presented.