Efficient pipelined tunable heterodyne notch filter implementation in FPGAs

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.

A new topology for a tunable microwave photonic notch filter, which achieves a wide and continuous tuning range of FSR/2, is presented. The novel principle of tuning is based on changing optical variable attenuators only; consequently, a fixed wavelength laser can be used as the optical source. Experimental filter tuning results demonstrate a wide fractional tuning range of 50%, continuous tuning capability, and a notch filter shape that does not change as it is tuned, in very good agreement with predictions.

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 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.

In mixed signal systems, a weak signal is buried in strong interferers. The signal to noise ratio is poor. To convert the signal to digital, the dynamic range of the analog to digital converter cannot be efficiently utilized. The interference has to be reduced before the conversion. A notch filter can remove this interference. To allow for the uncertainty of the interference frequency, process variations, and ageing of components, it has to be self-correcting. This paper presents a scheme that improves the signal to noise ratio. This system will form the front end of any mixed mode system where the signal is known to be buried in narrow-band noise. The self-tuned notch filter has two parts: a tunable notch filter (a transconductor implementation of the universal active filter) and a control circuit. This has been implemented in 0.35 /spl mu/m CMOS technology.

Angle tunable terahertz band notch filter with single-band and dual-band switching characteristics based on metallic strip structures

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.

High-Q biquadratic notch filter synthesis using nodal admittance matrix expansion

This paper presents tunable absorptive dual-notch filters using a stub-loaded coupled line with an inductor. The two-pole Butterworth filter function is modified to attain absorptive responses at a notch frequency. In addition, a stub-loaded coupled line with an inductor is employed to obtain dual-band bandstop responses, the required coupling coefficients, and quality factors based on the modified Butterworth function at two notch frequencies. In the proposed filter, tunable absorptive dual-notch responses are accomplished without using auxiliary circuits, such as an impedance matching network. The two resonant frequencies and the quality factors of the resonators are independently controlled by adjusting the three loading capacitances of the resonator. Three types of filters are designed and then built on a substrate with <i>ε<sub>r</sub></i> = 3.42 and <i>h</i> = 30 mils. The first filter (Filter A) attained a return loss of 11.2–17.1 dB/10.5–24.4 dB at 0.76–0.98 GHz/1.05–1.28 GHz. The measured return loss of the second filter (Filter B) was 12.5–14.8 dB/10.2–12.3 dB at 0.84–1.08 GHz/1.35–1.59 GHz. For Filter C, equipped with a 4-pole response achieved through the cascade connection of two 2-pole filters (Filter B), a return loss of 11.2–15.1 dB/14.2–27.3 dB was obtained at 0.9–1.1 GHz/1.38–1.63 GHz. The application areas of the proposed filters include cognitive radios and carrier aggregation systems requiring two transmit frequencies.

A microelectromechanical tunable notch filter using silicon-photonic freestanding waveguides is proposed, and the basic characteristics are experimentally investigated. The proposed filter is composed of a wavelength-tunable silicon microring resonator and a busline switch. The tunable microring consists of freestanding single-mode waveguides and air-gap directional waveguide couplers. The optical path length of the microring is varied physically by a displacement of electrostatic comb-drive actuator. The busline switch consists of a gap-variable waveguide coupling mechanism, which enables coupling the tunable microring with the busline by another electrostatic comb-drive actuator. During the wavelength tuning of microring, the busline can be disconnected from the microring. Therefore, the proposed device operates as a hitless wavelength-selective switch if they are connected in series. The waveguides are 320 nm in width and 340 nm in thickness. The resonant wavelength shift of the microring is 9.96 nm at the voltage of 26 V with the actuator displacement of 1.0 μm. The coupling to busline is adjusted from the switch-off state at the gap of 600 nm to the switch-on state corresponding to the critical coupling condition at the gap of 383 nm. The whole size of the wavelength-tunable filter with hitless mechanism is about 150 μm by 80 μm. Due to the capacitive operation of the comb-drive actuators, the power consumption is negligibly small.

In this work, a compact design of an electrically tunable notch filter, based on liquid crystal (LC) technology, has been designed, manufactured, and characterized. The proposal has been achieved through particular configuration schemes with low cost inverted-microstrip structures and conventional spurlines structures due to its ease of integration. Central frequency tunability has been induced by applying low ac voltages, thus involving low power consumption. For these devices, filter responses have been approached specifically at microwave C-band frequency allocated for many satellite communications applications. Also, it has taken advantage of new highly anisotropic nematic LC mixtures at those frequency ranges.

This paper discusses development of a fractional order resonator (FOR) using a single fractor, a capacitor and a resistor. The said fractor is an obtuse angle type inductive fractor and inclusion of such fractor makes the Q-factor of this FOR infinite (theoretically). Besides, the proposed FOR is tunable; varying the fractance, the resonating frequency can be tuned. Design, simulation and hardware realization of this tunable FOR have been presented here along with detail experimental results. Experimentally a Q factor more than 100 has been achieved in this work. As an application of this FOR, a tunable FO Notch filter has also been discussed at the end of this paper.

This thesis investigates Brillouin- and Kerr-active light sources in scalable silicon nitride platforms. We design waveguides that support both Brillouin scattering, a nonlinear optical process mediated by an acoustic wave, and the Kerr nonlinearity, an intensity-dependent refractive index. Using these waveguides, high spectral purity Brillouin lasers and broadband microcomb sources are realized by forming optical microresonators. In this work, we demonstrate an enhancement of Brillouin strength by several orders of magnitude, present multiple Brillouin photonic applications, realize Brillouin lasers and microcomb sources, and theoretically examine the interaction of competing Brillouin and Kerr gain in a single microcavity.<br/>Chapter 2 establishes the theoretical and technical background, covering nonlinear optics in integrated photonics, microring resonators, microcomb generation, and the principles of Brillouin scattering.<br/>In Chapter 3, we evaluate silicon nitride geometries including thick, symmetric dual-stripe, and asymmetric dual-stripe waveguides for SBS and Kerr nonlinearity. Optimized symmetric dual-stripe designs enabled low-loss fabrication (7 dB/m) and supported both Brillouin lasing and Brillouin-induced Kerr frequency combs.<br/>Chapter 4 introduces a numerical model of competing Brillouin and Kerr gain in microresonators. Simulations show that Brillouin microcombs can form in forward or backward directions depending on the free spectral range (FSR) and pump conditions. Acoustic detuning was found to be critical, as FSR values slightly below the Brillouin shift prevent suppression of Brillouin lasing by Kerr induced cross-phase modulation.<br/>In Chapter 5, we enable enhanced Brillouin gain by integrating silicon nitride with tellurite glass and coupling to surface acoustic waves (SAWs). This hybrid approach improved Brillouin strength by over two orders of magnitude, enabling demonstrations of a 10-dB optical amplifier, a tunable microwave notch filter with 2.2-MHz linewidth, and a Brillouin phonon laser with a record-low 7-Hz acoustic linewidth.<br/>Together, these results demonstrate that Brillouin and Kerr nonlinear sources can be integrated in silicon nitride, offering scalable routes to high-coherence lasers, frequency combs, and multifunctional microwave photonic devices. This establishes a foundation for applications ranging from optical frequency division to coherent phonon sources and advanced signal processing.<br/>