Resonator Notch Filter Research Articles

Tunable bandpass microwave photonic filter with largely reconfigurable bandwidth and steep shape factor based on cascaded silicon nitride micro-ring resonators.

Bandpass microwave photonic filter (MPF) can be achieved based on the well-known phase to intensity conversion method by using phase modulation and single micro-ring resonator (MRR) notch filter. Since MRR could introduce residual phase in handling one optical sideband, the out-of-band radio frequency (RF) rejection ratio and the shape factor of the bandpass MPF are very limited. Here, by introducing another MRR to handle the other optical sideband, the residual phase can be greatly suppressed, thus the filter's performance can be greatly improved. The proposed bandpass MPF was both verified theoretically and experimentally. Compared with the single MRR, the out-of-band RF rejection ratio and the shape factor were improved by 20 dB and 1.67, respectively. Furthermore, the bandpass MPF's bandwidth is reconfigurable by adjusting the optical carrier's frequency or the two MRRs' amplitude coupling coefficients. The bandpass MPF's center frequency is also tunable by changing the resonant wavelengths of two MRRs in the opposite direction simultaneously. Experimentally, bandwidth reconfiguration from 0.38 GHz to 15.74 GHz, the shape factor optimization from 2 to 1.23, and frequency tuning from 4 GHz to 21.5 GHz were achieved. We believe that the proposed bandpass MPF has great potential for microwave photonic signal processing.

THz guided-mode resonance notch filter with variable filtering strength

In this paper, we propose a terahertz (THz) guided-mode resonance (GMR) notch filter made of a monolithic polyethylene terephthalate (PET) film, which has a monolayer grating structure. The proposed configuration shows both polarization-dependent and polarization-independent notch filter characteristics for the incident THz wave depending on the rotation angle of the second grating film. When the rotation angle is 0°, the filtering strength (transmittance) at resonance frequency changes from 0.4 (0.996) to 99.0% (0.010) according to the incident polarization. The transmittance continuously decreases with increasing rotation angle until 90°. When the rotation angle is 90°, the transmittance converges to 0.065 (± 0.015) independent of the incident wave polarization. When the incident polarization angle ranges from 90° to 180°, paradoxically, the transmittance through the two GMR grating films is greater than the transmittance through only the first GMR grating film due to the enhancement of the vertical component of the THz wave. These results agree well with a calculation using a polar coordinate system.

Multiband notch filter based guided-mode resonance for mid-infrared spectroscopy

A dielectric guided-mode resonance (GMR) notch filter with multiple channels was designed to operate in the mid-wave infrared (MWIR, 3∼4μm). The transmission characteristics of filters were analyzed using a finite difference time domain (FDTD) method. In the structure of notch filter, two different periodic (p1=1.6μm and p2=2.0μm) silicon (Si) grating waveguide layers (GWLs) are constructed on the CaF2 substrate. Si waveguide layer thickness and CaF2 cladding layer thickness were designed based on optical interference principle to give maximum transmission across the MWIR. The transmission spectrum presents two narrow band located at 3.410μm and 3.833μm with not only a high bandstop coefficient (>99%), but also a broadband high transmission (>90%) off-resonance. The resonant wavelengths can be flexible modulated in wide range by changing grating periods or filling factors, and it is proved that filter is stable and useful in actual atmospheric conditions. Because of the good performance in the bandstop features, the multiband GMR notch filter designed in this method may have a potential for a variety of imaging or detection applications.

Thermal control of the magnon-photon coupling in a notch filter coupled to a yttrium iron garnet/platinum system

We report thermal control of mode hybridization between the ferromagnetic resonance (FMR) and a planar resonator (notch filter) working at 4.74 GHz. The chosen magnetic material is a ferrimagnetic insulator (Yttrium Iron Garnet: YIG) covered by 6 nm of platinum (Pt). A current induced heating method has been used in order to enhance the temperature of the YIG/Pt system. The device permits us to control the transmission spectra and the magnon-photon coupling strength at room temperature. These experimental findings reveal potentially applicable tunable microwave filtering function.

Performance analysis and improvement of semiconductor optical amplifier direct modulation with assistance of microring resonator notch filter

We demonstrate through numerical simulations that a passive single-bus microring resonator (MRR) employed as notch filter enables to directly modulate an ordinary semiconductor optical amplifier (SOA) at 10 Gb/s. This data rate constitutes a fourfold increase in the speed that it is possible to modulate the SOA due to its finite differential carrier lifetime. The theoretical analysis unveils how the MRR radius and detuning must be selected so that the MRR-based filtering scheme efficiently overcomes the pattern-dependent impairments incurred by the SOA narrow electrical bandwidth. Moreover, the small-signal analysis conducted to correlate the perturbations in power of the modulated optical signal inserted in the MRR with those at the MRR output confirms the enhancement in the electrical bandwidth of the SOA–MRR combination. Provided that the MRR response is tailored as suggested, which is technologically feasible, the MRR action permits the encoded signal to exhibit at extended data rate a pulse and eye diagram profile of acceptable quality, tolerable amplitude difference indices, an error probability below the forward error correction limit, and a sufficient system net gain for medium-haul transmission in standard single-mode fiber with dispersion compensation. These performance improvements can be beneficial for the direct modulation of standard SOAs. Together with SOAs inherent amplification capability, they can open new perspectives in using these active elements as external modulators in various target applications.

Mid-wave infrared narrow bandwidth guided mode resonance notch filter.

We have designed, fabricated, and characterized a guided mode resonance notch filter operating in the technologically vital mid-wave infrared (MWIR) region of the electromagnetic spectrum. The filter provides a bandstop at λ≈4.1 μm, with a 12 dB extinction on resonance. In addition, we demonstrate a high transmission background (>80%), less than 6% transmission on resonance, and an ultra-narrow bandwidth transmission notch (10 cm-1). Our filter is optically characterized using angle- and polarization-dependent Fourier transform infrared spectroscopy, and simulated using rigorous coupled-wave analysis (RCWA) with excellent agreement between simulations and our experimental results. Using our RCWA simulations, we are able to identify the optical modes associated with the transmission dips of our filter. The presented structure offers a potential route toward narrow-band laser filters in the MWIR.

Using a $\hbox{Si}_{3}\hbox{N}_{4}$ Ring Resonator Notch Filter for Optical Carrier Reduction and Modulation Depth Enhancement in Radio-Over-Fiber Links

Optical carrier reduction via the use of a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ring resonator notch filter (RRNF) is proposed and experimentally demonstrated as a means for improving the modulation efficiency in 10-GHz radio-over-fiber (RoF) links. The realized filter is characterized in both the optical and microwave domains and is then exploited in an RoF test bed. Experimental results show a modulation depth improvement of up to 9 dB.

Variable carrier reduction in radio-over-fiber systems for increased modulation efficiency using a Si_3N_4 tunable extinction ratio ring resonator

Variable optical carrier reduction via the use of a Si(3)N(4) ring resonator notch filter with tunable extinction ratio is demonstrated in a 10 GHz radio-over-fiber system for improving the modulation efficiency. The extinction of the filter notch is tuned with micro-heaters, by setting the Mach-Zehnder coupler of the ring. Experimental results showing a modulation depth improvement of up to 20 dB are provided.

Picosecond wavelength conversion using semiconductor optical amplifier integrated with microring resonator notch filter

In this paper, we analyse the picosecond wavelength conversion using semicon- ductor optical amplifier (SOA) with a novel technique. For an accurate and precise modelling, all the nonlinear effects that are relevant to picosecond and subpicosecond pulse regime, such as, self-phase modulation, nonlinear Kerr effect, spectral hole burning, carrier heating, carrier depletion, two-photon absorption and group velocity dispersion are taken into account in the SOA model. We integrate the structure with a microring resonator notch filter to eliminate the unwanted pump and probe signals at the output of the system. It shows that with the three coupled microring resonators, output four-wave mixing (FWM) signal generated by the SOA can be filtered accurately. Moreover, our results demonstrate that the microring resonator can be used for modifying the shape and spectrum of the output FWM signal. Simulation results show that this new technique enhances the output time bandwidth product.

On-Chip All-Optical Passive 3.55 Gbit/s NRZ-to-PRZ Format Conversion Using a High-Q Silicon-Based Microring Resonator

We report the experimental result of all-optical passive 3.55 Gbit/s non-return-to-zero (NRZ) to pseudo-return-to-zero (PRZ) format conversion using a high-quality-factor (Q-factor) silicon-based microring resonator notch filter on chip. The silicon-based microring resonator has 23800 Q-factor and 22 dB extinction ratio (ER), and the PRZ signals has about 108ps width and 4.98 dB ER.

Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings

An approach of enhanced light-trapping in a thin-film silicon solar cell by adding a two-filling-factor asymmetric binary grating on it is proposed for the wavelength of near-infrared. Such a grating-on-thin-film structure forms a guided-mode resonance notch filter to couple energy diffracted from an incident wave to a leakage mode of the guided layer in the solar cell. The resonance wave coupled between two-filling-factor gratings would laterally extend the optical power and induce multiple bounces within the active layer. The resonance effect traps light in the cell enhancing its absorption probability. A dynamic light-trapping behaviour in solar cells is observed. A photon dwelling time is proposed for the first time to quantify the light-trapping effect. Moreover, the light absorption probability is also quantified. As compared the grating-on-thin-film structure with the one of planar silicon thin film, simulation results reveal that it is 3-fold enhancement in the light absorption within a spectral range of 920-1040 nm. Moreover, such an enhancement can be maintained even the incident angle of near-IR broadband light wave varies up to +/-40 degrees.

Silicon Photonics Research in Hong Kong: Microresonator Devices and Optical Nonlinearities

In this review paper we showcase recent activities on silicon photonics science and technology research in Hong Kong regarding two important topical areas-microresonator devices and optical nonlinearities. Our work on silicon microresonator filters, switches and modulators have shown promise for the nascent development of on-chip optoelectronic signal processing systems, while our studies on optical nonlinearities have contributed to basic understanding of silicon-based optically-pumped light sources and helium-implanted detectors. Here, we review our various passive and electro-optic active microresonator devices including (i) cascaded microring resonator cross-connect filters, (ii) NRZ-to-PRZ data format converters using a microring resonator notch filter, (iii) GHz-speed carrier-injection-based microring resonator modulators and 0.5-GHz-speed carrier-injection-based microdisk resonator modulators, and (iv) electrically reconfigurable microring resonator add-drop filters and electro-optic logic switches using interferometric resonance control. On the nonlinear waveguide front, we review the main nonlinear optical effects in silicon, and show that even at fairly modest average powers two-photon absorption and the accompanied free-carrier linear absorption could lead to optical limiting and a dramatic reduction in the effective lengths of nonlinear devices.

Far infrared spectroscopy with high resolution cyclotron resonance filters

A new type of far infrared spectroscopy based on a cyclotron resonance notch filter is demonstrated. The resonant absorption energy of such a filter is tuned by an external magnetic field. GaAs/AlGaAs heterostructures with high mobility two-dimensional electron gas are used to obtain an optimal cyclotron resonance filter. With such a filter, we can analyze far infrared radiation in the range 40–150 cm−1 with a resolution of up to 2 cm−1. A procedure for the determination of the spectral characteristics of an unknown source from the detector signal is presented. We show that the cyclotron-resonance-notch-filter based spectrometer provides ultralow background radiation conditions for measurements. We also demonstrate the performance of the spectrometer by an analysis of electrostimulated far infrared emission of InSb, GaAs bulk crystals as well as of selectively doped quantum wells.

70 MHz surface-acoustic-wave resonator notch filter

A 70 MHz notch filter employing a surface-acoustic-wave resonator in a hybrid-coil circuit to produce a notch depth of 50 dB has been developed. The notch frequency is tunable over a 40 kHz range and the passband attenuation is approximately 7 dB.