Ring Filter Research Articles

Design and Analysis of a Tri-Band Dual-Mode Chip Filter for 60-, 77-, and 100-GHz Applications

A tri-band dual-mode chip filter, which is fabricated with a commercial monolithic microwave integrated circuit technology and suitable for millimeter-wave applications, is presented in this paper. This filter is constructed by using stacked ring resonators with individual perturbation and feeding capacitors, thus fractional bandwidths and center frequencies of three passbands can be flexibly controlled. An equivalent model of the tri-band filter that considers coupling effects between the stacked ring resonators is adopted, and then a new set of design equations that can determine element values of dual-mode ring filters realized with different length ratios of upper parts over lower parts of the ring resonators are derived and proposed to design the filters with desired characteristics. Theoretical and experimental results reveal that dual-mode ring filters realized with different length ratios can change the positions of transmission zeros while keeping their widths of passbands equal, provide different characteristics of roll-off rates, and stopband suppressions. By following proposed design guidelines, the layout pattern of the tri-band dual-mode filter can be determined quickly. To verify the proposed design concept, an experimental prototype, locating three passbands at 60, 77, and 100 GHz, respectively, was fabricated on GaAs substrate. The size of the filter is about 0.46 × 0.91 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the measured insertion losses in the three passbands are less than 2.4, 2.7, and 3.5 dB over the frequency bands of interest, and their associated return losses are greater than 18, 17, and 8 dB, respectively.

A Stable Narrow Line-Width Dual-Wavelength Fiber Laser Based on Nonlinear Polarization Rotation with a High Finesse Ring Filter

A stable narrow line-width dual-wavelength fiber laser based on nonlinear polarization rotation with a high finesse ring filter is proposed and demonstrated. A polarization-dependent-isolator (PDI) and a section of polarization maintaining fiber (PMF) form an equivalent birefringent filter. Moreover, a ring filter can produce high finesse due to the weak gain generated by the EDF. As a result, two stable wavelengths are generated which both have about 18dB extinction ratio, 16dB side mode suppression ratio (SMSR) and 0.16nm 3dB line-width. Plus, less than 2 pm of the wavelengths shift and smaller than 0.4 dB of the optical power fluctuation when the system is operating in room environment for a period of 40 minutes indicate that the ultra narrow line-width fiber laser is very stable.

Multi-Wavelength Fiber Laser Based on a High Finesse Fiber Ring Filter and Multimode FBG

A multi-wavelength fiber laser with a narrow bandwidth based on an erbium-doped fiber ring filter and multimode fiber Bragg grating (MM-FBG) has been proposed, a high finesse fiber ring filter are introduced .The fiber ring filter consists of two optical couplers and a section of weak pumped erbium-doped fiber (EDF）. Thanks to the delay of cavity length and the gain generated by the EDF, the filter has spectral response with a high finesse. The incorporation of the fiber ring filter leads to the suppression of undesirable mode and makes the output laser narrower bandwidth. With 980 nm LD pumped, at the room temperature, the space of the two wavelengths is 0.07nm, which improved the effect of the filter.

Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter

A dual-wavelength fiber laser with a narrow-linewidth, based on a P-F fiber filter has been proposed. Polarization-maintaining fiber Bragg grating (PM-FBG) and a F-P fiber filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device. The fiber F-P filter consists of two optical couplers and a section of un-pumped erbium-doped fiber (EDF). Due to the delay of cavity and the loss generated by the EDF, the filter has comb spectral response. The incorporation of the fiber F-P filter leads to the suppression of undesirable modes. At the room temperature, under 980nm LD pumped, the maximum output of the two wavelengths is respectively −2.259dBm and 0.568dBm, with the 3-dB bandwidth separately 0.1nm and 0.14nm, realizing the narrow linewidth and dual-wavelength output.

Si micro-ring MUX/DeMUX WDM filters

We demonstrate 3rd order micro-ring filters, 100 GHz-spaced 16 channels and 50 GHz-spaced 32 channels. Fabrication-induced resonant wavelength errors, σ = 0.237 nm, and temperature-dependent wavelength shift, 0.043 nm/°C tolerable to ΔT>10 °C, has been measured on filters based on the fundamental TM mode. The problem of CMOS-compatible photolithography is solved, while maintaining a small radius, R = 9 μm. As some dummy channels are arranged, it is shown that an on-chip optical network for many cores CPU can be constructed by 16 channel ring filters with the currently available technology.

GHz-bandwidth optical filters based on high-order silicon ring resonators

Previously demonstrated high-order silicon ring filters typically have bandwidths larger than 100 GHz. Here we demonstrate 1-2 GHz-bandwidth filters with very high extinction ratios (~50 dB). The silicon waveguides employed to construct these filters have propagation losses of ~0.5 dB/cm. Each ring of a filter is thermally controlled by metal heaters situated on the top of the ring. With a power dissipation of ~72 mW, the ring resonance can be tuned by one free spectral range, resulting in wavelength-tunable optical filters. Both second-order and fifth-order ring resonators are presented, which can find ready application in microwave/radio frequency signal processing.

A Wavelength-Tunable Single-Longitudinal-Mode Fiber Ring Laser With a Large Sidemode Suppression and Improved Stability

A high-performance single-longitudinal-mode (SLM) fiber ring laser incorporating a high finesse ring filter that contains a section of weakly pumped erbium-doped fiber is proposed and experimentally demonstrated. The incorporation of the high finesse ring filter can suppress multimode oscillation, improve power stability, and increase sidemode suppression ratio (SMSR). A stable SLM oscillation with a tunable range from 1522 to 1573 nm and an SMSR as high as 68 dB is experimentally demonstrated.

Miniaturized Wideband Ring-Type Bandpass Filters with Upper Stopband Characteristic

A new class of wideband ring-type microstrip bandpass filter is proposed under smaller size of three quarters waveguide length section. One via hole is placed at perpendicular position in a squared ring, whereas two short-circuited sections are formed in the ring-type microstrip bandpass filter similar to a dual-mode ring filter in shape, thereby making up a three quarters waveguide length ring-type microstrip bandpass filter. By adjusting the short-circuited sections, the bandwidth of the center frequency can be controlled easily. As a pair of open-circuited stubs is placed between the two ports, two extra resonances can be used to improve the out-of-band performance. Afterwards, a novel microwave microstrip filter has been successfully fabricated with the lower insertion loss S 21 of 0.48 dB, return loss S 11 of 30 dB, 3 dB bandwidth of 80%, and central frequency of 2.4 GHz. Simulated and measured results show good wideband filtering performance with widened upper stopband outside the wide passband.

Frequency-switchable microwave generation based on a dual-wavelength single-longitudinal-mode fiber laser incorporating a high-finesse ring filter

A wavelength-switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser (EDFL) incorporating a novel high-finesse ring filter is proposed and demonstrated. The ring filter consists of two optical couplers and a section of pumped erbium-doped fiber (EDF). Thanks to the gain generated by the EDF, the ring filter has spectral response with a high finesse. The incorporation of the ring filter leads to the suppression of undesirable modes in the dual-wavelength EDFL. An experiment is carried out. Two SLM wavelengths are generated. The side mode suppression ratio is greater than 50 dB. The wavelength spacing of the two wavelengths is tunable with a tuning step of approximately 10 GHz. A frequency switchable microwave signal from approximately 10 to approximately 40 GHz is thus generated by beating the two wavelengths at a photodetector (PD). The spectral width of the generated microwave signal is measured to be less than 5 kHz.

Adjusting resonant wavelengths and spectral shapes of ring resonators using a cladding SiN layer or KOH solution

It is shown that the resonant frequencies and the transmission spectra of ring resonators can be adjusted by depositing or etching the cladding nitride layer on the ring waveguide without introducing an extra loss or extra variations of channel spacing. The cladding nitride layer increases the minimum width of the gap in the coupling region to larger than 150nm which makes it possible to consider photolithography instead of E-beam lithography for the typical design rule of ring filters. KOH silicon etching can also adjust not only the resonance frequencies but also coupling coefficients with a small sacrifice of guiding loss.

Self-adaptive, narrowband tuning of a pulsed optical parametric oscillator and a continuous-wave diode laser via phase-conjugate photorefractive cavity reflectors: verification by high-resolution spectroscopy

A dynamic self-adaptive Bragg grating formed in a photorefractive crystal is shown to be a convenient way to attain single-longitudinal-mode (SLM) operation and narrowband tuning both in a pulsed, injection-seeded optical parametric oscillator (OPO) and in a continuous-wave (cw) extended-cavity diode laser. The pulsed OPO cavity comprises a Rh:BaTiO3 photorefractive (PR) crystal, a periodically poled KTiOPO4 nonlinear-optical crystal, and a dielectrically-coated end mirror. A continuous-wave seed beam at 820–850 nm from a tunable SLM diode laser traverses firstly the Rh:BaTiO3 crystal and then is retro-reflected by the end mirror; this creates a wavelength-selective Bragg grating reflector in the PR crystal, thereby completing the OPO cavity. The cavity stays automatically resonant with the seed radiation, with no need to actively control its length or to make any other mechanical adjustment. One form of injection seeder comprises a novel extended-cavity diode laser (ECDL) design incorporating a self-pumped photorefractive phase-conjugate reflector and a compact, high-finesse tunable intracavity ring filter. This combination facilitates robust tunable single-frequency operation with narrow optical bandwidth. The performance characteristics of the OPO and the ECDL are evaluated by recording high-resolution atomic and molecular spectra. Notably, fluorescence-detected sub-Doppler two-photon excitation at 822 nm, of the 8S←6S transition in atomic Cs, provides a crucial linewidth test.

UWB용 대역통과 링 필터의 설계

In this paper, a novel ultra-wide band filter which is operating at frequency bands from 3.1 ㎓ to 10.6 ㎓ is suggested. It is modified from the conventional ring filter and consisted of a ring with two parallel open-stub with length of λ/8. It improves the sharpness of the conventional ring filter and is compact. The measured results show that the fabricated filter has a insertion loss of 2.1 ㏈ and the measured group delay of the filter is less than 463 ps through UWB frequency bands.

Efficient phase locking of erbium-doped fiber ring lasers by a common ring filter

Efficient phase locking of two erbium-doped fiber ring lasers is demonstrated by constructing a common ring filter. The ring filter offers the functions of both mode selection and mutual injection coupling between the lasers. Thanks to the mutual injection locking between them, they achieve the phase locking state and coherently combine in the far-field. Moreover, a single-mode feedback fiber is introduced to filter the far-field pattern to make the phase locking state more stable. The spatial interference fringes, output powers and spectra all indicate that employing the common ring configuration can achieve efficient phase locking of multiple fiber ring lasers.

RF optoelectronic oscillator using a directly modulated semiconductor laser and a fiber optical ring filter

AbstractIn this article we present an RF optoelectronic oscillator based on directly modulated laser diode and an all optical RF filter. The system is modeled and simulated using standard simulators. Using commercial modules and standard single mode fiber, the implemented system shows an RF oscillation with 9.8 dBm at 1.1 GHz. We also show that the use of an all optical RF filter allows a sidemode suppression ratio more than 50 dB without affecting the signal purity. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 470–475, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24069

Dual-wavelength S-band erbium-doped fiber double-ring laser

We propose and demonstrate an S-band CW dual-wavelength erbium-doped fiber (EDF) dual-ring laser using a compound-ring filter (CRF) with various coupling losses inside the gain cavity. Employing a ring filter combined within the cavity, the fiber laser can lase a dual wavelength without any filter inside the ring loop. The dual-wavelength output exhibits a good performance having optical side-mode suppression ratios (SMSRs) of 31.6 and 31.8 dB and output powers of −9.6 and −9.3 dBm at 1505.58 and 1506.43 nm, respectively, when the coupling loss is 30% inside the cavity. In addition, the output stabilities of the dual-wavelength laser have also been analyzed.

Robust tunable single-frequency operation of a diode laser by a self-pumped phase-conjugate reflector and a high-finesse filter

A novel form of extended-cavity diode laser attains robust tunable single-frequency operation with narrow linewidth. The laser cavity includes a self-pumped photorefractive phase-conjugate reflector for wavelength-adaptive narrowband feedback and a compact high-finesse tunable intracavity ring filter for single-longitudinal-mode selectivity and control. Its performance around 830 nm is verified with a simple Fabry-Perot laser diode and by Doppler-free two-photon spectroscopy in atomic cesium.

Secondary effluent reclamation: combination of pre-treatment and disinfection technologies

A study was carried out to evaluate the efficiency of secondary effluent additional treatment, using a combination of pre-treatments (ring filter, physico-chemical and infiltration-percolation) followed by disinfection methods (chlorine dioxide, peracetic acid and ultraviolet light). Three different indicator microorganisms were determined: E. coli, total coliforms and somatic bacteriophages. The results show better efficiency of physico-chemical and infiltration-percolation processes. Bacteriophages were eliminated to a lesser extent than bacterial indicators in all the treatment systems. Chlorine dioxide and peracetic acid seems to be more efficient in disinfection than ultraviolet light when a ring filter is the pre-treatment used. For the same doses and contact times, the efficiency of the disinfection methods is higher when the pre-treatment used is the physico-chemical or the infiltration-percolation system. The final effluent quality from the physico-chemical treatment train and the infiltration-percolation treatment train, followed by the disinfectants, achieves an E. coli content that allows the reuse in most of the uses described in the Spanish legislation for wastewater reuse.

Multichannel silicon WDM ring filters fabricated with DUV lithography

We have fabricated 9-channel silicon wavelength-division-multiplexing (WDM) ring filters using 193nm deep-ultraviolet (DUV) lithography and investigated the spectral properties of the ring filters by comparing the transmission spectra with and without an upper cladding. The average channel-spacing of the 9-channel WDM ring filter with a polymeric upper cladding is measured about 1.86nm with the standard deviation of the channel-spacing about 0.34nm. The channel crosstalk is about −30dB, and the minimal drop loss is about 2dB.

Four-channel switched microwave filter based on optical ring resonators

A four-channel switched microwave filter was demonstrated incorporating a switched optical resonator, which is constructed by integrating a 1×4 space switch with arrayed ring filters featuring different free spectral ranges. The four channels centred at 10, 16, 18 and 20 GHz were individually selected to provide a bandpass filtering via the control voltage applied to the switched resonator.

A Compact Ultrawide Bandpass Filter on Thin-Film Substrate

This paper presents the ultrawideband filters for UWB fullband (range of 3.1-10.6 GHz) applications. This filter consists of ring filter for wide-bandwidth and coupled line structure for suppressing unwanted passband in upper and lower stopbands. Especially, the filter structure was realized on silicon substrate using thin film technology, adequate for wafer level packaging, which can be integrated with CMOS UWB chipset that is currently on development. To minimize the dimension of the filter, the Hilbert structure was applied in ring filter and the meander shaped broadside coupled structure was also adopted in the coupled line structure. The size of the fully realized filter structure is 4.4 x 3.6 mm 2 . The insertion loss in passband is 1.5 dB and the return loss is larger than 15 dB, respectively. The group delay in center frequency is 0.2ns and the group delay variation is less than 0.15 ns.