Ultra-narrow Bandpass Research Articles

Multi-Band OFDM Transmission at 100 Gbps With Sub-Band Optical Switching

In this paper, we present an original work on sub-wavelength optical switching performed over a coherent multi-band orthogonal frequency-division multiplexing (MB-OFDM) super-channel operating at 100 Gbps. After having demonstrated that dual-polarization MB-OFDM (DP-MB-OFDM) is as efficient as single-carrier dual-polarization quaternary phase shift keying (DP-QPSK) technology to transport 100 Gbps data-rate over a 10 × 100-km G.652 fiber-based transmission line, we show that optical add-drop of OFDM sub-bands as narrow as 8 GHz inside a 100 Gbps DP-MB-OFDM signal constituted of four sub-bands is feasible in the middle of this 1000-km transmission line. The flexible optical add-drop multiplexer (FOADM) implemented here is constituted by the association of an ultra-narrow pass-band and stop-band optical filter. The design and realization of such ultra-selective optical filters is presented, while the impact of their physical features over the quality of transmission is discussed. To prove that several add-drop multiplexers can be cascaded, our FOADM is introduced into a G.652 fiber-based recirculating loop and the impact of the cumulated filtering transfer function as well as the crosstalk inside the OADM are investigated. A typical use case for the introduction of such FOADM into long-haul transport networks is given, and the capital expenditure (CAPEX) cost advantage for the multi-layer transport networks is highlighted. By the proof of concept delivered here, combination of super-channel and sub-wavelength optical switching pushes network flexibility far away of what is today proposed by system vendors, opening new horizons for an optimized use of multi-layer transport networks.

Widely tunable wavelength spacing dual-wavelength single longitudinal mode erbium doped fiber laser

A simple widely tunable wavelength spacing dual-wavelength single longitudinal mode (SLM) erbium doped fiber laser (EDFL) based on cascaded fiber Bragg gratings (FBGs) and birefringent fiber filter is proposed and demonstrated. Experimental results show that the lasing wavelength spacing is widely tunable in a range from 2nm to 18nm, which has potential to generate frequency tunable terahertz (THz) waves by beating the lasing dual-wavelength in a high speed photodetector. The birefringent fiber filter acts as an ultra-narrow bandpass filter and benefits the simultaneous oscillation of dual-wavelength in a single laser cavity. The output peak power of the lasing dual-wavelength is approximately equalized at room temperature, and a high optical signal-to-noise ratio (OSNR) is realized in the whole tuning range. The SLM operation of dual-wavelength fiber laser is verified by Fabry–Perot (F–P) scanning interferometer, and the clear eye diagram proves that the proposed fiber laser is effective in the application of fiber optic communication system.

The enlargement of high reflectance range in ultra-narrow bandpass filter with disordered one-dimensional photonic crystal

The conventional ultra-narrow bandpass filter structure has only a very limited width of high-reflectance range. This study, by introducing disorder into one-dimensional (1D) photonic crystal, attempts to enlarge the width of high-reflectance range while keeping the ultra-narrow bandpass. Enlargement by 46.8% was obtained after theoretical design. Since this structure contains some degree of disorder already, it has a strong tolerance of the variation of layer thicknesses. Unlike studies using conventional periodic structures, theoretical statistical results in this study demonstrate that high quality remains even after allowing for ±5% variation of layer thicknesses. This indicates that only a very low thickness control precision is required in the future and the production difficulty is immensely lowered. To put the construction to test, a structure has been developed and demonstrated by a magnetron reactive sputtering coating system, which agrees with the theoretical result very well. By introducing disorder into the periodic 1D photonic crystal structure, the high-reflectance range is significantly extended by 37%, with an ultra-narrow pass band of 0.8 nm and intensity of 82%.

Design and Simulation of an IF MEMS Filter Based on Face Shear Mode Square Resonator

Intermediate frequency (IF) Filters with IC (Integrated circuit) compatibility, narrow bandwidth and large stop band rejection are in need for wireless communications. This paper presents the design and simulation of a 70 MHz IF Micro-electro-mechanical filter using two identical face shear mode square resonators. By carefully designing the supporting structure of the resonators, a quality factor above 100,000 is achieved in the best designed resonator. With these face shear mode square resonators, three filters are designed and the simulated transmission response shows that these filters can obtain unterminated transmission passbands of about 25 kHz to 35 kHz with the centre frequency of 70 MHz, which represents a 0.036% to 0.05% bandwidth. This ultra narrow bandwidth IF bandpass filter can be an attractive candidate for wireless receivers.

An Ultracompact OSNR Monitor Based on an Integrated Silicon Microdisk Resonator

Optical signal-to-noise ratio (OSNR) monitoring is essential for control and management of dynamic optical networks. Small footprint, low cost, and less power consumption are always desirable for such monitoring system. In this paper, we demonstrate an integrated dispersion-insensitive in-band OSNR monitor based on a compact silicon microdisk resonator (MDR) with only 5-μm radius. The MDR (Q ~ 54 000) functions as an ultranarrow bandpass filter in the measurement of the OSNR. The monitoring performance is evaluated in a 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) system and is shown to be insensitive to chromatic dispersion from 0 to 850 ps/nm. The input power requirement of the monitor is also studied, which is consistent with the desire for low-power operation. Finally, we analyze the sensitivity of this technique for various Q factors of the MDRs. The results indicate that the sensitivity of this scheme can be improved with higher Q factors.

A Narrow-Passband and Frequency-Tunable Microwave Photonic Filter Based on Phase-Modulation to Intensity-Modulation Conversion Using a Phase-Shifted Fiber Bragg Grating

A novel approach to implementing a narrow-passband and frequency-tunable microwave photonic filter (MPF) based on phase-modulation to intensity-modulation conversion in a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed MPF, a phase-modulated signal is sent to a PS-FBG. If one of the sidebands falls in the notch of the PS-FBG, the phase-modulated signal is converted to an intensity-modulated signal. Due to the ultra-narrow notch of the PS-FBG, a microwave filter with an ultra-narrow passband is realized. The tunability of the microwave filter is achieved by tuning the wavelength of the optical carrier. A theoretical analysis is performed in which the value of the phase shift and the location of the phase shift in the PS-FBG on the frequency response of the MPF are studied. Two PS-FBGs with different reflection bandwidths and different phase-shift values introduced at the center of the gratings are fabricated and incorporated into the proposed MPF. For the two PS-FBGs, the 3-dB bandwidths are 120 and 60 MHz and the tunable ranges are 5.5 and 15 GHz.

All-Optical Approach to Microwave Frequency Measurement With Large Spectral Range and High Accuracy

An all-optical approach for microwave frequency (MWF) measurement with a low-speed oscilloscope is proposed and experimentally demonstrated. In this scheme, an optical Alter with a single and ultranarrow passband, together with a tunable laser and a low-speed photodiode is utilized to calculate the MWF by measuring the time delay between the sweeping optical carrier and its upper/lower sideband passing through the filter. Single-frequency and multifrequency measurements are experimentally demonstrated. The measurement recognition, accuracy, and resolution are below 0.1, 0.09, and 0.2 GHz, respectively. This proposed scheme can be easily upgraded to higher frequencies using a modulator with higher bandwidth proportional to the desired measurement range.

Ultranarrow bandpass filter with wide nontransmission region composed of randomly distributed layer thicknesses

By introducing disorder into a periodic Fabry–Pérot type of ultranarrow bandpass (UNBP) filter, the nontransmission region of the filter can be remarkably enlarged while maintaining the UNBP. The filter that was used was fabricated by using electronic beam evaporation. The introduction of disorder into the periodic structure ensures that the nontransmission region is significantly extended by 14%, with a very narrow bandpass of full width at half maximum <1.9 nm and intensity=80%.

Metamaterials‐inspired technologies applied to ultra high‐frequency filtering structures

AbstractIn this letter, the design and comparative study of metamaterial‐inspired bandpass filters operating at G‐band (150 GHz) is presented. To this aim, filters based on split ring resonators (SRRs) and complementary SRRs are studied and compared on a scale compliant with MMIC technology. Technological issues impose severe constraints to the design of this type of devices. Specifically, the filter selectivity concern is addressed as a trade‐off between the acceptable insertion losses in the transmitted band and the achievable bandwidth. The addition of series gaps to previous unit cell configurations and suspended membrane structures are introduced to overcome these limitations, thus presenting improved upper band edges and rejection characteristics. In this context, the extension of metamaterial‐based filtering structures to higher frequencies and notably at millimeter waves is still lacking. Therefore, we present here the first contribution in this field by addressing the possibility to fabricate an ultra narrow bandpass filter for space applications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1868–1872, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25300

Note: An ultranarrow bandpass filter system for single-photon experiments in quantum optics

We describe a combined ultranarrow bandpass filtering setup for single-photon experiments in quantum optics. The filter is particularly suitable for single-photon electromagnetically induced transparency (EIT) experiments, but can also be used in several similar applications. A multipass planar Fabry-Perot etalon together with polarization filters and spatial filtering allows 114 dB pump beam suppression, while the signal beam is attenuated by just 4 dB, although both wavelengths are only separated by 0.025 nm (9.2 GHz). The multipass etalon alone accounts for 46 dB suppression while it has a peak transmission of 65%. We demonstrate EIT experiments in Cs vapor at room temperature with probe power in the femtowatt regime using this filter.

Flat-top and ultranarrow bandpass filter designed by sampled fiber Bragg grating with multiple equivalent phase shifts

We propose a novel approach to designing an optical filter with a flat-top and ultranarrow transmission band by using a sampled fiber Bragg grating (SFBG) having multiple equivalent phase shifts (EPSs). In the proposed approach, multiple EPSs are fabricated by adjusting several sampling periods of the SFBG. The obtained multiple EPSs are then arranged properly to get a flat-top transmission band in the narrow -1st reflection band of the SFBG, leading to the generation of a flat and ultranarrow transmission band. Filters with two or five EPSs are designed by simulation and experiment, with low ripples and ultranarrow 1 dB bandwidths observed in transmission bands.

基于啁啾莫尔光栅和半导体光放大器的多波长光纤激光器

A simple and cost-effective multi-wavelength fiber ring laser based on a chirped Moire fiber grating (CMFG) and a semiconductor optical amplifier (SOA) is proposed. Stable triple-wavelength lasing oscillations at room temperature are experimentally demonstrated. The measured optical signal-to-noise ratio (SNR) reaches the highest value of 50 dB and the power fluctuation of each wavelength is less than 0.2 dB within a 1-h period. To serve as a wavelength selective element, the CMFG possesses excellent comb-like filtering characteristics including stable wavelength interval and ultra-narrow passband, and its fabrication method is easy and flexible. The lasing oscillation shows a narrower bandwidth than SOA-based multi-wavelength fiber lasers utilizing some other kinds of wavelength selective components. Methods to optimize the laser performance are also discussed.

Photonic Bandgap Fiber Filter Design Based on Nonproximity Resonant Coupling Mechanism

The possibility of designing compact ultranarrow bandpass filters based on the phenomenon of nonproximity resonant tunneling in multicore photonic bandgap fibers is proposed and numerically demonstrated in this investigation by making use of versatile algorithms based on the finite-element method. The proposed multifunctional assembly exhibits bandpass transmission characteristics at four closed spaced wavelengths with a 3-dB bandwidth of about 1.2 nm and an insertion loss of about 0.8dB. The isolation level between neighbor channels, ranging from 12dB up to 15 dB, could be achieved at optical frequencies. The overall device performance offers some promising propagation characteristics for various all-fiber narrow bandpass filters.

Proposal for an Ultranarrow Passband Using Two Coupled Rings

We demonstrate theoretically that a simple two-coupled-ring structure yields very narrow resonances in the transmission spectra, provided the loss is very small. The linewidth is smallest when the path lengths of the two rings have a ratio of two. Relative to the single ring, the linewidth is reduced beyond the size scaling by the intensity buildup factor in the second ring. In the lossless case, the linewidth can be two orders of magnitude narrower. The enhancement can still be seen for experimentally demonstrated silicon-on-insulator microrings.

Single-longitudinal-mode fiber ring laser using internal lasing injection and self-injection feedback

A single-longitudinal-mode (SLM) fiber ring laser is demonstrated by introducing internal lasing injection and self-injection feedback. Internal lasing, generated in an auxiliary cavity, interacts with the laser oscillation in a main cavity to suppress mode hopping. Self-injection feedback loops are incorporated in the main cavity to serve as laser mode filters. Neither an ultra-narrow bandpass filter nor a precise control for laser cavity length is required in achieving stable SLM operation.

Single-longitudinal-mode dual-wavelength fiber ring laser by incorporating variable saturable absorbers and feedback fiber loops

A single-longitudinal-mode dual-wavelength fiber ring laser is proposed and demonstrated experimentally by introducing feedback fiber loops and a variable saturable absorber in a fiber ring cavity. A dynamic ultra-narrow bandpass filter is formed by the combined interactions of cascaded fiber Bragg gratings, feedback fiber loops and low-pumped erbium-doped fiber. Both ultra-narrow bandpass filter and accurate control for the cavity length are not required for the single-longitudinal-mode performance. The proposed scheme offers a possibility of generating terahertz waves by photomixing the lasing wavelengths in a high-speed photodetector.

Single-longitudinal-mode fiber ring laser using fiber grating-based Fabry–Perot filters and variable saturable absorbers

A single-longitudinal-mode (SLM) fiber ring laser is demonstrated by incorporating a fiber Bragg grating (FBG)-based Fabry–Perot (F–P) filter and a variable saturable absorber in a fiber ring cavity. An ultra-narrow bandpass filter is established by the combined mode filtering of the FBG-based F–P filter and the variable saturable absorber. No accurate control for cavity length is required, and stable single longitudinal-mode operation without mode hopping is conveniently achieved.

A high-performance ultra-narrow bandpass HTS filter and its application in a wind-profilerradar system

This paper reports a recent development of a narrowband high-temperaturesuperconducting (HTS) bandpass filter with a fractional bandwidth of 0.35%in the L band. The filter exhibits a 10-pole quasi-elliptic function responseimplemented with a cascaded quadruplet coupling structure. The measuredfilter shows a midband insertion loss of 0.26 dB and a return loss better than−15 dB overthe passband. Steep rejection slopes are obtained at the band edges and the measured skirt slope hasexceeded 120 dB MHz−1, resulting in an excellent out-of-band rejection very close to the band-edge. Combining thisfilter together with a special designed low-noise amplifier (LNA) as well as a cryo-cooler, anHTS subsystem was then constructed and mounted in the front end of a wind-profiler radarsystem, substituting the corresponding conventional parts. A field trial has shown that theHTS filter could markedly improve the sensitivity as well as the anti-interference capabilityof a wind-profiler radar system.

Ultranarrow bandpass hybrid filter with wide rejection band

The theoretical study and the experimental realization of an ultranarrow bandpass filter, joining a fiber Bragg grating and a dielectric mirror directly deposited at the extremity of the fiber tip, is presented. The features of such a filter are in very good accordance with the results of theoretical simulations.

Non-proximity resonant tunneling in multi-core photonic band gap fibers: An efficient mechanism for engineering highly-selective ultra-narrow band pass splitters

The objective of the present investigation is to demonstrate the possibility of designing compact ultra-narrow band-pass filters based on the phenomenon of non-proximity resonant tunneling in multi-core photonic band gap fibers (PBGFs). The proposed PBGF consists of three identical air-cores separated by two defected air-holes which act as highly-selective resonators. With a fine adjustment of the design parameters associated with the resonant-air-holes, phase matching at two distinct wavelengths can be achieved, thus enabling very narrow-band resonant directional coupling between the input and the two output cores. The validation of the proposed design is ensured with an accurate PBGF analysis based on finite element modal and beam propagation algorithms. Typical characteristics of the proposed device over a single polarization are: reasonable short coupling length of 2.7 mm, dual bandpass transmission response at wavelengths of 1.339 and 1.357 mum, with corresponding full width at half maximum bandwidths of 1.2 nm and 1.1 nm respectively, and a relatively high transmission of 95% at the exact resonance wavelengths. The proposed ultra-narrow band-pass filter can be employed in various applications such as all-fiber bandpass/bandstop filtering and resonant sensors.