A novel all fiber microwave transversal filter with complementary outputs

A novel all-fiber bipolar delay line filter is realized in a single-line cascaded high birefringence fiber structure. Optically coherent operation is achieved with suppression of interference noise. Complementary filter outputs give simultaneous lowpass and highpass responses.

A novel tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a DFB laser diode and fiber Bragg grating

We demonstrate experimentally a novel and simple tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a distribution feedback laser diode and high reflection fiber Bragg gratings (FBGs). In this filter, variable time delay is provided by cascaded high reflection fiber Bragg gratings (FBGs), and the tuning of the filter is realized by tuning different FBG to match the fixed carrier wavelength, or adjusting the carrier wavelength to fit different FBG. The incoherent negative tapping is realized by using the carrier depletion effect in a distribution feedback laser diode.

Novel design of FBG-based composite double notch VSB filter for DWDM systems

This paper proposes a novel design of optical filters based on a cascade of tailored fiber Bragg gratings (FBGs) operating in the transmission regime. As an example of the application of the proposed general technique, ultranarrow optical vestigial sideband (VSB) filtering based on two FBGs operating in the transmission regime was examined. This design can be easily implemented by writing FBG-based filters for each wavelengthdivision-multiplexing channel before multiplexing. © 2006 IEEE.

Passive scene imaging of absorbing gases by narrowband dielectric filter modulation

This paper examines a method for locating within a scene a distribution of an absorbing gas using a passive imaging technique. An oscillatory modulation of the angle of a narrowband dielectric filter located in front of a camera imaging a scene, gives rise to an intensity modulation that differs in regions occupied by the absorbing gas. A preliminary low cost system has been constructed from readily available components which demonstrates how the location of gas within a scene can be implemented. Modelling of the system has been carried out, especially highlighting the transmission effects of the dielectric filter upon different regions of the image.

Design of FBG-based ultra-narrow asymmetric filter for transmission with 0.8 bit/s/Hz spectral efficiency without polarisation multiplexing

We propose a novel approach to ultra-narrow optical filtering based on a specially designed slightly asymmetric filter, which can be fabricated using fibre Bragg gratings. A feasibility of 8×40 Gbit/s DWDM RZ transmission with 0.8 bit/s/Hz spectral efficiency (without polarisation multiplexing) over 1280 km of SMF/DCF link without FEC has been confirmed by numerical modelling. © 2004 Elsevier Inc. All rights reserved.

The effects of coloured light filter overlays on reading rates in age-related macular degeneration

Purpose: To determine the effect of coloured light filter overlays on reading rates for people with age-related macular degeneration (AMD). Method: Using a prospective clinical trial design, we examined the null hypothesis that coloured light filter overlays do not improve reading rates in AMD when compared to a clear filter. Reading rates for 12 subjects with non-exudative AMD, associated with a relative scotoma and central fixation (mean age 81 years, SD 5.07 years) were determined using the Rate of Reading Test® (printed, nonsense, lower case sans serif, stationary text) with 10 different, coloured light filter overlays (Intuitive Overlays®; figures in brackets are percentage transmission values); rose (78%), pink (78%), purple (67%), aqua (81%), blue (74%), lime-green (86%), mint-green (85%), yellow (93%), orange (83%) and grey (71%). A clear overlay (Roscolene # 00) (360 cdm-2) with 100% transmittance was used as a control. Results: ANOVA indicated that there was no statistically significant difference in reading rates with the coloured light filter overlays compared to the clear filter. Furthermore, chi-squared analysis indicated that the rose, purple and blue filters had a significantly poorer overall ranking in terms of reading rates compared to the other coloured and clear light filters. Conclusion: Coloured light filter overlays are unlikely to provide a clinically significant improvement in reading rates for people with non-exudative AMD associated with a relative scotoma and central fixation. Copyright © Acta Ophthalmol Scand 2004.

Multiwavelength generation in a random distributed feedback fiber laser using an all fiber Lyot filter

Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting subnanometer line-widths. A flat power distribution over multiple lines is obtained, which indicates that the power between lines is redistributed in nonlinear mixing processes. The multiwavelength generation is observed both in first and second Stokes waves. © 2014 Optical Society of America.

Pulse shaping in mode-locked fiber lasers by in-cavity spectral filter

We numerically show the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity. Depending on the amplitude transfer function of the filter, we are able to achieve various regimes of advanced temporal waveform generation, including ones featuring bright and dark parabolic-, flat-top-, triangular- and saw-tooth-profiled pulses. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for controlling the dynamics of mode-locked fiber lasers. © 2014 Optical Society of America.

A nonreciprocal wavelength-interleaving bidirectional coherent fiber transversal filter

A bidirectional nonreciprocal wavelength-interleaving filter based on an optically coherent high birefringence fiber transversal filter structure is demonstrated. Stable, low loss operation is achieved with reconfigurable transfer characteristics for interleaved channel spacing of 0.8 nm with >30 dB isolation and ultra-low chromatic dispersion.

An optical pump controlled tunable phase-shifted fiber grating transmission filter

Optical pump controlled, remotely tunable phase-shifted fiber grating transmission filters were analyzed. The transmission peak had a full width hail maximum (FWHM) bandwidth. With increasing control pump power, the resonant peak shifted towards the longer wavelength side. The efficiency of the system was largely affected by the greater number of sections of doped fiber as well as the absence of recirculation of unabsorbed pump beam. The configuration, besides its simplicity and cost-effectiveness, exhibited wavelength-independent pump-induced phase shifts and no anisotropic effects during operation.

Supermode-noise suppression using a nonlinear Fabry–Pérot filter in a harmonically mode-locked fiber ring laser

A simple efficient method for stabilizing a harmonically mode-locked fiber ring laser is proposed. In this method, a linear optical filter and a nonlinear Fabry–Pérot filter in which the refractive index is optical intensity dependent are located in the laser cavity. The linear filter is used to select a fixed lasing wavelength, and the Fabry–Pérot filter introduces a negative all-optical feedback mechanism that is able to suppress pulse-to-pulse amplitude fluctuations in the laser cavity. The scheme was experimentally demonstrated using a fiber Bragg grating as the linear filter and a laser diode biased below threshold as the nonlinear Fabry–Pérot, and stable harmonically mode-locked pulses with a supermode noise suppression ratio >55 dB were obtained.

A novel dual complementary output optical fiber transversal filter for DWDM applications

A novel dual complementary output optical fiber transversal filter is realized for DWDM applications. Stable, simultaneous complementary filter responses with flattened passbands and large sidelobe suppressions are achieved with a single-line cascaded Hi-Bi fiber structure.

Band-pass filter with flat time delay response based on fiber grating Sagnac loop

We have developed the analytic expressions for the phase response and time delay of FBGSL of arbitrary grating structure and found that the results from the modelling are in excellent agreement with that of the experimentally measured real devices. The theoretical and experimental investigation clearly reveals that FBGSLs utilizing uniform and linearly chirped gratings exhibit a near-constant time delay in the passbands. Such multi-channel bandpass filters should be highly attractive to WDM applications as they are operating in transmission regime and offering near-zero dispersion.