In-line Optical Filter Research Articles

Doubly electrically tuned cylindrical Bragg fiber waveguide inline optical filter for multiwavelength LASER applications

In present communication, doubly tuned Bragg fiber waveguide low power inline optical filter with voltage tunable single crystal PMMA defect cavity is theoretically modeled and discussed using Henkel formalism in a cylindrical coordinate system for multiwavelength LASER applications. The structure provides photonic band gap (PBG) with a resonant transmission peak in the obtained PBG region. The defect cavity thickness is controlled by applying an external electric DC voltage. Initially, PBG of the proposed inline optical filter may tune-up to 828nm by modulating the incidence angle upto 80°. Thus, the resonant transmission peak also blue-shifted by 243nm, which can further tuned in presence of DC voltages and so-called doubly electrically tuned. Further, in doubly electrically tuned mode, the application range of such a device is very large up to 129nm for a small change in voltage range about 20V. Thus, the present device can be utilized as multiwavelength laser sources.

A novel Bragg fiber waveguide based narrow band inline optical filter

Theoretical analysis of Bragg fiber waveguide based inline optical filter having a defect layer is presented. Defect layer is introduced in Bragg fiber waveguide by breaking its cladding layer periodicity. Considering the cylindrical wave equations, the transmittance of proposed waveguide is obtained using transfer matrix method. It is observed that the proposed Bragg waveguide represent photonic band gap and a narrow defect mode (pass band) is present in this band gap region. This defect mode can be obtained in any position between the wavelength ranges 1.241 μm–1.550 μm with the help of incident angle of light. The narrowness of the defect mode depends on the number of unit cell present in the cladding region. This proposed waveguide may be used to design a narrowband transmission filters.

Analysis of Fiber Bragg Gratings for the Elimination of Realignment During the Life of the System While FBG Is Spliced Directly to the Doped Fiber

Fiber Bragg Grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.

Timing and phase jitter suppression in coherent soliton transmission.

We have revisited soliton transmission in the new context of coherent optical detection optimizing and comparing digital backward propagation and in-line optical filtering as a means to suppress soliton timing and phase jitter. We find that in-line optical filtering allows one to improve the reach of the soliton system by up to the factor of 2. Our results show that nonlinear propagation can lead to performance beyond the nonlinear Shannon limit.

Compact in-line optical notch filter based on an asymmetric microfiber coupler

Novel compact in-line optical filters with narrow rejection bandwidths are proposed, and one is experimentally demonstrated based on asymmetric microfiber (MF) couplers. It is composed of silica and bismuth-oxide-glass MFs and less than 500μm long. Single transmission dips in a wavelength range of up to 300nm are obtained, and the transmission extinction ratio is more than 30dB. Additionally, a -20 dB bandwidth of 0.88nm is achieved. This narrow bandwidth of the transmission notch benefits from the huge refractive index difference between the two MFs. These experimental results agree well with the theoretical predictions. With the advantages of having a simple structure, being fiberized, and having a small footprint, this device can be an attractive element for micro/nanophotonics, optical sensing, optical signal processing, and optical fiber communications.

Symbol Spaced Adaptive MIMO Equalization for Ultrahigh Bit Rate Metro Coherent Optical Links

A novel approach to symbol spaced adaptive multiple-input-multiple-output (MIMO) equalization is proposed. Different functionalities are defined for static versus adaptive equalizers, to minimize noise enhancement. Static equalizers are used for anti-aliasing filtering and bulk CD compensation, and a newly proposed modified-LMS-based adaptive MIMO equalizer is used to compensate for fiber random impairments such as residual CD and PMD. In addition, the proposed technique enables the use of low-cost reduced bandwidth components in both transmit and receive sides, and supports aggressive in-line optical filtering in the existing WDM network. Moreover, the proposed technique perfectly suits coherent metro applications, allowing significant power savings in application specific integrated circuit implementation.

PMD penalties in long nonsoliton systems and the effect of inline filtering

We consider the polarization-mode dispersion (PMD) tolerance of long nonsoliton systems. We find that the effect of PMD in such systems is to derail the nonlinear evolution of the waveform from its PMD-free trajectory at an early stage of transmission, leading to extremely high penalties at the receiver end. It is shown that PMD affects the propagating bandwidth in a way that is strongly correlated with the received penalty. Use of inline optical filters is shown to be extremely efficient in reducing the penalties caused by PMD.

Simulation of single-channel optical systems at 100 Gb/s

With the help of a computer simulation, we have investigated the conditions under which the transmission of light pulses through optical fibers may be possible over thousands of kilometers at a bit rate of 100 Gb/s. Employing an amplifier spacing of only 20 km, nonreturn-to-zero (NRZ), return-to-zero (RZ), and dispersion-managed solitons (DMSs) may all be useful provided that certain additional conditions are met. These include dispersion management by means of a dispersion map, a reduced dispersion slope, low polarization mode dispersion (PMD), and in-line optical filters.

Soliton-based return-to-zero transmission over transoceanic distances by periodic dispersion compensation

The accumulation of Gordon–Haus jitter can be effectively suppressed by the use of periodic dispersion compensation and in-line optical filters. The feasibility of 20-Gbit/s soliton-based transoceanic systems has been confirmed through 1000-km loop transmission experiments and 8100-km straight-line transmission experiments that employed periodic dispersion compensation. For a 20-Gbit/s, 9000-km transmission system, a Q2 of 19 dB, a sufficient power window of 2.5 dB, and robustness to repeater output power reduction have been demonstrated, as has compatibility with the conventional supervision scheme. A dramatic increase in system capacity can be expected from soliton wavelength-division multiplexing with periodic compensation of dispersion and its slope.

10 Gbit/s RZ-signal transmission over 12960 km in the anomalous regime with optimised in-line optical filters

An in-line filter arrangement is investigated experimentally for single-channel long-distance optical transmission in the anomalous region with periodic dispersion compensation. The optimal arrangement, along with the optimum compensation ratio and in-line amplifier output power, allows a 10 Gbit/s RZ signal to be successfully transmitted over 12960 km in a 720 km recirculating loop.

Reduction of Gordon-Haus timing jitter by periodic dispersion compensation in soliton transmission

A novel soliton transmission scheme to suppress the accumulation of the Gordon-Haus jitter using periodic dispersion compensation and inline optical filters has been proposed. With 90% dispersion compensation rate and optimum optical filters, a Q/sup 2/ of 19 dB and a large power window of 2 dB were confirmed for a 20 Gbit/s, 9000 km transmission system by using a 1000 km-long recirculating loop.

1111 km, two channel IM-DD transmission experiment at 2.5 Gb/s through 21 in-line erbium-doped fiber amplifiers

Two-channel transmission is demonstrated in a 2.5 Gb/s intensity-modulated direct-detection system over a distance of 1111 km, using 21 in-line erbium-doped fiber amplifiers. The two channels incur virtually no penalty when they are transmitted simultaneously. Owing to the use of gain filtering in the amplifiers instead of discrete in-line optical filters, the overall bandwidth of the link is about 15 nm, for a sensitivity penalty smaller than 1 dB on one single transmitted channel. >

Inline optical filter using lifted-off GaAs/AlGaAs multilayer

A new inline optical filter is reported. A GaAs/AlGaAs multilayer interference filter was lifted off its GaAs substrate by selective etching, and was sandwiched between two gradient-index rod lenses. Near-theoretical performance was obtained, with over 20 dB rejection in the stop band and less than 0.5 dB insertion loss at transmission peaks. This type of filter could be extremely useful in wavelength division multiplexed systems.