Nonlinearly Chirped Fiber Bragg Grating Research Articles

Spectral properties of nonlinearly chirped fiber Bragg gratings for optical communications

Numerical investigation of spectral properties of nonlinearly chirped grating under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equations using transfer matrix method. Our findings show that, by optimizing the linear and higher-order nonlinear chirp coefficients, the reflection bandwidth, side lobes, and group delay could be tunable with the increment of the applied tension. Indeed, the fiber grating chirp is tunable by the applied tension represented by the increase of the reflection spectrum bandwidth and the decrease of the group delay ripples. Besides, the time delay curve typically exhibits two behaviors within the rejection bandwidth: a linear variation for large wavelengths and a quadratic variation for short wavelengths. Therefore, with such kind of grating, it is possible to compensate both linear and nonlinear dispersion in high speed optical networks.

The investigation of the parameter choice of the nonlinearly chirped FBG

Purpose – Correctly choosing the nonlinearly chirped fiber Bragg grating (NLCFBG) parameter is very important, which may instruct the effective manufacture grating. The purpose of this paper is to analyze some kinds of curve reflection spectrums and time delays of the FBG.Design/methodology/approach – In this paper, some kinds of curve reflection spectrums and time delays of the FBG are analyzed. The paper makes the numerical simulation of the spectrum character and time delay about some kinds of FBG. The relation between the modulation intensity and linear chirp coefficient c1 of the FBG is studied for the first time. The transformation of the curve about time delay is compared at different modulation intensity.Findings – The authors investigate the number of dots which is used to draw a graph of the spectrum character and time delay, and is found that the graph of the spectrum character and time delay is broken off when the graphed number of dots is too less. Also, the authors study the reflection spect...

Chirped RF Pulse Generation Based on Optical Spectral Shaping and Wavelength-to-Time Mapping Using a Nonlinearly Chirped Fiber Bragg Grating

Chirped radio-frequency (RF) pulse generation based on optical spectral shaping and nonlinear wavelength-to-time mapping in a nonlinearly chirped fiber Bragg grating (NLCFBG) is investigated. In the proposed approach, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is shaped by an optical filter that has a sinusoidal frequency response. The spectrum-shaped optical pulse is sent to the NLCFBG, to implement nonlinear wavelength-to-time mapping. A chirped electrical pulse with the central frequency and chirp rate determined respectively by the first- and second-order dispersions of the NLCFBG is then obtained at the output of a high-speed photodetector. An approximate model that describes the chirped RF pulse generation is derived, which is verified by numerical simulations. Chirped pulse generation with a pulse compression ratio as high as 450 is demonstrated. The key device in the chirped RF pulse generation system is the NLCFBG, which is investigated in detail with an emphasis on the influence of its group delay ripples on the performance of the pulse generation system. Techniques to design and fabricate the NLCFBG are also discussed. The proposed approach provides a potential solution for the generation of chirped RF pulse with a high central frequency and large chirp rate for applications in pulse compression radar systems.

Photonic Generation of Chirped Millimeter-Wave Pulses Based on Nonlinear Frequency-to-Time Mapping in a Nonlinearly Chirped Fiber Bragg Grating

A novel approach to optically generating chirped millimeter-wave pulses with tunable chirp rate based on spectral shaping and nonlinear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed approach, the optical power spectrum of an ultrashort pulse from a femtosecond pulsed laser is shaped by a two-tap Sagnac loop filter that has a sinusoidal frequency response. The spectrum-shaped optical pulse is then sent to a nonlinearly chirped fiber Bragg grating (NL-CFBG) with a tunable nonlinear group delay to serve as a high-order dispersive device to perform the nonlinear frequency-to-time mapping. A chirped electrical pulse with a high central frequency and large chirp rate is then generated at the output of a high-speed photodetector. The NL-CFBG used in the proposed system is produced from a regular linearly chirped fiber Bragg grating based on strain-gradient beam tuning. A detailed theoretical analysis on the chirped pulse generation is developed, which is verified by numerical simulations and experiments. Millimeter-wave pulses with a central frequency of around 35 GHz and instantaneous frequency chirp rates of 0.053 and 0.074 GHz/ps are experimentally generated.

Advances in the Design and Fabrication of High-Channel-Count Fiber Bragg Gratings

In this paper, we review our recent developments in the design and fabrication techniques for high-channel-count fiber Bragg gratings (FBGs). We have presented a theory for the phase-only sampled FBG and demonstrated that a sampled FBG of N channels would require radicN/etamiddot times higher maximum reflective index modulation than that of the single-channel FBG. We experimentally demonstrate a 45- and 81-channel linearly chirped FBG for nearly whole C-band dispersion compensation, which is fabricated with a novel diffraction precompensated phase mask. The grating specifications obtained agree well with the theoretical design. We have presented a novel method for multichannel FBG design, which enables us to design any kind of multichannel FBGs, where the spectrum response of each channel could be either identical or nonidentical. Particularly, the nine-channel nonlinearly chirped FBG, which is used as a simultaneous dispersion and dispersion slope compensator, has been demonstrated.

Thermally tunable dispersion compensator in 40-Gb/s system using FBG fabricated with linearly chirped phase mask

An improved design and fabrication method of nonlinearly chirped fiber Bragg gratings is demonstrated. Based on reconstruction-equivalent- chirp method, the nonlinearly chirped fiber Bragg grating is realized with a linearly chirped phase mask instead of a uniform one, which improves the performance of the device. Coated with uniform thin metal film, the obtained grating works as a tunable dispersion compensator with a tuning range ~200ps/nm, peak-to-peak group delay ripple <14ps and 3-dB bandwidth approximately 2nm. Employing this device, the power penalty in a 40- Gb/s X5/10km conventional single mode fiber using carrier suppressed return-to-zero format is less than 0.7dB at a BER=10-10.

Advanced design of a multichannel fiber Bragg grating based on a layer-peeling method

A multichannel fiber Bragg grating (FBG) design based on a discrete layer-peeling method is described. This novel method enables us to design any kind of multichannel FBG in which the spectrum responses of the channels can be either identical or nonidentical. In particular, a nine-channel dispersion-free FBG and a nine-channel nonlinearly chirped FBG used simultaneously as chromatic dispersion and dispersion slope compensators are described. Unlike the general multichannel FBG designed by a sampling method, these two gratings have ideal flat-topped profiles in both the transmission and the reflection spectra. By optimally detuning the relative phases for the multiple-spectrum channels with an iterative layer-peeling method, we can make maximum use of length-limited photosensitive fiber. Moreover, we show numerically that one can reduce or eliminate the oscillation that inherently exists in the index-change envelope of our multichannel FBG by accepting a decreased extinction ratio of the in-band signal to the out-of-band noises.

Tuning sampled nonlinearly chirped fiber Bragg gratings with adjustable chirp and fixed center wavelength

AbstractA simple method for tuning a sampled nonlinearly chirped fiber Bragg grating (SNCFBG) without a center‐wavelength shift is demonstrated experimentally. A uniform sampled fiber Bragg grating (SFBG) is adhered on a bent plastic plate along a precalculated curve. The nonlinear chirp among the SFBG channels is tuned when a displacement is applied to the free end of the plastic plate and the central wavelength of the grating is fixed. The dispersion varies from −996.3 to −117.9 ps/nm in the center channel and the center‐wavelength shift is as small as 0.06 nm in the tuning process. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 432–434, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20493

Using sampled nonlinearly chirped fiber Bragg gratings to achieve 40-Gbit/s tunable multi-channel dispersion compensation

We demonstrate tunable chromatic dispersion in a 4×40-Gbit/s wavelength-division-multiplexed (WDM) transmission experiments using single sampled nonlinearly chirped fiber Bragg grating (NC-FBG) with negligible errors from higher order dispersion or two cascaded inverse sampled NC-FBG to cancel the higher order dispersion within the data’s bandwidth. In both the single FBG and cascaded FBG configurations, <3 dB penalty is achieved for all four WDM channels even though the eye is completely closed without compensation.

Fabrication of Tunable Sampled Nonlinearly Chirped Fiber Bragg Gratings with a Simple Method

In this letter a simple method for fabricating tunable sampled nonlinearly chirped fiber Bragg gratings (SNCFBGs) is demonstrated experimentally. A SNCFBG is formed when tension is applied to an etched sampled fiber Bragg grating (SFBG), whose cross-section area's reciprocal varies along the length of the SFBG. The chirp of the grating period and the sampled period can be tuned by adjusting the strain gradients, and the dispersion and dispersion slope can also be compensated.

Real-time group-velocity dispersion monitoring and automated compensation without modifications of the transmitter

We show that the clock signal can be regenerated, or suffer fading, through a dispersive fiber link for NRZ or RZ data, respectively. The clock regenerating and fading effects can be used to monitor the accumulated chromatic dispersion for unambiguous windows of ±900 ps/nm for NRZ systems and ±640 ps/nm for RZ systems at 10 Gbit/s. We also demonstrate dynamic dispersion compensation for both NRZ and RZ data at 10 Gbit/s using the extracted power as a control signal to stretch a nonlinearly chirped fiber Bragg grating.

Electrically tunable dispersion compensator based on nonlinearly chirped fiber Bragg grating

AbstractA new prototype of a compact and power‐efficient tunable dispersion compensator is demonstrated. To our acknowledge, this is the first time a tunable dispersion compensator using nonlinearly chirped fiber Bragg grating, coated with on‐fiber uniform metal heater, has been realized. A remarkable degree of dispersion tunability, as much as approximately 800 ps/nm, has been demonstrated. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 288–292, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10897

A novel method for creating linearly and nonlinearly chirped fiber Bragg gratings

We propose a novel and flexible method for controlling the chirp rate of a linearly chirped fiber Bragg grating (FBG) and nonlinearly chirped FBG by adhering a uniform FBG onto a plastic plate with a pre-calculated curvature and applying an axial force on the plate. The center wavelength shift was measured to be only 0.1 nm, which is small compared with the previously reported techniques. The dispersions of the linearly chirped FBG and the nonlinearly chirped FBG were measured to be about 1200 ps/nm and 125 ps/nm/nm, respectively, and the bandwidth of the chirped FBG was about 0.5 nm.

Tunable chromatic dispersion compensation in 40-Gb/s systems using nonlinearly chirped fiber Bragg gratings

Chromatic dispersion management and tunable compensation are essential features of 40-Gb/s wavelength-division-multiplexed (WDM) systems. In this paper, we demonstrate both single and multi channel 40-Gb/s tunable dispersion compensation using nonlinearly chirped FBGs (NC-FBGs). For single channel compensation, we show that the NC-FBG can be tuned over a moderate range (/spl sim/400 ps/nm) with tolerable third-order dispersion (<200 ps/nm/sup 2/) within the channel's data bandwidth (intrachannel third-order dispersion). For multichannel systems, we demonstrate 4/spl times/40-Gb/s tunable dispersion compensation using sampled NC-FBGs in two configurations. First, we show that a single, sampled NC-FBG with fairly low intrachannel third-order dispersion induces negligible penalty on all four channels. This solution has a limited dispersion tuning range because of the deleterious intrachannel third-order dispersion. We show a moderate tuning range from -300 ps/nm to -700 ps/nm. Second, we demonstrate that two inverse, concatenated, sampled NC-FBGs can cancel the high deleterious intrachannel third-order dispersion, thus extending the dispersion tuning range. This solution provides both positive and negative dispersion values by stretching the two NC-FBGs separately. A tuning range of -300 ps/nm to +300 ps/nm with zero intrachannel third-order dispersion is shown.

Adaptive dispersion slope equalizer using a nonlinearly chirped fiber Bragg grating pair with a novel dispersion detection technique

We realized the first adaptive-dispersion equalizer that equalizes dispersion over a wide wavelength range (6 nm) in the zero-dispersion wavelength region of a dispersion-shifted fiber (DSF). The equalizer is based on a pair of nonlinearly chirped fiber Bragg gratings, which are designed to equalize exactly the dispersion profile of a DSF. The dispersion changes were tracked using a technique that employs opposite dispersion fibers to identify the sign of the dispersion change. Unlike previous approaches, no additional sources or changes in the source wavelength are required. We demonstrate the adaptive equalization of the dispersion changes in an 83-km DSF, induced by temperature changes between -10/spl deg/C and 60/spl deg/C.

A wavelength-tunable dispersion equalizer using a nonlinearly chirped fiber Bragg grating pair mounted on multilayer piezoelectric transducers

We realized a wavelength-tunable dispersion equalizer using a pair of nonlinearly chirped fiber Bragg gratings mounted on multilayer piezoelectric transducers. The operation region can be continuously tuned up to 7 nm by applying 50 V. This device enables us to equalize the second- and third-order dispersion of dispersion-shifted fibers with different zero dispersion wavelengths over 6 mn. This performance shows that our equalizer can be employed for adaptive equalization.

Tunable compensation of the dispersion slope mismatch in dispersion-managed systems using a sampled nonlinearly chirped FBG

We demonstrate dispersion slope compensation for three 10-Gbit/s wavelength-division-multiplexing (WDM) channels using a sampled nonlinearly chirped fiber Bragg grating (FBG) in a dispersion-managed transmission system. The replicated wavelength bands of the sampled FBG have a different wavelength separation than the WDM channels, causing each channel to experience a different dispersion compensation that can be tuned upon stretching of the FBG. We achieve significant power penalty reduction for all three channels using our dispersion-slope-compensation method with a tunable amount of dispersion over 900 and 1200 km fiber links.

Simultaneous tunable dispersion compensation of many WDM channels using a sampled nonlinearly chirped fiber Bragg grating

We fabricated and characterized a tunable dispersion compensator for multiple wavelength-division-multiplexed (WDM) channels using a sampled nonlinearly chirped fiber Bragg grating, the channel dispersion can be adjusted from -200 to -1200 ps/nm, we demonstrate tunable dispersion compensation for three channels in a 10-Gb/s WDM system. All three channels achieve a BER=10/sup -9/ after propagating through either 60 or 120 km of standard single-mode fiber.

Fabrication of non-linearly chirped fiber Bragg gratings for higher-order dispersion compensation

Broadband non-linearly chirped fiber Bragg gratings were fabricated by using a step-chirped phase mask. These gratings were used to construct a third-order dispersion compensator with a bandwidth of over 6 nm around the zero dispersion wavelength. The dispersion slope is sufficient for compensating a 60-km-long dispersion-shifted fiber.

Second- and third-order dispersion compensation of picosecond pulses achieved by combining two nonlinearly chirped fibre Bragg gratings

We used a combination of nonlinearly chirped fiber Bragg gratings to demonstrate for the first time to our knowledge, second- and third-order dispersion compensation for 1.6-ps and 3.5-ps pulses transmitted over a 66-km-long-shifted fiber around the zero-dispersion wavelength.