Chirped Fiber Gratings Research Articles

Simple model of errors in chirped fiber gratings

A simple etalon based model is presented to show the origin of the wavelength-dependent ripples in the group delay and phase, and in the intensity of optical signals reflected from chirped fiber gratings. The simplicity of the model allows intuitive understanding of the effects, and quantitative predictions. We derive accurate scaling laws that allow the experimenter to make quantitative connections between the grating writing process parameters and grating performance.

Reduction of group delay ripple of multi-channel chirped fiber gratings using adiabatic UV correction

We demonstrate reduction of group delay ripple (GDR) from 24 ps to 9 ps peak to peak in a four channel 43 Gb/s dispersion compensating chirped fiber grating by adiabatic UV post processing. The eye opening penalty due to the grating GDR was improved from ~2dB to <1dB for all of the channels over a range of carrier frequencies of 15GHz. Our results demonstrate that at 43 Gb/s, the adiabatic UV correction technique is sufficient to substantially improve multi-channel fiber grating performance. We also discuss three limitations of the correction technique which cause GDR to vary from channel to channel: Noise in the sampling function, cladding mode loss, and varying channel reflectivity. While these limitations are visible in our results they do not reduce the effectiveness of the adiabatic correction for our gratings.

Dispersion-order selectable chromatic dispersion compensator using strain-profile modification blocks

A new method for tuning the dispersion profile of a fiber grating is described. The method involves compressing the fiber grating attached to a structure in which the cross-sectional area varies with its position. Because the cross-sectional area defines the compression rate, the local Bragg reflection wavelength that determines the dispersion profile varies along the position. A structure in which the cross-sectional area can be simply altered by inserting-extracting a part of structure was designed. Therefore, the dispersion order of the fiber grating attached to the structure can be selected. Using the method, a linearly-quadratically chirped fiber grating was made and various group delay slopes depending on the applied stress were obtained.

Design of broadband and arbitrary profile filters using large chirped fiber grating

AbstractA method is presented for designing and fabricating broadband and arbitrary profile filters using large chirped fiber grating. The relationship between grating reflectivity and chirp coefficient is discussed. By changing the ultraviolet (UV) light exposure dose along the grating, the complex refractive index modulation profile can be obtained. A broadband filter used for sensing with a linear reflectivity profile is produced through this method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 115–117, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11143

Tunable dispersion compensator based on distributed Gires-Tournois etalons

We report a novel tunable dispersion compensator (TDC) based on all-fiber distributed Gires-Tournois etalons (DGTE), which is formed by overlapped chirped fiber gratings. Two DGTEs of opposite dispersion slope work together to generate a tunable periodical dispersion profile. The demonstrated TDCs have the advantages of multichannel operation, extremely low group-delay ripple, low loss, and low cost.

Improvement of composite second-order and composite triple-beat performances by using chirped fiber gratings in a wavelength-division-multiplexing transport system

We present a two-wavelength wavelength-division- multiplexing (WDM) externally modulated transport system that uses chirped fiber gratings (CFGs) to reduce the fiber dispersion and cross- phase modulation (XPM)-induced crosstalk simultaneously. In compari- son to a two-wavelength WDM externally modulated transport system without CFGs, good performances of composite second-order (CSO) >67 dB and composite triple-beat (CTB) >65 dB distortions are ob- tained, accompanied by acceptable carrier-to-noise ratio (CNR) >50 dB value in our proposed system over a 100-km single-mode fiber (SMF) transport. © 2003 Society of Photo-Optical Instrumentation Engineers.

A simple method for the fabrication of intrinsically apodized chirped fibre Bragg gratings

A new and simple fabrication technique is reported for the UV inscription of intrinsically apodized chirped fibre gratings at an arbitrary Bragg wavelength employing a single chirped phase-mask in a scanning Talbot interferometer set-up. Chirped gratings have been successfully produced over a large wavelength range and with bandwidths up to 5 nm. These gratings exhibit the time-delay response of a small ripple effect. In the present paper a comparison with previously reported fabrication methods is given, showing the advantages and disadvantages of the different methods.

Wideband true-time-delay beam former that employs a tunable chirped fiber grating prism.

A fiber grating prism that consists of four tunable chirped-grating delay lines for wideband true-time-delay beam forming is proposed and demonstrated. The chirped gratings are produced by use of the grating bending technique in which a uniform grating is surface mounted on a simply supported beam. We obtained chirped gratings with different chirp rates by bending the uniform gratings with different beam deflections. Four linear chirped fiber gratings with identical spectral width but linearly increased grating length are fabricated. The spectra and time-delay responses of the tunable chirped gratings are measured. A chirped-grating prism for wideband true-time-delay beam forming by use of four chirped gratings is constructed and tested experimentally. We obtained different time delays by tuning the wavelength of the optical carrier. The proposed true-time-delay beam former with a four-element phased-array steerer is suitable for continuous beam forming at microwave frequencies up to 20 GHz.

Improving the performance of fiber gratings with sinusoidal chirps.

Sinusoidal chirps are introduced in fiber gratings to improve their performance as dispersion compensators and multichannel filters. The sinusoidally chirped fiber gratings exhibit a flattop spectrum with steep edges and high reflectivity. The bandwidth utilization defined as the ratio of -1:-30-dB bandwidth could be very high (>0.85). This structure can be applied to the sampled fiber gratings to enhance channel uniformity. We demonstrate 264 uniform channels with a 25-GHz-spacing for high-density-wavelength multiplexing applications. Multichannel dispersion compensations with seven uniform channels of 50-GHz-spacing in short fiber gratings are also demonstrated. The impact of possible fabrication errors on the spectra of the gratings is discussed.

Study on sampled chirped fiber gratings

A new method on the basis of the coherence theory is presented to analyze the sampled chirped fiber gratings (SCFGs). Comparing with the usual transfer matrix method based on coupling-wave equation, this new method provides a more complete and correct analytical results. 10 channels wavelength SCFG are fabricated, with the dispersion of −1300 ps/nm, the wavelength spacing between two neighboring channels of 0.8 nm and the ripples of time delay of less than 50 ps in the bandwidth of 0.6 nm.

Dispersion compensation and crosstalk reduction in a bidirectional dense wavelength division multiplexing cable television system

We propose and demonstrate a bidirectional dense wave- length division multiplexing cable television system that uses large effec- tive area fibers (LEAFs) as transmission fibers and chirped fiber grating (CFG) as a dispersion compensation device to reduce the dispersion and cross-phase modulation (XPM)-induced crosstalk. By comparing the system link with the transmission length of a 50-km single-mode fiber (SMF) without CFG, good performances of carrier-to-noise ratio (CNR) >50 dB, a composite second order (CSO) >69 dB, and a composite triple beat (CTB) >66 dB are obtained in our proposed system over a 50-km LEAF transport. © 2003 Society of Photo-Optical Instrumentation Engineers. (DOI: ORACLE)

Influence of non-ideal chirped fibre grating characteristics on dispersion-compensated analogue optical links in presence of fibre-induced SPM

The impairments produced by fibre nonlinearities and non-ideal chirped fibre grating (CFG) characteristics in dispersion-compensated analogue optical systems are investigated. The simulation results show that the non-ideal CFG reflectivity and group delay characteristics give rise to amplitude ripple in the compensated system frequency response, whereas the fibre nonlinear effects set a maximum achievable performance that is dependent on the residual dispersion.

The Bragg reflection characteristics of the fibre grating formed by chirped ultr ashort laser pulses

Under the illumination of 800 nm femtosecond laser pulse, two-photon absorption phenomenon can occur in the photosensitive glass As2S3. When a chirped femtosecond laser pulse meets with another femtosecond laser pulse in an As2S3 fibre, the interference pattern can be recorded permanently as a chirped grating. In this paper, the relation between the structure of the chirped fibre grating and the parameters of the incident femtosecond pulse is described. Numerical calculations show that the chirped fibre grating has a broad Bragg reflection spectrum.

Multiwavelength Linear-Cavity Fiber Laser Source Using a Sagnac Interferemetric Filter and a Strain-Induced Chirped Fiber Grating

Multiwavelength Linear-Cavity Fiber Laser Source Using a Sagnac Interferemetric Filter and a Strain-Induced Chirped Fiber Grating

Highly tunable optically switched time delay line for transversal filtering

A novel tunable dispersion device, based on two chirped fibre gratings subjected to non-uniform magnetic fields, is presented. A large degree of tunability is achieved from 250 to 750 ps/nm. This is used to demonstrate RF filtering in the 3–11 GHz range.

Multiwavelength Linear-Cavity Fiber Laser Source Using a Sagnac Interferemetric Filter and a Strain-Induced Chirped Fiber Grating

A novel multiwavelength linear-cavity fiber laser source using a strain-induced chirped fiber Bragg grating, a Sagnac interferemetric filter, and Erbium-Ytterbium codoped fibers is proposed and demonstrated for the first time. The Sagnac interferemetric filter, which acts as a full-reflecting mirror, consists of a polarization-maintaining directional coupler and two pieces of polarization-maintaining fibers. The strain-induced chirped FBG, which acts as a partial-reflecting mirror, is achieved by bending a uniform FBG bonded at a slant onto the lateral surface of a simply supported beam. By tuning the strain-induced chirped FBG, desirable lasing wavelength and number can be easily achieved.

광변조기의 양방향 변조를 이용한 chirped fiber grating의 시간지연 측정법

광변조기의 양방향 변조를 이용한 chirped fiber grating의 시간지연 측정법

Group-delay-tailored chirped fiber Bragg gratings using a tapered elastic plate

A new method to induce a strain gradient on a fiber Bragg grating is described. The method can be used to generate arbitrary strain distributions along the fiber. The objective of the method was to apply strain to a fiber grating that is attached on an appropriately tapered elastic plate. Using this method, linearly/nonlinearly chirped fiber gratings were prepared. Various group delay slopes were obtained depending on the plate shape and the applied strain. In addition, the repeatability could be maintained by adopting a feedback control method for the strain adjustment.

Continuous true-time-delay beamforming for phased array antenna using a tunable chirped fiber grating delay line

In this letter, we demonstrate a new five-element true-time-delay (TTD) system that uses only a single tunable linear chirped fiber grating (TLCFG) delay line for continuous TTD beamforming. The system avoids the complicated wavelength tuning and synchronal control of the tunable lasers as well as the tunable bandpass filters. Different time delays are achieved by tuning the chirp rate of the TLCFG, to which a multiwavelength laser source that carries the RF signal is applied. The time delay responses of the TTD system are measured experimentally, which agree well with the theoretical analysis. The beampointing angle can be controlled continuously by changing the chirp rate of the TLCFG. The minimum time delay step can be much smaller than 1 ps thanks to the high position resolution of the actuator.

Dispersion Compensation in Externally Modulated Transmission System Using Chirped Fiber Grating

We present an externally modulated NTSC AM-VSB erbium-doped fiber amplifier (EDFA)-repeated system in the 1550 nm region which uses a chirped fiber grating (CFG) as a dispersion compensation device. In contrast to the conventional externally modulated fiber optical CATV systems, either with or without dispersion compensation fiber (DCF), good performances of carrier-to-noise ratio (CNR) S 50 dB, composite second order (CSO) S 74 dB, and composite triple beat (CTB) S 65 dB were achieved for the full channel band after a 100-km single-mode fiber (SMF) transmission.