Dispersion Slope Compensation Research Articles

Integrated-optic chromatic dispersion compensator with completely passive operation and wide operational bandwidth

I report on a fiber chromatic dispersion compensator comprising an array of 100 fixed delay lines sandwiched by a pair of arrayed-waveguide grating-type wavelength filters. The requisite delay for the dispersion compensation is allocated to each demultiplexed wavelength component after the first wavelength filter, and the wavelength components are again multiplexed at the second filter. The flexible capability of delay pattern arrangement enables us to realize various fixed dispersion compensation characteristics. I show transmittance and relative delay time characteristics of a multichannel dispersion compensator for short-distance wavelength division multiplexing communication, and its application to dispersion compensation for a pulse amplitude modulation four signal. I also demonstrate the realization of a dispersion slope compensator for a dispersion-shifted fiber with this configuration.

Analysis of fiber Bragg grating with exponential–linear and parabolic taper profiles for dispersion slope compensation in optical fiber links

In this paper, the effect of various taper profiles on dispersion slope compensation in optical fiber links is studied. Theoretical and numerical investigation of the linear and nonlinear group delays of tapered fiber Bragg grating's (T-FBG) under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equation using transfer matrix method. Our study shows that the linear tapered FBG profile provide the best result than the linear-exponential profile which can compensate up to 500km. As result, the spectral characteristics of tapered grating allow them to be used efficiently in high bit rates WDM and long-haul optical communication systems for chromatic dispersion of single-mode fiber.

Broadband dispersion compensation of conventional single mode fibers using microstructure optical fibers

This paper presents a microstructure optical fiber for dispersion compensation in a wide range of wavelengths. The finite-element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed novel dispersion compensating fiber shows that it is possible to obtain a larger negative dispersion coefficient of about −130 to −360ps/(nmkm), better dispersion slope compensation, better compensation ratio, and lower confinement losses less than 10−2dB/km in the entire telecommunication (1400–1600nm) band by using a modest number of design parameters and very simple cladding design.

S+C+L波段色散斜率补偿光子准晶体光纤

针对光纤通信中的色散补偿,尤其是密集波分复用系统的多信道同时补偿的需求,提出了一种用于宽带色散斜率补偿的光子准晶体光纤.该光纤结构包层空气孔为准晶体排列,并且在纤芯引入了中心缺陷.通过对光纤特性的数值分析表明,在1 460-1 625 nm的光通信波段,该结构光纤的相对色散斜率为0.004 4-0.002 9 nm^-1,相对色散斜率与标准单模光纤近似相等,且负色散值达-2 476 ps·nm^-1·km^-1.对标准单模光纤进行色散补偿后,在S＋C＋L波段色散值为（-0.5-0）ps·nm^-1·km^-1.该光纤可用于对当前光纤通信系统进行宽带色散补偿,实现多信道同时补偿,简化结构,并降低补偿成本.

Design of Broadband Dispersion Compensating Photonic Crystal Fiber

This paper presents a triangular-lattice photonic crystal fiber for broadband dispersion compensation. The finite element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed dispersion compensating fiber shows that it is possible to obtain a larger negative dispersion coefficient of ?360 ps/(nm.km) at 1.55 ?m, better dispersion slope compensation, better compensation ratio in the entire telecommunication (1460-1640 nm) band by using a modest number of design parameters and very simple cladding design.

Higher-order dispersion compensation to enable a 36 μs wavelength-maintaining delay of a 100 Gb/s DQPSK signal

We demonstrate a method for dispersion slope compensation of a conversion/dispersion-based optical delay to enable 100 Gb/s operation based on a spatial light modulator and fiber Bragg gratings. A continuous delay of up to 3.6 micros for 100, 80, and 20 Gb/s differential quadrature phase-shift-keyed (DQSPK) and 50, 40, and 10 Gb/s differential phase-shift-keyed (DPSK) waveforms is shown. A time-delay bit-rate product of approximately 360,000 for 100 Gb/s DQPSK with wavelength-maintaining operation is achieved.

Simultaneous dispersion and dispersion-slope compensator based on a doubly sampled ultrahigh-channel-count fiber Bragg grating

A simultaneous dispersion and dispersion-slope compensator based on a doubly sampled fiber Bragg grating (FBG) with 153 channels has been demonstrated, which is obtained by simultaneously chirping the period of the seed grating and the periods of the two sampling functions. These two sampling functions are optimized with the simulated annealing algorithm and the Gerchberg-Saxton iterative method. Moreover, the spectral inclination (in reflection) inherently due to the different magnitudes of the channel dispersion has been successfully equalized.

Design of High-Channel-Count Multichannel Fiber Bragg Gratings Based on a Largely Chirped Structure

We propose a novel technique to design a high-channel-count, multichannel fiber Bragg grating (FBG) based on a largely chirped structure. The minimization of refractive-index modulation has been widely discussed in the previously demonstrated multichannel grating designs. The complexity of the grating structure, however, is also important from the point of view of practical fabrication. In this paper, the degree of grating complexity (DGC) is defined. We show that the DGC of a multichannel grating can be significantly reduced by designing a grating with a largely chirped structure. A detailed grating design process based on this technique is discussed, by which four multichannel gratings are designed and numerically studied, for applications such as periodic and nonperiodic spectral filtering, chromatic dispersion compensation and dispersion slope compensation. The proposed theory and examples show that different gratings with high-channel-count and multichannel responses can be designed and fabricated using a single commercially available phase mask, and all the gratings can be realized by a conventional FBG fabrication facility since the gratings have a low DGC with low index modulation.

Novel broadband dispersion compensating photonic crystal fibers: Applications in high-speed transmission systems

This paper reveals a novel dispersion compensating photonic crystal fiber (DC-PCF) for wide-band high-speed transmission systems. The finite-difference method with an anisotropic perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed novel DC-PCF shows that it is possible to obtain a larger negative dispersion coefficient, better dispersion slope compensation, and confinement losses less than 10 −4 dB/m in the entire S+C+L telecommunication band by using a modest number of design parameters. The proposed module can be used in 40 Gb/s dense wavelength division multiplexing (DWDM) systems in optical fiber communication networks.

Tunable dispersion slope compensator using two uniform fiber Bragg gratings mounted on S-shape plate

We propose and experimentally demonstrate a novel method for tunable dispersion slope compensation. We use two uniform fiber Bragg gratings (FBGs), a spatially designed S-bending stage and 4-port circulator. Two FBGs are mounted on each surface of a metal plate along the calculated quadratic curve. The dispersion slope (DS) can be tuned by adjusting a nonlinear strain along two uniform FBGs without changing second order dispersion as well as the central wavelength. In the experiment, a DS tuning range from -13.9 to -54.8 ps/nm(2) is achieved with the bandwidth of larger than 2.0 nm.

Reconfigurable Dispersion Equalizer Based on Phase-Apodized Fiber Bragg Gratings

We present a novel dispersion equalizer design for the compensation of chromatic dispersion and chromatic dispersion slope in WDM systems. The device is based on a cascade of complex quasi-periodic chirped fiber Bragg gratings. We show that the use of a low chirp results in the distribution of the resonating cavities along the optical fiber length, which allows reconfiguration of the spectral characteristics by the application of a temperature profile. This paper exposes in detail the numerical techniques used in the optimization of the fiber Bragg grating filters taking into account fabrication imperfections. We present a specific design for a 32-channel dispersion equalizer for 10 Gbit/s and a 50-GHz channel spacing. We examine the spectral characterization of a device fabricated using a phase-apodized mask for various settings of the chromatic dispersion profile. We demonstrate a tuning range of plusmn800 ps/nm over a bandwidth of 30 GHz. On average, the standard deviation of the phase ripple was below 0.1 rad. Finally, we evaluate the performance of this device by bit error rate measurements.

Novel complex gratings with third-order group-delay variations for tunable pure dispersion slope compensation

We present a novel tunable dispersion compensator that can provide pure slope compensation. The approach uses two specially designed complex fiber Bragg gratings (FBGs) with reversely varied third-order group delay curves to generate the dispersion slope. The slope can be changed by adjusting the relative wavelength positions of the two FBGs. Several design examples of such complex gratings are presented and discussed. Experimentally, we achieve a dispersion slope tuning range of +/- 650 ps/nm(2) with > 0.9 nm usable bandwidth.

Reflection equalization of the simultaneous dispersion and dispersion-slope compensator based on a phase-only sampled fiber Bragg grating

A novel approach for the reflection equalization of a phase-only sampled fiber Bragg grating (FBG) is presented, where the grating is specially designed as a simultaneous dispersion and dispersion-slope compensator with channels up to 51. The sampling-function used is given with an analytical form with a linearly-chirped sampling period and is optimized by using the simulated annealing algorithm.

Tunable chromatic dispersion and dispersion slope compensator using a planar lightwave circuit lattice-form filter

A tunable chromatic dispersion and dispersion slope compensator is proposed that has a single lattice-form filter configuration. Wavelength dependence is intentionally added to its tunable couplers, which produces dispersion slope compensation in addition to the dispersion compensation. Dispersion tunability of +/- 500 ps/nm and a slope of -4.9 ps/nm(2) over 40 GHz are successfully demonstrated, thus meeting the requirement for 40 Gbits/s differential quadrature phase shift keying transmission with an 80 km long nonzero dispersion-shifted fiber.

General Design Rules for the Synthesis of Dispersion and Dispersion Slope Compensation FIR and IIR Filters With Reduced Complexity

Chromatic dispersion is one of the main transmission impairments in optical systems with high bit rates, because the dispersion limit scales with the square of the data rate. Optical delay-line filters can be used to compensate dispersion and dispersion slope. They can be designed as feedforward finite-impulse response filters or as all-pass infinite-impulse response filters. Due to the time-variant property of the dispersion, those filters have to be adaptive, which requires fast and reliable calculation of the filter coefficients. In this paper, a new approach to calculate filter coefficients by applying analytical methods is presented. Design examples are given, and the filter performance is discussed.

Adjustable Group Velocity Dispersion and Dispersion Slope Compensation Devices With Wavelength Tunability Based on Enhanced Thermal Chirping of Fiber Bragg Gratings

We demonstrate group velocity dispersion (GVD) and dispersion slope (DS) compensation devices based on enhanced thermal chirping of glued fiber Bragg gratings (FBGs). By gluing a uniform FBG onto a uniform Zn channel for the GVD compensator and a linearly tapered Zn channel for the DS compensator, the thermal sensitivity of the FBG is enhanced. The thermal chirping of the FBG is given by the thermal expansion of a Zn channel, the thermooptic effect, and the thermal expansion of the optical fiber. Controlling the temperature distributions of the uniform FBG performs the tuning of GVD and/or DS, as well as their center wavelengths. These compensation devices can tune their GVD or DS while maintaining a constant center wavelength and change their center wavelengths while preserving constant GVD or DS values. The GVD can be tuned from -123.39 to -57.29 ps/nm with the center wavelength at 1552.9 nm, while the center wavelength can be shifted 2.2 nm with a GVD value of about -105 ps/nm. On the other hand, the DS can be tuned from -8.88 to -24.44 ps/nm2 with the center wavelength at 1554.5 nm, while the center wavelength can be shifted 0.6 nm with a DS value of about -10.4 ps/nm2.

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.

Demonstration of 80-km-Long SMF Transmission on Time-Spread Wavelength-Hopping-Type OCDM With Dispersion Compensators

We demonstrate the novel dispersion compensation for time-spread/wavelength-hop (TS-WH) optical code-division multiplexing (OCDM). The single-mode-fiber transmission, up to 80 km long, on TS-WH OCDM was achieved by a combination of the dispersion-compensated decoder and the multichannel-type dispersion-slope compensator.

Two-User 150-km Field Fiber Security Enhanced SPECTS O-CDMA Transmission

We demonstrate two-user error-free performance of security enhanced spectral phase-encoded time-spreading optical code-division multiple-access across a 150-km field fiber link. The testbed incorporates a 64-mode optical frequency comb source, a fully integrated silica arrayed waveguide grating spectral phase encoder/decoder, and a tunable dispersion slope compensator. Physical layer security is enhanced by using a bright code/dark code modulation format

Tunable Dispersion and Dispersion Slope Compensator Using Strain-Chirped Fiber Bragg Grating

We propose a tunable dispersion and dispersion slope compensator based on induced strain-chirp in a uniform fiber Bragg grating. A specially designed mechanical rotator concatenated with a metal beam with linear thickness variation along its height was used to induce a quadratic strain gradient along the grating. We successfully demonstrated the dispersion and dispersion slope change by adjusting the rotation angle and feasibility of dispersion and dispersion slope compensation at 160-Gb/s nonreturn-to-zero transmission by simulation