Superstructured Fiber Bragg Grating Research Articles

Tunable superstructure fiber Bragg grating with chirp-distribution modulation based on the effect of external stress

We report an external stress modulation method for producing a superstructure fiber Bragg grating (FBG) with approximate cascaded resonant cavities composed of different index chirp distributions. The 15 mm uncoated apodized uniform-period FBG is pressed by the vertical stress from the upper 11 pieces of the pattern plate controlled by a piezoelectric ceramic actuator. The piece length is 1 mm, and the interval of the adjacent pieces is 0.4 mm. The reflectivity of the modulated FBG gradually shows six obvious multichannel 75%-85% reflection peaks with the increase of the vertical stress of each pattern-plate piece from 0 to 30 N. The channel spacing is steady at about 10 GHz for a C-band wavelength division multiplexing system.

Multi-channel optical code-division multiple-access scheme based on super-structure fiber Bragg gratings

We propose a novel simultaneous multi-user en/decoder using super-structure fiber Bragg gratings (SFBGs) for multi-channel optical code-division multiple-access (OCDMA) applications. Each channel can generate and recognize codes for users individually. Therefore, the SFBG can make full use of the wavelength resource to enlarge the system capacity. In this paper, a 2-channel, 4-channel and 8-channel en/decoders are designed in a single SFBG with optimized performance for their auto-correlation peak over the maximum wing level ratios and peak over the maximum cross-correlation level ratios being larger than 17 and 10.2dB, respectively.

Chromatic dispersion compensation and coherent Direct-Sequence OCDMA operation on a single super structured FBG

We have proposed, fabricated and demonstrated experimentally a set of Coherent Direct Sequence-OCDMA en/decoders based on Super Structured Fiber Bragg Gratings (SSFBGs) which are able to compensate the fiber chromatic dispersion at the same time that they perform the en/decoding task. The proposed devices avoid the use of additional dispersion compensation stages reducing system complexity and losses. This performance was evaluated for 5.4, 11.4 and 16.8 km of SSMF. The twofold performance was verified in Low Reflectivity regime employing only one GVD compensating device at decoder or sharing out the function between encoder and decoder devices. Shared functionality requires shorter SSFBGs designs and also provides added flexibility to the optical network design. Moreover, dispersion compensated en/decoders were also designed into the High Reflectivity regime employing synthesis methods achieving more than 9 dB reduction of insertion loss for each device.

Numeral analysis of spectral shaping based on superstructure fiber Bragg grating in high-power Nd:glass chirped pulse amplification system

Using the genetic algorithm, we design a superstructure fiber Bragg grating (SSFBG) to pre-compensate gain narrowing and gain saturation effects in a high-power Nd:glass chirped pulse amplification system. An inverse engineering operation of chirped pulse amplification processing is used to calculate the target spectrum of the seed pulse and then the response function of the SSFBG can be obtained. Some numerical simulations are given to realize a 20μJ, 15nm ultrashort seed pulse to the hundreds Joules, 8nm optimal fourth order super-Gaussian chirped pulses in a high power Nd:glass amplification system. The results show that the gain narrowing and gain saturation effects will be reduced largely when a SSFBG, which has a proper refractive index modulation distribution, chirp coefficient and length, is used. It is believed that this proposed method will provide a theoretical direction for the future experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.

Inter-Band Crosstalk Reduction Using Sinc Apodization of Super-Structured Fiber Bragg Gratings for Hybrid WDM/OCDM Add/Drop Filters

Here, we propose a newly developed hybrid system of wavelength-division multiplexing (WDM) and optical code-division multiplexing (OCDM) with phase-shifted coherent time-spreading for the future metro-access integrated network. In order to suppress the inter-band crosstalk from the WDM interfering channels, the sinc-apodizing technique is proposed for the super-structured fiber Bragg gratings (SSFBGs) as the add/drop filters. The suppression of crosstalk is demonstrated by two-channel WDM and OCDM experiments, compared with conventional SSFBGs with uniform index profile. The proposed method suppresses the crosstalk and shows the feasibility of the 160 (10 WDM 16 OCDM)-channel system.

SpontaneousPTsymmetry breaking in Dirac-Kronig-Penney crystals

We introduce a non-Hermitian $\mathcal{PT}$ invariant extension of the Dirac-Kronig-Penney model, describing the motion of a Dirac quasiparticle in a locally periodic sequence of imaginary $\ensuremath{\delta}$-Dirac barriers and wells, and propose its optical realization using superstructure fiber Bragg gratings with alternating regions of optical gain and absorption. For the infinite crystal, we determine the band structure and show that the $\mathcal{PT}$ phase is always broken. For a finite crystal, we derive analytical expressions for reflection and transmission probabilities, and show that the $\mathcal{PT}$ phase is unbroken below a finite threshold of the $\ensuremath{\delta}$-barrier area. In the proposed optical realization, the onset of $\mathcal{PT}$ symmetry breaking in the finite crystal corresponds to the lasing condition for the grating superstructures.

WDM-Coherent OCDMA over one single device based on short chip Super structured fiber Bragg gratings

We theoretically propose and demonstrate experimentally a Coherent Direct Sequence OCDMA en/decoder for multi-channel WDM operation based on a single device. It presents a broadband spectral envelope and a periodic spectral pattern that can be employed for en/decoding multiple sub-bands simultaneously. Multi-channel operation is verified experimentally by means of Multi-Band Super Structured Fiber Bragg Gratings with binary phase encoded chips fabricated with 1mm inter-chip separation that provides 4x100 GHz ITU sub-band separation at 1.25 Gbps. The WDM-OCDMA system verification was carried out employing simultaneous encoding of four adjacent sub-bands and two different OCDMA codes.

Research on Half of the Bandwidth of the En-/Decoding Spectrum Application Based on SSFBG

Abstract A scheme for half of the bandwidth of the en-/decoding spectrum application based on superstructured fiber Bragg grating (SSFBG) is presented in this paper. As verified by theoretical and simulation analysis, the half of the bandwidth of the en-/decoding spectrum has already contained all code information and en-/decoding function can be completed as long as the reflection spectrum covers half of the original bandwidth (half of the bandwidth of the en-/decoding spectrum). As indicated by the en-/decoding experiment, the en-/decoding performance of the half of the bandwidth of the en-/decoding spectrum application is better than that of the conventional mode of center alignment. The half of the bandwidth of the en-/decoding spectrum application shall choose half of en-/decoding spectrum inclining to Level 0, thus both ensuring auto-/cross-correlation of the en-/decoding and minimizing insertion loss. The half of the bandwidth of the en-/decoding spectrum application reduces costs for light sources and improves performance of the receiver, being conducive to the practical design of the system.

Novel architecture of WDM/OCDMA-PON based on SSFBG and wavelength re-modulation technology

A novel architecture of wavelength-division multiplexing/optical code division multiplexing access-passive optical network (WDM/OCDMA-PON) based on superstructure fiber Bragg grating (SSFBG) and wavelength re-modulation technology is proposed. In this scheme, WDM is overlaid on OCDMA channel in a single network by virtue of a kind of SSFBG, and the total capacity of hybrid PON can be extended by regulating the transmission power reasonably. Re-modulation technology is also a good method to save wavelength-specific components at the optical network unit (ONU) and cost of wavelength management on the customer side. In simulation system, 1.25 Gb/s up/downstream data are transported with good performance. In addition the crosstalk penalties from adjacent wavelength channels (with the same OC) are found to be negligible in upstream and downstream transmissions.

Synthesis of fiber Bragg grating for gain-narrowing compensation in high-power Nd: Glass chirped pulse amplification system

We propose and analyze theoretically a method to compensate gain-narrowing effect by using the spectral shaping technology based on superstructure fiber Bragg grating (SSFBG) in high-power Nd:glass chirped pulse amplification system. The target spectrum is firstly calculated from hundreds joules amplified chirped Gaussian or super-Gaussian pulse by an inverse engineering operation. A genetic algorithm is used to design the SSFBG and obtain the index modulation distribution of grating which can transform the initial seed pulse to the target spectrum. The numerically simulations show that the spectral narrowing effect of chirped pulse amplification will be reduced largely and the ideal pulse spectrum (Gaussian or super-Gaussian) is also obtained. It is believed that this proposed method will provide a theoretical direction for the following experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.

A novel architecture of optical code label generation and recognition for optical packet switching

A novel architecture of optical code (OC) label generation and recognition for optical packet switching (OPS) by using super structured fiber Bragg grating (SSFBG) is proposed. The OC label is generated and recognized by a label generator and recognizer, respectively. The label generator is composed of N encoders in parallel, and it can generate 2N kinds of serial optical code labels (SOCLs) for indicating 2N network routing information. The label recognizer can decode SOCLs by N decoders in parallel and provides label information to the switching control unit so that clock information is not required during the decoding process. In the switch nodes, handling of the high-speed information payload stream and the recognition of the OC label are performed in the optical domain, while processing of the routing information remains in the electrical domain. This approach could be a promising solution for an OPS network with high capacity, good quality of service (QoS), multi-service function and high security. In this experiment, we demonstrate 40 Gbps 256 label optical packet switching that employs clockless SOCL processing.

Investigation of superstructured fiber Bragg grating-based OCDMA system

The bit error rate (BER) performance of a superstructured fiber Bragg grating (SSFBG)-based optical code division multiple access (OCDMA) system is investigated with different input pulse widths and grating refractive index modulation amplitudes, and the corresponding crosstalk ratio is considered at different data-rates. Simulation results show that increasing the input pulse width or grating refractive index modulation amplitude will degrade the BER performance apparently. Moreover, with fixed code length and chip-rate detection, a lower data-rate system has better tolerance to an increasing input pulse width, while a higher data-rate system has better tolerance to an increasing grating refractive index modulation amplitude.

Security Improvement Using $\pm\pi/2$-Phase-Shifted SSFBG En/Decoder in Time-Spreading OCDMA

The existence of dips in the waveform encoded by 0/π-phase-shifted superstructured fiber Bragg grating (0/π -SSFBG) allows eavesdroppers to extract code sequence straightforwardly. In this letter, the code extraction technique for 0/π-SSFBG is summarized and demonstrated. To address this security issue, we propose using ±π/2-phase-shifted ±π/2-SSFBG as encoder/decoder to improve security in time-spreading optical code-division multiple-access. The security and coding performances for both ±π/2-SSFBG and 0/π-SSFBG are compared; ±π/2-SSFBG exhibits improved security and better coding performance. The influence of input pulse over the security performance for ±π/2 -SSFBG is discussed. Short input pulse can improve the security of the encoded signal.

10 Gb/s-Based PON Over OCDMA Uplink Burst Transmission Using SSFBG Encoder/Multi-Port Decoder and Burst-Mode Receiver

In this paper, we propose a novel 10 Gb/s-based passive optical network (PON) over optical code division multiple access (OCDMA) system to realize the new generation full capacity optical access network which is easily upgraded from existing time division multiplexing PON (TDM-PON) without sacrificing the currently uplink bandwidth assigned to the individual user. 16-ONU (4-OCDMA x 4-packet) uplink burst transmission, an upgrade scenario by a factor of four of conventional 10 Gb/s-based PON, is experimentally demonstrated by using multi-level phase-shift-keying (PSK) super-structured fiber Bragg grating (SSFBG) encoder/multi-port decoder and burst-mode receiver. In the discussions, it will be shown that 32 users can be accommodated in 10 Gb/s-based PON over OCDMA system, and a key is newly introduced multi-level phase-shifted en/decoding, of which auto-correlation waveform can be preferably adopted in the burst-mode reception at 10 Gb/s.

Efficient All-Optical Wavelength-Conversion Scheme Based on a Saw-Tooth Pulse Shaper

We experimentally demonstrate the use of saw-tooth optical pulses, generated using a superstructured fiber Bragg grating, to achieve high performance and efficient all-optical wavelength conversion in a scheme based on cross-phase modulation in a highly nonlinear fiber, with subsequent offset filtering. Compared to the use of more conventional waveforms, such as Gaussian pulses, the purpose-shaped saw-tooth pulses allow an improvement in the optical signal-to-noise ratio of the wavelength-converted signal of around 15 dB as well as a more than 6-dB improvement in receiver sensitivity.

Elimination of Multiple Access Interference in Ultrashort Pulse OCDMA Through Nonlinear Polarization Rotation

A multiple access interference elimination scheme based on nonlinear polarization rotation (NPR) is proposed for ultrashort pulse optical code-division multiple access (OCDMA). This scheme is experimentally investigated in a four-user and 2.5-Gb/s coherent OCDMA system encoded/decoded by 127-chip superstructured fiber Bragg gratings. The measured bit-error-rate results of the NPR-based thresholder are also compared with those of a conventional supercontinuum-based thresholder in both the back-to-back and 20-km transmission cases. Our proposed scheme has the advantage of colorless operation over <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band.

Millimeter-wave pulse generation based on pulse reshaping using superstructure fiber Bragg grating

A novel optical approach is proposed to generate millimeter wave (MMW) pulse signal based on the pulse reshaping of superstructure fiber Bragg grating (SSFBG). In our scheme, one input pico-second Gaussian pulse is transformed into n Gaussian pulses by the SSFBG reshaping firstly, and then the pulse train is replicated to form a required frequency modulation MMW optical pulse envelope by the linear chirped fiber Bragg grating (LCFBG) or other highly dispersive element. The high-speed photodetector (PD) and band-pass filter can transform the MMW optical pulse into an MMW pulse signal ultimately. Depending on this scheme, MMW signals with frequency up to 10 GHz can be easily generated by the completed fiber components.

Simultaneous measurement of temperature and tensile loading using superstructure FBGsdeveloped by laser direct writing of periodic on-fiber metallic films

This paper addresses the development of superstructure fiber Bragg gratings (FBGs)by laser-assisted direct writing of on-fiber metallic films. A novel laser directwrite method is characterized to fabricate periodic films of silver nanoparticles onthe non-planar surface of as-fabricated FBGs. Silver films with a thickness of9 µm are fabricated around a Bragg grating optical fiber. The performance of the superstructureFBG is studied by applying temperature and tensile stress on the fiber. Anopto-mechanical model is also developed to predict the optical response of the synthesizedsuperstructure FBG under thermal and structural loadings. The results show that thereflectivity of sidebands in the reflection spectrum can be tuned up to 20% and 37%under thermal and structural loadings, respectively. In addition, the developedsuperstructure FBG is used for simultaneous measurement of force and temperature toeliminate the inherent limitation of regular FBGs in multi-parameter sensing.

Numerical Investigation of Ultrashort Complex Pulse Generation Based on Pulse Shaping Using a Superstructure Fiber Bragg Grating

A technique for ultrashort complex pulse generation based on the pulse shaping of superstructure fiber Bragg grating (SSFBG) is presented. We apply this technique to illuminate the mutual transformation between Gaussian pulse and soliton pulse, generations of double optical pulse and complex millimeter wave (MMW) pulse by phase and amplitude profiling of 1-ps transform-limited pulse. The designed principle of grating is demonstrated; the corresponding refractive index distribution, the reflection spectrum and the characteristics of pulse transmission are also simulated. The results of this study indicate that this design method is very flexible for complex pulse generations. Finally, some potential applications for these complex pulses in the areas of ultrafast photonics, optical measurement, novel devices for optical communication system and so on are also listed and discussed.

Photonic True-Time Delay Beamforming Based on Superstructured Fiber Bragg Gratings With Linearly Increasing Equivalent Chirps

A photonic true-time delay beamforming system for phased array antennas based on superstructured fiber Bragg gratings (SFBGs) with linearly increasing equivalent chirps is proposed and demonstrated. The theory behind SFBGs with equivalent chirps is detailed and a closed-form equation for the equivalent dispersion is presented for the first time. Array factors, calculated based on the experimentally measured time delays are shown for different wavelengths of the photonic beamformer. An analysis of the errors present in the group delay responses of the fabricated SFBGs is also presented.