Ultrawideband Doublet Pulses Research Articles

Theoretical demonstration of all-optical switchable and tunable UWB doublet pulse train generator utilizing SOA wavelength conversion and tunable time delay

An all-optical ultrawide band (UWB) doublet pulse train signal generator is proposed and theoretically simulated by utilizing an inverse wavelength conversion base on the cross-gain modulation (XGM) effect in a semiconductor optical amplifier (SOA) and controllable time delay in two optical delay lines (ODLs). The proposed scheme is not only optically switchable in the polarity of pulse by switching the polarity of input pulse but also tunable in signal pulse width and radiofrequency (RF) spectrum by tuning the ODLs.

Generation of UWB Doublet Pulse Based on Directly Modulated Laser and Chromatic Dispersion

An ultra-wideband (UWB) doublet pulse generation technique in the optical domain for UWB-over-fiber systems is presented. Our solution is based on the direct modulation of a semiconductor laser, optical filtering, and chromatic dispersion in a transmission fiber. When the integration of the transmitter in optical access network infrastructure is considered, the transmission length difference, or the difference in accumulated dispersion, is an issue to exactly obtain the desired pulse shape. To solve this problem, we propose to adjust the transmitter operation point, specifically the laser chirp, with respect to the targeted transmission fiber length. Bit error rate measurements prove that doublet pulses can be achieved with fiber length variation from 15 to 40 km of single-mode fiber.

A Novel Approach to Photonic Generation and Modulation of Ultra-Wideband Pulses

AbstractA novel approach to photonic generation of ultra-wideband (UWB) signals is proposed in this paper. The proposed signal generator is capable of generating UWB doublet pulses with flexible reconfigurability, and many different pulse modulation formats, including the commonly used pulse-position modulation (PPM) and bi-phase modulation (BPM) can be realized. Moreover, the photonic UWB pulse generator is capable of generating UWB signals with a tunable spectral notch-band, which is desirable to realize the interference avoidance between UWB and other narrow band systems, such as Wi-Fi. A mathematical model describing the proposed system is developed and the generation of UWB signals with different modulation formats is demonstrated via computer simulations.

UWB Doublet Generation Employing Cross-Phase Modulation in a Semiconductor Optical Amplifier Mach–Zehnder Interferometer

In this paper, a novel method to generate ultrawideband (UWB) doublets is proposed and experimentally demonstrated, which is based on exploiting the cross-phase modulation in a semiconductor optical amplifier (SOA). The key component is an integrated SOA Mach-Zehnder interferometer pumped with an optical carrier modulated by a Gaussian pulse. The transfer function of the nonlinear conversion process leads to the generation of UWB doublet pulses by tuning the SOA currents to different values.

All-optical UWB doublet pulses generation by using a delay interferometer

We demonstrated a simple scheme to generate ultra wideband (UWB) doublet pulses by inputting a dark return-to-zero (RZ) signal into a fiber delay interferometer (FDI). An 0.625-Gbit/s dark-RZ pulse train where the pulse width is 120ps was inputted into a FDI where the free spectral range (FSR) is 0.16nm (∼20GHz, according time delay is ∼50ps) and the extinction ratio (ER) is 9dB, and the phase difference of the two fiber arms was changed and controlled by adjusting the operation temperature of the FDI, by do so, UWB doublet pulses were directly generated at an output port of the FDI. The system parameter effects on the output UWB pulses were discussed. Moreover, we also numerically demonstrated that the UWB quadruplet pulses can be generated in the same set by optimizing system parameters. This scheme has some distinct advantages including easy integration, convenient tuning, good stability, and so on. Presented method also accords with the general features in future applied UWB-Over-Fiber communication system, such as, single optical source input, simple configuration and passive device.

Photonic generation of ultra-wideband doublet pulse using a semiconductor-optical-amplifier based polarization-diversified loop

We propose and demonstrate a novel scheme of ultra-wideband (UWB) doublet pulse generation using a semiconductor optical amplifier (SOA) based polarization-diversified loop (PDL) without any assistant light. In our scheme, the incoming gaussian pulse is split into two parts by the PDL, and each of them is intensity modulated by the other due to cross-gain modulation (XGM) in the SOA. Then, both parts are recombined with incoherent summation to form a UWB doublet pulse. Bi-polar UWB doublet pulse generation is demonstrated using an inverted gaussian pulse injection. Moreover, pulse amplitude modulation of UWB doublet is also experimentally demonstrated. Our scheme shows some advantages, such as simple implementation without assistant light and single optical carrier operation with good fiber dispersion tolerance.

Filter-free ultra-wideband doublet pulses generation based on wavelength conversion and fiber dispersion effect

Filter-free ultra-wideband (UWB) doublet pulse generation is experimentally demonstrated in the optical domain based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) and UWB-over-fiber technology is implemented by exploiting dispersion-induced pulse broadening effect in single-mode fiber (SMF). In our proposed system, the SOA generates a polarity-inversed Gaussian pulse train with respect to the injected one through the XGM. After a piece of SMF, the bandwidth of polarity-reversed Gaussian pulse broadens due to the induced dispersion. After the combination of the two light waves with a suitable time delay between them, UWB pulse is obtained. The key parameters for UWB pulse, including central frequency, 10dB bandwidth, as well as fractional bandwidth are experimentally obtained with 8GHz, 9.9GHz and 123% respectively. The generated UWB doublet pulse conforms with the UWB definition of Federal Communications Commission (FCC).

Bismuth Nonlinear Optical Fiber for Photonic Ultrawideband Radio-Signal Processing

The feasibility of using a bismuth-oxide-based nonlinear optical fiber (Bi-NLF) for the implementation of ultrawideband (UWB) radio-signal-processing schemes is experimentally investigated. The use of two different types of nonlinear signal processors for the generation of UWB pulses is demonstrated. One processor uses cross-phase modulation for monocycle pulse generation, whereas the other uses nonlinear polarization rotation for doublet pulse generation. It is experimentally shown that UWB monocycle and doublet pulses can be successfully generated using the Bi-NLF-based nonlinear signal processors. Moreover, the system performance for the generation of UWB pulses is evaluated by performing a transmission experiment over a 20-km-long nonzero dispersion-shifted fiber (NZ-DSF) link. Error-free and penalty-free UWB doublet signal transmission is achieved.

Optical arbitrary waveform generator applicable to pulse generation and chromatic dispersion compensation of a remote UWB over fiber system

Optical arbitrary waveform generator (OAWG), which can generate pre-distorted ultra-wideband (UWB) pulses to tolerate the chromatic dispersion (CD) of the fiber without any other CD compensation solutions, provides a good solution for the UWB over fiber system. In our paper, we experimentally demonstrate a new OAWG scheme based on multiple incoherent continuous wave lights by double side band with suppressed carrier (DSB-SC) modulation. UWB Gaussian monocycle and doublet pulses are generated and the chromatic dispersion of 20-km, 50-km and 100-km single-mode fiber (SMF) are compensated by the OAWG system without any other CD compensation solutions.

All-optical pulse shaping for ultrawideband doublet pulses using nonlinear optical loop mirror with optical parametric amplification

We propose and experimentally demonstrate an alternative photonic scheme for the generation of ultrawideband (UWB) doublet pulses, which is based on an optical fiber-based nonlinear optical loop mirror (NOLM) incorporating the optical parametric amplification (OPA) effect. The proposed scheme uses both cross-phase modulation and OPA within an optical fiber-based NOLM to produce an ideal transfer function for the shaping of input soliton pulses into doublet pulses. Using the proposed scheme, a successful conversion of input soliton pulses into doublet pulses is readily demonstrated. The system performance of UWB doublet pulses is also assessed by propagating the 1.25 Gbit/s doublet pulses over a fiber link. Error-free UWB doublet signal transmission is demonstrated.

Photonic Generation of UWB Pulses Using a Nonlinear Optical Loop Mirror and Its Distribution Over a Fiber Link

A novel approach is proposed for generating ultra-wideband (UWB) doublet pulses using a nonlinear optical loop mirror (NOLM). In this scheme, a polarization controller is used to shift the NOLM transfer function so that for a fixed operating condition (pump power), we can access the nonlinear portion of the transfer function. The UWB doublet pulses are then modulated using on-off keying and transmitted over a 10-km span of standard single-mode fiber to assess system performance. Error-free transmission is achieved with a power penalty of 1.5 dB compared with the back-to-back measurement.

Photonic Ultrawideband Pulse Generation With HNL-DSF-Based Phase and Intensity Modulator

We propose and experimentally demonstrate a photonic ultrawideband (UWB) pulse (monocycle and doublet) generator based on a highly nonlinear dispersion-shifted fiber (HNL-DSF). The pulsed pump, located in the anomalous group-velocity dispersion regime of the HNL-DSF, performs as both an intensity and a phase modulator in our scheme. We experimentally prove, for the first time to the best of our knowledge, that the UWB doublet pulse can be generated when the optical carrier is located at the center of a narrow tunable filter's passband. Furthermore, the encoded doublet signal, fully compliant with the Federal Communications Commission (FCC) regulations, is transmitted at 950 Mb/s through a 25-km single-mode fiber without introducing any obvious pulse distortion.

Generation and Distribution of 1.25 Gb/s Ultrawideband Doublet Pulses Based on the Combination of Nonlinear Polarization Rotation and Parametric Amplification

We propose an alternative photonic scheme to generate a doublet ultrawideband (UWB) pulse, which is based on the combined use of nonlinear polarization rotation (NPR) and optical parametric amplification (OPA). The proposed scheme uses NPR together with OPA in a highly nonlinear dispersion-shifted fiber to produce an ideal transfer function with which input Gaussian pulses are successfully converted into doublet pulses. An experimental demonstration was carried out to verify the working principle. The system performance of the generated UWB doublet pulses was assessed by propagating them over a 20-km-long fiber link, followed by wireless transmission. Error-free transmission was successfully achieved at a data rate of 1.25 Gb/s.

All-optical switchable UWB pulses generation, modulation and transmission

We proposed and demonstrated all-optical polarity- and shape-switchable ultrawideband (UWB) Gaussian pulses generation schemes using a single polarization interferometer (PI) or a semiconductor optical amplifier (SOA) cascaded by a PI. When an optical signal with dark return-to-zero (RZ) format propagates directly through a single PI, a pair of polarity-reversed UWB monocycle pulses and a positive UWB doublet pulse is acquired respectively only by adjusting the polarization controllers, without changing the bias of the intensity modulator. If a SOA is connected at the input of the PI to firstly implement the first-order differential function to the input dark RZ pulse utilizing gain saturation effect of the SOA, both polarity- and shape-switchable UWB Gaussian monocycle and doublet pulses are all acquired from the cascaded system. Moreover, if a nonreturn-to-zero control signal is introduced into the SOA, utilizing the cross-gain modulation (XGM) effect of the SOA and the differential characteristic of PI, all-optical shape modulation to UWB signals can be realized, and the polarity of the modulated UWB pulses can also be switched. Also, UWB signal transmission characteristics in fiber link were investigated.

Ultrawideband doublet pulse generation based on nonlinear polarization rotation of an elliptically polarized beam and its distribution over a fiber/wireless link

Proposed herein is an alternative photonic scheme for the generation of a doublet UWB pulse, which is based on the nonlinear polarization rotation of an elliptically polarized probe beam. The proposed scheme is a modified optical-fiber Kerr shutter that uses an elliptically polarized probe beam together with a linearly polarized control beam. Through theoretical analysis, it was shown that the optical-fiber-based Kerr shutter is capable of producing an ideal transfer function for the successful conversion of input Gaussian pulses into doublet pulses under special elliptical polarization states of the probe beam. An experimental verification was subsequently carried out to verify the working principle. Finally, the system performance of the generated UWB doublet pulses was assessed by propagating them over a 25-km-long standard single-mode fiber link, followed by wireless transmission. Error-free transmission was successfully achieved.

Ultrawideband Doublet Pulse Generation Based on a Semiconductor Electroabsorption Modulator and Its Distribution Over a Fiber/Wireless Link

An alternative photonic-generation scheme of ultrawideband (UWB) doublet pulses based on a semiconductor electroabsorption modulator (EAM) is proposed. The use of EAMs for doublet pulse generation has not been reported due to the difficulty of producing a U-shaped electrical-to-optical (E-O) transfer function. It is shown in the study that the creation of a U-shaped E-O transfer function from multi-quantum-well-based EAMs can be easily done under special conditions. An experiment is subsequently conducted to demonstrate the successful generation of UWB doublet pulses. The system performance of the generated UWB doublet pulses is then evaluated through a range of signal transmission experiments over a fiber/wireless transmission link. Error-free UWB doublet signal transmission is demonstrated.

Switchable UWB pulse generation using a polarization maintaining fiber Bragg grating as frequency discriminator

We propose and successfully demonstrate a novel approach to optically generate ultrawideband (UWB) pulse with switchable shape and polarity by using a polarization-maintaining fiber Bragg grating (PM-FBG) as frequency discriminator. Depending on the shape of the reflective spectrum of the PM-FBG, the system can function as a first- or second-order differentiator for the generation of Gaussian UWB monocycle or doublet pulses. Consequently, the shape and the polarity of the generated UWB pulse can be switched by simple adjustment of a polarization controller (PC). Gaussian monocycle and doublet pulses were successfully obtained with fractional bandwidths of about 188% and 152%, respectively. Higher-order UWB pulses with spectrum covering from 2.9 GHz to 9.8 GHz have also been obtained through adjustment of the PC.

Polarity- and Shape-Switchable UWB Pulse Generation Based on a Photonic Microwave Delay-Line Filter With a Negative Tap Coefficient

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel and simple scheme to implement a two- or three-tap photonic microwave filter with one negative coefficient for polarity- and shape-switchable ultrawideband (UWB) pulse generation is proposed and demonstrated. The entire system can be reconfigured as a two- or three-tap microwave delay-line filter with one negative coefficient realized by operating a balanced photodetector (BPD) as a single photodetector or a BPD for the generation of UWB monocycle or doublet pulses. The polarity of the generated UWB pulses can be switched by tuning the transmission axis of the arbitrary wave plate. The proposed scheme is experimentally demonstrated. Gaussian monocycle and doublet pulses with fractional bandwidths of about 174% and 141% are generated. </para>

Photonic generation of ultrawideband monocycle and doublet pulses by using a semiconductor-optical-amplifier-based wavelength converter

Photonic generation of ultrawideband (UWB) monocycle and doublet pulses is experimentally demonstrated using a cascaded electroabsorption modulator (EAM) and semiconductor optical amplifier by exploiting a combination of cross-absorption modulation and cross-gain modulation. The polarities and shapes of UWB monocycle and doublet pulses can be simply controlled using an optical time-delay controller and the reverse voltage applied to the EAM. The corresponding measured rf spectra meet the UWB criteria.

All-optical ultra-wideband pulse generation based on semiconductor optical amplifiers

Several all-optical methods for ultra-wideband (UWB) pulse generation based on various nonlinearities of single semiconductor optical amplifiers (SOAs), namely cross phase modulation (XPM), cross gain modulation (XGM), and a hybrid of self phase modulation (SPM) and XGM, have been demonstrated. In the first method, UWB doublet pulses are realized with XPM. The input optical Gaussian pulse will be converted to two polarity-reversed monocycle pulses by a blue shifted and a red shifted optical bandpass filters respectively. These two monocycle pulses are then combined with proper time delay to generate two polarity-reversed doublet pulses. Second, two polarityreversed monocycle pulses are obtained based on XGM of the SOA and group delay of the single mode fiber (SMF). In the scheme, two polarity-reversed Gaussian pulses are generated due to XGM, and then the mixed signal is converted to a monocycle shape due to the group delay of the SMF. Finally, we present UWB doublet generation based on SPM. The monocycle pulse is generated from a dark return-to-zero (RZ) signal and converted to a doublet pulse by injecting an additional probe signal with the SMF transmission. For the first time and to the best of our knowledge, we report that the generated doublet pulses are transmitted over 5 km SMF by proper dispersion compensation without distortion. The configuration of our alloptical methods is compact and simple. The feasibility to implement the pulse shape modulation and pulse polarity modulation is discussed.