Ultra-wideband Signal Generation Research Articles

High-speed microwave photonic switch for millimeter-wave ultra-wideband signal generation

We propose a scheme for generating millimeter-wave (MMW) ultra-wideband (UWB) signal that is free from low-frequency components and a residual local oscillator. The system consists of two cascaded polarization modulators and is equivalent to a high-speed microwave photonic switch, which truncates a sinusoidal MMW into short pulses. The polarity switchability of the generated MMW-UWB pulse is also demonstrated.

Photonic multi-shape UWB pulse generation using a semiconductor optical amplifier-based nonlinear optical loop mirror

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband (UWB) signal generation using a semiconductor optical amplifier (SOA) based nonlinear optical loop mirror (NOLM). By employing the cross phase modulation (XPM) effect, cross gain modulation (XGM), or both, multi-shape UWB waveforms are generated including monocycle, doublet, triplet, and quadruplet pulses. Both the shapes and polarities of the generated pulses are flexible to adjust, which may be very useful in UWB pulse shape modulation and pulse polarity modulation.

Generation of ultra-wideband signals by directly current-modulating distributed feedback laser diode subjected to optical feedback

The chaotic ultra-wideband (UWB) pulse signals are generated by directly modulating semiconductor laser subjected to optical feedback. We simulate that the -10 dB bandwidth and the central frequency of the RF spectrum of the chaotic UWB signals are influenced by the bias current and feedback strength. The research results demonstrate that the -10 dB bandwidth of the RF spectrum of the UWB signals increases with the increases of the bias current of the semiconductor laser and the feedback, the central frequency also increases with the increases of the bias current and the feedback. In our experiments, chaotic UWB signals with steerable and flatted power spectrum are generated by directly modulating DFB-LD subjected to optical feedback. The power spectrum of UWB signals is fully compliant with the FCC indoor mask, while a large fractional bandwidth of 133% and a central frequency of 6.6 GHz are achieved. The central frequency and -10 dB bandwidth of the chaotic UWB signals are on a large scale tunable by adjusting the bias current and feedback power. In addition, the chaotic UWB signals transmit through a 34.08 km single mode fiber and the power spectrum does not have any discrete spectrum line.

System Wide Implementation of Photonically Generated Impulse Radio Ultra-Wideband for Gigabit Fiber-Wireless Access

In this paper, we comprehensively review our research work on system wide implementation of photonically generated IR-UWB signals based on relaxation oscillations of a semiconductor laser. Firstly, we present our novel approach as a flexible method for photonic generation of high speed impulse radio ultra-wideband (IR-UWB) signals at 781.25 Mbps with on-off keying (OOK) and binary phase shift keying (BPSK) modulation formats. We further advance the state-of-the-art to include multi-Gigabit IR-UWB signal generation. Both OOK and BPSK signals comply with the Federal Communications Commission (FCC) regulation. Secondly, we implement UWB fiber transmission systems and study hybrid fiber-wireless transmission performance at a system level. This is accomplished by employing our digital signal processing (DSP) assisted receiver. The photonic generation method is superior to the state-of-the-art electronic generation method in terms of transmission bit-error rate performance. Moreover, photonic IR-UWB generation is shown to be capable of longer wireless reach due to its lower bandwidth limitation. Finally, we experimentally demonstrate the integration of a relaxation oscillations-based UWB photonic generation system into existing wavelength division multiplexing passive optical networks (WDM-PON) infrastructure. This provides converged Gigabit indoor wireless and wireline access services.

Photonic generation of impulse ultrawideband signals with switchable shapes and polarities based on frequency-to-time mapping

A photonic approach to generate impulse ultrawideband (UWB) signals with switchable shapes and polarities based on the frequency-to-time mapping technique is proposed and demonstrated. UWB monocycle, doublet, and triplet signals with two polarities can be obtained by adjusting the switchable spectrum shaper.

Photonic generation of ultrawideband signals based on frequency-dependent gain saturation in a reflective semiconductor optical amplifier

A novel scheme to generate ultrawideband (UWB) pulses with different polarities is proposed and experimentally demonstrated based on a reflective semiconductor optical amplifier (RSOA). Because the gain saturation in the RSOA is more evident when the injected optical signal has a lower modulation frequency, the RSOA operated at the gain saturation regime can shape a dark or bright return-to-zero pulse to a UWB pulse. An experiment is performed. The fractional bandwidth of the generated UWB pulse is more than 89%. The generated UWB signals with on-off keying format are transmitted in a 20km single-mode fiber. The power penalty is less than 1.2dB. Since the RSOA is possibly a key device in wavelength-division multiplexed passive optical networks (WDM-PONs), the proposed optical UWB generator can be used to provide UWB services in a WDM-PON system without significantly increasing the cost.

Photonic generation of high order UWB signals

A simple method is proposed to generate high order optical ultra-wideband (UWB) signals. A fiber Bragg grating (FBG) filter is used as a frequency discriminator to convert phase modulation to intensity modulation when generating high order UWB signals. Simulation results show that the fractional bandwidths of the generated signals are over 50%, which are in accordance with the FCC definition of UWB signal. By adjusting the laser's center wavelength, we can increase the order of the generated UWB signal, and thus make the generated signal more consistent with the pulse selection criteria of UWB signal.

Photonic Generation of Ultrawideband (UWB) Pulse With Tunable Notch-Band Behavior

A photonic approach to generating the ultrawideband (UWB) pulses with tunable band-rejection behavior based on a negative coefficient two-tap microwave photonic filter is proposed and experimentally demonstrated. To avoid the interference between UWB and the Wireless Fidelity system, the UWB pulse with the “batwing” shape, which corresponds to the 5-GHz notch-band in frequency domain, is generated. Moreover, the band-notched position of the generated UWB signals could be tuned by adjusting the basic delay of the microwave photonic filter. Utilizing the optically tunable band-rejection character, the UWB systems can coexist with existing and future wireless network technologies almost without interference, as well as provide the opportunity for the combination between UWB-over-fiber and cognitive radio.

Performance evaluation of photonic UWB generation based on silicon MZM

Silicon photonics has emerged as the premier candidate for the photonic systems-on-chip (SoC). The scheme based on the silicon Mach-Zehnder modulator (MZM) to generate photonic ultra-wideband (UWB) signals is helpful to the integration of the UWB system with other optical networks on a single silicon-based chip. In this paper, according to the influence of the nonlinear free carrier dispersion (FCD) effect and the free carrier absorption (FCA) effect, the performance of two typical UWB generation schemes is numerically analyzed. The double side-band UWB (DSB-UWB) generation scheme needs the DC reverse bias which increases the complexity of the modulator and there is a residual chirp resulting from the FCD effect even the push-pull operation is adopted. The quasi single-sideband UWB (QSSB-UWB) generation scheme doesn't have these problems. However there is the asymmetric amplitude peak in the generated UWB signal. The property of the large singal modulation is also investigated to improve the signal-to-noise ratio (SNR).

Photonic generation and transmission of chaotic ultra wideband signals

We propose and experimentally demonstrate a chaotic ultra wideband (UWB) over fiber link based on optical feedback laser diode, in which UWB signals are generated and transmitted at three different bit rates of 360, 720 Mbit/s, and 1.44 Gbit/s respectively. Without utilizing any dispersion compensation module, the signal at a bit rate of 1.44 Gbit/s is detected using a digital signal processing receiver after 10 km fiber and 0.6 m wireless channel transmission. The power spectrum does not have any discrete spectral line because of the random output of the chaotic pulses, which means that the harmful effects of discrete spectral lines could be avoided with this method.

Upconversion of Gain-Switched Laser Pulses for Optical Generation of UWB Signals

We propose and experimentally demonstrate a simple, low-cost optical ultra-wide band (UWB) pulse generation method. A gain-switched laser pulse is dispersed by optical fiber propagation and upconverted to the center of the US Federal Communications Commission (FCC) mask using an optical intensity modulator. The generated UWB pulses comply with the FCC mask with relatively high power efficiencies. We also show that the optical fiber can be replaced with a fiber Bragg grating filter to make the transmitter compact. Wireless propagation of the UWB impulses is investigated by offline signal processing. A linear receiver and an energy detector are implemented. The linear filter shows a better BER performance, particularly in worse channel conditions. We reach the FEC limit of 10-3 after 3.5 m of wireless propagation at 856 Mb/s.

Photonic generation of millimeter-wave ultra-wideband signal using phase modulation to intensity modulation conversion and frequency up-conversion

We propose and experimentally demonstrate the generation of a pair of polarity-reversed 24GHz millimeter-wave (MMW) ultra-wideband (UWB) monocycles. The scheme is realized by using delay interferometer (DI) based phase modulation to intensity modulation (PM–IM) conversion and carrier suppression modulation (CSM) based frequency up-conversion. The phase modulation is realized by using either electro-optic phase modulator (EOPM) or cross phase modulation (XPM) in semiconductor optical amplifier (SOA), which is an all-optical approach to obtaining baseband UWB signals, respectively. After frequency up-converted by using CSM in a Mach–Zehnder modulator (MZM), a pair of polarity-reversed 24GHz MMW-UWB signals complying with the Federal Communication Committee (FCC) requirements is generated. The bi-phase modulation (BPM) of 24GHz MMW-UWB signals can also be realized by electrically switching the bias voltage of delay interferometer.

6-channel photonic generation of ultra-wideband signals using multiple nonlinear characteristics in a parallel FOPA structure

We propose an approach to generating 6-channel polarity-inverted ultra-wideband (UWB) doublets by utilizing the parallel fiber-optical parametric amplifier (FOPA) configuration. The pulse-splitting effect in a highly nonlinear fiber (HNLF) is exploited to generate the double-overshoot and the double-undershoot, which are the basic components required to form a UWB pulse. Under the circumstances of different relative time advance/delays (RTADs) and different initial Gaussian pulse durations, the key parameters, including center frequency (Fc), 10-dB bandwidth (BW10dB) and fractional bandwidth (FBW) for a UWB doublet are systematically investigated, eventually proved in line with the U. S. Federal Communications Commission (FCC) regulation.

All-optical UWB signal generation and multicasting using a nonlinear optical loop mirror

An all-optical scheme for ultra-wideband (UWB) signal generation (positive and negative monocycle and doublet pulses) and multicasting using a nonlinear optical loop mirror (NOLM) is proposed and demonstrated. Five UWB signals (1 monocycle and 4 doublet pulses) are generated simultaneously from a single Gaussian optical pulse. The fractional bandwidths of the monocycle pulses are approximately 100% while those of the doublet pulses range from 100% to 133%. The UWB signals are then modulated using a 2(15)-1 pseudorandom bit sequence (PRBS) and error-free performance for each multicast channel is obtained.

Experimental Analysis of 60-GHz VCSEL and ECL Photonic Generation and Transmission of Impulse-Radio Ultra-Wideband Signals

Optical generation of impulse-radio ultra-wideband (UWB) signals in the 60-GHz band is proposed and experimentally demonstrated. External-cavity laser (ECL) and vertical-cavity surface-emitting laser (VCSEL) is employed for frequency up-conversion by heterodyne mixing with a UWB optical signal for comparison purposes. Real-time bit-error-rate (BER) performance of generated signals at 3.125 Gb/s is evaluated combining fiber and 2-m wireless transmission. Different optical fiber types including 1-km bend-insensitive single-mode fiber and 20-km nonzero dispersion-shifted fiber is evaluated. BER <; 10-9 for the ECL and BER <; 2.2·10-3 for the VCSEL requiring higher received optical power than the ECL is demonstrated employing electrical power detection.

All-optical binary phase-coded UWB signal generation for multi-user UWB communications

An all-optical incoherent scheme for generation of binary phase-coded ultra-wideband (UWB) signals is proposed and experimentally demonstrated. The binary phase coding is performed based on all-optical phase modulation in a semiconductor optical amplifier (SOA) and phase modulation to intensity modulation (PM-IM) conversion in a fiber delay interferometer (DI) that serves as a multichannel frequency discriminator. By locating the phase-modulated light waves at the positive and negative slopes of the DI transmission spectra, binary phase encoded UWB codes (0 and π) are generated. We also experimentally demonstrate a bipolar UWB coding system with a code length of 4, operating at 1.25 Gb/s. And the decoding is analyzed as well. Our proposed system has potential application in future high-speed UWB impulse radio over optical fiber access networks.

Widely Tunable Ultra-Wideband Signals Generation Utilizing Optically Injected Semiconductor Laser

We propose and experimentally demonstrate an approach to generate ultra-wideband (UWB) pulse based on period-one oscillation of semiconductor laser. The baseband UWB signal with 10-dB bandwidth of 5.59 GHz is generated when the gain-switched pulse train is injected into the slave laser diode. Moreover, the center frequency of the generated UWB signal can be continuously tuned and converted up to 19.53 GHz by adjusting the optical frequency detuning in optical domain directly.

Optical Generation and Distribution of OFDM Ultrawideband Signals Over Fiber

In this paper is presented an architecture aiming the distribution of orthogonal frequency division multiplexing (OFDM) signals, compatible with ultra-wide band (UWB) standards, in wavelength division multiplexing (WDM) radio-over-fiber (RoF) scenario. The suggested WDM architecture allows unicast and multicast transmission of OFDM signals within the standard millimeter-wave (mm-wave) UWB bands, from 3.1 to 10.6 GHz and from 57 to 64 GHz, respectively 8 GHz and 60 GHz. The generation of the OFDM-UWB signals with the desired mm-wave carriers' frequencies is made using an optical frequency-quadrupling technique, thus with lower bandwidth requirements for the optical modulator, and allowing the use of a lower frequency electrical drive signal. The OFDM-UWB signals distribution is fully passive, recurring to a cyclic AWG (Arrayed Waveguide Grating). Two types of modulation are used, double side band (DSB) for up-/down-link unicast transmission and DSB with carrier suppression for down-link multicast. In this later case, we avoid the need for high precision filtering, to remove the optical carrier at the receiver, providing a system with greater tolerance to frequency variations. The system's performance is evaluated for different bit rates, input powers and transmission distances, allowing transmission up to 12 km over single mode fiber (SMF), with a maximum EVM below the maximum permissible relative constellation error which is set to a root mean square (RMS) EVM of 14.13% ECMA-368 International Standard: High rate ultra wide-band PHY and MAC Standard, 2007.

Chaotic ultra-wideband microwave signal generation utilizing an optical injection chaotic laser diode

The ideal ultra-wideband (UWB) microwave pulses that fully comply with the indoor spectrum mask governed by Federal Communications Commission(FCC Indoor Mask)are generated by using continuous-wave optical injection to a chaotic laser diode. We firstly simulate and demonstrate the photonic generation of the chaotic UWB signal according to the rate equations of laser diode with optical feedback and injection. The simulations display that the -10 dB bandwidth of UWB signal increases with the increases of optical injection strength, frequency detuning, linewidth enhancement factor and with the decrease of bias current of the slave laser, and the UWB signal central frequency changes in a range from 5 to 8 GHz. We further experimentally obtain tunable chaotic UWB microwave signals with a rate up to 500 Mbit/s by tuning optical injection strength when the other parameters are fixed. The experimental results are in accordance with the theoretical analyses.

An All-Optical Transformer From Differential NRZ Data to Ultra-Wideband Pulse Stream

We propose and experimentally demonstrate a compact and cost-effective scheme based on a fiber Sagnac structure to realize real time conversion from differential nonreturn-to-zero (NRZ) data to ultra-wideband (UWB) pulse stream. The proposed conversion system for the UWB signal generation consists of a single-wavelength laser, a phase modulator, several polarization controllers, and optical couplers. Due to the optical interference between the two phase-modulated light waves with slight phase difference in the Sagnac loop, two sharp optical pulses with opposite polarities are obtained. With proper time delay, a UWB monocycle pulse stream is generated from the original differential NRZ data. Our proposed method gives a reliable, easy, and low-cost transformer from differential NRZ signal to UWB pulse stream, and no high-speed arbitrary waveform generator (AWG) is required in this all-optical transformer.