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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 2 — Jan. 16, 2012
  • pp: 1184–1201
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Photonic ultra-wideband pulse generation, hybrid modulation and dispersion-compensation-free transmission in multi-access communication systems

Kang Tan, Jing Shao, Junqiang Sun, and Jian Wang  »View Author Affiliations


Optics Express, Vol. 20, Issue 2, pp. 1184-1201 (2012)
http://dx.doi.org/10.1364/OE.20.001184


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Abstract

We propose and demonstrate a scheme for optical ultrawideband (UWB) pulse generation by exploiting a half-carrier-suppressed Mach–Zehnder modulator (MZM) and a delay-interferometer- and wavelength-division-multiplexer-based, reconfigurable and multi-channel differentiator (DWRMD). Multi-wavelength, polarity- and shape-switchable UWB pulses of monocycle, doublet, triplet, and quadruplet are experimentally generated simply by tuning two bias voltages to modify the carrier-suppression ratio of MZM and the differential order of DWRMD respectively. The pulse position modulation, pulse shape modulation, pulse amplitude modulation and binary phase-shift keying modulation of UWB pulses can also be conveniently realized with the same scheme structure, which indicates that the hybrid modulation of those four formats can be achieved. Consequently, the proposed approach has potential applications in multi-shape, multi-modulation and multi-access UWB-over-fiber communication systems.

© 2012 OSA

1. Introduction

Ultra-wideband (UWB) is a promising technology in many applications, especially for short-range high-data-rate wireless communication systems and broadband sensor networks, since it has distinct advantages of high data capacity, huge bandwidth, low power spectral density (PSD), and immunity to multipath fading. The Federal Communications Commission (FCC) has allocated 7.5-GHz spectral band from 3.1 to 10.6 GHz for unlicensed use of UWB with a PSD of less than −41.3 dBm/MHz and a 10-dB spectral bandwidth larger than 500 MHz or a fractional bandwidth greater than 20% [1

1. G. R. Aiello and G. D. Rogerson, “Ultra-wideband wireless systems,” IEEE Microw. Mag. 4(2), 36–47 (2003). [CrossRef]

].

In order to take advantage of low transmission loss and extremely broad bandwidth offered by optical communication systems, the generation and modulation of UWB pulses directly in the optical domain have been considered to be of importance for UWB-over-fiber (UWBoF) technology [2

2. D. Porcino and W. Hirt, “Ultra-wideband radio technology: potential and challenges ahead,” IEEE Commun. Mag. 41(7), 66–74 (2003). [CrossRef]

]. Hence, promising solutions for UWB pulse generation and modulation in the optical domain for single- or multi-user UWBoF communication systems have acquired special attention [3

3. J. Yao, F. Zeng, and Q. Wang, “Photonic Generation of Ultrawideband Signals,” J. Lightwave Technol. 25(11), 3219–3235 (2007). [CrossRef]

5

5. R. C. Qiu, H. Liu, and X. Shen, “Ultra-wideband for multiple access communications,” IEEE Commun. Mag. 43(2), 80–87 (2005). [CrossRef]

]. Zeng et al. proposed an approach to UWB doublet pulse generation and distribution over optical fiber by combining an electro-optic phase modulator, a length of single-mode fiber (SMF), and a photo-detector (PD) to form an all-optical microwave bandpass filter [6

6. F. Zeng and J. Yao, “An approach to ultrawideband pulse generation and distribution over optical fiber,” IEEE Photon. Technol. Lett. 18(7), 823–825 (2006). [CrossRef]

]. Dong et al. reported a UWB monocycle generation scheme utilizing gain saturation of dark return-to-zero signal in an SOA [7

7. J. Dong, X. Zhang, J. Xu, and D. Huang, “All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier,” Opt. Lett. 32(15), 2158–2160 (2007). [CrossRef] [PubMed]

]. Bolea et al. presented a photonic structure for arbitrary waveform generation applicable to multiband UWB communications, which was based on a dispersive element and a balanced PD [8

8. M. Bolea, J. Mora, B. Ortega, and J. Capmany, “Photonic arbitrary waveform generation applicable to multiband UWB communications,” Opt. Express 18(25), 26259–26267 (2010). [CrossRef] [PubMed]

]. Huang et al. suggested UWB pulse generation by use of a nonlinear-optical-loop-mirror-based optical switch [9

9. H. Huang, K. Xu, J. Li, J. Wu, X. Hong, and J. Lin, “UWB Pulse Generation and Distribution Using a NOLM Based Optical Switch,” J. Lightwave Technol. 26(15), 2635–2640 (2008). [CrossRef]

]. Li et al. demonstrated an approach to UWB monocycle or doublet pulse generation using cross-gain modulation in highly-nonlinear-fiber-based optical parametric amplifier [10

10. J. Li, B. P. P. Kuo, and K. Kin-Yip Wong, “Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier,” IEEE Photon. Technol. Lett. 21(4), 212–214 (2009). [CrossRef]

]. Wang et al. proposed all-optical UWB pulse generation based on the quadratic nonlinear interactions and sum-frequency generation in periodically poled lithium niobate waveguides [11

11. J. Wang and J. Sun, “All-Optical Ultrawideband Monocycle Generation Using Quadratic Nonlinear Interaction Seeded by Dark Pulses,” IEEE Photon. Technol. Lett. 22(3), 140–142 (2010). [CrossRef]

13

13. J. Wang, J. Sun, X. Zhang, and D. Huang, “All-optical ultrawideband pulse generation using cascaded periodically poled lithium niobate waveguides,” IEEE J. Quantum Electron. 45(3), 292–299 (2009). [CrossRef]

]. A scheme for UWB pulse generation exploiting a Sagnac-interferometer-based intensity modulator was presented, which can provide flexible pulse shape and polarity control of monocycles and doublets [14

14. J. Li, K. Xu, S. Fu, J. Wu, J. Lin, M. Tang, and P. Shum, “Ultra-wideband pulse generation with flexible pulse shape and polarity control using a Sagnac-interferometer-based intensity modulator,” Opt. Express 15(26), 18156–18161 (2007). [CrossRef] [PubMed]

]. Switchable UWB pulse generation of monocycle and doublet by using a polarization maintaining fiber Bragg grating as frequency discriminator was reported [15

15. X. Feng, Z. Li, B.-O. Guan, C. Lu, H. Y. Tam, and P. K. A. Wai, “Switchable UWB pulse generation using a polarization maintaining fiber Bragg grating as frequency discriminator,” Opt. Express 18(4), 3643–3648 (2010). [CrossRef] [PubMed]

]. Photonic generation of UWB signals by direct current modulation of semiconductor lasers was proposed [16

16. V. Torres-Company, K. Prince, and I. T. Monroy, “Fiber transmission and generation of ultrawideband pulses by direct current modulation of semiconductor lasers and chirp-to-intensity conversion,” Opt. Lett. 33(3), 222–224 (2008). [CrossRef] [PubMed]

, 17

17. H. Lv, Y. Yu, T. Shu, D. Huang, S. Jiang, and L. P. Barry, “Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser,” Opt. Express 18(7), 7219–7227 (2010). [CrossRef] [PubMed]

]. Some promising schemes have been presented for generating power-efficient UWB waveforms, utilizing the techniques of arbitrary waveform generation or the combination of a number of low-order derivatives of Gaussian pulses [18

18. M. Abtahi, M. Dastmalchi, S. LaRochelle, and L. A. Rusch, “Generation of Arbitrary UWB Waveforms by Spectral Pulse Shaping and Thermally-Controlled Apodized FBGs,” J. Lightwave Technol. 27(23), 5276–5283 (2009). [CrossRef]

, 19

19. S. T. Abraha, C. M. Okonkwo, E. Tangdiongga, and A. M. J. Koonen, “Power-efficient impulse radio ultrawideband pulse generator based on the linear sum of modified doublet pulses,” Opt. Lett. 36(12), 2363–2365 (2011). [CrossRef] [PubMed]

]. Moreover, some optical UWB generation techniques supporting various modulation formats have been demonstrated, which are capable to achieve two or three modulation formats with the same scheme structure, such as on-off keying (OOK) and binary phase-shift keying (BPSK) [20

20. M. Mirshafiei, M. Dastmalchi, M. Abtahi, S. LaRochelle, and L. A. Rusch, “Optical distribution of UWB: Low complexity pulse generation supporting OOK and PSK,” in Proceedings of IEEE Topical Meeting on Microwave Photonics (MWP) 2010, pp. 346–349 (2010).

, 21

21. Y. Dai and J. Yao, “High-Chip-Count UWB Biphase Coding for Multiuser UWB-Over-Fiber System,” J. Lightwave Technol. 27(11), 1448–1453 (2009). [CrossRef]

]. Besides, the effects of fiber dispersion on UWB waveforms have also been studied, which can be compensated in some schemes by using special elements, such as dispersion compensation fiber, or by modifying the parameters of UWB generation system in order to reduce the unwanted dispersion-induced distortion [22

22. M. Jazayerifar, B. Cabon, and J. A. Salehi, “Transmission of Multi-Band OFDM and Impulse Radio Ultra-Wideband Signals Over Single Mode Fiber,” J. Lightwave Technol. 26(15), 2594–2603 (2008). [CrossRef]

24

24. X. Yu, T. B. Gibbon, and I. T. Monroy, “Experimental Demonstration of All-Optical 781.25-Mb/s Binary Phase-Coded UWB Signal Generation and Transmission,” IEEE Photon. Technol. Lett. 21(17), 1235–1237 (2009). [CrossRef]

]. In addition, since information is transmitted independently and concurrently over a shared physical channel in a multi-access UWBoF communication systems, extensive research appears in a multiple access UWB system using time division multiple access or code division multiple access techniques in order to separate the multiple users and avoid the crosstalk from other channels [25

25. Y. Wang and X. Dong, “A time-division multiple-access SC-FDE system with IBI suppression for UWB communications,” IEEE J. Sel. Areas Comm. 24(4), 920–926 (2006). [CrossRef]

, 26

26. S. H. Song and Q. T. Zhang, “CDMA-PPM for UWB Impulse Radio,” IEEE Trans. Vehicular Technol. 57(2), 1011–1020 (2008). [CrossRef]

]. Phase-coded UWB sequence generator for multiple access UWB communications based on a polarization modulator or phase modulator and a fiber-Bragg-grating (FBG) -based multi-channel frequency discriminator has been demonstrated [27

27. P. Ou, Y. Zhang, and C.-X. Zhang, “Optical generation of binary-phase-coded, direct-sequence ultra-wideband signals by polarization modulation and FBG-based multi-channel frequency discriminator,” Opt. Express 16(7), 5130–5135 (2008). [CrossRef] [PubMed]

, 28

28. Y. Dai and J. Yao, “Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating,” J. Lightwave Technol. 26(15), 2513–2520 (2008). [CrossRef]

], avoiding using bulky FBG array with low stability. Recently, Abraha et al. have proposed, for the first time, service multicasting by all-optical routing of 1 Gb/s impulse-radio (IR) UWB using cross-gain modulation of SOA, which has potential applications for integrating IR-UWB with wavelength-division-multiplexed passive optical networks and in-building networks [29

29. S. Abraha, N. Tran, C. Okonkwo, H. Chen, E. Tangdiongga, and A. Koonen, “Service Multicasting by All-Optical Routing of 1 Gb/s IR UWB for In-Building Networks,” in Proceedings of Optical Fiber Communications Conference/National Fiber Optic Engineers Conference (OFC/NFOEC) 2011, paper JWA68 (2011).

].

Most of those approaches are efficient for UWB pulse generation of monocycles and doublets applied to two or three modulation formats with the same scheme structure, while there appears less research, especially the experimental demonstration, on higher order derivatives of Gaussian pulses that are capable for multi-modulation formats, which would be better for matching the FCC mask in theory and more flexible for future UWBoF systems [30

30. S. Abraha, C. Okonkwo, H. Yang, D. Visani, Y. Shi, H.-D. Jung, E. Tangdiongga, and T. Koonen, “Performance Evaluation of IR-UWB in Short-Range Fiber Communication Using Linear Combination of Monocycles,” J. Lightwave Technol. 29(8), 1143–1151 (2011). [CrossRef]

]. Besides, limited by FCC mask from 3.1 to 10.6 GHz, the width of UWB pulses cannot be as narrow as required to further increase the transmission rate in a single channel. Especially, when pulse position modulation (PPM) is applied, the transmission rate of UWB pulses will be further restricted to a lower value since there should remain certain time spacing between pulses for PPM.

2. Operating principle

Figure 1
Fig. 1 Schematic diagram of the proposal for UWB pulse generation
shows the schematic diagram of the proposal for UWB pulse generation with switchable pulse shape and polarity.

A laser beam of continuous-wave (CW) at wavelength λs is injected into an MZM in order to generate the signal pulse sequence. At the output of MZM, the field amplitude Es(t) of the signal light can be approximately expressed by [31

31. G. Qi, J. Yao, J. Seregelyi, S. Paquet, and C. Belisle, “Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique,” IEEE Trans. Microw. Theory Tech. 53(10), 3090–3097 (2005). [CrossRef]

]
Es(t)=Es0cos{Φ[V(t)]2}cos(ωst),
(1)
where Es0 and ωs are field amplitude and angular frequency of the input CW respectively. V(t) is the applied electrical drive voltage, by which the optical phase difference Φ[V(t)] is caused between the two arms of the MZM. When the MZM is driven by cosine electrical signal and biased at voltage Vbias1, Φ[V(t)] can be written as
Φ[V(t)]=ϕbias1+πVπVmcos(ωmt)=πVπVbias1+πVπVmcos(ωmt),
(2)
where ϕbias1 is the phase shift determined by Vbias1, Vπ is the half-wave voltage of the MZM, Vm and ωm are the amplitude and angular frequency of the electrical drive signal, respectively. Substituting Eq. (2) into Eq. (1), the electric field amplitude of the output optical signal can be expanded in terms of the first kind Bessel functions as
Es(t)=Es0cos{12[ϕbias1+πVπVmcos(ωmt)]}cos(ωst)=Es0cos(ϕbias12)J0(β)cos(ωst)+Es0cos(ϕbias12)×{n=1J2n(β)[cos(ωst2nωmt+nπ)+cos(ωst+2nωmtnπ)]}Es0sin(ϕbias12)×{n=1J2n1(β)[sin(ωst(2n1)ωmt+nππ2)sin(ωst+(2n1)ωmtnπ+π2)]},
(3)
where Jn(β) denotes the n-th order first kind Bessel function and β=πVm2Vπ is the phase modulation index. Equation (3) shows that the power of the input optical carrier will be expanded among the first-order, second-order, and higher order optical sidebands, of which the amplitude distribution can be optimized by modifying the parameters β and ϕbias1. For example, when ϕbias1 is set as odd multiples of π by tuning Vbias1, the optical carrier and all even-order sidebands are suppressed by transferring their power to the odd-order ones.

Under small signal modulation condition, only the optical carrier and the first order sidebands need to be considered, hence Eq. (3) can be simplified to

Es(t)Es0cos(ϕbias12)J0(β)cos(ωst)Es0sin(ϕbias12)×{J1(β)[sin(ωstωmt+π2)sin(ωst+ωmtπ2)]}.
(4)

When the MZM is driven by a Gaussian pulse sequence, each sideband would be broadened due to the Fourier transform relation between the time and frequency domains. Similarly, by tuning Vbias1 to set ϕbias1 close to odd multiples of , partial suppression of the frequency components near the optical carrier, which could be called the half-carrier-suppressed Mach–Zehnder modulation, would be achieved, while the generated optical spectrum is expected for the UWB pulses according to the relation between the optical spectra of UWB pulses and the FCC spectral mask. We have designed an experiment to substantiate the deduction above and truly got pulses in the shape of doublets at the output of the MZM, as shown in Fig. 1. The corresponding electrical spectrum of generated doublets is presented by an inset at the lower left of Fig. 1. Therefore, with the optimization of ϕbias1 determined by , the output signals of the MZM can be shaped as Gaussian pulses or doublets alternatively.

Coupled with continuous probe light at wavelength λp, the signal pulses at λs from MZM are then fed into a highly nonlinear fiber (HNLF), arousing the cross-phase modulation (XPM) of the continuous probe light. Thus, the modulated probe light (Ep(t)) after HNLF obtains a phase variation (φ(t)) that is approximately proportional to the optical power of input Gaussian pulses or doublets (Ps(t)).

Then the two light beams are sent into the DWRMD formed by connecting a 40GHz DI with an 8-channel 200GHz wavelength-division multiplexer (WDM), which is served as a filter to get rid of the unnecessary signal pulses at λs and a first-order or second-order multi-channel differentiator when the bias voltage (Vbias2) of DI and wavelength of probe light are properly set.

After injected into DI, the phased-modulated probe light is divided equally into two parts by a 3dB coupler, with a time delay difference of τ induced by a different path length in one arm and a phase shift of φbias2 induced by applied on the other. Through another 3dB-and 2 × 2 coupler, the signals from two arms are recombined together. Thus, the signals at the two output ports can be expressed as
[Eo(t)E¯o(t)]=12Epmeiωpt[ei[φ(t)+φbias2]ei[φ(tτ)ωpτ]ei[φ(t)+φbias2+π2]+ei[φ(tτ)ωpτ+π2]].
(5)
where Epm and ωp are the electric field amplitude and optical carrier angular frequency of the phase-modulated probe light at the output of HNLF. Hence, the output optical power (Po(t) and P¯o(t)) of the probe light can be represented by

[Po(t)P¯o(t)][Eo(t)Eo(t)E¯o(t)E¯o(t)]=12|Epm|2[1sin[φ(t)φ(tτ)+ωpτ+φbias2+π2]1+sin[φ(t)φ(tτ)+ωpτ+φbias2+π2]].
(6)

Deduced from Eq. (6), the transmission spectrum of DI is periodic. When is 25 ps for 40GHz DI and is 1550 nm, the transmission spectrum period of 40GHz DI (λTDI) is 0.32 nm. Considering the channel spacing of the 200GHz WDM (λTWDM) is 1.6 nm, the whole DWRMD is multi-channel with a channel spacing of 1.6 nm since λTWDM=5λTDI.

When detected by PD that works in the linear response region, the probe light at the output ports converts to photocurrent, the AC terms of which can be approximately written as

[io(t)i¯o(t)][sin[φ(t)φ(tτ)+φbias2+ωpτ+π2]sin[φ(t)φ(tτ)+φbias2+ωpτ+π2]].
(7)

By choosing appropriate φbias2 though tuning Vbias2 to let φbias2+ωpτ+π2 equal Nπ (N should be an integer) and considering that φ(t)φ(tτ) is small enough due to relatively low cross-phase modulation index and small , Eq. (7) can be simplified to

[io(t)i¯o(t)][sin[φ(t)φ(tτ)]±sin[φ(t)φ(tτ)]][[φ(t)φ(tτ)]±[φ(t)φ(tτ)]][[Ps(t)Ps(tτ)]±[Ps(t)Ps(tτ)]]
(8)

Considering that the output signals are proportional to the first-order difference of the signal pulses generated by MZM and is sufficiently small, the signals at the output of DI can be approximated as the first-order differential of the pulses generated from MZM. Moreover, the polarity of the output pulses from each port can be changed conveniently by setting N as an odd or even, which means that pairs of UWB pulses with inverted polarity can be simultaneously obtained from corresponding ports and the polarity of pulses from each port can be easily changed by tuning Vbias2. Comparing the short time shift (mostly less than 3 fs) induced by a π phase shift of the DI at the frequency of the optical carrier (lager than 190 THz) with the bit period of a UWB pulse (mostly more than 1 ns), the polarity of UWB pulses can be switched nearly without time shift or pulse position shift. Hence, when the hybrid modulation format of PPM and BPSK is applied, the influence of pulse position shift on PPM, which is caused by BPSK, is small enough to be ignored.

When the wavelength of the probe light (λp) is located on the top flat of super-Gaussian spectral transmittance curve of one WDM channel, the WDM only acts as a filter and DI performs as a first-order differentiator, forming a first-order multi-channel differentiator with conveniently tuning characteristics. Moreover, the large slope variation range of super-Gaussian transfer function of each WDM channel is beneficial for optimizing the spectral response of DI, which indicates that it is possible to achieve desired positive and negative quadrature slopes of the whole DWRMD spectral transmittance curve by adjusting Vbias2. Therefore, the DWRMD could also be reconfigured to be a second-order differentiator when the optical carrier of the phase-modulated probe light is located at those positions with quadrature slopes.

Considering that the device properties and the experimental conditions cannot be ideal and that there are some parasitic effects in the whole UWB pulse generation system, there would be slight differences between the pulse shapes predicted by the developed theory and the experimental results. Firstly, the MZM may not provide ideal transformation from electrical signals to optical ones, while the Vbias1 may jitter or not be properly set. Secondly, when probe lights and signal light propagate in the HNLF, there also exist some other nonlinear effects besides XPM, such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) and four-wave mixing (FWM). Since the wavelength spacing of about 1.6 nm is relatively large and the power of probe light in each channel is set to be relatively low, the crosstalk between the adjacent channels which is caused by SBS, SRS and FWM is very small but still has a little influence on the waveforms at the output of the HNLF. Thirdly, the DWRMD may also induce some distortion when spectral transmittance curve of WDM is not ideal or Vbias2 jitters or is not properly set.

As a consequence, by tuning Vbias1 of the MZM to generate Gaussian pulses and Vbias2 of the DI to reconfigure the DWRMD as a first-order or second-order multi-channel differentiator, monocycles or doublets with inverted polarity at different wavelengths are obtained, as shown by the four insets from A to D at the upper right of Fig. 1. Similarly, by tuning Vbias1 of the MZM to generate doublets and Vbias2 of the DI to reconfigure the DWRMD as a first-order or second-order multi-channel differentiator, triplets or quadruplets with inverted polarity at different wavelengths are also achieved, as shown by the four insets from E to H at the lower right of Fig. 1. Moreover, since the DWRMD is multi-channel with a channel spacing of 1.6 nm, more CW probes could be added as communication channels for more users in order to establish a multi-access UWB systems.

3. Experimental demonstration and discussion

The experimental setup is shown in Fig. 2
Fig. 2 The experimental setup for UWB pulse generation, transmission and multicasting. TLS: tunable laser source; PC: polarization controller; MZM: Mach–Zehnder modulator; BPG: bit pattern generator; EDFA: erbium-doped fiber amplifier; OC: optical coupler; HNLF: highly nonlinear fiber; DI: delay interferometer; WDM: wavelength-division multiplexer; SMF: single-mode fiber; PD: photo-detector; ESA: electrical spectrum analyzer; DCA: digital communication analyzer.
. Emitted by a tunable laser source, the CW at 1542 nm (λs) with an output power of 13 dBm is sent into MZM through a polarization controller, which is used for adjusting the polarization of the CW to be optimal for MZM. The MZM is driven by a bit pattern generator (BPG) and biased at different voltages (Vbias1) to generate Gaussian pulses or doublets. The BPG is used for generating electrical Gaussian pulse train with a fixed pattern “0000 0000 1000 0000” (one “1” per 16 bits) at a bit rate of 10 Gbit/s, corresponding to the pulse repetition rate of 0.625 GHz.

Firstly, we would like to take the signals from ch5 of the WDM as an example to observe the waveforms and spectra of generated UWB pulses. When the MZM is reconfigured properly to generate Gaussian pulses, polarity- and shape-switchable monocycles and doublets can be obtained by tuning the bias voltage () of the DWRMD. The monocycles with positive and negative polarity are shown by the red dashed curve and blue solid curve respectively in Fig. 3(a)
Fig. 3 Waveforms and spectra of the generated monocycles. (a) Waveforms of the positive (red dashed line) and negative (blue solid line) monocycles. (b) Corresponding electrical spectrum with FCC mask in green dashed line.
. The upper full-width at half-maximum (FWHM) and lower FWHM of the positive monocycle are about 52 and 42 ps, respectively, while the monocycle with negative polarity has the upper and lower FWHM of approximately 50 and 42 ps respectively. Given by Fig. 3(b), the corresponding electrical spectrum shows a central frequency of about 5.4 GHz and a 10-dB bandwidth of about 9.25 GHz, indicating that the fractional bandwidth is about 171%. Displayed in Fig. 4(a)
Fig. 4 Waveforms and spectra of the generated doublets. (a) Waveforms of the positive (red dashed line) and negative (blue solid line) doublets. (b) Corresponding electrical spectrum with FCC mask in green dashed line.
with red dashed curve and blue solid curve, the positive and negative doublet possesses the FWHMs of ~48 and ~40 ps, while the central frequency and 10-dB bandwidth of doublets, shown in Fig. 4(b), are ~8.69 and ~11.22 GHz, corresponding to a fractional bandwidth of ~129%.

When the MZM is reconfigured to produce doublets, triplets and quadruplets can be generated by adjusting . As depicted in Fig. 5(a)
Fig. 5 Waveforms and spectra of the generated triplets. (a) Waveforms of the positive (red dashed line) and negative (blue solid line) triplets. (b) Corresponding electrical spectrum with FCC mask in green dashed line.
, the upper and lower FWHM of the positive triplet is about 36 and 40 ps respectively, while the negative triplet is illustrated with the upper and lower FWHM of approximately 30 and 42 ps respectively. The corresponding electrical spectrum, as shown in Fig. 5(b), has a central frequency of ~8.93 GHz, a 10-dB bandwidth of ~9.26 GHz and a fractional bandwidth of ~104%. Finally, the positive and negative quadruplets are displayed in Fig. 6(a)
Fig. 6 Waveforms and spectra of the generated quadruplets. (a) Waveforms of the positive (red dashed line) and negative (blue solid line) quadruplets. (b) Corresponding electrical spectrum with FCC mask in green dashed line.
with the red dashed curve and blue solid curve, the FWHMs of which are ~40 and ~30 ps, respectively. As depicted in Fig. 6(b), the central frequency and 10-dB bandwidth are ~10.43 and ~7.14 GHz, presenting a fractional bandwidth of ~68%.

After propagating over 75-km SMF, the generated triplets are analyzed as the bias voltage of DWRMD (Vbias2) tunes continuously in the range of 0-4V. Figure 9
Fig. 9 Central frequency and 10-dB bandwidth of UWB pulses as a function of Vbias2 after 75km-length SMF transmission
reveals the central frequency and 10-dB bandwidth as a function of Vbias2. As shown in Fig. 9, there is no UWB pulses generated when is tuned in the range of 2.4-3.4V due to the coherent cancellation in DI influenced by the corresponding φbias2, while the left and right parts are UWB regions. The central frequency and 10-dB bandwidth have the overall growth of different levels when is tuned from 0 to 1.6V. Meanwhile, they slightly decreases when is set in the range of 1.6-2.4V and 3.4-4.0V. Thus, to some extent, the DWRMD might also be reconfigured to slightly optimize the corresponding electrical spectra obtained in base station in order to better meet the FCC’s definition by appropriately tuning Vbias2 in a small range.

The WDM transmission system for the multi-access of UWB signal is shown in Fig. 10
Fig. 10 WDM-UWB transmission system for multi-access. AWG: arrayed waveguide grating.
. A pair of AWGs is applied to multiplex and demultiplex the generated UWB pulses at eight different wavelengths as different communication channels for different users, while the polarity of the UWB pulses at each wavelength can be changed by choosing corresponding output ports for multiplexing. The optical spectra of the eight-wavelength probe lights after multiplexing are shown by an inset in Fig. 10. Since the pulse repetition rate for every channel is 1.25 GHz, the total transmission rate of UWB pulses in the SMF after multiplexing reaches 10 Gbit/s. Figure 11
Fig. 11 The UWB pulses generated at different wavelengths as different communication channels. (a) Pulsewidth, (b) central frequency and 10-dB bandwidth of the negative triplets versus the wavelength.
depicts the pulse width, the central frequency and 10-dB bandwidth of the triplets propagating over 25-km SMF as a function of the eight wavelengths of the probe light, corresponding to the eight communication channels. Since the wavelength spacing of adjacent probe lights may not be precisely equal to the integral multiples of the period of DI (), the upper and lower FWHM fluctuates a little as shown in Fig. 11(a), which influences little on the temporal shape as shown by the insets for the waveforms of ch1, ch4 and ch8. Meanwhile, for the same reason, there appears very slight fluctuation of the central frequency and the 10-dB bandwidth in different channels, as displayed in Fig. 11(b). By well tuning the wavelength for each channel, the fluctuations can be minimized and a better performance for multi-access communication can be obtained. Though the conversion bandwidth of XPM in HNLF is very wide, the features of devices limit the available bandwidth for wavelength-division multiplexing. Mainly considering the 3-dB bandwidth of the gain spectrum of EDFA implemented for pre-amplifying the probe lights before transmission and the wavelength spacing of 1.6 nm, the number of efficient wavelengths for multiplexing may reach about 25 in the proposal when the number of WDM channels increases synchronously.

Additionally, most approaches for UWB generation exploiting nonlinearities will be involved in the estimation of power budget and system efficiency, mainly due to the relatively low nonlinearity efficiency [7

7. J. Dong, X. Zhang, J. Xu, and D. Huang, “All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier,” Opt. Lett. 32(15), 2158–2160 (2007). [CrossRef] [PubMed]

, 9

9. H. Huang, K. Xu, J. Li, J. Wu, X. Hong, and J. Lin, “UWB Pulse Generation and Distribution Using a NOLM Based Optical Switch,” J. Lightwave Technol. 26(15), 2635–2640 (2008). [CrossRef]

, 11

11. J. Wang and J. Sun, “All-Optical Ultrawideband Monocycle Generation Using Quadratic Nonlinear Interaction Seeded by Dark Pulses,” IEEE Photon. Technol. Lett. 22(3), 140–142 (2010). [CrossRef]

13

13. J. Wang, J. Sun, X. Zhang, and D. Huang, “All-optical ultrawideband pulse generation using cascaded periodically poled lithium niobate waveguides,” IEEE J. Quantum Electron. 45(3), 292–299 (2009). [CrossRef]

]. However, considering that large numbers of probe lights can be added for providing additional channels without changing the signal light power according to the principle of XPM, the system efficiency in the proposed scheme will increase a lot compared with conventional cases. Moreover, when the materials or structures with high nonlinearity are implemented, the system efficiency will be further improved. For example, the chalcogenide rib waveguide or fiber taper can be applied for arousing the XPM, which provides the nonlinearity parameter of several hundred or thousand times that in HNLF [32

32. B. J. Eggleton, B. Luther-Davies, and K. Richardson, “Chalcogenide photonics,” Nat. Photonics 5, 141–148 (2011).

].

Finally, it is worth noting that the proposal may show some features for the potentiality to be robust to some effects of the antenna and wireless channel. For example, considering that the pulse shape can vary a lot from monocycle to quadruplet by tuning Vbias1 and Vbias2, the two bias voltages are beneficial to modify the UWB pulse shape for pre-distortion correction in order to compensate the shape distortion introduced from the antenna or wireless channel.

4. Demonstration and discussion on hybrid modulation

The above experiments demonstrate that the proposed scheme is efficient for multi-wavelength, polarity- and shape-switchable UWB pulse generation and transmission. According to the analysis of reconfiguring methods in principle, the modulation formats of PPM, PSM, PAM and BPSK can also be accomplished independently with the same structure.

One way for realizing the PPM is to change the position of “1” in the fixed pattern for generating UWB pulses, but it is an electrical method for multicasting, only providing discrete pulse positions for PPM. Considering λTWDM=5λTDI, there are, in every channel, at least three wavelengths of probe light that can be chosen to generate the same UWB pulses, which can be used in all-optical PPM applied for wavelength division multiplexing together with chromatic dispersion in fiber since the UWB pulses are tolerant to chromatic dispersion as substantiated in the experiments. Assuming the chromatic dispersion of the SMF for transmission at wavelength λp is 17 ps/nm/km, the differences of group delay between those three wavelengths of probe light per kilometer in SMF are about λTDI×17=5.44 ps/km and 2×λTDI×17=10.88 ps/km. Hence, when the SMF length is 20 km, the time shift of 108.8 ps and 217.6 ps is obtained only by changing the wavelength of probe light. Moreover, when the length and chromatic dispersion of SMF for transmission is fixed, with the λp tuned continuously together with Vbias2 in order to let φbias2+ωpτ remain constant or have even multiples of π shift, the all-optical continuous change of pulse position in the range of more than 200 ps could be easily achieved without changing the shape, polarity or amplitude of UWB pulses.

To implement PSM of UWB pulses from monocycle to quadruplet for multicasting, Vbias1 and Vbias2 should be modified simultaneously for tuning the carrier-suppression ratio and the differential order of the DWRMD respectively. Here we take the PSM of monocycles and triplets as an example. Considering that those two kinds of UWB pulses can be regarded as the first order differential of Gaussian pulses and doublets, we can firstly tune to let equal (N is an integer) so that the DWRMD performs as a first order differentiator. Then, by tuning to adjust the carrier-suppression ratio for alternatively generating the Gaussian pulses or doublets, the PSM of monocycles and triplets can be obtained without changing other characteristics of UWB pulses for other three modulation formats.

For PAM, we can dynamically set a proper power of 1480-nm pump light for EDFA (PEP), which is used for amplifying the signal pulses generated from MZM. Considering the cross-phase modulation index is proportional to the amplitude of those signal pulses, the amplitude of the generated UWB pulses can be modified by continuously changing the power of the 1480-nm pump light, presenting that the all-optical PAM with continuous tuning characteristics can be realized for multicasting. Similar to PPM and PSM, the PAM also has no influence on the other three modulation formats.

Since two groups of output ports of DWRMD can simultaneously provide pairs of polarity-inverted UWB pulses (E0(t) and E¯0(t)), there are two methods for realizing BPSK. One method applied for wavelength division multiplexing is to apply certain optical switches between UWB pulse generator and AWG for multiplexing in order to alternatively choose the required polarity of UWB pulses from two groups of output ports of DWRMD, one group of which is from ch1 to ch8 and the other is from ch1¯ to ch8¯. The other method for multicasting is to tune Vbias2 to let φbias2+ωpτ have a shift of odd multiples of π. Thus, the influence on the other three modulation formats, which is caused by BPSK, is also negligible.

Therefore, as PSM, BPSK, PPM and PAM can be independently achieved for multicasting applications by tuning , , λp and PEP which contribute four degrees of freedom for modulation, the hybrid modulation of those four formats can potentially be obtained for multicasting.

As there is only one BPG in our laboratory that is not enough to implement the four modulation formats together with the generation, the hybrid modulation format for UWB pulses is numerically simulated by using Optisystem 7.0.

The transmission rate of UWB pulses is 1.25 Gbit/s, while the length and chromatic dispersion of SMF for transmission is 25 km and 17 ps/nm/km respectively. Thus, when we choose the different wavelengths with the shift of one spectrum period of DI, the time shift for PPM between two differently modulated pulses is approximately 136 ps. As shown in Fig. 12
Fig. 12 Demonstration of UWB hybrid modulation format of PPM, PSM, PAM and BPSK. The matrixes in green color describe the corresponding values of the four parameters for tuning.
, the numerical results present that, with the hybrid modulation of four formats, the UWB signal sequence of 16 pulses can convey 16 states of information in Gray code from 0000 to 1000, which means that the signals of 16 pulses transmit totally the data of 64 bits over the fiber link. The PPM, PSM, PAM and BPSK represent the 4 bits from the highest to lowest respectively. For PPM, pulse position of approximate 450 and 314 ps, measured starting from the beginning of the pulse period, represent 0 and 1, which is technically achieved by setting the wavelength of probe light as λp0 and λp1 respectively. For PSM, monocycle and triplet represent 0 and 1, which is technically obtained by setting the bias voltage of MZM as Vbias10 and Vbias11 respectively. For PAM, the half amplitude and the full one represent 0 and 1, which is technically accomplished by setting the pump light power for EDFA as PEP0 and PEP1 respectively. For BPSK, the negative and positive polarity represent 0 and 1, which is technically realized by setting the bias voltage of DWRMD as Vbias20 and Vbias21 respectively. One of the methods for the technical implementation in a practical way is to use a dual-drive MZM, a 40GHz DI with RF input port for injecting high speed signals in order to induce rapid phase shifting between the two arms, a single-drive MZM and a 80GHz DI with RF input port as a wavelength switch for tuning , Vbias2, PEP and λp respectively, which is also the technical scheme chosen for the simulation [33

33. S. Pan and J. Yao, “Performance evaluation of UWB signal transmission over optical fiber,” IEEE J. Sel. Areas Comm. 28(6), 889–900 (2010). [CrossRef]

].

The transient state between “0” and “1” or “1” and “0” in the data signal generates some undesirable parasitic pulses as shown in Fig. 12, which may deteriorate the performance of a UWB communication system. Methods to get rid of the parasitic pulses are under investigation.

Considering that a bit group of digital sequences for information communication is mostly coded from a corresponding sampling value of an analog signal that often changes continuously, the adjacent bit groups may often vary in only one bit with Gray code applied. Therefore, by using hybrid modulation formats and Gray coding, the adjacent UWB pulses may often vary in only one characteristic among position, shape, amplitude and polarity, which is relatively convenient for detection and demodulation in practical applications.

The above demonstration performs well when 4-bit groups code the analog signals. If more bits are used for coding and the number of bits in use is integer multiples of 4, which is common in actual coding process such as the 8-bit bytes for computing, we can divide one whole bit group that represents one sampling value of analog signals into several parts with every part consisting of 4 bits. Additionally, when the number of bits in bit group is not the integer multiples of 4, the division should start from the lowest bit to the highest one so that only the part including the highest bit do not consists of 4 bits. Then the part less than 4 bits can be represented by less than four corresponding formats for hybrid modulation, while the other formats are ignored in demodulation. Thus, the 4-bit Gray coding for hybrid modulation in proposed scheme can also function well. Each pair of corresponding 4-bit parts or shorter than 4-bit parts in adjacent bit groups remains the same or varies in only one bit at most times, indicating that each pair of corresponding UWB pulses in adjacent pulse groups also stays the same or varies in only one characteristic mostly.

5. Conclusion

Acknowledgments

This work was supported by the National High Technology Research and Development Program of China (Grant No.2009AA03Z410) and the National Natural Science Foundation of China (Project number: 60977044 and 61077051).

References and links

1.

G. R. Aiello and G. D. Rogerson, “Ultra-wideband wireless systems,” IEEE Microw. Mag. 4(2), 36–47 (2003). [CrossRef]

2.

D. Porcino and W. Hirt, “Ultra-wideband radio technology: potential and challenges ahead,” IEEE Commun. Mag. 41(7), 66–74 (2003). [CrossRef]

3.

J. Yao, F. Zeng, and Q. Wang, “Photonic Generation of Ultrawideband Signals,” J. Lightwave Technol. 25(11), 3219–3235 (2007). [CrossRef]

4.

S. Pan and J. Yao, “UWB-Over-Fiber Communications: Modulation and Transmission,” J. Lightwave Technol. 28(16), 2445–2455 (2010). [CrossRef]

5.

R. C. Qiu, H. Liu, and X. Shen, “Ultra-wideband for multiple access communications,” IEEE Commun. Mag. 43(2), 80–87 (2005). [CrossRef]

6.

F. Zeng and J. Yao, “An approach to ultrawideband pulse generation and distribution over optical fiber,” IEEE Photon. Technol. Lett. 18(7), 823–825 (2006). [CrossRef]

7.

J. Dong, X. Zhang, J. Xu, and D. Huang, “All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier,” Opt. Lett. 32(15), 2158–2160 (2007). [CrossRef] [PubMed]

8.

M. Bolea, J. Mora, B. Ortega, and J. Capmany, “Photonic arbitrary waveform generation applicable to multiband UWB communications,” Opt. Express 18(25), 26259–26267 (2010). [CrossRef] [PubMed]

9.

H. Huang, K. Xu, J. Li, J. Wu, X. Hong, and J. Lin, “UWB Pulse Generation and Distribution Using a NOLM Based Optical Switch,” J. Lightwave Technol. 26(15), 2635–2640 (2008). [CrossRef]

10.

J. Li, B. P. P. Kuo, and K. Kin-Yip Wong, “Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier,” IEEE Photon. Technol. Lett. 21(4), 212–214 (2009). [CrossRef]

11.

J. Wang and J. Sun, “All-Optical Ultrawideband Monocycle Generation Using Quadratic Nonlinear Interaction Seeded by Dark Pulses,” IEEE Photon. Technol. Lett. 22(3), 140–142 (2010). [CrossRef]

12.

J. Wang, Q. Sun, J. Sun, and W. Zhang, “All-optical UWB pulse generation using sum-frequency generation in a PPLN waveguide,” Opt. Express 17(5), 3521–3530 (2009). [CrossRef] [PubMed]

13.

J. Wang, J. Sun, X. Zhang, and D. Huang, “All-optical ultrawideband pulse generation using cascaded periodically poled lithium niobate waveguides,” IEEE J. Quantum Electron. 45(3), 292–299 (2009). [CrossRef]

14.

J. Li, K. Xu, S. Fu, J. Wu, J. Lin, M. Tang, and P. Shum, “Ultra-wideband pulse generation with flexible pulse shape and polarity control using a Sagnac-interferometer-based intensity modulator,” Opt. Express 15(26), 18156–18161 (2007). [CrossRef] [PubMed]

15.

X. Feng, Z. Li, B.-O. Guan, C. Lu, H. Y. Tam, and P. K. A. Wai, “Switchable UWB pulse generation using a polarization maintaining fiber Bragg grating as frequency discriminator,” Opt. Express 18(4), 3643–3648 (2010). [CrossRef] [PubMed]

16.

V. Torres-Company, K. Prince, and I. T. Monroy, “Fiber transmission and generation of ultrawideband pulses by direct current modulation of semiconductor lasers and chirp-to-intensity conversion,” Opt. Lett. 33(3), 222–224 (2008). [CrossRef] [PubMed]

17.

H. Lv, Y. Yu, T. Shu, D. Huang, S. Jiang, and L. P. Barry, “Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser,” Opt. Express 18(7), 7219–7227 (2010). [CrossRef] [PubMed]

18.

M. Abtahi, M. Dastmalchi, S. LaRochelle, and L. A. Rusch, “Generation of Arbitrary UWB Waveforms by Spectral Pulse Shaping and Thermally-Controlled Apodized FBGs,” J. Lightwave Technol. 27(23), 5276–5283 (2009). [CrossRef]

19.

S. T. Abraha, C. M. Okonkwo, E. Tangdiongga, and A. M. J. Koonen, “Power-efficient impulse radio ultrawideband pulse generator based on the linear sum of modified doublet pulses,” Opt. Lett. 36(12), 2363–2365 (2011). [CrossRef] [PubMed]

20.

M. Mirshafiei, M. Dastmalchi, M. Abtahi, S. LaRochelle, and L. A. Rusch, “Optical distribution of UWB: Low complexity pulse generation supporting OOK and PSK,” in Proceedings of IEEE Topical Meeting on Microwave Photonics (MWP) 2010, pp. 346–349 (2010).

21.

Y. Dai and J. Yao, “High-Chip-Count UWB Biphase Coding for Multiuser UWB-Over-Fiber System,” J. Lightwave Technol. 27(11), 1448–1453 (2009). [CrossRef]

22.

M. Jazayerifar, B. Cabon, and J. A. Salehi, “Transmission of Multi-Band OFDM and Impulse Radio Ultra-Wideband Signals Over Single Mode Fiber,” J. Lightwave Technol. 26(15), 2594–2603 (2008). [CrossRef]

23.

M. Abtahi and L. A. Rusch, “RoF Delivery over PONs of Optically Shaped UWB Signals for Gigabit/s Wireless Distribution in the Home,” IEEE J. Sel. Areas Comm. 29(6), 1304–1310 (2011). [CrossRef]

24.

X. Yu, T. B. Gibbon, and I. T. Monroy, “Experimental Demonstration of All-Optical 781.25-Mb/s Binary Phase-Coded UWB Signal Generation and Transmission,” IEEE Photon. Technol. Lett. 21(17), 1235–1237 (2009). [CrossRef]

25.

Y. Wang and X. Dong, “A time-division multiple-access SC-FDE system with IBI suppression for UWB communications,” IEEE J. Sel. Areas Comm. 24(4), 920–926 (2006). [CrossRef]

26.

S. H. Song and Q. T. Zhang, “CDMA-PPM for UWB Impulse Radio,” IEEE Trans. Vehicular Technol. 57(2), 1011–1020 (2008). [CrossRef]

27.

P. Ou, Y. Zhang, and C.-X. Zhang, “Optical generation of binary-phase-coded, direct-sequence ultra-wideband signals by polarization modulation and FBG-based multi-channel frequency discriminator,” Opt. Express 16(7), 5130–5135 (2008). [CrossRef] [PubMed]

28.

Y. Dai and J. Yao, “Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating,” J. Lightwave Technol. 26(15), 2513–2520 (2008). [CrossRef]

29.

S. Abraha, N. Tran, C. Okonkwo, H. Chen, E. Tangdiongga, and A. Koonen, “Service Multicasting by All-Optical Routing of 1 Gb/s IR UWB for In-Building Networks,” in Proceedings of Optical Fiber Communications Conference/National Fiber Optic Engineers Conference (OFC/NFOEC) 2011, paper JWA68 (2011).

30.

S. Abraha, C. Okonkwo, H. Yang, D. Visani, Y. Shi, H.-D. Jung, E. Tangdiongga, and T. Koonen, “Performance Evaluation of IR-UWB in Short-Range Fiber Communication Using Linear Combination of Monocycles,” J. Lightwave Technol. 29(8), 1143–1151 (2011). [CrossRef]

31.

G. Qi, J. Yao, J. Seregelyi, S. Paquet, and C. Belisle, “Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique,” IEEE Trans. Microw. Theory Tech. 53(10), 3090–3097 (2005). [CrossRef]

32.

B. J. Eggleton, B. Luther-Davies, and K. Richardson, “Chalcogenide photonics,” Nat. Photonics 5, 141–148 (2011).

33.

S. Pan and J. Yao, “Performance evaluation of UWB signal transmission over optical fiber,” IEEE J. Sel. Areas Comm. 28(6), 889–900 (2010). [CrossRef]

34.

R. C. Qiu, “A study of the ultra-wideband wireless propagation channel and optimum UWB receiver design,” IEEE J. Sel. Areas Comm. 20(9), 1628–1637 (2002). [CrossRef]

35.

I. S. Lin and A. M. Weiner, “Selective Correlation Detection of Photonically Generated Ultrawideband RF Signals,” J. Lightwave Technol. 26(15), 2692–2699 (2008). [CrossRef]

36.

J. Dederer, B. Schleicher, A. Trasser, T. Feger, and H. Schumacher, “A fully monolithic 3.1-10.6 GHz UWB Si/SiGe HBT Impulse-UWB correlation receiver,” in Proceedings of IEEE International Conference on Ultra-Wideband, ICUWB 2008, pp. 33–36 (2008).

37.

T. Li, H. Zhou, and M. Yi, “Gray Coded PPM Performance with Imperfect Slot Synchronization in Optical Communication,” in Proceedings of Conference on Lasers and Electro-Optics/Pacific Rim 2009, (Optical Society of America, 2009), paper TUP11_30 (2009).

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2330) Fiber optics and optical communications : Fiber optics communications
(070.1170) Fourier optics and signal processing : Analog optical signal processing
(350.4010) Other areas of optics : Microwaves
(060.5625) Fiber optics and optical communications : Radio frequency photonics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: September 6, 2011
Revised Manuscript: November 23, 2011
Manuscript Accepted: December 12, 2011
Published: January 5, 2012

Citation
Kang Tan, Jing Shao, Junqiang Sun, and Jian Wang, "Photonic ultra-wideband pulse generation, hybrid modulation and dispersion-compensation-free transmission in multi-access communication systems," Opt. Express 20, 1184-1201 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-2-1184


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References

  1. G. R. Aiello and G. D. Rogerson, “Ultra-wideband wireless systems,” IEEE Microw. Mag.4(2), 36–47 (2003). [CrossRef]
  2. D. Porcino and W. Hirt, “Ultra-wideband radio technology: potential and challenges ahead,” IEEE Commun. Mag.41(7), 66–74 (2003). [CrossRef]
  3. J. Yao, F. Zeng, and Q. Wang, “Photonic Generation of Ultrawideband Signals,” J. Lightwave Technol.25(11), 3219–3235 (2007). [CrossRef]
  4. S. Pan and J. Yao, “UWB-Over-Fiber Communications: Modulation and Transmission,” J. Lightwave Technol.28(16), 2445–2455 (2010). [CrossRef]
  5. R. C. Qiu, H. Liu, and X. Shen, “Ultra-wideband for multiple access communications,” IEEE Commun. Mag.43(2), 80–87 (2005). [CrossRef]
  6. F. Zeng and J. Yao, “An approach to ultrawideband pulse generation and distribution over optical fiber,” IEEE Photon. Technol. Lett.18(7), 823–825 (2006). [CrossRef]
  7. J. Dong, X. Zhang, J. Xu, and D. Huang, “All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier,” Opt. Lett.32(15), 2158–2160 (2007). [CrossRef] [PubMed]
  8. M. Bolea, J. Mora, B. Ortega, and J. Capmany, “Photonic arbitrary waveform generation applicable to multiband UWB communications,” Opt. Express18(25), 26259–26267 (2010). [CrossRef] [PubMed]
  9. H. Huang, K. Xu, J. Li, J. Wu, X. Hong, and J. Lin, “UWB Pulse Generation and Distribution Using a NOLM Based Optical Switch,” J. Lightwave Technol.26(15), 2635–2640 (2008). [CrossRef]
  10. J. Li, B. P. P. Kuo, and K. Kin-Yip Wong, “Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier,” IEEE Photon. Technol. Lett.21(4), 212–214 (2009). [CrossRef]
  11. J. Wang and J. Sun, “All-Optical Ultrawideband Monocycle Generation Using Quadratic Nonlinear Interaction Seeded by Dark Pulses,” IEEE Photon. Technol. Lett.22(3), 140–142 (2010). [CrossRef]
  12. J. Wang, Q. Sun, J. Sun, and W. Zhang, “All-optical UWB pulse generation using sum-frequency generation in a PPLN waveguide,” Opt. Express17(5), 3521–3530 (2009). [CrossRef] [PubMed]
  13. J. Wang, J. Sun, X. Zhang, and D. Huang, “All-optical ultrawideband pulse generation using cascaded periodically poled lithium niobate waveguides,” IEEE J. Quantum Electron.45(3), 292–299 (2009). [CrossRef]
  14. J. Li, K. Xu, S. Fu, J. Wu, J. Lin, M. Tang, and P. Shum, “Ultra-wideband pulse generation with flexible pulse shape and polarity control using a Sagnac-interferometer-based intensity modulator,” Opt. Express15(26), 18156–18161 (2007). [CrossRef] [PubMed]
  15. X. Feng, Z. Li, B.-O. Guan, C. Lu, H. Y. Tam, and P. K. A. Wai, “Switchable UWB pulse generation using a polarization maintaining fiber Bragg grating as frequency discriminator,” Opt. Express18(4), 3643–3648 (2010). [CrossRef] [PubMed]
  16. V. Torres-Company, K. Prince, and I. T. Monroy, “Fiber transmission and generation of ultrawideband pulses by direct current modulation of semiconductor lasers and chirp-to-intensity conversion,” Opt. Lett.33(3), 222–224 (2008). [CrossRef] [PubMed]
  17. H. Lv, Y. Yu, T. Shu, D. Huang, S. Jiang, and L. P. Barry, “Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser,” Opt. Express18(7), 7219–7227 (2010). [CrossRef] [PubMed]
  18. M. Abtahi, M. Dastmalchi, S. LaRochelle, and L. A. Rusch, “Generation of Arbitrary UWB Waveforms by Spectral Pulse Shaping and Thermally-Controlled Apodized FBGs,” J. Lightwave Technol.27(23), 5276–5283 (2009). [CrossRef]
  19. S. T. Abraha, C. M. Okonkwo, E. Tangdiongga, and A. M. J. Koonen, “Power-efficient impulse radio ultrawideband pulse generator based on the linear sum of modified doublet pulses,” Opt. Lett.36(12), 2363–2365 (2011). [CrossRef] [PubMed]
  20. M. Mirshafiei, M. Dastmalchi, M. Abtahi, S. LaRochelle, and L. A. Rusch, “Optical distribution of UWB: Low complexity pulse generation supporting OOK and PSK,” in Proceedings of IEEE Topical Meeting on Microwave Photonics (MWP) 2010, pp. 346–349 (2010).
  21. Y. Dai and J. Yao, “High-Chip-Count UWB Biphase Coding for Multiuser UWB-Over-Fiber System,” J. Lightwave Technol.27(11), 1448–1453 (2009). [CrossRef]
  22. M. Jazayerifar, B. Cabon, and J. A. Salehi, “Transmission of Multi-Band OFDM and Impulse Radio Ultra-Wideband Signals Over Single Mode Fiber,” J. Lightwave Technol.26(15), 2594–2603 (2008). [CrossRef]
  23. M. Abtahi and L. A. Rusch, “RoF Delivery over PONs of Optically Shaped UWB Signals for Gigabit/s Wireless Distribution in the Home,” IEEE J. Sel. Areas Comm.29(6), 1304–1310 (2011). [CrossRef]
  24. X. Yu, T. B. Gibbon, and I. T. Monroy, “Experimental Demonstration of All-Optical 781.25-Mb/s Binary Phase-Coded UWB Signal Generation and Transmission,” IEEE Photon. Technol. Lett.21(17), 1235–1237 (2009). [CrossRef]
  25. Y. Wang and X. Dong, “A time-division multiple-access SC-FDE system with IBI suppression for UWB communications,” IEEE J. Sel. Areas Comm.24(4), 920–926 (2006). [CrossRef]
  26. S. H. Song and Q. T. Zhang, “CDMA-PPM for UWB Impulse Radio,” IEEE Trans. Vehicular Technol.57(2), 1011–1020 (2008). [CrossRef]
  27. P. Ou, Y. Zhang, and C.-X. Zhang, “Optical generation of binary-phase-coded, direct-sequence ultra-wideband signals by polarization modulation and FBG-based multi-channel frequency discriminator,” Opt. Express16(7), 5130–5135 (2008). [CrossRef] [PubMed]
  28. Y. Dai and J. Yao, “Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating,” J. Lightwave Technol.26(15), 2513–2520 (2008). [CrossRef]
  29. S. Abraha, N. Tran, C. Okonkwo, H. Chen, E. Tangdiongga, and A. Koonen, “Service Multicasting by All-Optical Routing of 1 Gb/s IR UWB for In-Building Networks,” in Proceedings of Optical Fiber Communications Conference/National Fiber Optic Engineers Conference (OFC/NFOEC) 2011, paper JWA68 (2011).
  30. S. Abraha, C. Okonkwo, H. Yang, D. Visani, Y. Shi, H.-D. Jung, E. Tangdiongga, and T. Koonen, “Performance Evaluation of IR-UWB in Short-Range Fiber Communication Using Linear Combination of Monocycles,” J. Lightwave Technol.29(8), 1143–1151 (2011). [CrossRef]
  31. G. Qi, J. Yao, J. Seregelyi, S. Paquet, and C. Belisle, “Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique,” IEEE Trans. Microw. Theory Tech.53(10), 3090–3097 (2005). [CrossRef]
  32. B. J. Eggleton, B. Luther-Davies, and K. Richardson, “Chalcogenide photonics,” Nat. Photonics5, 141–148 (2011).
  33. S. Pan and J. Yao, “Performance evaluation of UWB signal transmission over optical fiber,” IEEE J. Sel. Areas Comm.28(6), 889–900 (2010). [CrossRef]
  34. R. C. Qiu, “A study of the ultra-wideband wireless propagation channel and optimum UWB receiver design,” IEEE J. Sel. Areas Comm.20(9), 1628–1637 (2002). [CrossRef]
  35. I. S. Lin and A. M. Weiner, “Selective Correlation Detection of Photonically Generated Ultrawideband RF Signals,” J. Lightwave Technol.26(15), 2692–2699 (2008). [CrossRef]
  36. J. Dederer, B. Schleicher, A. Trasser, T. Feger, and H. Schumacher, “A fully monolithic 3.1-10.6 GHz UWB Si/SiGe HBT Impulse-UWB correlation receiver,” in Proceedings of IEEE International Conference on Ultra-Wideband, ICUWB 2008, pp. 33–36 (2008).
  37. T. Li, H. Zhou, and M. Yi, “Gray Coded PPM Performance with Imperfect Slot Synchronization in Optical Communication,” in Proceedings of Conference on Lasers and Electro-Optics/Pacific Rim 2009, (Optical Society of America, 2009), paper TUP11_30 (2009).

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