- Email: [email protected]
Photonic generation of millimeter-wave ultra-wideband signal using microfiber ring resonator
Optics Communications 284 (2011) 1803–1806
Contents lists available at ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Discussion
Photonic generation of millimeter-wave ultra-wideband signal using microfiber ring resonator Yu Zhang a,d, Xinliang Zhang a,⁎, Fangzheng Zhang b, Jian Wu b, Guanghui Wang c, Perry Ping Shum c a
Wuhan National Laboratory for Optoelectronics and Institute of Optoelectronics Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Key Laboratory of Information Photonics and Optical Communications, Ministry of Education in China, Beijing University of Posts and Telecommunications, Beijing 100876, China Network Technology Research Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 637553, Singapore d Chongqing Optoelectronics Research Institute, Chongqing 400060, China b c
a r t i c l e
i n f o
Article history: Received 19 June 2010 Received in revised form 10 September 2010 Accepted 10 September 2010 Available online 19 October 2010 Keywords: Microfiber Ring resonator Millimeter-wave Ultra-wideband
a b s t r a c t The photonic generation of millimeter-wave (MMW) ultra-wideband (UWB) signal using microfiber ring resonator (MRR) is proposed. The central frequency and 10-dB bandwidth of generated MMW-UWB signal varying with Q factor of MRR are analyzed. We successfully demonstrate a generation of 24-GHz MMW-UWB signal by utilizing a microfiber ring resonator with free spectrum range of 20 GHz and Q factor of 19,000. The generated MMW-UWB signal has a power spectrum density complying with Federal Communication Committee requirements. © 2010 Published by Elsevier B.V.
1. Introduction Ultra-wideband (UWB) technology has attracted significant attention for a promising solution of short-range high speed wireless communication and sensor network, because the UWB system has many intrinsic advantages, such as low power consumption, immunity to multipath fading, high data-rate, low required signal-to-noise ratio (SNR) and huge bandwidth [1]. Recently, there has been substantial research effort devoted to the UWB system merged into the optical fiber system, including photonic generation, modulation, and distribution of the UWB signal [2–6]. According to the regulation developed by the Federal Communication Committee (FCC), the UWB signal has a 10-dB bandwidth of larger than 500 MHz or a fractional bandwidth greater than 20% with a power spectral density limit of −41.3 dBm/MHz. Besides baseband (7.5 GHz spectral band from 3.1 GHz to 10.6 GHz), several frequency bands (24 GHz and 60 GHz) have been allocated by FCC to UWB application in the millimeter-wave (MMW) band. The 24 GHz UWB signal is regulated for the vehicular radar applications in the frequency band of 22–29 GHz [7]. Various approaches of MMW-UWB signal generation via up-conversion have been proposed, which are demonstrated by using semiconductor optical amplifier [8], highly nonlinear fiber [9], Arrayed waveguide grating [10], and special Mach– Zehnder modulator (MZM) [11,12].
⁎ Corresponding author. E-mail address: [email protected] (X. Zhang). 0030-4018/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.optcom.2010.09.091
In this letter, we propose and demonstrate a photonic generator of a 24 GHz MMW-UWB signal by utilizing a microfiber ring resonator (MRR). Two tones of optical-carrier suppression (OCS) modulation signal generated by biasing MZM at transmission null are both modulated by a phase modulator (PM), subsequently, the two modulated tones are aligned to two linear slopes of MRR with a comb transmission spectrum to accomplish the conversion from phase modulation to intensity modulation. For each tone, the conversion principle is similar to the principle of the photonic generation of the baseband UWB signal based on phase-modulation-to-intensity-modulation conversion by using microring resonator [13] or asymmetric Mach–Zehnder interferometer [14]. After the two tones beating at the Photodetector (PD), the MMW-UWB can be achieved. In addition, we analyze the central frequency and 10-dB bandwidth of the generated MMW-UWB signal varying with Q factor of MRR. 2. Operation principle As we know, when an MZM under a push–pull operation mode is driven by an electrical sinusoidal signal with frequency of fm and biased at transmission null, an OCS modulation can be achieved, and two tones λ−1 and λ+1 of the OCS signal can beat to generate a MMW signal with a frequency of 2fm. If the two tones of the OCS signal are modulated by a phase modulator driven by an electrical Gaussian pulse with a repetition rate of fs, the two tones will both have temporal chirps, which are the firstorder derivative of phase variation. The positive and negative values of chirps with monocycle shape represent the blueshift and redshift of two
λ-1
λ +1
beating
MRR
Time
Time
Wavlength
Power (10dB/div)
-30 -40
8
-50 -60 -70 10
15 20 25 Frequency (GHz)
30
7
24.5
24.0
-30 -40 -50 -60 -70 10
6 15 20 25 Frequency(GHz)
20000
25000
10-dB bandwidth (GHz)
Time
25.0
Power (10dB/div)
a
Centralfrequency (GHz)
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
Amplitude
1804
30
30000
35000
40000
Q factor Chirp
Fig. 2. Central frequency and 10-dB bandwidth of the generated MMW-UWB signal vary with the Q factor of MRR.
Amplitude
b
Chirp
operated under a temperature controller, the transmission spectrum can be shifted to the generated polarity-inversed MMW-UWB signal.
Time beating
3. Experimental results and discussion
λ +1
Power
λ-1
MRR
Time
Time
Wavlength
Chirp
Chirp
Fig. 1. Operation principle of generating different polarity MMW-UWB signal. (a) Two phase modulated tones aim at the two positive slopes of MRR, and (b) two phase modulated tones aim at the two negative slopes of MRR.
tones, respectively. When the two modulated tones are aligned to two positive slopes or two negative slopes of MRR with free spectrum range (FSR) of 2fm, as shown in Fig. 1, the conversion from phase modulation to intensity modulation of two tones can be accomplished by employing the two same slopes of MRR as two frequency discriminators. Finally, the MMW-UWB signal can be achieved after the two tones beating at PD. MRR is an all-pass type microring resonator fabricated with microfiber, so it has a periodical notch transmission spectrum. For the MRR with different Q factor, the positive slope or negative slope of every notch has different inclined extents, which can affect the conversion from phase modulation to intensity modulation. The simulation result shows that the central frequency and 10-dB bandwidth of the generated MMW-UWB signal are dependent on the Q factor of MRR, when the fm is fixed. In this simulation, the fm is 10 GHz, fs is 625 MHz, the full-width at halfmaximum (FWHM) of Gaussian pulse is 100 ps, the two tones are both aligned to the positive slopes, the FSR of MRR is 20 GHz, and the extinction ratio of MRR is 15 dB. From Fig. 2, it can be observed that the higher Q factor of MRR results in lower central frequency and narrower 10-dB bandwidth of the MMW-UWB signal. Therefore, the central frequency and 10-dB bandwidth can be adjusted when the Q factor is tuned by changing the coupling coefficient of the twisted region in MRR. However, the Q factor of MRR should be controlled to be less than 40,000, because a larger Q factor results in a sharper slope, which will induce the chirp value overstepping the range of the slope. Furthermore, when the MRR is
Fig. 3 shows the experimental setup for generation of the 24 GHz MMW-UWB signal. A tunable laser diode is used to generate a continuous-wave light at 1552.53 nm with 5-dBm output power, which is modulated by a MZM under the push–pull operation mode. The MZM is driven by a 10-GHz RF signal, and biased at transmission null to generate the OCS signal. The carrier suppression ratio is higher than 20 dB, and the frequency spacing between the two tones is 20 GHz, which is shown as blue lines in Fig. 4. A pulse pattern generator (PPG) is used to generate an electrical Gaussian pulse train with a fixed pattern “1000 0000 0000 0000” (one “1” per 16 bits) at a bit rate of 10 Gb/s, which implies that the pulse repetition rate is 625 MHz and the FWHM of Gaussian pulse is about 100 ps. After amplification by a broadband electrical amplifier, the Gaussian pulse train is utilized to drive a phase modulator and modulate two tones of the OCS signal. Then, the two modulated tones aim at the periodical linear slopes of MRR with a FSR of 20 GHz, as shown in Fig. 4. After PD detection, the generated MMW-UWB signal is measured by communication signal analyzer (CSA) and electrical spectrum analyzer (ESA). The MRR is a key device in our experiment scheme, so the fabricating and adjusting of MRR are presented here. The microfibers are silica wires with a diameter of several micrometers for low-loss optical wave guiding [15], which are fabricated by exploiting standard single mode fiber through the method of flame-heated taper drawing. The MRR is assembled with microfibers under an optical microscope [16–18]. Firstly, the microfiber is drawn out from fiber with one end connecting to the fiber taper, and then the freestanding end of the microfiber is assembled into an un-tightened knot. Fig. 3(a) shows the scanning electron microscope (SEM) image of an MRR, and the diameter of the microfiber is 3 μm as shown in Fig. 3(b). Fig. 3(c) is the magnification of the twisted area with an overlap length of more than 150 μm; the twisted structure offers a long and stable overlap for effective coupling. Therefore, through tightening or loosening the knot, we can fabricate a MRR with a FSR of 20 GHz with a ring diameter of 3.3 mm, which corresponds to the 20-GHz frequency spacing of two tones in our experiment. The measured insertion loss and Q factor of the MRR is about 8 dB and 19,000, respectively, and the transmission spectra of MRR are shown as black and purple solid lines in Fig. 4, which has an extinction ratio of about 11 dB. When the two modulated tones are located at two positive slopes of MRR shown as purple lines in Fig. 4, the 24-GHz MMW-UWB signal can be obtained after PD detection. Fig. 5 (a) shows the waveform of
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
1805
Fig. 3. Experimental scheme of 24 GHz MMW-UWB over the fiber system. (a) Experimental setup; (b) SEM image of MRR; (c) SEM image of the single microfiber with a diameter of 3 μm; and (d) SEM of the coupling area.
the 24-GHz MMW-UWB signal, in which, the repetition rate of pulse is 20 GHz, and the envelope of pulse accords with a monocycle pulse indicated as a red dashed line. The corresponding power spectrum is shown in Fig. 5(b), which has a central frequency of 23.4 GHz and a 10-dB bandwidth of 6.0 GHz (from 20.4 GHz to 26.4 GHz). Then, two negative slopes of MRR are aligned to two tones through finely adjusting the coupling area and the ring diameter of MRR shown as black lines in Fig. 4. Thus, a 24-GHz polarity-inversed MMW-UWB signal can be generated. Fig. 5 (c) shows the waveform of the 24-GHz polarity-inversed MMW-UWB signal, which has an envelope according with the polarity-inversed monocycle pulse shown as red dashed line. Fig. 5(d) shows that the power spectrum of the 24-GHz polarityinversed MMW-UWB signal has a central frequency of 23.8 GHz and 10-dB bandwidth of 6.8 GHz (from 20.4 GHz to 27.2 GHz). In addition, this approach can also be used to generate the 60-GHz MMW-UWB signal by changing the frequency of the RF signal driving the MZM to 30 GHz and adjusting the FSR of MRR to 60 GHz. 4. Conclusion We have proposed a novel and simple approach to generate a MMW-UWB signal by using a microfiber ring resonator. The simulation exhibits a higher Q factor of MRR results in a lower central
Acknowledgements This work was supported by the National High Technology Research and Development Program of China (Grant No. 2006AA03Z414), the National Natural Science Foundation of China (Grant No. 60877056, No. 60901006 and No. 60707005). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
[11] [12] [13] [14] [15] [16] [17] [18]
-10
Power (dBm)
frequency and a narrower 10-dB bandwidth of the MMW-UWB signal. Through adjusting the transmission spectrum of MRR, we experimentally demonstrated the 24-GHz MMW-UWB signals with opposite polarities, which have the power spectra complying with the FCC regulation.
-20 -30 -40 -50 -60
1552.2
1552.4
1552.6
1552.8
ength
Wavel
1553
(nm)
Fig. 4. Measured transmission spectrum of MRR and optical spectra after MZM, PM, and MRR.
J.P. Yao, et al., J. Lightwave Technol. 25 (Nov 2007) 3219. F. Zeng, J.P. Yao, IEEE Photonics Technol. Lett. 18 (Sep-Oct 2006) 2062. J.J. Dong, et al., Opt. Lett. 32 (May 2007) 1223. M. Bolea, et al., Opt. Express 17 (Mar 2009) 5023. T.B. Gibbon, et al., IEEE Microw Wirel. Compon. Lett. 20 (Feb 2010) 127. S.L. Pan, J.P. Yao, IEEE Photonics Technol. Lett. 21 (Oct 2009) 1381. FCC, “Second report and order and second memorandum opinion and order,” FCC 04–285, Dec. 2004. S. Fu, et al., IEEE Photonics Technol. Lett. 20 (May-Jun 2008) 1006. J. Li, et al., IEEE Photonics Technol. Lett. 21 (Sep 2009) 1172. T. Kuri, et al., “Optical transmitter and receiver of 24-GHz ultra-wideband signal by direct photonic conversion techniques,” presented at the 2006 International Topical Meeting on Microwaves Photonics, New York, 2006. Q.J. Chang, et al., IEEE Photonics Technol. Lett. 20 (Sep-Oct 2008) 1651. Y. Guennee, R. Gary, IEEE Photonics Technol. Lett. 19 (Jul-Aug 2007) 996. F. Liu, et al., Electron. Lett 45 (Nov 2009) 1247. S.L. Pan, J.P. Yao, Opt. Lett. 34 (Jan. 2009) 160. L.M. Tong, et al., Nature 426 (Dec 18 2003) 816. X.S. Jiang, et al., Appl. Phys. Lett. 88 (May 29 2006) 223501. M. Sumetsky, J. Lightwave Technol. 26 (Jan-Feb 2008) 21. F. Xu, G. Brambilla, IEEE Photonics Technol. Lett. 19 (Sep-Oct 2007) 1481.
1806
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
Fig. 5. Measured waveforms and power spectra of the 24-GHz MMW-UWB signal. (a), (c) Waveforms of a pair of polarities MMW-UWB signal; and (b), (d) power spectra of a pair of opposite polarities MMW-UWB signal.
Contents lists available at ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Discussion
Photonic generation of millimeter-wave ultra-wideband signal using microfiber ring resonator Yu Zhang a,d, Xinliang Zhang a,⁎, Fangzheng Zhang b, Jian Wu b, Guanghui Wang c, Perry Ping Shum c a
Wuhan National Laboratory for Optoelectronics and Institute of Optoelectronics Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Key Laboratory of Information Photonics and Optical Communications, Ministry of Education in China, Beijing University of Posts and Telecommunications, Beijing 100876, China Network Technology Research Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 637553, Singapore d Chongqing Optoelectronics Research Institute, Chongqing 400060, China b c
a r t i c l e
i n f o
Article history: Received 19 June 2010 Received in revised form 10 September 2010 Accepted 10 September 2010 Available online 19 October 2010 Keywords: Microfiber Ring resonator Millimeter-wave Ultra-wideband
a b s t r a c t The photonic generation of millimeter-wave (MMW) ultra-wideband (UWB) signal using microfiber ring resonator (MRR) is proposed. The central frequency and 10-dB bandwidth of generated MMW-UWB signal varying with Q factor of MRR are analyzed. We successfully demonstrate a generation of 24-GHz MMW-UWB signal by utilizing a microfiber ring resonator with free spectrum range of 20 GHz and Q factor of 19,000. The generated MMW-UWB signal has a power spectrum density complying with Federal Communication Committee requirements. © 2010 Published by Elsevier B.V.
1. Introduction Ultra-wideband (UWB) technology has attracted significant attention for a promising solution of short-range high speed wireless communication and sensor network, because the UWB system has many intrinsic advantages, such as low power consumption, immunity to multipath fading, high data-rate, low required signal-to-noise ratio (SNR) and huge bandwidth [1]. Recently, there has been substantial research effort devoted to the UWB system merged into the optical fiber system, including photonic generation, modulation, and distribution of the UWB signal [2–6]. According to the regulation developed by the Federal Communication Committee (FCC), the UWB signal has a 10-dB bandwidth of larger than 500 MHz or a fractional bandwidth greater than 20% with a power spectral density limit of −41.3 dBm/MHz. Besides baseband (7.5 GHz spectral band from 3.1 GHz to 10.6 GHz), several frequency bands (24 GHz and 60 GHz) have been allocated by FCC to UWB application in the millimeter-wave (MMW) band. The 24 GHz UWB signal is regulated for the vehicular radar applications in the frequency band of 22–29 GHz [7]. Various approaches of MMW-UWB signal generation via up-conversion have been proposed, which are demonstrated by using semiconductor optical amplifier [8], highly nonlinear fiber [9], Arrayed waveguide grating [10], and special Mach– Zehnder modulator (MZM) [11,12].
⁎ Corresponding author. E-mail address: [email protected] (X. Zhang). 0030-4018/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.optcom.2010.09.091
In this letter, we propose and demonstrate a photonic generator of a 24 GHz MMW-UWB signal by utilizing a microfiber ring resonator (MRR). Two tones of optical-carrier suppression (OCS) modulation signal generated by biasing MZM at transmission null are both modulated by a phase modulator (PM), subsequently, the two modulated tones are aligned to two linear slopes of MRR with a comb transmission spectrum to accomplish the conversion from phase modulation to intensity modulation. For each tone, the conversion principle is similar to the principle of the photonic generation of the baseband UWB signal based on phase-modulation-to-intensity-modulation conversion by using microring resonator [13] or asymmetric Mach–Zehnder interferometer [14]. After the two tones beating at the Photodetector (PD), the MMW-UWB can be achieved. In addition, we analyze the central frequency and 10-dB bandwidth of the generated MMW-UWB signal varying with Q factor of MRR. 2. Operation principle As we know, when an MZM under a push–pull operation mode is driven by an electrical sinusoidal signal with frequency of fm and biased at transmission null, an OCS modulation can be achieved, and two tones λ−1 and λ+1 of the OCS signal can beat to generate a MMW signal with a frequency of 2fm. If the two tones of the OCS signal are modulated by a phase modulator driven by an electrical Gaussian pulse with a repetition rate of fs, the two tones will both have temporal chirps, which are the firstorder derivative of phase variation. The positive and negative values of chirps with monocycle shape represent the blueshift and redshift of two
λ-1
λ +1
beating
MRR
Time
Time
Wavlength
Power (10dB/div)
-30 -40
8
-50 -60 -70 10
15 20 25 Frequency (GHz)
30
7
24.5
24.0
-30 -40 -50 -60 -70 10
6 15 20 25 Frequency(GHz)
20000
25000
10-dB bandwidth (GHz)
Time
25.0
Power (10dB/div)
a
Centralfrequency (GHz)
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
Amplitude
1804
30
30000
35000
40000
Q factor Chirp
Fig. 2. Central frequency and 10-dB bandwidth of the generated MMW-UWB signal vary with the Q factor of MRR.
Amplitude
b
Chirp
operated under a temperature controller, the transmission spectrum can be shifted to the generated polarity-inversed MMW-UWB signal.
Time beating
3. Experimental results and discussion
λ +1
Power
λ-1
MRR
Time
Time
Wavlength
Chirp
Chirp
Fig. 1. Operation principle of generating different polarity MMW-UWB signal. (a) Two phase modulated tones aim at the two positive slopes of MRR, and (b) two phase modulated tones aim at the two negative slopes of MRR.
tones, respectively. When the two modulated tones are aligned to two positive slopes or two negative slopes of MRR with free spectrum range (FSR) of 2fm, as shown in Fig. 1, the conversion from phase modulation to intensity modulation of two tones can be accomplished by employing the two same slopes of MRR as two frequency discriminators. Finally, the MMW-UWB signal can be achieved after the two tones beating at PD. MRR is an all-pass type microring resonator fabricated with microfiber, so it has a periodical notch transmission spectrum. For the MRR with different Q factor, the positive slope or negative slope of every notch has different inclined extents, which can affect the conversion from phase modulation to intensity modulation. The simulation result shows that the central frequency and 10-dB bandwidth of the generated MMW-UWB signal are dependent on the Q factor of MRR, when the fm is fixed. In this simulation, the fm is 10 GHz, fs is 625 MHz, the full-width at halfmaximum (FWHM) of Gaussian pulse is 100 ps, the two tones are both aligned to the positive slopes, the FSR of MRR is 20 GHz, and the extinction ratio of MRR is 15 dB. From Fig. 2, it can be observed that the higher Q factor of MRR results in lower central frequency and narrower 10-dB bandwidth of the MMW-UWB signal. Therefore, the central frequency and 10-dB bandwidth can be adjusted when the Q factor is tuned by changing the coupling coefficient of the twisted region in MRR. However, the Q factor of MRR should be controlled to be less than 40,000, because a larger Q factor results in a sharper slope, which will induce the chirp value overstepping the range of the slope. Furthermore, when the MRR is
Fig. 3 shows the experimental setup for generation of the 24 GHz MMW-UWB signal. A tunable laser diode is used to generate a continuous-wave light at 1552.53 nm with 5-dBm output power, which is modulated by a MZM under the push–pull operation mode. The MZM is driven by a 10-GHz RF signal, and biased at transmission null to generate the OCS signal. The carrier suppression ratio is higher than 20 dB, and the frequency spacing between the two tones is 20 GHz, which is shown as blue lines in Fig. 4. A pulse pattern generator (PPG) is used to generate an electrical Gaussian pulse train with a fixed pattern “1000 0000 0000 0000” (one “1” per 16 bits) at a bit rate of 10 Gb/s, which implies that the pulse repetition rate is 625 MHz and the FWHM of Gaussian pulse is about 100 ps. After amplification by a broadband electrical amplifier, the Gaussian pulse train is utilized to drive a phase modulator and modulate two tones of the OCS signal. Then, the two modulated tones aim at the periodical linear slopes of MRR with a FSR of 20 GHz, as shown in Fig. 4. After PD detection, the generated MMW-UWB signal is measured by communication signal analyzer (CSA) and electrical spectrum analyzer (ESA). The MRR is a key device in our experiment scheme, so the fabricating and adjusting of MRR are presented here. The microfibers are silica wires with a diameter of several micrometers for low-loss optical wave guiding [15], which are fabricated by exploiting standard single mode fiber through the method of flame-heated taper drawing. The MRR is assembled with microfibers under an optical microscope [16–18]. Firstly, the microfiber is drawn out from fiber with one end connecting to the fiber taper, and then the freestanding end of the microfiber is assembled into an un-tightened knot. Fig. 3(a) shows the scanning electron microscope (SEM) image of an MRR, and the diameter of the microfiber is 3 μm as shown in Fig. 3(b). Fig. 3(c) is the magnification of the twisted area with an overlap length of more than 150 μm; the twisted structure offers a long and stable overlap for effective coupling. Therefore, through tightening or loosening the knot, we can fabricate a MRR with a FSR of 20 GHz with a ring diameter of 3.3 mm, which corresponds to the 20-GHz frequency spacing of two tones in our experiment. The measured insertion loss and Q factor of the MRR is about 8 dB and 19,000, respectively, and the transmission spectra of MRR are shown as black and purple solid lines in Fig. 4, which has an extinction ratio of about 11 dB. When the two modulated tones are located at two positive slopes of MRR shown as purple lines in Fig. 4, the 24-GHz MMW-UWB signal can be obtained after PD detection. Fig. 5 (a) shows the waveform of
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
1805
Fig. 3. Experimental scheme of 24 GHz MMW-UWB over the fiber system. (a) Experimental setup; (b) SEM image of MRR; (c) SEM image of the single microfiber with a diameter of 3 μm; and (d) SEM of the coupling area.
the 24-GHz MMW-UWB signal, in which, the repetition rate of pulse is 20 GHz, and the envelope of pulse accords with a monocycle pulse indicated as a red dashed line. The corresponding power spectrum is shown in Fig. 5(b), which has a central frequency of 23.4 GHz and a 10-dB bandwidth of 6.0 GHz (from 20.4 GHz to 26.4 GHz). Then, two negative slopes of MRR are aligned to two tones through finely adjusting the coupling area and the ring diameter of MRR shown as black lines in Fig. 4. Thus, a 24-GHz polarity-inversed MMW-UWB signal can be generated. Fig. 5 (c) shows the waveform of the 24-GHz polarity-inversed MMW-UWB signal, which has an envelope according with the polarity-inversed monocycle pulse shown as red dashed line. Fig. 5(d) shows that the power spectrum of the 24-GHz polarityinversed MMW-UWB signal has a central frequency of 23.8 GHz and 10-dB bandwidth of 6.8 GHz (from 20.4 GHz to 27.2 GHz). In addition, this approach can also be used to generate the 60-GHz MMW-UWB signal by changing the frequency of the RF signal driving the MZM to 30 GHz and adjusting the FSR of MRR to 60 GHz. 4. Conclusion We have proposed a novel and simple approach to generate a MMW-UWB signal by using a microfiber ring resonator. The simulation exhibits a higher Q factor of MRR results in a lower central
Acknowledgements This work was supported by the National High Technology Research and Development Program of China (Grant No. 2006AA03Z414), the National Natural Science Foundation of China (Grant No. 60877056, No. 60901006 and No. 60707005). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
[11] [12] [13] [14] [15] [16] [17] [18]
-10
Power (dBm)
frequency and a narrower 10-dB bandwidth of the MMW-UWB signal. Through adjusting the transmission spectrum of MRR, we experimentally demonstrated the 24-GHz MMW-UWB signals with opposite polarities, which have the power spectra complying with the FCC regulation.
-20 -30 -40 -50 -60
1552.2
1552.4
1552.6
1552.8
ength
Wavel
1553
(nm)
Fig. 4. Measured transmission spectrum of MRR and optical spectra after MZM, PM, and MRR.
J.P. Yao, et al., J. Lightwave Technol. 25 (Nov 2007) 3219. F. Zeng, J.P. Yao, IEEE Photonics Technol. Lett. 18 (Sep-Oct 2006) 2062. J.J. Dong, et al., Opt. Lett. 32 (May 2007) 1223. M. Bolea, et al., Opt. Express 17 (Mar 2009) 5023. T.B. Gibbon, et al., IEEE Microw Wirel. Compon. Lett. 20 (Feb 2010) 127. S.L. Pan, J.P. Yao, IEEE Photonics Technol. Lett. 21 (Oct 2009) 1381. FCC, “Second report and order and second memorandum opinion and order,” FCC 04–285, Dec. 2004. S. Fu, et al., IEEE Photonics Technol. Lett. 20 (May-Jun 2008) 1006. J. Li, et al., IEEE Photonics Technol. Lett. 21 (Sep 2009) 1172. T. Kuri, et al., “Optical transmitter and receiver of 24-GHz ultra-wideband signal by direct photonic conversion techniques,” presented at the 2006 International Topical Meeting on Microwaves Photonics, New York, 2006. Q.J. Chang, et al., IEEE Photonics Technol. Lett. 20 (Sep-Oct 2008) 1651. Y. Guennee, R. Gary, IEEE Photonics Technol. Lett. 19 (Jul-Aug 2007) 996. F. Liu, et al., Electron. Lett 45 (Nov 2009) 1247. S.L. Pan, J.P. Yao, Opt. Lett. 34 (Jan. 2009) 160. L.M. Tong, et al., Nature 426 (Dec 18 2003) 816. X.S. Jiang, et al., Appl. Phys. Lett. 88 (May 29 2006) 223501. M. Sumetsky, J. Lightwave Technol. 26 (Jan-Feb 2008) 21. F. Xu, G. Brambilla, IEEE Photonics Technol. Lett. 19 (Sep-Oct 2007) 1481.
1806
Y. Zhang et al. / Optics Communications 284 (2011) 1803–1806
Fig. 5. Measured waveforms and power spectra of the 24-GHz MMW-UWB signal. (a), (c) Waveforms of a pair of polarities MMW-UWB signal; and (b), (d) power spectra of a pair of opposite polarities MMW-UWB signal.