Optical mm-wave DWDM signal generation with photonic frequency quadruple by only one external...

matching. Nice results from this work prove the adopted LNAarchitecture to be very suitable for designing high-performanceK-band or higher frequency-band LNAs.

ACKNOWLEDGMENT

This work is supported by the National Science Council of theR.O.C. under Contracts NSC95- 2221-E-260–032 and NSC-095-SAF-I-564–630-TMS. The authors are also very grateful for thesupports from National Chip Implementation Center (CIC), Tai-wan, for chip fabrication and high-frequency measurements.

REFERENCES

1. K.W. Yu, Y.L. Lu, D.C. Chang, V. Liang, and M.F. Chang, K-bandlow-noise amplifiers using 0.18 �m CMOS technology, IEEE Micro-wave Wireless Compon Lett 14 (2004), 106–108.

2. G. Xiang and A. Hajimiri, A 24-GHz CMOS front-end, IEEE J Solid-State Circ 39 (2004), 368–373.

3. S.C. Shin, M.D. Tsai, R.C. Liu, K.Y. Lin, and H. Wang, A 24-GHz3.9-dB NF low-noise amplifier using 0.18 �m CMOS technology, IEEEMicrowave Wireless Compon Lett 15 (2005), 448–450.

4. H.W. Chiu, S.S. Lu, and Y.S. Lin, A 2.17-dB NF 5-GHz-band mono-lithic CMOS LNA with 10-mW DC power consumption, IEEE TransMicrowave Theory Tech 53 (2005), 813–824.

5. M.L. Edwards and J.H. Sinsky, A new criterion for linear 2-portstability using geometrically derived parameters, IEEE Trans Micro-wave Theory Tech 40 (1992), 2303–2311.

6. H.K. Chen, D.C. Chang, Y.Z. Juang, and S.S. Lu, A compact widebandCMOS low noise amplifier using shunt resistive-feedback and seriesinductive-peaking techniques, IEEE Microwave Wireless Compon Lett17 (2007), 616–618.

7. D. Barras, F. Ellinger, H. Jackel, and W. Hirt, A low supply voltageSiGe LNA for ultra-wideband frontends, IEEE Microwave WirelessCompon Lett 14 (2004), 469–471.

© 2008 Wiley Periodicals, Inc.

OPTICAL MM-WAVE DWDM SIGNALGENERATION WITH PHOTONICFREQUENCY QUADRUPLE BY ONLYONE EXTERNAL MODULATOR

Ying Li,1,2 Lin Chen,2 Shuangchun Wen,2 and Dianyuan Fan1

1 Department of Optical Science and Engineering, Fudan University,Shanghai 200433, China2 School of Computer and Communication, Hunan University,Changsha 410082, China; Corresponding author:scwen@vip.sina.com

Received 29 September 2007

ABSTRACT: We have proposed a novel scheme to generate opticalmm-wave DWDM signals with four time frequency of the local oscillatorby using only one external modulator. By incorporating the proper di-rect current (DC) bias on the external modulator to suppress the firstorder sideband in central office (CO), and using optical filtering tech-nique to separate the optical mm-wave and optical carrier in the basestation, the dense wavelength division multiplexing (DWDM) opticalmillimeter-wave (mm-wave) signals are generated with four timesfrequency of the LO signal. We have experimentally demonstratedfour-channel DWDM optical mm-wave signal generation with a re-petitive frequency up to 40 GHz by 10 GHz LO, and down-streamsignal delivery over 20-km fiber with 0.7-dB power penalty. © 2008Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1152–1155,2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23328

Key words: radio-over-fiber (ROF); optical millimeter wave; DWDM;external modulator

1. INTRODUCTION

There is a strong interest in providing broadband wireless accessservice in the emerging optical-wireless network [1]. Optical mil-limeter (mm)-wave generation is a key technique in the radio-over-fiber (ROF)-based optical-wireless access networks [2]. To reducethe total cost of the central station (CS) and base station (BS) andconnect as many users as possible, the dense wavelength divisionmultiplexing (DWDM) technique is a strong candidate to bettersupport the connections between CSs and BSs [3–4]. In [5–8],there have been several reports on WDM ROF system to reducethe complexity and cost of the system. But the LO frequency ishalf of the repetitive frequency of the optical mm-wave carrier. Tofurther reduce the LO frequency and bandwidth of the externalmodulator, an optical mm-wave generation scheme has proposedin [9] by multiple double-frequency technique through properlyadjusting DC bias on external modulator. However in [9], justsingle channel optical mm-wave carrier has been generated with-out carrying any baseband data signal. For WDM ROF systems, itis necessary that the base-band data of the downlink for eachchannel are up-converted to the millimeter-wave frequency usinga cost-efficient and high performance scheme. In conventionaloptical mm-wave generation scheme, the optical base band signalis generated using a single-electrode Mach-Zehnder modulator(MZM), and then up-converted using a dual-electrode MZM [3].In this article, we have proposed a novel scheme for generation ofoptical DWDM mm-wave carriers with four time frequency of thelocal oscillator and simultaneous up-conversion of base band datasignal by using only one external modulator. We experimentallydemonstrated that four channels optical mm-waves with a repeti-tive frequency up to 40 GHz that carry 2.5-Gb/s downlink base-band data are simultaneously generated by using 10 GHz LOfrequency and transmitted over 20-km conventional single-modefiber (SMF-28).

2. PRINCIPLE

Figure 1 shows the principle to generate optical DWDM mm-wavesignals with photonic frequency quadrupling and simultaneoussignal up-conversion by only one external modulator for ROFsystem. In the central office, for each channel, the base-bandsignals of the downlink data are up-converted with the RF carrier

data1

RF1 (f0)

IM

Downlink fiber IL

IM

downlinkreceiverOF1

OF2 Uplink data

Central Office

Base Station

RF2data2

RF4data4

MUXDFB1

DFB4

Figure 1 Principle of the optical mm-wave DWDM signals with pho-tonic frequency quadrupling and simultaneous signal up-conversion byonly one external modulator for ROF system. IL: interleaver, IM: intensitymodulator, OF: optical filter. [Color figure can be viewed in the onlineissue, which is available at www.interscience.wiley.com]

1152 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 DOI 10.1002/mop

of LO frequency by an electrical mixer. Each CW lightwave ismodulated via a LiNbO3 external modulator (MOD) driven by theup-converted signal. Here we assume that the MOD is an ideal onewith symmetrical DC-biased performance as shown in Figure 2. Ifthe MOD is DC-biased at the top peak output power when the LOsignal are removed as shown in Figure 2(a), the odd-order modescan be suppressed as shown in Figure 2(b). Therefore, the opticalmm-wave carrier with four times of LO frequency is generated.The optical mm-waves including the central optical carrier and thesecond order sidebands of multiple channels are combined by aMUX and delivered to the base station by the downlink fiber. Inthe base station, an optical interleaver with two output ports is usedto separate the central optical carriers and the second-order side-band. After optical interleaver, the second order sidebands of thedesired channel are selected by a tunable optical filter (TOF1). Thetwo peak modes of the second sidebands will be beat to generatemm-wave with frequency quadrupling RF signal when they aredetected by a downlink receiver. The remaining optical carrier canbe used as uplink optical carrier after it is selected by a tunableoptical filter (TOF2). By the proposed scheme, DWDM optical

mm-wave signals at four times the frequency of the electrical drivesignal can be generated, and simultaneously frequency up-con-verted by using only one modulator, which significantly reduce thecost and bandwidth of the external modulator and the requirementof high frequency RF source.

3. EXPERIMENTAL SETUP AND RESULTS

The experimental setup for optical mm-wave DWDM signal gen-eration and transmission is shown in Figure 3. A laser array withfour DFB-LDs was employed to generate four wavelength CWlight-waves from 1538.19 to 1542.94 nm with 200-GHz channelspacing. An arrayed waveguide (AWG) was used to combine thefour CW light-waves before they were modulated by an externalmodulator. The 2.5 Gb/s base-band electrical signal of the down-link data with a pseudorandom binary sequence (PRBS) length of231-1 is up-converted with the 10 GHz RF microwave signal (LOsignal) with a peak to peak voltage of 7 V by an electrical mixer.The four CW light-waves of DWDM channel were modulated viaa LiNbO3 (LN) MZM modulator biased at the top peak outputpower when the LO signal and data signal are removed. Thehalf-wave voltage of the LN MZM is 3.8 V. The DWDM opticalspectra before and after modulation are inserted in Figure 3 as inset(i) and (ii), respectively. After modulation, it is can be seen that theodd-order modes are almost suppressed, and the power of theoptical carriers is 12 dB larger than that of the second-order modesfor all channels. The wavelength spacing between the two second-order modes for each channel is 0.32 nm (40 GHz). We used anoptical interleaver (IL) with 100/50 GHz channel spacing to sup-press other higher-order modes. The optical spectrum after passingthrough the first IL is inserted in Figure 3 as inset (iii). We can seethat the fourth- and sixth-order modes are removed for all chan-nels. The eye diagrams of optical mm-wave for four channelsbefore transmission are shown in Figure 4. After transmission over20 km SMF-28 with dispersion of 17 ps/(nm km), the eye diagramsof optical mm-wave for four channels are shown in Figure 5. Wecan see that the eye diagrams of optical mm-wave for four chan-nels are still clearly open after transmission. We use another ILwith 50/25 GHz channel spacing to separate the optical carriersand optical mm-wave of DWDM channels. This interleaver has a3 dB passing band-width of 0.15 nm, insert loss of 2 dB and nopolarization sensitivity. The optical spectra from the two outputs ofthe second IL are inserted in Figure 3 as inset (iv) and (v). Afterpassing through the second IL, the second-order modes is 14 dBlarger than the optical carrier as shown in inset (iv). Figure 3 (v)shows the optical spectrum of the remaining optical carrier whichcan be used for uplink optical carrier. After EDFA, we employeda TOF to select the desired channel. As an example, the opticalspectrum of channel 3 and channel 4 are shown in Figure 6. AfterTOF, the desired channel optical mm-wave was detected via PINPD with a 3-dB bandwidth of 60 GHz for O/E conversion. Theconverted electrical signal was amplified by an electrical amplifier(EA) with a bandwidth of 10 GHz centered at 40 GHz. We use amixer to down-convert the electrical millimeter-wave signal. Afterthe down conversion, the 2.5 Gbit/s signal was detected by a BERtester. Figure 7 shows the BER cures and eye diagrams of channel3 after transmission over 20-km SMF. Since all channels haveidentical performance after transmission, we only show one chan-nel’s BER and eye diagram in Figure 7. It can be seen from Figure7, for a BER of 10�9, the receiver sensitivity for a back-to-back(B-T-B) signal is �33.6 dBm, and the power penalty after 20-kmtransmission at a BER of 10�9 is 0.7 dB for all channels.

DC bias

Transmission function

Optical carrier

eveneven

odd

(a)

(b)

Figure 2 Modulation principle for photonic frequency quadruplingscheme. (a) Modulation performance, (b) optical spectrum at the output ofthe modulator

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 1153

4. CONCLUSION

In this letter, we have proposed and experimentally demonstrateda novel DWDM ROF downstream link with optical mm-wavegeneration with four times frequency of the local oscillator (LO)signal and simultaneous up-conversion of base-band signals byusing only one external modulator. So the lower frequency devicesuch as RF source, electrical mixer, and optical modulator can beused to generate high frequency optical mm-wave DADM signals,which significantly reduce the cost of the DWDM ROF system.We have demonstrated that four channels optical mm-wave carrierup to 40 GHz were generated by using 10 GHz LO RF signal, and

IM

PM-coupler

10GHz LO

2.5Gbit/s

50/100GHzIL, Optoplex

25/50GHzIL

O/E

LPF

MIX

EA

Powerdivider

0.5nmTOFEDFA

20kmSMF-28

1538 1539 1540 1541 1542 1543-80-70-60

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1538 1539 1540 1541 1542 1543-80-70-60-50-40-30-20-10

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1538 1539 1540 1541 1542 1543-80-70-60-50-40-30-20-10

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tical

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wer

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m)

Wavelength (nm)

(i)

(ii)

(iii)

(iv)

(V)

DFB-1

DFB-4

Figure 3 Experimental setup for DWDM mm-wave generation and transmission. The resolution for all optical spectra is 0.01 nm. [Color figure can beviewed in the online issue, which is available at www.interscience.wiley.com]

Ch 1 Ch 2

Ch 3 Ch 4

100ps/div 100ps/div

100ps/div100ps/div

Figure 4 Eye diagrams of optical mm-wave for four channels beforetransmission. [Color figure can be viewed in the online issue, which isavailable at www.interscience.wiley.com]

ch1 ch2

ch3 ch4

100ps/div100ps/div

100ps/div 100ps/div

Figure 5 Eye diagrams of optical mm-wave after transmission over20-km SMF-28. [Color figure can be viewed in the online issue, which isavailable at www.interscience.wiley.com]

1538 1539 1540 1541 1542 1543-80-70-60

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ch3 ch4

Figure 6 The optical spectra of channel 3 and channel 4 after opticalfilter

1154 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 DOI 10.1002/mop

2.5-Gb/s down-stream data signal were delivered over 20-km fiberwith 0.7-dB power penalty.

ACKNOWLEDGMENT

This work is partially supported by the program of the Ministry ofEducation of China for New Century Excellent Talents in Univer-sity, and the Hunan Provincial Natural Science Foundation ofChina (Grant No. 06JJ50108).

REFERENCES

1. A. Kim, Y. Joo, and Y. Kim, 60 GHz wireless communication systemswith radio-over-fiber links for indoor wireless LANS, IEEE TransConsum Electrics 50 (2004), 517–520.

2. S.-C. Chan, S.-K. Hwang, and J.-M. Liu, Radio-over-fiber AM-to-FMup-conversion using an optically injected semiconductor laser, Opt Lett31 (2006), 2254–2256.

3. L. Chen, H. Wen, and S.C. Wen, A radio-over-fiber system with a novelscheme for millimeter-wave generation and wavelength reuse for up-link connection, IEEE Photon Technol Lett 18 (2006), 2056–2057.

4. T. Kuri and K. Kitayama, Optical heterodyne detection technique fordensely multiplexed millimeter-wave-band radio-on-fiber systems, JLightwave Technol 21 (2003), 3167–3179.

5. M. Attygalle, C. Lim, and A. Nirmalathas, Extending optical transmis-sion distance in fiber wireless links using passive filtering in conjunctionwith optimized modulation, J Lightwave Technol 24 (2006), 1703–1709.

6. T. Kuri and K. Kitayama, Optical heterodyne detection technique fordensely multiplexed millimeter-wave-band radio-on-fiber systems,IEEE Photon Technol Lett 21 (2003), 3167–3169.

7. X. Zhang, B. Liu, J. Yao, and R. Kashap, A novel millimeter-wave-bandradio-over-fiber system with dense wavelength-division multiplexingbus architecture, IEEE Trans Microwave Tech 54 (2006), 929–937.

8. L. Chen, X.-Y. Lei, S.-C. Wen, and J.-G. Yu, A novel radio over fibersystem with DWDM mm-wave generation and wavelength reuse forupstream data connection, Opt Express 15 (2007), 5893–5897.

9. G. Qi, J. Yao, J. Seregelyi, S. Paquet, and C. Belisle, Generation anddistribution of a wide-band continuously tunable millimeter-wave sig-nal with an optical external modulation technique, IEEE Trans Micro-wave Theory Tech 53 (2005), 3090–3097.

© 2008 Wiley Periodicals, Inc.

NARROW-SLOT BANDPASS FILTERBASED ON FOLDED SUBSTRATE-INTEGRATED WAVEGUIDE WITH WIDEOUT-OF-BAND REJECTION

Wang Lei,1 Wenquan Che,1,2 Kuan Deng,1 and Shiwei Dong3

1 Department of Electrical Engineering Nanjing University of Scienceand Technology 210094 Nanjing, China; Corresponding author:yeeren_che@yahoo.com.cn2 Institute for High Frequency Engineering Technische UniversitaetMunchen, Arcisstrasse 21, D-80333 Munchen, Germany3 National Key Laboratory of Space Microwave Technology, Xi’an,China

Received 29 September 2007

ABSTRACT: The folded substrate-integrated waveguide (FSIW) takesthe advantages of more compact size and higher integration than theconventional SIW structures, probably resulting in a very compact de-sign. One simple narrow-slot bandpass filter is thus proposed and im-plemented to demonstrate the superiority of FSIW structure. The designstrategies of the bandpass filter are introduced. One prototype withthree narrow slots in the middle layer of FSIW is fabricated to demon-strate the validity of the proposed design. For the sake of measurement,one back-to-back stripline transition is also designed. The measuredresults are in good agreement with the HFSS-simulated results, whichindicates that the bandwidth is about 15%; the insertion loss is less than1.5 dB. In addition, the rejection band of this filter is quite wide, imply-ing very good harmonic rejection. © 2008 Wiley Periodicals, Inc.Microwave Opt Technol Lett 50: 1155–1159, 2008; Published online inWiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23327

Key words: folded substrate-integrated waveguide (FSIW); narrow-slot;bandpass filter; stripline transition; out-of-band rejection

1. INTRODUCTION

The rectangular waveguide (RWG) structures have advantagesover other planar transmission lines for millimeter wave bandapplications because of its low loss and high Q. However, they aredifficult to manufacture and integrate with planar circuitry becauseof their 3D geometry. In recent years, some scholars have pro-posed substrate-integrated waveguide (SIW) to solve these prob-lems. The original SIW, as shown in Figure 1(a), largely preservesthe advantages of conventional RWG [1, 2] and microstrip, i.e.,high Q, low cost, low profile, easy connection with microstrip orcoplanar circuit, and easy adoption into filters and antennas [3–6].However, its width may be too large for some circuits. Therefore,width reduction and compact integration is still desirable. Toreduce the width, Chen et al. [7] studied the folded regularwaveguide (FRWG), i.e., of solid walls. Grigoropoulos et al. [8]then introduced the concept and geometry of the folded SIW(FSIW) with walls of cylindrical vias, as illustrated in Figure 1(b).In Figure 1(a), a[prime] is the SIW width, h is the height of thesubstrate with dielectric constant �r, the cylinder radius and spac-ing are R and W, respectively. In Figure 1(b), a2 is the width ofFSIW, g[prime] is the gap between the central metal septum andthe right sidewall. It may be noted that the horizontal section ofFSIW is only half of the original SIW structure, implying morecompact size and higher integration. We have derived the desiredformulas of FSIW [9], i.e., the propagation constant and cutofffrequency as a function of all the parameters of the SIW, as wellas the gap width between the central metal septum and the rightsidewall of the FSIW. The accuracies of those formulas have beenverified by numerical HFSS simulations and experiments [9].

-38 -36 -34 -32 -30 -28 -26 -24

10

9

8

7

6

5

11

B-T-B 20km

-log(

BE

R)

Received power (dBm)

All channels have identical performance

Down-converted100ps/div, after 20km

Figure 7 BER curve and eye diagram of channel 3 after transmissionover 20-km SMF. [Color figure can be viewed in the online issue, which isavailable at www.interscience.wiley.com]

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 1155