STUDY OF OPTICALLY CONTROLLEDHIGH TEMPERATURESUPERCONDUCTING MICROWAVEVARIABLE ATTENUATOR

Lin Liu, Yutang Ye, Yunfeng Wu, Zhenlong Chen, andYulin WangSchool of Optoelectronic Information, University of Electronic Scienceand Technology of China, Chengdu 610054, China

Received 16 November 2006

ABSTRACT: A novel optically controlled HTS (high temperature su-perconducting) microwave variable attenuator was proposed and a sam-ple was tested, which can be used solely, or be integrated into the HTSsystem. Utilizing the very low microwave superficial resistance and su-perexcellent optically response character of YBCO film, the insertionloss of sample is lower than 0.2 dB and variable attenuation precisionis 0.01 dB at least. © 2007 Wiley Periodicals, Inc. Microwave OptTechnol Lett 49: 1539–1541, 2007; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.22494

Key words: high temperature superconducting; attenuator; laser radia-tion; insertion loss; attenuation precision

1. INTRODUCTION

Follows the extensive application of YBCO HTS (High tempera-ture superconducting) film and its relative devices in the realm ofaviation, spaceflight and military [1], it is a direction to enhancethe integration degree of HTS system which is very important toimprove the capability and minish the bulk of systems [2].

Attenuator, as the important device in a HTS system [3], exertsgreat functions in leveling off signal, improving receiving andtransmitting quality, and avoiding the influences of climate andother environments [4]. An attenuator, which possesses superex-cellent capabilities including low insertion loss, high tuning pre-cision, and working in liquid nitrogen temperature(the base ofattenuator integrated into a HTS system), is greatly important tothe development and application of HTS system [5]. However, it isa pity that compared with the HTS system, the insertion loss andtuning precision of attenuators in being, are going beyond 1–2orders of magnitude [6]; on the other hand, the attenuators existingcan not work in liquid nitrogen temperature [7]. For above reasons,it is necessary to develop a novel attenuator specially used in HTSsystem.

A novel optically controlled HTS microwave variable attenu-ator is proposed in this article. Utilizing the very low microwavesuperficial resistance [8] and superexcellent laser response ability[9] of YBCO HTS film, this attenuator possesses low insertion lossand high tune precision and expediently integrated into a HTSsystem. As we known, it is the first time to be proposed.

2. FABRICATION AND TEST OF OPTICALLY CONTROLLEDHTS MICROWAVE VARIATION ATTENUATOR

The configuration of optically controlled HTS microwave variableattenuator sample is shown in Figure 1. The main parts includehousing box (1), RF (radio frequency) SMA joint (2), HTS circuit(3), cover box (4), and fiber plug (5). The material of housing boxand cover board are respectively, cuprum and transparent organicglass (can work in liquid nitrogen temperature). Through thetransparent glass, we can realize the collimation between laserfacula and HTS microstrip.

To test the attenuator in liquid nitrogen, we adopt the config-uration as shown in Figure 1, and the dimension of circuit sample

Figure 1 Configuration of optically controlled HTS microwave variableattenuator

Figure 2 Test system of optically controlled HTS microwave variableattenuator

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 7, July 2007 1539

is 12 mm � 8 mm � 0.5 mm. In fact, when the optically controlledHTS attenuator is integrated into a HTS system, because the innerworking condition of HTS system is completely adapting to theoptically controlled HTS attenuator, the dimension and weight willbe minished much more for the cancel of housing box. We can seethat integrated optically controlled HTS attenuator in system takegreat advantages than solely used.

We test the parameters of attenuator in liquid nitrogen byHP8720 (DC–20G) Network analyzer (as shown in Fig. 2). Thelaser radiation (with wavelength 0.68 �m, laser power tune range0–40 mw, distance between fiber to microstrip 1 mm, and thediameter of laser focula about 1 mm) can cover the whole micros-trip.

A lot of paper about optically controlled HTS switch is re-ported. For the superexcellent response capability of YBCO HTSfilm, the isolation reached exceeding 60 dB and responding dura-tion is lower than 1 ms. For the limitation of paper contents, theabove two parameters are not reported in this article repeatedly.

3. EXPERIMENTAL CONCLUSION

3.1. Insertion LossThe whole loss of HTS receiver front-end existing is lower than 1dB, but the insertion loss of a common attenuator is 1 dB at least.So, if we adapt the common attenuator outside of the HTS system,the superexcellent performance will be influenced greatly. Forabove reasons, the attenuator integrated in HTS system mustpossess the performance of very low insertion loss.

The insertion loss of optically controlled HTS microwave vari-able attenuator sample fabricated in experiment is shown in Figure3. Y-coordinate denotes insertion loss and each lattice is 0.1 dB.Before the attenuator joined into the test system, the test systemmust adjust to about 0 dB [as shown in Fig. 3(a)]; after attenuatorjoined (no laser radiation), the insertion loss increase to about 0.2dB [as shown in Fig. 3(b)].

3.2. High Precision Tuning of Attenuation Scale by Laser PowerControllingTwo tuning modes including continuum tuning and digital tuningall can be realized for the character of laser power tuning, and wecan select any mode based on the need.

Through experiments, we obtain the changeable characters ofinsertion loss of attenuator follows the laser power change (asshown in Fig. 4). Y-coordinate denotes insertion loss and eachlattice is 0.02 dB. The insertion loss values are respectively, 0,0.01, 0.02, 0.03, 0.05, 0.06, 0.07, and 0.08 dB when the laserpower are respectively, 0, 5, 10, 15, 20, 25, 30, and 35 mw. We cansee when the pace of laser power is about 5 mw the changeablevalue of insertion loss is about 0.01 dB. Compare with the com-mon attenuator, the tuning precision of optically controlled HTSattenuator improves 1–2 orders of magnitude at least. It is greatworthy for HTS system to improve performance farther.

Figure 3 Test curve of HTS attenuator insertion loss

Figure 4 Change process of attenuation of superconductor attenuatorfollowing laser power

1540 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 7, July 2007 DOI 10.1002/mop

Through the computer disposal, we obtain the changeable curveof insertion loss follows laser power (as shown in Fig. 5). Thechangeable rate exist difference for the influence of differentresponse character of YBCO to laser in different power. From 0 to15 mw of laser power, the changeable rate of insertion lossrepresent linearity character, and in this phase, the main influenceof laser is radiant heat. When the laser power exceeds 15 mw,fluctuation appears and complicated nonequilibrium optical re-sponse [10] replaces the simplex heat response. It’s very importantto design the proper tuning pace of laser power.

4. CONCLUSIONS

A novel optically controlled HTS microwave variable attenuator isproposed in this article, which can be used solely, or be integratedinto the HTS system. It is very important to improve the perfor-mance of HTS system. From now on, attention should be given tothe integration and miniaturization technologies.

ACKNOWLEDGMENT

This study was supported by the National Nature Science Foun-dation of China (Grant No. 60277008), the Research Foundationfrom Ministry of Education of China (Grant No. 03147), theScience and Technology Foundation of State Key Laboratory(Grant No. 514910501005DZ0201), the Science and TechnologyBureau of Sichuan Province (Grant No. 04GG021–020-01).

REFERENCES

1. D.C. Niu, T.W. Huang, H.J. Lee, et al., An X-band front-end moduleusing HTS technique for a commercial dual mode radar, IEEE TransAppl Supercond 15 (2005), 1008–1011.

2. T.L. Wilson, A high-temperature superconductor energy-momentumcontrol system for small satellites, IEEE Trans Appl Supercond 13(2003), 2287–2290.

3. J.F. Seaux, C. Lascaux, and V. Madrangeas, Interest of the supercon-ductivity at 30 GHz: Application to the HTS preselect receive filtersfor satellite communications, IEEE MTT-S Int Microwave Symp Dig2 (2004), 1121–1124.

4. K.O. Sun, M.K. Choi, and D.D. Van Weide, A PIN diode controlledvariable attenuator using a 0-dB branch-line coupler, IEEE MicrowaveCompon Lett 15 (2005), 440–442.

5. E.R. Soares, J.D. Fuller, and P.J. Marozick, Applications of high-temperature- superconducting filters and cryo-electronics for satellitecommunication, IEEE Trans Microwave Theory Tech 48 (2000),1190–1198.

6. K.O. Sun and D.D. Van Weide, Design of pin diode controlled

variable attenuator using slow wave microstrip lines, Microwave OptTechnol Lett 47 (2005), 323–327.

7. C.E. Saavedra and Y. Zheng, Ring-hybrid microwave voltage-variableattenuator using HFET transistors, IEEE Trans Microwave TheoryTech 53 (2005), 2430–2433.

8. R.M. Raafat, Microwave superconductivity, IEEE Trans MicrowaveTheory Tech 50(2002), 750–759.

9. K.A. Kouzakov and J.S. Berakdar, Photoinduced emission of cooperpairs from superconductors, Phys Rev Lett 91(2003), 257007/1–257007/4.

10. P.W. Kruse, High Tc superconducting IR detectors, Proc SPIE Int SocOpt Eng 1292 (1990), 108–177.

© 2007 Wiley Periodicals, Inc.

TIME RESPONSE OF ASE-XGMWAVELENGTH CONVERSION IN SOAsUSING ULTRASHORT PULSES

Rafael de Oliveira Ribeiro,1 Maria Jose Pontes,2

Rodolfo A. A. Lima,1 Maria Thereza M. R. Giraldi,3 andMaria Cristina R. Carvalho1

1 CETUC - Centro de Estudos em Telecomunicacoes, PUC-Rio -Pontifıcia Universidade Catolica do Rio de Janeiro, Rua Marques deSao Vicente, 225/7° andar K, 22451–900 Rio de Janeiro, RJ, Brazil2 Universidade Federal do Espırito Santo, ES, Brazil3 Instituto Militar de Engenharia - IME, Rio de Janeiro, Brazil

Received 22 November 2006

ABSTRACT: The time response of a semiconductor optical amplifierwavelength converter based on the ASE-XGM technique was experimentallyobtained using ultra-short pump optical pulses. The results were comparedwith the pump & probe technique and show similar time responses. Theconversion efficiency of the ASE-XGM technique was measured for differentpump power levels and presented promising results. © 2007 Wiley Periodi-cals, Inc. Microwave Opt Technol Lett 49: 1541–1544, 2007; Publishedonline in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22492

Key words: wavelength conversion; semiconductor optical amplifiers;cross-gain modulation; nonlinear effects

1. INTRODUCTION

All-optical wavelength conversion devices are strongly desired innext-generation optical networks, mainly in the context of wave-length-routed optical networks. They represent a powerful tool tooptimize the utilization of the available wavelengths in the net-work, reducing the blocking rate for lightpath requests. Wave-length converters can be useful in the wavelength allocation,allowing the use of different wavelengths on the links along theroute [1, 2]. The main advantage of all-optical processes is thatthey do not require conversion to the electrical domain—this isespecially true as bit rates increase to 10 Gb/s and beyond [3].

The use of semiconductor optical amplifiers (SOAs) as wave-length converters is very attractive due to its small size andpossibility of integration, using fabrication techniques similar tothose used for silicon-based integrated circuits. Several convertermechanisms have been shown to achieve efficient wavelengthconversion [3, 4]. Those can be used in ultrahigh-speed switches,routers, and related applications.

Most techniques of wavelength conversion in SOAs are accom-plished by the use of nonlinear effects, such as cross-gain modu-lation (XGM), cross-phase modulation, and four-wave mixing[2–7]. Usually, such approaches require an extra light source,

Figure 5 Graph of insertion loss correspond to laser

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 7, July 2007 1541