Measurement Error Estimation of Electro-Optic Probe by using Electro-Magnetic Field Simulator

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1 Measurement Error Estimation of Electro-Optic Probe by using Electro-Magnetic Field Simulator Tomoya Naoe 1, a, Mitsuru Shinagawa 1, Jun Katsuyama 2, Hiroaki Tanaka 2, and Yoshinori Matsumoto 2, b 1 Faculty of Science and Engineering, Hosei University, 3-7-2, Kajino-cho, Koganei-shi, Tokyo, , Japan 2 Innovation Center Marketing Headquarters, Yokogawa Electric Corporation, , Nakacho, Musashino-shi, Tokyo, , Japan a <tomoya.naoe.4n@stu.hosei.ac.jp>, b <Yoshinori.Matsumoto@jp.yokogawa.com> Keywords: electro-optic probe, electro-optic crystal, measurement error, electro-magnetic field simulator Abstract. This paper describes a measurement error estimation of an electro-optic (EO) probe system. The system uses an EO crystal and a laser source for wideband and noncontact measurement. When the EO crystal is positioned in an electro-magnetic field, the crystal disturbs the field. As a result, the EO probe system might have a measurement error. ZnTe and LiNbO 3 are widely used as the EO crystals for the EO probe system. We examined the measurement error with ZnTe and LiNbO 3 by using an electro-magnetic field simulator. We found that the measurement error with ZnTe was smaller than that with LiNbO 3. The measurement error became larger when the EO crystal was positioned closer to the device under test. When the EO crystal was far from the device under test, the measurement error was negligibly small. 1. Introduction An electro-optic (EO) probe system [1]-[6] based on a laser source and an EO crystal is used for wideband and noncontact measurement. The EO crystal disturbs the electro-magnetic field from the device under test, which might cause a measurement error. We examined the measurement error with ZnTe [7][8] and LiNbO 3 [9] by using an electro-magnetic field simulator.

2 Linearly Circularly Elliptically Laser diode EO crystal Photo receiver Wave plate Polarizer Output signal Electric field Fig. 1. EO probe system configuration. Fig. 1 shows the configuration of the EO probe system. A linearly from a laser diode is converted into a circularly by a wave plate. The circularly is converted into an elliptically by passing through the EO crystal coupled with the electric field from the device under test. The change in polarization is converted into a change in intensity by a polarizer. The light with the intensity change is converted into an electrical signal by a photo receiver. 2. Simulation Model Fig. 2 shows our electro-magnetic field simulation model including a microstrip line and an EO crystal according to an organic photovoltaics (OPV) model [10]-[]. We used an electro-magnetic field simulator based on the finite-difference time-domain method. The EO crystal is positioned over the microstrip line. The signal electrode and the ground electrode are made of copper. The substrate is made of glass epoxy. ZnTe and LiNbO 3 are used as the EO crystals. The relative permittivities of ZnTe, LiNbO 3, and glass epoxy are 10, 32, and 4.6 respectively. The probe point is in the center of the EO crystal. The electric field strength in the Z-direction is obtained at the probe point. The distance D from the top surface of the signal electrode to the probe point is changed from 1 mm to 10 mm. The input signal is a sinusoidal signal with an amplitude of 1 V p-p and a frequency of 100 MHz. z y x 1 mm EO crystal 13 mm 10 mm 3 mm Signal electrode Substrate mm D Probe point Signal electrode mm 160 mm 80 mm Input signal Ground electrode Fig. 2. Simulation model.

3 3. Simulation Results Proceedings of International Conference Fig. 3 shows simulation results. Circle marks ( ), rectangle marks ( ), and triangle marks ( ) show the electric field strength without an EO crystal, that with ZnTe, and that with LiNbO 3, respectively. The electric field with the EO crystal was smaller than that without the EO crystal due to the dielectric property of the EO crystal. Electric field strength [V/m] Without EO crystal With ZnTe With LiNbO D [mm ] Fig. 3. Simulation results. The measurement error with ZnTe, E ZT (D), and that with LiNbO 3, E LN (D), at distance D are defined as E ZT (D) = ( E 0 (10 mm ) / E ZT (10 mm )) E 0 (D) E ZT (D) E 0 (D) 100 [%], (1) E LN (D) = ( E 0 (10 mm ) / E LN (10 mm )) E 0 (D) E LN (D) E 0 (D) 100 [%]. (2) Here, E 0 (D) is the electric field strength without the EO crystal, E ZT (D) is that with ZnTe, and E LN (D) is that with LiNbO 3 at distance D. Measurement error E ZT, E LN [%] With ZnTe With LiNbO D [mm ] Fig. 4. Measurement error. Fig. 4 shows the characteristics of the measurement error with ZnTe and LiNbO 3. Rectangle marks ( ) and triangle marks ( ) show the measurement error with ZnTe and LiNbO 3 respectively. E ZT and E LN were larger than 4% in a distance range of 2 mm. It was also found that E ZT was

4 smaller than E LN. As D increased, the measurement error decreased to less than 4%, which satisfies the specifications of an OPV model measurement system [10]. 4. Conclusion We examined the measurement error of an EO probe system for an OPV model with ZnTe and LiNbO 3 by using an electro-magnetic field simulator. When the EO crystal was far from the device under test in a distance range of > 2 mm, the measurement error was negligibly small. In the distance range of 2 mm, the measurement error with ZnTe was smaller than that with LiNbO 3. This means that the electro-magnetic field disturbance by ZnTe is smaller than that by LiNbO 3. Acknowledgements We thank Ryo Saito, Yukihiro Ishihara, and Masahiro Yada for their useful comments and the discussions they had with us. References [1] J. A. Valdmanis, G. A. Mourou, and C. W. Garbel, Subpicosecond Electrical Sampling, IEEE Journal Quantum Electronics, vol. 19, no. 4, pp , Apr [2] H. K. Heinrich, B. R. Hemenway, K. A. McGroddy, and D. M. Bloom, Measurement of real-time digital signals in a silicon bipolar junction transistor using a noninvasive optical probe, Electronics Letters, vol. 22, no., pp , Jun [3] J. Nees, and G. Mourou, Noncontact electro-optic sampling with a GaAs injection laser, Electronics Letters, vol. 22, no. 17, pp. 1032, Aug [4] J. A. Valdmanis, 1 THz-bandwidth proper for high-speed devices and integrated circuits, Electronics Letters, vol. 23, no. 24, pp , Nov [5] K. J. Weingarten, M. J. W. Rodwell, and D. M. Bloom, Picosecond Optical Sampling of GaAs Integrated Circuits, IEEE Journal Quantum Electronics, vol. 24, no. 2, pp , Feb [6] M. Shinagawa, and T. Nagatsuma, A laser-diode-based picosecond electrooptic prober for high-speed LSIs, IEEE Transactions on Instrumentation and Measurement, vol. 41, no. 3, pp , Jun [7] H. Takahashi, S. Aoshima, and Y. Tsuchiya, Sampling and Real-Time Methods in Electro-optic Probing System, IEEE Transactions on Instrumentation and Measurement, vol. 44, no. 5, pp , Oct [8] H. Takahashi, K. Kuroyanagi, S. Aoshima, and Y. Tsuchiya, Ultrafast E-0 Sampling using ZnTe Crystal and Ti:sapphire Laser, Microwave Photonics, MWP '96. Technical Digest., 1996 Internatonal Topical Meeting on, pp , Dec [9] S. R. M. Robertson, and A. J. Rogers, Measurement of DC electric fields using the electro-optic effect, IEE Proceedings J Optoelectronics, vol. 132, no. 3, pp , Jun

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