- Email: [email protected]
Multi-channel light modulation based on the attenuation total reflection
Available online at www.sciencedirect.com
Optics & Laser Technology 37 (2005) 225 – 228 www.elsevier.com/locate/optlastec
Multi-channel light modulation based on the attenuation total re&ection Yanfang Yanga;∗ , Zhuangqi Caoa , Qishun Shena , Jumin Haob , Ling Qiub , Yuquan Shenb , Wen Yuanc , Pingping Xiaoc a Department
b Technical
of Applied Physics, Shanghai Jiao Tong University, Shanghai 200030, China Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100101, China c Department of Physics, Jiangxi Normal University, Nanchang 330027, China
Received 16 September 2003; received in revised form 27 February 2004; accepted 19 March 2004 Available online 7 June 2004
Abstract Multi-channel light modulation, which is based on the attenuated total re&ection (ATR) con
1. Introduction Poled polymers with second-order optical nonlinearity show great promise for use in electro-optic devices, because the materials themselves are inexpensive, and they oBer large susceptibilities, fast-response time, excellent mechanical and physical properties, and can be easily deposited onto many substrates. Particularly, organic polymers have much lower dielectric constants than nonlinear inorganic crystals, allowing higher bandwidth and lower drive power in traveling wave devices [1]. Thus a good electro-optic polymer will have many potential applications, such as the polymer modulators for lightwave data transmission systems. In recent years, there has been considerable progress made in the
Corresponding author. E-mail address: [email protected] (Y. Yang).
0030-3992/$ - see front matter ? 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2004.03.013
multi-channel electro-optic polymer modulators. Girton et al. have reported on a
226
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
2. Theory 1.0
Fig. 1. Con
Reflectivity
0.8 0.6 0.4
TM0
TM1
0.2 TM5
0.0
TM4 TM 3
55
TM2
60 65 70 Incident Angle (degree)
75
80
Fig. 2. ATR spectrum of the prism-polymer optical waveguide coupling system.
Reflectivity
The con
1.0
∆ ∆
0.8
∆I
∆I 0.6 0.4
TM2
S
S
TM1
0.2
0.0 61.9
62.0
62.1
63.2
63.4
θ Fig. 3. Shift of the ATR spectrum under the in&uence of the electric
refractive index of the polymer in the absence of an applied
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
227
Fig. 4. Experimental setup of the multi-lightwave modulation. P is a polarizer, BS1 , BS2 , beam splitters, M1 , M2 mirrors.
3. Sample preparation and experiment details The fabrication process of the modulator is as follows: a cross-linked polymer (n3 =1:69; r33 =30 Pm=V) layer of 3– 4 m thickness, which can support four or
(a)
(b)
(c)
Fig. 5. Oscilloscope traces of the light re&ectivity vs. time of beam 1 (upside) and the light re&ectivity vs. time of beam 2 (downside) with the modulation voltage 25 V at 50 MHz in three diBerent ways: (a) same wavelength ( = 832 nm) modulation with TM1 and TM2 modes; (b) diBerent wavelength (1 = 832 nm; 2 = 980 nm) modulation with same TM1 mode; (c) diBerent wavelength (1 = 832 nm; 2 = 980 nm) modulation with TM1 and TE2 modes.
TM-polarized or TE-polarized light. The ATR electro-optic modulator is mounted on a computer-controlled =2 goniometer to control accurately the incident angle. The intensities of the two re&ected lights are detected with two photodiodes by averaging of the output signals respectively. In the experiment the =2 goniometer keeps rotating to generate the ATR spectrum shown on the computer screen. The =2 goniometer stops in the midst of an appropriate fall-oB re&ection dip in the ATR spectrum that is the experiment’s working angle for light beam 1. Then the =2 goniometer is kept unmoved and the light beam 2 is regulated until the working’s angle of the light beam 2 is just at the midst of the fall-oB of another re&ection dip. After applying an electrical signal across the EO polymer, according to the shifted tiny P , we can record the alteration of the two re&ected intensities PI . So two re&ected light beams are then modulated simultaneously. Fig. 5 shows the oscilloscope traces of the light re&ectivity vs. time of beam 1 (upside) and the light re&ectivity vs. time of beam 2 (downside) with the modulation voltage at 25 V in three diBerent types. In it, (a) using the same wavelength ( = 832 nm) modulation with TM1 and TM2 modes, in this model, the guided modes serve as operation channels; (b) using the diBerent wavelengths (1 = 832 nm, 2 = 980 nm) modulation with the same TM1 mode, in this model, special light wavelength serve
228
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
Table 1 Modulation value of three diBerent types at modulation voltage 25 V
ri3 (Pm/V) PI (V)
Re&ectivity index (%)
Modulation
(a)
r33 = 30 at 832 nm
(b)
r33 = 18:5 at 980 nm
(c)
r13 = 6:2 at 980 nm
3 V@TM1, 2:8 V@TM2 3 V@832 nm, 2:6 V@980 nm 3 V@832 nm@TM1, 0:8 V@980 nm@TE2
42.9 40 42.9 36.7 42.9 14
as operation channels; (c) using the diBerent wavelengths (1 = 832 nm, 2 = 980 nm) modulation with TM1 and TE2 modes, in this model, both the guided mode and the light wavelength together serve as operation channel. The modulation value of three diBerent types at the same modulation voltage 25 V is shown in Table 1. Higher modulation index can be attained from any of the above three diBerent types. Here, we have presented the results of the doublechannel light modulation using the organic polymer electro-optic modulator based on the attenuated total re&ection. It is possible to extend this method to three or more channel lightwave modulation. In our experiment, owing to modulating the same electrical signals in both channels, there is no measurable electrical cross-talk. So we can obtain the stable modulation trace of the light re&ectivity. The bandwidth is a very essential parameter of EO modulator. Compared with the former work about lightwave transmission using the organic polymer electro-optic phase modulator with propagation geometry, the bandwidth of the intensity modulator used in the experiment is lower, which cannot be beyond 100 GHz like a traveling wave modulator [14]. However, the optical response speed of the ATR electro-optic modulator is mainly restricted to the electric capacity eBect cause by the two electrodes. To improve the response time of this modulator to meet the practical transmission, it is necessary to reduce the size of the bottom electrode to get a higher response speed. The theoretical 3 dB bandwidth is beyond 3:0 GHz when the area of the bottom electrode is lower than 1 mm2 . In the present modulator, the real region of the electrodes are approximately 6 mm × 6 mm, and a modulation bandwidth larger than 50 MHz has been obtained, which is suRcient to transmit multiple television signals. 4. Conclusion We have demonstrated a double-channel light polymer modulator based on the attenuated total internal re&ection con
extremely simple. The con
Optics & Laser Technology 37 (2005) 225 – 228 www.elsevier.com/locate/optlastec
Multi-channel light modulation based on the attenuation total re&ection Yanfang Yanga;∗ , Zhuangqi Caoa , Qishun Shena , Jumin Haob , Ling Qiub , Yuquan Shenb , Wen Yuanc , Pingping Xiaoc a Department
b Technical
of Applied Physics, Shanghai Jiao Tong University, Shanghai 200030, China Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100101, China c Department of Physics, Jiangxi Normal University, Nanchang 330027, China
Received 16 September 2003; received in revised form 27 February 2004; accepted 19 March 2004 Available online 7 June 2004
Abstract Multi-channel light modulation, which is based on the attenuated total re&ection (ATR) con
1. Introduction Poled polymers with second-order optical nonlinearity show great promise for use in electro-optic devices, because the materials themselves are inexpensive, and they oBer large susceptibilities, fast-response time, excellent mechanical and physical properties, and can be easily deposited onto many substrates. Particularly, organic polymers have much lower dielectric constants than nonlinear inorganic crystals, allowing higher bandwidth and lower drive power in traveling wave devices [1]. Thus a good electro-optic polymer will have many potential applications, such as the polymer modulators for lightwave data transmission systems. In recent years, there has been considerable progress made in the
Corresponding author. E-mail address: [email protected] (Y. Yang).
0030-3992/$ - see front matter ? 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2004.03.013
multi-channel electro-optic polymer modulators. Girton et al. have reported on a
226
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
2. Theory 1.0
Fig. 1. Con
Reflectivity
0.8 0.6 0.4
TM0
TM1
0.2 TM5
0.0
TM4 TM 3
55
TM2
60 65 70 Incident Angle (degree)
75
80
Fig. 2. ATR spectrum of the prism-polymer optical waveguide coupling system.
Reflectivity
The con
1.0
∆ ∆
0.8
∆I
∆I 0.6 0.4
TM2
S
S
TM1
0.2
0.0 61.9
62.0
62.1
63.2
63.4
θ Fig. 3. Shift of the ATR spectrum under the in&uence of the electric
refractive index of the polymer in the absence of an applied
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
227
Fig. 4. Experimental setup of the multi-lightwave modulation. P is a polarizer, BS1 , BS2 , beam splitters, M1 , M2 mirrors.
3. Sample preparation and experiment details The fabrication process of the modulator is as follows: a cross-linked polymer (n3 =1:69; r33 =30 Pm=V) layer of 3– 4 m thickness, which can support four or
(a)
(b)
(c)
Fig. 5. Oscilloscope traces of the light re&ectivity vs. time of beam 1 (upside) and the light re&ectivity vs. time of beam 2 (downside) with the modulation voltage 25 V at 50 MHz in three diBerent ways: (a) same wavelength ( = 832 nm) modulation with TM1 and TM2 modes; (b) diBerent wavelength (1 = 832 nm; 2 = 980 nm) modulation with same TM1 mode; (c) diBerent wavelength (1 = 832 nm; 2 = 980 nm) modulation with TM1 and TE2 modes.
TM-polarized or TE-polarized light. The ATR electro-optic modulator is mounted on a computer-controlled =2 goniometer to control accurately the incident angle. The intensities of the two re&ected lights are detected with two photodiodes by averaging of the output signals respectively. In the experiment the =2 goniometer keeps rotating to generate the ATR spectrum shown on the computer screen. The =2 goniometer stops in the midst of an appropriate fall-oB re&ection dip in the ATR spectrum that is the experiment’s working angle for light beam 1. Then the =2 goniometer is kept unmoved and the light beam 2 is regulated until the working’s angle of the light beam 2 is just at the midst of the fall-oB of another re&ection dip. After applying an electrical signal across the EO polymer, according to the shifted tiny P , we can record the alteration of the two re&ected intensities PI . So two re&ected light beams are then modulated simultaneously. Fig. 5 shows the oscilloscope traces of the light re&ectivity vs. time of beam 1 (upside) and the light re&ectivity vs. time of beam 2 (downside) with the modulation voltage at 25 V in three diBerent types. In it, (a) using the same wavelength ( = 832 nm) modulation with TM1 and TM2 modes, in this model, the guided modes serve as operation channels; (b) using the diBerent wavelengths (1 = 832 nm, 2 = 980 nm) modulation with the same TM1 mode, in this model, special light wavelength serve
228
Y. Yang et al. / Optics & Laser Technology 37 (2005) 225 – 228
Table 1 Modulation value of three diBerent types at modulation voltage 25 V
ri3 (Pm/V) PI (V)
Re&ectivity index (%)
Modulation
(a)
r33 = 30 at 832 nm
(b)
r33 = 18:5 at 980 nm
(c)
r13 = 6:2 at 980 nm
3 V@TM1, 2:8 V@TM2 3 V@832 nm, 2:6 V@980 nm 3 V@832 nm@TM1, 0:8 V@980 nm@TE2
42.9 40 42.9 36.7 42.9 14
as operation channels; (c) using the diBerent wavelengths (1 = 832 nm, 2 = 980 nm) modulation with TM1 and TE2 modes, in this model, both the guided mode and the light wavelength together serve as operation channel. The modulation value of three diBerent types at the same modulation voltage 25 V is shown in Table 1. Higher modulation index can be attained from any of the above three diBerent types. Here, we have presented the results of the doublechannel light modulation using the organic polymer electro-optic modulator based on the attenuated total re&ection. It is possible to extend this method to three or more channel lightwave modulation. In our experiment, owing to modulating the same electrical signals in both channels, there is no measurable electrical cross-talk. So we can obtain the stable modulation trace of the light re&ectivity. The bandwidth is a very essential parameter of EO modulator. Compared with the former work about lightwave transmission using the organic polymer electro-optic phase modulator with propagation geometry, the bandwidth of the intensity modulator used in the experiment is lower, which cannot be beyond 100 GHz like a traveling wave modulator [14]. However, the optical response speed of the ATR electro-optic modulator is mainly restricted to the electric capacity eBect cause by the two electrodes. To improve the response time of this modulator to meet the practical transmission, it is necessary to reduce the size of the bottom electrode to get a higher response speed. The theoretical 3 dB bandwidth is beyond 3:0 GHz when the area of the bottom electrode is lower than 1 mm2 . In the present modulator, the real region of the electrodes are approximately 6 mm × 6 mm, and a modulation bandwidth larger than 50 MHz has been obtained, which is suRcient to transmit multiple television signals. 4. Conclusion We have demonstrated a double-channel light polymer modulator based on the attenuated total internal re&ection con
extremely simple. The con