Application Cases

Experiment Name: Research on Electro-Optic Switches Based on the Goos-Hänchen Effect

Test Equipment: High-voltage amplifier, Signal generator, Oscilloscope, Tunable laser, etc.

Experimental Process:

Figure 1: Experimental setup diagram

The experimental setup is shown in Figure 1. A laser with a wavelength of 860.00 nm emitted from a tunable laser passes through a polarizer and two 0.1 mm diameter pinholes to obtain TE-polarized and collimated laser light, which is then incident on the upper metal layer of a double-metal-clad waveguide. The polarizer and the two pinholes are spaced approximately 0.5 m apart, and a plane mirror is inserted into the optical path to make the setup more compact. The PMN-PT transparent ceramic measures 5.62 mm × 4.2 mm × 3.00 mm (l × w × h) and forms the double-metal-clad waveguide, which is fixed on a double-angle rotary stage (see photo in Figure 3.13). Electrodes are connected to the upper and lower metal layers of the double-metal-clad waveguide using conductive silver adhesive. The external voltage is first generated as a small signal by a programmable signal generator, then amplified by a high-voltage amplifier, and finally applied to the two electrodes of the double-metal-clad waveguide. A three-hole array with a hole diameter of 0.1 mm and a hole spacing of 0.4 mm is precisely placed in the direction of the reflected light so that when no external voltage is applied, the reflected light passes through channel 1. During the experiment, both the voltage signal from the signal generator and the reflected light intensity signal are received and measured by a digital oscilloscope.

Experimental Results:

Figure 2: Experimental results of reflected light intensity and GH shift versus applied voltage. The insets show the reflected light spots at applied voltages of 0 V, 500 V, and 650 V.

To measure the voltages required for the optical signal to pass through channels 2 and 3, we first replaced the three-hole array and photodiode in the reflected light direction with a position-sensitive detector (PSD) to measure the relationship between the GH shift of the reflected light and the applied voltage. The experimental results of reflected light intensity and GH shift versus applied voltage are shown in Figure 2, with the applied voltage range from 0 to 650 V in 50 V increments. In the experiment, the incident angle was fixed at the position where the reflected light intensity is maximum. At this point, the incident light is almost not coupled into the waveguide layer, so the GH shift is minimal and can be used as a reference point for measuring the GH shift. The voltage signal from the signal generator was set to a rectangular wave with a frequency of 1 Hz. Due to the low signal frequency, a high-speed PSD was not required to measure the GH shift. When any external voltage is applied, the refractive index of the PMN-PT transparent ceramic waveguide layer increases, while its thickness decreases. At lower applied voltages, the ultra-high-order guided mode shifts to the left because the inverse piezoelectric effect dominates at this stage, resulting in ΔN < 0. When the applied voltage exceeds 400 V, the ultra-high-order guided mode begins to shift to the right. Since the effective refractive index has a quadratic relationship with the electro-optic effect, at higher applied voltages, the electro-optic effect begins to dominate, resulting in ΔN > 0. As explained in the experimental principles, whether the ultra-high-order guided mode shifts left or right, it can cause changes in the GH shift of the reflected light intensity. When the applied voltage increases from 0 V to 200 V, the GH shift increases from 0 μm to 290 μm. When the voltage further increases to 400 V, the GH shift decreases to 32 μm. As the applied voltage continues to increase to 650 V, the GH shift increases again to 830 μm. The three insets in Figure 2 show the reflected light spots at applied voltages of 0 V, 500 V, and 650 V, confirming the theoretical result that a larger GH shift corresponds to smaller reflected light intensity and a larger spot radius. When the applied voltage is 830 V (not shown in Figure 2), the GH shift of the reflected light reaches its maximum value of 1040 μm, and the reflectivity of the reflected light is only 0.11. Such a large GH shift is not suitable for electro-optic switches because the reflected light spot becomes severely distorted or even splits.

Figure 3: Experimental results of periodic modulation of the electro-optic switch with a modulation period of 20 microseconds.

When the signal generator frequency was set to 50 kHz, the experimental response results of the electro-optic switch based on the GH shift effect are shown in Figure 3. When no external voltage is applied (not shown in Figure 3), the reflected light exits from channel 1 with an insertion loss of 0.22 dB, and the crosstalk of channels 2 and 3 relative to channel 1 are -29.8 dB and -32.7 dB, respectively. As shown in Figure 3(a), when the peak-to-peak voltage signal from the signal generator is 179 mV with a bias voltage of 80 mV, the voltage amplified by the high-voltage amplifier and applied to the PMN-PT transparent ceramic is 537 V. At this point, the reflected light exits from channel 2, with insertion losses of 3.77 dB in the on-state and 36.5 dB in the off-state, and the crosstalk of channels 1 and 3 relative to channel 2 are -29.2 dB and -37.4 dB, respectively. Similarly, when the peak-to-peak voltage signal from the signal generator is 214 mV, the amplified applied voltage is 642 V, and the reflected light exits from channel 3, with insertion losses of 6.12 dB in the on-state and 41.2 dB in the off-state (see Figure 3(b)). The crosstalk of channels 1 and 3 relative to channel 2 are -32.6 dB and -31.3 dB, respectively. The switching times for channels 2 and 3 are shown in Figure 3(c). The turn-on time (defined as the time required for the light intensity to increase from 10% to 90% of its maximum value) is 0.42 μs and 0.28 μs, respectively, while the turn-off time (defined as the time required for the light intensity to decrease from 90% to 10% of its maximum value) is 0.94 μs and 1.63 μs, respectively.

Figure: ATA-7100 High-Voltage Amplifier Specifications

The experimental materials in this article have been compiled and released by Xi'an Aigtek Electronics. For more experimental solutions, please continue to follow the Aigtek official website. Aigtek is a high-tech enterprise in China specializing in the research, development, production, and sales of measurement instruments. The company has consistently focused on the R&D and manufacturing of test instrument products such as high-voltage amplifiers, voltage amplifiers, power amplifier modules, and high-precision current sources.