waveguide:manual
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| waveguide:manual [2016/01/28 01:17] – [Connections and Controls] Michael Radunsky | waveguide:manual [2021/08/26 15:26] (current) – external edit 127.0.0.1 | ||
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| =====Operation===== | =====Operation===== | ||
| - | The LS-105 is shipped with a 5 V power supply and a cable for connection to the SEEOR, as shown in < | + | The LS-105 is shipped with a 5 V power supply and a cable for connection to the SEEOR, as shown in < |
| - | < | + | < |
| <WRAP right round box 550px>< | <WRAP right round box 550px>< | ||
| - | The cable plugs into the LS-105 with a push connector. | + | The cable plugs into the LS-105 with a push connector |
| ===Prototype EO Scanner Optical Head=== | ===Prototype EO Scanner Optical Head=== | ||
| Line 129: | Line 129: | ||
| When designing LC-drive electronics there are two important inherent properties. First, for a typical nematic LC, the EO response is via an induced dipole interaction. This means that the LC-molecules respond to the magnitude of the applied electric field but not the sign. Second, it is necessary that the time-averaged voltage across an LC optic is “DC-balanced” to have zero or minimal offset. This can be critical for both the operation and lifetime of the device. Prolonged time-averaged DC offsets will drive ion-migration inside the LC material, which can be deleterious for both the short-term performance and ultimately the lifetime of the device. On short timescales ion-migration will create a shielding field to cancel the applied voltage, which will cause the LC molecules to “relax” or “sag.” Precision applications can be sensitive to this sag even during short timescales. On long timescales ion-migration can result in the build up of permanent charge layers within the LC, thereby causing a “burn-in” which may forever degrade the operation of the device. The LC-drive electronics must account for both the “induced dipole” response and the “DC-balance” constraint.\\ | When designing LC-drive electronics there are two important inherent properties. First, for a typical nematic LC, the EO response is via an induced dipole interaction. This means that the LC-molecules respond to the magnitude of the applied electric field but not the sign. Second, it is necessary that the time-averaged voltage across an LC optic is “DC-balanced” to have zero or minimal offset. This can be critical for both the operation and lifetime of the device. Prolonged time-averaged DC offsets will drive ion-migration inside the LC material, which can be deleterious for both the short-term performance and ultimately the lifetime of the device. On short timescales ion-migration will create a shielding field to cancel the applied voltage, which will cause the LC molecules to “relax” or “sag.” Precision applications can be sensitive to this sag even during short timescales. On long timescales ion-migration can result in the build up of permanent charge layers within the LC, thereby causing a “burn-in” which may forever degrade the operation of the device. The LC-drive electronics must account for both the “induced dipole” response and the “DC-balance” constraint.\\ | ||
| An optimum voltage waveform that satisfies both of these LC requirements is a high quality square wave with no DC offset. Since the LC material only responds to the magnitude of the electric field and not the sign, by rapidly switching the voltage polarity the LC material will see the same E-field magnitude and simultaneously the need for DC balance will be satisfied. While in principle the square wave provides the ideal waveform, for anyone who has ever worked with square waves they will know that a high quality square wave is easier said than done. This is especially true when driving capacitive loads such as LC cells. Furthermore, | An optimum voltage waveform that satisfies both of these LC requirements is a high quality square wave with no DC offset. Since the LC material only responds to the magnitude of the electric field and not the sign, by rapidly switching the voltage polarity the LC material will see the same E-field magnitude and simultaneously the need for DC balance will be satisfied. While in principle the square wave provides the ideal waveform, for anyone who has ever worked with square waves they will know that a high quality square wave is easier said than done. This is especially true when driving capacitive loads such as LC cells. Furthermore, | ||
| - | <WRAP center round box 90%>[{{: | + | <WRAP center round box 90%>< |
| </ | </ | ||
| - | Common problems with square waves are illustrated on the left of Figure 7. Typically, the square wave is generated via amplification of a low voltage clock from a function generator or other clock source. Frequently, amplifiers are susceptible to several common problems: offsets (often frequency dependent which hampers trimming), limited slew rates, limited settling times (can cause overshoot and ringing), and limited current output. As shown on the left of Figure 7, all of these problems can have dramatic impacts on the magnitude of the electric field, i.e. what the LC responds to. For high-speed LC devices, the slew rate required to minimize any transient LC response during the polarity switch can be >100 Volts/ms, which is beyond the capabilities of most amplifiers when driving a capacitive load. The right hand side of Figure 7 shows an ideal square wave and its associated constant E-field magnitude. | + | Common problems with square waves are illustrated on the left of <imgref waveform> |
| | | ||
| - | <WRAP center round box 450px>[{{ : | + | <WRAP center round box 450px>< |
| </ | </ | ||
waveguide/manual.1453943869.txt.gz · Last modified: 2021/08/26 14:26 (external edit)