Amplitude Modulator Crystal
Orientation (Click to Enlarge)
The electro-optic amplitude modulator (EO-AM) is a Pockels cell type modulator consisting of two matched lithium niobate crystals (see figure 2 on the Graph Tab) packaged in a compact housing with an RF input connector. Applying an electric field to the crystal induces a change in the indices of refraction (both ordinary and extraordinary) giving rise to an electric field dependent birefringence which leads to a change in the polarization state of the optical beam. The EO crystal acts as a variable waveplate with retardance linearly dependent on the applied electric field. By placing a linear polarizer at the exit, the beam intensity through the polarizer varies sinusoidally with linear change in applied voltage.
Our EO phase modulators provide a variable phase shift on a linearly polarized input beam. The input beam is linearly polarized along the vertical direction which is the Z-axis of the crystal. A voltage at the RF input is applied across the Z-axis electrodes inducing a change in the crystal's extraordinary index of refraction thereby causing a phase shift in the optical signal.
The control signal may be a DC or a time varying RF signal. When the control voltage is a time varying signal, the optical beam undergoes frequency modulation whereby some of the energy at the fundamental frequency is converted into sidebands separated from the fundamental frequency by the integer multiples of the modulating frequency. The amount of energy converted into sidebands is determined by the depth of modulation. The graph to the right shows a plot of relative sideband strength as a function of depth of modulation.
100 mA Pulsed Output Current (100 mA continuous)
-20X Voltage Gain
The Thorlabs HVA200 High Voltage Amplifier is designed to directly drive our Electro-Optic Modulators. The amplifier has many features, including a ±200 V output, a continuous current output of 100 mA, a 1 MHz bandwidth, and low noise. The voltage gain of -20 boosts the input up to the high voltages needed to drive our lithium niobate broadband modulators. An adjustable bias allows for precise DC offset control.
The HVA200 uses a high voltage, wideband, high slew rate output amplifier to achieve the desired output. The input amplifier includes a summing junction, which allows an adjustable DC bias to be added to the input modulation. This composite signal is then boosted by a fixed voltage gain of 20 by the output amplifier up to a maxiumum output of ±200 V. For example, if the HVA200 is sweeping from -200 to 200 V and a 10 V DC Bias is applied, the output of the HVA200 will be from -190 to 200 V (i.e., the sweep is clipped because the maximum voltage output was reached). If, however, the HVA is swept from -100 to 100 V and the same 10 V DC Bias is applied, the output will sweep from -90 to 110 V.
For added safety, a front panel HV Enable button must be pressed to connect the HV output to the output BNC. The DC Bias control consists of a rotary encoder, which allows precise control and repeatability. The bias adjustment is typically used to shift the DC level of the output as needed by the application. A voltage monitor output is provided to allow real-time monitoring of the high voltage output. The monitor has a scaling of 20:1 (when used with high impedance detectors) so that an output of 200 V results in a 10 V monitor voltage.
Easily Rotates Into and Out of Beam Path
13mm Diameter Aperture for Use With GTH5M
#2-56 Mounting Screw and Washer Included
The EO-PMT allows for easy interface of a Glan Thompson polarizer (GTH5M) to our Electro-Optic Modulators. The single mounting point allows the mount to swivel the polarizer into and out of the light path; a useful feature that allows for alignment and adjustment of the electro-optic modulators. The EO-GTH5M packages the Glan Thompson polarizer (GTH5M) with the mounting adapter.
The FT-EOMA is a mounting bracket used to mount an Electro-Optic (EO) Modulator onto a FiberBench. The length of the bench needs to be at least 70 mm in the direction you wish to mount the modulator. Incorporation of the optional EO Modulator optic mount and polarizer (EO-GTH5M) will require a longer FiberBench. The Linear Polarizer modules are well suited for use with an EO Modulator in a FiberBench System. The application picture to the right shows an EO Modulator with an FT-38X100 Multi-Axis FiberBench, one PCB Linear Polarizer, and two PAF FiberPorts.