Specifications

Features

High Contrast Ratios

The extinction ratio is limited by refractive index distortions in the electro-optic crystals that impart wavefront distortion to the optical beam. For these devices, the on:off extinction ratio is typically 50:1 for a 0.5-mm diameter beam. Higher values can be achieved by focusing your beam.

Alignment Made Simple

The crystals in these modulators are mounted at 45° so that your input polarization can be either vertical or horizontal. To minimize thermal birefringence, we use two matched crystals arranged in series. This results in amplitude modulators that exhibit less than 1 mrad/°C of temperature-dependent polarization rotation. In addition, the mechanical aperture make aligning your beam through the modulator simple.

Resonant Designs Offer Low Drive Voltages

We offer both broadband modulators that can be used at a wide range of frequencies and resonant modulators that operate at a single frequency with much lower drive voltage requirements. The resonant modulators feature a resonant tank circuit to maximize power transfer from driver to crystal, thereby maximizing the voltage across the crystal, lowering required drive voltages. Each resonant phase modulator is built to the your exact specified frequency.

Optical Chopping With Amplitude Modulators

One application of these modulators is high-frequency optical chopping. Although mechanical choppers are frequently used, they modulate the optical intensity at rates of only a few kilohertz. This frequency is often not high enough to get away from the 1/f noise of the detection system. An optical amplitude modulator, such as the Model 410X can be used to chop the beam at 1 MHz, thus giving you shot-noise-limited detection.

Amplitude Stabilizer Application

Another common use for an amplitude modulator is as the actuator in an amplitude stabilizer as shown. Here, a photodetector measures a portion of the laser intensity which the servo uses to adjust the transmission of the amplitude modulator. An important consideration in this application is the nonlinear response of the modulator. The changing slope of the modulator's response to input voltage leads to a change in the closed-loop transfer function which could destabilize the feedback loop.

An amplitude modulator can be used to reduce the amplitude fluctuations.

Amplitude Modulator Transfer Function

The transfer function of an amplitude modulator between crossed polarizers is a sin2 function. You can achieve linear amplitude modulation with small modulation voltages by biasing the modulator at the 50% transmission point, either with a quarter-wave plate or by applying a DC voltage to the modulator.

Resources

Manuals