Attenuating a laser beam with a Model 4104NFamplitude modulator. The beam passes through the modulator followed by a polarizer (Modulator Accessories). A Model 3211 broadband-modulator driver is used to drive the modulator. Innovative design minimizes thermal birefringence
High-quality lithium niobate crystals provide high contrast and low drive voltages
Can be used as electronically variable wave plates
New Focus™ amplitude modulators are specifically designed for high performance at modulation frequencies of up to 200 MHz. The Model 4102NF / 4104NF broadband amplitude modulator can be operated from DC to 200 MHz. The Model 4101NF / 4103 is a resonant device that can be built to operate at any frequency from 0.01 to 200 MHz.
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.
Since our modulators don’t include external polarizers, they can be used as electronically variable wave plates. To use the device as an amplitude modulator, a polarizer is needed at the output.
The Model 4101NF / 4103 can be driven with a low-voltage function generator or the Model 3363 resonant-modulator drivers. The Model 4102NF / 4104NF can be driven using our Model3211 broadband-modulator drivers with a function generator. Call us or visit the support section of our website for driver recommendations.
Attenuating a laser beam with a Model 4104NFamplitude modulator. The beam passes through the modulator followed by a polarizer (Modulator Accessories). A Model 3211 broadband-modulator driver is used to drive the modulator.
The extinction ratio of an amplitude modulator is the ratio between the optical power at maximum and minimum transmission. A high extinction ratio indicates a good modulator. For our Model 410X modulators, 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.
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.