Is there such a thing as a switched beam splitter? I am designing an experiment, and it would be extremely useful to me to have a "switched" beam splitter - a beam splitter wherein I could apply a voltage to some leads on the beam splitter to adjust the percent of light that is transmitted through versus reflected. I think that a light valve that had a mirror effect instead of going completely black could fit the bill. 
Does such a device/mechanism exist? I am a novice with optics, and I've designed a setup that accomplishes the same goal - the setup is complicated and has poor results. My guess is that such a thing could exist, I just don't know words I should be searching for. 
 A: There are numerous ways to do this, with the best one depending on the operating wavelength, power handling requirement, switching speed requirement, etc.
You can use a liquid crystal to rotate the beam polarization, and then a polarizing beam splitter to direct the beam depending on the state of the LC.
You can use a an electro-optic modulator in one arm of a Mach-Zehnder interferometer to produce destructive interference at one output and constructive interference at the other, depending on the electric signal driving the modulator.
You can use a Pockels cell with a polarizer to very quickly block and unblock a beam.
You can use an acousto-optic modulator to redirect a (portion of a) beam by a controllable angle.
Etc.
A: Combined with a polarizing beamsplitter, anything that can alter the polarization of a light beam produces a switchable beamsplitter.  Whether that would work for your purpose depends on the experiment you're setting up.
Liquid crystal displays work by altering the polarization of transmitted or reflected light, and have a switching speed on the order of 1 kHz.  There are other electro-optical devices like Faraday rotators that similarly alter the polarization of light.  If speed is not an issue you could just drive a variable beamsplitter with a stepping motor or other electrical actuator.
