There are basically 4 types of filters, short and long pass, bandpass (narrow) and beamsplitters (dichroics). In fluorescence microscopy these are usually combined in a filter block as is illustrated below.

The excitation and barrier filter can be either a short, long or bandpass. It's purpose is to only allow the required excitation light to pass to the specimen. The dichroic is positioned at an angle of 45 degrees and will reflect down the excitation light to the specimen and then allow the longer fluorescent light to pass through it to the detector. The final filter which is known as a barrier filter can once again be any of the short, long or bandpass. It's purpose is to block any of the excitation light and only pass the required emitted fluorescent light.

Below is an example of a transmission curve of a filter block that could be used for a UV excitable dye. The blue curve shows you the excitation light the green curve shows you the dichroic which will reflect most of the excitation light but block its transmission and the red curve is the barrier filter which is a bandpass filter only allowing light between 430 and 490 nm to pass to the detector.

In today's modern confocals the emissions are able to be separated with even finer precision. Each confocal achieves this slightly differently.