High density recording system using side-by-side information and servo tracks

An information signal recording system comprising:

• means for rotating a recording disc;
• means for producing two light beams;
• means for producing and sequentially switching first and second reference signals which have different frequencies, such that said reference signals correspond to each rotating period of the recording disc, and means for further producing a third reference signal which has a frequency that is different from the frequencies of the first and second reference signals, said third signal being produced responsive to said switching of the first and second reference signals;
• means for adding said third reference signal and an information signal which are to be recorded;
• a first light modulating means for modulating one of said two light beams with the output signal of said adding means;
• a second light modulating means for modulating the other of said two light beams responsive to the first and second reference signals;
• and
• recording means for simultaneously forming an information signal track on the recording disc responsive to the light beam modulated by the first light modulating means and a reference signal track on an intermediate part of said recording disc between center lines of adjacent information signal tracks, said recorded signals being responsive to the light beam modulated by the second light modulating means,
• said first and second reference signals being alternately recorded on the reference signal track each rotating period of the recording disc, said third reference signal being recorded at a predetermined position on the information signal track each rotating period of the recording disc.