Fraction-order sideband generation in an optomechanical system

We propose a scheme for generating a new kind of sideband, i.e., the fraction-order sideband, in an optomechanical system. In the conventional scheme of high-order sideband generation [ Opt. Lett. 38 , 353 ( 2013 ) OPLEDP 0146-9592 10.1364/OL.38.000353 ], the sideband interval has a minimum frequency limitation, which is equal to the mechanical frequency ω b , and this limits the precision of the sideband comb. With our proposed fraction-order sidebands, the sideband interval can break that limitation and reach ω b / n ( n is an integer). The scheme we propose can be realized by driving the optomechanical system with three laser fields, including a control field ( ω c ) and two probe fields ( ω p , ω f ), in which the detuning between ω c and ω p is equal to the mechanical frequency ω b , while the detuning between ω c and ω f is equal to ω b / n . In this case, we find that not only the integer-order (high-order) sidebands, but also the fraction-order sidebands, and the sum and difference sidebands between the integer- and fraction-order sidebands, will appear in the output spectrum. Moreover, the sideband interval becomes ω b / n , and it can be decreased by increasing n . Our work paves the way to achieve a tunable optical frequency comb based on the optomechanical system.