Parametric oscillator

A parametric oscillator is a <a href="/facts/Harmonic_oscillator/7IQNToGt">driven harmonic oscillator</a> in which the oscillations are driven by varying some parameters of the system at some frequencies, typically different from the <a href="/facts/Natural_frequency/pqTgYguB">natural frequency</a> of the oscillator. A simple example of a parametric oscillator is a child pumping a <a href="/facts/Swing_(seat)/JjXkbLVe">playground swing</a> by periodically standing and squatting to increase the size of the swing's oscillations. The child's motions vary the <a href="/facts/Moment_of_inertia/TpLLAVl7">moment of inertia</a> of the swing as a <a href="/facts/Pendulum/D2hQXwlI">pendulum</a>. The "pump" motions of the child must be at twice the frequency of the swing's oscillations. Examples of parameters that may be varied are the oscillator's resonance frequency 
 
 
 
 ω
 
 
 {\displaystyle \omega }
 
 and damping 
 
 
 
 β
 
 
 {\displaystyle \beta }
 
.
Parametric oscillators are used in several areas of physics. The classical <a href="/facts/Varactor/Kfd2nv5k">varactor</a> parametric oscillator consists of a semiconductor <a href="/facts/Varactor_diode/Kfd2nv5k">varactor diode</a> connected to a <a href="/facts/Resonant_circuit/tzEfI7Hf">resonant circuit</a> or <a href="/facts/Cavity_resonator/NjC413Gn">cavity resonator</a>. It is driven by varying the diode's capacitance by applying a varying <a href="/facts/Bias_voltage/lK0e6hbK">bias voltage</a>. The circuit that varies the diode's capacitance is called the "pump" or "driver". In microwave electronics, <a href="/facts/Waveguide_(electromagnetism)/M60l8qrm">waveguide</a>/<a href="/facts/Yttrium_aluminum_garnet/U6m3FjcR">YAG</a>-based parametric oscillators operate in the same fashion. Another important example is the <a href="/facts/Optical_parametric_oscillator/K6RBDNjY">optical parametric oscillator</a>, which converts an input <a href="/facts/Laser/jk6PTvvT">laser</a> light wave into two output waves of lower frequency (
 
 
 
 
 ω
 
 s
 
 
 ,
 
 ω
 
 i
 
 
 
 
 {\displaystyle \omega _{s},\omega _{i}}
 
).
When operated at pump levels below oscillation, the parametric oscillator can <a href="/facts/Amplifier/pnRgxncC">amplify</a> a signal, forming a parametric amplifier (paramp). <a href="/facts/Varactor/Kfd2nv5k">Varactor</a> parametric amplifiers were developed as <a href="/facts/Noise_(electronics)/Izbv38Rr">low-noise</a> amplifiers in the radio and microwave frequency range. The advantage of a parametric amplifier is that it has much lower noise than an amplifier based on a gain device like a <a href="/facts/Transistor/Bmr8zwL0">transistor</a> or <a href="/facts/Vacuum_tube/VHd1BNLq">vacuum tube</a>. This is because in the parametric amplifier a <a href="/facts/Electrical_reactance/LnvyrUnM">reactance</a> is varied instead of a (noise-producing) <a href="/facts/Electrical_resistance/hxSt0UAj">resistance</a>. They are used in very low noise radio receivers in <a href="/facts/Radio_telescope/SxIXUowL">radio telescopes</a> and <a href="/facts/Spacecraft_communication/YQqQaUw0">spacecraft communication</a> antennas.
Parametric resonance occurs in a mechanical system when a system is parametrically excited and oscillates at one of its resonant frequencies. Parametric excitation differs from forcing since the action appears as a time varying modification on a system parameter.

Parametric oscillator open-in-new

Parametric oscillator