1550nm 80MHz Acousto-optic Frequency Shifter
Low insertion loss
|Average optical power||KW||0.5|
|Peak (pulse) optical power||kW||0.5|
|Ultrasonic sound velocity||m/s||4200|
|Voltage standing wave ratio||1.5:1|
|Fiber type||Single mode|
|Fiber optic interface||FC/APC|
When light is diffracted at the traveling refractive index grating in an acousto-optic modulator, the diffracted light experiences a shift of optical frequency which is plus or minus the acoustic (or drive) frequency. That effect (which can be interpreted as a Doppler shift) is exploited in acousto-optic frequency shifters.
Drive frequencies are typically between some tens and hundreds of megahertz, rarely more than 1 GHz. The resulting change of optical wavelength is quite small. For larger frequency shifts, or for realizing very small frequency shifts (e.g. only a few MHz), one may cascade two or more devices. It is also possible to use a double pass through a single device in order to obtain twice the frequency shift.
Frequency shifters may either be operated with a fixed drive frequency, generating a fixed optical frequency offset, or with a variable drive frequency. In the latter case, one needs to consider the fact that the beam direction will change with the drive frequency; if that is detrimental, one may use methods to minimize such effects. It is also possible to operate a frequency shifter with several drive frequencies at the same time.
The optical input beam is typically a laser beam from a single-frequency laser. However, a frequency shifter would also work with a multimode beam, if its bandwidth is not too large.
Most acousto-optic frequency shifters are bulk devices, but there are also compact fiber-coupled versions (fiber-pigtailed AOFS). Light from the input fiber is first collimated, then sent through the modulator crystal and finally focused into the output fiber. There are also all-fiber frequency shifters (perhaps not commercially available) where the frequency shift is created within an optical fiber.
Transmission through an acousto-optic (AO) device causes the input light to experience a frequency shift equal to the RF drive frequency. Our acousto-optic frequency shifters (AOFS) are optimized for the needs of applications like interferometry, with the ability to achieve high extinction ratio between modes.