Description

1550nm 80MHz Acousto-optic Frequency Shifter

Key performance

Low insertion loss

compact

Stable performance

parameter	Unit	Min	Max	conventional
material				TeO2
wavelength	nm	1520	1580	1550
Average optical power	KW		0.5
Peak (pulse) optical power	kW		0.5
Ultrasonic sound velocity	m/s			4200
Insertion loss	dB		3	2
Extinction Ratio	dB	50
Return loss	dB	40
Rising time	ns		55	45
frequency	MHz			80
Frequency shift	MHz			+/-80
RF power	W			2
Voltage standing wave ratio			1.5:1
input resistance	Ω			50
Device interface				SMA
Fiber type				Single mode
Fiber optic interface				FC/APC
Fiber length	m			1.5
Operating temperature	℃			-20~+60
storage temperature	℃			-30~+70

 

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.