26-05-2012, 01:28 PM
Continuous phase stabilization and active interferometer control using
two modes
Continuous phase stabilization and active interferometer control.pdf (Size: 2.18 MB / Downloads: 42)
The ability to continuously adjust and stabilize the
optical phase dierence between two arms of an interfer-
ometer is of great importance to a wide range of appli-
cations including homodyne detection for quantum state
tomography [1], phase-shift keying in optical telecommu-
nications [2], phase-shifting interferometry [3], ultrafast
pump-probe spectroscopy [4{6], interference-based op-
tical lattices [7] and near-eld scanning microscopy [8].
Previous approaches typically relied on fringe-lock meth-
ods, in which a useful error signal can only be produced
near integer multiples of =2. These methods are prone
to fringe skipping, where noise causes the phase lock cir-
cuit to hop to a neighboring interference fringe, a half
wavelength away. In many applications the ability to
continuously adjust the phase dierence to an arbitrary
value is required, which cannot be achieved with fringe-
lock methods. Continuous phase locking has been previ-
ously accomplished in two ways. An arbitrary phase can
be locked by modulation of one of the interfering beams
and detection at the fundamental and second harmonic
of the modulation frequency [9]. This method, which
produces a sinusoidal error signal, is still susceptible to
fringe skipping. Furthermore, the phase modulation re-
quires specialized signal analysis and is undesirable when
signal acquisition rates faster than the modulation fre-
quency are necessary. A recent technique that utilizes
tilting of the beam in one arm of the interferometer and
spatially resolved measurements at the output to cre-
ate a linear error signal was introduced [10]. However,
this scheme requires precise alignment and stabilization
of photodetector positioning, and suers from chromatic
aberrations of the glass wedge used for the tilt.
Conclusion
In conclusion, we have shown a general approach to
interferometric phase control capable of locking to any
chosen phase value. The key element in this scheme is
the use of two orthogonal modes with known, xed phase
oset to obtain a precise estimate of the interferometer
phase for arbitrary path length dierence. This enables
highly accurate feedback control of the system. Depend-
ing upon the nature of the interferometer to be stabi-
lized, in particular, considering the main sources of phase
noise, choice of what degree of freedom to utilize can be
made to optimize the stabilization scheme. This general
approach to phase stabilization allows control under di-
verse noise conditions. Polarization modes are extremely
useful when there is little change in birefringence be-
tween the two interferometer arms as demonstrated here.
Frequency modes could be used in optical ber based
interferometers where the dispersion is known.