There are no practical optics capable of being frequency modulated.
Lasers by defininition can't be frequency modulated.
The use of AM versus FM has nothing to do with "precision".
You have no clue what modulation is.
http://www.opticsinfobase.org/abstract.cfm?URI=JLT-16-4-656 quote:
"This paper proposes a scheme for the generation of optical frequency
modulation (FM) signals through direct modulation and injection locking
of semiconductor lasers. The method is simple and effective. The
amplitude modulation of the AM-FM optical carrier generated through
direct modulation can be drastically reduced by an injection-locked
semiconductor laser. For this purpose, the AM limiting property of the
injection-locked semiconductor laser has been investigated
theoretically in detail. The FM index and the second harmonic
distortion of the resulting FM signal at the output of the AM limiter
has also been calculated."
http://www.stanford.edu/~siegman/fm_laser_buildup.pdf
http://www.stanford.edu/~siegman/current_research.html quotes:
"FM laser operation" is a rather unusual type of laser operation
discovered by Steve Harris in the early 1960s in which an intracavity
phase modulator that is tuned a small amount away from the exact axial
mode spacing of the laser causes the laser to operate in a purely
frequency modulated (FM) manner, with the axial modes locked together
in a classic Bessel-function frequency modulated spectrum."
"FM laser operation is thus quite different in character from the
better known "FM mode-locked" type of operation which produces short
mode-locked output pulses, although FM laser operation can easily be
converted into FM mode locked (i.e., pulsed) operation in the same
laser simply by tuning the intracavity phase modulation frequency more
or less exactly to the axial mode spacing frequency."
"FM laser operation can be of some interest and possibly even some
practical application in situations -- such as perhaps in broadband
fiber lasers -- where one wants to create a very wide "comb" spectrum
with known and coherent phases between the individual spectral
components of the comb, while at the same time avoiding nonlinear or
other problems that may be associated with a short-pulse type of
mode-locked operation."
"Unfortunately, recent experiments seem to show that although a very
broadband type of FM laser operation can easily be achieved in a fiber
laser, the resulting oscillation spectrum can also be quite noisy. The
noise fluctuations in this case are associated with the fact that the
oscillation spectrum in an FM laser only converges quite slowly to the
desired FM-laser steady-state spectrum when the phase modulator is
first turned on, or only slowly converges back to steady-state
following any transient disturbances in the laser."
http://www.ece.drexel.edu/CMLE/papers/mmilifm/mmilifm.htm quote:
"Using the Maxwell-Bloch equations, we have studied dynamics associated
with an electro-optically tunable laser modulated by a sinusoidal
signal with a frequency near the cavity free spectral range. We find
that FM modelocking may occur when a higher order FM mode acquires the
lowest threshold. For short-cavity lasers, the pulse waveform at
modelocking is complicated, and unlike the simple Gaussian shape
suggested by previous studies. In order to explain instability observed
in laser FM operation, we develop a linear stability analysis for the
lasing FM mode. Our analysis shows that this type of instability is
attributed to mode competition and to laser relaxation dynamics. We
then confirm these analytic results by numerical simulations. "
http://digitalcommons.stevens.edu/dissertations/AAI3160412/ quote:
"This work presents a novel phase-amplitude-modulation principle of
active ranging and its application to laser ranging and
vibrodiagnostics. An exact theoretical description of the proposed
technique is given. Based on the developed theoretical model we present
a laser-phase-amplitude-modulation vibrometer and a simple system for
measurements of the length of optical fibers as practical applications
of phase-amplitude-modulation technique. Both systems have been
assembled and successfully tested. In the last chapter we present a
wide-band phase-amplitude-modulation technique and its application to
active ranging. Experimental results being obtained during experiments
promise that both developed systems might be a serious alternative to
all existing similar systems due to its low cost and simple assembly."
You just need to
