Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analog FM free-space optical communication based on a mid-infrared
  quantum cascade laser frequency comb   Quantum cascade laser frequency combs are nowadays well-appreciated sources
for infrared spectroscopy. Here their applicability for free-space optical
communication is demonstrated. The spontaneously-generated intermodal beat note
of the frequency comb is used as carrier for transferring the analog signal via
frequency modulation. Exploiting the atmospheric transparency window at 4
$\mu$m, an optical communication with a signal-to-noise ratio up to 65 dB is
realized, with a modulation bandwidth of 300 kHz. The system tolerates a
maximum optical attenuation exceeding 35 dB. The possibility of parallel
transmission of an independent digital signal via amplitude modulation at 5
MS/s is also demonstrated.

33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga