Abstract
Frequency quadrupling for tunable microwave and sub-terahertz generation
using a single polarization modulator (PolM) in a Sagnac loop without using
an optical filter or a wideband microwave phase shifter is proposed and experimentally
demonstrated. In the proposed system, a linearly polarized continuous wave
from a tunable laser source (TLS) is split into two orthogonally polarized
optical waves by a polarization beam splitter (PBS) and sent to the Sagnac
loop traveling along the clockwise and counter-clockwise directions. A PolM
to which a reference microwave signal is applied is incorporated in the loop.
The PolM is a traveling-wave modulator, due to the velocity mismatch only
the clockwise light wave is effectively modulated by the reference microwave
signal, and the counter-clockwise light wave is not modulated. This is the
key point that ensures the cancelation of the optical carrier without the
need of an optical filter. Along the clockwise direction, the joint operation
of the PolM, a polarization controller (PC), and a polarizer corresponds to
a Mach–Zehnder modulator (MZM) with the bias point controlled to suppress
the odd-order sidebands. The optical carrier is then suppressed by the counter-clockwise
light wave at the polarizer. As a result, only two ±2nd-order sidebands are generated,
which are applied to a photodetector (PD) to generate a microwave signal with
a frequency that is four times that of the reference microwave signal. A theoretical
analysis is developed, which is validated by an experiment. A frequency-quadrupled
electrical signal with a large tunable range from 2.04 to 100 GHz is generated.
The performance of the proposed system in terms of stability and phase noise
is also evaluated.
© 2013 IEEE
PDF Article
More Like This
Cited By
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Contact your librarian or system administrator
or
Login to access Optica Member Subscription