Amplification assisted difference frequency
generation for efficient mid-infrared conversion
based on monolithic tandem lithium niobate
superlattice
TAO CHEN,HAO LIU,WEI KONG, AND RONG SHU*
Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences,
Shanghai 200083, China
*Corresponding author: shurong@mail.sitp.ac.cn
Received 15 February 2017; revised 4 May 2017; accepted 5 May 2017; posted 9 May 2017 (Doc. ID 286845); published 13 July 2017
We report the investigation on the performance of an amplification assisted difference frequency generation
(AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem
lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the
DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump
pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion
efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equa-
tions. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler
conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the
reduction in conversion efficiency resulting from wider acce ptance bandwidths for the input lasers. We believe
that such systems combining the merits of high stability inherited from cavity-free configuration and high
efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community,
especially when the pulse shaping technique is incorporated.
© 2017 Chinese Laser Press
OCIS codes: (190.4970) Parametric oscillators and amplifiers; (190.4410) Nonlinear optics, parametric processes; (140.3070)
Infrared and far-infrared lasers.
https://doi.org/10.1364/PRJ.5.000355
1. INTRODUCTION
To date, mid-infrared (MIR) lasers have become the work-
horses for scientific research, environmental monitoring, and
defense systems, enabling high-resolution operation in the tem-
poral, spectral, and spatial domains [1–3]. Among all the MIR
generation methods, the optical parametri c oscillator (OPO)
stands out from its counterparts due to its broad operating tem-
perature, wide wavelength tuning range, and high power scal-
ability. Since its advent, this method has been extensively
adopted to generate MIR radiation with output durations from
continuous wave (CW) to femtosecond [4–10]. However, the
pump-to-idler conversion efficiency of a conversional OPO is
intrinsically restricted by the Manley–Rowe relations, in which
the generation of any demanded MIR idler photons is always
accompanied by the same amount of unwanted near-infrared
signal photons. In addition, the inefficient parametric conver-
sion during the buildup phase and probable parametric back-
conversion during oscillation will further reduce the actual
pump-to-idler conversion efficiency in practice.
To tackle this crisis, the scheme of the cascaded OPO
(COPO) was proposed, in which the generated intracavity signal
photons were recycled partly to produce the idler photons once
more via a secondary optical parametric amplification (OPA)
process [11]. Thanks to the prosperity of quasi-phase-matching
technology, COPOs harnessed by monolithic aperiodically poled
or tandem structured ferroelectric crystals have been demon-
strated theoretically and/or experimentally, in either nanosecond
[12–18]orpicosecond[19] regime. Nevertheless, inevitable
drawbacks inherited from the oscillating cavity remained for both
OPOs and COPOs, including compli cated coating, susceptibility
to misalignment, mode hopping, and thermal induced instability.
Especially when pumped by lasers with high repetition rate and
high average power, the thermal bistable behavior of such OPOs
or COPOs may hinder them from operating in pulse-on-demand
mode [20], which happens to be one of the favorite operation
modes for biomedical research or MIR countermeasures.
As an alternative, amplification assisted difference frequency
generation (AA-DFG) featuring cavity-free configuration can
Research Article
Vol. 5, No. 4 / August 2017 / Photonics Research 355
2327-9125/17/040355-07 Journal © 2017 Chinese Laser Press