By adopting self-injection locking (SIL) technology in an external injection locking (EIL) optoelectronic oscillator (OEO), a highly improved side mode suppression ratio (SMSR) and low phase noise microwave signal generator is designed. The EIL ranging is closely related to the frequency spacing ranging of the free-running OEO, which is the reverse of the oscillation loop length, and limits the phase noise performance. Here SIL technology is introduced to significantly increase the Q-factor of the OEO without degrading the SMSR by setting the longer loop without oscillation. Both the simulation and experimental results are carried out to confirm the conclusion. Additionally, an SMSR up to 86 dB and phase noises as low as
−
88.80
d
B
c
/
H
z
@
100
H
z
and
−
122.83
d
B
c
/
H
z
@
10
k
H
z
, respectively, are demonstrated. Furthermore, the frequency overlapping Allan deviation of the proposed OEO scheme is also enhanced by
1
0
3
times, which benefits from the external injection technology compared with the free-running OEO. In addition, the SMSR and phase noise modification dependence on the fiber length, the RF source quality and external injection power, as well as the frequency tunability, are detailed and discussed to reveal the compatibility combination mechanism of the EIL and the SIL.
An active mode-locked optoelectronic oscillator (AML-OEO) based on the simulated Brillouin scattering (SBS) effect without an electrical filter is demonstrated here. By using phase modulation and SBS-based selective sideband amplification, the central frequency of the proposed SBS-AML-OEO is easily adjusted by simply changing the pump laser frequency instead of the filters. A microwave frequency comb signal with an adjustable central frequency and fixed bandwidth are generated by injecting a mode-locking external RF synchronizing with the free spectral ranging FSR. In addition, the harmonic SBS-AML-OEO is also achieved by harmonic signal injection. The proposed method reveals a simple solution to tune the central frequency and has the potential to be integrated on a chip since there is no structure changing in the scheme.
A coherent dual-band microwave photonic (MWP) radar system is proposed and experimentally demonstrated in this paper.In the transmitter, coherent dual band linear frequency modulation (LFM) waves with the characteristics of tunable central frequency and the same large bandwidth are generated based on an improved optical frequency operation module (OFOM).In the receiver, the information of targets is obtained after the echoes at two bands are received and de-chirp processed simultaneously. Experimentally, the presented coherent dual-band MWP radar system operating in X band and Ku band with an instantaneous bandwidth of 3GHz is constructed. A target-detection experiment verifies that centimetre level resolution can be achieved by the system.
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