Photonic microwave generation using period-one nonlinear dynamics of semiconductor lasers suffers from poor spectral purity. A stabilization approach based on optical modulation sideband injection locking is investigated. An optical signal carrying a highly correlated modulation sideband comb simultaneously injection-locks the regeneration of the optical carrier and the lower oscillation sideband in the dynamics, establishing a phase-locking between the two spectral components. A linewidth of below 1 Hz is therefore achieved for microwave generation up to at least 40 GHz. Because of the frequency multiplication in yielding the comb-like optical signal, only an electronic microwave reference at the tenth subharmonic or higher of the generated microwave frequency is required.

Photonic microwave stabilization for period-one nonlinear dynamics of semiconductor lasers using optical modulation sideband injection locking

Phase noise of the period-one (P1) nonlinear dynamical oscillation in an optically injected semiconductor laser is numerically investigated. The P1 dynamics causes the laser output intensity to oscillate at a widely tunable frequency for photonic microwave generation, although the intrinsic spontaneous emission in the laser inevitably degrades the microwave signal and manifests as the oscillation phase noise. To characterize the phase noise, the P1 microwave linewidth is first numerically examined through the rate equations with a Langevin term. The P1 microwave linewidth is found to vary with the injection parameters. It is nearly minimized when the microwave power maximizes. Owing to the laser nonlinearities, the P1 microwave linewidth can even be smaller than the free-running optical linewidth. By adding an optical feedback to the laser, the P1 microwave linewidth is found to reduce as the feedback strength and feedback delay increase, in which an inverse-square dependency is followed asymptotically. By modification to a dual-loop feedback, noisy side peaks around the central P1 frequency are effectively suppressed through the Vernier effect. The dual-loop feedback maintains a low phase noise variance over a wide tuning range of the P1 frequency, while allowing long delay times for significant P1 microwave linewidth narrowing.

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Phase noise characteristics of microwave signals generated by semiconductor laser dynamics

Effects of optical feedback on period-one nonlinear dynamics of an optically injected semiconductor laser are numerically investigated. The optical feedback can suppress the period-one dynamics and excite other more complex dynamics if the feedback level is high except for extremely short feedback delay times. Within the range of the period-one dynamics, however, the optical feedback can stabilize the period-one dynamics in such a manner that significant reduction of microwave linewidth and phase noise is achieved, up to more than two orders of magnitude. A high feedback level and/or a long feedback delay time are generally preferred for such microwave stabilization. However, considerably enhanced microwave linewidth and phase noise happen periodically at certain feedback delay times, which is strongly related to the behavior of locking between the period-one microwave oscillation and the feedback loop modes. The extent of these enhancements reduces if the feedback level is high. While the microwave frequency only slightly changes with the feedback level, it red-shifts with the feedback delay time before an abrupt blue-shift occurs periodically. With the presence of the laser intrinsic noise, frequency jitters occur around the feedback delay times leading to the abrupt blue-shifts, ranging from the order of 0.1 GHz to the order of 1 GHz.

/pdf/optical-feedback-stabilization-of-photonic-microwave-5a0od6lf1b.pdf

Optical feedback stabilization of photonic microwave generation using period-one nonlinear dynamics of semiconductor lasers

For radio-over-fiber links, microwave-modulated optical carriers with high optical modulation depth are preferred because high optical modulation depth allows generation of high microwave power after photodetection, leading to high detection sensitivity, long transmission distance, and large link gain. This study investigates the period-one nonlinear dynamics of semiconductor lasers for optical modulation depth improvement to achieve photonic microwave amplification through modulation sideband enhancement. In our scheme, only typical semiconductor lasers are required as the amplification unit. The amplification is achieved for a broad microwave range, from less than 25 GHz to more than 60 GHz, and for a wide gain range, from less than 10 dB to more than 30 dB. The microwave phase quality is mainly preserved while the microwave power is largely amplified, improving the signal-to-noise ratio up to at least 25 dB. The bit-error ratio at 1.25  Gbits/s is better than 10−9, and a sensitivity improvement of up to at least 15 dB is feasible.

Photonic microwave amplification for radio-over-fiber links using period-one nonlinear dynamics of semiconductor lasers

We propose and experimentally demonstrate an approach to generating reconfigurable radar waveforms based on an optically injected semiconductor laser. In the proposed system, the semiconductor laser is operated at period-one oscillation state, in which an optical output signal containing a microwave modulation on the intensity is generated. After photo detection, a frequency-tunable microwave signal is obtained with its instantaneous frequency determined by the optical injection strength and/or the detuning frequency between the master and slave lasers. Since the dynamical behavior of a semiconductor laser evolves at a subnanosecond time scale, by properly designing a control signal to manipulate the optical injection strength, reconfigurable microwave waveforms with desired parameters can be generated for radar and other applications. In particular, the generation of continuous-wave or pulsed, linearly chirped, and frequency-hopping microwave waveforms with reconfigurable parameters are experimentally demonstrated. In addition, a high-resolution distance measurement experiment is performed to verify the feasibility of applying the proposed microwave waveform generator to radar applications.

Reconfigurable Radar Waveform Generation Based on an Optically Injected Semiconductor Laser

To distribute microwaves over fibers, optical single-sideband (SSB) modulation signals are preferred to optical double-sideband (DSB) modulation signals. This study investigates an optically injected semiconductor laser at period-one nonlinear dynamics for optical DSB-to-SSB conversion. For the operating microwave frequencies up to 40 GHz investigated in this study, the proposed system regenerates or even enhances the microwave features of an optical DSB input while converting its optical feature into SSB with an intensity difference of at least 20 dB. The bit-error ratio at 622 Mb/s is down to 10(-9) with a sensitivity improvement of up to 3 dB. The proposed system can be self-adapted to certain changes in the operating microwave frequency and can operate stably under certain fluctuations in the input optical power and frequency.

Optical double-sideband modulation to single-sideband modulation conversion using period-one nonlinear dynamics of semiconductor lasers for radio-over-fiber links.

When a semiconductor laser is subject to an incoming optical carrier, equivalently an external optical injection, it
can enter nonlinear period-one dynamics through Hopf bifurcation due to the radical modification in field-carrier
coupling of the injected laser which results from the dynamical competition between injection-imposed laser oscillation
and injection-shifted cavity resonance. Equally-separated spectral components appear, of which intensity
and frequency depend strongly on the injection level and frequency. This suggests that a dynamical amplitude
or frequency variation of the incoming optical signal, such as amplitude-shift keying (ASK) or frequency-shift
keying (FSK), respectively, would lead to corresponding dynamical variation in amplitude and frequency of each
spectral component. Therefore, by properly selecting the optical frequency of the output optical carrier and
by minimizing the residual ASK and FSK modulation, both ASK-to-FSK and FSK-to-ASK conversions can be
achieved, where bit-error ratio down to 10 -12 is achieved with a slight power penalty. Only a typical semiconductor
laser is necessary as the key conversion unit. In addition, frequency shifts of the optical carrier can also
be achieved, which allows a simultaneous frequency conversion of the optical carrier if required.

http://ir.lib.ncku.edu.tw/retrieve/123799/Conversion+between+Optical+ASK+and+Optical+FSK+Using+Nonlinear+Dynamics+of+Semiconductor+Lasers_Presentation.pdf

Cheng Hao Chu

Papers

Optical double-sideband modulation to single-sideband modulation conversion using period-one nonlinear dynamics of semiconductor lasers for radio-over-fiber links.

Conversion between Optical ASK and Optical FSK Using Nonlinear Dynamics of Semiconductor Lasers

Rare-earth metal complexes supported by indolyl-based NCN-pincer ligand and their efficient catalysis for isoprene polymerization