Nonlinear dynamics of semiconductor lasers under individually optoelectronic feedback (OEF) and optical feedback (OF) is attracted much attention in these two decades. In this paper, nonlinear dynamics of single-mode distributed feedback (DFB) semiconductor laser subject to dual feedback composed of both optical feedback and optoelectronic feedback are investigated experimentally. The dynamical states shown in individual system are observed, quasi-periodic (QP) oscillation and pulsation, regular pulsation (RP), chaotic oscillation (CO) and pulsation (CP). To explore the microwave signals generated by quasi-periodic states in the dual feedback system, we also measure the suppression ratio of unwanted frequency side peak and RF spectral linewidth in frequency domain. On the other hand, the corresponding time series are also considered and discussed by calculating the amplitude variation of regular pulses and pulse widths. Moreover, a side peak suppression ratio of about 56 dB is achieved when applying the hybrid feedback scheme. The amplitude variation ratio of regular pulses is optimized to 0.008 and the pulse-width is approximately 0.12 ns which is smaller than those coefficient when applying individual OF and OEF system. The improved percentage of averaged amplitude variation in regular pulses of around 60 percent is also obtained. Furthermore, the complexity of chaotic waveforms generated by hybrid feedback system are discussed and calculated.
Optical feedback (OF) system plays an important role in nonlinear dynamics because of low cost, less complexity, and well-maintained. Rich nonlinear characteristics of semiconductor laser under optical feedback are investigated, including period-one oscillation (P1), period-two oscillation (P2), quasi-period (QP), and chaotic oscillation (CO) states. However, the stability of the states generated is the most important issue to be solved and improved. In this paper, the polarization rotated feedback is purposed to be an alternative approach that possesses the characteristic of improving the signal quality compared to optical feedback. We focused on the generation of P1 states and on the performance of the noise reduction of the P1 states by utilizing incoherent OF. The polarization rotated feedback system is built up by OF systems under the orthogonally polarized feedback. The optical components that we used in the scheme for generating of the polarization rotated feedback are Faraday rotator (FR) and polarizer to provide the incoherent optical feedback, rich dynamics is obtained compared to those observed in traditional feedback system. Moreover, noise reduction of the P1 states caused by the delay loop frequencies in feedback scheme is realized by applying the orthogonally polarized feedback to the already-generated P1 states by the traditional scheme. To explore the quality of the generated P1 states, the measurements of the amplitude of side peaks, the spectral linewidths, and amplitude variation of P1 states under traditional OF and polarization rotated feedback in both frequency and time domain observed by electrical power spectrum and oscilloscopes are examined and analyzed, respectively. As a result, effective noise reduction in P1 states is achieved while applying a polarization rotated feedback.
Nonlinear dynamics of semiconductor lasers under individually optoelectronic feedback (OEF) and optical feedback (OF) is attracted much attention in these two decades. However, according to my knowledge, there is no related research results in dual-feedback system composed of optical and optoelectronic feedbacks. In this paper, the nonlinear dynamics of the dual-feedback system is studied and applications in generation of broadband chaos and stabilized pulses based on quasi-periodic (QP) states are achieved. Generally, QP states do not have contributed application which limited the research attention in recent years. Here we focused on the QP state and turned it to be the useful chaos and pulses. The QP is firstly generated by pure OEF system and then applying an additional OF system to obtain the chaos and pulses by tuning the controllable conditions of feedback strength and delay time. To explore the rich dynamics of the dual feedback system, mappings of each dynamical states are calculated, including regular pulsing, periodic oscillation, and chaotic oscillation and pulsing states. Furthermore, chaos bandwidth and amplitude variation of regular pulses are examined to quantify the signals generated. A 2-fold improvement of chaotic oscillation frequency is observed in dual feedback system compared to the chaos generated by pure OEF system. Broadband bandwidth of chaotic oscillation is obtained in dual-feedback system when using a relaxation oscillation frequency of 2.5 GHz laser in the free-running condition. Moreover, the improved percentage of averaged amplitude variation in regular pulses is around 81.6% compared to those generated by pure OEF scheme.
Optoelectronic feedback (OEF) system plays an important role in nonlinear dynamics because of low-cost and easy to generate dynamical states, including regular pulsing (RP), quasi-pulsing (QP), and chaotic pulsing (CP). However, the non-ignored noise naturally generated by delay-loop frequency in the dynamical states is the most important problem to be solved. In this paper, we focused on the generation of RP states and also on the improvement of the noise reduction in the RP states by utilizing the double-delay system. The double-delay system is built up by optical feedback (OF) and OEF systems. When adjusting four controllable parameters of OEF delay time, OEF feedback strength, OF delay time, and OF feedback strength, more complex dynamics are obtained compared to those observed in individual OF and OEF system. Moreover, noise reduction of the RP states caused by the mixing of delay loop frequencies in double-delay scheme is realized by applying an additional OF delay loop to the already-generated RP states by OEF scheme. To explore the quality of the generated RP states, the measurements of amplitude variation in time series and the single-side band phase noise in frequency domain are examined. As a result, effective noise reduction in RP states is achieved while applying a weak OF feedback strength and a short OF delay time. Furthermore, no common factor in these two delays is necessary to observe stabilized RPs and the amplitude variation down to 0 which is equal to 100 percentage noise reduction is achieved while fine-tuning the controllable parameters carefully.
Microwave frequency combs utilizing hybrid optical injections schemes by varying the operational parameters, injection strength, repetition frequency, and detuning frequency are demonstrated and characterized. The dynamical hybrid optical injections are realized by both optical pulse injection and optical cw injection to the slave laser simultaneously under the condition of zero detuning frequency between two injecting source lasers. For pure pulse injection case, the amplitude variation of ±27.3 dB in a 30 GHz range is obtained. By further applying the injection strength of the cw injection to the pulses injected semiconductor laser, the amplitude variation of ±3.3 dB in a 30 GHz range in microwave frequency combs are observed when operating the cw injection system in a stable locking state. In order to examine the microwave frequency comb precisely, each operational parameters of the hybrid optical injections schemes are analyzed. The amplitude variation of microwave frequency combs is also strongly influenced by operating the cw injection system in different states. Comparing to the cw injection system operated in period-one states, the amplitude variation is reduced when operated in the stable locking states. Moreover, the bandwidth broadening in microwave frequency comb is expected when the cw injection system operating in a stable locking state. In this paper, strongly improve the amplitude variation of the microwave frequency combs generated utilizing hybrid injections scheme compared to single injection case are obtained and compared.
We demonstrate and characterize the microwave frequency combs utilizing both the dynamical single-beam and dual-beam injection schemes numerically. The dynamical single-beam injection scheme is realized by optical pulse injection to the slave laser (SL) from a pulsed laser. When the SL subjected to only the optical pulse injection from the pulsed laser, microwave frequency combs are generated by the nonlinear dynamics of the frequency-locked states with different locking ratios. The amplitude variation of ±18 dB in a 30 GHz range is obtained by precisely varying the operational parameters, injection strength, repetition frequency, and detuning frequency. In this paper, we propose the dynamical dual-beam injection scheme to improve the amplitude variation of the microwave frequency comb generated. The dynamical dual-beam injection is realized by both optical pulse injection and optical cw injection to the semiconducor laser. By utilizing the hybrid scheme consists of double optical injections, the advantages of each individual dynamical system are added and enhanced. As the result, the amplitude variation of the microwave frequency comb of ±3.0 dB in a 30 GHz range is achieved when operating the cw and pulse injection to the slave laser in stable locking and frequency locked states, respectively. In addition, the bandwidth enhancement of over 25 GHz is also observed.
We demonstrate and characterize arbitrary channel selection utilizing both the double phase-locked and optical
injection schemes experimentally. The double phase-locked scheme is realized by both optical injection and electrical
modulation to the slave laser (SL) from a pulsed laser. The pulsed laser is generated by the semiconductor
laser under optoelectronic feedback, which outputs repetitive pulse train with the repetition frequency controlled
by the feedback delay time and feedback strength. When the SL subject to only the optical pulse injection from
the pulsed laser, a broadband microwave frequency comb with amplitude variation ±5 dB in a 20 GHz range is
generated. By further applying an electrical modulation to form a double phase-locked condition, a main channel
can be selected accordingly. The advantages of large channel suppression ratio, system stabilization, and spurious
noise reduction are obtained by using the double phase-locked technique. Moreover, by further applying an
optical cw injection from a tunable laser, we demonstrate the selection of a secondary channel. A selection range
of about 7.2 GHz is achieved by adjusting the cw injection strength. Average channel suppression between the
main and secondary channels to the undesired channels with ratios of 41.8 and 25.9 dB are obtained, respectively.
The single sideband (SSB) phase noise of -60 dBc/kHz (-90 dBc/Hz estimated) is achieved at offset frequencies
of 25 and 200 kHz for the main and secondary channels, respectively. Demonstration of communication between
the main and secondary channels is also demonstrated.
We numerically investigate high-frequency microwave signal generation utilizing a double injection locking technique.
A slave laser (SL) is strongly injected by a master laser 1 (ML1) and a master laser 2 (ML2) optically.
Stable locking states are observed when the SL is subject to optical injection by either the ML1 or the ML2
individually. By utilizing the hybrid scheme consists of double optical injections, the advantages of each individual
dynamical system are added and enhanced. Comparison of the performances of the spectral width, power
fluctuation, and frequency tunability between the signal generated in the double injection locking scheme and
the similar period-one (P1) oscillation signal generated in a conventional single injection scheme is studied. A
3-fold linewidth reduction is achieved by utilizing the double injection locking scheme benefitted by the strong
phase-locking and high coherence when operating at the stable injection locking state. Moreover, for the double
injection locking scheme, a wide continuous tuning range of more than 100 GHz is obtained by adjusting the
detuning frequency of the two master lasers. The performances of narrow linewidth, wide tuning range, and
frequency continuity show the great advantages of the high-frequency microwave signal generated by the double
injection locking technique.
Characteristics of the frequency-locked states generated by nonlinear dynamical behaviors of semiconductor
lasers under periodical optical injection are investigated experimentally. The periodic optical waveforms used
for injection, including repetitive pulses and sine oscillations, are generated from a laser (master laser) through
self optoelectronic feedback and direct current modulation, respectively. Under proper operational conditions,
namely the repetition frequency and injection strength of the injected light, microwave frequency combs are
observed at the output of the injected laser (slave laser). In generating the microwave frequency combs, the
pulse injection scheme shows the best performance compared to the sine modulation and cw optical injection
schemes. The potential applications of these microwave frequency combs in frequency division and multiplexing
are demonstrated.
The nonlinear dynamics of a semiconductor laser (slave laser) injected by optical pulses with high repetition rate
are investigated experimentally. The pulses for injection are generated from a laser (master laser) subjected to
either an optoelectronic feedback or an optical feedback. The repetition rates of the pulses are controlled by
varying the delay time and the feedback strength of the feedback loop. By injecting the repetitive optical pulses
of different intensities and repetition frequencies into another laser (slave laser), rich dynamical states including
regular pulsations, frequency beatings, and chaotic pulsations are observed. Moreover, frequency-locked states
with different winding number, the ratio of the main pulsation frequency of the slave laser and the repetition
frequency of the injected pulses, are also found. Compared to a laser subject to a sine modulated optical injection,
the linewidths of the high-order microwave components in the output spectrum of the slave laser are substantially
narrower for the laser under repetitive optical pulse injection.
We investigate the nonlinear dynamics of a pulse injected semiconductor laser that a laser is optically injected
by repetitive pulses. Rich dynamics, including both oscillation and pulsation states, are found by varying the
intensity and repetition rate of the injection pulses. The laser enters into chaotic pulsation (CP) and chaotic
oscillation (CO) states through individual period-double routes. Under proper injection, frequency-locked states
with different winding numbers, the ratio of the oscillation relaxation frequency and the repetition frequency
of the injection pulses, are observed. The winding numbers reveal a Devil's staircase structure, where a Farey
tree showing the relation between the neighboring states is presented. Moreover, the bandwidth enhancement
phenomenon of the chaotic states under repetitive pulse injection is also discussed.
A tracking system utilizing tunable liquid lens is proposed and demonstrated. Adapting the concept of EWOD
(electrowetting-on-dielectric), the curvature of a droplet on a dielectric film can be controlled by varying the applied
voltage. When utilizing the droplet as an optical lens, the focal length of this adaptive liquid lens can be adjusted as
desired. Moreover, the light that passes through it can therefore be focused to different positions in space. In this paper,
the tuning range of the curvature and focal length of the tunable liquid lens is investigated. Droplet transformation is
observed and analyzed under a CCD camera. A tracking system combining the tunable liquid lens with a laser detection
system is also proposed. With a feedback circuit that maximizing the returned signal by controlling the tunable lens, the
laser beam can keep tracked on a distant reflected target while it is moving.
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