Secure and high-speed optical communications are of primary focus in information transmission. Although it is widely accepted that chaotic secure communication can provide superior physical layer security, it is challenging to meet the demand for high-speed increasing communication rate. We theoretically propose and experimentally demonstrate a conceptual paradigm for orbital angular momentum (OAM) configured chaotic laser (OAM-CCL) that allows access to high-security and massive-capacity optical communications. Combining 11 OAM modes and an all-optical feedback chaotic laser, we are able to theoretically empower a well-defined optical communication system with a total transmission capacity of 100 Gb/s and a bit error rate below the forward error correction threshold 3.8×10−3. Furthermore, the OAM-CCL-based communication system is robust to 3D misalignment by resorting to appropriate mode spacing and beam waist. Finally, the conceptual paradigm of the OAM-CCL-based communication system is verified. In contrast to existing systems (traditional free-space optical communication or chaotic optical communication), the OAM-CCL-based communication system has three-in-one characteristics of high security, massive capacity, and robustness. The findings demonstrate that this will promote the applicable settings of chaotic laser and provide an alternative promising route to guide high-security and massive-capacity optical communications.
Optical chaos generated by perturbing semiconductor lasers has been viewed, over recent decades, as an excellent entropy source for fast physical random bit generation (RBG) owing to its high bandwidth and large random fluctuations. However, most optical-chaos-based random bit generators perform their quantization process in the electrical domain using electrical analog-to-digital converters, so their real-time rates in a single channel are severely limited at the level of Gb/s due to the electronic bottleneck. Here, we propose and experimentally demonstrate an all-optical method for RBG where chaotic pulses are quantized into a physical random bit stream in the all-optical domain by means of a length of highly nonlinear fiber. In our proof-of-concept experiment, a 10-Gb/s random bit stream is successfully generated on-line using our method. Note that the single-channel real-time rate is limited only by the chaos bandwidth. Considering that the Kerr nonlinearity of silica fiber with an ultrafast response of few femtoseconds is exploited for composing the key part of quantizing laser chaos, this scheme thus may operate potentially at much higher real-time rates than 100 Gb/s provided that a chaotic entropy source of sufficient bandwidth is available.
Miniaturization and high accuracy are the future directions of the solar-blind ultraviolet imaging system. Based on the principle of quantum dot photoluminescence and one-dimensional photonic crystal, we design an ultraviolet–visible spectral converter for an ultraviolet imaging system. In addition to the advantages of small size, high precision, and low-voltage power requirement, our design avoids the use of image intensifiers and light-cone couples. We propose three stacks of photonic crystals structures, which provide band-pass in the solar-blind range and a wide stopband in the visible range. This structure has a local effect on the excitation light of the quantum dots and can effectively enhance the brightness. The spectral converter utilizes the light-to-light conversion, which breaks away from the photoelectric conversion mode of the past and puts forward ideas for the future development.
A high-speed physical random number generator based on a chaotic laser was proposed and experimentally demonstrated.
The broadband chaotic laser generated by an external cavity laser diode was employed as the physical entropy source.
The chaotic signal was sampled and converted by an 1-bit analog-to-digital converter to a binary sequence with the rate
of up to 1 Gb/s. To overcome the periodicity in random sequence due to the photo round trip time in the external cavity,
the exclusive-or (XOR) operation on corresponding random bits in samples of the chaotic signal and its time-delay signal
from a same single chaotic laser was executed. The scheme was simpler than the present random number generator in
which random number sequences were obtained real-timely by doing XOR operation on the binary sequences from two
chaotic semiconductor lasers. In addition, the proper selection of delay length was analyzed. A large number experiments
show that when the corresponding delay time of autocorrelation trace with correlation coefficient of less than 0.007 is
considered as the delay time between the chaotic signal and its time-delay signal, streams of random numbers can be
generated with verified randomness.
We numerically study the message filtering characteristics of semiconductor laser as a receiver in optical chaos
communication. The transmitter is an external-cavity laser subjecting to optical feedback that operates in a chaotic
regime. The receiver can operate at a chaotic regime either similar to the transmitter (closed-loop scheme) or without
optical feedback (open-loop scheme). We study the effects of frequency detuning and parameters mismatch between
transmitter and receiver on quality of the recovered signal in both open and closed loop schemes. We find that the
closed-loop scheme has, in general, a higher quality of recovered signal compared with the open-loop. We also study the
effects of message frequency on quality of the recovered signal in the two types of schemes. The results demonstrate that
the filtering effect of semiconductor laser receiver is larger for low frequency message and decreases as the message
frequency approaches the relaxation oscillation frequency of semiconductor laser. The SNR of the recovered signal of the
open-loop scheme remains higher than that of the closed-loop scheme when the message frequency is in high frequency
region.
A novel chaotic lidar with high resolution is proposed and studied theoretically. In chaotic lidar system, the
chaotic laser emitted from chaotic laser diode is split into two beams: the probe and the reference light. The
ranging is achieved by correlating the reference waveform with the delayed probe waveform backscattered from
the target. In chaotic lidar systems presented previously, the chaotic signal source is laser diode with optical
feedback or with optical injection by another one. The ranging resolution is limited by the bandwidth of chaotic
laser which determined by the configuration of chaotic signal source. We proposed a novel chaotic lidar which
ranging resolution is enhanced significantly by external optical injected chaotic laser diode. With the
bandwidth-enhanced chaotic laser, the range resolution of the chaotic lidar system with optical injection is
roughly two times compared with that of without optical injection. The resolution increases with injection
strength increasing in a certain frequency detuning range.
We experimentally investigated the wavelength matching between the probe light and injection-locked modes of FP-LD
(Fabry-Perot laser diode) for wavelength conversion configuration. Wavelength conversion from 1552.9nm to 1548.5nm
was obtained experimentally based on cross-gain modulation with the 10GHz repetition rate optical pulse train in a
FP-LD. Our results indicate that there always exists a selected longitudinal mode of the probe light in the FP-LD to
maximize the extinction ratio of the conversion signal. Moreover, there also exists an optimum injection signal pulse
power to improve the conversion signal further under the same matching mode of probe light wavelength with the
constant input power, and the constant detuning between the probe light and signal pulse wavelengths and the locked
modes of FP-LD with a certain bias current range.
We propose and experimentally demonstrate a novel technique that uses a single Fabry-Perot laser diode (FP-LD) to
perform simultaneous all-optical clock division and wavelength conversion. Utilizing the period-two oscillations
characteristics in an optically injected semiconductor laser and the cross-gain modulation effect of the injection locked
semiconductor laser, we achieve the simultaneous all optical clock division and wavelength conversion in a single FP-LD.
Clock frequency division of 12.8 GHz to 6.4 GHz with simultaneous wavelength conversion from 1550.24 nm to
1545.91 nm is obtained. The experimental results indicate there is a certain injection signal power to obtain stable clock
frequency division in an optimum wavelength detuning. It was empirically found that the best clock division and
wavelength conversion occurred when the injected signal power was approximately 2~2.5 times as the injected probe
light power, and the range of optimum wavelength detuning was about from -0.01 nm to 0.06 nm. Moreover, the FP-LD's
bias current also influence the clock frequency divisions, we demonstrate that the most effective conversion can be
obtain when bias current is located in the range of 1.6Ith~2.3Ith. The experimental investigations further show that there
is an optimum matching mode between the FP-LD and the probe light for obtaining the largest extinction ratio in
wavelength conversion.
We investigate the feasibility of multi-target ranging using broad-band chaotic laser numerically and experimentally.
Chaotic laser generated by semiconductor laser with optical feedback can be utilized as chaotic signal source for target
ranging and detection. Chaotic laser is split into reference beam and signal beam, the ranging is realized by correlating
the reference waveform with the time-delayed signal waveform reflected back from the target. Simulation results
indicate that the signal beam can be divided into several portions, by correlating the reference waveform with several
time-delayed signal waveforms backscattered from multi-targets, the range measurements of multi-targets are achieved
in real time. We design a proof-of-concept experiment to confirm the simulation results and realize the range
measurements of two targets simultaneously.
The effects of dispersion on optical fiber chaotic secure communication are numerically investigated. A theoretical model
for fiber chaotic secure communication system which is consisted of a pair of synchronized chaotic lasers and an optical
fiber channel is presented. Chaotic secure communication for a 1-GHz sinusoidal message after propagating several
hundred kilometers is numerically analyzed. By numerically studying the effects of dispersion on the system's
performance, we show that the synchronization progressively degrades and the signal-to-noise ratio of the recovered
message decreases as the fiber length increases. We also find that the signal-to-noise ratio descends when the modulation
frequency of the encoding message increases. We propose a dispersion management scheme to compensate the
dispersion in fiber chaotic secure communication system. The proposed dispersion management map is consisted of a
segment of 5-km dispersion-compensating fiber with value of dispersion β2=-49ps2/km, a segment of 245-km nonzero dispersion-shifted fiber with value of dispersion β2=1ps2/km and optical amplifiers. The results show that the
signal-to-noise ratio of the extracted 1-GHz sinusoidal message increases from 2.75dB to 14.02dB when the length of
fiber is set to 500km.
Extensive experiment studies are performed in the evolved process from low-frequency fluctuations to
chaos. The low-frequency fluctuations and high dimension chaos with 12.2 correlation dimension are
generated experimentally by a DFB semiconductor laser with optical feedback. Meanwhile, the effects
of pumping current and feedback strength on the average duration and the peak-peak value of
low-frequency fluctuations are experimentally analyzed. Our results show that there exists an
obvious critical point for the bias current of the semiconductor laser. When the bias current Ib is set
below 1.03Ith, the peak-peak value of the low-frequency fluctuations is increasing at first and then
decreasing with the feedback strength decreasing, while its average duration is decreasing but chaos
don't appear in the whole performance. However, when the bias current Ib is set above 1.03Ith, the output of the laser can evolutes from low-frequency fluctuations chaos with the feedback strength
decrease. Moreover the peak-peak value of the low-frequency fluctuation is increasing continually and
its average periodic time is decreasing with the decrease of the feedback strength.
We experimentally study the period doubling phenomenon of gain-switched multiple quantum well Fabry-Perot laser
diodes with/without external optical injection. The relations between resonance frequency and modulation frequency are
analyzed detailedly when period doubling occurs. The obtained research results indicate that external optical injection
may be an effective technique to suppress or enhance period doubling of a gain switched laser diode with injection
optical power. Experiments show that the period doubling would appear in a broader frequency range with external
optical injection, and indicate that period doubling occurs over a wide range of modulation frequency in laser diode as
the injection power increases. Moreover, we have studied in detail that period doubling easily occurs when bias current is
located between 1.1Ith and 1.3Ith, and modulation current is set between 0.5Idc and 2.5Idc.
Temporal coherence property of supercontinuum (SC) generated in a polarization-maintaining photonic crystal fiber
(PM-PCF) pumped by Ti:sapphire fs laser was experimentally studied by using a modified Michelson interferometer.
The coherence length of supercontinuum light was measured to characterize the temporal coherence property. The
coherence lengths of supercontinuum and pump laser were measured to be 6.5 μm and 59.14 μm, respectively. The
shortened coherence length of supercontinuum output from the PM-PCF was due to the broadened spectrum. Moreover,
the interferogram evolution versus the supercontinuum spectra was also investigated. It was indicated that the flatter the
supercontinuum was, the better the interferogram was.
Range finding with continuous-wave chaotic laser train generated from laser diode with optical feedback is investigated
theoretically. Chaotic laser is split into probe beam flighting to target and reference beam, and then, the distance of target
can be calculated from the flight time obtained by correlating the time-delayed probe beam with the reference one.
Effects of noise and waveform error on correlation performances for different chaotic states are investigated to study the
system tolerance of environmental noise. Simultaneously, the effects of chaotic state characterized by the largest
Lyapunov exponent and correlation dimension on correlation performances are demonstrated theoretically to select
satisfying chaotic laser used as probe light. Simulated results indicate that ideal chaotic laser train should have high
dimension and have smooth spectrum with broad bandwidth for ranging with high resolution. For the simulated system,
ranging resolution within 1.5cm range independent of target location can be achieved using the chaotic lasers generated
in middle of the chaos-generated regime of feedback level.
The multi-pulse operation of the Yb3+-doped fiber mode-locked laser with a polarization sensitive isolator and two
polarization controllers is reported. Dual- and triple-pulse of the Yb3+-doped fiber mode-locked laser in the normal
dispersion are achieved as the pumping power is increased. The fiber laser can achieve different multi-pulse outputs by
adjusting the polarization controllers or increasing the pump power. The results show that over-driving of the fast
artificial saturable absorber induced the generation of the multi-pulse.
We report a high-power diode-double-end-pumped Q-switched Nd:YVO4 red laser through intracavity
frequency-doubling with a type-I critical phase-matched LBO crystal. At the repetition frequency of 26 kHz, the
maximum quasi-continuous-wave (QCW) output power at 671 nm was measured to be 9.2 W at the incident pump power
of 62.4 W with the corresponding optical conversion efficiency of 14.7%; the pulse width of about 106 ns; the pulse
energy of 353.8μJ; the peak power of 3.34 kW, respectively. The perfect performance indicated that the
double-end-pumped technique could effectively diminish the thermal lens effect, extend the range of the stable resonator
region and achieve a high optical conversion efficiency to obtain a high output power.
We propose a technique for measuring the pulse width jitter of high repetition rate optical pulse trains. The technique is
based on spectral measurement of three different harmonics of the detected pulse train. The simulation results show that
the pulse width jitter would contribute a great amount of noise power to the total noise power when the product of pulse
width and angular frequency is larger than 1. We apply the proposed technique to characterize noise of a Fabry-Perot
Laser Diode. The pulse width jitter is estimated to be 2.3ps. Compared with the calculated 1.8% amplitude noise and
5.1ps timing jitter, the pulse width jitter is found not to be negligible.
The stark energy level split of (2F7/2, 2F5/2) of ytterbium ion in glasses are derived from room temperature absorption and emission spectra. It is shown that the stark energy split increases as the base varies from phosphate to tellurite glasses, and the first and second stark energy levels lay in range of 150 - 250 cm-1, 350 - 450 cm-1 over ground, the first over ground has smaller energy and thus larger Boltzmann heat effect and is difficult in lasing at this terminal level. The second level is 350 cm-1 over ground and can be considered as the terminal level whose lasing wavelength varies from 1000 nm to 1020 nm. The partition function ratio of the upper and lower levels of ytterbium ion is calculated and more accurate reciprocity equation by which emission cross section is determined from absorption spectra is obtained from stark energy levels.
The paper presents both numerical and experimental investigations on the behavior of 1.55 micrometers distributed feedback (DFB) laser diode (LD) driven by strong RF power. The picosecond dynamic response of gain-switched DFB LD can be analyzed by appropriate rate equations. The results of experimental research are generally in good agreement with the numerical calculations and the minimum pulse width is about 17 ps under 1 GHz, 20 dBm RF modulation.
This paper reviews recent progress in ultrafast optoelectronic measurement techniques utilizing ultrafast optical pulses, with particular emphasis on the wide range of novel applications of ultrafast optoelectronics for generation and measurement of ultrafast electrical signal. Such specific high-speed optoelectronic measurement techniques as photoconductive sampling, electro-optic sampling, picosecond photoemissive sampling etc. are described.
This paper describes the method of measurement ultrafast electrical pulses with a gain switch semiconductor laser and a LiTaO3 probe tip. The results are presented. The results are comparable to the digital sampling oscilloscope with 20 GHZ bandwidth. The minimum detectable voltage is 1.54 mv, the temporal resolution is 25 ps. The voltage sensitivity of 5.4 uv/(root)Hz. This system has compactness stability and broad application prospects.
This paper describes the performances of Cr:GaAs photoconductive switch that is conducted with a gain switch semiconductor laser. This photoconductive switch generates stable and reliable electrical pulses. This system has compactness, high efficiency, and bright application prospects.
Electro-Optic (EO) sampling is a potentially powerful technique to characterize very high speed electrical wave forms in the time domain and to examine wave forms internal to integrated circuits, where external connections cannot be made. It is more attractive when the semiconductor laser is used as a laser source because of its compactness, inexpensiveness and arbitrary repetition rate for gain-switched operation. However such laser systems have limitations for practical use, i.e. the poor voltage sensitivity, which is caused by laser power. Noise suppression is the most important point in EO sampling system using a laser diode.
The soft x-ray time-resolved spectroscopy is composed of a soft x-ray spectroscopic head and a soft x-ray streak camera. Because the soft x-ray spectroscopic head possesses a spectral resolution of 0.1 angstrom, the performances of the whole system mainly depend on the characteristics of the soft x-ray streak camera. In this paper, therefore, the design features and characterization of the soft x-ray streak camera are mainly described. In order to record the spectrum ranging from 30 angstroms to 230 angstroms on a limited photocathode slit length, the whole camera including the photocathode can be shifted along the spectrum without dismantling the camera from the soft x-ray generating chamber. The soft x-ray streak image tube possesses a specially designed vacuum-tight valve, which could be closed or opened in the vacuum chamber operated by a step motor, to prevent the photocathode sensitive to soft x- ray and internal intensified microchannel plate from pollution by water vapor or dust in the atmosphere. In order to test its dynamic performances, a soft x-ray diode was developed. The dynamic testing shows that the temporal resolution of this camera is 5 ps, which is limited by our soft x-ray source, dynamic spatial resolution is 20 lp/mm which implies the spectral resolution of 0.25 angstroms. Because of using CsI or KI photocathode deposited on a 1000 angstrom thick parylence film, the spectral responses range is approximately 0.05 to 10 KeV.
On the basis of theoretical and experimental study a new picosecond and nanosecond framing camera has been developed. The details associated with the design features of a framing image tube and its controlling circuitry are outlined and the experimental results obtained with this camera are shown in this paper. Recently experimental results have shown that this camera can provide 25 lp/mm, 17 lp/mm and 12 lp/mm with the exposure time (FWHM) of 5 ns, 250 ps, and 77 ps for each of 3 framing images, respectively. The pulse circuit for 6 frame images has been developed and the camera equipped with this circuit is being further tested. It is expected to obtain the same performances as stated above. This camera also can be used as a picosecond streak camera.
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