A three-dimensional structure device that realizes electromagnetic-induced transparency (EIT) in the terahertz band is designed. We use metamaterials to simulate electromagnetic-induced transparency phenomena, through the design of effective metamaterial unit structures, acquire high transmittance while achieving strong dispersion, reducing the absorption of light waves by the medium in the slow light process. EIT’s frequency response is expressed as a narrowband transparent window formed in a large block peak. There are two coupling methods for metamaterials to achieve EIT: bright-bright mode coupling and bright-dark mode coupling. Obviously, the structures in the bright-mode coupled metamaterial unit can be directly excited by incident waves to form a resonant mode, that is, there are at least two radiating mode resonators, which are generally two-dimensional planar structures such as double strips, double rings, etc. This work breaks through the traditional planar patch structure, connects the two resonant rings with cylinders, and innovatively constructs a three-dimensional metamaterial unit. We successfully achieve EIT in the range of 1.06THz to 1.41THz, at a resonance frequency of 1.26THz, the two narrow-band resonance peaks of EIT are located at 1.22THz and 1.30 THz. Realizing EIT through terahertz metamaterials, thereby realizing slow light effect, have paved the way for the design of slow-light devices to meet the future demand for ultra-fast optical signal processing and promote the development of next-generation communication technologies.
A nested resonant ring structure composed of double split square ring based on frequency selective surface (FSS) is proposed to realize ultra-wide bandstop filter. To begin with, the structure is supposed by a single layer, adding the number of resonant rings and metal-dielectric layers to adjust frequency points and bandwidth. Through numerical simulation, we found that the location of the frequency points depended on horizontal nested rings and the transmission coefficient improved by multiply layers. In order to enhance the flatness of stopband, the depth and size of slots are calculated, showing 1.72THz stop-band from 1.27THz to 2.99THz. The result demonstrates that the range of bandwidth achieve 1.5THz with transmission depth up to 20dB, and flat bandstop as well as out-band rejection are well-performed compared with traditional slot structure.
Super-continuum Generation is demonstrated in air-holes silica photonic crystal fiber using soliton pulse. Fiber nonlinearity is investigated according to ratio between d and Λ. Third-order dispersion is investigated on suppression of soliton splitting.
We describe the nonlinear optical response of low-loss Si0.6Ge0.4/Si waveguides in the mid-IR between 3.3 μm and 4 μm using femtosecond long pulses. Furthermore, we estimate the three-photon and four-photon absorption coefficients together with the nonlinear refractive index of Si0.6Ge0.4/Si waveguides, which are found to be comparable to previous work on the same material but with different waveguide length and geometries, and with longer optical pulses. Therefore, this work corroborates the previous measurements and thus provides some guidelines for future nonlinear device work. Using the estimated coefficients, the nonlinear FOM of Si0.6Ge0.4/Si waveguides in the mid-infrared(mid-IR) is evaluated. An optimum FOM is observed around 4 μm due to the decrease of the three-photon absorption coefficient, together with a small four-photon absorption coefficient. We find that this optimum of the FOM also depends on the coupled peak intensity since the three and four-photon absorption scales differently with this parameter. Finally, we compare the impact of free carrier absorption at mid-infrared wavelengths versus near-infrared (near-IR) wavelengths for these femtosecond long pulses, and highlights the need to accurately account for free carrier effects even when using ultrashort optical pulses in the mid-IR. This work provides useful groundwork for the design of photonic devices such as supercontinuum sources based on this material platform.
As an important modern measurement equipment of the electromagnetic field, electric field probe can measure the
industrial, scientific and medical aspects of the leakage field. In the Electro Magnetic Compatibility (EMC) experiment, it can also check the high-frequency-sensitive parts of the devices and the parasitic radiations due to the mechanical movement. Especially in the field of Electromagnetic Compatibility, electric field probe is one of the most important test equipment. This paper introduces a type of optical electric field probe. In the system, a kind of antenna, which could provide a response nearly isotropic for all polarizations of the incident field, is used for receiving the signal of the electric field. The high-frequency signal received by the antenna then is detected by Schottky barrier diode detector. This low-frequency or Direct Current (DC) signal can be modulated to the band of light by the Electro-Absorption-Distributed Feed Back (EA-DFB) modulator, thus the probe can provide a wild band responds. Through the optical fiber, the optical signal is sent to the photoelectric detector. Based on the optical power value, the field intensity can be calculated. In this system, compared with traditional transmission line, optical fiber can minimize the electromagnetic interference and transmission-line attenuation. In addition to this, the system also has high test sensitivity and wide measurement bandwidth. Furthermore, the whole system has a simple structure and low manufacturing cost.
When we want to analyze the characteristics of doping fiber laser, we must establish mathematical model and use numerical solving method then obtain the relations among the various parameters of the doping fiber laser. In this paper, we select the erbium-doping fiber laser (EDFL) which pump wavelength lies to 980 nm as a typical example and analyze the EDFL characteristics. When the numerical model of the EDFL is solved, sometimes there is a trouble which is the solution of the rate equation or propagation equation having not the convergence value. For this reason, a simple iteration method is provided to solve this problem. This method is simple and feasible, and it can decrease the calculation time largely. The conclusion of the theory analysis is more close to the experiment result.
Using broadband dispersion compensation CFBGs, over 500km-40Gbps NRZ transmission
system on G.652 fiber will be demonstrated without electric regenerator, FEC and Raman amplifier.
The power penalty is about 2dB @ BER =10-10.The CFBGs have better performance: 3dB band is
about 1.2nm, group delay ripple is less than 25ps near center wavelength, power ripple is less than 2dB,
and DGD is less than 1ps. In order to stabilize the DC bias of the LiNbO3 MZ modulator, a
semiconductor cooler is applied to control the temperature. The effect is perfect.
Chirped fiber Bragg gratings are supposed to be cascaded for multi-channel dispersion compensation in DWDM
systems. The interaction between them restricts their employment. Gaussian and Super Gaussian apodization are used to
reduce the out-of-band reflection so as to suppress the interaction of the cascaded gratings. The increase of the channel
spacing can also diminish the interaction.
We fabricated linearly chirped fiber gratings by using uniform phase mask instead of chirped mask. The chirp of the grating is realized by precisely setting the distance between the fiber and the phase mask at every point of the fiber. In experiments we derived linearly chirped fiber grating which has dispersion -1102ps/nm, time delay ripple is 17ps. And also the asymmetry high order apodization method is used successfully to reduce the time delay ripple. The experiment results consistent with the simulation results. We can fabricate gratings with different chirp extent use one uniform phase mask conveniently by only changing the curve function of the fiber.
System performance degradation caused by group delay ripples of chirped fiber Bragg grating dispersion compensators is analyzed in detail with considerations for the ripple period, amplitude and phase offset. And the induced different kinds of signal distortions are also shown and explained.
The dispersion of 8×10Gb/s wavelength division multiplex (WDM) system has been compensated by the cascaded chirped fiber Bragg gratings(CFBGs), with ITU-T standard wavelengths and wavelength grid. The ASE of the EDFA could be reduced, the OSNR of the transmitted signal could be increased and the fluctuation of the EDFA gain could be controlled in the certain scope by the dispersion compensated CFBGs' WDM system. Impact of cascaded CFBGs' delay ripple on dispersion compensation has been analyzed. Experiment of error-free 8×10Gb/s 2015km transmission without forward error correction (FEC) and electronic repeaters were demonstrated. In the transmission, simplex CFBGs compensators were used and no other form of dispersion compensators were adopted. The experiment result showed that the consistency of the dispersion compensating in each channel is perfect over 2015km optical fiber transmission. The experiment result does agree with the theoretic analysis.
KEYWORDS: Fiber Bragg gratings, Semiconductor lasers, Control systems, Wavelength tuning, Voltage controlled current source, Fiber lasers, Light emitting diodes, LED displays, Power supplies, Lithium
In this paper,we introduce a novel tunable external-cavity semiconductor laser that simultaneously achieves rapid tuning rate and tuning precision by mechanical control. A stepping motor is applied in the tuning system. By control of the angular displacement of stepping motor, we can modify the centre wavelength of FBG.
The necessity of packaging and the basic principle of temperature compensation package for fiber gratings are expatiated. A method of packaging fiber gratings with the negative temperature coefficient material is introduced, and the temperature characteristic and long-term stability of packaged fiber gratings are measured. This packaging keeps the compact structure and doesn't influence the intrinsic characteristic of fiber gratings. In addition, its temperature coefficient is reduced to 0.0005nm/°C, and this result reaches applicable request. The more important is this packaging can keep good long-term stability. After half a year, the characteristic, reflecting wavelength and temperature coefficient of the packaged fiber gratings have little changed, and this result realizes the high stability packaging for fiber gratings.
In this paper, we present the design of a new type of high speed electro-optic (EO) modulator based on long period fiber grating (LPG). The outer layer of the LPG is fabricated by material with high EO coefficient, and a special material with ultra-negative temperature coefficient is used for the temperature compensation. This
modulator can work steadily with low power microwave driver, its speed is very high and its cost is low. To our knowledge, this is the first time for a modulator designed with such a simple and effective structure.
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