The focusing characteristics of Fresnel zone plate (FZP) on vortex beams at 1550 nm are investigated. Employing the Fresnel diffraction integral, the diffraction characteristics on different circular structures are calculated. Many calculations and measurements of the transmission light field-phase distribution demonstrate that the focusing characteristics of the vortex beam through FZP are similar to Gaussian beam. The effect of radius-dependent phase delay on the focus position is verified. At the same time, it is proved that the topological charge has nothing to do with the major focal position and the FZP will not change the topological charge of the incident vortex beam.
Due to the epsilon near zero (ENZ) effect, indium tin oxide (ITO) can be used in optical modulators and reduce the modulator’s size dramatically. The tunability of optical properties and the CMOS compatible capability make ITO more attractive. To study the properties of ITO thin films, several works have been done. Firstly, thin ITO thin films were obtained by magnetron sputtering with different oxygen flow rates ranging from 0 to 50sccm. Secondly, EDS was carried out to investigate the elements' content. It can be found that increasing oxygen flow rate increases the percentage of oxygen atom and Sn atom of ITO thin films. Thirdly, surface profiler was used to measure the stress value of the ITO thin films. We find that the tensile stress of ITO thin films tends to transform into compressive stress when the oxygen flow rate rises, which is worth considering in the design of devices. Fourthly, spectrometer and Hall effect measurement were applied to measure the normal incidence transmittance and electrical properties of the ITO thin films. Larger oxygen flow rate leads to the normal incidence transmittance of ITO thin films becoming larger. Hall effect measurement contributes to the conclusion that the carrier concentration of ITO thin films is able to range from 1019 to 1021 cm-3, and that when the oxygen flow rate is not too large, as the environment oxygen increases, the carrier concentration decreases and the mobility increases. This research can contribute to the design of compact ITO based optical modulators so as to achieve a better performance, which can further the integration of optical modulators.
Neuromorphic engineering has a wide range of applications in the fields of machine learning, pattern recognition, adaptive control, etc. Photonics, characterized by its high speed, wide bandwidth, low power consumption and massive parallelism, is an ideal way to realize ultrafast spiking neural networks (SNNs). Synaptic plasticity is believed to be critical for learning, memory and development in neural circuits. Experimental results have shown that changes of synapse are highly dependent on the relative timing of pre- and postsynaptic spikes. Synaptic plasticity in which presynaptic spikes preceding postsynaptic spikes results in strengthening, while the opposite timing results in weakening is called antisymmetric spike-timing-dependent plasticity (STDP) learning rule. And synaptic plasticity has the opposite effect under the same conditions is called antisymmetric anti-STDP learning rule. We proposed and experimentally demonstrated an optical implementation of neural learning algorithms, which can achieve both of antisymmetric STDP and anti-STDP learning rule, based on the cross-gain modulation (XGM) within a single semiconductor optical amplifier (SOA). The weight and height of the potentitation and depression window can be controlled by adjusting the injection current of the SOA, to mimic the biological antisymmetric STDP and anti-STDP learning rule more realistically. As the injection current increases, the width of depression and potentitation window decreases and height increases, due to the decreasing of recovery time and increasing of gain under a stronger injection current. Based on the demonstrated optical STDP circuit, ultrafast learning in optical SNNs can be realized.
A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is demonstrated with a precision delay feedback loop cascaded with a terahertz optical asymmetric demultiplexer (TOAD)-based power equalizer. Its feasibility has been verified by experiments, which show a multiplication for PRBS at cycle 2^7−1 from 2.5 to 10 Gb/s. This scheme can be employed for the rate multiplication of a much longer cycle PRBS at a much higher bit rate over 40 Gb/s if the time-delay, the loss, and the dispersion of an optical delay line are all precisely managed.
The semiconductor optical amplifier (SOA) is a key device for all optical signal processing based on its nonlinearity, which depends on its group velocity dispersion (GVD). A simple scheme to measure the GVD of the SOA is proposed with some computations from the measured gain spectra based on the relationship between GVD and the optical gain from the Kramers-Kronig relation. The dispersion is relatively flat in the range of 1530 nm~1610 nm, and lightly depends on the input power and the injection current. The peak-gain wavelength and zero-dispersion wavelength red-shift with the input power increasing and blue-shift with the injection current increasing, and the zero-dispersion wavelength is greater than the peak-gain wavelength on the longer wavelength side.
The slow light is always at the cost of the signal distortion when the periodic rectangular signal propagates in
Erbium-doped fiber (EDF), which is confirmed by the implemented simulations and measurements. A new definition of
Fundamental Harmonic Fractional Delay (FHFD) is proposed based on the fundamental harmonic phase delay with the
consideration of signal distortion to evaluate the slow light effect. The influences of signal power, modulation depth and
duty ratio on slow light effect are studied, and the relationship between Fundamental Harmonic Fractional Delay (FHFD)
and Total Harmonic Distortion (THD) is given.
Briefly compare the polarization rotation speed of Mach-Zehnder interferometer, lithium crystal, LCD and
semiconductor optical amplifier (SOA), etc. Then propose a program of high-speed ternary optical multiplier based on
SOA’s nonlinear polarization rotation. Finally, the theoretical analysis and simulation research of SOA’s nonlinear
polarization rotation indicate that the ternary optical multiplier is one of the possible options to achieve high-speed
optical computing, and may be widely applied to optical computer.
An all-optical multibit correlator using the multistage cascaded quantum dots semiconductor optical amplifiers Mach-Zehnder interferometer (QD-SOA MZI) is presented with the example of an 8-bits correlator. The simulations demonstrate the correlator pulse with ultrahigh quality at the bit rate of 500 Gbps. For the ultrahigh bit-rate applications, the ultrafast dynamics of the QD-SOA are investigated with the pulse/spectra distortion, gain dynamics, phase dynamics, and the frequency chirp of the optical pulse. All-optical logical gates XOR and AND based on the QD-SOA MZI are simulated with the consideration of many nonlinear dynamics, such as the carrier injection, carrier depletion, carrier density fluctuation, carrier heating, and the spectra hole-burning in the rate equations scheme.
The amplified Spontaneous Emission (ASE) is the important noise source for EDFA, affecting the EDFA based fiber laser seriously. The theory and practice have shown that the ASE is closely related with pump methods, so the study on the ASE of EDF under the condition of the pulse pumping has important academic significations. What’s more, the mode-locked laser based on EDFA fiber ring could be pumping by the pulse to realized mode-lock, and the ASE will impact its characteristics. In this paper, the effects of pump pulse with different width and amplitude on the ASE were investigated by the theoretical and experiment methods. Beginning with the carrier density rate equation, we can get each level of the distribution of the number of particles carriers along with the change of time based on the relationship between the average number of photons of the spontaneous radiation and the number of particles carriers distribution. An approximate analytic solution of output ASE noise average is derived when pump signal is small.Building an experimental system, the results show that the output amplitude of ASE is proportional to the input width of pump pulse when the pump pulse is small. It's also shows that the output amplitude of ASE is proportional to the input amplitude of pump pulse. The new phenomena can be used for the all-optical measurement of a pulse width.
A prototype of the temperature sensor based on the nano-wire Silicon-on-Insulator (SOI) waveguides, with air cladding
or SiO2 cladding, is proposed with the principle of two mode interference (TMI) in the two mode nano-wire SOI
waveguides. The beatlength, between the two modes with same polarization in the two-mode regime, are shown with the
dependence on the waveguide parameters. The effects of the birefringence on the temperature sensor are discussed.
A high multiplexing capability and ultrahigh resolution interrogation scheme for optical fiber Bragg grating sensing
system was proposed. A scan ring laser based on semiconductor optical amplifier (SOA) and tunable Fabry-Perot
interferometer can provide 70nm bandwidth and 32 monitoring channels, and therefore the interrogator can
simultaneously detect more than 1000 fiber Bragg grating (FBG) sensors. In the interrogation scheme, a gas absorption
spectral line was used as a wavelength reference, and a comb filter was designed as a standard device that can
dynamically calibrate the wavelength of FBG sensors. Therefore, the wavelength resolution can reach to 0.5 pm.
We propose a novel photonic crystal fiber (PCF) design for single-polarization single-mode (SPSM) operation. The
proposed SPSM-PCF characteristics are investigated by using a full-vector finite element method (FEM) with perfect matched layer
(PML) boundary conditions. The proposed SPSM-PCF performs SPSM operation for a wide range of wavelength. The results show
that this is a good design methodology to realize broadband SPSM operation.
KEYWORDS: Signal to noise ratio, Optical networks, Switches, Packet switching, Control systems, Interference (communication), Fiber couplers, Networks, Signal attenuation
In this paper, a novel all optical buffer based on cascaded double-loop all optical buffer (DLOB) unites is
proposed and demonstrated experimentally with the SNR analyze. This buffer is compact, simple, and inherently stable,
the delay can be adjusted in the range of 0 to 250us. By injecting a synchronizing control pulse, the operation of reading
and writing can be realized easily and the switch time is up to 20ps. The new optical buffer can be used in optical routers to
solve the packets contention.
The semiconductor optical amplifiers (SOAs) are employed in all optical networking and all optical signal processing due to the excellent nonlinearity and high speed. The gain recovery time is the key parameter to describe the response speed of the SOA. The relationship between the gain dynamics and a few operation parameters is obtained in this article. A few simple formula and some simulations are demonstrated, from which, a few methods to improve the response speed of the SOA can be concluded as following, lengthening the active area, or lessening the cross area, increasing the injection current, increasing the probe power, operating with a CW holding beam.
KEYWORDS: Dispersion, Waveguides, All optical signal processing, Photonic crystal fibers, Birefringence, Optical signal processing, Interferometers, Control systems, Nonlinear optics, Signal processing
A squeezed elliptical hole air-silica photonic crystal fibre is reported for all optical signal processing, which
has some novel properties of high birefringence and high nonlinearity, according with tailorable dispersion at 1550nm.
The influence of the extinction ratio (ER) of the input signal on the copying optical signal
are analyzed theoretically for the first time to our knowledge and the deterioration of the ER of the
output signal result from continuous - wave (CW) is noticed. The relationship between the ER of the
output and the input signals are given quantificationally. The experiment results are agree with the
theory. The recopied optical signal using fiber ring cavity is realized in experiment by reducing CW.
An Erbium-doped optical fiber amplifier (EDFA) is employed for compensating the round - trip loss
of the fiber ring cavity and a semiconductor optical amplifier (SOA) is used for the power
equalizing of the output signal, the tenth copied optical signal is implemented.
The transmission properties of a uniform Fiber Bragg Grating (FBG) in a photonic crystal fiber (PCF) with C6v symmetry are studied in this article. The Bragg wavelength λB, increases asymptotically to a particular wavelength as the number of air-hole ring or the hole pitch Λf increases; on the contrary, it decreases as the relative hole size (hole-pitch ratio f) increases. The coupling coefficient between the forward and backward propagating fundamental modes decreases as Λf increases and increases as f increases.
Index-guiding photonic crystal fibers (PCFs) with appropriate structural parameters support the fundamental and second order modes over a practically infinite wavelength range. The potential applications of such PCFs are discussed.
In a long period grating (LPG) made on a silica-based single material photonic crystal fiber (PCF), the effect of material dispersion on the resonance wavelength of the LPG is negligible. The resonance wavelength, the period and length of the LPG, and the diameter and pitch of the air -hole lattice of the PCF are found to obey a scaling law. Simulations show that the resonance wavelength has a non-monotonic dependence on the grating period and, for a particular grating period, there could exist dual resonance wavelengths and hence double transmission dips due to phase matching between the fundamental core mode and a cladding mode simultaneously at two wavelengths. This phenomenon may be explored for novel devices and sensor applications.
In this paper, we proposed a novel SPSM PCF and analyzed its optical properties with a full vector model. Considering the opposite parity of each guided mode in the fiber with symmetric structure, we improved the full vector model we developed previously. The numerical result demonstrated that the algorithm proposed is very efficient for analyzing the PCFs with symmetric structure. It only needs relatively few terms to obtain good results that the computation time can be reduced greatly. It is also confirmed that the fiber structure proposed is very efficient and can operate at SPSM region from the wavelength 1.37mm to 1.70mm.
A novel supercell overlapping method is developed to analyze the PCFs. The dielectric constant of the PCF is considered as the sum of two different periodic dielectric structures which can be expanded in cosine functions.
Long period fiber gratings couple the fundamental guided mode to forward propagating cladding modes. A Characteristic of LPGs in SMF is that their spectral properties (resonant wavelength and coupling strength) are sensitive to the refractive index of the surface surrounding the cladding region. Because of this, LPGs are typically packaged unrecoated to obtain insensitive spectral properties. In this paper the effective index model combined with the coupling-mode theory are used to study the characteristics of LPGs based on photonic crystal fiber (PCF). After plenty of numerical simulation, the results demonstrate that PCF-based LPGs will be more insensitive to the surrounding medium than those written in SMF.
Combining perfectly matched layer (PML) for the boundary treatment, we present an efficient compact 2-dimensional finite-difference time-domain (2D FDTD) method for modeling photonic crystal fibers. For photonic crystal fibers, if we assume that the propagation constant along the propagation direction is fixed, three-dimensional hybrid guided modes can be calculated by using only a two-dimension mesh. Because of using the real variable method, the computation time, i.e., it is of order N. Comparing with the plane wave expansion method, FDTD make the computation time and computer memory are significantly reduced. The numerical results for a triangular lattice
photonic crystal fiber are in very good agreement with the results from the local basis function method. This method can easily be used for any complicated inclusions.
A full vector method based on supercell lattice method is applied for modeling the microstructured optical fibers (MOF). With this new method, the class and degeneracy of modes in MOF are discussed based on symmetry analysis. We classify the modes of MOF into nondegenerate or degenerate pairs according to the minimum waveguide sectors
and its appropriate boundary conditions. It is shown that the modes of MOF can be labeled by its step index fiber analogs, except the modes with the same symmetry as MOF. The doublet of the degenerate pairs in which both have the same symmetry as MOF will be split into two nondegenerate modes by the reduced symmetry of the fiber.
Twin core erbium-doped fiber is fabricated using a combination of MCVD, solution doping and post processing technique. This paper mainly study the birefringence of twin-core Erbium doped fiber including geometrical and stress birefringence. First we analysis the mode distribution of twin core fiber and geometrical birefringence by supercell lattice orthogonal function method using the structure parameters measured. Then the geometrical birefringence also calculated from the couple theory. The calculated result showed that two elliptical cores would have higher geometrical birefringence than two circular cores. Generally the Er-doped fiber is high Germanium doped to keep high Numerical Aperture (NA), which cause high thermal expansion coefficient difference between the core and the cladding, and the stress birefringence is anisotropic. According the distribution of stress field, we calculated the stress birefringence in the area of assembling of light power, which approximate to 10-4. The investigation proved that twin core Erbium doped
fiber has high birefringence and good polarization maintaining characteristics.
Using the experiment results of RH. Stolen's, we got the polynomial formula of the SRS Stokes spectrum by sampling and digital fitting. Based on the formula, the Raman gain and noise figure properties of multi-wavelength pumping broadband Raman amplifier are obtained with considering the inter-amplifying between multi pumps. After numerical analyze, we got the properties of the gain and the noise figure of different Raman amplifiers in different fibers G652, G653, G655 and LEAF.
In this paper we propose a novel structure to enhance pump conversion efficiency and noise characteristics of L-band EDFAs. By adding only a input-reflect fiber Bragg grating and reflecting fractional backward ASE power as a secondary forward pump to further amplify the signal light, larger than 20dB small signal gain improvement and 1dB NF decrease can be achieved. We also investigate the influences of different wavelength FBGs. Experimental results agree well with numerical simulations.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.