Based on the principle of space-time duality, time lens can be used for reference in theoretical research and practical application. As an optical device, the advantages of time lens lie in its simple structure and diversified functions. So far, the time lens has realized the functions of broadening, compressing, Fourier transform and time reversal of optical signal waveforms. In this paper, the time reversal function of the time lens imaging system is used to realize the effect of the optical logic "NOT" gate, which greatly simplifies the logical "NOT" operation system and greatly improves the operation speed. The research on the use of the optical logic "NOT" gate as Manchester code signal generator is also carried out.
In the paper, we have proposed a structure with only one photonic crystal (PC) micro-cavity side-coupled to a PC
one-way waveguide to generate strong on-resonance optical delay. According to the coupled mode theory (CMT),
the resonator system can maintain a 100% transmission spectrum throughout the complete resonant bandwidth,
which is also demonstrated by the numerical results calculated by the finite element method (FEM). As a temporal
Gaussian pulse is launched, the simulation results show that the device introduces a strong pulse delay while
maintaining total transmission efficiency within the resonant bandwidth, and the resonator structure may be of great
significance for making delay lines in optical buffer applications.
We design a highly efficient channel drop filter (CDF) with only one channel drop micro-cavity based on photonic
crystal (PC) one-way waveguide. By means of the new nature of waveguide-cavity interaction, over 95% channel drop
efficiency can be realized in the structure. Some multichannel drop filters with high drop efficiencies are also engineered
based on such the structure. These numerical results are all calculated by using the finite element method (FEM), which
agrees well with the theoretical analysis result.
When an optical pulse with super-Gaussian shape is transmitted in fiber, it will gradually evolve to Gaussian function
shape under suffered all kinds of effects, such as group velocity dispersion (GVD), third order dispersion (TOD), forth
order dispersion (FOD), and nonlinear effects. An interesting phenomenon is observed, that is, TOD will transfer energy
of super-Gaussian pulse from one half to another within total flat top, but TOD will split Gaussian optical pulse and bring
strong oscillation structure in the edge of pulse. Corresponding to frequency domain, super-Gaussian pulse has two
evident slide slobs arranged in both sides of main peak, but TOD can make slobs fade away and transform frequency
spectral to Gaussian function shape. In a densely dispersion managed (DDM) fiber system, the propagation performance
of super Gaussian pulse with sub-picosecond pulse width is investigated. From clear eye-diagram of propagating over
1000 km, we can conclude that the DDM fiber system is very suitable for super Gaussian optical pulse transmission
under low system power condition.
Based on typical triangular arrangement of air holes with equivalent diameter size, enlarging eight air holes of arranged
in the diamond shape closing to the core of photonic crystal fiber (PCF) to form asymmetry structure of section, this kind
of peculiar arrangement of air holes in inner-cladding can make modal field present some birefringence character and
birefringence degree can be obtained at the magnitude of 10-4. Here, a series of characters about designed PCFs, such as
modal field, dispersion, effective refractive index in two orthogonal directions, and birefringence are investigated.
Generally, in the section of photonic crystal fiber, all air holes are arranged to a triangular regulation, when the size of air holes, the pitch of between neighboring air holes, and refractive index of background material are mapped optimally, one missing air hole in the central of section can localize optical field and form a single mode fiber. Here, each air hole is replaced by twin air holes with fixed distance and axis direction. Accordingly, we can think the central of
section where twin air holes missing is the core of fiber, and optical field is guided in here. In the novel photonic crystal
fiber, all twin air holes arranged according to identical axis direction in the cladding of PCF bring an asymmetry structure of section, and birefringence can come into being in this novel PCFs. After some parameters are selected optimally, the effective refractive index difference between two orthogonal directions Δneff can reach the magnitude of 10-4. From the result of numerical calculation, we also can see that the birefringence parameter Δneff can increase
slightly when the distance between twin air holes is shortened a little but keeping each air holes size and the pitch of
neighboring cell composed by twin air holes.
By numerical simulation, we show that the fourth-order dispersion (FOD) makes sub-picosecond optical pulse broaden as second-order dispersion (SOD), makes optical pulse oscillate simultaneously as third-order dispersion (TOD). Based on above two reasons, sub-picosecond optical pulse will be widely broaden and lead to emission of continuum radiation during propagation. Here, resemble to two- and third-order dispersion compensation, fourth-order dispersion compensation is also suggested in a dispersion-managed optical fiber link, which is realized by arranging two kinds of fiber with opposite dispersion sign in each compensation cell. For sake of avoiding excessively broadening, ultra short scale dispersion compensation cell is required in ultra high speed optical communication system. In a full dispersion compensation optical fiber system which path average dispersion is zero about SOD, TOD, and FOD, even suffering from affection of high order nonlinear like self-steep effect and self-frequency shift, 200 fs gauss optical pulse can stable propagate over 1000 km with an optimal initial chirp. When space between neighboring optical pulse is only 2 picoseconds corresponding to 500 Gbit/s transmitting capacity, eye diagram is very clarity after 1000 km. The results demonstrate that ultra short scale dispersion compensation including FOD is need and effective in ultra-high speed optical communication.
We design a kind of dual-cladding photonic crystal fiber (DC-PCF), in which air holes arranged in the vicinity of the core (inner-cladding) is smaller than the other air holes (outer-cladding). By numerical simulation, the dispersion characteristic of this novel PCF is investigated. Dispersion curves will become comparatively flat while gradually reducing the air holes arranged in inner cladding under fixing the air holes of outer cladding. An ultra-flattened dispersion can be realized when the air holes size of inner-cladding dwindling down to an optimum size. As an example, the DC-PCF demonstrates an extraordinary flattened dispersion around 9.8ps/nm.km within ±0.4ps/nm/km fluctuation range in an ultra-broad wavelength range from 1.0μm to 2.0μm . Furthermore, when the air holes arranged in the second layer nearing the core is reduced slightly, the flattened dispersion curve even can parallel shift from 11.8ps/nm/km to 7.8ps/nm/km, 6.2ps/nm/km, 4.0ps/nm/km at the wavelength around 1.55μm.
A model of photonic crystal fiber (PCF) with tapered high-index core by GeO2 doped in silica glasses is supposed. Based on finite different approximation of the semi-vector helm-holtz equation, the character of dispersion and modal field areas about this kind of PCF are investigated. Results demonstrate that dispersion parameter can change gradually in positive dispersion region or negative dispersion region, even can change from positive to negative dispersion region when the air hole and pitch are fixed, only the core radius of the PCF is tapered. The kind of PCF is designed for special dispersion-related applications. Especially, it can offer dispersion self-compensation in some optical devices.
Our researches are based on such a system architecture that is intended to utilize the good characteristic of the interaction between millimeter-wave and lightwave to implement the 60GHz short millimeter-wave broadband wireless access system over fiber links. The networks include fiber optic links between the center stations (CS) and the base stations (BSs) and millimeter-wave air channel between the BSs and the networks terminals. The polymer optical fiber (POF) is deployed as optical fiber link medium due to its marked competitiveness in short haul, large capability communication systems. In this paper, we focus on suppressing dispersion of the radio-over-fiber transmission system. The POF is a dominant fiber chromatic dispersion source, which behaves multi-mode properties and produces inter-mode dispersion to heavily cause the POF bandwidth degradation. We present analysis on modal dispersion characteristics of 60 GHz short millimeter-wave broadband wireless access system over polymer optical fiber (POF) transmission link and present our scheme, which chooses proper launch condition to control the number of low-order modes and high-order modes excited in the POF link to improve system dispersion characteristic.
Analysis of monolithic integrated MQW waveguide and passive waveguide with ATG structure is presented by using normal modes theory. It is based on the analysis of normal modes of asymmetric five-layer waveguide, combined with theoretic model of MQW waveguide. The electromagnetic field distribution, dispersion equation, calculation and simulation results are reported.
A novel photonic crystal fiber with ultra-flattened dispersion and large mode area is demonstrated. All air holes are arranged in the section according to triangular regulation and with identical spacing. The thirteen air holes, which in the middle of the section arrayed in the shape of snowflake, are smaller than the other air holes in the outer cladding region, form the large core region of PCF. Because the effective refractive index of the core region is higher than the cladding region, total internal reflective (TIR) can occur in the interface between the core and cladding, and optical field can be located mainly within the region of snowflake form. Obviously, this kind of PCF has large mode area because the thirteen holes holding together increase the core area of PCF visibly. On the other hand, not only ultra-flattened dispersion character can be realized in a broadband wavelength range, but also the flattened dispersion curve can easily be shifted in parallel from negative to zero, even to positive when the air holes of the core region is changed while the air holes size of cladding and spacing in the whole section remain fixed. Desired dispersion character and modal area can be realized in our designed PCFs with special section structure by optimizing the match of the spacing and air hole size in core and cladding regions.
A novel design method about photonic crystal fiber (PCF) with large area model field (LAMF) is demonstrated. Different from ordinarily design that the core of PCF formed by missing one air holes in the center of section, many air holes distributed in heartland all together come into being the core region. Air holes are arranged regularly in core region and outer cladding regions according to different periodical character, respectively. The effective refractive index (n eff ) of core region should be higher than cladding region because of total internal reflection (TIR) requirement. In this paper, two kinds of typical scheme are offered to realize LAMF-PCF. First, Λ, the spacing of neighboring air holes in whole section is fixed, once the radius of air holes in the core region rc is smaller than the cladding air holes rcla, LAMF-PCF will be formed. The modal area only lessens a little as rc is reduced. Especially, optimal size of rc can nearly make MFA insensitive to wavelength. On the contrary, dispersion parameter of PCF will take place visible change along with rc reduced, and ultra-flattened dispersion character can be realized when rc is optimized. Another method of designing LAMF-PCF is keeping all air holes uniform in the whole section of PCF, but the space of neighboring air holes in the core region Λc is longer than the cladding region Λcla, so neff of core region is higher than the cladding region and TIR can take place.
We demonstrate a novel kind of dense dispersion-managed fiber line, which gradually decrease not only local dispersion in each fiber segment, but also averaged dispersion in every dispersion compensation cell during an amplified period. When an amplifier period contains several or more dispersion compensation cell (La/Lc >> 1), short dispersion compensation period can greatly reduce the degree of optical pulse breathing and interaction between neighboring pulse. Loss can make the Kerr effect becomes weaker when optical pulse propagating in an optical amplified length, so better counterbalance between dispersion and nonlinear effect can be obtained by appropriately reducing local and averaged dispersion parameter. Some results show that this kind of optical fiber links have some excellent advantages over constant local and averaged dispersion system, can greatly improve the performance on high speed optical fiber transmission system.
A novel design of densely dispersion-managed optical fiber transmission systems with decreasing average dispersion and decreasing local dispersion (dual-decreasing DDM) is proposed. The system is characterized by gradually decreasing not only local dispersion in each fiber segment, but also average dispersion in every dispersion compensation cell. When an optical pulse propagates along an optical fiber link, transmission loss weakens the Kerr effect to break the balance between dispersion and nonlinearity. To deal with the problem, dispersion parameters in a densely dispersion-managed system are made to vary gradually to counterbalance the nonlinearity. This novel approach has a number of advantages over ordinary densely dispersion-managed (DDM) soliton transmission systems, including allowing higher pulse power and reduction of optical pulse broadening, hence there is less interaction between neighboring pulses. Simulation results indicate that the dual-decreasing DDM has better propagation performance in comparison with the ordinary DDM in a high-speed optical communication system.
In this paper the liquid thermal diffusivity measurement through pulsed photothermal deflection in a modified collinear configuration is presented and discussed. The condition that the pulsed beam is regarded as in the form of a Dirac delta function here is given out. Comparison between theory and experiment is also shown.
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