A non-uniform rectangular slow-wave structure relativistic backward wave oscillator (RBWO) is designed in order to realize the miniaturization of high-power microwave (HPM) systems. the structure is Optimized through simulation software to find and analyze the best magnetic field strength, the diode voltage and beam current value of the RBWO. Simulation results found that a microwave with a frequency of 3.533 GHz and a power of 1.19 GW is obtained with an efficiency of 26.3% when the guiding magnetic field 0.24 T, the diode voltage 713 KV and the beam current 6.3 KA. Experimental research is carried out: an output microwave with an average power of 1 GW, a frequency of 3.589 GHz and a pulse width of 95 ns is generated when the external magnetic field is 0.24 T on the high current electron beam accelerator platform. The experimental results lay a good foundation for miniaturization of highpower microwave systems.
It is a professional degree course textbook for the Nation-class Specialty—Optoelectronic Information Science and Engineering, and it is also an engineering practice textbook for the cultivation of photoelectric excellent engineers. The book seeks to comprehensively introduce the theoretical and applied basis of optoelectronic technology, and it’s closely linked to the current development of optoelectronic industry frontier and made up of following core contents, including the laser source, the light's transmission, modulation, detection, imaging and display. At the same time, it also embodies the features of the source of laser, the transmission of the waveguide, the electronic means and the optical processing methods.
In this paper, we demonstrate the buried waveguides directly writing in LiNbO3 crystal by a tightly focused femtosecond laser with repetition rate 75MHz, and the femtosecond laser was focused by the microscope objective of which NA is 0.65. Fabricating nine carved paths in LiNbO3 crystal by moving three-dimensional electric translation stage at different speeds varying from 2mm/s to 10mm/s, controlled by a computer. Analyzing the structure of the end face of the directly writing region by laser Raman, which shows the large-scale defects are generated in the center of the etching region, densification induced by the thermal effect of high repetition rate femtosecond laser interaction of LiNbO3 were generated below and down of the center of the etching region. Using a He-Ne laser focused by a microscope objective with NA 0.65 coupling to the end face of the prefabricated nine carved paths, which shows two waveguides are generated in the top and below of the inscribing region. Testing the insert loses of these waveguides with an optical power meter, the result shows that the insert loses of the waveguides fabricated at speed of 8~10mm/s is low to 3dB·cm-1, and the insert loses was low to 1.5 dB·cm-1 when the scanning speed is 9mm/s, moreover, the insert loses of the below region was low to the top region.
We used a commercially available 75 MHz regeneratively amplified laser system emitting 50 femtosecond pulses of
energies up to 3nJ at a wavelength of 800 nm. All waveguides were fabricated by focussing the femotsecond pulse train
polarised parallel to the x-axis to a distance of approximately 125 μm below the sample surface using a 0.65 NA, ×40
microscope objective and translating the sample along the y axis. To find the optimum waveguide fabrication parameters
the translation speed was varied from 2 to 100 μm/s. We introduces a method of measuring the refractive index of
optical waveguide in ten micrometer. Useing CCD to measure the two-dimensional near-field light intensity distribution
of the output cross-section of the waveguide, by measuring the two-dimensional near-field light intensity distribution of
the output cross-section of the waveguide can be calculated the two-dimensional distribution of refractive index of
waveguides. The context detailedly gives measurement results about femtosecond laser inducing the near-field intensity
of lithium niobate optical waveguide cross-section and calculations of refractive index of optical waveguide. The results
show that the refractive index of waveguides showed a large central, gradually reduce and the change of refractive index
in the range of 0.001. This method is of great significance to measure the optical waveguide refractive index
In recent years, the microfabrication of Lithium Niobate (LiNbO3) based optical integrated devices by using femtosecond laser pulses has been attracting increasing attention. One key current challenge is to understand the mechanism of the interaction of femtosecond laser pulses on LiNbO3 crystal, which is still elusive. Here we demonstrate the etching of LiNbO3 crystal surface by using tightly focused femtosecond laser pulses with repetition rate 75 MHz, pulse duration 50 fs, and single pulse energy 3nJ. The morphology of the etched area is observed by a scanning electron microscope (SEM) which shows the laser illuminated area has obvious thermal damage. When the etching time is 30 seconds and the etched area is 42μm in diameter, thermal damage is observed within the area with 28μm diameter, redeposition is observed in between 28-34μm diameter, and modification is observed in between 34-42μm diameter. A theoretical thermal diffusion model is built to simulate the temperature distribution in the area etched by laser pulses with repetition rates 1 kHz, 1 MHz, and 75 MHz, respectively. The simulation result from 75 MHz repetition rate matches experimental observation very well. The results show that there is thermal damage when LiNbO3 crystal is illuminated with high repetition rate femtosecond laser pulses.
We have fabricated waveguides in z-cut Lithium niobate using focussed femtosecond pulses inscription of the bulk
material. The form of modified regions and their relationship with writing pulse energy and scan speed is examined.
The damage threshold and morphology of optical material have been investigated by 800nm,
75MHz, 30fs laser pulses, in 40 magnification and 0.65 numerical aperture (NA) objective in the
Z-LiNbO3 crystals. The influence of several experimental parameters, for example energy per
pulse, a ser scanning speed, or repeat time on writing quality and the characters of relative
microstructures has been analyzed and studied in theory. The damage structural change, from
small refractive index changes to micro explosion structure in LiNbO3 induced by high intensity
nanosecond laser is studied. Nonlinear interactions of nanosecond laser and transparent material
The subsurface morphology of the processed structures inside the LiNbO3 was obtained by a
Nikon optical microscope. Particularly, we find that the wider width of the buried channel with the
increase of energy per pluse, repeat time and the reduce of scanning speed. It was caused by the
avalanche ionization and multi-photon absorption of lithium on the processed area, and which is
also lead to the refractive index change rang by the writing conditions. The result shows that the
propagation of optical waveguide could achieve ideal effect when the energy per pluse is under
300mW, the scanning speed is from 0.05mm/s to 0.2mm/s, and the focus depth is from 350μm to
400μm.At last, in this approach, the insertion loss of 1×4 optical splitter is less than 1dB/cm.
A electric field technique was developed to fabricate 1×4 buried channel waveguides on
optical glass. The 40V voltage was applied on the glass to accelerate the exchange of sodium ions
in the glass and cesium ions in the salt melt. As a result, the optical loss of 0.1dB/cm was obtained
for channel waveguides of 20μm depth with the 1.550μm laser, and a 3D buried channel
waveguide is produced by the non-uniform field ion exchange under 1μm height inclined on glass.
The variable separation method and coordinate transformation is presented for solving the
refractive index distribution of the regular hexagon GRIN lens. Through the software
programming, the exact solution of the refractive index distribution is proved by the correctness.
The result is obtained for the manufacture of imaging systems and characteristics. The model can
be extended to solve the even-numbered polygon edges in the positive refractive index distribution
of GRIN lens.
A high electric field technique was developed to fabricate buried optical waveguide modulator on K9 optical
glass. The 80V voltage was applied on the glass to accelerate the field-driven ion exchange process by expeditiously
replacing host sodium ions in the glass with silver ions. As a result, the optical loss for optical waveguide modulator
was measured using the edge coupling technique with a 0.6328μm He-Ne laser. Loss of 0.20 dB/cm was obtained
for channel waveguides of 25μm in depth, relatively low for waveguides of such depth at red wavelength.
Ion-exchange technique in glass was developed to fabricate gradient refractive index optical devices. In this paper, the
Finite Difference Method(FDM), which is used for the solution of ion-diffusion equation, is reported. This method
transforms continual diffusion equation to separate difference equation. It unitizes the matrix of MATLAB program to
solve the iteration process. The collation results under square boundary condition show that it gets a more accurate
numerical solution. Compared to experiment data, the relative error is less than 0.2%. Furthermore, it has simply
operation and kinds of output solutions. This method can provide better results for border-proliferation of the hexagonal
and the channel devices too.
Square Gradient-index Selfoc lenses (GRIN) were successfully prepared by Tl+ and K+ ion-exchange. The ion
concentration equation in square class fiber was calculated by variable separation method. The refractive-index profile of
Square GRIN lenses analytic solution is got based on the linear relation between refractive-index and ion concentration.
The computation results are in good agreement with the measured ones. MATLAB partial differential toolbox was used
to numerically solve ion diffusion equation on square boundary conditions, this works is easy to be handled and redound
to the research on Square GRIN Lenses. The refractive-index analytic solution can be predigested and modeled by a
square law function with introducing the concept of incidence directions angle. Based on the function, the ray's
trajectory equation and Numerical Aperture were got. This work shows that the optical properties of Square GRIN lenses
are related to the directions angle.
The GRIN lens is widely used in optical communication and imaging systems. Its array can be used to design integrated
optic imaging system, especially for hexagonal GRIN. In this paper, the analytic solution of refractive-index distribution
of regularly hexagonal GRIN was obtained by separating variables and transforming coordinate. Having been simulated
and compared, the correctness of this analytic solution was proved qualitatively and quantitatively. It has great benefit
for further research of regular hexagonal GRIN lens and compound eye imaging system. Furthermore, a universal
solution of the refractive-index distribution of a regular N-gon (N is even) lens was obtained by this method.
The buried channel waveguides on optical glass is fabricated by a high electric field technique. The 900V voltage was applied on the glass to accelerate the field-driven ion exchange process by expeditiously replacing host sodium ions in the glass with silver ions. As a result, the lowest optical loss was achieved on waveguides fabricated at 350°C. The optical loss for channel waveguides was measured using the interference technique with a 0.6328μm He-Ne laser. And the loss of 0.30 dB/cm was obtained for channel waveguides of 20μm in depth, relatively low for waveguides of such depth at red wavelength. A nearly Gauss refractive index profile was observed from every channel waveguide fabricated.
With the thermal diffusion method, the Tl+ -ion diffusion process in Tl+-Na+ ion-exchanged glass is in details described by the electroneutrality field and the stress, which are generated by the huge dimension difference for Tl+ and Na+ ions and the large difference in diffusion coefficients between Tl+ and Na+ ions. The results of the theoretical analysis and the experiment data by X-ray energy dispersive spectra indicate that the Tl+ diffusion process is found to be a new diffusion law.
A detailed theoretical and experimental study of the buried waveguide contour, which depends on exchange time and window width by Tl+-Na+ exchange techniques, is reported. Modeling, which includes the effect of ion-exchange time and window width, agrees well with our experiments showing that a buried waveguide contour depends on the relation of τ = square root of Defft and W/2. The same index profile is formed a curve in the interference fringes, and the refractive index profile is a semicircular or semielliptical in waveguide. These results may be used in the proper design of integrated optical circuits and self-focus microlens that need the semicircular or semielliptical waveguides at different sections, such as optical power splitters, diffractive waveguide gratings, and so on.
A theoretical and experimental study of the semicircular waveguide dependence of Tl+-Na+ ion-exchange waveguide on exchange-time and line breadth is reported. Modeling, which includes the effect of ion-exchange time t and line breadth W, agrees well with our experiments showing that a semicircular waveguide depends on the longer exchange time and the narrower line breadth. The result may be used in arrayed microlens and integrated optical circuits, such as diffractive waveguide gratings, and so on.
A theoretical and experiment analysis of two-step ion-exchanged glass optical power splitter is reported. In order to facilitate quantitative analysis, we propose the rational model of physics for a 1×4 S-branch power splitter in glass. These surface half-round channel waveguides are fabricated by first performing a thermal exchange in Tl2SO4 through a mask patterned on the glass surface. The channel waveguides are then buried by second thermal Na+ exchange, unmasked ion exchange, in melt NaNO3. A buried optical power splitter of low insertion loss and uniformity loss has been realized.