High-order diffraction suppression using modulated groove position gratings
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Conventional diffraction gratings composed of a series of equally spaced slits suffer from wavelength overlapping caused by high-order diffraction. Here modulated groove position gratings (MGPGs) are proposed to significantly suppress the high diffraction orders. Both numerical solution and experimental results demonstrate the effectiveness of MGPGs. The suppression ratio is determined by the number of grating grooves used. By using an MGPG with 10,000 grooves, a suppression ratio as high as 18,000 can be obtained. In addition, the minimum linewidth is kept to 1/4 of the grating period, which enables grating realization with high line density employing today's nanofabrication technology. Our results should be of great interest in both diffraction grating theory and applications, particularly due to MGPGs' applicability in a wide wavelength range and realizability with high line density.Keywords:
Laser linewidth
Diffraction efficiency
Groove (engineering)
Ultrasonic grating
The high diffraction efficiency and high dispersion ability of diffraction grating plays a very important role in laser systems. Fused-silica transmission gratings not only have board band, high diffraction efficiency and high damage threshold, but also have the advantage of light path without shelter comparing to reflective gratings. In this paper, the study of polarization-independent transmission fused-silica grating is carried out, and the influence of rectangular and trapezoidal grating microstructures on the -1st diffraction efficiency of grating is analyzed. For trapezoidal groove structure, in the range of 80 to 90 degrees, the distributions of diffraction efficiency at different bottom angle are calculated and analyzed. The structure parameters of the grating are optimized by rigorous coupled wave theory. The designed grating groove density is 1440 lines/mm. The -1st diffraction efficiency of the grating is over 96% for both of TE and TM polarized waves at the Littrow angle (49.7 degrees) with the center wavelength of 1060nm. Within the bandwidth of 42nm (from 1039 to 1081nm), the -1st diffraction efficiency of the designed grating is theoretically greater than 90% for both of TE and TM polarized waves.
Diffraction efficiency
Ultrasonic grating
Electromagnetically induced grating
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In order to study the diffraction characteristics of blazed gratings and analyze the influence of grating parameters on diffraction efficiency, the dependence of diffraction efficiency on the different grating structure parameters and wavelengths was obtained based on the rigorous coupled-wave electromagnetic theory. Calculation results showed that the larger the slot angle, the smaller the blazed angle and the diffraction efficiency, and the bigger the wavelength, the smaller the diffraction efficiency and the bigger the blazed angle. Finally,the polarization phenomenon of a blazed grating was analyzed. The obtained results are helpful for the grating design.
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Ultrasonic grating
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Diffraction grating of high diffraction efficiency and low polarization dependent loss is a key component of the integrated wavelength division-multiplexing device. It has an important application in optics communication. Using the method of rigorous coupled-wave theory to compute the diffraction efficiency of a grating, the program for calculating diffraction efficiency for both TE and TM polarization is made. By changing grating profile, finally the grating profile that has high diffraction efficiency and low polarization dependence loss is gained.
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Ultrasonic grating
Electromagnetically induced grating
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The theoretical and experimental study of the diffraction efficiency of a volume transmission diffraction grating when illuminated by an arbitrary direction reconstruction beam was realized. It was found that on the contrary of what is usually expected, the diffraction efficiency could be increased by a rotation of the grating around its K vector, although the exact Bragg condition is no longer satisfied. Theoretically, the diffraction efficiency can be increased up to 100% for any grating, if we discard the reflection on the grating boundary, and absorption on the holographic media.
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Electromagnetically induced grating
Reflection
Ultrasonic grating
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Diffraction gratings are used in many optical systems as beam splitters. In these applications the diffraction grating must (1) have high diffraction efficiency and (2) produce uniform intensities in the central block of diffracted beams. High diffraction efficiency is attained by making the grating a phase grating. In this paper we discuss in some detail the use of pulse width modulation (PWM) and pulse position modulation (PPM) to create grating structures that produce uniform central diffracted beams. By using these modulation techniques and proper phase relief for the grating, the diffraction grating can have a diffraction efficiency of 70% or more. Some examples of multiple beam diffraction gratings produced by using PWM and PPM are shown.
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Ultrasonic grating
Electromagnetically induced grating
Beam splitter
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Diffraction gratings are very important in hyperspectral imaging. Their desired diffraction efficiency is dictated by the sensitivity of the detector in the spectral band of interest and the luminance of the scene to be observed. If the desired diffraction efficiency curve is established in this spectral band of interest, the remaining work is to design a diffraction grating that meets this demand. This paper is concerned with blazed gratings in reflection, and the geometry of the grating will therefore depend on this reference curve, the spectral band, and the optimization order. The simplest form is a grating with a uniform profile that is optimized at a single-blaze wavelength. It is a monoblaze grating. When such grating cannot meet the requirements in terms of diffraction efficiency, a multiblaze grating optimized at several blaze wavelengths is required. The objective of this paper is to propose a method of optimization of this multiblaze grating, i.e., how to find the number of blaze wavelengths necessary as well as their value to answer the requirements in term of diffraction efficiency.
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Ultrasonic grating
Reflection
Electromagnetically induced grating
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The next-generation diffraction grating not only requires a nonmechanical control and a remote control to generate a diffraction pattern but also requires a tunable period. Here, we propose a stimuli-responsive liquid crystal (LC) phase grating with a tunable period and a diffraction order. The stimuli-responsive LC diffraction grating is composed of periodically arranged electrodes on a double-sided glass substrate. By adjusting the driving scheme, the pitch and diffraction order of the LC grating can be switched between three different modes. The experimental results show that the LC grating has a lower driving voltage (∼5 V). In addition, the tunable LC grating can achieve more diffraction orders, which can be applied to a holographic display to achieve a wide-viewing angle and an enlarged size.
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Ultrasonic grating
Electromagnetically induced grating
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The formation mechanism of ultrasonic grating is analyzed,analytical expression for the light intensity distribution of diffraction pattern of ultrasonic grating is derived,as well as a comparative study of diffraction pattern of ultrasonic grating and plane transmission grating is given by theoretical analysis and numerical simulation.The results show that the diffraction principal maximum satisfies the similar grating equation,but the intensity distribution of the pattern is different,capable of generating the phenomenon of missing order,but the law is different,and the ultrasonic grating is a dynamic grating,the frequency of every diffraction fringe is also different.
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Electromagnetically induced grating
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One of the factors determining the diffraction efficiency of the grating of a surface-relief hologram is the refractive index of the material. The refractive index of the photopolymer constituting a reproduced grating is smaller than that of the photoresist constituting the master grating. To reproduce the grating with a high diffraction efficiency, we studied how to optimize the grating shape. We found that a grating 0.5 μm wide required a master grating 0.9 μm wide to get the highest diffraction efficiency and that the reproduced grating had to be at least 1 μm deep. We fabricated a master and stamp and replicated gratings with a diffraction efficiency of 78 ±5%.
Diffraction efficiency
Electromagnetically induced grating
Ultrasonic grating
Photoresist
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Based on Kogelnik's coupled-wave theory, diffraction efficiency equation of transmission volume Bragg grating is derived. By numerical simulation, it is analyzed that influence of writing parameters such as refractive index modulation, grating thickness, phase-mismatching parameters, deviation of angles and wavelengths on diffraction efficiency The study is shown that the maximal diffraction efficiency is obtained when phase-mismatching do not occur between the incident waves and the diffraction waves, and diffraction efficiency will be improved at the incidence of Bragg angle when the grating thickness and the refractive index modulation increases. When the incident light met all Bragg conditions,diffraction efficiency of the...
Diffraction efficiency
Ultrasonic grating
Fiber Bragg Grating
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