China
Africa
Explore chapters and articles related to this topic
Diffractive Optical Elements
Published in Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young, Polarized Light and Optical Systems, 2018
Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young
Two common periodic gratings are the rectangular grating and the blazed grating depicted in Figure 23.5. As shown in Figure 23.5a, a rectangular grating contains a repeating rectangular profile. A blazed grating has a triangular profile. Consider light reflecting from a grating facet. A blazed grating will tend to have high efficiency in orders near the reflected direction. Thus, blazing is used to maximize the diffraction efficiency into a desired order. Arbitrary shape gratings are those with the arbitrary profiles. Several terminologies and notations of these periodic grating structures used in the following sections are highlighted in Table 23.1.
The Diffraction Grating
Published in Abdul Al-Azzawi, Photonics, 2017
Figure 19.4 illustrates the cross-sections of basic grating profiles. There are many designs for the shapes of the grooves in a grating. The groove profile determines the relative strengths of diffracted orders produced. Types (a) and (b) in Figure 19.4 are called blazed grating (triangular and sawtooth). The wavelength dispersion of the blazed grating depends on the blaze angle of the profile. Grating grooves having two or more different blaze angles can be combined on a single diffraction grating, as shown in Figure 19.1. This structure allows for wavelength dispersion over a wider range. Type (c) in Figure 19.4 is called an unblazed profile. Type (d) in Figure 19.4 is called a rectangular profile. The blazed gratings are the most popular groove profiles because they allow a very high proportion of power to be transferred into the first order mode. However, a particular blazed grating will operate efficiently over only a very restricted range of wavelengths.
Passive Optical Components
Published in Jerry D. Gibson, The Communications Handbook, 2018
WDM systems carrying more than two channels require more complex multiplexers/demultiplexers. Two such devices are sketched in Fig. 50.12. One uses a GRIN rod to collimate the beam diverging from the input fiber. The collimated beam strikes the blazed grating, which directs different wavelengths into different directions. The lens then refocuses the collimated (but redirected) beams onto different output fibers leading to the receivers. In the second device, a curved reflector performs the same function as the GRIN rod lens. Both of these components can multiplex/demultiplex 10 or more channels (wavelengths). Insertion losses and isolations are on the order of 1 dB and 25 dB, respectively.
Rapid phase calibration of a spatial light modulator using novel phase masks and optimization of its efficiency using an iterative algorithm
Published in Journal of Modern Optics, 2020
Amar Deo Chandra, Ayan Banerjee
The final segment of our work deals with exploring methods to improve the diffraction efficiency of a phase limited SLM. It has been shown [11,12] that there is often a mismatch between the intended gray level and the actual gray level displayed on the SLM which diminishes its diffraction efficiency. A mitigation technique based on global linear corrections in the look-up table (LUT) has been suggested [12] to improve the diffraction efficiency of SLMs which exhibit limited phase depth. A given LUT is quantified in terms of the slope of the linear function which maps the input gray level to the output gray level and is referred to as the contrast (C). The ideal LUT is shown in Figure 13(a) which has a contrast of unity. The method involves making incremental changes in the contrast of the LUT and measuring the corresponding first order diffraction efficiency obtained using a blazed grating. We implement this method based on global linear corrections in the LUT by modified phase encoding of the blazed grating (having periodicty of 16 pixels) displayed on the SLM. To begin with, we measure the power in the first diffraction order using the blazed grating (having C=1) displayed on the SLM. In the subsequent steps, we modify the phase encoding of the blazed grating by using the updated output gray level information computed using the desired LUT mapping function (having variable contrast) to obtain the modified blazed grating. The LUT, having a maximum contrast of 255, maps a blazed grating to a binary grating. We iterate this process using LUTs having different contrasts (some modified LUTs are shown in Figure 13) and measure the resultant first order diffraction efficiency.
Quantitative modelling towards trace spectroanalysis of dielectrics by sliding spark plasma
Published in Radiation Effects and Defects in Solids, 2023
Spectral measurements were made using a spectrometer with holographic blazed grating (1600 grooves/mm, blaze 220 nm, blazing angle 5, entry slit width 11 × 35 μm), focal length 150 mm, reciprocal linear dispersion of 4.2 nm/mm and measuring in the range 210 ≤ λ ≤ 510 nm by use of three CCDs each consisting of 2100 pixels. The spectrometer was spectrally calibrated using hollow cathode lamps and pure analytical grade compounds (18).
Technique for detecting flaws in metallic surfaces using an optical system with phase-type blazed gratings
Published in Journal of Modern Optics, 2019
Takuma Ogawa, Takashi Fukuda, Akira Emoto
Here, these theoretical treatments are based on an assumption that both the aperture and blazed gratings are relatively thin and placed on the focal plane of L2. A standard image of the sample surface was captured without using blazed gratings [Figure 3(a)]. The sample has a large unintended flaw, as indicated by the arrow in the central region of Figure 3(a). Figure 3(b and c) were captured using Diffraction gratings W and N, respectively. These images show the effect of the low-pass filtering: obvious blurring can be seen in the images captured with the diffraction gratings, particularly in the regions indicated by the circles in Figure 3. This effect was caused by a modulation in the spatial frequencies by the blazed gratings, as evidenced by the Fourier spectra shown in the insets corresponding to each captured image. In order to compare the Fourier spectra in more detail, cross-sectional distributions were extracted from the central regions of the two-dimensional distributions along the horizontal direction and plotted in Figure 4. These results show that spatial frequencies larger than 2.5 (line pairs/mm) were reduced substantially in the surface image captured with the Diffraction gratings N. This is attributed to the grating period of the blazed grating because high spatial frequency modulation in the gratings strongly influences the high spatial frequencies of the wavefront reflected from the sample surface; on the other hand, the low spatial frequencies of the wavefront are largely undisturbed by the relatively high spatial frequency modulation in the gratings. As a result, the high spatial frequencies are modulated while the low spatial frequencies are enhanced (i.e. low-pass filtering). The results show that the Diffraction gratings N can be used as effective low-pass filters for observing metallic sample. However, one challenge was that the two-dimensional Fourier spectrum was distributed anisotropically as shown in Figure 3(c). This problem is addressed in Section 3.4.