Experiment evaluation of speckle suppression efficiency of 2D quasi-spiral M-sequence-based diffractive optical element

Abstract

The quasi-spiral 2D diffractive optical element (DOE) based on M-sequence of length N=15 is designed and manufactured. The speckle suppression efficiency by the DOE rotation is measured. The speckle suppression coefficients of 10.5, 6, and 4 are obtained for green, violet, and red laser beams, respectively. The results of numerical simulation and experimental data show that the quasi-spiral binary DOE structure can be as effective in speckle reduction as a periodic 2D DOE structure. The numerical simulation and experimental results show that the speckle suppression efficiency of the 2D DOE structure decreases approximately twice at the boundaries of the visible range. It is shown that a replacement of this structure with the bilateral 1D DOE allows obtaining the maximum speckle suppression efficiency in the entire visible range of light.

Dispersion of speckle suppression efficiency for binary DOE structures: spectral domain and coherent matrix approaches

“…The method based on DOE was firstly introduced in 1998 for speckle reduction in a laser projection system [11]. Thereafter, many works have been done to improve the DOE structures and optimize DOE activities for more effective speckle suppression and miniaturize the laser projection systems [12][13][14][15][16][17][18][19][20]. Two kinds of DOE structures, the one-sided 2D DOE (OSDOE) and the two-sided 1D DOE (TSDOE), have been examined for the speckle contrast and speckle suppression range [12][13][14][15].…”

“…Thereafter, many works have been done to improve the DOE structures and optimize DOE activities for more effective speckle suppression and miniaturize the laser projection systems [12][13][14][15][16][17][18][19][20]. Two kinds of DOE structures, the one-sided 2D DOE (OSDOE) and the two-sided 1D DOE (TSDOE), have been examined for the speckle contrast and speckle suppression range [12][13][14][15]. In addition, binary phase codes with pseudorandom sequences [13], Barker codes [16,[18][19] and the Hadamard matrix [10,17] have been developed for DOEs used in laser projection systems for speckle suppression.…”

“…Two kinds of DOE structures, the one-sided 2D DOE (OSDOE) and the two-sided 1D DOE (TSDOE), have been examined for the speckle contrast and speckle suppression range [12][13][14][15]. In addition, binary phase codes with pseudorandom sequences [13], Barker codes [16,[18][19] and the Hadamard matrix [10,17] have been developed for DOEs used in laser projection systems for speckle suppression. Furthermore, various activation methods, such as mechanical movements including linear shift, rotation and step-wise shift, as well as methods based on switching DOE structures, have been investigated for decorrelating laser beams [12][13][17][18][19][21][22].…”

“…In addition, binary phase codes with pseudorandom sequences [13], Barker codes [16,[18][19] and the Hadamard matrix [10,17] have been developed for DOEs used in laser projection systems for speckle suppression. Furthermore, various activation methods, such as mechanical movements including linear shift, rotation and step-wise shift, as well as methods based on switching DOE structures, have been investigated for decorrelating laser beams [12][13][17][18][19][21][22]. It was shown that DOE based on binary pseudorandom sequences can be realized as 1D and 2D DOE structures and both structures can use linear shift to achieve the best speckle suppression [18][19].…”

“…It has been shown that an OSDOE based on pseudorandom sequences has narrower speckle suppression range than the visible range [12][13]15]. It has also been shown that a TSDOE has speckle suppression range wider than the visible range, and therefore, it can be the optimal solution of speckle suppression problem [12][13][14][15]. It is important to know whether this property is true for any OSDOE and any TSDOE, for example for a DOE based on Hadamard matrix.…”