Ultra-short embedded long-period waveguide grating for broadband mode conversion

Opto-Electronics Review

“…Operation principle of the mode coupling converters is based on the coupling between the fundamental and the selected high-order mode under the condition of their phase matching. Such a mode coupling is usually achieved by using ADC, [44][45][46][47][48][49][50][51][52][53][54][55][56][57]73,78], ring [58,59], LPG [60][61][62][63][64][65]72,74,75], BG [66,67], dielectric metasurface structure [68][69][70], and grating-assisted coupler [71], and so on. Their key performances have been summarized in Table 2 in the Appendix.…”

Compact, broadband, and efficient LP01 -LP11a mode converter based on cascaded asymmetric Y-junction

“…In an MDM optical transmission system, a mode converter that serve to convert a particular mode into another mode is often needed at both the input and output ends, and therefore, is a key component [3,4]. In view of this, numerous research efforts have been made toward the development of high-performance mode converters and consequently, various types of mode converters based on bulk-optic components [5,6], optical bers [7,8], and planar lightwave circuit (PLC) [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] have been demonstrated now. Among them, PLC-based mode converters attract more interest because of their distinctive advantages including compactness, material and structure diversity, design and fabrication exibility, and integration capability.…”

“…Among them, PLC-based mode converters attract more interest because of their distinctive advantages including compactness, material and structure diversity, design and fabrication exibility, and integration capability. These previously reported PLC-based mode converters employed various structures, including trench [9] or slot waveguide [10], asymmetric directional couplers [11][12][13], multimode interference coupler [14,15], grating-assisted couplers [16], Bragg grating [17], long-period gratings (LPG) [18][19][20], asymmetric Y-junction [21][22][23][24][25], integration of asymmetric Y-junction with thermo-induced LPG [26], Mach-Zehnder interferometer [27][28][29], dielectric metasurface [30], and so on.…”

Spot-Size Converter Based on Long-Period Grating

“…As is well known, at resonance wavelengths, an LPG can couple the mode of the cladding into the mode of the core completely and vice versa [19], [20]. By exploiting this unique capability, LPG-based wavelength filter [21]- [23], mode filter [24], [25], mode switch [26], mode converter [27]- [30], grating coupler [31], and optical-fiber-to-waveguide coupler [32] have been proposed and demonstrated recent years. Note that the transfer of light power between the fiber and the waveguide in [32] is based on the grating-assisted transverse coupling, not butt coupling via the facets of the fiber and the waveguide.…”

“…Therein, the LPG achieves a maximum mode conversion efficiency of 90% between the two E x 11 modes of the polymer cladding and the Si 3 N 4 core. The 3-dB bandwidth of the device is 4 nm, but it can be dramatically enlarged by optimizing the design of the grating, such as by using the chirped grating [33] or the length-apodized grating [25], [29], or by operating an LPG at its turning point along its phase-matching curve [30], [34].…”