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5.3: Invited Paper: High Efficiency Phase Modulators
Author(s) -
Lu Jiangang,
Luo Yuxiang,
Huang Kai
Publication year - 2021
Publication title -
sid symposium digest of technical papers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.351
H-Index - 44
eISSN - 2168-0159
pISSN - 0097-966X
DOI - 10.1002/sdtp.14363
Subject(s) - liquid crystal on silicon , materials science , optics , optoelectronics , diffraction efficiency , liquid crystal , grating , phase modulation , birefringence , physics , phase noise
In communication networks, wavelength selective switch (WSS) is one of the key components in reconfigurable optical add‐drop multiplexer (ROADM) [1]. Several technologies have been developed to achieve a high‐performance WSS, such as micro electromechanical systems (MEMS) [2], liquid crystal on silicon (LCOS) [3], arrayed waveguide grating (AWG) [4], and hybrid planar lightwave circuit (PLC)‐MEMS [5]. Among these, LCOS‐based WSS is most attractive for the next‐generation optical networks due to its controllability with individual electrical control on pixel. It shows advantages of flexible bandwidth adjustment, adaptive alignment, and robustness without mechanical movements. A LCOS exhibiting a high diffraction efficiency at a large deflection angle is demonstrated [6]. A liquid crystal (LC) mixture with a large birefringence (Δn = 0.27, at λ = 1550 nm) and a large dielectric constant (Δε = 10.4) is developed to obtain the high‐phase retardation, more than 4π, at 1550 nm within a relatively low operation voltage of 5.5 V on LCOS. When compared with the conventional modulation method of 2π phase retardation, both grating period and phase retardation are doubled in 4π modulo modulation. Using the high‐phase retardation modulation method, the LCOS may achieve high diffraction efficiency, more than 56.6% at 4.5° deflection angle of C‐band wavelength with an optimized phase retardation profile. A polarization‐independent blue phase liquid crystal on silicon (BPLCoS) device with low operation voltage for 2π phase depth is proposed [7]. With optimized reflection structure and two reflection films, the incident light may experience multifold optical path and 2π phase depth can be obtained. For the polarization‐independence, an inclined electric field made by periodical gradient voltage is applied on the blue phase liquid crystal (BPLC) to match the light propagation direction. With the structure, the operation voltage can be lowered to 5.5 V in simulation and 5.9 V in experiment for 2π phase modulation at 1550 nm. The high diffraction efficiency and polarization‐independent phase modulators show the great potential application of beam steering for the optical communication and the holographic display.