Long Low-Loss-Litium Niobate on Insulator Waveguides with Sub-Nanometer Surface Roughness

Wu, Rongbo; Wang, Min; Xu, Jian; Qi, Jia; Chu, Wei; Fang, Zhiwei; Zhang, Jianhao; Zhou, Junxia; Qiao, Lingling; Chai, Zhifang; Lin, Jintian; Cheng, Ya

doi:10.3390/nano8110910

Cited by 158 publications

(106 citation statements)

References 37 publications

(40 reference statements)

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“…First, a thin layer of chromium (Cr) with a thickness ranging from 600 nm to ∼1 μm was deposited on LNOI by magnetron sputtering. The thin layer of Cr serves as a protection mask once being patterned by either laser ablation or optical lithography . Second, the Cr foil will be selectively removed with a high spatial precision using femtosecond laser ablation.…”

Section: Technical Details Of Cmplmentioning

confidence: 99%

“…The ion beam etching inevitably leaves behind a surface roughness on the order of a few nanometers, which limits the ultimate Q factor of a freestanding LN microdisk to ~10 6 . The problem has recently been resolved by first patterning a chromium (Cr) thin film coated on the top surface of LNOI into a hard mask with a femtosecond laser, followed by the chemo‐mechanical polish (CMP) for structuring the LNOI into the microdisk . We will show below that the CMP lithography (CMPL) can enable ultrahigh performance LNOI photonic structures, opening the venue toward large scale, low loss, reconfigurable PICs for numerous applications.…”

Section: Introductionmentioning

confidence: 99%

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Chemo‐mechanical polish lithography: A pathway to low loss large‐scale photonic integration on lithium niobate on insulator

Wang

Lin

et al. 2019

Quantum Engineering

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129

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We discuss the recent breakthrough in the field of photonic integrated circuits for generating high-quality photonic structures on lithium niobate (LN) on insulator (LNOI). This is enabled by the development of chemo-mechanical polish lithography (CMPL). We begin with a brief introduction of the background, followed by the description of the CMPL technique that holds the promise for realizing LNOI waveguides of ultralow propagation loss approaching the absorption limit of LN. We demonstrate fabrication of low loss optical waveguides with the CMPL and construction of beamsplitters with the fabricated LNOI waveguides. At last, some conclusions and future perspectives will be given.A video abstract of this article can be found at: https://youtu.be/sgnecU_QzcY KEYWORDS chemo-mechanical polish lithography (CMPL), femtosecond laser micromachining, lithium niobate on insulator (LNOI), photonic integrated circuit (PIC), waveguides Quantum Engineering. 2019;1:e9.wileyonlinelibrary.com/journal/que2

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Section: Technical Details Of Cmplmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chemo‐mechanical polish lithography: A pathway to low loss large‐scale photonic integration on lithium niobate on insulator

Wang

Lin

et al. 2019

Quantum Engineering

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129

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“…Lithium niobate on insulator (LNOI) is an emerging platform which has shown promising potential for integrated photonics due to its numerous advantages of high refractive-index contrast, wide transparent window (0.35-5 μm), large nonlinear coefficient, and excellent electro-optic characteristics [1][2][3][4][5]. In recent years, photonic devices based on LNOI, including waveguides [6,7], microring resonators [1,8], microdisk resonators [9][10][11], and photonic crystal cavities [12,13] have been developed. On-chip functionalities, such as second harmonic generation [13][14][15][16][17][18], electro-optic modulator [3,[19][20][21][22][23], and optical frequency comb [24,25], have experienced rapid progress with the above-mentioned LNOI micro-/nanodevices.…”

Section: Introductionmentioning

confidence: 99%

“…On-chip functionalities, such as second harmonic generation [13][14][15][16][17][18], electro-optic modulator [3,[19][20][21][22][23], and optical frequency comb [24,25], have experienced rapid progress with the above-mentioned LNOI micro-/nanodevices. Importantly, many integrated on-chip lithium niobate (LN) devices developed recently already feature low propagation losses [6][7][8]10], which is critical for practical applications. However, some challenges are yet to be overcome.…”

Section: Introductionmentioning

confidence: 99%

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber

Ni¹,

Zhou²,

Gao³

et al. 2020

Opt. Express

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A lithium niobate on insulator ridge waveguide allows constructing high-density photonic integrated circuits thanks to its small bending radius offered by the high index contrast. Meanwhile, the significant mode-field mismatch between an optical fiber and the single-mode lithium niobate waveguide leads to low coupling efficiencies. Here, we demonstrate, both numerically and experimentally, that the problem can be solved with a tapered single mode fiber of an optimized mode field profile. Numerical simulation shows that the minimum coupling losses for the TE and TM mode are 0.32 dB and 0.86 dB, respectively. Experimentally, though without anti-reflection coating, the measured coupling losses for TE and TM mode are 1.32 dB and 1.88 dB, respectively. Our technique paves a way for a broad range of on-chip lithium niobate applications.

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“…A basic challenge in the production of M-ZI modulators in LNOI is the fabrication of high-quality waveguide structures. A few techniques have been developed for fabricating waveguides in LN,, proton exchange (PE) [23], and chemo-mechanical polishing [24]. Compared with other methods, PE is low-cost, has low propagation loss, and is a mature manufacturing method that is compatible with the LN optical waveguide industry [25,26].…”

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confidence: 99%

Design and Optimization of Proton Exchanged Integrated Electro-Optic Modulators in X-Cut Lithium Niobate Thin Film

et al. 2019

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In this study, we designed, simulated, and optimized proton exchanged integrated Mach-Zehnder modulators in a 0.5-µm-thick x-cut lithium niobate thin film. The single-mode conditions, the mode distributions, and the optical power distribution of the lithium niobate channel waveguides are discussed and compared in this study. The design parameters of the Y-branch and the separation distances between the electrodes were optimized. The relationship between the half-wave voltage length production of the electro-optic modulators and the thickness of the proton exchanged region was studied.Electro-Optic (E-O) modulators have recently attracted growing attention in ultra-compact photonic integrated circuits (PICs) [1]. They have extensive applications in optical telecommunication networks and microwave-photonic systems [2]. The Mach-Zehnder interferometer (M-ZI) is one of the most important interference structures in modulators because of its simple design and manufacture, with the existence of a reference arm that compensates for the common-mode effect [3]. Many types of M-ZI-based applications for optical communication have been investigated, such as switches/modulators [4,5], multi/demultiplexers [6,7], and splitters [8,9].Lithium niobate (LiNbO 3 , LN) is one of the most remarkable optical crystal materials due to its combination of excellent E-O and nonlinear optical characteristics [10]. Due to the high E-O coefficient (r 33 = 31.2 pm/V) in LN, high-quality E-O modulators of this type are very valuable in optical communication [11][12][13][14][15]. In the last decade, high-refractive-index contrast in the form of lithium niobate thin film bonded to a SiO 2 layer (lithium niobate on insulator, LNOI) has emerged as an ideal platform for integrated high-performance modulators [16][17][18][19]. A basic challenge in the production of M-ZI modulators in LNOI is the fabrication of high-quality waveguide structures. A few techniques have been developed for fabricating waveguides in LN,, proton exchange (PE) [23], and chemo-mechanical polishing [24]. Compared with other methods, PE is low-cost, has low propagation loss, and is a mature manufacturing method that is compatible with the LN optical waveguide industry [25,26]. Compared with rough-etched side walls, PE waveguides have smooth boundaries. However, to the best of the authors' knowledge, to date there have been few reports on proton-exchanged electro-optic modulators in LNOI [23].In this research, we simulated and analyzed a proton-exchanged E-O M-ZI modulator in an x-cut LNOI. Based on the full-vectorial finite-difference method [27], the single-mode conditions of the PE waveguides were investigated, the bending losses of the Y-branch structures were analyzed, and the propagation losses of the PE waveguides with different separation distances between electrodes were simulated. The half-wave voltages of the devices were calculated using the finite difference beam propagation method (FD-BPM) [28,29]. The optimized half-wave voltage-length product (V π ·L) was approxi...

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Long Low-Loss-Litium Niobate on Insulator Waveguides with Sub-Nanometer Surface Roughness

Cited by 158 publications

References 37 publications

Chemo‐mechanical polish lithography: A pathway to low loss large‐scale photonic integration on lithium niobate on insulator

Chemo‐mechanical polish lithography: A pathway to low loss large‐scale photonic integration on lithium niobate on insulator

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber

Design and Optimization of Proton Exchanged Integrated Electro-Optic Modulators in X-Cut Lithium Niobate Thin Film

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