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Journal of Physics B Atomic Molecular and Optical Physics

Avoiding lateral mode leakage in thin film lithium niobate waveguides for the generation of spectrally pure photons at telecom wavelengths

Muskan Arora, Pranav Chokkara, Jasleen Lugani

Published Jun 27, 2024• 3 citations
Publisher

Abstract

Abstract Photonic integrated optical components, notably straight waveguides, serve as pivotal elements for on-chip generation and manipulation of quantum states of light. In this work, we focus on optimizing waveguides based on lithium niobate on insulator (LNOI) to generate photon pairs at telecom wavelengths using spontaneous parametric down-conversion (SPDC). Specifically, we investigate lateral leakage for all possible SPDC processes involving type 0, type I, and type II phase matching conditions in an X-cut lithium niobate waveguide and provide a recipe to avoid leakage loss for the interacting photons. Furthermore, focusing on type II phase matching, we engineer the waveguide in the single-mode regime such that it also satisfies group index matching for generating spectrally pure single photons with high purity (99.33%). We also address fabrication imperfections of the optimized design and find that the spectral purity of the generated photons is robust to fabrication errors. This work offers guidance for the suitable selection of morphological parameters to obtain lossless, single-mode LNOI waveguides for building linear optical circuits and photon pair generation at telecom wavelengths using desired phase-matching conditions.

DOI
10.1088/1361-6455/ad5c3e

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arXiv:2412.11372•Laser & Photonics Review•Aug 23, 2024•17 citations
Abstract Photonic integrated optical components, notably straight waveguides, serve as pivotal elements for on-chip generation and manipulation of quantum states of light. In this work, we focus on optimizing waveguides based on lithium niobate on insulator (LNOI) to generate photon pairs at telecom wavelengths using spontaneous parametric down-conversion (SPDC). Specifically, we investigate lateral leakage for all possible SPDC processes involving type 0, type I, and type II phase matching conditions in an X-cut lithium niobate waveguide and provide a recipe to avoid leakage loss for the interacting photons. Furthermore, focusing on type II phase matching, we engineer the waveguide in the single-mode regime such that it also satisfies group index matching for generating spectrally pure single photons with high purity (99.33%). We also address fabrication imperfections of the optimized design and find that the spectral purity of the generated photons is robust to fabrication errors. This work offers guidance for the suitable selection of morphological parameters to obtain lossless, single-mode LNOI waveguides for building linear optical circuits and photon pair generation at telecom wavelengths using desired phase-matching conditions.
Photonic integrated optical components, notably straight waveguides, serve as pivotal elements for on-chip generation and manipulation of quantum states of light. In this work, we focus on optimizing waveguides based on lithium niobate on insulator (LNOI) to generate photon pairs at telecom wavelength using spontaneous parametric down-conversion (SPDC). Specifically, we investigate lateral leakage for all possible SPDC processes involving type 0, type I and type II phase matching conditions in an X-cut lithium niobate waveguide and provide a recipe to avoid leakage loss for the interacting photons. Furthermore, focusing on type II phase matching, we engineer the waveguide in the single mode regime such that it also satisfies group index matching for generating spectrally pure single photons with high purity (99.33%). We also address fabrication imperfections of the optimized design and found that the spectral purity of the generated photons is robust to fabrication errors. This work serves as a tutorial for the appropriate selection of morphological parameters to obtain lossless, single mode LNOI waveguides for building linear optical circuits and photon pair generation at telecom wavelengths using desired phase-matching conditions.
In this work, we focus on optimizing waveguides based on Lithium Niobate on Insulator (LNOI) for the generation of cross-polarized spectrally pure photons at telecommunication wavelength using type II spontaneous Parametric Down-Conversion (SPDC) process. Our optimization process is based on avoiding lateral leakage losses for all the modes involved in considered SPDC process by choosing waveguide parameters appropriately. In addition, we also ensure single mode operation for all the interacting wavelengths. We further engineer the waveguide such that it satisfies group index matching for generating spectrally pure single photons with high purity (⪆95 %). Such single-mode and loss-free waveguides are poised to have broad applications in both classical and quantum optical fields.
Sources of spectrally engineered photonic states are a key resource in several quantum technologies. Of particular importance are the so-called factorizable biphoton states which possess no spectral entanglement and hence, are ideal for heralded generation of high-purity single photons. An essential prerequisite for generating these states through nonlinear frequency conversion is the control over the group indices of the photonic modes of the source. Here, we show that thin-film lithium niobate on insulator (LNOI) is an excellent platform for this purpose. We design and fabricate periodically poled ridge waveguides in LNOI to demonstrate group index engineering of its guided photonic modes and harness this control to experimentally realize on-chip group index matched type-II sum-frequency generation (SFG) and photon-pair creation through spontaneous parametric down-conversion (SPDC). Also, we numerically study the role of the top cladding layer in tuning the dispersion properties of the ridge waveguide structures and reveal a distinctive difference between the air and silica-clad designs which are currently among the two most common device cladding configurations in LNOI. We expect that these results will be relevant for various classical and quantum applications where dispersion control is crucial in tailoring the nonlinear response of the LNOI-based devices.
Abstract Spontaneous parametric down-conversion (SPDC), especially in non-linear waveguides, serves as an important process to generate quantum states of light with desired properties. In this work, we report on a design of a strongly dispersive, singly poled thin film lithium niobate (TFLN) waveguide geometry which acts as a convertible source of photon pairs across telecom band with tunable spectral properties. Through our simulations, we demonstrate that by using this optimized waveguide geometry, two completely different yet desirable type II phase-matched SPDC processes are enabled using a single poling period. One process generates spectrally correlated non-degenerate photon pairs with one photon at 1310nm (telecom O band) and the other at 1550nm (telecom C band). The second SPDC process results in spectrally uncorrelated photon pairs in telecom C band at 1533nm and 1567nm respectively.We attribute this versatility of TFLN waveguide to its strong dispersion properties and make a comparative study with the existing weakly dispersive waveguide platforms.We believe that such a versatile source of photon pairs will serve as an important ingredient in various quantum optical tasks which require photons at different telecom bands and desired spectral properties.
Abstract Broadband photon pairs are highly desirable for quantum metrology, quantum sensing, and quantum communication. Such sources are usually designed through type-0 phase-matching spontaneous parametric down-conversion (SPDC) that makes the photon pairs hard to separate in the frequency-degenerate case and thus limits their applications. In this paper, we design a broadband frequency-degenerate telecom-band photon pair source via the type-II SPDC in a dispersion-engineered thin-film lithium niobate waveguide, where the polarization modes of photon pairs are orthogonal and thus are easily separated deterministically. With a 5-mm-long waveguide, our design can achieve a bandwidth of 5.56 THz (44.8 nm), which is 8.6 times larger than that of the bulk lithium niobate, and the central wavelength can be flexibly adjusted. Our design is a promising approach towards high-quality integrated photon sources and may have wide applications in photonic quantum technologies.
Abstract Thin‐film lithium niobate on insulator (LNOI) emerges as a promising platform for integrated quantum photon source, enabling scalable on‐chip quantum information processing. The most popular technique to overcome the phase mismatching between interacting waves in waveguide is periodic poling, which is intrinsically sensitive to poling uniformity. Here, an alternative strategy to offset the phase mismatching of spontaneous parametric down‐conversion (SPDC) process, so‐called modal phase matching, in a straight waveguide fabricated on a dual‐layer LNOI is reported. The dual‐layer LNOI consists of two 300 nm lithium niobates with opposite directions, which significantly enhances the spatial overlap between fundamental and high‐order modes and thus enables efficient SPDC. This dual‐layer waveguide generates photon pairs with pair generation rate of 41.77 GHz , which exhibits excellent signal‐to‐noise performance with coincidence‐to‐accidental ratio up to 58298 1297. Moreover, a heralded single‐photon source with second‐order autocorrelation and heralded rate exceeding 100 kHz is observed. The results provide an experiment‐friendly approach for efficient generation of quantum photon sources and benefit the on‐chip quantum information processing based on LNOI.