Encyclopedia > letter P > periodic poling

Periodic Poling

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: a technique for achieving quasi-phase matching of nonlinear interactions in a transparent crystal material

Categories: article belongs to category optical materials optical materials, article belongs to category nonlinear optics nonlinear optics, article belongs to category methods methods

DOI: 10.61835/h5v Cite the article: BibTex plain text HTML Link to this page LinkedIn

Periodic poling of nonlinear crystal materials is a technique for obtaining quasi-phase matching [1] of nonlinear interactions. It involves a process which generates a periodic reversal of the domain orientation (domain inversion) in a nonlinear crystal so that the sign of the nonlinear coefficient also changes.

Ferroelectric Domain Engineering

The most common technique for periodic poling is ferroelectric domain engineering [2]. This involves the application of a strong electric field to a ferroelectric crystal via patterned electrodes on the crystal surface, which typically have a period between a few microns and some tens of microns, and are usually produced with a photolithographic process. The poling period (i.e. the period of the electrode pattern) determines the wavelengths for which certain nonlinear processes can be quasi-phase-matched. Domain reversal occurs for a field strength above the so-called coercive field strength, which is e.g. ≈ 21 kV/mm in congruent lithium niobate (LiNbO₃). Such high field strengths have to be applied with great care to avoid discharges in air and destruction of the crystal.

The process is particularly challenging for thick samples (more than 0.5 mm), where the poling quality is sometimes good only near the electrodes. Another challenge is to achieve a high poling quality for small poling periods (well below 10 μm), as required, e.g., for frequency doubling to the visible spectral range. Stoichiometric lithium niobate (SLN) has a much lower coercive field strength of roughly 2 kV/mm, which greatly facilitates periodic poling, even for thicker samples.

Ferroelectric nonlinear crystal materials which are suitable for periodic poling with electric fields include lithium niobate (LiNbO₃), lithium tantalate (LiTaO₃), potassium titanyl phosphate (KTP, KTiOPO₄) and potassium titanyl arsenate (KTA, KTiOAsO₄). The periodically poled materials are often given a name beginning with “PP”, for example PPKTP (periodically poled KTP), PPLN (periodically poled lithium niobate) and PPLT (periodically poled lithium tantalate). PPLN and PPLT crystals are often used in, e.g., optical parametric oscillators and frequency doublers, and are also available in the form of nonlinear waveguides. The combination of the high nonlinearity of PPLN with strong confinement in a waveguide allows for efficient nonlinear interactions even at fairly low power levels.

Note that the details of the poling process have to be optimized for each particular type of nonlinear crystal; this can involve the preparation of crystal surfaces, the choice of electrode materials and details of electrode fabrication, the magnitude, shape and duration of applied electric pulses (often actively controlled with real-time monitoring e.g. of the flown electric charge or optical polarization changes), and the choice of temperature during the poling process. There are also methods to suppress domain back-switching, or to exploit backswitching for high-quality poling [4].

It is possible to periodically pole a large proportion of a whole crystal wafer, e.g. of lithium niobate or tantalate, in a single process, and later cut that wafer into many small crystals. In that way, the processing cost can be relatively low for fabrication of large quantities, whereas periodically poled materials are usually expensive when made in small quantities.

Periodic Poling of Glasses

There have also been interesting attempts to perform periodic poling of optical glass fibers. This is possible because the application of a strong electric field (often applied in a vacuum chamber, together with elevated temperature) for some time can induce a <$\chi^{(2)}$> nonlinearity in the originally isotropic glass. Even if the effective nonlinear coefficient achieved is not very high, some moderate length of glass with a decent poling quality permits efficient nonlinear frequency conversion within all-fiber devices [6].

Fabrication of Orientation-patterned Semiconductors

It is also possible to fabricate semiconductor materials such as gallium arsenide (GaAs) with periodic patterns of domain orientation, which lead to a periodically changing sign of the effective nonlinear coefficient. However, this is not achieved by application of an electric field; gallium arsenide, for example, is not ferroelectric, so that such a technique could not work. Other techniques have been worked out for such periodic patterning, but they are usually not called periodic poling. The article on orientation-patterned semiconductors contains more details.

More to Learn

Encyclopedia articles:

Bibliography

[1]	P. A. Franken and J. F. Ward, “Optical harmonics and nonlinear phenomena”, Rev. Mod. Phys. 35, 23 (1963) (first report of periodic poling); https://doi.org/10.1103/RevModPhys.35.23
[2]	M. Yamada et al., “First-order quasi-phase matched LiNbO₃ waveguide periodically poled by applying an external field for efficient blue second-harmonic generation”, Appl. Phys. Lett. 62, 435 (1993); https://doi.org/10.1063/1.108925
[3]	G. Miller, “Periodically poled lithium niobate: modeling, fabrication, and nonlinear-optical performance”, http://nlo.stanford.edu/content/periodically-poled-lithium-niobate-modeling-fabrication-and-nonlinear-optical-performance, Ph. D. thesis at the University of Stanford (1998); see also references therein
[4]	R. G. Batchko et al., “Backswitch poling in lithium niobate for high-fidelity domain patterning and efficient blue light generation”, Appl. Phys. Lett. 75, 1673 (1999); https://doi.org/10.1063/1.124787
[5]	K. Nakamura et al., “Periodic poling of magnesium-oxide-doped lithium niobate”, J. Appl. Phys. 91 (7), 4528 (2002); https://doi.org/10.1063/1.1456965
[6]	A. Canagasabey et al., “High-average-power second-harmonic generation from periodically poled silica fibers”, Opt. Lett. 34 (16), 2483 (2009); https://doi.org/10.1364/OL.34.002483

(Suggest additional literature!)

Suppliers

The RP Photonics Buyer's Guide contains 84 suppliers for nonlinear crystal materials. Among them:

Optogama

Optogama supplies different types of nonlinear crystals for fundamental, applied research and industrial applications: BBO, LBO, KTP, KDP, DKDP, LiNbO₃, AGaSe₂, AGaS₂, ZGeP₂, GaSe, CdSe. The crystals are used for harmonic generation, sum and difference frequency mixing, optical parametric oscillators and amplifiers, electro-optical modulation and Q-switching, terahertz generation and terahertz detectors, as well as for characterization of ultrashort laser pulses by FROG, XFROG, SPIDER, dispersion scan, and chirp scan methods.

HC Photonics

HC Photonics (HCP) provides various high efficiency nonlinear crystals to enable full-spectrum applications, including periodically poled lithium niobate (pp-LiNbO₃, PPLN) and periodically poled lithium tantalate (LiTaO₃)/PPLT.

Features and service:

more than 250 commercial off-the-shelf PPMgO:LN bulk crystals for wavelength conversions: QPM pattern: single, multiple, and fan-out; configuration: SHG, SFG, DFG, OPG, OPO, OPA; wavelength range: UV (355 nm) to mid-infrared (5000 nm)
custom-made solutions: QPM period: 2–1000 μm; QPM pattern: single, multiple, fan-out, chirped, cascade, 2D; dimension: length 0.3–80 mm, width 0.1–40 mm, thickness 0.2–5 mm); configuration: SHG, SFG, DFG, OPG, OPO, OPA, THG, SHG+SFG; wavelength range: UV (355 nm) to mid-infrared (5000 nm) and THz; material: PPMgO:LN or PPMgO:LT
PPLN waveguides: excellent performance, i.e. >50% overall efficiency. Fibered module generating >2 W at 780 nm (1560 nm SHG) is off-the-shelf. Crystals for other wavelengths are also available or can be designed upon request.

Raicol Crystals

Raicol Crystals offers a wide range nonlinear crystal materials:

LBO e.g. for high-power applications
BBO e.g. for UV applications
flux-grown KTP and RTP with its high nonlinearity, also in variants with high gray tracking resistance
periodically poled crystal materials like PPKTP, PPSLT and Mg-doped LiNbO₃

Our crystals are used in a wide range of applications, including various kinds of nonlinear frequency conversion and electro-optics, but also quantum technology.

Laserton

Laserton offers various types of nonlinear crystals, including β-BBO, KTP and KTA, KDP & KD^*P, LiNbO₃, LBO, SBN and RTP.

GWU-Lasertechnik

GWU-Lasertechnik offers all standard nonlinear crystals like LBO, BBO and KTP with a broad variety of specifications. Beside the well-established materials, innovative crystals like CLBO or BiBO with outstanding properties for e. g. deep-UV generation or high-power ultrashort pulse lasers are available. No matter if individual pieces for R & D purposes are required or cost-efficient numbers in small, medium or large batches with in-time delivery for the production line are needed: GWU’s dedicated service helps to find the best core components for your application. GWU-Lasertechnik has more than 30 years of experience in distributing laser crystals. Choose GWU to benefit from our wide knowledge and in-field experience!

Shalom EO

Shalom EO offers a vast selection of nonlinear crystals, including BBO, KDP and KD^*P, LBO, KTP, HGTR KTP, KTA, BIBO, LiIO₃, LiNbO₃, MgO:LiNbO₃, RTP, ultra-thin BBO, LBO crystals and infrared nonlinear crystals ZnGeP₂ (ZGP).

Our nonlinear crystals are excellent for applications ranging from frequency conversion to short-pulse generation. The NLO crystals offer reliable performance for harmonic generation (SHG, THG, 4HG, 5HG), sum and difference frequency generation (SFG, DFG), for optical parametric oscillators (OPOs) and optical parametric amplifiers (OPAs). Off-the-shelf and customized crystals are optional for our customers. Miscellaneous coating options including uncoated, AR, HR, HT, PR coatings, and custom coatings can be tailored. All the crystals will undergo rigorous inspection before dispatch.

In addition, electro-optic (EO) crystals and acousto-optic (AO) crystals are also available.

Covesion

Non-linear Optical (NLO) crystals provide an enormously flexible solution for generating new wavelengths from existing, off-the-shelf laser sources. The optical wavelength spectrum is utilized by a large and continually expanding variety of applications, from manufacturing of medical lasers, quantum networking & computing through to environmental sensing as well as many others.

With its high non-linear coefficient, ability to be periodically poled and broad optical transmission, MgO:PPLN becomes a highly flexible solution for the generation wavelengths from the blue (400 nm) through the mid-IR and beyond (THz).

ALPHALAS

Most of the standard nonlinear crystals like BBO, LBO, BiBO or KTP for frequency doubling, tripling and quadrupling of the fundamental laser radiation are available from stock. Customer-specific dimensions and AR coatings are also offered at competitive prices.

EKSMA OPTICS

EKSMA Optics offers a complete portfolio of nonlinear optical crystals: BBO, LBO, KTP, KDP, DKDP, LiIO₃, LiNbO₃, MgO:LiNbO₃, AGS, AGSe, ZGP, GaSe, CdSe from stock or manufactured according to customers specifications or for specific applications.

Artifex Engineering

Artifex Engineering provides finished crystal optics for non-linear applications. Visit our product page for more information. We look forward to your inquiry.

Edmund Optics

Nonlinear crystals of either β-barium borate (BBO) or lithium triborate (LBO) are used for frequency conversion of laser sources. BBO crystals feature thicknesses from 0.2 mm to 0.5 mm to minimize group velocity mismatch and are ideal for frequency doubling or tripling of Ti:sapphire and Yb:doped laser pulses. The critical and noncritical phase matching LBO crystals are ideal for second or third harmonic generation of Nd:YAG and Yb:doped lasers.

Nonlinear crystals with 20-10 surface quality and λ/10 (LBO) or λ/8 (BBO) surface flatness provide the broad transparency range and large nonlinear coefficient needed for the harmonic generation of fundamental laser frequencies. Each crystal features a protective anti-reflection (AR) coating that minimizes reflection and limits fogging from ambient conditions.

Questions and Comments from Users

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.