• Website search
  • Distributor login
  • Quote
  • Solution finder
Covesion Logo
    • EN
      • 简体中文
  • Home
  • Products
  • Applications
  • Resources
    • Case Studies
    • Publications
    • Technical Guides
    • Whitepapers
    • FAQs
  • News & Insights
    • Company News
  • About Us
    • Why Choose Covesion
    • Careers
    • Customers & Partners
    • Research Projects
  • Contact Us
    • International Distributors
  • Home
  • Products
    • Components and Modules
    • Custom PPLN
    • MgO:PPLN Crystals and Chips
    • PPLN Accessories
  • Applications
    • Space & Defence
    • Spectroscopy & Environmental Science
    • Scientific Instrumentation
    • Research
    • Quantum Science
  • News & Insights
    • Company News
  • About Us
    • Why Choose Covesion
    • Customers & Partners
    • Research Projects
  • Resources
    • Publications
    • Technical Guides
    • FAQs
  • Contact Us

Components and Modules

Custom PPLN

MgO:PPLN Crystals and Chips

PPLN Accessories

  • Fiber Coupled Bulk Crystal Module
  • Ruggedised Waveguide Package
  • Component Waveguide: Fiber
  • Component Waveguide: Free-space

We offer a range of custom design packages including; one-off crystals, OEM prototyping and large-volume manufacture.

Custom PPLN
  • SHG Crystals
  • OPO Crystals
  • DFG Crystals
  • SFG Crystals
  • Waveguide Chip
  • PPLN Ovens
  • Temperature Controllers
  • PPLN Crystal Clip Kits
  • PPLN Oven Mount Adapters
  • Waveguide Accessory Pack
Space & Defence
Scientific Instrumentation
Spectroscopy & Environmental Science
Research
Quantum Science
View All Applications

Suggested Searches

MgO:PPLN Crystals Custom PPLN Crystals PPLN Accessories PPLN Waveguides

Can’t find what you’re looking for?

Contact Us

Electron Dynamics is now part of Covesion

Read Blog Post

ResourcesMaterial properties of Lithium Niobate

Material properties of Lithium Niobate

12th Nov 2020
  • Lithium Niobate
  • MgO:PPLN
image from Covesion ©
  • Share

Second Order Nonlinearity

The second order nonlinear polarisation of lithium niobate can be written as,

Second order nonlinear polarisation of lithium niobate

The 2-D matrix describes the non-susceptibility tensor χ(2). For 5% MgO doped lithium niobate (MgO:LN) at 1064nm, d31=4.4pm/V, d33=25pm/V [1].

The highest nonlinear coefficient is d33=25pm/V, which corresponds to interactions that are parallel to the z-axis, i.e. type-0 phase matching. In other words, all interactive waves must be e-polarized in order to achieve the highest conversion efficiency. All of our crystals are designed to access this d33 coefficient. For periodically poled MgO:LN, the effective nonlinear coefficient deff is typically 14pm/V.

NOTE: Covesion can offer custom crystals for type I or type II interactions, for example for entangled photon systems for the generation of orthogonally polarized pairs.

Material deff (pm/V)
MgO:PPLN 14pm/V (typical)
KTP 3.4pm/V
BBO 2.5pm/V
LBO 0.85pm/V

Refractive Index

The temperature dependent refractive index is described by the Sellmeier equation:

Sellmeier equation

 

Where the temperature dependent parameter f is defined as,

Where T is temperature in °C

and the Sellmeier coefficients are,

Sellmeier Coefficient 5% MgO:LN [2] Undoped LN [3]
a1 5.756 5.35583
a2 0.0983 0.100473
a3 0.2020 0.20692
a4 189.32 100
a5 12.52 11.34927
a6 1.32E-02 1.5334E-02
b1 2.860E-06 4.629E-07
b2 4.700E-08 3.862E-08
b3 6.113E-08 -8.9E-09
b4 1.516E-04 2.657E-05

Using these parameters in the Sellmeier equation, you can calculate the refractive index variation with wavelength and temperature. The table below has a few examples.

Temperature 532nm 780nm 1064nm 1550nm 3500nm
30°C 2.2260 2.1715 2.1496 2.1320 2.0732
100°C 2.2485 2.1929 2.1708 2.1530 2.0938
150°C 2.2673 2.2108 2.1884 2.1705 2.1110

PPLN has a high index of refraction that results in a ~14% Fresnel loss per uncoated surface. To increase transmission through our crystals, the crystal input and output facets are AR coated, thus reducing the reflections at each surface to less than 1%.

Transmission

MgO:LN and LN have very similar transmission curves and are highly transparent from 400-4000nm. Material absorption occurs below 400nm and above 4000nm where PPLN can still be used as long as the losses can be overcome. For example, a pulsed mid-infrared OPO generating 7.3um has been demonstrated in PPLN [4], although more commonly, PPLN-based OPOs are often operated up to 4.5-5um. Similarly, for the UV region, generation at 386nm [5] and 370nm [6] has been demonstrated using 3rd order QPM in MgO:PPLN.

Work by Schwesyg et al. have analysed the absorption losses of MgO:LN between 300 and 2950nm [7]. Their data (shown below) provides an accurate measurement of the absorption coefficient between 400-800nm. Their experiment also found no measurable absorption bands between 800-2000nm.

Measurable absorption bands

The figure below shows the transmission curves of LN and MgO:LN measured by Covesion, showing the roll-off of transmission for both materials. The measurement includes Fresnel reflections off both input and output facets of the measured samples, which accounts for a loss of approximately 30% due to Fresnel reflections.

NOTE: There is an OH-absorption band at 2826nm with a measured absorption coefficient of 0.088cm-1 [7].

MgO:PPLN vs undoped PPLN

Undoped PPLN is usually operated at temperatures between 100°C and 200°C, to minimize the photorefractive effect that can damage the crystal and cause the output beam to become distorted. Since the photorefractive effect is more severe in PPLN when higher energy photons in the visible part of the spectrum are present, it is especially important to use the crystal only in the recommended temperature range.

The addition of 5% MgO to lithium niobate significantly increases the optical and photorefractive resistance of the crystal while preserving its high nonlinear coefficient. With a higher damage threshold, MgO:PPLN is more suitable for high power applications. It can also be operated from room temperature up to 200°C, significantly increasing the wavelength tunability of the device. Moreover, in some special cases, the MgO:PPLN can be operated at room temperature and without the need for temperature control e.g. Our MSHG1550-0.5-1 (1mm long) can be used for generating 780nm from 1560nm femtosecond fibre laser.

Power Handling and Damage Threshold

Lifetime testing of our crystals is an on-going process at Covesion. Using a 10W 1064nm CW laser, we have generated 2.2W at 532nm. With a pump intensity of >500KW/cm2 and operating temperature of 35degC, our PPLN maintained the 2.2W SHG output power over a period of 2000hrs, with no signs of damage to the crystal and no evidence of beam distortion due to photorefraction.

Lifetime testing of our crystals

The damage threshold of MgO:PPLN or PPLN depends on wavelength as well as whether the source is CW or pulsed. In the CW regime, the threshold depends on the intensity and is lower when visible wavelengths are involved. For pulsed sources, the damage threshold depends on wavelength, pulse duration, average power and the repetition rate. Often the damage threshold will be higher for low repetition rate sources.

If you think that you are working close to the damage threshold, then a good tip is to test the damage threshold in an unpoled region of the crystal. Covesion crystals have a standard width of 10mm, but the poled gratings cover a maximum width ~7mm. You can use the unpoled areas to carefully test for damage as long as it is still within the AR coated region.

Note: The damage threshold in a poled region will be lower if you are generating visible wavelengths. Always increase the pump power gradually, whilst monitoring the beam for any distortions or a sudden drop in power.

The table below shows a collection of data from Covesion and from customers showing the power handling or damage thresholds under various regimes. We are continuously working together with our customers to increase the amount of information available on crystal damage thresholds. If you would like to contribute to this, please email sales@covesion.com.

Regime Peak Intensity/ Energy Density Damage? Notes
CW 500KW/cm2 N 1064nm, 10W, SHG (Covesion)
CW 500KW/cm2 N 1560nm, 30W, (Australian National University [8])
CW 200kW/cm2 N 532nm, 2.2W, (from 1064nm SHG) (Covesion)
ns 100MW/cm2 or 2J/cm2 Y 1064nm, ~30um period, single pass, 10-20ns, 21Hz, (Covesion)
ps 100MW/cm2 N 1060nm OPO, 20ps, 115MHz, 24W (ORC Southampton, [9])
ps 1.5GW/cm2 N 1064nm OPG for MIR: 7ps, 400Hz
ps 1.8MW/cm2 Y 530nm OPO, 20ps, 230MHz, 500mW, (ORC Southampton, [10])
ps 7.5MW/cm2 Y 530nm OPO, 20ps, 230MHz, 1W->100mW chopped, (ORC Southampton, [10])
ps 468MW/cm2 N 1064nm, 7ps, 17W, 80MHz, (National University of Singapore [11])
fs 4GW/cm2 Y 1550nm, 200fs, 200mW, 80MHz, SHG

 

Damage Mechanisms

The Photorefractive Effect

Under conditions of high intensity, LiNbO3 and MgO: LiNbO3 are prone to the photorefractive effect, which is an optically induced change in refractive index. (N.B. The threshold is higher for MgO: LiNbO3).

In a region of high optical intensity, electrons are released as free carriers and then redistribute in an area of lower optical intensity. This causes a spatially varying refractive index within the material that can be observed as beam distortions. This can result in permanent damage to the crystal. However, under some circumstances, if the effects are small the damage can be reversed by heating the crystal to 200°C for a couple of hours to allow all the charge carriers to re-diffuse.

If you are working near the damage threshold, it is recommended that you operate at high temperatures between 150-200°C.

Green Induced Infrared Absorption

Green Induced Infrared Absorption, or GRIIRA, is an effect where the presence of green light allows infrared to be absorbed. This causes local heating which can offset the phase matching temperature of your interaction, but it can also eventually lead to crystal damage.

The mechanism for GRIIRA comes from the creation of polarons from crystal defects such as, Nb ions occupying Li ion sites (known as antisite defects), and Fe ion impurities. Doping lithium niobate with MgO reduces the onset of GRIIRA, as it allows Mg ions to replace the Nb antisite defects.

IR absorption due to blue light also occurs by the same mechanisms, and is known as BLIIRA (blue induced infrared absorption).

References

1. Compact blue-green lasers”, W. P. Risk, T. R. Gosnell and A. V. Nurmikko, Cambridge University Press, 2003
2. Gayer et al., Applied Physics B 91, 343-348 (2008)
3. D.H.Jundt, Optics Letters V.22 N.20 p.1553-1555 (1997)
4. M. A. Watson et al., Optics Letters, vol. 27, no. 23, pp. 2106–8, ( 2002)
5. R.T. White et al., Applied Physics B: Lasers and Optics, 77(6-7), 547–550 (2003)
6. J. Kim, et al., 2013 IEEE Photonics Society Summer Topical Meeting Series (pp. 183–184) (2013)
7. J. R. Schwesyg et al., Advances in Optical Materials, AIThE3, (2011)
8. S. S. Sané et al., Optics Express, vol. 20, no. 8, pp. 8915–9, (2012)
9. F. Kienle et al., Optics Express, vol. 18, no. 8, pp. 7602–10, (2010)
10. F. Kienle et al., Journal of the Optical Society of America B, vol. 29, no. 1, p. 144, (2011)
11. P. K. Upputuri and H. Wang, Applied Physics B, vol. 112, no. 4, pp. 521–527, (2013)

  • Share

Related Articles

  • Covesion Guide to PPLN: Introduction

    Read Article
  • Principles of nonlinear frequency conversion

    Read Article
  • How to Use PPLN

    Read Article
  • Example uses of PPLN

    Read Article

Get Updates

Subscribe to our e-newsletter for the latest information

By completing this form you agree to our Privacy Policy and Terms and Conditions. We will never pass your information to any third party. Learn more about our Privacy and Data Policy.

  • *
    By completing this form you are agreeing to our Privacy Policy and Terms & Conditions. We will never pass your information onto any 3rd parties. Learn more about our privacy and data policy.

Subscribe to our e-newsletter for the latest information

By completing this form you agree to our Privacy Policy and Terms and Conditions. We will never pass your information to any third party. Learn more about our Privacy and Data Policy.

BACK TO THE TOP
  • Careers
  • Products
  • Applications
  • Resources
  • Publications
  • Technical Guides
  • FAQs
  • News & Insights
  • About Us
  • Customers & Partners
  • International Distributors
Address
Unit F3, Adanac North, Adanac Drive, Nursling, Southampton, SO16 0BT, United Kingdom
  • Email
    sales@covesion.com
  • Telephone
    +44 (0)1794 521638
Find us
  • Privacy & Cookies
  • Website Terms of Use
  • Accessibility
  • Contact Us
  • Sitemap
© 2023 © 2021 Covesion Ltd. All Rights Reserved | Covesion UK Registration Number 06338847, VAT Number 943 1896 00 Website by ExtraMile Communications

Subscribe to our e-newsletter for the latest information

By completing this form you agree to our Privacy Policy and Terms and Conditions. We will never pass your information to any third party. Learn more about our Privacy and Data Policy.

  • By completing this form you are agreeing to our Privacy Policy and Terms & Conditions. We will never pass your information onto any 3rd parties. Learn more about our privacy and data policy.
Close