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Broadband Second Harmonic Generation using Fixed-Period Periodically Poled Lithium Niobate

Yongjoo Kim, Yijia Cai, Zhixin Liu

TL;DR

This work tackles the limited SHG bandwidth in standard PPLN caused by quasi-phase matching. It introduces a practical method: use a commercially available multi-period PPLN and angle-tune the crystal to sample multiple fixed poling periods, enabling broadband SHG without custom-fabricated devices. The authors demonstrate a 17.56 nm SHG bandwidth centered at 780 nm using an optical frequency comb around 1555 nm, achieving a 1.6x improvement over the no-angle case. The approach offers a straightforward path to broadband frequency doubling with standard PPLN, with potential impact on broadband frequency comb generation in visible and near-infrared regions.

Abstract

Periodically poled lithium niobate (PPLN) is a widely used nonlinear optical device for second harmonic generation (SHG). Despite its wide adoption in commercial systems, its bandwidth for SHG is fundamentally limited by the quasi-phase matching condition. This can be overcome by aperiodic or chirped PPLN structures; however, such devices are typically custom-fabricated and not readily available commercially. In this study, we investigate an alternative approach to achieving broadband SHG by using a standard PPLN crystal containing multiple fixed poling periods. Broadband operation is realized by angle tuning the crystal relative to input beam in free-space. The effect of angle tuning is examined over a range of incident angles, and an 1.6x enhancement in SHG bandwidth is demonstrated. These results suggest a practical and efficient strategy for broadband SHG using standard PPLN devices.

Broadband Second Harmonic Generation using Fixed-Period Periodically Poled Lithium Niobate

TL;DR

This work tackles the limited SHG bandwidth in standard PPLN caused by quasi-phase matching. It introduces a practical method: use a commercially available multi-period PPLN and angle-tune the crystal to sample multiple fixed poling periods, enabling broadband SHG without custom-fabricated devices. The authors demonstrate a 17.56 nm SHG bandwidth centered at 780 nm using an optical frequency comb around 1555 nm, achieving a 1.6x improvement over the no-angle case. The approach offers a straightforward path to broadband frequency doubling with standard PPLN, with potential impact on broadband frequency comb generation in visible and near-infrared regions.

Abstract

Periodically poled lithium niobate (PPLN) is a widely used nonlinear optical device for second harmonic generation (SHG). Despite its wide adoption in commercial systems, its bandwidth for SHG is fundamentally limited by the quasi-phase matching condition. This can be overcome by aperiodic or chirped PPLN structures; however, such devices are typically custom-fabricated and not readily available commercially. In this study, we investigate an alternative approach to achieving broadband SHG by using a standard PPLN crystal containing multiple fixed poling periods. Broadband operation is realized by angle tuning the crystal relative to input beam in free-space. The effect of angle tuning is examined over a range of incident angles, and an 1.6x enhancement in SHG bandwidth is demonstrated. These results suggest a practical and efficient strategy for broadband SHG using standard PPLN devices.
Paper Structure (4 sections, 3 figures)

This paper contains 4 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Conclusion

Figures (3)

  • Figure 1: Experimental setup. (a) A schematic of setup. (b) (Left) Optical layout of the free-space optics stage. (Right) Spot diagrams of 1500 nm (blue), 1550 nm (green), and 1600 nm (red) at the mid plane of the PPLN, confirming diffraction-limited performance of the optics design. The Airy radius (the black solid circle): 15.10 $\mu$m
  • Figure 2: PPLN configuration for angle tuning
  • Figure 3: (a) EDFA output spectrum (b) PPLN output spectra for tilt angles from 0 to 40$^\circ$