Neodymium-doped Lithium Niobate Research Articles

Electro-optically tunable single-frequency lasing from neodymium-doped lithium niobate microresonators.

Tunable light sources are a key enabling technology for many applications such as ranging, spectroscopy, optical coherence tomography, digital imaging and interferometry. For miniaturized laser devices, whispering gallery resonator lasers are a well-suited platform, offering low thresholds and small linewidths, however, many realizations suffer from the lack of reliable tuning. Rare-earth ion-doped lithium niobate offers a way to solve this issue. Here we present a single-frequency laser based on a neodymium-doped lithium niobate whispering gallery mode resonator that is tuned via the linear electro-optic effect. Using a special geometry, we suppress higher-order transverse modes and hence ensure single-mode operation. With an applied voltage of just 68 V, we achieve a tuning range of 3.5 GHz. The lasing frequency can also be modulated with a triangular control signal. The freely running system provides a frequency and power stability of better than Δ ν=20MHz and 6 %, respectively, for a 30-minute period. This concept is suitable for full integration with existing photonic platforms based on lithium niobate.

Quasi-phase-matched self-pumped optical parametric oscillation in a micro-resonator.

Lasing and self-pumped optical parametric oscillation (self-OPO) are achieved in a high-Q whispering-gallery-mode micro-resonator, made of neodymium-doped lithium niobate. A laser process providing 5 mW output power at 1.08 μm wavelength is sufficient to pump a self-OPO process within the same high-Q cavity. At 6 mW lasing output power, the sum of signal and idler output powers exceeds 1.2 mW. The wavelength of the generated light ranges from 1.5 to 3.8 μm. Phase matching is provided by a radial quasi-phase-matching structure, which is generated by a current-controlled calligraphic poling technique. To the best of our knowledge, this is the first demonstration of a quasi-phase-matched self-pumped nonlinear optical process in a micro-resonator, as well as the first self-OPO in a micro-resonator. The concept bears the potential for a highly integrated and wavelength-tunable coherent light source at low cost.

Self-frequency doubling in a laser-active whispering-gallery resonator.

Lasing and self-frequency doubling are achieved in a millimeter-sized laser-active whispering-gallery resonator made of neodymium-doped lithium niobate. A low-cost 808-nm laser diode without external frequency stabilization is sufficient to pump the neodymium ions. Laser oscillation around 1.08μm drives a frequency-doubling process within the same cavity providing green light. The electrical-optical efficiency of the system reaches up to 2×10-4. To the best of our knowledge, this is the first demonstration of combining lasing and χ(2) frequency conversion in a single high-Q whispering-gallery resonator. This approach is general and can be applied to other materials and other nonlinear optical processes.

Characterization of active waveguides fabricated by ultralow-fluence swift heavy ion irradiation in lithium niobate crystals

We report on the fabrication of neodymium-doped lithium niobate active planar waveguides based on the generation of non-overlapping nano-tracks by ultralow-fluence swift heavy ions. A combination of confocal luminescence, Raman and surface second harmonic investigations have evidenced the simultaneous presence of partial amorphization, damage and local compression of the lithium niobate network along the ion path, with these effects being at the basis of the refractive index modification. The potential application of the obtained waveguides in multi-functional laser devices has been discussed.

Ultraviolet nanosecond laser-assisted micro-modifications in lithium niobate monitored by Nd3+ luminescence

This work reports on the microstructural modifications produced by nanosecond ultraviolet ablation in neodymium doped lithium niobate crystals. The neodymium ions have been used as optical probes to determine the extension and nature of the modified bulk material. From micro-luminescence experiments we have been able to determine the spatial distribution of the UV ablation induced material densification, local disorder and defect creation. Results have been compared to those previously obtained from femtosecond irradiated lithium niobate crystals.

Self-optical parametric oscillation in periodically poled neodymium-doped lithium niobate

Self-optical parametric oscillation is demonstrated for the first time to our knowledge in a periodically poled neodymium-doped lithium niobate (Nd:PPLN) crystal. The crystal is pumped by a cw Ti:sapphire laser at 813.5 nm. The Nd(3+) ions absorb the 813.5-nm radiation to generate 1084-nm laser oscillation. The internally Q switched 1084-nm radiation pumps the periodically poled lithium niobate host matrix to generate optical parametric oscillation at 1.55 and 3.6 microm . Up to 24% conversion efficiency from laser to signal is observed.

Luminescence from chromium–neodymium-doped lithium niobate

Luminescence from chromium–neodymium-doped lithium niobate (LiNbO 3) was experimentally measured to determine the degree of non-radiative energy transfer between chromium and neodymium ions. Evidence is presented for two different time constants for emission from chromium ions in the material, indicating that non-radiative transfer does occur. Differences between quasi-continuous pumping and pulsed excitation are discussed.

Optical waveguide fabrication in neodymium-doped lithium niobate

We report the realisation of high-quality, proton-exchanged optical waveguide structures in neodymium-doped lithium niobate. Measurements indicate that the presence of the neodymium does not alter the proton exchange rate, and the presence of the protons does not affect the emission and absorption spectra of the bulk material significantly. Such waveguides will permit the realisation of highly efficient semiconductor laser pumped amplifiers and laser structures integrated with electro-optic and/or acousto-optic elements.

CW laser oscillations and tuning characteristics of neodymium-doped lithium niobate crystals

We have obtained over 250 mW of CW laser emission at 1084 nm from a neodymium-doped single crystal of lithium niobate when the rod was end pumped by 1 W from a Kr+ laser at 752 nm. Thresholds of less than 30 mW are obtained with a weak output coupler, rising to 220 mW with a 35 percent transmitting output mirror. The laser could be tuned over 3 nm around the peak at 1084.4 nm with a thin, uncoated etalon in the cavity.

Laser healing of thermally induced optical damage and its relationship with the spectral characteristics of neodymium-doped lithium niobate

An investigation was made of the polarization dependence of the kinetics of laser healing of thermally induced optical damage (TIOD) in LiNbO3:Nd crystals and its relationship with the polarized absorption spectra. It was observed that the kinetics of healing of TIOD differed when the crystal was illuminated by extraordinarily and ordinarily polarized beams. The nature of the healing of TIOD is discussed. Some features of the polarization-dependent absorption spectra of crystals with and without optical inhomogeneities are considered.