Continuous wave waveguide laser at room temperature in Nd3+-doped Zn:LiNbO3

Abstract

This work reports continuous laser action at room temperature in LiNbO 3 :Nd 3ϩ channel waveguides, fabricated by Zn diffusion. The absorbed pump power at the threshold was 1.25 mW and a slope efficiency of 20% was obtained. With our available pump power the laser could emit up to 0.14 mW without exhibiting any photorefractive damage. © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1427426͔ Lithium niobate is an attractive and widely used active integrated-optical medium due to its excellent electro-optic, acousto-optic, and nonlinear properties. Rare-earth doped LiNbO 3 allows the fabrication of efficient waveguide lasers and amplifiers. 1 The integration of phase or amplitude modulators allows the construction in this material of many interesting systems, including mode-locked or Q-switched laser devices. 2 Neodymium doped LiNbO 3 can be operated in a four level scheme and it was the first rare-earth ion to lead to laser action in this host. 3,4 However, pump induced photorefractive damage limited the laser oscillation to pulsed operation with low efficiencies. A few years later, it was discovered that MgO codoping reduced the photorefractive damage, 5 and more efficient laser oscillation was reported in Nd:MgO:LiNbO 3 . 6,7 The following step in the use of this material has been the generation of devices in waveguide configuration. Several techniques have been used to produce low loss waveguides in LiNbO 3 such as proton exchange, titanium indiffusion or ion implantation, which have provided methods to produce efficient laser operation in Nd-doped LiNbO 3 waveguides. The first waveguide laser was demonstrated by using proton exchange in a Nd:MgO:LiNbO 3 substrate, 8 which was followed by ion implanted and titanium in-diffused efficient channel waveguide laser. 9,10 Nevertheless due to the high density of photons in the waveguide all these devices suffered from photorefractive damage, limiting the performance to pulsed operation or requiring the continuous annealing at high temperature. 11,12 It should be also mentioned that MgO codoping reduces the solubility of Nd ions in LiNbO 3 , then limiting the number of active ions in the host, and it also reduces the optical quality of the crystals. To date cw lasing operation at room temperature was only reported by Amin et al. 13,14 in the Nd-diffused Ti:LiNbO 3 waveguide, using Z-propagating waveguides and a -polarized pump beam in order to minimize the photorefractive damage. Unfortunately with this configuration not only is the pump efficiency reduced ͑the optimum pump in these materials is polarized͒ but also it is not possible to use the highest electro-optic LiNbO 3 coefficient r 33 to integrate active functions within the same optical chip.An alternative possibility in order to use transverse propagation ͑to the z axis͒ keeping a low photorefractive damage could be based in the fabrication of channel waveguides by Zn diffusion. This fabrication technique 15,16 produces waveguides that support both TE and TM modes, regardless of the crystal cut. Also, i...

Dual-polarization-pump CW laser operation in Nd3+:LiNbO3 channel waveguides fabricated by reverse proton exchange

“…In order to fit the experimental threshold (P th = 3 mW) and slope efficiency (/ = 2.8%) values, we find that the overall propagation losses are d % 2. This value is substantially higher than that estimated from the nominal reflectivity values of the cavity mirrors and the estimated waveguide attenuation (around 0.5 dB/cm), probably due to imperfect matching with the gain medium, as it has been previously reported when using butted mirrors cavities [20].…”

“…Substituting this value in Eq. 1, 2, together with the experimental spectroscopic parameters (s = 5 ls, g % 1, r e = 2.7 · 10 À19 cm 2 [18]) the threshold and slope efficiency can be calculated [20]. In order to fit the experimental threshold (P th = 3 mW) and slope efficiency (/ = 2.8%) values, we find that the overall propagation losses are d % 2.…”

“…It addition to this qualitative explanation, it is also possible to give quantitative prediction of the laser characteristics under TM pumping. In this case, pump and signal beams present a high overlap, and it is possible to describe the laser characteristics, such as laser pump threshold and slope efficiency, by using compact expressions [20] …”

Continuous-wave laser action at λ=1064.3 nm in proton- and carbon-implanted Nd:YAG waveguides

“…5,8 It is well known that when the Nd 3ϩ -doped waveguides are coupled to a resonant cavity, they can operate as a fourlevel scheme to lead laser action. 10 The inset of Fig. 2 shows a photograph, taken by a digital camera through an infrared viewer, of the output waveguide laser focused on a screen when the proton-implanted Nd:YAG waveguide was coupled to the resonant cavity ͑see Fig.…”

Red, green, and blue simultaneous generation in aperiodically poled Zn-diffused LiNbO3:Er3+/Yb3+ nonlinear channel waveguides

“…7,10,11 In the present work, the metal diffusion was performed following a two-step procedure ͑exchange and diffusion͒ [12][13][14] which preserves the initial wafer ferroelectric pattern. 15 The exchange process at 550°C for 2 h was performed followed by annealing in open atmosphere at 850°C for 4 h. These conditions produce a 4 m depth Gaussian index profile, with a maximum index change of 0.15% and 0.20% in the extraordinary and ordinary refractive indices, respectively.…”