Ultrafast Laser Inscription and ∼2 μm Laser Operation of Y-Branch Splitters in Monoclinic Crystals

Abstract

We report on the first active surface Y-branch waveguide in the ∼2 µm spectral range. Depressed-cladding rectangular-cross-section surface waveguides with a splitting ratio of 1 × 2 are fabricated by femtosecond direct laser writing in a thulium (Tm 3+ ) doped monoclinic double tungstate crystal. Confocal laser microscopy and µ-Raman spectroscopy reveal well preserved crystallinity of the waveguide core. Under high-brightness laser pumping at 0.8 µm, a simultaneous continuous-wave laser operation in both arms is achieved resulting in a total output power of 0.46 W at ∼1.84 µm with a slope efficiency of 40.6% and a laser threshold of 0.28 W. The laser output is linearly polarized and spatially multimode (TE 12 /TE 22 ) with a power splitting ratio between arms of 52.1/47.9%). The waveguide propagation losses at 1.84 µm are ∼1.6 dB/cm and the loss from the Y-junction is 0.1 dB. The fabricated waveguides represent a route towards advanced photonic micro-structures such as a Mach-Zehnder interferometer for bio-sensing at ∼2 µm.

Controllable Dynamic Single‐ and Dual‐Channel Graphene Q‐Switching in a Beam‐Splitter‐Type Channel Waveguide Laser

“…[1,2] In addition to straight channels, on-demand curveshaped channel WGs based on fs-DLW have been demonstrated and provide significant potential for diverse functional optical elements. [3,4] Beam-splitter-type (BS) WGs fabricated by fs-DLW are used not only in passive devices, [5,6] but also for continuous-wave (cw) laser operation in the 1 [7][8][9] and 2 μm [10] wavelength range. Such BS WG lasers providing multiple lasing output signals from a single pump could be utilized in quantum optics, optical sensing, and communication applications.…”

“…Beam‐splitter‐type (BS) WGs fabricated by fs‐DLW are used not only in passive devices, [ 5,6 ] but also for continuous‐wave (cw) laser operation in the 1 [ 7–9 ] and 2 µm [ 10 ] wavelength range. Such BS WG lasers providing multiple lasing output signals from a single pump could be utilized in quantum optics, optical sensing, and communication applications.…”

“…The present study is mainly focused on the validation of the striking dual-channel Q-switched operation and its controllability by a single pump source. Even though BS WG lasers have recently been recognized as an interesting approach with a strong potential, [7][8][9][10][11][12] the beam-splitting ratio as the parameter of paramount importance for BSs has previously been studied only for a particular splitting value and a widely tunable beam-splitting ratio in BS WG lasers has not been demonstrated so far.…”

Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances

“…Beyond a normal straight laser cavity, it is also possible to achieve efficient optical feedback for lasing oscillation in curved and branched cavity geometry owing to an enhanced optical gain of a waveguide laser. For example, in femtosecond laser-written 3D structures, compact waveguide lasers at 1 μm have been proposed in different functionalities, such as S-curved, 159,194 Y-branches, 97,180,208,216 1 × 2 and 1 × 4 beam splitting, 101 ring-shaped beam transformation, 100,132 and optical-lattice-like lasing 75 [Figs. 13(a)-13(e)].…”

“…Recently, MIR (∼2 μm) waveguide lasers, typically obtained from Tm 3þ -and Ho 3þ -doped materials, have attracted much attention from researchers. For a gain medium of Tm∶ KLuðWO 4 Þ 2 , efficient waveguide lasers at ∼1.8 μm operating both in the CW and Q-switched regimes have been reported by Kifle et al in various laser-written waveguide structures, such as Y-branch splitters, 208 surface cladding, 205 buried circular cladding, 166,206 and photonic-lattice-like cladding prototypes. 207 In addition, their group has demonstrated a low-loss (<0.1 dB∕cm) waveguide laser in a Tm 3þ ∶MgWO 4 crystal at ∼2.02 μm with a slope efficiency of 64.4%.…”