Poling-free integrated second-order nonlinear optics with evaporated organic thin films

Integrated second-order [χ (2) ] photonics underpins next-generation classical and quantum technologies, enabling applications ranging from frequency conversion and high-speed modulation to entangled photon generation. However, the field is now limited by a lack of materials that combine high nonlinear performance with scalable, CMOS-compatible fabrication. Vapor-deposited organic thin films having large χ (2) nonlinearities without electric field poling offer a versatile solution, theoretically enabling both standalone organic circuits and heterogeneous integration on passive platforms. Yet, the translation of these films into functional photonic devices has remained speculative. Here, we demonstrate phase-matched second-harmonic generation in strip-loaded waveguides by harnessing the film’s giant birefringence (Δ n ≈ −0.2) to match fundamental modes (TE 00 → TM 00 ), thereby maintaining high modal overlap. The resulting efficiency of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">η</mml:mi> <mml:mi>L</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>29</mml:mn> <mml:mo>%</mml:mo> <mml:msup> <mml:mi mathvariant="normal">W</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mtext>cm</mml:mtext> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> rivals that of strip-loaded waveguides on thin-film lithium niobate. These results establish spontaneously oriented organics as a promising material class for the integration of second-order nonlinear functionalities on arbitrary substrates.