Ductile dicing of LiNbO ₃ ridge waveguide facets to achieve 0.29 nm surface roughness in single process step

Abstract

A single-step ductile dicing process capable of manufacturing optical quality facets in lithium niobate (LiNbO 3 ) ridge waveguides with an average surface roughness of 0.29 nm is reported. This result is comparable with surface roughnesses achieved by lapping and polishing and represents an order of magnitude improvement over the prior state of the art in LiNbO 3 waveguide facet dicing.Introduction: Dicing, a form of mechanical sawing, is commonly used in semiconductor and photonics processing to separate individual die from wafers. In most semiconductor processes where functional elements are accessed from the top of the die, dicing speed is more critical than quality and often performed in a 'brittle' regime where cracks and edge chipping on the order of tens of microns are common. In photonics, optical components are more often accessed (launched) from the side of the die and require a surface roughness of a few nanometres to prevent unwanted loss by scatter. Such roughness is typically achieved by laborious extra stages of lapping and polishing, in which individual components are manually handled through multiple mounting and cleaning steps.In recent work, we have demonstrated optical quality dicing of micron-order ridge waveguide structures in germanium telluride with a facet roughness of 3.0 nm (Sa) [1]. Here, we present results in lithium niobate (LiNbO 3 ), a popular nonlinear optical material for use in laser wavelength conversion [2][3][4][5][6]. A single-step ductile dicing process was developed to achieve sub-nanometre surface roughness on periodically poled LiNbO 3 (PPLN) facets, circumventing the need for lapping and polishing. This represents an order of magnitude improvement in surface roughness over previous publications in the field [5].

Zn-indiffused diced ridge waveguides in MgO:PPLN generating 1 watt 780 nm SHG at 70% efficiency

“…(2) this metallic layer is indiffused in a furnace with an oxygen atmosphere at around 950 • C, which is below the crystal's Curie temperature and ensures spontaneous domain inversion does not occur; (3) ridge waveguide structures are cut into the wafer using optical quality dicing to achieve sub-nanometer surface roughness [24][25][26]. The cut depth exceeds the indiffusion layer thickness (solid lines), ensuring the ridge waveguide geometry.…”

1.6-micron Er:YGG waveguide amplifiers

“…Ridge waveguides were fabricated on the PLD-grown Er:YGG films by ultra-precision dicing, utilizing ductile mode machining [11,12]. Dicing saws are often used to separate dies from wafers in the semiconductor industry.…”

Zn:MgO:PPLN Waveguides for Rb Cold Atom Trap Based Quantum Gravitometry in a CubeSat

“…These low insertion losses can be attributed to both the symmetric pump mode of the waveguides enabling efficient mode matching and low amounts of optical scattering from waveguide sidewall roughness. We have shown ductile dicing to produce an average surface roughness of 0.29 nm (Sa) on waveguide facets in a single processing step [4].We will present our latest work on ruggedised Zn:MgO:PPLN ridge waveguides and report on fabrication, insertion/waveguide loss, second harmonic generation spectra/efficiency, vibration and radiation testing of our waveguides for operation in space, and their use in the CASPA project.…”

“…These low insertion losses can be attributed to both the symmetric pump mode of the waveguides enabling efficient mode matching and low amounts of optical scattering from waveguide sidewall roughness. We have shown ductile dicing to produce an average surface roughness of 0.29 nm (Sa) on waveguide facets in a single processing step [4].…”