Abstract
Photonic integrated circuits (PICs) written with an ultrashort pulsed laser provide advantages in a range of applications, such as photon-based quantum information processing, where low insertion loss and low polarization dependence are critical concerns. Here we demonstrate the inscription of hybrid waveguides in fused silica at a pulse repetition rate of 1MHz that fulfill both these criteria. The mechanisms for propagation and coupling losses are identified and decoupled, with separate sections of the waveguide minimizing for each and an adiabatic mode conversion between the two. Moreover, differing sources of birefringence were revealed to be non-parallel for the waveguides, such that structures can be designed where these competing sources cancel to remove any polarization dependence.
Highlights
Photonic integrated circuits (PICs) that are employed in quantum information processing (QIP) can be categorized into two groups according to their fabrication techniques: direct written waveguide circuits [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] and waveguide circuits fabricated with complementary metal-oxide-semiconductor (CMOS) processing technology [18,19,20,21,22,23]
A drawback of ultrashort-pulsed laser written (UPLW) waveguide circuits is that the propagation losses have been typically higher than their CMOS-process based counterparts [24]
An approach to fabrication of waveguides with low propagation and insertion losses and low polarization dependence at the same time was demonstrated as a proof-ofprinciple
Summary
Photonic integrated circuits (PICs) that are employed in quantum information processing (QIP) can be categorized into two groups according to their fabrication techniques: direct written waveguide circuits [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] and waveguide circuits fabricated with complementary metal-oxide-semiconductor (CMOS) processing technology [18,19,20,21,22,23]. The work presented here focuses on single-mode laser written waveguides at wavelength of around 800 nm, based on the wavelength of the SPDC photon source [15,16,17, 32] of our intended QIP applications. Considering that Rayleigh scattering is a major loss mechanism [40], the propagation loss of a waveguide at 1550 nm wavelength tends to be significantly lower than that at around 800 nm Among those reported waveguides, polarization dependency of the waveguides has not been extensively investigated, Nasu et al have measured the polarization-dependent loss of the written waveguide [36]. We first investigated the relationship between the writing parameters and the properties of the straight waveguides written in pure fused silica, in term of propagation loss, insertion loss coupled from a single-mode fibre and polarization dependency. It is worth to mention that in this work only the single-scan writing approach was used, since the multiple-scan is intrinsically less efficient and in principle suffers from higher scattering loss due to the non-uniformity introduced by the separations of the different scanning passes
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