[Brief network outage provoked this far-too-long answer ;) ]

I'm pretty sure anyone who's dealt with fibre optics would disagree.

> Einstein

This likely refers to the behaviour of a classical beam of light in General Relativity passing through vacuum near a massive object sourcing an exterior Schwarzschild metric (e.g. a non-rotating but otherwise typical star).

There are redundant degrees of freedom in such a system. Normally one would set a coordinate condition or fix a gauge such that the beam of light is moving across star-centred/star-fixed coordinates [1], and one would say that the path it takes is curved compared to a beam that started parallel with the "curved" beam at a great distance from the star, and which never gets very close to the star.[2] Thus, the star's mass curves the beam of light, or equivalently, the beam(s) of light pass through curved spacetime (more technically they each follow a null geodesic of the Schwarzschild solution), with the near-to-star region of spacetime being more curved than the far-from-star region of spacetime.

In Special Relativity, spacetime is flat, so in vacuum beams of light that start parallel will always remain parallel.

Of course, when one introduces non-vacuum media (including hollow optical fibres with vacuum cores) or even a mirror, then a classical beam of light can be made to follow very different paths than it would in free space.

I think in this context that to the extent that Einstein would focus more on the non-vacuum behaviour of light and -- if we are talking about modern optical computing -- not consider the behaviour of a classical beam of light but rather a set of photons interacting with matter in a way in which quantum mechanical behaviour is not just observable but outright relevant. This would be directly analogous to considering the behaviour of fundamental charges in semiconductors in modern electronic computing, as quantum mechanical behaviour is often un-ignorable.

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[1] One could choose any arbitrary coordinate condition. For instance (this is something we can do in GR that is very non-Special Relativity-like) one could fix a set of coordinates on the notional leading edge of a (non-eternal) beam of light and treat the curvature of spacetime as a force acting on the beam, increasing in magnitude near the star, and pointing towards the star. While this is wholly legitimate -- the covariant formulation of the physics is identical -- one would generally take the position that the gauge discussed above is preferable as the behaviour of the light is simpler to describe (there's no need to consider the restoration of the behaviour of the beam of light as it leaves the region near the star or to consider any (pseudo-) force fields).

[2] Strictly speaking this is the path through spacetime, however, one could certainly consider deviation in the spacelike non-g_tt directions, and quantify this with the geodesic deviation equation applied between the two originally-parallel beams. In any event, a curved path through spacetime is shorter than a non-curved path, which is markedly different from Euclidean geometry in which a curved path through space is longer than a non-curved path.[3]

[3] Compare a path of a pulse of light through an optical microchip in a lab here on Earth, propagating from one edge of the chip to another. In the lab one will measure the non-straight path through curved waveguides or reflecting off mirrors as longer -- and taking longer -- than a straight path. But that's because the spacetime in the lab is so very nearly flat that it can't presently be distinguished from flat on the length scale of a (parallel-to-the-floor) microchip.