Yes weather is still a challenge for space to ground communication. However there are numerous techniques being developped to handle this. One is to use adaptive optics similar to what is used by telescopes, a similar approach can be done digitally (like MIMO antennas in wireless). Now if the sky is overcast all these techniques don't help, however you only need relatively few ground stations to essentially get to above 99% availability.
That said the first rollout of optical comms is to intersatellite links. There the only issue is loss due to diffraction (and pointing etc., but that's a different discussion). Optics has a big advantage because diffraction is proportional to the inverse of wavelength, and the wavelength of light is several orders of magnitude smaller. This determines the size of the transmit and receive antennas/apertures needed, or the loss for a given size. For realistic parameters optics would have 30-50dB less loss which is translates directly to SNR and thus allows the much higher rates.
Can confirm this from my own experience.
Just elaborating on the availability requirements, the idea is that clouds aren't everywhere at the same time, so if you have enough in-space bandwidth, you can hop your traffic around the constellation until you reach a satellite that is above a cloud-free area.
Can orbital angular momentum modulation help here? I'm a deepnoob here but iirc some forms of polarisation are more or less affected by 'water in the sky' and masks.
That said the first rollout of optical comms is to intersatellite links. There the only issue is loss due to diffraction (and pointing etc., but that's a different discussion). Optics has a big advantage because diffraction is proportional to the inverse of wavelength, and the wavelength of light is several orders of magnitude smaller. This determines the size of the transmit and receive antennas/apertures needed, or the loss for a given size. For realistic parameters optics would have 30-50dB less loss which is translates directly to SNR and thus allows the much higher rates.
Source: Doing research in this area