$$G \sim \left( \frac{\pi d}{\lambda} \right)^2$$$$G \sim 20 \times \log_{10}\left( \frac{\pi d}{\lambda} \right)$$
put gain equation in decibels to match free space equation
tl;dr: Considering Voyager-like conditions, going from 3.66 and 70 meter dishes to 0.5 and 5 meter telescopes, and from 3.6 cm to 1.55 micron wavelengths, we get an increase in received power of 10,000 times and an increase in data rate of 1,000 times!
I will leave further discussion of photon counting to a future question and answer session. Instead of photomultiplier tubes which work well for visible and just barely infrared (say 800 nm) what is in vogue now is superconducting nanowire position-sensitive photon detectors for the downlink receivers at least. See the images below for example (demonstrated by LADEE's Lunar Laser Communication Demonstration.
According to Spaceflight 101's Lunar Laser Communication Demonstration and ESA's LADEE efficiencies are in the Lunar XXX with LADEE)range of 1 bit per detected photon. It relies on precision timing of the photons and a bit more math than I'd like to learn today to show this.
So instead, I'll just quote @MarkAddler:
No, you don't need "at least some photons per data bit". 13 bits per photon has been demonstrated with laser communications.
You should read the full answer for context and to view the sources cited.
That's a (potential) increase in received data rate of 1,000 times!
Screenshots from Overview and Status of the Lunar Laser Communications Demonstration:
I will leave further discussion of photon counting to a future question and answer session. Instead of photomultiplier tubes which work well for visible and just barely infrared (say 800 nm) what is in vogue now is superconducting nanowire position-sensitive photon detectors for the downlink receivers at least. See the images below for example (demonstrated by the Lunar XXX with LADEE)
Screenshots from Overview and Status of the Lunar Laser Communications Demonstration:
tl;dr: Considering Voyager-like conditions, going from 3.66 and 70 meter dishes to 0.5 and 5 meter telescopes, and from 3.6 cm to 1.55 micron wavelengths, we get an increase in received power of 10,000 times and an increase in data rate of 1,000 times!
I will leave further discussion of photon counting to a future question and answer session. Instead of photomultiplier tubes which work well for visible and just barely infrared (say 800 nm) what is in vogue now is superconducting nanowire position-sensitive photon detectors for the downlink receivers at least. See the images below for example (demonstrated by LADEE's Lunar Laser Communication Demonstration.
According to Spaceflight 101's Lunar Laser Communication Demonstration and ESA's LADEE efficiencies are in the range of 1 bit per detected photon. It relies on precision timing of the photons and a bit more math than I'd like to learn today to show this.
So instead, I'll just quote @MarkAddler:
No, you don't need "at least some photons per data bit". 13 bits per photon has been demonstrated with laser communications.
You should read the full answer for context and to view the sources cited.
That's a (potential) increase in received data rate of 1,000 times!
Screenshots from Overview and Status of the Lunar Laser Communications Demonstration: