I don't think there is only one judge involved. This from Wikipedia:
When the court was founded, it was composed of seven
federal districtjudges appointed by the
Chief Justice of the United States, each serving a seven-year term, with one judge being appointed each year. In 2001, the
USA PATRIOT Act expanded the court from seven to eleven judges, and required that at least three of the Court's judges live within twenty miles (32 km) of the
District of Columbia. No judge may be appointed to this court more than once, and no judge may be appointed to both the Court of Review and the FISA court.
Chief Justice John Roberts has appointed all of the current judges.
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Edit:
Guess this comment requires a correction:
https://www.lawfareblog.com/how-fisa-court-really-works
"Applications under FISA are heard by a single FISC judge, and by
statute and
rule the government may not ask a second judge to consider an application for electronic surveillance or a physical search after one FISC judge has denied it. Instead, if a judge denies such an application, the government’s only statutory remedy is to take an appeal to the Foreign Intelligence Surveillance Court of Review."
(FISA is also known as FISC)