This web site (in German) is dedicated to the history of the Jews of the Niederlausitz region, which contains Calau:
You will find several pages about the history of the Jews in the region.
A list of names is found here:
The birth records up to September 1874 will be at the Brandesburgisches Landeshauptarchiv. The archives are closed due to COVID-19 and will not be opened before January. They can only be used in person, and the documents will have to be ordered in advance.
Those from October 1874 and later will be at the Archives of the Oberspreewald-Lausitz district.
Telefon: (03573) 8700
Fax: (03573) 870-1010
Andreas Schwab, Montreal, Canada