There are so many ways :)
1st Way:
string[] folders = Directory.GetDirectories(path, "*", SearchOption.TopDirectoryOnly);
string jsonString = JsonConvert.SerializeObject(folders);
2nd Way:
string[] folders = new DirectoryInfo(yourPath).GetDirectories().Select(d => d.Name).ToArray();
3rd Way:
string[] folders =
new DirectoryInfo(yourPath).GetDirectories().Select(delegate(DirectoryInfo di)
{
return di.Name;
}).ToArray();