On which dates did the episodes directed by TR Babu Subramaniam air?
CREATE TABLE "table1_17355820_1" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text
);
SELECT "original_air_date" FROM "table1_17355820_1" WHERE "directed_by"='TR Babu Subramaniam';