A fiber optical circulator includes a first collimator and a second collimator sandwiching a circulator core therebetween. The first collimator and the second collimator respectively define Port 1 and Port 2 thereof, and the first collimator further defines Port 3 thereof. The circulator core includes a first crystal and a second crystal at two ends respectively confronting the first collimator and the second collimator aside. The circulator core further includes a first group of two half-wavelength waveplates and a first Faraday rotator, and second subassembly a second group of two half-wavelength waveplates and a second Faraday rotator. A third crystal is disposed between the first subassembly and the second subassembly wherein a backward light path from Port 2 to Port 3 passes the third crystal and is deflected by the third crystal toward the first collimator though total internal reflection.