Fabrication of an 8× 8 Multimode Interference Optical Coupler on a BK₇ Glass Substrate by Ion-Exchange

Based on the principle of the graded-index multimode interference (MMI), an 8×8 MMI optical coupler is designed and fabricated by using K⁺- Na⁺ ion-exchange technique on a BK₇ glass substrate. The performance of the device is tested. The output of optical coupler has a high uniformity of approximately 0.72dB.