Abstract

In integrated optical devices, the constituent waveguides invariably undergo bends and curvature, causing excess radiation losses. To utilize the maximum "real estate", the packing density of the components on a single substrate can be increased by decreasing the bending radii. This will increase the bending losses substantially if the mode size is not decreased. On the other hand, efficient fiber-guide coupling requires mode sizes In the range of 7-10μm for 1.3μm operating wavelength. The solution lies in tapered structures ^[1] Although fiber compatible waveguides in BK7 with fiber-guide thruput losses below 1 dB in a 20 mm long device have been reported^[2] by K⁺ - Na⁺ ion exchange, the maximum index change is limited to 0.009^[3] which does not permit small mode sizes at 1.3μm wavelength. Therefore the K⁺ - Na⁺ exchange does not allow fabrication of useful tapers. Recently Mahapatra and Connors^[4] reported thermal tapering of Ag⁺ - Na⁺ exchanged channel guides in soda-lime glass where a total thruput loss of 2.2 dB in a 7mm long device was achieved at a wavelength of 0.8μm with an excess loss of 0.4 dB in the 3 mm taper. This large excess loss appears to be caused by the nonadiabatic transition and the large thruput loss appears to be associated with the high silver concentration in the glass.

© 1989 Optical Society of America