Along with recent increase in integration density of LSIs, internal circuit patterns have been scaled-down further. This scaling-down causes reduction of cross sectional area of wiring transmitting signals, thereby increasing the wiring resistance, and moreover causes the space between the adjacent wirings to reduce, thereby increasing the inter-wiring capacitance.
As a result, the wiring delay (or propagation delay) time determined by the wiring resistance and the wiring capacitance increases, which makes it difficult to further increase the operating speed of LSIs. Furthermore, along with core multiplication and the three-dimensional integration of memory in the LSIs, signal propagation in a large amount of capacities between the cores or between the core and the memory has become essential. Thus, the signal propagation speed via electricity is the bottleneck against the higher performance of the LSIs.
As a technique for solving the problem with wiring delay caused along with the increase in density of LSIs, an optical interconnection (optical wiring) technique in which an electric signal is replaced by an optical signal has been attracting attention. The optical interconnection technique is a technique for propagating signals using an optical waveguide instead of using a metal wiring, and can be expected to achieve higher-speed operation because the aforementioned increase in wiring resistance or inter-wiring capacitance due to the scaling-down does not occur.
In a semiconductor laser (LD) used as a light source in the optical interconnection technique, an element conventionally used in optical communication has a width of several micrometers and a length of hundred micrometers, which is extremely huge as compared with a transistor or a wiring pitch of an LSI. This interrupts the replacement of electric wiring with optical interconnection. In view of this, a microring laser including a microring resonator as a compact light source has recently been attracting attention.
For achieving the optical interconnection on an LSI chip, it is necessary to form an optical transmission-reception system by integrating compactly a light-receiving element (reception part) together with a light-emitting element (transmission part) as a light source, and an optical waveguide (propagation part) in addition to a driver circuit and an amplifier circuit on the same chip.
Since a microring laser provides light rays rotating in different directions in a resonator, it is difficult to stably extract and transmit (or propagate) only one light ray as an output. Even though only one light ray can be extracted stably, the loss would increase by the amount of the other light ray.