A new structure optical switch with an p/n/p/n current blocking layer has been designed. In TIR(Total Internal Reflection) optical switches, efficient current confinement of the reflection region is required to obtain the large refractive index change. The current injection region of the new optical switch, which is embedded with Zn-diffusion and p/n/p/n current blocking layer, is formed at the intersection of two rib waveguides. This optical switch has the groove etched InGaAs cap layer. This optical switch is a self-aligned structure. The current spreading effect can be minimized using the p/n/p/n blocking layer, thus the injected current can be confined efficiently in the reflection region. And this structure can provide a large p-contact area, leading to small contact resistance.
The opeation current and the carrier lifetime has been calculated as a function of the cross angle of the optical switch in order to understand the parameter specifications of the optical switch. Following the calculated results, the operation current density is 2.73 kA/㎠ for total reflection in the optical switch with 6 ˚ crossing angle and InGaAsP(Eg=0.953eV, 0.8㎛ thick) core layer.
The 2×2 InGaAsP/InP optical switch with an p/n/p/n current blocking layer has been fabricated using MOCVD crystal growth, selective wet-etching, Zn-diffusion, and metallization. The width of the waveguide was 7㎛ while that in the intersecting region was controlled to be 17㎛. The total length of the switch was 3mm. The area of the current path is 250×3.5μ㎡. A very low operation current of 20 mA has been achieved for the first time with an 2×2 InGaAsP/InP TIR optical switch with 6 ˚ crossing angle. This operation current corresponds to a current density of 2.3 kA/㎠. This results are rather well agree with the calculated results. From the above results, it can be concluded that efficient current confinement is obtained using the p/n/p/n current blocking layer. The measured crosstalk was -8.2 dB for 0 mA and -9.7 dB for 20 mA, and the total insertion loss was about 20 dB. The 3-dB bandwidth of the optical switch was 59 MHz at the injection current of 20 mA. The extracted carrier-lifetime is 2.7 ns.