LASER-DIODES IN PHOTON NUMBER SQUEEZED STATE

A laser diode with an intrinsic layer as the space charge limited curr ent region is expected to emit a low noise (less than the shoe noise l evel) light. However, when one applies the intrinsic layer to the Base r diode, he faces severe difficulty. Because the intrinsic layer has a very high resistivity, the applied voltage to operate the laser diode is too large and causes catastrophic damage to the laser diode, Here we propose novel laser diodes which emit a low noise light, The first is an AlGaAs laser diode having an undoped layer between the active la yer and the cladding layer which acts as the space charge limited curr ent region, Fano factor, F-m, of this laser diode is 28% smaller than the shot noise level (standard quantum limit, Fm = 1) at 21 mA (output power, P-o = 20 mW). The second cane is an InGaAsP laser diode having two tunnel barrier layers whose bandgap energy is larger than that of the cladding layer, The region between the barriers acts as the space charge limited current region, Fano factor, F-m of this laser diode i s 47% smaller than the shot noise level at 21 mA (P-o = 10 mW). On the other hand, an AlGaAs laser diode with the two tunnel barrier layers has Fano factor, F-m which is 43% smaller than the shot noise level at 21 mA (Po = 20 mW). The calculated amplitude noise spectral densities of the latter two laser diodes are in good agreement with the calcula ted values from Langevin method. However the calculated amplitude nois e spectral density of the former laser diode does not agree with the c alculated value from Langevin method. This disagreement is also discus sed.