In this paper, we report on the first ever demonstration of a continuous-wave operation of an injection-type membrane distributed-reflector (DR) laser at room temperature. A threshold current of 250 µA was obtained with a stripe width of 0.7 µm, a DFB region length of 30 µm, and a DBR region length of 90 µm. An external differential quantum efficiency of 11% with a light output ratio between the front and the rear of 6.7 was obtained at the front waveguide.

Low-power consumption directly-modulated lasers are a key device for on-chip optical interconnection. We fabricated a GaInAsP/InP membrane DFB laser that exhibited a low-threshold current of 0.21 mA and single-mode operation with a sub-mode suppression ratio of 47 dB at a bias current of 2 mA. A high modulation efficiency of 11 GHz/mA^1/2 was obtained. A 10 Gbit/s direct modulation using a non-return-to-zero 2³¹-1 pseudo-random bit sequence signal was performed with a bias current of 1 mA, which is the lowest bias current ever reported for direct modulation of a DFB laser. A bit-error rate of 10^-9 was successfully achieved.

The temperature dependence of a GaInAsP/InP membrane distributed-reflector laser bonded on a Si substrate — which showed a low threshold current (0.29 mA) and a relatively high differential quantum efficiency (23% from the front side) at 20 °C — was measured. A characteristic temperature of the threshold current, T0, of 84 K and a sub-mA threshold current operation up to 90 °C were obtained under a continuous-wave (CW) condition. Furthermore, single-mode operation up to 80 °C was also obtained.

To advance on-chip optical interconnections, membrane distributed-reflector (DR) lasers with low threshold current and high-efficiency operation at one side output were realized. First, a membrane distributed Bragg reflector (DBR) laser with 80-µm-long active section and 50-µm-long DBR section was fabricated to clarify the DBR reflectivity. An external differential quantum efficiency of 35% for the output from the front facet was obtained, and the DBR reflectivity was estimated to be 75%. Next, a membrane DR laser with 61-µm-long distributed feedback section and 50-µm-long DBR section was fabricated. A threshold current of 0.48 mA, external differential quantum efficiency from the front side waveguide of 26%, and light output ratio from the front to the rear sides of 13 were obtained. The lasing spectrum showed a single-mode operation with a side-mode suppression-ratio (SMSR) of 40 dB. Finally, small-signal direct modulation was carried out and a modulation current efficiency factor of 7.9 GHz/mA 1/2 and 7 GHz/mA 1/2 were, respectively, obtained for the 30-µm-long and 61-µm-long devices.

On-chip optical interconnection is a promising technology for wiring future large-scale integrated circuits, as a means to mitigate the considerable power dissipation of traditional wiring layers. Here, we fabricate an integrated optical link using a membrane distributed-feedback (DFB) laser and a p-i-n photodiode (PD) in a butt-jointed built-in coupling geometry. The optical link is formed on a Si substrate by benzocyclobutene bonding. The integrated DFB laser shows a low-threshold current of 0.48 mA. Light transmission between the DFB laser and the p-i-n PD is confirmed with static measurements of the optical link. The optical link has a 3-dB bandwidth of 11.3 GHz at a 2.73 mA DFB laser bias current and a -3 V p-i-n PD bias voltage. A data transmission experiment of the optical link is performed, using a nonreturn to zero, pseudorandom-bit-sequence with a word length of 2 31 -1 signals. With a DFB laser bias current of 2.5 mA, 10 Gbit/s data transmission with a bit-error-rate of 6 × 10 -7 is successfully achieved.