Kai Fukuda

Room-temperature continuous-wave operation of membrane distributed-reflector laser

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-bias current 10 Gbit/s direct modulation of GaInAsP/InP membrane DFB laser on silicon.

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/mA1/2 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.

High-modulation efficiency operation of GaInAsP/InP membrane distributed feedback laser on Si substrate

The direct modulation characteristics of a membrane distributed feedback (DFB) laser on a silicon substrate were investigated. Enhancement of the optical confinement factor in the membrane structure facilitates the fabrication of a strongly index-coupled (κ(I) = 1500 cm(-1)) DFB laser with the cavity length of 80 µm and a threshold current of 270 µA. Small-signal modulation measurements yielded a -3dB bandwidth of 9.5 GHz at 1.03-mA bias current, with modulation efficiency of 9.9 GHz/mA(1/2), which is, to the best of our knowledge, the highest value among those reported for DFB lasers.

High-Efficiency Operation of Membrane Distributed-Reflector Lasers on Silicon Substrate

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-<italic>μ</italic>m-long active section and 50-<italic>μ</italic>m-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- <italic>μ</italic>m-long distributed feedback section and 50-<italic>μ</italic>m-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-<italic>μ</italic>m-long and 61-<italic>μ</italic>m-long devices.

Integrated Optical Link on Si Substrate Using Membrane Distributed-Feedback Laser and p-i-n Photodiode

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 231-1 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.

10 Gbps operation of membrane DFB laser on silicon with record high modulation efficiency

We successfully demonstrated high-speed direct modulation of GaInAsP/InP membrane DFB laser on Si substrate for on-chip optical interconnection. The device showed threshold current of 0.21mA and single-mode operation with SMSR = 47dB. From small signal modulation, a record high modulation efficiency of 11GHz/mA1/2 was obtained. A 10 Gbps direct modulation with a bit-error-rate (BER) <; 10-9 was demonstrated at 1mA bias current.

High efficiency operation of membrane distributed-reflector laser with reduced index coupling coefficient structure

High efficiency operation of membrane distributed-reflector laser was demonstrated by both an improvement in differential quantum efficiency and a reduction of differential resistance. A threshold current of 0.44 mA, an external differential quantum efficiency for the front-side output of 36%, and a maximum power conversion efficiency of 14.6% were obtained for a device with a DFB section length of 40 μm.

Preliminary reliability test of lateral-current-injection GaInAsP/InP membrane distributed feedback laser on Si substrate fabricated by adhesive wafer bonding

A preliminary reliability test was performed for lateral-current-injection GaInAsP/InP membrane Distributed Feedback (DFB) lasers fabricated by multi-regrowth and adhesive wafer bonding. The measurement was conducted for lasers with two different types of p-side electrode: Ti/Au and Au/Zn/Au. The device with the Au/Zn/Au electrode, which had better current–voltage (I–V) characteristics, showed no degradation of differential quantum efficiency and threshold current after continuous aging for 310 h at a bias current density of 5 kA/cm2. This result indicates that the multi-regrowth and bonding process for the GaInAsP/InP membrane DFB laser will not impact the initial reliability.

90 °C continuous-wave operation of GaInAsP/InP membrane distributed-reflector laser on Si substrate

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, T 0, 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.

High-differential quantum efficiency operation of GaInAsP/InP membrane distributed-reflector laser on Si

The high-external differential quantum efficiency operation of a GaInAsP/InP membrane distributed-reflector laser bonded on a Si substrate was achieved by adopting a short cavity design and reducing the waveguide loss and differential resistance. A threshold current of 0.21 mA, an external differential quantum efficiency of 32% for the front-side output, and a power-conversion efficiency of 12% were obtained with a 32-µm distributed feedback section length, a 50-µm distributed-Bragg-reflector section, and a 0.8-µm stripe width. A side-mode suppression ratio of 41 dB was obtained at a bias current of 1 mA.