John E. Bowers

Gain-assisted hybrid silicon microring electro-absorption modulators

Energy consumption and device footprint are major limiting factors in scaling current optical interconnect architectures to reach multi-terabit per second data transmission. Hybrid integration of III-V on Si using a low-temperature O2 plasma-assisted wafer bonding technique is an attractive platform for integrating active elements on Si in a low optical loss and high density manner. Further scaling on individual devices could enable hybrid photonic integrated circuits with complex functionality and low power consumption. A microring resonator is widely regarded as an ideal structure for very compact passive and active devices, e.g., recently demonstrated hybrid Si microring lasers [3]. Although microring structures are wavelength sensitive, they have several advantages viz. small size, resonance-enhanced efficiency and no intrinsic reflections. We propose a novel microring modulator design by incorporating a gain and a loss section in the same microring cavity. Separately biasing the two sections best uses the properties of a microring resonator. We compare this design with two other techniques that were previously employed on III-V-based electro-absorption (EA) microring modulators. We also show the promise of the design in achieving high efficiency modulation with respect to some state of the art Si ring modulator results.

Study of Hybrid Silicon Microring Lasers with Undercut Active Region

We report a study of hybrid silicon microring lasers with undercut active region, showing threshold reduction and output power enhancement due to better gain/optical mode overlap. Negative effects from excessive undercutting are also discussed.

Development of quantum and interband cascade lasers on silicon (Conference Presentation)

We are developing midwave infrared (mid-IR) quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) bonded to silicon. The heterogeneous integration of mid-IR photonic devices with silicon promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and electronic technologies. The first Fabry-Perot QCLs on silicon were bonded to pre-patterned silicon-on-nitride-on-insulator (SONOI) substrates. Lateral tapers in the III-V mesas transferred the optical mode from the hybrid III-V/Si active region into the passive silicon waveguides, with feedback provided by reflections from both the III-V tapers and the polished passive silicon facets. Lasing was observed at uf06c uf0bb 4.8 uf06dm with threshold current densities as low as 1.6 kA/cm2 when operated in pulsed mode at T = 20 oC. The first mid-IR DFB lasers integrated on silicon employed gratings patterned into the silicon waveguides before bonding. Over 200 mW of pulsed power was generated at room temperature, and operated to 100 °C with T0 = 199 K. Threshold current densities were measured below 1 kA/cm2.The grating imposed considerable wavelength selectivity and 22 nm of thermal tuning, even though the emission was not spectrally pure. Ongoing research focuses on flip-chip bonding to improve heat sinking for continuous-wave operation, and arrayed waveguide gratings for beam combining. ICLs have also been bonded to silicon and the GaSb substrate has been chemically removed with an InAsSb etch-stop layer. Tapered ICL ridges designed for lasing in a hybrid III-V/Si mode have been processed above passive silicon waveguides patterned on SOI. A goal is to combine the power generated by arrays of QCLs and ICLs residing on the same chip into a single, high-quality output beam.

Defect-related degradation of III-V/Silicon 1.55 µm DBR laser diodes

This paper reports on an extensive investigation on the degradation mechanisms that may limit the long term reliability of heterogeneous III-V/Silicon DBR laser diodes for integrated telecommunication applications in the 1.55 μm window. The devices under test, aged for up to 500 hours under different bias conditions, showed a gradual variation of both optical (L-I) and electrical (I-V, C-V) characteristics. In particular, the laser diodes exhibited an increase in the threshold current, a decrease of the turn-on voltage and an increase in the apparent charge density within the space-charge region, which was extrapolated from C-V measurements. For longer stress times, these two latter processes were found to be well correlated with the worsening of the optical parameters, which suggests that degradation occurred due to an increase in the density of defects within the active region, with consequent decrease in the non-radiative (SRH) lifetime. This conclusion is also supported by the fact that during stress the apparent charge profiles indicated a re-distribution of charge within the junction. A preliminary investigation on the physical origin of the defects responsible for degradation was carried out by DLTS measurements, which revealed the presence of five different deep levels, with a main trap located around 0.43 eV above the valence band energy. This trap was found to be compatible with an interface defect located between the In0.53AlxGa0.47-xAs SCH region and the InP layer.

High performance quantum dot lasers epitaxially integrated on Si

Silicon photonics promises scalable manufacturing of integrated photonic devices through utilization of established CMOS processing techniques and facilities. Unfortunately, the silicon photonics platform lacks a viable light source, which has historically been overcome through heterogeneous integration techniques. To further improve economic viability, the platform must transition to direct epitaxy on Si to bypass the scaling limits imposed by the small sizes and high cost of III-V substrates in heterogeneous integration. InAs quantum dots have demonstrated themselves as the most promising candidate for achieving high performance light emitters epitaxially grown on Si. Using molecular beam epitaxy, we have grown quantum dot lasers composed of InAs dot-in-a-well active layers on industry-standard, on-axis (001) Si substrates. In this report, we utilized p-doping of the quantum dot active region to increase gain for improved dynamic performance and reliability. These devices have been subjected to accelerated aging conditions at 60°C and a bias multiple of twice threshold current density. After 2,750 hours of continuous aging, an extrapolated lifetime of more than 100,000 hours has been calculated.

Hybrid Silicon-AlGaInAs Lasers and Optical Modulators

A number of important breakthroughs in the past decade have focused attention on Si as a photonic platform. We review here recent progress on efforts to make lasers on or in silicon and on silicon optical modulators.