Gyeong Cheol Park

Hybrid grating reflector with high reflectivity and broad bandwidth

We suggest a new type of grating reflector denoted hybrid grating (HG) which shows large reflectivity in a broad wavelength range and has a structure suitable for realizing a vertical cavity laser with ultra-small modal volume. The properties of the grating reflector are investigated numerically and explained. The HG consists of an un-patterned III-V layer and a Si grating. The III-V layer has a thickness comparable to the grating layer, introduces more guided mode resonances and significantly increases the bandwidth of the reflector compared to the well-known high-index-contrast grating (HCG). By using an active III-V layer, a laser can be realized where the gain region is integrated into the mirror itself.

Hybrid grating reflectors: Origin of ultrabroad stopband

Hybrid grating (HG) reflectors with a high-refractive-index cap layer added onto a high contrast grating (HCG) provide a high reflectance close to 100% over a broader wavelength range than HCGs. The combination of a cap layer and a grating layer brings a strong Fabry-Perot (FP) resonance as well as a weak guided mode (GM) resonance. Most of the reflected power results from the FP resonance, while the GM resonance plays a key role in achieving a reflectance close to 100% as well as broadening the stopband. An HG sample with 7 InGaAlAs quantum wells included in the cap layer has been fabricated by directly wafer-bonding a III-V cap layer onto a Si grating layer. Its reflection property has been characterized. This heterogeneously integrated HG reflector may allow for a hybrid III-V on Si laser to be thermally efficient, which has promising prospects for silicon photonics light sources and high-speed operation.

Polarization-Independent Wideband High-Index-Contrast Grating Mirror

Island-type two-dimensional high-index-contrast grating mirror based on a standard silicon-on-insulator wafer have been experimentally demonstrated. The measured spectra shows a bandwidth of ~192 nm with a reflectivity over 99% as well as polarization independence. Numerical simulations show that the designed mirror has large tolerance to fabrication errors.

III-V/SOI vertical cavity laser structure for 120 Gbit/s speed

Ultrashort-cavity structure for III-V/SOI vertical cavity laser with light output into a Si waveguide is proposed, enabling 17 fJ/bit efficiency or 120 Gbit/s speed. Experimentally, 27-GHz bandwidth is demonstrated at 3.5 times of threshold.

Ultrahigh-speed Si-integrated on-chip laser with tailored dynamic characteristics

For on-chip interconnects, an ideal light source should have an ultralow energy consumption per bandwidth (operating en-ergy) as well as sufficient output power for error-free detection. Nanocavity lasers have been considered the most ideal for smaller operating energy. However, they have a challenge in obtaining a sufficient output power. Here, as an alternative, we propose an ultrahigh-speed microcavity laser structure, based on a vertical cavity with a high-contrast grating (HCG) mirror for transverse magnetic (TM) polarisation. By using the TM HCG, a very small mode volume and an un-pumped compact optical feedback structure can be realised, which together tailor the frequency response function for achieving a very high speed at low injection currents. Furthermore, light can be emitted laterally into a Si waveguide. From an 1.54-μm optically-pumped laser, a 3-dB frequency of 27 GHz was obtained at a pumping level corresponding to sub-mA. Using measured 3-dB frequen-cies and calculated equivalent currents, the modulation current efficiency factor (MCEF) is estimated to be 42.1 GHz/mA1/2, which is superior among microcavity lasers. This shows a high potential for a very high speed at low injection currents or avery small heat generation at high bitrates, which are highly desirable for both on-chip and off-chip applications.

Hybrid III-V/SOI resonant cavity enhanced photodetector

A hybrid III-V/SOI resonant-cavity-enhanced photodetector (RCE-PD) structure comprising a high-contrast grating (HCG) reflector, a hybrid grating (HG) reflector, and an air cavity between them, has been proposed and investigated. In the proposed structure, a light absorbing material is integrated as part of the HG reflector, enabling a very compact vertical cavity. Numerical investigations show that a quantum efficiency close to 100 % and a detection linewidth of about 1 nm can be achieved, which are desirable for wavelength division multiplexing applications. Based on these results, a hybrid RCE-PD sample has been fabricated by heterogeneously integrating an InP-based material onto a silicon-on-insulator wafer and has been characterized, which shows a clear enhancement in photo-current at the designed wavelength. This indicates that the HG reflector provides a field enhancement sufficient for RCE-PD operation. In addition, a capability of feasibly selecting the detection wavelength during fabrication as well as a possibility of realizing silicon-integrated bidirectional transceivers are discussed.

III–V/SOI vertical cavity laser with in-plane output into a Si waveguide

We experimentally demonstrate an optically-pumped III-V-on-SOI hybrid vertical-cavity laser that outputs light into an in-plane Si waveguide, using CMOS-compatible processes. The laser operates ~1.49 μm with a side-mode suppression ratio of ~27 dB and has a similar threshold as long-wavelength VCSELs.

Hybrid III-V/SOI single-mode vertical-cavity laser with in-plane emission into a silicon waveguide

We report a III-V-on-SOI vertical-cavity laser emitting into an in-plane Si waveguide fabricated by using CMOS-compatible processes. The fabricated laser operates at 1.54 μm with a SMSR of 33 dB and a low threshold.

Hybrid Si-on-chip lasers with nano structures

For silicon photonics, specifically chip-level optical interconnects, an ultrahigh-speed low-energy-consuming laser that can be integrated onto a silicon (Si) wafer is an ideal element. Here, we report on a hybrid Si-on-chip micro-cavity laser structure with a potential of providing such characteristics. As shown in Fig. 1a, the laser structure is a vertical cavity, consisting of a high contrast grating (HCG) mirror formed in the Si layer of a Si-on-insulator wafer, an InP-based active material, and a dielectric distributed Bragg reflector [1-3]. ‘Hybrid’ reflects the heterogeneous integration of III-V material onto Si. In HCGs, the two propagating Bloch mode interplay with each other, providing a rich control over optical properties for vertical cavities as photonic crystals do for in-plane cavities. These include a small mode volume, control of in-plane group velocity, engineering dispersion, photonic hetero-structure [4], etc. These properties will be discussed in the talk.

Ultrabroadband hybrid III-V/SOI grating reflector for on-chip lasers

We report on a new type of III-V/SOI grating reflector with a broad stopband of 350 nm. This reflector has promising prospects for applications in high-speed III-V/SOI vertical cavity lasers with an improved heat dissipation capability.