Jeongkug Lee

Fiber-coupled surface-emitting photonic crystal band edge laser for biochemical sensor applications

We report on a refractive index sensor platform based on a surface-emitting photonic crystal (PC) Γ-point band edge laser (BEL). A simple butt-end fiber coupling makes the BEL system compact, while the translational symmetry of the PC pattern removes the necessity of fiber alignment. The laser wavelength shifts linearly to longer wavelengths as the refractive index of the environmental medium increases. Our BEL system had an index resolution of ∼10−3. Taking into account the alignment-free nature, as well as its ultracompactness and high fiber-coupled laser output, the BEL system is well suited to a label-free sensor platform for biochemical applications.

Free-Standing GaN-Based Photonic Crystal Band-Edge Laser

We report the fabrication of a GaN-based membrane-type photonic crystal (PC) band-edge laser (BEL) that requires a smaller PC active area than previous designs due to strong field confinement. A honeycomb-lattice PC was designed such that the Γ1 monopole band-edge mode fell within the emission band of InGaN quantum wells. The BEL exhibited pulsed lasing at room-temperature when optically pumped above its threshold pump energy density of ~ 15.5 mJ/cm2. Based on polarization angle analysis, we confirmed that the BEL indeed lased at the Γ1 monopole band-edge mode.

High-power and large-alignment-tolerance fiber coupling of honeycomb-lattice photonic crystal Γ-point band-edge laser

Butt-end fiber coupling is a compact and efficient scheme especially suitable for a surface-emitting photonic crystal (PC) band-edge laser. The honeycomb-lattice PC offers a relatively large intact area without air-holes, and therefore, a high optical gain. The use of a Γ-point band-edge mode allows vertical laser emission, yielding a fiber-coupled output power of more than 30 μW. The system is virtually alignment-free in the lateral directions; however, it exhibits oscillatory decay in the vertical direction, which can be significantly suppressed by using an angle-cleaved fiber tip.

Milliwatt-level fiber-coupled laser power from photonic crystal band-edge laser

We report unprecedentedly high output powers measured from large area two-dimensional square-lattice photonic-crystal band-edge lasers (BELs), patterned by holographic lithography. In order to ensure mechanical rigidity, the BELs were fabricated in an InP-based epilayer bonded onto a fused silica substrate beforehand. The BEL devices, employing the surface-emitting Γ-point monopole band-edge mode, provide a fiber-coupled single mode output power as high as 2.6 mW and an external differential quantum efficiency of ~4%. The results of a three-dimensional finite-difference time-domain simulation agree with the experimental observation that the large BELs are beneficial for achieving both high power output and high differential quantum efficiency.

Over 1 hour continuous-wave operation of photonic crystal lasers

We report on the long lifetime (>1 hour) of photonic crystal (PC) lasers under continuous-wave (CW) operation. For stable CW operation, we van-der-Waals-bonded our PC lasers to a novel submount structure consisting of MgF2-diamond bilayers on silicon substrate, which simultaneously ensures vertical mode confinement and efficient heat spread/dissipation. The combination of a Γ-point band-edge mode and butt-end fiber coupling yielded high CW fiber-coupled output power (~200 μW). The results demonstrate that the CW lifetime of PC lasers can be extended to the level for practical applications.

Band-edge lasers based on randomly mixed photonic crystals.

By employing two-dimensional InGaAsP photonic band-edge lasers, we have experimentally demonstrated that a random mixture of two different photonic crystals (PCs) possesses a new band structure that is intermediate to that of the two host PCs. The photonic band-edges shift monotonically, but with a strong bowing effect, as the mixed PC system is systematically transformed from one PC to the other. The experimental observations are in excellent agreement with finite-difference time-domain simulations and model calculations based on virtual-crystal approximation with compositional disorder effect included.

Photonic crystal digital alloys and their band structure properties

We investigated semi-disordered photonic crystals (PCs), digital alloys, and made thorough comparisons with their counterparts, random alloys. A set of diamond lattice PC digital alloys operating in a microwave regime were prepared by alternately stacking two kinds of sub-PC systems composed of alumina and silica spheres of the same size. Measured transmission spectra as well as calculated band structures revealed that when the digital alloy period is short, band-gaps of the digital alloys are practically the same as those of the random alloys. This study indicates that the concept of digital alloys holds for photons in PCs as well.

Anderson localizations and photonic band-tail states observed in compositionally disordered platform

The strength of photon localization in the band-tail states is determined by the degree of disorder and state energy. Anderson localization in random structures is an intriguing physical phenomenon, for which experimental verifications are far behind theoretical predictions. We report the first experimental confirmations of photonic band-tail states and a complete transition of Anderson localization. An optically activated photonic crystal alloy platform enables the acquisition of extensive experimental data exclusively on pure eigenstates, revealing direct evidence of band-tail states and Anderson localization transition within the band-tail states. Analyses of both experimental and simulated data lead to a comprehensive picture of photon localization that is highly consistent with theories by Anderson and others. We believe that our results provide a strong experimental foundation upon which both the fundamental understandings and application possibility of Anderson localization can be promoted significantly.

High Fiber-coupled Output Power from Continuous-wave Photonic Crystal Band-edge Laser

We demonstrate continuous-wave operation of surface-emitting photonic crystal band-edge laser wafer-bonded onto a substrate of efficient thermal dissipation. Using a butt-end fiber coupling scheme, high laser output power of ~200 ?W is achieved.

Lasing Actions of Extended and Localized Modes in Mixed Photonic Crystals

By employing band-edge laser platforms, we produced randomly mixed photonic crystals in binary format, a photonic analogy to mixed semiconductors. Lasing actions of both extended and localized modes were achieved using the mixed photonic crystals.