Quantum Cascade Photonic Crystal Surface-Emitting Laser With Lateral Coupling Cavity at 9.4 μ m

On-chip photonic crystal surface-emitting lasers

GaN-based 2-D photonic crystal (PC) surface-emitting lasers (PCSELs) with AlN/GaN distributed Bragg reflectors are fabricated and investigated. A clear threshold characteristic under the optical pumping at room temperature is observed at about 2.7 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with PC lattice constant of 234 nm. Above the threshold, only one dominant peak appears at 401.8 nm with a linewidth of 0.16 nm. The laser emission covers whole circular 2-D PC patterns of 50 mu m in diameter with a small divergence angle. The lasing wavelength emitted from 2-D PC lasers with different lattice constants occurs at the calculated band edges, showing different polarization angles due to the light diffracted in specific directions, corresponding exactly to Gamma -, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -, and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -directions in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> space. The PCSEL also shows a spontaneous emission coupling factor beta of 5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and a characteristic temperature of 148 K. Furthermore, the coupled-wave model in 2-D hexagonal lattice is applied to distinguish the discrepancy in threshold power and the corresponding coupling coefficient. The results show that the lasing actions within Gamma, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> , and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> modes have a substantial relation between the threshold energy density and the coupling coefficient.

By altering the lattice geometry of the photonic crystal (PhC) surface-emitting lasers (PCSELs), we tune the regular lasing band edges of quadratic dispersions to form a single accidental Dirac point of linear dispersion at the Brillouin zone center. This not only increases the mode spacing by orders of magnitude but also eliminates the distributed in-plane feedback to enable single-mode PCSELs of substantially larger area and thus substantially higher output power. The advantages of using accidental Dirac cones are systematically evaluated through two-dimensional in-plane calculations and confirmed by three-dimensional simulations of PhC slab devices.

We experimentally and theoretically investigate the optical properties of GaN-based photonic crystal surface emitting lasers( PCSELs). We discuss the effects of lattice constant,boundary shape,and lattice type of photonic crystal( PC) on lasing characteristics. The PCSEL structures are fabricated using the metal-organic chemical vapor deposition,the electron beam lithography,and inductively coupled plasma reactive ion etching technique. The optical properties of PCSEL which include the diffraction pattern,emission spectrum,divergence angle and so on are measured by the angular-resolved photoluminescence system. Meanwhile,the plane wave expansion and multiple scattering method( MSM) are used to calculate the band diagram and threshold gain of PCSELs,respectively. The results reveal that the lattice constant plays an important role in selection of lasing mode. Despite the lasing wavelength and linewidth of circular and hexagonal shapes PCSELs are almost the same,the threshold excitation energy density of circular shape PCSEL is 0. 3 mJ /cm2 smaller than that ofhexagonal PCSEL. The PCSEL with honeycomb lattice shows the lower excitation energy density of1. 6 mJ /cm2 and divergence angle of 1. 3°. In case of square lattice,the excitation energy density is twice as large as that of honeycomb lattice. The overall results show that the single-mode emission,low divergence angle,and so on can be produced from GaN-based PCSEL. On the other hand,the numerical results calculated using the MSM are in good agreement with experimental results. The MSM could be a fast and cost-effective approach for predicting the lasing characteristic. We believe that these contributions provide guidance for the development of GaN-based PCSEL.

All-semiconductor photonic crystal surface-emitting lasers (PCSELs) operating in CW mode at room temperature and coherently coupled arrays of these lasers are reviewed. These PCSELs are grown via MOVPE on GaAs substrates and include QW active elements and GaAs/InGaP photonic crystal (PC) layer situated above this active zone. Atoms of triangular shapes have been shown to increase optical power from the PCSEL but are also shown to result in a competition between lasing modes. Simulation shows that the energy splitting of lasing modes is smaller for triangular atoms, than for circles making high power single-mode devices difficult to achieve. In this work we experimentally investigate the effect of lateral optical feedback introduced by a facet cleave along one or two perpendicular PCSEL edges. This cleavage plane is misaligned to the PC resulting in a periodic variation of facet phase along the side of the device. Results confirm that a single cleave selects the lowest threshold 2D lasing mode, resulting in a ~20% reduction in threshold current and favours single-mode emission. The addition of a second cleave at right-angles to the first has no significant effect upon threshold current. The virgin device is shown to have a symmetric far-field (1 degree) whilst a single cleave produces a 1 degree divergence perpendicular to cleave and 5 degree parallel to cleave. The second orthogonal cleave results in the far field becoming symmetric again but with a divergence angle of 1 degree indicating that single-mode lasing is supported over a wider area.

Photonic crystal lasers can be realized either based on photonic bandgap defect mode or defect-free bandedge mode, while the bandgap is not essential for the latter. We review here defect-free bandedge mode based photonic crystal surface-emitting lasers (PCSELs) for on-chip integration. We first discuss ultra-thin membrane reflector vertical-cavity surface-emitting lasers (MR-VCSELs), where single layer photonic crystal slabs can be designed as a broadband membrane reflector. Later, we discuss another type of defect-free PCSELs where the lasing cavity is formed based on evanescent coupling of gain medium with the photonic crystal bandedge mode near bandedge. Cavity designs were carried out for the optimal modal overlap and high confinement factors. Lateral cavity size scaling was also investigated both theoretically and experimentally in PCSELs. Buried tunnel junction based InGaAsP quantum well heterostructures were also designed and incorporated into electrically injected PCSELs. Finally, discussions are given toward energy efficient lasers.

Photonic crystal surface-emitting lasers (PCSELs), which use a two-dimensional photonic crystal as the laser cavity, can achieve both high output powers and narrow beam divergence angles owing to single-mode lasing over a large area. High-speed, high-power, direct modulation of PCSELs is expected to realize compact and power-saving optical transmitters without bulky lens systems and fiber amplifiers for free-space optical communications. In this paper, we realize high-speed, high-power, free-space optical communication via directly modulated watt-class photonic-crystal surface-emitting lasers. We first numerically investigate the intrinsic (optical) and parasitic (electrical) frequency response characteristics of watt-class PCSELs with large lasing areas, and we show that several-GHz-class direct modulation is feasible even in watt-class PCSELs. Then, we fabricate a 500-µm-diameter PCSEL and simultaneously realize watt-class continuous-wave operation and several-GHz-class direct modulation. Finally, by directly modulating the developed PCSEL with a quadrature amplitude modulation (QAM) signal, we demonstrate free-space optical communication with over 10 Gbit/s high-speed transmission and virtual 5-km-class long-distance transmission even without using a transmitter lens.

A lateral cavity photonic crystal (PhC) surface-emitting laser is realized on a commercial epitaxial waveguide wafer without a distributed Bragg reflector first. Energy is coupled from the lateral resonance to surface-emitting light through the Γ band edge of the PhC with a square lattice. Electrically driven 1553.8 nm surface-emitting lasing action is observed at room temperature. The threshold current density of 667 A/cm2 is ultralow for the surface-emitting laser.

We report on the design of a photonic crystal surface emitting laser (PCSEL) with an all-semiconductor (InGaP/GaAs) photonic crystal suitable for very-large-area emission and high-power operation. Using coupled-wave theory for PCSELs we model infinite- and finite-size cavity PCSELs and show that a photonic crystal unit cell with square lattice periodicity and a rotated and stretched triangular feature is suitable for the realization of PCSELs with very large areas (1 mm&lt;L &lt; 3 mm for a square cavity of size L × L) while maintaining high mode discrimination between the fundamental laser mode and higher order cavity modes as well as high external efficiency. This was achieved by exploiting a single-lattice photonic crystal unit cell design that minimizes one-dimensional coupling in the photonic crystal, providing a promising alternative to double-lattice PCSELs.

We propose and demonstrate free-space optical (FSO) communication using photonic crystal surface-emitting lasers (PCSELs). Unlike other types of conventional semiconductor lasers, such as edge-emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs), PCSELs achieve much larger area single-mode coherent lasing, and this unique feature enables high-power (>watt) and lens-free operations at the same time. To date, these advantages have been recognized to be game changing, especially in light detection and ranging (LiDAR) and laser processing applications. In this work, we show that FSO communication can also benefit from these advantages of PCSELs; more specifically, conventional transmitters that include low-power semiconductor lasers, optical lenses, and fiber-based amplifiers could be replaced with a single PCSEL. Since fiber amplifiers usually consist of bulky components and have low conversion efficiencies, PCSELs can offer more space- and power-saving solutions. Moreover, the narrow beam divergence angles directly obtained from large-area single-mode PCSELs can also eliminate the need for lens systems on the transmitter side. To experimentally verify these potential advantages, we performed FSO transmission experiments based on PCSELs and successfully transmitted 480-MHz and 864-MHz orthogonal frequency division multiplexed (OFDM) signals over 1.1 m using a 500-μm PCSEL in a lens-free transmitter configuration. We believe that PCSELs open new possibilities and choices in FSO communication.

We propose and investigate a novel coherent laser array design based on laterally coupled photonic crystal surface-emitting lasers (PCSELs). As a new type of semiconductor laser technology, PCSELs have field confinement in a planar cavity and laser beam emission in the surface normal direction. By engineering lateral couplings between PCSELs with heterostructure photonic crystal designs, we can achieve coherent operations from an array of PCSELs. In this paper, we demonstrate coherent operation from a passively coupled PCSEL array design. We fabricated PCSEL array devices on a GaAs-based quantum well heterostructure at a target wavelength of 1040 nm. Experimental results show that the 2-by-2 PCSEL arrays have spectral linewidth of 0.14–0.22 nm. Beam combining performance was characterized by self-interference experiments. Similar coherency between the PCSEL array and single PCSEL device was observed. Our compact PCSEL array designs by passive lateral coupling have potential applications in fields of on-chip photonic computing, quantum, and information processing.

The device characteristics of GaSb-based mid-infrared (MIR) photonic-crystal (PC) surface-emitting lasers (SELs) were investigated with respect to depths of etched PC holes. Measurement of below-threshold emission spectra identifies the bandgap as well as band-edge modes. The bandgap separation, which is a function of feedback coupling, increases with increasing depth. From within, the Bragg frequencies and their detuning from lasing frequencies can be determined. Moreover, with increasing depth, the threshold pumping density decreases exponentially to a saturation level, which is assigned to minimum device modal gain of certain value. The relative threshold gain is then plotted as a function of normalized frequency detuning. The gain-detuning relationship of PCSELs is similar to that of one-dimensional (1D) distributed feedback (DFB) lasers.

InP-based InGaAs/GaAsSb ‘W’-type quantum well (QW) photonic-crystal (PC) surface- emitting lasers (SELs) of 2.2 μm wavelength range are fabricated and room-temperature lasing emissions by optical pumping are demonstrated for the first time. Photonic-crystal surface-emitting laser (PCSEL) devices are investigated in terms of PC parameters of etch depth, lattice period, and filling factor. The lasing emissions cover wavelengths from 2182 nm to 2253 nm. The temperature-dependent lasing characteristics are also studied in terms of lattice period. All PCSELs show consistent lasing wavelength shift against temperature at a rate of 0.17 nm/K. The characteristic temperatures of PCSELs are extracted and discussed with respect to wavelength detuning between QW gain peak and PC cavity resonance.

Photonic crystal (PhC) surface emitting lasers (PCSELs) utilizing Bragg diffraction mechanism have considerable amounts of publication during the past few years1,2,3,4. Such PhC lasers have many excellent advantages to attract the attention especially in controlling the specific lasing modes such as longitudinal and transverse modes, lasing phenomenon over the large area, and narrow divergence beam. Therefore, we fabricated the GaN-based PCSELs devices with AlN/GaN distributed Bragg reflectors (DBR) and analyzed the PhC laser characteristics caused by the surrounding PhC nanostructure. However, there were many theoretical methods calculating the photonic band diagrams and the distribution of electric or magnetic field of the PhC nanostructure in the past few years, such as 2-D plane wave expansion method (PWEM)2,5, finite difference time domain (FDTD)6,7, transfer matrix method, and multiple scattering method (MSM), etc. Many different advantages and limitations occur while using these methods. Therefore, in our case, we applied the MSM and PWEM to calculate the PhC threshold gain and photonic band diagram by using our PCSEL device structure.

We report experimental demonstration of a hybrid III-V/Si photonics crystal surface-emitting laser (PCSEL) based on membrane transfer printing technique. Single mode operation was observed with linewidth of 5 A and side-mode suppression ratio (SMSR) greater than 20 dB.