Aiyi Qi

Design and Analysis of Laser Diodes Based on the Longitudinal Photonic Band Crystal Concept for High Power and Narrow Vertical Divergence

High-power low-vertical-divergence laser diodes based on the longitudinal photonic band crystal (PBC) concept are investigated at a wavelength of 900 nm. The thicknesses of the layers in the longitudinal PBC waveguide are prudently optimized by mode analysis, and the lowest vertical far-field angle is found to be achieved by mode coupling. A self-consistent model is also utilized to study the device performances in detail, which shows excellent optical properties without obvious electronic performance degradation. In the experiment, continuous wave power up to 1 W/facet and vertical far-field angles of less than 10° (full-width at half-maximum) and ~50° (with 95% power content) are achieved simultaneously, with epitaxial wafer containing PBC layers of ten periods. The agreement among the design, simulation, and experiment shows a bright prospect for further reduced vertical divergence angle with high power output.

Lateral cavity photonic crystal surface-emitting laser with ultralow threshold

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.

Hybrid III–V-silicon single-mode laser with periodic microstructures

In this Letter, a III-V/silicon hybrid single-mode laser operating at C band for photonic integration circuit is presented. The InGaAlAs gain structure is bonded onto a patterned silicon-on insulator through wafer to wafer directly. The mode selected mechanism based on a hybrid III-V/silicon straight cavity with periodic microstructures is applied, which only need low cost i-line projection photolithography in the whole technological process. At room temperature, we obtain 0.62 mW output power in continuous-wave. The side mode suppression ratio of larger than 20 dB is obtained from experiments. [corrected].

A novel lateral cavity surface emitting laser with top sub-wavelength grating

We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer without the distributed Bragg reflector and it needs no wafer bonding. It exhibits a side mode suppression ratio of 23.0 dB and a high output power of 5.32 mW at 1552.44 nm. The specific single mode lasing agrees well with the band edge mode calculation of the grating. In 3D simulation, we observe obvious light output from the grating.

High-brightness diode laser arrays integrated with a phase shifter designed for single-lobe far-field pattern.

High-brightness 910 nm wavelength edge-emitting laser arrays integrated with a phase-shifter have been designed. Over 450 mW/facet with M2 <; 3 is achieved experimentally. Such devices show bright future for low cost and easy fabrication.

Lateral cavity photonic crystal surface emitting laser based on commercial epitaxial wafer

A lateral cavity photonic crystal surface emitting laser (LC-PCSEL) with airholes of cone-like shape etched near to the active layer is fabricated. It employs only a simple commercial epitaxial wafer without DBR and needs no wafer bonding technique. Surface emitting lasing action at 1575 nm with power of 1.8 mW is observed at room temperature, providing potential values for mass production of electrically driven PCSELs with low cost. Additionally, Fano resonance is utilized to analyze aperture equivalence of PC, and energy distribution in simplified laser structure is simulated to show oscillation and transmission characteristics of laser.

Lateral Cavity Photonic Crystal Surface Emitting Laser With Narrow Divergence Angle

We demonstrate an electrical injection lateral cavity photonic crystal surface emitting laser (LC-PCSEL) with a narrow divergence angle of less than 4.8° and nearly circular beam at communication wavelength. Different etching depth of PC air hole results in varied divergence angle for both PC element and PC array structure. Shallow-etching PC array structure has a great advantage in achieving a narrow divergence angle, nearly circular beam, high far-field intensity, and large fabrication tolerance. By rotating the device from 0° to 180°, the measured divergence angles are less than 4.8°. Therefore, a narrow divergence angle LC-PCSEL with circular beam is achieved due to six-fold rotational symmetry. This is a demonstration of the 2-D coherent oscillations, which reflects the nature of 2-D PC. Our demonstration promises to realize extensive applications in on-chip communication, and interconnects for surface emitting laser in communication wavelength.

The development of high sensitivity silicon avalanche photodiode array

The high sensitivity APD arrays have more and more application in the data transmission, LIDAR, remote sensing, medical image diagnosis system, environmental monitoring, military reconnaissance and etc. A preliminary study of Si APD was carried out, including the simulation of the photoelectric characteristics of Si APD, the experiment of Si APD single chip and array, and the test of Si APD. The APD gain is above 100, dark current is several nA, the rise time is nanosecond level. The 4×4, 1×16 Si APD arrays with high gain, quick response and low dark current have been made by means of available conventional semiconductor technology. The pulse width of the transient response under 1064 nm pulse LD illuminated is less than 100 ns at 100 V bias voltage which the pulse width is limited by the following amplification circuit. Some measures to improve the responsivity of APD at 1064nm is discussed. The next step is to develop the CMOS compatible high sensitivity APD array integrated with CMOS readout circuit.

Effect of ridge structure on electro-optical characteristics of ridge-waveguide lasers with low vertical divergence based on photonic crystal structure

Ridge-waveguide (RW) lasers based on photonic crystal structure were fabricated and measured. We investigated the effect of residual layer thickness (corresponding to etching depth) and ridge width on electro-optical characteristics of RW lasers. For deep-etching RW lasers, although lateral beam quality factor M2 is better than that of shallow-etching RW lasers, the other characteristics such as output power are much less than that of shallow-etching RW lasers. The calculating results indicate that RW lasers with ridge width w ≥ 8 μm will operate in mixing mode. The experimentally results of various ridge width RW lasers show that RW laser with 7 μm ridge operated in single mode over the whole measurement range and RW laser with 8 μm ridge change from single-mode operation to mixing-mode operation with the increasing of driving current. The device with 7-μm-wide ridge and 3-mm-long cavity obtain 2 W single-transverse-mode optical power and 59% maximum power conversion efficiency. The lateral beam quality factors M2 values are less than 1.7 over the whole measuring range.

High efficiency single transverse mode photonic band crystal lasers with low vertical divergence

High efficiency 980 nm longitudinal photonic band crystal (PBC) edge emitting laser diodes are designed and fabricated. The calculated results show that eight periods of Al0.1Ga0.9As and Al0.25Ga0.75As layer pairs can reduce the vertical far field divergence to 10.6° full width at half maximum (FWHM). The broad area (BA) lasers show a very high internal quantum efficiency ηi of 98% and low internal loss αi of 1.92 cm-1. Ridge waveguide (RW) lasers with 3 mm cavity length and 5um strip width provide 430 mW stable single transverse mode output at 500 mA injection current with power conversion efficiency (PCE) of 47% under continuous wave (CW) mode. A maximum PCE of 50% is obtained at the 300 mA injection current. A very low vertical far field divergence of 9.4° is obtained at 100 mA injection. At 500 mA injection, the vertical far field divergence increases to 11°, the beam quality factors M2 values are 1.707 in vertical direction and 1.769 in lateral direction.