Edge-emitting Lasers Research Articles

Real-Time 1.25-Gb/s Transmission Over 50-m SI-POF Using a Green Laser Diode

A real-time 1.25-Gb/s transmission over a 50-m step-index plastic optical fiber (SI-POF) with -12.5-dBm sensitivity at bit error rate equal to 10-9 was achieved. The binary modulated signal was received and post-equalized using a fully integrated optical receiver. A green edge-emitting laser diode with 520 nm is used, which gives a lower attenuation over POF compared to the traditional 650-nm red laser. The launched optical power is 1 dBm, which ensures eye-safety (class 1 M) with 6-dB power margin.

7.3-Gb/s Transmission Over Microstructured Polymer Optical Fiber for In-Home Networks

Polymer optical fiber (POF) links typically have a limited bandwidth due to heavy modal dispersion. In order to achieve higher data throughput, advanced signal modulation formats and transceivers have been investigated for improved spectral efficiency. However, emerging new fibers such as microstructured POFs (mPOF) can further improve transmission performance by offering a larger bandwidth at lower loss. In this letter, we report multigigabit transmission over high-bandwidth mPOF. A gross data rate of 7.3 Gb/s is achieved after a transmission length of 50 m using discrete multitone modulation in an intensity-modulated direct-detection system using a directly modulated edge-emitting laser diode at 650 nm and an avalanche silicon photodiode. The achieved spectral efficiency is 3.4 bits/(s Hz) considering the uncoded net bit rate with bit-error rate below 10-3.

GaAs-Based High Power Diode Laser

High-power diode lasers based on GaAs semiconductor bars are well established as reliable and highly efficient laser sources. The device structure and stack technology of edge-emitting diode laser were presented briefly as well as the development of electro-optical conversion efficiency ,lifetime , power .The technology of ten-thousand –watt level high power diode laser was introduced as a new generation of laser processing equipment. In order to output high power, we utilized polarization coupling technology to couple two 808nm and 880nm laser diode stack together, and designed the optical system to expand and focus the beam, through the experiment; we realize the overall efficiency more than 90%, power output 1000W.

조명 및 무선통신이 동시에 가능한 가시광 송수신기에 관한 연구

본 연구는 조명 및 무선통신이 동시에 가능한 가시광 송수신기에 대해 가시광 통신 본연의 가시성, 무선 통신의 사용 편의성 그리고 고속의 통신 속도를 고려해 edge-emitting laser diode와 silicon photo diode를 기반으로한 고속 가시광 무선 송수신기를 구현하였다. 제안된 가시광 무선 송수신기는 120Mbit/s의 고속에서 양방향 전송이 가능하도록 설계되었으며 이때 발생하는 누화(crosstalk)를 방지하기 위한 방법으로 shielding 방식을 적용해 가시광 송수신기의 성능을 실험적으로 측정 분석하였다. 또 수신기의 시야각 확대를 위한 방법으로는 새로운 구조의 광학적 antenna를 적용해 광학적 antenna가 없는 두 개의 송수신기 사이의 전송링크 특성과 광학적 antenna를 사용한 두 개의 송수신기 사이의 전송링크 특성을 2차원 평면상에서 전송거리, 적용범위 그리고 기울임 정도를 변화시켜 실험과 시뮬레이션을 통해 그 성능을 비교 분석하였다. We investigated the performance of a visible light communication (VLC) transceiver applicable to both of illumination and wireless communication. we considered the visibility of VLC, the easy connection for wireless communication and high-speed transmission and implemented VLC transceiver based on edge-emitting laser diode and silicon photodiode. The proposed VLC transceiver is designated to operate in a full duplex mode at high speed of 120 Mbit/s. The shielding method that is employed as a means to reduce the light cross coupling effect inside the VLC transceiver is proposed and its performance is experimentally measured. We also applied optical antenna to have the larger angle of field of view (FOV) to novel structure of VLC transceiver and examined and analyzed their bit error rate performance, photometric result with respect to the transmission distance, the coverage range and the tilt degree as transmission link characteristic between two transceivers without optical antenna and with optical antenna.

Spectrally narrow mid-infrared optically pumped lasers with partial surface DBR

An optically pumped mid-infrared edge-emitting laser is described, in which a Distributed Bragg Reflector grating partially occupies the surface, and provides spectral narrowing in a high power device. A quasi-continuous-wave power of 3 Watts is obtained at 3.6 µm that is contained within a spectral width of 7 nm.

Superradiance dynamics in semiconductor laser diode structures

We analyze theoretically the superradiant emission (SR) in semiconductor edge-emitting laser heterostructures using InGaN/GaN heterostructure quantum well (QW) as a model system. The generation of superradiant pulses as short as 500 fs at peak powers of over 200 W has been predicted for InGaN/GaN heterostructure QWs with the peak emission in the blue/violet wavelength range. Numerical simulations based on semiclassical traveling wave Maxwell-Bloch equations predict building up of macroscopic coherences in the ensemble of electrons and holes during SR pulse formation. We show that SR is covered by the Ginzburg-Landau equation for a phase transition to macroscopically coherent state of matter. The presented theory is applicable to other semiconductor materials.

Ultralow Beam Divergence and Increased Lateral Brightness in Optically Pumped Midinfrared Laser

An optically pumped edge-emitting semiconductor laser emitting near 4.1 μm was designed with weak transverse mode confinement resulting in an exceptionally large transverse optical mode size. Consequently, a laser device is reported that exhibits a fast-axis divergence angle of ~4.2° full-width at half-maximum (FWHM). More notably, a large reduction of the lateral axis divergence is also observed as a result of the increased lateral coherency. The reduced confinement factor and differential gain serves to suppress lateral filamentation. Despite the higher threshold and lower power, a lateral divergence angle of ~3.2° FWHM and increased lateral brightness is achieved.

Semiconductor laser simulations using non-equilibrium Green’s functions

We present a novel method to simulate quantum well, edge-emitting semiconductor lasers in non-equilibrium steady-state. Our method is based on non-equilibrium Green’s functions approach which allows for a fully quantum mechanical description of carrier and photon dynamics. This microscopic approach significantly reduces the number of phenomenological parameters needed to simulate laser. General equations for photon Green’s functions and polarizations are derived as well as their coupling to electron Green’s functions through self-energies. Series of approximations are done to photon Green’s function to allow for efficient numerical approach. All equations are written in the non-orthogonal basis suitable for numerical calculations. As an example, the theory is applied to analyze Al0.2Ga0.8As/GaAs quantum well laser with the effective mass Hamiltonian. Major laser characteristics such as material and modal gain, threshold parameters, carrier and current densities were determined.

A radiation tolerant 5 Gb/s Laser Driver in 130 nm CMOS technology

The GigaBit Transceiver (GBT) project aims at the design of a radiation tolerant chip set for high speed optical data transmission. The chipset includes the GigaBit Laser Driver (GBLD), a radiation tolerant ASIC designed in a standard CMOS 130 nm technology. The GBLD is a laser driver designed to work to up to 5 Gb/s and capable to drive both Vertical Cavity Surface Emitting Lasers (VCSELs) and Edge Emitting Lasers (EELs). The GBLD can provide a modulation current up to 24 mA and a bias current up to 43 mA with the pre-emphasis function to compensate for external capacitive load.

Large spot size and low-divergence angle operation of 917-nm edge-emitting semiconductor laser with an asymmetric waveguide structure

GaInAs/AlGaAs comprehensive-strained three-quantum-well lasers with asymmetric waveguide are designed and optimized. With this design, the optical field in the transverse direction is extended, and a semiconductor laser with large spot is obtained. For a 300-μm cavity length and 100-μm aperture device under continuous wave (CW) operation, the measured vertical and horizontal far-field divergence angles are 12.2° and 3.0°, respectively. The slope efficiency is 0.44 W/A and the lasing wavelength is 917 nm. The equivalent transverse spot size is 3 \mu m for the fundamental transverse mode, which is a sufficiently large value for the purpose of coupling and manipulation of light.

Long-wavelength MBE grown GaInNAs quantum well laser emitting at 1270 nm

In this paper, we report on comprehensive theoretical optical properties analysis and experimental device electrical-optical characterization of long wavelength GaInNAs edge-emitting laser diode. The theoretical analysis demonstrates that a high quality GaInNAs active region and device design are devised, where high material gain near 1.3 μm and optimal optical mode confinement are calculated. Experimentally, room temperature lasing emission around 1.27 μm with threshold current densities of 670–810 A/cm2 is obtained from the fabricated broad area GaInNAs edge-emitting laser grown by molecular beam epitaxy technique.

Third-order photonic-crystal distributed-feedback quantum cascade lasers

We demonstrate room-temperature operation of broad-area edge-emitting photonic-crystal distributed-feedback quantum cascade lasers at λ∼4.6μm. The lasers use a weak-index perturbed third-order photonic-crystal lattice to control the optical mode in the wafer plane. Utilizing this coupling mechanism, the near-diffraction-limited beam quality with a far-field profile normal to the facet can be obtained. Single-mode operation with a signal-to-noise ratio of about 20dB is achieved in the temperature range of 85–290K. The single-facet output power is above 1W for a 55μm×2.5mm laser bar at 85K in pulsed mode.

Reduced auger recombination in mid-infrared semiconductor lasers

A quantum-design approach to reduce the Auger losses in λ = 2 μm InGaSb type-I quantum well edge-emitting lasers is reported. Experimentally realized structures show a ∼3 × reduction in the threshold, which results in 4.6 × lower Auger current loss at room temperature. This is equivalent to a carrier lifetime improvement of 5.7 × and represents about a 19-fold reduction in the equivalent “Auger coefficient.”

PERFORMANCE ENHANCEMENT OF InGaN-BASED LASER DIODES USING A STEP-GRADED AlxGa1-xN ELECTRON BLOCKING LAYER

A step-graded Al x Ga 1- x N electron blocking layer (EBL) is introduced to the InGaN -based edge-emitting blue-violet laser diode (LD) structure to suppress the undesired built-in interface polarization charges. When compared to a conventional abrupt Al 0.18 Ga 0.82 N EBL design, the step-graded Al x Ga 1- x N EBL design may help reduce the electron accumulation at the edge of the active region and hence improve the quantum efficiency in LD operation. The effects of the step-graded Al x Ga 1- x N EBL on the fabricated device performance are also investigated. LDs with the step-graded Al x Ga 1- x N EBL demonstrated significantly reduced threshold current density and increased slope efficiency under the continuous-wave operation.

High-Power Versatile Picosecond Pulse Generation from Mode-Locked Quantum-Dot Laser Diodes

This paper presents the current status of our research in mode-locked quantum-dot edge-emitting laser diodes, particularly highlighting the recent progress in spectral and temporal versatility of both monolithic and external-cavity laser configurations. Spectral versatility is demonstrated through broadband tunability and novel mode-locking regimes that involve distinct spectral bands, such as dual-wavelength mode-locking, and robust high-power wavelength bistability. Broad tunability of the pulse repetition rate is also demonstrated for an external-cavity mode-locked quantum-dot laser, revealing a nearly constant pulse peak power at different pulse repetition rates. High-energy and low-noise pulse generations are demonstrated for low-pulse repetition rates. These recent advances confirm the potential of quantum-dot lasers as versatile, compact, and low-cost sources of ultrashort pulses.

Toward Frequency-Domain Modeling of Mode Locking in Semiconductor Lasers

In this paper, a frequency-domain harmonic balance method is developed for solving the Maxwell-Bloch equations or simplified versions thereof for semiconductor lasers. The numerical algorithms are formulated to track stationary, periodic, and quasi-periodic steady-state behavior, including passive-mode-locking operation. The nonlinear set of equations with the Fourier coefficients and the fundamental angular frequency as unknowns is solved by a Newton method. Special focus is put on the derivation of a comprehensive bifurcation analysis tool including homotopy, continuation, stability analysis, bifurcation detection, and methods to handle branch switching. As an illustrative example of the method, nonlinear multimode characteristics of an edge-emitting laser are presented.

Toward 1550-nm GaAs-Based Lasers Using InAs/GaAs Quantum Dot Bilayers

By choice of appropriate growth conditions and optimization of the strain interactions between two closely stacked InAs/GaAs quantum dot (QD) layers, the emission wavelength of the QDs can be significantly extended, giving room-temperature emission from highly uniform QD ensembles in excess of 1500 nm. These QD bilayers are incorporated into edge-emitting laser structures and room-temperature ground-state lasing at 1420 nm and electroluminescence at 1515 nm are observed. Under high-bias conditions, asymmetric broadening of peaks in the laser gain spectra are observed, extending positive net modal gain from the devices to beyond 1500 nm, and the origin of this broadening is discussed.

Comprehensive electro-optical analysis of long wavelength GaInNAs edge-emitting laser diode

Comprehensive analysis of GaInNAs edge-emitting laser operating near 1300nm wavelength are made to underline the behavioural features of the proposed laser device, in view of the analytical investigation for various material and device electrical-optical parameters analysis such as band diagram, material gain, quantum well emission wavelength, optical wave and mode profiles, light-current-voltage characteristic, output mode spectrum, current distribution and far-field profile. The material analysis indicates that a high quality GaInNAs active region is designed, where high material gain and photoluminescence wavelength near 1.3μm are achieved. The device obtains low threshold current operation with lasing emission around 1.285μm.

Timing Jitter Characterization of a Free-Running SESAM Mode-locked VECSEL

We present timing jitter measurements of an InGaAs quantum well vertical external cavity surface emitting laser (VECSEL) passively mode locked with a quantum dot semiconductor saturable absorber mirror (SESAM) at 2-GHz repetition rate. It generates 53-mW average output power in 4.6-ps pulses at 953 nm. The laser housing was optimized for high mechanical stability to reduce acoustic noise. We use a fiber-coupled multimode 808-nm pump diode, which is mounted inside the laser housing. No active cavity length stabilization is employed. The phase noise of the free-running laser integrated over a bandwidth from 100 Hz to 1 MHz corresponds to an RMS timing jitter of ≈212 fs, which is lower than previously obtained for mode-locked VECSELs. This clearly confirms the superior noise performance expected from a high-Q-cavity semiconductor laser. In contrast to edge-emitting semiconductor diode lasers, the cavity mode is perpendicular to the quantum well gain layers, which minimizes complex dispersion and nonlinear dynamics.

Room-temperature low-threshold current-injection InGaAs quantum-dot microdisk lasers with single-mode emission

We fabricated current-injection InGaAs quantum-dot microdisk lasers with benzocyclobutene cladding in this work. The microdisk pedestal diameter is carefully designed to facilitate carrier injection and modal control. With this structure, low threshold current of 0.45 mA is achieved at room temperature from a device of 6.5 μm in diameter with single-mode emission from quantum-dot ground states. The negative characteristic temperature T0 of threshold current is observed between 80 K and 150 K. The transition temperature from negative T0 to positive T0 is 150 K which is higher than that of the edge-emitting lasers fabricated from the same wafer. This phenomenon indicates the lower loss level of our microdisk cavities. These microdisk lasers also show positive T0 significantly higher than that of the edge-emitting lasers from the same wafer.