High Optical Output Power Research Articles

Single-mode high-power interband cascade lasers for mid-infrared absorption spectroscopy.

For high-sensitivity absorption spectroscopy, single-mode light sources capable of emitting high optical output power in the 3 to 5 µm wavelength range are vital. Here, we report on interband cascade lasers that emit 20 mW of optical power in a single spectral mode at room temperature and up to 40 mW at 0 °C using second-order laterally coupled Bragg gratings for distributed feedback. The lasers employ a double-ridge design with a narrow 3-µm-wide top ridge to confine the optical mode and a 9-µm-wide ridge for current confinement. The lasers were developed for an integrated cavity output spectroscopy instrument for stratospheric detection of hydrogen chloride at a wavelength of 3.3746 µm and emit at the target wavelength with more than 34 mW of single-mode power.

High optical output power in the UVA range of a frequency-doubled, strain-compensated AlGaInP-VECSEL

We present a maximum continuous-wave optical output power of 260 mW from an optically pumped, frequency-doubled vertical-external-cavity surface-emitting laser with wavelengths ranging from 325 to 332 nm. The device consists of a GaInP/AlGaInP multi-quantum-well structure grown using metal–organic vapour-phase epitaxy. We use strain compensation in the active region of the laser chip to for better performance at short wavelengths. In addition to wavelength-tuning results in the UVA region, power transfer measurements of the fundamental mode exceeding 1.2 W are presented.

Effect of the energy barrier in the base of the transistor laser on the recombination lifetime

Data are presented to quantify the effect of the conduction band energy barrier (ΔEC,B) in the base region of the transistor laser on the minority carrier transport dynamics, recombination lifetime in the base region, and frequency response of the device. A greater ΔEC,B results in lower transistor current gain (β) and higher optical output power, indicating increased carrier confinement and recombination in the base. For a device with ΔEC,B = 41 meV, the measured bias-dependent optical frequency response and subsequent data fitting yield a short recombination lifetime of 30 ps in the base and a small resonance peak of 1.5 dB. A device with ΔEC,B = 82 meV exhibits a longer recombination lifetime of 70 ps and a larger resonance peak of 4 dB.

Compact 100 Gb/s Ethernet Transmitter Optical Sub-Assembly Using Polarization Beam Combiner

A compact transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s Ethernet system with a long transmission distance of 40 km over single-mode fiber. The TOSA consists of electro-absorption modulator integrated distributed feedback laser diode arrays and a polarization beam combiner for wavelength multiplexing to obtain a high optical output power and a high dynamic extinction ratio. We confirmed that the TOSA successfully achieved an error-free four-lane ×25.8 Gb/s transmission, i.e., a total bit-rate of 100 Gb/s, over 40 km.

Large Signal Analysis of Distributed Feedback Laser with Three Types Spatial Chirped Grating and High Reflection: Anti Reflection Facets

In this paper, based on the coupled mode and carrier rate equations, the effects of different types of spatial chirped grating on a laser with distributed feedback (DFB), λ/4 phase shift, uniform injection current on the laser and high reflection in the rear facet were simulated and investigated for the first time. By using dynamic analysis with improved finite difference time domain (FDTD) numerical method in a single mode DFB laser with two way linear spatial chirped grating, the extinction ratio (ER) and high bit rate as a direct modulator and also making a high output optical power, were computed and analyzed. By adjusting the parameters such as spatial chirped grating, uniform injection current and the other physical parameters, the optical output power and side mode suppression ratio were obtained more than 28 mW and 80 dB respectively. Also by optimizing the physical parameters in DFB laser which is worked as a direct modulator, the bit rate and extinction ratio respectively 15 Gb and 50 dB were obtained. The obtained results from this simulation showed that using the reflection in the rear facet with a two way linear spatial chirped in the waveguide of the DFB laser improved output responses such as output optical power, side mode suppression ratio, (ER) and high bit rate in the direct modulator situation.

Single package directly modulated laser bidirectional optical subassembly using a modified mini-dual-in-line package for 10 Gbps passive optical networks

A bidirectional optical subassembly comprised of a 2.5 Gbps distributed feedback (DFB) laser diode (LD) directly modulated laser transmitter and a 10 Gbps positive intrinsic negative photodiode receiver was developed for an optical network unit of a 10 Gbps passive optical network. Here, a low-cost mini-dual-in-line package was modified to contain whole components of a transmitter and receiver in a single space while satisfying the requirements of 10 Gbps micro-device package standards. The transmitter was fabricated to achieve high optical output power by placing a micro aspheric lens very close to the DFB LD and reducing the thermal resistance between an LD chip and heat sink to bring down the DFB LD chip temperature. As a result, the transmitter output power was 3.5 dB higher than a conventional transistor outline can BOSA due to a high optical coupling efficiency of more than 70% and a low thermal resistance for heat dissipation. The receiver sensitivity was −21 dBm at a bit error rate of 10−3 and the sensitivity penalty of the receiver due to signal crosstalk was less than 0.3 dB.

Contact-geometry engineering in a circular light-emitting diode (LED) for improved electrical and optical performances

GaN light-emitting diodes (LEDs) based on circular mesa structure are fabricated and their electrical and optical characterizations are performed. The uniform current flow in the circular LED (C-LED) was conducted in the radial direction, from the n-type GaN island electrode at the center to the p-type GaN ring electrode around the perimeter. The symmetric electrode structuring substantially improved the electrical and optical performances. The operating voltage for C-LED at a reference current (100 mA) was 20.9% lower than that of a conventionally structured LED (CV-LED). Also, C-LED showed 19.4% higher optical output power than CV-LED.

Watt-class green-emitting laser modules using direct second harmonic generation of diode laser radiation

Large-area high-resolution displays, using a flying-spot to create the picture, require light sources in the red, green and blue wavelength range with a high optical output power and nearly diffraction limited beam. In this paper we present experimental results of high-brightness distributed Bragg reflector tapered diode lasers at 106x nm that can be used for single-pass second harmonic generation into the green. Based on these lasers we developed compact (2.5 cm3) green laser modules with an output power of 1W at 53x nm and an electro-optical conversion efficiency of about 5%. The output power stability is better than 2% and the wavelength stability is ±10 pm. The excellent beam quality Mδ2 < 2 of the green light allows operation in flying spot application systems. Furthermore, we estimate that our concept allows power scaling up to 2W by using nonlinear planar waveguide crystals and into the multi-watt level by spectral beam combining.

Tapered diode lasers and laser modules near 635nm with efficient fiber coupling for flying-spot display applications

Flying-spot displays require light sources in the red, green and blue with a high optical output power and nearly diffraction limited beams. In this paper we present experimental results of red-emitting, AlGaInP based, tapered diode lasers and their integration into diode laser modules. The laser modules emit a collimated, almost diffraction limited beam with an optical output power as high as 1W at a wavelength close to 635 nm. The tapered laser chips were designed with emphasis on achieving a good beam quality in vertical and lateral directions of a collimated beam. To test the suitability for flying-spot display applications, we performed fiber coupling experiments with a low mode number optical fiber with an etendue as low as 6 × 10−6 mm2 sr. A maximum transmission of 70% of the launched power behind the uncoated fiber as well as a usable power in excess of 580mW were measured.

Improved Electrical and Optical Properties of ITO/Ag/ITO Films by Using Electron Beam Irradiation and Their Application to Ultraviolet Light-Emitting Diode as Highly Transparent &lt;I&gt;p&lt;/I&gt;-Type Electrodes

We have investigated the effect of insertion of a Ag layer in ITO film as well as electron beam irradiation to the multilayer films on the electrical and optical properties of the ITO-based multilayer deposited by magnetron sputtering method at room temperature. Inserting a very thin Ag layer between ITO layers resulted in a significant decrease in sheet resistance and increased the optical band gap of the ITO/Ag/ITO multilayer to 4.35 eV, followed by a high transparency of approximately 80% at a wavelength of 375 nm. We have also fabricated ultraviolet light-emitting diodes (LED) by using the ITO/Ag/ITO p-type electrode with/without electron beam irradiation. The results show that the UV-LEDs having ITO/Ag/ITO p-electrode with electron beam irradiation produced 19% higher optical output power due to the low absorption of light in the p-type electrode.

Tunable Short Cavity 10-Gb/s 1550-nm DFB-Laser With Integrated Optical Amplifier and Taper

A novel tunable 1550-nm buried heterostructure (BH-) distributed feedback (DFB)-laser is presented consisting of a phase tuning section, a short cavity complex coupled DFB section, and an amplifier section with integrated optical taper. The device shows a narrow optical far-field, a high optical output power, up to 10-Gb/s direct modulation capability and a wavelength tuning range of several nanometers by varying the current in the phase section only.

Effects of a step-graded AlxGa1−xN electron blocking layer in InGaN-based laser diodes

A step-graded AlxGa1-xN electron blocking layer (EBL) is studied on InGaN-based laser diodes (LDs). Its efficacy on device performance is investigated with respect to stimulated emission properties, internal quantum efficiency, internal loss, and temperature-dependent characteristics. When compared to a LD structure with an abrupt Al0.18Ga0.82N EBL design, the LD with the step-graded AlxGa1-xN EBL design demonstrates lower threshold current density and higher slope efficiency. The threshold current density is reduced from 4.6 kA/cm2 to 2.5 kA/cm2 under pulsed-current operation and the corresponding slope efficiency is increased from 0.72 W/A to 1.03 W/A. The insertion of the step-graded AlxGa1−xN EBL leads to a dramatic enhancement in internal quantum efficiency from 0.60 to 0.92, while internal loss keeps at 9 ∼ 10 cm−1. The temperature-dependent measurement also shows that the step-graded AlxGa1−xN EBL can improve the thermal stability with reduced red-shift from 0.05 nm/K to 0.034 nm/K. This simple yet efficient structural design change provides an effective way to achieve high-performance InGaN-based LDs with higher optical-output power and lower electric-power consumption.

Light extraction enhancement from GaN‐based thin‐film LEDs grown on silicon after substrate removal using HNA solution

AbstractOne of the promising methods to obtain high optical output power from LEDs grown on Si is to eliminate the absorptive Si substrate. In this paper, we report how GaN‐based thin‐film LEDs grown on silicon (111) substrates by MOCVD were successfully transferred to a copper substrate by room‐temperature electroplating and how the original Si substrate was removed by HNA solution. After fabrication, the III‐nitride LED thin films showed no cracks or degradation. And the light output power of LEDs after Si removal increased by ∼ 30% compared with conventional ones before the Si removal. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

True green InGaN laser diodes

AbstractWe present true green InGaN ridge waveguide (RWG) laser diodes (LDs) at 520 nm on c‐plane GaN substrates in pulse operation at room temperature. Defect reduction in the In‐rich quantum wells by improving growth conditions of the epitaxial layers is the key parameter to demonstrate laser operation at this wavelength. Carrier lifetime measurements in combination with electroluminescence (EL) data and simulations of competing recombination processes below laser threshold confirm that the reduction of defects in the light emitting InGaN quantum wells is essential to realize true green nitride‐based LDs with low laser threshold of 125 mA and good slope efficiency of 220 mW/A for optical output power level up to 50 mW. Investigation of the lateral far field of 520 nm RWG LDs shows a perfect beam quality. The measured vertical far field shows a substrate mode due to leakage into the transparent GaN substrate supported by waveguide simulations with an additional internal loss of less than 1 cm−1. Mounted InGaN‐based ridge LDs at 500 nm demonstrate high optical output power of 35 mW in cw operation with good wall plug efficiency of 3.5% at room temperature.

Supermodes in Broad Ridge (Al,In)GaN Laser Diodes

Broad area (Al,In)GaN laser diodes (LDs) are suitable for high optical output power in the near UV to blue spectral range. But for ridge widths larger than a few micrometers, the occurrence of filamentation is well known. We present experimental evidence that the single filaments tend to be phase-locked with defined phase offset and build up a so called supermode. Depending on driving current a coherent or incoherent superposition of different supermodes can be observed, which has a significant impact on the corresponding lateral far-field pattern. By a simulated reconstruction of the lateral mode profile of the laser mode propagating in free space we retrieve the field and phase distribution of the laser mode in the waveguide. In this context the coupling mechanism is discussed and the mode behavior is compared to supermodes in GaAs laser diode arrays.

Novel monolithic integration scheme for high-speed electroabsorption modulators and semiconductor optical amplifiers using cascaded structure

A new monolithic integration scheme, namely cascaded-integration (CI), for improving high-speed optical modulation is proposed and demonstrated. High-speed electroabsorption modulators (EAMs) and semiconductor optical amplifiers (SOAs) are taken as the integrated elements of CI. This structure is based on an optical waveguide defined by cascading segmented EAMs with segmented SOAs, while high-impedance transmission lines (HITLs) are used for periodically interconnecting EAMs, forming a distributive optical re-amplification and re-modulation. Therefore, not only the optical modulation can be beneficial from SOA gain, but also high electrical reflection due to EAM low characteristic impedance can be greatly reduced. Two integration schemes, CI and conventional single-section (SS), with same total EAM- and SOA- lengths are fabricated and compared to examine the concept. Same modulation-depth against with EAM bias (up to 5V) as well as SOA injection current (up to 60mA) is found in both structures. In comparison with SS, a < 1dB extra optical-propagation loss in CI is measured due to multi-sections of electrical-isolation regions between EAMs and SOAs, suggesting no significant deterioration in CI on DC optical modulation efficiency. Lower than -12dB of electrical reflection from D.C. to 30GHz is observed in CI, better than -5dB reflection in SS for frequency of above 5GHz. Superior high-speed electrical properties in CI structure can thus lead to higher speed of electrical-to-optical (EO) response, where -3dB bandwidths are >30GHz and 13GHz for CI and SS respectively. Simulation results on electrical and EO response are quite consistent with measurement, confirming that CI can lower the driving power at high-speed regime, while the optical loss is still kept the same level. Taking such distributive advantage (CI) with optical gain, not only higher-speed modulation with high output optical power can be attained, but also the trade-off issue due to impedance mismatch can be released to reduce the driving power of modulator. Such kind of monolithic integration scheme also has potential for the applications of other high-speed optoelectronics devices.

8 W single-emitter InGaN laser in pulsed operation

We present the investigation of an optimized epitaxial layer structure in order to reach high optical output powers of several watts. The influence of an interlayer, which is located between the multiple quantum well layers and the electron blocking layer, is analysed carefully. For high current densities the leakage current density increases with increasing interlayer thickness. Correlating the leakage current density with the injection efficiency it is found that by decreasing the interlayer thickness constant injection efficiency for high current regions can be reached. This is essential for a linear laser characteristic up to high optical output power levels. Further enhancement can be achieved by enlarging the total waveguiding layer structure. As a result the optical power density in the resonator was decreased. With these improvements threshold current density and slope efficiency of 2.7 kA/cm 2 and 2.1 W/A can be achieved. The optical output power is increased to 8.7 W for a 20 μm broad single-emitter ridge-waveguide laser in pulsed operation.

InGaN Light-Emitting Diode With Quasi-Quantum-Dot-Shaped Active Layer Using SiCN Interfacial Layer

A quasi-quantum-dot (QQD)-shaped InGaN-GaN multilple-quantum-well light-emitting diode (LED) was achieved using a silicon carbon nitride (SiCN) interfacial layer. QQDs with ~100-nm diameter and ~4-nm height were uniformly formed inside the InGaN active layer due to strain and affinity difference between the InGaN and SiCN layer. The surface morphology and structural properties of QQD-LED were measured with atomic force microscopy, secondary ion mass spectrometry, and X-ray diffraction. Device performance of QQD-LEDs were evaluated and compared with normal LEDs. The QQD-LED showed ~15% higher photoluminescence intensity and ~10% higher optical output power

60 mW continuous-wave operation of InGaN laser diodes made by plasma-assisted molecular-beam epitaxy

We demonstrate continuous-wave operation at 411nm of InGaN multi-quantum-well laser diodes (LDs) made by plasma-assisted molecular-beam epitaxy (PAMBE). The threshold current density and voltage for these LDs are 4.2kA∕cm2 and 5.3V, respectively. High optical output power of 60mW is achieved. The LDs are fabricated on low-dislocation-density bulk GaN substrates, at growth conditions which resemble liquid-phase epitaxy. We show that use of such substrates eliminates spiral growth, which is the dominant growth mechanism for PAMBE on high-dislocation-density substrates. Therefore, PAMBE opens new perspectives for next generation of InGaN LDs.

1300-nm horizontal-cavity surface-emitting BH-DFB lasers for uncooled operation

We present a novel type of 1300-nm horizontal-cavity surface-emitting buried heterostructure distributed feedback (DFB) lasers showing high optical output power and uncooled direct modulation capability of 7.5 Gb/s. These lasers can be fabricated and tested using on-wafer techniques only, so the overall fabrication costs are considerably lower than with conventional edge-emitting DFB lasers.