Sean Coleman

High-temperature continuous-wave operation of low power consumption single-mode distributed-feedback quantum-cascade lasers at λ∼5.2 μm

Continuous-wave operation of a distributed-feedback quantum-cascade laser in a packaged module is demonstrated up to a heat sink temperature of 80 °C with an output power of greater than 10 mW and a power consumption of less than 3.8 W. Single longitudinal mode emission near 5.24 μm is observed over a temperature range from 10 to 80 °C with a side mode suppression ratio greater than 20 dB limited by the instrumentation. A single spatial mode is determined with far-field pattern measurement. The above performance is achieved using a buried heterostructure and a small cavity of 7.6 μm×1.5 mm.

Carrier Transport in InGaN MQWs of Aquamarine- and Green-Laser Diodes

We studied experimentally and theoretically the substrate-orientation impact on carrier transport and capture in InGaN multiple quantum well (MQW) laser diodes (LDs) with emission in the aquamarine-green spectral range. A new simulation approach was developed to analyze this behavior of LEDs and LDs emitting at these wavelengths. We show that due to deep carrier confinement, the thermal escape from a QW in such devices is negligible. The carrier distribution among QWs is therefore determined by the carrier transport and capture rates. We also show that the ballistic transport mechanism is dominant in this type of MQW active region. In c-plane structures, this mechanism is tunneling-assisted, and therefore, the transport is much slower than in nonpolar and semipolar structures. Because of this, a strong carrier injection nonuniformity observed in c-plane LDs, causes the threshold current increase when number of QWs is >;2. This effect is not observed in semipolar LDs because the carrier transport rate is faster than the capture rate.

High-power high-Modulation-speed 1060-nm DBR lasers for Green-light emission

We report on the static and dynamic performance of high-power and high-modulation-speed 1060-nm distributed Bragg reflector (DBR) lasers for green-light emission by second-harmonic generation. Single-wavelength power of 387 mW at 1060-nm wavelength and green power as high as 99.5 mW were achieved. A thermally induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. Measured rise-fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the lasers suitable for >50-MHz green-light modulation applications

304 mW green light emission by frequency doubling of a high-power 1060-nm DBR semiconductor laser diode

We report for the first time, to the best of our knowledge, 304 mW green light emission generated by frequency doubling of the output from a 1060-nm DBR semiconductor laser using a periodically poled MgO-doped lithium niobate waveguide in a compact single-pass configuration. The excellent performance of these DBR lasers, including a kink-free power greater than 750 mW, single-spatial-mode output beam, single-wavelength emission spectra, and high wavelength-tuning efficiency, plays an important role in the generation of high-power green light.

Room Temperature CW Operation of Mid-IR Distributed Feedback Quantum Cascade Lasers for

We present the design and the performance of midinfrared distributed feedback (DFB) quantum cascade lasers (QCLs) made of strain balanced Ga_xIn_1-xAs/Al_yIn_1-yAs material on InP substrates for sensing CO₂, N₂O, and NO in the middle wavelength range of mid-IR from 4 to 6 μm. We present the performances of our DFB QCLs at three different aspects: high power, low threshold power consumption, and wide wavelength coverage. We demonstrated a continuous wave (CW) DFB QCL with an output power of 220mW at 20°C, a CW DFB QCL with low threshold voltage of 8V and low-divergent far-field angles of 27.5° × 32.9° by reducing the number of quantum cascaded stages, a CW DFB QCL with a low threshold power consumption of 0.7W by reducing doping density in the active core, and DFB QCLs wide wavelength coverage of 325 cm^-1, 16.9% of center wavelength at 5.2 μm, within one wafer by changing the grating period. 12 DFB QCL chips have being aged for 3000 h under 25°C and a constant quasi-CW current of 0.37 A. No decrease in power was observed.

\hbox{CO}_{2}, \hbox{N}_{2}

We studied characteristic temperatures (T0) of laser diodes (LDs) grown on semipolar GaN substrates and emitting in the green spectral range. For several semipolar laser designs with and without an electron blocking layer (EBL), T0 remains higher (161–246 K) than that typically reported for c-plane green LDs. The slope efficiency measured in the pulsed regime is nearly temperature independent. These observations indicate that T0 is mainly determined by intrinsic quantum well (QW) properties, such as higher differential gain. A high T0 and a sufficient injection efficiency allow the achievement of a continuous wave output power of 60 mW for an LD without an EBL.

O, and NO Gas Sensing

We report on the design, fabrication and performance of high-power and high-modulation-speed 1060-nm DBR lasers for green-light emission by second harmonic generation. Single-spatial-mode and single-wavelength power more than 450 mW of 1060-nm wavelength was achieved with a 3-section DBR laser with non-absorbing DBR and phase sections created by an impurity-free quantum-well intermixing technique. A thermally-induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. The green power as high as 104.6 mW was demonstrated by coupling the DBR laser output to a second-harmonic-generation waveguide. Measured rise/fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the DBR lasers suitable for >=50-MHz green-light-modulation applications. The detrimental thermally-induced patterning effect and a differential-phase modulation scheme as a solution are discussed.

60 mW Pulsed and Continuous Wave Operation of GaN-Based Semipolar Green Laser with Characteristic Temperature of 190 K

We present the design and the performance of mid-infrared distributed feedback quantum cascade lasers made of strain-balanced GaxIn1-xAs/AlyIn1-yAs material on InP substrates for wavelength near 5 μm. By changing the grating period within one wafer, we demonstrated wide wavelength coverage of 325 and 282 cm-1 (16.3% and 14.1% of the center wavelength) under room temperature pulsed and continuous wave (CW) operation, respectively. The variation of pulsed and CW laser performance as a function of wavelength detuning from the gain peak was studied and correlated to the amplified spontaneous emission spectra. We conclude that a slight positive detuning within 5% of the center wavelength favors CW performance especially for high-temperature operation.

High-power distributed Bragg reflector lasers for green-light generation

We demonstrated the room temperature continuous wave (CW) operation of mid-infrared distributed feedback (DFB) quantum cascade lasers (QCLs) made of strain balanced GaInAs/AlInAs material on InP substrates for sensing CO2 isotope and N2O gas for potential applications that need battery powered portable devices in a sensor network. For the former device at 4.35 μm wavelength, we demonstrated a low threshold voltage of less than 8 V for battery operation and a near circular far field pattern with small divergent angles of 33 by 28 degrees full width at half maximum (FWHM) in vertical and horizontal directions, respectively, for easy collimation. For the latter device at 4.5 μm wavelength, we demonstrated a low CW threshold power consumption of 0.7 W at 20 °C. A side mode suppression ratio (SMSR) of 30 dB was achieved within the whole operating current and temperature ranges for both lasers.

Impact of Wavelength Detuning on the Performance of Mid-IR Distributed Feedback Quantum Cascade Lasers

We characterized the performance of sampled-grating distributed Bragg reflectors (SG DBR) quantum cascade lasers (QCLs) and demonstrated a wide wavelength tuning from 4.48 to 4.69 μm (100cm-1) by injecting current into the SGDBR sections.