Richard Maulini

3 W Continuous-Wave Room Temperature Single-Facet Emission From Quantum Cascade Lasers Based On Nonresonant Extraction Design Approach

A strain-balanced, InP-based quantum cascade laser structure, designed for light emission at 4.6 μm using a new nonresonant extraction design approach, was grown by molecular beam epitaxy. Removal of the restrictive two-phonon resonant condition, currently used in most structure designs, allows simultaneous optimization of several design parameters influencing laser performance. Following the growth, the structure was processed in buried heterostructure. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of 5 mm×11.6 μm. Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and 0.86 kA/cm2.

1.6W high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 4.6μm

A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.

External cavity quantum cascade laser

In this paper we review the progress of the development of mid-infrared quantum cascade lasers (QCLs) operated in an external cavity configuration. We concentrate on QCLs based on the bound-to-continuum design, since this design is especially suitable for broadband applications. Since they were first demonstrated, these laser-based tunable sources have improved in performance in terms of output power, duty cycle, operation temperature and tuneability. Nowadays they are an interesting alternative to FTIRs for some applications. They operate at room temperature, feature a high spectral resolution while being small in size. They were successfully used in different absorption spectroscopy techniques. Due to their vast potential for applications in industry, medicine, security and research, these sources enjoy increasing interest within the research community as well as in industry.

Broadband tuning of external cavity bound-to-continuum quantum-cascade lasers

A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ≅10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse.

External cavity quantum-cascade laser tunable from 8.2to10.4μm using a gain element with a heterogeneous cascade

A heterogeneous quantum-cascade structure based on two bound-to-continuum designs emitting at 9.6 and 8.4μm is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of 350cm−1 and shows a variation of intensity of less than 20% over more than 200cm−1. External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over 265cm−1 from 8.2to10.4μm, that is, over 24% of the center wavelength.

High power thermoelectrically cooled and uncooled quantum cascade lasers with optimized reflectivity facet coatings

We present a method of preserving the device wall-plug efficiency by adjusting mirror losses with facet coatings for longer cavity quantum cascade lasers. An experimental study of output power and wall-plug efficiency as functions of mirror losses was performed by varying the front facet coating reflectivity with a high-reflectivity-coated rear facet. The use of optimized reflectivity coatings on 7-mm-long chips resulted in continuous-wave output power of 2.9 W at 293 K for thermoelectrically cooled devices mounted on AlN submounts and average and continuous-wave output power in excess of 1 W for uncooled devices emitting at 4.6 m.

Continuous-wave operation of a broadly tunable thermoelectrically cooled external cavity quantum-cascade laser

Continuous-wave operation of an external cavity quantum-cascade laser on a thermoelectric cooler is reported. The active region of the gain element was based on a bound-to-continuum design emitting near 5.15 microm. The external cavity setup was arranged in a Littrow configuration. The front facet of the gain chip was antireflection coated. The laser could be tuned over more than 170 cm(-1) from 4.94 to 5.4 microm and was single mode over more than 140 cm(-1). The output power was in excess of 10 mW over approximately 100 cm(-1) and in excess of 5 mW over approximately 130 cm(-1) at -30 degrees C.

Direct measurement of the linewidth enhancement factor by optical heterodyning of an amplitude-modulated quantum cascade laser

A measurement of the linewidth enhancement factor α of a distributed feedback quantum cascade laser is presented. The measurement is based on a heterodyning experiment, in which one of the lasers is modulated at radio frequency. A value of α=0.02±0.20 is obtained for a modulation frequency of 500MHz. As the frequency is decreased, α increases and is consistent with a thermal chirp effect.

λ~7.1 μm quantum cascade lasers with 19% wall-plug efficiency at room temperature

Strain-balanced In0.6Ga0.4As/Al0.56In0.44As quantum cascade lasers emitting at a wavelength of 7.1 μm are reported. The active region is based on a three-phonon-resonance quantum design with a low voltage defect of 120 meV at injection resonance. A maximum wall-plug efficiency of 19% is demonstrated in pulsed mode at 293 K. Continuous-wave output power of 1.4 W and wall-plug efficiency of 10% are measured at the same temperature, as well as 1.2 W of average power in uncooled operation. A model for backfilling of the lower laser level which takes into account the number of subbands in the injector is presented and applied to determine the optimum value of the voltage defect to maximize wall-plug efficiency at room temperature, which is found to be ~100 meV, in good agreement with experimental results.

High-performance continuous-wave room temperature 4.0-μm quantum cascade lasers with single-facet optical emission exceeding 2 W

A strain-balanced, AlInAs/InGaAs/InP quantum cascade laser structure, designed for light emission at 4.0 μm using nonresonant extraction design approach, was grown by molecular beam epitaxy. Laser devices were processed in buried heterostructure geometry. An air-cooled laser system incorporating a 10-mm × 11.5-μm laser with antireflection-coated front facet and high-reflection-coated back facet delivered over 2 W of single-ended optical power in a collimated beam. Maximum continuous-wave room temperature wall plug efficiency of 5.0% was demonstrated for a high-reflection-coated 3.65-mm × 8.7-μm laser mounted on an aluminum nitride submount.