Burc Gokden

High-power, room-temperature, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ∼4.8μm

A high-power continuous-wave (CW) operation of distributed-feedback quantum-cascade lasers using a buried grating with epitaxial regrowth up to temperatures of above 60°C is demonstrated. For a high-reflectivity-coated 13μm-wide and 3mm-long cavity, CW output powers of 135mW at 25°C and still 37mW at 60°C are obtained. The device exhibits a CW threshold current density of 1.1kA∕cm2, a maximum CW wall-plug efficiency of 1.48% at 25°C, and a characteristic temperature of 177K in pulsed mode. Single-mode emission near 4.8μm with a side-mode suppression ratio of >30dB and a tuning range of ∼8.1cm−1 (i.e., tunability of 0.18cm−1∕K) in the temperature range from 15to60°C is observed.

High power broad area quantum cascade lasers

Broad area quantum cascade lasers (QCLs) are studied with ridge widths up to 400 μm, in room temperature pulsed mode operation at an emission wavelength around 4.45 μm. The peak output power scales linearly with the ridge width. A maximum total peak output power of 120 W is obtained from a single 400-μm-wide device with a cavity length of 3 mm. A stable far field emission characteristic is observed with dual lobes at ±38° for all tested devices, which suggests that these broad area QCLs are highly resistant to filamentation.

High power quantum cascade lasers

We report the most recent state-of-art quantum cascade laser results at wavelengths around 4.8 and 10 μm. At 4.8 μm, a room temperature wall plug efficiency (WPE) of 22 and 15.5% are obtained in pulsed mode and continuous wave (cw) mode, respectively. Room temperature cw output power reaches 3.4 W. The same laser design is able to reach a WPE of 36% at 120 K in pulsed mode. At 10 μm, room temperature average power of 2.2 W and cw power of 0.62 W are obtained. We also explore lasers utilizing the photonic crystal distributed feedback mechanism, and we demonstrate up to 12 W peak power operation at three different wavelengths around 4.7 μm with a waveguide width of 100 μm and diffraction limited beam quality.

Demonstration of a Quantum Controlled-NOT Gate in the Telecommunications Band

We present the first quantum controlled-not (cnot) gate realized using a fiber-based indistinguishable photon-pair source in the 1.55 microm telecommunications band. Using this free-space cnot gate, all four Bell states are produced and fully characterized by performing quantum-state tomography, demonstrating the gates unambiguous entangling capability and high fidelity. Telecom-band operation makes this cnot gate particularly suitable for quantum-information-processing tasks that are at the interface of quantum communication and linear optical quantum computing.

Watt level performance of quantum cascade lasers in room temperature continuous wave operation at λ∼3.76 μm

An InP-based quantum cascade laser heterostructure emitting at 3.76 μm is grown with gas-source molecular beam epitaxy. The laser core is composed of strain balanced In0.76Ga0.24As/In0.26Al0.74As. Pulsed testing at room temperature exhibits a low threshold current density (1.5 kA/cm2) and high wall plug efficiency (10%). Room temperature continuous wave operation gives 6% wall plug efficiency with a maximum output power of 1.1 W. Continuous wave operation persists up to 95 °C.

Broad area photonic crystal distributed feedback quantum cascade lasers emitting 34 W at λ∼4.36 μm

We demonstrate room temperature, high power, single mode, and diffraction limited operation of a two dimensional photonic crystal distributed feedback quantum cascade laser emitting at 4.36 μm. Total peak power up to 34 W is observed from a 3 mm long laser with 400 μm cavity width at room temperature. Far-field profiles have M2 figure of merit as low as 2.5. This device represents a significant step toward realization of spatially and spectrally pure broad area high power quantum cascade lasers.

Photonic crystal distributed feedback quantum cascade lasers with 12 W output power

We demonstrate room temperature, high power, and diffraction limited operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting around 4.7 μm. PCDFB gratings with three distinctive periods are fabricated on the same wafer. Peak output power up to 12 W is demonstrated. Lasers with different periods show expected wavelength shifts according to the design. Dual mode spectra are attributed to a purer index coupling by putting the grating layer 100 nm away from the laser core. Single lobed diffraction limited far field profiles are observed.

Current status and potential of high-power mid-infrared intersubband lasers

Some of the recent advances in high power quantum cascade laser development will be reviewed in this paper. Research areas explored include short wavelength (λ<4 μm) lasers, high performance strain-balanced heterostructures, and high power long wavelength (7< λ< 16 μm) lasers. Near λ=4.5 μm, highlights include demonstration of 18% continuous wave wallplug efficiency at room temperature, 53% pulsed wallplug efficiency at 40 K, and 120 W of peak power output from a single device at room temperature. Near λ~10 μm, up to 0.6 W of continuous output power at room temperature has also been demonstrated, with pulsed efficiencies up to 9%.

Widely tunable single-mode high power quantum cascade lasers

We demonstrate widely tunable high power distributed feedback quantum cascade laser array chips that span 190 nm and 200 nm from 4.4 um to 4.59 um and 4.5 um to 4.7 um respectively. The lasers emit single mode with a very narrow linewidth and side mode suppression ratio of 25 dB. Under pulsed operation power outputs up to 1.85 W was obtained from arrays with 3 mm cavity length and up to 0.95 W from arrays with 2 mm cavity length at room temperature. Continuous wave operation was also observed from both chips with 2 mm and 3 mm long cavity arrays up to 150 mW. The cleaved size of the array chip with 3 mm long cavities was around 4 mm x 5 mm and does not require sensitive external optical components to achieve wide tunability. With their small size and high portability, monolithically integrated DFB QCL Arrays are prominent candidates of widely tunable, compact, efficient and high power sources of mid-infrared radiation for gas sensing.

High power 1D and 2D photonic crystal distributed feedback quantum cascade lasers

For many practical applications that need bright sources of mid-infrared radiation, single mode operation and good beam quality are also required. Quantum cascade lasers are prominent candidates as compact sources of mid-infrared radiation capable of delivering very high power both CW and under pulsed operation. While 1D photonic crystal distributed feedback structures can be used to get single mode operation from quantum cascade lasers with narrow ridge widths, novel 2D photonic crystal cavity designs can be used to improve spectral and spatial purity of broad area quantum cascade lasers. In this paper, we demonstrate high power, spatially and spectrally pure operation at room temperature from narrow ridge and broad area quantum cascade lasers with buried 1D and 2D photonic crystal structures. Single mode continuous wave emission at λ = 4.8 μm up to 700 mW in epi-up configuration at room temperature was observed from a 11 μm wide 5 mm long distributed feedback quantum cascade laser with buried 1D gratings. High peak powers up to 34 W was obtained from a 3mm long 400 μm wide 2D photonic crystal distributed feedback laser at room temperature under pulsed operation. The far field profile had a single peak normal to the laser facet and the M2 figure of merit was as low as 2.5. Emission spectrum had a dominating single mode at λ = 4.36 μm.