We report the design and manufacturing of a tunable VCSEL with an HCG MEMS mirror and an integrated detector oblique to the optical cavity for measuring output power without disturbing the laser cavity. This allows for a single laser device with integrated power monitoring capabilities that can be used in concert with external electronics to stabilize the power or monitor optical feedback of the device for sensing applications. The HCG tunable VCSEL is modified to incorporate a sacrificial layer capable of detecting light at the VCSEL’s operating wavelength. For the MEMS release process, the sacrificial layer is removed from the optical cavity defined by the VCSEL mirrors and active region. The release process is designed to create a cavern around the optical cavity and walls of such cavern are composed by sacrificial layer material. Thus, the sacrificial layer material is removed from the optical cavity, but is kept surrounding it. Light scattered at the interface semiconductor-air hits the cavern walls and modifies current through the MEMS terminals (Idet). Any change in VCSEL output power (Pout) is directly related to a change on Idet through MEMS terminal, creating a direct relationship of Pout vs. Idet. To the best of our knowledge, there is no previous report of a VCSEL with integrated oblique intracavity detector.
We report recent advances in electrically-pumped 1050 nm and 1550 nm micro-electro-mechanically-tunable verticalcavity surface emitting-lasers (MEMS-VCSELs). We demonstrate a single-mode, continuous, mechanical tuning range of 73 nm with high output power and low threshold current performance for the 1050 nm devices. To the best of our knowledge, 73 nm is a record tuning value for an electrically-pumped tunable VCSEL with a tuning speed >250 kHz, making them highly desirable for next generation OCT and other swept source applications. 10 Gbps 1550-nm DWDM tunable SFP+ modules based on an HCG-VCSEL are demonstrated with an embedded communications channel for automatic wavelength tuning and locking for low cost FTTx and front haul network applications.
We present the recent development of high performance compact THz sources based on intracavity nonlinear
frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz
sources with respect to the continuous wave THz power output, monolithic THz tuning, and widely frequency are
achieved by systematic optimization of the device's active region, waveguide design, and chip bonding strategy.
Room temperature continuous wave THz power of more than 10 μW at 3.4 THz is demonstrated at room
temperature. Monolithic THz tuning of a chip-based THz source from 2.6 to 4.2 THz with power up to 0.1 mW is
achieved. Surface emission from the substrate via a diffraction grating with THz power up to 0.5 mW is also
obtained. The developing characteristics show the potential for these THz sources as local oscillators for many
astronomical and medical applications.
We present the recent development of high performance compact THz sources based on intracavity nonlinear frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources with respect to the continuous wave THz power output, monolithic THz tuning, and widely frequency are achieved by systematic optimization of the device's active region, waveguide design, and chip bonding strategy. Room temperature continuous wave THz power of more than 10 μW at 3.4 THz is demonstrated at room temperature. Monolithic THz tuning of a chip-based THz source from 2.6 to 4.2 THz with power up to 0.1 mW is achieved. Surface emission from the substrate via a diffraction grating with THz power up to 0.5 mW is also obtained. The developing characteristics show the potential for these THz sources as local oscillators for many astronomical and medical applications.
We demonstrate the first room temperature continuous wave THz sources based on intracavity difference frequency
generation from mid-infrared quantum cascade lasers. This accomplishment was enabled by integration of several key
technologies, resulting in a new high efficiency waveguide design and improved thermal dissipation. Room temperature
single mode emissions at 3.6 THz with an emitting power of 3 μW and a mid-IR-to-THz conversion efficiency of 0.44
mW/W2 are obtained in continuous wave mode. THz peak power up to 1.4 mW in pulsed mode operation with a mid-IRto-
THz conversion efficiency of 0.8 mW/W2 at 3.5 THz is also demonstrated.
We present the recent development of high performance compact THz sources based on intracavity nonlinear
frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz
sources in the spectral purity, frequency coverage as well as THz power are achieved by systematic optimizing the
device's active region, waveguide, phase matching scheme, and chip bonding strategy. Room temperature
single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Čerenkov phase-matched
THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via
epi-down mounting of our THz device. The THz power is later scaled up to mW level by increased the mid-IR
power and conversion efficiency. The rapid development renders this type of THz sources promising local oscillators
for many astronomical and medical applications.
We present the high performance THz sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers. Room temperature single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Cerenkov phase-matched THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via epi-down mounting of our THz device. The rapid development renders this type of THz sources promising local oscillators for many astronomical and medical applications.
This paper describes our development efforts at Northwestern University regarding dual-section sampled
grating distributed feedback (SGDFB) QCLs. These devices are the same size, but have much wider electrical tuning,
than a traditional DFB laser. In this paper, I will show how we have dramatically extended the monolithic tuning range
of high power quantum cascade lasers with high side mode suppression. This includes individual laser element tuning of
up to 50 cm-1 and 24 dB average side mode suppression. These lasers are capable of room temperature continuous
operation with high power (<100 mW) output. Additionally, we have demonstrated a broad spectral coverage of over
350 cm-1 on a single chip, which is equivalent to 87.5% of the gain bandwidth. The eventual goal is to realize an
extended array of such laser modules in order to continuously cover a similar or broader spectral range, similar to an
external cavity device without any external components.
Quantum Cascade Lasers (QCLs), operating in continuous wave (cw) at room temperature
(rt) in 3-3.5μm spectral range, which overlaps the spectral fingerprint region of many hydrocarbons,
is essential in spectroscopic trace gas detection, environment monitoring, and pollution control. A
3μm QCL, operating in cw at rt is demonstrated. This initial result makes it possible, for the most
popular material system (AlInAs/GaInAs on InP) used in QCLs in mid-infrared and long-infrared, to
cover the entire spectral range of mid-infrared atmospheric window (3-5μm).
In0.79Ga0.21As/In0.11Al0.89As strain balanced superlattice, which has a large conduction band
offset, was grown. The strain was balanced with composite barriers (In0.11Al0.89As /In0.4Al0.6As) in
the injector region, to eliminate the need of extremely high compressively strained GaInAs, whose
pseudomorphic growth is very difficult.
We demonstrate room temperature terahertz (THz) quantum cascade laser (QCL) sources with a broad spectral coverage based on intracavity difference-frequency generation. Dual mid-infrared (mid-IR) active cores based on the single-phonon resonance scheme are designed with a THz nonlinearity specially optimized for the high operating fields that correspond to the highest mid-infrared output powers. Integrated dual-period distributed feedback (DFB) gratings with different grating periods are used to purify and tune the mid-IR and THz spectra. Two different phase matching schemes are used for THz generation. The first is the collinear modal phase matching scheme, wherein the wafer is grown on a n+ InP substrate. Room temperature single mode operation THz emission with frequency tuning range from 3.3 to 4.6 THz and THz power up to 65 mW at 4.0 THz are realized. The mid-IR to THz power conversion efficiency is 23 uW/W2. The second is the Čerenkov phase-matching scheme, wherein the wafer is grown on a semi-insulating InP substrate, and device’s facet is polished into 20-30 degrees for THz extraction. Room temperature single mode emissions from 1.0 to 4.6 THz with a side-mode suppression ratio and output power up to 40 dB and 32 µW are obtained, respectively. The mid-IR to THz power conversion efficiency is 50 uW/W2.
We demonstrate room temperature, continuous wave operation of quantum cascade ring lasers around 5 μm with single
mode operation up to 0.51 W output power. Single mode operation persists up to 0.4 W. Light is coupled out of the ring
cavity through the substrate with a second order distributed feedback grating. The substrate emission scheme allows for
epilayer-down bonding, which leads to room temperature continuous wave operation. The far field analysis indicates that
the device operates in a high order mode.
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.
We demonstrate room temperature, high power, single mode and diffraction limited operation of a two dimensional
photonic crystal distributed feedback (PCDFB) 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 towards realization of spatially and spectrally pure broad
area high power 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.
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