Show all abstracts
View Session
- Front Matter: Volume 9767
- Structure and Cavity Developments
- Materials Developments
- Blue/Green Emitters
- Quantum Dots
- Cavity Effects and Mode-Locking
- DFB and DBRs
- Lasers on Silicon
- Interband and Quantum Cascade Lasers
- QCLs: Combs and Mode-Locking II
- New Device Concepts
- High-Brightness Lasers
- QCLs: Cavities, Integration, and Applications
- Poster Session
Front Matter: Volume 9767
Front Matter: Volume 9767
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9767, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
Structure and Cavity Developments
Type-I QW cascade diode lasers for spectral region above 3 um
Show abstract
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of
GaSb-based diode lasers operating in spectral region from 3.1 to 3.3 μm. The experiment showed that the increase
of the number of cascades from two (previously used in record cascade 3 μm emitters) to three led to critical
enhancement of the differential gain and reduction of the threshold current density of λ > 3 μm lasers. Light p-doping
of the AlGaAsSb graded section did not introduce extra optical loss but aided hole transport as required for
realization of the efficient multi-stage cascade pumping scheme. Corresponding coated three-stage devices with
~100-μm-wide aperture and 3-mm-long cavity demonstrated CW output power of 500 mW near 3.18 μm at 17 °C –
more than twofold increase as compared to previous state-of-the-art diode lasers emitting only 200 mW. Three-stage
lasers with quantum wells designed to emit in the middle of methane absorption band near 3.25 μm demonstrated
record output power levels above 350 mW – nearly threefold improvement over previous non-cascade state-of-the-art
diodes. Utilization of the different quantum wells in cascade laser heterostructure was demonstrated to yield
wide gain lasers as often desired for tunable laser spectroscopy. Two step etching was applied in effort of
simultaneous minimization of both internal optical loss and the lateral current spreading in narrow ridge lasers.
Generation of 7W nanosecond pulses with 670nm ridge-waveguide lasers
A. Klehr,
T. Prziwarka,
A. Liero,
et al.
Show abstract
The aim of this paper is to present detailed experimental and theoretical investigations of the behavior of ridge-waveguide
(RW) lasers emitting at 670 nm under injection of sub-ns current pulses with high amplitudes. The
RW lasers are based on strained GaInP double quantum wells embedded in an asymmetric AlGaInP/AlInP
waveguide structure. The width of the ridge is 15 μm and the cavity length 3 mm.
The laser diode is mounted on an in-house developed laser driver with a final stage based on GaN transistors,
which generates nearly rectangular shaped current pulses with amplitudes up to 30 A and widths down to 300 ps.
The pulse width can be varied electronically between 300 ps and 1.2 ns with a repetition frequency up to 1 MHz,
which results in a variation of the pulse width of the emitted optical pulses between 200 ps and 1.2 ns. The
maximum pulse power depends on the electrical pulse width and reaches 7.2 W for a ridge width of 15 μm. At
high pulse current amplitudes the pulse power saturates. Time-dependent simulations with the drift-diffusion
simulator WIAS-TeSCA reveal that accumulation of excess electrons under the ridge is the root cause for the
power saturation, limiting the maximum achievable output power.
GaAs-based self-aligned stripe superluminescent diodes processed normal to the cleaved facet
Show abstract
We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned
stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application
of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband
manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for
high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of
Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet
demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real
estate.
Materials Developments
Microscopic modelling of opto-electronic properties of dilute bismide materials for the mid-IR
Show abstract
Fully microscopic many-body models are used to determine important material characteristics of GaAsBi and InAsBi
based devices. Calculations based on the band anti-crossing (BAC) model are compared to first principle density
functional theory (DFT) results. Good agreement between BAC-based results and experimental data is found for
properties that are dominated by states close to the bandgap, like absorption/gain and photo luminescence. Using the
BAC model for properties that involve states in the energetic region of the BAC defect level, like Auger losses and free
carrier absorption results in a sharp resonance in the dependence of these quantities for Bismuth concentrations for which
the bandgap becomes resonant with the spin-orbit splitting or the BAC-splitting of the light and heavy hole bands. DFT
calculations show that the BAC model strongly over-simplifies the influence of the bismuth atoms on the bandstructure.
Taking into account the more realistic results of DFT calculations should lead to a reduction of the sharp resonance and
lead to enhancements or suppressions for other Bismuth concentrations and spectral regions.
First demonstration of orange-yellow light emitter devices in InGaP/InAlGaP laser structure using strain-induced quantum well intermixing technique
Show abstract
In this paper, a novel strain-induced quantum well intermixing (QWI) technique is employed on InGaP/InAlGaP material system to promote interdiffusion via application of a thick-dielectric encapsulant layer, in conjunction with cycle
annealing at elevated temperature. Broad area devices fabricated from this novel cost-effective QWI technique lased at
room-temperature at a wavelength as short as 608nm with a total output power of ~46mW. This is the shortest-
wavelength electrically pumped visible semiconductor laser, and the first report of lasing action yet reported from post-
growth interdiffused process. Furthermore, we also demonstrate the first yellow superluminescent diode (SLD) at a
wavelength of 583nm with a total two-facet output power of ~4.5mW - the highest optical power ever reported at this wavelength in this material system. The demonstration of the yellow SLD without complicated multiquantum barriers to
suppress the carrier overflow will have a great impact in realizing the yellow laser diode.
Blue/Green Emitters
Room-temperature continuous-wave operation of BeZnCdSe quantum-well green-to-yellow laser diodes with sub-10 mA threshold current
Show abstract
Low threshold current BeZnCdSe single quantum-well (SQW) laser diodes (LDs) have been developed. The waveguide
was formed of a ridge structure with etching away the top p-type BeMgZnSe/ZnSe:N short-period superlattice cladding
layer, and then covered with a thick SiO2 layer and planarized with chemical-mechanical polishing and reactive ion
etching process. Three type LDs with different SQW thickness and Cd content were developed and compared at varying
waveguide width and length. Lasing wavelength of 535, 563, and 567 nm were realized respectively, at room-temperature
continuous-wave condition with the laser cavity formed by the cleaved waveguide facets coated with high-reflectivity
dielectric films. Compared with our previously developed gain-guided diode structure for a 5-μm-wide, 800-
μm-long gain-guided green laser with a threshold current and voltage of 68 mA and 10.4 V, a 535-nm green laser with 7-
nm-thick SQW can realize a threshold current and voltage of 7.07 mA and 7.89 V, respectively, for a cavity width of 4
μm and length of 300 μm. A 563-nm yellow LD with 4-nm-thick SQW was also developed with 7.4-mA and 8.48-V
threshold current and voltage for a 3-μm-wide, 300-μm-long cavity. A 567-nm yellow LD with 7-nm-thick SQW can
achieve a threshold current and voltage of 10.8 mA and 8.4 V, respectively, for a cavity length of 300 μm and width of 7
μm. The threshold current and voltage were decreased due to the reinforced confinement of carriers in cavities. The
device performance can be significantly improved with much lower power consumption. The threshold current and
power consumption is also sufficiently low compared with that of InGaN/GaN green LDs, which will benefit the
potential application for ZnSe-based LDs as light sources in full-color display as well as some biomedical devices.
Studies on 405nm blue-violet diode laser with external grating cavity
Show abstract
Spectroscopy applications of free-running laser diodes (LD) are greatly restricted as its broad band spectral emission.
And the power of a single blue-violet LD is around several hundred milliwatts by far, it is of great importance to obtain
stable and narrow line-width laser diodes with high efficiency. In this paper, a high efficiency external cavity diode laser
(ECDL) with high output power and narrow band emission at 405 nm is presented. The ECDL is based on a
commercially available LD with nominal output power of 110 mW at an injection current of 100 mA. The spectral width
of the free-running LD is about 1 nm (FWHM). A reflective holographic grating which is installed on a home-made
compact adjustable stage is utilized for optical feedback in Littrow configuration. In this configuration, narrow line-width
operation is realized and the effects of grating groove density as well as the groove direction related to the beam
polarization on the performances of the ECDL are experimentally investigated. In the case of grating with groove density
of 3600 g/mm, the threshold is reduced from 21 mA to 18.3 mA or 15.6 mA and the tuning range is 3.95 nm or 6.01 nm
respectively when the grating is orientated in TE or TM polarization. In addition, an output beam with a line-width of 30
pm and output power of 92.7 mW is achieved in TE polarization. With these narrow line-width and high efficiency, the
ECDL is capable to serve as a light source for spectroscopy application such as Raman scattering and laser induced
fluorescence.
Large TE polarized optical gain from AlInN-delta-GaN quantum well for ultraviolet lasers
Show abstract
Ultraviolet (UV) lasers with wavelength (λ) < 300 nm have important applications in free-space communication, water/air purification, and biochemical agent detection. Conventionally, AlGaN quantum wells (QWs) are widely used as active region for UV lasers. However, high-efficiency electrically injected mid-UV lasers with λ ~ 250-300 nm are still very challenging as the corresponding AlGaN QWs suffer from severe band-mixing effect due to the presence of the valence sub-band crossover between the heavy-hole (HH) and crystal-field split off (CH) sub-bands, which would result in very low optical gain in such wavelength regime.
Therefore, in this work, we propose and investigate the use of AlInN material system as an alternative for mid-UV lasers. Nanostructure engineering by the use of AlInN-delta-GaN QW has been performed to enable dominant conduction band – HH sub-band transition as well as optimized electron-hole wave function overlap. The insertion of the ultra-thin delta-GaN layer, which is lattice-matched to Al0.82In0.18N layer, would localize the wave functions strongly toward the center of the active region, leading to large transverse electric (TE) polarized optical gain (gTE) for λ~ 250- 300 nm. From our finding, the use of AlInN-delta-GaN QW resulted in ~ 3-times enhancement in TE-polarized optical gain, in comparison to that of conventional AlGaN QW, for gain media emitting at ~ 255 nm. The peak emission wavelength can be tuned by varying the delta layer thickness while maintaining large TE gain. Specifically, gTE ~ 3700 cm-1 was obtained for λ ~ 280-300 nm, which are very challenging for conventional AlGaN QW active region.
Quantum Dots
1.5-um quantum dot laser material with high temperature stability of threshold current density and external differential efficiency
Show abstract
Self-organized InAs quantum dot (QD) lasers based on InP substrate were grown by means of solid source molecular beam epitaxy (SSMBE). Six InAs QD layers with high dot density and highly uniform dot sizes were used as active medium. Broad area (BA) and ridge waveguide (RWG) lasers with different cavity lengths were processed and characterized. Also the influence of a post-growth rapid thermal annealing (RTA) process on the laser characteristics was investigated. The lasers showed a high modal gain of 12 - 14.5 cm-1 per dot layer and a threshold current density for infinite cavity length of 120 A/cm2 per dot layer. In pulsed operation, as-cleaved BA lasers with a cavity length of 292 μm can be operated up to 120 °C. High characteristic temperature values were obtained with T0 = 125 K (20 °C to 45 °C) and T0 = 100 K up to 120 °C. The slope efficiency of about 0.28 W/A can be kept constant over a wide operating temperature range of up to 100 °C. Mounted RWG lasers with 388 μm cavity length and operated in pulsed mode showed a maximum output power of 120 mW a slope efficiency of 0.42 W/A at 15 °C. The lasers can be operated at 150 °C with 25 mW output power. These results demonstrate very well the temperature insensitive lasing performance expected in nearly ideal QD lasers due to the high density of states localized at the transition energy, which allow a very robust ground state lasing.
High-temperature continuous wave operation (up to 100C) of InAs/InGaAs quantum dot electrically injected microdisk lasers
Show abstract
In this work, electrically-injected microdisk lasers with diameter varied from 15 to 31μm based on an InAs/InGaAs QD
active region have been fabricated and tested in continuous wave regime. At room temperature, lasing is achieved at
wavelength around 1.26…1.27 μm with threshold current density about 900 A/cm2. Specific series resistance is
estimated to be about 10-4 Ohm•cm2. The lasers were tested at elevated temperatures. Lasing is achieved up to 100°C
with threshold current of 13.8mA and lasing wavelength of 1304nm in device with 31μm diameter. To the best of our
knowledge, this is the highest CW lasing temperature and the longest lasing wavelength ever reported for injection QD
microdisk/microring lasers on GaAs substrates. Emission spectrum demonstrates single-mode lasing with side mode
suppression ration of 24dB and dominant mode linewidth of 35pm. The far field radiation pattern demonstrates two
narrow maxima off the disk plane. A combination of device characteristics achieved (low threshold, long wavelength,
operation at elevated temperatures) makes them suitable for application in future optoelectronic circuits for optical
interconnect systems.
High-speed directly modulated 1.5-um quantum dot lasers
Show abstract
Due to the discrete density of states distribution and spatial localization of carriers in quantum dot (QD) material, the
dynamics should be strongly enhanced in comparison to quantum well material. Based on improved 1.5 μm
InAs/InGaAlAs/InP QD gain material short cavity ridge waveguide lasers were fabricated. Devices with cavity, lengths
of 230 to 338 μm with high reflection coatings on the backside exhibit record value for any QD laser in small and large
signal modulation performance with up to 15 GHz and 36 GBit/s, respectively, obtained at 14 °C. Due to the high
temperature stability of threshold current and external differential efficiency, the lasers exhibit also nearly constant
modulation bandwidth between 14-60 °C.
Cavity Effects and Mode-Locking
Timing jitter performance of mode-locked external cavity multi-quantum-well semiconductor lasers
Show abstract
Mode-locked semiconductor lasers are a promising source for applications such as ultrafast optical sampling. For such
an application, the reduction of timing jitter of the pulse source in a cost-effective manner is a key challenge. While
monolithic devices have been the source of much recent interest, external cavity lasers have been less well studied. In
this work, the noise of an external cavity laser under passively mode-locked operation is evaluated. A ridge-waveguide
super-large optical cavity material system is used.
Interaction of phase and amplitude shaping in an external cavity semiconductor laser
Show abstract
Ultrashort pulse generation with semiconductor lasers poses a promising alternative to currently available femtosecond laser sources like solid state and fiber lasers. Semiconductor devices can be produced inexpensively, are energy efficient and their wavelength can be designed by band gap engineering. Furthermore they feature a tunable repetition rate. Yet pulse duration and peak power of those devices limit their potential for applications so far. However, recent research demonstrated a reduction of the pulse width from 534 fs (full width half maximum) to 216 fs by shaping the spectrally resolved spectral phase and amplitude inside the cavity. The utilized system consisted of a mode-locked edge emitting semiconductor laser diode, a spatial light modulator inside the external cavity to carry out the pulse shaping and an evolutionary algorithm to optimize the phase and amplitude. Here we present the results of separate phase and amplitude shaping as well as their interaction if optimized together at the same time. Furthermore we demonstrate the flexibility of the phase and amplitude shaping with respect to each other. Thus we expect of our system to enable adaptation to a resonator external dispersion.
DFB and DBRs
Narrow-linewidth 1.5-um quantum dot distributed feedback lasers
Show abstract
The ever-growing need for higher data rates is a driving force for the implementation of higher order coherent communication formats. A key element in coherent detection is the local oscillator (LO) of the decoding unit. This device has to provide coherent light with a narrow linewidth in order to distinguish between different phase and amplitude states of the incoming signal. As predicted by theory, a drastic linewidth reduction is expected from quantum dot (QD) laser materials by the quasi zero-dimensional nature of the gain function. The impact of different gain materials consisting of different numbers of QD layers on the linewidth of distributed feedback (DFB) lasers was investigated and shows an unambiguous dependence on the layer design. Intrinsic linewidths as low as 110 kHz could be determined.
Pulsed hybrid dual wavelength Y-branch-DFB laser-tapered amplifier system suitable for water vapor detection at 965 nm with 16 W peak power
Show abstract
A master oscillator power amplifier system emitting alternatingly at two neighbored wavelengths around 965 nm is presented. As master oscillator (MO) a Y-branch DFB-laser is used. The two branches, which can be individually controlled, deliver the two wavelengths needed for a differential absorption measurement of water vapor. Adjusting the current through the DFB sections, the wavelength can be adjusted with respect to the targeted either “on” or “off” resonance, respectively wavelength λon or wavelength λoff. The emission of this laser is amplified in a tapered amplifier (TA). The ridge waveguide section of the TA acts as optical gate to generate short pulses with duration of 8 ns at a repetition rate of 25 kHz, the flared section is used for further amplification to reach peak powers up to 16 W suitable for micro-LIDAR (Light Detection and Ranging). The necessary pulse current supply user a GaN-transistor based driver electronics placed close to the power amplifier (PA). The spectral properties of the emission of the MO are preserved by the PA. A spectral line width smaller than 10 pm and a side mode suppression ratio (SMSR) of 37 dB are measured. These values meet the demands for water vapor absorption measurements under atmospheric conditions.
Difference frequency modulation of multi-section dual-mode lasers with nanoscale surface gratings
Show abstract
Dual-mode multi-section quantum-well distributed feedback lasers with surface gratings have been fabricated, without regrowth, at 1310 and 1550 nm using UV nano-imprint lithography. Several laser and grating sections have been employed to control and stabilize the dual-mode emission and to reduce mode competition. Frequency differences between 15 GHz and 1 THz were achieved for different longitudinal structures. Frequency difference variations of several GHz have been measured under bias modulation with rates up to a few GHz. Higher frequency difference modulation rates are expected from improved measurement setups and from employing quantum dot active regions for further reduction of mode competition.
5,000 h reliable operation of 785nm dual-wavelength DBR-RW diode lasers suitable for Raman spectroscopy and SERDS
Show abstract
Monolithic wavelength stabilized diode lasers, e.g. distributed Bragg reflector (DBR) ridge waveguide (RW) lasers,
are well-suited light sources for compact and portable Raman spectroscopic systems. In the case of in situ and
outdoor investigations, the weak Raman lines are often superimposed by daylight, artificial light sources or
fluorescence signals from the samples under study. Among others, shifted excitation Raman difference spectroscopy
(SERDS) has been demonstrated as a powerful and easy-to-use technique to separate the Raman lines from
disturbing background signals. SERDS is based on subsequential excitation of the sample with two slightly shifted
wavelengths. The Raman lines follow the change in the excitation wavelength whereas the non-Raman signals
remain unchanged. For SERDS dual-wavelength light sources, e.g., mini-arrays containing two DBR-RW lasers, are
requested. Moreover, for portable Raman instruments such as handheld devices robust and reliable excitation light
sources with lifetimes > 1,000 h are preferred.
In this work, reliability investigations of dual-wavelength DBR-RW mini-arrays over a total test time of 5,000 h are
presented. Wavelength stabilization and narrowing of the spectral emission is realized by 10th-order DBR surface
gratings defined by i-line wafer stepper technology. The DBR-section has a length of 500 μm, the devices a total
length of 3 mm. The ridge waveguide has a stripe width of 2.2 μm. Maximum output powers up to 215 mW per
emitter were measured. Over the whole power range, 95 % of the emitted power is within a spectral width of 0.15 nm
(2.5 cm−1), which is smaller than the spectral width needed to resolve most Raman lines of solid and liquid samples.
In a step-stress test, the devices were tested at 50 mW, followed by 75 mW and finally at 100 mW per emitter.
Electro-optical and spectral measurements were performed before, during and after the test. All emitters under study
did not show any deterioration of their electro-optical and spectral properties demonstrating their applicability for
portable Raman systems.
First demonstration of single-mode distributed feedback type-I GaSb cascade diode laser emitting near 2.9 um
Mathieu Fradet,
Takashi Hosoda,
Clifford Frez,
et al.
Show abstract
We demonstrate GaSb-based laterally-coupled distributed-feedback type-I cascade diode lasers emitting near 2.9 μm as
potential sources for OH measurements. The laser heterostructures consist of two GaInAsSb quantum well stages in
series separated by GaSb/AlSb/InAs tunnel junction and InAs/AlSb electron injectors. Single-mode emission is
generated using second order lateral Bragg grating etched alongside narrow ridge waveguides. The lasers were
fabricated into 2-mm-long devices, solder-mounted epi-up on copper submounts, and operate at room temperature. With
an anti-reflection coating at the emission facet, the lasers exhibit a typical current threshold of 110 mA at 20 °C and emit
more than 14 mW of output power. The Bragg wavelength temperature tuning rate was 0.29 nm/°C.
Lasers on Silicon
Cavity enhanced 1.5-um LED with silicon as a hole injector
Show abstract
Here we report the demonstration of a Si/InAlGaAs/InP PIN cavity enhanced LED around 1.5 um by using membrane
transfer method. The silicon layer is acting not only as the optical guiding layer but also the hole injection layer. The
new hybrid integrated LED could be further developed as laser source for silicon photonics.
Photonic-crystal lasers on silicon for chip-scale optical interconnects
Show abstract
Optical interconnects are expected to reduce the power consumption of ICT instruments. To realize chip-to-chip or chip-scale
optical interconnects, it is essential to fabricate semiconductor lasers with a smaller energy cost. In this context, we
are developing lambda-scale embedded active-region photonic-crystal (LEAP) lasers as light sources for chip-scale
optical interconnects.
We demonstrated the first continuous-wave (CW) operation of LEAP lasers in 2012 and reported a record low threshold
current and energy cost of 4.8 μA and 4.4 fJ/bit at 10 Gbit/s in 2013. We have also integrated photonic crystal
photodetectors on the same InP chip and demonstrated waveform transfer along 500-μm-long waveguides. Although
LEAP lasers exhibit excellent performance, they have to be integrated on Si wafers for use as light sources for chip-scale
optical interconnects.
In this paper, we give a brief overview of our LEAP lasers on InP and report our recent progress in fabricating them on
Si. We bonded the InP wafers with quantum-well gain layers directly on thermally oxidized Si wafers and performed all
process steps on the Si wafer, including high-temperature regrowth. After this process modification, we again achieved
CW operation and obtained a threshold current of 57 μA with a maximum output power of more than 3.5 μW at the
output waveguides. An output light was successfully guided through 500 × 250-nm InP waveguides.
Interband and Quantum Cascade Lasers
Interband cascade laser sources in the mid-infrared for green photonics
Show abstract
Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool for gas sensing applications with
significant advantages compared to other techniques. These advantages include real time measurement, standoff
detection and ruggedness of the sensor. Especially the Mid-Infrared (MIR) wavelength region from 3 to 6 microns is of
great interest for industrial process control and the reduction of pollutants. In this contribution we present novel ICL
devices developed to address the crucial air pollutant sulfur dioxide SO2 at its transition around 4 μm. In general,
interband cascade lasers (ICLs) have evolved into important laser sources for the MIR spectral range. Compared to
quantum cascade lasers, they offer significant advantages with respect to threshold power density as well as overall
power consumption. In contrast to conventional diode lasers, ICLs are able to cover the entire MIR wavelength range of
interest.
For application in TLAS, single-mode devices are required. In this work application-grade distributed feedback (DFB)
ICL devices for addressing SO2 at the wavelength range around 4 μm are presented. A lateral metal grating, defined by
electron beam lithography, is used to achieve DFB operation and hence spectrally single-mode emission. Continuous
wave laser operation with threshold power consumption below 100 mW at room temperature, side mode suppression
ratio of > 30 dB and wavelength tuning range up to 28 nm are demonstrated.
Step-taper active-region quantum cascade lasers for carrier-leakage suppression and high internal differential efficiency
Show abstract
By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting
quantum cascade lasers (QCLs) virtually complete carrier-leakage suppression is achieved, as evidenced by
high values for both the threshold-current characteristic temperature coefficient T0 (283 K and 242 K) and the slope-efficiency
characteristic temperature coefficient T1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for
low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept
relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm2 and 1.88 kA/cm2, respectively. In addition, due
to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In
turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30-
40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both
efficient carrier-leakage suppression as well as fast and efficient carrier extraction, the values for the internal differential
efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting
in the 7-11 μm wavelength range.
Surface-emitting quantum cascade laser with 2nd-order metal-semiconductor gratings for single-lobe emission
Show abstract
Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) are demonstrated with high-power, single-lobe surface emission. A 2nd-order Au-semiconductor distributed-feedback (DFB)/ distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length
of 5.1 mm. The lasers are designed to operate in a symmetric longitudinal mode by causing resonant coupling of the guided optical mode to the antisymmetric surface-plasmon modes of the
2nd-order metal/semiconductor grating. In turn, the antisymmetric longitudinal modes are strongly absorbed by the metal in the grating, causing the symmetric longitudinal mode to be favored to
lase, which produces a single lobe beam over a grating duty-cycle range of 36-41 %. Simulations
indicate that the symmetric mode is always favored to lase, independent of the random phase of
residual reflections from the device’s cleaved ends. Peak pulsed output powers of ~ 0.4 W were measured with single-lobe, single-mode operation near 4.75 μm.
QCLs: Combs and Mode-Locking II
Frequency comb operation of long-cavity terahertz quantum-cascade lasers
Show abstract
We investigated the multi-mode operation of long-cavity terahertz quantum-cascade lasers (l ≥ 7.5 mm). For QCLs based on an active region design with longitudinal optical (LO) phonon transitions, emission with 30–40 strong modes in a range of more than 270 GHz (9 cm-1) is observed. For certain operating conditions, we found evidence for stable frequency comb operation, which has been further proven by a self-mixing technique. In general, the multimode dynamics is characterized by a complex alternation of broad- and narrow-beat note regimes for these devices. In contrast, only a single narrow-beat note regime was observed for a different long-cavity device based on a bound-to-continuum active region, for which the emission comb spans only 33 GHz (1.1 cm-1). We further report a technique based on a tunable bandpass filter to confirm the presence of weak emission modes in the periphery of THz combs, which allowed for the unambiguous detection of modes within a dynamic range of 35 dB. We found that the 35-dB width of the comb can exceed the 20-dB width by a factor of two.
New Device Concepts
Quantum dots as active material for quantum cascade lasers: comparison to quantum wells
Show abstract
We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.
High-Brightness Lasers
DBR tapered diode laser at 1030 nm with nearly diffraction-limited narrowband emission and 12.7 W of optical output power
Show abstract
Nearly diffraction-limited emission from a distributed Bragg reflector (DBR) tapered diode laser is presented. Intrinsic
wavelength stabilization is achieved with a 3rd order DBR grating manufactured by electron beam lithography. At a
heatsink temperature of 15°C an optical output power of 12.7 W with an electro-optical efficiency > 40% is obtained.
The corresponding emission wavelength is 1030.57 nm and spectral bandwidths of 0.02 nm are measured over the whole
power range. At 10.5 W of optical power 8.1 W are contained in the central lobe. The measured beam propagation ratio
and brightness are 1.1 (1/e2) and 700 MWcm-2 sr-1, respectively. With these parameters, the laser is suitable for
applications such as non-linear frequency conversion.
High performances of very long (13.5mm) tapered laser emitting at 975 nm
Show abstract
Mode-locked semiconductor laser technology is a promising technology candidate considered by European
Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision
optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these
applications, we have realised a multi-section monolithic-cavity tapered laser diode with a record cavity
length of 13.5 mm. The laser operates at 975 nm wavelength. It is designed for the emission of ultra-short
optical pulses (<1 ps) at a repetition rate of 3 GHz with an average optical power of 600 mW. It is based on a
MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal
losses and low series resistance. The first results obtained under CW pumping of such centimetre-long laser at
20 °C heatsink temperature show the lasing threshold current as low as 1.27 A and the differential external
efficiency as high as 0.55 W/A.
Three-section master oscillator power amplifier at 1.57 um for LIDAR measurements of atmospheric carbon dioxide
Show abstract
We present experimental results on a three-section master oscillator power amplifier at 1.57 μm to be applied in an integrated path differential absorption LIDAR system for column-averaged atmospheric CO2 measurements. The application requires high power and good beam quality together with spectral purity and modulation capacity to be used in a random modulation CW LIDAR system. The device consists of a distributed feedback laser acting as master oscillator, a bent modulator section and a tapered optical amplifier section with a tilted front facet to avoid coupled cavity effects. The modulator section acts as an absorber or amplifier when driven at zero or positive bias. Devices with different geometries and epitaxial structures were fabricated and characterized, presenting CW output powers higher than 350 mW and stable single mode emission. At the frequency required by the application (12.5 MHz) a high optical modulation amplitude and extinction ratio were achieved.
Novel approaches to increasing the brightness of broad area lasers
Show abstract
Progress in studies to increase the lateral brightness Blat of broad area lasers is reviewed. Blat=Pout/BPPlat is maximized by
developing designs and technology for lowest lateral beam parameter product, BPPlat, at highest optical output power
Pout. This can be achieved by limiting the number of guided lateral modes and by improving the beam quality of low-order
lateral modes. Important effects to address include process and packaging induced wave-guiding, lateral carrier
accumulation and the thermal lens profile. A careful selection of vertical design is also shown to be important, as are
advanced techniques to filter out higher order modes.
QCLs: Cavities, Integration, and Applications
Monolithic integration of a quantum cascade laser array and an echelle grating multiplexer for widely tunable mid-infrared sources
Show abstract
In the mid-infrared (Mid-IR), arrays of distributed feedback Quantum Cascade Lasers (QCL) have been developed as a
serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth,
single mode operation and wide tunability are then gathered together on a single chip with high compactness and
intrinsic stability. In order to benefit from this extended wavelength range in a single output beam we have developed a
platform for InP-based photonics. After the validation of all required building blocks such as straight waveguides,
adiabatic couplers between active and passive waveguides, and echelle grating multiplexers, we are tackling the
integration into a single monolithic device.
We present the design, fabrication and performances of a tunable source, fully monolithic based on the echelle grating
approach. Advantages are design flexibility, relatively simple processing and the need for one single epitaxial growth for
the entire structure. The evanescent coupler has been designed to transfer all light adiabatically from the active region to
a low loss passive waveguide, while taking advantage of the high gain available in the quantum wells. The multiplexer is
based on an etched diffraction grating, covering the whole range of the 30 lasers of the array while keeping a very
compact size. These results show the first realization of a monolithic widely tunable source in the Mid-IR and would
therefore benefit to the development of fully integrated spectroscopic sensor systems.
Regrowth-free mid-infrared distributed feedback quantum cascade lasers with sub-watt power consumption
Ryan M. Briggs,
Clifford Frez,
Mathieu Fradet,
et al.
Show abstract
We report on room-temperature, continuous-wave operation of single-mode quantum cascade lasers designed for
minimal threshold power consumption in the 4 to 10 μm spectral range. Narrow-ridge distributed feedback lasers were
developed with plasma-etched sidewall corrugations and infrared-transparent dielectric cladding, enabling fabrication
without any epitaxial steps beyond the initial growth of the planar laser wafer. The devices exhibit single-mode emission
with stable, mode-hop-free tuning and side-mode suppression greater than 25 dB. We demonstrate packaged single-mode
devices with continuous-wave threshold power consumption near 1 W above room temperature.
Spectroscopic benzene detection using a broadband monolithic DFB-QCL array
Show abstract
Quantitative laser spectroscopic measurements of complex molecules that have a broad absorption spectra require broadly tunable laser sources operating preferably in the mid-infrared molecular fingerprint region. In this paper a novel broadband mid-infrared laser source comprising of an array of single-mode distributed feedback quantum cascade lasers was used to target a broadband absorption feature of benzene (C6H6), a toxic and carcinogenic atmospheric pollutant.
The DFB-QCL array is a monolithic semiconductor device with no opto-mechanical components, which eliminates issues with mechanical vibrations. The DFB-QCLs array used in this work provides spectral coverage from 1022.5 cm-1 to 1053.3 cm-1, which is sufficient to access the absorption feature of benzene at 1038 cm-1 (9.64 μm).
A sensor prototype based on a 76 m multipass cell (AMAC-76LW, Aerodyne Research) and a dispersive DFB-QCL array beam combiner was developed and tested. The Allan deviation analysis of the retrieved benzene concentration data yields a short-term precision of 100 ppbv/Hz1/2 and a minimum detectable concentration of 12 ppbv for 200 s averaging time. The system was also tested by sampling atmospheric air as well as vapors of different chemical products that contained traces of benzene.
Cascade laser applications: trends and challenges
Show abstract
When analyses need rapid measurements, cost effective monitoring and miniaturization, tunable semiconductor lasers
can be very good sources. Indeed, applications like on-field environmental gas analysis or in-line industrial process
control are becoming available thanks to the advantage of tunable semiconductor lasers.
Advances in cascade lasers (CL) are revolutionizing Mid-IR spectroscopy with two alternatives: interband cascade lasers
(ICL) in the 3-6μm spectrum and quantum cascade lasers (QCL), with more power from 3 to 300μm. The market is
getting mature with strong players for driving applications like industry, environment, life science or transports.
CL are not the only Mid-IR laser source. In fact, a strong competition is now taking place with other technologies like:
OPO, VCSEL, Solid State lasers, Gas, SC Infrared or fiber lasers. In other words, CL have to conquer a share of the
Mid-IR application market.
Our study is a market analysis of CL technologies and their applications. It shows that improvements of components
performance, along with the progress of infrared laser spectroscopy will drive the CL market growth. We compare CL
technologies with other Mid-IR sources and estimate their share in each application market.
Single-mode enhancement in coupled-cavity quantum cascade lasers
Show abstract
This paper reports on numerical analysis of longitudinal mode discrimination in coupled-cavity AlInAs/InGaAs/InP
quantum cascade lasers. Using a three dimensional, self-consistent model of physical phenomena in edge emitting laser
we performed exhaustive analysis of geometrical parameters of CC QCL on spectral characteristics. We discuss the
enhancement of the single mode operation in multi-section designs concerning variable dimensions of sections and air
gaps between sections and provide designing guidelines assuring single-mode operation. We also show impact of
independent current tuning of laser sections inducing Stark effect and heating as additional elements enhancing single
mode operation.
Poster Session
Simulation of broad spectral bandwidth emitters at 1060 nm for optical coherence tomography
Show abstract
The simulation of broad spectral bandwidth light sources (semiconductor optical amplifiers (SOA) and superluminescent
diodes (SLD)) for application in ophthalmic optical coherence tomography is reported. The device
requirements and origin of key device parameters are outlined, and a range of single and double InGaAs/GaAs
quantum well (QW) active elements are simulated with a view to application in different OCT embodiments. We
confirm that utilising higher order optical transitions is beneficial for single QW SOAs, but may introduce deleterious
spectral modulation in SLDs. We show how an addition QW may be introduced to eliminate this spectral modulation,
but that this results in a reduction of the gain spectrum width. We go on to explore double QW structures where the
roles of the two QWs are reversed, with the narrow QW providing long wavelength emission and gain. We show how
this modification in the density of states results in a significant increase in gain-spectrum width for a given current.
Three-dimensional finite-difference time-domain modelling of photonic crystal surface-emitting lasers
Show abstract
We investigate the beam divergence in far-field region, diffraction loss and optical confinement factors of all-semiconductor
and void-semiconductor photonic-crystal surface-emitting lasers (PCSELs), containing either
InGaP/GaAs or InGaP/air photonic crystals using a three-dimensional FDTD model. We explore the impact
of changing the PC hole shape, size, and lattice structure in addition to the choice of all-semiconductor or
void-semiconductor designs. We discuss the determination of the threshold gain from the diffraction losses,
and explore limitations to direct modulation of the PCSEL.