Fiber-based quantum networks require on-demand sources of entangled photons in the telecom C-band for long distance information transfer. Historically, the field of in-fiber entanglement distribution has been dominated by photons provided via spontaneous processes. In recent years, semiconductor quantum dots have emerged as strong competitors in terms of generating single and entangled photons due to their promise of deterministic qubit generation in the NIR wavelength region. Here, we show the on-demand generation of polarization entangled photons in the telecom C-band based on InAs/GaAs quantum dots grown via metal-organic vapor-phase epitaxy. By employing a robust phonon-assisted two-photon excitation scheme, we are able to generate pairs of entangled photons with a concurrence of 91.4 ± 3.8 % and a maximum fidelity to the Bell state Φ+ of 95.2 ± 1.1 %.
Over the last few years, significant progresses have been made on photonic crystal based surface-emitting lasers on silicon. Both membrane-reflector VCSELs (MR-VCSELs) and bandedge effect based PCSELs have been reported with silicon based photonic crystal cavities and hybrid integrated compound semiconductor gain materials. In this talk, we will report recent advances in these laser structures. Lasing characteristics will be reported considering different coupling efficiencies for both low and room temperature operations. The lateral cavity size effect will also be discussed in making low threshold lasers with small cavity sizes. Finally the integration of other coupling structures will be discussed for beam routing in-plane.
Work is supported by ARO, AFOSR, and NSF.
Quantum structures base on type-II In(Ga)Sb quantum dots (QDs) embedded in an InAs matrix were used as active
material for achieving long-wavelength infrared (LWIR) photodetectors in this work. Both InAs and In(Ga)Sb are
narrow band semiconductor materials and known to possess a large number of surface states, which apparently play
significant impact for the detector’s electrical and optical performance. These surface states are caused not only by
material or device processing induced defects but also by surface dangling bonds, oxides, roughness and contaminants.
To experimentally analyze the surface states of the QD structures treated by different device fabrication steps, atomic
force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray
photoelectron spectroscopy (XPS) measurements were performed. The results were used to optimize the fabrication
process of the LWIR photodetectors in our ongoing project. The dark current and its temperature dependence of the
fabricated IR photodetectors were characterized in temperature range 10 K to 300 K, and the experiment results were
analyzed by a theoretic modeling obtained using simulation tool MEDICI.
We report on the device characterization of In(Ga)Sb/InAs quantum dots (QDs) based photodetectors for long wave IR
detectors. The detection principle of these quantum-dot infrared photodetectors (QDIPs) is based on the spatially indirect
transition between the In(Ga)Sb QDs and the InAs matrix, as a result of the type-II band alignment. Such photodetectors
are expected to have lower dark currents and higher operating temperatures compared to the current state of the art InSb
and mercury cadmium telluride (MCT) technology.
The In(Ga)Sb QD structures were grown using metal-organic vapour-phase epitaxy and explored using structural,
electrical and optical characterization techniques. Material development resulted in obtaining photoluminescence up to
10 μm, which is the longest wavelength reported in this material system. We have fabricated different photovoltaic IR
detectors from the developed material that show absorption up to 8 μm. Photoresponse spectra, showing In(Ga)Sb QD
related absorption edge, were obtained up to 200 K. Detectors with different In(Ga)Sb QDs showing different cut-off
wavelengths were investigated for photoresponse. Photoresponse in these detectors is thermally activated with different
activation energies for devices with different cut-off wavelengths. Devices with longer cut-off wavelength exhibit higher
activation energies. We can interpret this using the energy band diagram of the dots/matrix system for different QD sizes.
Narrow bandgap semiconductors GaSb, InAs, and InSb are important building blocks for infrared photodetectors based
on type-II InSb quantum dots or an InAs/GaSb strained layer superlattice. Understanding the surface chemical
composition of these materials can provide valuable information that enables optimization of device surface passivation
techniques leading towards surface leakage free IR photodetectors. We report on an investigation into Ga-, In-, Sb-, and
As-oxides and other chemical species on the surface of untreated, dry etched and thermally treated GaSb, InAs and InSb
samples by x-ray photoelectron spectroscopy. The experimental results reveal the presence of Sb- and Ga-oxides on the
surfaces of the untreated and treated GaSb samples. Both Sb- and In-oxides were observed on the surface of all InSb
samples, and especially the dry etched sample had thicker oxide layers. In the case of the InAs samples, not only In- and
As-oxides XPS signals were obtained, but also AsCl species were found on the ICP dry etched sample. These results
helped to analyze the dark current of our fabricated IR detectors.
We report on the optical and structural characterization of InSb QDs in InAs matrix, grown on InAs (100) substrates, for
infrared photodetection. InSb has 7% lattice mismatch with InAs forming strained QDs, which are promising for longwave
IR applications, due to their type-II band alignment. This report contains material development results of InSb QDs
for increasing their emission wavelength towards long-wave IR region. Samples were grown by two techniques of MBE
and MOVPE, with different InSb coverage on InAs (100) substrates. Structures grown by MBE reveal QD related
photoluminescence at 4 μm. AFM investigations of the MBE grown structures showed uncapped dots of ~ 35 nm in size
and ~ 3 nm in height, with a density of about 2 x 1010 cm-2. Cross-section TEM investigations of buried InSb layers
grown by MBE showed coherently strained QDs for nominal InSb coverage in the range of 1.6 - 2 monolayers (MLs).
Layers with InSb coverage more than 2MLs contain relaxed QDs with structural defects due to large amount of strain
between InSb and InAs. Samples with such large dots did not show any InSb related luminescence. The MOVPE grown
InSb samples exhibit a strong QD related emission between 3.8 to 7.5 μm, depending on the amount of InSb coverage
and other growth parameters. We report the longest wavelength observed so far in this material system.
Nowadays novel micro-fabrication and wafer-based manufacturing approach allows realizing micro-optics in a way
scientists have dreamt for generations, in particular, utilizing nano-imprint lithography as fabrication tooling enables
greatly accelerating the micro-optics technology to its frontier. In this report, we present wafer-scale fabrication of
various types of micro-optical elements based on photoresist, benzocyclobutene, photocurable imprint resist, and
semiconductor materials by using thermal reflow, reactive ion etching, and imprint techniques. Especially, several
concave or convex 3-dimensional micro-optical structures shaped by imprint method are detailed. These micro-optical
elements can be monolithically or hybrid integrated onto optoelectronics devices, such as photodetectors and emitters as
optical beam focuser, collimator, filter, or anti-reflectance elements. As application examples, polymer microlenses were
integrated directly on the top of UV dual functional devices and quantum dot long wavelength infrared photodetectors,
respectively.
A high-power single-mode 1.3-μm InGaAs/GaAs vertical-cavity surface-emitting laser (VCSEL)
structure employing a novel concept of engineering the optical mode profile to match the gain profile is
suggested and demonstrated experimentally and theoretically. In contrast to various singlemode
VCSEL approaches reported in the literature so far, based on selective loss or anti-resonant effects to
suppress higher order modes, it is due to a novel design to increase the active region size while
maintaining single mode emission. The shape of the fundamental mode profile is engineered to be
similar to the gain profile which resembles a doughnut shape especially in intra-cavity contacted
devices. In this way, the fundamental mode with the best fit to the gain profile can reach the lasing
condition earliest and consume all the optical gain, leading to a suppression of higher order modes.
Notably, despite this engineered shape of the mode profile, the far field shape remains close to
Gaussian. The mode shaping can be achieved by introducing a shallow intracavity patterning before
depositing the top mirror. Fabricated device structures consist of a A-Si/SiN/SiO2 top mirror,
modulation-doped current spreading layers, re-grown current confinement layers, three InGaAs/GaAs
quantum wells, and a GaAs/AlGaAs bottom mirror. Single mode operation is demonstrated even for
devices with active region as large as 10μm.
Historically IRnova has exclusively been a company, focused on manufacturing of QWIP detectors. Nowadays, besides
continuous improvements of the performance of QWIP FPAs and development of new formats IRnova is involved in
development of QWIP detectors for special applications and has started the development of the next generation infrared
detectors, as well.
In the light of the development of new formats we validate experimentally theoretical calculations of the response of
QWIPs for smaller pixel size. These results allow for the development of high performance megapixel QWIP FPA that
exhibit the high uniformity and operability QWIP detectors are known for. QWIP is also being considered for space
applications. The requirements on dark current and operating temperature are however much more stringent as compared
to the terrestrial applications. We show ways to improve the material quality with as a result a higher detector operating
temperature.
IRnova is also looking at antimony-based strained superlattice material for the LWIR region together with partners at the
IMAGIC centre of excellence. One of the ways to overcome the problem with surface currents is passivating
overgrowth. We will report the status and results of overgrowing the detector mesas with AlGa(As)Sb in a MOVPE
system. At the same centre of excellence a novel material concept is being developed for LWIR detection. This new
material contains a superlattice of vertically aligned and electronically coupled InAs and GaSb quantum dots.
Simulations show that it should be possible to have LWIR detection in this material. We will present the current status
and report results in this research.
In this article, we report on long wavelength (1.27 μm) single-mode micro-structured photonic crystal strained InGaAs
quantum wells VCSELs for optical interconnection applications. Single fundamental mode room-temperature
continuous-wave lasing operation was demonstrated for devices designed and processed with different two-dimensional
etched patterns. The conventional epitaxial structure was grown by Metal-Organic Vapor Phase Epitaxy (MOVPE) and
contains fully doped GaAs/AlGaAs DBRs, one oxidation layer and three strained InGaAs quantum wells. The holes were
etched half-way through the top-mirror following various designs (triangular and square lattices) and with varying hole's
diameters and pitches.
We obtained up to 1.7 mW optical output power and more than 30 dB Side-Mode Suppression Ratio (SMSR) at
room temperature and in continuous wave operation. Systematic static electrical, optical and spectral characterization
was performed on wafer using an automated probe station. Numerical modeling using the MIT Photonic-Bands (MPB
[1]) package of the transverse modal behaviors in the photonic crystal was performed using the plane wave method in
order to understand the index-guiding effects of the chosen patterns, and to further optimize the design structures for
mode selection at the given wavelength.
FTTH networks require implementing a diplexer at each user termination. According to most of the standards, this
diplexer detects a download signal beam at 1.49μm and emits an upload signal beam at 1.31μm on the same single
mode fibre. Both signals exhibit datarate speed below 2.5Gbps. Today, most of the diplexers are obtained by actively
aligning a set of individual optoelectronic components and
micro-optics. However, new manufacturing solutions
satisfying very low cost and mass production capability requirements of this market would help to speed the massive
spreading of this technology. In this paper, we present an original packaging design to manufacture Diplexer Optical
Sub-Assembly for FTTH application. A dual photodiode is stacked over a VCSEL and detects both the download
signal beam at 1.49μm passing through the laser and one part of the upload signal beam at 1.31μm for monitoring.
To satisfy this approach, an innovative VCSEL has been designed to have a very high transmission at 1.49μm. All
these components are mounted on a very small circuit board on glass including also integrated circuits such as
transimpedance amplifier. So, the device combines advanced optoelectronic components and highly integrated
Multi-Chip-Module on glass approach using collective wafer-level assembling technologies. For the single mode
fibre optical coupling, active and passive alignment solutions are considered.
GaAs-based VCSELs emitting near 1.3 μm are realized using highly strained InGaAs quantum wells and a large
detuning of the cavity resonance with respect to the gain peak. The VCSELs have an oxide aperture for current and
optical confinement and an inverted surface relief for suppression of higher-order transverse modes. The inverted surface
relief structure also has the advantage of suppressing oxide modes that otherwise appear in VCSELs with a large
detuning between the cavity resonance and the gain peak. Under large signal, digital modulation, clear and open eyes and
error free transmission over 9 km of single mode fiber have been demonstrated at the OC-48 and 10 GbE bit rates up to
85°C. Here we review these results and present results from a complementary study of the RF modulation characteristics,
including second order harmonic and third order intermodulation distortion, relative intensity noise (RIN), and spurious
free dynamic range (SFDR). RIN levels comparable to those of single mode VCSELs emitting at 850 nm are
demonstrated, with values from -140 to -150 dB/Hz. SFDR values of 100 and 95 dB•Hz2/3 were obtained at 2 and 5 GHz,
respectively, which is in the range of those required in radio-over-fiber systems.
In this article, we report our results on 1.3&mgr;m VCSELs for optical interconnection applications. Room
temperature continuous-wave lasing operation is demonstrated for top emitting oxide-confined devices with three
different active materials, highly strained InGaAs/GaAs(A) and GaInNAs/GaAs (B) multiple quantum wells (MQW) or
InAs/GaAs (C) quantum dots (QD). Conventional epitaxial structures grown respectively by Metal Organic Vapour
Phase Epitaxy (MOVPE), Molecular Beam Epitaxy (MBE) and MBE, contain fully doped GaAs/AlGaAs DBRs. All
three epilayers are processed in the same way. Current and optical confinement are realized by selective wet oxidation.
Circular apertures from 2 (micron)m to 16 (micron)m diameters are defined.
At room temperature and in continuous wave operation, all three systems exhibit lasing operation at
wavelengths above 1 275nm and reached 1 300nm for material (A). Typical threshold currents are in the range [1-
10]mA and are strongly dependent firstly on oxide diameter and secondly on temperature. Room temperature cw
maximum output power corresponds respectively to 1.77mW, 0.5mW and 0.6mW. By increasing driving current,
multimode operation occurs at different level depending on the oxide diameter. In case (A), non conventional modal
behaviors will be presented and explained by the presence of specific oxide modes.
Thermal behaviors of the different devices have been compared. In case (A) and (C) we obtain a negative T0.
We will conclude on the different active materials in terms of performances with respect to 1300nm VCSEL
applications.
We report on a quantum dot (QD) structure grown on a 4'' GaAs substrate by metal organic vapor phase epitaxy (MOVPE), which consists of five stacked InAs/InGaAs/GaAs QD layers embedded in the center of a typical in-plane waveguide. The density of the QDs is about 2.5 x 1010 cm-2 per QD layer. The photoluminescence (PL) peak wavelength at 1322 nm corresponding to the interband transition of the QD ground states was observed at room temperature with a full width at half-maximum of 49 meV. A good uniformity of the QD structure across the 4'' wafer was verified with a variation of the PL peak wavelength of 0.9 % from the wafer center to the edge. Top p-contacts and a bottom n-contact were processed on the QD structure, and electroluminescence (EL) spectra were measured at different temperatures. An EL peak corresponding to the QD ground states emission was obtained at 1325 nm at room temperature.
A novel electrical and optical confinement scheme for surface emitting optoelectronic devices is presented. The scheme
is based on epitaxial regrowth of a pnp current blocking layer structure around a mesa etched in the vertical cavity region
of the device. The lateral size and orientation of the mesa is defined lithographically and dry etching is used to create
vertical mesa sidewalls. By orienting the mesa sidewalls in certain crystallographic directions, it is possible to selectively
grow a current blocking pnp layer structure on the exposed n-type lower cladding layer of the cavity whithout
obstructing the electrical injection into the active region. The concept is evaluated in 1.2-μm GaAs-based light emitting
diodes with InGaAs quantum wells. This type of structure can easily be used as the amplifying region of a vertical cavity
laser, providing a good alternative to selective oxidation confinement.
In the context of optical interconnection applications, we report on results obtained on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs). Our devices are top p-type DBR oxide-confined VCSEL, grown by metalorganic vapour-phase epitaxy (MOVPE). These lasers exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm at room temperature is reached for a 4 μm oxide diameter VCSEL. The particular design of the active layer based on a large detuning between the gain maximum and the cavity resonance gives our devices a very specific thermal and modal behaviour. Therefore, we study the spectral and spatial distributions of the transverse modes by near field scanning optical microscopy using a micropolymer tip at the end of an optical fibre.
We report results on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs) for optical interconnection applications. The structure was grown by metalorganic vapour-phase epitaxy (MOVPE) and processed as top p-type DBR oxide-confined device. Our VCSELs exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm is demonstrated at room temperature. The thermal behaviour of our devices is explained through the threshold current-temperature characteristics. Furthermore, the effective index model is used to understand the modal behaviour.
We describe the development of long-wavelength InGaAs/GaAs vertical-cavity surface emitting lasers (VCSELs). Using highly strained double-quantum wells (DQWs) in combination with negative gain-cavity detuning we have been able to realise such VCSELs with emission wavelength up to 1300 nm. High-performance device characteristics include mW-range output power, mA-range threshold currents, 10 Gbit/s data transmission and very good temperature stability with continuous-wave operation up to at least 140°C. Singlemode emission is realised using an integrated mode filter consisting of a patterned silicon layer on the out-coupling mirror surface, yielding output power and threshold currents for 1270-nm devices of 1.2 - 0.5 mW and 2.3 - 0.6 mA, respectively, over a temperature interval of 10 - 140°C. Multimode devices have been found to deliver more than 2 mW at 1290 nm. Preliminary lifetime measurements do not reveal any intrinsic reliability problems related to the highly strained quantum wells.
In this work we present performance characteristics of metalorganic vapor-plase epitaxy grown GaInNAs and InGaAs quantum-well (QW) vertical-cavity lasers (VCLs) for 1.3-μm applications. The InGaAs VCLs emit in a wavelength range from 1200 to somewhat above 1260 nm, while the GaInNAs VCLs operate from 1264 to 1303 nm. The InGaAs VCLs are based on highly strained InGaAs double QWs, with photoluminescence (PL) maximum around 1190 nm, and extensive negative gain-cavity detuning. As a consequence, these devices are strongly temperature sensitive and the minimum threshold current is found at very high temperature (~90-100°C). Both kind of VCLs work continuous-wave well above 100°C, and while the InGaAs VCLs reach slightly higher light output power, they show significantly larger threshold currents. In addition, the large device detuning also has profound effects on the high-frequency response. Nevertheless, for a 1260-nm device, 10 Gb/s transmission is demonstrated in a back-to-back configuration. We also show that by further optimization of the InGaAs QWs the PL peak wavelength can be extended to at least 1240 nm. The incorporation of such QWs in the present VCL structure should considerably improve the device performance, resulting in higher light output power, lower threshold current, and reduced temperature sensitivity with a shift of the minimum threshold current towards room temperature, thus approaching standard VCL tuning.
We compare GaInNAs and highly strained InGaAs quantum-wells (QWs) for applications in metal-organic vapor-phase epitaxy (MOVPE)-grown GaAs-based 1300-nm vertical-cavity lasers (VCLs). While the peak wavelength of InGaAs QWs can be extended by a small fraction of N, the luminescence efficiency degrades strongly with wavelength. On the other hand, using highly strained InGaAs QWs in combination with a large VCL detuning it is also possible to push the emission wavelength towards 1.3 μm. The optimized MOVPE growth conditions for such QW and VCL structures are discussed in some detail. It is noted that GaInNAs and InGaAs QWs preferably are grown at low temperature, but with quite different V/III ratios and growth rates. We also point out the importance of reduced doping concentration and growth temperature of the n-doped bottom DBR to minimize optical loss and for compatibility with GaInNAs QWs. InGaAs VCLs with emission wavelength beyond 1260 nm is demonstrated. This includes mW-range output power, mA-range threshold current and 10 Gb/s data transmission.
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