This PDF file contains the front matter associated with SPIE
Proceedings Volume 6908, including the Title Page, Copyright
information, Table of Contents, Introduction (if any), and the
Conference Committee listing.
This article outlines development work at JDSU on InGaNAs based vertical cavity surface emitting lasers (VCSELs)
operating at 1270nm and their use in 10Gbps SFP+ modules. DC and AC performance of die and transmit optical
subassemblies (TOSAs) will be described. Due to their low power consumption, LW VCSELs are ideal for use in
SFP+; module performance will be described as well.
Over the past 3 years laser based tracking systems for optical PC mice have outnumbered the traditional VCSEL market
datacom by far. Whereas VCSEL for datacom in the 850 nm regime emit in multipe transverse modes, all laser based
tracking systems demand for single-mode operation which require advanced manufacturing technology. Next generation
tracking systems even require single-polarization characteristics in order to avoid unwanted movement of the pointer
due to polarization flips. High volume manufacturing and optimized production methods are crucial for achieving the
addressed technical and commercial targets of this consumer market. The resulting ideal laser source which emits
single-mode and single-polarization at low cost is also a promising platform for further applications like tuneable diode
laser absorption spectroscopy (TDLAS) or miniature atomic clocks when adapted to the according wavelengths.
In 2007 Finisar® completed the transfer of an entire epitaxial and fabrication line from one facility to another. During
this period, reliability models had to be re-validated and product continuity maintained. In this paper we describe the
activities necessary to support such a transition, and we extend previously published VCSEL failure atlases.
InP-based, long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) with buried tunnel junction are
presented for high-power applications. Various studies of single-devices with large apertures and monolithically
integrated two-dimensional VCSEL arrays are shown. The influence of aperture and array size on laser power, efficiency
and divergence angle is investigated in detail. Unlike GaAs-based devices, large apertures are not favorable due to
thermal issues. Accordingly, we focused on VCSEL arrays and derived scaling rules for optimum performance. This
allows manufacturing high-power devices achieving continuous-wave (CW) optical powers in excess of 3 W at -11°C
heat-sink temperature, circular far-field, low divergence angles around 20° and power densities of 130 W/cm2 at
1.55 μm. To the best of our knowledge, this is the highest power ever reported for a monolithic VCSEL array. At room
temperature, more than 2 W is still available and high-temperature operation up to 70°C is applicable. The driving
voltages around 1.2 V are significantly low, enabling single battery mobile operation. The wall-plug efficiency at room
temperature exceeds 20% in a wide range. Addressing the array in sectors, we found that the array is very homogenous
in performance with a standard deviation of less than 2.8%. Therefore, high-power applications can also be
accomplished by VCSEL technology. As these novel devices with emission wavelengths beyond 1400 nm are less
restrictive with respect to eye-safety, they are also favorable for free-space applications. Additionally, the devices may
be used as concealed infra-red headlights that are invisible for all silicon-based detectors.
We review recent results on high-power, high-efficiency two-dimensional vertical-cavity surface-emitting laser
(VCSEL) arrays emitting around 980nm. Selectively oxidized, bottom-emitting single VCSEL emitters with 51% power
conversion efficiency were developed as the basic building block of these arrays. More than 230W of continuous-wave
(CW) power is demonstrated from a ~5mm x 5mm array chip. In quasi-CW mode, smaller array chips exhibit 100W
output power, corresponding to more than 3.5kW/cm2 of power density. High-brightness arrays have also been
developed for pumping fiber lasers, delivering a fiber output power of 40W. We show that many of the advantages of
low-power single VCSEL devices such as reliability, wavelength stability, low-divergence circular beam, and low-cost
manufacturing are preserved for these high-power arrays. VCSELs thus offer an attractive alternative to the dominant
edge-emitter technology for many applications requiring compact high-power laser sources.
In this paper we summarize production data from serial 10 Gb/s devices and report on 850 nm VCSEL arrays with
channel speeds up to 25 Gb/s. The production data demonstrates that robustness of the basic technology as well as its
suitability for cost effective, high volume production. The >10 Gb/s measurements on two dimensional arrays show that
850 nm VCSEL technology can be extended well beyond the 10 Gb/s links currently beginning to be deployed by
volume field users.
Polarization stability of vertical-cavity surface-emitting lasers (VCSELs) is of crucial importance in particular for single-mode devices used in optical communications and optical sensing. We
will consider major approaches to polarization control and then focus on surface gratings, which provide a monolithically integrated type of polarization-dependent feedback. Single-mode as well as multimode grating VCSELs have been fabricated in large
quantity and have been shown to be polarization-stable with high orthogonal polarization suppression ratio not only for static operation but also under digital and analog modulation, temperature variation, optical feedback, as well as externally
applied stress. After reviewing published work on grating VCSELs,
we will discuss grating design variations by means of extensive
vectorial simulations. The reliability of polarization control is then investigated by studying the characteristics of several thousand VCSELs on a given sample. Finally, as an application example in optical communications, we demonstrate free-space transmission of an aggregate data rate of 16 Gbit/s using polarization division multiplexing with two multimode grating VCSELs.
We describe a robust manufacturing process for single-mode photonic crystal (PhC) vertical-cavity surface-emitting
lasers (VCSELs). The fabrication of the PhC VCSELs is based on a high tolerance manufacturing process only using
optical lithography. We investigate various photonic crystal designs to determine endlessly single mode designs,
whereby the same photonic crystal design yields single mode operation for three different wavelengths (780 nm, 850 nm,
and 980 nm). The PhC VCSELs demonstrate a maximum output power greater than 1 mW under continuous wave
operation with side-mode suppression ratio greater than 35 dB.
In this paper, we present the design and manufacturing of photonic-crystal long-wavelength VCSELs. They were
developed to provide a high-performance low-cost alternative to Fabry-Perot and DFB lasers for 2.5 Gbps applications
within the intermediate range access network. The paper covers photonic-crystal long-wavelength device design,
manufacturing process, DC and AC characteristics, as well as reliability studies. The addition of photonic-crystal
structures to the long-wavelength vertical-cavity surface-emitting lasers allows us to increase the oxide diameter. This
reduces the series resistance as well as the thermal resistance resulting in increased single-mode output-power and an
enhanced high-temperature performance of our devices.
In this article, we present our results on long wavelength (1.1 μm) single-mode micro-structured photonic crystal
strained InGaAs quantum wells VCSELs for optical interconnection applications. Single fundamental mode roomtemperature
continuous-wave lasing operation was demonstrated for devices designed and processed with a number of
different two-dimensional etched patterns. The conventional epitaxial structure was grown by Molecular Beam Epitaxy
(MBE) 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.
At room temperature and in continuous wave operation, micro-structured 50 µm diameter mesa VCSELs with
10 μm oxidation aperture exhibited more than 1 mW optical power, 2 to 5 mA threshold currents and more than 30 dB
side mode suppression ratio at a wavelength of 1090 nm. These structures show slight power reduction but similar
electrical performances than unstructured devices. Systematic static electrical, optical and spectral characterization was
performed on wafer using an automated probe station. Numerical modeling using the MIT Photonic-Bands (MPB )
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 extended wavelength range.
A detailed study of the high-power pulsed operation of C-band optically-pumped GaInNAsSb vertical cavity surface emitting lasers is reported.
The devices employ a resonant periodic gain structure grown by molecular beam epitaxy on a GaAs substrate with a 31-pair GaAs/AlAs bottom
distributed Bragg reflector and a 4-λ,
GaAs-based resonant cavity containing 10 GaInNAsSb quantum wells distributed among the 7 antinodes of the electric field.
A dual-pump-band SiO2/TiO2 dielectric top mirror allows efficient optical pumping via low reflectivities at 808nm and 1064nm
while providing very high reflectivity at the 1.55μm target emission wavelength. The laser characteristics were evaluated using both a Q-switched Nd:YAG
1064nm pump and a 20W-peak 180ns-pulsed 850nm diode laser. The importance of the gain-cavity detuning was evident from time-dependent spectral
measurements of laser material
subjected to post-growth annealing at different temperatures between 725 and 775°C. The highest annealing temperature produces the largest blue shift of the
gain peak relative to the cavity resonance, resulting in the best power transfer characteristics as well as reduced temperature sensitivity.
For a long time, only a small wavelength range of Vertical-Cavity Surface-Emitting Lasers (VCSEL) was available.
The current evolution in process technology allows the fabrication of long wavelength VCSEL that is
interesting for Telecom systems because they offer a higher integration level than the existing optical sources
at lower costs since they are fabricated in arrays. We propose to focus our investigation on the behavior of
singlemode 1.55μm VCSEL. We aim at precisely knowing their spectral properties under direct modulation.
We present a study about the linewidth measurement and the linewidth enhancement factor, also called the
Henry - or the alpha - factor. Many studies have been reported but only a few of them are really efficient. Two
different set-ups are presented here to extract alpha factor. The first one uses an interferometer based on the
heterodyne technique and the second uses the dispersive properties of an optical fiber. We compare both results
and discuss about each set-up.
There are many potential applications of visible, red (650nm - 690nm) vertical cavity surface emitting lasers (VCSELs)
including high speed (Gb) communications using plastic optical fiber (POF), laser mouse sensors, metrology, position
sensing. Uncertainty regarding the reliability of red VCSELs has long been perceived as the most significant roadblock
to their commercialization. In this paper we will present data on red VCSELs optimized for performance and reliability
that will allow exploitation of this class of VCSEL in a wide range of high volume consumer, communication and
VCSELs operating at ~665nm have been fabricated on 4" GaAs substrates using MOCVD as the growth process and
using standard VCSEL processing technology. The active region is AlGaInP-based and the DBR mirrors are made from
AlGaAs. Threshold currents are typically less than 2mA, the devices operate up to >60C and the light output is polarized
in a stable, linear characteristic over all normal operating conditions. The 3dB modulation bandwidth of the devices is in
excess of 3GHz and we have demonstrated the operation of a transceiver module operating at 1.25Gb/s over both SI-POF
Ageing experiments carried out using a matrix of current and temperature stress conditions allows us to estimate that the
time to failure of 1% of devices (TT1%F) is over 200,000h for reasonable use conditions - making these red VCSELs
ready for commercial exploitation in a variety of consumer-type applications. Experiments using appropriate pulsed
driving conditions have resulted in operation of 665nm VCSELs at a temperature of 85°C whilst still offering powers
useable for eye-safe free space and POF communications.
Improving the image quality and speed is an endless demand for printer applications. To meet the market requirements,
we have launched the world first laser printer (DocuColor 1256 GA) introducing 780-nm single-mode 8×4 VCSEL
arrays in the light exposure system in 2003. The DocuColor 1256 GA features 2400 dots per inch (dpi) resolution which
is the highest in the industry and a speed of 50 pages per minute (ppm). A VCSEL array design has an advantage that it
can increase the pixel density and also increase the printing speed by simultaneously scanning the 32-beam to the
photoconductor in the exposure process. Adopting VCSELs as a light source also contributes to the reduction of the
machine's power consumption. The VCSELs are industrially manufactured based on the original in-situ monitored
oxidation process to control the oxide aperture size. As a result, uniform characteristics with a less than 5% variation in
both output power and divergence angle are obtained. Special care is also taken in the assembly process to avoid
additional degradation in performance and quality. This technology is currently extended to high-end tandem color
machines (2400 dpi, 80 ppm) to grasp on-demand publishing market. This paper will cover the key technologies of the
VCSEL based light exposure system as well as its manufacturing process to assure its quality.
There are many applications for non-contact measurement of the displacement and velocity of moving objects, especially
when achieved at low cost. An optical displacement sensor has been developed that can be compared to expensive laser-interferometry
sensors, however at a cost compatible with requirements for consumer products. This miniature Laser-Doppler Interferometer works on all light scattering surfaces. The first large-scale application is in PC-mice.
The measurement principle employs so-called "Laser Self Mixing", which occurs when laser light scattered on a surface,
within the coherence length, is coupled back into the laser cavity. When the object is moving, the back-scattered light is
continuously shifting in phase relative to the laser light at the laser mirror. This results in a periodic perturbation of the
feedback into the laser cavity, which causes modulations of the light intensity in the cavity. The frequency of these
modulations is proportional the speed of the object. A VCSEL, optimized for this application, is used as light source, a
photo-diode in the sensor measures the intensity fluctuations and, finally, an integrated circuit transfers the photo-diode
signal into velocity or displacement information. To determine the direction of the movement, a triangle modulation of
the laser-current is used, which modulates the laser-temperature and hence the laser frequency.
Next to the applications in PC-mice a much wider range of applications as input device in consumer products can be
envisaged. For instance menu navigation by finger movement over a sensor in remote controls, mobile phones and lap
tops. Furthermore a wide field of applications is envisaged in the manufacturing of industrial equipment, which requires
non-contact measurement of the movement of materials. The small form factor of less than 0.2 cubic centimeters allows
applications previously considered impossible.
Low cost and intrinsic performances of 850 nm Vertical Cavity Surface Emitting Lasers (VCSELs) compared
to Light Emitting Diodes make them very attractive for high speed and short distances data communication
links through optical fibers. Weight saving and Electromagnetic Interference withstanding requirements have
led to the need of a reliable solution to improve existing avionics high speed buses (e.g. AFDX) up to 1Gbps
To predict and optimize the performance of the link, the physical behavior of the VCSEL must be well
understood. First, a theoretical study is performed through the rate equations adapted to VCSEL in large
signal modulation. Averaged turn-on delays and oscillation effects are analytically computed and analyzed
for different values of the on- and off state currents. This will affect the eye pattern, timing jitter and Bit Error
Rate (BER) of the signal that must remain within IEEE 802.3 standard limits. In particular, the off-state
current is minimized below the threshold to allow the highest possible Extinction Ratio. At this level, the
spontaneous emission is dominating and leads to significant turn-on delay, turn-on jitter and bit pattern
effects. Also, the transverse multimode behavior of VCSELs, caused by Spatial Hole Burning leads to some
dispersion in the fiber and degradation of BER. VCSEL to Multimode Fiber coupling model is provided for
prediction and optimization of modal dispersion. Lastly, turn-on delay measurements are performed on a real
mock-up and results are compared with calculations.
We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple
quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented
sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final
200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 nm In0.1Ga0.9N well. The peak
emission of the as-grown MQWs sample was ~420nm. A dielectric distributed Bragg reflectors (DBR) were then coated
on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk
GaN bottom surface. The cavity has a quality factor of ~520 from 400-490nm. The device was pumped by a focused CW
HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum
centered at the designed MQW wavelength was observed as expected. However, when the focused position was moved
toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the
designed MQW wavelength.
We have proposed and demonstrated the principle of optical decoupling of the AC modulation component in a lossmodulated
Vertical Cavity Surface Emitting Laser (VCSEL) using a detuned duo-cavity device. This approach allows
the VCSEL power to be modulated without changing the photon density in the active region. Analysis of reflectivity
spectra of a Fabri-Perot cavity with absorber shows that at a certain detuning from the resonance wavelength, reflectivity
is almost independent of absorption magnitude. At this spectral detuning between the active region cavity and modulator
cavity, a feedback-free transmission modulation of the VCSEL output is possible. The use a multiple-double-QW
(MDQW) electroabsorption modulator allows absorption swing between 0.2% and 2% per pass. Optical power
modulation of transmission with contrasts up to 40% and chirp of less than 0.05 nm at 930 nm was demonstrated with
our design. Initial cavity resonance detuning is controlled through growth and was determined to be ideally ~0.7 nm
from analysis of stand-alone absorber cavities. Resonance coupling (splitting) was calculated to be less than 0.3 nm in
case of matching resonances. Applying bias at the MDQW modulator section allows adjustment of detuning between
cavities by changing the top cavity resonance wavelength mainly via Kramers-Kronig relations. The high frequency
modulation characteristics can be tuned in this manner to show little or no sign of resonance, in which case the high
frequency roll-off of the modulation response is entirely determined by parasitics of the modulator section. We have
demonstrated a flat (+/-3db) response up to 20 GHz.
Proc. SPIE 6908, GaInNAsSb/GaAs vertical cavity surface-emitting lasers (VCSELs): current challenges and techniques to realize multiple-wavelength laser arrays at 1.55 μm, 69080N (1 February 2008); doi: 10.1117/12.762311
Multiple-wavelength laser arrays at 1.55 μm are key components of wavelength division multiplexing (WDM) systems
for increased bandwidth. Vertical cavity surface-emitting lasers (VCSELs) grown on GaAs substrates outperform their
InP counterparts in several points. We summarize the current challenges to realize continuous-wave (CW) GaInNAsSb
VCSELs on GaAs with 1.55 μm emission wavelength and explain the work in progress to realize CW GaInNAsSb
VCSELs. Finally, we detail two techniques to realize GaInNAsSb multiple-wavelength VCSEL arrays at 1.55 μm. The
first technique involves the incorporation of a photonic crystal into the upper mirror. Simulation results for GaAs-based
VCSEL arrays at 1.55 μm are shown. The second technique uses non-uniform molecular beam epitaxy (MBE). We have
successfully demonstrated 1x6 resonant cavity light-emitting diode arrays at 850 nm using this technique, with
wavelength spacing of 0.4 nm between devices and present these results.