We present the results of the implementation of two VCSEL-based optoelectronic oscillators (VBO) using one on-chip 850-nm vertical-cavity surface-emitting laser (VCSEL). The reported VBOs are implemented at 10 and 12 GHz using a direct-modulated VCSEL. The laser direct modulation bandwidth is 13.3 GHz. The VBOs performance is described through the phase noise and time-domain stability.
Due to expected capacity bottlenecks of exploited microwave technologies, feeder links for data relay or broadband access systems will require the implementation of high capacity optical communication links between space and ground. In this context, it is necessary a detailed investigation of the optical technologies and techniques that could enable the transmission of high data rates at optical frequencies through the Earth’s atmosphere, with regard to all kinds of atmospheric phenomena. In particular, the adverse effects of atmospheric turbulence fading are of special relevance to optical communication systems for ground-to-space uplink applications. Although previous studies and experiments have demonstrated the feasibility of such optical links at low data rate, research is still needed to identify technical solutions and strategies adapted to the specific constraints imposed to these high-speed links in order to ensure the required level of performance. Against this background, various test benches have been developed in order to characterize different modulation and detection techniques for optical communication systems prior to be incorporated in the conceptual design of future 1-Tb/s ground-space optical links. The expected performances of such an experimental demonstration are derived based on simulation models taking into account atmospheric turbulence effects, in order to prove the feasibility of reliable ground-space high date rate optical communication links. Our first simulation studies, considering On-Off Keying (OOK) and Differential Phase Shift Keying (DPSK) modulations, have allowed us to understand the complexity of the link and to optimize both the transmitter and the receiver to achieve acceptable performance levels.
Interest in free space optical communications has increased in the last decades as it has many advantages over RF communications, especially for space-borne applications. However, high power, good spectral quality and beam quality are needed for efficient data transmission over long distances. To meet the need of having lightweight and compact laser sources with such qualities for FSO, semiconductor based MOPA systems (Master Oscillator Power Amplifier) have been developed. In this paper we present the experimental results and compare them to simulation results for a threesection monolithically integrated semiconductor Master Oscillator Power Amplifier emitting at 1.5 μm wavelengths, designed for LIDAR applications that can also be used for free space telecommunications. The MOPA includes a distributed feedback laser section for single mode light emission, an intermediate section for data modulation and a flared semiconductor optical amplifier section for power amplification, which allows us to generate a high power beam with good spectral characteristics. The impact of bias conditions of the different device sections and device design on performances have been studied. Single mode operation at 4 different wavelengths near 1550 nm is achieved for optical output power up to 400 mW in continuous-wave (CW) regime for a SOA current of 3 A and 800 mW for SOA pulsed operation for currents up to 5 A. Near-field profile is also analyzed for different modulator current. Small-signal dynamic response is measured and analyzed.
By using existing single mode components developed for fiber technologies (optical detectors and amplifiers, MUX/DEMUX...), the very high throughput of future satellite-to-ground optical communication links might be achievable at a reasonable cost.
The optical injection locking (OIL) technique is proposed to reduce the phase noise of a carrier generated for a vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator. The OIL technique permits the enhancement of the VCSEL direct modulation bandwidth as well as the stabilization of the optical noise of the laser. A 2-km delay line, 10-GHz optical injection-locked VCSEL-based optoelectronic oscillator (OILVBO) was implemented. The internal noise sources of the optoelectronic oscillator components were characterized and analyzed to understand the noise conversion of the system into phase noise in the oscillator carrier. The implemented OILVBO phase noise was −105.7 dBc/Hz at 10 kHz from the carrier; this value agrees well with the performed simulated analysis. From the computed and measured phase noise curves, it is possible to infer the noise processes that take place inside the OILVBO. As a second measurement of the oscillation quality, a time-domain analysis was done through the Allan’s standard deviation measurement, reported for first time for an optoelectronic oscillator using the OIL technique.
In this paper, optical uplink and downlink are studied in order to ensure the feeder link of the next generation of broadband geostationary satellite with capacity around 1Tbps. For such capacity, optical links are commonly based on pre-amplified optical receiver with Single Mode Fiber (SMF) optical amplifier. Adaptive optic systems are necessary to compensate the distortions embedded by the atmospheric turbulences that decrease the injection efficiency of the downlink and the pointing accuracy of uplink. This paper is focused on the performances achievable with a simple system based on a single fine pointing mechanism. Considering a digital optical feeder link that is transparent with respect to the user segment, a promising capacity per satellite of 300GHz is achieved.
KEYWORDS: Free space optics, Modulation, Receivers, Signal detection, Digital signal processing, Signal attenuation, Phase shift keying, Satellites, Adaptive optics, Modulators
The use of optical communication to transfer data between LEO satellite and optical ground station is being studied. It
creates the opportunities to highly increase a transmitted data rate across a free space. The optical propagation channel
has specificities that imply the potential use of error correcting code (ECC) and interleaving at physical and higher layer.
The study aims to assess the performance of a combination of ECC and interleaving in presence of various channel
scenarios and receiver architectures. As a result of these studies, a functional physical layer simulator is provided. The
simulator emulates a signal generation and applies time series representing the propagation channel with an effect of
receiver front-ends. It also features various detection methods and computes mutual information (MI) in order to
approximate ECC performances. A number of receiver architectures and channel scenarios were studied. The channel
scenarios combine a direct coupling of the received signal into the photo-detector (PD) and among other assume the use
of pre-amplified receiver implying the signal coupling into a standard single mode fiber (SSMF) prior to the detection.
Time series were generated and represent the power received at PD input depending on the chosen scenarios (without
adaptive optics (AO), with tip-tilt correction, with no dynamical coupling losses or with higher order AO correction).
Two modulations of OOK and DBPSK along with various detection methods were examined. The tuning of ECC
parameters was studied through the computation of mutual information. Additionally two cases of physical and higher
layer interleaving were implemented providing an excellent diversity to the channel seen by the codeword of ECC.
In this article we propose a long wavelength VCSEL by VCSEL Optoelectronic Oscillator to generate high frequency carriers. Stability and quality are key factors to use Vertical-Cavity Surface-Emitting Lasers (VCSELs) in VCSEL Based Optoelectronic Oscillators (VBO). To enhance the performance of a 2.49 GHz VBO presented in [1]. The use of the optical injection locking technique applied to the VBO laser pump contributes to the VCSEL Relative Intensity Noise (RIN) reduction, and the increase of the modulation bandwidth that leads to a carrier phase noise reduction. The Injection Locked VCSEL Based Oscillator (ILVBO) performance will be presented and discussed taking into account the injection locking conditions of the laser source.
In this paper, we study the critical parameters of 1550 nm vertical-cavity surface-emitting lasers (VCSEL) for several applications in space environment like satellite (telecommunications and observation) and deep space (probes and rover). The analysis is focus in the main parameters degrading the VCSEL behavior in wide application field. These parameters are the optical output power, the threshold current and the relative noise intensity (RIN) according to the temperature that affects the storage and mostly the operation of the laser diode. Characterization processes and results are presented here.
Optical links at 1.55μm are envisaged to cope with the increasing capacity demand from geostationary telecom satellite
operators without the need of Radio Frequency (RF) coordination. Due to clouds blockages, site diversity techniques based
on a network of Optical Ground Stations (OGS) are necessary to reach the commonly required link availability (e.g. 99.9%
over the year). Evaluation of the N Optical Ground Station Network (N-OGSN) availability is based on Clouds Masks
(CMs) and depends on the clouds attenuation taken in the optical communication budget link. In particular, low attenuation
of high semitransparent clouds (i.e. cirrus) could be incorporated into the budget link at the price of larger or more powerful
optical terminals. In this paper, we present a method for the calibration of the attenuation at 1.55 μm of high semitransparent
clouds. We perform OGS localization optimization in Europe and we find that the incorporation of thin cirrus attenuation
in the budget link reduces by 20% the number of handover (i.e. switches OGS) and the handover rate. It is also shown that
the minimum number of station required in Europe to reach 99.9% link availability is 10 to 11. When the zone of research
is enlarged the Africa, this number is reduced to 3 to 4.
We present here a 1.55 μm single mode Vertical-Cavity Surface-Emitting Laser (VCSEL) based low phasenoise
ring optoelectronic (OEO) oscillator operating at 2.49 GHz for aerospace, avionics and embedded systems
applications. Experiments using optical fibers of different lengths have been carried out to obtain optimal results.
A phase-noise measurement of -107 dBc/Hz at an offset of 10 kHz from the carrier is obtained. A 3-dB linewidth
of 16 Hz for this oscillator signal has been measured. An analysis of lateral mode spacing or Free Spectral Range
(FSR) as a function of fiber length has been carried out. A parametric comparison with DFB Laser-based and
multimode VCSEL-based opto-electronic oscillators is also presented.
Optical communication systems have been widely preferred for network communications, especially for
Datacoms Local Area Network links. The optical technology is an excellent candidate for on-board systems
due to the potential weight saving and EMC immunity. According to the short length of the link and a cost
saving, Vertical Cavity Surface Emitting Laser (VCSEL) and multimode fiber are the best solution for gigabit
systems. In this context, we propose a modeling of 850nm VCSEL based on the rate equations analysis to
predict the optical interconnect performances (jitter, bit error rate). Our aim is to define the operation
conditions of VCSEL under large signal modulation in order to maximize the Extinction Ratio (current IOFF
below threshold) without affecting link performances. The VCSEL model is developed to provide large signal
modulation response. Biasing below threshold causes stochastic turn-on delay. Fluctuations of this delay
occur, due to the spontaneous emission. This leads to additional turn-on jitter. These stochastic effects are
included in the model by adding the Langevin photon and electron noise sources.
The VCSEL behavior under high-speed modulation is studied to observe the transient response and extract the
resonance frequency, overshoot and turn-on delay. The associated jitter is evaluated with the standard
deviation of the turn-on delay probability density function.
Simulations of stochastic and deterministic jitters are realized under different conditions of modulation (OFF
current levels). Comparing simulations with measurement results carried out on VCSEL and a short haul
gigabit link validates the approach.
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
over 100m.
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.
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.
Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers
(VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain best
current confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent
electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy to
integrate with classical software for circuit studies, this model which is widely adaptable for different structures takes
into account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10
GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic values
for the VCSEL intrinsic parameters.
Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current and
voltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz for
monomodal emitter.
The integration of different components in optoelectronics modules, such as VCSEL and photodiode arrays, optical guides and electronics, introduces optoelectronical, thermal and mechanical interactions. In this context, a thermal and optoelectronic model of VCSEL array is proposed. The self and cross heating of VCSEL arrays have been simulated. The thermal behavior of VCSEL in the array can be modeled by an equivalent circuit model. A small signal electrical equivalent circuit is also presented. This model is obtained from the electrical effects in the component structure and the identification with the rate equations. The models have been validated with 850nm VCSEL arrays characterization.
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