43,864 research outputs found
Thermal analysis of high-bandwidth and energy-efficient 980ânm VCSELs with optimized quantum well gain peak-to-cavity resonance wavelength offset
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 111, 243508 (2017) and may be found at https://doi.org/10.1063/1.5003288.The static and dynamic performance of vertical-cavity surface-emitting lasers (VCSELs) used as light-sources for optical interconnects is highly influenced by temperature. We study the effect of temperature on the performance of high-speed energy-efficient 980ânm VCSELs with a peak wavelength of the quantum well offset to the wavelength of the fundamental longitudinal device cavity mode so that they are aligned at around 60â°C. A simple method to obtain the thermal resistance of the VCSELs as a function of ambient temperature is described, allowing us to extract the active region temperature and the temperature dependence of the dynamic and static parameters. At low bias currents, we can see an increase of the â3âdB modulation bandwidth fâ3dB with increasing active region temperature, which is different from the classically known situation. From the detailed analysis of fâ3dB versus the active region temperature, we obtain a better understanding of the thermal limitations of VCSELs, giving a basis for next generation device designs with improved temperature stability
High Efficiency Power Amplifier Based on Envelope Elimination and Restoration Technique
Due to complex envelope and phase modulation employed in modern transmitters it is necessary to use power amplifiers that have high linearity. Linear power amplifiers (classes A, B and AB) are commonly used, but they suffer from low efficiency especially if the transmitted signal has high peak to average power ratio (PAPR). Kahn's technique based on envelope elimination and restoration (EER) is based on idea that high efficiency power supply (envelope amplifier) could be used to modulate the envelope of high efficient non linear power amplifiers (classes D or E). This paper presents solutions for power amplifier that performs envelope modulation and class E amplifier that is used as a non linear amplifier. The envelope amplifier is implemented as a multilevel converter in series with linear regulator and can provide up to 100 W of instantaneous power and reproduce 2 MHz sine wave. The implemented Class E amplifier can operate at 120 MHz with efficiency near to 85%. The envelope amplifier and class E amplifier have been integrated and efficiency and linearity of the implemented transmitter has been measured and presente
On the Power Spectral Density of the GSM Signaling Scheme
In this paper, the Power Spectral Density of encoded Gaussian Minimum Shift Keying
(GMSK) which is the Signaling Scheme of the Global System for Mobile Communication
(GSM) is derived by a combined approach of the autocorrelation method and Markov
Process. In the analysis, the Amplitude Modulated Pulse decomposition proposed by P.
Laurent is employed to ease computation. Encoding of the message data utilizes
Convolutional Code of rate1/2. Results are for both the uncoded and coded waveform
comparing variation in power spread over a range of frequency
Mid-Infrared nonlinear silicon photonics
Recently there has been a growing interest in mid-infrared (mid-IR) photonic technology with a wavelength of operation approximately from 2-14 mu m. Among several established mid-IR photonic platforms, silicon nanophotonic platform could potentially offer ultra-compact, and monolithically integrated mid-IR photonic devices and device arrays, which could have board impact in the mid-IR technology, such as molecular spectroscopy, and imaging. At room temperature, silicon has a bandgap similar to 1.12 eV resulting in vanishing two-photon absorption (TPA) for mid-IR wavelengths beyond 2.2 mu m, which, coupled with silicon's large nonlinear index of refraction and its strong waveguide optical confinement, enables efficient nonlinear processes in the mid-IR. By taking advantage of these nonlinear processes and judicious dispersion engineering in silicon waveguides, we have recently demonstrated a handful of silicon mid-IR nonlinear components, including optical parametric amplifiers (OPA), broadband sources, and a wavelength translator. Silicon nanophotonic waveguide's anomalous dispersion design, providing four-wave-mixing (FWM) phase-matching, has enabled the first demonstration of silicon mid-IR optical parametric amplifier (OPA) with a net off-chip gain exceeding 13 dB. In addition, reduction of propagation losses and balanced second and fourth order waveguide dispersion design led to an OPA with an extremely broadband gain spectrum from 1.9-2.5 mu m and > 50 dB parametric gain, upon which several novel silicon mid-IR light sources were built, including a mid-IR optical parametric oscillator, and a supercontinuum source. Finally, a mid-IR wavelength translation device, capable of translating signals near 2.4 mu m to the telecom-band near 1.6 mu m with simultaneous 19 dB gain, was demonstrated
Broadband energy-efficient optical modulation by hybrid integration of silicon nanophotonics and organic electro-optic polymer
Silicon-organic hybrid integrated devices have emerging applications ranging
from high-speed optical interconnects to photonic electromagnetic-field
sensors. Silicon slot photonic crystal waveguides (PCWs) filled with
electro-optic (EO) polymers combine the slow-light effect in PCWs with the high
polarizability of EO polymers, which promises the realization of
high-performance optical modulators. In this paper, a broadband,
power-efficient, low-dispersion, and compact optical modulator based on an EO
polymer filled silicon slot PCW is presented. A small voltage-length product of
V{\pi}*L=0.282Vmm is achieved, corresponding to an unprecedented record-high
effective in-device EO coefficient (r33) of 1230pm/V. Assisted by a backside
gate voltage, the modulation response up to 50GHz is observed, with a 3-dB
bandwidth of 15GHz, and the estimated energy consumption is 94.4fJ/bit at
10Gbit/s. Furthermore, lattice-shifted PCWs are utilized to enhance the optical
bandwidth by a factor of ~10X over other modulators based on
non-band-engineered PCWs and ring-resonators.Comment: 12 pages, 4 figures, SPIE Photonics West Conference 201
On the Performance of Single- and Multi-carrier Modulation Schemes for Indoor Visible Light Communication Systems
In this paper, we investigate and compare the performance of single- and
multi-carrier modulation schemes for indoor visible light communication (VLC).
Particularly, the performances of single carrier frequency domain equalization
(SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying
(OOK) with minimum mean square error equalization (MMSE) are analyzed in order
to mitigate the effect of multipath distortion of the indoor optical channel
where nonlinearity distortion of light emitting diode (LED) transfer function
is taken into account. Our results indicate that SCFDE system, in contrast to
OFDM system, does not suffer from high peak to average power ratio (PAPR) and
can outperform OFDM and OOK systems. We further investigate the impact of LED
bias point on the performance of OFDM systems and show that biasing LED with
the optimum value can significantly enhance the performance of the system.
Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE
systems to further compensate signal degradation due to inter-symbol
interference (ISI) and LED nonlinearity.Comment: 6 Pages, IEEE Globecom conference 201
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