KEYWORDS: Data centers, Modulation, Transmitters, Single mode fibers, Wavelength division multiplexing, Eye, Transmittance, Digital signal processing, Laser sintering, Optical amplifiers
A 200-Gb / s wavelength-division multiplexing transmission system using multiwavelength directly modulated transmitter optical subassemblies for data center has been proposed and demonstrated experimentally. The 8 × 25 Gb / s PAM-4 optical transmission system over 10 km of standard single-mode fiber is tested. The penalty variation within 1 dB for eight channels indicates that colorless transmission operation in the C-band is feasible with stable performance. Clear eye openings without any distortion show a good linearity characteristic for the optical transmission system. The advantages of integration, channelization, miniaturization, and low power consumption of the proposed scheme present a promising result for data center interconnection.
In this paper, the influence of packaging on the high speed performance of photodetector (PD) is systematically and comprehensively studied. Combined with the equivalent circuit, the RF attenuation induced by packaging in PD module is investigated in detail. The microwave transmission performance of the PD module has been analyzed and optimized in three regions: the RF substrate, the connection between the coaxial connector and the substrate, and the parasitic parameters introduced by packaging. With the optimized scheme, a packaged PD module with a 3dB bandwidth of 23GHz is fabricated and its bandwidth has no degradation compared to the photodiode chip. The results indicate that the performance of the PD module can be compensated by optimizing the packaging design and the optimized scheme can be used for PD module which has a higher response speed.
KEYWORDS: Free space optics, Telecommunications, Atmospheric turbulence, Free space optical communications, Signal to noise ratio, Atmospheric optics, Turbulence, Acquisition tracking and pointing, Modulation, Transmitters
The performance of a free-space optical communication system is highly affected by the atmospheric turbulence in terms of scintillation. An optical communication system based on intensity-modulation direct-detection was built with 1-km transmission distance to evaluate the bit error rate (BER) performance over real atmospheric turbulence. 2.5-, 5-, and 10-Gbps data rate transmissions were carried out, where error-free transmission could be achieved during over 37% of the 2.5-Gbps transmissions and over 43% of the 5-Gbps transmissions. In the rest of the transmissions, BER deteriorated as the refractive-index structure constant increased, while the two measured items have almost the same trend.
KEYWORDS: Modulation, Analog electronics, Semiconductor lasers, Intermodulation, Radio optics, Laser optics, Microwave radiation, Laser applications, Signal to noise ratio, Photodetectors
We fabricated a narrow linewidth 1.55μm directly-modulated distributed-feedback (DFB) laser. The laser exhibits an
output power of 14mW at 100mA, flat frequency response with -3 dB bandwidth of 18 GHz, the third-order
intermodulation distortion (IMD3) with 39.8dBm, narrow optical linewidth with 181kHz, and RIN below -135.7dB/Hz
in the 0.1-10GHz range along with the high side-mode suppression ratio (<52dB). We also experimentally verified the
modulation bandwidth, linearity, and linewidth is related to the bias current. The characteristics of the laser, namely
sufficient modulation bandwidth, high linearity, low relative intensity noise (RIN) and narrow linewidth, make it the
perfect candidates for high dynamic directly modulated analog optical link.
An ultra wideband optical frequency comb (OFC) generator based on semiconductor Quantum dot F-P cavity is packaged by our group. The free spectral rage (FSR) of the OFC can be tunable from 97GHz to 100GHz and the pulse width of the 100GHz OFC is 1.2ps.The full span of the OFC spectra is 80nm with a Gaussian shaped, and in span of 10nm, the flatness of the OFC can be limited to 1.7dB. The OFC has the advantages of small volume, simple and compact structure, low power dissipation, and has an ultra-wide bandwidth and flat spectrum, which can be used in the field of arbitrary waveform generation, channel information processing, and optical frequency division multiplexing.
The dynamic control for the spectra of the Ultra-wideband (UWB) signals, which is the key for implementing the dynamic spectrum access in the cognitive radio, is still a challenge due to the limited processing speed of the electronic devices. In this paper, we have summarized our recent work about controlling the spectrum shape of the UWB signals in optical domain, in addition to reviewing the other groups’ related research work. The experiment setups and results based on nonlinear dynamics of the optoelectronic oscillator and transfer response of the phase or polarization-to-intensity convertor will be described in detail respectively, in which the controllable frequency suppress for the optical UWB signals at specific frequency positions were implemented. Particularly, the UWB pulse with the special shape, which corresponds to the 5-GHz band-rejection in frequency domain, was generated in order to avoid the interference between UWB and Wireless Fidelity system in practice. In addition, the UWB signals whose center frequency could be continuously tuned and converted up to the frequency range of millimeter wave were generated by utilizing the polarization modulator based optical switch. The areas for future development and the challenge of implementing these techniques for the applications in practice will also be discussed.
In this letter, we put forward a new kind of polarization-maintaining index-guiding photonic crystal fiber (PM-IG-PCF).
It is made up of a solid silica core, two big circular air holes near the core and a cladding with elliptical air holes. By
making use of a full-vector finite-element method (FEM), we study the modal birefringence and polarization mode
dispersion (PMD) as a function of the normalized wavelength of fundamental modes in the PM-IG-PCF we proposed.
Numerical results show that very high modal birefringence with magnitude of order of 10-3 has been obtained, which is
higher than the birefringence induced by adding two big air holes near the core or elliptical air holes in cladding
separately. Furthermore, the chromatic dispersion curves of the two orthogonal polarizations for the birefringence PCF
are presented as a function of the normalized wavelength.
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