New 40 Gbit/s GaAs Modulators with Low Drive Voltage
u²t Photonics of Berlin, Germany, has announced the availability of new Mach-Zender modulators based on gallium arsenide semiconductor technology.
The new modulators are designed for telecommunications applications and are suitable microwave photonics uses as well. Drive voltage of 3V, bandwidth of 30 GHz, and highly accurate modulation characteristics are combined on a platform capable of exploiting high-volume manufacturing processes.
From the press release:
“This robust manufacturing capability makes it ideal for highly integrated products, especially for complex modulation schemes such as DQPSK and DP-QPSK which form the u²t modulator product family.”
The new Mach-Zender modulators complement u²t’s photodetector and photoreceiver products offered with a bandwidth of up to 100 GHz.
For more information on the new modulators, click here.
A new generation of PM-DPSK coherent optical transceivers include sophisticated new DSP chips running algorithms for clock and data recovery, polarization demultiplexing and mitigation of impairments such as PMD, CD, and OSNR.
The challenge for these new polarization-sensitive transceivers is to guarantee that they can continue to send and receive signals even when the state of polarization (SOP) changes rapidly, as can be the case in aerial fiber plant or when moving fibers in the central office.
New Ridge Technologies’ NRT-2500 Polarization Control Platform provides a comprehensive toolkit for testing polarization-sensitive transceivers. The NRT-2500 can set, scramble, randomize and track polarization state to support a wide variety of polarization-related test scenarios. An overview of these capabilities is available here, with a video overview of the platform here.
A new capability, called the Spinner Mode, was designed specifically for testing 40G and 100G polarization sensitive transponders. In this mode, a rotating ½-waveplate is simulated with a user-settable SOP rotation speed up to 50 kHz (300,000 Radians/sec for linear polarized light). In addition to being super fast, the Spinner mode changes the SOP in an endless, controllable and repeatable manner, covering all tilts, angles and ellipticities on the Poincaré Sphere.
This is the ultimate tool for testing the polarization tracking capability of DSP-equalized transceivers. View a demonstration of the Polarization Spinner feature of the NRT-2500 Polarization Control Platform by clicking here.
Advanced Silicon Photonics at UW
The University of Washington in Seattle has launched Optoelectronic Systems Integration in Silicon (OpSIS), a center for accelerating innovation in silicon photonics technologies.
The new silicon wafer service enables researchers to pool resources for optoelectronic chip fabrication. Cost sharing across multiple research projects lowers costs for creating complex photonic-electronic microcircuits on the scale of today’s CPUs.
OpSIS is a component of the UW’s Institute for Photonic Integration under director Michael Hochberg and is co-funded with Intel (INTC). Additional partners are the US Air Force and BAE Systems.
Hochberg was quoted in the Wall Street Journal citing applications in biomedical sensing and radar where significant advances await the kind of deep integration that will be made more widely available to researchers through OpSIS. A similar effort was undertaken a generation ago at the University of Southern California and helped fuel the massive integration of microelectronic systems that are at the heart of today’s technological wonders. OpSIS has the potential to drive similar advances in chips that use both electrons and photons to process information.
Mitigating PMD for High Speed Optical Transmission
Polarization Mode Dispersion (PMD) analyzers are available on the market today that provide reliable assessment of PMD contribution in each span of an optical link, measured from a single end.
By providing span-level assessment, network operators can mitigate problems by rerouting or upgrading just a section of an entire link, with a dramatic cost savings over the option of replacing an entire fiber run.
EXFO’s FTB-5600 Distributed PMD Analyzer is a single-ended instrument that requires only one technician with minimal technical expertise to troubleshoot PMD in a fiber run. It not only measures the PMD from the far-end connector, but uses distributed Rayleigh backscattering to actually measure cumulative PMD on the entire fiber link.
For more information, download an application note here.
ROADM Validation and 40G Commissioning Issues
John Lastowka, President of All-Tech Communications, LLC, was recorded speaking about Optical Signal to Noise (OSNR) measurements in 40G optical networks.
In-band OSNR measurements assure network engineers that crosstalk will not be a significant factor affecting their ability to meet SLA requirements, according to Lastowka.
The video was produced and posted by EXFO of Quebec, Canada. You can view it here.
Measuring Impact of Second-Order PMD
Second-order Polarization Mode Dispersion (SOPMD) is an important consideration when calculating statistical availability of an optical link. This in an assertion of Henry Yaffe, PhD, President of New Ridge Technologies of Owings Mills, Maryland, USA.
PMD-caused outages of a network will be underestimated if only first-order PMD (also known as Differential Group Delay, DGD) is considered.
“Statistically, the SOPMD level positively correlates with the DGD level. The magnitude of the depolarization component of SOPMD increases with increasing DGD in a linear manner. As DGD gets worse, SOPMD also gets worse. Moreover SOPMD depends on the modulation bandwidth of the signal. As bit rates increase the SOPMD also increases.”
New Ridge Technologies specializes in characterization of PMD tolerance of optical networks and includes both DGD and SOPMD assessment to determine overall network PMD tolerance.
A definition of SOPMD and discussion of its importance is available here. New Ridge Technologies’ range of PMD sources and emulators is described here.
Graphical display of SOPMD can be extracted from measured Jones Matrix data, as outlined in a whitepaper from Luna Technologies of Blacksburg, Virginia. Details on measurement of Jones Matrix elements using a swept-wavelength Optical Vector Analyzer can be found here.
PMD and Mode-Coupling in Telecom Fibers
EXFO’s Francis Audet has written a cautionary application note warning that PMD measurements in the field should be made with instrumentation accuracy specified for conditions that will be obtained on real-world fibers.
“Some test equipment vendors base their accuracy specifications on weak-mode coupling, a condition never seen in network scenarios and that is extremely easy to measure and qualify. An accuracy value based on a test scenario that will never be seen in the field cannot guarantee anything on real-world fibers. Some other test equipment vendors tackle the challenge and specify accuracy with strong-mode coupling. This accuracy is often not as good as the values quoted on weak-mode coupling, but it is a usable number and certainly has a true accuracy rate that is much higher than those specifying only weak-mode coupling values, which are in reality focusing on a specification rather than an application.”
The application note can be found here. A collection of resources for PMD measurement can be found here.
20 GHz Mini Microwave Photoreceiver
Linear Photonics’ MiniPR represents a breakthrough in size and ease of use, enabling connection of microwave analog photoreceivers directly to optical and RF
connectors.
MiniPR is available in bandwidths of 12 or 20 GHz, with options for either RF-coupled or internal DC biasing. It is also available with either FC/PC or FC/APC optical connector. The datasheet is available here. Resources for microwave photonic applications can be found here.
Avionics Optical Link Health Monitoring
The unique characteristics of optical fiber installations in aircraft call for specialized measurement techniques.
In a paper by Roger G. Duncan, et al, of Luna Technologies of Blacksburg, VA, measurement techniques suitable for fault location in short-run optical communication links are described. Precise localization and identification of cracks and breaks, as well as losses due to bends, splices and connectors is outlined.
Assessment of optical link health may also include measurement of temperature and strain variations on the fiber itself. Distributed temperature and strain measurements along a fiber run may also identify loss or nascent fault conditions arising from careless or poorly routed installation.
The whitepaper can be downloaded here. Additional articles on applications of optical fiber in avionics can be found here.
Microwave Photonics Links to 30 GHz
Microwave photonic links permit the distribution of communication and sensing signals over large distances between facilities, or within a single facility, on optical fiber, without the signal degradation found in coax copper signal distribution. Electromagnetic susceptibility is eliminated, longer distances can be traversed without signal loss, and the communications traffic is more secure.
Inter-facility links with flat gain and RF bandwidth of 5, 12, or 30 GHz can be used for signal and antenna remoting applications, radar and information processing.
A datasheet can be found here. Additional resources on microwave photonics applications can be found here.
