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O-Band Fiber Amplifier (PDFA)![]()
PDFA100 Single Mode PDFA, FC/APC 50 GBaud/s PAM4 Eye Diagram from the PDFA100 ![]() Please Wait ![]() Click to Enlarge Typical gain spectrum for the PDFA100 optical amplifier. A complete set of performance graphs is available on the Graphs tab. ![]() Click to Enlarge Operating Principle of the PDFA Features
Applications
Thorlabs' Praseodymium-Doped Fiber Amplifier (PDFA) offers high gain (>20 dB small signal gain), high output power (>16 dBm), and a low noise figure (<8 dB), making it ideal for use within optical networks as either a booster amplifier or preamplifier. As Pr ions in silica transition to a lower excited state nonradiatively, these PDFAs are designed and manufactured by Thorlabs using proprietary fluoride fiber. Please see the PDF Emission tab for more information on light emission in Pr-doped fluoride fibers (PDF). The PDFA incorporates a relatively short length of PDF, which results in a signal latency <100 ns. Fiber amplifier technology offers key advantages over semiconductor optical amplifiers (SOAs) when used for boosting communication signals. Distortion effects typically associated with the saturation mechanism and gain dynamics of SOAs do not exist in PDFAs, leading to improved compatibility with wavelength division multiplexed systems, advanced modulation formats, and high data rates. In particular, undesirable distortion effects such as cross-gain modulation and pattern dependence are eliminated in the PDFA as a result of its high saturation energy and slow gain dynamics. The PDFA gain dynamics are independent of pulse shape or modulation format due to a long upper-state lifetime that leads to negligible cross-talk between adjacent channels. For a comparison between the resulting PDFA and SOA eye diagrams, please see the PDFA vs. SOA tab. Featuring a ripple-free, or flat, gain spectrum, the PDFA produces uniform gain over a number of channels, which eliminates channel mismatches at the end of a link. The resulting clean, stable output is ideal for improving the power budget in data center applications. As shown in the schematic to the right, the main components of the PDFA include a wavelength-division multiplexer (WDM), input and output isolators, and a PDF. The WDM is used to combine the pump laser and O-band signal light before the PDF, while the isolators, which only allow light to travel in one direction, prevent lasing by minimizing back reflections. The input and output isolators also serve to prevent any spontaneous emission signal from entering the amplifier and the pump light from exiting the amplifier, respectively. Each fiber amplifier is enclosed in a compact benchtop package with FC/APC (2.0 mm narrow key) input and output connectors. The instrument's front panel includes an adjustment knob for tuning the pump current of the PDFA. This device also features a display screen that shows the pump level, as well as the temperature and emission status. To show when the internal laser is active, an indicator LED is included on the enable button; this will blink rapidly for three seconds before the amplifier turns on. For additional safety, the user may connect an interlock circuit to the BNC connector on the rear panel. The PDFA uses a universal power supply allowing operation over 100 - 240 VAC without the need to select the line voltage. A region-specific power cord is included. Operation Modes The command line interface can also be used to enable or disable the amplifier, set the current level in the ACC mode, or read status indicators. The indicators available through the USB interface include temperature error, interlock status, and emission status. For more details on these features, please refer to the instrument manual. For applications that require PDFAs with custom form factors, power consumption, or optical specifications, please contact Tech Support. Thorlabs also offers Ytterbium-Doped Fiber Amplifiers (YDFAs) and Erbium-Doped Fiber Amplifiers (EDFAs), which operate in the 1025 - 1075 nm and 1530 - 1565 nm (C-band) wavelength ranges, respectively.
Performance GraphsPerformance may vary from unit to unit; this data reflects the typical performance of our PDFAs, and is presented for reference only. The guaranteed specifications are shown in the Specs tab. Wavelength Dependence![]() Click to Enlarge Click for Raw Data The typical gain as a function of the wavelength. The blue-shaded region denotes the specified operating wavelength range. Data is measured with the pump level set at 100%. ![]() Click to Enlarge Click for Raw Data The typical noise figure as a function of the wavelength. The blue-shaded region denotes the specified operating wavelength range. Data is measured with the pump level set at 100%. Input Power and Pump Level Dependence at 1310 nm![]() Click to Enlarge Click for Raw Data The typical output power as a function of input power at 1310 nm. Data is measured with the pump level set at 100%. ![]() Click to Enlarge Click for Raw Data The typical noise figure as a function of input power at 1310 nm. Data is measured with the pump level set at 100%. ![]() Click to Enlarge Click for Raw Data The typical gain as a function of input power at 1310 nm. Data is measured with the pump level set at 100%. Distortion-Free Amplification![]() Click to Enlarge 50 GBaud/s Eye Diagram for a Commerically Available SOA ![]() Click to Enlarge 50 GBaud/s Eye Diagram for the PDFA100 Fiber Amplifier One advantage of Praseodymium-Doped Fiber Amplifiers (PDFAs), in comparison to semiconductor optical amplifiers (SOAs), is their slow gain dynamics. Communication signals include pulse sequences with random patterns. In the simple case of an on-off-keying (OOK) and non-return-to-zero (NRZ) format, the pulses have identical amplitudes but their width can vary from one bit period (20 ps for 50 Gb/s data rate) to many bit periods, depending on the type of data being transmitted. As a result, if the amplifier gain saturation has a time constant comparable to the bit period, the gain of the amplifier exhibits pattern dependence. This effect can result in severely distorted optical signals when the amplifier is driven into saturation. SOAs typically have carrier lifetimes on the order of tens of picoseconds, and pattern dependence is observed at standard communication data rates when they are driven into saturation. In contrast, PDFAs have an upper-state lifetime in the millisecond range, which makes them immune to this pattern dependence. This distinguishing characteristic between SOAs and fiber amplifiers has been previously studied for OOK with return-to-zero (RZ) and NRZ modulation formats1. Signal distortion becomes a more severe issue in modern modulation formats, such as 4-level pulse amplitude modulation (PAM4). Footnotes
The Praseodymium-Doped Fluoride Fiber Amplifier (PDFA) achieves signal gain through stimulated emission, which is when an incident photon causes an excited-state ion to relax to a lower energy state by emitting a photon. For this fiber amplifier, silica cannot be used as the host material because the excited state decays to the ground state nonradiatively via phonon relaxation. Materials with lower phonon energies, such as fluorides or chalcogenide glasses, are more suitable hosts. Thorlabs uses proprietary fluoride fiber doped with the rare-earth metal praseodymium to generate radiative emission and achieve signal gain. ![]() Click to Enlarge Schematics showing Pr3+ ion excitation and emission processes. 3H4, 3H5, and 1G4 are the ground, intermediate, and excited energy levels, respectively. Stimulated Emission in the PDFA Note that the electronic states of the Pr3+ ion are energy bands and not discrete energy levels, and there is a range of wavelengths the emission processes occur over, i.e. the PDFA bandwidth. This is as a result of the Stark-splitting caused by the local electric fields from the surrounding host lattice acting on the Pr3+ ion, as well as site-to-site variation within the amorphous host. Stimulated vs. Spontaneous Emission Front and Back Panels![]() Click to Enlarge Back Panel ![]() Click to Enlarge Front Panel
The PDFA100 contains the following components:
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