Lack of reliable high-speed internet access in rural regions, due to complicated logistics and the considerable costs involved to extend land-based networks to these areas, has inspired a wave of next-generation applications that will provide greater accessibility and reliability. Making use of “space laser” networks, these revolutionary solutions can relay digital traffic via low Earth orbit (LEO) satellite systems to provide low-latency, high-speed broadband services to communities typically beyond the reach of standard wireless and fiber networks.
Used in traditional optical transmission networks, the amplification technique of employing erbium-doped fiber amplifiers (EDFA) to directly amplify optical signals (without conversion to electrical signals) has now expanded to help boost laser-based signals for orbiting satellite communication networks.
Optical amplifiers are primarily evaluated with gain and noise figures (NF) via an optical spectrum analyzer (OSA) to measure the optical spectra of input, using Trace A and Trace B respectively. For select applications, a polarization scrambler is placed before the OSA to reduce the effects of the OSA's polarization dependence.
To obtain accurate gain and NF, it is necessary to exclude the source spontaneous emission (SSE) of the light source being amplified. The gain and NF is then calculated for each channel of the input optical signal. As needed, analysis parameters such as channel detection and amplified spontaneous emission (ASE) level detection should be incorporated to hone results. This can be applied to dense wavelength division multiplexing (DWDM) systems as well.
To accurately measure the characteristics of an optical amplifier, perform the following steps first:
Connect the internal calibration light source out to the optical input port with a single-mode fiber. If an internal calibration light source is not present, calibrate using a single wavelength light source with stable output, such as a DFB-LD.
Calibrate the resolution bandwidth of an OSA to the equivalent noise bandwidth (required by IEC standards for optical amplifier measurement) using an external light source. Resolution calibration is recommended due to the filter response of an OSA not typically being rectangular. Because of this, the resolution bandwidth (defined as FWHM) differs slightly from the equivalent noise bandwidth. This step is especially effective when wavelength resolution is 0.05 nm or less (e.g., the difference becomes prominent). With an external light source, use a stabilized single-mode laser light source with an output power of -20 dBm or more, a level stability of 0.1 dBp-p or less, and output line width of 5 MHz or less.
Next, calibrate the absolute power reading of the OSA. For the measurement light source, use a single-wavelength light source with stable output, such as DFB-LD and calculate the power correction factor (PCF) using the formula PCF (dB) = P_OPM (dBm) - P_OSA (dBm), where P-OPM is the optical power value on the optical power meter and P-OSA is the spectral peak power value on the OSA.
If optical connectors, splitters, or switches are inserted between the light source and the EDFA input or between the EDFA output and the OSA, researchers must compensate for those losses. After calibrating the absolute power using an optical power meter, double check if there is extra loss that causes errors in the absolute power reading. If additional losses in the input and output paths of EDFA are uncovered, adjust correction values based upon interpolation.
Depending upon EDFA analysis needs there are multiple parameters to consider. The most-commonly used include:
Optical amp gain and NF are obtained after measuring the signal power via the optical amp (as the output light leaves the optical amp). Peak setting is typically employed because a continuous wave (CW) laser light source is used for the EDFA measurements.
Because amplified spontaneous emission (ASE) generated by an optical amplifier is superimposed on the output light, it is important to measure this noise component separately in optical amplifier evaluation. Optical amplifier analysis identifies the ASE component using the curve fitting and interpolation methods.
IEC-based calculations for optical amplifier test methods using multichannel parameters (interpolated source subtraction with an OSA) utilize optical power (dBm), optical frequency (Hz), and frequency resolution (Hz) for EDFA analysis.
The general amplifier gain and NF measurement principles are well-established for traditional land-based optical networks that use fiber as the transmission medium. With the push for greater accessibility and more reliable and affordable networking services, EDFA analysis algorithms with optical amplifiers have shown to be directly applicable in free-space applications as well. The tried-and-true technologies and test methods that revolutionized long-haul optical transport networks in decades past are once again pioneering communications with cutting-edge laser-based orbiting satellite networks.
High Stability reference laser light sources for DWDM channel measurements. The one or two channel modules are part of an integrated optical device testing solution for the AQ2200 series frame controller platform.
The AQ2200-212 is single channel sensor module with an analog output port.
Ideal for measuring output power of transmission equipment and optical fiber amplifiers.
Increase your testing power and capability with the AQ2200-222 sensor module.
With built-in optical power meter for monitoring power
Compact and lightweight optical variable attenuator.
SM, GI50 and GI62.5 optical fiber models available.
High Performance LONG WAVELENGTH
The AQ6375B is a bench-top optical spectrum analyzer covering the long wavelengths, 1200 to 2400 nm, with the added benefits of gas purging input ports / output ports, a built-in cut filter for high order diffracted light, and a novel double speed mode which increases the sweep speed up to 2 times compared to the standard sweep mode.
MWIR WAVELENGTH with internal gas purge and cut filter
The AQ6376 is the latest version of our bench-top optical spectrum analyzer extending the wavelength coverage well beyond the NIR range of our previous models into the MWIR region from 1500 to 3400 nm.
Popular applications include the detection of gases such as carbon oxides (COx), nitrogen oxides (NOx), and hydrocarbon gas (CxHy) for environmental studies.
AQ6380 OSA: 5 pm high wavelength resolution, ±5 pm accuracy, 65 dB wide close-in dynamic range, 80 dB high stray light suppression
A modular test platform with a wide selection of modules allows optimal configuration of test solutions for optical component and network systems manufacturing.