The evaluation of materials used in optical communication devices often requires high sensitivity measurements in the near infrared region. The optical elements that are used, such as band pass and cut-off filters, are designed to preferentially select the wavelengths that are used for the communication signal and reject the wavelengths that contribute noise. The filters must be designed so that the maximum signal amplitude is obtained after passing through the optical element.
This application note demonstrates the high sensitivity measurement of optical elements using a V-780 with an InGaAs detector.
UV-0010, V-780, UV-Visible/NIR, Materials, Near-infrared, InGaAs detector
Comparison with PbS Detector
Figure 1 shows the results for a 1.3 µm band frequency cut-off filter used for optical communications. The spectra were obtained using two different V-700 UV-visible/NIR spectrophotometers; one using a PbS detector (V-770) and the other an InGaAs detector (V-780). As seen in Figure 1, the spectra obtained with the InGaAs detector shows a much higher S/N than those with a PbS detector.
High Resolution Measurement
Figure 2 shows the results of a 1050 nm laser cut filter at varying spectral bandwidths. Small bandwidths enable high-resolution visualization of the edge of the cut-off filter, as well as the interference curve of a multi-layer filter. Both characteristics are not observed at larger bandwidths and at the smallest bandwidth – 0.2 nm, good S/N is still maintained.
|Measurement Range||1150-950 nm|
|Bandwidth||0.2 nm||0.4 nm||1.0 nm||1.0 nm|
|Scan Speed||10 nm/min||10 nm/min||20 nm/min||200 nm/min|
|Data Interval||0.05 nm||0.1 nm||0.2 nm||0.5 nm|
High Scan Speed Measurement
Figure 3 shows the results of a 1.3 µm band frequency cut-off filter at varying scan speeds. The data indicate that even at the maximum scan speed of 400 nm/min, good S/N and spectral shape are well maintained.
|Measurement Range||1600-850 nm|
|Scan Speed||4000 nm/min||1000 nm/min||200 nm/min||100 nm/min|
|Data Interval||2 nm||1 nm||1 nm||1 nm|
Variable Angle Measurement using the Integrating Sphere
The absolute reflectance measurement system with an integrating sphere was used to measure a 1050 nm laser cut-off filter. Figure 4 shows the measurements at varying incident angles with a spectral a bandwidth of 1 nm. While integrating spheres are known to decrease sensitivity, the use of the InGaAs detector with the integrating sphere enables high S/N and resolution.
|Scan Speed||200 nm/min||Data Interval||0.2 nm|
Required Products and Software
A high sensitivity UV-Visible/NIR Spectrophotometer with InGaAs detector for wavelengths up to1600nm
Wide range UV-Visible/Near Infrared Spectrophotometer with PbS detector for wavelengths up to 3200nm