High Sensitivity Near Infrared Absolute Reflectance Measurement of Materials

Download PDF October 10, 2017

Introduction

High Sensitivity Near Infrared Absolute Reflectance Measurement of Materials
V-780 UV-Visible/NIR Spectrophotometer

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.

Keywords

UV-0010, V-780, UV-Visible/NIR, Materials, Near-infrared, InGaAs detector

Results

Figure 1. Transmission spectra of 1.3 µm band frequency cut filter. The spectrum (left) was zoomed in between 1200 and 1350 nm to illustrate the difference in S/N between the two detectors.

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.

Figure 2. Transmission spectra of a 1050 nm laser cut-off filter at varying bandwidths. The spectrum (left) was zoomed in
between 1020 and 1075 nm to illustrate the higher S/N.

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 Conditions
Measurement Range1150-950 nm
ResponseSlow
Bandwidth0.2 nm0.4 nm1.0 nm1.0 nm
Scan Speed10 nm/min10 nm/min20 nm/min200 nm/min
Data Interval0.05 nm0.1 nm0.2 nm0.5 nm
Figure 3. Transmission spectra of 1.3 µm band frequency cut-off filter. The spectrum (left) was zoomed in
between 1200 and 1350 nm to illustrate the high S/N.

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 Conditions
Measurement Range1600-850 nm
Bandwidth4.0 nm
ResponseQuickFastMediumSlow
Scan Speed4000 nm/min1000 nm/min200 nm/min100 nm/min
Data Interval2 nm1 nm1 nm1 nm
Figure 4. Transmission spectra of a 1050 nm laser cut-off filter at the following incident angles:
0 (red), 10 (blue), 20 (green), 30 (pink), and 40 (teal) degrees.

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.

Measurement Conditions
ResponseFastBandwidth1.0 nm
Scan Speed200 nm/minData Interval0.2 nm

Required Products and Software

V-780
ARMN-921i

About the Author

Toshifumi Uchiyama is a member of the electronic spectroscopy team located at the JASCO main laboratory in Tokyo