1. Lecture-2 Insertion Loss Measurements

2. Insertion Loss Measurements • The insertion loss of optical components used in a transmission link define the system’s power budget and the system margin. • Insertion loss measurement is always a two step procedure. • In the first step, the input power to the test device is measured. • In the second step, the test device is inserted and the power is measured again. • The two power results are divided by each other, and the attenuation is usually expressed in dB.

3. Insertion Loss Measurements • Single wavelength loss measurements • Historically, most insertion-loss measurements were carried out using sources with fixed wavelengths, mostly Fabry-Perot (FP) lasers. • Other possible optical sources for single-wavelength measurement are: a) Surface-emitting LEDs. b) Distributed-feedback lasers (DFBs).

4. Insertion Loss Measurements • Polarization dependent loss measurements • There are two popular method for PDL measurement. a) Polarization Scanning Method. b) Mueller method.

5. Insertion Loss Measurements • Polarization Scanning Method. Laser Source Polarization Controller DUT Power meter Record min/max Power values Fiber-loop design recommended Generate all polarization states Figure: Principle setup for measuring the PDL of optical filters.

6. Insertion Loss Measurements • Polarization Scanning Method. To obtain good accuracy in this measurements, the following is important. 1. Constant input power to DUT. 2. Generation of all polarization states.

7. Insertion Loss Measurements • Mueller method. Polarization controller Laser Source DUT Power meter Record power at four states P Q H Waveplate design recommended Generate four Polarization states: Linear horizontal (0o) Linear vertical (90o) Linear diagonal (45o) Right-hand circular Figure: Principle setup for measuring the PDL using Muller method.

8. Insertion Loss Measurements • Wavelength dependent loss measurements • Loss measurements with a Tunable Laser and a power meter • In wavelength-dependent insertion-loss measurements the most obvious quality criteria of the TLS is its wavelength accuracy. • Optical interface effects need to be avoided during the measurements. • Spontaneous emission causes limitations.

9. Insertion Loss Measurements • Wavelength dependent loss measurements • Loss measurements with a TLS and OSA • TLS/OSA measurement range. • Limited Filter rejection in the Stop band. • Dynamic range improvement due to using an OSA.

10. Insertion Loss Measurements • Wavelength dependent loss measurements • Loss measurements using a broadband source There are several considerations that must be made in comparing broadband sources. 1. Spectral density. 2. Wavelength coverage. 3. Smoothness of the spectral shape. 4. Power stability over time. 5. Source polarization state. 6. Reflection sensitivity and 7. Cost