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Fiber Isolator Lab Facts

Fiber Isolator Lab Facts

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Thorlabs Lab Fact: Isolation & Transmission Properties of IO-F and IO-H Fiber Isolators

Light Propagation Through a Polarization-Independent Isolator
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Figure 1: IO-H Series Polarization-Independent Isolator Schematic
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Light Propagation Through a Polarization-Independent Isolator
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Figure 2: IO-F Series Polarization-Independent Isolator Schematic

We present laboratory measurements of the isolation and transmission properties of our IO-H and IO-F series of fiber-coupled optical isolators. Generally, an isolator uses a Faraday rotator in conjunction with a half-wave plate, between two beam-displacement polarizers, to provide isolation from back reflections. While both series provide excellent isolation from optical feedback, they do so through different geometries. As a result, these two series offer different optimized performance specifications. The IO-H series (see Figure 1) is optimized for performance at a specific wavelength (e.g., 1550 nm for the IO-H-1550APC). The IO-F series (see Figure 2), however, is designed as a more versatile platform and offers customized performance over various wavelength bands. These bands are defined by the choice of half-wave plate and collimating lenses.

For this experiment the laser source was Thorlabs' TLK-L1550R Tunable Laser Kit, swept through 1505 – 1593 nm. The fiber-coupled laser beam was fed through a 99:1 fiber coupler, allowing 1% of the TLK’s power to be sent to an OSA203 Optical Spectrum Analyzer to monitor and record the TLK’s center wavelength at each data point. The remaining power was split in half by a 50:50 fiber coupler, which created two paths. One path was designated as a reference path and was fed directly into an integrating sphere; the other path was designated as the test path. The isolator was placed in the test path and then attached to an integrating sphere. For this experiment, the IO-H-1550APC and IO-F-1550APC isolators were tested. Either the transmission (when the isolator was integrated into the test path in the forward direction) or isolation (when the isolator was integrated into the path in the reverse direction) was measured. Since both reference and test path data were taken simultaneously, the exact transmission or isolation could be extracted along with peak wavelength data from the OSA.

Figures 3 and 4 summarize the measured results for the IO-H series isolator and compare those results to those reported on our website. Figure 3 shows that for the two tested IO-H-1550APC isolators, the real transmission is a few percentage points higher than the specified value on the website (i.e., the performance exceeds the specification). It also shows a slight etalon effect caused by the front window of the OSA detector. Figure 4 details the isolation for the same set of isolators and shows a slight increase in isolation and similar bandwidth as the web specifications. Figures 5 and 6 summarize the measured results for the IO-F series isolator. The two tested isolators show a >5% increase over the specified transmission, and an additional etalon effect from the internal half-wave plate is observed as well. Figure 6 shows that the measured isolators again have higher isolation than specified but also have a variance in the peak isolated wavelength. For details on the experimental setup employed and the results summarized here, please click here.

Polarization through prism
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Figure 3: IO-H Series Transmission
Stress Induced Shifts
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Figure 4: IO-H Series Isolation
Stress Induced Shifts
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Figure 5: IO-F Series Transmission
Stress Induced Shifts
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Figure 6: IO-F Series Isolation

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