The optical isolation or non-reciprocal absorption is an important magneto-optical effect. It describe the difference of light absorption in two opposite direction of light propagation.

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Zayets et al, Patent appl., 2016-126905, 2016; in Japanese; in English

 

 

Figure 1 shows the setup for measurements of the non-reciprocal loss . The optical 2x2 switch can switched between its two states by a control voltage. Both the light source and the light detector are connected to one side of the switcher. Other side of the switcher is connected to two opposite sides of the sample. The fiber collimators are used for light coupling between fibers and free space. The two switching states are absolutely identical except propagation directions of light in the sample are opposite. When the control voltage is off, the light propagation direction is from up to down. When the control voltage is on, the light propagation direction is from down to up.  The difference of the detected light for two switching states corresponds to the non-reciprocal absorption in the sample.

 

 

 

Linear transverse magneto-optical effect (See here) is one source of the non-reciprocal absorption.

 

 

 

 

 

 

 

 

 

Figure 2 shows the setup for measurements of the non-reciprocal loss using the lock-in technique. The 2x2 switch is switching between two opposite directions of light propagation. The pulse generator generates a sequence of electrical pulses, which switch the 2x2 switcher between its two states. Also, the pulses are used as the reference signal for the lock-in amplifier. The detected signal is modulated at the same frequency as the switcher is switched. The amplitude of the modulation is proportional to the value of the non-reciprocal loss of the sample. The lock-in amplifier is able to measure this modulation with a high precision and a high sensitivity.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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2x2 optical switch

There are many 2x2 switches on market. All, I know, have a fiber for input and output. I do not know any bulk-type 2x2 optical switch. I believe it is possible to make a bulk-type 2x2 optical switch using mirrors. A bulk-type 2x2 optical switch could be very useful in a measurement setup with a camera.

For MO and non-linear measurement, the critical parameter for a 2x2 switch is the cross-talk between input 1 and input 2. It should be minimized as much as possible!!!

 

The optical properties of a sample is measured for two opposite directions of light propagation. Since the direction of light is changed by a 2x2 optical switch without any change or distortion of the optical alignment,  a tiny difference of optical properties for opposite propagation directions can be measured with a high precision.