At the same time the output of U3A presents a positive going signal to U2. When both op amp inputs are equal, the output of U1 stops integrating. U3-B turns on and provides a positive going feedback signal. At any rate, the LM358 is very inexpensive.Ī positive signal input causes the output of U1 to shift positive. There is the LM321 single op amp, but it is unpopular and comes only in the SO-23-5 SMD package. I do this because there is no DIP single device that will do the job (that I know of). I generally use the LM358 dual op amp whenever I need a single ground sensing op amp. To maintain a high voltage rating, use two single devices and match the CTR to some degree. However, that power may be substantially reduced with further optimization.While DIP optical couplers have up to about 5kV isolation capability, this circuit cannot support above about 100V or so because one of the outputs is fed back to the input amplifier –this puts the voltage isolation between adjacent pins on the device rather than across the device. The main limitations are that the usable optical bandwidth is small and that a substantial electric power is required to drive piezo actuators creating the sound wave. This operation principle allows one to realize rather compact isolators for use on photonic chips. If those optical residences are positioned such that the ring is resonant for one propagation direction, resident coupling of the ring to the straight waveguide can cause substantial propagation losses.įor the opposite propagation direction, the induced loss can be much lower. Here, the rotation of the acoustic field causes a direction-dependent shift of resonance frequencies. In particular, it has been demonstrated that one can utilize rotating sound waves in a ring-shaped waveguide resonator, coupled to a straight waveguide. Therefore, alternative methods are under development, where non-reciprocal light propagation is obtained based on completely different physical mechanisms, not involving magnetic fields. Here, the requirement of a strong magnetic field is a major problem.Īs mentioned above, conventional types of optical isolators based on the Faraday effect are hard to implement in the context of photonic integrated circuits. However, it is hard to develop ultra-compact devices for use in photonic integrated circuits. Relatively compact low-power isolators can also be made.Power limitations arise due to thermal effects (particularly thermal lensing and depolarization) associated with parasitic absorption. Such devices can be made for operation with very high optical powers by using a sufficiently large beam area.Faraday isolators can be made for a wide range of optical wavelengths.Īlthough each device works well only within a limited bandwidth, that bandwidth can be substantial – sufficient for a wide range of applications.
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