Hi
I am thinking and reading a lot on ECDL based on transmission VBG. First reflection based VBG bragg condition looks good but in case of Trasmission based VBG plane of VBG seems parallel to incoming light , than how reflection for feedback happen ?
Does reflected light and transmitted light in steady state transmission VBG are same? Because in ECDL based on grating in Littrow configuration have 1st order as feedback while zeroth order light went as output
Hi Emma,
VBGs are not like traditional diffraction gratings. They are more related to dielectric mirrors. You have in the glass repeating low and high refractive index structures (very small refractive index difference) and the light falling onto it interferes constructively when reflected from the boundaries - then it works like a mirror. If the waves interfere destructively in the backward direction then you have good transmission. Bragg gratings are often written inside single mode
fibre core too (FBG). Sometimes they are chirped which results in different wavelengths being reflected from different depths of the mirror - this is then used for dispersion compensation. You can use for instance the OptiGrating software to play around with the parameters - they have an unrestricted demo with time limitation.
What perfectly shows the relation between dielectric mirrors and Bragg gratings is that there are for instance chirped mirror which are also used for dispersion compensation using the same principle.
Best regards,
Daniel