How to use a fiber to create delay line in Practice

[Taiwo Ambali Abiola]

What is the exact length of the fiber that can be used to create a time delay of 50ns between two optical signal. I am currently implementing a system that requires splitting the pulse light into two, delay one by 50ns and later recombine the signal (a form of MZI). Actually, I am suppose to use a phase modulator on the delayed harm but it seems the effect of phase modulator can only come through with high frequency RF signal. But since my Photo detectors at the receiver can not support high frequency, I resulted into using fiber delay. What is the length of the fiber that could be used to get exact 50ns time delay.

[Taiwo Ambali Abiola]

How then can we convert the time delay into delay angle difference. I am actually trying to make the delay between the two signals to be (pie or 180 degree) difference. How do I go about the calculations.

Thanks so much and hope to hear from you soonest,.

[Abhishek Shrama]

Hi Taiwo
Have you tried to delay signal with time component from library? Or you can can only want to delay signal with fiber?

[Taiwo Ambali Abiola]

Actually I am talking about laboratory experimental setup not optisystem. Thanks

[Alessandro Festa]

Hi Taiwo, since the speed of the optical signals into fiber is v=c/n, where c is the speed of light into vacuum and n is the effective index of the fiber (1.5 about), to create a delay = T you need an amount of fiber equal to L = v * T.
In your case T = 50ns, so L = 10m. Depending on the precision you need on the 50ns, you need to know very well the n of the fiber.

[Taiwo Ambali Abiola]

whaooo, this is quite helpful. Thanks so much Alessandro. I now got the delay to be 50ns as attached in the image.

Really appreciate this.

[Alessandro Festa]

You are very welcome, it is my pleasure to helpforum members whenever I can!

[Taiwo Ambali Abiola]

I also got the method to convert it to angle to be = (360*time delay)/Period
where Period = 1/F(frequency).

So with that, my 50 ns delay is equivalent to 180degree (Pie) delay since I am running on 10MHz frequency which means the period= 100ns

Thanks a lot.

[Ashu verma]

Hello Taiwo
Alessandro almost explained the concept of delay.I just want to add that you should be familiar to the fiber parameters for exact calculation.One important oint i want to add is delay also depends upon your wavelength.For examples for a specific fiber (for which i have calculated) gives me results 49.16nm for 1310nm and 49.21ns for 1550.So if you are looking for exact delay then consider this point also.Thank you

[Taiwo Ambali Abiola]

I see! Thanks alot Samsung. Actually I am working with 1550 nm windows and the problem has been solved by Alessandro suggestion. I think the refractive index also comes to play there. Perhaps the refractive index of the fiber I used coincides with the one that could give 50ns though I didn’t check the refractive index.

Thanks so much for you suggestions.

[Ashu verma]

Welcome Taiwo
I just explained the effect of wavelength,because some times delay should be accurate.Otherwise Alessandro made a very good point and explained all.

[Taiwo Ambali Abiola]

Yes, I understand. Thanks so much

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