Applications of photonic systems

Microwave photonics link

Let’s assume a fiber-optic link based on an externally modulated laser. For the purpose of this exercise we can further assume that both the transmitter and the receiver are impedance matched.

Question 1:

An external modulator has an optical loss of 5 dB, Vπ of 5V and input resistance of 50 Ω . Find the    ratio of the squared modulated optical power to the electrical input power for optical input power to the modulator of 10 mW.

Question 2:

A detector has responsivity of 0.9 A/W and is connected to a load of resistance of 50 Ω . What is the ratio of electrical output power to squared modulated optical input power?

Question 3:

If the modulator in question 1 is connected to an optical link with 10 dB loss, followed by the detector in question 2, what will be the electrical gain of the link?

Question 4:

If the laser input power to the modulator is increased to 100 mW, how much will the electrical gain of the link increase by?

When in trouble, refer to:

1       C. H. Cox, G. E. Betts and L. M. Johnson, "An analytic and experimental comparison of direct and external

modulation in analog fiber-optic links," in IEEE Transactions on Microwave Theory and Techniques, vol.

38, no. 5, pp. 501-509, May 1990, doi: 10.1109/22.54917.

2       Charles H. Cox, III “Analog Optica Links Theory and Practice”, Cambridge University Press,  2004,

https://doi.org/10.1017/CBO9780511536632

Question 5 - Optical heterodyning

If two lasers (λ1= 1550nm, λ1= 1549nm) are combined at a photdodiode, what frequency signal will be generated at the output?

Question 6 - Optical ring resonators

What would be the circumference of an optical ring resonator if its free spectral range (FSR) is 20 GHz. Consider silicon nitride on silicon oxide platform. with group refractive index of 1.72 and a minimum bending radius of 80 um.

What is the propagation loss through ring resonators?