High School

There is a DFB-LD composed of InGaAsP with a central wavelength of 1550 nm and an effective refractive index of 3.6.

(a) The change in oscillation wavelength according to the temperature of the DFB-LD is +0.1 nm/°C. Assuming that wavelength tuning is performed due to the temperature change of the TEC, what is the wavelength tuning range \([A]\) if it is operated between -20 °C and 80 °C?

(b) We intend to produce a tunable laser array that can use the entire C-band (1525 nm to 1565 nm) using multiple channels of DFB-LD with different center wavelengths. If the temperature range of the TEC is operated between -20 °C and 80 °C, what is the minimum number of channels of DFB-LD required?

Answer :

A) the wavelength tuning range A if it is operated between -20 °C and 80 °C is 10 nm

B) the minimum number of channels of DFB-LD required to span the entire C-band would be 4 channels.

(a) The change in oscillation wavelength according to the temperature of DFB-LD is +0.1 nm/°C.

Assuming that wavelength tuning is performed due to the temperature change of TEC, what is the wavelength tuning range A if it is operated between -20 °C and 80 °C?

The wavelength tuning range is determined by the minimum temperature of -20°C and the maximum temperature of 80°C, with a range of 100°C. For every degree of temperature increase, the oscillation wavelength increases by 0.1 nm.

The oscillation wavelength range can be found using the following equation:

A = Δλ/ΔT x ΔT

Where,

Δλ/ΔT = Temperature Coefficient of the device

ΔT = Change in temperature

A = Wavelength tuning range, we have,

Δλ/ΔT = +0.1 nm/°C

ΔT = (80 - (-20))°C = 100°C

So,

A = Δλ/ΔT x ΔT = +0.1 nm/°C x 100°C= 10 nm

(b) We intend to produce a tunable laser array that can use the entire C-band (1525 nm to 1565 nm) using multiple channels of DFB-LD with different center wavelengths. If the temperature range of the TEC is operated between -20 °C and 80 °C, what is the minimum number of channels of DFB-LD required?

To span the entire C-band (1525 nm to 1565 nm), we need to find the range of center wavelengths that is required. We can find this by finding the difference between the maximum wavelength of the C-band and the minimum wavelength of the C-band, which is,

1565 nm - 1525 nm = 40 nm

We know that for every degree of temperature increase, the oscillation wavelength increases by 0.1 nm. So, to span a wavelength range of 40 nm, we need to change the temperature by:

40 nm / 0.1 nm/°C = 400°C

To cover this range, we have a temperature range of 80 - (-20) = 100°C available to us.

Therefore, the minimum number of channels required to cover the full C-band would be:

400°C / 100°C = 4 channels

Hence, the minimum number of channels of DFB-LD required to span the entire C-band would be 4 channels.

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