Gain and NF Characteristics of the EDZF

106

Figure 44: Excess 980 nm pump power as a function of the input 980 nm pump power for the 2 m and 3 m long EDZFs

This validates the spectral plots obtained in Figure 42 to Figure 44. The data also shows that further experimentation with the EDZF, such as gain and NF measurement as well as examinations of its non-linear characteristics are better conducted using the 3 m long EDZF, as the operational limits of the 2 m EDZF are reached too quickly.

107 external signal source in the form of a Tunable Laser Source (TLS). The modified setup is shown in Figure 45.

Figure 45: Experimental setup for gain and NF measurement of 3 m long EDZF

The external signal is generated from a Yokogawa AQ2200 TLS, which has an operational wavelength range of 1460 nm to 1640 nm. The signals generated by the TLS have a linewidth of 0.015 nm, with a maximum average output power of 12.8 dBm³³. An optical isolator is placed just after the output of the TLS to prevent any backward propagating signals from the DUT from reaching the TLS and possibly damaging it.

The gain and NF levels obtained by the EDZF based amplifier is similar to that of other amplifiers using highly-doped active media. The pump power of the system is kept at 170.1 mW, and two input signals at -30 dBm and 0 dBm are measured over a wavelength range of 1530 nm to 1590 nm, in 10 nm intervals. The -30 dBm signal represents a Low signal, or a low powered signal that is typically observed in optical transmission lines after a certain distance, due to the attenuation experienced by the signal. The 0 dBm signal on the other hand represents a saturated input signal, typically experienced near the source. These signals represent the different conditions under which the EDZF can be deployed, namely as an in-line

33 It must be noted that the maximum output power of 12.8 dBm is not the highest power that can be obtained by the TLS, as it can be configured to deliver signals of higher power. In this work however the maximum power for the TLS is set at 12.8 dBm, for the purpose of preventing damage to the system as well as to avoid decreasing its operation lifespan.

DUT: 3 m EDZF

OSA WDM COUPLER

980 nm LD

ISOLATOR

TLS

ISOLATOR

108 amplifier, or as a booster amplifier. The gain performance of the EDZF as an amplifier is given in Figure 46.

Figure 46: Gain of the EDZF imparted to Low (-30 dBm) signal and High (0 dBm) input signals.

It can be seen immediately from Figure 46 that the EDZF amplifier can impart very high gain levels, ranging from approximately 28.0 dB near the central region of 1530 nm, as well as a high gain level of between 22.0 to 25.0 dB at what would be the plateau region of the EDZF’s ASE output. Outside of this region however, the gain begins to decline, as expected, and finally reaches a relatively low value of around 5.0 dB at 1590 nm. The same observation can also be made for the gain experienced by the High signal, with a relatively flat gain output of around 10.0 dB from 1530 nm to about 1570 nm, before the gain begins to drop to about 2.0 or 3.0 dB at 1590 nm.

However, the high gain levels imparted by the EDZF are also accompanied by relatively high NF levels. In the case of the 0 dBm input signal, the NF is initially recorded at high levels, approximately 14.1 dB before quickly dropping to 9.3 dB over a wavelength range of 1530 to 1550 nm. A subsequent increase in the input wavelength sees the NF decrease further, though not as steeply as before, reaching a value of 7.7 dB at 1580 nm. However, as the input wavelength continues to increase,

0 5 10 15 20 25 30

1520 1530 1540 1550 1560 1570 1580 1590 1600

Gain (dB)

Wavelegnth (nm)

Input Signal = -30 dBm Input Signal = 0 dBm

109 the NF begins to rise again, now increasing to 8.3 dB at 1590 nm. In the case of the -30 dBm input signal, a similar observation is made, with the initial high NF of 12.2 dB decreasing quickly to only 4.9 dB over a wavelength range of 1530 to 1550 nm.

Subsequently increases in the input wavelength at this power see a further drop in the NF to 2.8 dB, before it rises slightly to approximately 3.9 dB at 1590 nm. The NF of the EDZF based amplifier, as a function of the wavelength, is given in Figure 47.

Figure 47: NF of the EDZF imparted to Low (-30 dBm) signal and High (0 dBm) input signals

The high NF levels can be attributed to the high ASE levels also encountered at this region. In fact, if one were to overlay the ASE spectrum against the gain and NF values obtained over the wavelength range, it would be seen that both the gain and NF follow a relatively similar pattern, with a peak value corresponding to the peak region of the ASE spectrum, followed by an almost constant region that where the plateau region of the ASE lies. This gives the EDZF some advantages, on particular the ability to provide almost constant gain over wavelength region, although at the cost of the high NF levels. The gain and NF values obtained in this work correspond to that previously obtained by M. C. Paul, et. al. in references [24] and [78].

0 2 4 6 8 10 12 14 16

1520 1530 1540 1550 1560 1570 1580 1590 1600

NF (dB)

Wavelegnth (nm)

Input Signal = -30 dBm Input Signal = 0 dBm

110