The Report of Gain Performance Characteristics of the Erbium Doped Fiber Amplifier (EDFA)

Transcription

1 The Report of Gain Performance Characteristics of the Erbium Doped Fiber Amplifier (EDFA) Masruri Masruri (186520) 22/05/ Laboratory Setup The laboratory setup using in this laboratory experiment is depicted in Fig. 1. Fig.1: The Laboratory Setup of EDFA This figure is the realization of EDFA with the pump light copropagates with the signal light and is set up according to the schema in Fig. 1. This schema uses the component devices: tunable laser to represent the signal C band isolator (2 units) Attenuator of 15dB for C band pumping laser Pirelli with I max = 190mA and the P max = 98mW WDM 980/ m of Erbium doped fiber 2 Experiment 1 In this experiment we measure the reference power, P in, of the fiber amplifier. Using OSA we connect the P in in Fig. 1 to the input of OSA. By varying the desired parameters we measured the effective power, P in : 1

2 On the tunable laser we set the wavelength λ = 1530, 1550, 1565 nm and varie the power between -30 dbm and 0 dbm, which the step difference is 5 dbm. We used the attenuator of 15 db for the power 25dBm. On the tunable laser we set the power -30, -20, -10, dbm, and varie the wavelength between λ = 1525, and 1565 nm, which the step difference is 5 nm. We used the attenuator 15 db for the power 25dBm. OSA is set with the resolution bandwidth 0.5 nm, and the sensitivity HIGH Result and Analysis The results for the setting to fix desired wavelength (λ = 1530, 1550, 1565 nm ) and varies the power are described in Fig Fig.2: The Effective power for λ = 1530nm Fig.3: The Effective power for λ = 1550nm The trajectory line is the power set to the tunable laser while the full line is the effective power. Fig. 2-4 describe that there are losses of power around 1-2dB if we measure the power in the point 2

3 Fig.4: The Effective power for λ = 1565nm of P in in Fig. 1 using the reference of power have been set in the tunable laser. These losses are caused by the loss in the devices, isolator and attenuator, and also in the connector. Fig. 5-8 describe the tunable laser being set to fix power (-30,-20,-10, and 0 dbm) and varying the wavelength between 1525 and 1565 nm for each of the power. Fig.5: The Effective power for P ower = 30dBm In fig. 5-8 we put the reference power and here we see that the effective power varies according to the wavelength. As the power increases the effective power much more stabil for each of the wavelength. We will use the effective power obtained here both variying the power and varying the wavelength as the input power to measure the Gain of the amplifier. 3 Experiment 2 In this experiment we will measure the spectrum of ASE (Amplified Spontaneous Emission) using the OSA which is connected to the output of the second isolator (see Fig. 2). Using the schema in 3

4 Fig.6: The Effective power for P ower = 20dBm Fig.7: The Effective power for P ower = 10dBm 4

5 Fig.8: The Effective power for P ower = 0dBm Fig. 1 we turn on the pump laser using the injected current of 150 ma while maintain the tunable laser turn off. Fig. 9 describes the ASE spectrum. Fig.9: ASE spectrum (resolution bandwidth 0.05, sensitivity HIGH 3) Fig. 9 shows that for the C band, the peak power happens on the wavelength around 1530 nm and after that the power decreases in the increase of the wavelength. 4 Experiment 3 In this experiment, by fixing the wavelength at 1530 nm, 1550 nm, and 1565 nm, and the pumping power at P pump,max we will determine the saturation curve, G versus P out, of the amplifier. We will also determine the output saturation power, P sat as the varying of the wavelength. P sat is defined as the output power in which it has the half of the maximum gain (or G max 3dB). OSA is set with resolution bandwidth 0.5 nm, and sensitivity HIGH 3, the same parameters as Experiment 1 when we measured the reference power. 5

6 Fig describe the saturation curve for λ = 1530, 1550, and 1565 nm, respectively. The P sat for each wavelength is described in Table 1. Fig.10: Saturation curve for λ = 1530nm Fig.11: Saturation curve for λ = 1550nm λ(nm) P sat (mw ) Table 1. Saturation Power, P sat 5 Experiment 4 In this experiment we will fix the power of the tunable laser at -30 dbm, -20dBm, -10dBm, 0 dbm and varying the wavelength between 1525 and 1565 nm. The pumping laser is set with maximum power. 6

7 Fig.12: Saturation curve for λ = 1565nm Fig describe the output G versus λ for each of the power have explained above. The maximum gain achieves by the power -30 dbm in the wavelength 1535 nm which is 45 db, while the gain for other wavelengths remain small. The power -20 dbm has the maximum gain around 33 db at the wavelength 1530 nm and at the wavelength 1535 around 31.5dB, while the gain for other wavelengths also remain small. At the power -10 dbm, the maximum gain is achieved at 1530 nm but we can see that the gain curve is more flat than before. As the power increases in this case 0 dbm the gain curve is more flat. Here we can conlude that the more power of tunable laser increases the balance is achieved. In this case, the condition of saturation is achieved so that all the wavelengths have the gain maximum as demonstrated in Fig.16. When the signal power is low, the characteristic of gain curve is similar with the characteristic of ASE curve which the maximum gain is around the wavelength of 1530 nm. Fig.13: G versus λ for Power=-30 dbm 7

8 Fig.14: G versus λ for Power=-20 dbm Fig.15: G versus λ for Power=-10 dbm 8

9 Fig.16: G versus λ for Power=0 dbm 6 Experiment 4 In this experiment we will fix the power of the tunable laser at -30 dbm and varying the wavelength between 1525 and 1565 nm. The laser pump is set with half of the maximum power, P pump,max /2. Fig. 17 describes the curve Gain versus λ at the power of tunable laser set to -30 dbm. Fig.17: G versus λ for Power=-30 dbm using P pump = P pump,max/2 The curve is nearly similar to the gain curve using the maximum pumping power with the power of tunable laser set to -20 dbm as depicted in Fig. 14, but here the maximum gain is around 34 db, while Fig. 14 is 33 db. Here the characteristics of gain curve is still the same with the ASE curve which the maximum gain is in the wavelength around 1530 nm. The signal power is not enough to burst the gain of signal in the wavelength being set. The signal power of wavelength in C-band ( nm) should be bigger enough to induce stimulated emission in excited erbium ions which has been pumped by pumping laser in order to this wavelength could be amplified. Fig. 18 describes the spectrum of wavelength 1550 nm which is amplified. In this experiment, the power signal is set to 0 dbm and the pumping laser is set with the injected current 150 ma. 9

10 Fig.18: spectrum fiber amplifier for λ = 1550nm (OSA resolution bandwidth 0.05, sensitivity HIGH 3) 7 Theoritical Analysis Fig. 19 describes the erbium energy level scheme. Using the Fig.1, Light from the pump supplies energy to elevate the erbium ions to the 4 I 13/2 first excited state. The excitation energy of this state corresponds to wavelengths near the minimum optical loss of silica optical fibers ( 1550 nm). Optical signals propagating through the EDFA with wavelengths between about 1525 and 1565 nm induce stimulated emission in excited erbium ions and are thereby amplified.[1] Fig.19: Erbium Energy Level Scheme 7.1 Gain Gain is the fundamental characteristic of an amplifier. Optical amplifier gain is defined as the ratio of the output signal power to the input signal power, G(λ) = P out P in = L 0 g(λ, z).dz, (1) and it is obtained by integrating the gain coefficient g(λ) over the length L of the erbiumdoped fiber. The gain coefficient, normally expressed in units of decibels per meter, is the sum of the emission coefficient g (λ) = Γ s n ER σ e (λ) and the absorption coefficient α(λ) = Γ s n ER σ a (λ) 10

11 weighted by the fractional populations N 2 and N l, respectively, of the first excited and ground states of erbium: g(λ, z) = 1 dp (λ, z) = g (λ).n 2 (z) α(λ).n 1 (z) (2) P (λ, z) dz where Γ, is the confinement factor of the signal mode in the fiber core, n Er is the concentration of Er ions in the core, and σ e (λ) and σ a (λ),are, respectively,the signal emission and absorption cross sections as functions of wavelength. 7.2 Output Power Saturation The output power is approximately proportional to the pump power when signal levels are high and the amplifier is saturated. This is a characteristic of the three-level erbium laser system as can be understood by reference to the erbium energy-level scheme (Fig. 13); when the amplifier is saturated, pump absorption from the ground state is balanced by stimulated emission from the first excited state induced by the signal. The higher the pump power is, the higher the signal power at which this balance occurs. P sat is measured as the output power in which it has the half of the maximum gain. References [1] Ivan P. Kaminov, T.L Koch, Optical Fiber Telecommunications IIIB. Academic Press