**3.2.2 Static characteristics**

The static photo-detection current is not given data in data sheets of traditionally used SOAs. In unsaturated regime this curve can be approximate calculated from the optical gain (proportional with G-1) and the input optical power (proportional with Pin). However in several cases it can only be determined by measurements.

Fig.8a depicts the electrical current as a function of the input optical power of SOA-detector. The relationship between the input optical power and the output electrical current is given by the detector responsivity, it can be determined from this curve. However this static photo-detection current is operation point and temperature sensitive. Fig.8b represents the shape of the calculated curve (based on optical gain-bias current curve), that follows the measured data.

Multi-Functional SOAs in Microwave Photonic Systems 93

of the incoming intensity modulated signal. The detected current is directly proportional to the modulation depth. Thus, the difference between the two electrical powers is about 14dB.

> 50 100 150 200 250 Bias Current [mA]

Fig. 10. Measured detected electrical power versus operation point of SOA-detector with different modulation depths, Optical power at the detector input=5µW, Modulation frequency=3GHz, Optical wavelength=1550nm, Temperature=20C, Applying isolators to

The result of the detection experiments over input optical power and temperature are depicted in Fig.11. In the unsaturated regime the detected electrical signal is square proportional to the optical power, but in the saturation regime the relation goes to linear proportionality. The detection is also temperature sensitive, because the operation of semiconductor devices depends on the temperature. The measurement results show, that

> -94 -93 -92 -91 -90 -89 -88 -87 -86 -85

**Detected Electrical Power[dBm]**

Fig. 11. Measured detected electrical power versus average input optical power (a) and temperature (b). Optical wavelength=1550nm, Bias current=200mA, Modulation

The responsivity of the SOA-detector can be calculated from the measurement. If the input signal is intensity modulated, the fluctuation in the optical intensity due to modulation will

15 20 25 30 **Temperature [˚C]**


eliminate the optical reflection effect


**Detected Electrical Power [dBm]**

Detected Electrical Power [dBm]

m=25% m=7%

the detection efficiency decreases, when the temperature increases.


frequency=3GHz, Modulation depth=25%, Isolators

**3.2.4 Responsivity extraction from the measurements** 

Fig. 8. Static detection characteristics of SOA-detector

Optical wavelength=1550nm, Applying isolators to eliminate the optical reflection effect (a) Measured current change versus average optical power, at different temperatures, Bias Current=150mA

(b) Current change versus SOA operation point for different input optical power, Comparison of measurement and calculation results, Temperature=20C
