Biophotonics_Concepts_to_Applications

Anoptical circulatoris a non-reciprocal multi-port passive device that directs
light sequentially from port to port in only one direction. As illustrated in Fig.5.15
for a 3-port circulator, an optical input signal A on port 1 is sent out on port 2, an
input B on port 2 is sent out on port 3, and an input C on port 3 is sent out on port 1.
Available configurations include jacketed opticalfiber attachments andfibers with
connector terminations. Table5.5 lists some average values of key operating

Table 5.4 Common specifications for opticalfiber couplers

Coupler parameter Specification

Coupling ratio 1/99–50/50

Directivity ≥50 dB (1×2)

≥60 dB (2×2)

Reflectance ≥−55 dB

Polarization dependent loss (PDL) ≥0.1 dB (≥0.3 dB for taps of≥15 %)

Operating bandpass ±40 nm

Operating temperature: −40 to +85 °C

Standard lead length 1 m

Port 1 Port 2

Port 3

B

A A

B

C

C

Circulator

Fig. 5.15 Operational concept of a three-port optical circulator

Table 5.5 Typical values of key operating parameters for commercial 3-port and 4-port optical
circulators (WDLwavelength dependent loss;PDLpolarization dependent loss)

Parameter 3-Port circulator 4-Port circulator

Center wavelength 1310 or 1550 nm

(±20 nm)

1290 – 1330, 1525–1565, or 1570–

1610 nm

Isolation 50 dB 50 dB

Insertion loss 0.8 dB 0.6 dB

WDL 0.20 dB 0.15 dB

PDL 0.20 dB 0.10 dB

Power handling 500 mW 500 mW

Size 5.5 mm×60 mm 5.5 mm×60 mm

Operating

temperature

0 to +70 °C 0 to +70 °C

142 5 Fundamentals of Optical Detectors