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• FAQ for Differential Group Delay

General Photonics’ high-speed variable differential group delay (DGD) line provides a variable amount of group delay difference between two linear orthogonal polarization states. DGD is a key component for PMD emulation and compensation. ProDelay™ can digitally vary the amount of 1st order PMD from -45 ps to 45 ps with a resolution of 1.36 ps (6-bit resolution) in less than 250 μs. With an integrated circuit board and a software package, the device can easily be controlled with a computer or a microprocessor. The circuit board has a 10-pin TTL digital I/O port to interface with any digital control signal, either from a control circuit board or a computer. An optional Labview PMD emulation software can also available to generate Maxwellian DGD distribution of any average value. In addition to PMD compensation and emulation, this patented device can be used for precision TDM bit alignment.

• Digitally switched DGD
• 250 µs delay switching speed
• ± 45 ps or 90 ps total DGD
• 6-bit (1.36 ps) delay resolution
• Compact
• Patented

• Polarization mode dispersion compensation
                         
• PMD emulation
• TDM bit alignment

Insertion Loss	1.5 dB max.
Return Loss	55 dB
PDL	0.2 dB over all DGD values
PDL Variation	± 0.15 dB over all DGD values
Wavelength Dependent Loss	0.25 dB over C band
1st order PMD	-45 ~ +45 ps, 0 ~ 90 ps optional, others specify
DGD Varying Resolution	1.36 ps
2nd order PMD	90 ps2 max.
Transient DGD	1.36 ps max.
Transient Loss	0.5 dB per bit max.
Number of Control Bits	6
Delay Variation Speed	250 μs
Operating Wavelength	1550 ± 50 nm, or 1310 ± 50 nm
Optical Power Handling	300 mW min.
Electrical Interface	10 pin digital port to accept any 6 bit TTL control
Electrical Power Supply	9 VDC/0.6A
Software	DGDPro-I for computer printer port (included) DGDPro-II for a digital I/O card and PMD emulation (optional)
Operating Temperature	0 ~ 50 °C
Dimensions	7.3" × 9.0" × 2.5" (L × W × H)