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Home > Products > Optical Phase Demodulators > DPSK Demodulator / Delay Line Interferometer
DPSK Demodulator / Delay Line Interferometer  
Optoplex DPSK Demodulator - Delay Line Interferometer
Optoplex DPSK Demodulator - Delay Line Interferometer
Optoplex DPSK Demodulator - Delay Line Interferometer
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  • Description
  • Features
  • Applications
  • Specification
  • Typical Performance
  • Parameter Definition
Product Description - DPSK Demodulator
Optical differential-phase shift keying (DPSK) provides a desired modulation format that offers high receiver sensitivity, high tolerance to major nonlinear effects in high-speed transmissions, and high tolerance to coherent crosstalk. In DPSK, data information is carried by the optical phase difference between adjacent bits. For direct detection of DPSK signal (by conventional intensity detectors), a DPSK demodulator is needed to convert the phase-coded signal into an intensity-coded signal.

Optoplex's Optical DPSK Demodulator, also known as Delay Line Interferometer (DLI), converts phase modulation to amplitude modulation over the entire C+L band in support of data transmission rates of 2.5, 10 or 40 Gb/s. The DPSK Demodulator is designed for phase modulated optical communication systems utilized in commercial, defense and space exploration markets. The DPSK device plays a key role in improving signal quality and performance to meet the expanding demand for higher data rates and more complex transmission formats within current and next generation systems without major capital expenditure. Optoplex's DPSK Demodulator is based on a patented free-space optical design, which is compact, athermal and polarization-independent. The measured frequency drift over temperature is only ~0.02 GHz/°C for our standard passive device. Further, this DPSK Demodulator exhibits a total polarization-dependent phase shift (PDPS) of less than 2 degrees over the entire operating temperature range with a high extinction ratio. Optoplex's DPSK Demodulators can be configured to be fully tunable, semi-tunable or purely passive.

Optoplex provides three types of DPSK demodulators:

  1. Tunable DPSK demodulator
  2. Passive DPSK demodulator
  3. Semi-tunable DPSK demodulator

Tunable DPSK demodulator: A tunable DPSK demodulator is the DPSK demodulator whose spectral response can be tuned along the frequency axis while keeping the FSR unchanged.

Passive DPSK demodulator: To avoid system control involving complicated feedback algorithm and power consumption, a passive DPSK demodulator can be built. As indicated by its name, a passive DPSK demodulator does not have the tuning capability and its phase, or spectral constructive/destructive peaks, is fixed when it is built. By “passive” it means that the DPSK demodulator does not contain spectral tuning element in the device.

Semi-tunable DPSK demodulator: Considering the contribution of TDFS to the channel misalignment and that TDFS does not scale down with FSR as does the FSR-error, the passive solution will not work well for a low-bit-rate system. However, by combining the features of tunable and passive DPSK demodulators, Optoplex developed semi-tunable DPSK demodulator, also known as Colorless DPSK Demodulator. A colorless DPSK demodulator is a special tunable DPSK demodulator whose optical performance is the same as passive DPSK demodulator, but, like a tunable DPSK demodulator, equipped with a tuner for providing a few GHz tuning capability. Its FSR can be either 25 GHz or 50 GHz so that it can be used in systems with channel spacing being a multiple of the FSR. As a result, Optoplex’s colorless DPSK demodulator combines the advantages of both tunable and passive DPSK demodulators and can serve the ever-demanding needs of system providers.

Dual-Rate DPSK Demodulator is also available. For DQPSK demodulator, please visit DQPSK demodulator page.

Features and Benefits of DPSK Demodulator
  • Athermal design
  • C+L band coverage by a single device
  • Low temperature-dependent frequency shift (TDFS)
  • Low polarization-dependent frequency shift (PDFS)
  • Wide bandwidth
  • Low insertion loss & PDL
  • High power handling
  • Passive, semi-tunable and fully tunable operation
  • Suitable for both RZ and NRZ modulation format
  • Single or dual data rate operation
  • Telcordia GR-1221 qualified
DPSK Demodulator Applications
  • 2.5, 10, 20 or 40 Gb/s commercial DPSK signal reception
  • Customized data rate for advanced applications
  • Data rate optimization
  • Extend transmission distance
Standard Specifications of DPSK Demodulator
Parameter Unit
Wavelength Range (C-Band) nm
1527 to 1567
Wavelength Range (L-Band) nm
1567 to 1607
Free Spectral Range (FSR)1 GHz
10.7, 43, 50, 67
10.0, 12.5, 40, 50, 66.67
FSR Error M%
< 1
< 0.015
Insertion Loss2 (including 2 connectors) dB
1.7 Typical; 2.2 Maximum
Extinction Ratio2 dB
> 18
> 18
> 20
PMD2 ps
< 0.1
Return Loss dB
> 40
< 0.2
PDFS2 deg
< 3
< 1.5
Optical Path Delay2 (between the 2 receiving ports) ps
< 1.0
Tuning Range -
1.5 x FSR
± 3 GHz
Tuning Time Constant3 sec
~ 1.0
~ 6.0
Power Consumption W
0.5 Typical, 1.0 Maximum
Tuning Voltage V
0 to 5
Maximum Input Optical Power mW
Operating Temperature °C
0 to 70
Storage Temperature °C
-40 to 85
Dimension (L x W x H)4 mm
~ 39x26x11 for 10~12.5 GHz
~ 26x24x9 for >40 GHz
~51x30x18 for 10 or 12.5 GHz
~25x25x11 for 40 GHz
Connector Type -
Fiber Pigtail Type -
SMF-28 with 900 µm loose tube
Fiber pigtail length m
1.0 ± 0.1


  1. Only typical values are listed. Optoplex can provide devices with FSR ranging from 5 to 160 GHz.
  2. Over the stated spectral and operating temperature ranges and all polarization states.
  3. Defined as the time required to reach half-way from the starting and ending points.
  4. Excluding two collimator sleeves extending out from the two adjacent sides by 21 mm with diameter of 8 mm.
  5. Excluding two collimator sleeves extending out from one shorter side by 17 mm with diameter of 6.3 mm.
Typical Performance of DPSK Demodulator

Typical spectra of Optoplex DPSK demodulator

Parameter Definition of DPSK Demodulator

Parameter Definition


Wavelength Range is defined as spectral range over which the DPSK demodulator can operate.

1528.77 ~ 1563.86 nm

DPSK is acronym for Differential Phase-Shift Keying


DLI is acronym for Delay Line Interferometer.


DQPSK is acronym for Differential Quaternary Phase-Shift Keying


DPSK Demodulator is a component that converts phase modulation into amplitude modulation.


Insertion Loss (dB) is the relative peak power level transmitted to the output ports referenced to the 0-dB reference level when the DPSK demodulator is inserted. "On" and "Off" ports are reported separately.

1.7 dB

Insertion Loss Uniformity (dB) is defined as maximum insertion loss difference between the adjacent channels of the two output ports across the whole operating wavelength range.

0.5 dB

Isolation/Extinction Ratio (dB) is defined as the power difference between peak and valley of the spectrum. "On" and "Off" ports are reported separately.

18 dB

Polarization Dependent Loss (PDL) (dB) is the power difference between the two extreme polarization states. "On" and "Off" ports are reported separately.

0.2 dB

Polarization Dependent Frequency Shift (PDFS) (deg) is the maximum frequency difference measured at the valley of power spectrum among all polarization states.

3 deg

Optical Return Loss (dB) is the ratio between the input power and the reflected power over all polarization states at each port , RL = -10×log10(Pr/Pin).

40 dB

Tuning Range (TR) (GHz) is the maximum shift variation of a center frequency of the spectrum driven by applying control voltage to DPSK demodulator.


Tuning Speed (TS) (second) is the time needed by the device to tune the frequency to its half of target position.

1 s

Operating Temperature (°C) is the ambient temperature range over which the device's performance spec can be met.

-5 to 65 °C

Storage Temperature (°C) is the ambient temperature range over which the device can be stored without affecting its intended application afterwards.

-40 to 85 °C

Product Request and Ordering Information
Please speak to Optoplex Sales persons. If you request custom-designed DPSK demodulator product, please provide the following parameters:
  • Wavelength range
  • Free spectral range (FSR)
  • Passive, semi-tunable or fully tunable
  • Fiber length
  • Optical connector type