Carrier-Suppressed Return-to-Zero
Carrier-Suppressed Return-to-Zero (CSRZ) is an optical line code. In CSRZ the field intensity drops to zero between consecutive bits (RZ), and the field phase alternates by π radians between neighbouring bits, so that if the phase of the signal is e.g. 0 in even bits (bit number 2n), the phase in odd bit slots (bit number 2n+1) will be π, the phase alternation amplitude. In its standard form CSRZ is generated by a single Mach–Zehnder modulator (MZM), driven by two sinusoidal waves at half the bit rate BR, and in phase opposition. This gives rise to characteristically broad pulses (duty cycle 67%).
The signal format Alternate-Phase Return-to-Zero (APRZ) can be viewed as a generalisation of CSRZ in which the phase alternation can take up any value ΔΦ (and not necessarily only π) and the duty cycle is also a free parameter.
CSRZ can be used to generate specific optical modulation formats, e.g. CSRZ-OOK, in which data is coded on the intensity of the signal using a binary scheme (light on=1, light off=0), or CSRZ-DPSK, in which data is coded on the differential phase of the signal, etc. CSRZ is often used to designate APRZ-OOK.
The characteristic properties of an CSRZ signal are those to have a spectrum similar to that of an RZ signal, except that frequency peaks (still at a spacing of BR) are shifted by BR/2 with respect to RZ, so that no peak is present at the carrier and power is ideally zero at the carrier frequency (hence the name).
Compared to standard RZ-OOK, the CSRZ-OOK is considered to be more tolerant to filtering and chromatic dispersion, thanks to its narrower spectrum.
Further reading
- Savard, John J. G. (2018) [2006]. "Digital Magnetic Tape Recording". quadibloc. Archived from the original on 2018-07-02. Retrieved 2018-07-16.
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- t
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- Unipolar encoding
- Bipolar encoding
- On-off keying
- Mark and space
- Return to zero (RZ)
- Non-return-to-zero, level (NRZ/NRZ-L)
- Non-return-to-zero, inverted (NRZ-I)
- Non-return-to-zero, space (NRZ-S)
- Manchester
- Differential Manchester/biphase (Bi-φ)
- See also: Baseband
- Baud
- Bit rate
- Digital signal
- Digital transmission
- Ethernet physical layer
- Pulse modulation methods
- Pulse-amplitude modulation (PAM)
- Pulse-code modulation (PCM)
- Serial communication
- Category:Line codes