OCPM stands for Optical Channel Performance Monitor used for monitoring the health of DWDM networks in optical layer. It embraces the essential functions of optical channel monitor (OCM), optical performance monitor (OPM), optical power meter, and optical wavelength meter, and more importantly measures OSNR. BaySpec’s OCPM measures continuous spectra, rather than monitoring discrete channels.
Wavelength Range (nm) is the spectral region over which the spectral engine and detectors are operated. BaySpec’s technology ensures to work in the C-band & L-band.
Absolute Wavelength Accuracy (pm) is the maximally allowed wavelength errors ±Dm centered at 0 error. For an OCPM, the measurement wavelength errors must be within the limits of [-Dm, +Dm], i.e.,
Max(|Dl|) = Max(|lOCPM – lc|) <=Dm or -Dm<= Dl <=+Dm
where Dl = lOCPM – lc is the wavelength error of an arbitrary channel, lOCPM is the peak wavelength reported by an OCPM and lc is the wavelength measured by a calibrated wavelength meter (e.g., OSA or wavemeter). Max(|Dl|) is the absolute value of the maximum wavelength error among all channels.
Relative Wavelength Accuracy: There are two different definitions that have been used.
Definition 1: Relative Wavelength Accuracy (pm) is the maximally allowed wavelength error span (dm) over all channels. For an OCPM, the maximum wavelength error span is:
dlm = DlMax – DlMin <= dm
where DlMax and DlMin are the maximum and minimum wavelength errors reported by the OCPM.
Definition 2: Relative Wavelength Accuracy (pm) is defined as ±dm/2, where dm is the maximally allowed wavelength error span. It may not be centered at 0 error.
The two different definitions for relative wavelength accuracy describe the same phenomenon.
The absolute wavelength accuracy determines the maximally allowed wavelength errors whereas the relative wavelength accuracy determines the uniformity of wavelength errors over all channels.
Wavelength Resolution (Spectral Resolution) (pm) is the full-width-half-maximum (FWHM) resolution. It is the spectral width at the half power level that the OCPM can resolve with high confidence level. In the other words, the wavelength resolution is the minimum resolvable wavelength separation between two nearby power spectra.
Note: Some customers define “resolution” as “readout resolution”, i.e., the number of significant digits returned from the measurement through the communications interface. This applies to “Wavelength” and “Power”.
Dynamic Range (dB) is the optical power range where an OCPM is operated. It is approximately expressed as
Dynamic Range = Upper Limit of Channel Input Power – Noise Floor
Note that OSNR is a relative measure. For example, Upper Limit of Channel Input Power = -20 dBm and Noise Floor = -80 dBm, yields the Dynamic Range = 60 dB.
Channel Input Power Range (dB) specifies the operating power range of an OCPM. The detection sensitivity determines its lower limit. Beyond its upper limit, the device becomes saturated.
Channel Input Power Range = Upper limit of channel input power – Lower limit of channel input power
Channel Power Accuracy (dB) is the maximally allowed power errors centered at 0 error. It is a measurement tolerance of power obtained with respect to the actual power value against all wavelengths. It is calibrated based on power meter.
Channel Power Repeatability (dB) measures the channel power accuracy over a given time period. BaySpec’s channel power repeatability is defined as the power fluctuation over 24 hours of continuous measurement.
OSNR (dB) of a channel is defined as an absolute ratio of the clean optical signal power P(signal) to noise power P(noise), measured in units of dB, i.e.,
OSNR = 10 × log10[ P(signal)/ P(noise)]
In practice, we approximate P(signal) = P(mixed) – P(noise) since the clean optical signal is not obtainable, where P(mixed) is the total power measured at the corresponding channel wavelength.
Noise Floor (dBm) is the lowest power level detectable by the OCPM, which is limited by the electronic system. An optical noise level lower than the noise floor would not be recognized and, as a result, OCPM will give the noise floor value instead.
Response Time (ms) is the aggregate time span of that OCPM needs to give a complete measurement. It includes intensity response time, calculation time and display time. In total, it is less than 20 ms for BaySpec’s OCPMs.
Operating Temperature (°C) is the temperature range over which the device can be operated and maintain its specifications.
Storage Temperature (°C) is the temperature range over which the device can be stored without damage and can be operated over operating temperature according to its specifications.