Optical Spectrum Analyzers - Confused on Units

[cambridgejohn]

Hi!

I am new to these, and off the bat am confused by the units.

Manufacturers quote resolution either in units of length, e.g. 0.04 nm, or HZ. For example,

0.04 pm / 5MHz
0.16 pm / 20 MHz
0.8 pm / 100 MHz.

I am thrown by this since I thought frequency was the inverse of wavelength. I get the length part and can understand when I look at a plot of Power vs. Wavelength.

I know I am overlooking something obvious...please help!

Thanks!
John

 

[AlephZero]

The numbers are not frequencies and wavelengths. The are differences between (or errors in the measurement of) in frequencies and wavelengths.

If a frequency f has wavelength $\lambda$, then
a frequency of f + 5 Mhz has a wavelength of approximately $\lambda$ - 0.04pm, and so on

 

[cambridgejohn]

Thanks. The error concept part helps. I can understand when a wavelength is being measured a higher resolution helps out, and that one needs to only buy an OSA which will discern a certain wavelength spectra. And I can understand how the difference part makes sense for the wavelength.

What are the units of the proportion between the frequencies and wavelengths measured?

 

[cambridgejohn]

ok. it all makes sense now. just needed to run through some numeric examples using the speed of light to get numbers. thanks again for your help.