Measuring Apparatus and Method for Optical Receiver
A CMRR measurement device of the present disclosure uses a wideband light source as a test beam instead of modulated light that needs to be swept by a light component analyzer (LCA). By using a spectrum analyzer or an A/D converter as an electrical signal measuring instrument, it is possible to acquire a CMRR with a low-price general-purpose measuring instrument. It is also possible to use a combination of a wideband light source and a continuous wave (CW) light source as the test beam. An expensive measuring instrument such as an LCA is unnecessary and repetition of sweep of modulated light is not required, and it is therefore possible to acquire the CMRR in an extremely short time.
1 . A measurement device for a common mode rejection ratio (CMRR) of a coherent optical receiver having a signal light input terminal and a local light input terminal, the coherent optical receiver including an optical hybrid connected to the signal light input terminal and the local light input terminal and a photodiode connected to an output of the optical hybrid, the measurement device comprising:
a wideband light source for outputting a test beam having a coherence length and a spectral wavelength width, the coherence length being longer than an optical path length of one interferometer inside the optical hybrid, and the spectral wavelength width corresponding to twice or more a frequency band of the CMRR to be measured; and
an electrical measuring instrument for an electrical signal from the coherent optical receiver,
wherein for each of numerator measurement and denominator measurement of CMRR, the test beam from the wideband light source is provided to at least one of the signal light input terminal or the local light input terminal.
2 . The measurement device according to claim 1 , wherein the test beam from the wideband light source is provided to only one of the signal light input terminal or the local light input terminal for the numerator measurement of CMRR.
3 . The measurement device according to claim 1 , wherein the test beam is provided from the wideband light source to both the signal light input terminal and the local light input terminal for the denominator measurement of CMRR.
4 . The measurement device according to claim 1 , wherein combined light of the test beam from the wideband light source and CW light from a continuous wave (CW) light source is provided to either the signal light input terminal or the local light input terminal for the numerator measurement of CMRR, and the CW light has a wavelength included in a wavelength bandwidth of the test beam.
5 . The measurement device according to claim 1 , wherein the test beam from the wideband light source is provided to the signal light input terminal, and CW light from a continuous wave (CW) light source is provided to the local light input terminal for the denominator measurement of CMRR.
6 . The measurement device according to claim 1 , wherein
light intensity of the test beam from the wideband light source in the numerator measurement and that in the denominator measurement are adjusted such that a sum of power supply currents of two photodiodes when the test beam is provided to either the signal light input terminal or the local light input terminal in the denominator measurement of CMRR becomes equal to a sum of power supply currents of the two photodiodes in the numerator measurement of CMRR, or
a value of each of the sums of the power supply currents is used to correct a result of the numerator measurement and a result of the denominator measurement to calculate the CMRR.
7 . The measurement device according to claim 1 , wherein the wideband light source is any one of an amplified spontaneous emission (ASE) light source, a super-continuum (SC) light source, or a superluminescent diode (SLD) light source.
8 . A measurement method for a common mode rejection ratio (CMRR) of a coherent optical receiver having a signal light input terminal and a local light input terminal, the coherent optical receiver including an optical hybrid connected to the signal light input terminal and the local light input terminal and a photodiode connected to an output of the optical hybrid, the measurement method comprising:
providing a test beam from a wideband light source to at least one of the signal light input terminal or the local light input terminal to obtain a first electrical signal by an electrical measuring instrument in numerator measurement of CMRR;
providing the test beam from the wideband light source to at least one of the signal light input terminal or the local light input terminal to obtain a second electrical signal by the electrical measuring instrument in denominator measurement of CMRR; and
calculating the CMRR based on the first electrical signal and the second electrical signal,
wherein the test beam has a coherence length longer than an optical path length of one interferometer inside the optical hybrid and has a spectral wavelength width corresponding to twice or more a frequency band of the CMRR to be measured.