Method and device for measuring a noise figure in optical amplifiers

A method for measuring noise figures of an optical amplifier, comprising the steps of:

• generating first and second modulation clocks in anti-phase, the first and second modulation clocks having a period which is shorter than a time constant of extinction of the optical amplifier;
• generating short wavelength light pulses which have different wavelengths .lambda..sub.1 .about..lambda..sub.n/2 and are modulated by the first modulation clock;
• generating long wavelength light pulses which have different wavelengths .lambda..sub.(n/2)+1 .about..lambda..sub.n and are modulated by the second modulation clock;
• mixing the short and long wavelength light pulses to generate a continuous light;
• supplying the continuous light to the optical amplifier;
• supplying the output light of the optical amplifier to an instrument for distinctively measuring powers of spectrums of the output light through an optical switch;
• switching the optical switch in synchronization with the first or second modulation clock so that powers PAMP.sub.1 .about.PAMP.sub.(n/2) at the wavelengths .lambda..sub.1 .about..lambda..sub.n/2 of an amplified light which corresponds to the short wavelength pulses and powers P.sub.ASE(n/2)+1 .about.P.sub.ASEn at the wavelengths .lambda..sub.(n/2)+1 .about..lambda..sub.n of a light which is outputted when the amplified light is not outputted from the optical amplifier are measured by the instrument;
• switching the optical switch in synchronization with the first or second modulation clock so that powers PAMP.sub.(n/2)+1 .about.PAMP.sub.n at the wavelengths .lambda..sub.(n/2)+1 .about..lambda..sub.n of an amplified light which corresponds to the long wavelength pulses and powers P.sub.ASE1 .about.P.sub.ASE(n/2) at the wavelengths .lambda..sub.1 .about..lambda..sub.n/2 of a light which is outputted when the amplified light is not outputted from the optical amplifier are measured by the instrument;
• calculating noise figures NF.sub.1 .about.NF.sub.n at the wavelengths .lambda..sub.1 .about..lambda..sub.n of the optical amplifier as described below;
• NF.sub.k =(P.sub.ASEk /h.nu..sub.k G.sub.k Bo)+(1/G.sub.k) (k=1.about.n)
• wherein h is Planck's constant;
• .nu..sub.k (k=1.about.n) are light frequencies of the light pulses;
• G.sub.k (k=1.about.n) are gains at the wavelengths .lambda..sub.k (k=1.about.n) of the optical amplifier;
• and Bo is a band width of a pass band of the instrument used for measuring the powers P.sub.ASE1 .about.P.sub.ASEn.

A method for measuring noise figures of an optical amplifier, comprising the steps of:

• generating a modulation clock having a period which is shorter than a time constant of extinction of the optical amplifier;
• generating a continuous wave light which has a wavelength .lambda..sub.1 ;
• generating light pulses which has a wavelength .lambda..sub.n and the amplitude is modulated by the modulation clock;
• supplying the continuous wave light and the light pulse to the optical amplifier;
• supplying the output light of the optical amplifier to an instrument for distinctively measuring powers of spectrums of the output light through an optical switch;
• changing the wavelength .lambda..sub.n of the light pulses and switching the optical switch in synchronization with the modulation clock so that power PAMP.sub.n at the wavelengths .lambda..sub.n of an amplified light which corresponds to the light pulse and a power P.sub.ASEn at the wavelengths .lambda..sub.n of a light which is outputted when the amplified light is not outputted from the optical amplifier are measured by the instrument;
• calculating noise figures NF.sub.n at a plurality of wavelengths .lambda..sub.n of the optical amplifier as described below;
• NF.sub.n =(P.sub.ASEn /h.nu..sub.n G.sub.n Bo)+(1/G.sub.n)
• wherein h is Planck's constant;
• .nu..sub.n is light frequency of the light pulse;
• G.sub.n is a gain at the wavelength .lambda..sub.n of the optical amplifier;
• and Bo is a band width of a pass band of the instrument used for measuring the power P.sub.ASEn.