CN104764592A - Measurement method of chirp parameters of electro-optic intensity modulator - Google Patents

Abstract

The invention discloses a measurement method of chirp parameters of an electro-optic intensity modulator and belongs to the field of photo-electronic technologies. The method includes the steps that a beam of optical carrier is divided into two beams through a beam splitter, one beam is modulated by a sine microwave signal through the electro-optic intensity modulator to be measured, the other beam is subjected to frequency shift, two optical signals are combined through a beam combiner and then are sent into a photoelectric detector for photovoltaic conversion, and therefore a beat frequency signal is obtained; the amplitude of a specific frequency component in the beat frequency can reach the maximum value and the minimum value by adjusting offset voltage of the electro-optic intensity modulator to be measured, and the chirp parameters of the electro-optic intensity modulator are obtained through calculation according to the maximum amplitude value and the minimum amplitude value of the specific frequency component; the frequency of the sine microwave signal is changed, the process is repeated, and finally a curve of the chirp parameters, changing along with the modulation frequency, of the electro-optic intensity modulator is obtained. Compared with the prior art, the measurement method can substantially improve the measurement resolution ratio and enlarge the frequency range, and is suitable for electro-optic intensity modulators with any limited splitting ratio.

Description

A kind of measuring method of electro-optic intensity modulator chirp parameter

Technical field

The invention belongs to photoelectron technical field, be specifically related to a kind of measuring method of electro-optic intensity modulator chirp parameter.

Background technology

Along with optical fiber telecommunications system towards at a high speed, wide bandwidth and future development at a distance, electro-optic intensity modulator one of Primary Component becoming speed fiber optic communication systems gradually.The electro-optic intensity modulator of traditional mach zhender waveguiding structure, due to the difference of driving voltage loss in the asymmetry of mach zhender waveguiding structure and two-arm, result in electro-optic intensity modulator and have the formation of the chirp parameter that is closely connected along with fibre-optical dispersion, become the key factor of restriction high speed long-haul transport, therefore in order to improve the overall transfer performance of an optical fiber communication, the measurement for chirp parameter is very important.

At present, the method measuring the chirp parameter of the electro-optic intensity modulator of mach zhender structure is roughly divided into electrical domain mensuration and area of light mensuration, Typical Representative is spectrographic method (Y.Q.Shi, L.S.Yan, A.E.Willner, " High-speed electrooptic modulator characterization using optical spectrum analysis, " Journal of Lightwave Technology.2003,21 (10): 2358-2367, N.Courjal and J.M.Dudley, " Extinction-ratio-independent method for chirp measurements of Mach-Zehndermodulators, " Optics Express.2004,12 (3): 442-448.), the method utilizes the light carrier in spectrum to obtain the chirp parameter of electro-optic intensity modulator with the ratio of sideband, but be limited to the restriction of resolution (0.01nm) and the impact of laser linewidth of commercial spectroanalysis instrument wavelength, cannot measure the chirp parameter in low-frequency range accurately, electrical domain mensuration comprises light frequency-discrimination method (J.Provost and F.Grillot, " Measuring the Chirp and theLinewidth Enhancement Factor of Optoelectronic Devices with a Mach – ZehnderInterferometer, " IEEE Photonics Journal.2011,3 (3): 476-488, J.S.Bakos, G.P.Djotyan, P.N.Ignacz, el al. " Generation of frequency-chirped laser pulses by an electro-opticamplitude modulator, " Optics and Lasers in Engineering.2009, 47 (1): 19-23.), phase-comparison method (L.S.Yan, Q.Yu, and A.E.Willner, " Measurement of the chirp parameter ofelectro-optic modulators by comparison of the phase between two sidebands, " OpticsLetters.2003, 28 (13): 1114-1116.), process of heterodyning (C.E.Rogers, J.L.Carini, J.A.Pechkis, el al. " Characterization and compensation of the residual chirp in a Mach-Zehnder-typeelectro-optical intensity modulator, " Optics Express.2010, 18 (2): 1166-1176, D.J.Krauseand J.C.Cartledge, " Technique for Measuring the Optical Phase Transfer Function, " IEEEPhotonics Journal.2004, 16 (8): 1915-1917.), Optical Fiber Transmission method (F.Devaux, Y.Sorel and J.F.Kerdiles, " Simple measurement of fiber dispersion and of chirp parameter of intensitymodulated light emitter, " Journal of Lightwave Technology.1993, 11 (12): 1937-1940.), wherein light frequency-discrimination method utilizes interferometer mode to extract for measuring chirp parameter by the amplitude of test component and phase response, but interferometer temperature influence is very large, and have very large requirement to the high bandwidth of the Free Spectral Range (FSR) of interferometer and high resolving power, and regulate complicated, phase-comparison method utilizes wave filter to form single-sideband modulation, obtains chirp parameter by the ratio of phase place extracting sideband, but to the resolution of wave filter and bandwidth requirement very high, and regulate difficulty when measuring multifrequency point, process of heterodyning utilizes the ratio of the phase place of light heterodyne technology measuring modulator and amplitude information directly to obtain chirp parameter, but is subject to the impact of laser stability, and is confined to the time domain measurement in low broadband, the dissemination of Optical Fiber Transmission method using degree modulated light signal in dispersive optical fiber obtains chirp parameter, but is usually subject to fiber lengths and environmental impact is very large.

Summary of the invention

Technical matters to be solved by this invention is that overcoming existing electro-optic intensity modulator chirp parameter measures the problem that medium frequency resolution is low, frequency range is narrow, a kind of electro-optic intensity modulator chirp parameter measuring method is proposed, can realize the wideband of electro-optic intensity modulator chirp parameter, high-resolution is measured, simplified measurement system, reduction measure cost.

The present invention is to achieve these goals by the following technical solutions:

A kind of measuring method of electro-optic intensity modulator chirp parameter, the light carrier that laser instrument sends is divided into two bundles through beam splitter, wherein light beam carrier wave is formed intensitymodulated optical signals via electro-optic intensity modulator to be measured by a sinusoidal signal modulation, another bundle light carrier forms shift frequency light signal after frequency shifter, two-beam signal sends into photodetector opto-electronic conversion after closing bundle by bundling device, obtains beat signal; Regulate the bias voltage of electro-optic intensity modulator to be measured respectively, the amplitude of characteristic frequency composition in beat signal is made to reach maximal value and minimum value, utilize maximal value and the minimum value of the characteristic frequency composition of record, calculate the chirp parameter obtaining electro-optic intensity modulator to be measured; Change the frequency of described sinusoidal signal and repeat said process, obtaining the variation relation of electro-optic intensity modulator chirp parameter to be measured with modulating frequency.

The measuring method of electro-optic intensity modulator chirp parameter provided by the invention, its specific implementation comprises the following steps:

The sinusoidal signal frequency that step 1, setting are loaded into electro-optic intensity modulator to be measured is f _m, the shift frequency amount of frequency shifter is f _s;

Step 2, progressively regulate the bias voltage of electro-optic intensity modulator to be measured, observe f in the beat signal that photodetector exports _sand f _m± f _srange value i (the f of frequency _s) and i (f _m± f _s), record i (f _s) maximum amplitude value and i (f _m± f _s) minimum amplitude value, be designated as i respectively ₀(f _s), i ₀(f _m± f _s); Progressively regulate the bias voltage of electro-optic intensity modulator to be measured again, observe f in the beat signal of photodetector output _sand f _m± f _srange value i (the f of frequency _s) and i (f _m± f _s), record i (f _s) minimum amplitude value and i (f _m± f _s) maximum amplitude value, be designated as i respectively _π(f _s), i _π(f _m± f _s);

Step 3, to solve electro-optic intensity modulator to be measured in modulating frequency be f _mchirp parameter, solution formula is:

$a_0\left(f_m\right)=\frac{i_0\left(f_s\right)\×i_0(f_m\±f_s)+i_{\mathrm{\π}}\left(f_s\right)\×i_{\mathrm{\π}}(f_m\±f_s)}{i_0\left(f_s\right)\×i_{\mathrm{\π}}(f_m\±f_s)-i_{\mathrm{\π}}\left(f_s\right)\×i_0(f_m\±f_s)}$

Step 4, calculate the symbol table value indicative s of electro-optic intensity modulator chirp parameter to be measured, when s be greater than 1 or be less than-1 time, chirp parameter a ₀for positive sign, when s is between-1 and 1, chirp parameter a ₀for negative sign, when s equals 1 or-1, chirp parameter is 0; The computing formula of s is:

$s\left(f_m\right)=\frac{i_0(f_m\±f_s)+i_{\mathrm{\π}}(f_m\±f_s)}{i_0(f_m\±f_s)-i_{\mathrm{\π}}(f_m\±f_s)}\·\frac{i_0\left(f_s\right)+i_{\mathrm{\π}}\left(f_s\right)}{i_0\left(f_s\right)-i_{\mathrm{\π}}\left(f_s\right)}$

The frequency f of step 5, change sinusoidal signal _mrepeat step 2 ~ step 4 and can obtain chirp parameter with modulating frequency f _mchange curve.

In technique scheme, in described beat signal, characteristic frequency composition refers to f _sand f _m± f _sradio-frequency component, its amplitude changes by regulating the bias voltage of electro-optic intensity modulator to be measured, reaches maximal value and minimum value respectively.

In technique scheme, described frequency shifter is acousto-optic frequency translation or modulation shift frequency, and before and after shift frequency, the centre frequency of light carrier has changed f _s.

In technique scheme, i in the solution formula of described chirp parameter ₀(f _m± f _s) and i _π(f _m± f _s) Xiang Zhongjun gets+number or all get-number.

Compared with prior art, the present invention has following beneficial effect:

The present invention measures electro-optic intensity modulator chirp parameter in the electrical domain exactly, improves resolution and the frequency range of optoelectronic device measurement.

Present invention achieves the calibration measurement of unevenness response and the light beam instability effectively avoiding photodetector, improve the accuracy that electro-optic intensity modulator chirp parameter is in the electrical domain measured.

Present invention achieves the chirp parameter of the electro-optic intensity modulator of the mach zhender structure measuring arbitrary finite splitting ratio in the electrical domain.

Accompanying drawing explanation

Fig. 1 is the device schematic diagram of a kind of electro-optic intensity modulator chirp parameter of the present invention measuring method.

Embodiment

Below in conjunction with embodiment, the invention will be further described, and described embodiment is only the present invention's part embodiment, is not whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making other embodiments used obtained under creative work prerequisite, belongs to protection scope of the present invention.

Light beam carrier wave is divided into two through beam splitter, a branch of by electro-optic intensity modulator to be measured, modulator loads a sinusoidal modulation signal, another Shu Jinhang shift frequency, and two bundles close through bundling device and send into photodetector after bundle and carry out opto-electronic conversion, obtain beat signal; By regulating the bias voltage of electro-optic intensity modulator to be measured, record Amplitude maxima and the minimum value of characteristic frequency composition in beat signal, thus calculate acquisition electro-optic intensity modulator chirp parameter to be measured; Change the frequency of sinusoidal modulation signal, repeat said process, obtain the change curve of electro-optic intensity modulator chirp parameter to be measured with modulating frequency.

In order to understand this technological invention scheme better, below measuring principle is briefly introduced:

Laser instrument export light carrier be divided into two bundles by beam splitter, a branch of through electro-optic intensity modulator to be measured modulate by sinusoidal signal, electro-optic intensity modulator output optical signal to be measured is expressed as

Wherein A ₁and f ₀be respectively amplitude and the frequency of light carrier, γ is the splitting ratio of the two-arm of electro-optic intensity modulator to be measured, m ₁and m ₂be respectively the light phase amplitude caused by modulation signal be loaded in electro-optic intensity modulator two-arm to be measured, f _mfor the frequency of sinusoidal modulation signal, for the phase offset that the bias voltage be loaded on modulator causes.

Another bundle that beam splitter exports carries out shift frequency through frequency shifter, and the light field of output is expressed as:

E ₂＝A ₂exp(j2πf ₀t+j2πf _st) (2)

A ₂for the amplitude of this bundle light carrier, f _sfor the frequency of acousto-optic frequency shifters, intensitymodulated optical signals and shift frequency light signal close road by bundling device and export and be:

E＝E ₁+ηE ₂exp(jψ) (3)

Wherein η, ψ are the relative amplitude of intensitymodulated optical signals when superposing with shift frequency light signal and phase place, form beat frequency photocurrent and export and be after photodetector opto-electronic conversion:

In formula, R is photodetector frequency response, (4) formula Bessel's function is launched also abbreviation to be:

Wherein J _n() is Bessel function of the first kind, and (5) formula medium frequency is f _sand f _m± f _srange value be

In small signal approximation situation (| m ₁|, | m ₂| <<1), change i (f by regulating bias voltage size _s), i (f _m± f _s) amplitude size, when being in bias point time, i (f _m± f _s) amplitude reach minimum value and be:

i ₀(f _m±f _s)＝R(f _m±f _s)ηA ₁A ₂(m ₁+γm ₂) (7)

I (f simultaneously _s) amplitude reach maximal value and be:

i ₀(f _s)＝2R(f _s)ηA ₁A ₂(1+γ) (8)

When being in bias point time, i (f _m-f _s) amplitude reaches maximal value and is:

i _π(f _m±f _s)＝R(f _m±f _s)ηA ₁A ₂(m ₁-γm ₂) (9)

Beat frequency sideband i (f simultaneously _s) reach minimum value and be:

i _π(f _s)＝2R(f _s)ηA ₁A ₂(1-γ) (10)

Comprehensively (7) ~ (10) formula, obtaining electro-optic intensity modulator to be measured in modulating frequency is f _mtime chirp parameter be:

$a_0\left(f_m\right)=\frac{m_1+{\mathrm{\&gamma;}}^2{m}_2}{\mathrm{\&gamma;}(m_1-m_2)}=\frac{i_0\left(f_s\right)\&times;i_0(f_m\&PlusMinus;f_s)+i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}{i_0\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)-i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_0(f_m\&PlusMinus;f_s)}---\left(11\right)$

The symbolic representation function of definition chirp parameter

$s\left(f_m\right)=\frac{m_1}{{\mathrm{\&gamma;}}^2{m}_2}=\frac{i_0(f_m\&PlusMinus;f_s)+i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}{i_0(f_m\&PlusMinus;f_s)-i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}\&CenterDot;\frac{i_0\left(f_s\right)+i_{\mathrm{\&pi;}}\left(f_s\right)}{i_0\left(f_s\right)-i_{\mathrm{\&pi;}}\left(f_s\right)}---\left(12\right)$

The judgement positive and negative for electro-optic intensity modulator chirp parameter to be measured then can be judged by the size of s value, if s is (f _m) >1 or s (f _m) <-1, then a ₀(f _m) be positive number, if-1<s is (f _m) <1, then a ₀(f _m) be negative, if s is (f _m)=1 or-1, then a ₀(f _m) be zero.

Embodiment 1

Electro-optic intensity modulator to be measured is a mach zhender electro-optic intensity modulator, and the frequency that laser instrument exports light carrier is f ₀=193.1THz, is divided into two bundles through beam splitter, a branch ofly enters electro-optic intensity modulator to be measured, the frequency f that signal source exports _mthe sinusoidal signal of=10GHz is loaded into electro-optic intensity modulator to be measured, the intensitymodulated optical signals of formation.Another bundle light carrier enters frequency shifter, and carry out shift frequency by acoustooptic modulation, shift frequency frequency is f _s=70MHz, intensitymodulated optical signals and shift frequency light signal are after bundling device closes and restraints, and carry out Photoelectric Detection by photodetector, the beat signal of generation is sent into spectrum analysis module and analyzed, and observes 70MHz (f _s), 9.93GHz (f _m-f _s) or 10.07GHz (f _m+ f _s) amplitude of three radio-frequency components, be designated as i (f respectively _s), i (f _m-f _s), i (f _m+ f _s).

Progressively regulate the bias voltage of electro-optic intensity modulator to be measured, when being in bias point time, i (f _s) reach maximum amplitude value i ₀(f _s)=0.6573, i (f _m-f _s) reach minimum amplitude value i ₀(f _m-f _s)=0.0040, when being in bias point time, i (f _s) reach minimum amplitude value i _π(f _s)=0.1712, i (f _m-f _s) reach maximum amplitude value i _π(f _m-f _s)=0.0165, record beat frequency sideband i _π(f _s)=0.1712, i _π(f _m-f _s)=0.0165, substitutes into formula (12) and calculates electro-optic intensity modulator to be measured at modulating frequency f _mthe chirp parameter of=10GHz is

$a_0\left(f_m\right)=\frac{i_0\left(f_s\right)\&times;i_0(f_m-f_s)+i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m-f_s)}{i_0\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m-f_s)-i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_0(f_m-f_s)}=0.5368$

The judgement positive and negative for electro-optic intensity modulator chirp parameter then can be calculated by symbolic representation function s, and expression formula is

$s\left(f_m\right)=\frac{m_1}{m_2{\mathrm{\&gamma;}}^2}=\frac{[i_0(f_m-f_s)+i_{\mathrm{\&pi;}}(f_m-f_s)]\&times;[}{[i_0(f_m-f_s)-i_{\mathrm{\&pi;}}(f_m-f_s)]\&times;[}\&CenterDot;\frac{i_0\left(f_s\right)+i_{\mathrm{\&pi;}}\left(f_s\right)]}{i_0\left(f_s\right)-i_{\mathrm{\&pi;}}\left(f_s\right)]}=2.7869$

Due to s>1, therefore a ₀symbol be positive sign, namely electro-optic intensity modulator to be measured has positive chirp parameter when modulating frequency is 10GHz, i.e. a ₀=0.5368.

The frequency f of signal source is changed by control and data processing module _m, to electro-optic intensity modulator to be measured at bias point in situation, the i (f in beat signal _s), i (f _m-f _s), i (f _m+ f _s) composition observes, record i ₀(f _s) maximum amplitude value and i ₀(f _m-f _s), i ₀(f _m+ f _s) minimum amplitude value; Again to electro-optic intensity modulator to be measured at bias point in situation, the i (f in beat signal _s), i (f _m-f _s), i (f _m+ f _s) composition observes, record i _π(f _s) minimum amplitude value and i _π(f _m-f _s), i _π(f _m+ f _s) maximum amplitude value; Calculate the chirp parameter under different modulating frequency, namely obtain the frequency response characteristic of electro-optic intensity modulator chirp parameter to be measured.

Claims (7)

1. a measuring method for electro-optic intensity modulator chirp parameter, is characterized in that comprising the following steps:

The light carrier that step 1, laser instrument send is divided into two bundles through beam splitter,

Step 2, wherein light beam carrier wave are formed intensitymodulated optical signals via electro-optic intensity modulator to be measured by a sinusoidal signal modulation, and another bundle light carrier forms shift frequency light signal after frequency shifter,

Step 3, two-beam signal send into photodetector opto-electronic conversion after closing bundle by bundling device, obtain beat signal;

Step 4, regulate the bias voltage of electro-optic intensity modulator to be measured, make the amplitude of characteristic frequency composition in beat signal reach maximal value and minimum value,

Step 5, the maximal value utilizing the characteristic frequency composition of record and minimum value calculate the chirp parameter obtaining electro-optic intensity modulator to be measured;

Step 6, change described sinusoidal signal frequency and repeat said process, obtain the variation relation of electro-optic intensity modulator chirp parameter to be measured with modulating frequency.

2. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 1, is characterized in that, the sinusoidal signal frequency being loaded into electro-optic intensity modulator to be measured in step 2 is f _m, the shift frequency amount of frequency shifter is f _s.

3. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 1, it is characterized in that, step 4 specifically comprises following:

Progressively regulate the bias voltage of electro-optic intensity modulator to be measured, observe f in the beat signal of photodetector output _sand f _m± f _srange value i (the f of frequency _s) and i (f _m± f _s), record i (f _s) maximum amplitude value and i (f _m± f _s) minimum amplitude value, be designated as i respectively ₀(f _s), i ₀(f _m± f _s); Progressively regulate the bias voltage of electro-optic intensity modulator to be measured again, observe f in the beat signal of photodetector output _sand f _m± f _srange value i (the f of frequency _s) and i (f _m± f _s), record i (f _s) minimum amplitude value and i (f _m± f _s) maximum amplitude value, be designated as i respectively _π(f _s), i _π(f _m± f _s).

4. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 1, is characterized in that, solving electro-optic intensity modulator to be measured in step 5 in modulating frequency is f _mchirp parameter a ₀solution formula be:

$a_0\left(f_m\right)=\frac{i_0\left(f_s\right)\&times;i_0(f_m\&PlusMinus;f_s)+i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}{i_0\left(f_s\right)\&times;i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)-i_{\mathrm{\&pi;}}\left(f_s\right)\&times;i_0(f_m\&PlusMinus;f_s)}$

The symbol table value indicative surveying electro-optic intensity modulator chirp parameter is s, when s be greater than 1 or be less than-1 time, chirp parameter a ₀for positive sign, when s is between-1 and 1, chirp parameter a ₀for negative sign, when s equals 1 or-1, chirp parameter is 0; The computing formula of s is:

$s\left(f_m\right)=\frac{i_0(f_m\&PlusMinus;f_s)+i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}{i_0(f_m\&PlusMinus;f_s)-i_{\mathrm{\&pi;}}(f_m\&PlusMinus;f_s)}\&CenterDot;\frac{i_0\left(f_s\right)+i_{\mathrm{\&pi;}}\left(f_s\right)}{i_0\left(f_s\right)-i_{\mathrm{\&pi;}}\left(f_s\right)}$

5. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 2, it is characterized in that, in described beat signal, characteristic frequency composition refers to f _sand f _m± f _sradio-frequency component, its amplitude changes by regulating the bias voltage of electro-optic intensity modulator to be measured, reaches maximal value and minimum value respectively.

6. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 1, is characterized in that, described frequency shifter is acousto-optic frequency translation or modulation shift frequency, and before and after shift frequency, the centre frequency of light carrier moves f _s.

7. the measuring method of a kind of electro-optic intensity modulator chirp parameter according to claim 4, is characterized in that, i in the solution formula of described chirp parameter ₀(f _m± f _s) and i _π(f _m± f _s) Xiang Zhongjun gets+number or all get-number.