INTERNATIONALE IECINTERNATIONAL STANDARD 61280-2-10 Première éditionFirst edition2005-07 Procédures d'essai des sous-systèmes de télécommunications à fibres optiques – Partie 2-10: Sys
Appareillage
Le montage de la méthode du discriminateur en fréquence est représenté à la Figure 7
Figure 7 – Montage de la méthode du discriminateur en fréquence
Système de lentille Lame demi-ronde
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To obtain low dispersion, a double-pass configuration is typically used
Figure 6 – Double-pass monochromator configuration
In this method, Table 1 is filled out column by column, with the monochromator fixed at frequency \( f_k \) A time waveform, \( P(t_1, f_k) \) to \( P(t_n, f_k) \), is recorded using an optical oscilloscope, while \( P(t) \) is measured with the monochromator filter centered on the signal The calculation of \( \Delta f(t) \) is performed using Equation (7).
Among the three methods discussed, only the frequency discriminator and monochromator techniques are viable for TRC measurements The subsequent sections will outline the equipment and procedures necessary for their application.
The set-up for the frequency discriminator method is shown in Figure 7
Figure 7 – Setup for the frequency discriminator method
Lens system Half-wave plate Aperture (slit)
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
Le générateur de profil fournit le signal de modulation à séquence binaire pseudo-aléatoire au
The DEE and triggering on the optical oscilloscope require specific modulation speeds and formats It is essential that the length of the pseudo-random binary sequence profile is 2^5 - 1 or longer While shorter profile lengths can be utilized, they do not allow for a comprehensive examination of the wavelength fluctuation effects dependent on the profile Longer profiles can be employed, but they will increase the measurement time The triggering signal must be synchronized with the pseudo-random binary sequence profile, rather than with the clock.
The erbium-doped fiber amplifier is optional and only required if the optical power from the DEE is insufficient to deliver an adequate signal level to the optical oscilloscope For optical frequencies outside the C or L bands, alternative amplifier technologies must be employed.
If the interferometer is highly sensitive to polarization, the state of polarization (SOP) at its input must be optimized The polarization state controller should be capable of transforming any arbitrary polarization state at its input into the required polarization state at its output Three designs of the device, utilizing either a rotating wave plate or a palette, can meet this requirement.
The article discusses a Mach-Zehnder interferometer featuring a sufficiently broad spectral range to accommodate fluctuations in the peak wavelength It emphasizes the need for a variable delay, denoted as ∆t, which allows for the adjustment of the DEE wavelength at points A and B in Figure 3 The specific value of ∆t is provided.
∆ (7) ó f o est la fréquence porteuse optique
The optical oscilloscope consists of a wideband continuous coupling optical-to-electrical converter and a sampling oscilloscope The combined frequency response of the optical-to-electrical converter and the oscilloscope should be at least twice the bit rate, ensuring that the impulse response exhibits no oscillation or overshoot, either positive or negative It must accept a trigger input and provide means to set the trigger along with an observable time range.
Procédure
To connect the device as shown in Figure 7, an erbium-doped fiber amplifier is only necessary if the power from the DEE is insufficient to provide a sufficiently high signal level to the optical oscilloscope Adjust the time range on the optical oscilloscope to display the desired number of bits, and set the number of data points, \( n \), to achieve the required temporal resolution, with a typical value of \( n \) being 1,000.
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
The pattern generator provides the PRBS modulation signal and trigger to the DUT and optical oscilloscope, ensuring that the modulation rate and format meet the specifications required by the DUT.
For optimal results, the PRBS pattern length should be at least \(2^5 - 1\) to effectively explore pattern-dependent chirp effects While shorter patterns can be utilized, they may not capture all relevant effects Conversely, longer patterns can be employed, but they will extend the measurement duration It is crucial that the trigger signal is synchronized with the PRBS pattern rather than the clock.
The erbium-doped fibre amplifier is optional It is required only if the optical power from the
DUT is too low to provide sufficient signal level to the optical oscilloscope For optical frequencies other than the C or the L-bands, alternative amplifier technologies must be used
To ensure optimal performance in a highly polarization-sensitive interferometer, it is essential to optimize the state-of-polarization (SOP) at the input A polarization state controller must effectively transform any arbitrary SOP at its input to the desired SOP at its output This requirement can be met using three paddle or rotating waveplate designs.
This Mach-Zehnder configuration features a sufficiently wide free spectral range (FSR) to accommodate peak chirp The variable delay is designed with a range, ∆t, allowing for precise adjustment of the device under test (DUT) wavelength to specific points.
A and B in Figure 3 The value of ∆t is:
∆ (7) where f o is the optical carrier frequency
The optical oscilloscope features a DC-coupled broadband optical-to-electrical converter paired with a sampling oscilloscope To ensure accurate measurements, the combined frequency response of these components must exceed twice the bit rate, while the impulse response should be free from ringing, overshoot, or undershoot Additionally, it is essential for the oscilloscope to accept a trigger input and provide a method for setting both the trigger and observable time range.
To conduct the procedure, first connect the equipment as illustrated in Figure 7 An EDFA is necessary only if the power from the DUT does not deliver a high enough signal level for the optical oscilloscope Next, adjust the time range on the optical oscilloscope to show the desired number of bits, and set the number of data points, \( n \), to ensure the required time resolution, with a typical value of \( n \) being 1,000.
Licensed to MECON Limited for internal use in Ranchi/Bangalore, supplied by Book Supply Bureau Adjust the polarization controller to achieve the maximum signal level on the optical oscilloscope Set the variable delay element to the quadrature point A as shown in Figure 11 and take measurements.
V A (t i ) ó 1 ≤ i ≤ n f) Régler l’élément de retard variable au point de quadrature B et mesurer V B (t i ) ó 1≤ t i ≤ n g) Calculer:
Appareillage
Le montage de la méthode du monochromateur est représenté à la Figure 8
Figure 8 – Montage de la méthode du monochromateur
Le générateur de profil fournit le signal de modulation à séquence binaire pseudo-aléatoire au
The DEE and triggering on the optical oscilloscope require specific modulation speeds and formats It is essential that the length of the pseudo-random binary sequence profile is 25-1 or longer While shorter profile lengths can be utilized, they may not fully capture the effects of wavelength fluctuations dependent on the profile Longer profiles can be employed, but they will increase measurement time The triggering signal must be synchronized with the pseudo-random binary sequence profile, rather than with the clock.
The erbium-doped fiber amplifier is optional and only required if the optical power from the DEE is insufficient to deliver an adequate signal level to the optical oscilloscope For optical frequencies outside the C or L bands, alternative amplifier technologies must be employed.
To optimize signal levels, adjust the polarization controller for maximum output on the optical oscilloscope Next, set the variable delay element to the quadrature point A as illustrated in Figure 11 and take the necessary measurements.
V A (t i ) where 1≤ i ≤ n f) Adjust the variable delay element to quadrature point B and measure V B (t i ) where 1≤ t i ≤ n g) Compute:
The set-up for the monochromator method is shown in Figure 8
Figure 8 – Set-up for the monochromator method
The pattern generator provides the PRBS modulation signal and trigger to the DUT and optical oscilloscope, ensuring that the modulation rate and format meet the specifications required by the DUT.
For optimal results, the PRBS pattern length should be at least \(2^5 - 1\) to effectively capture pattern-dependent chirp effects; shorter lengths may not provide comprehensive exploration While longer patterns can be utilized, they will extend the measurement duration It is crucial that the trigger signal is synchronized with the PRBS pattern rather than the clock.
The erbium-doped fibre amplifier is optional It is required only if the optical power from the
DUT is too low to provide sufficient signal level to the optical oscilloscope For optical frequencies other than the C or the L-bands, alternative amplifier technologies must be used
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
The monochromator features an adjustable bandwidth ranging from 100 pm to 500 pm, accommodating signal bit rates between 10 Gbit/s and 2.5 Gbit/s It is designed as a double-pass monochromator, ensuring that the chromatic dispersion is nominally zero at the center of the band In practical terms, it achieves a chromatic dispersion of less than 10 ps/nm, a polarization dependence of less than 0.5 dB, and an insertion loss that is minimized.
A minimum of 10 dB is required, and other filtering technologies that meet these criteria can also be utilized It is important for the monochromator to exhibit low polarization dependence or for the input polarization state to be adjusted to maximize the signal level.
NOTE Afin d’obtenir une dispersion faible et une dépendance en polarisation faible, un monochromateur compensé en polarisation à double pas est généralement utilisé
The optical oscilloscope consists of a wideband continuous-coupling optical-to-electrical converter and a sampling oscilloscope The combined frequency response of the optical-to-electrical converter and the oscilloscope should be at least twice the bit rate, ensuring that the impulse response exhibits no oscillations or overshoot It must accept a trigger input and provide means to set the trigger and an observable time range Additionally, the bandwidth should exceed twice the bit rate.
Procédure
To connect the device as shown in Figure 8, ensure that the erbium-doped fiber amplifier is used only if the power from the DEE is insufficient to provide a high enough signal level for the optical oscilloscope Adjust the time range on the optical oscilloscope to display the desired number of bits, and set the number of data points, \( n \), to achieve the required temporal resolution, with a typical value of \( n = 1,000 \) Finally, configure the bandwidth of the monochromator to match the spectral width of the signal.
A typical value for a non-return-to-zero transmitter operating at 10 Gb/s is 500 pm To analyze the system, center the monochromator's bandwidth on the transmitter and measure \( P(t_i) \) for \( 1 \leq i \leq n \) Next, adjust the monochromator's central frequency from \( f_A \) to \( f_B \) in equal steps, where \( f_A \) and \( f_B \) are the frequencies at which the response is 10 dB below the peak A common value for the number of steps, \( m \), is 10 Finally, for each frequency \( f_k \) of the monochromator, measure \( P(t_i, f_k) \) for \( 1 \leq i \leq n \) and \( 1 \leq k \leq m \).
Se référer au Tableau 1 h) Calculer la fréquence absolue pour chaque intervalle de temps:
( 1 ≤ i ≤ n (11) i) Calculer la fréquence moyenne dans le temps: n t f f n i
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The monochromator features an adjustable bandwidth ranging from 100 pm to 500 pm, accommodating signal bit rates between 10 Gbit/s and 2.5 Gbit/s It is designed as a double pass monochromator, ensuring that chromatic dispersion is nominally zero at the band center In practical applications, it must achieve a chromatic dispersion of less than 10 ps/nm, a polarization dependence of under 0.5 dB, and an insertion loss of less than 10 dB Additionally, alternative filter technologies can be employed to meet these specifications To optimize signal levels, the monochromator should exhibit low polarization dependence, or the input state of polarization should be adjusted accordingly.
NOTE To obtain low dispersion and low polarization dependence, a double-pass polarization compensated monochromator is typically used
The optical oscilloscope features a DC-coupled broadband optical-to-electrical converter paired with a sampling oscilloscope To ensure accurate measurements, the combined frequency response of these components must exceed twice the bit rate, while the impulse response should be free from ringing, overshoot, or undershoot Additionally, the device must accept a trigger input and provide a method for setting the trigger and observable time range, with a bandwidth that is greater than twice the bit rate.
To conduct the procedure, first connect the equipment as illustrated in Figure 8, ensuring that the EDFA is utilized only if the DUT's output power is inadequate for a high signal level on the optical oscilloscope Next, adjust the oscilloscope's time range to display the desired bit count and set the number of data points, typically around 1,000, to achieve the necessary time resolution Finally, configure the monochromator's bandwidth to match the spectral width of the DUT.
A typical value for a 10-Gb/s NRZ transmitter is 500 pm To analyze the transmitter, center the monochromator passband on it and measure \( P(t_i) \) for \( 1 \leq i \leq n \) Next, tune the monochromator's center frequency from \( f_A \) to \( f_B \) in \( m \) equal steps, where \( f_A \) and \( f_B \) are the frequencies at which the response is 10 dB below the peak, with \( m \) typically set to 10 Finally, at each monochromator frequency \( f_k \), measure \( P(t_i, f_k) \) for \( 1 \leq i \leq n \) and \( 1 \leq k \leq m \).
Table 1 h) Compute the absolute frequency for each time slot:
( 1 ≤ i ≤ n (11) i) Compute the time average frequency: n t f f n i
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU. j) Calculer la fluctuation de la longueur d’onde:
Based on the power, P(t), and the fluctuation of the wavelength, ∆f(t), of the measured and calculated waveforms in sections 7.2 or 8.2, the alpha factor can be determined Three forms of the alpha factor are essential for analyzing transient wavelength fluctuations.
Facteur alpha en fonction du temps, α(t)
Facteur alpha en fonction de la puissance, α (P)
Facteur alpha en fonction du temps, α (t)
La conversion de l’expression continue de α(t) donnée en [2] dans une forme discrète afin d’utiliser les données mesurées donne:
An example of the α(t) trace is shown in Figure 9 for an electro-absorption modulated laser, along with the P(t) trace The time range was selected to illustrate how α varies during the rise time of a single data bit The alpha factor exhibits significant variation during this period Typically, α(t) is calculated only during transitions of the power waveform, specifically between the 10% and 90% points This is due to the increased uncertainties in the calculation when ∆P/∆t is small.
Fact eu r al ph a ra d
Figure 9 – Exemple de tracé du facteur alpha en fonction du temps pour un laser modulé à électro-absorption
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU. j) Compute the chirp:
From the power, P(t), and chirp, ∆f(t), waveforms measured and calculated in 7.2 or 8.2, alpha factor can be calculated Three forms of alpha-factor are useful for transient chirp analysis:
Converting the continuous expression for α(t) given in [2] to discrete form in order to utilize the measured data gives:
Figure 9 illustrates the plot of α(t) for an EML alongside P(t), highlighting the significant variation of α during the rise time of a single data bit The selected time range emphasizes this variation, as α(t) is typically calculated only during power waveform transitions, specifically between the 10% and 90% points, due to increased calculation uncertainties when ∆P/∆t is minimal.
Figure 9 – An example plot of alpha versus time for an EML
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
Facteur alpha moyen, α moy
Le facteur alpha moyen est simplement la moyenne sur la fenêtre de temps sélectionnée n t n i
For a directly modulated laser, the alpha factor is theoretically constant over time, making this term meaningful In contrast, for an electro-absorption modulated laser, as shown in Figure 9, the alpha factor varies with time, rendering the average value less useful.
Apparatus
The set-up for the frequency discriminator method is shown in Figure 7
Figure 7 – Setup for the frequency discriminator method
Lens system Half-wave plate Aperture (slit)
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
Le générateur de profil fournit le signal de modulation à séquence binaire pseudo-aléatoire au
The DEE and triggering on the optical oscilloscope require specific modulation speeds and formats It is essential that the length of the pseudo-random binary sequence profile is 2^5 - 1 or longer While shorter profile lengths can be utilized, they do not allow for a comprehensive examination of the wavelength fluctuation effects dependent on the profile Longer profiles can be employed, but they will increase the measurement time The triggering signal must be synchronized with the pseudo-random binary sequence profile, rather than with the clock.
The erbium-doped fiber amplifier is optional and only required if the optical power from the DEE is insufficient to deliver an adequate signal level to the optical oscilloscope For optical frequencies outside the C or L bands, alternative amplifier technologies must be employed.
If the interferometer is highly sensitive to polarization, the state of polarization (SOP) at its input must be optimized The polarization state controller should be capable of transforming any arbitrary polarization state at its input into the required polarization state at its output Three designs of the device, utilizing either a rotating wave plate or a palette, can meet this requirement.
The article discusses a Mach-Zehnder interferometer featuring a sufficiently broad free spectral range to accommodate fluctuations in the peak wavelength A variable delay, denoted as ∆t, is necessary to adjust the wavelength of the DEE at points A and B in Figure 3 The value of ∆t is provided.
∆ (7) ó f o est la fréquence porteuse optique
The optical oscilloscope consists of a wideband continuous-coupling optical-to-electrical converter and a sampling oscilloscope The combined frequency response of the optical-to-electrical converter and the oscilloscope should be at least twice the bit rate, ensuring that the impulse response exhibits no oscillation or overshoot, either positive or negative It must accept a trigger input and provide means to set the trigger and an observable time range.
To connect the device, refer to Figure 7 The use of an erbium-doped fiber amplifier is only necessary if the power from the DEE is insufficient to provide a high enough signal level for the optical oscilloscope Adjust the time range on the optical oscilloscope to display the desired number of bits, and set the number of data points, \( n \), to achieve the required temporal resolution, with a typical value of \( n \) being 1,000.
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
The pattern generator provides the PRBS modulation signal and trigger to the DUT and optical oscilloscope, ensuring that the modulation rate and format meet the specifications required by the DUT.
For optimal results, the PRBS pattern length should be at least \(2^5 - 1\) to effectively capture pattern-dependent chirp effects While shorter patterns can be utilized, they may not adequately explore these effects Conversely, longer patterns can be employed, but they will extend the measurement duration It is crucial that the trigger signal is synchronized with the PRBS pattern rather than the clock.
The erbium-doped fibre amplifier is optional It is required only if the optical power from the
DUT is too low to provide sufficient signal level to the optical oscilloscope For optical frequencies other than the C or the L-bands, alternative amplifier technologies must be used
To ensure optimal performance in a highly polarization-sensitive interferometer, it is essential to optimize the state-of-polarization (SOP) at the input A polarization state controller must effectively transform any arbitrary SOP at its input to the desired SOP at its output Designs utilizing three paddles or rotating waveplates can successfully meet this requirement.
This Mach-Zehnder configuration features a sufficiently wide free spectral range (FSR) to accommodate peak chirp The variable delay is designed with a range, ∆t, allowing for precise adjustment of the device under test (DUT) wavelength to specific points.
A and B in Figure 3 The value of ∆t is:
∆ (7) where f o is the optical carrier frequency
The optical oscilloscope features a DC-coupled broadband optical-to-electrical converter paired with a sampling oscilloscope To ensure accurate measurements, the combined frequency response of these components must exceed twice the bit rate, while the impulse response should be free from ringing, overshoot, or undershoot Additionally, it is essential for the oscilloscope to accept a trigger input and provide a method for setting the trigger and observable time range.
Procedure
To set up the equipment, connect it as illustrated in Figure 7, ensuring that the EDFA is used only if the power from the DUT is inadequate for a high signal level on the optical oscilloscope Next, adjust the time range on the oscilloscope to show the desired number of bits, and configure the number of data points, n, to attain the necessary time resolution, with a typical value of n being 1,000.
Licensed to MECON Limited for internal use in Ranchi/Bangalore, supplied by Book Supply Bureau Adjust the polarization controller to achieve the maximum signal level on the optical oscilloscope Set the variable delay element to the quadrature point A as shown in Figure 11 and take measurements.
V A (t i ) ó 1 ≤ i ≤ n f) Régler l’élément de retard variable au point de quadrature B et mesurer V B (t i ) ó 1≤ t i ≤ n g) Calculer:
Le montage de la méthode du monochromateur est représenté à la Figure 8
Figure 8 – Montage de la méthode du monochromateur
Le générateur de profil fournit le signal de modulation à séquence binaire pseudo-aléatoire au
The DEE and triggering on the optical oscilloscope require specific modulation speeds and formats It is essential that the length of the pseudo-random binary sequence profile is 2^5 - 1 or longer While shorter profiles can be utilized, they may not fully capture the effects of wavelength fluctuations dependent on the profile Longer profiles can be employed, but they will increase measurement time The triggering signal must be synchronized with the pseudo-random binary sequence profile, rather than with the clock.
The erbium-doped fiber amplifier is optional and only required if the optical power from the DEE is insufficient to deliver an adequate signal level to the optical oscilloscope For optical frequencies outside the C or L bands, alternative amplifier technologies must be employed.
To optimize signal levels, adjust the polarization controller for maximum output on the optical oscilloscope Next, set the variable delay element to the quadrature point A as illustrated in Figure 11 and proceed to measure the results.
V A (t i ) where 1≤ i ≤ n f) Adjust the variable delay element to quadrature point B and measure V B (t i ) where 1≤ t i ≤ n g) Compute:
Apparatus
The set-up for the monochromator method is shown in Figure 8
Figure 8 – Set-up for the monochromator method
The pattern generator provides the PRBS modulation signal and trigger to the DUT and optical oscilloscope, ensuring that the modulation rate and format meet the specifications required by the DUT.
The PRBS pattern length should be at least \(2^5 - 1\) to effectively explore pattern-dependent chirp effects, although shorter lengths can be utilized with limitations While longer patterns can be employed, they will extend the measurement duration It is crucial that the trigger signal is synchronized with the PRBS pattern rather than the clock.
The erbium-doped fibre amplifier is optional It is required only if the optical power from the
DUT is too low to provide sufficient signal level to the optical oscilloscope For optical frequencies other than the C or the L-bands, alternative amplifier technologies must be used
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
The monochromator features an adjustable bandwidth ranging from 100 pm to 500 pm, accommodating signal bit rates between 10 Gbit/s and 2.5 Gbit/s It is designed as a double-step monochromator, ensuring that the chromatic dispersion is nominally zero at the center of the band In practical terms, it achieves a chromatic dispersion of less than 10 ps/nm, a polarization dependence of less than 0.5 dB, and an insertion loss that is minimized.
A minimum of 10 dB is required, and other filtering technologies that meet these criteria can also be utilized It is important for the monochromator to exhibit low polarization dependence, or the input polarization state should be adjusted to optimize the signal level.
NOTE Afin d’obtenir une dispersion faible et une dépendance en polarisation faible, un monochromateur compensé en polarisation à double pas est généralement utilisé
The optical oscilloscope consists of a wideband optical-to-electrical converter with continuous coupling and a sampling oscilloscope The combined frequency response of the optical-to-electrical converter and the oscilloscope should be at least twice the bit rate, ensuring that the impulse response exhibits no oscillation or overshoot, either positive or negative It must accept a trigger input and provide means to set the trigger and an observable time range Additionally, the bandwidth should exceed twice the bit rate.
To connect the device, follow the representation in Figure 8 An erbium-doped fiber amplifier is only necessary if the power from the DEE is insufficient to provide a sufficiently high signal level to the optical oscilloscope Adjust the time range on the optical oscilloscope to display the desired number of bits Set the number of data points, \( n \), on the optical oscilloscope to achieve the required temporal resolution, with a typical value of \( n = 1,000 \) Finally, adjust the bandwidth of the monochromator to match the spectral width.
A typical value for a non-return-to-zero transmitter operating at 10 Gb/s is 500 pm To analyze the system, center the monochromator's bandwidth on the transmitter and measure \( P(t_i) \) for \( 1 \leq i \leq n \) Next, adjust the monochromator's central frequency from \( f_A \) to \( f_B \) in \( m \) equal steps, where \( f_A \) and \( f_B \) are the frequencies at which the response is 10 dB below the peak A common value for \( m \) is 10 Finally, for each frequency \( f_k \) of the monochromator, measure \( P(t_i, f_k) \) for \( 1 \leq i \leq n \) and \( 1 \leq k \leq m \).
Se référer au Tableau 1 h) Calculer la fréquence absolue pour chaque intervalle de temps:
( 1 ≤ i ≤ n (11) i) Calculer la fréquence moyenne dans le temps: n t f f n i
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
The monochromator features an adjustable bandwidth ranging from 100 pm to 500 pm, accommodating signal bit rates between 10 Gbit/s and 2.5 Gbit/s It is designed as a double pass monochromator, ensuring that chromatic dispersion is nominally zero at the band center To achieve optimal performance, it requires a chromatic dispersion of less than 10 ps/nm, a polarization dependence of less than 0.5 dB, and an insertion loss of under 10 dB Additionally, alternative filter technologies that meet these specifications may be utilized It is essential for the monochromator to exhibit low polarization dependence, or for the input state-of-polarization to be adjusted to enhance the signal level.
NOTE To obtain low dispersion and low polarization dependence, a double-pass polarization compensated monochromator is typically used
The optical oscilloscope features a DC-coupled broadband optical-to-electrical converter paired with a sampling oscilloscope To ensure accurate measurements, the combined frequency response of these components must exceed twice the bit rate, while the impulse response should be free from ringing, overshoot, or undershoot Additionally, the device must accept a trigger input and provide a method for setting both the trigger and observable time range, with a bandwidth that is greater than twice the bit rate.
Procedure
To set up the equipment, connect it as illustrated in Figure 8, ensuring that the EDFA is included only if the DUT's output power is inadequate for a high signal level on the optical oscilloscope Next, adjust the oscilloscope's time range to capture the desired number of bits, and configure the number of data points, typically set to 1,000, to achieve the necessary time resolution Finally, set the monochromator's bandwidth to match the spectral width of the DUT.
A typical value for a 10-Gb/s NRZ transmitter is 500 pm To conduct measurements, center the monochromator passband on the transmitter and record P(t_i) for indices 1 through n Next, adjust the monochromator's center frequency from f_A to f_B in m equal steps, where f_A and f_B are the frequencies at which the response is 10 dB below the peak, with m typically set to 10 Finally, at each monochromator frequency f_k, measure P(t_i, f_k) for indices 1 through n and k from 1 to m.
Table 1 h) Compute the absolute frequency for each time slot:
( 1 ≤ i ≤ n (11) i) Compute the time average frequency: n t f f n i
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU. j) Calculer la fluctuation de la longueur d’onde:
Based on the power, P(t), and the fluctuation of the wavelength, ∆f(t), of the measured and calculated waveforms in sections 7.2 or 8.2, the alpha factor can be determined Three forms of the alpha factor are essential for analyzing transient wavelength fluctuations.
Facteur alpha en fonction du temps, α(t)
Facteur alpha en fonction de la puissance, α (P)
9.1 Facteur alpha en fonction du temps, α (t)
La conversion de l’expression continue de α(t) donnée en [2] dans une forme discrète afin d’utiliser les données mesurées donne:
An example of the α(t) trace is shown in Figure 9 for an electro-absorption modulated laser, along with the P(t) trace The time range was selected to illustrate how α varies during the rise time of a single data bit The alpha factor exhibits significant variation during this period Typically, α(t) is calculated only during transitions of the power waveform, specifically between the 10% and 90% points This is due to the increased uncertainties in the calculation when ∆P/∆t is small.
Fact eu r al ph a ra d
Figure 9 – Exemple de tracé du facteur alpha en fonction du temps pour un laser modulé à électro-absorption
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU. j) Compute the chirp:
From the power, P(t), and chirp, ∆f(t), waveforms measured and calculated in 7.2 or 8.2, alpha factor can be calculated Three forms of alpha-factor are useful for transient chirp analysis:
Alpha factor versus time, α (t)
Converting the continuous expression for α(t) given in [2] to discrete form in order to utilize the measured data gives:
Figure 9 illustrates the plot of α(t) for an EML alongside P(t), highlighting the significant variation of α during the rise time of a single data bit The selected time range emphasizes this variation, as α(t) is typically calculated only during power waveform transitions, specifically between the 10% and 90% points, due to increased calculation uncertainties when ∆P/∆t is minimal.
Figure 9 – An example plot of alpha versus time for an EML
LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.
Le facteur alpha moyen est simplement la moyenne sur la fenêtre de temps sélectionnée n t n i
For a directly modulated laser, the alpha factor is theoretically constant over time, making this term meaningful In contrast, for an electro-absorption modulated laser, as shown in Figure 9, the alpha factor varies with time, rendering the average value less useful.
9.3 Facteur alpha en fonction de la puissance, α (P)
A graph of the alpha factor as a function of power is a valuable tool for analyzing transient wavelength fluctuations The alpha value, denoted as α(t), is computed using equation (15) and plotted as an x-y scatter diagram alongside the corresponding power value P(t) The calculations focus specifically on the transition segments of the power waveform.
La Figure 10 représente le facteur alpha en fonction des graphiques de puissance pour (a) un laser modulé directement et pour (b) un laser modulé à électro-absorption
Fact eu r al ph a ra d
Fact eu r al ph a ra d
Figure 10 – Facteur alpha en fonction de la puissance pour (a) un laser modulé directement et (b) un laser modulé à électro-absorption
For many data transitions, the alpha factor for directly modulated lasers varies between approximately 0.2 and 3.5 In the case of electro-absorption modulated lasers, it follows a linear power function ranging from 0.2 to 1.4 These specific characteristics are influenced by the excitation level and polarization.
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Average alpha factor, α avg
The average alpha factor is simply the average over the selected time window n t n i
In directly modulated lasers, the alpha parameter remains theoretically constant over time, making it a significant factor In contrast, for an Electro-absorption Modulated Laser (EML), as illustrated in Figure 9, the alpha value fluctuates with time, rendering the average value less meaningful.
Alpha factor versus power, α (P)
A valuable tool for analyzing transient chirps is the graph of the alpha factor against power The alpha factor, denoted as α(t), is derived from Equation (15) and plotted as an x-y scatter chart alongside the corresponding power values P(t) This analysis focuses specifically on the transition segments of the power waveform.
Figure 10 shows Alpha factor versus power graphs for (a) a directly modulated laser and (b) for an EML
Figure 10 – Alpha factor versus power for (a) a DM laser and (b) an EML
The alpha factor for data transitions in DM ranges from approximately 0.2 to 3.5, while for EML, it exhibits a linear relationship with power, varying from 0.2 to 1.4 These specific characteristics are influenced by the drive level and bias.
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Vérification du montage de la fluctuation de la longueur d’onde résolue dans le temps et des calculs
The application of wavelength-resolved fluctuation equipment and calculations can be validated through independent measurements using an alternative method While this is challenging for signals that combine intensity and frequency modulation, a signal with only phase modulation can be utilized for this purpose A phase-modulated signal can be generated using a microwave signal driving a Mach-Zehnder type phase modulator.
By comparing the measured sideband level on an ASO with the amplitude of frequency modulation (phase) obtained from the time-resolved wavelength fluctuation measurement setup, the validity of the time-resolved wavelength fluctuation measurement can be established.
La relation entre le spectre de l’ASO et la fluctuation de la longueur d’onde est donnée par: m m f
J 0 est la fonction de Bessel d'ordre zéro du premier type
J 1 est la fonction de Bessel de premier ordre du premier type
∆f est la fluctuation de la longueur d’onde de crête
P bandelatérale est la puissance de la bande latérale (watts)
P porteuse est la puissance porteuse (watts)
Figure A-1 illustrates the measurements of a 10.25 GHz phase-modulated signal on an ASO, along with a time-resolved wavelength fluctuation setup The symmetry in the sidebands on the ASO and the flat power over time in the wavelength fluctuation graph indicate the absence of intensity modulation By applying Equation (A-1), the correlation between the two methods can be verified.
F luc tu at io n Hz
Figure A.1 – Modulation seulement en phase observée sur (a) un ASO et (b) un montage de mesure de la fluctuation e la longueur d’onde résolue dans le temps
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Verification of TRC set-up and calculations
The verification of TRC hardware and calculations can be achieved through independent alternatives Although challenging for signals with both intensity and frequency modulation, a signal featuring only phase modulation is suitable for this verification A pure phase-modulated signal can be produced using a microwave signal to drive a Mach-Zehnder phase modulator, allowing for the comparison of sideband levels as measured.
OSA with the amplitude of the frequency (phase) modulation obtained from the TRC measurement set-up, the validity of the TRC measurement can be established
The relationship between OSA spectrum and the chirp is given by: m m f
J 0 is the zero order Bessel function of the first kind
J 1 is the first order Bessel function of the first kind
P sideband is the sideband power (watts)
P carrier is the carrier power (watts)
Figure A.1 shows measurements of a 10,25 GHz phase modulated signal on an OSA and a
The TRC setup demonstrates symmetry in the sidebands observed on the OSA, along with a consistent power level over time in the TRC graph, indicating the absence of intensity modulation The relationship between these two methods can be confirmed using equation (A.1).
Figure A.1 – Pure phase modulation observed on (a) an OSA and
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Méthodes de modulation de l’émetteur optique
Directly modulated lasers (DM) are the most common, especially for short-range systems, due to their lower cost and higher wavelength fluctuation In a directly modulated laser, the diode current consists of two components: a fixed current that sets the operating point (average power) and a modulation current that determines the modulation level Both components are adjusted to achieve the desired average power and extinction ratio However, directly modulated lasers typically exhibit greater wavelength fluctuation at higher extinction ratios, resulting in a trade-off between extinction ratio and wavelength fluctuation penalty.
Diode laser Sortie de lumière
Figure B.1 – Représentation schématique d’un laser modulé directement
In a directly modulated laser, the presence of the data signal causes a change in the effective refractive index within the laser cavity This results in phase shifts (transient wavelength fluctuations) during data transitions, as well as a long-term shift in the laser frequency (adiabatic wavelength fluctuations).
La Figure B.2 représente P(t) et ∆f(t) pour un laser à rétroaction répartie modulé directement
There is a significant fluctuation in the transient and adiabatic wavelength These transitions stimulate relaxation oscillations within the device, leading to variations in instantaneous optical power and frequency.
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Directly modulated (DM) lasers are the most common, particularly for short-reach systems
DM lasers are cost-effective and typically exhibit a high chirp value In a DM laser, the diode current comprises two components: Idc, which establishes the operating point (average power), and Idata, which dictates the modulation level These components are fine-tuned to attain the desired average power and extinction ratio However, DM lasers tend to generate increased chirp at higher extinction ratios, creating a trade-off between extinction ratio and chirp penalty.
Figure B.1 – Schematic representation of a directly modulated laser
In a DM laser, the data signal alters the effective index of refraction within the laser cavity, leading to phase shifts during data transitions, known as transient chirp, as well as a long-term frequency shift referred to as adiabatic chirp.
Figure B.2 illustrates the behavior of P(t) and ∆f(t) in a directly modulated DFB laser, highlighting the presence of significant transient and adiabatic chirp These transitions trigger relaxation oscillations within the device, resulting in ringing effects in both the instantaneous optical power and frequency.
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Un laser modulé directement a une fluctuation de la longueur d’onde transitoire et adiabatique significative
Figure B.2 – Fluctuation de la longueur d’onde transitoire et adiabatique dans un laser modulé directement
Electro-absorption modulated lasers consist of a single longitudinal mode laser, typically a distributed feedback laser, combined with an integrated electro-absorption modulator (EAM) that operates on the same wavelength This configuration is cost-effective compared to fully integrated modulators and offers superior performance in wavelength fluctuation compared to directly modulated lasers.
In theory, when the modulation element is detached from the laser cavity, there are no adiabatic wavelength fluctuations The constant frequency generated by the laser is only altered in amplitude and phase as the light passes through the modulation section.
En pratique, d’autres effets tels que les parasites électriques, les réflexions optiques et les interactions thermiques peuvent provoquer des caractéristiques adiabatiques