© ISO 2013 Optics and photonics — Measurement method of semiconductor lasers for sensing Optique et photonique — Méthode de mesure des lasers semi conducteurs pour la sensibilité TECHNICAL SPECIFICATI[.]
General
The methods described in this Technical Specification are to be followed in accordance with ISO 13695.
Tunable semiconductor laser spectroscopy is extensively utilized in engineering, particularly for bio-sensing and environmental monitoring Semiconductor lasers play a crucial role in these applications, serving as essential components for developing effective sensing equipment Detailed descriptions of semiconductor lasers and sensing techniques can be found in sections 3.2 to 3.6.
Semiconductor laser
A semiconductor laser is an optical device that emits coherent light through stimulated emission, which occurs when an electric current surpasses the threshold current The generation of coherent optical radiation can be categorized into two mechanisms: (1) electron-hole recombination from interband transitions between the conduction and valence bands (bulk type) or between quantized states (quantum well type), and (2) intraband transitions between quantized states (quantum cascade type).
Edge-emitting lasers, particularly distributed feedback (DFB) lasers, are traditionally favored in sensing equipment due to their high power and single lasing modes In contrast, surface-emitting lasers are popular in sensing systems for their ease of handling These lasers are categorized into several types, as outlined in sections 3.2.2 to 3.2.5.
Semiconductor lasers can be categorized into two main types based on their emission structure The edge emitting type semiconductor laser emits coherent optical radiation parallel to the junction plane, while the surface emitting type emits radiation perpendicular to the junction plane A notable example of the surface emitting type is the vertical cavity surface emitting laser (VCSEL).
Transverse mode stabilizing structures in semiconductor lasers can be categorized into two types: gain guiding and refractive index guiding Gain guiding involves a semiconductor laser where the emitted light travels through the gain region created by carrier injection, with amplification occurring via stimulated emission Planar type lasers are commonly associated with gain guiding In contrast, refractive index guiding utilizes a stripe-shaped active layer or junction to create a significant refractive index difference between the stripe and its surrounding area, with buried heterostructures (BH) being a typical example of this guiding method.
The mode (wavelength) selection structures in semiconductor lasers include several types: a) Distributed feedback (DFB) semiconductor lasers utilize a grating to select stimulated emission, functioning in a single longitudinal mode; b) Distributed Bragg reflector (DBR) semiconductor lasers employ a Bragg grating adjacent to the light-emitting layer, also operating in a single longitudinal mode; c) Fabry-Perot (FP) semiconductor lasers generate stimulated emission between two mirror facets, typically operating in multiple longitudinal modes; and d) External cavity controlled semiconductor lasers consist of an optical cavity with one internal mirror and an external mirror, such as a grating, allowing for stimulated emission in the semiconductor part and usually operating in a single longitudinal mode.
The active layer structure of semiconductor lasers includes several types: a) Double heterostructure semiconductor lasers feature an active layer sandwiched between two heterojunctions, enabling efficient light emission b) Quantum well semiconductor lasers produce coherent optical radiation through stimulated emission from electron-hole recombination in quantized states, utilizing single or multiple quantum well layers, with quantum wire and quantum dot lasers representing two-dimensional and three-dimensional structures, respectively c) Strained quantum well semiconductor lasers also emit coherent radiation via stimulated emission from free electron-hole recombination in strained quantum well layers d) Quantum cascade semiconductor lasers generate coherent optical radiation through electron transitions between quantized states, operating without electron-hole recombination and utilizing quantum cascade layers for their light-emitting structure.
Common sensing technique and equipment using semiconductor laser
Semiconductor lasers, particularly quantum cascade lasers, offer numerous benefits such as compact size, lightweight design, low power consumption, and the ability to easily control wavelength through pulsed or continuous wave operation These advantages have led to extensive research and development of sensing techniques and equipment utilizing semiconductor lasers in both academic and industrial sectors Key sensing methods are detailed in sections 3.3.2 to 3.3.4.
3.3.2 Tunable laser absorption spectroscopy (TLAS)
The absorption spectrum is analyzed by repeatedly scanning the wavelength of light emitted from a semiconductor laser This process allows for both qualitative and quantitative assessment of the material composition based on the monitored spectrum's shape, peak wavelength, and intensity The lasing wavelength of the semiconductor laser is adjusted by controlling the ambient temperature or the injected current.
Figure 1 — Basic concept of tunable laser absorption spectroscopy (two absorption peaks are observed)
3.3.3 Cavity ring down spectroscopy (CRDS)
This technique, derived from tunable semiconductor laser spectroscopy, is primarily employed for detecting trace elements The material under analysis is placed within a cavity formed by two mirrors A light pulse of a specific wavelength is introduced into the cavity, where it is repeatedly reflected between the mirrors and passes through the material Some of the reflected light escapes through one of the mirrors, allowing for the monitoring of a pulse train with a time interval determined by the cavity length.
``,,`````,,```,,,```,````,`,-`-`,,`,,`,`,,` - trace element is qualitatively and quantitatively analysed with the decay time of the pulse train and the wavelength of the light.
Figure 2 — Basic concept of cavity ring down spectroscopy
When laser light illuminates a material, it is absorbed, causing lattice vibrations that generate a detectable supersonic wave This wave can be captured using a microphone, allowing for the quantitative analysis of the material's elements by monitoring the frequency and intensity of the emitted sound.
Figure 3 — Basic concept of photoacoustic spectroscopy
Temperature and current dependence of wavelength
The lasing wavelength of semiconductor lasers can be adjusted through several methods In external cavity control semiconductor lasers, the wavelength is selectable by manipulating the angle of an external grating mirror This technique allows for a broad scanning of the lasing wavelength by varying the grating angle.
In semiconductor lasers, the lasing wavelength is primarily regulated by adjusting the ambient temperature and the injected current, particularly in tunable semiconductor laser spectroscopy These adjustments affect the band-gap due to temperature variations and the band-filling effect from carrier injection into the active layer Additionally, changes in the refractive index of the active layer, influenced by temperature and carrier density, play a crucial role in altering the lasing wavelength The rate at which these physical properties change dictates the conventional dependence of the lasing wavelength on temperature and current This section elucidates the physical mechanisms behind the control of lasing wavelength through temperature and current adjustments.
Several factors govern the change in lasing wavelength of semiconductor lasers as shown in Figure 4
A change in the refractive index of the active region affects the threshold carrier density, leading to a corresponding shift in the lasing wavelength of Fabry-Pérot (FP) modes in FP-lasers This effect, driven by plasma interactions in semiconductors, results in shorter or longer lasing modes depending on whether the refractive index increases or decreases In distributed feedback (DFB) lasers, a decrease in effective grating pitch, caused by changes in the refractive index, also influences the lasing mode Additionally, temperature variations play a crucial role, as rising temperatures increase the refractive index and shift the gain envelope of FP-modes to longer wavelengths, while lowering temperatures have the opposite effect due to changes in band-gap energy.
Before lasing, the peak wavelength of FP-modes decreases due to the band-filling effect, while the DFB-mode wavelength also shortens as the injected carrier density rises, leading to a reduction in the refractive index After lasing begins, the primary influence shifts to thermal effects, as the threshold carrier density remains constant Consequently, Joule heating occurs, causing variations in light output power in relation to the injected current at a stable carrier density.
Semiconductor lasers can alter their lasing wavelength through several fundamental mechanisms A key method involves adjusting the ambient temperature while maintaining a constant current, which primarily affects the band-gap in Fabry-Pérot (FP) lasers and the refractive index in Distributed Feedback (DFB) lasers.
``,,`````,,```,,,```,````,`,-`-`,,`,,`,`,,` - lasing wavelength with the magnitude of injected current also occurs by the band-gap change due to
Joule heating occurs at the active layer, or pn-junction, due to the nearly constant injected carrier density after lasing This article analyzes the temperature and current dependence of the lasing wavelength in Distributed Feedback (DFB) lasers, focusing on the implications of thermal conductivity.
2 energy level change due to band filling
3 band gap change due to temperature increase
4 refractive index change due to carrier (plasma) effect
5 refractive index change due to heating
Figure 4 — Main factor of lasing-wavelength change
NOTE 2 The sample is a 1 300 nm-band FP semiconductor laser The labels indicated by 1, 2, 3 and 4 indicate the responsible parts of heat conduction for the heat generated at the active layer.
Figure 5 (b) — Estimated temperature rise in active layer as a function of pulse width
Effect of current injection on lasing wavelength
The temperature change rate in the active layer of a semiconductor laser is influenced by heat conduction and Joule heating, which diffuses from the active layer to its surroundings The change in lasing wavelength is significantly affected by the mounting configuration and packaging structure For a 1,300 nm-band FP semiconductor laser, the active layer temperature can be estimated from the junction voltage, which decreases linearly with temperature Monitoring the junction voltage at 1 mA after turning off a 100 mA pulsed current allows for accurate temperature assessment, as the monitoring current is set to minimize Joule heating effects The temperature dependence of the junction voltage is approximately 1 mV/°C As the pulse width increases, Joule heating diffuses through the laser chip and into the active layer, heat sink, package stem, and equipment, demonstrating that the transient heat conduction phenomenon is critical in determining the active layer's temperature and is affected by the laser-chip mounting configuration.
These behaviours are closely related to the rate and range of wavelength change under current modulation
In Figure 6, the horizontal axis represents modulation frequency while the vertical axis shows frequency deviation, which relates to wavelength variation As the modulation frequency increases from 100 Hz, the frequency deviation decreases due to a reduced response to heat conduction This trend is also evident in Figure 5, where the current pulse width aligns with the modulation frequency of the semiconductor laser concerning heat conduction A notable dip occurs after 100 kHz in Figure 6, beyond which the plasma effect prevails, leading to a blue shift in the lasing wavelength This frequency deviation is referred to as FM-response or chirping in optical fiber communication The frequency range for tunable semiconductor laser spectroscopy lies below the dip frequency and where heat influence is dominant, resulting in a red shift.
Y frequency deviation, in GHz/mA
NOTE The modulation current was a 0,5 mA peak-to-peak sinusoidal wave and the DC bias was set at 60 mA.
Figure 6 — Lasing frequency (wavelength) deviation for a 1 300 nm-band DFB semiconductor laser as a function of frequency
When the injected current changes rapidly, the resulting temperature increase is insufficient and does not reach saturation The temperature difference between the active layer and the package temperature varies with the magnitude of the injected current, especially when the package temperature is held constant Consequently, the current dependence is not uniform and fluctuates with the rate of current increase However, if the monitoring time intervals are kept constant, these dependencies stabilize, significantly influenced by the materials used and the chip-mount configuration.
Effect of ambient temperature on lasing wavelength
Heat is transferred inversely from the surrounding environment to the active layer of a semiconductor laser when there are changes in ambient or package temperature The heat conductance of the package, package stem, and heat sink remains consistent during the diffusion of Joule heating at the active layer Consequently, a specific time interval is required for the active layer's temperature to equal that of the ambient environment, as illustrated in Figure 5.
The temperature dependence of wavelength and absorption peak wavelength varies based on the monitoring time interval after altering the ambient temperature When the package temperature change rate exceeds 1 second, the temperature dependence remains consistent, as the temperature change diffuses to the active layer In contrast, at scanning rates corresponding to a package temperature change of less than 1 second, the absorption peak for CO₂ gas shows a shift in position towards the temperature scan direction, with a decrease in peak magnitude These effects are attributed to the heat diffusion time constant between the package and the active layer, which is crucial to consider during measurements.
The relationships between various factors are influenced by changes in ambient temperature, which simultaneously affect threshold current density and band-gap energy, leading to complex variations in lasing wavelength These dependencies are contingent upon the specific material utilized, the mounting configuration, and the monitoring time interval Therefore, the rate of change in injected current and ambient conditions plays a crucial role in these dynamics.
(package) temperature has to be constant during tumble semiconductor laser spectroscopy to eliminate wavelength error, although the dependence differs with the change rate.
NOTE A 2 000 nm-band semiconductor laser was used in this experiment.
Figure 7 — Shape change in absorption spectrum monitored at different scanning rates of the package temperature for one of CO 2 -gas absorption peaks
4 Measurement method for temperature dependence of wavelength
General
Semiconductor lasers, as outlined in Clause 3, utilize temperature control to either scan or fix their lasing wavelength for sensing applications The temperature dependence of these lasers indicates the magnitude of the lasing wavelength shift, which is crucial for accurate sensing Typically, a semiconductor laser employed in sensing operates as a single longitudinal mode laser, with the wavelength shift monitored in relation to changes in peak-emission wavelength due to temperature or current variations Detailed measurement methods for assessing temperature dependence are provided in sections 4.2 to 4.4.
Description of measurement setup and requirements
The measurement setup is depicted in Figure 8. © ISO 2013 – All rights reserved 9
2 device (semiconductor laser) being measured
9 power supply of thermoelectric cooler
Figure 8 — Basic measurement setup of temperature dependence of lasing wavelength
The LD driver provides current to the semiconductor laser, delivering continuous wave operation during measurements If the laser cannot maintain this mode, it supplies pulsed current, particularly for lasers like quantum cascade lasers.
A spectrometer, also known as a spectrophotometer or spectroscope, analyzes the spectral components of incoming light by utilizing a wavelength-tunable optical filter It outputs light corresponding to individual spectral components within a specific wavelength range, employing devices such as a diffraction grating or Fabry-Perot interferometer as the tunable optical filter.
The optical spectrum analyser can effectively monitor light signals when properly calibrated, serving as an alternative to traditional spectrometers and optical detectors In addition to diffraction-grating and Fabry-Perot interferometer-based analysers, Michelson interferometer-based spectrum analysers are also viable options, as they provide the autocorrelation function of the input light signal.
Precautions to be observed
The linearity of optical detector response should be maintained within the input and output range during measurement.
The spectral response of the optical detector shall be calibrated.
The wavelength resolution and the bandwidth of the spectrometer shall be such that the measurement is carried out with adequate accuracy.
For measurement, light reflected into the laser shall be minimized to ensure that the spectral response is not significantly affected.
The temperature monitoring point should be set at the device being measured as close as possible.
To ensure accurate measurements, the temperature change rate must remain constant, unless there are significant deviations in the monitoring data This constant rate should be established by considering the time constant of heat conductance between the device's active layer and its packaging.
Measurement procedures
The specified current, cw or pulse, is applied to the device being measured.
The spectrometer's wavelength is fine-tuned to achieve the highest reading on the optical detector, and the wavelength at this peak value is noted This recorded wavelength is identified as the peak-emission wavelength.
The temperature of the device being measured is changed with a constant rate The peak-emission wavelength is continuously monitored with a constant temperature interval.
The change in the peak-emission wavelength is linearly proportional to the temperature of the device being measured.
The temperature dependence of the peak-emission wavelength is determined by calculating the slope of the change in peak-emission wavelength with respect to temperature In cases where the relationship is nonlinear, calculations should be confined to the linear range for accuracy.
The wavelength temperature tuning range is defined by the kink point, which marks the deviation from a linear relationship at both low and high temperature extremes.
5 Measurement method for current dependence of wavelength
General
The lasing wavelength of semiconductor lasers varies with injected current, making it crucial for sensing applications This current dependence indicates the extent of lasing wavelength shifts, serving as a key measure of wavelength changes due to current control Understanding this characteristic is essential for optimizing semiconductor lasers in sensing Detailed measurement methods for assessing current dependence are outlined in sections 5.2 to 5.4.
Description of measurement setup and requirements
The measurement setup is depicted in Figure 9. © ISO 2013 – All rights reserved ``,,`````,,```,,,```,````,`,-`-`,,`,,`,`,,` - 11
2 device (semiconductor laser) being measured
9 power supply of thermoelectric cooler
Figure 9 — Diagram of measurement setup for current dependence of lasing wavelength
The LD driver provides current to the semiconductor laser, delivering continuous wave operation during measurements If continuous wave operation is not feasible, it supplies pulsed current to lasers, including quantum cascade lasers.
A spectrometer, also known as a spectrophotometer or spectroscope, analyzes the spectral components of incoming light by utilizing a wavelength-tunable optical filter It outputs light corresponding to individual spectral components within a specific wavelength range, employing devices such as a diffraction grating or Fabry-Perot interferometer as the tunable optical filter.
The optical spectrum analyser can effectively monitor light signals when properly calibrated, serving as an alternative to traditional spectrometers and optical detectors In addition to diffraction-grating and Fabry-Perot interferometer-based analysers, Michelson interferometer-based spectrum analysers are also viable options, as they provide the autocorrelation function of the input light signal.
Precautions to be observed
The linearity of optical detector response should be maintained within the input and output range during measurement.
The spectral response of the optical detector shall be calibrated.
The wavelength resolution and the bandwidth of the spectrometer shall be such that the measurement is carried out with adequate accuracy.
For measurement, light reflected into the semiconductor laser shall be minimized to ensure that the spectral response is not significantly affected.
The temperature monitoring point should be set at the device being measured as close as possible.
To ensure accurate measurements, the rate of current change must remain constant, unless there are significant deviations in the monitoring data This constant rate should be established by considering the time constant of heat conductance between the active layer and the device package being measured.
Measurement procedures
The specified injected current, cw or pulse, is applied to the device being measured.
The specified temperature is set to the device being measured.
The spectrometer's wavelength is fine-tuned to achieve the highest reading on the optical detector, and the wavelength at this peak value is noted This recorded wavelength is identified as the peak-emission wavelength.
The injected current of the device being measured is changed with a constant rate The peak-emission wavelength is monitored continuously or with a constant current interval.
The change in the peak-emission wavelength is linearly proportional to the magnitude of the injected current of the device being measured.
The relationship between the peak-emission wavelength and the magnitude of the injected current is analyzed by calculating the slope of their change In cases where this relationship is nonlinear, it is essential to conduct the calculations within the linear region to obtain accurate results.
The tuning range of the wavelength current is defined by the kink point, which marks the deviation from a linear relationship at both low and high levels of injected current.
For lasers that cannot operate in continuous wave mode near room temperature, the designated pulsed current is adjusted according to the device being measured The pulse height is modified while maintaining a constant pulse width and duty cycle, with all other procedures remaining consistent as previously outlined.
The specified injected current, cw, is applied to the device being measured.
The specified temperature is set to the device being measured.
An etalon plate, also known as a Fabry-Perot etalon, is utilized in place of the spectrometer as shown in Figure 9 It is precisely adjusted to achieve the necessary finesse, defined as the ratio of the free spectral range (FSR) to the full width at half maximum (FWHM) of the resonance peak The optical detector is capable of monitoring the cavity modes with this finesse.
A small signal current, sinusoidal wave, is biased to the laser under tested in addition to the specified current.
The width of the peak deviation is divided with the peak height of injected current, and the dynamic current dependence is calculated in unit of Hz/mA.
6 Measurement method of spectral line width
General
Lasing spectral line width is a key characteristic of single-mode semiconductor lasers, particularly when operating in continuous wave While it is generally uncritical for most sensing applications, it becomes crucial when monitoring narrow absorbing lines at low pressure If the spectral line width exceeds that of the absorption line shapes, the measured line shape appears broadened and unclear Thus, understanding the lasing spectral line width is essential for certain sensing applications involving semiconductor lasers The measurement method for this characteristic is detailed in sections 6.2 to 6.4.
Description of measurement setup and requirements
The measurement setup is depicted in Figure 10 a), Figure 10 b) and Figure 10 c).
Figure 10 (a) — Lasing spectrum line width measurement system: Optical heterodyne fibre system
Figure 10 (b) — Lasing spectrum line width measurement system: Optical heterodyne system © ISO 2013 – All rights reserved 15
4 optical fibre for phase delay
Figure 10 (c) — Lasing spectrum line width measurement system: Self-delayed optical heterodyne fibre system
Figure 10 illustrates three types of heterodyne systems: (a) a two-laser fiber system, (b) a two-laser system without fiber, and (c) a self-delayed system Both the systems in (a) and (c) utilize optical fiber, with the optical output power from the semiconductor laser being coupled to the fiber using lenses These systems are interconnected through single-mode optical fibers.
The beam optic system illustrated in (b) operates without fiber, utilizing a semiconductor laser to generate a laser beam This beam is transformed into a parallel beam using a lens before it traverses various optical components and equipment Typically, beam optic systems are employed for lasers that emit light at wavelengths exceeding 2 µm.
The polarization controller is controlling the polarization direction of light transmitted through the fibre and adjusting the two light from the device being measured and local oscillator.
The optical fibre of phase delay is delaying the phase of transmitted light The length of the fibre influences monitoring resolution.
The optical frequency modulator adjusts the frequency of light using a fiber coupler, creating a difference in frequency from the light transmitted through an alternate fiber path for heterodyne detection Typically, an acousto-optical modulator serves as the modulating device.
Precautions to be observed
To ensure accurate measurements, it is essential to suppress light reflected into the semiconductor laser to below -50 dB using an optical isolator, as back-reflected light significantly impacts spectral line width Additionally, applying an anti-reflecting film to all optical components, as shown in Figure 7, is recommended to minimize back-reflection.
To ensure optimal performance in setups utilizing single mode optical fibre, it is essential to minimize back-reflection at the connection point between fibres to below -50 dB by employing appropriate fibre types.
The electrical source driving the semiconductor lasers has to be low noise to eliminate its influence on the spectral line width For instance, battery cell is favourable.
The optical isolation of the isolator has to be set at the value of less than −50 dB.
The spectral response of the optical detector should be calibrated.
The rf spectral analyser should be corrected.
The beat frequency of the both semiconductor lasers or the frequency of optical modulator should be relatively high frequency to eliminate the influence of 1/f noise.
Measurement procedures
6.4.1 System employing two semiconductor lasers [shown in Figures 10 (a) and (b)]
The specified injected current is applied to the device being measured.
The specified temperature is set to the device being measured.
The specified wavelength is set to the device being measured, and the wavelength of the local oscillator is set at a required value which determines the beat frequency.
The frequency range of the rf spectrum analyser is adjusted within the required range for monitoring the beat frequency.
The polarization controller regulates the polarization to ensure that the peak value of the beat signal on the RF spectrum analyzer is maximized in fiber systems, as illustrated in Figure 10 (a).
If the beam system is used [Figure 10 (b)], the polarization of the both semiconductor lasers have to be adjusted.
The spectral line width is read on the rf spectrum analyser at 3 dB-down point or other values such as
The 20 dB-down point was calculated, revealing that the spectral line width observed on the RF spectrum analyzer is the combined result of the line widths of both semiconductor lasers, which exhibit Lorentzian line shapes.
The homodyne detection technique occurs when the lasing wavelengths of both semiconductor lasers coincide This monitoring procedure resembles that of the heterodyne technique, but it uniquely observes the beat spectrum at 0 Hz, allowing for the direct measurement of the spectral line width.
6.4.2 Self-delayed heterodyne [shown in Figure 10 (c)]
The specified injected current is applied to the device being measured.
The specified temperature is set to the device being measured.
The specified wavelength is set to the device being measured.
The frequency range of the rf spectrum analyser is adjusted within the required range for monitoring the beat frequency. © ISO 2013 – All rights reserved 17
The light frequency modulation is performed with the optical frequency modulator.
The beat spectrum on the rf spectrum analyser is confirmed to appear at the modulation frequency.
The polarization is controlled by the polarization controller so that the peak value of beat signal on rf spectrum analyser is the maximum.
If the beam system without optical fibre is used, the polarization of the semiconductor laser has to be adjusted.
The spectral line width is read on the rf spectrum analyser at 3 dB-down point or other values such as
20 dB-down point and calculated Here, the spectral line width monitored on the rf spectrum analyser is twice of the true value under consumption of a Lorentzian line shape.
The self-delayed homodyne detection technique occurs when the lasing wavelengths of both semiconductor lasers align, despite the significant impact of 1/f noise In systems utilizing fiber optics, the optical modulator is not required The monitoring process resembles that of the heterodyne technique, with the beat spectrum detected at 0 Hz, allowing for the measurement of the spectral line width.
Semiconductor lasers exhibit complex device characteristics, with various electrical and optical properties detailed in this Technical Specification Annex A provides examples of absolute maximum ratings, essential ratings, and key characteristics for semiconductor lasers housed in TO-can packages and fiber-pigtail modules.
Table A.1 — Symbols (and abbreviated terms)
Symbol Unit Term ϕ e W radiant power η e , h W/A radiant power efficiency η ed , η d W/A differential radiant power efficiency η s W/A slope efficiency
Lϕ e % linearity (in current – radiant power relation) λ air m wavelength in air
The spectral radiant power distribution, denoted as \$P(\lambda)\$ in W/m, describes the variation of radiant power across a specific wavelength tuning range Key parameters include the peak-emission wavelength \$\lambda_p\$ and the central wavelength \$\lambda_m\$ Additionally, the rms spectral radiation bandwidth is represented as \$\Delta\lambda_{rms}\$, while the spectral line width is indicated by the full width at half maximum (FWHM), denoted as \$\Delta\lambda_L\$ in either meters or Hertz.
The SMS dB side mode suppression ratio, denoted as Δλ, indicates the spectral shift (δλ) in relation to temperature (T) and current (I) dependencies The change in radiant power (ΔP_t) is calculated as the difference between the end (P_e1) and opposite end (P_e2) of the tuning range Additionally, the maximum wavelength range maintains a constant ratio of wavelength to current or temperature It is essential to determine the required time for the lasing wavelength shift to stabilize within a defined value after altering the current or temperature.
Symbol Unit Term Δλ tr m wavelength tuning range b Δ λ tt s wavelength tuning time c
R(f) or RIN dB relative intensity noise (RIN)
The carrier-to-noise ratio (C/N dB) is a critical parameter in assessing signal quality, while key timing metrics such as turn-on delay time (\$t_{d(on)}\$), rise time (\$t_{r}\$), turn-on time (\$t_{on}\$), turn-off delay time (\$t_{d(off)}\$), fall time (\$t_{f}\$), and turn-off time (\$t_{off}\$) are essential for evaluating device performance The cut-off frequency (\$f_{c}\$) is significant in modulation applications, and the change in radiant power (\$ΔP_{t} = P_{e1} - P_{e2}\$) is measured across a defined temperature or current tuning range, where \$P_{e1}\$ and \$P_{e2}\$ represent the power at the ends of the tuning range Additionally, the maximum wavelength range maintains a constant ratio of wavelength to current or temperature, and the required time for the lasing wavelength shift to stabilize after a change in current or temperature is also crucial for optimal operation.
A.3 Essential ratings and characteristics of TO can laser devices
The TO can laser device consists of the following basic parts:
Semiconductor laser: InP, GaAs, InGaAs, InAlAs, InGaAsP, etc.
Monitor photodide: Ge, Si, InGaAs, etc.
Semiconductor laser: Fabry Perot, Distributed feedback (DFB), buried heterostructure (BH), ridge waveguide, vertical cavity surface emitting (VCSEL), quantum well (QW), Multiple QW (MQW), strained MQW, quantum cascade, etc.
A.3.4 Details of outline and encapsulation
A.3.4.1 ISO and/or IEC and/or national reference number of the outline drawing.
A.3.4.2 Method of encapsulation: glass/metal/plastic/other.
A.3.5 Limiting values (absolute maximum system) over the operating temperature range, unless otherwise stated
Table A.2 — Characteristics and requirements of the limiting values
Min Max Unit General conditions
A.3.5.3 Soldering temperature: (at specified soldering time and minimum distance to case T sld x °C
A.3.5.6 CW radiant output power at optical port ϕ e x W
A.3.5.7 Maximum radiant output power at specified pulse width and duty cycle ϕ ep x W
A.3.5.8 ESD-Voltage (both polarities) Human Body model V ESD x V
A.3.5.11 ESD-Voltage (both polarities) Human Body model V mESD x V
Table A.3 — Electrical and optical characteristics
Min Max Unit Semiconductor laser
A.3.6.2 Radiant output power at optical port at I F ( I (TH) + ΔI F ) specified (where appropriate for maximum value) ϕ e x x W
A.3.6.4 Differential efficiency at ϕ e ± Δϕ e specified or at I F ± ΔI F specified η d x x W/A
A.3.6.5 Linearity of radiant output power between ϕ e1 and ϕ e2 specified (where appropriate) L d x %
A.3.6.6 Radiant output power at optical port at I (TH) (where appropriate) ϕ (TH) x W
A.3.6.7 Forward voltage at ϕ e or I F specified V F x V
A.3.6.8 Differential resistance above threshold (where appropri- ate) R d x x Ω/A
A.3.6.9 Side mode suppression ratio SMS x dB
NOTE Characteristics with “+” in the symbol column indicate that minimum and maximum values of the characteristics shall be taken over whole operating temperature range. © ISO 2013 – All rights reserved 21
Min Max Unit Semiconductor laser
A.3.6.12 Thermal resistance junction-case (where appropriate) T th(j-c) x K/W
A.3.6.13 Reverse dark current at ϕ e = 0 at V R specified I mR0 x A
A.3.6.14 Monitor photodiode output current at ϕ e and V R speci- fied I m x x A
A.3.6.15 Linearity of monitor diode current to radiant output power from the optical port over the specified range from I F1 to I F2 or ϕ e1 to ϕ e2
A.3.6.16 Capacitance at V R and f specified C tot x F
A.3.6.17 Central (RMS) wavelength of the maximum spectrum at radiant output power ϕ e specified λ x x m
A.3.6.18 RMS spectral bandwidth at a) ϕ e or I F specified (under CW conditions) or b) ϕ e mean or I F mean and ϕ e specified (under modula- tion conditions)(where appropriate) Δλ rms x x W/A
A.3.6.19 Rise time of radiant output power between 90 % and
10 % of the radiant output power ϕ e or I F and R L speci- fied t r x s
A.3.6.20 Fall time of radiant output power between 10 % and
90 % of the radiant output power ϕ e or I F and R L speci- fied t f x s
A.3.6.21 Relative intensity noise at ϕ e or I F specified, ϕ e and Δ f specified, optical reflection specified (where appropri- ate)
Semiconductor laser (and monitor photodiode)
Characteristics over the operating temperature range specified
A.3.6.23 Differential efficiency at ϕ e ± Δϕ e specified or at I F ± ΔI F specified η d+ x x W/A
A.3.6.24 Tracking error at ϕ e specified referring to
A.3.6.25 Central (RMS) wavelength of the spectrum at radiant output power ϕ e specified λ + x x m
A.3.6.26 Linearity of radiant output power between ϕ e1 and ϕ e2 specified (where appropriate) L n+ x %
NOTE Characteristics with “+” in the symbol column indicate that minimum and maximum values of the characteristics shall be taken over whole operating temperature range.
Min Max Unit Semiconductor laser
A.3.6.31 Optical power variation across wavelength (frequency) tuning range ΔP t x W
The dark current of the monitor photodiode at the specified reverse voltage \( V_R \) is denoted as \( I_R(D) + x \, A \) Characteristics marked with a “+” in the symbol column indicate that both minimum and maximum values must be considered across the entire operating temperature range.
A.4 Essential ratings and characteristics of modules with pigtail fibre
The laser module with pigtail fibre consists of the following basic parts:
A.4.2.1 Semiconductor laser: InP, GaAs, InGaAs, InAlAs, InGaAsP, etc.
A.4.2.2 Monitor photodiode: Ge, Si, InGaAs, etc.
Semiconductor laser: Fabry Perot, Distributed feedback (DFB), buried heterostructure (BH), ridge waveguide, vertical cavity surface emitting (VCSEL), quantum well (QW), Multiple QW (MQW), strained MQW, quantum cascade, etc.
A.4.4 Details of outline and encapsulation
A.4.4.1 ISO and/or IEC and/or national reference number of the outline drawing.
A.4.4.2 Method of encapsulation: glass/metal/plastic/other.
A.4.4.4 Information on pigtail fibre: type of fibre, kinds of protection, connector, length, etc.
A.4.4.5 Information on the heatsinking of the package.
Table A.3 (continued) © ISO 2013 – All rights reserved ``,,`````,,```,,,```,````,`,-`-`,,`,,`,`,,` - 23
A.4.5 Limiting values (absolute maximum system) over the operating temperature range, unless otherwise stated
Table A.4 — Characteristics and requirements of limit values
Min Max Unit General conditions
A.4.5.3 Soldering temperature: (at specified soldering time and minimum distance to case T sld x °C
A.4.5.4 Minimum bending radius of pigtail (at specified dis- tance from case) r x m
Tensile strength along cable axis:
A.4.5.9 CW radiant output power at pigtail output ϕ e x W
A.4.5.10 Maximum radiant output power at specified pulse width and duty cycle ϕ ep x W
A.4.5.11 ESD-Voltage (both polarities) Human Body model V ESD x V
A.4.5.14 ESD-Voltage (both polarities) Human Body model V mESD x V
Table A.5 — Electrical and optical characteristics
Min Max Unit Semiconductor laser
A.4.6.2 Radiant output power at pigtail output at I F ( I (TH) + Δ I F ) specified (where appropriate for maximum value) ϕ e x x W
NOTE Characteristics with “+” in the symbol column indicate that minimum and maximum values of the characteristics shall be taken over whole operating temperature range.
Min Max Unit Semiconductor laser
A.4.6.4 Differential efficiency at ϕ e ± Δϕ e specified or at I F ± ΔI F specified η d x x W/A
A.4.6.5 Linearity of radiant output power between ϕ e1 and ϕ e2 specified (where appropriate) L d x %
A.4.6.6 Radiant output power at pigtail output at I (TH) (where appropriate) ϕ TH x W
A.4.6.7 Forward voltage at ϕ e or I F specified V F x V
A.4.6.8 Differential resistance above threshold (where appro- priate) R d x x Ω/A
A.4.6.9 Side mode suppression ratio SMS x dB
A.4.6.12 Thermal resistance junction-case (where appropriate) T th(j-c) x K/W
A.4.6.13 Reverse dark current at ϕ e = 0 at V R specified I mR0 x A
A.4.6.14 Monitor photodiode output current at ϕ e and V R speci- fied I m x x A
A.4.6.15 Linearity of monitor diode current to radiant output power from the optical port over the specified range from I F1 to I F2 or ϕ e1 to ϕ e2
A.4.6.16 Capacitance at V R and f specified C tot x F
A.4.6.17 Central (RMS) wavelength of the maximum spectrum at radiant output power ϕ e specified λ x x m
A.4.6.18 RMS spectral bandwidth at: a) ϕ e or I F specified (under CW conditions) or b) ϕ e mean or I F mean and ϕ e specified (under modula- tion conditions)(where appropriate) Δλ rms x x W/A
A.4.6.19 Rise time of radiant output power between 90 % and
10 % of the radiant output power ϕ e or I F and R L speci- fied t r x s
A.4.6.20 Fall time of radiant output power between 90 % and
10 % of the radiant output power ϕ e or I F and R L speci- fied t f x s
A.4.6.21 Relative intensity noise at ϕ e or I F specified, ϕ e and Δf specified, optical reflection specified (where appropri- ate)
Semiconductor laser (and monitor photodiode)
The characteristics specified for the operating temperature range indicate that those marked with a “+” in the symbol column require the minimum and maximum values to be considered across the entire temperature range.
Table A.5 (continued) © ISO 2013 – All rights reserved ``,,`````,,```,,,```,````,`,-`-`,,`,,`,`,,` - 25
Min Max Unit Semiconductor laser
A.4.6.23 Differential efficiency at ϕ e ± Δ ϕ e specified or at I F ± Δ I F specified η d+ x x W/A
A.4.6.24 Tracking error at ϕ e specified referring to
A.4.6.25 Central (RMS) wavelength of the spectrum at radiant output power ϕ e specified λ + x x m
A.4.6.26 Linearity of radiant output power between ϕ e1 and ϕ e2 specified (where appropriate) L n+ x %
A.4.6.31 Optical power variation across wavelength (frequency) tuning range ΔP t x W
The dark current of the monitor photodiode at the specified reverse voltage \( V_R \) is denoted as \( I_R(D) + x \, A \) Characteristics marked with a “+” in the symbol column indicate that both minimum and maximum values must be considered across the entire operating temperature range.
[1] ISO 11145, Optics and photonics — Lasers and laser-related equipment — Vocabulary and symbols
[2] IEC 60747-5-1, Discrete semiconductor devices and integrated circuits, Optoelectronic devices — General
[3] IEC 60747-5-2, Discrete semiconductor devices and integrated circuits, Optoelectronic devices —
[4] IEC 60825, Safety of laser products
[5] IEC 62007-1, Semiconductor optoelectronic devices for fiber optic system applications — Part 1:
[6] Publication 50(521), IEC International Electrotechnical Vocabulary, Chapter 521: Semiconductor devices and integrated circuits 1)
1) Withdrawn. © ISO 2013 – All rights reserved 27