ISO/TS 17915:2013
(Main)Optics and photonics — Measurement method of semiconductor lasers for sensing
Optics and photonics — Measurement method of semiconductor lasers for sensing
ISO/TS 17915:2013 describes methods of measuring temperature, injected current dependence and lasing spectral line width in relation to semiconductor lasers for sensing applications. ISO/TS 17915:2013 is applicable to all kinds of semiconductor lasers, such as edge-emitting type and vertical cavity surface emitting type lasers, bulk-type and (strained) quantum well lasers, and quantum cascade lasers, used for optical sensing in e.g. industrial, medical and agricultural fields. ISO/TS 17915:2013 is an application of ISO 13695, in which the physical bases are explained.
Optique et photonique — Méthode de mesure des lasers semi-conducteurs pour la sensibilité
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Standards Content (Sample)
TECHNICAL ISO/TS
SPECIFICATION 17915
First edition
2013-07-15
Optics and photonics —
Measurement method of
semiconductor lasers for sensing
Optique et photonique — Méthode de mesure des lasers semi-
conducteurs pour la sensibilité
Reference number
ISO/TS 17915:2013(E)
©
ISO 2013
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ISO/TS 17915:2013(E)
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ISO/TS 17915:2013(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Optical sensing using semiconductor lasers . 1
3.1 General . 1
3.2 Semiconductor laser. 1
3.3 Common sensing technique and equipment using semiconductor laser . 3
3.4 Temperature and current dependence of wavelength . 5
3.5 Effect of current injection on lasing wavelength . 7
3.6 Effect of ambient temperature on lasing wavelength . 8
4 Measurement method for temperature dependence of wavelength .9
4.1 General . 9
4.2 Description of measurement setup and requirements . 9
4.3 Precautions to be observed .10
4.4 Measurement procedures.11
5 Measurement method for current dependence of wavelength .11
5.1 General .11
5.2 Description of measurement setup and requirements .11
5.3 Precautions to be observed .12
5.4 Measurement procedures.13
6 Measurement method of spectral line width .13
6.1 General .13
6.2 Description of measurement setup and requirements .14
6.3 Precautions to be observed .17
6.4 Measurement procedures.17
Annex A (informative) Essential ratings and characteristics .19
Bibliography .27
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ISO/TS 17915:2013(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
The committee responsible for this document is ISO/TC 172, Optics and photonics, Subcommittee SC 9,
Electro-optical systems.
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TECHNICAL SPECIFICATION ISO/TS 17915:2013(E)
Optics and photonics — Measurement method of
semiconductor lasers for sensing
1 Scope
This Technical Specification describes methods of measuring temperature, injected current dependence
and lasing spectral line width in relation to semiconductor lasers for sensing applications. This Technical
Specification is applicable to all kinds of semiconductor lasers, such as edge-emitting type and vertical
cavity surface emitting type lasers, bulk-type and (strained) quantum well lasers, and quantum
cascade lasers, used for optical sensing in e.g. industrial, medical and agricultural fields. This Technical
Specification is an application of ISO 13695, in which the physical bases are explained.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 13695, Optics and photonics — Lasers and laser-related equipment — Test methods for the spectral
characteristics of lasers
3 Optical sensing using semiconductor lasers
3.1 General
The methods described in this Technical Specification are to be followed in accordance with ISO 13695.
Optical sensing using tunable semiconductor laser spectroscopy has been widely used in various
engineering fields. For example, optical sensing is being used for bio-sensing and environmental
monitoring. Semiconductor lasers are key devices for those applications and are indispensable for
building sensing equipment. Semiconductor lasers and sensing techniques are described in 3.2 to 3.6.
3.2 Semiconductor laser
3.2.1 General
A semiconductor laser is an optical semiconductor device that emits coherent optical radiation in a
certain direction through stimulated emission resulting from electron transition when excited by an
electric current that exceeds the threshold current of the semiconductor laser. Here, the mechanism
of coherent optical radiation is divided into two categories, (1) electron-hole recombination due to
interband electron transition between conduction and valence band (bulk type) or between two
quantized states (quantum well type, see 3.2.5) and (2) intraband electron transition between two
quantized states (quantum cascade type, see 3.2.5).
Edge-emitting types with single lasing modes, such as distributed feedback (DFB) lasers, have been
conventionally used in sensing equipment because of their high power and single lasing modes. Surface-
emitting types are also widely used in sensing systems because they are easy to handle. Some names are
given to those lasers from various aspects. Those lasers are briefly categorized in 3.2.2 to 3.2.5.
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3.2.2 Basic structure
a) Edge emitting type semiconductor laser: a semiconductor laser that emits coherent optical radiation
in the direction parallel to junction plane.
b) Surface emitting type semiconductor laser: a semiconductor laser that emits coherent optical
radiation in the direction normal to junction plane. Vertical cavity surface emitting type
semiconductor laser (VCSEL) is the typical one.
3.2.3 Transverse mode stabilizing structure
a) Gain guiding: a semiconductor laser in which emitted light propagates along the gain region
generated by carrier injection and is amplified by stimulate emission along the gain region. Planar
type lasers are typical ones in gain guiding.
b) Refractive index guiding: a semiconductor laser in which a stripe-shape active layer (light emitting
layer) or junction is formed to introduce effective refractive index difference between the stripe and
the outer region. Buried heterostructure (BH) is typical in refractive index guiding.
3.2.4 Mode (wavelength) selection structure
a) Distributed feedback (DFB) semiconductor laser: a semiconductor in which stimulated emission is
selected by a grating (equivalent to distributed mirror). This laser operates in single longitudinal mode.
b) Distributed Bragg reflector (DBR) semiconductor laser: a semiconductor laser in which stimulated
emission is selected by a Bragg grating (equivalent to distributed mirror) jointed at a side or the
both sides of light emitting layer. This laser operates in single longitudinal mode.
c) Fabry-Perot (FP) semiconductor laser: a semiconductor laser in which stimulated emission is
generated between two mirror facets. This laser normally operates in multiple longitudinal modes.
d) External cavity controlled semiconductor laser: a semiconductor laser in which the optical cavity is
composed of one mirror and an external mirror (ex. grating) set on the opposite side of the mirror.
Stimulated emission is generated at the semiconductor part in the optical cavity. This laser normally
operates in single longitudinal mode.
3.2.5 Active layer structure
a) Double heterostructure semiconductor laser: a semiconductor laser in which the active layer (light
emitting layer) is sandwiched with two heterojunctions (pn- and iso-junction).
b) Quantum well semiconductor laser: a semiconductor laser that emits coherent optical radiation
through stimulated emission resulting from the recombination of electrons and holes between
two quantized states. Here, the light emitting layer is composed of a single quantum well layer
or multiple quantum well layers. Quantum wire and quantum dot (box) semiconductor laser are
included in this category but the light emitting area of quantum wire and dot is two-dimensional
and three-dimensional structure, respectively.
c) Strained quantum well semiconductor laser: a semiconductor laser that emits coherent optical
radiation through stimulated emission resulting from the recombination of free electrons and holes
between two quantized states. Here, the light emitting layer is composed of strained single quantum
well layer or multiple quantum well layers.
d) Quantum cascade semiconductor laser: a semiconductor laser that emits coherent optical radiation
through stimulated emission resulting from electron transition between two quantized states without
any electron-hole recombination. The light emitting layer is composed of quantum cascade layers.
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3.3 Common sensing technique and equipment using semiconductor laser
3.3.1 General
Semiconductor lasers including quantum cascade semiconductor lasers have various advantages:
compact size, light weight, low power consumption, easy controlling of wavelength by pulsed or
continuous wave operation, etc. Sensing techniques and equipment using such semiconductor lasers
have been researched and developed in academic and industrial fields. The main sensing techniques are
described in 3.3.2 to 3.3.4.
3.3.2 Tunable laser absorption spectroscopy (TLAS)
Absorption spectrum is monitored by scanning repeatedly the wavelength of light emitted from
semiconductor laser as shown in Figure 1. The composition of material and mixture to be examined are
qualitatively and quantitatively analysed based on the monitored spectrum (shape, peak wavelength
and intensity). The lasing wavelength of semiconductor laser is scanned by controlling the ambient
temperature or injected current in this technique.
Key
X wavelength
Y optical intensity
1 tunable laser diode
2 lens
3 cell
4 element to be detected
5 optical detector
Figure 1 — Basic concept of tunable laser absorption spectroscopy (two absorption peaks
are observed)
3.3.3 Cavity ring down spectroscopy (CRDS)
This technique is usually used for detecting trace element and originated from tunable semiconductor
laser spectroscopy. Material to be analysed is introduced into the cavity built up with two mirrors
as shown in Figure 2. Light pulse (with a certain wavelength) introduced to the cavity is repeatedly
reflected between the mirror and passes through the material. A part of reflecting light escapes through
the mirror, and a pulse train with a time interval determined with the cavity length is monitored. The
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trace element is qualitatively and quantitatively analysed with the decay time of the pulse train and the
wavelength of the light.
Key
X wavelength
Y optical intensity
A optical pulse
B optical pulse train
1 tunable laser diode
2 lens
3 cell
4 element to be detected
5 optical detector
6 mirror
Figure 2 — Basic concept of cavity ring down spectroscopy
3.3.4 Photoacoustic spectroscopy (PAS)
When material to be analysed is illuminated with laser light, the light is absorbed at the material. The
light power absorbed induces lattice vibration, and the vibration results in the emission of a supersonic
wave as shown in Figure 3. The supersonic wave is detectable with a microphone, and the element
contained in the material is quantitatively analysed by monitoring the frequency and intensity.
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Key
1 tunable laser diode
2 lens
3 cell
4 element to be detected
5 supersonic wave
6 microphone
Figure 3 — Basic concept of photoacoustic spectroscopy
3.4 Temperature and current dependence of wavelength
The lasing wavelength of semiconductor lasers is changed by various methods. In external cavity
control semiconductor lasers, the lasing wavelength can be selected by controlling the angle of grating
if a grating is set as an external mirror. The lasing wavelength is widely scanned by controlling the
grating angle.
In normal semiconductor lasers, their lasing wavelength is ordinarily controlled by varying the ambient
temperature and injected current in tunable semiconductor laser spectroscopy. These variables
corresponding to band-gap change due to ambient temperature and the band-filling effect induced
by carrier injected into the active layer of semiconductor lasers. In addition, refractive index change
of the active layer, which is induced by temperature and injected carrier density, takes the important
role of changing the lasing wavelength. The changing rate of these physical properties determines
the conventionally used temperature and current dependence of lasing wavelength. The physical
mechanisms of temperature and current control of the lasing wavelength are explained in this subclause.
Several factors govern the change in lasing wavelength of semiconductor lasers as shown in Figure 4.
A decrease (an increase) in the refractive index of the active region originates from an increase (a
decrease) in threshold carrier density and shortens (lengthens) the lasing wavelength of each Fabry-
Pelot (FP)-mode in FP-lasers. This phenomenon is induced by the plasma effect related to carrier density
in semiconductors. In DFB lasers, the lasing mode is shortened (lengthened) with a decrease (an increase)
in effective grating pitch introduced by the decrease (increase) in the refractive index. The increase
(decrease) in the refractive index is introduced by rising (lowering) temperature. In addition, the rising
(lowering) temperature shifts the envelope of FP-modes (gain envelope) to the longer (shorter) range.
This is due to a reduction (an increase) of the band-gap energy.
Before lasing, the peak wavelength of FP-modes shortens due to the band-filling effect, and that of DFB-
mode also shortens as the injected carrier density increases through the refractive index reduction.
After lasing, the main factor is the thermal effect because threshold carrier density is fixed at the
threshold value after lasing. Joule heating is generated and light output power changes in response to
injected current under the constant carrier density.
These are basic mechanisms for changing lasing wavelength in semiconductor lasers. Among them, the
change in lasing wavelength by controlling ambient temperature under a constant current is mainly
generated by band-gap change in FP-lasers and refractive index change in DFB lasers. Controlling the
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lasing wavelength with the magnitude of injected current also occurs by the band-gap change due to
Joule heating at the active layer (or pn-junction) because the injected carrier density is nearly constant
after lasing. The temperature and current dependence of lasing wavelength is analysed in DFB lasers
from the viewpoint of thermal conductivity in the following parts.
Key
X wavelength
Y intensity
1 gain envelope
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
6 each lasing mode
Figure 4 — Main factor of lasing-wavelength change
Key
1 semiconductor laser
2 active layer
3 heat sink
4 package stem
5 heat flow
Figure 5 (a) — Sample configuration
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Key
X current pulse width
Y active layer temperature, in ° C
1 LD chip
2 heat sink
3 package stem
4 package
NOTE 1 Pulse height: 100 mA.
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
3.5 Effect of current injection on lasing wavelength
The rate of temperature change in the active layer depends on a transient phenomenon determined
by heat conduction. The Joule heating generated at the active layer gradually diffuses from the active
layer to the surrounding region, and thus the change rate in lasing wavelength strongly depends on
the mounting configuration and packaging structure. Figure 5 shows an example of active layer
temperature increase as a function of the current pulse width for a 1 300 nm-band FP semiconductor
laser. The active layer temperature is estimated from the junction voltage because the junction voltage
linearly decreases with temperature. The junction voltage at 1 mA is monitored just after turning off
the 100 mA-pulsed current. The pulsed current and the monitoring current of the junction voltage is
set at 100 and 1 mA, respectively. Here, the value of the monitoring current is determined so that the
Joule heating due to the current is negligible. The temperature dependence of the junction voltage is
about 1 mV/°C in the 1 300 nm-band semiconductor lasers. The Joule heating due to current injection
diffused within the laser chip and then towards the outside of the active layer, heat sink, package stem,
package, and equipment, as the pulse width was widened. This heat conduction transient phenomenon
governs the temperature of the active layer and is influenced by the laser-chip mounting configuration
(configuration of the heat-conducting path).
These behaviours are closely related to the rate and range of wavelength change under current modulation.
In Figure 6, the horizontal axis indicates modulation frequency and the vertical axis corresponds to the
frequency deviation, which corresponds to the wavelength variation. As modulation frequency increases
from 100 Hz, the frequency deviation decreases because the response to heat conduction is gradually
small. This behaviour is also recognized in Figure 5, in which the current pulse width corresponds to the
modulation frequency of the semiconductor laser from the viewpoint of heat conduction. A dip appears
after 100 kHz in Figure 6. After the dip, the plasma effect is dominant and the lasing wavelength tends
to be shortened (blue shift). This frequency deviation is called FM-response or chirping in the optical
[4]
fibre communication field. The frequency range used for tunable semiconductor laser spectroscopy is
below the dip frequency and the frequency at which the influence of heat is dominant (red shift).
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Key
X modulation frequency
Y frequency deviation, in GHz/mA
1 Joule heating (lengthening)
2 dip
3 plasma effect (shortening)
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 is quickly changed, the increase in the temperature is not sufficient and
the increase is not saturated. The temperature difference between the active layer and the package
temperature becomes large or small in response to the magnitude of injected current when the package
temperature is set at a constant temperature. The current dependence is, therefore, not constant and
varies with the rate of current increase. Their dependences are, however, kept at fixed values if the time
interval of monitoring are fixed at the constant values and strongly influenced by the materials used and
the chip-mount configuration.
3.6 Effect of ambient temperature on lasing wavelength
Heat is inversely transmitted from the ambient to the active layer of the semiconductor laser through
the package when the ambient temperature or package temperature is changed. The heat conductance
of the package, package stem, and heat sink is the same for the case of the diffusion of Joule heating at
the active layer, and a certain time interval is needed until the temperature of the active layer is equal to
the ambient temperature as shown in Figure 5.
The temperature dependence of wavelength and absorption peak wavelength vary depending on the
time interval of monitoring after changing the ambient temperature. If the change rate of package
temperature is set at values of more than 1 s, the temperature dependence is the same because the change
in package temperature can diffuse to the active layer (see Figure 5). Figure 7 shows a set of the change
in absorption peak in the spectrum monitored at different scanning rate of the package temperature
for one of CO -gas absorption peaks. (The CO -gas pressure is set at an atmospheric pressure, and the
2 2
spectral width is broadened because of Doppler shift.) These scanning rates correspond to the package-
temperature change rate of less than 1 s. As the rate is high, the peak position shifts to the direction of
the temperature scan and the magnitude of the absorption peak tends to be small. These phenomena are
caused by the time constant of heat diffusion between the package and active layer, and should be paid
attention under measurement.
These dependences are governed by the change of each factor discussed in 3.4. When ambient temperature
is changed, for example, threshold current density and band-gap energy vary simultaneously and lasing
wavelength changes complicatedly. The dependences result from the overall change in the factors.
Consequently, the dependences will vary with the material used, the mounting configuration, the
monitoring time interval, etc. It can be said that the change rate of the injected current and ambient
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(package) temperature has to be constant during tumble semiconductor laser spectroscopy to eliminate
wavelength error, although the dependence differs with the change rate.
Key
X package case temperature, in °C
Y light power, in a.u
1 temperature scan
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 -gas absorption peaks
2
4 Measurement method for temperature dependence of wavelength
4.1 General
As described in Clause 3, the lasing wavelength of semiconductor lasers is scanned or fixed by temperature
control when they are used for sensing application. The temperature dependence corresponds to the
magnitude of lasing wavelength shift and is a measure of the lasing wavelength change with temperature.
This characteristic is therefore important for semiconductor lasers for sensing. A semiconductor laser
used for sensing is normally a single longitudinal mode laser (see 3.2 and Figure 4), and the shift value
of wavelength is, for instance, monitored with the amount of the change in peak-emission wavelength
under temperature or current variation. The measurement method of the temperature dependence is
described in 4.2 to 4.4.
4.2 Description of measurement setup and requirements
The measurement setup is depicted in Figure 8.
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Key
1 LD driver
2 device (semiconductor laser) being measured
3 lens
4 spectrometer
5 attenuator
6 optical detector
7 thermoelectric cooler
8 controller of power supply
9 power supply of thermoelectric cooler
Figure 8 — Basic measurement setup of temperature dependence of lasing wavelength
The LD driver is supplying current to the semiconductor laser, and if the laser is not capable of operating
in continuous wave throughout measurement, is supplying pulsed current to the lasers, such as quantum
cascade ones.
The spectrometer (spectrophotometer or spectroscope) is resolving the spectral components of input
light in corresponding to the wavelength by wavelength-tunable optical filter and outputting light of the
individual spectral components within a certain wavelength range. A diffraction grating or Fabry-Perot
interferometer is used as the tunable optical filter.
The optical spectrum analyser is applicable to monitor, instead of the spectrometer and optical
detector, if th
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