JP2006086431A - Wavelength variable light source and wavelength characteristics measuring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength variable light source where producibility of light intensity of output light is satisfactory, even if wavelength is swept a plurality number of times, and to provide a wavelength characteristic measuring system that uses the wavelength variable light source. <P>SOLUTION: The wavelength variable light source, having a semiconductor laser outputting a laser beam for a prescribed wavelength range, a laser drive circuit supplying laser-driving current to the semiconductor laser, a light-receiving part receiving the laser beam which the semiconductor laser outputs and a current control part for controlling the laser drive current which the laser-driving circuit outputs, based on light intensity of the laser beam which the light-receiving part receives is improved. The light source has a storage part for storing the value of the light intensity at each wavelength and an operation means comparing the value of the light intensity outputted from the light-receiving part with the value of light intensity in the storage part and obtaining laser drive current which the laser-driving circuit outputs. The storage part stores the value of the light intensity, in a range where a change of light intensity of the laser beam becomes constant with respect to the increase/decrease of the laser drive current. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a semiconductor laser that outputs laser light over a predetermined wavelength range, a laser drive circuit that supplies a laser drive current to the semiconductor laser, a light receiving unit that receives the laser light output from the semiconductor laser, and the light receiving unit In particular, the present invention relates to a wavelength tunable light source including a current control unit that controls a laser drive current output from a laser drive circuit based on the light intensity of laser light received by the laser, and a wavelength characteristic measurement system using the wavelength tunable light source. The present invention relates to a wavelength tunable light source with good reproducibility of the intensity of output light even if wavelength sweeping is performed a plurality of times, and a wavelength characteristic measurement system using the wavelength tunable light source.

  The wavelength tunable light source can change the wavelength of the output light over a wide range. Wavelength sweeping is performed with such a wavelength tunable light source, and wavelength characteristics of optical components, measuring instruments, and the like are measured. For example, the transmission characteristics of the wavelength filter, the branching ratio characteristics of the beam splitter, the switching characteristics of the optical switch, and the like are measured.

  In the measurement method, output light from a wavelength tunable light source is input to an object to be measured (optical component, measuring instrument, etc.). Then, the output light from the measurement target is measured by an optical measuring instrument such as an optical spectrum analyzer or an optical power meter. Further, the wavelength characteristic of the measurement target is measured by sweeping the wavelength of the wavelength tunable light source (see, for example, Patent Document 1 and Patent Document 2).

  Usually, it is difficult for a wavelength tunable light source to output output light having a constant light intensity (also referred to as optical power) over a wide wavelength range (for example, several hundred [nm]). This is because the light intensity of the laser light from the semiconductor laser varies depending on the wavelength even if the laser drive current for driving the semiconductor laser is constant.

  For this reason, when measuring the wavelength characteristic of the object to be measured, the wavelength sweep is performed twice. First, without connecting the object to be measured, the wavelength variable light source and the optical measuring device are directly connected to sweep the wavelength, and the first measurement is performed. Next, the object to be measured is connected between the wavelength tunable light source and the optical measuring device, the wavelength is swept, and the second measurement is performed. Then, by taking the difference between the first measurement and the second measurement, the wavelength characteristic of the measurement target can be measured with high accuracy.

  Incidentally, when the light intensity is stabilized and output, APC (Automatic Power Control) control is performed to change the laser drive current or using an optical attenuator.

  Next, FIG. 4 is a diagram showing the characteristics (so-called IL characteristics) of the laser drive current to the semiconductor laser and the light intensity of the laser light. In FIG. 4, the horizontal axis represents the current value of the laser drive current, and the vertical axis represents the light intensity of the laser light. Until the predetermined current value It, almost no laser beam is output. When the current value It is exceeded, the output increases in proportion to the increase in current, that is, with linearity. Further, when the predetermined current value Is is exceeded, the output is saturated. Further, if the current value is increased even if the current value Is is exceeded, the optical output decreases and the semiconductor laser may be destroyed. Usually, it is driven at a current value Id before the output is saturated.

  When the environment (for example, temperature) of the semiconductor laser changes or the temperature of the semiconductor laser itself changes due to the amount of laser drive current injected into the semiconductor laser, the IL characteristic also changes. This will be specifically described with reference to FIG. FIG. 5 is a diagram showing a change in IL characteristics due to a change in temperature. Here, the same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 5, when the temperature changes from T to T1, T2 (T ≠ T1 ≠ T2), the characteristic curve also changes from A to A1, A2, but the curve only changes along the horizontal axis, and the shape is It is similar. Therefore, even if the temperature changes, the light intensity varies uniformly over the wavelength range to be swept, and APC is easy.

JP 2001-308455 A JP 2002-299757 A

  Thus, since the measurement is performed twice and the difference is taken, the characteristics of the measurement target can be measured even if the light intensity of the output light of the wavelength tunable light source differs depending on the wavelength.

  However, the IL characteristics of an actual semiconductor laser are not limited to those having good linearity as shown in FIG. 4 over all wavelengths. This will be described with reference to FIG. FIG. 6 is a diagram showing other IL characteristics. Here, the same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. Depending on the wavelength, there are irregularities as shown in FIG. 6 (a), and the output decreases as the current increases, and as shown in FIG. 6 (b), a large current is required to output laser light. A value It is required, and various characteristics such as a laser beam that is not output due to a slight temperature change are provided.

  Therefore, when the temperature changes between the first and second measurements and the IL characteristic also changes, a wavelength that cannot be APC controlled in the wavelength range to be swept may be generated. Therefore, the reproducibility of the output light is deteriorated in the first time and the second time, and there is a problem that it is difficult to accurately measure the wavelength characteristic of the measurement target.

  Accordingly, an object of the present invention is to realize a wavelength tunable light source with good reproducibility of the light intensity of output light even if wavelength sweep is performed a plurality of times, and a wavelength characteristic measurement system using the wavelength tunable light source.

The invention according to claim 1
A semiconductor laser that outputs laser light over a predetermined wavelength range;
A laser driving circuit for supplying a laser driving current to the semiconductor laser;
A light receiving portion for receiving laser light output from the semiconductor laser;
In the wavelength tunable light source including the current control unit that controls the laser driving current output from the laser driving circuit based on the light intensity of the laser beam received by the light receiving unit,
A storage unit for storing a light intensity value for each wavelength;
Comparing a light intensity value output from the light receiving unit with a light intensity value of the storage unit to obtain a laser drive current output from the laser drive circuit, and the storage unit, A light intensity value within a range in which a change in the light intensity of the laser light is constant with respect to increase / decrease in the laser drive current is stored.

The invention according to claim 2 is the invention according to claim 1,
The storage unit stores a light intensity value corresponding to a current value approximately in the center of the range.

The invention described in claim 3
In the wavelength characteristic measurement system that measures the wavelength characteristics of the measurement target,
The wavelength tunable light source according to claim 1 or 2,
Measuring the first output light from the wavelength tunable light source obtained without passing through the measurement object and the second output light from the wavelength tunable light source obtained through the measurement object; It has an optical measuring device for measuring the wavelength characteristic of the object to be measured from the difference between the output light and the second output light.

The present invention has the following effects.
According to the first and second aspects, the storage unit stores in advance a light intensity value within a range in which the amount of change is constant with respect to increase or decrease of the laser drive current. Then, when performing wavelength sweeping of the output light, the calculation means obtains the laser drive current based on the light intensity value of the storage unit and the light intensity value from the light receiving unit. Thereby, even if the IL characteristic changes due to a temperature change or the like, the APC control cannot be performed at some wavelengths. Therefore, even if the wavelength sweep is performed a plurality of times, the reproducibility of the light intensity of the output light is good, and the wavelength characteristics of the measurement target can be measured with high accuracy.

  According to the second aspect of the present invention, the storage unit stores the light intensity value corresponding to the current value near the center of the range having a good linearity with the IL characteristic, so that it is affected by the fluctuation of the IL characteristic. The light intensity is more reproducible.

  According to claim 3, since the output light of the wavelength tunable light source according to claim 1 or 2 is used, the reproducibility of the light intensity of the output light is good even if the wavelength sweep is performed a plurality of times. As a result, the wavelength characteristics of the object to be measured can be accurately measured even when measurement is performed by performing multiple wavelength sweeps.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a first embodiment of the present invention. There are two types of wavelength tunable light sources: an external resonator type and an internal resonator type. Here, an external resonator type wavelength tunable light source having a wide wavelength tunable range will be described as an example. In addition, the description will be made with a Littman arrangement type in which mode hops do not occur.

  In FIG. 1, the optical amplification unit 10 includes a semiconductor laser 11, a first lens 12, and a second lens 13. The semiconductor laser 11 has an antireflection film 11a at one end. The first lens 11 emits the light emitted from one end of the semiconductor laser 11 (the end surface having the antireflection film 11a) as parallel light. The second lens 13 condenses laser light emitted from the other end of the semiconductor laser 11.

  The wavelength selection unit 20 includes a diffraction grating 21, a wavelength selection mirror 22, and a mirror rotation unit 23. The wavelength selection unit 20 selects the wavelength of light incident from one end of the optical amplification unit 10 and feeds it back to the optical amplification unit 11. The diffraction grating 21 wavelength-disperses the light from the optical amplification unit 10 and the light from the wavelength selection mirror 22. The wavelength selection mirror 22 is a reflection unit, and reflects the light, which is wavelength-dispersed by the diffraction grating 21, to the diffraction grating 21. The mirror rotating unit 23 rotates the wavelength selection mirror 22 and performs wavelength selection of light that the diffraction grating 21 returns to the optical amplification unit 10.

  The laser drive circuit 30 outputs a laser drive current for driving the semiconductor laser 11 to the semiconductor laser 11. The optical coupler 40 receives the laser beam condensed by the second lens 13, splits the incident laser beam into two, and outputs one branched beam as output light. The light receiving unit 50 receives the other branched light branched by the optical coupler 40 and outputs the value of the light intensity of the received laser light.

  The current control unit 60 includes a calculation unit 61 and controls the current value of the laser drive current output from the laser drive circuit 30 based on the light intensity of the laser light (the other branched light) received by the light receiving unit 50. The storage unit 70 stores a light intensity value for each wavelength within a predetermined wavelength range, that is, a wavelength variable range. Further, the calculating means 61 compares the value of the light intensity of the laser beam output from the light receiving unit 50 with the value of the light intensity of the storage unit 70 to obtain the laser driving current output from the laser driving circuit 30.

The operation of such an apparatus will be described.
First, an operation of storing the light intensity value at each wavelength in the storage unit 70 will be described. The IL characteristic of the semiconductor laser 11 is measured for each predetermined wavelength, for example, at an interval of 1 [nm]. Specifically, the current value output from the laser drive circuit 30 is measured with an ammeter, and the light intensity received by the light receiving unit 50 is measured. Or you may measure the output light of a wavelength variable light source with an optical power meter.

  Then, from the obtained IL characteristic, a range where the change in the light intensity of the laser light is constant with respect to the increase / decrease of the laser drive current, that is, a range with good linearity is searched for, The light intensity value stored in the storage unit 70 is preferably stored in the storage unit 70 in this range, which corresponds to the current value near the center.

  This will be described with reference to FIG. FIG. 2 shows the IL characteristics shown in FIGS. 4 and 6. The same components as those in FIGS. 4 and 6 are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 2, the light intensity value corresponding to the current value at the approximate center of the range with good linearity is stored in the storage unit 70. For example, in FIG. 2A, the light intensity value P (a) corresponding to the current value Id (a), and in FIG. 2B, the light intensity value P corresponding to the current value Id (b). In FIG. 2B and FIG. 2C, the light intensity value P (c) corresponding to the current value Id (c) is stored in the storage unit 70. Note that the storage in the storage unit 70 is preferably performed at the time of adjustment before shipping the device or at the time of calibration of the device.

  In the range where the light intensity is saturated (current value larger than Is) and the range before the laser beam is output (range of 0 to It), the change is constant (change = 0) and the linearity is Of course, these ranges are out of scope.

Next, the operation for measuring the measurement target will be described.
The laser drive circuit 30 outputs a laser drive current having a current value set as an initial value to the semiconductor laser 11. Thereby, the light emitted from one end of the semiconductor laser 11 is converted into parallel light by the first lens 12 and enters the diffraction grating 21. Then, the light incident on the diffraction grating 21 is diffracted by the diffraction grating 21, is wavelength-dispersed at different angles for each wavelength, and enters the wavelength selection mirror 22. Further, only the light having a desired wavelength out of the light incident on the wavelength selection mirror 22 is reflected by the diffraction grating 21 through the same optical path. The mirror rotating means 23 selects the wavelength that is reflected by the same optical path.

  Then, the light incident on the diffraction grating 21 is wavelength-dispersed again, and only the light having the wavelength selected by the wavelength selection unit 20 is converged by the semiconductor laser 11 by the first lens 12 and returned. Here, an external resonator is formed by the other end of the semiconductor laser 11 and the wavelength selection mirror 22, and laser oscillation is performed.

  On the other hand, the laser light emitted from the other end not provided with the antireflection film 11 a is condensed by the second lens 13 and enters the optical coupler 40. Then, the optical coupler 40 splits the laser light into two, one branched light is output as output light of the variable wavelength light source, and the other branched light is received by the light receiving unit 50.

  A photodiode (not shown) provided in the light receiving unit 50 outputs a photocurrent corresponding to the light intensity of the other branched light. Then, an IV conversion circuit (not shown) provided in the light receiving unit 50 converts the photocurrent into a voltage. Further, an AD conversion circuit (not shown) provided in the light receiving unit 50 converts analog data into digital data. Then, the light receiving unit 50 outputs at least one of the voltage value of the analog data output from the IV conversion circuit or the voltage value of the digital data output from the AD conversion circuit to the current control unit 60 as a light intensity value.

  Then, the current control unit 60 selects the light intensity value corresponding to the wavelength to be output from the light intensity values P (a) to P (c) stored in the storage unit 70, for example, the value P (a). Is read. Further, the calculation means 61 of the current control unit 60 compares the light intensity value from the light receiving unit 50 with the light intensity value P (a) read from the storage unit 70, and outputs the laser to the laser driving circuit 30. Determine the value of the drive current. Further, the current control unit 60 controls the laser driving circuit 30 to output a laser driving current having the obtained current value to the semiconductor laser 11. That is, the current control unit 60 is also an APC circuit.

  Further, by rotating the wavelength selection mirror 22 by the mirror rotating means 23, the wavelength of the light returning from the wavelength selection unit 20 to the optical amplification unit 10 can be varied, and the wavelength of the output light is swept. Of course, in accordance with the rotation of the mirror rotating means 23, the light intensity values P (b) and P (c) corresponding to the wavelength to be output next are read from the storage unit 70, and the calculating means 61 calculates the laser drive current. To do. Then, the current control unit 60 controls the laser drive circuit 30 to cause the semiconductor laser 11 to output a laser drive current.

  As described above, the storage unit 70 stores in advance the light intensity values P (a) to P (c) within a range in which the amount of change is constant with respect to increase and decrease of the laser drive current. When the wavelength sweep of the output light is performed, the calculation unit 61 obtains a laser drive current based on the light intensity value in the storage unit 70 and the light intensity value from the light receiving unit 50. Thereby, even if the IL characteristic changes due to a temperature change or the like, the APC control cannot be performed at some wavelengths. Therefore, even if the wavelength sweep is performed a plurality of times, the reproducibility of the light intensity of the output light is good, and the wavelength characteristics of the measurement target can be measured with high accuracy.

  In addition, the storage unit 70 provides light intensity values P (a) to P (c) corresponding to current values Id (a) to Id (c) in the vicinity of the center of the range having a good linearity with IL characteristics. Since the data is stored, the light intensity is less affected by fluctuations in the IL characteristic, and the light intensity reproducibility is further improved.

[Second Embodiment]
Next, an example of a wavelength characteristic measurement system that measures the wavelength characteristic of the measurement target using the wavelength variable light source shown in FIG. 1 will be described. Here, FIG. 3 is a block diagram showing a second embodiment of the present invention. In FIG. 3, a wavelength tunable light source 100 is the light source shown in FIG. The optical measuring device 101 is, for example, an optical power meter, an optical spectrum analyzer, or the like, and receives output light from the wavelength variable light source 100. The measurement target 102 is connected between the variable wavelength light source 100 and the optical measuring device 101.

The operation of such an apparatus will be described.
First, the wavelength variable light source 100 and the optical measurement device 101 are directly connected without connecting the measurement target 102 and the wavelength is swept to perform the first measurement. Then, the optical measuring device 101 measures and stores the light intensity of the first output light from the wavelength variable light source 100 obtained without going through the measurement target 102.

  Next, the object to be measured 102 is connected between the wavelength tunable light source 100 and the optical measuring instrument 101, the wavelength is swept, and the second measurement is performed. Then, the optical measuring device 101 measures and stores the light intensity of the second output light from the variable wavelength light source 100 obtained via the measurement target 102.

  Further, the optical measuring device 101 measures the wavelength characteristic of the measurement object 102 from the difference between the first output light and the second output light.

  Thus, since the output light of the wavelength tunable light source 100 is used, the reproducibility of the light intensity of the output light is good even if the wavelength sweep is performed a plurality of times. As a result, the wavelength characteristics of the object 102 to be measured can be accurately measured even when measurement is performed by performing multiple wavelength sweeps.

In addition, this invention is not limited to this, The following may be sufficient.
In the apparatus shown in FIG. 1, the configuration of the Littman arrangement type external resonator type tunable light source is shown. However, the external resonator may have any configuration. For example, only the mirror which is a reflection means may be provided in the wavelength selection unit 20, and this mirror may be moved along the optical axis. Alternatively, only the diffraction grating as the reflection means may be provided in the wavelength selection unit, and this diffraction grating may be moved along the optical axis. Further, an internal resonator type may be used instead of an external resonator type.

  In the apparatus shown in FIG. 1, the configuration in which the light intensity values P (a) to P (c) are stored in the storage unit 70 at intervals of 1 [nm] is shown. May be.

  In the apparatus shown in FIG. 1, the configuration using the optical coupler 40 as an example of the optical branching unit is shown, but a beam splitter, a half mirror, or the like may be used. The point is that any laser beam from the semiconductor laser 11 can be branched at a stable branching ratio.

  In the apparatus shown in FIG. 3, an example is given in which output light from the variable wavelength light source 100 is directly measured, and then the measurement target 102 is connected and measured. However, the measurement order may be reversed. That is, after the measurement object 102 is connected and measured, the measurement object 102 may be removed and the output light from the variable wavelength light source 100 may be directly measured.

It is the block diagram which showed the 1st Example of this invention. 6 is a diagram illustrating light intensity values P (a) to P (c) stored in a storage unit 70. FIG. It is the block diagram which showed the 2nd Example of this invention. It is the figure which showed the IL characteristic of a semiconductor laser. It is the figure which showed the change of the IL characteristic by a temperature change. It is the figure which showed the other IL characteristic of the semiconductor laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor laser 30 Laser drive circuit 50 Light-receiving part 60 Current control part 61 Calculation means 70 Memory | storage part 100 Wavelength variable light source 101 Optical measuring device 102 Object to be measured

Claims (3)

A semiconductor laser that outputs laser light over a predetermined wavelength range;
A laser driving circuit for supplying a laser driving current to the semiconductor laser;
A light receiving portion for receiving laser light output from the semiconductor laser;
In the wavelength tunable light source including the current control unit that controls the laser driving current output from the laser driving circuit based on the light intensity of the laser beam received by the light receiving unit,
A storage unit for storing a light intensity value for each wavelength;
Comparing a light intensity value output from the light receiving unit with a light intensity value of the storage unit to obtain a laser drive current output from the laser drive circuit, and the storage unit, A wavelength tunable light source that stores a value of light intensity within a range in which a change in light intensity of laser light is constant with respect to increase / decrease in laser drive current.   The wavelength tunable light source according to claim 1, wherein the storage unit stores a light intensity value corresponding to a current value substantially in the center of the range. In the wavelength characteristic measurement system that measures the wavelength characteristics of the measurement target,
The wavelength tunable light source according to claim 1 or 2,
Measuring the first output light from the wavelength tunable light source obtained without passing through the measurement object and the second output light from the wavelength tunable light source obtained through the measurement object; A wavelength characteristic measurement system comprising: an optical measuring device that measures the wavelength characteristic of the measurement target from the difference between the output light and the second output light.

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