Laser diode device, laser diode operation method, and scanning microscope device equipped with laser diode

Abstract

A laser diode device is provided, comprising a laser diode, a driver (EPS) for supplying AC power to the laser diode, a first feedback component (FB1), and a second feedback component (FB2). The first feedback component (FB1) is configured to detect an optical output of the laser diode and controls a first waveform characteristic of the AC power to adjust the detected optical output (P M ) as the first target value (P D ) The second feedback component (FB2) controls the temperature (T EST ) and controlling a second waveform characteristic of the AC power, which is different from the first waveform characteristic, to estimate the estimated temperature (T EST ) to the second target value (T OPT ) configured to maintain the temperature at or near the

Description

[Technical field]

[0001] This application relates to laser diode devices. The present application further relates to a method of operating a laser diode. The present application further relates to a scanning microscope apparatus equipped with a laser diode. [Background technology]

[0002] Laser diodes have a wide range of applications. As an example, laser diodes are used in scanning probe microscopy (SPM) instruments. In an SPM instrument, a probe mounted on a flexible carrier is scanned along the surface of a sample. The deflection of the light beam from a laser diode mounted on a flexible carrier is detected, and the detected signal is analyzed to measure the physical properties of the sample. It is then important that the light beam rendered by the laser diode is as stable as possible to minimize noise in the detected signal. Other applications include optical fiber communication, barcode readers, laser pointers, CD / DVD / Blu-ray disc reading / recording, laser printing, laser scanning, and light beam illumination, which also require a stable light beam.

[0003] Especially when used in an SPM device, the beam needs to be highly pointing stable, in other words, the angle fluctuation of the beam needs to be small. Summary of the Invention [Problem to be solved by the invention]

[0004] It is a first object of the present disclosure to provide an improved laser diode device that reduces angular variations in the rendered laser beam.

[0005] A second object of the present disclosure is to provide an improved method of operating a laser diode that reduces angular variations in the rendered laser beam.

[0006] A third object of the present disclosure is to provide a scanning microscope apparatus equipped with an improved laser diode. [Means for solving the problem]

[0007] According to a first object, there is provided a laser diode apparatus comprising a laser diode, a driver, a first feedback component, and a second feedback component, where the driver is configured to supply AC power to the laser diode having a first waveform characteristic and a second controlled waveform characteristic different from the first waveform characteristic.

[0008] The first feedback component includes an optical power control module configured to detect an optical output of the laser diode and configured to control a first waveform characteristic to maintain the detected optical output near a first target value.

[0009] The second feedback component has a temperature control module configured to estimate a temperature of the laser diode by detecting a voltage-current characteristic of the laser diode and to control a second waveform characteristic to maintain the estimated temperature near a second target value.

[0010] By estimating the temperature of the laser diode from the detected voltage-current characteristic, material costs are minimized. A separate temperature sensor is not required, nor are additional connections to such a sensor. Instead, the second feedback component can directly detect the voltage across and the current through the laser diode. In one example, the second feedback component comprises a look-up table (LUT) having a plurality of addressable entries for each pair of voltage and current ranges, the look-up table including a representation of a temperature value of the laser diode associated with each pair of said voltage and current ranges. In another example, the temperature value is estimated using an approximate polynomial relationship that specifies the temperature as a function of the measured voltage and current. In yet another example, the temperature is estimated using an analytical equation that specifies the temperature as a function of the voltage and current.

[0011] Each feedback element controls one of the waveform characteristics to maintain both light output and a stable operating temperature.

[0012] In one embodiment, the first waveform characteristic controlled by the optical power control module of the first feedback component is the amplitude of the power parameter and the second waveform characteristic controlled by the temperature control module of the second feedback component is the duty cycle, whereby the optical power control module is configured to control a change in the amplitude having a sign equal to the sign of the difference between the first target value and the detected optical power, and the temperature control module is configured to control a change in the duty cycle having a sign equal to the sign of the difference between the second target value and the estimated temperature.

[0013] In an alternative embodiment, the first waveform characteristic controlled by the optical power control module of the first feedback component is the duty cycle of the power parameter, and the second waveform characteristic controlled by the temperature control module of the second feedback component is the amplitude. In operation, the optical power control module adjusts the first target value (P D) and the detected light output, and the temperature control module is configured to control a change in amplitude having a sign opposite to the sign of the difference between the second target value and the estimated temperature.

[0014] In some examples, the controlled amplitude is the amplitude of the current supplied to the laser diode. In this case, the voltage across the laser diode is the dependent parameter and is approximately proportional to the logarithm of the supplied current. In other embodiments, the controlled amplitude is the amplitude of the voltage supplied to the laser diode. In this case, the current through the laser diode is the dependent parameter and is approximately proportional to an exponential function of the supplied voltage. Of these embodiments, direct control of the supplied current has the advantage that it can be more easily stabilized to a constant value.

[0015] In some examples, the laser diode device disclosed herein further comprises an optimal temperature calculation module configured to calculate an optimal junction temperature at which the laser diode can generate an optical output equal to the first target value as a second target value. In some applications, different optical outputs may be required depending on the circumstances. In practice, the optimal temperature at which the pointing stability is maximized varies depending on the optical output provided.

[0016] In one embodiment, the waveform at which power is applied is a square wave, which is advantageous in that it can be implemented with relatively simple power control components, namely a controlled switching element with a controllable voltage or current source to control the amplitude of the square wave and a pulse width modulator to modulate the pulse width at which power is delivered.

[0017] In another embodiment, the waveform to which power is applied is sinusoidal. This mode of operation is suitable for operation at high frequencies where the parasitic input capacitance of the LD prevents the use of pulse width modulated (PWM) signals.

[0018] According to a second object of the present disclosure, providing power having a first waveform characteristic and a second waveform characteristic of a power parameter to a laser diode; detecting the optical output of the laser diode; controlling the first waveform characteristic to maintain the detected optical output near a first target value; estimating a temperature of the laser diode by detecting a voltage-current characteristic of the laser diode; A method of operating a laser diode is provided that includes controlling a second waveform characteristic to maintain the estimated temperature near a second target value.

[0019] According to a third aspect of the present disclosure, a probe having a tip that is scanned over the surface of a sample; a signal generator for generating an input signal for inducing an acoustic signal in the probe, tip or sample; an embodiment of a laser diode device as described above for generating a light beam emitted towards the probe and generating a secondary light beam reflected by the probe; a photodetector providing an output signal indicative of the direction of the secondary light beam; A scanning probe microscope (SPM) apparatus is provided that includes a signal analysis module that outputs an output signal indicative of a characteristic of the sample based on the input signal and the output signal.

[0020] The implementation of the SPM device may involve the photodetector of the SPM device having the ability to detect the optical output of the laser diode, for example by using the sum of the response of the four quadrants of the photodetector. In practice, however, such a measurement method is not accurate in most applications due to the effects of cantilever movement, speckle interference, and the optical propagation medium. For example, in some applications, the SPM cantilever and sample are immersed in a liquid. For this reason, it is usually preferable to provide a dedicated optical output sensor close to the laser diode. Typically, the laser diode is provided in the same package as such a sensor.

[0021] These and other aspects will now be described in more detail with reference to the drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 shows a schematic diagram of a first embodiment of a laser diode device. [Diagram 2] FIG. 2 shows a schematic diagram of a second embodiment of a laser diode device. [Diagram 3] FIG. 13 is a diagram illustrating a third embodiment of a laser diode device. [Figure 4] FIG. 13 is a diagram illustrating a fourth embodiment of a laser diode device. [Diagram 5] FIG. 10 is a schematic diagram illustrating a fifth embodiment of a laser diode device. [Figure 6] FIG. 13 is a schematic diagram illustrating a sixth embodiment of a laser diode device. [Figure 7] FIG. 1 is a diagram showing a schematic diagram of a scanning probe microscope (SPM) device. [Figure 8] FIG. 1 shows measurement results obtained with a controlled driven laser diode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the various drawings, like reference numbers refer to like elements unless otherwise noted.

[0024] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In certain instances, well-known methods, procedures, and components are not described in detail so as not to obscure aspects of the present invention.

[0025] 1 is a schematic diagram of a laser diode apparatus comprising a laser diode LD connected to a driver EPS configured to supply AC power to the laser diode LD having a first controlled waveform characteristic of a power parameter and a second controlled waveform characteristic different from the first controlled waveform characteristic. The laser diode apparatus further comprises a first feedback component FB1 and a second feedback component FB2.

[0026] The first feedback component FB1 is configured to detect the optical output of the laser diode LD and controls the first waveform characteristic to detect the detected optical output P M The first target value P D In the illustrated example, the first feedback component FB1 comprises a monitor diode MD arranged in the vicinity of the laser diode LD, e.g. housed together with the laser diode LD in a common package. A subtraction element, such as a differential amplifier, is arranged to maintain the first target value P D and the detected optical output P M Difference with E P , which is output as an input to the optical power control module OPCM. In response, the optical power control module OPCM outputs a control signal C A The driver EPS supplies AC power to the laser diode LD with this first waveform characteristic. D is set, for example, by an operator or a lead administrator.

[0027] The second feedback component FB2 determines the temperature T of the laser diode LD by detecting the voltage-current characteristics of the laser diode LD. EST and controlling the second waveform characteristic to estimate the estimated temperature T EST Set the second target value T OPTIn the illustrated embodiment, the second feedback component FB2 comprises a voltage sensor SV that detects the voltage drop across the laser diode LD and outputs an output signal V LD to the temperature estimation module TEM. Furthermore, the driver EPS outputs an output signal I LD to the temperature estimation module TEM. In some examples, the output signal V LD and output signal I LD and represent the instantaneous voltage across and the instantaneous current through the laser diode LD, respectively. LD and output signal I LD indicates for example the respective peak value or the respective average value. The temperature estimation module TEM estimates the output signal V LD and output signal I LD Based on the detected voltage-current characteristic indicated by EST In the illustrated example, the temperature estimation module TEM comprises a look-up table having a number of addressable entries for each pair of voltage range and current range.

[0028] A subtraction element such as a differential amplifier subtracts the signal T OPT The second target value T is the value of the junction temperature at which stable operation is achieved, denoted by OPT and signal T EST The difference between the estimated temperature and the T In the illustrated example, the second target value T OPT As a result, the laser diode LD reaches the first target value P D An optimum temperature calculation module OTCM is provided which is configured to calculate an optimum junction temperature capable of producing an optical output having an output equal to T OPT A fixed value is specified as

[0029] In the embodiment of Fig. 1, the power parameter to be controlled is the current supplied to the laser diode LD. The first waveform characteristic controlled by the optical power control module OPCM of the first feedback component FB1 is the amplitude of the supplied current. In operation, the optical power control module OPCM controls the amplitude of the supplied current to a first target value P D and the detected optical output P M Difference with E P For example, the target optical output P D The optical output P M If this is exceeded, the driver EPS supplies a current with increased amplitude.

[0030] The second waveform characteristic controlled by the temperature control module TCM of the second feedback component FB2 is the current I PWM is the duty cycle at which the second target value T OPT The estimated temperature T EST Difference with E T For example, the estimated temperature T EST is the second target value T OPT If higher than the difference E TThe sign of is negative, and the temperature control module TCM decreases the duty cycle. Therefore, this means a decrease in the optical power, but typically the first feedback component FB1 can correct the optical power relatively quickly compared to the change caused by the change in the duty cycle for the temperature change. This is because the junction temperature is related to the integral of the power consumed therein, and the optical power is directly related to the power supplied. However, the response speed of the first feedback component FB1 and the second feedback component FB2 may be appropriately set as required. For example, the first feedback component FB1 may be a proportional-differential (PD) controller with a differential component D added to the proportional component P to increase the response speed, and / or the second feedback component FB2 may be a proportional-integral (PI) controller with an integral component I added to the proportional component P to decrease the response speed.

[0031] It is further noted that the laser diode device may comprise a feed-forward control module that specifies reference values ​​for the amplitude and the duty cycle based on prior estimations, where the first feedback component FB1 and the second feedback component FB2 specify adaptations to the respective reference values ​​to approximate a target operating temperature and a target optical power.

[0032] 1, the controlled amplitude is the amplitude of the current supplied to the laser diode LD. In this case, the voltage across the laser diode LD is the dependent parameter, which is approximately proportional to the logarithm of the current supplied according to the response characteristic of the laser diode LD.

[0033] FIG. 2 shows another embodiment corresponding to the embodiment of FIG. 1, except that the amplitude controlled is the amplitude of the voltage supplied to the laser diode LD. In this case, the output signal C of the optical power control module OPCM Ais the pulse-width modulated voltage V supplied to the laser diode LD by the driver EPS. PWM Specifies the amplitude of .

[0034] In that case, the current through the laser diode LD is a dependent parameter, approximately proportional to an exponential function of the supplied voltage.Of these embodiments, direct control of the supply current has the advantage that it can be more easily stabilized to a constant value.

[0035] FIG. 3 shows yet another embodiment. As in the embodiment of FIG. 1, the driver EPS supplies a controlled pulse-width modulated current I PWM to the laser diode LD, except that in this case the optical power control module OPCM of the first feedback component FB1 controls the duty cycle of the current and the second feedback component FB2 controls the amplitude of the current.

[0036] During operation, the optical power control module OPCM maintains a first target value P D and the detected optical output P M Difference with E P For example, the detected light output P M is the first target value P D If it is smaller, the difference E P The sign of is positive, and the optical power control module OPCM controls a positive change in the duty cycle.

[0037] During operation, the temperature control module TCM adjusts the second target value T OPT The estimated temperature T EST Difference with E T For example, the estimated temperature T EST is the second target value T OPT Below the difference E T If the sign of is positive, the temperature control module TCM controls the driver EPS to generate a lower amplitude pulse width modulated current I PWM If the first feedback component FB1 is not present, the junction temperature will be equal to the second target value TOPT However, due to the relatively fast response of the optical power control module OPCM, the duty cycle is increased to maintain the specified output, so that the combined effect of the first feedback component FB1 and the second feedback component FB2 achieves a fixed value with a lower amplitude and a larger duty cycle, which results in an increase in the junction temperature and a decrease in the second target value T OPT can get closer to

[0038] Figure 4 shows another embodiment corresponding to that of Figure 3, except that the amplitude that is controlled is that of the voltage supplied to the laser diode LD.

[0039] Further details of the embodiment of FIG. 2 are shown in FIG. 5. As shown therein, the driver EPS is a controllable voltage supply module EPS V and controllable pulse width modulator module EPS DC Equipped with a controllable voltage supply module EPS V is the input voltage V from an external power source such as a battery. IN and receives the amplitude control signal C A Pulse width modulator module EPS with voltage controllable according to DC In response to this, the controllable pulse width modulator module EPS DC is the duty cycle control signal C DC The laser diode LD is supplied with a controlled voltage having a duty cycle specified by . Note that due to the presence of the sense resistor SR, the amplitude of the voltage across the laser diode LD will be slightly smaller than that due to the driver EPS. In practice, this does not matter, since the two feedback components FB1, FB2 will tend to control the driver EPS in any case so that the target operating temperature and the target optical power are achieved.

[0040] Further details of the embodiment of FIG. 3 are shown in FIG. 6. As shown therein, the driver EPS includes a controllable pulse width modulator module EPSDC and controllable current supply module EPS I Equipped with a controllable pulse width modulator module EPS DC is the input voltage V from an external power source such as a battery. IN and receiving a duty cycle control signal C DC A current supply module EPS capable of controlling a controlled pulse width modulated supply voltage having a duty cycle specified by I The controllable current supply module EPS I is the amplitude control signal C A Amplitude and pulse width modulator module EPS controlled by DC A current having a pulse width modulated by is supplied to the laser diode LD.

[0041] FIG. 7 is a schematic diagram of a scanning probe microscope (SPM) device comprising a probe P, a signal generator SG, an optical laser diode device LDC, a laser diode LD, a photodetector DT and a signal analysis module AM. The optical laser diode device LDC, the laser diode LD are, for example, one of the embodiments as shown in FIG. 1 to FIG. 6. Here, the controlled laser driver LDC is a combination of a driver EPS, a first feedback component FB1 and a second feedback component FB2. The interconnection between the block LDC and the laser diode LD represents the power supply line to the laser diode LD and the output from the optical sensor MD integrated with the laser diode LD in a common package. A separate temperature sensor line is not required since the second feedback component FB2 is configured to estimate the junction temperature from the voltage-current characteristic of the laser diode LD.

[0042] In an SPM device, a probe P has a tip T that is scanned over the surface of a sample S. The tip T is, for example, mounted on a cantilever, membrane or other flexible carrier. A signal generator SG receives an input signal S into induce an acoustic signal at the probe P, tip T or sample S. A laser diode LD is arranged to generate a steady light beam B which is emitted towards the probe P. This causes a secondary light beam Br to be reflected by the probe P and detected by a photodetector DT, such as a quadrant detector. In response, the photodetector DT produces an output signal S which is indicative of the direction of the secondary light beam Br. out Since the secondary ray Br results from the reflection of the original ray B on the probe P, the detected direction indicates the deformation of the probe P and thus the surface or subsurface features of the sample S. Accordingly, the signal analysis module AM ​​outputs the input signal S in and the output signal S out The output signal San, which indicates a characteristic of the sample S, is output based on the output signal S. Due to the fact that the controlled laser driver LDC drives the laser diode LD so that the laser diode LD generates a stable output beam B of controlled power, the output signal S out The noise can be minimized.

[0043] Figure 8 shows the results from a series of 400 measurements performed with an HL6320G TO-9 laser diode. For this experiment, the temperature of the laser diode was increased in 400 steps of 0.005°C from 23 to 25°C. In each of the 400 measurements, the power was swept from 0.2mW to 2.7mW. A quad cell was used to measure the noise level of the laser diode at each combination of temperature and power.

[0044] The left side of Figure 8 shows the measured noise level in arbitrary units. The vertical axis shows the number of measurements, and the horizontal axis shows the power in mW. The brightness shows the measured noise level. The right side of Figure 8 shows the temperature set for each measurement on the horizontal axis and the number of measurements on the vertical axis. It can be seen that it is difficult to reduce the position noise when operating at low power, for example below 0.3 mW. However, above this power level, the noise can be minimized by properly controlling the junction temperature. For example, if the power is 1.0 mW, the temperature should be maintained within the range of about 23.8 °C to about 24.5 °C. If the power is 2.5 mW, the temperature should be maintained within the range of about 23.3 °C to about 24.1 °C.

[0045] Although the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate many modifications and variations within the scope of the present invention, which is determined by the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single component or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope of the present invention.

Claims

1. A laser diode (LD), A driver (EPS) that supplies AC power having first and second controlled waveform characteristics of power parameters to the laser diode (LD), wherein the second controlled waveform characteristic is different from the first controlled waveform characteristic, configured to detect the optical output of the laser diode (LD), and controlling the first waveform characteristic to detect the optical output (P Ｍ ), and a first feedback component (FB1) having an optical power control module (OPCM) configured to maintain the optical output near a first target value (P Ｄ ); By detecting the voltage-current characteristics of the laser diode (LD), the temperature (T ＥＳＴ ) of the laser diode (LD) is estimated, and the estimated temperature (T ＥＳＴ ) is controlled by controlling the second waveform characteristic so as to be maintained near a second target value (T ＯＰＴ ), and a second feedback component (FB2) having a temperature control module (TCM) configured to maintain the temperature control module (TCM).

2. The first waveform characteristic controlled by the optical power control module (OPCM) of the first feedback component (FB1) is the amplitude of the power parameter, and the optical power control module (OPCM) is configured to control a change in amplitude having a sign equal to the sign of the difference (E Ｄ ) between the first target value (P Ｍ ) and the detected optical output (P Ｐ ). The second waveform characteristic controlled by the temperature control module (TCM) of the second feedback component (FB2) is a duty cycle, and the temperature control module (TCM) is the second target value (T ＯＰＴ ) and the estimated temperature (T ＥＳＴ ) and the difference (E Ｔ ) is configured to control a change in the duty cycle having a sign equal to the sign of the difference, the optical laser diode device according to claim 1.

3. The first waveform characteristic controlled by the optical power control module (OPCM) of the first feedback component (FB1) is the duty cycle of the power parameter, and the optical power control module (OPCM) is configured to control a change in the duty cycle having a sign equal to the sign of the difference (E Ｄ ) between the first target value (P Ｍ ) and the detected optical output (P Ｐ ). The second waveform characteristic controlled by the temperature control module (TCM) of the second feedback component (FB2) is amplitude, and the temperature control module (TCM) is the second target value (T ＯＰＴ ) and the estimated temperature (T ＥＳＴ ) and the difference (E Ｔ ) is configured to control a change in amplitude having a sign opposite to the sign of the difference, the optical laser diode device according to claim 1.

4. The optical laser diode device according to claim 2 or 3, wherein the amplitude to be controlled is the amplitude of the current supplied to the laser diode (LD).

5. The optical laser diode device according to claim 2 or 3, wherein the amplitude to be controlled is the amplitude of the voltage supplied to the laser diode (LD).

6. The optimal junction temperature at which the laser diode (LD) can generate an optical output having an output equal to the first target value (P Ｄ ), is calculated as the second target value (T ＯＰＴ ), and further includes an optimal temperature calculation module (OTCM) configured to calculate the optical laser diode device according to any one of claims 1 to 3.

7. Supplying AC power having first and second controlled waveform characteristics of power parameters to a laser diode (LD), wherein the second controlled waveform characteristic is different from the first controlled waveform characteristic, Detecting the optical output of the laser diode (LD), The optical output (P Ｍ ) detected by controlling the first waveform characteristic is maintained near a first target value (P Ｄ ), and Estimating the temperature (T ＥＳＴ ) of the laser diode (LD) by detecting the voltage-current characteristics of the laser diode (LD); Controlling the second waveform characteristic to maintain the estimated temperature (T ＥＳＴ ) near a second target value (T ＯＰＴ ), a method for operating a laser diode.

8. The first controlled waveform characteristic is the amplitude of the power parameter, The controlled change in the amplitude has the same sign as the sign of the difference (E Ｄ ) between the first target value (P Ｍ ) and the detected optical output (P Ｐ ). The second controlled waveform characteristic is the duty cycle, The controlled change of the duty cycle is equal to the sign of the difference (E ＯＰＴ between the second target value (T ＥＳＴ and the estimated temperature (T Ｔ ), the method according to claim 7).

9. The first controlled waveform characteristic is the duty cycle of the power parameter, and the controlled change in the duty cycle has the same sign as the sign of the difference (E Ｄ ) between the first target value (P Ｍ ) and the detected optical output (P Ｐ ). The second controlled waveform characteristic is the amplitude, The controlled change in the amplitude has a sign opposite to the sign of the difference (E ＯＰＴ between the second target value (T ＥＳＴ ) and the estimated temperature (T Ｔ ), according to the method of claim 8.

10. The method according to claim 8 or 9, wherein the amplitude to be controlled is the amplitude of the current supplied to the laser diode (LD).

11. The method according to claim 8 or 9, wherein the amplitude to be controlled is the amplitude of the voltage supplied to the laser diode (LD).

12. The method according to any one of claims 7 to 9, further comprising calculating an optimum junction temperature at which the laser diode (LD) can generate an optical output having an output equal to the first target value (P Ｄ ) as the second target value (T ＯＰＴ ).

13. A probe (P) having a tip (T) that is scanned over the surface of a sample (S), An input signal (S ｉｎ ) for inducing an acoustic signal to the probe (P), the tip (T), or the sample (S), and a signal generator (SG) that generates the input signal (S The laser diode device according to any one of claims 1 to 3, which generates a light beam (B) directed at the probe (P) and generates a secondary light beam (Br) reflected by the probe (P). An optical detector (DT) that outputs an output signal (S ｏｕｔ ) indicating the direction of the secondary light beam (Br); The input signal (S ｉｎ ), and a signal analysis module (AM) that outputs an output signal (San) indicating the characteristics of the sample (S) based on the output signal (S ｏｕｔ ), a scanning probe microscope (SPM) apparatus comprising the same.

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