JP6848217B2 - Laser diode module - Google Patents

Description

The present invention relates to a laser diode module using a laser diode such as a vertical cavity surface emitting laser (Vertical Cavity Surface Emitting LASER, abbreviated as VCSEL).

In recent years, with the miniaturization and cost reduction of the Fourier transform infrared spectrophotometer (FTIR), a laser diode module (hereinafter, LD module) using a vertical resonator surface emitting laser as an alternative to the HeNe laser as a reference light source. ) Is adopted.

The vertical resonator surface emitting laser is composed of a laser diode, has a reflecting mirror in the direction perpendicular to the semiconductor substrate, and emits light to the reflecting mirror. Vertical resonator surface emitting lasers are used because of their low cost and low power consumption.

However, the vertical resonator surface emitting laser has a large fluctuation amount of the oscillation wavelength with respect to temperature, and this fluctuation amount is the horizontal axis (wave number) of the spectrum acquired by the infrared detector provided in the Fourier transform infrared spectrophotometer. Means that fluctuates. Therefore, S (signal) / N (noise) deteriorates, and qualitative analysis of the spectrum becomes difficult. As a result, it is necessary to take measures such as suppressing the temperature fluctuation inside the apparatus, adjusting the temperature of the vertical resonator surface emitting laser, and sequentially performing wave number calibration.

In the Fourier transform infrared spectrophotometer, the S / N can be improved by increasing the amount of light of the IR light source and increasing the signal S. However, since the IR light source itself generates heat, the temperature inside the device rises. Then, the temperature of the vertical resonator surface emitting laser chip of the LD module is shaken by the ambient temperature and rises, and the oscillation wavelength fluctuates. Therefore, in order to stabilize the oscillation wavelength, the temperature of the LD module is generally controlled by the thermo module.

U.S. Pat. No. 6,654,125B2

However, due to the influence of the thermal resistance between the LD chip and the temperature sensor, the temperature of the LD chip could not be accurately monitored and was affected by the ambient temperature.

Further, there is known a method of acquiring the spectrum of a known sample and feeding back the fluctuation amount of the spectrum peak to correct the wavelength of the laser beam (Patent Document 1). However, the wavelength of the laser must be monitored at certain time intervals. In addition, a function for automatically switching known samples is also required, which makes the device expensive.

An object of the present invention is to provide a laser diode module capable of achieving a high level of temperature stability with a simple structure.

The laser diode module according to the present invention is a laser diode module which is a reference light source of a Fourier transformed infrared spectrophotometer in order to solve the above problems, and includes a pedestal, a laser element having a laser diode chip inside, and a laser element. A laser element block in which the laser element is incorporated and an opening is formed so that the pedestal is exposed to the surrounding environment by contacting the outer peripheral portion of the pedestal, and a laser element block provided in the laser element block and from the laser element. A lens holder to which a collimating lens that collimates light is adhered, a temperature adjusting element that adjusts the temperature of the laser element block, and a hole formed in the laser element block are inserted, and a part of the laser element block is exposed to the surrounding environment. The laser element block is provided with a temperature sensor for detecting the temperature of the laser element block, and the fluctuation amount of the oscillation wavelength of the laser element with respect to the temperature fluctuation of the ambient environment is 0.01 nm or less .

According to the present invention, the outer periphery of the pedestal of the laser element comes into contact with the laser element block, an opening is formed so that the pedestal is exposed to the ambient environment, and a part of the temperature sensor is exposed to the ambient environment. can temperature sensor detects the temperature of the laser element block of the surrounding environment, Runode the laser element and the temperature sensor are both affected by external temperature variations, controlling the degree of influence. Therefore, a high level of temperature stability can be achieved with a simple structure.

It is sectional drawing of the laser diode module of Example 1. FIG. It is a figure which shows the stability of the wavelength with respect to the temperature change of the laser diode module of Example 1. It is a block diagram of the Fourier transform infrared spectrophotometer provided with the laser diode module of Example 1.

Hereinafter, embodiments of the laser diode module of the present invention will be described in detail with reference to the drawings.

(Example 1)
First, the fluctuation of the oscillation wavelength allowed by the vertical resonator surface emitting laser is 0.02 nm or less, and assuming that the temperature coefficient of the laser diode chip is 0.06 nm / ° C, the laser diode temperature is about 0.3 ° C. It becomes the temperature fluctuation of. When the IR light source is used with an increased amount of light, the temperature inside the device rises from room temperature (about 20 ° C.) to a maximum of about 60 ° C.

Further, in the case of portable FTIR, the operating temperature range is around 0 ° C. to 40 ° C. in order to assume an outdoor environment. From the above, temperature stability is required in which the ambient temperature fluctuation is about 40 ° C. and the laser diode temperature is 0.3 ° C., that is, the temperature coefficient is 0.75% or less. The configuration of the embodiment for achieving this temperature stability will be described below.

FIG. 1 is a cross-sectional view of the laser diode module. The laser diode module shown in FIG. 1 includes a laser element 1, an LD block 2, a ring screw 3, a collimating lens 4, a lens holder 5, a thermo module 6, a heat dissipation plate 7, a thermistor 8, and screws 9 and 10. ..

The laser element 1 is a vertical resonator surface emitting laser composed of a 850 nm vertical single mode CAN type laser diode, has a reflector in the direction perpendicular to the substrate, and emits light to the reflector. The laser element 1 has a pedestal 1a as a base and three pins 1b. The outer circumference of the pedestal 1a is in contact with the LD block 2 corresponding to the laser element block of the present invention.

The LD block 2 is formed with an opening 2b so that the central portion of the pedestal 1a is exposed to the surrounding environment. The three pins 1b are composed of a positive electrode pin, a negative electrode pin, and a ground pin.

A hole 2a having a diameter larger than that of the opening 2b is formed in the LD block 2, and a screw groove 2c is formed on the outer periphery of the hole 2a. The main body of the laser element 1 is incorporated in the hole 2a, and the three pins 1b of the laser element 1 are exposed to the surrounding environment through the opening 2b.

The ring screw 3 is screwed into the screw groove 2c, and by screwing the ring screw 3 into the screw groove 2c, the laser element 1 and the pedestal 1a can be fastened to the LD block 2.

The collimating lens 4 is provided in the hole 2a and collimates the laser beam from the laser element 1. A collimating lens 4 is adhered to the lens holder 5, and a screw groove (not shown) is formed, and the screw groove is screwed into the screw groove 2c. The optical axis with the laser element 1 is adjusted using the screw groove 2c. A space A surrounded by the laser element 1, the LD block 2, and the lens holder 5 is formed.

The thermo module 6 corresponds to the temperature adjusting element of the present invention and is arranged below the LD block 2 to adjust the temperature of the LD block 2. The heat radiating plate 7 is arranged below the thermo module 6 and dissipates the heat of the thermo module 6 to the outside.

The thermistor 8 is inserted into the hole 2a formed in the LD block 2, and a part including the pin is exposed to the surrounding environment. The thermistor 8 corresponds to the temperature sensor of the present invention and detects the temperature of the LD block 2.

The screw 9 is inserted into the hole 2a formed in the LD block 2 and tightened to fix the lens holder 5. The screw 10 is inserted into the hole 2a formed in the LD block 2 and tightened to fix the ring screw 3.

As described above, according to the laser diode module of the first embodiment, the outer periphery of the pedestal 1a of the laser element 1 comes into contact with the LD block 2, and the opening 2b is formed so that the central portion of the pedestal 1a is exposed to the surrounding environment. Since a part of the thermistor 8 is exposed to the surrounding environment, the laser element 1 and the thermistor 8 are affected by the external temperature fluctuation, and the degree of the influence can be controlled. Therefore, a high level of temperature stability can be achieved with a simple structure.

FIG. 2 is a diagram showing wavelength stability with respect to a temperature change of the laser diode module of the first embodiment. In the example shown in FIG. 2, the amount of fluctuation of the oscillation wavelength when the environmental temperature is changed from 5 ° C. to 60 ° C. is shown.

As can be seen from FIG. 2, the fluctuation amount of the oscillation wavelength was 0.01 nm or less. Since the temperature coefficient of the LD chip is 0.06 nm / ° C., when converted to the LD temperature, it is 0.16 ° C. or less, and the temperature coefficient of 0.3% or less can be achieved.

FIG. 3 is a block diagram of a Fourier transform infrared spectrophotometer including the laser diode module of the first embodiment. The Fourier transform infrared spectrophotometer includes a laser element 1, an IR light source 21, a fixed mirror 22, a movable mirror 23, a beam splitter 24, a sample 25, a detector 26, mirrors 27 and 28, and a photodiode 29.

The IR light source 21 leads to the beam splitter 24 via the mirror 27. The beam splitter 24 splits the light from the mirror 27 into one light and the other light. One light is reflected by the fixed mirror 22 and returned to the beam splitter 24, the other light is reflected by the movable mirror 23 and returned to the beam splitter 24, and is combined by the beam splitter 24 to generate a first interference wave.

The first interference wave is sent to the detector 26 via the mirror 28 and the sample 25. The detector 26 performs a Fourier transform process based on the first interference wave. Since different interference waves are obtained depending on the position of the movable mirror 23, the detector 26 separates the signal intensity of the interference wave at each position into the light intensity of each wave number component by the Fourier transform process.

Further, the laser element 1 shown in FIG. 3 is the laser element 1 shown in FIG. 1 and is a reference light source of the Fourier transform infrared spectrophotometer. The laser beam from the laser element 1 is guided to the beam splitter 24 through the mirror 27. The beam splitter 24 splits the light from the mirror 27 into one light and the other light. One light is reflected by the fixed mirror 22 and returned to the beam splitter 24, the other light is reflected by the movable mirror 23 and returned to the beam splitter 24, and is combined by the beam splitter 24 to generate a second interference wave.

The second interference wave is detected by the photodiode 29 via the mirror 28. The output detected by the photodiode 29 is used for the analysis of the first interference wave detected by the detector 26.

As described above, the laser element 1 of the laser diode module of the first embodiment can be used for the Fourier transform infrared spectrophotometer.

In the present invention, as the laser element 1, a vertical resonator surface emitting laser having a reflecting mirror in the direction perpendicular to the substrate and emitting light to the reflecting mirror is used, but instead of this, the end surface of the semiconductor substrate is used. An end face emitting laser composed of a laser diode having a reflecting mirror and emitting light in a direction parallel to the substrate may be used.

The laser diode module according to the present invention can be applied to a Fourier transform infrared spectrophotometer and a portable Fourier transform infrared spectrophotometer.

1 Laser element 1b, 8a Pin 2 LD block 2a Hole 2b Opening 2c Thread groove 3 Ring screw 4 Collimating lens 5 Lens holder 6 Thermo module 7 Heat dissipation plate 8 Thermistor 9, 10 Screw 21 IR light source 22 Fixed mirror 23 Movable mirror 24 Beam Splitter 25 Sample 26 Detector 27,28 Mirror 29 Photodiode

Claims (3)

A laser diode module that is a reference light source for a Fourier transform infrared spectrophotometer.
A pedestal, a laser element having a laser diode chip inside, and
A laser element block in which the laser element is incorporated and an opening is formed so as to come into contact with the outer peripheral portion of the pedestal and expose the pedestal to the surrounding environment.
A lens holder provided in the laser element block and adhered with a collimating lens that collimates the light from the laser element.
A temperature adjusting element that adjusts the temperature of the laser element block, and
A temperature sensor that is inserted into a hole formed in the laser element block, is arranged so that a part of the laser element block is exposed to the surrounding environment, and detects the temperature of the laser element block.
Equipped with a,
A laser diode module characterized in that the amount of fluctuation of the oscillation wavelength of the laser element with respect to the temperature fluctuation of the ambient environment is 0.01 nm or less. The laser diode module according to claim 1, wherein said laser device, characterized by comprising a vertical cavity surface emitting laser. The laser diode module according to claim 1 or 2, wherein the laser element comprises an end face emitting laser.

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