JP2011054664A - Etalon filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a laser device to be used, even in the case of occurrence of an angle error in mounting. <P>SOLUTION: An etalon filter is used for the laser device whose atmospheric temperature can be changed by a temperature controller, and disposed in a predetermined path of laser light emitted by the laser device. The etalon filter is formed from a crystal member, and in the etalon filter, an incident surface, on which the laser light is made to be incident, is formed in parallel with a C axis of the crystal. The etalon filter is constituted so that the C axis is parallel with or orthogonal to a direction of an incident polarized wave of the laser light. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an etalon filter used in a laser device.

  Conventionally, a laser apparatus includes a semiconductor laser, an optical system that collimates laser light emitted from the semiconductor laser, a beam splitter that divides the laser light into two systems, and a predetermined wavelength for one of the divided laser lights. This is mainly composed of a Fabry-Perot resonator that resonates and a photodetector to which the laser light is incident.

  In the laser device configured as described above, a structure using two reflectors for a Fabry-Perot resonator is known. The Fabry-Perot resonator having this structure is required to have high installation accuracy of the two reflecting plates. For example, there is a problem in that the light transmission characteristics of the laser light change unless the two reflectors are installed with a parallelism in seconds (for example, see Patent Document 1).

Therefore, a laser apparatus using an etalon filter instead of the Fabry-Perot resonator has been proposed. This laser device incorporates a semiconductor laser module in which the semiconductor laser, optical system, beam splitter, etalon filter, and photodetector are modularized.
The etalon filter used in this semiconductor laser module is made of quartz or quartz (see, for example, Patent Document 2). For example, when quartz is used for the etalon filter, the C axis of the quartz is parallel to the incident direction of the laser light. It is formed as follows.
Such an etalon filter can be mounted on a semiconductor laser module while maintaining parallelism by parallelizing the incident side surface and the emission side surface of the laser light.

Japanese Patent No. 283068 JP 2003-004940 A

However, in the semiconductor laser module having such a structure, the angle of the etalon filter is adjusted so that light of wavelength λ can be monitored before the etalon filter is fixed to the substrate used in the module. In some cases, the etalon filter cannot be removed and the entire module may be discarded.
This is because the graph showing the relationship between the wavelength and transmittance used at a predetermined temperature condition of the etalon filter mounted as a module does not match the graph when the etalon filter is mounted at the normal position, and the desired This is because it becomes impossible to use the laser device so as to emit laser light at the performance to be performed, particularly at the reference wavelength.
It is also conceivable to reattach the etalon filter by adjusting the attached angle. However, since the etalon filter is already fixedly mounted, there is a problem that the angle cannot be changed.

  Accordingly, an object of the present invention is to provide an etalon filter that solves the above-described problems and enables the laser device to be used even if an angular error occurs in mounting.

  In order to solve the above-mentioned problems, the present invention is an etalon filter used in a laser device whose ambient temperature can be changed by a temperature control device and disposed in a predetermined path of laser light emitted by the laser device. The incident surface is made of a quartz member, and the incident surface on which the laser beam is incident is formed parallel to the C axis of the quartz crystal.

According to such an etalon filter, since the incident surface of the laser beam is formed in parallel with the C axis of the crystal, an error occurs in the mounting angle due to the mounting, and the wavelength and transmittance used under a predetermined temperature condition. Even if the graph showing the relationship with the etalon filter does not match the graph when the etalon filter is mounted at the normal position, the wavelength is shifted by adjusting the ambient temperature with the temperature control device provided in the laser device. The graph showing the relationship with the transmittance can be matched or approximated to the graph when the etalon filter is mounted at the normal position.
Thereby, even if an error occurs in the mounting angle due to the mounting of the etalon filter, the module can be used without being discarded.

It is a conceptual diagram which shows an example of the state which mounted the etalon filter which concerns on 1st embodiment of this invention in the module used for a laser apparatus. It is a conceptual diagram which shows an example of the etalon filter which concerns on 1st embodiment of this invention. It is a graph which shows the relationship between the transmittance | permeability in predetermined temperature, and a frequency. It is a conceptual diagram which shows an example of the etalon filter which concerns on 2nd embodiment of this invention.

  The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described in detail with reference to the drawings as appropriate. Note that each component is exaggerated for easy understanding of the state.

(First embodiment)
FIG. 1 is a conceptual diagram showing an example of a state in which the etalon filter according to the first embodiment of the present invention is mounted on a module used in a laser device. FIG. 2 is a conceptual diagram showing an example of an etalon filter according to the first embodiment of the present invention. FIG. 3 is a graph showing the relationship between transmittance and frequency at a predetermined temperature.
As shown in FIG. 1, an etalon filter 10A according to a first embodiment of the present invention is used in a laser device (not shown) whose ambient temperature can be changed by a temperature control device 200. Laser light to be irradiated (hereinafter referred to as “light”) is used by being mounted on a predetermined path of LT.

  In this laser apparatus, the etalon filter 10A of the present invention is used by being incorporated in a module 100 on which various optical components are mounted when mounted on a predetermined light path.

First, an example of the configuration of the module 100 will be described.
The module 100 mainly includes optical components such as an etalon filter 10A, a semiconductor laser 20, optical lenses 30a to 30e, an optical fiber 40, a beam splitter 50, a first detector 60, and a second detector 70.

  In this module 100, a semiconductor laser 20, an etalon filter 10A, optical lenses 30a to 30d, an optical fiber 40, a beam splitter 50, and a second detector 70 are linearly arranged, and the beam splitter 50, the optical lens 30e, The first detector 60 is arranged linearly.

  Here, optical lenses 30 a and 30 b are arranged between the semiconductor laser 20 and the optical fiber 40. The light LT emitted from the semiconductor laser 20 is collected on the optical fiber 40 via the optical lenses 30a and 30b.

On the other hand, optical lenses 30c and 30d are disposed between the semiconductor laser 20 and the second detector 70 in a direction opposite to the light LT, and a beam splitter is disposed between the optical lenses 30c and 30d. 50 and the etalon filter 10A are disposed.
In such an arrangement, the light LT emitted from the semiconductor laser 20 is converted into parallel light by the optical lens 30 c and branched in two directions by the beam splitter 50.
One of the branched lights LT is incident on an etalon filter 10A (see FIGS. 1 and 2) made of quartz that is placed so that the C-axis is orthogonal to the transmission direction of the light LT.

The light LT having a wavelength which is incident on the etalon filter 10A and resonates is condensed on the second detector 70 made of, for example, a photodiode via the optical lens 30d.
The other branched light is condensed on the first detector 60 made of, for example, a photodiode via the optical lens 30e, and the oscillation light power is monitored.

  By comparing the output value of the first detector 60 and the output value of the second detector, the wavelength of the semiconductor laser 20 is measured, and the temperature and injection current of the temperature control device 200 described later are changed. The wavelength can be controlled.

  The temperature control device 200 uses, for example, a Peltier element, and can raise or lower the ambient temperature. This temperature control device 200 is provided in the lower part of the module 100, and can adjust the temperature around the etalon filter 10A.

The etalon filter 10A mounted on such a module 100 is made of quartz.
As shown in FIG. 2, the etalon filter 10 </ b> A has a configuration in which the C axis, which is the optical axis of crystal, is orthogonal to the incident direction of the incident light LT. That is, in the etalon filter 10A, the incident surface 11 on which the light LT is incident is formed in parallel with the C axis of the crystal.
Specifically, the C axis of the etalon filter 10A is parallel to the direction of the incident polarization NHP of the light LT incident on the etalon filter 10A. At this time, as for the other axes of the etalon filter 10A, the A axis is parallel to the incident direction of the light LT, and the B axis is orthogonal to the A axis and the C axis. In addition, the other axis of the etalon filter 10A may be configured such that the B axis is parallel to the incident direction of the light LT and the A axis is orthogonal to the B axis and the C axis.

The etalon filter 10A configured as described above can be used even when the mounting angle is deviated.
Here, the principle of adjustment when the mounting angle of the etalon filter 10A is shifted will be described.
As shown in FIG. 3A, the transmittance and wavelength when the mounting angle of the etalon filter 10A is 0 ° in advance, that is, when the incident surface 11 of the etalon filter 10A is mounted perpendicular to the incident direction of the light LT. Create a transmission waveform graph showing the relationship.
Using this graph of the transmission waveform, the value of the wavelength at the transmission intensity of light having a predetermined value is determined.
For example, the wavelength when the transmittance corresponding to the predetermined transmission intensity and the graph of the transmission waveform intersect is used as a reference. The reference wavelength is λ = a.

Here, it is assumed that the attachment angle of the etalon filter 10A is deviated from the light incident direction. For example, as shown in FIG. 3B, the case where the mounting angle shift is 1 ° will be described as an example.
A transmission waveform graph showing the relationship between the light transmittance and the wavelength when the mounting angle is shifted by 1 ° is created. Here, it is assumed that the wavelength when the transmittance corresponding to the predetermined transmission intensity intersects with the graph of the transmission waveform when shifted by 1 ° is λ = B.

The graph of the transmission waveform when the mounting angle is shifted by 1 ° is compared with the graph of the transmission waveform as a reference, and it is confirmed that the two graphs do not match.
This shows that the graph of the transmission waveform used as a reference is in a shifted state due to the mounting angle being shifted by 1 °.
At this time, the reference wavelength λ = A in the reference transmission waveform graph is shifted to the wavelength λ = B because the mounting angle is shifted by 1 °.
The shift amount at this time is expressed by Equation 1.
Shift amount Δλ = | A−B |

Here, the optical length L of the entrance surface 11 and the exit surface, which are two reflecting surfaces with respect to the temperature of the etalon filter 10A, can be approximated by Equation 2.
L = n0 × L0 × (1 + ΔT × (α + (1 / n0) × (dn / dT))) Equation 2
Where n0 is the refractive index of the crystal at room temperature T0, dn / dT is the amount of change in refractive index with respect to temperature, ΔT is the amount of temperature change from room temperature T0, L0 is the physical length of the etalon filter 10A at room temperature T0, and α is a line. Indicates the expansion coefficient.
Further, the transmission intensity T (λ) of the etalon filter 10A can be expressed by Expression 3 and Expression 4.
T (λ) = (1−R) ² / ((1−R) ² + 4 × R × sin ² (σ / 2)) Equation 3
σ = 4πL / λ Equation 4
Here, R indicates the reflectance of the incident surface and the exit surface.

  Using these equations, the wavelength B when the transmittance corresponding to the predetermined transmission intensity and the graph of the shifted transmission waveform intersect is used as the reference transmission waveform graph and the transmission corresponding to the predetermined transmission intensity. The temperature to be adjusted is determined so that the wavelength A when the rate intersects is obtained.

For example, using these equations, the shift amount of the wavelength with respect to the temperature is calculated, and this is compared with the shift amount obtained by Equation 1, and the temperature to be adjusted is set.
For example, the shift amount per 1 ° C. in the etalon filter 10A of the present embodiment is 13 pm / ° C. (pm: picometer).
Thus, after the etalon filter 10A is attached, the laser device can be used at the reference wavelength λ = A by adding the temperature for adjustment set from the obtained shift amount.

Thus, when the temperature is adjusted by the temperature control device 200, the shifted transmission waveform graph matches the reference transmission waveform graph. Therefore, by using the temperature control device 200 provided in the laser device, the module 100 can be used without being discarded even when the attachment angle of the etalon filter 10A is deviated.
For example, in a conventional etalon filter formed so that the C-axis of quartz is parallel to the incident direction of laser light, the wavelength shift amount with respect to temperature is 5 pm / ° C., and the present invention is smaller than the conventional one. It can be seen that a large correction effect can be obtained by adjusting the temperature. Further, in the conventional etalon filter formed of quartz, the shift amount of the wavelength with respect to the temperature is 10 pm / ° C., and it can be seen that the present invention can obtain a large correction effect with a small temperature adjustment as compared with the conventional case. In addition, since the thermal conductivity of quartz is approximately 2.5 times or more that of quartz, there is an effect of improving the responsiveness and stability of the etalon filter characteristics with respect to temperature adjustment.

(Second embodiment)
FIG. 4 is a conceptual diagram showing an example of an etalon filter according to the second embodiment of the present invention.
As shown in FIG. 4, the etalon filter 10B according to the modification of the second embodiment of the present invention is different from the first embodiment in that the C axis is orthogonal to the direction of the incident polarization NHP. Different.
As described above, in the etalon filter 10B according to the modification of the second embodiment of the present invention, the C axis is orthogonal to the direction of the incident polarization NHP. That is, in the etalon filter 10B, the incident surface 11 on which the light LT is incident is formed in parallel with the C axis of the crystal.
For example, the shift amount per 1 ° C. in the etalon filter 10B of the present embodiment is 15 pm / ° C. (pm: picometer).
Even if comprised in this way, there exists an effect similar to 1st embodiment.

DESCRIPTION OF SYMBOLS 100 Module 200 Temperature control apparatus 10A, 10B Etalon filter 11 Incident surface 20 Semiconductor laser 30a-30e Optical lens 40 Optical fiber 50 Beam splitter 60 1st detector 70 2nd detector

Claims (1)

An etalon filter used in a laser device whose ambient temperature can be changed by a temperature control device and disposed in a predetermined path of laser light emitted by the laser device,
An etalon filter formed from a quartz member, wherein an incident surface on which laser light is incident is formed in parallel with the C-axis of the quartz crystal.

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