JP5088866B2 - Temperature controller for wavelength locker, wavelength locker and optical module - Google Patents

Description

  The present invention relates to an element structure of a wavelength detection element for optical communication, and more particularly to a temperature control device for an independent temperature control type wavelength locker, a wavelength locker provided with the temperature control device, and an optical module provided with the wavelength locker. .

In the development of wavelength division multiplexing optical communication technology (WDM), the oscillation wavelength of a semiconductor laser for communication is permanently within +/− 2 pm at intervals of 100 GHz or 50 GHz centering on 193.1 THz (1552.52 nm). It is desired to stabilize.
In recent years, in response to such technical requirements, a CW (continuous oscillation) laser module for communication is equipped with a functional element that detects a wavelength and an optical output, which is called a wavelength locker. (For example, see Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1).

The structure of a typical wavelength locker is shown in FIGS. In these wavelength lockers, as shown in FIG. 10, generally, light (laser beam) emitted from a laser element (not shown) is converted into a parallel beam by a beam splitter 3 or the like, and the beam diameter is divided into two equal parts. The etalon element 5 is inserted, and the light 7A that has passed through the etalon element 5 and the light 7B that has not passed through the etalon element 5 are received by the dedicated photodiodes 1 and 2, respectively. , Or as shown in FIG. 11, light (laser beam) 7 emitted from a laser element (not shown) is cut out for light output and wavelength detection by a beam splitter 3 or the like, and an etalon element is placed in one optical path. 5 is inserted, and the light 7A that has passed through the etalon element 5 and the light 7B that has not passed through the etalon element 5 are respectively converted into dedicated photodiodes. It received 1, 2, taking a method for detecting the wavelength and light output from the output of the photodiodes 1 and 2. Here, the photodiode 1 is a wavelength detection photodiode, and the photodiode 2 is a light output monitoring photodiode.
From the output of the photodiode (PD) 1 for wavelength detection, a photocurrent signal that periodically oscillates with respect to the wavelength as shown in FIG. 12 can be detected.

  As a wavelength fixing method (control method), an oscillation wavelength detection photodiode at that time under a specific wavelength generation condition (a condition in which a target wavelength is oscillated by setting a control temperature and a drive current value of the laser diode) In general, the wavelength is fixed by applying negative feedback control of the control temperature of a laser diode (not shown) so that the detection current from 1 becomes constant.

  In that case (for example, the method described in Non-Patent Document 1), the wavelength detection signal current value generated through the etalon element 5 with respect to the target wavelength is always the current as shown in FIG. In the region connecting the maximum value and the minimum value, it should be in the region of a single decrease of about 85% or a single increase around the point of (maximum value−minimum value) / 2.

  This is because, in the characteristics shown in FIG. 13, the wavelength range that can be selected is very wide in the region near the apex and the lowest point of the current waveform, although the wavelength detection current value is the same. This is because it cannot be controlled. For this reason, when the wavelength locker is manufactured, particularly when the etalon element 5 is mounted, the mounted etalon element 5 is slightly rotated to finely adjust the incident angle of the light incident on the etalon element 5, It is necessary to adjust the transmission characteristics. However, changing the incident angle of the light incident on the etalon element 5 also changes the FSR (the output period of the etalon element 5) as it is, so that the etalon element prepared with characteristics of 100 GHz intervals or 50 GHz intervals is used. 5, the output cycle is slightly shifted. Therefore, when only one wavelength is fixed, sufficient wavelength control and wavelength locker can be manufactured by the above method. However, a tunable laser (for example, a DBR (distributed black reflector) laser) or a multi-channel laser (wavelength It is difficult to fix the wavelength using the etalon element 5 in an element whose wavelength changes in a wide band such as a selective laser.

  In recent years, as described in Non-Patent Document 1 in order to solve this difficult problem, in a wavelength selective laser or the like, two temperature controllers (Peltier elements) are mounted in the same module, and the temperature of the etalon element is made independent. Thus, a technique that can stably use the period of the etalon element 5 in a wide band has been proposed.

JP 2004-153176 A Y. Yokoyama et al., “Multiwavelength locker integrated wide-band wavelength-selectable light source module”, IEEE Photonics Tech.Let., Vol.15, No.2, 2003. "Tunable LD Module with Wavelength Looker-FLD2F15CA-K" FUJITSU COMPOUND SEMICONDUCTOR, INC., March 2001, p.1-5 N. Fujiwara et al., “Tuning range enhanced self-phase adjustment in mode-hop free short-active-region DBR laser”, IEEE J. Sel. Topics Quantum Electron. Vol.11, No.5, pp.939- 944, 2005.

  However, even with the improvement technique described in Non-Patent Document 1 described above, when the use environment temperature fluctuates, the ambient temperature inside the laser module changes. Therefore, the control temperature of the etalon element 5 and the etalon element 5 There is a problem to be solved in that a difference occurs between the actual temperature and the wavelength resolution ability that can be controlled is reduced.

  In the wavelength locker that independently controls the temperature of the etalon element part, the above problem that the actual temperature of the etalon element is affected by the change of the outside air temperature (environment temperature) and its transmission characteristics are changed. This can be solved by changing the mounting method of the temperature detection resistor element (thermistor element) in the element section, and the wavelength locker can be provided which controls the temperature of the etalon element with high accuracy and is not affected by the outside air temperature fluctuation.

  As an example of the mounting method of the thermistor element, as in Patent Document 1, by defining the thickness range of the insulating plate that is the same material as the etalon element, a temperature monitor that follows the change in the etalon temperature with respect to the change in the outside air temperature Thus, stable temperature control is possible within a wavelength shift amount of ± 0.5 pm of the etalon characteristic.

  However, as a matter of fact, the insulating plate that enables stable temperature control as described above is affected not only by the thickness but also by the width and length. Considering the aspect ratio of the insulating plate in particular, it is considered that the width is more susceptible to changes in environmental temperature than the length. That is, it is necessary to consider not only the thickness of the insulating plate but also the width dependency as in the prior art.

  FIG. 14 is a sectional view of the etalon element and the thermistor element mounting portion of the wavelength locker. In FIG. 14, 6 is a wavelength locker substrate, 5 is an etalon element, 8 is a thermistor element mounting insulating plate, and 4 is a thermistor element. The etalon element 5 is mounted on the wavelength locker substrate 6. The insulating plate 8 is mounted on the wavelength locker substrate 6 adjacent to the etalon element 5. The thermistor element 4 is mounted on the insulating plate 8. The insulating plate 8 and the thermistor element 4 constitute a wavelength locker temperature control device.

The thickness (height) of the etalon element 5 is t1, the width is w1, the thickness (height) of the insulating plate 3 is t2, and the width is w2. Here, the etalon element 5 and the insulating plate 8 are fixed to the wavelength locker substrate 6 by some adhesive (epoxy resin, solder, etc.). Here, the insulating plate 8 is assumed to have the same material as the etalon element 2 or an equivalent thermal conductivity (unit: W / K / m). The material of the etalon element 5 is, for example, quartz or fused quartz. Examples of the material used for the insulating plate 8 include ceramics such as alumina (Al ₂ O ₃ ) having the same thermal conductivity when the etalon element 5 is quartz, for example, in addition to the same crystal or fused quartz as the etalon element 5. Is mentioned. As the material of the wavelength locker substrate 6, a material having high thermal conductivity, such as aluminum nitride (AlN), is used.

In FIG. 14, the laser beam passes near the central portion (width w1 / 2, thickness t1 / 2) of the etalon element 5. In order to control the temperature of the central portion of the etalon element 5 so that the temperature of the central portion of the etalon element 5 is always constant even when the environmental temperature changes, the temperature of the thermistor element 4 on the insulating plate 8 is Need to follow the temperature. Here, when the environmental temperature Ta the temperature was controlled to a constant wavelength locker substrate 6 changes to 70 ° C. from 0 ° C., the temperature variation in the central portion of the etalon device 5 and [Delta] T _E.

FIG. 15A is a schematic view showing the temperature distribution in the insulating plate 8 with respect to the distance from the wavelength locker substrate 6 when the temperature of the wavelength locker substrate 6 is constant and the environmental temperature Ta is changed. In FIG. 15A, the solid line is Ta = 70 ° C., and the dotted line is Ta = 0 ° C. At this time, the temperature variation on the uppermost surface of the insulating plate 8 (the surface on which the thermistor element 4 is mounted) is defined as ΔT. If the temperature of the thermistor element 4 follows the temperature of the etalon element 5, then ΔT = ΔT _E. FIG. 15B shows a relative temperature change of the thermistor element 4 with respect to the etalon element 5 when the environmental temperature changes.

If ΔT> ΔT _E as shown in (i) of FIG. 15B, for example, when the environmental temperature is 70 ° C., a temperature higher than the actual temperature (the temperature of the etalon element 5) is observed, and conversely, the environmental temperature At 0 ° C., a temperature lower than the actual temperature is observed. Therefore, the thermistor relative temperature shows an in-phase change with respect to the environmental temperature change, and the change amount is ± 0.5 × (ΔT−ΔT _E ) (° C.). As shown in (ii) of FIG. 15B, when ΔT <ΔT _E , the phase is opposite to that of (i).

FIG. 16 is a diagram showing a change in ΔT with respect to a change in the thickness t2 of the insulating plate 8 using the width w2 as a parameter. The etalon element 5 and the insulating plate 8 are both made of quartz, and are placed so that the c-axis of the quartz is perpendicular to the wavelength locker substrate 6. The width of the etalon element 5 was 1 mm and the thickness was t1 = 2 mm, and the length of the insulating plate 8 was approximately the same as that of the etalon element 5. An epoxy resin (adhesive layer thickness 100 μm) was used as an adhesive for adhering the etalon element 5 and the insulating plate 8 to the wavelength locker substrate 6. As shown in FIG. 16, ΔT increases as the thickness t2 increases, and ΔT decreases as the width w2 increases. This indicates that when the thickness t2 is increased, it is easily affected by the environmental temperature, and when the width w2 is widened, it is easily affected by the temperature of the wavelength locker substrate 6 (it is less susceptible to the environmental temperature). The dotted line in FIG. 16 indicates ΔT _E , which is 0.77 ° C. here.

  FIG. 17 shows the change in the relative temperature of the thermistor element 4 and the change in the monitor wavelength calculated from the change in the environmental temperature. The thickness t2 of the insulating plate 8 is constant (1.1 mm) and the width w2 is 0.5 mm ( It is the figure compared with (circle) of FIG. 16, and 1 mm (circle of FIG. 16). In FIG. 17, the solid line a indicates a width w2 of 0.5 mm, and the dotted line b indicates a width w2 of 1 mm. When the width w2 is 0.5 mm, the fluctuation of the monitor wavelength is within ± 0.5 pm. However, when the width w2 is 1 mm, a change as shown in (ii) of FIG. A wavelength shift of ± 0.7 pm occurs at 15 ° C. and the wavelength. Here, 600 MHz / ° C. was used as the frequency temperature characteristic of the etalon element 5 and 8 pm / 1 GHz was used as the wavelength / frequency conversion. Thus, even if only the thickness t2 of the insulating plate 8 is defined, the stable control within the wavelength shift amount ± 0.5 pm becomes difficult due to the change of the width w2.

  Therefore, as a means for solving the above problems, in the present application, in the wavelength locker that independently controls the temperature of the etalon element portion, the actual temperature of the etalon element is affected by the change of the outside air temperature (environment temperature), and the transmission characteristics thereof are changed. A design guideline that takes into account not only the thickness but also the width of an insulating plate for mounting a temperature detection element such as a temperature detection resistance element (thermistor element) of the etalon element portion when changing is shown.

  Specifically, the wavelength locker temperature control device, wavelength locker, and optical module of the present invention have the following characteristics.

That is, the wavelength locker temperature control device of the first invention is a wavelength locker temperature control device adjacent to an etalon element mounted on a wavelength locker substrate,
An insulating plate mounted on the wavelength locker substrate adjacent to the etalon element, and a temperature detecting element mounted on the insulating plate,
The insulating plate has the same thermal conductivity as the etalon element;
The etalon element and the insulating plate are arranged such that the material thereof is quartz and the c-axis of the quartz is perpendicular to the wavelength locker substrate,
The width and thickness of the insulating plate are set so that the temperature fluctuation on the surface of the insulating plate on which the temperature detecting element is mounted follows the temperature fluctuation at the center of the etalon element when the environmental temperature changes. And
When the temperature variation at the center of the etalon element is ΔT _E and the temperature variation on the surface of the insulating plate on which the temperature detecting element is mounted is ΔT, the width and thickness of the insulating plate are ΔT = ΔT _{E In the} temperature control device for wavelength locker set so that ΔT follows ΔT _E within a range of ± 0.2 ° C.
When the width of the etalon element is w1, the thickness is t1, the width of the insulating plate is w2, and the thickness is t2,
The width w2 and thickness t2 of the insulating plate are either w2 / w1 or t2 / t1 where w2 / w1 obtained by normalizing w2 by w1 and t2 / t1 obtained by normalizing t2 by t1. Is a first line representing the relationship between w2 / w1 and t2 / t1 where ΔT = ΔT _E + 0.2 ° C. and ΔT = ΔT _E −0.2 ° C. It is set so that it may become in the range enclosed by the 2nd line showing the relationship of w2 / w1 and t2 / t1.

The wavelength locker second invention is characterized in that it has a temperature control device for a first shot Ming wavelength locker.

Further, the optical module of the third invention, an optical module, characterized in that it has a wavelength locker of the second aspect of the invention, a semiconductor laser.

  According to the wavelength control device for wavelength locker of the present invention, the temperature of the etalon element is obtained by using the insulating plate for mounting the temperature detection element such as the temperature detection resistance element (thermistor element) having the same thermal conductivity as the etalon element. Can be controlled with high accuracy, and a wavelength locker and an optical module can be realized in which the element operation is not affected by changes in the outside air temperature.

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

  The configuration of the wavelength locker etalon element and the thermistor element mounting portion in each of the following embodiments is the same as the configuration of FIG. 14 described above, and therefore, the illustration and detailed description thereof will be omitted with reference to FIG. In addition, this wavelength locker can control the temperature of the etalon element 5 part independently using the thermistor element 4 for temperature control. That is, this wavelength locker is provided with a temperature control element (not shown) such as a Peltier element under the wavelength locker substrate 6, and the detected temperature of the thermistor element 4 mounted on the insulating plate 8 (the temperature of the etalon element 5). ), The temperature of the etalon element 5 is controlled by controlling the temperature control element (Peltier element). The temperature control of the etalon element 5 is performed independently of the temperature control of the semiconductor laser by other temperature control elements (Peltier elements).

  In the wavelength locker in each of the following embodiments, the etalon element 5 has a width w1 = 1 mm and a thickness t1 = 2 mm. In addition, since the length of the insulating plate and the etalon is sufficiently longer than the width, the influence on the temperature change is small enough to be ignored. Therefore, the length of the insulating plate 8 is approximately the same as that of the etalon element 5.

In addition, the design of the width w2 and the thickness t2 of the insulating plate 8 of the wavelength locker in each of the following embodiments was performed using simulation software. First, use the simulation software “Solid Works” (manufactured by Solid Works Japan Co., Ltd.) to create a model for calculation of dimensions, materials, etc., and then the simulation software “Cosmos Works” (manufactured by Solid Works Japan Co., Ltd.) ) To calculate the width w2 and thickness t2 of the insulating plate 8 from the heat conductivity, heat transfer coefficient, and heat radiation rate.
Here, the thermal conductivity corresponds to the rate (speed) at which the inside of the material conducts heat, and the heat transfer rate corresponds to the rate (speed) at which heat is transferred from the outside air (air) to the material.
The following was used for thermal conductivity (unit: W / m / K).
That is, BK7; 1.4, AlN (aluminum nitride); 150, quartz (c-axis direction); 10.4, quartz (perpendicular to c-axis); 6.2 were used.
The heat transfer coefficient was 10.4 (W / m ² / K), and the heat radiation coefficient was 0.92.

<First Embodiment>
FIG. 1 is the same as FIG. 16, and in this embodiment also, the material (material) of the etalon element 5 and the insulating plate 8 is quartz, and the c-axis of the quartz is perpendicular to the wavelength locker substrate 6. Are disposed on the wavelength locker substrate 6. In FIG. 1, the hatched portion indicates a range of ΔT = ΔT _E ± 0.2 ° C. As described above, the material of the insulating plate 8 may be alumina (Al ₂ O ₃ ) having a thermal conductivity equivalent to that of the etalon element 5 (quartz).

  FIG. 2 shows a first embodiment of the present invention. 2 normalizes the relationship between the width w2 and the thickness t2 of the insulating plate 8 included in the shaded temperature range of FIG. 1 by the width w1 and the thickness t1 of the etalon element 5 (w2 / w1, t2 / t1).

In FIG. 2, the dotted line indicates the relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) when ΔT = ΔT _E. For example, the optimum thickness t2 when the width w2 is 0.2 mm, 0.5 mm, 0.7 mm, and 1 mm is about 0.6 mm, about 1.1 mm, about 1.3 mm, and about 1.6 mm, respectively. . In FIG. 2, the solid line 1 as the first line is ΔT = ΔT _E + 0.2 ° C., and the solid line 2 as the second line is the relationship between w 2 and t 2 when ΔT = ΔT _E −0.2 ° C. (w 2 / W1 and t2 / t1), and by using w2 and t2 in the range surrounded by the solid lines 1 and 2, the thermistor element 4 mounted on the insulating plate 8 The temperature can be detected with high accuracy. Accordingly, the temperature of the etalon element 5 is accurately controlled by a temperature control element (Peltier element) (not shown) installed under the wavelength locker substrate 6 based on the temperature detected by the thermistor element 4. For example, when the reference temperature of the etalon element 5 is set to 40 ° C., if the temperature of the etalon element 5 rises from 40 ° C. to 0.2 ° C. due to the influence of the outside air temperature (environmental temperature), this implementation follows the temperature rise. The thermistor element 4 on the insulating plate 8 in the form detects the temperature of the etalon element 5 with high accuracy. The etalon element 5 is cooled by the temperature control element (Peltier element) based on the detected temperature, and the temperature of the etalon element 5 is maintained at 40 ° C. As a result, stable and highly accurate temperature control within a monitor wavelength deviation of ± 0.5 pm can be performed. For example, when the width w2 of the insulating plate 8 is 0.2 mm, the thickness t2 of the insulating plate 8 may be set between approximately 0.4 mm and 0.7 mm. When the width w2 is 0.5 mm, the thickness t2 is between 0.8 and 1.3 mm. When the width w2 is 0.7 mm, the thickness t2 is between 1.0 and 1.6 mm. Further, when the width w2 is 1 mm, the thickness t2 may be set between 1.2 and 1.9 mm.

  In a region where the size of the insulating plate 8 exceeds the size of the etalon element 5 (1 <w2 / w1, 1 <t2 / t1), radiation from the upper wall and side wall of the module, etc. from outside the wavelength locker substrate 6 and the ambient temperature Therefore, it is not realistic to use the insulating plate 8 having such a size. Also, in the region of w2 / w1 <0.5, it is possible to select the insulating plate 8 having such a size considering that the size of a general small thermistor element is about 0.5 mm square. Not realistic.

In this embodiment, an epoxy resin is used as an adhesive for bonding the etalon element 5 and the insulating plate 8 to the wavelength locker substrate 6. However, another adhesive having a thermal conductivity equivalent to this epoxy resin is used. But the result is the same. As described above, alumina (Al ₂ O ₃ ) having a thermal conductivity equivalent to that of the etalon element 5 (quartz) may be used as the material of the insulating plate 8.

<Second Embodiment>
FIG. 3 shows a second embodiment of the present invention. FIG. 3 shows the first embodiment (the etalon element 5 and the insulating plate 8 are both made of quartz, and the etalon element 5 and the insulating plate 8 so that the c-axis of the crystal is perpendicular to the wavelength locker substrate 6. And the thickness of the epoxy resin adhesive layer that adheres the etalon element 5 and the insulating plate 8 to the wavelength locker substrate 6 is reduced to about 10 μm (1/10 of the epoxy resin adhesive layer thickness of the first embodiment). The result is 1/200 of the thickness of the etalon element, which corresponds to the result when an adhesive means having high thermal conductivity such as soldering is used. Compared with FIG. 1 for the same size insulating plate 8, the adhesive layer thickness of the epoxy resin is reduced, and it appears that the thermal conductivity of the insulating plate 8 has increased, so ΔT decreases. However, ΔT _E also decreases from 0.77 ° C. to 0.46 ° C. In FIG. 3, the shaded area indicates a range of ΔT = ΔT _E ± 0.2 ° C., as in FIG.

FIG. 4 shows the relationship between the width w2 and the thickness t2 of the insulating plate 8 included in the temperature range of the shaded portion in FIG. In FIG. 4, the dotted line is ΔT = ΔT _E , the solid line 1 as the first line is ΔT = ΔT _E + 0.2 ° C., and the solid line 2 as the second line is ΔT = ΔT _E −0.2 ° C. The relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) is shown. By applying w2 and t2 in the range surrounded by the solid lines 1 and 2 in FIG. 4 to the insulating plate 8, the etalon element 5 is affected by the outside air temperature (environment temperature) as in the case of the first embodiment. When the temperature fluctuates, the thermistor element 4 on the insulating plate 8 according to the present embodiment accurately detects the temperature of the central portion of the etalon element 5 following the temperature fluctuation. Therefore, the temperature detected by the thermistor element 4 Based on the above, the temperature of the etalon element 5 is accurately controlled by a temperature control element (Peltier element) (not shown) installed under the wavelength locker substrate 6. As a result, stable and highly accurate temperature control within a monitor wavelength deviation of ± 0.5 pm can be performed.

  When w2 and t2 in the range surrounded by the solid lines 1 and 2 in FIG. 4 are compared with FIG. 1, the dotted lines almost coincide (especially in the region where w2 / w1 is 0.5 or more). For example, the optimum thickness t2 when the width w2 is 0.2 mm, 0.5 mm, 0.7 mm, and 1 mm is about 0.7 mm, about 1.2 mm, about 1.4 mm, and about 1.6 mm, respectively. . On the other hand, the allowable range of the thickness t2 with respect to the width w2 of the insulating plate 8 is increased by about 1.3 to 1.6 times by reducing the thickness of the adhesive layer of the epoxy resin as compared with the case where the thickness of the adhesive layer of the epoxy resin is 100 μm. It was enlarged. For example, when the width w2 is 0.2 mm, the thickness t2 is approximately between 0.6 and 1 mm, and when the width w2 is 0.5 mm, the thickness t2 is between 0.8 and 1.5 mm. When w2 is 0.7 mm, the thickness t2 may be set between 1.0 and 1.7 mm, and when the width w2 is 1 mm, the thickness t2 may be set between 1.1 and 2 mm. .

<Third Embodiment>
FIG. 5 shows a third embodiment of the present invention. Also in this embodiment, the materials of the etalon element 5 and the insulating plate 8 are both quartz. However, in this embodiment, the etalon element 5 and the insulating plate 8 are arranged so that the c-axis of the crystal is parallel to the wavelength locker substrate 6. Therefore, the thermal conductivity of the etalon element 5 and the insulating plate 8 in the direction perpendicular to the wavelength locker substrate 6 is about 3/5 of FIG. 2 (when the c-axis is perpendicular to the wavelength locker substrate 6). An epoxy resin (adhesive layer thickness 100 μm) was used as an adhesive for adhering the etalon element 5 and the insulating plate 8 to the wavelength locker substrate 6.

In FIG. 5, the dotted line is ΔT = ΔT _E , the solid line 1 as the first line is ΔT = ΔT _E + 0.2 ° C., and the solid line 2 as the second line is ΔT = ΔT _E −0.2 ° C. The relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) is shown. By applying w2 and t2 in the range surrounded by the solid lines 1 and 2 in FIG. 5 to the insulating plate 8, the etalon element 5 is affected by the outside air temperature (environment temperature) as in the case of the first embodiment. When the temperature fluctuates, the thermistor element 4 on the insulating plate 8 according to the present embodiment accurately detects the temperature of the central portion of the etalon element 5 following the temperature fluctuation. Therefore, the temperature detected by the thermistor element 4 Based on the above, the temperature of the etalon element 5 is accurately controlled by a temperature control element (Peltier element) (not shown) installed under the wavelength locker substrate 6. As a result, stable and highly accurate temperature control within a monitor wavelength deviation of ± 0.5 pm can be performed.

The relationship between w2 and t2 when ΔT = ΔT _{E in} FIG. 5 (the relationship between w2 / w1 and t2 / t1) is substantially the same as FIG. For example, the optimum thickness t2 when the width w2 is 0.2 mm, 0.5 mm, and 1 mm is about 0.7 mm, about 1.1 mm, and about 1.5 mm, respectively. On the other hand, when the thermal conductivity of the insulating plate 8 is 3/5, the allowable range of the thickness t2 with respect to the width w2 of the insulating plate 8 is reduced to about 3/5 compared with FIG.

<Fourth Embodiment>
FIG. 6 shows a fourth embodiment of the present invention. In the present embodiment, the materials of the etalon element 5 and the insulating plate 8 are both fused silica or BK7. The thermal conductivity of fused quartz or BK7 is an order of magnitude smaller than that of quartz. BK7 is borosilicate crown optical glass, which has a high transmittance in the visible light region and relatively low dispersion, and is the most common and inexpensive optical material for optical glass. An epoxy resin (adhesive layer thickness 100 μm) was used as an adhesive for adhering the etalon element 5 and the insulating plate 8 to the wavelength locker substrate 6.

In FIG. 6, the dotted line is ΔT = ΔT _E , the solid line 1 as the first line is ΔT = ΔT _E + 0.2 ° C., and the solid line 2 as the second line is ΔT = ΔT _E −0.2 ° C. The relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) is shown. By applying w2 and t2 in the range surrounded by solid lines 1 and 2 in FIG. 6 to the insulating plate 8, the etalon element 5 is affected by the outside air temperature (environment temperature) as in the case of the first embodiment. When the temperature fluctuates, the thermistor element 4 on the insulating plate 8 according to the present embodiment accurately detects the temperature of the central portion of the etalon element 5 following the temperature fluctuation. Therefore, the temperature detected by the thermistor element 4 Based on the above, the temperature of the etalon element 5 is accurately controlled by a temperature control element (Peltier element) (not shown) installed under the wavelength locker substrate 6. As a result, stable and highly accurate temperature control within a monitor wavelength deviation of ± 0.5 pm can be performed.

The relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) when ΔT = ΔT _{E in} FIG. 6 is substantially the same as FIG. For example, the optimum thickness t2 when the width w2 is 0.2 mm, 0.5 mm, and 1 mm is about 0.6 mm, about 1.1 mm, and about 1.6 mm, respectively. On the other hand, the allowable range of the thickness t2 with respect to the width w2 of the insulating plate 8 is reduced to about 1/10 compared with FIG.

Summarizing the results of FIG. 2, FIG. 4, FIG. 5, and FIG. 6, the relationship between w2 and t2 (the relationship between w2 / w1 and t2 / t1) when ΔT = ΔT _E is almost the same in each figure. Only the allowable range of the thickness t2 with respect to the width w2 of the insulating plate 8 changes. In addition, the allowable range expands and contracts in proportion to the thermal conductivity of the material. That is, the optimum range of w2 and t2 in FIGS. 2, 5, and 6 is almost included in the range shown in FIG. Of the materials that can be used for the etalon element 5, the one having the highest thermal conductivity is considered to be quartz, and the production tolerance of the insulating plate 8 is the widest in that case.

  FIG. 7 shows a change in the monitor wavelength observed by the thermistor element 4 with respect to a change in the environmental temperature using the multi-wavelength light source module with a built-in wavelength locker produced by the thermistor mounting method of the present invention. As in FIG. 16, not only the width w2 of the insulating plate 8 is changed from 0.5 mm to 1 mm, but also the thickness t2 is changed from 1.1 mm to 1.7 mm, thereby stabilizing the monitor wavelength fluctuation within ± 0.5 pm. Temperature control could be realized. This result applies to all cases where the insulating plate 8 is made of the same material as the etalon element 5 or a material having the same thermal conductivity, and the adhesive layer thickness is 100 μm or 10 μm, or an adhesive such as an epoxy resin. However, the same result is obtained with soldering.

<Fifth Embodiment>
The fifth embodiment relates to an optical module equipped with the wavelength locker of the first embodiment. FIG. 8 shows the configuration of the optical module of the fifth embodiment.

  As shown in FIG. 8, a part of the output light 7 of the semiconductor laser 11 is branched by the beam splitter 3, and one of the branched lights 7 B is detected by the photodiode 2 to control the output of the semiconductor laser 11. Feedback 9 is provided to the laser 11. The other branched light 7A passes through the etalon element 5 and is detected by the photodiode 1 and fed back to the semiconductor laser 11 in order to control the wavelength of the semiconductor laser 11. The temperature of the etalon element 5 is measured by the thermistor element 4 on the thermistor element mounting insulating plate 8. The material of the etalon element 5 is quartz, the width w1 is 1 mm, and the thickness t1 is 2 mm. The material of the thermistor element mounting insulating plate 8 is quartz, the width w2 is 0.2 mm, and the thickness t2 is 0.5 mm.

  As the semiconductor laser 11, a DBR laser that is a wavelength tunable laser was used (Non-patent Document 3). This DBR laser was oscillated with 8 wavelengths (wavelength interval of 0.449 nm from 1549.72 nm to 1552.52 nm), and the wavelength of the laser output light was controlled using the wavelength locker of the first embodiment. FIG. 9 shows the temperature change of the wavelength of the laser output light 7. The wavelength of the laser output light 7 does not vary even when the ambient temperature is changed from 0 ° C. to 70 ° C. As described above, in the optical module of the present embodiment, the oscillation wavelength of the wavelength tunable laser can be stably controlled under the environmental temperature fluctuation.

  In this embodiment, a DBR laser is used as a light source for outputting multi-wavelength laser light. However, a multi-wavelength laser integrated with a DFB laser may be used. Of course, it is possible to control a laser that outputs a single wavelength. Moreover, although the wavelength locker of the said 1st Embodiment was mounted in the optical module of this embodiment, of course, you may mount the wavelength locker of the said 2nd or 3rd embodiment in an optical module.

  As described above, according to the present invention, in the wavelength locker that independently controls the temperature of the etalon element portion, the actual temperature of the etalon element is affected by the change of the outside air temperature (environment temperature), and its transmission characteristics By optimizing both the width and thickness of the insulating plate for mounting the temperature sensing resistor element (thermistor element) with the same material or thermal conductivity as the etalon element Thus, it is possible to provide a wavelength locker that can control the temperature of the etalon element with high accuracy and is not affected by fluctuations in the outside air temperature, and a multi-wavelength light source module incorporating the wavelength locker.

  In addition, the optimum thickness and width parameters of the insulating plate for the etalon element provided by the present invention are not the optimum values themselves due to differences in the handling of radiation parameters and material boundary conditions, etc., from a normal simple heat conduction model. It may not be found. The present invention is a result of structural analysis based on knowledge obtained from many experimental results, and it is clear that the present invention is not in a range that can be easily inferred from existing technologies.

  The present invention relates to a temperature controller for wavelength lockers, a wavelength locker, and an optical module, and particularly applied to the case where the oscillation wavelength of a semiconductor laser for communication is permanently stabilized in the development of wavelength division multiplexing optical communication technology (WDM). It is useful.

It is a graph showing the change of (DELTA) T with respect to insulation plate thickness (etalon element; quartz crystal (board | substrate ⊥ c axis), insulation plate; quartz crystal (substrate ⊥ c axis), adhesive layer thickness: 100 μm). FIG. 5 is a diagram showing the relationship between the width and thickness of an insulating plate that allows the relative temperature change of the thermistor element to the etalon element to ± 0.2 ° C. according to the first embodiment of the present invention (etalon element; crystal (substrate (C axis), insulating plate: quartz (substrate c axis), adhesive layer thickness: 100 μm). It is a graph showing the change of (DELTA) T with respect to the thickness of an insulating plate (etalon element; quartz crystal (board | substrate ⊥ c-axis), insulating plate; quartz crystal (board | substrate ⊥ c-axis), adhesive layer thickness: 10 micrometers). FIG. 6 is a diagram showing a relationship between the width and thickness of an insulating plate that is a second embodiment of the present invention and allows a relative temperature change of ± 0.2 ° C. of the thermistor element (etalon element; crystal (substrate c axis) Insulating plate; quartz (substrate c axis), adhesive layer thickness: 10 μm). FIG. 9 is a diagram showing the relationship between the width and thickness of an insulating plate that is a third embodiment of the present invention and allows a relative temperature change of the thermistor element to the etalon element up to ± 0.2 ° C. (Etalon element: crystal (substrate // c axis), insulating plate: crystal (substrate // c axis), adhesive layer thickness: 100 μm). FIG. 10 is a diagram showing the relationship between the width and thickness of an insulating plate that allows the relative temperature change of the thermistor element to ± 0.2 ° C. according to the fourth embodiment of the present invention (etalon element; BK7, insulation) Plate; BK7, adhesive layer thickness: 100 μm). It is the figure which compared the shift amount of the monitor wavelength of the thermistor element with respect to an etalon element when the environmental temperature by the thermistor mounting method of this invention changes with 0.5 mm and 1 mm of insulating plate widths. It is a block diagram of the optical module of the 5th Embodiment of this invention. It is a figure which shows the change by the environmental temperature of the wavelength of laser output light. It is a figure showing the 1st example of the conventional typical wavelength locker structure. It is a figure showing the 2nd example of the conventional typical wavelength locker structure. It is a figure showing the transmission characteristic of the light of an etalon element. It is a figure showing the detail of the light transmission characteristic of an etalon element. It is sectional drawing of the etalon element and thermistor element mounting part on the board | substrate of a wavelength locker. (A) is a figure showing the temperature distribution inside an insulating plate when environmental temperature Ta changes, (b) is a figure which shows the relative temperature change of the thermistor element with respect to etalon element temperature when environmental temperature changes. It is a graph showing the change of (DELTA) T with respect to insulation plate thickness (etalon element; quartz crystal (board | substrate ⊥ c axis), insulation plate; quartz crystal (substrate ⊥ c axis), adhesive layer thickness: 100 μm). It is the figure which compared the relative temperature change of the thermistor element with respect to the etalon element when environmental temperature changed, and the shift amount of the monitor wavelength in 0.5 mm and 1 mm of insulating plate widths (etalon element; crystal (substrate ⊥ c axis) , Insulating plate; quartz (substrate ⊥ c-axis), adhesive layer thickness: 100 μm).

Explanation of symbols

1, 2 Photodiode 3 Beam splitter 4 Thermistor element 5 Etalon element 6 Wavelength locker substrate 7 Laser output light 7A, 7B Branched laser output light 8 Insulating plate 9, 10 Feedback 11 Semiconductor laser

Claims (3)

A temperature control device for a wavelength locker adjacent to an etalon element mounted on a wavelength locker substrate,
An insulating plate mounted on the wavelength locker substrate adjacent to the etalon element, and a temperature detecting element mounted on the insulating plate,
The insulating plate has the same thermal conductivity as the etalon element;
The etalon element and the insulating plate are arranged such that the material thereof is quartz and the c-axis of the quartz is perpendicular to the wavelength locker substrate,
The width and thickness of the insulating plate are set so that the temperature fluctuation on the surface of the insulating plate on which the temperature detecting element is mounted follows the temperature fluctuation at the center of the etalon element when the environmental temperature changes. And
When the temperature variation at the center of the etalon element is ΔT _E and the temperature variation on the surface of the insulating plate on which the temperature detecting element is mounted is ΔT, the width and thickness of the insulating plate are ΔT = ΔT _{E In the} temperature control device for wavelength locker set so that ΔT follows ΔT _E within a range of ± 0.2 ° C.
When the width of the etalon element is w1, the thickness is t1, the width of the insulating plate is w2, and the thickness is t2,
The width w2 and thickness t2 of the insulating plate are either w2 / w1 or t2 / t1 where w2 / w1 obtained by normalizing w2 by w1 and t2 / t1 obtained by normalizing t2 by t1. Is a first line representing the relationship between w2 / w1 and t2 / t1 where ΔT = ΔT _E + 0.2 ° C. and ΔT = ΔT _E −0.2 ° C. A temperature control device for a wavelength locker, characterized in that it is set within a range surrounded by a second line representing the relationship between w2 / w1 and t2 / t1. A wavelength locker comprising the temperature control device for a wavelength locker according to claim 1 . An optical module comprising the wavelength locker according to claim 2 and a semiconductor laser.

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