JP2004153176A - Wavelength locker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength locker that can independently control the temperature of an etalon element in high accuracy and is not influenced by the change of outside air temperature. <P>SOLUTION: A thermistor 4 for temperature control is placed on the center of the side of the etalon element 5 or adjacent to the center thereof, and a thermistor electrode 7 led out from the side of the etalon element to its upper surface is provided. The thermistor fitting side of the etalon element is preferably arranged directing in such a direction that it is difficult to be given by radiation from a module side wall surface. In another case, the thermistor for temperature control is mounted to an insulation plate (dummy etalon plate) that is made of a material same as the etalon element or having the same thermal conductivity, and the thickness of the insulation plate may be set to be 1/2 to 2/3 of that of the etalon element. A cover made of glass may be used to cover the etalon element and the thermistor for temperature control. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an element structure of a wavelength detecting element for optical communication, and more particularly to an independent temperature control type wavelength locker.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in the development of wavelength division multiplexing optical communication technology (WDM), the oscillation wavelength of a semiconductor laser for communication has a permanent wavelength within +/- 2 pm at intervals of 100 GHz or 50 GHz centered on 193.1 THz (155.52 nm). It is hoped that it will be stable in nature. In recent years, in response to such technical requirements, a CW (continuous wave) laser module for communication is equipped with a functional element called wavelength locker, which detects wavelength and optical output, as a standard. (For example, see Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1).
[0003]
FIGS. 9 and 10 show the structure of a typical conventional wavelength locker. First, as shown in FIG. 9, generally, light emitted from a laser element (not shown) is converted into a parallel beam by a beam splitter 3 or the like, and an etalon element 5 is inserted so as to bisect the beam diameter. The light passing through 5 and the light not passing through etalon element 5 are received by dedicated photodiodes 1 and 2, respectively, and the wavelength and light output are detected from the outputs of photodiodes 1 and 2, or as shown in FIG. As described above, the laser beam is cut out for light output and wavelength detection by the beam splitter 3 or the like, and the etalon element 5 is inserted into one optical path, and the light that has passed through the etalon element 5 and does not pass through the etalon element 5 in the same manner as described above. Light is received by dedicated photodiodes 1 and 2, respectively, and the wavelength and light output are detected from the outputs of photodiodes 1 and 2. Here, the photodiode 1 is a photodiode for detecting a wavelength, and the photodiode 2 is a photodiode for monitoring an optical output.
[0004]
From the output of the photodiode (PD) 1 for wavelength detection, a photocurrent signal that periodically oscillates with respect to the wavelength can be detected as shown in FIG. As a method of fixing the wavelength (control method), 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 a laser diode), a photodiode for detecting an oscillation wavelength at that time Generally, a method of fixing the wavelength by performing negative feedback control on the control temperature of a laser diode (not shown) so that the detection current from 1 becomes constant.
[0005]
In the case of the conventional method (for example, the method described in Non-Patent Document 1), the current value of the wavelength detection signal generated through the etalon element 5 for the target wavelength is always shown in FIG. Thus, in the region connecting the maximum value and the minimum value of the current value, it must be in a region of a single decrease or a single increase of about 85% around the point of (maximum value-minimum value) / 2. . This is because, in the characteristics shown in FIG. 12, the range of selectable wavelengths becomes very wide near the apex and the lowest point of the current waveform while having the same wavelength detection current value. Is not controllable. 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 light incident on the etalon element 5, It is necessary to adjust the transmission characteristics.
[0006]
However, changing the angle of incidence of light incident on the etalon element 5 changes the FSR (period of output of the etalon element 5) as it is, so that the etalon element prepared with the characteristics of 100 GHz intervals or 50 GHz intervals at all. 5, the output cycle is slightly shifted. Therefore, when only one wavelength is fixed, it is possible to perform sufficient wavelength control and manufacture of a wavelength locker by the above method. However, a wavelength tunable laser (for example, a DBR (distributed black reflector) laser) or a multi-channel laser (wavelength It is difficult to fix the wavelength using an etalon element 5 in an element such as a selective laser whose wavelength changes over a wide band.
[0007]
In recent years, in order to solve this difficulty, as shown in FIG. 9 of Patent Document 1, in a wavelength selection laser or the like, two temperature controllers (Peltier elements) are mounted in the same module, and an etalon element is mounted. A technique has been proposed in which the temperature of the etalon element 5 can be stably used over a wide band by controlling the temperature independently.
[0008]
[Patent Document 1]
JP-A-2002-185074 (FIG. 9)
[0009]
[Non-patent document 1]
“NEC Data Sheet (Tentative) Laser Diode NX8570 Series”, Document No. PL 10135JJ01V0V0DS (1st edition), NEC Compound Semiconductor Devices 2002, April 2002, p. 1, 2, 11-13
[0010]
[Non-patent document 2]
"Tunable LD Module with Wavelength Locker-FLD2F15CA-K" FUJITSU COMPOUND SEMICONDUCTOR, INC. , March 2001, p. 1-5
[0011]
[Problems to be solved by the invention]
However, even with the improved technology described in the above-mentioned Patent Document 1, if the use environment temperature fluctuates, the ambient temperature inside the laser module changes, so that the control temperature of the etalon element 5 and the etalon element 5 There is a problem to be solved in that a difference is generated from the actual temperature, and the controllable wavelength resolving power is reduced.
[0012]
Therefore, an object of the present invention is to provide a wavelength locker that independently controls the temperature of an etalon element portion, in which the actual temperature of the etalon element is affected by a change in the outside air (environmental temperature) temperature to change its transmission characteristics. The above-mentioned problem was solved by changing the mounting method of the etalon element and the mounting method of the temperature detection resistor element (thermistor element) in the etalon element section, controlling the temperature of the etalon element with high accuracy and reducing the outside air temperature fluctuation. It is to provide a wavelength locker that is not affected.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a wavelength locker of the present invention is a wavelength locker that independently controls the temperature of an etalon element portion using a temperature control thermistor, wherein the temperature control thermistor is located at the center of the side surface of the etalon element or the temperature control thermistor. A thermistor electrode is disposed near the center and has a thermistor electrode extending from a side surface of the etalon element to an upper surface of the etalon element.
[0014]
Here, preferably, the temperature control thermistor mounting side of the etalon element may be arranged in a direction less likely to receive radiant heat from a module side wall surface.
[0015]
Another aspect of the wavelength locker of the present invention is a wavelength locker that independently controls the temperature of an etalon element using a temperature control thermistor, which is installed near the etalon element and has the same material as the etalon element. The temperature control thermistor was mounted on an insulating plate made of a material or a material having the same thermal conductivity, and the thickness of the insulating plate was set to be between か ら and ／ of the thickness of the etalon element. It is characterized by the following.
[0016]
Here, preferably, a glass lid for covering the etalon element and the temperature control thermistor and blocking radiant heat from the upper surface may be provided.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
The present invention focuses on the method of measuring the temperature of the etalon element of the wavelength locker, and proposes a method and structure for mounting a thermistor element on the etalon element as shown in FIGS.
[0019]
(1st Embodiment)
The first embodiment of the present invention shown in FIG. 1 has a structure in which the thermistor 4 is directly attached to the etalon element 5 in order to grasp the substantial temperature of the etalon element 5 more. A pair of thermistor electrodes 7 extending from the upper surface to the side surfaces through which the laser beam of the etalon element 5 mounted on the wavelength locker does not transmit is provided, and the thermistor 4 is mounted on the thermistor electrode 7. Further, a thermal contact metal layer is formed on the remaining side and bottom surfaces of the etalon element 5 through which the laser beam does not pass.
[0020]
The mounting of the thermistor 4 on the etalon element 5 itself is a technique within a range that can be easily inferred from the prior art. However, in the present invention, a thermistor electrode 7 extending from the upper surface to the side surface of the etalon element 5 is formed and shown in FIG. As described above, the thermistor 4 is mounted at the center of the side surface of the etalon element 5 far from (ie, inside) the module outer peripheral wall 17. By the effect of the mounting position, the effect of the radiant heat 12 from the LD module upper plate 6 and the side wall 17 can be reduced.
[0021]
That is, the laser beam emitted from the semiconductor laser 13 and having passed through the first lens 15 and the isolator 16 is split in two directions by the first stage of the beam splitter 3 in the wavelength locker, and one reflected beam is used for monitoring the optical output. The incident light is incident on the photodiode (PD) 2, and the other straight beam is further split in two directions by the second stage of the beam splitter 3, and one straight beam is guided to the optical fiber 14, while the other reflected beam is The light enters the photodiode (PD) 5 for wavelength detection through the etalon element 5. At this time, the radiant heat 12 from the LD module upper plate 6 and the side wall 17 is directed to the etalon element 5. However, in the first embodiment of the present invention, the thermistor electrode 7 extending from the upper surface to the side surface of the etalon element 5 is formed, and the thermistor electrode 4 is provided at the center of the side surface of the etalon element 5 far from (ie, inside) the module outer peripheral wall 17. Is mounted, the effect of the radiant heat 12 from the LD module upper plate 6 and the side wall 17 can be reduced.
[0022]
Further, since the thermistor 4 is provided at the center of the side surface of the etalon element 5 as described above, it is possible to monitor the temperature substantially at the center of the heat distribution inside the etalon element 5, so that even if the internal temperature of the module changes, A sufficiently effective temperature of the etalon element 5 can be measured, and fluctuations in the transmission characteristics of the etalon element 5 can be kept very small.
[0023]
(Second embodiment)
In the second embodiment of the present invention shown in FIG. 3, a pseudo etalon element plate (a plate made of the same material as the etalon element) 8 is arranged in parallel near the side surface of the etalon element 5 at intervals. It has a structure with the thermistor 4 mounted. By adjusting the thickness t of the pseudo etalon element plate 8 at the time of design, the temperature measured by the thermistor 4 approaches the effective temperature of the etalon element 5, and the thermistor 4 is directly mounted at the center of the side surface of the etalon element 5. The same effect as that shown in FIG. 1 can be obtained.
[0024]
Next, the operation of the above-described embodiment of the present invention will be described.
[0025]
A case where the thermistor 4 is mounted on the wavelength locker substrate 6 of the conventional example as shown in FIG. 10, a case where the thermistor 4 is mounted on the etalon element 5 of the comparative example, and an etalon element according to the present invention as shown in FIG. FIGS. 4 and 5 show a comparison of characteristics with the case where the thermistor element 4 is mounted on the side surface of FIG.
[0026]
FIG. 4 shows a characteristic change of the etalon element 5 due to an external temperature change when the thermistor 4 is mounted on the wavelength locker substrate 6. The frequency is shown on the horizontal axis, but it can be understood that the change is about 8 pm due to a temperature change of 50 ° C. in terms of wavelength. This change can be reduced to about 2 to 5 pm by changing the material of the etalon element 5 to a material having high thermal conductivity. However, the difference between the temperature observed by the thermistor 4 and the actual temperature of the etalon element 5 does not disappear. Absent.
[0027]
FIG. 5 shows that the laser element 13 inside the LD module is controlled by the output value from the wavelength detecting PD (photodiode) 1 while controlling the temperature outside the LD module (environmental temperature) using a high-speed thermostat while controlling the wavelength. 10 shows the results of measuring the amount of change in the control wavelength when the cycle was changed from 20 ° C. to 70 ° C. at 30 minute intervals. From the chain line waveform in FIG. 5A, when the thermistor 4 is mounted on the wavelength locker substrate 6 (conventional example), as the outside air temperature changes and the inside of the module is heated, the control wavelength is also increased to about 8 pm on the long wave side (plus side). It can be seen that the degree has shifted by about This is because the temperature of the etalon element 5 rises as the temperature inside the module rises, and means that a difference occurs between the temperature observed by the thermistor element 4 and the actual temperature of the element 5. In the case of the thermistor element 4, a temperature lower than the effective temperature of the etalon element 5 is observed.
[0028]
On the other hand, when the thermistor 4 is mounted above the etalon element 5 (comparative example), the control wavelength shifts to the shorter wavelength (minus side) as shown by the broken line waveform in FIG. You can see that it is doing. At the position above the etalon element 5, the amount of radiant heat from the upper part of the module is larger than that of the etalon element 5, and the amount of heat at the upper end inside the etalon element 5 is observed and rubbed. Since the temperature higher than the average temperature of the etalon element 5 has been measured, it is considered that the cooling was performed excessively and thus shifted to the minus side.
[0029]
In the mounting position according to the present invention shown in FIG. 1, the thermistor 4 measures a temperature exactly midway between the upper and lower surfaces, and is a position where it does not receive excessive radiant heat. A temperature approximately equal to can be measured. Therefore, as shown by the solid waveform in FIG. 5C, the control wavelength could be stabilized to a variation of 0.5 pm or less as a whole.
[0030]
Also, in the case of the present invention in which the thermistor 4 is mounted on the pseudo etalon element plate 8 shown in FIG. 3, the thickness t of the plate 8 is １ ／ of the thickness T of the etalon element 5 as shown in FIG. By setting to ／, the same effect as in the case of FIG. 1 can be obtained, and a stable performance of 0.5 pm or less can be confirmed for the control wavelength.
[0031]
[Example]
Further, specific embodiments of the present invention will be described with reference to the drawings.
[0032]
FIGS. 7 and 8 show the inside of an LD module on which a tunable laser (see FIG. 2) according to the first and second embodiments of the present invention is mounted. Next, with reference to FIGS. 7 and 8, a procedure for manufacturing these wavelength lockers will be described.
[0033]
First, a deposition layer 11 made of nickel and metal is placed on the mounting position of the thermistor 4 and the etalon element 5 on the aluminum nitride substrate 6, the position of the thermistor relay electrode 10, and the mounting position of the PDs (photodiodes) 1 and 2, respectively. Was formed and sintered, and then a high-melting point solder layer was deposited on the mounting positions of the PDs 1 and 2 and the mounting side wall of the etalon element 5.
[0034]
Thereafter, the beam splitters 3 are fixed with an ultraviolet curing epoxy resin (UV), and light is incident on each beam splitter 3 from a normal laser beam incident position using a red laser 13 having a beam diameter of 670 μm as a marker. The PDs 1 and 2 are fixed with solder in accordance with the reflection path of the red light.
[0035]
At the time of this solder fixing, the mounting side wall 9 of the etalon element 5 is also mounted by soldering. Subsequently, the etalon element 5 and the thermistor 4 mounted on the pseudo etalon element plate 8 are fixed with an ultraviolet curable epoxy resin while checking the path of red light.
[0036]
At this time, the angle of incidence on the etalon element 5 is 0 degree. Thereafter, wiring is bonded from the thermistor electrode 7 to the thermistor relay electrode 10 to complete the wavelength locker structure. FIG. 8 of the second embodiment shows that, in addition to the steps of FIG. 7, the etalon element mounting side wall 9 is mounted on the thermistor 4 side in the same procedure, and finally the radiant heat 12 from the upper surface is cut off. A glass lid 18 was placed over both side walls 9 so as to cover the etalon element 5 and the thermistor element 4.
[0037]
The completed wavelength locker is mounted inside the LD module as shown in FIG. 2 to complete the module. The completed module exhibited substantially the same wavelength stability performance as the wavelength fluctuation characteristic indicated by the solid line waveform in FIG. However, in the first embodiment and the second embodiment, the average value was about 0.08 pm, and the stability of the second embodiment was improved.
[0038]
Further, the thickness of the pseudo etalon element plate 8 similarly mounted is (1 / T) 0.6 in the standardized thickness in the first embodiment and 0.5 in the second embodiment. Stability was obtained.
[0039]
【The invention's effect】
As described above, according to the present invention, in the wavelength locker that independently controls the temperature of the etalon element portion, the mounting position of the etalon element and the mounting position of the temperature detection resistance element (thermistor element) in the etalon element section are conventionally determined. By changing the temperature of the etalon element, the actual temperature of the etalon element is affected by changes in the outside air (environmental temperature), and the transmission characteristics can be changed. This provides an effect of being able to provide a wavelength locker that is not affected by changes in the outside air temperature.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a structure of an etalon element according to a first embodiment of the present invention.
FIG. 2 is a schematic plan view showing an arrangement configuration in which a wavelength locker in which the etalon element of FIG. 1 is arranged is built in an LD (laser diode) module.
FIG. 3 is a diagram showing a thermistor mounting structure according to the present invention.
FIG. 4 is a waveform chart showing an influence of an etalon element due to a change in external temperature.
FIG. 5 is a waveform chart showing a comparison of wavelength fluctuation of a control wavelength depending on a mounting position of a thermistor.
FIG. 6 is a characteristic diagram showing the thickness and wavelength stability of a pseudo etalon element plate.
FIGS. 7A and 7B are diagrams showing the structure of the wavelength locker according to the first embodiment of the present invention, wherein FIG. 7A is a plan view and FIG.
8A and 8B are diagrams showing a structure of a wavelength locker according to a second embodiment of the present invention, wherein FIG. 8A is a plan view and FIG. 8B is a front view.
FIG. 9 is a plan view showing a first example of a conventional typical wavelength locker structure.
FIG. 10 is a plan view showing a second example of a conventional typical wavelength locker structure.
FIG. 11 is a waveform chart showing light transmission characteristics of the etalon element.
FIG. 12 is a waveform diagram showing details of light transmission characteristics of the etalon element.
[Explanation of symbols]
1 PD (photodiode) for wavelength detection
2 Optical output monitor PD (photodiode)
3 Beam splitter (light splitting mirror)
4 Thermistor element (thermal resistance thermometer)
5 Etalon element 6 Wavelength locker substrate (LD module top plate)
Reference Signs List 7 Thermistor electrode 8 Pseudo etalon element plate 9 Side wall for mounting etalon element 10 Relay electrode for thermistor 11 Thermal contact metal layer 12 Radiant heat 13 Semiconductor laser 14 Optical fiber 15 First lens 16 Isolator 17 Module outer peripheral wall (side wall)
18 Quartz glass lid

Claims (4)

In a wavelength locker that independently controls the temperature of the etalon element using a temperature control thermistor,
The temperature control thermistor is disposed at or near the center of the side surface of the etalon element,
A wavelength locker having a thermistor electrode extending from a side surface of the etalon element to an upper surface of the etalon element. 2. The wavelength locker according to claim 1, wherein the temperature control thermistor mounting side of the etalon element is arranged in a direction that is less likely to receive radiant heat from a module side wall surface. 3. In a wavelength locker that independently controls the temperature of the etalon element using a temperature control thermistor,
The temperature control thermistor is mounted on an insulating plate that is installed near the etalon element and is made of the same material or the same thermal conductivity as the material of the etalon element,
2. A wavelength locker according to claim 1, wherein the thickness of said insulating plate is set between 1/2 and 2/3 of the thickness of said etalon element. 4. The wavelength locker according to claim 3, further comprising a glass lid that covers the etalon element and the temperature control thermistor to block radiant heat from an upper surface. 5.

Images