WO2018236167A1

WO2018236167A1 - Laser device including filter and operation method therefor

Info

Publication number: WO2018236167A1
Application number: PCT/KR2018/007041
Authority: WO
Inventors: 김정수
Original assignee: 김정수
Priority date: 2017-06-22
Filing date: 2018-06-21
Publication date: 2018-12-27
Also published as: KR20190000078A

Abstract

Disclosed are a laser device including a filter and an operation method therefor. According to an aspect of the present embodiment, the purpose of the present invention is to provide a low-cost subminiature TO type laser device that emits laser light having a reduced oscillation line width, and to provide an optical element which maintains the characteristics of a laser optimized for long-distance transmission and in which the variation in laser wavelength according to variations in the temperature of the external environment is minimized so that the optical element can even be applied in DWDM in which the wavelength spacing is 100 GHz or even 50 GHz.

Description

Laser device including filter and method of operation

The present invention relates to a laser apparatus and a method of operating the same, and more particularly, to a laser apparatus capable of being fabricated in an extremely small size equipped with a wavelength stabilizing apparatus including a filter and capable of reducing the line width of laser light emitted from the package, And a method of operating the laser device.

The contents described in this section merely provide background information on the present embodiment and do not constitute the prior art.

Recently, communication services such as a video service of a smart phone and the like have been introduced with a great communication capacity. Accordingly, there has been a great need to increase the conventional communication capacity, and a DWDM (Dense Wavelength Division Multiplexing) communication method has been adopted in order to increase the communication capacity using the optical fiber that has been conventionally installed. DWDM is a method of simultaneously transmitting light of various wavelengths with one optical fiber. Even if optical signals of various wavelengths are simultaneously transmitted to one optical fiber, no interference occurs between signals.

In order to expand the optical communication at a low cost, DWDM, which can use the existing optical fiber as it is, is preferably applied because the portion where the most cost is consumed in the optical communication is the optical fiber installation part. In DWDM, DWDM with a frequency interval of 100 GHz is now subdivided into DWDM with a frequency interval of 50 GHz. In such a 100 GHz and 50 GHz, and furthermore, a very fine DWDM of 25 GHz, it is preferable that each optical device generates a constant wavelength irrespective of changes in the external environmental temperature.

A semiconductor laser typically used for optical communication exhibits a wavelength change of about 90 pm with respect to a temperature change of 1 占 폚. The thermoelectric cooler (TEC), which can control the temperature electrically, has the function of keeping the temperature of the device such as the laser diode chip constant. However, the thermoelectric element merely controls the temperature of the element thermally coupled to the upper plate by measuring the temperature in the vicinity of the upper surface of the thermoelectric element, and can not substantially control the temperature of the semiconductor laser diode chip. Therefore, there is a problem that it is difficult to precisely control the temperature of the laser diode chip even if a thermoelectric element is used, when the temperature inside the optical element changes due to external temperature change. This causes a ripple change of the laser diode chip.

The stability of the wavelength of the laser diode is more important in DWDM where the wavelength interval is narrowed, that is, the frequency interval is narrowed. The International Telecommunication Union Telecommunication Standardization Sector (ITU-T), which defines the communication standard, permits the following wavelength changes. At a frequency interval of 200 GHz, only a wavelength change of +/- 300 pm at the center wavelength specified by the standard, only a wavelength change of +/- 100 pm at the central wavelength defined by the standard at the 100 GHz frequency interval, Only wavelength variations of +/- 20 pm at the center wavelength are allowed.

In addition, recently, optical communication has been speeding up, and long distance has been demanded. When a transmitting device directly modulates a DFB-LD (Distributed Feedback Laser diode) and transmits a high-speed signal of 10 Gbps or higher, chirp phenomenon generated when a semiconductor laser diode is directly modulated is combined with the dispersion of the optical fiber, It is difficult.

In order to solve this problem, Applicant has proposed a method of mounting an optical filter in a TO-can type optical device package in US 9,515,454. FIG. 1 shows a TO-can type laser which realizes the characteristics of a laser capable of long-distance transmission at high speed as described in the above-mentioned invention.

Also, as shown in FIG. 2, the present invention proposes a method in which an optical element is mounted on a support such as a silicon or the like having a good heat conductivity and disposed on a 45-degree reflection mirror. It has been demonstrated that optical devices fabricated in this way can transmit more than 100Km at a high-speed transmission rate of 10Gbps.

However, there is a problem in the above-mentioned stabilization of the wavelength by the method mentioned in the above-mentioned invention. The wavelength stabilization mentioned in the above-mentioned invention is only a relative wavelength stabilization of the wavelength of the optical filter and the laser diode having the characteristics of the etalon.

According to a further study by the present applicant, the temperature of the optical filter changes with the temperature of the external environment although the thermoelectric element is at a constant temperature. As the material of the optical filter including the etalon in the stand structure shown in FIG. 2, glass or quartz is used as the material having a small refractive index change depending on the temperature, and these materials have a very low thermal conductivity.

The temperature control of the TEC is the main purpose of temperature control of the TEC top plate, and the thermally contacted stand with the thermoelectric device controls the temperature of the etalon filter by transmitting heat. However, as shown in FIG. 3, when the temperature of the external environment changes when the thermoelectric element is at a constant temperature, conduction by the thermal radiation 60 occurs from the cap 50 of the package. The etalon filter is thermally balanced between the conduction from the cap 50 of the package and the heat transfer by the stand 10.

According to the experiment of the present applicant, when the external temperature changes while the thermoelectric element is fixed at a predetermined temperature in a state where the etalon filter 30 is attached to the stand 10 thermally coupled to the thermoelectric element by the method as shown in FIG. 4 , The temperature of the etalon filter was found to undergo a temperature change corresponding to almost half of the external temperature change.

The temperature change of the etalon filter means that the temperature of the etalon filter changes by about 20 ° C, for example, when a change in the external environment temperature of 40 ° C occurs even when the thermoelectric element is maintained at a constant temperature . Even if the refractive index change rate is low depending on the temperature such as glass or Quartz, the temperature change of the etalon filter has a temperature change of about 12 pm per degree centigrade. Therefore, even if the thermoelectric element is maintained at a constant temperature, the etalon peak (wavelength of the etalon filter) itself shows a wavelength change of about 6.25 pm per 1 deg.

For effective long-distance transmission, the laser oscillation wavelength should be adjusted to have a certain relative position with the etalon peak by changing the laser temperature. At this time, the temperature change of the external environment at 40 ° C changes the transmission wavelength of the etalon peak by about 240 pm, so that the laser wavelength itself needs to be changed by about 240 pm to enable long distance transmission. Therefore, the conventional method can be applied only to DWDM with a wavelength interval of 200 GHz or more.

The present invention provides a low-cost TO type laser device that emits a laser beam having a small size and a small oscillation line width in order to solve the above problems. And to provide optical devices that can be applied to DWDM with a wavelength interval of 100 GHz and further with a wavelength of 50 GHz.

According to an aspect of the present invention, there is provided a laser device comprising: a laser diode chip for emitting laser light; An FP (Fabry-Perot) type etalon filter or a thin film filter; A heat sink having a good heat transfer coefficient to surround an outer circumferential surface of the wavelength selective filter; a collimating lens provided on an optical path between the laser diode chip and the wavelength selective filter for collimating light emitted from the laser diode chip; A 45-degree partial reflective mirror that deflects laser light traveling horizontally to a laser beam that travels perpendicular to the package's bottom surface; And a photodiode monitoring photodiode disposed on the optical path through which the laser beam reflected by the wavelength selective filter after being emitted from the laser diode chip passes through the 45 degree partial reflecting mirror.

Further, a photodiode for monitoring the light intensity may be further disposed on one side of the 45-degree partial reflection mirror and disposed on an optical path that is diverged from the laser diode chip and transmits the 45-degree partial reflection mirror.

It is preferable that the laser diode chip, the collimating lens, the wavelength selective filter, the 45-degree partial reflection mirror, and the photodiode for monitoring the wavelength are fixed on the thermoelectric element and disposed inside the TO (transistor outline) package.

In addition, the material having a high thermal conductivity to surround the wavelength selective filter is preferably a thermal conductive adhesive such as silver epoxy or silicone or AlN or a metal having high thermal conductivity, and is simultaneously in thermal contact with the wavelength selective filter and the stand. In particular, it is preferable that the heat sink having a good thermal conductivity to surround the wavelength selective filter is protruded so that the wavelength selective filter is buried, and the size of the protrusion is preferably 200 μm or more.

It is also possible to cover the upper part of the heat sink having such protruding shape with a window cover of a glass.

When the temperature of the wavelength selective filter is affected by the external environment temperature regardless of the temperature of the thermoelectric element, the temperature of the thermoelectric element is reset to a temperature that cancels the change of the external environment temperature. The wavelength of the laser light emitted from the laser diode chip is adjusted by adjusting the current passing through the semiconductor laser to adjust the wavelength of the laser irrespective of the thermoelectric element so that the transmission curve of the wavelength selective filter has a predetermined transmission / Lt; / RTI >

The reflectance of the 45-degree partial reflection mirror is preferably 80% to 98%.

In addition, the package housing in which the laser diode chip, the collimating lens, the wavelength selective filter, the 45-degree partial reflection mirror, the photodiode for optical intensity monitoring, the photodiode for optical wavelength monitoring and the thermoelectric element are disposed, .

As described above, according to the present embodiment, in the optical device directly modulating using the DFB-LD, a wavelength selective filter such as an etalon filter is mounted inside the optical device package, Quot; signal and the " 0 " signal, the relative wavelengths of the wavelength selective filter and the laser wavelength can be adjusted so that the transmittance passing through the wavelength selective filter is different. Therefore, the optical device according to an embodiment of the present invention facilitates long-distance transmission in high-speed operation and suppresses the change in the laser oscillation wavelength as a result of temperature change of the wavelength selective filter due to a change in the external environmental temperature can do. The optical device according to an embodiment of the present invention further includes a window glass covering a heat radiating plate, a protruding heat radiating plate and a protruding heat radiating plate outside the wavelength selective filter so that the entire wavelength selective filter can more easily exchange heat with the thermoelectric element. Such that the wavelength selective filter responds to the effect of ambient temperature at a minimum. As a result, the laser wavelength changes to a minimum extent to the external environmental temperature change, allowing the optical device to be used for the denser DWDM methods such as 100 GHz and 50 GHz.

1 shows a conventional TO-can type optical device for high-speed long distance transmission

Fig. 2 is a view of a stand on which a wavelength selective filter is mounted in a conventional TO-can optical device for high-speed long distance transmission

3 is a view showing that a wavelength selective filter has a temperature different from that of a thermoelectric element by thermal radiation in a conventional TO-can type optical element for high-speed long distance transmission

4 is a view showing a wavelength selective filter mounted on a stand in a conventional TO-can type optical device for high-speed long distance transmission exposed to thermal radiation from an optical device package

5 is a schematic diagram showing a relationship between a wavelength selective filter and a laser wavelength when a wavelength selective filter is mounted so that a conventional direct modulation DFB-LD can be used for high-speed long-

6 is a view of a wavelength selective filter in which a heat sink is paved around the wavelength selective filter according to the present invention

Fig. 7 is a view of a wavelength selective filter in which a heat sink is protruded around the wavelength selective filter according to the present invention

8 is a view of a wavelength selective filter in which a window is mounted on a heat sink having a protruding shape around the wavelength selective filter according to the present invention

Fig. 9 is a graph showing the influence of the external environment temperature on the temperature of the wavelength selective filter in the structures of Figs. 4, 6, and 7 according to the present invention

FIG. 10 is a graph illustrating a change in the wavelength of the laser when the external environment temperature changes when the C-structure of FIG. 7 is used

Fig. 11 is a graph showing the relationship between the temperature of the thermoelectric element and the wavelength of the laser, in order to compensate for the fact that the change in the external environment temperature substantially changes the temperature of the wavelength selective filter. A schematic diagram for explaining the process of shifting the current flowing to a wavelength having a predetermined transmission band of the wavelength selective filter

12 is a schematic diagram for stabilizing a wavelength using a monitoring photodiode

13 is a flowchart of a method for stabilizing a wavelength using the present invention

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals even though they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. Throughout the specification, when an element is referred to as being "comprising" or "comprising", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise . In addition, '... Quot ;, " module ", and " module " refer to a unit that processes at least one function or operation, and may be implemented by hardware or software or a combination of hardware and software.

FIG. 1 shows a TO-can type optical device having a wavelength selective filter having a transmission distance of 20 Km by directly modulating a DFB-LD at a 10 Gbps level in a conventional 1.55-μm long wavelength band.

FIG. 2 shows a stand in which a wavelength selective filter is mounted in a conventional TO-can type optical device having a wavelength selective filter for high-speed long-distance transmission. A hole is formed in the stand 10, and a 45-degree partial reflecting mirror for dividing the laser beam is mounted in the hole. The stand can usually be made of silicon with good thermal conductivity.

FIG. 3 is a graph showing the relationship between the wavelength of the radiation from the cap 50 forming the outer periphery of the TO-can type optical device in the TO-can type optical device having the wavelength selective filter for high-speed long- And the like. Referring to FIG. 1, it is preferable that the laser light proceeding to the wavelength selective filter passes through the center of the wavelength selective filter. The wavelength selective filter typically has a very low thermal conductivity and has a refractive index different from that of a ceramic material such as glass or quartz Reflective layer is used coated. Since the heat is directly transferred to the front surface of the wavelength selective filter by thermal radiation, even if the wavelength selective filter is thermally coupled to the stand close to the temperature of the thermoelectric element due to its high thermal conductivity, the temperature of the central part of the wavelength selective filter becomes Otherwise, it may vary depending on the temperature change of the external environment.

FIG. 4 is a view showing in detail a process of heat transfer to a wavelength selective filter mounted on a stand by heat radiation. FIG. 5 shows a case in which a DFB-LD is directly subjected to high- This is a graph showing that this is possible.

Referring to FIG. 5 (a), the optical signal emitted from the laser is composed of a "1" signal having a large signal intensity and a "0" signal having a weak signal intensity. The chirp phenomenon of the optical transmission is a phenomenon in which the wavelength varies depending on the current density injected into the semiconductor laser. When the magnitude of the injection current of the "1" signal and the "0" signal largely changes, a large chirp characteristic occurs. chirp property occurs. Therefore, in order to minimize the chirp characteristic, it is preferable that the difference in the current magnitude between the " 1 " signal and the " 0 " However, from the viewpoint of signal discrimination, if the signal magnitudes of the "1" signal and the "0" signal do not differ greatly, the signal discrimination becomes disadvantageous. Therefore, if the difference in the current magnitude between the "1" signal and the "0" signal is increased, chirp characteristics become worse and transmission becomes difficult. If the difference between the "1" signal and the "0" signal is small, the signal discrimination becomes difficult. Referring to FIG. 5, when the " 1 " signal of the laser light generated in the laser diode chip in the structure of A-CASE is matched to the region having the greatest transmittance of the wavelength selective filter, the " 0 " Is disposed in the falling area. Accordingly, since the attenuation of the " 0 " signal becomes larger than that of the signal " 1 ", the signal intensity difference between the " 1 " Do.

However, in the structure of B-CASE, when the laser's "0" signal is fitted to the wavelength region of the highest transmittance of the wavelength selective filter, the "1" signal lies in a region with a relatively low transmittance. As a result, the "1" signal is relatively much attenuated and the "0" signal is less attenuated, so the signal intensity difference between the "1" signal and the "0" signal is rather reduced. Therefore, when the wavelength of the signal from the laser is combined with the wavelength-selective filter in the form of B-CASE, the transmission characteristics are deteriorated. Accordingly, it is very important to adjust the wavelength of the laser light emitted from the laser to match the " 1 " signal to the maximum transmittance wavelength band of the wavelength selective filter.

The wavelength of the laser and the wavelength selective filter and the relative position are usually controlled by the temperature change of the thermoelectric element at a specific current condition. That is, the semiconductor laser has a wavelength change rate of about 90 pm / ° C., and the wavelength selective filter such as a glass typically shows a wavelength change rate according to a temperature of about 12 pm / ° C. Therefore, the wavelength of the laser should be adjusted so that the temperature of the thermoelectric element is adjusted so that the "1" signal is at the desired position of the wavelength selective filter. Since the wavelength selective filter does not change the wavelength depending on the temperature, the wavelength of the laser should be adjusted to a wavelength having a good transmission quality by changing the wavelength of the laser. However, when the transmission peak of the wavelength selective filter is far away from the predetermined channel, the wavelength of the laser light itself deviates far from the predetermined channel in order to improve the transmission characteristic.

6 is a graph of the temperature of the center of the wavelength selective filter when the temperature of the thermoelectric element is fixed at 40 ° C and the external environment temperature is changed from 20 to 80 ° C. Referring to FIG. 6, the A-structure is the temperature at the center of the wavelength selective filter measured in the structure shown in FIG. 4, and the B-structure and the C-structure are the same as those of the heat sink 120 ) Is the temperature at the center of the wavelength selective filter in the padded structure. When the external temperature changes by 40 ° C in the A-structure, the temperature of the central part of the wavelength selective filter shows a temperature change of about 20 ° C even though the thermoelectric element is maintained at a constant temperature.

The temperature change of the wavelength selective filter at 20 캜 changes the transmission wavelength of the wavelength selective filter by about 240 pm and the wavelength of the laser light can be adjusted by adjusting the temperature of the thermoelectric device to the wavelength. That is, since the wavelength of the laser diode chip varies by about 90 pm / C, when the temperature of the thermoelectric element rises by about 2.5 ° C, the "1" signal can be placed in the appropriate region of the wavelength selective filter. The transmission wavelength of the wavelength selective filter increases again by about 30 pm, which can be canceled by the increase of the temperature of the thermoelectric element by about 0.3 ° C. By repeating this process, the temperature of the thermoelectric element In FIG. 1, the two monitor photodiodes measure the reflectance of the wavelength selective filter to adjust the wavelength of the laser light in the appropriate region of the wavelength selective filter. In this process, the wavelength of the laser is determined by the transmission wavelength of the wavelength selective filter.

However, in the conventional technique of FIG. 4, since the wavelength selective filter is sensitive to changes in the external environment temperature, it is difficult to apply it to wavelength DWDM having a wavelength interval of 100 GHz, further, 50 GHz.

In the structure of FIG. 4, the difference between the temperature of the wavelength selective filter 30 and the temperature of the thermoelectric element is significant because the characteristic of the wavelength selective filter 30 is poor in thermal conductivity, Because it affects the center of the image.

In order to solve such a problem, the present invention attaches a heat sink 120 having a good thermal conductivity around the wavelength selective filter 130 as shown in FIGS. The heat sink 120 facilitates the heat exchange with the thermoelectric element even in a region remote from the stand 110, thereby making the temperature of the central portion of the wavelength selective filter closer to the temperature of the thermoelectric element.

Figure 7 is an embodiment of a B-structure. At least one side of the stand 110 may include a wavelength selective filter 130 and the wavelength selective filter 130 may be coupled to the stand 110 in a cantilever fashion. The wavelength selective filter 130 may be coupled to the stand 110 only on one side or may be coupled to the plurality of stands 110 on a plurality of sides. The surface to which the wavelength selective filter 130 is bonded is preferably a side surface of the wavelength selective filter 130. In addition, the shape to which the wavelength selective filter 130 is coupled can be coupled horizontally with the lower surface of the stand 110 (FIG. 7 is an embodiment combined horizontally) .

In addition, a side surface of the wavelength selective filter 130 that is not coupled to the stand 110 may be coupled to the heat sink 120. The width of the heat sink 120 may be approximately equal to the thickness of the wavelength selective filter 130. The heat sink 120 may be installed on the side surface of the wavelength selective filter 130, or on a portion of the top surface and the bottom surface through which light does not pass.

8, the width of the heat sink 120 is larger than the thickness of the wavelength selective filter 130 so that the heat sink 120 is out of the region of the wavelength selective filter and the upper surface of the wavelength selective filter 130 and / And may be formed in a protruding shape in a bottom direction. The protruding heat sink 120 prevents the thermal radiation line, which is transmitted in a linear form, from reaching the wavelength selective filter 130 directly, thereby bringing the temperature of the wavelength selective filter 130 closer to the thermoelectric element.

The heat sink 120 may protrude more than 100 袖 m, preferably 200 to 500 袖 m, more than the thickness of the wavelength selective filter.

In addition, the heat sink 120 may further include a cover 140 that absorbs heat to the protruded heat sink of the thermoelectric element. The cover portion 140 includes a feature that blocks heat radiation similarly to the protruding heat sink 120, and light passes therethrough. The cover portion 140 may block the radiant heat 60 that can reach the wavelength selective filter so that the temperature of the wavelength selective filter is closer to the temperature of the thermoelectric element.

It is preferable that the cover portion 140 is coated with an anti-reflective coating on the surface through which the light passes. The heat sink 120 attached to the wavelength selective filter 130 may be formed of a material having a good thermal conductivity. Such a material may be a metal material such as Cu, Al, or CuW, or a ceramic material such as AlN or Silicon have. Preferably, the heat sink 120 is coupled to the wavelength selective filter with a thermally conductive adhesive, and one of the heat sinks is preferably in thermal contact with the stand with an adhesive.

7 to 9, the wavelength selective filter 130 can be less affected by changes in the external environmental temperature. Accordingly, even if the external environmental temperature changes, the wavelength of the laser beam passing through the wavelength selective filter 130 is relatively stable as compared with the conventional one. This process is supported by the graph shown in FIG.

FIG. 10 is a graph showing a change in the wavelength of the laser as the external environment temperature changes when the C-structure of FIG. 8 is used.

Fig. 10 illustrates the structure of Fig. 8 (C-structure) as an example. When the ambient temperature rises by 40 ° C, the temperature of the center of the wavelength selective filter shows a temperature rise of about 2 ° C. Therefore, it is assumed that the transmission wavelength band of the wavelength selective filter is set to the channel set by the ITU-T when the external environment temperature is 40 ° C, as indicated by the solid line in FIG. 10 (a). When the ambient temperature rises to 80 ° C, the temperature of the wavelength selective filter rises by about 2 ° C. At this time, since the wavelength selective filter has a temperature dependence of about 12 pm / C wavelength, the center wavelength of the wavelength selective filter is deviated by about 24 pm from the ITU-T setting channel as indicated by the dotted line in Fig. 10 (a). In order to improve the transmission quality, the " 1 " signal of the laser light must shift to the transmission wavelength peak of the wavelength selective filter, and therefore, the thermoelectric element should be raised by about 0.3 DEG C as shown in FIG. This is because the wavelength of the laser deviates more than 20 pm from the channel set by the ITU-T, and this structure can be applied to 100 GHz DWDM, but it is difficult to apply to 50 GHz DWDM requiring a wavelength stability range of 20 pm or less.

Another embodiment of the present invention is to eliminate the dependence of the wavelength selective filter on the external environmental temperature, which is difficult to completely remove, so that the wavelength of the laser passing through the wavelength selective filter can always have a constant value.

Fig. 11 is a graph showing the relationship between the temperature of the thermoelectric element and the wavelength of the laser, in order to compensate for the fact that the change in the external environment temperature substantially changes the temperature of the wavelength selective filter. And the current is changed to a wavelength having a predetermined transmission band of the wavelength selective filter.

The solid line in FIG. 11 (a) shows a case where the transmission peak of the wavelength-selective filter matches the ITU-T channel at an external temperature of 40 ° C / TEC setting temperature of 40 ° C. The dotted line in FIG. 11 (a) shows the transmission peak of the wavelength selective filter at an external temperature of 80 ° C / TEC setting temperature of 40 ° C. In the case of the dotted line, the wavelength selective filter is affected by the external temperature and shows that the wavelength has already shifted. The broken line in FIG. 11 (a) shows the transmission peak of the wavelength selective filter when the external temperature is 80 ° C / TEC setting temperature 38 ° C. This shows that the transmission wavelength of the wavelength selective filter can be matched to the original ITU-T setting channel by adjusting the temperature of the thermoelectric device in such a way that the laser device compensates for the influence of the external temperature change on the wavelength selective filter In the drawing, the solid line and the dashed line do not coincide with each other, but this is to make a dashed line appear. The setting temperature of the thermoelectric element for canceling the change in the external temperature of the laser device can be predetermined and stored in the memory, and the TEC setting temperature can be appropriately set according to the external temperature.

However, as shown in FIG. 11 (b), when the TEC set temperature changes from 40 ° C to 38 ° C, the oscillation wavelength of the laser deviates from the ITU-T channel by 180 pm or more. At this time, if the temperature of the thermoelectric device is adjusted again, the temperature of the thermoelectric device changes so that the transmission wavelength of the wavelength selective filter deviates from the ITU-T channel. Therefore, in such a situation, there is a need for a method capable of matching the laser wavelength to the appropriate region of the transmission peak of the wavelength selective filter by changing only the laser wavelength without changing the temperature of the thermoelectric element.

When a current is injected, the wavelength of the semiconductor laser can be varied by self-heating or the like. In the case of a general semiconductor laser, a wavelength change of 10 to 20 pm / mA occurs. Taking the wavelength change of 15 pm / mA as an example, a wavelength change of 180 pm can be generated by injecting a current of about 12 mA into the laser diode chip. Since the heat generated by the current flowing through the laser is absorbed by the thermoelectric element and the thermoelectric element is at a constant temperature regardless of the current flowing through the laser diode chip, the transmission peak of the wavelength selective filter, which depends only on the temperature of the thermoelectric element, It becomes irrelevant to the current. That is, by injecting a current into the laser diode chip, the wavelength oscillated in the laser diode chip can be matched to the appropriate region of the wavelength selective filter. Since the temperature of the thermoelectric device is reset by the method of canceling the influence of the external environmental temperature, the transmission wavelength of the wavelength selective filter can coincide with the channel set by ITU-T. The laser oscillation wavelength is placed in the appropriate region of the wavelength selective filter by the current flowing to the laser diode chip, so that it can be applied to 50 GHz DWDM which does not deviate from the wavelength set by the external environment change while enabling high speed long distance transmission. Optical devices can be made.

12 is a diagram showing a configuration of a laser device for stabilizing the wavelength of the laser of the present invention.

The laser device may further include a thermoelectric element for controlling the temperature of the laser and the wavelength selective filter, and a further lens capable of collimating the laser light. The laser apparatus includes a 45-degree partial reflection mirror 230 for dividing the laser light passing through the lens, a first monitoring photodiode 210 for monitoring the intensity of laser light on the optical path passing through the 45-degree partial reflection mirror, And the wavelength selective filter 130 may be disposed on the optical path reflected from the 45-degree partial reflection mirror. The laser device further includes a second monitoring photodiode 220 for monitoring the intensity of the reflected light in the wavelength selective filter of the laser light on the optical path through which the light reflected by the wavelength selective filter passes through the 45- .

In the conventional laser apparatus, the wavelength selective filter is in contact with the upper plate of the thermoelectric element by a stand or the like having a high thermal conductivity by a stand or the like, but is spaced apart from the upper plate of the thermoelectric element and relatively close to the outer wall of the package I was on the street. Therefore, a considerable temperature difference can be generated between the temperature of the thermoelectric device upper plate and the wavelength selective filter, so that the temperature of the thermoelectric device is kept constant, and the temperature of the wavelength selective filter is constant . Therefore, the present invention has the characteristic of complementing the conventional laser device.

Of course, the present invention can be implemented by using a TO-can type package, and a stand having a 45-degree partial reflection mirror and a wavelength selective filter is made of a material having a high thermal conductivity such as Silicon . The wavelength selective filter may be any one of an etalon filter having a high refractive index and a low refractive index on both surfaces of a ceramic material such as glass or quartz and a wavelength selective filter in the form of a single pass filter for forming a reflective film on one surface Can be implemented.

The first monitoring photodiode 210 monitors the output P (t) of the laser beam passing through the partial reflection mirror 230 having the transmittance A. The monitored power (which may be current or voltage depending on the situation) is P1 = A * P (t). (1-A) P (t), the intensity of the laser beam reflected by the 45-degree partial reflection mirror 230 becomes (1-A) P ). Here, F (t) is a function of the wavelength change depending on the temperature of the wavelength selective filter 130. At this time, if the transmission wavelength is exactly matched, F (t) will be very small, and if the transmission wavelength is changed by external influence, F (t) will become large.

The reflected output is again received by the second monitoring photodiode 220 through the 45-degree partial reflecting mirror 230 and its output P2 is (1-A) A * P (t) F (t) do. Accordingly, the ratio (P1 / P2) of the output (any one of power, current, and voltage) of the first and second monitoring photodiodes becomes (1-A) F (t) Is only a function of the wavelength change with the temperature of the wavelength selective filter 130.

The present invention can confirm the correct value of the wavelength output using the ratio of the monitored power of the first and second monitoring photodiodes and can stabilize the wavelength using the ratio value.

The process of stabilizing the wavelength is as follows.

First, after the temperature of the thermoelectric element (TEC) is set, the laser apparatus monitors the temperature of the external environment and controls the temperature of the thermoelectric element corresponding to the external environment temperature to a predetermined temperature (predetermined temperature is applied to the memory value of the system in advance . Then, the laser device adjusts the oscillation wavelength of the laser by adjusting the amount of current applied to the laser so that the ratio of the output of the first and second monitoring photodiodes to a predetermined value is varied according to the temperature of the thermoelectric element.

Thereafter, the laser apparatus monitors the values of the outputs of the first and second monitoring photodiodes in real time or with a predetermined period, and adjusts the oscillation wavelength of the laser by adjusting the current applied to the laser. The oscillation wavelength of the laser can be finely adjusted so that the optimum wavelength for the system performance can be obtained.

Accordingly, in the present invention, in order to eliminate the influence of the external environmental temperature on the wavelength selective filter, when the preset temperature of the thermoelectric element is set according to the external environment temperature, the current applied to the laser is applied to the first and second monitoring photodiodes A method of adjusting the ratio of the flowing current (voltage, electric power) of the battery pack to a predetermined value can be used.

The foregoing description is merely illustrative of the technical idea of the present embodiment, and various modifications and changes may be made to those skilled in the art without departing from the essential characteristics of the embodiments. Therefore, the present embodiments are to be construed as illustrative rather than restrictive, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Patent Application Serial No. 119 (a) (35 USC § 119 (a)) to U.S. Patent Application No. 10-2017-0078949, filed on June 22, 2017, All content is incorporated herein by reference. In addition, the present patent application is also incorporated in the present patent application as a reference, if the priority is given to the countries other than the US for the same reason as above.

Claims

A wavelength selective filter in which a wavelength of transmitted light is selected in accordance with a change in temperature,

A stand coupled to at least one side of the wavelength selective filter;

A heat sink coupled thermally to the other surface of the wavelength selective filter not associated with the stand;

Wherein the heat dissipation plate is not formed in a region through which the light of the wavelength selective filter passes.
The method according to claim 1,

Wherein the wavelength selective filter is cantilevered to the stand,

Wherein the heat dissipating plate is coupled to at least one surface of the one surface of the coupling surface.
3. The method of claim 2,

Wherein the width of the heat sink is equal to or greater than the thickness of the wavelength selective filter.
The method of claim 3,

Further comprising a cover portion having a characteristic that light passes through an upper side of the heat dissipation plate when the width of the heat dissipation plate is larger than the thickness of the wavelength selection type filter.
In a laser device in which a data signal is modulated and oscillated,

A thermoelectric element for compensating an external temperature at which the laser device is operated;

A wavelength selective filter capable of selecting a wavelength transmitted by a temperature change of the thermoelectric element;

And a laser diode whose wavelength is changed by a temperature change of the thermoelectric element and whose data signal is directly modulated.
6. The method of claim 5,

Wherein a wavelength of light oscillated by receiving a predetermined current is varied in the laser diode.
1. A method of operating a laser device including a filter whose wavelength transmitted by a thermoelectric element is selectively variable, a laser diode whose data signal is directly modulated and whose wavelength is oscillated by the temperature of the thermoelectric element,

Setting a temperature of the thermoelectric element;

Measuring an external temperature change of the laser device;

And varying a set temperature of the thermoelectric device when the measured external temperature changes.
8. The method of claim 7,

And compensating for a change in an oscillated wavelength caused by a temperature variation of the thermoelectric element.
9. The method of claim 8,

Wherein the step of compensating further comprises adjusting a current applied to the laser diode such that the ratio of the output of the first and second monitoring photodiodes is a constant ratio.