Optical receiving module and optical receiving device having multiple tunable filters

Abstract

The present invention provides an optical receiving device and an optical receiving module having a tunable wavelength filter. [Solution] The optical receiving device includes a thermoelectric element 320 arranged on a substrate 310, a first tunable wavelength filter 330 with one end positioned on one side of the thermoelectric element and the other end positioned lower and inclined than the plane of the thermoelectric element, which transmits only a first wavelength that varies according to the temperature of the thermoelectric element, a second tunable wavelength filter 350 positioned above the first tunable wavelength filter and spaced apart on one side of the thermoelectric element, which transmits only a second wavelength that varies according to the temperature of the thermoelectric element, a first detector 360 positioned on the substrate at a distance from the thermoelectric element and on the optical axis of the received signal, which detects signals that pass through both the first tunable wavelength filter and the second tunable wavelength filter, and a second detector 370 positioned at a distance from the first detector on the substrate and which detects signals that have passed through the second tunable wavelength filter and are reflected by the first tunable wavelength filter.

Description

Technical Field

[0001] The present invention relates to an optical receiver having a plurality of wavelength-variable filters.

Background Art

[0002] Currently, the world has reached an agreement on the NG-PON2 (Next Generation-passive Optical Network version 2) standard. In such an NG-PON2 standard, four channels with a signal speed of the order of 10 Gbps are set for the downstream optical signal from the telephone exchange to the subscriber. Such a wavelength interval between the four channels is set to a wavelength interval of 100 GHz or 200 GHz. [[ID=thirteen]]

[0003] In such an NG-PON2 standard, one subscriber must select one wavelength for optical reception. Such wavelength separation can be achieved by inputting a channel optical signal of a specific wavelength into an optical receiver using a fixed device that separates wavelengths, thereby receiving the downstream optical signal. However, in an optical receiver configured to separate such fixed wavelengths into specific optical fibers and perform optical reception regardless of the type of wavelength coupled to the specific optical fiber, optical line allocation is not performed dynamically, making optical line management difficult.

[0004] FIG. 1 and FIG. 2 are diagrams for explaining an NG-PON2 (Next Generation-passive Optical Network) TWDM-PON (Tunable Wavelength Division Multiplexing-passive Optical Network) communication network.

[0005] As shown in Figure 1, an NG-PON2 (Next Generation-Passive Optical Network) TWDM-PON (Tunable Wavelength Division Multiplexing-passive Optical Network) communication network consisting of four wavelength channels is shown. In a four-channel NG-PON2, each subscriber transmits data to the telephone exchange using the wavelength of the channel assigned to them for the time allocated to them, and each subscriber receives data transmitted from the telephone exchange to the subscriber for the time allocated to them using the wavelength channel, thereby facilitating communication.

[0006] In this type of TWDM-PON, four OLT (Optical Line Terminal) optical modules in the telephone exchange and 32 or up to 64 subscriber optical modules form a single set to construct a communication network. Each subscriber uses a designated wavelength channel to communicate with multiple subscribers by dividing the channel over time. The splitter 100 is a passive element that simply divides and supplies optical power equally to multiple subscribers; this splitter does not have the function of setting the optical path according to wavelength. The optical power transmitted from the OLT (Optical Line Terminal) in the telephone exchange is distributed equally at the optical splitter regardless of wavelength and transmitted to the subscriber ONU (Optical Network Unit), where the subscriber ONU optical element uses the wavelength of the channel assigned to it to communicate. In NG-PON2, four channels can be used to assign diverse transmission characteristics to each channel, and by changing the wavelengths allowed to subscribers according to these channel-specific transmission characteristics, the communication characteristics of subscribers can be changed. Therefore, with a 4-channel tunable wavelength system, communication characteristics can be set separately for up to four different wavelengths, enabling the construction of a more effective communication network.

[0007] As can be seen in Figure 2, using 8 wavelength channels allows for a wider variety of services compared to 4 channels. Compared to existing NG-PON2, which can perform different types of communication using 4 different wavelengths, increasing the number of allowed channels to 8 channels allows for a wider variety of services, thus increasing the number of channels in tunable communication from 4 to 8 channels brings considerable economic benefits.

[0008] However, increasing the number of channels can lead to a variety of problems because it expands the temperature range of the tunable filter. Specifically, if the NG-PON2 standard has a wavelength spacing of 100 GHz for four channels, and a tunable filter (e.g., an etalon filter) has a change in transmission wavelength with temperature of 10 GHz / °C, then the wavelength spacing between the first and fourth channels is 300 GHz, and the temperature of the tunable filter must be changed by at least 30°C to change the receiving channel. If this standard is applied to eight channels, the wavelength spacing between the first and eighth channels is 700 GHz, and the temperature of the tunable filter must be changed by at least 70°C to receive the receiving channel. Such large temperature changes can lead to problems such as reduced durability of various components inside the optical receiver, decreased long-term reliability of epoxy used in assembly, resulting in airtightness issues, and increased power consumption. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention was proposed to solve the problems of the conventional invention, and the object of the present invention is to provide an optical receiving module and optical receiving device having multiple tunable filters, which can reduce the temperature variation range of the tunable filters and improve the reliability of the optical receiving element when receiving many channels, compared to using a single tunable filter. [Means for solving the problem]

[0010] An optical receiving module having multiple tunable filters to solve the aforementioned problems may include: a thermoelectric element disposed on a substrate and whose temperature is changed; a first tunable filter, one end of which is disposed on one side of the thermoelectric element and the other end of which is disposed lower than the plane of the thermoelectric element and is inclined, which transmits only a first wavelength of the received signal that is variable according to the temperature of the thermoelectric element; a heater disposed on one side, which is disposed on one side of the thermoelectric element and spaced above the first tunable filter, which transmits only a second wavelength of the received signal that is variable according to the temperature of the thermoelectric element and the heater; a first detector, which is disposed on the substrate spaced apart from the thermoelectric element and positioned on the optical axis of the received signal, which detects a signal corresponding to one channel of the N received received channel signals that is transmitted by the first tunable filter, after multiple channel signals have been transmitted by the second tunable filter; and a second detector, which is disposed on the substrate spaced apart from the first detector, which detects a signal that has been transmitted by the second tunable filter and is reflected by the first tunable filter.

[0011] The thermoelectric element may include an inclined surface on one side of the thermoelectric element that is tilted at a certain angle with respect to the plane of the thermoelectric element, and the first tunable filter may be coupled to the inclined surface and arranged at an angle.

[0012] The thermoelectric element may include a housing groove containing an inclined surface of the housing groove that is tilted at a certain angle in the plane of the thermoelectric element, and the first tunable filter may be housed in the inclined surface of the housing groove and arranged at an angle.

[0013] The thermoelectric element includes a protrusion that is inclined at a certain angle with respect to the plane of the thermoelectric element, and the first tunable filter may be coupled to the inclined surface of the protrusion and arranged at an angle.

[0014] The second detector may be positioned on a signal path where the first tunable filter is tilted, and the signal that has passed through the second tunable filter is reflected from the upper surface of the first tunable filter, then from the lower surface of the second tunable filter, and this process is repeated until the signal is ultimately directed downwards.

[0015] The first tunable filter has a first wavelength interval smaller than the overall wavelength interval between the N receiving channels, and the second tunable filter has a second wavelength interval smaller than the wavelength interval between the N receiving channels, characterized in that the first wavelength interval and the second wavelength interval are different from each other.

[0016] The heater can adjust the temperature of the second tunable filter.

[0017] A second tunable filter is located on one side and may further include a heater for adjusting the temperature of the second tunable filter.

[0018] The second tunable filter may further include a reflective coating layer located on at least one of the upper and lower parts of the second tunable filter, excluding the region where the heater is located.

[0019] The second tunable filter further includes a reflective coating layer located on at least one of the upper and lower parts of the second tunable filter, and the heater may be located on the upper side of the reflective coating layer.

[0020] The second tunable filter may further include an electrode connected to the heater at a position corresponding to the lower surface of the heater, and an electrical resistance lower than the electrical resistance of the second tunable filter, formed at a position corresponding to the lower surface of the heater and formed around the electrode.

[0021] An optical receiving module having multiple tunable filters may further include a thermal barrier member positioned between the upper part of the thermoelectric element and the lower part of the second tunable filter, which prevents heat generated by the heater from being transferred to the thermoelectric element and forms a temperature difference between the thermoelectric element and the heater.

[0022] The wavelength of the first tunable filter may be determined according to the temperature change caused by the thermoelectric element, and the wavelength of the second tunable filter may be determined according to the temperature change caused by the thermoelectric element and the heater.

[0023] The optical receiving module having multiple tunable filters further includes a transimpedance amplifier located on top of the substrate, and the second detector may be located on top of the transimpedance amplifier.

[0024] A light receiving device having multiple tunable filters according to yet another embodiment of the present invention includes a thermoelectric element disposed on a substrate and whose temperature is changed; a first tunable filter, one end of which is disposed on one side of the thermoelectric element and the other end of which is disposed lower than the plane of the thermoelectric element and is inclined, which transmits only a first wavelength of the received signal that is variable according to the temperature of the thermoelectric element; a heater disposed on one side, which is disposed on one side of the thermoelectric element and spaced above the first tunable filter, which transmits only a second wavelength of the received signal that is variable according to the temperature of the thermoelectric element and the heater; and a receiving device disposed on the substrate spaced apart from the thermoelectric element and which transmits The system may include: a first detector positioned on the optical axis of the signal, which detects a signal corresponding to one channel among the N received channel signals that is transmitted by the first tunable filter, after multiple channel signals have been transmitted by the second tunable filter; a second detector positioned on the substrate at a distance from the first detector, which detects a signal that has been transmitted by the second tunable filter and then reflected by the first tunable filter; and a control unit that determines which of the first and second tunable filters the signal has been transmitted through, according to the signals detected by the first and second detectors.

[0025] The control unit can determine that if no signal is detected by the first detector and the second detector, the signal corresponding to any one of the N receiving channels could not pass through the second tunable filter; if no signal is detected by the first detector and a signal is detected by the second detector, the control unit can determine that the signal corresponding to any one of the N receiving channels passed through the second tunable filter but could not pass through the first tunable filter; and if a signal is detected by the first detector and no signal is detected by the second detector, the control unit can determine that the signal corresponding to any one of the channels passed through both the first and second tunable filters and was received normally.

[0026] The control unit changes the temperatures of the thermoelectric element and the heater until a signal is detected by the second detector to change the wavelength of the second wavelength-variable filter, sets the temperature at which the signal is detected by the second detector as the set temperature of the second wavelength-variable filter, and then controls to maintain the set temperature of the second wavelength-variable filter using the heater. After passing through the second wavelength-variable filter, the temperature of the thermoelectric element is changed until a signal is detected by the first detector after passing through the wavelength-variable filter and the signal is detected by the first detector, and the temperature at which the signal is detected by the first detector can be set as the set temperature of the first wavelength-variable filter.

Effect of the Invention

[0027] According to the present invention, by using a plurality of wavelength-variable filters, the temperature change range of the wavelength-variable filter can be reduced to enhance the reliability of the optical receiving element.

[0028] By realizing different wavelength intervals between a plurality of wavelength-variable filters, it is possible to prevent signals corresponding to two channels from passing through the plurality of wavelength-variable filters simultaneously.

Brief Description of the Drawings

[0029] [Figure 1-2] It is a diagram for explaining an NG-PON2 (Next Generation-passive Optical Network) TWDM-PON (Tunable Wavelength Division Multiplexing-passive Optical Network) communication network. [Figure 3] It is a diagram for explaining an optical receiving module and an optical receiving device having a plurality of wavelength-variable filters according to an embodiment of the present invention. [Figure 4-5] It is a diagram for explaining a process of selecting a wavelength using one wavelength-variable filter, [Figure 6] It is a diagram for explaining a process of selecting a wavelength using a plurality of wavelength-variable filters. [Figure 7-9]This figure illustrates a coupling configuration of a thermoelectric element and a first tunable filter according to one embodiment of the present invention. [Figure 10] This figure illustrates a coupling configuration of a thermoelectric element and a first tunable filter according to yet another embodiment of the present invention. [Figure 11] This figure illustrates a coupling configuration of a thermoelectric element and a first tunable filter according to yet another embodiment of the present invention. [Figure 12] This figure illustrates an optical receiving module and optical receiving device having multiple tunable filters according to yet another embodiment of the present invention. [Figure 13-14] This figure illustrates the resistance formed in a second wavelength tunable filter according to one embodiment of the present invention. [Figure 15] This diagram illustrates the transmittance of the second tunable filter as it depends on the angle of incidence relative to the optical axis. [Modes for carrying out the invention]

[0030] The specific details for carrying out the invention will be described below with reference to the attached drawings.

[0031] Figure 3 is a diagram illustrating an optical receiving module and optical receiving device having multiple tunable filters according to one embodiment of the present invention.

[0032] As shown in Figure 3, the optical receiving device includes a substrate 310, a thermoelectric element 320, a first tunable filter 330, a thermal shielding member 340, a second tunable filter 350, a first detector 360, a second detector 370, a lens 380, and a control unit 390. In the present invention, the receiving module may also include a substrate 310, a thermoelectric element 320, a first tunable filter 330, a thermal shielding member 340, a second tunable filter 350, a first detector 360, a second detector 370, and a lens 380.

[0033] A thermoelectric element 320 refers to an element that utilizes the thermoelectric phenomenon, and has a structure in which a P-type thermoelectric element and an N-type thermoelectric element are joined between metal electrodes to form a PN junction pair. For example, a thermoelectric element 320 refers to an element that can cool or heat by utilizing the Peltier effect, which is a phenomenon in which heat is absorbed or released by electric current.

[0034] The thermoelectric element 320 is positioned on top of the substrate 310 and its temperature can be changed. For example, the wavelength transmitted by the first tunable filter 330 and the second tunable filter 350 is changed according to the changed temperature of the thermoelectric element 320.

[0035] The thermoelectric element 320 can be implemented in a variety of configurations other than those shown in Figure 3.

[0036] The first tunable filter 330 may be positioned with one end on one side of the thermoelectric element 320 and the other end positioned lower than the plane of the thermoelectric element 320 and tilted. The tilt is achieved at an angle that allows the signal transmitted through the second tunable filter 350 to be reflected from the upper surface of the first tunable filter 330 and then reflected again from the lower surface of the second tunable filter 350. For example, if the first tunable filter 330 is positioned tilted downward by approximately 3 degrees with respect to the plane of the thermoelectric element 320, the incident angle of the signal reflected from the upper surface of the first tunable filter 330 and incident on the second tunable filter 350 becomes 6 degrees, allowing the second tunable filter 350 to reflect the most signal. Here, the explanation is based on the first tunable filter 330 being positioned tilted downward by approximately 3 degrees with respect to the plane of the thermoelectric element 320, but it can be achieved in various ways, such as 1 to 5 degrees. The reason for arranging the first tunable filter 330 at an angle is to ensure that the signal incident vertically and transmitted through the second tunable filter 350 is reflected from the upper surface of the first tunable filter 330, and then reflected again from the lower surface of the second tunable filter 350, and this process is repeated. Various angles can be achieved.

[0037] Figure 15 illustrates the transmittance of the second tunable filter as it depends on the angle of incidence relative to the optical axis.

[0038] As shown in Figures 3 and 15, when a signal transmitted perpendicularly through the second tunable filter 350 is reflected by the first tunable filter 330, which is tilted 3 degrees relative to the second tunable filter 350, the angle of reflection will be 6 degrees from the perpendicular of the second tunable filter 350. Referring to Figure 15, it can be confirmed that a signal with a 6-degree angle cannot be transmitted through the second tunable filter 350 and is reflected. Here, the angle of reflection can be realized in various ways.

[0039] The first tunable filter 330 can selectively transmit only the signal corresponding to one of the multiple channels of signals that have been transmitted through the second tunable filter 350, which are varied according to the temperature of the thermoelectric element 320, from the signal received from the outside.

[0040] The thermal barrier member 340 is positioned between the top of the thermoelectric element 320 and the bottom of the second wavelength tunable filter 350, preventing heat generated by the heater 355, positioned on one side of the second wavelength tunable filter 350, from being transferred to the thermoelectric element 320. Physically, solids cannot completely block heat transfer, and in the case of materials with low thermal conductivity, it is possible to prevent heat generated from the heater 355 from being transferred to the thermoelectric element 320. This obstruction of heat transfer creates a temperature difference between the thermoelectric element 320 and the heater 355 due to the thermal barrier member 340. By utilizing this temperature difference between the thermoelectric element 320 and the heater 355, the second wavelength tunable filter 350 acquires the characteristic of being regulated at a temperature independent of the first wavelength tunable filter 330. Therefore, the thermal barrier member 340 does not need to completely block heat; it only needs to have a heat transfer coefficient that can generate a temperature difference between the thermoelectric element 320 and the heater 355. For example, the thermal barrier member 340 can be made of a material such as glass or quartz, and can be made of a material with a heat transfer coefficient of 0.1 W / mK to 30 W / mK.

[0041] The second tunable filter 350 can be positioned above the first tunable filter 330 at a distance and on one side of the thermoelectric element 320. For example, if there is no thermal barrier member 340, the first tunable filter 330 can be positioned on the side of the thermoelectric element 320, and the second tunable filter 350 can be positioned on the upper surface of the thermoelectric element 320, thereby positioning them at a distance from each other. Another example is if there is a thermal barrier member 340, the first tunable filter 330 can be positioned on the upper or side of the thermoelectric element 320, and the second tunable filter 350 can be positioned above the thermal barrier member 340, thereby positioning them at a distance from each other. In addition to the arrangements described above, various other configurations can be realized in which the second tunable filter 350 is positioned above the first tunable filter 330 at a distance.

[0042] The second tunable filter 350 can transmit signals only at the second wavelength, which is variable according to the temperature of the thermoelectric element 320 and repeats at a fixed periodic interval, from the signals received from the outside. For example, the second tunable filter 350 can transmit multiple channel signals out of N received channel signals. When a designer adjusts the wavelength interval of the wavelength signal of the second tunable filter 350, multiple channel signals may be transmitted unintentionally. Alternatively, a designer can intentionally adjust the wavelength interval of the wavelength signal of the second tunable filter 350 so that multiple channel signals are transmitted.

[0043] The first tunable filter 330 has a first wavelength spacing smaller than the overall wavelength spacing between the N receiving channels, and the second tunable filter 350 has a second wavelength spacing smaller than the wavelength spacing between the N receiving channels. Here, the first wavelength spacing and the second wavelength spacing are different from each other. A detailed explanation of this is given in Figure 6 below.

[0044] The wavelength of the first tunable filter 330 is determined according to the temperature change caused by the thermoelectric element 320, and the wavelength of the second tunable filter 350 is determined according to the temperature change caused by the thermoelectric element 320 and the heater 355.

[0045] The heater 355 is positioned on one side of the second tunable filter 350 and can adjust the temperature of the second tunable filter 350. For example, the heater 355 can be positioned in various locations, such as above or below the second tunable filter 350.

[0046] The reflective coating layer 351 is positioned on the top and bottom of the second tunable filter 350 to adjust the transmission linewidth of the second tunable filter 350. For example, the reflective coating layer 351 may be positioned on only a portion of the top or bottom of the second tunable filter 350 (e.g., the portion excluding the area where the heater 355 is located). Alternatively, the reflective coating layer 351 may be positioned on the entire top or bottom of the second tunable filter 350.

[0047] There is no major problem if the reflective coating layer 351 is placed on all or part of the upper and lower parts of the second tunable filter 350. However, if the heater 355 is placed on top of the reflective coating layer 351 formed on the upper part of the second tunable filter 350, it may prevent the heat from the heater 355 from being transferred to the second tunable filter 350. This may result in unnecessary energy loss when regulating the temperature of the second tunable filter 350, and the temperature of the heater 355 may rise excessively compared to the second tunable filter 350, potentially impairing the stability of the heater 355. Therefore, it is more preferable that the heater 355 is placed in direct contact with the upper part of the second tunable filter 350, and that the reflective coating layer 351 is formed excluding the area where the heater 355 is placed.

[0048] Furthermore, the reflective coating layer 351 may be composed of a material with low thermal conductivity, such as SiNx, SiO2, or Al2O3. This allows the reflective coating layer 351 to create an additional temperature difference between the thermoelectric element 320 and the heater 355, independently of the thermal barrier member 340. Therefore, the reflective coating layer 351 in the lower layer of the second wavelength tunable filter 350 can produce the same effect as the thermal barrier member 340.

[0049] The first detector 360 is positioned on the substrate 310 at a distance from the thermoelectric element 320. The first detector 360 is positioned on the optical axis of the received signal. The second tunable filter 350 allows multiple channel signals from the N received channel signals to pass through, and the first tunable filter 330 allows only one channel from the multiple channel signals passed through by the second tunable filter 350 to pass through. As a result, the first detector 360 can detect the signal corresponding to the one channel that has passed through the first tunable filter 330.

[0050] The first detector 360 is used to detect a signal for a specific channel that has passed through both the tunable filters 330 and 350 from the signals received from the outside.

[0051] For example, the first detector 360 can detect a signal if the wavelength of the signal corresponding to the first channel among the eight receiving channels passes through the first tunable filter 330 and the second tunable filter 350. Similarly, the first detector 360 can detect signals corresponding to the second to eighth channels as the wavelengths transmitted by the tunable filters 330 and 350 change in response to temperature changes.

[0052] The second detector 370 is positioned on the substrate 310, separate from the first detector 360, and can detect signals that have passed through the second tunable filter 350 and been reflected by the first tunable filter 330.

[0053] The second detector 370 is positioned on the signal path where the signal transmitted through the second tunable filter 350 is reflected from the upper surface of the first tunable filter 330, then from the lower surface of the second tunable filter 350, and this process is repeated until the signal is ultimately directed downwards, thereby detecting the signal. For this reason, it is preferable that the right end portion of the first tunable filter 330 is located inside the right end portion of the second tunable filter 350. In other words, it is preferable that the right end portion of the second tunable filter 350 is located outside (to the right in the drawing) the right end portion of the first tunable filter 330.

[0054] The second detector 370 is used to monitor whether or not a signal is generated that is transmitted through the second tunable filter 350 but not through the first tunable filter 330, as described above.

[0055] The transimpedance amplifier (TIA) 375 may be placed on top of the substrate 310. The second detector 370 may be placed on top of the transimpedance amplifier 375.

[0056] The lens 380 is positioned between the first tunable filter 330 and the first detector 360, so that the parallel light signals transmitted through the first tunable filter 330 and the second tunable filter 350 are focused and incident on the first detector 360.

[0057] Since the transmittance of a tunable filter is related to the angle of light incident on the filter, it is preferable that the light transmitted through the tunable filter is parallel light. However, the diameter of a Gbps-class high-speed photodetector may be smaller than 20 μm, and lens 380 may be necessary to focus the light transmitted through the tunable filter as parallel light into the active region of the first photodetector (360).

[0058] The control unit 390 can determine which of the first tunable filter 330 and the second tunable filter 350 the signal passed through, based on the signals detected by the first detector 360 and the second detector 370.

[0059] If no signal is detected by the first detector 360 and the second detector 370, the control unit 390 determines that the signal corresponding to any one of the N receiving channels could not pass through the second tunable filter. In other words, the control unit 390 determines that the received signal could not pass through any of the tunable filters.

[0060] The control unit 390 determines that if no signal is detected by the first detector 360 but a signal is detected by the second detector 370, the signal corresponding to one of the N receiving channels passed through the second tunable filter 350 but not through the first tunable filter 330. In other words, the control unit 390 determines that the received signal passed through the second tunable filter 350 but not through the first tunable filter 330. In other words, a channel of a specific wavelength in the received signal was passed through the second tunable filter 350 but not through the first tunable filter 330.

[0061] The control unit 390 can determine that if a signal is detected by the first detector 360 but not by the second detector 370, the signal corresponding to one of the N received channels has passed through both the first tunable filter 330 and the second tunable filter 350 and been received normally. In other words, the control unit 390 determines that if a signal is detected by the first detector 360, the signal corresponding to a specific channel has passed through both the first tunable filter 330 and the second tunable filter 350 and been received normally, and therefore, no signal is detected by the second detector 370.

[0062] Here, the fact that the detector does not detect a signal does not mean that no signal is detected at all. This is because the tunable filter has some transmission characteristics even in the wavelength range that it blocks. Therefore, rather than detecting a signal based on whether or not a signal is received, the detector determines that a signal has been detected successfully if the intensity of the received signal is higher than a pre-set reference value, and that it has not been detected successfully if it is lower than a pre-set reference value. In other words, the detector can determine whether or not a signal has been detected successfully based on the intensity of the received signal.

[0063] The control unit 390 can change the temperature of the thermoelectric element 320 and the heater 355 to change the wavelength of the second tunable filter 350 until a signal is detected by the second detector 370, and set the temperature at which the signal is detected by the second detector 370 to the set temperature of the second tunable filter 350. For example, the control unit 390 can change the temperature of the thermoelectric element 320 to 38 degrees and change the temperature of the heater 355 to continuously change the wavelength of the second tunable filter 350. The control unit 390 can change the temperature of the heater 355 and detect the temperature at which a signal is detected by the second detector 370 (for example, it may be 42 degrees), and set the detected temperature (for example, 42 degrees) to the set temperature of the second tunable filter 350.

[0064] Next, the control unit 390 can continuously change the temperature of the thermoelectric element 320 using the heater 355, while controlling it so that the set temperature of the second tunable filter (for example, 42 degrees) is maintained, until a signal ("a signal that has passed through the second tunable filter 350 and then through the first tunable filter 330") is detected by the first detector 360. While changing the temperature of the thermoelectric element 320 (by raising or lowering it by 38 degrees), the control unit 390 can detect the temperature at which the signal is detected by the first detector 360 (for example, it may be 40 degrees), and set the detected temperature (for example, 40 degrees) to the set temperature of the first tunable filter 330.

[0065] Figures 4 and 5 illustrate the process of selecting a wavelength using one tunable filter, while Figure 6 illustrates the process of selecting a wavelength using multiple tunable filters.

[0066] As shown in Figures 3, 4, and 5, when using one tunable filter for 8 channels (CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8), the wavelength spacing of the tunable filter must be greater than the overall wavelength spacing of the 8 channels. If the tunable filter (e.g., an etalon filter) has a change in transmission wavelength with temperature of 10 GHz / °C, the wavelength spacing between the 1st and 8th channels is 700 GHz, and the temperature of the tunable filter must be changed by at least 70°C (the temperature difference required to change from CH1 to CH8) in order to receive all receiving channels. If CH1 is set to 40°C, then CH8 will be at a temperature of 110°C. Such large temperature changes can lead to reliability problems in the optical receiver.

[0067] On the other hand, as shown in Figures 3 and 6, the present invention applies to cases where multiple tunable filters (for example, two) are used for 8 channels (CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8).

[0068] The wavelength signal 610 of the first tunable filter 330 periodically has high transmittance at wavelengths FA1, FA2, and FA3, and the wavelength signal 610 has a first wavelength interval 611 that is smaller than the overall wavelength interval 601 for the eight receiving channels 600.

[0069] The wavelength signal 620 of the second tunable filter 350 periodically has high transmittance at FB1, FB2, and FB3 wavelengths, and the wavelength signal 620 has a second wavelength interval 621 that is smaller than the overall wavelength interval 601 for the eight receiving channels 600. Herein, the first wavelength interval 611 and the second wavelength interval 621 are different from each other.

[0070] The second tunable filter 350 must transmit only one channel ("e.g., CH1"). However, referring to Figure 6, when adjusting the interval of the wavelength signals 620, the signal of the first channel ("e.g., CH1") may be transmitted at the FB1 wavelength, and some signals from the fifth and sixth channels may be transmitted at the FB2 wavelength ("located between the fifth and sixth channels"). In this case, from the detector's perspective, two signals may be detected ("first channel signal / signal between the fifth and sixth channels"), making it impossible to determine exactly which channel's signal was received.

[0071] Therefore, in this embodiment, the wavelength signal 610 of the first tunable filter 330 may have a configuration that transmits only one of the two signals ("first channel signal / signal between the fifth channel and the sixth channel") that have been transmitted through the second tunable filter 350. For example, the wavelength signal 610 of the first tunable filter 330 has a second wavelength interval 621 that is different from the first wavelength interval 611, and transmits the signal corresponding to the first channel ("transmits at the FA1 wavelength") and blocks the signal between the fifth channel and the sixth channel ("blocks at the FA2 to FA3 wavelengths"). In other words, the wavelength signal 610 of the first tunable filter 330 can transmit only the signal corresponding to the first channel, thereby enabling only one of the signals that have been transmitted through the second tunable filter 350 to be received by the first detector 360.

[0072] As an example of the process of changing the received channel signal, if the goal is to allow the entire first channel (CH1) to pass through, the temperatures of the first tunable filter 330 and the second tunable filter 350 can be adjusted to shift the FA1, FA2, and FA3 wavelengths of the first tunable filter 330 and one of the FB1, FB2, and FB3 wavelengths of the second tunable filter 350 to the wavelength corresponding to the first channel (CH1). This allows the signal corresponding to the first channel (CH) to be transmitted. By adjusting the first tunable filter 330 and the second tunable filter 350 respectively and repeating the above process, it is possible to control the transmission of signals corresponding to each of the eight channels (CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8).

[0073] This allows the first tunable filter 330 to transmit only one of the multiple signals that have passed through the second tunable filter 350, thereby preventing all of the multiple signals that have passed through the second tunable filter 350 from being incident on the first detector 360.

[0074] Figures 7, 8, and 9 illustrate a coupling configuration of a thermoelectric element and a first tunable filter according to one embodiment of the present invention.

[0075] Figure 7 is a cross-sectional view of the thermoelectric element according to this embodiment, and Figure 8 is a perspective view of the thermoelectric element according to this embodiment.

[0076] As shown in Figures 7 and 8, the thermoelectric element 320 may include a housing groove 321 containing a housing groove inclined surface 321-1 that is inclined at a certain angle in the plane of the thermoelectric element. The housing groove 321 may be configured in a way that can accommodate the first wavelength tunable filter, and the position of the housing groove 321 can be realized in various ways.

[0077] When the first wavelength tunable filter 330 is housed in the housing groove 321 and positioned on the inclined surface 321-1 of the housing groove, it can be positioned at an angle equal to the inclination of the inclined surface 321-1 in the plane of the thermoelectric element 320. Here, the first wavelength tunable filter 330 can be fixed with an epoxy such as H2OE, which has a good heat transfer coefficient.

[0078] As shown in Figure 9, a first tunable filter 330 may be placed in the housing groove 321 of the thermoelectric element 320, a thermal barrier member 340 may be placed on top of the thermoelectric element 320, and a second tunable filter 350 may be placed on top of the thermal barrier member 340. In this way, the first tunable filter 330 can be positioned at a constant incline with the housing groove 321 connected, and the second tunable filter 350 can be positioned on top of the thermal barrier member 340 and parallel to the plane of the thermoelectric element.

[0079] Figure 10 is a side view illustrating the coupling configuration of a thermoelectric element and a first tunable filter according to another embodiment of the present invention.

[0080] As shown in Figure 10, the thermoelectric element 320 includes a projection 322 which includes an inclined surface of the projection that is tilted at a certain angle with respect to the plane of the thermoelectric element. Here, the projection 322 may be formed only in a part of the thermoelectric element 320 or may be formed to be long in a specific longitudinal direction.

[0081] The first tunable filter 330 may be coupled to the inclined surface of the protrusion 322 and positioned at an angle to the plane of the thermoelectric element 320.

[0082] Figure 11 is a side view illustrating the coupling configuration of a thermoelectric element and a first tunable filter according to another embodiment of the present invention.

[0083] As shown in Figure 11, the thermoelectric element 320 may include an inclined surface 323 on one side that is tilted at a certain angle with respect to the plane of the thermoelectric element. Here, the inclined surface may be formed only in a part of the thermoelectric element 320, or it may be formed over a specific length.

[0084] The first tunable filter 330 may be coupled to the inclined surface 323 and positioned at an angle with respect to the plane of the thermoelectric element 320.

[0085] Figure 12 illustrates an optical receiving module and optical receiving device having multiple tunable filters according to another embodiment of the present invention.

[0086] As shown in Figures 11 and 12, the second tunable filter 350 may have reflective coating layers 351 formed on its upper and lower surfaces, and the heater 355 may be positioned above the reflective coating layer 351 formed on the upper surface of the second tunable filter 350.

[0087] The remaining configuration is the same as in Figure 11, so it will be omitted.

[0088] Figures 13 and 14 illustrate the resistors formed in a second tunable filter according to one embodiment of the present invention.

[0089] As shown in Figures 13 and 14, the second tunable filter 350 may include a current-carrying resistor 1310 formed at a position corresponding to the lower surface of the heater 355 and around the electrode 1300. For example, the second tunable filter 350 may be made of a material such as silicon, and specifically, the second tunable filter 350 may be made of a low-doped, un-doped, or semi-insulating silicon substrate. Here, the current-carrying resistor 1310 may be formed by ion implantation or diffusion.

[0090] The current-carrying resistance 1310 has lower electrical resistance than the second wavelength tunable filter 350, which is made of low-doped or undoped semi-insulating silicon. As a result, current flows more easily through the current-carrying resistance 1310 than through the second wavelength tunable filter 350, which has relatively higher electrical resistance. Therefore, it is possible to prevent the current generated by the electrode 1300 from spreading to the second wavelength tunable filter 350, and to keep the heat generated by the current and electrical resistance confined to the vicinity of the electrode 1300.

[0091] In this way, by forming an electrical resistance 1310 so that heat is generated only around the electrode 1300, the heat-generating area can be limited by the electrical resistance 1310.

[0092] Furthermore, the second wavelength tunable filter 350 includes a region that protrudes outward (to the right in the drawing) relative to the thermoelectric element 320 ("cantilevered beam configuration"), and this cantilevered beam configuration corresponds to the region through which the received signal is transmitted. Since the cantilevered beam configuration region is suspended in the air, almost no heat is released to the outside. As a result, there is no heat generation or dissipation in the cantilevered beam configuration region, and therefore a constant temperature can be maintained without temperature differences ("temperature changes"). This can be understood from the basic theory of thermodynamics that if there is no heat generation or dissipation, dQ=0, and therefore dT is also 0. This makes it possible to improve the temperature uniformity of the cantilevered beam configuration region ("light transmission region") of the second wavelength tunable filter 350.

[0093] The described embodiments can also be configured by selectively combining all or part of each embodiment to allow for a variety of variations.

[0094] It should be noted that the examples provided are for illustrative purposes only and not limiting. Furthermore, a typical expert in the technical field of the present invention will understand that a variety of embodiments are possible within the scope of the technical concept of the present invention.

Claims

1. A thermoelectric element placed on a substrate, whose temperature is changed, A first tunable wavelength filter is provided, with one end positioned on one side of the thermoelectric element and the other end positioned lower and tilted below the plane of the thermoelectric element, which transmits only a first wavelength of the received signal that varies according to the temperature of the thermoelectric element. A second tunable filter, which includes a heater positioned on one side, is positioned on one side of the thermoelectric element, spaced above the first tunable filter, and transmits only a second wavelength of the received signal that varies according to the temperature of the thermoelectric element and the heater, A first detector is positioned on the substrate at a distance from the thermoelectric element and on the optical axis of the received signal, and detects a signal corresponding to one channel that is transmitted by the first tunable filter from among the N received channel signals, through which multiple channel signals are transmitted by the second tunable filter. An optical receiving module having a plurality of tunable filters, including a second detector which is positioned on the substrate at a distance from the first detector and detects a signal that has passed through the second tunable filter and has been reflected by the first tunable filter.

2. The aforementioned thermoelectric element is An optical receiving module having a plurality of tunable filters according to claim 1, wherein one side of the thermoelectric element includes an inclined surface that is tilted at a certain angle with respect to the plane of the thermoelectric element, and the first tunable filter is coupled to the inclined surface and arranged at an inclination.

3. The aforementioned thermoelectric element is An optical receiving module having a plurality of tunable filters according to claim 1, comprising a housing groove including a housing groove inclined surface that is inclined at a certain angle in the plane of a thermoelectric element, wherein the first tunable filter is housed in the housing groove inclined surface and arranged at an inclination.

4. The aforementioned thermoelectric element is An optical receiving module having a plurality of tunable filters according to claim 1, wherein the module includes a protrusion that includes an inclined surface of the protrusion that is tilted at a certain angle with respect to the plane of the thermoelectric element, and the first tunable filter is coupled to the inclined surface of the protrusion and arranged at an inclination.

5. The second detector is, An optical receiving module having a plurality of tunable filters according to claim 1, wherein the first tunable filter is arranged at an angle, and the signal that has passed through the second tunable filter is reflected by the upper surface of the first tunable filter and then by the lower surface of the second tunable filter, and this process is repeated until the signal is ultimately directed downward.

6. The first tunable filter is, The first wavelength interval is smaller than the overall wavelength interval between the N receiving channels, The second tunable filter is, An optical receiving module having a plurality of tunable filters according to claim 1, wherein the first wavelength interval and the second wavelength interval are different from each other, and a second wavelength interval is smaller than the overall wavelength interval between the N receiving channels.

7. The aforementioned heater is An optical receiving module having a plurality of tunable filters according to claim 1, wherein the temperature of the second tunable filter is adjusted.

8. The aforementioned heater is It is positioned in direct contact with the second tunable filter, The second tunable filter is, An optical receiving module having a plurality of tunable filters according to claim 7, further comprising reflective coating layers disposed above and below the second tunable filter, excluding the region where the heater is located.

9. The second tunable filter is, The second tunable filter further includes a reflective coating layer disposed on at least one of the upper and lower parts, The aforementioned heater is An optical receiving module having a plurality of tunable filters according to claim 7, disposed above the reflective coating layer.

10. The second tunable filter is, An electrode connected to the heater is positioned at a location corresponding to the lower surface of the heater, An optical receiving module having a plurality of tunable filters according to claim 7, further comprising current-carrying resistance formed around the electrode, having an electrical resistance lower than the electrical resistance of the second tunable filter, and being formed at a position corresponding to the lower surface of the heater.

11. An optical receiving module having a plurality of tunable filters according to claim 7, further comprising a thermal barrier member disposed between the upper part of the thermoelectric element and the lower part of the second tunable filter, which prevents heat generated by the heater from being transferred to the thermoelectric element and forms a temperature difference between the thermoelectric element and the heater.

12. The wavelength of the first tunable filter is Determined according to the temperature change caused by the thermoelectric element, The wavelength of the second tunable filter is An optical receiving module having a plurality of tunable wavelength filters according to claim 7, which are determined according to the temperature change caused by the thermoelectric element and the heater.

13. A thermoelectric element placed on a substrate, whose temperature is changed, A first tunable wavelength filter is provided, with one end positioned on one side of the thermoelectric element and the other end positioned lower and at an angle below the plane of the thermoelectric element, which transmits only a first wavelength of the received signal that varies according to the temperature of the thermoelectric element. A second tunable filter, which includes a heater positioned on one side, is positioned above the first tunable filter and separated from the thermoelectric element, and transmits only a second wavelength of the received signal that varies according to the temperature of the thermoelectric element and the heater, A first detector is positioned on the substrate at a distance from the thermoelectric element and on the optical axis of the received signal, and detects a signal corresponding to one channel among the N received channel signals that is transmitted by the first tunable filter, after multiple channel signals have been transmitted by the second tunable filter from among the multiple transmitted channel signals. A second detector is positioned on the substrate at a distance from the first detector and detects signals that have passed through the second tunable filter and have been reflected by the first tunable filter. An optical receiving device having a plurality of tunable filters, including a control unit that determines which of the first tunable filter and the second tunable filter the signal has passed through, in accordance with the signals detected by the first detector and the second detector.

14. The control unit, If no signal is detected by the first detector and the second detector, it is determined that the signal corresponding to any one of the N receiving channels could not pass through the second tunable filter. If no signal is detected by the first detector and a signal is detected by the second detector, it is determined that the signal corresponding to one of the N receiving channels passed through the second tunable filter but not through the first tunable filter. An optical receiving device having a plurality of tunable filters according to claim 13, wherein if a signal is detected by the first detector and no signal is detected by the second detector, it is determined that a signal corresponding to either one channel has passed through both the first tunable filter and the second tunable filter and has been received normally.

15. The control unit, An optical receiving device having a plurality of tunable filters according to claim 13, wherein the temperature of the thermoelectric element and the heater is changed to change the wavelength of the second tunable filter until a signal is detected by the second detector, the temperature at which a signal is detected by the second detector is set to the set temperature of the second tunable filter, the temperature of the thermoelectric element is changed while controlling the heater to maintain the set temperature of the second tunable filter, the temperature at which a signal is detected by the first detector is changed by passing through the second tunable filter, and the temperature at which a signal is detected by the first detector is set to the set temperature of the first tunable filter.

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