DWDM optical device with two light source chips

Abstract

The present invention relates to a DWDM optical device having two light source chips in which two or more semiconductor laser diode chips, each corresponding to a plurality of wavelength channels, are combined into one optical device package, and the respective semiconductor lasers are driven simultaneously to obtain twice the transmission speed compared to when a single semiconductor laser is driven.

Description

[Technical field]

[0001] The present invention relates to a DWDM optical device, and more particularly to a DWDM optical device having two light source chips in which two or more semiconductor laser diode chips, each corresponding to a plurality of wavelength channels, are combined into one optical device package, and the respective semiconductor lasers are driven simultaneously to obtain twice the transmission speed compared to when a single semiconductor laser is driven. [Background technology]

[0002] Conventionally, various methods have been proposed for assembling laser diode (LD) chips into one package.

[0003] US Patent US7,184,621 in FIG. 1 presents a method of manufacturing four laser diode chips with wavelength intervals of about 20 nm or more, such as 12757 nm, 13002 nm, 13247 nm, and 13492 nm, as one package. A beam spilting filter (or beam combining filter) is used to combine two different wavelengths into one optical path, and the beam spilting filter is a filter that transmits a specific wavelength and reflects a specific wavelength. Such a beam spilting filter can combine light with different wavelengths into one optical path according to the path of the incident light, and can also simultaneously perform the function of separating different wavelengths having the same optical path into different optical paths. Therefore, the beam spilting filter can also simultaneously perform the function of a beam combining filter. In the US Patent No. 7,184,621, in order to collect laser beams having wavelength intervals of about 20 nm or more into one optical path, the optical path of each laser beam is adjusted using a filter arranged to have an incident angle of 45 degrees with respect to each laser beam. However, in the case of a filter arranged at 45 degrees, the transmission / reflection wavelength shifts according to the incident angle of the laser beam incident on each filter.

[0004] Figure 2 shows that in the case of a dichroic filter, whose transmission / reflection changes according to wavelength, the wavelength band that is transmitted / reflected changes according to the angle of incident light. In the 1300~1600nm wavelength band, a dichroic filter causes a shift in the transmitted / reflected wavelength of about 6nm when the incident angle of light changes by about 1 degree based on 45 degrees. Therefore, when using a 45 degree filter, there will be wavelength bands where the transmission / reflection characteristics cannot be controlled by adjusting the incident angle of light.

[0005] FIG. 3 shows the transmission / reflection / guardband of a wavelength filter. As defined in FIG. 3, the precision of the incident angle of light entering the dichroic filter must be adjusted depending on the width of the guardband wavelength between the transmission wavelength band and the reflection wavelength band.

[0006] That is, as in the US Patent No. 7,184,621, when the guardband between the wavelength bands to be combined is 6 nm or more, it is possible to adjust the incidence angle of light incident on the 45 degree dichroic filter within ±1 degree. However, when using a 45 degree dichroic filter, if the guardband is within 0.6 nm, it is inconvenient to have to adjust the incidence angle of light incident on the dichroic filter very precisely within 0.1 degree.

[0007] That is, in order to combine two or more wavelengths into one optical path using an existing 45-degree dichroic filter, an appropriate guardband must exist between each wavelength band.

[0008] In optical communication, a technology that uses multiple wavelengths simultaneously on one optical fiber, called Wavelength Division Multiplexing (WDM), is used to increase the utility of optical fibers. Among these methods, WDM with narrow wavelength spacing, where the wavelength spacing of each optical communication channel is 100GHz (approximately 0.6nm to 0.8nm), is called Dense WDM (DWDM). DWDM has a short wavelength spacing of 100GHz, and when the guardband, which is the minimum wavelength spacing between channels, is 0.6nm to 0.8nm or less, it is necessary to adjust the angle of incidence of light incident on the filter very precisely within 0.1 degree. However, this method is practically impossible, so the method of the US Patent No. 7,184,621 is difficult to apply to the combination of lasers with a guardband of 0.8nm or less, which is DWDM class.

[0009] Meanwhile, instead of using a 45 degree dichroic filter as in US Patent No. 7,184,621, there is a method of muxing multiple wavelengths into one optical fiber as a method of reducing the angle of incidence into the dichroic filter. In FIG. 4, the angle of incidence into the dichroic filter in US Patent No. 8,488,244 is reduced to about 7 degrees and optically commercialized, but the angle of incidence of the laser light incident on each dichroic filter is about 7 degrees. If the angle of incidence is shifted by about + / - 1 degree in such an angle of incidence, a shift in wavelength occurs as shown in FIG. 2. In this case, a shift in wavelength of about + / - 1 nm occurs, so if the guardband is 1 nm or more, multiple laser lights can be muxed into one optical path using such a zig-zag dichroic filter method. However, to mix wavelengths with a short guardband of about 0.2 nm, the size of the zig-zag filter must be very large to increase the tolerance of the incidence angle to about + / - 1 degree. Currently, zig-zag filters with an incidence angle of 7 degrees to the dichroic filter are mainly used to mix wavelengths with a guardband of 32 nm, and the size of such zig-zag filters is about 4 to 5 mm in length. However, if a zig-zag filter with an incidence angle of 2 degrees to the dichroic filter is used to mix wavelengths with a guardband of about 1 nm, the size of the zig-zag filter must be long, about 16 to 20 mm in length. This size is very difficult to manufacture and occupies a large volume, making it difficult to manufacture small optical devices.

[0010] Recently, in order to increase the efficiency of optical fiber utilization, Dense Wavelength Division Multiplexing (DWDM) techniques with wavelength intervals of 200 GHz, 100 GHz, or 50 GHz between channels are used. One example of such a DWDM network is NG-PON2. NG-PON2 is composed of 4 or 8 channels with 100 GHz intervals, and current telecommunications companies use a method of bundling the channels of such optical elements to increase the communication capacity of one network access point, thereby achieving communication capacity at speeds two, three, or four times faster than when using a single optical element. In the structure of FIG. 1 or FIG. 4, the wavelength interval is at least 3 nm or more, and the channel width allowed for each optical element is several nm. Since the semiconductor laser changes by about 0.1 nm per 1°C, the allowable temperature range of each laser diode reaches several tens of degrees Celsius in the conventional structure of FIG. 1 or FIG. 4, and it is not necessary to precisely adjust the temperature of each laser diode chip by installing two or three optical elements. However, NG-PON2 has a wavelength spacing of 100 GHz, which means that the total channel width is only 0.8 nm, and at least 0.2 nm on either side of the 0.8 nm must be used as a guardband with adjacent channels. Therefore, the laser diode chip temperature allowed for each channel must be within at least + / - 2°C, and preferably each laser diode chip must be precisely adjusted to within + / - 1°C of the channel center wavelength.

[0011] When applying the method of mounting two or more semiconductor lasers as one as shown in Figures 1 and 4 and driving the two semiconductor lasers independently or simultaneously to increase communication capacity through channel bundling to DWDM, each laser must be simultaneously controlled to within + / - 100 pm at the center wavelength of each communication channel, i.e., the temperature of each laser diode chip must be controlled within + / - 1°C under optimal conditions.

[0012] Since the oscillation wavelength of each semiconductor laser is determined according to the temperature during the manufacturing process, two or more semiconductor lasers are mounted in one optical element, and in order to simultaneously tune each semiconductor laser to the central wavelength of the allowable channel, each laser must be precisely temperature-controlled independently. In the case of FIG. 4, although not shown in the drawing, four semiconductor lasers are mounted on one thermoelectric element, and all four semiconductor lasers are driven at the same temperature. However, in the case of FIG. 4, the allowable wavelength range of each laser reaches 3 to 4 nm, which has an allowable temperature range of 40°C. Although the oscillation wavelength can be measured very precisely in each laser diode chip state, this has a wavelength inaccuracy of at least + / - 5°C when packaged at this wavelength when the chip is not packaged. However, in the case of FIG. 4, since there is an allowable range of + / - 20°C, it is possible to select chips that can operate each channel at the same temperature during the chip selection process. However, with a channel spacing of 100 GHz, two laser diode chips cannot be operated simultaneously on one thermoelectric element unless the chips are grouped at the same temperature of + / - 1°C after packaging, which is practically impossible due to wavelength inaccuracies during chip selection.

[0013] As another method, it is possible to arrange multiple thermoelectric elements on one optical element, arrange a laser diode chip on each thermoelectric element, and independently tune the oscillation wavelength of each laser diode chip to an allowed channel. However, this is an economically disadvantageous method because it increases the number of thermoelectric elements, increases the number of thermistors for measuring the temperature of each thermoelectric element, and complicates the assembly process.

[0014] In addition, NG-PON2 and Google's Super-PON networks operate laser diodes in burst mode in TDM (Time Division Multiplexing) networks where multiple subscribers share one channel at the DWDM level. In burst mode, the laser diode chip is completely off during times not permitted for each subscriber, and when a burst-on signal is received and the laser diode chip starts to operate, the current for driving the laser diode is concentrated in the active layer of the laser diode chip, generating heat and light. Therefore, when burst mode operation begins, the temperature of the semiconductor laser active layer changes, and the laser diode oscillation wavelength changes accordingly. The temperature change of the semiconductor laser active layer that occurs when burst mode begins easily exceeds 10°C, which corresponds to a wavelength shift of about 10 nm, making burst mode operation difficult in the 100 GHz-spaced DWDM optical communication method.

[0015] Increasing the speed of a laser diode chip in an optical device reduces the receiving sensitivity, making it difficult to increase the maximum number of subscribers. Therefore, since it is possible to increase the number of subscribers by using multiple low-speed channels rather than high-speed signals, a method is required to integrate multiple low-speed laser diode chips into one optical device, accurately align the wavelength of light emitted from each laser diode chip with a channel allowed in DWDM, and suppress wavelength shift of the laser diode chip in burst mode. The above-mentioned conventional technology has problems in terms of DWDM, integration of multiple low-speed laser diode chips, and burst mode operation, and a method is required to solve these problems. [Prior art documents] [Patent documents]

[0016] [Patent Document 0001] US Patent US7,184,621B1 (registered 2007.2.27) [Patent Document 0002] US Patent US8,488,244B1 (registered July 16, 2013) Summary of the Invention [Problem to be solved by the invention]

[0017] The present invention has been proposed to solve the problems that arise in conventional DWDM, and an object of the present invention is to provide a DWDM optical element in which the guardband between channels is within 1 nm, two or more wavelength-tunable optical elements are arranged in one optical element, and the optical elements are driven simultaneously to double the transmission speed.

[0018] Another object of the present invention is to provide a DWDM optical device in which a heater is mounted on a laser diode chip, and when the laser diode operates in burst mode, the temperature of the laser diode chip changes due to heat generated by the laser diode chip itself when it is driven, thereby suppressing the change in laser wavelength caused by the change in the temperature of the chip, and at the same time, the wavelength of light emitted from a plurality of laser diodes can be accurately matched to a channel by using one thermoelectric element and a heater mounted on at least one laser diode chip.

[0019] This patent is the result of research conducted under the following national research and development program: Project number: RS-2022-TI016661 Department name: Small and Medium-sized Venture Business Department Issue Management (Professional Agency) Name: Small and Medium Enterprise Technology Information Promotion Agency Research project name: Investment-based R&D (Scale-Up Tips) Research title: Development of 10Gbps-based 8-channel up / down 80Gbps NG-PON2 extended optical element Contribution ratio: 1 / 1 Project execution organization name: Forbel Co., Ltd. Research period (total): 2022-12-01~2024-11-30 [Means for solving the problem]

[0020] In order to achieve the above object, an optical device according to the present invention provides a wavelength tunable laser, in which one thermoelectric element is disposed in one optical device package, and two or more laser diode chips are disposed on the thermoelectric element, and at least one of the laser diode chips has a heater attached to an upper portion of the laser diode chip, and at least one laser diode chip operates an additional heater disposed thereon at a given temperature of the thermoelectric element to secure the wavelength of a communication channel, thereby allowing at least two laser diode chips to independently emit laser beams as center wavelengths of different communication channels.

[0021] The laser beams emitted from the laser diode chips are polarized orthogonally to each other, and then combined by a polarized light coupler and transmitted to an optical fiber.

[0022] In addition, a half-wavelength polarizing plate is disposed on at least one optical path of the laser light emitted from each of the laser diode chips to convert the polarization of the laser diode chip into an orthogonal polarization, and then the laser light emitted from the two laser diode chips can be combined by a polarizing optical coupler and optically transmitted to an optical fiber.

[0023] At this time, it is preferable that the polarizations of the laser beams emitted from the respective laser diode chips are arranged to be orthogonal to each other by disposing the respective laser diode chips in different positions.

[0024] Meanwhile, the laser diodes serving as the multiple light sources may have a structure including any one of a distributed feedback laser diode (DFB-LD), an electro absorption modulator (DFB-LD-EAM), a distributed Bragg reflection laser diode (DBR-LD-EAM), a semiconductor optical amplifier (DFB-LD-EAM-SOA), and a DBR-LD-EAM-SOA, and multiple light sources can be formed by combining light source chips having the above structure.

[0025] Here, the laser diode chip can be operated in a burst mode.

[0026] It is preferable to modulate the amount of heater-generated heat injected into the laser diode chip equipped with the heater operating in burst mode to compensate for part or all of the heat generated by Joule heat of the laser diode chip itself operating in burst mode.

[0027] In addition, it is preferable that the sum of the amount of heat generated by the heater and the amount of heat generated by the laser diode, which are injected into the laser diode chip equipped with the heater operating in the burst mode, is maintained constant regardless of the burst on-off state.

[0028] It is preferable that the laser diode chip has a reverse mesa ridge structure, and a heater is mounted on the top of the reverse mesa ridge structure.

[0029] Also, the laser diode chip may be provided with a wavelength locker function capable of measuring the wavelength of laser light emitted from at least one of the laser diode chips. Effect of the Invention

[0030] In the present invention, in an optical element having two or more light source chips mounted thereon in a DWDM optical communication network with a wavelength interval of 200 GHz or 100 GHz or less, precise wavelength control of each light source is performed by adjusting the temperature of a thermoelectric element mounted in common to each optical element and by using a heater built into at least one light source chip to adjust the emission wavelengths of multiple light source chips to match a set DWDM channel, thereby reducing the number of thermoelectric elements to ensure economy, and also increasing the DWDM-level data transmission capacity of the optical element by operating multiple light source chips simultaneously.

[0031] In addition, when operating in burst mode, it has the effect of suppressing fluctuations in laser light emitted from each laser diode chip due to joule heating, thereby achieving smooth transmission. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a configuration diagram showing a conventional method for realizing four laser diode chips having wavelength intervals of 20 nm or more as one optical element. [Diagram 2] 1 is a graph showing transmission wavelength characteristic curves according to the angle of incidence for a 45-degree filter. [Diagram 3] 1 is a conceptual diagram of transmission / reflection / guardband of a wavelength filter. [Figure 4] FIG. 1 is a configuration diagram showing a conventional method for realizing four chips having a guardband of 4 nm as one optical element. [Diagram 5] 1 is a graph showing the transmission / reflection characteristics of a polarized light coupler as a function of the angle of incidence. [Figure 6] This is an example of the temperature change in the LD active layer region when 100 mW is applied to the LD active layer region. [Figure 7] This is an example of the temperature change in the LD active region when the application of 100 mW to the heater region is interrupted midway. [Figure 8]This is an example of the temperature change in the LD active region when 100 mW is applied to the heater region and then interrupted, and the laser diode is driven at 100 mW. [Figure 9] 1 is a diagram showing the combination configuration of multiple light source chips for DWDM channels having wavelength spacing narrower than 200 GHz proposed in the present invention. [Figure 10] 1 is a conceptual diagram of how a heater is used to make the wavelength of an upper channel chip reach the target wavelength when the wavelength of a lower channel light source first reaches the target wavelength through a thermoelectric element according to the present invention. [Figure 11] 1 is a conceptual diagram of how a heater is used to make a lower channel chip's wavelength reach a target wavelength when the wavelength of the upper channel light source first reaches a target wavelength through a thermoelectric element according to the present invention. [Figure 12] FIG. 1 is a conceptual diagram showing a method for adjusting the amount of heat generated by the LD and heater when the wavelength reaches the target wavelength by the thermoelectric element. [Figure 13] FIG. 1 is a conceptual diagram showing a method for adjusting the amount of heat generated by the LD and heater when the wavelength reaches the target wavelength due to the thermoelectric element + heater power. [Figure 14] FIG. 1 is a conceptual diagram showing a method of electrically driving the LD and heater when the wavelength reaches the target wavelength due to the thermoelectric element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention will now be described with reference to specific examples, without the precondition that the scope of the present invention is not limited thereto.

[0034] The present invention will be described as being applied to an optical element for Dense Wavelength Division Multiplexing (DWDM) channels in which the spacing between channels is 200 GHz or less.

[0035] However, the concept of the present invention can be applied and utilized in various forms regardless of the description of the present invention, and all such applications are within the scope of the concept of the present invention.

[0036] FIG. 5 is a graph showing the characteristics of a polarization coupler applied to the present invention.

[0037] Polarization couplers are made by evaporating multiple thin layers with high and low refractive index on materials that are transparent to light, such as glass and quartz. In Figure 5, even if the angle of incidence is shifted to 42 degrees or 48 degrees based on the angle of incidence of 45 degrees, more than 90% of P-polarized light is transmitted and more than 90% of S-polarized light is reflected in the wavelength range of about 40 nm. Therefore, when this type of polarization coupler is used as an optical coupler that combines the paths of two lights, it can eliminate the problem of the transmission / reflection ratio changing greatly even with a slight change in the angle of incidence, as shown in Figure 2.

[0038] Figure 6 shows the temperature change over time in the laser active region when 100mW of power is applied to the active layer in a ridge-structure DFB-LD (Distributed Feedback Laser Diode) in burst mode. Typically, the duration of the burst signal reaches about 10 micro-sec, during which the laser active region experiences a temperature change of more than 8°C, which is a wavelength change large enough to affect adjacent channels. Therefore, there is a reason to suppress such wavelength changes.

[0039] Figure 7 shows the temperature change in the laser active layer when a heater is evaporated on top of a ridge-structure DFB-LD and the heater is turned off at a power of 100 mW just as the laser burst operation begins.

[0040] Figure 8 shows the temperature change in the laser active region when the heater is turned off in response to a burst signal while the 100mW heater is operating, and the laser diode is simultaneously driven at 100mW. The LD on effect and heater off effect show that the temperature change in the LD active region is effectively suppressed.

[0041] FIG. 9 is a conceptual diagram showing a method of coupling multiple light source chips for DWDM channels having wavelength intervals narrower than 200 GHz proposed in the present invention.

[0042] 9 shows an example in which two laser diode chips are integrated into one optical element, but more laser diode chips can be mounted. In the present invention, it is assumed that heaters are mounted on both the lower channel laser diode chip 100 and the upper channel laser diode chip 110, but a heater can be mounted on only one of the chips. In this case, the wavelength of the chip not equipped with a heater is adjusted by the thermoelectric element 900.

[0043] In the embodiment of the present invention, the lower channel laser diode chip 100 and the upper channel laser diode chip 110 are each configured for four channels.

[0044] Although each of the laser diode chips 100, 110 has been described as having p-polarized light, they may both have s-polarized light, or one may have s-polarized light and the other may have p-polarized light. If the laser diode chips 100, 110 have different polarizations, the half-wave polarizer 310 of the present invention may not be necessary. The p-polarized laser light emitted from the laser diode chips 100, 110 is collimated into parallel light through the respective parallel light lenses 200, 210. The half-wave polarizer 310 is placed on the optical path of one of the two p-polarized lights to change the p-polarized light to s-polarized light. A total reflection mirror 410 is placed on the optical path with the changed polarization to send the s-polarized light to the polarized light combiner 500.

[0045] The polarized optical coupler 500 reflects s-polarized light and transmits p-polarized light, combining the light emitted from each laser diode chip 100, 110 regardless of wavelength and sending it to an optical fiber (not shown) to transmit a signal. An optical element having a plurality of laser diode chips 100, 110 thus manufactured can be manufactured, and the wavelengths of the plurality of laser diode chips 100, 110 can be independently and accurately matched to the central wavelength of a predetermined channel by using the thermoelectric element 900 and heaters deposited on the laser diode chips 100, 110.

[0046] FIG. 10 shows that in FIG. 9, the wavelength of the laser diode chip 100 for the lower channel is adjusted by the thermoelectric element 900 (4-b). At this time, when the wavelength of the laser diode chip 110 for the upper channel does not reach the target wavelength (4-c), the heater of the laser diode chip 110 is additionally driven to adjust the temperature, so that the frequency of the laser diode 110 light source for the upper channel can be moved to accurately match the center frequency (wavelength) of the assigned channel (4-d).

[0047] FIG. 11 shows that in FIG. 9, the wavelength of the laser diode chip 110 for the upper channel is adjusted by the thermoelectric element 900 (4-b). At this time, when the wavelength of the laser diode chip 100 for the lower channel does not reach the target wavelength (4-c), the heater of the lower laser diode chip 100 is driven to adjust the temperature, so that the frequency of the light source of the laser diode chip 100 for the lower channel can be moved to accurately match the center frequency (wavelength) of the assigned channel (4-d).

[0048] 6 and 8, the heater power and the power injected into the laser diode are equivalently converted into heat. However, while the power injected into the heater is converted into heat, the power injected into the laser diode is converted into heat and light, and the effect on the temperature of the laser diode active region is the portion of the power injected into the laser diode that is converted into heat, excluding the portion that is converted into light and escapes.

[0049] As shown in FIG. 12, when the laser diode chip reaches the target wavelength using only the thermoelectric element, the heat generated by the laser diode (LD) can be injected in place of the heater power to offset the wavelength change caused by Joule heating of the laser diode (LD) itself due to burst mode.

[0050] As shown in FIG. 13, when the thermoelectric element and the heater are operated simultaneously and the laser diode chip reaches the target wavelength, the heater power can be modulated and injected as shown in FIG. 13 to offset the wavelength change caused by Joule heating of the laser diode itself due to the burst mode.

[0051] In FIG. 12 and FIG. 13, it is preferable that the sum of the heat amount generated by driving the laser diode (LD) and the heater heat amount is maintained constant regardless of the presence or absence of the burst operation.

[0052] 12 and 13, a compensation process for the amount of heat generated by driving a laser diode is explained. From an electrical perspective, only a part of the electrical power input to the laser diode (LD) is converted into heat.

[0053] As shown in Fig. 14, the electrical power of the heater to offset this is smaller than the electrical power injected into the laser diode (LD) in Fig. 14. Therefore, the electrical power injected into the laser diode (LD) and the electrical power injected into the heater may be substantially different between the burst mode operation and the idle mode.

[0054] The present invention may include all processes of precisely matching multiple laser diodes to a targeted optical channel using a thermoelectric element and a heater, and modulating the heater power to partially or completely offset the laser diode wavelength change caused by the generation of Joule heat in the laser diode (LD) itself.

[0055] Meanwhile, in the description of the present invention, the light source chip (laser diode chip) is exemplified as a DFB-LD, but it can be applied to a light source having a structure of DFB-LD-Electro Absorption Modulator (EAM) or light sources having various structures such as DFB-LD-EAM, DBR-LD-EAM (Distributed Bragg Reflection Laser Diode EAM), DFB-LD-EAM (semiconductor optical amplifier), etc., and a combination of such various light source chips is also possible.

[0056] In a preferred embodiment of the present invention, the DFB-LD, DFB-LD-EAM, DBR-LD, etc. preferably have a ridge structure with a heater attached, and in particular, it is preferred that the heater be attached on the ridge structure of a reverse mesa structure so that it is easy to attach the heater to the top of the light source.

[0057] Although not described in the present invention, it is also preferable that a wavelength locker function capable of measuring the wavelength of at least one laser diode chip is further added in the optical device package.

[0058] Thus, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and variations can be made by those having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the claims described below.

Claims

1. In tunable lasers, A thermoelectric element disposed in one optical element package; At least two laser diode chips are disposed on the thermoelectric element; At least one of the laser diode chips includes a heater mounted on the laser diode chip; having and applying a temperature obtained by operating the heater in addition to a temperature generated by the thermoelectric element so that the wavelength of the at least one laser diode chip coincides with a center wavelength of a predetermined communication channel, thereby allowing the at least two laser diode chips to independently emit laser beams having center wavelengths of different communication channels.

2. 2. The optical element according to claim 1, further comprising a polarizing optical coupler that combines the laser beams emitted from the respective laser diode chips into mutually orthogonal polarized beams and transmits the combined laser beams to an optical fiber.

3. a half-wave polarizing plate disposed on an optical path of the laser light emitted from any one of the laser diode chips and converting the polarization of the laser diode chip into an orthogonal polarization; The polarization optical coupler includes:

3. The optical device according to claim 2, wherein the laser light received from the half-wavelength polarizer and the laser light received in the remaining laser diode chip without passing through the half-wavelength polarizer are combined and optically transmitted to an optical fiber.

4. The polarization of the laser light emitted from each of the laser diode chips is 2. The optical element according to claim 1, wherein the laser diode chips are arranged in different positions so as to have mutually orthogonal polarizations.

5. The laser diodes, which are the plurality of light sources, have a structure including any one of a distributed feedback laser diode (DFB-LD), an electro absorption modulator (DFB-LD-EAM), a distributed bragg reflection laser diode (DBR-LD-EAM), a semiconductor optical amplifier (DFB-LD-EAM-SOA), and a semiconductor optical amplifier (DBR-LD-EAM-SOA).

2. The optical element according to claim 1, wherein a plurality of light sources are formed by combining light source chips having the above structure.

6. 2. The optical device of claim 1, wherein the laser diode chip operates in a burst mode.

7. 7. The optical element of claim 6, wherein the heater operating in burst mode modulates the amount of heater-generated heat injected into the laser diode chip on which the heater is mounted to compensate for a part or all of the amount of heat generated by Joule heat of the laser diode chip itself operating in burst mode.

8. 7. The optical device of claim 6, wherein the sum of the amount of heat generated by the heater injected into the laser diode chip having the heater operating in burst mode and the amount of heat generated by the laser diode is maintained constant regardless of burst on-off.

9. 2. The optical device of claim 1, wherein the laser diode chip has a reverse mesa ridge structure, and a heater is mounted on an upper portion of the reverse mesa structure.

10. 2. The optical device according to claim 1, further comprising a wavelength locker function capable of measuring a wavelength of laser light emitted from at least one of the laser diode chips.

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