Optical element

Abstract

The present invention provides an optical device including a first cladding layer formed on the upper part of a substrate, a MQW (Multiple Quantum Well) active layer formed on the upper part of the first cladding layer over the entire light source region and modulator region, a second cladding layer formed on the upper part of the MQW active layer, and a heater that applies heat to the MQW active layer corresponding to the light source region to adjust the energy bandgap of the light source.

Description

Technical Field

[0001] The present invention relates to an optical device that integrally realizes a light source and a modulator having the same active layer in a DFB-LD (Distributed Feedback laser diode) or DBR-LD (Distributed Bragg Reflector) structure.

Background Art

[0002] Currently, for optical communication, a laser light source with a direct laser modulation structure such as a DFB-LD (Distributed Feedback laser diode) or a DBR-LD (Distributed Bragg Reflector) is used, or an external modulation method that integrates a DFB-LD or a DBR-LD with an EA (Electro-absorption) modulator or an MZ (Mach Zhender) modulator is used.

[0003] An EML (Electro Modulated Laser) in which a light source such as a DFB-LD and an EA (Electro-absorption) modulator or an MZ (Mach Zhender) modulator are integrated minimizes the chirp phenomenon that occurs when directly current-modulating a light source such as a DFB-LD, enabling high-speed and long-distance communication.

[0004] In particular, in the case of an EML light source in which an EA modulator is integrated, it is preferable that the bandgap wavelengths of the semiconductor materials in the DFB-LD region and the EA modulator region have different characteristics. Usually, the bandgap wavelength of the optical gain region such as a DFB-LD preferably has a wavelength that is about 20 nm to 40 nm longer than the bandgap wavelength of the EA modulator region. In epitaxial crystal growth for fabricating a laser light source, methods for making the bandgap wavelengths of the DFB-LD region and the EA modulator region different, such as the SAG (Selective Area Growth) technique, have been very restrictively applied. Usually, after crystal growth in the DFB-LD region, the epi-crystal for the DFB-LD in the portion where the modulator is to be inserted is removed, and an appropriate epi-crystal for the modulator is regrown, etc. There are disadvantages such as the manufacturing method being very difficult and the unit price of the optical device being high.

[0005] FIG. 1 is a diagram for explaining a conventional modulator integrated light source (EML).

[0006] As shown in FIG. 1, the modulator integrated light source (EML) 100 may include a substrate 110, a first cladding layer 120, a first MQW active layer 131, a second MQW active layer 132, a second cladding layer 141, and a third cladding layer 142. Here, multiple quantum well (MQW) is an abbreviation for Multiple Quantum Well.

[0007] The first cladding layer 120 is formed on the upper part of the substrate 110.

[0008] The first MQW active layer 131 is formed on one side (the left side with reference to FIG. 1) above the first cladding layer 120.

[0009] The second MQW active layer 132 is formed on the other side (the right side with reference to FIG. 1) above the first cladding layer 120. Here, the first MQW active layer 131 and the second MQW active layer 132 may be provided in the same plane and may be formed above the first cladding layer 120 in various ways.

[0010] The first MQW active layer 131 region corresponds to a light source, and the second MQW active layer 132 region corresponds to a modulator.

[0011] The energy bandgap of the second MQW active layer 132 is larger than that of the first MQW active layer 131.

[0012] The second cladding layer 141 is formed on top of the first MQW active layer 131.

[0013] The third cladding layer 142 is formed on top of the second MQW active layer 132.

[0014] Thus, a conventional modulator integrated light source (EML) forms a first MQW active layer 131 and a second MQW active layer 132 with different energy bandgaps so that the energy bandgap of the light source region has a smaller value than that of the modulator region.

[0015] To form the first MQW active layer 131 and the second MQW active layer 132 with different energy bandgaps, the first MQW active layer 131 is grown first, the first MQW active layer 131 in the region where the modulator is to be grown is etched, and the second MQW active layer 132 of the modulator is grown in the etched region. In such a process, adjusting the etching depth, stabilizing the etching surface, and regrowing the epitaxial crystal are very difficult processes, and various problems occur in such a process.

[0016] FIG. 2 is a diagram for explaining the path through which heat generated from a heater with a conventional structure is transmitted.

[0017] As shown in FIG. 2, the first cladding layer 210 is formed on top of the substrate 200.

[0018] The second cladding layer 211 is formed on both sides of the upper part of the first cladding layer 210.

[0019] . The MWQ active layer 220 is formed in the center of the second cladding layer 211. As shown in FIG. 2, the width of the MWQ active layer 220 has a very narrow width (for example, about 1.5 um to 2 um).

[0020] In such a prior art, the heat generated from a heater (not shown) is not concentrated and transmitted to the MWQ active layer 220, but is transmitted (240) to the entire surrounding area. Therefore, since all the heat generated from the heater does not contribute to the temperature rise of the MWQ active layer 220, there is a problem that the heat is transmitted inefficiently and the overall energy efficiency is significantly reduced.

[0021] In addition, since the spatial resolution of the semiconductor lithography method used in normal optoelectronic device fabrication is about 1 um, it is very difficult to fabricate a heater on the narrow MWQ active layer 220 with a width of about 1.5 um to 2 um.

[0022] Currently, in internationally standardized communication systems such as NG-PON2 (IEEE G.989.2), the light source uses the TDM (Time domain multiplexing) method, where multiple subscribers time-division share one optical wavelength channel. That is, the laser light source of a subscriber not using communication must be completely turned off. Therefore, in the time-division method (TDM), the light source is completely turned on and off alternately. The semiconductor laser is sensitive to changes in the oscillation wavelength with temperature. Therefore, the light source of an EML device in which a light source such as a DFB-LD device and a modulator are combined must also be turned on and off ("burst mode"). When the light source is turned on in the time-division method, a problem occurs in that the temperature of the light source changes due to self-heat generated from the light source, and thereby the wavelength of the light source changes.

[0023] The matters described in this background art section are created to facilitate the understanding of the background of the invention and may include matters that are not prior art known to those of ordinary skill in the art to which this technology belongs.

[0024] [National Research and Development Project that Supported this Invention] [Subject Specific Number]2022000523 [Subject Number]2022-0-00523 [Name of Ministry]Ministry of Science, Technology, Information and Communications [Name of Project Management (Specialty) Organization]Information and Communications Planning and Evaluation Institute [Name of Research Project]Broadcasting and Communication Industry Technology Development [Name of Research Topic]Development of 25Gbps-based 4-channel 100Gbps NG-PON2+ Transceiver [Contribution Rate]1 / 1 [Name of Project Implementing Organization]PHOVEL Co., Ltd. [Research Period]April 1, 2022 ~ December 31, 2024

Summary of the Invention

Problems to be Solved by the Invention

[0025] An object of the present invention is, in a situation where the energy band gaps of the light source region and the modulator region are the same, to reduce the energy band gap of the light source region by using a heater, so that the energy band gap of the light source region is smaller than the energy band gap of the modulator region, enabling the modulator to operate normally.

[0026] Another object of the present invention is to form the second cladding layer in a structure where the width increases upward, so that electrodes and the like can be conveniently formed upward with a wide width, making the manufacturing very easy.

[0027] Another object of the present invention is to form the second cladding layer in a structure where the width increases upward, so that the heat generated from the heater can be concentrated in the active region without being dispersed, enabling the desired heat to be transmitted to the active region in a short time and providing an optical element with excellent thermal energy efficiency because the heat is not dispersed.

[0028] Another object of the present invention is to control the thermoelectric power of the heater so as to cancel out the thermoelectric power generated when the light source is turned on during the time when the light source is turned on in burst mode, so that the overall thermoelectric power is maintained constant during the entire time, and not only the wavelength of the light source remains constant as time changes, but also the energy bandgap becomes constant.

Means for Solving the Problems

[0029] The optical element according to this embodiment includes a first cladding layer formed on the upper part of a substrate, a MQW (Multiple Quantum Well) active layer formed on the upper part of the first cladding layer over the entire light source region and modulator region, a second cladding layer formed on the upper part of the MQW active layer, and a heater that applies heat to the MQW active layer corresponding to the light source region to adjust the energy bandgap of the light source.

[0030] The heater applies heat to the MQW active layer corresponding to the light source region to increase the temperature, so that the light source energy bandgap is reduced, and the light source energy bandgap is smaller than the modulator energy bandgap in the modulator region.

[0031] The second cladding layer in the light source region has a shape in which the width of the lower side is smaller than the width of the upper side.

[0032] The optical element further includes a first electrode formed on the upper part of the second cladding layer and an insulating film formed on the upper part of the first electrode, and the heater is formed on the upper part of the insulating film.

[0033] The second cladding layer is formed such that the height of the cladding layer formed in the light source region and the modulator region is higher than the cladding layer formed between the light source region and the modulator region.

[0034] The optical element further includes a second electrode formed on the upper part of the second cladding layer in the modulator region.

[0035] The heater maintains the thermoelectric power (P) for forming a desired light source energy band gap in the light source region. However, when the optical element is driven in burst mode, during the time when the light source is on in burst mode and thermoelectric power (R) is generated, the thermoelectric power (P) of the heater is changed to "thermoelectric power (P) - thermoelectric power (R)" so that the thermoelectric power (P) is constantly maintained even when driven in burst mode.

Advantages of the Invention

[0036] In the present invention, in a situation where the energy band gaps of the light source region and the modulator region are the same, by using a heater to reduce the energy band gap of the light source region, the energy band gap of the light source region can be made smaller than that of the modulator region, enabling the modulator to operate normally.

[0037] Moreover, in the present invention, by forming the second cladding layer with a structure that becomes wider towards the upper side, electrodes and the like can be conveniently formed on the wider upper side, making the manufacturing very easy.

[0038] Furthermore, in the present invention, by forming the second cladding layer with a structure that becomes wider towards the upper side, the heat generated from the heater can be concentrated in the active region without being dispersed, so that the desired heat can be transmitted to the active region in a short time. Also, since the heat is not dispersed, the thermal energy efficiency is excellent.

[0039] Also, in the present invention, by controlling the thermoelectric power of the heater so as to cancel out the thermoelectric power generated when the light source is on during the time when the light source is on in burst mode, not only can the overall thermoelectric power be constantly maintained throughout the entire time and the wavelength of the light source remain constant even when the time changes, but also the energy band gap can be made constant.

Brief Description of the Drawings

[0040]

Figure 1

Figure 2

Figures 3-4

Figures 5-6

Figures 7-10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0041] Hereinafter, specific contents for carrying out the invention will be described in detail with reference to the accompanying drawings.

[0042] FIG. 3 and FIG. 4 are diagrams for explaining the light emission principle and the light absorption principle.

[0043] As shown in FIG. 3, when current is injected in a p-n junction structure, electron movement exceeding the energy band gap 330 between the conduction band 310 and the valence band 320 appearing due to the semiconductor epitaxial crystal structure occurs, and photons having a wavelength corresponding to this energy are emitted.

[0044] As shown in FIG. 4, when light is absorbed by a semiconductor, electrons move from the valence band 320 to the conduction band 310 by absorbing photon energy exceeding the energy band gap 330, and light absorption occurs.

[0045] Therefore, if the light source and the modulator have the same energy gap, the light emitted from the light source is easily absorbed by the modulator, resulting in a decrease in the transmittance of the modulator.

[0046] FIG. 5 and FIG. 6 are diagrams for explaining the optical modulation principle in an optical element in which a light source and a modulator are integrated.

[0047] In FIGS. 5 and 6, optical modulation is explained based on the case where the energy band gap 430 of the modulator region is larger than the energy band gap 330 of the light source region.

[0048] As shown in FIG. 5, the light source and the modulator are divided into a light source region 300 and a modulator region 400.

[0049] In the light source region 300, electron transfer occurs across the energy band gap 330 of the light source between the conduction band 310 and the valence band 320, and photons of a wavelength corresponding to this energy are emitted.

[0050] In the modulator region 400, since no reverse voltage is applied to the modulator, if the size of the energy band gap 430 of the modulator between the conduction band 410 and the valence band 420 does not change, the energy band gap 430 of the modulator region 400 is larger than the energy band gap of the light source region, so the light of the energy emitted from the light source passes through the modulator without being absorbed.

[0051] As shown in FIG. 6, when a reverse voltage is applied to the modulator, the energy band gap 430 of the modulator is reduced (440) due to the QCSE (Quantum Confined Stark Effect) (for example, it can be the same as the energy band gap 330 of the light source). In this case, the modulator region can well absorb the light emitted from the light source and exhibit the basic characteristics (functions) of the modulator. Thus, it can be confirmed that when the energy band gap of the modulator region is made larger than that of the light source region, the modulator operates well.

[0052] FIGS. 7, 8, 9, and 10 are diagrams for explaining an optical element according to an embodiment of the present invention.

[0053] As shown in FIG. 7, the optical element 700 may include a substrate 710, a first cladding layer 720, an MQW active layer 730, a second cladding layer 740, a first electrode 750, an insulating film 760, a heater 770, a second electrode 780, and a control unit.

[0054] The light source included in the optical element 700 may have a DFB-LD or DBR-LD structure.

[0055] The first cladding layer 720 may be formed on the upper part of the substrate 710.

[0056] The MQW active layer 730 may be formed on the upper part of the first cladding layer 720. The MQW active layer 131 may be formed by a single epitaxial growth covering both the light source region 800 which is the left region with reference to FIG. 7 and the modulator region 900 which is the right region with reference to FIG. 7. Instead of different MQW active layers, the same one MQW active layer may be formed on the upper part of the first cladding layer 720.

[0057] The second cladding layer 740 may be formed on top of the MQW active layer 730. The height of the cladding layer formed in the light source region 800 and the modulator region 900 of the second cladding layer 740 may be substantially the same, and the cladding layer formed between the light source region 800 and the modulator region 900 may be formed lower than the cladding layer formed in the light source region 800 and the modulator region 900.

[0058] The second cladding layer 740 may further include a grating portion 740 on the inner lower side.

[0059] As another example, the grating portion 740 may be formed on top of the first cladding layer 720 instead of the second cladding layer 740.

[0060] The first electrode 750 may be formed on top of the second cladding layer 740 in the light source region 800.

[0061] The first electrode 750 is a P electrode, and electrons in the electrode move to the MQW active layer 730 through the second cladding layer 740.

[0062] The insulating film 760 may be formed between the first electrode 750 and the heater 770. The insulating film 760 can insulate between the first electrode 750 and the heater 770.

[0063] The heater 770 generates heat, and the generated heat can be transmitted to the MQW active layer 730 through the first electrode 750 and the second cladding layer 740, etc.

[0064] The second electrode 780 may be formed on top of the second cladding layer 740 in the modulator region 900.

[0065] The second electrode 780 is an electrode used to apply a reverse voltage to the modulator. When a reverse voltage is applied to the modulator using the second electrode 780, the energy bandgap 930 of the modulator is reduced by QCSE (Quantum confined stark effect).

[0066] Since the MQW active layer 730 is formed identically across the light source region 800 and the modulator region 900, the light source energy band gap 830 between the conduction band 810 and the valence band 820 in the light source region 800 and the modulator energy band gap 930 between the conduction band 910 and the valence band 920 in the modulator region 900 are the same.

[0067] A control unit (not shown) can control the driving of the configuration formed on the optical element. For example, the control unit (not shown) can control the first electrode, the second electrode, the heater, etc. according to the input control signal.

[0068] The connection part between the light source and the modulator conversion part can be an electrically isolation region.

[0069] FIG. 8 is a view of the second cladding layer 740, the first electrode 750, the insulating film 760, and the heater 770 seen from the "A direction" shown in FIG. 7.

[0070] As shown in FIG. 8, the second cladding layer 740 has a shape in which the lower width 742 is smaller than the upper width 743. For example, the second cladding layer 740 may have a reverse mesa structure.

[0071] Since the second cladding 740 has the structure as shown in FIG. 8, the first electrode 750, the insulating film 760, and the heater 770 can be installed in a wide place like the upper width 743 of the second cladding layer 740 instead of being formed in a narrow place like the lower width 742 of the second cladding layer 740, so the production is very easy.

[0072] FIG. 9 is a diagram for explaining the path through which the heat generated from the heater in FIG. 8 moves.

[0073] As shown in FIG. 9, the heat generated from the heater 770 can move (744) intensively without being dispersed into the active region 731 of the MQW active layer 730 along the structure of the second cladding layer 740.

[0074] According to this embodiment, by having a structure in which the heat generated from the heater 770 is concentrated in the active region 731 without being dispersed, not only can the desired heat be transmitted to the active region 731 in a short time, but also since the heat is not dispersed, the thermal energy efficiency is very excellent.

[0075] FIG. 10 is a view of the second cladding layer 740 and the second electrode 780 as seen from the “B direction” shown in FIG. 7.

[0076] As shown in FIG. 10, the second cladding layer 740 in the modulator region may be formed in a direction perpendicular to the MQW active layer 730. For example, the second cladding layer 740 may have a vertical mesa structure, but is not limited to such a structure and the second cladding layer 740 may be formed in various structures.

[0077] The second electrode 780 may be formed on the upper side of the second cladding layer 740.

[0078] FIG. 11 is a diagram for explaining a method of adjusting an energy band gap in an optical element according to an embodiment of the present invention.

[0079] Referring to FIG. 11, as described in FIG. 7, the light source energy band gap 1130 of the light source region 1000 and the modulation energy band gap 1230 of the modulator region 1020 have the same value.

[0080] However, in order to exhibit normal modulator characteristics (performance), the light source energy band gap 1130 must be smaller than the modulation energy band gap 1230 of the modulator region 1020.

[0081] Therefore, in the present invention, heat can be applied to the light source region 1000 using a heater to increase the temperature and reduce the light source energy band gap 1130.

[0082] For example, when the energy band gap is reduced by temperature, the energy band gap is usually reduced by 0.4 to 0.5 nm / °C when converted to wavelength. That is, a temperature increase of about 40°C results in a shift of the band gap wavelength of about 20 nm or a reduction in the energy band gap.

[0083] As described above, heat can be applied to the light source region 1000 to reduce the light source energy band gap 1130 to be like the light source energy band gap 1130 of the light source region 1010. Thereby, the light source energy band gap 1130 can be made smaller than the modulator energy band gap 1230 of the modulation region 1020.

[0084] In this way, after the light source energy band gap 1130 becomes smaller than the modulator energy band gap 1230 of the modulation region 1020, in the modulator region 1020, when a reverse voltage is not applied to the modulator and the size of the modulator energy band gap 1230 between the conduction band 1210 and the valence band 1220 does not change, since the energy band gap 1230 of the modulator region 1020 is larger than the reduced energy band gap 1230 of the light source region 1010, the light of the energy emitted from the light source passes through without being absorbed by the modulator.

[0085] If a reverse voltage is applied to the modulator, the energy band gap 1230 of the modulator region 1030 is reduced by the quantum confined stark effect (QCSE) (for example, it can become the same as the reduced energy band gap 1130 of the light source region 1010). In this case, the modulator region absorbs the light emitted from the light source well and exhibits the basic characteristics (functions) of the modulator.

[0086] In this embodiment, by using a heater to reduce the energy band gap of the light source region so that the energy band gap of the light source region is smaller than the energy band gap of the modulator region, the modulator can operate normally.

[0087] FIG. 12 is a diagram for explaining a method of controlling a heater when an optical element according to an embodiment of the present invention operates in a burst mode.

[0088] Referring to FIGS. 7, 8, 9, 10, 11, and 12, in the time-division multiplexing (TDM) method, the light source is alternately completely turned on and off (on-off). Therefore, the light source of the optical element according to this embodiment must also be turned on and off ("burst mode").

[0089] The heater 770 can generate a thermoelectric power (P) to obtain a desired energy band gap 1130 of the light source (1200).

[0090] When the light source is turned on in the burst mode, a thermoelectric power (R) is generated, and when the light source is turned off, the thermoelectric power becomes 0 (1210).

[0091] If the thermoelectric power (P) generated from the heater 770 and the thermoelectric power (R) generated when the light source is turned on in the burst mode are directly combined, the thermoelectric power is not constant and changes to "P + R" and "P" power (1220). In this case, not only does the wavelength of the light source change due to the thermoelectric power, but also the energy band gap changes over time.

[0092] Therefore, the heater 770 of the present invention changes the thermoelectric power of the heater 770 from "P → P - R" during the time when the thermoelectric power (R) is generated when the light source is turned on in the burst mode (1230). A control unit (not shown) can control the heater 770 to operate as described above.

[0093] By changing and controlling the thermoelectric power of the heater 770 from "P → P-R", even when the light source turns on in burst mode and thermoelectric power (R) is generated and combined with the thermoelectric power of the heater 770, the thermoelectric power (P) can be maintained constant.

[0094] As a result, even when the light source turns on in burst mode, the overall thermoelectric power can be maintained constant. Therefore, not only can the wavelength of the light source be kept constant over time, but the energy bandgap can also be maintained constant.

[0095] All or part of each embodiment can be selectively combined and configured so that the above-described embodiments can be variously modified.

[0096] It should also be noted that the embodiments are for illustrative purposes and not for restrictive purposes. Also, those of ordinary skill in the technical field of the present invention will be able to understand that various embodiments are possible within the scope of the technical idea of the present invention.

Claims

1. A first cladding layer formed on the upper part of a substrate, A MQW (Multiple Quantum Well) active layer formed on the upper part of the first cladding layer over the entire light source region and modulator region, A second cladding layer formed on the upper part of the MQW active layer, An optical element including a heater that applies heat to the MQW active layer corresponding to the light source region to adjust the energy bandgap of the light source.

2. The heater is characterized in that heat is applied to the MQW active layer corresponding to the light source region to increase the temperature so that the light source energy bandgap is reduced, and the light source energy bandgap becomes smaller than the modulator energy bandgap in the modulator region, according to the optical element described in Claim 1.

3. The second cladding layer in the light source region has a shape in which the width of the lower side is smaller than the width of the upper side, according to the optical element described in Claim 1.

4. Further includes a first electrode formed on the upper part of the second cladding layer, And an insulating film formed on the upper part of the first electrode, The heater is formed on the upper part of the insulating film, according to the optical element described in Claim 3.

5. The second cladding layer is characterized in that the height of the cladding layer formed in the light source region and the modulator region is formed higher than the cladding layer formed between the light source region and the modulator region, according to the optical element described in Claim 1.

6. Further includes a second electrode formed on the upper part of the second cladding layer in the modulator region, according to the optical element described in Claim 5.

7. The heater is characterized in that it maintains the thermoelectric power (P) for forming the desired light source energy bandgap in the light source region, but when the optical element is driven in burst mode, during the time when the light source is on (on) in burst mode and thermoelectric power (R) is generated, the thermoelectric power (P) of the heater is changed to "thermoelectric power (P) - thermoelectric power (R)" so that the thermoelectric power (P) is constantly maintained even when driven in burst mode, according to the optical element described in Claim 1.

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