WO2022137418A1 - 光半導体素子 - Google Patents
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- WO2022137418A1 WO2022137418A1 PCT/JP2020/048403 JP2020048403W WO2022137418A1 WO 2022137418 A1 WO2022137418 A1 WO 2022137418A1 JP 2020048403 W JP2020048403 W JP 2020048403W WO 2022137418 A1 WO2022137418 A1 WO 2022137418A1
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/1003—Waveguide having a modified shape along the axis, e.g. branched, curved, tapered, voids
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/14—External cavity lasers
- H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
- H01S5/142—External cavity lasers using a wavelength selective device, e.g. a grating or etalon which comprises an additional resonator
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
- G02F1/025—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction in an optical waveguide structure
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- H01S5/00—Semiconductor lasers
- H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
- H01S5/0078—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for frequency filtering
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- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
- H01S5/0422—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer
- H01S5/0424—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer lateral current injection
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- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
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- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
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- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
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- H01S5/00—Semiconductor lasers
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- H01S5/023—Mount members, e.g. sub-mount members
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
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- H01S5/1014—Tapered waveguide, e.g. spotsize converter
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- H01S5/00—Semiconductor lasers
- H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
Definitions
- the present invention relates to an optical semiconductor device including a semiconductor laser and an optical filter. Regarding.
- a diffraction grating having a ⁇ / 4 phase shift has been used as a typical structure of an optical resonator for single mode.
- the phase is inverted by the phase shifter formed in a part of the uniform diffraction grating, and single mode oscillation at the Bragg wavelength is possible.
- This laser is called a ⁇ / 4 shift DFB (Distributed Feedback) laser and has already been put into practical use.
- the line width of the laser related to the signal quality is important, and the narrower the line width is, the better.
- the line width ⁇ of the semiconductor laser is given by the equation (1) based on the relational expression of Showlow Towns.
- h Planck's constant
- ⁇ is the oscillation frequency
- P0 is the laser output
- vg is the group velocity
- ⁇ m is the resonator loss
- ⁇ 0 is the waveguide loss
- F is the output coefficient
- K is the Petermann's factor
- L a is the active layer length
- L p is the resonator length
- n sp is the emission recombination constant
- ⁇ is the line width increase coefficient. From the equation (1), it is effective to suppress the resonator loss of the semiconductor laser in order to narrow the line width of the laser.
- the resonator loss is suppressed and the Q value of the resonator is increased, the light is strongly localized in the phase shift region. In this localized region of strong light, a large amount of carriers are consumed, so that the carrier density decreases.
- Such a phenomenon that a carrier distribution is generated in the resonator due to the light intensity distribution in the laser is called spatial hole burning.
- a decrease in carrier density results in a decrease in refractive index.
- a distribution is generated in the refractive index inside the resonator.
- the distribution of the refractive index leads to a decrease in the reflectance of the optical resonator and a decrease in mode selectivity, and the oscillation mode of the laser becomes unstable.
- One of the measures to narrow the line width is to use the optical feedback effect. This effect can be achieved by forming an external mirror on the semiconductor laser and returning the reflected light from the mirror to the semiconductor laser to narrow the line width.
- the DFB laser and the etalon filter are connected via a spatial optical system, and the reflected light from the etalon filter is returned to the DFB laser to realize a narrow line width.
- a DFB laser and a ring resonator are hybridly integrated to obtain the same effect.
- a measure to increase the Q value of the optical filter can be considered in order to increase the amount of frequency noise attenuation, but in this case, the phase delay in the optical filter becomes large, the frequency noise on the high frequency side cannot be reduced, and as a result, it becomes narrow. It was controlling the line width.
- the optical semiconductor element according to the present invention comprises, in order, a semiconductor laser, an optical waveguide, a loop waveguide, and a ring resonator optically coupled to the loop waveguide.
- the distance between the semiconductor laser and the ring resonator is 1 ⁇ m or more and 200 ⁇ m or less.
- the optical semiconductor device is characterized in that the semiconductor laser, the optical waveguide, and the DBR grating are provided in this order, and the distance between the semiconductor laser and the DBR grating is 1 ⁇ m or more and 200 ⁇ m or less.
- FIG. 1 is a schematic diagram showing a configuration of an optical semiconductor device according to the first embodiment of the present invention.
- FIG. 2A is a bird's-eye view showing the configuration of a semiconductor laser of an optical semiconductor device according to the first embodiment of the present invention.
- FIG. 2B is a front sectional view showing the configuration of a semiconductor laser of an optical semiconductor device according to the first embodiment of the present invention.
- FIG. 3 is a diagram showing the characteristics of the optical semiconductor device according to the first embodiment of the present invention.
- FIG. 4 is a diagram showing the characteristics of the optical semiconductor device according to the first embodiment of the present invention.
- FIG. 5 is a schematic diagram showing a configuration of an optical semiconductor device according to a second embodiment of the present invention.
- FIG. 6 is a diagram showing the characteristics of the optical semiconductor device according to the second embodiment of the present invention.
- FIG. 7 is a schematic diagram showing the configuration of the optical semiconductor device according to the present invention.
- FIG. 8 is a schematic diagram showing the configuration of the optical semiconductor device according to the present invention.
- the optical semiconductor device 10 includes a first optical waveguide 11_1, a semiconductor laser 12, a second optical waveguide 11_2, and an optical filter.
- the optical filter in the present embodiment is composed of a loop waveguide 13 and a ring resonator 14 coupled to the loop waveguide 13.
- the laser beam can be directly output from the end face (right end in the figure) of the semiconductor laser 12.
- the optical semiconductor element 10 is configured by a laminated structure on a Si substrate 1.
- a Si waveguide composed of, for example, a Si core and a SiO2 cladding is used as the second optical waveguide 11_2 and the optical filter. Since the Si waveguide has a large difference in refractive index between the core and the cladding, it enables steep bending and is suitable for small size and high integration.
- the width of the waveguide structure used for the second optical waveguide 11_2 and the optical filter is 400 nm, and the layer thickness of the waveguide core is 220 nm.
- the length of the second optical waveguide 11_2 connecting the semiconductor laser 12 and the loop waveguide 13 is about 50 ⁇ m.
- the loop waveguide 13 in the optical filter may have a configuration in which the light incident from the semiconductor laser 12 is coupled to the ring resonator 14 and returned to the semiconductor laser 12, and as shown in FIG. 1, the upper surface shape has an angular angle. It may be a curved polygon. Alternatively, the top surface shape may be a circle or an ellipse.
- the radius is about 20 ⁇ m.
- the ring resonator 14 in the optical filter may have a structure in which the incident light coupled from the loop waveguide 13 circulates, and as shown in FIG. 1, the upper surface shape may be circular. Alternatively, the top surface shape may be an ellipse or a polygon. If the upper surface of the ring resonator 14 is circular, the radius of the ring resonator 14 is about 50 ⁇ m.
- the gap between the loop waveguide 13 and the ring resonator 14 may be 50 ⁇ m and may be long enough to be optically coupled.
- the semiconductor laser 12 has a thin film lateral current injection structure.
- the semiconductor laser 12 is, in order, a multiple quantum well (Multi-Quantum Well, MQW) 1204, which is an active layer (light emitting layer), on the SiO 2 clad 1202 covering the Si waveguide (core) 1203 on the Si substrate 1. It is provided with SiN grating 1205 and SiO 2 1212.
- MQW multiple quantum well
- p-InP1206 and n-InP1207 are provided on both sides of the MQW1204, and on the p-InP1206, in order, on the p-InGaAs1208, the p-electrode 1210, and the n-InP1207.
- n-InGaAs1209 and n-electrode 1211 are provided.
- the InP tapered waveguide 1213 is connected to the MQW1204 in the waveguide direction of the laser light, and the laser light is coupled from the InP tapered waveguide 1213 to the Si waveguide 1203 to guide the Si waveguide 1203.
- the element length of the semiconductor laser 12 is 500 ⁇ m.
- the laser beam can be coupled to the Si waveguide 1203 even in the InP tapered waveguide 1213 having a length of about 10 ⁇ m (Non-Patent Document 3).
- the laser beam emitted from the semiconductor laser 12 passes through the second optical waveguide 11_2 and is incident on the ring resonator 14.
- the ring resonator 14 converts the frequency fluctuation of light into the amplitude fluctuation.
- the converted light with amplitude fluctuation returns to the semiconductor laser 12. This amplitude fluctuation works to cancel the frequency fluctuation.
- the increase (attenuation) of the oscillation frequency is changed to the increase (attenuation) of the amplitude by the ring resonator 14, and the amplitude of the feedback light is increased (attenuation).
- the feedback light increases (attenuates)
- the photon density of the DFB laser increases (attenuates)
- the refractive index inside the DFB laser decreases (increases). Since the decrease in the refractive index decreases (increases) the oscillation frequency, the feedback light acts as negative feedback so as to cancel the change in the oscillation frequency.
- the feedback length is the distance between the semiconductor laser 12 and the ring resonator 14. Specifically, the feedback length is the distance from the end of the semiconductor laser 12 on the optical filter side to the portion where the ring resonator 14 couples the loop waveguide 13.
- FIG. 3 shows the calculation result of the frequency noise spectrum.
- the spectrum of frequency noise was calculated based on the optical transfer function.
- the results when the feedback length is 1 cm (101 in the figure) and 100 ⁇ m (102 in the figure) are shown, and the results when the feedback length is not provided for comparison (free running, 100 in the figure) are also shown. ..
- the frequency noise is attenuated on the low frequency side and not attenuated on the high frequency side.
- the frequency noise is attenuated at about 8 GHz or less.
- the feedback length is 100 ⁇ m, the frequency noise is attenuated at about 30 GHz or less. In this way, as the feedback length increases, frequency noise can be attenuated in a wide frequency range. This is because when the feedback length (distance between the semiconductor laser 12 and the ring resonator 14) is long, a phase delay occurs.
- the noise attenuation band can be expanded without causing damping.
- the feedback length is preferably 5 ⁇ m or more, and can be 1 ⁇ m or more, in consideration of the configuration of the element.
- the semiconductor laser 12 and the optical filter can be monolithically integrated on the Si substrate. Further, the taper length can be shortened by using the lateral current injection structure of the thin film for the semiconductor laser 12 structure. In this way, the semiconductor laser 12 and the optical filter can be connected with a short feedback length. As a result, the frequency noise attenuation band can be expanded.
- the ring resonator 14 is used for the optical filter, the increase in the phase delay can be suppressed by adjusting the Q value of the ring resonator 14, and the frequency noise attenuation band can be set. Can be expanded.
- FIG. 4 shows the calculation results of the frequency noise spectrum when the Q value of the ring resonator 14 is low (103 in the figure) and high (104 in the figure).
- the value of the low Q value was set to 1000
- the value of the high Q value was set to 10000.
- the frequency noise is attenuated at about 30 GHz or less, and the noise attenuation amount is about 2.5 dB.
- the frequency noise is attenuated at about 20 GHz or less, and the noise attenuation amount is about 10 dB or more.
- the noise attenuation when the Q value is low, the noise attenuation is small and the frequency noise attenuation band is wide, and when the Q value is high, the noise attenuation is large and the frequency noise attenuation is narrow.
- the attenuation of frequency noise changes depending on the G value, and there is a trade-off relationship between the noise attenuation band and the attenuation amount.
- the frequency noise attenuation can be changed by changing the configuration and changing the Q value.
- the optical semiconductor device 20 according to the second embodiment has the configuration of the optical semiconductor device 20 according to the first embodiment, and further, between the semiconductor laser 12 and the loop waveguide 13.
- a semiconductor optical amplifier 15 is provided in any of the second optical waveguides 11_2.
- the Q value is set low, and the laser beam is amplified by the semiconductor optical amplifier 15 to improve the noise attenuation amount.
- the Q value can be reduced by reducing the distance between the ring resonator 14 and the loop waveguide 13 in the optical semiconductor element 20.
- the Q value can be set to about 100 to 1000.
- the Q value can be reduced by reducing the diameter of the ring resonator 14. For example, by setting the diameter of the ring resonator 14 to about 10 to 100 ⁇ m, the Q value can be set to about 100 to 1000.
- the distance between the ring resonator 14 and the loop waveguide 13 (or the diameter of the ring resonator 14) is 0.3 ⁇ m, and the Q value is set to 1000.
- the semiconductor optical amplifier 15 can amplify the feedback amplitude fluctuation, the feedback gain can be increased and the noise attenuation amount can be increased. Since the frequency band of the semiconductor optical amplifier 15 is as high as several THz, a wide band noise attenuation is possible. That is, the semiconductor optical amplifier 15 makes it possible to achieve both a wide band of frequency noise attenuation and an improvement in the amount of noise attenuation.
- the frequency noise can be attenuated at about 50 GHz or less in both the case without SOA (201 in the figure) and the case with SOA (202 in the figure).
- the noise attenuation is about 2.5 dB.
- the noise attenuation is about 13 dB.
- the frequency noise can be attenuated in a wide range and the noise attenuation amount can be improved.
- the optical semiconductor device 20 As described above, according to the optical semiconductor device 20 according to the present embodiment, it is possible to realize an optical semiconductor device having low frequency noise.
- the optical filter is configured by the Si waveguide
- an InP waveguide may be used.
- the InP waveguide since both the semiconductor laser 12 and the waveguide are composed of the InP-based semiconductor material, it is not necessary to connect the InP-based semiconductor laser and the Si waveguide between different materials, and the size and frequency are further reduced. It is possible to widen the band of noise attenuation.
- SiN waveguide or a SiO x Ny waveguide may be used. Since SiN has a lower thermo-optical coefficient than Si and InP, it is stable against thermal fluctuations. Therefore, the intrinsic frequency noise is low. Further, since the light power resistance is high, the nonlinear optical effect is unlikely to occur even at high power, which is effective for increasing the light output.
- the Q value can be set low by reducing the depth of the diffraction grating groove of the DBR grating 16.
- the Q value can be set to 50 to 1000 by setting the diffraction grating to a depth of 0.01 to 0.2 ⁇ m.
- the distance (feedback length) between the semiconductor laser and the DBR grating is set to 200 ⁇ m or less, the noise attenuation band can be expanded without causing damping.
- the feedback length is preferably 5 ⁇ m or more, and can be 1 ⁇ m or more, in consideration of the configuration of the element.
- this configuration may be applied to the optical semiconductor device 10 according to the first embodiment, and the semiconductor optical amplifier may not be arranged.
- the optical semiconductor element 20 according to the second embodiment is further attached to the second embodiment.
- a coupled waveguide including the loop waveguide 13_2 and the third optical waveguide 11_3 may be provided to take out the laser beam, and the laser beam may be output from the coupled waveguide.
- the laser beam is output only from the tip of the coupled waveguide (only in the left direction in the figure), twice the output can be obtained as compared with the case where it is output from both sides, and the output can be increased. Further, this configuration may be applied to the optical semiconductor device 10 according to the first embodiment.
- the present invention can be applied to transmission and reception station emission sources in digital coherent communication.
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Abstract
Description
に関する。
本発明の第1の実施の形態に係る光半導体素子を、図1~図4を参照して説明する。
第1の実施の形態に係る光半導体素子10は、図1に示すように、第1の光導波路11_1と、半導体レーザ12と、第2の光導波路11_2と、光フィルタとを備える。本実施の形態における光フィルタは、ループ導波路13と、ループ導波路13と結合するリング共振器14から構成される。ここで、第1の光導波路11_1を備えなくても、半導体レーザ12の端面(図中右端)から直接レーザ光を出力できる。
半導体レーザ12から発せられたレーザ光は、この第2の光導波路11_2を通りリング共振器14に入射する。このリング共振器14により、光の周波数揺らぎが振幅揺らぎに変換される。
本発明の第2の実施の形態に係る光半導体素子を、図5~図6を参照して説明する。
11_1、11_2 光導波路
12 半導体レーザ
13 ループ導波路
14 リング共振器
Claims (7)
- 順に、半導体レーザと、
光導波路と、
ループ導波路と、
前記ループ導波路と光結合するリング共振器とを備え、
前記半導体レーザと前記リング共振器との距離が1μm以上200μm以下である
ことを特徴とする光半導体素子。 - 前記光導波路のいずれかの部分に半導体光増幅器
を備える請求項1に記載の光半導体素子。 - 前記ループ導波路と前記リング共振器との間の距離が、0.1μm以上0.5μm以下であることを特徴とする請求項1又は請求項2に記載の光半導体素子。
- 前記リング共振器の半径が、10μm以上1000μm以下である
ことを特徴とする請求項1又は請求項2に記載の光半導体素子。 - 前記リング共振器において、前記ループ導波路が結合する部分とは異なる部分に結合する他のループ導波路と、
前記他のループ導波路に接続する他の光導波路と
を備える請求項1から請求項4のいずれか一項に記載の光半導体素子。 - 順に、半導体レーザと、
光導波路と、
DBRグレーティングとを備え、
前記半導体レーザと前記DBRグレーティングとの距離が1μm以上200μm以下である
ことを特徴とする光半導体素子。 - 前記光導波路のいずれかの部分に半導体光増幅器
を備える請求項6に記載の光半導体素子。
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Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20060127007A1 (en) * | 2002-10-09 | 2006-06-15 | Moti Margalit | Optical filtering device and method |
JP2010177539A (ja) * | 2009-01-30 | 2010-08-12 | Nec Corp | 送信光源及びその製造方法 |
JP2015230991A (ja) * | 2014-06-05 | 2015-12-21 | 富士通株式会社 | 変調光源 |
WO2016152274A1 (ja) * | 2015-03-20 | 2016-09-29 | 古河電気工業株式会社 | 波長可変レーザ素子およびレーザモジュール |
JP2017022247A (ja) * | 2015-07-09 | 2017-01-26 | 富士通株式会社 | 波長選択素子及び波長可変光源 |
JP2017168545A (ja) * | 2016-03-15 | 2017-09-21 | 富士通株式会社 | 光モジュール |
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20060127007A1 (en) * | 2002-10-09 | 2006-06-15 | Moti Margalit | Optical filtering device and method |
JP2010177539A (ja) * | 2009-01-30 | 2010-08-12 | Nec Corp | 送信光源及びその製造方法 |
JP2015230991A (ja) * | 2014-06-05 | 2015-12-21 | 富士通株式会社 | 変調光源 |
WO2016152274A1 (ja) * | 2015-03-20 | 2016-09-29 | 古河電気工業株式会社 | 波長可変レーザ素子およびレーザモジュール |
JP2017022247A (ja) * | 2015-07-09 | 2017-01-26 | 富士通株式会社 | 波長選択素子及び波長可変光源 |
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