WO2017056474A1 - Semiconductor laser light source - Google Patents

Semiconductor laser light source Download PDF

Info

Publication number
WO2017056474A1
WO2017056474A1 PCT/JP2016/004339 JP2016004339W WO2017056474A1 WO 2017056474 A1 WO2017056474 A1 WO 2017056474A1 JP 2016004339 W JP2016004339 W JP 2016004339W WO 2017056474 A1 WO2017056474 A1 WO 2017056474A1
Authority
WO
WIPO (PCT)
Prior art keywords
semiconductor laser
optical
light source
laser
single mode
Prior art date
Application number
PCT/JP2016/004339
Other languages
French (fr)
Japanese (ja)
Inventor
裕幸 山崎
洋 八坂
Original Assignee
日本電気株式会社
国立大学法人東北大学
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日本電気株式会社, 国立大学法人東北大学 filed Critical 日本電気株式会社
Priority to JP2017542740A priority Critical patent/JP6729857B2/en
Publication of WO2017056474A1 publication Critical patent/WO2017056474A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers

Definitions

  • the present invention relates to a semiconductor laser light source, and more particularly to a narrow line width semiconductor laser light source used in the optical communication field and the optical measurement field.
  • a fiber laser or a semiconductor laser having an external resonator configuration is used as the narrow linewidth laser light source.
  • a fiber laser is disclosed in Non-Patent Document 1, for example.
  • FIG. 1 is a diagram illustrating a configuration example of a fiber laser disclosed in Non-Patent Document 1.
  • resonators using a polarization maintaining fiber 03 are arranged in a ring shape, and a polarization maintaining type ⁇ / 4 shift diffraction is partly provided.
  • An Er 3+ doped fiber laser 01 with a grating is provided.
  • An excitation light source 02 having a wavelength of 1480 nm is coupled to a resonator via a polarization maintaining WDM (wavelength division multiplex) coupler 04.
  • WDM wavelength division multiplex
  • the light extracted from the polarization maintaining coupler 05 inserted into the resonator is extracted to the outside as an optical output 08 through the polarization maintaining optical isolator 06 and the optical bandpass filter 07.
  • a polarization maintaining optical isolator 06 is also inserted in the resonator between the fiber laser 01 and the polarization maintaining coupler 05.
  • a specific wavelength can be selectively oscillated by exciting the resonator with the pumping light source 02, and by reducing the length of the ring-shaped resonator, narrow linewidth light can be obtained. It can oscillate.
  • Non-Patent Document 2 Non-Patent Document 3
  • Non-Patent Document 4 Non-Patent Document 5
  • FIG. 2 is a diagram illustrating a configuration example of an external resonator laser using a bulk diffraction grating disclosed in Non-Patent Document 2.
  • the external resonator laser disclosed in Non-Patent Document 2 uses a bulk diffraction grating mirror 10 as an external mirror.
  • the light reflected by the bulk diffraction grating mirror 10 is optically coupled to the optical fiber 13 through the lens 11, the semiconductor gain medium 09, the lens 11, the optical isolator 12, and the lens 11, as shown in FIG.
  • the light reflected by the bulk diffraction grating mirror 10 is optically coupled to the optical fiber 13 through the lens 11, the semiconductor gain medium 09, the lens 11, the optical isolator 12, and the lens 11, as shown in FIG.
  • FIG. 3 is a diagram showing a configuration example of an external resonator laser using a fiber Bragg diffraction grating disclosed in Non-Patent Document 3.
  • the external cavity laser disclosed in Non-Patent Document 3 uses a fiber Bragg diffraction grating 14 as an external mirror.
  • the light emitted from the semiconductor gain medium 09 and reflected by the fiber Bragg diffraction grating 14 is optically coupled to the optical fiber 13 via the optical isolator 12.
  • FIG. 4 is a diagram showing a configuration example of an external resonator laser using a waveguide type diffraction grating disclosed in Non-Patent Document 4.
  • the external cavity laser disclosed in Non-Patent Document 4 uses a waveguide type diffraction grating 15 as an external mirror.
  • the light reflected by the waveguide type diffraction grating 15 is optically coupled to the optical fiber 13 through the lens 11, the semiconductor gain medium 09, the lens 11, the optical isolator 12, and the lens 11, as shown in FIG. Is done.
  • FIG. 5 is a diagram illustrating a configuration example of an external resonator laser using a ring filter disclosed in Non-Patent Document 5.
  • the external cavity laser disclosed in Non-Patent Document 5 is an optical light whose core is a semiconductor optical amplification medium (semiconductor gain medium) 09 and nitrogen-doped silica (SiON) as an external cavity.
  • a three-stage ring filter 16 using a waveguide is hybrid-integrated on a Si platform 17.
  • the semiconductor optical amplifying medium 09 does not have a wavelength selection function, and it is necessary to use a multi-stage ring resonator for making the oscillation light into a single mode.
  • FIG. 5 is a diagram illustrating a configuration example of an external resonator laser using a ring filter disclosed in Non-Patent Document 5.
  • the external cavity laser disclosed in Non-Patent Document 5 is an optical light whose core is a semiconductor optical amplification medium (semiconductor gain medium) 09 and nitrogen
  • the light reflected by the three-stage ring filter 16 and amplified by the semiconductor optical amplifying medium (semiconductor gain medium) 09 passes through the lens 11, the optical isolator 12, and the lens 11 to the optical fiber. 13 is optically coupled.
  • Patent Document 1 discloses a “laser light source” that includes a laser that oscillates in a single mode and a narrow-band filter that is disposed at the output end of the laser and that has a center wavelength that matches the oscillation wavelength.
  • a multilayer interference film filter is used as a narrow band filter.
  • Patent Document 2 discloses an erbium fiber laser that generates a clean optical carrier.
  • the erbium fiber laser disclosed in Patent Document 2 includes a ring-like or linear erbium-doped fiber and a pump laser that pumps the erbium-doped fiber.
  • the ring-shaped erbium-doped fiber is used as a laser cavity and is connected by a coupler to an optical fiber coupled to a pump laser and an output fiber.
  • the laser cavity includes an optical isolator and a Fabry-Perot interferometer.
  • a grating structure may be provided instead of the Fabry-Perot / interferometer.
  • Linear erbium-doped fiber includes a combination of grating and mirror.
  • Patent Document 3 discloses a distributed feedback semiconductor laser that suppresses the Fabry-Perot mode and oscillates in a distributed feedback mode in a temperature range from the operation guarantee upper limit temperature to the operation guarantee lower limit temperature.
  • the distributed feedback semiconductor laser disclosed in Patent Document 3 includes a semiconductor region having one end surface and the other end surface, a reflection film, and an antireflection film.
  • the reflective film is provided on one end surface of the semiconductor region and functions as a first filter portion.
  • the antireflection film is provided on the other end surface of the semiconductor region and functions as a second filter portion.
  • the semiconductor region includes an active layer provided between the p-type cladding layer and the n-type cladding layer, and a Bragg diffraction grating optically coupled to the active layer.
  • the p-type cladding layer, the n-type cladding layer, and the active layer are provided on the substrate.
  • the oscillation wavelength in the distributed feedback mode (DFB mode) of the semiconductor laser has temperature dependence.
  • Patent Document 4 discloses an “integrated semiconductor light source” in which a single mode semiconductor laser and a ring-shaped semiconductor optical waveguide are integrated on the same semiconductor substrate.
  • An integrated semiconductor light source disclosed in Patent Document 4 is produced on a distributed feedback type (Distributed FeedBack, DFB) laser produced on an InP substrate and on the InP substrate for returning the optical output to the DFB laser again.
  • DFB distributed FeedBack
  • a ring-shaped optical waveguide The output light from both ends of the DFB laser can be returned to itself.
  • a light output waveguide is further provided, and this light output waveguide is coupled by a light combiner / demultiplexer to obtain a light output from the light output waveguide.
  • Antireflection films are formed on both ends of the optical output waveguide and on both optical output end faces of the integrated semiconductor light source to prevent unstable operation due to reflection of oscillation light.
  • the DFB laser oscillates by current injection from the electrodes.
  • the oscillation light of the DFB laser propagates through the ring-shaped optical waveguide and returns to itself again.
  • the DFB laser and the ring-shaped optical waveguide constitute the resonator of this light source.
  • Non-Patent Documents 1 to 5 above increase the resonance characteristics of the resonator by increasing the length of the external resonator, and in addition, an unnecessary longitudinal mode is generated using the wavelength selection characteristics of the external resonator.
  • the spectral line width is reduced by the removal.
  • a long external resonator is indispensable, and the light source has become large. For this reason, it has become indispensable to realize a small laser light source having a narrow spectral line width.
  • Patent Document 1 merely discloses a laser light source including a laser that oscillates in a single mode and a narrow-band filter disposed at the output end of the laser. That is, in such a configuration, since the light emitted from the laser is simply output through the filter, it is difficult to reduce the frequency noise generated by the laser itself. Further, in the laser light source disclosed in Patent Document 1, since the laser and the filter are composed of separate parts that are separately separated, there is a problem that the laser light source becomes large.
  • Patent Document 2 merely discloses an erbium fiber laser in which an erbium-doped fiber is pumped with a pump laser. That is, in such a configuration, since the light emitted from the pump laser is only output through the erbium-doped fiber, the frequency noise generated by the pump laser itself is reduced as in Patent Document 1. Difficult to do.
  • the erbium fiber laser disclosed in Patent Document 2 also has a problem that the pump laser and the erbium-doped fiber are made up of separate parts and thus become large.
  • Patent Document 3 merely discloses a distributed feedback semiconductor laser that oscillates in a distributed feedback mode.
  • the distributed feedback semiconductor laser disclosed in Patent Document 3 includes first and second filter units therein. In such a configuration, it is difficult to reduce the frequency noise generated in the distributed feedback semiconductor laser itself, as in Patent Documents 1 and 2.
  • Patent Document 4 discloses an integrated semiconductor light source in which output light emitted from both ends of a DFB laser can be returned to itself via a ring-shaped optical waveguide.
  • the combination of the BFB laser and the ring-shaped optical waveguide constitutes an integrated semiconductor light source resonator. This improves the resonance characteristics of the resonator.
  • the ring-shaped optical waveguide becomes relatively large.
  • this integrated semiconductor light source further requires a light output waveguide and a light combiner / splitter. As a result, there is a problem that the light source becomes relatively large.
  • An object of the present invention is to provide a semiconductor laser light source that solves the above-described problems.
  • One embodiment of the present invention includes a single mode semiconductor laser having a first end and a second end facing each other, and an optical filter provided outside the single mode semiconductor laser.
  • the laser and the optical filter are fabricated on the same substrate, the optical filter is provided in the vicinity of the first end of the single mode semiconductor laser, and the optical filter is the first end of the single mode semiconductor laser. Operates as an optical negative feedback optical circuit that negatively feeds back the original light emitted from the first mode to the first end of the single mode semiconductor laser, and the output light from the second end of the single mode semiconductor laser
  • a semiconductor laser light source configured to be emitted to
  • FIG. It is a figure which shows the structural example of the fiber laser disclosed by the nonpatent literature 1.
  • FIG. It is a figure which shows the structural example of the external resonator laser using the bulk diffraction grating disclosed by the nonpatent literature 2.
  • FIG. It is a figure which shows the structural example of the external resonator laser using the fiber Bragg diffraction grating disclosed by the nonpatent literature 3.
  • FIG. It is a figure which shows the structural example of the external resonator laser using the waveguide type diffraction grating disclosed by the nonpatent literature 4.
  • FIG. It is a figure which shows the structural example of the external resonator laser using the ring filter disclosed by the nonpatent literature 5.
  • FIG. 1 is a structural diagram of a semiconductor laser light source according to a first embodiment of the present invention.
  • FIG. 7 is a diagram showing a reflection characteristic (the principle of optical negative feedback) of an optical waveguide ring resonator used in the semiconductor laser light source shown in FIG. 6.
  • FIG. 6 is a structural diagram of a semiconductor laser light source according to a second embodiment of the present invention.
  • a semiconductor laser light source has a light source configuration in which an optical circuit for optical negative feedback composed of an optical filter is coupled to a semiconductor laser that oscillates in a single mode. It is. With such a configuration, a small semiconductor laser light source having a low frequency noise characteristic and a narrow spectral line width was realized without improving the resonance characteristics of the single mode semiconductor laser resonator.
  • FIG. 6 is a structural diagram showing the semiconductor laser light source 110 according to the first embodiment of the present invention.
  • an optical beam comprising a ring optical waveguide 103-1, a straight optical waveguide 103-2, and an interference light extraction optical waveguide 103-3.
  • the waveguide ring resonator 103 is used as an optical circuit for optical negative feedback.
  • a semiconductor laser light source 110 includes a distributed feedback (DFB) laser 101 fabricated on an InP substrate 100, an optical waveguide ring resonator 103 fabricated on the same substrate 100, and the like. And an optical coupling loss adjuster 102.
  • the DFB laser 101 has a first end 101a and a second end 101b facing each other.
  • the optical waveguide ring resonator 103 is also called an optical filter.
  • the optical waveguide ring resonator (optical filter) 103 is provided in the vicinity of the first end 101 a of the DFB laser 101.
  • the semiconductor laser light source 110 is configured such that the DFB laser 101 and the optical waveguide ring resonator (optical filter) 103 are coupled (bad coupling) via the optical coupling loss adjuster 102.
  • the optical waveguide ring resonator (optical filter) 103 is an optical negative feedback optical circuit that negatively feeds back the original light emitted from the first end 101 a of the DFB laser 101 to the first end 101 a of the DFB laser 101. Operate. Output light emitted from the second end 101 b of the DFB laser 101 is emitted to the outside of the semiconductor laser light source 110 and is optically coupled to the optical fiber 13.
  • the optical coupling loss adjuster 102 is used to adjust the amount of feedback from the optical filter 103 so that the optical filter 103 does not become an external resonator of the DFB laser 101.
  • This adjuster 102 introduces a structure using an electroabsorption effect based on the principle of band edge wavelength change due to an electric field applied to a semiconductor material or a structure using a free carrier absorption effect due to a change in carrier density during electric field application and current injection. And realized.
  • a highly reflective film 104 having a reflectivity of 95% is formed on the other output waveguide end face of the linear optical waveguide 103-2 of the optical waveguide ring resonator 103. Both ends of the interference light extraction optical waveguide 103-3 are installed on the top of the InP substrate 100, and an antireflection film 105 is formed to prevent reflection at the end face that affects the filter characteristics.
  • the length from the left end (first end) 101a of the DFB laser 101 to the coupling portion between the ring optical waveguide 103-1 and the linear optical waveguide 103-2 is the phase delay in the optical circuit for optical negative feedback. In order to reduce the amount, it was set to 0.5 mm (1 mm or less).
  • the radius of the ring optical waveguide 103-1 of the optical waveguide ring resonator 103 was 270 ⁇ m, and the free spectrum range of the resonance characteristics was set to 50 GHz.
  • a light wave having an optical frequency that can be a standing wave in the ring optical waveguide 103-1 is emitted from the side surface of the semiconductor substrate provided with the antireflection film 105 by being coupled to the optical waveguide 103-3 for extracting interference light. It does not reflect toward the light source 110 side. For this reason, the reflection characteristic of the optical waveguide ring resonator 103 shows a characteristic (resonance characteristic) in which the reflectance decreases at intervals of 50 GHz. When one of the resonance spectra is taken out, the reflectance shows frequency dependence as shown in FIG.
  • the frequency noise of the laser is reduced through the following steps, and the narrow spectral line width of the semiconductor laser light source 110 according to the first embodiment is realized.
  • the characteristics can be realized.
  • the oscillation light frequency of the DFB laser 101 is shifted to the high frequency side. 2. Increasing the reflectivity of the optical waveguide ring resonator 103 3. The amount of reflected light from the optical waveguide ring resonator 103 increases and the amount of feedback injection to the DFB laser 101 increases. 4. The photon density in the resonator of the DFB laser 101 is increased. 5. The carrier density in the resonator of the DFB laser 101 is reduced due to the stimulated emission phenomenon. 6. Refractive index increase in the resonator of the DFB laser 101 due to plasma effect The oscillation light frequency of the DFB laser 101 is shifted to the lower frequency side.
  • the oscillation light frequency of the DFB laser 101 When the oscillation light frequency of the DFB laser 101 is shifted to the low frequency side, the oscillation light frequency can be shifted to the high frequency side through the reverse process (negative feedback operation).
  • the optical negative feedback optical circuit (the optical waveguide ring resonator 103 in the first embodiment) composed of the optical filter constituting the semiconductor laser light source 110 according to the first embodiment of the present invention is the frequency of the semiconductor laser 101. It can be seen that the circuit operates as an optical circuit that operates to reduce noise and efficiently reduces the line width of the semiconductor laser 101.
  • a spectral line width of 5 kHz or less can be achieved with a light source having an element size of only 1 mm 2 or less.
  • the semiconductor laser light source 110 introduces the optical negative feedback operation by providing the semiconductor laser 101 with the optical circuit 103 for optical negative feedback composed of an optical filter. It was clarified that a semiconductor laser light source with a narrow spectral line width can be realized. Although the DFB laser 101 is taken up as the original light source in the first embodiment, it goes without saying that a light source having the same characteristics can be realized with other single mode semiconductor lasers.
  • FIG. 8 is a structural diagram showing a semiconductor laser light source 120 according to the second embodiment of the present invention.
  • an optical waveguide type realized by forming a high coupling constant diffraction grating 106 and a high reflection film 104 at the end face in a linear optical waveguide.
  • the Fabry-Perot filter 107 is used as an optical circuit for optical negative feedback.
  • the length from the left end (first end) 101a of the DFB laser 101 to the right end of the high coupling constant diffraction grating 106 is 0 in order to reduce the phase delay amount in the optical circuit for optical negative feedback. 3 mm (1 mm or less).
  • the semiconductor laser light source 120 of the second embodiment includes a DFB laser 101 fabricated on an InP substrate 100, an optical waveguide Fabry-Perot filter 107 fabricated on the same substrate 100, an optical coupling loss adjuster 102, Consists of.
  • the DFB laser 101 has a first end 101a and a second end 101b facing each other.
  • the optical waveguide Fabry-Perot filter 107 is also simply called an optical filter.
  • An optical waveguide type Fabry-Perot filter (optical filter) 107 is provided in the vicinity of the first end 101 a of the DFB laser 101.
  • the semiconductor laser light source 120 is configured such that the DFB laser 101 and the optical waveguide Fabry-Perot filter 107 are coupled (bad coupling) via the optical coupling loss adjuster 102.
  • the optical waveguide type Fabry-Perot filter (optical filter) 107 is an optical circuit for negative optical feedback that negatively feeds back the original light emitted from the first end 101 a of the DFB laser 101 to the first end 101 a of the DFB laser 101.
  • Output light emitted from the second end 101 b of the DFB laser 101 is emitted to the outside of the semiconductor laser light source 120 and is optically coupled to the optical fiber 13.
  • the optical coupling loss adjuster 102 is used to adjust the amount of feedback light from the optical filter 107 so that the optical filter 107 does not become an external resonator of the DFB laser 101.
  • This adjuster 102 introduces a structure using an electroabsorption effect based on the principle of band edge wavelength change due to an electric field applied to a semiconductor material or a structure using a free carrier absorption effect due to a change in carrier density during electric field application and current injection. And realized.
  • a diffraction grating 106 having a high coupling constant of 200 cm ⁇ 1 and a length of 150 ⁇ m is formed, and the reflectance of the other output waveguide end face is 95%.
  • the high reflection film 104 is formed.
  • the free spectral range was set to 50 GHz by setting the straight waveguide length to 860 ⁇ m.
  • the reflection characteristics of the optical waveguide type Fabry-Perot filter 107 were almost the same as those shown in FIG.
  • a spectral line width of 10 kHz or less can be achieved with a light source having an element size of only 1 mm ⁇ 0.5 mm or less.
  • the semiconductor laser light source 120 introduces the optical negative feedback operation by providing the semiconductor laser 101 with the optical circuit for optical negative feedback including the optical filter 107. It was clarified that a semiconductor light source with a narrow spectral line width can be realized. Although the DFB laser 101 is taken up as the original light source in the second embodiment, it goes without saying that a light source having the same characteristics can be realized with other single mode semiconductor lasers.
  • the frequency of the optical negative feedback optical circuit configured by the optical filter is simply applied to the single mode semiconductor laser without improving the resonance characteristics of the semiconductor laser resonator.
  • a semiconductor laser light source with low noise and narrow spectral linewidth characteristics can be realized. Since there is no need to improve the resonance characteristics, the semiconductor laser light source according to the present invention is characterized in that it can be provided in a very small shape.

Abstract

In order to provide a semiconductor laser light source, which is ultra-small, and has a narrow spectrum width, this semiconductor laser light source is provided with: a single-mode semiconductor laser having a first end and a second end facing each other; and an optical filter that is provided outside of the single-mode semiconductor laser. The single-mode semiconductor laser and the optical filter are formed on a same substrate. The optical filter is provided close to the first end of the single-mode semiconductor laser. The optical filter operates as a light negative-feedback optical circuit that performs negative feedback of original output light to the first end of the single-mode semiconductor laser, said original output light having been outputted from the first end of the single-mode semiconductor laser. Output light from the second end of the single-mode semiconductor laser is to be outputted to the outside.

Description

半導体レーザ光源Semiconductor laser light source
　本発明は、半導体レーザ光源に関し、特に、光通信分野や光計測分野に用いられる、狭線幅半導体レーザ光源に関するものである。 The present invention relates to a semiconductor laser light source, and more particularly to a narrow line width semiconductor laser light source used in the optical communication field and the optical measurement field.
　光通信システムの大容量化、長距離化に向けて、光の位相を用いたデジタルコヒーレント光通信システムの研究開発が盛んに行われている。本デジタルコヒーレント光通信システムでは、光の位相揺らぎを小さくする必要があり、位相揺らぎが小さく、周波数雑音が低い、狭線幅レーザ光源が必要不可欠である。 Research and development of a digital coherent optical communication system using the phase of light is being actively promoted for increasing the capacity and the distance of optical communication systems. In this digital coherent optical communication system, it is necessary to reduce the phase fluctuation of light, and a narrow linewidth laser light source that has low phase fluctuation and low frequency noise is indispensable.
　狭線幅レーザ光源としては、ファイバレーザや外部共振器構成の半導体レーザが用いられている。ファイバレーザは、例えば、非特許文献１に開示されている。 As the narrow linewidth laser light source, a fiber laser or a semiconductor laser having an external resonator configuration is used. A fiber laser is disclosed in Non-Patent Document 1, for example.
　図１は、非特許文献１に開示されたファイバレーザの構成例を示す図である。図１に示されるように、非特許文献１に開示されたファイバレーザは、偏波保持ファイバ０３を用いた共振器をリング状に配置し、その一部に偏波保持型λ/4シフト回折格子を有するEr3+ドープファイバレーザ０１を配備している。1480nmの波長を持つ励起光源０２は、偏波保持ＷＤＭ（wavelength division multiplex）カプラ０４を介して共振器に結合されている。共振器に挿入された偏波保持カプラ０５から取り出された光は、偏波保持光アイソレータ０６および光バンドパスフィルタ０７を介して光出力０８として外部へ取り出される。ファイバレーザ０１と偏波保持カプラ０５との間の共振器にも偏波保持光アイソレータ０６が挿入されている。 FIG. 1 is a diagram illustrating a configuration example of a fiber laser disclosed in Non-Patent Document 1. As shown in FIG. 1, in the fiber laser disclosed in Non-Patent Document 1, resonators using a polarization maintaining fiber 03 are arranged in a ring shape, and a polarization maintaining type λ / 4 shift diffraction is partly provided. An Er 3+ doped fiber laser 01 with a grating is provided. An excitation light source 02 having a wavelength of 1480 nm is coupled to a resonator via a polarization maintaining WDM (wavelength division multiplex) coupler 04. The light extracted from the polarization maintaining coupler 05 inserted into the resonator is extracted to the outside as an optical output 08 through the polarization maintaining optical isolator 06 and the optical bandpass filter 07. A polarization maintaining optical isolator 06 is also inserted in the resonator between the fiber laser 01 and the polarization maintaining coupler 05.
　このような構成のファイバレーザでは、励起光源０２により共振器を励起することで特定の波長を選択的に発振できる構成とし、そのリング状の共振器長を長くすることで、狭線幅光を発振することができる。 In the fiber laser having such a configuration, a specific wavelength can be selectively oscillated by exciting the resonator with the pumping light source 02, and by reducing the length of the ring-shaped resonator, narrow linewidth light can be obtained. It can oscillate.
　また、外部共振器構成の半導体レーザにおいては、光増幅媒体として半導体を用いている。そのような外部共振器レーザは、例えば、非特許文献２、非特許文献３、非特許文献４、および非特許文献５に開示されている。 Further, in a semiconductor laser having an external resonator configuration, a semiconductor is used as an optical amplification medium. Such external cavity lasers are disclosed in Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4, and Non-Patent Document 5, for example.
　図２は、非特許文献２に開示された、バルク回折格子を用いた外部共振器レーザの構成例を示す図である。図２に示されるように、非特許文献２に開示された外部共振器レーザは、バルク回折格子ミラー１０を外部鏡として用いている。このバルク回折格子ミラー１０で反射された光は、図２に示されるように、レンズ１１、半導体利得媒体０９、レンズ１１、光アイソレータ１２、およびレンズ１１を介して、光ファイバ１３に光結合される。 FIG. 2 is a diagram illustrating a configuration example of an external resonator laser using a bulk diffraction grating disclosed in Non-Patent Document 2. As shown in FIG. 2, the external resonator laser disclosed in Non-Patent Document 2 uses a bulk diffraction grating mirror 10 as an external mirror. The light reflected by the bulk diffraction grating mirror 10 is optically coupled to the optical fiber 13 through the lens 11, the semiconductor gain medium 09, the lens 11, the optical isolator 12, and the lens 11, as shown in FIG. The
　図３は、非特許文献３に開示された、ファイバブラッグ回折格子を用いた外部共振器レーザの構成例を示す図である。図３に示されるように、非特許文献３に開示された外部共振器レーザは、ファイバブラッグ回折格子１４を外部鏡として用いている。図３に示されるように、半導体利得媒体０９から出射され、ファイバブラッグ回折格子１４で反射された光は、光アイソレータ１２を介して、光ファイバ１３に光結合される。 FIG. 3 is a diagram showing a configuration example of an external resonator laser using a fiber Bragg diffraction grating disclosed in Non-Patent Document 3. As shown in FIG. 3, the external cavity laser disclosed in Non-Patent Document 3 uses a fiber Bragg diffraction grating 14 as an external mirror. As shown in FIG. 3, the light emitted from the semiconductor gain medium 09 and reflected by the fiber Bragg diffraction grating 14 is optically coupled to the optical fiber 13 via the optical isolator 12.
　図４は、非特許文献４に開示された、導波路型回折格子を用いた外部共振器レーザの構成例を示す図である。図４に示されるように、非特許文献４に開示された外部共振器レーザは、導波路型回折格子１５を外部鏡として用いている。この導波路型回折格子１５で反射された光は、図４に示されるように、レンズ１１、半導体利得媒体０９、レンズ１１、光アイソレータ１２、およびレンズ１１を介して、光ファイバ１３に光結合される。 FIG. 4 is a diagram showing a configuration example of an external resonator laser using a waveguide type diffraction grating disclosed in Non-Patent Document 4. As shown in FIG. 4, the external cavity laser disclosed in Non-Patent Document 4 uses a waveguide type diffraction grating 15 as an external mirror. The light reflected by the waveguide type diffraction grating 15 is optically coupled to the optical fiber 13 through the lens 11, the semiconductor gain medium 09, the lens 11, the optical isolator 12, and the lens 11, as shown in FIG. Is done.
　図５は、非特許文献５に開示された、リングフィルタを用いた外部共振器レーザの構成例を示す図である。図５に示されるように、非特許文献５に開示された外部共振器レーザは、半導体光増幅媒体（半導体利得媒体）０９と、外部共振器としての窒素添加シリカ（SiON）をコアとする光導波路を用いた３段リングフィルタ１６をSiプラットフォーム１７上にハイブリッド集積したレーザである。本構成では、半導体光増幅媒体０９は波長選択機能を持たず、発振光の単一モード化のために複数段構成のリング共振器を用いる必要がある。図５に示されるように、３段リングフィルタ１６で反射され、半導体光増幅媒体（半導体利得媒体）０９で増幅された光は、レンズ１１、光アイソレータ１２、およびレンズ１１を介して、光ファイバ１３に光結合される。 FIG. 5 is a diagram illustrating a configuration example of an external resonator laser using a ring filter disclosed in Non-Patent Document 5. As shown in FIG. 5, the external cavity laser disclosed in Non-Patent Document 5 is an optical light whose core is a semiconductor optical amplification medium (semiconductor gain medium) 09 and nitrogen-doped silica (SiON) as an external cavity. In this laser, a three-stage ring filter 16 using a waveguide is hybrid-integrated on a Si platform 17. In this configuration, the semiconductor optical amplifying medium 09 does not have a wavelength selection function, and it is necessary to use a multi-stage ring resonator for making the oscillation light into a single mode. As shown in FIG. 5, the light reflected by the three-stage ring filter 16 and amplified by the semiconductor optical amplifying medium (semiconductor gain medium) 09 passes through the lens 11, the optical isolator 12, and the lens 11 to the optical fiber. 13 is optically coupled.
　また、本発明に関連する他の先行技術文献（特許文献）も種々知られている。 Various other prior art documents (patent documents) related to the present invention are also known.
　例えば、特許文献１は、単一モード発振するレーザと、このレーザの出力端に配置されて、中心波長が発振波長と一致した狭帯域なフィルタと、から成る「レーザ光源」を開示している。特許文献１において、狭帯域なフィルタとして、例えば多層膜の干渉膜フィルタを用いている。 For example, Patent Document 1 discloses a “laser light source” that includes a laser that oscillates in a single mode and a narrow-band filter that is disposed at the output end of the laser and that has a center wavelength that matches the oscillation wavelength. . In Patent Document 1, for example, a multilayer interference film filter is used as a narrow band filter.
　また、特許文献２は、クリーンな光搬送波を発生させる、エリビウム・ファイバ・レーザを開示している。特許文献２に開示されたエリビウム・ファイバ・レーザは、リング状又は線形のエリビウム・ドーピング・ファイバと、そのエリビウム・ドーピング・ファイバを励起（ポンピング）するポンプレーザとを備える。リング状エリビウム・ドーピング・ファイバは、レーザキャビティとして用いられ、ポンプレーザに結合された光ファイバと出力ファイバとに結合器で接続されている。レーザキャビティは、光アイソレータとファブリペロ・干渉計とを含む。ファブリペロ・干渉計の代わりに格子構造を設けてもよい。線形エリビウム・ドーピング・ファイバは、格子とミラーとの組み合わせを含む。 Patent Document 2 discloses an erbium fiber laser that generates a clean optical carrier. The erbium fiber laser disclosed in Patent Document 2 includes a ring-like or linear erbium-doped fiber and a pump laser that pumps the erbium-doped fiber. The ring-shaped erbium-doped fiber is used as a laser cavity and is connected by a coupler to an optical fiber coupled to a pump laser and an output fiber. The laser cavity includes an optical isolator and a Fabry-Perot interferometer. A grating structure may be provided instead of the Fabry-Perot / interferometer. Linear erbium-doped fiber includes a combination of grating and mirror.
　さらに、特許文献３は、動作保証上限温度から動作保証下限温度までの温度範囲においてファブリペロモードを抑制し分布帰還モードで発振する分布帰還型半導体レーザを開示している。この特許文献３に開示された分布帰還型半導体レーザは、一端面および他端面を有する半導体領域と、反射膜と、反射防止膜とを備える。反射膜は、半導体領域の一端面に設けられ、第１のフィルタ部として働く。反射防止膜は、半導体領域の他端面に設けられ、第２のフィルタ部として働く。半導体領域は、ｐ型クラッド層とｎ型クラッド層との間に設けられた活性層と、該活性層に光学的に結合されたブラッグ回折格子とを含む。ｐ型クラッド層、ｎ型クラッド層および活性層は、基板上に設けられている。半導体レーザの分布帰還モード（ＤＦＢモードにおける発振波長は温度依存性を有している。半導体レーザは、前方光および背面光を出射する。 Further, Patent Document 3 discloses a distributed feedback semiconductor laser that suppresses the Fabry-Perot mode and oscillates in a distributed feedback mode in a temperature range from the operation guarantee upper limit temperature to the operation guarantee lower limit temperature. The distributed feedback semiconductor laser disclosed in Patent Document 3 includes a semiconductor region having one end surface and the other end surface, a reflection film, and an antireflection film. The reflective film is provided on one end surface of the semiconductor region and functions as a first filter portion. The antireflection film is provided on the other end surface of the semiconductor region and functions as a second filter portion. The semiconductor region includes an active layer provided between the p-type cladding layer and the n-type cladding layer, and a Bragg diffraction grating optically coupled to the active layer. The p-type cladding layer, the n-type cladding layer, and the active layer are provided on the substrate. The oscillation wavelength in the distributed feedback mode (DFB mode) of the semiconductor laser has temperature dependence. The semiconductor laser emits front light and back light.
　特許文献４は、単一モード半導体レーザとリング状半導体光導波路とを同一の半導体基板上に集積した「集積型半導体光源」を開示している。特許文献４に開示された集積型半導体光源は、ＩｎＰ基板上に作成された分布帰還型（Distributed FeedBack, ＤＦＢ）レーザと、その光出力を再度ＤＦＢレーザへ帰還するために該ＩｎＰ基板上に作製されたリング状光導波路とを備える。DFBレーザの両端からの出力光を自身へ帰還できる構造となっている。本集積型半導体光源では、光出力導波路を更に配備し、この光出力導波路を光合成分波器により結合することで光出力導波路から光出力を得る構成となっている。光出力導波路の両端、集積型半導体光源の両光出力端面は発振光の反射による不安定動作を防止するために反射防止膜が形成されている。ＤＦＢレーザは、電極からの電流注入で発振を行う。ＤＦＢレーザの発振光はリング状光導波路を伝搬し、再び自身に戻ってくる構成となっている。ＤＦＢレーザ及びリング状光導波路が本光源の共振器を構成することなる。 Patent Document 4 discloses an “integrated semiconductor light source” in which a single mode semiconductor laser and a ring-shaped semiconductor optical waveguide are integrated on the same semiconductor substrate. An integrated semiconductor light source disclosed in Patent Document 4 is produced on a distributed feedback type (Distributed FeedBack, DFB) laser produced on an InP substrate and on the InP substrate for returning the optical output to the DFB laser again. A ring-shaped optical waveguide. The output light from both ends of the DFB laser can be returned to itself. In this integrated semiconductor light source, a light output waveguide is further provided, and this light output waveguide is coupled by a light combiner / demultiplexer to obtain a light output from the light output waveguide. Antireflection films are formed on both ends of the optical output waveguide and on both optical output end faces of the integrated semiconductor light source to prevent unstable operation due to reflection of oscillation light. The DFB laser oscillates by current injection from the electrodes. The oscillation light of the DFB laser propagates through the ring-shaped optical waveguide and returns to itself again. The DFB laser and the ring-shaped optical waveguide constitute the resonator of this light source.
特開平０４－１５５９８０号公報Japanese Patent Laid-Open No. 04-155980 特開平０４－２８７３８４号公報Japanese Patent Laid-Open No. 04-287384 特開２００７－０１２６９１号公報JP 2007-012691 A 特開２０１５－００２３３５号公報JP2015-002335A
　しかしながら、上記非特許文献１～５に記述したレーザ光源は、外部共振器長を長くすることで共振器の共振特性を高め、加えて外部共振器の波長選択特性を用いて不要な縦モードを除去することでスペクトル線幅を低減している。その結果、共振器の共振特性を向上するために長大な外部共振器が必要不可欠であり、光源が大型になっていた。このため、狭スペクトル線幅を有する小型レーザ光源の実現が必要不可欠となっていた。 However, the laser light sources described in Non-Patent Documents 1 to 5 above increase the resonance characteristics of the resonator by increasing the length of the external resonator, and in addition, an unnecessary longitudinal mode is generated using the wavelength selection characteristics of the external resonator. The spectral line width is reduced by the removal. As a result, in order to improve the resonance characteristics of the resonator, a long external resonator is indispensable, and the light source has become large. For this reason, it has become indispensable to realize a small laser light source having a narrow spectral line width.
　また、上記特許文献１～４に開示された先行技術には、それぞれ、次に述べるような問題点がある。 Also, each of the prior arts disclosed in Patent Documents 1 to 4 has the following problems.
　特許文献１は、単に、単一モード発振するレーザと、このレーザの出力端に配置された狭帯域なフィルタと、から成るレーザ光源を開示しているに過ぎない。すなわち、このような構成では、レーザから出射された光を単にフィルタを介して出力しているだけなので、レーザそれ自身で発生した周波数雑音を低減することが困難である。また、特許文献１に開示されたレーザ光源においては、レーザとフィルタとは別々に分離した個別部品から構成されているので、大型になってしまうという問題もある。 Patent Document 1 merely discloses a laser light source including a laser that oscillates in a single mode and a narrow-band filter disposed at the output end of the laser. That is, in such a configuration, since the light emitted from the laser is simply output through the filter, it is difficult to reduce the frequency noise generated by the laser itself. Further, in the laser light source disclosed in Patent Document 1, since the laser and the filter are composed of separate parts that are separately separated, there is a problem that the laser light source becomes large.
　特許文献２は、単に、ポンプレーザでエリビウム・ドーピング・ファイバを励起（ポンピング）するようにした、エリビウム・ファイバ・レーザを開示しているに過ぎない。すなわち、このような構成では、ポンプレーザから出射された光を、エリビウム・ドーピング・ファイバを介して出力しているだけなので、特許文献１と同様に、ポンプレーザそれ自身で発生した周波数雑音を低減することが困難である。また、特許文献２に開示されたエリビウム・ファイバ・レーザにおいても、ポンプレーザとエリビウム・ドーピング・ファイバとは別々に分離した個別部品から構成されているので、大型になってしまうという問題もある。 Patent Document 2 merely discloses an erbium fiber laser in which an erbium-doped fiber is pumped with a pump laser. That is, in such a configuration, since the light emitted from the pump laser is only output through the erbium-doped fiber, the frequency noise generated by the pump laser itself is reduced as in Patent Document 1. Difficult to do. In addition, the erbium fiber laser disclosed in Patent Document 2 also has a problem that the pump laser and the erbium-doped fiber are made up of separate parts and thus become large.
　特許文献３は、単に、分布帰還モードで発振する分布帰還型半導体レーザを開示しているに過ぎない。特許文献３に開示された分布帰還型半導体レーザは、その内部に、第１及び第２のフィルタ部を備えている。このような構成では、上記特許文献１および２と同様に、分布帰還型半導体レーザそれ自身で発生した周波数雑音を低減することが困難である。 Patent Document 3 merely discloses a distributed feedback semiconductor laser that oscillates in a distributed feedback mode. The distributed feedback semiconductor laser disclosed in Patent Document 3 includes first and second filter units therein. In such a configuration, it is difficult to reduce the frequency noise generated in the distributed feedback semiconductor laser itself, as in Patent Documents 1 and 2.
　特許文献４は、DFBレーザの両端から出射された出力光を、リング状光導波路を介して、自身へ帰還できるようした、集積型半導体光源を開示している。ＢＦＢレーザとリング状光導波路との組み合わせによって、集積型半導体光源の共振器を構成している。これにより、共振器の共振特性を向上させている。しかしながら、このような構成では、リング状光導波路が比較的大きくなってしまう。加えて、この集積型半導体光源は、光出力導波路および光合成分波器をも、更に必要とする。その結果、光源が比較的大きくなってしまうという問題がある。 Patent Document 4 discloses an integrated semiconductor light source in which output light emitted from both ends of a DFB laser can be returned to itself via a ring-shaped optical waveguide. The combination of the BFB laser and the ring-shaped optical waveguide constitutes an integrated semiconductor light source resonator. This improves the resonance characteristics of the resonator. However, with such a configuration, the ring-shaped optical waveguide becomes relatively large. In addition, this integrated semiconductor light source further requires a light output waveguide and a light combiner / splitter. As a result, there is a problem that the light source becomes relatively large.
　本発明の目的は、上記した課題を解決する、半導体レーザ光源を提供することにある。 An object of the present invention is to provide a semiconductor laser light source that solves the above-described problems.
　本発明の一形態は、互いに対向する第１の端及び第２の端を持つ単一モード半導体レーザと、この単一モード半導体レーザの外部に具備した光フィルタと、を備え、単一モード半導体レーザと光フィルタとは同一の基板上に作製され、光フィルタは、単一モード半導体レーザの第１の端の近傍に設けられており、光フィルタは、単一モード半導体レーザの第１の端から出射された原出射光を、単一モード半導体レーザの第１の端へ負帰還する光負帰還用光回路として動作し、単一モード半導体レーザの第２の端からの出力出射光が外部へ出射されるように構成されている、半導体レーザ光源である。 One embodiment of the present invention includes a single mode semiconductor laser having a first end and a second end facing each other, and an optical filter provided outside the single mode semiconductor laser. The laser and the optical filter are fabricated on the same substrate, the optical filter is provided in the vicinity of the first end of the single mode semiconductor laser, and the optical filter is the first end of the single mode semiconductor laser. Operates as an optical negative feedback optical circuit that negatively feeds back the original light emitted from the first mode to the first end of the single mode semiconductor laser, and the output light from the second end of the single mode semiconductor laser A semiconductor laser light source configured to be emitted to
　本発明によれば、超小型でかつスペクトル幅の狭い半導体レーザ光源を提供することが可能となる。 According to the present invention, it is possible to provide a semiconductor laser light source having a very small size and a narrow spectrum width.
非特許文献１に開示された、ファイバレーザの構成例を示す図である。It is a figure which shows the structural example of the fiber laser disclosed by the nonpatent literature 1. FIG. 非特許文献２に開示された、バルク回折格子を用いた外部共振器レーザの構成例を示す図である。It is a figure which shows the structural example of the external resonator laser using the bulk diffraction grating disclosed by the nonpatent literature 2. FIG. 非特許文献３に開示された、ファイバブラッグ回折格子を用いた外部共振器レーザの構成例を示す図である。It is a figure which shows the structural example of the external resonator laser using the fiber Bragg diffraction grating disclosed by the nonpatent literature 3. FIG. 非特許文献４に開示された、導波路型回折格子を用いた外部共振器レーザの構成例を示す図である。It is a figure which shows the structural example of the external resonator laser using the waveguide type diffraction grating disclosed by the nonpatent literature 4. FIG. 非特許文献５に開示された、リングフィルタを用いた外部共振器レーザの構成例を示す図である。It is a figure which shows the structural example of the external resonator laser using the ring filter disclosed by the nonpatent literature 5. FIG. 本発明の第１の実施例による半導体レーザ光源の構造図である。1 is a structural diagram of a semiconductor laser light source according to a first embodiment of the present invention. 図６に示した半導体レーザ光源に使用される、光導波路リング共振器の反射特性 (光負帰還の原理)を示す図である。FIG. 7 is a diagram showing a reflection characteristic (the principle of optical negative feedback) of an optical waveguide ring resonator used in the semiconductor laser light source shown in FIG. 6. 本発明の第２の実施例による半導体レーザ光源の構造図である。FIG. 6 is a structural diagram of a semiconductor laser light source according to a second embodiment of the present invention.
　以下、本発明の実施形態について説明する。 Hereinafter, embodiments of the present invention will be described.
　上記課題を解決するために、本発明の一実施形態に係る半導体レーザ光源は、単一モードで発振する半導体レーザに、光フィルタで構成される光負帰還用光回路を直近に結合する光源構成である。このような構成により、単一モード半導体レーザ共振器の共振特性を向上することなく、低周波数雑音特性を有し狭スペクトル線幅な小型半導体レーザ光源を実現した。 In order to solve the above problems, a semiconductor laser light source according to an embodiment of the present invention has a light source configuration in which an optical circuit for optical negative feedback composed of an optical filter is coupled to a semiconductor laser that oscillates in a single mode. It is. With such a configuration, a small semiconductor laser light source having a low frequency noise characteristic and a narrow spectral line width was realized without improving the resonance characteristics of the single mode semiconductor laser resonator.
　図６は、本発明の第１の実施例に係る半導体レーザ光源１１０を示す構造図である。 FIG. 6 is a structural diagram showing the semiconductor laser light source 110 according to the first embodiment of the present invention.
　図６に示されるように、本発明の第１の実施例による半導体レーザ光源１１０では、リング光導波路１０３－１、直線光導波路１０３－２、および干渉光取出用光導波路１０３－３からなる光導波路リング共振器１０３を光負帰還用光回路として用いる。 As shown in FIG. 6, in the semiconductor laser light source 110 according to the first embodiment of the present invention, an optical beam comprising a ring optical waveguide 103-1, a straight optical waveguide 103-2, and an interference light extraction optical waveguide 103-3. The waveguide ring resonator 103 is used as an optical circuit for optical negative feedback.
　本第１の実施例に係る半導体レーザ光源１１０は、ＩｎＰ基板１００上に作製された分布帰還型(Distributed FeedBack,ＤＦＢ)レーザ１０１と、同一基板１００上に作製された光導波路リング共振器１０３と、光結合損失調整器１０２と、から成る。ＤＦＢレーザ１０１は、互いに対向する第１の端１０１ａおよび第２の端１０１ｂを持つ。光導波路リング共振器１０３は光フィルタとも呼ばれる。光導波路リング共振器（光フィルタ）１０３は、ＤＦＢレーザ１０１の第１の端１０１ａの近傍に設けられている。従って、半導体レーザ光源１１０は、ＤＦＢレーザ１０１と光導波路型リング共振器（光フィルタ）１０３とが光結合損失調整器１０２を介して結合（バッドカップリング）される構成となっている。光導波路リング共振器（光フィルタ）１０３は、ＤＦＢレーザ１０１の第１の端１０１ａから出射された原出射光を、ＤＦＢレーザ１０１の第１の端１０１ａへ負帰還する光負帰還用光回路として動作する。ＤＦＢレーザ１０１の第２の端１０１ｂからの出力出射光は、当該半導体レーザ光源１１０の外部へ出射され、光ファイバ１３に光結合される。 A semiconductor laser light source 110 according to the first embodiment includes a distributed feedback (DFB) laser 101 fabricated on an InP substrate 100, an optical waveguide ring resonator 103 fabricated on the same substrate 100, and the like. And an optical coupling loss adjuster 102. The DFB laser 101 has a first end 101a and a second end 101b facing each other. The optical waveguide ring resonator 103 is also called an optical filter. The optical waveguide ring resonator (optical filter) 103 is provided in the vicinity of the first end 101 a of the DFB laser 101. Therefore, the semiconductor laser light source 110 is configured such that the DFB laser 101 and the optical waveguide ring resonator (optical filter) 103 are coupled (bad coupling) via the optical coupling loss adjuster 102. The optical waveguide ring resonator (optical filter) 103 is an optical negative feedback optical circuit that negatively feeds back the original light emitted from the first end 101 a of the DFB laser 101 to the first end 101 a of the DFB laser 101. Operate. Output light emitted from the second end 101 b of the DFB laser 101 is emitted to the outside of the semiconductor laser light source 110 and is optically coupled to the optical fiber 13.
　光結合損失調整器１０２は、光フィルタ１０３がＤＦＢレーザ１０１の外部共振器とならないように、光フィルタ１０３からの帰還光量を調整するために用いられる。本調整器１０２は、半導体材料への電界印加によるバンド端波長変化を原理とした電界吸収効果を用いた構造あるいは電界印加および電流注入時のキャリア密度変動による自由キャリア吸収効果を用いた構造を導入して実現される。 The optical coupling loss adjuster 102 is used to adjust the amount of feedback from the optical filter 103 so that the optical filter 103 does not become an external resonator of the DFB laser 101. This adjuster 102 introduces a structure using an electroabsorption effect based on the principle of band edge wavelength change due to an electric field applied to a semiconductor material or a structure using a free carrier absorption effect due to a change in carrier density during electric field application and current injection. And realized.
　光導波路リング共振器１０３の直線光導波路１０３－２のもう一方の出力導波路端面には、反射率が９５％の高反射膜１０４が形成されている。干渉光取出用光導波路１０３－３の両端は、ＩｎＰ基板１００の上部に設置し、フィルタ特性に影響を与える端面での反射を防ぐための反射防止膜１０５が形成されている。図６における、ＤＦＢレーザ１０１の左端（第１の端）１０１ａから、リング光導波路１０３－１と直線光導波路１０３－２の結合部までの長さは、光負帰還用光回路での位相遅延量を低減するために０．５ｍｍ (１ｍｍ以下)とした。 A highly reflective film 104 having a reflectivity of 95% is formed on the other output waveguide end face of the linear optical waveguide 103-2 of the optical waveguide ring resonator 103. Both ends of the interference light extraction optical waveguide 103-3 are installed on the top of the InP substrate 100, and an antireflection film 105 is formed to prevent reflection at the end face that affects the filter characteristics. In FIG. 6, the length from the left end (first end) 101a of the DFB laser 101 to the coupling portion between the ring optical waveguide 103-1 and the linear optical waveguide 103-2 is the phase delay in the optical circuit for optical negative feedback. In order to reduce the amount, it was set to 0.5 mm (1 mm or less).
　光導波路リング共振器１０３のリング光導波路１０３－１の半径は２７０μｍとし、共振特性のフリースペクトルレンジを５０ＧＨｚに設定した。リング光導波路１０３－１で定在波となり得る光周波数を有する光波は、干渉光取出用光導波路１０３－３へ結合することで反射防止膜１０５を施した半導体基板側面から放射されるため、レーザ光源１１０側へは反射しない。このために、光導波路リング共振器１０３の反射特性は、５０ＧＨｚ間隔で反射率が低下する特性(共振特性)を示す。その中の１本の共振スペクトルを取り出すと、反射率は図７に示すような周波数依存性を示す。 The radius of the ring optical waveguide 103-1 of the optical waveguide ring resonator 103 was 270 μm, and the free spectrum range of the resonance characteristics was set to 50 GHz. A light wave having an optical frequency that can be a standing wave in the ring optical waveguide 103-1 is emitted from the side surface of the semiconductor substrate provided with the antireflection film 105 by being coupled to the optical waveguide 103-3 for extracting interference light. It does not reflect toward the light source 110 side. For this reason, the reflection characteristic of the optical waveguide ring resonator 103 shows a characteristic (resonance characteristic) in which the reflectance decreases at intervals of 50 GHz. When one of the resonance spectra is taken out, the reflectance shows frequency dependence as shown in FIG.
　ＤＦＢレーザ１０１の発振周波数を図７の「動作点」に設定することで、以下の工程を経てレーザの周波数雑音低減が実現され、本第１の実施例による半導体レーザ光源１１０の狭スペクトル線幅特性を実現できる。 By setting the oscillation frequency of the DFB laser 101 to the “operating point” in FIG. 7, the frequency noise of the laser is reduced through the following steps, and the narrow spectral line width of the semiconductor laser light source 110 according to the first embodiment is realized. The characteristics can be realized.
　１．ＤＦＢレーザ１０１の発振光周波数が高周波数側へシフト
　２．光導波路リング共振器１０３の反射率増加
　３．光導波路リング共振器１０３からの反射光量が増加し、ＤＦＢレーザ１０１への帰還注入光量が増加
　４．ＤＦＢレーザ１０１の共振器内の光子密度が増加
　５．誘導放出現象によりＤＦＢレーザ１０１の共振器内のキャリア密度が低下
　６．プラズマ効果によりＤＦＢレーザ１０１の共振器内の屈折率増加
　７．ＤＦＢレーザ１０１の発振光周波数が低周波数側へシフト 1. 1. The oscillation light frequency of the DFB laser 101 is shifted to the high frequency side. 2. Increasing the reflectivity of the optical waveguide ring resonator 103 3. The amount of reflected light from the optical waveguide ring resonator 103 increases and the amount of feedback injection to the DFB laser 101 increases. 4. The photon density in the resonator of the DFB laser 101 is increased. 5. The carrier density in the resonator of the DFB laser 101 is reduced due to the stimulated emission phenomenon. 6. Refractive index increase in the resonator of the DFB laser 101 due to plasma effect The oscillation light frequency of the DFB laser 101 is shifted to the lower frequency side.
　ＤＦＢレーザ１０１の発振光周波数が低周波数側へシフトした際にも、逆の過程を経て発振光周波数を高周波数側へシフトできる(負帰還動作)。 When the oscillation light frequency of the DFB laser 101 is shifted to the low frequency side, the oscillation light frequency can be shifted to the high frequency side through the reverse process (negative feedback operation).
　つまり、本発明の第１の実施例による半導体レーザ光源１１０を構成する光フィルタからなる光負帰還用光回路(本第１の実施例では光導波路リング共振器１０３)は、半導体レーザ１０１の周波数雑音を低減するように動作し、半導体レーザ１０１の線幅を効率的に低減する光回路として動作することがわかる。 That is, the optical negative feedback optical circuit (the optical waveguide ring resonator 103 in the first embodiment) composed of the optical filter constituting the semiconductor laser light source 110 according to the first embodiment of the present invention is the frequency of the semiconductor laser 101. It can be seen that the circuit operates as an optical circuit that operates to reduce noise and efficiently reduces the line width of the semiconductor laser 101.
　本第１の実施例による半導体レーザ光源１１０を作製することで、わずか１ｍｍ２以下の素子サイズの光源で５ｋＨｚ以下のスペクトル線幅を達成できることが確認できた。 It was confirmed that by producing the semiconductor laser light source 110 according to the first embodiment, a spectral line width of 5 kHz or less can be achieved with a light source having an element size of only 1 mm 2 or less.
　以上説明したように、本発明の第１の実施例による半導体レーザ光源１１０によって、半導体レーザ１０１へ光フィルタからなる光負帰還用光回路１０３を付与して光負帰還動作を導入することで、スペクトル線幅の狭い半導体レーザ光源を実現できることを明らかにした。なお、本第１の実施例では、元光源としてＤＦＢレーザ１０１を取り上げたが、他の単一モード半導体レーザでも同様の特性を有する光源を実現できることは言うまでもない。 As described above, the semiconductor laser light source 110 according to the first embodiment of the present invention introduces the optical negative feedback operation by providing the semiconductor laser 101 with the optical circuit 103 for optical negative feedback composed of an optical filter. It was clarified that a semiconductor laser light source with a narrow spectral line width can be realized. Although the DFB laser 101 is taken up as the original light source in the first embodiment, it goes without saying that a light source having the same characteristics can be realized with other single mode semiconductor lasers.
　図８は、本発明の第２の実施例に係る半導体レーザ光源１２０を示す構造図である。 FIG. 8 is a structural diagram showing a semiconductor laser light source 120 according to the second embodiment of the present invention.
　図８に示されるように、本発明の第２の実施例による半導体レーザ光源１２０では、直線光導波路に高結合定数回折格子１０６と端面の高反射膜１０４を形成することで実現した光導波路型ファブリペロフィルタ１０７を光負帰還用光回路として用いる。図８における、ＤＦＢレーザ１０１の左端（第１の端）１０１ａから、高結合定数回折格子１０６の右端までの長さは、光負帰還用光回路での位相遅延量を低減するために、０．３ｍｍ (１ｍｍ以下)とした。 As shown in FIG. 8, in the semiconductor laser light source 120 according to the second embodiment of the present invention, an optical waveguide type realized by forming a high coupling constant diffraction grating 106 and a high reflection film 104 at the end face in a linear optical waveguide. The Fabry-Perot filter 107 is used as an optical circuit for optical negative feedback. In FIG. 8, the length from the left end (first end) 101a of the DFB laser 101 to the right end of the high coupling constant diffraction grating 106 is 0 in order to reduce the phase delay amount in the optical circuit for optical negative feedback. 3 mm (1 mm or less).
　本第２の実施例の半導体レーザ光源１２０は、ＩｎＰ基板１００上に作製されたＤＦＢレーザ１０１と、同一基板１００上に作製された光導波路型ファブリペロフィルタ１０７と、光結合損失調整器１０２とから成る。ＤＦＢレーザ１０１は、互いに対向する第１の端１０１ａおよび第２の端１０１ｂを持つ。光導波路型ファブリペロフィルタ１０７は、単に、光フィルタとも呼ばれる。光導波路型ファブリペロフィルタ（光フィルタ）１０７は、ＤＦＢレーザ１０１の第１の端１０１ａの近傍に設けられている。半導体レーザ光源１２０は、ＤＦＢレーザ１０１と光導波路型ファブリペロフィルタ１０７が光結合損失調整器１０２を介して結合（バッドカップリング）される構成となっている。光導波路型ファブリペロフィルタ（光フィルタ）１０７は、ＤＦＢレーザ１０１の第１の端１０１ａから出射された原出射光を、ＤＦＢレーザ１０１の第１の端１０１ａへ負帰還する光負帰還用光回路として動作する。ＤＦＢレーザ１０１の第２の端１０１ｂからの出力出射光は、当該半導体レーザ光源１２０の外部へ出射され、光ファイバ１３に光結合される。 The semiconductor laser light source 120 of the second embodiment includes a DFB laser 101 fabricated on an InP substrate 100, an optical waveguide Fabry-Perot filter 107 fabricated on the same substrate 100, an optical coupling loss adjuster 102, Consists of. The DFB laser 101 has a first end 101a and a second end 101b facing each other. The optical waveguide Fabry-Perot filter 107 is also simply called an optical filter. An optical waveguide type Fabry-Perot filter (optical filter) 107 is provided in the vicinity of the first end 101 a of the DFB laser 101. The semiconductor laser light source 120 is configured such that the DFB laser 101 and the optical waveguide Fabry-Perot filter 107 are coupled (bad coupling) via the optical coupling loss adjuster 102. The optical waveguide type Fabry-Perot filter (optical filter) 107 is an optical circuit for negative optical feedback that negatively feeds back the original light emitted from the first end 101 a of the DFB laser 101 to the first end 101 a of the DFB laser 101. Works as. Output light emitted from the second end 101 b of the DFB laser 101 is emitted to the outside of the semiconductor laser light source 120 and is optically coupled to the optical fiber 13.
　光結合損失調整器１０２は、光フィルタ１０７がＤＦＢレーザ１０１の外部共振器とならないように光フィルタ１０７からの帰還光量を調整するために用いられる。本調整器１０２は、半導体材料への電界印加によるバンド端波長変化を原理とした電界吸収効果を用いた構造あるいは電界印加および電流注入時のキャリア密度変動による自由キャリア吸収効果を用いた構造を導入して実現される。 The optical coupling loss adjuster 102 is used to adjust the amount of feedback light from the optical filter 107 so that the optical filter 107 does not become an external resonator of the DFB laser 101. This adjuster 102 introduces a structure using an electroabsorption effect based on the principle of band edge wavelength change due to an electric field applied to a semiconductor material or a structure using a free carrier absorption effect due to a change in carrier density during electric field application and current injection. And realized.
　光導波路型ファブリペロフィルタ１０７のＤＦＢレーザ１０１側には、２００ｃｍ－１の高結合定数を持つ、長さ１５０μｍの回折格子１０６が形成され、もう一方の出力導波路端面には反射率が９５％の高反射膜１０４が形成されている。 On the DFB laser 101 side of the optical waveguide Fabry-Perot filter 107, a diffraction grating 106 having a high coupling constant of 200 cm −1 and a length of 150 μm is formed, and the reflectance of the other output waveguide end face is 95%. The high reflection film 104 is formed.
　この高結合定数回折格子１０６と高反射膜１０４を端面鏡とした光導波路型ファブリペロフィルタ１０７では、直線導波路長を８６０μｍとすることで、そのフリースペクトルレンジを５０ＧＨｚに設定した。光導波路型ファブリペロフィルタ１０７の反射特性は、図７に示したものとほぼ同様な特性を示した。 In the optical waveguide Fabry-Perot filter 107 using the high coupling constant diffraction grating 106 and the high reflection film 104 as end mirrors, the free spectral range was set to 50 GHz by setting the straight waveguide length to 860 μm. The reflection characteristics of the optical waveguide type Fabry-Perot filter 107 were almost the same as those shown in FIG.
　第２の実施例に係る半導体レーザ光源１２０の動作原理は、上記第１の実施例に係る半導体レーザ光源１１０において記載したものと同様であるので、その説明を省略する。 Since the operating principle of the semiconductor laser light source 120 according to the second embodiment is the same as that described in the semiconductor laser light source 110 according to the first embodiment, description thereof is omitted.
　本第２の実施例による半導体レーザ光源１２０を作製することで、わずか１ｍｍ×０．５ｍｍ以下の素子サイズの光源で、１０ｋＨｚ以下のスペクトル線幅を達成できることが確認できた。 It was confirmed that by producing the semiconductor laser light source 120 according to the second embodiment, a spectral line width of 10 kHz or less can be achieved with a light source having an element size of only 1 mm × 0.5 mm or less.
　以上説明したように、本発明の第２の実施例による半導体レーザ光源１２０によって、半導体レーザ１０１へ光フィルタ１０７からなる光負帰還用光回路を付与して光負帰還動作を導入することで、スペクトル線幅の狭い半導体光源を実現できることを明らかにした。なお、本第２の実施例では、元光源としてＤＦＢレーザ１０１を取り上げたが、他の単一モード半導体レーザでも同様の特性を有する光源を実現できることは言うまでもない。 As described above, the semiconductor laser light source 120 according to the second embodiment of the present invention introduces the optical negative feedback operation by providing the semiconductor laser 101 with the optical circuit for optical negative feedback including the optical filter 107. It was clarified that a semiconductor light source with a narrow spectral line width can be realized. Although the DFB laser 101 is taken up as the original light source in the second embodiment, it goes without saying that a light source having the same characteristics can be realized with other single mode semiconductor lasers.
　以上説明したように、本発明によれば、光フィルタで構成される光負帰還用光回路を単一モード半導体レーザへ付与するだけで、半導体レーザ共振器の共振特性を改善することなく、周波数雑音が低く、狭スペクトル線幅特性を有する半導体レーザ光源を実現できる。共振特性を改善する必要が無いことから、本発明による半導体レーザ光源は超小型な形状で提供できることが特徴となる。 As described above, according to the present invention, the frequency of the optical negative feedback optical circuit configured by the optical filter is simply applied to the single mode semiconductor laser without improving the resonance characteristics of the semiconductor laser resonator. A semiconductor laser light source with low noise and narrow spectral linewidth characteristics can be realized. Since there is no need to improve the resonance characteristics, the semiconductor laser light source according to the present invention is characterized in that it can be provided in a very small shape.
　また、本発明の具体的な構成は前述の実施形態（実施例）に限られるものではなく、この発明の要旨を逸脱しない範囲の変更があってもこの発明に含まれる。 In addition, the specific configuration of the present invention is not limited to the above-described embodiment (example), and changes in a range not departing from the gist of the present invention are included in the present invention.
　以上、実施の形態（実施例）を参照して本願発明を説明したが、本願発明は上記実施の形態（実施例）に限定されるものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。 Although the present invention has been described with reference to the embodiment (example), the present invention is not limited to the above embodiment (example). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
　この出願は、２０１５年９月２８日に出願された日本出願特願２０１５－１８９４１０を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2015-189410 filed on September 28, 2015, the entire disclosure of which is incorporated herein.
　１００：　ＩｎＰ基板
　１０１：　ＤＦＢレーザ
　１０１ａ：　第１の端
　１０１ｂ：　第２の端
　１０２：　光結合損失調整器
　１０３：　光導波路リング共振器（光フィルタ）
　１０３－１：　リング光導波路
　１０３－２：　直線光導波路
　１０３－３：　干渉光取出用光導波路
　１０４：　高反射膜
　１０５：　反射防止膜
　１０６：　高結合定数回折格子
　１０７：　光導波路型ファブリペロフィルタ（光フィルタ）
　１１０：　本発明の第１の実施例による半導体レーザ光源
　１２０：　本発明の第２の実施例による半導体レーザ光源 DESCRIPTION OF SYMBOLS 100: InP board | substrate 101: DFB laser 101a: 1st end 101b: 2nd end 102: Optical coupling loss regulator 103: Optical waveguide ring resonator (optical filter)
103-1: Ring optical waveguide 103-2: Linear optical waveguide 103-3: Interference light extraction optical waveguide 104: High reflection film 105: Antireflection film 106: High coupling constant diffraction grating 107: Optical waveguide type Fabry-Perot filter ( Optical filter)
110: Semiconductor laser light source according to the first embodiment of the present invention 120: Semiconductor laser light source according to the second embodiment of the present invention

Claims (6)

  1. 　互いに対向する第１の端及び第２の端を持つ単一モード半導体レーザと、該単一モード半導体レーザの外部に具備した光フィルタと、を備え、
    　前記単一モード半導体レーザと前記光フィルタとは同一の基板上に作製され、前記光フィルタは、前記単一モード半導体レーザの前記第１の端の近傍に設けられており、
    　前記光フィルタは、前記単一モード半導体レーザの前記第１の端から出射された原出射光を、前記単一モード半導体レーザの前記第１の端へ負帰還する光負帰還用光回路として動作し、
    　前記単一モード半導体レーザの前記第２の端からの出力出射光が外部へ出射されるように構成されている、半導体レーザ光源。     A single mode semiconductor laser having a first end and a second end facing each other, and an optical filter provided outside the single mode semiconductor laser,
    The single mode semiconductor laser and the optical filter are fabricated on the same substrate, and the optical filter is provided in the vicinity of the first end of the single mode semiconductor laser,
    The optical filter operates as an optical negative feedback optical circuit that negatively feeds back the original light emitted from the first end of the single mode semiconductor laser to the first end of the single mode semiconductor laser. And
    A semiconductor laser light source configured to emit output light from the second end of the single mode semiconductor laser to the outside.
  2. 　前記単一モード半導体レーザは、分布帰還型半導体レーザから成る、請求項１記載の半導体レーザ光源。 The semiconductor laser light source according to claim 1, wherein the single mode semiconductor laser is a distributed feedback semiconductor laser.
  3. 　前記光フィルタは、光導波路により構成されたリング共振器から成る、請求項１又は２に記載の半導体レーザ光源。 3. The semiconductor laser light source according to claim 1, wherein the optical filter includes a ring resonator configured by an optical waveguide.
  4. 　前記光フィルタは、回折格子および高反射膜でミラーを構成した光導波路型ファブリペロフィルタから成る、請求項１又は２に記載の半導体レーザ光源。 3. The semiconductor laser light source according to claim 1, wherein the optical filter comprises an optical waveguide type Fabry-Perot filter in which a mirror is formed by a diffraction grating and a highly reflective film.
  5. 　前記単一モード半導体レーザと前記光フィルタとが、同一ＩｎＰ基板上にモノリシック集積され、バッドカップリングされている、請求項１乃至４のいずれか１つに記載の半導体レーザ光源。 5. The semiconductor laser light source according to claim 1, wherein the single mode semiconductor laser and the optical filter are monolithically integrated on the same InP substrate and are badly coupled.
  6. 　前記単一モード半導体レーザと前記光フィルタとが、同一ＩｎＰ基板上にモノリシック集積され、光結合損失調整器を介して前記バッドカップリングされている、請求項５に記載の半導体レーザ光源。 6. The semiconductor laser light source according to claim 5, wherein the single mode semiconductor laser and the optical filter are monolithically integrated on the same InP substrate and are badly coupled via an optical coupling loss adjuster.
PCT/JP2016/004339 2015-09-28 2016-09-26 Semiconductor laser light source WO2017056474A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2017542740A JP6729857B2 (en) 2015-09-28 2016-09-26 Semiconductor laser light source

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2015189410 2015-09-28
JP2015-189410 2015-09-28

Publications (1)

Publication Number Publication Date
WO2017056474A1 true WO2017056474A1 (en) 2017-04-06

Family

ID=58423280

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2016/004339 WO2017056474A1 (en) 2015-09-28 2016-09-26 Semiconductor laser light source

Country Status (2)

Country Link
JP (1) JP6729857B2 (en)
WO (1) WO2017056474A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110649462A (en) * 2019-09-02 2020-01-03 上海科技大学 Method for compressing spectral line width of quantum cascade laser
JP7437682B2 (en) 2020-03-16 2024-02-26 株式会社デンソー laser light source

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04343283A (en) * 1991-05-20 1992-11-30 Nippon Telegr & Teleph Corp <Ntt> Integrated semiconductor laser ray source
JPH06326410A (en) * 1993-05-14 1994-11-25 Nippon Telegr & Teleph Corp <Ntt> Integrated semiconductor laser beam source

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04343283A (en) * 1991-05-20 1992-11-30 Nippon Telegr & Teleph Corp <Ntt> Integrated semiconductor laser ray source
JPH06326410A (en) * 1993-05-14 1994-11-25 Nippon Telegr & Teleph Corp <Ntt> Integrated semiconductor laser beam source

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110649462A (en) * 2019-09-02 2020-01-03 上海科技大学 Method for compressing spectral line width of quantum cascade laser
JP7437682B2 (en) 2020-03-16 2024-02-26 株式会社デンソー laser light source

Also Published As

Publication number Publication date
JPWO2017056474A1 (en) 2018-07-12
JP6729857B2 (en) 2020-07-29

Similar Documents

Publication Publication Date Title
JPH11214799A (en) Semiconductor laser module
JP7060648B2 (en) Raman amplification light source, Raman amplification light source system, Raman amplifier, Raman amplification system
JP2005123612A (en) Broadband light source using semiconductor optical amplifier
JP4063908B2 (en) Light source device, optical amplifier, and optical communication system
US7599406B2 (en) Fiber ring laser
JP3250428B2 (en) Optical amplifier
JPH041614A (en) Optical amplifying device
WO2022054860A1 (en) Light source, light source device, method for driving light source, raman amplifier, and raman amplification system
JP6729857B2 (en) Semiconductor laser light source
Bowers Integrated microwave photonics
JP2012256667A (en) Semiconductor laser light source
EP4042529A1 (en) Wavelength control of multi-wavelength laser
JP2010050162A (en) Semiconductor wavelength variable laser
Yeniay et al. High-performance integrated erbium/sup+ 3/-ytterbium/sup+ 3/codoped glass waveguide laser
JP6083644B2 (en) Integrated semiconductor light source
WO2016182068A1 (en) Light source for raman amplification, light source system for raman amplification, raman amplifier, raman amplifying system
EP1087479B1 (en) Stabilized laser source
US20050226283A1 (en) Single-mode semiconductor laser with integrated optical waveguide filter
JP2016152253A (en) Semiconductor laser element
US20220344887A1 (en) Photonic device
JP2002374037A (en) Semiconductor laser module, fiber-optic amplifier using the same and optical communication system
US20100296159A1 (en) Wavelength-variable light source
JP2005276904A (en) Semiconductor light-emitting element
JP5058087B2 (en) Tunable semiconductor laser
JP6929226B2 (en) Higher Seedless Raman Pumping

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 16850654

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 2017542740

Country of ref document: JP

Kind code of ref document: A

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 16850654

Country of ref document: EP

Kind code of ref document: A1