CN112600068A - Narrow linewidth external cavity semiconductor laser linear array based on diffraction grating array - Google Patents

Narrow linewidth external cavity semiconductor laser linear array based on diffraction grating array Download PDF

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CN112600068A
CN112600068A CN202011601590.5A CN202011601590A CN112600068A CN 112600068 A CN112600068 A CN 112600068A CN 202011601590 A CN202011601590 A CN 202011601590A CN 112600068 A CN112600068 A CN 112600068A
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diffraction grating
semiconductor laser
array
linear array
lens
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杨明来
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Zhejiang Changxin Photoelectric Technology Co Ltd
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Zhejiang Changxin Photoelectric Technology Co Ltd
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    • 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
    • H01S5/0267—Integrated focusing lens
    • 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
    • H01S5/005—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
    • 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
    • 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
    • H01S5/0268—Integrated waveguide grating router, e.g. emission of a multi-wavelength laser array is combined by a "dragon router"

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)

Abstract

The invention discloses a narrow linewidth external cavity semiconductor laser linear array based on a diffraction grating array, which comprises a semiconductor laser linear array, wherein the semiconductor laser linear array consists of a gain waveguide, a fast axis collimating mirror and a waveguide grating, a small lens, a half-wave plate, a large lens and the diffraction grating array are sequentially arranged along the laser output direction of the semiconductor laser linear array, and the distance from the small lens to the semiconductor laser linear array is the focal length f of the small lens1The small lens and the large lens are arranged in a confocal manner to form an inverted telescopic system, and the distance between the large lens and the diffraction grating array is the focal length f of the large lens2The half-wave plate is positioned at the focus of the small lens and the large lens, the diffraction grating array is formed by gluing diffraction grating units with different rotation angles, and each diffraction grating unit is placed in a Littrow structure.

Description

Narrow linewidth external cavity semiconductor laser linear array based on diffraction grating array
Technical Field
The invention relates to a narrow linewidth external cavity semiconductor laser linear array based on a diffraction grating array.
Background
The manufacturing process of bonding the laser linear array strip and the heat sink has internal thermal stress, so that all the light-emitting units in the linear array strip are not on the same straight line and are bent. When the spectrum compression is performed by using the external cavity feedback of the whole diffraction grating, as shown in fig. 1, the light-emitting unit a and the off-axis light-emitting unit b on the optical axis (z axis) are incident on the grating at different angles, and when the diffraction grating is of a littrow structure, the central wavelengths of the feedback light returned from the original path are different, so that the central wavelengths of the spectrums output by the on-axis light-emitting unit and the off-axis light-emitting unit are different, and the whole spectrum of the semiconductor laser linear array is the superposition of the spectrums of each light-emitting unit, so. Typically a bend of 1 μm causes a spectral broadening of 40GHz [ appl.opt.44(15), 3101(2005) ].
In the CN1960093A scheme, the grating outer cavity adopts a Littman structure, the first-order diffraction light of the grating is incident on the feedback mirror, the light beam is incident on the grating after being reflected by the feedback mirror, and the first-order diffraction light returns to each light-emitting unit of the laser diode array along the original path, thereby oscillating and amplifying. The zero order diffracted light of the grating is output as laser light. In the scheme, the feedback mirror is composed of a plurality of reflecting mirrors, and the line width narrowing caused by the bending of the semiconductor laser linear array strip is reduced by adjusting the angle of the feedback mirror. The disadvantage of this solution is that, because of the grating littman structure, when the light is reflected by the feedback mirror and re-enters the grating, the first order diffracted light is fed back to the laser, and the zero order diffracted light is lost, so the output power is lower. In addition, because the introduction of the feedback mirror increases the number of optical elements, the adjustment of the optical path is complicated and difficult. The diffraction grating array external cavity semiconductor laser linear array of patent No. 2007200944437 has the problems of complex structure, multiple optical path elements and linear array spectrum broadening of the diffraction grating array external cavity semiconductor laser linear array.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a narrow linewidth external cavity semiconductor laser linear array based on a diffraction grating array.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array comprises a semiconductor laser linear array, wherein the semiconductor laser linear array consists of a gain waveguide, a fast axis collimating mirror and a waveguide grating, a small lens, a half-wave plate, a large lens and a diffraction grating array are sequentially arranged along the output direction of laser of the semiconductor laser linear array, the distance from the small lens to the semiconductor laser linear array is the focal distance f1 of the small lens, the small lens and the large lens are arranged at the confocal point to form an inverted telescopic system, the distance from the large lens to the diffraction grating array is the focal distance f2 of the large lens, the half-wave plate is positioned at the focal point of the small lens and the large lens, the diffraction grating array is formed by gluing diffraction grating units with different rotation angles, each diffraction grating unit is arranged in a salutary structure, one or more light emitting units of the semiconductor laser linear array are incident on the, and adjusting each diffraction grating unit to enable the incident angles theta and phi of the light beams a and b of the optical axis and the off-axis light-emitting unit to be equal or very close to each other.
Preferably, the small lens and the large lens are both convex lenses, and the focal length of the large lens is 3 to 10 times that of the small lens.
Preferably, the small lens, the half-wave plate and the large lens are coated with antireflection films with working wavelengths, and each diffraction grating unit in the diffraction grating array is coated with a high-reflection film with the working wavelength.
Preferably, the fast axis collimating lens is prepared by adopting a plasma coupling dry etching and high-quality optical dielectric film deposition technology, preparing a curved side wall groove by reasonably selecting etching process parameters, and depositing an optical dielectric material in the groove.
Preferably, the waveguide grating is prepared by adopting high-precision mask preparation and a plasma coupling dry etching technology and reasonably selecting etching process parameters.
The invention has the following beneficial effects: the invention integrates gain waveguide, fast axis collimating mirror and waveguide grating by semiconductor laser linear array, so that the semiconductor laser linear array with narrow line width replaces discrete semiconductor laser linear array without grating and fast axis collimating mirror, combines rear end lens group and diffraction grating, makes one or more light-emitting units of semiconductor laser linear array incident on a diffraction grating unit, makes the central wavelength of feedback light returned along the original path after the light-emitting units with different bending degrees pass through the diffraction unit very close by adjusting each diffraction grating unit, and makes the central wavelength of littrow first-order diffraction feedback light have a certain shift by adjusting the angle, so that the central wavelength of light-emitting unit output light with different bending degrees is very close, and because the central wavelength of waveguide grating spectrum and external cavity grating feedback spectrum has a certain shift, the spectrum superposition similar to vernier effect is formed, achieving the purpose of reducing the whole spectrum line width, meanwhile, the structure of the light path is simplified, and the stability of the device is improved.
Drawings
Fig. 1 is a diagram of light paths of a light-emitting unit a on an optical axis (z axis) and an off-axis light-emitting unit b incident on a diffraction grating at different angles when external cavity feedback is performed by using the whole diffraction grating. a is the light output emitted by the on-axis light-emitting unit, b is the light beam emitted by the on-axis light-emitting unit, theta is the included angle between the light beam a and the normal of the diffraction grating,
Figure BDA0002871246830000031
the angle between the light beam b and the normal of the diffraction grating is shown as 501, and the diffraction grating unit is shown as 501.
Fig. 2 is a schematic diagram of a diffraction grating array external cavity narrow linewidth semiconductor laser linear array structure. The device comprises a gain waveguide 101, a fast axis collimating mirror 102, a waveguide grating 103, a semiconductor laser linear array 1, a small lens 2, a half-wave plate 3, a large lens 4, a diffraction grating array 5 and a diffraction grating unit 501.
Fig. 3 is a light path diagram of the external cavity feedback by using the diffraction grating array, in which the light emitting unit a on the z-axis of the optical axis and the off-axis light emitting unit b are incident on the grating at different angles, a is a light beam emitted by the on-axis light emitting unit, b is a light beam emitted by the on-axis light emitting unit, θ is an included angle between the light beam a and the normal of the diffraction grating unit, and Φ is an included angle between the light beam b and the normal of the diffraction grating unit.
Fig. 4 is a schematic diagram of an integrated narrow-linewidth semiconductor laser linear array unit of the improved fast axis collimating mirror, where 101 is a gain waveguide, 102 is an integrated optical medium fast axis collimating mirror, and 103 is a waveguide grating.
FIG. 5 is a schematic view of vernier effect of laser spectra. The solid line oscillogram is the frequency-selecting spectrum of the waveguide grating, and the dotted line is the feedback spectrum of the diffraction grating.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings of the specification:
the present invention is further described with reference to fig. 2, fig. 3, fig. 4, fig. 5 and the embodiments, but the present invention is not limited to these embodiments.
Example (b):
as shown in fig. 2, 3 and 4, the narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array comprises a semiconductor laser linear array 1, wherein the semiconductor laser linear array 1 is composed of a gain waveguide 101, a fast axis collimator 102 and a waveguide grating 103, a small lens 2, a half-wave plate 3, a large lens 4 and a diffraction grating array 5 are sequentially arranged along the laser output direction of the semiconductor laser linear array, the distance from the small lens 2 to the semiconductor laser linear array 1 is the focal length f1 of the small lens 2, and the small lens 2 and the large lens 4 are arranged in a confocal manner to form an inverted telescopic system for compressing the divergence angle in the x direction of the slow axis, and if the amplification factor of the inverted telescopic system is n, the divergence angle of the slow axis can be compressed by n times. The distance between the large lens 4 and the diffraction grating array 5 is f2 of the focal length of the large lens 4, the half-wave plate 3 is located at the focal point of the small lens 2 and the large lens 4, and the output power of the laser can be adjusted by rotating the half-wave plate 4. The diffraction grating array 5 is formed by gluing diffraction grating units 501 with different rotation angles, each diffraction grating unit 501 is placed in a littrow structure, namely, zero-order diffraction light is output light, and first-order diffraction light returns to each light-emitting unit of the lens integrated semiconductor laser linear array 1 along the original path. One or more light emitting units of the semiconductor laser linear array 1 are incident on a corresponding diffraction grating unit 501, and each diffraction grating unit 501 is adjusted to make the incident angles theta and phi of the light beams a and b of the off-axis light emitting units incident on the diffraction grating unit 501 equal to or very close to each other, that is, theta is phi. Such first order littrow formula: the 2dsin theta can be known as lambda, the central wavelength of the light feedback optical axis along the original path is close to the central wavelength of the off-axis light emitting unit, and the central wavelength of the littrow first-order diffraction feedback light is shifted to a certain extent by adjusting the angle, so that the central wavelengths of the light output by the light emitting units with different bending degrees are very close to each other, and meanwhile, because the central wavelengths of the waveguide grating spectrum and the external cavity grating feedback spectrum have a certain deviation, the spectrum superposition similar to a vernier effect is formed, the purpose of reducing the whole line width is achieved, the light path structure is simplified, and the stability of the device is. Thus, the center wavelengths of the spectrums output by the on-axis light-emitting unit and the off-axis light-emitting unit are equal, so that the integral spectral line width of the semiconductor laser linear array is reduced.
As shown in fig. 2, the small lens 2 and the large lens 4 are both convex lenses, and the focal length of the large lens 4 is 3 to 10 times the focal length of the small lens 2.
As shown in fig. 2, the small lens 2, the half-wave plate 3 and the large lens 4 are coated with antireflection film of the operating wavelength, and each diffraction grating unit 501 in the diffraction grating array 5 is coated with high reflection film of the operating wavelength.
As shown in fig. 2, the fast axis collimating lens 102 is prepared by adopting a plasma coupled dry etching and high-quality optical dielectric film deposition technology, curved sidewall grooves are prepared by reasonably selecting etching process parameters, and the fast axis collimating lens 102 is prepared by depositing an optical dielectric material in the grooves, so as to realize an on-chip integrated fast axis collimating laser linear array.
As shown in fig. 2, the waveguide grating 103 is prepared by using a high-precision mask preparation and a plasma coupling dry etching technique, and the waveguide grating 103 is prepared by reasonably selecting etching process parameters, so that frequency selection and spectrum narrowing of the laser linear array are realized.
FIG. 5 is a schematic view of vernier effect of laser spectra. The solid line oscillogram is the frequency-selecting spectrum of the waveguide grating, and the dotted line oscillogram is the feedback spectrum of the diffraction grating. The overlapping area between the solid line waveform diagram and the dotted line waveform diagram is the final spectrum of the laser unit, namely the waveform diagram indicated by an arrow, and the spectral line width of the invention is small as can be seen from fig. 5.
The invention makes one or more light-emitting units of the laser linear array incident on one diffraction grating unit through the external cavity feedback of the diffraction grating array, makes the central wavelength of the feedback light returned by the light-emitting units with different bending degrees along the original path after passing through the diffraction unit very close by adjusting each diffraction grating unit, and makes the central wavelength of the littrow first-order diffraction feedback light generate certain deviation by adjusting the angle, so that the central wavelength of the output light of the light-emitting units with different bending degrees is very close, and simultaneously, because the central wavelength of the waveguide grating spectrum and the central wavelength of the external cavity grating feedback spectrum have certain deviation, the spectrum superposition similar to the vernier effect is formed, thereby effectively reducing the spectral line width of the laser unit and the whole linear array.
It should be noted that the above list is only one specific embodiment of the present invention. It is clear that the invention is not limited to the embodiments described above, but that many variations are possible, all of which can be derived or suggested directly from the disclosure of the invention by a person skilled in the art, and are considered to be within the scope of the invention.

Claims (5)

1. The narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array is characterized by comprising a semiconductor laser linear array (1), wherein the semiconductor laser linear array (1) consists of a gain waveguide (101), a fast axis collimating mirror (102) and a waveguide grating (103), a small lens (2), a half-wave plate (3), a large lens (4) and a diffraction grating array (5) are sequentially arranged along the laser output direction of the semiconductor laser linear array, and the distance from the small lens (2) to the semiconductor laser linear array (1) is the focal length f of the small lens (2)1The small lens (2) and the large lens (4) are arranged in a confocal manner to form an inverted telescopic system, and the distance between the large lens (4) and the diffraction grating array (5) is the focal length f of the large lens (4)2The half-wave plate (3) is located at the focus of the small lens (2) and the large lens (4), the diffraction grating array (5) is formed by gluing diffraction grating units (501) with different rotation angles, each diffraction grating unit (501) is placed in a littrow structure, one or more light emitting units of the semiconductor laser linear array (1) are incident on the corresponding diffraction grating unit (501), and each diffraction grating unit (501) is adjusted to enable the incident angles theta and phi of light beams a and b of the optical axis and the off-axis light emitting units to be equal or very close to each other when the light beams a and b are incident on the diffraction grating unit (501).
2. The array of narrow linewidth external cavity semiconductor lasers based on a diffraction grating array as claimed in claim 1, wherein the small lens (2) and the large lens (4) are both convex lenses, and the focal length of the large lens (4) is 3-10 times of that of the small lens (2).
3. The narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array as claimed in claim 1, wherein the small lens (2), the half-wave plate (3) and the large lens (4) are coated with antireflection film with working wavelength, and each diffraction grating unit (501) in the diffraction grating array (5) is coated with high reflection film with working wavelength.
4. The narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array as claimed in claim 1, wherein the fast axis collimating mirror (102) is prepared by adopting plasma coupled dry etching and high-quality optical dielectric film deposition technology, preparing a curved sidewall groove by reasonably selecting etching process parameters, and depositing optical dielectric material in the groove.
5. The narrow linewidth external cavity semiconductor laser linear array based on the diffraction grating array as claimed in claim 1, wherein the waveguide grating (103) is prepared by adopting high-precision mask preparation and plasma coupling dry etching technology and reasonably selecting etching process parameters.
CN202011601590.5A 2020-12-30 2020-12-30 Narrow linewidth external cavity semiconductor laser linear array based on diffraction grating array Pending CN112600068A (en)

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