CN117791273A - Ultra-narrow linewidth sweep frequency laser - Google Patents

Abstract

The invention provides an ultra-narrow linewidth sweep frequency laser, which comprises an outer cavity, an optical path device and a control system, wherein the optical path device is arranged in the outer cavity and comprises a semiconductor gain chip, an aspheric lens, an etalon, a single optical fiber coupler, a double optical fiber coupler, a transmission grating, an MEMS (micro-electromechanical system) reflector and an optical waveguide coupler which are sequentially arranged; the semiconductor gain chip emits divergent laser; the beam is condensed and collimated by an aspheric lens, and then the spectrum is selected by an etalon; the laser beam is converted into a collimated laser beam with ultra-narrow linewidth through a single optical fiber coupler and a double optical fiber coupler; selecting specific wavelength through a transmission grating and an MEMS reflector to obtain accurate spectrum filtering laser output, and returning a small part of the laser output after reflection for continuously exciting the semiconductor gain chip; most of the laser beams are transmitted to the optical waveguide coupler to be subjected to light splitting, light is emitted after fusion, and ultra-narrow line width laser with the line width of a target is obtained, so that the laser beams can be widely applied to the fields of high-precision optical ranging, imaging and the like of laser radars and the like.

Description

Ultra-narrow linewidth sweep frequency laser

[ field of technology ]

The invention relates to the field of laser radars or optical communicators, in particular to a sweep frequency laser of a laser radar or an optical communicator.

[ background Art ]

In the current laser radar system or optical communication device, a laser source mainly adopts a low-power laser with MHz laser pulse repetition frequency, the laser pulse width is wider, and the distance resolution of distance measurement is limited. In order to obtain higher precision, continuous wave laser with narrower linewidth is required to be used for continuous wave frequency modulation so as to improve the distance resolution.

The narrow linewidth continuous wave laser source commonly used in the industry comprises semiconductor laser and fiber laser with stable external cavity, but the output power of the external cavity stable laser is lower; while the injection locking laser can obtain higher output power, the linewidth can only reach the MHz magnitude, and the distance resolution is not high.

The disadvantages of current narrow line laser technology are as follows:

1. the output power of the narrow-line laser is limited, and the application requirement of the laser radar is difficult to meet.

2. The line width is difficult to achieve KHz magnitude, the frequency stability is poor, and the distance resolution and the measurement accuracy are required to be improved.

3. The continuous tunable range is narrow, the modulation rate is slow, and the frequency scanning performance is limited.

4. The multi-parameter comprehensive optimization such as extremely narrow line width, wide modulation range, high modulation rate and the like is not realized.

Therefore, the development of a novel ultra-narrow linewidth sweep frequency laser of the laser radar has important significance in realizing breakthrough of performance.

[ invention ]

The technical problem to be solved by the invention is to provide the ultra-narrow linewidth sweep frequency laser which can realize ultra-narrow linewidth, has smaller linewidth magnitude, supports long cavity configuration, has stable frequency sweep, small jitter and can rapidly and continuously sweep frequency.

The invention is realized in the following way: the ultra-narrow linewidth sweep frequency laser comprises an outer cavity, an optical path device and a control system, wherein the optical path device is arranged in the outer cavity, and comprises a gain chip, an aspheric lens, an etalon, a single optical fiber coupler, a double optical fiber coupler, a transmission grating, an MEMS reflector and an optical waveguide coupler which are sequentially arranged;

the MEMS reflector is provided with an MEMS driving module, and the MEMS driving module and the etalon are connected with an adjustable voltage power supply; the voltage of the adjustable voltage power supply is controlled and regulated by the control system; the MEMS drive module provides accurate scanning of the MEMS mirror in multiple degrees of freedom;

the light path direction of the light path device is as follows:

the semiconductor gain chip is used as a pumping light source to provide the required laser gain and emit divergent laser;

the aspheric lens is used for converging and collimating divergent laser emitted by the semiconductor gain chip to obtain collimated laser;

the etalon is used as a frequency spectrum filter element, and the frequency spectrum of the collimated laser is selected according to the voltage of the adjustable voltage power supply to obtain the laser of a target range wave band;

the single-fiber coupler is used for spatial filtering and guiding of laser and comprises a first incidence lens, a single fiber and a first emergent lens, wherein the first incidence lens focuses and couples the laser of the target range wave band, then enters the single fiber, and a laser mode field is obtained after the laser mode field is transmitted and filtered through the single fiber and is converted into a first collimated laser beam by the first emergent lens;

the double-fiber coupler comprises a second incidence lens, a double-fiber and a second emergent lens, wherein the second incidence lens focuses and couples the first collimated laser beam and then enters the double-fiber, and the second collimated laser beam is transmitted and filtered through the double-fiber and then converted into a second collimated laser beam by the second emergent lens and then sent to the transmission grating;

wherein the total length of the single optical fiber and the double optical fiber is controlled according to the requirement;

the transmission grating and the MEMS reflector select specific wavelengths of the second collimated laser beams according to the target wavelengths of the finally output ultra-narrow linewidth laser, and accurate spectrum filtering laser output is obtained; the MEMS reflector continuously tunes the frequency scanning output of the accurate spectrum filtering laser output, then reflects the accurate spectrum filtering laser output, and enters the transmission grating at an angle continuously changed in a given mode under the driving of the MEMS driving module, and adjusts the incident angle of reflected light entering the transmission grating;

the transmission grating is transmitted back to the double-fiber coupler;

the double-fiber coupler transmits a small part of the reflected light back to the semiconductor gain chip by the single-fiber coupler and the etalon in sequence, and the double-fiber coupler is used for continuously exciting the semiconductor gain chip; simultaneously directing a substantial portion of said reflected light to an optical waveguide coupler;

the optical waveguide coupler splits most of reflected light and outputs light after fusion, and ultra-narrow linewidth laser with a target linewidth magnitude is obtained.

Further, the total length of the single optical fiber and the double optical fiber is adjusted according to the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude, namely:

the smaller the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is, the longer the total length of the single optical fiber and the double optical fibers is, and the shorter the total length of the single optical fiber and the double optical fibers is otherwise.

Further, the MEMS mirror performs continuously tunable frequency scan output on the accurate spectrum filtered laser output according to the following rule:

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is smaller, the scanning angle adopted by the MEMS reflector is larger, and the scanning frequency is higher;

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is larger, the scanning angle adopted by the MEMS reflector is smaller, and the scanning frequency is lower.

Further, a small portion of the reflected light accounts for 10% of the reflected light.

The invention has the advantages that: the ultra-narrow linewidth sweep frequency laser adopts the quantum dot gain medium, ensures that the gain linewidth is extremely narrow, can realize extremely narrow linewidth by modifying the lengths of single optical fiber and double optical fibers, has linewidth magnitude up to KHz magnitude, and greatly improves the resolution of laser distance measurement; the applicability is very wide, and the product can be realized by modifying the coating of SLED and selecting etalons with different free spectrum ranges according to the requirements of different fields; the MEMS reflector is adopted to switch the wavelength, so that the wavelength is fast, the scanning range is wide, the scanning space is larger, the modulation rate is obviously improved and can reach more than 1000 times per second, and the frequency scanning is more flexible and efficient; the design of the integral light path effectively improves the output power, the output seed power can reach 50 milliwatts, and the device is suitable for various environmental applications; the frequency stability is greatly optimized, and the ranging accuracy and reliability are obviously improved; the cost is low.

[ description of the drawings ]

The invention will be further described with reference to examples of embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of the optical path structure of an ultra-narrow linewidth swept laser.

Fig. 2 is a schematic diagram of the effect of the aspherical lens in condensing and collimating the divergent laser light emitted from the semiconductor gain chip according to an embodiment of the present invention.

Fig. 3 is a schematic diagram illustrating a state after the laser spectrum is selected by the standard tool according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of a state of a laser for realizing ultra-narrow linewidth light emission according to requirements in an embodiment of the present invention.

Fig. 5 is a graph of the laser spectrum of the final output in an embodiment of the invention.

[ detailed description ] of the invention

The embodiment of the invention can realize extremely narrow linewidth, smaller linewidth magnitude, support long cavity configuration, stable frequency sweep, small jitter and rapid and continuous frequency sweep by providing the ultra-narrow linewidth frequency sweep laser.

The technical scheme in the embodiment of the invention aims to solve the problems, and the overall thought is as follows: the gain chip comprises a gain chip, and a quantum dot gain medium is adopted to ensure that the gain linewidth is extremely narrow; by modifying the lengths of the single optical fiber and the double optical fiber, the extremely narrow linewidth reaches the KHz magnitude; a long cavity structure is built according to requirements through a single fiber coupler and a double fiber coupler so as to obtain corresponding high interference stability; line width is controlled through closed loop feedback; the MEMS reflector is adopted to carry out wavelength scanning with large angle and high frequency, so that a rapid scanning and accurate low-jitter frequency sweeping scheme is realized; power stabilization techniques. The technology breaks through the limit of the line width and the sweep rate of the current sweep laser, and can be widely applied to the fields of high-precision optical ranging, imaging and the like of laser radars and the like.

In order to better understand the above technical solutions, the following detailed description will refer to the accompanying drawings and specific embodiments.

Referring to fig. 1 to 5, an ultra-narrow linewidth swept laser according to an embodiment of the invention includes an external cavity, an optical path device, and a control system. The optical path device is arranged in the outer cavity, comprises a gain chip, an aspheric lens, an etalon, a single optical fiber coupler, a double optical fiber coupler, a transmission grating, an MEMS reflector and an optical waveguide coupler which are sequentially arranged;

the MEMS reflector is provided with an MEMS driving module, and the MEMS driving module and the etalon are connected with an adjustable voltage power supply; the voltage of the adjustable voltage power supply is controlled and regulated by the control system; the MEMS drive module provides accurate scanning of the MEMS mirror in multiple degrees of freedom;

as shown in fig. 1, the path direction of the optical path device is as follows:

the semiconductor gain chip is used as a pumping light source to provide the required laser gain and emit divergent laser; the light emitting film of the semiconductor gain chip can be selected or replaced, so that the wavelength of the scattered laser can be adjusted through the selection of the light film, and the required laser gain is realized.

The aspheric lens is used for converging and collimating divergent laser emitted by the semiconductor gain chip to obtain collimated laser;

the etalon is used as a frequency spectrum filter element, and the frequency spectrum of the collimated laser is selected according to the voltage of the adjustable voltage power supply to obtain the laser of a target range wave band; since the free spectral range of the fixed interval is also different for different etalons, the selection of the target range band laser spectrum can also be achieved by the selection of the etalon.

The single-fiber coupler is used for spatial filtering and guiding of laser and comprises a first incidence lens, a single fiber and a first emergent lens, wherein the first incidence lens focuses and couples the laser of the target range wave band, then enters the single fiber, and a laser mode field is obtained after the laser mode field is transmitted and filtered through the single fiber and is converted into a first collimated laser beam by the first emergent lens;

the double-fiber coupler comprises a second incidence lens, a double-fiber and a second emergent lens, wherein the second incidence lens focuses and couples the first collimated laser beam and then enters the double-fiber, and the second collimated laser beam is transmitted and filtered through the double-fiber and then converted into a second collimated laser beam by the second emergent lens and then sent to the transmission grating;

wherein the total length of the single optical fiber and the double optical fiber is controlled according to the requirement; when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is smaller, the total length of the single optical fiber and the double optical fibers is longer, and conversely, the total length of the single optical fiber and the double optical fibers is shorter.

The transmission grating and the MEMS reflector select specific wavelengths of the second collimated laser beam according to a diffraction equation and the target wavelength of the finally output ultra-narrow linewidth laser, so that accurate spectrum filtering laser output is obtained;

the MEMS reflector can perform large-angle and high-frequency wavelength scanning, continuously tuneable frequency scanning output is performed on the accurate spectrum filtering laser output, then the laser is reflected, and the laser enters the transmission grating in a continuously changing angle of a given mode under the driving of the MEMS driving module, and the incident angle of reflected light entering the transmission grating is adjusted;

the MEMS reflector continuously tunes the frequency scanning output of the accurate spectrum filtering laser output according to the following rules:

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is smaller, the scanning angle adopted by the MEMS reflector is larger, and the scanning frequency is higher;

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is larger, the scanning angle adopted by the MEMS reflector is smaller, and the scanning frequency is lower.

The transmission grating is transmitted back to the double-fiber coupler;

the double-fiber coupler transmits a small part of the reflected light back to the semiconductor gain chip through the single-fiber coupler and the etalon in sequence, and the double-fiber coupler is used for keeping seed light in a laser to be continuously amplified, oscillating back and forth and continuously exciting the semiconductor gain chip; simultaneously directing a substantial portion of said reflected light to an optical waveguide coupler; for example, the reflected light may be as follows: 9, 10% of the reflected light is transmitted back to the semiconductor gain chip and 90% of the reflected light is transmitted to the optical waveguide coupler.

The optical waveguide coupler splits most of reflected light and outputs light after fusion, and ultra-narrow linewidth laser with a target linewidth magnitude is obtained.

Example 1:

referring to fig. 1 to 5, the semiconductor gain chip provides the required laser gain, the wavelength range of the emitted divergent laser after being coated is 1300nm to 1650nm, and finally the laser output with the wavelength of 1550 or 1553nm and the ultra-narrow line width is realized, and the parameters of the optical path are selected or controlled as follows:

the collimated laser obtained after the divergent laser of the semiconductor gain chip is condensed and collimated by the aspheric lens is shown in figure 2;

an etalon with a fixed interval and a free spectrum range of 400GHz is adopted as a frequency spectrum filter element, the frequency spectrum of the collimated laser is selected according to the voltage of an adjustable voltage power supply, and as shown in figure 3, the laser with a target range wave band is obtained;

controlling the total length of a single optical fiber of the single optical fiber coupler and a double optical fiber of the double optical fiber coupler to be 2469 cm;

the transmission grating and the MEMS reflector select specific wavelengths of the second collimated laser beam according to a diffraction equation and the target wavelength of the finally output ultra-narrow linewidth laser, wherein as shown in FIG. 4, 5V of adjustable power supply voltage is applied to the MEMS driving module, and therefore accurate spectrum filtering laser output of 1549.98nm can be obtained; applying 18V adjustable voltage to the MEMS driving module to obtain 1553.16nm accurate spectrum filtering laser output;

the dual-fiber coupler transmits about 10% of the reflected light back to the semiconductor gain chip by the single-fiber coupler and the etalon in sequence for continuously exciting the semiconductor gain chip; while directing about 90% of said reflected light to an optical waveguide coupler;

the optical waveguide coupler adopts a 2×2 optical waveguide coupler and is used for carrying out light splitting on most of reflected light to be converged and then outputting the light, as shown in fig. 5, the ultra-narrow line width laser with the target line width of 5000HZ is obtained at the position of the full width half maximum 3dB bandwidth as can be seen from the frequency spectrum.

While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that the specific embodiments described are illustrative only and not intended to limit the scope of the invention, and that equivalent modifications and variations of the invention in light of the spirit of the invention will be covered by the claims of the present invention.

Claims (4)

1. An ultra-narrow linewidth sweep frequency laser is characterized in that: the optical path device is arranged in the outer cavity, comprises a semiconductor gain chip, an aspheric lens, an etalon, a single optical fiber coupler, a double optical fiber coupler, a transmission grating, an MEMS reflector and an optical waveguide coupler which are sequentially arranged;

the MEMS reflector is provided with an MEMS driving module, and the MEMS driving module and the etalon are both connected with an adjustable voltage power supply; the voltage of the adjustable voltage power supply is controlled and regulated by the control system; the MEMS drive module provides accurate scanning of the MEMS mirror in multiple degrees of freedom;

the light path direction of the light path device is as follows:

the semiconductor gain chip is used as a pumping light source to provide the required laser gain and emit divergent laser;

the aspheric lens is used for converging and collimating divergent laser emitted by the semiconductor gain chip to obtain collimated laser;

the etalon is used as a frequency spectrum filter element, and the frequency spectrum of the collimated laser is selected according to the voltage of the adjustable voltage power supply to obtain the laser of a target range wave band;

the single-fiber coupler is used for spatial filtering and guiding of laser and comprises a first incidence lens, a single fiber and a first emergent lens, wherein the first incidence lens focuses and couples the laser of the target range wave band, then enters the single fiber, and a laser mode field is obtained after the laser mode field is transmitted and filtered through the single fiber and is converted into a first collimated laser beam by the first emergent lens; wherein the length of the single optical fiber is controlled according to the requirement;

the double-fiber coupler comprises a second incidence lens, a double-fiber and a second emergent lens, wherein the second incidence lens focuses and couples the first collimated laser beam and then enters the double-fiber, and the second collimated laser beam is transmitted and filtered through the double-fiber and then converted into a second collimated laser beam by the second emergent lens and then sent to the transmission grating;

wherein the total length of the single optical fiber and the double optical fiber is controlled according to the requirement;

the transmission grating and the MEMS reflector select specific wavelengths of the second collimated laser beams according to the target wavelengths of the finally output ultra-narrow linewidth laser, and accurate spectrum filtering laser output is obtained; the MEMS reflector continuously tunes the frequency scanning output of the accurate spectrum filtering laser output, then reflects the accurate spectrum filtering laser output, and enters the transmission grating at an angle continuously changed in a given mode under the driving of the MEMS driving module, and adjusts the incident angle of reflected light entering the transmission grating;

the transmission grating is transmitted back to the double-fiber coupler;

the double-fiber coupler transmits a small part of the reflected light back to the semiconductor gain chip by the single-fiber coupler and the etalon in sequence, and the double-fiber coupler is used for continuously exciting the semiconductor gain chip; simultaneously directing a substantial portion of said reflected light to an optical waveguide coupler;

the optical waveguide coupler splits most of reflected light and outputs light after fusion, and ultra-narrow linewidth laser with a target linewidth magnitude is obtained.

2. An ultra-narrow linewidth swept laser as claimed in claim 1, wherein: the total length of the single optical fiber and the double optical fiber is adjusted according to the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude, namely:

the smaller the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is, the longer the total length of the single optical fiber and the double optical fibers is, and the shorter the total length of the single optical fiber and the double optical fibers is otherwise.

3. An ultra-narrow linewidth swept laser as claimed in claim 1, wherein: the MEMS reflector continuously tunes the frequency scanning output of the accurate spectrum filtering laser output according to the following rules:

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is smaller, the scanning angle adopted by the MEMS reflector is larger, and the scanning frequency is higher;

when the target linewidth magnitude of the ultra-narrow linewidth laser of the target linewidth magnitude is larger, the scanning angle adopted by the MEMS reflector is smaller, and the scanning frequency is lower.

4. An ultra-narrow linewidth swept laser as claimed in claim 1, wherein: a small portion of the reflected light accounts for 10% of the reflected light.