WO2012126427A2

WO2012126427A2 - Laser with tunable outer cavity and method for using same

Info

Publication number: WO2012126427A2
Application number: PCT/CN2012/075816
Authority: WO
Inventors: 陈波; 高磊; 张光勇; 陈熙
Original assignee: 华为技术有限公司
Priority date: 2012-05-21
Filing date: 2012-05-21
Publication date: 2012-09-27
Also published as: CN102812602A; WO2012126427A3; CN102812602B

Abstract

Provided in embodiments of the present invention are a laser with tunable outer cavity and a method for using the same, wherein the laser with tunable outer cavity comprises a gain chip, a collimating mirror, a wavelength selecting element, and an optical path difference generating optical passageway; a cavity surface of the gain chip is located in a focal plane of the collimating mirror; the wavelength selecting element is located between the collimating mirror and the optical path difference generating optical passageway; light beams emitted from the cavity surface of the gain chip are collimated by the collimating mirror to form parallel beams which are sent to the wavelength selecting element; the wavelength selecting element filters the parallel beams from the collimating mirror and then sends them to the optical path difference generating optical passageway; the optical path difference generating optical passageway splits the parallel beams entering the optical path difference generating optical passageway into at least two branch beams, and reflects each of the branch beams in the incident direction to the gain chip, wherein the optical path difference generating optical passageway is capable of adjusting the optical path difference between the optical paths of the branch beams. Since the optical path difference generating passageway serves to roughly select mode without the need for precious control and adjustment, the process of wavelength tuning and selecting is made easier.

Description

External cavity tunable laser, and method of use thereof

TECHNICAL FIELD The present invention relates to the field of optical technologies, and in particular, to an external cavity tunable laser and a method of using the same. Background technique

Large-capacity high-speed optical transmission and a more flexible optical network structure are the development trend of optical communication. In order to achieve a single-wave transmission rate greater than 40 Gbps, high-order modulation and coherent reception techniques are generally used, which requires an optical carrier linewidth of less than ΙΟΟΚΗζ to suppress phase noise and detect signal phase. On the other hand, the intelligent and flexible optical network has the characteristics of dynamic wavelength distribution, which can be realized by adjusting the wavelength or frequency of the optical carrier. Therefore, a narrow linewidth tunable laser is of great significance to the evolution of optical communication systems.

At present, the implementation of a narrow-width tunable laser with a linewidth less than ΙΟΟΚΗζ is mainly realized by an external cavity tunable laser, and the existing external cavity tunable laser performance is not ideal, and the tuning speed is low, the control is complicated, and the assembly tolerance is Small, low reliability and other issues. The external cavity tunable laser shown in Figure 1 comprises a gain chip, a collimating mirror, a wavelength selective element, and a mirror. The external cavity tunable laser shown in Figure 1 can achieve single longitudinal mode lasing, mainly by using the overlapping of the transmission spectra of two wavelength tunable components to select a fine wavelength, that is, using a cursor (Vernier) effect. The specific principle is as follows: After the beam emitted from the gain chip (12) is collimated and collimated by the collimating mirror (20), it passes through two tunable wavelength selecting elements (24) and (26), which are tunable The wavelength selective elements (24) and (26) filter the outgoing beam incident on the mirror (14), which is then reflected by the mirror (14) and folded back completely to the active area of the gain chip (12) according to the original incident path. Cavity resonance. The transmission spectra of the tunable wavelength selective elements (24) and (26) are shown in the two free spectral regions (Free Spectral Range 1, 2, FSR1 and FSR2) of Figure 2, since the transmission peaks of FSR1 and FSR2 are only at λΐ There is overlap at the wavelength, so that when λΐ corresponds to the longitudinal mode of the external cavity laser, a single longitudinal mode lasing of wavelength λΐ can be achieved.

The Vernier effect employed in the prior art is by adjusting the wavelength selection elements of the two FSRs. The transmission spectrum is such that only one transmission peak coincides and the remaining transmission peaks are staggered to achieve a single longitudinal mode lasing corresponding to the coincident transmission peak. However, in order to accurately implement single longitudinal mode lasing, it is necessary to "simultaneously control" the transmission spectrum distribution of the two wavelength selective elements, making control extremely difficult, and thus the control system is complicated and the tuning rate is low. SUMMARY OF THE INVENTION Embodiments of the present invention provide an external cavity tunable laser, and a method of using the same, to make the wavelength tuning selection process faster and easier.

An external cavity tunable laser comprising:

Gain chip, collimating mirror, wavelength selecting component, optical path difference generating optical path;

A cavity surface of the gain chip is located at a focal plane of the collimating mirror; a wavelength selecting component is located between the collimating mirror and the optical path difference generating optical path; and the collimating mirror collimates the light beam emitted from the cavity surface of the gain chip to form a parallel And transmitting the light beam to the wavelength selective element; the wavelength selecting element filters the parallel light beam from the collimating mirror and sends the light beam to the optical path difference generating optical path;

The optical path difference generating optical path divides the parallel light beam of the incident optical path difference generating optical path into at least two branch light beams, and reflects the respective branch light beams in the incident direction to the gain chip, wherein the optical path difference generating optical path can be adjusted The optical path difference between the optical paths of the branch beams.

A method of using an external cavity tunable laser, comprising:

After the gain chip of the external cavity tunable laser according to any one of the embodiments of the present invention is excited to generate a light beam, adjusting the optical path difference to generate an optical path difference between optical paths of the respective branch beams in the optical path, so that The external cavity tunable laser implements a wavelength tuning function.

As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages: The external cavity resonant optical path includes a gain chip, a collimating mirror, a wavelength selecting element, and an optical path difference generating optical path. The wavelength selecting component can play the role of the primary filtering mode selection; the optical path difference generating optical path serves as the second filtering mode selection, and can further select the desired lasing from the mode selected by the initial filtering with a certain frequency interval. Mode, and suppress the remaining modes to achieve single longitudinal film lasing. Since the optical path difference generation circuit functions as a coarse selection mode, precise adjustment adjustment is not required, making the wavelength tuning selection process faster and easier. DRAWINGS In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be described below. It is obvious that the drawings in the following description are only some embodiments of the present invention. Other drawings may also be obtained from those of ordinary skill in the art in view of these drawings without the inventive labor.

1 is a schematic structural view of a prior art external cavity tunable laser;

2 is a schematic diagram of a free spectral region adjusted with the external cavity tunable laser shown in FIG. 1; FIG. 3 is a schematic structural view of an exceptional cavity tunable laser according to the present invention;

4 is a schematic structural view of an exemplified cavity tunable laser according to the present invention;

5 is a transmission spectrum formed by Etalon-1 filtering and an interference spectrum formed by two-beam interference according to an embodiment of the present invention;

6 is a mode gain spectrum diagram of a common filtering effect of an Etalon-1 and an optical path difference generating optical path according to an embodiment of the present invention;

7a is a 增益=29.15μηι mode gain spectrum diagram of an embodiment of the present invention;

Figure 7b is a 增益 = 29.17μηι mode gain spectrum diagram of an embodiment of the present invention;

Figure 8 is a partial view of a transmission spectrum of an embodiment of the present invention;

9 is a schematic structural view of an exemplified cavity tunable laser according to the present invention;

10 is a schematic structural view of an exemplified cavity tunable laser according to the present invention;

FIG. 11 is a schematic flowchart of a method according to an embodiment of the present invention. The present invention will be further described in detail with reference to the accompanying drawings, in which FIG. An embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

An embodiment of the present invention provides an external cavity tunable laser, as shown in FIG. 3, including: a gain chip 100, a collimating mirror 200, a wavelength selecting component 300, and an optical path difference generating optical path 400; wherein the gain shown in FIG. Both ends of the chip 100 are the cavity surface 1001 and the cavity surface 1002; such marks are also used in the subsequent figures, and are not described again.

One cavity surface of the gain chip 100 is located at the focal plane of the collimating mirror 200; In the focal plane of the collimating mirror 200; the wavelength selecting component 300 is located between the collimating mirror 200 and the optical path difference generating optical path 400;

The collimating mirror 200 collimates the light beam emitted from the cavity surface of the gain chip 100 to form a parallel beam and transmits it to the wavelength selecting element 300. The wavelength selecting element 300 filters the parallel beam from the collimating mirror 200 and transmits it to The optical path difference generating optical path 400; the wavelength selective element 300 shown in FIG. 3 is sent to the filtered parallel light beam 600 of the optical path difference generating optical path 400;

The optical path difference generating optical path 400 divides the parallel light beam of the incident optical path difference generating optical path 400 into at least two branched light beams, and reflects the respective branch light beams to the gain chip 100 in the incident direction, as shown in FIG. The light beam 700 and the branch light beam 800, the optical path difference generating light path 400, can adjust the optical path difference between the optical paths of the respective branch light beams.

In the above embodiment, the external cavity resonant optical path includes a gain chip, a collimating mirror, a wavelength selecting element, and an optical path difference generating optical path. The wavelength selecting component can play the role of the primary filtering mode selection; the optical path difference generating optical path functions as the second filtering mode selection, and can further select the desired excitation from the mode selected by the initial filtering and having a certain frequency interval. Shooting, and suppressing the remaining modes to achieve single longitudinal film lasing. Since the optical path difference generation circuit functions as a coarse selection mode, precise adjustment adjustment is not required, making the wavelength tuning selection process faster and easier.

Optionally, in the embodiment of the present invention, two specific configurations of the optical path difference generating optical path 400 are provided. It should be noted that in the following embodiments, the branch beam is a two-way structure, and the branch beam is two. The principle of the above road is the same as that of the following embodiment. Therefore, the structure of the two-way branch beam in the following embodiments should not be construed as limiting the embodiment of the present invention.

Embodiment 1 As shown in FIG. 4, the optical path difference generating optical path 400 includes: at least two mirrors 401 (two mirrors shown in FIG. 4: a mirror 401A and a mirror 401B), and at least one reflection The position of the mirror 401 is adjustable; the position of the mirror 401 A can be adjusted, or the position of the mirror 401B can be adjusted, or the positions of the mirror 401A and the mirror 401B can be adjusted.

Each of the mirrors 401 is located in the propagation direction of the branch beam generated by the incident optical path difference generating optical path 400 and the reflecting surface of each of the mirrors 401 is perpendicular to the propagation direction of the branch beam; the position of the adjusting mirror 401 is adjustable. The position of at least one of the mirrors 401 changes the optical path difference between the optical paths of the respective branch beams incident on the respective mirrors 401 in the optical path difference generating optical path 400. For example: the position of the mirror 401A is adjustable, then the position of the mirror 401A is adjusted (for example, parallel movement in front and rear) The mirror 401A) changes the optical path of the branch beam of the mirror 401A such that the difference between the optical path of the branch beam of the mirror 401A and the optical path of the branch beam of the mirror 401B follows the position of the mirror 401A. The change has changed.

It should be noted that in the embodiment of the present invention, the mirror may be a common mirror or a full-reflecting mirror, and the embodiments of the present invention may be implemented and achieve corresponding effects. Since the total reflection mirror has a higher effect on the reflectance of light, it is preferable to use a total reflection mirror.

Based on the first embodiment, the working principle of the external cavity tunable laser is as follows: Wavelength selection element 300 The position of the mirror 401B is different such that there is an optical path difference between the optical paths of the respective branch beams. The corresponding reflected branch beam having an optical path difference is completely folded back along the original incident optical path, and after focusing by the collimating mirror 200, the combined wave is interfered and enters the inner cavity of the gain chip 100.

As shown in Fig. 4, the equivalent cavity length (Lc) of the outer cavity is set to 1.2163 cm (cm), and the longitudinal mode formed by the outer cavity is about 0.0988 nm (nm). Here, a Fabry Perot etalon Etalon (referred to as Etalon-1) is used as the wavelength selecting element 300 shown in Fig. 4, and the transmission peak interval is 0.4 nm. At this time, the transmission spectrum after Etalon-1 filtering is shown in Fig. 5. The horizontal axis is the wavelength (wavelength), indicating the spectrum; the vertical axis is the normalized power, and the horizontal axis of the subsequent FIG. 6, FIG. 7a and FIG. 7b is the wavelength, indicating the spectrum; the vertical axis is the normalized intensity; Transmission spectra and interference spectra are also illustrated, and subsequent figures are no longer described. Figure 5 shows the interference spectrum formed by the transmission spectrum and double beam interference after Etalon-1 filtering. As can be seen from Fig. 5, because Etalon-1 has a small FSR and high filtering precision, it can be used for many existing The cavity longitudinal mode is initially selected such that only a few longitudinal modes exit at a transmittance close to one. At the same time, the broken line of Fig. 5 also shows the interference spectrum obtained by the interference of the two branches of the optical path difference. As shown in Fig. 4, the optical path difference is determined by the position difference Μ=29.17μηι of the two mirrors 401A and The mirror 401B is introduced. It can be seen that the peak of the interference spectrum is located at λ = 1535.7 nm, which corresponds to one of the modes obtained after the initial selection of the Etalon-1 filter, and the residual mode deviating from λ = 1535.7 nm is suppressed by the distribution of the interference spectrum, thereby forming enough The gain difference is such that only the longitudinal mode mode with λ = 1535.7 nm can lasing, that is, the mode gain spectrum corresponding to the common filtering effect of the Etalon-1 and the optical path difference generating optical path shown in FIG. Since the interference spectrum formed by the interference of the two beams is a relatively slowly varying envelope, even if the position difference of the two mirrors is M = 29.17 μm (μηι), as shown in Fig. 7a, Μ = 29.15 μηι and Fig. 7b Μ = 29.19 In the case of μηι, it is still possible to make the longitudinal mode of λ = 1535.7 nm have a gain close to 1, while continuing to effectively suppress The gain of the residual mode deviating from λ = 1535.7 nm is maintained, and the single longitudinal mode lasing state is maintained. This means that the control of the position difference M does not need to be performed to a very precise degree, thereby effectively increasing the wavelength tuning rate and improving the reliability of the mode selection. In order to achieve wavelength adjustment, it is necessary to adjust the transmission spectrum of Etalon-1 and the distribution of the interference interference spectrum. The wavelength ληι corresponding to the transmission peak of Etalon is determined by equation (1):

2nd cos Θ where n = 1 is the refractive index, d = 2.0445mm is the gap between the front and back reflection surfaces of Etalon, Θ = o° is the angle between the incident light and the Etalon surface, and m is the wavelength number. In order to tune the mode selection wavelength to λ = 1540 nm, d is reduced by 40 nm, at which time the transmission spectrum of Etalon-1 becomes the distribution shown in Fig. 8. At the same time, M increases by 130 nm on the basis of the original 29.17μηι, so that the peak of the interference spectrum shifts to the longitudinal mode position of λ = 1540 nm, so as to achieve the single longitudinal film lasing of λ = 1540 nm by suppressing other longitudinal modes.

Embodiment 2 As shown in FIG. 9, the optical path difference generating optical path 400 includes: a beam splitting mirror 402; at least two mirrors 403 (two mirrors shown in FIG. 9: a mirror 403 A and a mirror 403B) At least one of the mirrors 403 is adjustable in position; specifically, the position of the mirror 403A is adjustable, or the position of the mirror 403B is adjustable, and the positions of the mirror 403A and the mirror 403B are both adjustable.

The beam splitter 402 is located in the optical path of the parallel beam incident on the optical path difference generating optical path 400 for splitting the parallel beam of the incident beam splitter 402 into at least two branch beams;

The number of the mirrors 403 is the same as the number of the branches, the mirror 403 is located in the beam path of the beam, and the reflecting surface of each mirror 403 is perpendicular to the branch beam of the optical path; the adjusting mirror 403 The position of the at least one mirror 403, which is positionally adjustable, causes an optical path difference between the optical paths of the respective branch beams incident on each of the mirrors 403 in the optical path difference generating optical path 400 to be changed. For example: the position of the mirror 403A is adjustable, then adjusting the position of the mirror 403A changes the optical path of the branch beam of the mirror 403A, so that the optical path of the branch beam of the mirror 403A and the branch beam of the mirror 403B are The difference between the optical paths varies with the change in the position of the mirror 403A.

Based on the second embodiment, the working principle of the external cavity tunable laser is as follows: The outgoing beam filtered by the wavelength selecting component 300 is incident on the beam splitting mirror 402 and is divided into two branches, one of which is reflected by the mirror 403 and is reflected. Fold back along the original incident path; the other branch is reflected by the mirror 403 and folded back along the original incident path. The two branches will be led by the relative positions of the two mirrors 403. The optical path difference is entered, and is folded back into the inner cavity of the gain chip 100 along the final interference. At least one of the two mirrors 403 is positionally adjustable, by which the optical path difference of the branch beam is adjusted to finally change the spectral distribution of the interference multiplex, and wavelength tuning is achieved.

In order to increase the light transmittance of the beam splitter 402, the surface of the beam splitter mirror 402 is optionally plated with an anti-reflection film. In the structure shown in Fig. 9, the beam splitting surface of the beam splitter 402 has a transmittance and a reflectance of 50%, and the four light-passing surfaces are coated with an anti-reflection film.

Further, as shown in FIG. 10, the laser further includes: a focusing mirror 500, wherein the focusing mirror 500 is located between the wavelength selecting component 300 and the optical path difference generating optical path 400;

The wavelength selecting component 300 filters the parallel beam from the collimating mirror 200 and transmits it to the optical path difference generating optical path 400.

The wavelength selecting element 300 filters the parallel beam from the collimating mirror 200 and sends it to the focusing mirror 500. The focusing mirror 500 narrows the spot of the parallel beam from the wavelength selecting unit 300, and transmits the parallel beam after the spot is reduced to the optical path difference. An optical path 400 is generated.

The focusing mirror 500 and the collimating mirror 200 constitute a two-lens system, and the gain chip 100 and the two-lens system, and the mirror 403 (or the mirror 401) of each branch beam together constitute a retro-reflection structure. It is not sensitive to the lateral displacement variation of the gain chip, thereby improving the assembly tolerance of the device. Because the external cavity optical path is a two-lens system, wherein the focusing mirror and the collimating mirror form a double lens, the gain chip-double lens system-mirror forms a quasi-4f system, and is a back-reflecting structure, which is simulated and tested by practice. Insensitive to lateral displacement, it helps to improve the tolerance of actual device assembly.

Optionally, the wavelength selecting component 300 is specifically: a Fabry Perot etalon.

Optionally, the wavelength selecting component 300 is: a fixed wavelength selecting component having a fixed frequency interval, or a tunable wavelength selecting component. The tunable wavelength selecting element is relative to the fixed wavelength selecting element, and the tunable wavelength selecting element is an element having a function of adjusting the wavelength of the transmitted light, and a plurality of tunable ways of realizing the selected wavelength are For example, the filtering of the incident spectrum can be achieved by reflection or diffraction or transmission, thereby realizing the selection of light of a desired wavelength from the incident light containing a plurality of wavelengths. The tunable wavelength selective component can be an optic containing an Etalon, grating, etc., and the tunable meaning is by changing the device parameters of the tunable wavelength selection component, such as Etalon's mirror spacing, or temperature; For the grating, which is the angle between the incident light and the normal to the grating, by changing these parameters, the tunable wavelength selective component can be made. The flexible selection of the desired wavelength, such as A working conditions, can use the wavelength selection component to select the "wavelength = lambda-1"light; under the B operating conditions, the parameters of the wavelength selection component can be changed to select "wavelength = Lambda — 2" light.

Optionally, the tunable wavelength selection component is: one of a thermal-modulated Fabry-Perot etalon, a liquid crystal voltage-tuned Fabry-Perot etalon, or a pitch-adjustable Fabry-Perot etalon Kind.

Further, the above laser further includes:

A microelectromechanical system or piezoelectric ceramic, the microelectromechanical system or piezoelectric ceramic connected to a positionally adjustable mirror for driving and tuning the position of the positionally adjustable mirror.

The embodiment of the invention further provides a method for using an external cavity tunable laser, as shown in FIG. 11, comprising:

1101: The gain chip of any of the above-mentioned external cavity tunable lasers provided by the embodiment of the present invention is excited to generate a light beam;

1102: After the gain chip of any of the above-mentioned external cavity tunable lasers is excited to generate a light beam, the optical path difference between the optical paths of the respective branch beams in the optical path is adjusted, so that the above The external cavity tunable laser implements a wavelength tuning function.

Specifically, if the optical path difference generating optical path comprises: at least two mirrors, and at least one of the mirror positions is adjustable; wherein the adjusting the optical path difference generates an optical path difference between optical paths of the respective branch beams in the optical path Includes:

The position of the at least one mirror whose position is adjustable in the adjustment mirror is adjusted such that the optical path difference between the optical paths of the respective branch beams incident on the optical path in the optical path is changed.

Specifically, if the external cavity tunable laser comprises: a micro electromechanical system or a piezoelectric ceramic;

The microelectromechanical system or piezoelectric ceramic is activated such that the microelectromechanical system or piezoelectric ceramic drives the positionally adjustable mirror in the mirror to tune the position of the positionally adjustable mirror.

In addition, those skilled in the art can understand that all or part of the steps in implementing the foregoing method embodiments may be performed by a program to instruct related hardware, and the corresponding program may be stored in a computer readable storage medium. The storage medium may be a read only memory, a magnetic disk or an optical disk or the like.

The above is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can lightly within the technical scope disclosed by the embodiments of the present invention. Variations or substitutions that are conceivable are intended to be encompassed within the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

Rights request

1. An external cavity tunable laser, comprising:

a gain chip (100), a collimating mirror (200), a wavelength selecting element (300), and an optical path difference generating optical path (400);

A cavity surface of the gain chip (100) is located at a focal plane of the collimating mirror (200); a wavelength selective element

(300) is located between the collimating mirror (200) and the optical path difference generating optical path (400); the collimating mirror (200) collimates the light beam emitted from the cavity surface of the gain chip (100) to form a parallel beam and Sending it to the wavelength selection component (300); the wavelength selection component (300) filters the parallel beam from the collimating mirror (200) and sends it to the optical path difference generating optical path (400);

The optical path difference generating optical path (400) divides the parallel light beam of the incident optical path difference generating optical path (400) into at least two branched light beams, and reflects the respective branch light beams to the gain chip (100) according to the incident direction. The optical path difference generating optical path (400) can adjust the optical path difference between the optical paths of the respective branch beams.

2. The laser according to claim 1, wherein the optical path difference generating optical path (400) comprises: at least two mirrors (401), and at least one of the mirrors (401) is positionally adjustable;

Each of the mirrors (401) is located in a propagation direction of the branch beam generated by the incident optical path difference generating optical path (400) and a reflecting surface of each of the mirrors (401) is perpendicular to a propagation direction of the branching beam;

The optical path difference generating optical path (400) can adjust an optical path difference between optical paths of the respective branch beams, specifically: adjusting a position of the at least one mirror (401) whose position is adjustable in the mirror (401), The optical path difference between the optical paths of the respective branch beams incident on each of the mirrors (401) in the optical path difference generating optical path (400) is changed.

3. The laser according to claim 1, wherein said optical path difference generating optical path (400) comprises: a beam splitting mirror (402); at least two mirrors (403), and at least one mirror (403) ) adjustable position;

The beam splitter (402) is located in the optical path of the parallel beam of the incident optical path difference generating optical path (400) for dividing the parallel beam of the incident beam splitter (402) into at least two bundles of light beams;

The number of the mirrors (403) is the same as the number of the branches, and one mirror (403) is located in the beam path of a bundle of beams, and the reflection surface of each mirror (403) and the branch of the optical path there are The beam is vertical; The optical path difference generating optical path (400) can adjust an optical path difference between optical paths of the respective branch beams, specifically: adjusting a position of the at least one mirror (403) whose position is adjustable in the mirror (403), so that The optical path difference between the optical paths of the respective branch beams incident on each of the mirrors (403) in the optical path difference generating optical path (400) is changed.

4. A laser according to claim 3, characterized in that the surface of the beam splitter (402) is coated with an anti-reflection film.

The laser according to any one of claims 1 to 4, characterized in that the laser further comprises: a focusing mirror (500), the focusing mirror (500) is located at the wavelength selecting element (300) and the optical path difference is generated. Between the light paths (400);

The wavelength selecting component (300) filters the parallel beam from the collimating mirror (200) and sends it to the optical path difference generating optical path (400).

The wavelength selecting component (300) filters the parallel beam from the collimating mirror (200) and sends it to the focusing mirror (500), which narrows the spot of the parallel beam from the wavelength selecting unit (300) and reduces The parallel beam behind the spot is sent to the optical path difference generating optical path (400).

6. A laser according to any one of claims 1 to 4, characterized in that

The wavelength selecting element (300) is specifically: a Fabry Perot etalon.

7. A laser according to any one of claims 1 to 4, characterized in that

The wavelength selective component (300) is: a fixed wavelength selective component having a fixed frequency spacing, or a tunable wavelength selective component.

8. The laser of claim 7 wherein:

The tunable wavelength selective component is one of: a thermally tuned Fabry Perot etalon, a liquid crystal voltage tuned Fabry Perot etalon or a pitch adjustable Fabry Perot etalon.

The laser according to any one of claims 2 to 8, further comprising: a micro electromechanical system or a piezoelectric ceramic, the microelectromechanical system or the piezoelectric ceramic being connected to the positionally adjustable mirror, Drive and tune the position of the positionally adjustable mirror.

10. A method of using an external cavity tunable laser, comprising:

After the gain chip of the external cavity tunable laser according to any one of claims 1 to 9 is excited to generate a light beam, adjusting the optical path difference between the optical paths of the respective branch beams in the optical path generating optical path, so that said The external cavity tunable laser implements a wavelength tuning function.

11. The method according to claim 10, wherein if the optical path difference generates an optical path package Included: at least two mirrors, and at least one of the mirror positions is adjustable; wherein the adjusting the optical path difference to generate the optical path difference between the optical paths of the respective branch beams in the optical path includes:

12. The method according to claim 10, wherein if the external cavity tunable laser comprises: a micro electromechanical system or a piezoelectric ceramic; wherein the adjusting the optical path difference generates an optical path of each branch beam in the optical path such that each The optical path difference between the optical paths of the branch beams includes: