A laser tunable device

Abstract

The present invention provides a laser tunable device, comprising: a light source module for emitting incident laser light; a cavity mode selector disposed on the optical path of the laser, including a frequency response of a mode selection pattern, capable of aligning the frequency in the cavity mode selector with one of a plurality of cavity modes, for exciting the laser light emitted preferentially by the marked selected cavity mode over other cavity modes and changing the optical path of the laser; a double-sided mirror disposed on the optical path of the laser, for reflecting the incident laser light when rotating to change the reflection angle of the laser, when the double-sided mirror rotates by an angle θ, the incident angle of the laser incident on the cavity film selector after being reflected by the double-sided mirror rotates by 2θ; a first lens group and a second lens group are respectively disposed on both sides of the double-sided mirror, for reflecting the laser light reflected by the double-sided mirror multiple times so that the output laser light is parallel to the incident laser light; an end mirror is disposed on the output path of the output laser light, for receiving and outputting the laser light. The present invention can achieve jump-free tuning.

Description

Technical Field

[0001] The present invention relates to a laser light source, and particularly to a laser tunable device. Background Art

[0002] Tunable external cavity lasers have been favored in many fields because of their narrow linewidth, high stability, continuous tuning without mode hopping and other characteristics. For example, metrology, spectroscopy, laser measurement, laser cooling, etc.

[0003] Currently, the tunable external cavity laser light sources on the market are all based on diffraction gratings to form tuning schemes (mainly evolved from the Littrow method and the Littman-Metcalf method). These tuning schemes rely on rotating the grating and simultaneously moving the spatial position of the grating to synchronize the change of the external cavity longitudinal mode wavelength / frequency with the grating diffracted light wavelength / frequency, so as to achieve continuous non-mode-hopping tuning of the laser. These lasers have made very remarkable developments in recent years, especially after the application of MEMS (Micro-Electro-Mechanical System) technology, achieving substantial progress in being smaller, faster, more precise, etc. However, such schemes also have unsolvable problems. For example, non-mode-hopping tuning can only be carried out within a certain range (λ / 4, where λ is the laser wavelength). Once beyond this range, the laser will mode-hop, that is, jump from one operating longitudinal mode to another adjacent longitudinal mode. During the mode-hopping process, the laser will be unstable for a period of time. The new laser mode needs a certain time to resonate again, and at the same time, the continuous wavelength / frequency change will also be broken. In mechanical design, since the angle and spatial position of the grating need to be changed simultaneously, these mechanical movements require a stable and strong fulcrum to support the movement of the grating or the mirror. For lasers that need to work quickly for a long time, this mechanical movement fulcrum is usually the first to be damaged, and its lifespan is extremely short compared with other devices or optical equipment. Often, the damage of the fulcrum means the scrapping of the entire laser because the cost and difficulty of repair and maintenance are quite high.

[0004] Some lasers with non-mechanical tuning modes avoid the above drawbacks. They use electro-optic crystals (KTN) or acousto-optic crystals (AOM) instead of mechanical devices, and use current or acoustic waves to change the angle of light in the crystal, thereby changing the position where the light hits the grating, and thus changing the wavelength / frequency. This tuning method has obvious advantages compared with mechanical tuning. It saves space and the tuning speed is not in the same order of magnitude at all (it can reach GHz while the rotation speed of a mechanical galvanometer can only reach kHz). This advantage makes such lasers particularly favored in the field of OCT (optical coherence tomography). However, this tuning method also has drawbacks. The change in the external cavity wavelength / frequency is not synchronized with the grating diffraction wavelength / frequency, resulting in frequent mode hopping of the intracavity laser. Moreover, the fixed positions of the grating and the crystal make it difficult for the laser to operate in a single mode.

[0005] There are also some non-external-cavity tunable lasers that also have their uses in some fields, such as vertical-cavity surface-emitting lasers (VCSELs). Such lasers can make the laser cavity very small, so that only one longitudinal mode operates in the entire laser cavity, thus eliminating mode interference or mode hopping. By changing the refractive index of the cavity or slightly changing the cavity length, the tuning of the laser wavelength / frequency can be achieved. Such lasers generally have a high cost, and at the same time, the defects in the coherence length corresponding to the short cavity also affect the application of such lasers. Summary of the Invention

[0006] In order to overcome the above technical defects, the present invention provides a laser tunable device that can achieve mode-hop-free tuning.

[0007] To solve the above problems, the present invention is implemented according to the following technical solutions:

[0008] A laser tunable device, comprising:

[0009] A light source module for emitting incident laser light;

[0010] A cavity mode selector disposed on the optical path of the laser. The cavity mode selector includes a frequency response of a mode selection mode. The mode selection mode can align the frequency in the cavity mode selector with one of a plurality of cavity modes, for exciting the laser marked as the selected cavity mode to emit laser light preferentially over other cavity modes and changing the optical path of the laser;

[0011] A double-sided mirror disposed on the optical path of the laser. The double-sided mirror is used for reflecting the incident laser light when rotating to change the reflection angle of the laser light. When the double-sided mirror rotates by an angle θ, the incident angle of the laser light incident on the cavity mode selector after being reflected by the double-sided mirror rotates by 2θ;

[0012] The first lens group and the second lens group are respectively arranged on both sides of the double-sided mirror, and are used for reflecting the laser reflected by the double-sided mirror multiple times so that the emitted laser is parallel to the incident laser;

[0013] The end mirror is arranged on the output path of the emitted laser and is used for receiving and outputting the laser.

[0014] Compared with the prior art, the laser tunable device of the present invention has the following beneficial effects: in the laser cavity formed among the light source module, the lens group, and the laser output element, when the double-sided mirror rotates by an angle θ, the optical path change of the laser in the laser cavity is an expression only related to cos 2θ. The incident angle of the laser incident on the cavity mode selector after being reflected by the double-sided mirror rotates by 2θ. That is to say, the optical path change has nothing to do with the placement positions of the light source module and the double-sided mirror, and even the rotation fulcrum of the double-sided mirror, which enables a large tolerance error in the installation of the light source module and the mirror, realizes the synchronous change of the cavity mode (double-sided mirror) and the mode selection mode (incidence on the cavity mode selector), and thus realizes perfect tuning.

[0015] As a further improvement of the present invention, the cavity mode selector includes: an etalon, which has opposite partially reflective surfaces defining a plurality of etalon modes and is used for changing the optical path of the laser.

[0016] As a further improvement of the present invention, the cavity mode selector further includes: a filter, the etalon is coated to form the filter, and the filter is used for frequency alignment with the mode selection mode selected by the cavity mode selector and aligned with the cavity mode. The aligned frequency response is combined with the frequency response of the cavity mode selector to generate a combined frequency response that excites the selected cavity mode to emit laser preferentially over other cavity modes.

[0017] As a further improvement of the present invention, the first lens group includes: a first mirror surface and a second mirror surface, and the second lens group includes: a third mirror surface and a fourth mirror surface. The first mirror surface and the third mirror surface are parallel, and the second mirror surface and the fourth mirror surface are parallel.

[0018] As a further improvement of the present invention, the cavity mode selector is arranged between the first lens group and the double-sided mirror, or the cavity mode selector is arranged between the second lens group and the double-sided mirror.

[0019] As a further improvement of the present invention, the present invention further includes a first driving and rotating component for driving the double-sided mirror to rotate relative to the first lens group, the second lens group, the cavity mode selector, and the light source module.

[0020] As a further improvement of the present invention, the present invention further includes a second driving and rotating member for driving the first mirror group, the second mirror group, the cavity mode selector, and the light source module to rotate relative to the double-sided mirror.

[0021] As a further improvement of the present invention, the cavity mode selector is disposed between the light source module and the double-sided mirror. When the double-sided mirror rotates by an angle θ, the cavity mode selector rotates by an angle 2θ.

[0022] As a further improvement of the present invention, both the first mirror group and the second mirror group are right-angled plane mirrors or right-angled triangular prisms.

[0023] As a further improvement of the present invention, the end mirror is a total reflection mirror, so that the output laser returns to the light source module along the original optical path, passes through the lens and the laser in the light source module in sequence, and is output on the side of the laser without an anti-reflection coating.

[0024] As a further improvement of the present invention, a micro-spherical array mirror is disposed on the surface of the total reflection mirror close to the double-sided mirror.

[0025] As a further improvement of the present invention, the total reflection mirror is a curved mirror.

[0026] As a further improvement of the present invention, a cylindrical mirror is disposed on the surface of the total reflection mirror close to the double-sided mirror.

[0027] As a further improvement of the present invention, the total reflection mirror is a triangular prism.

[0028] As a further improvement of the present invention, a grating mirror is disposed on the surface of the total reflection mirror close to the double-sided mirror.

[0029] As a further improvement of the present invention, a reflection grating is disposed on the surface of the total reflection mirror away from the double-sided mirror.

[0030] As a further improvement of the present invention, the double-sided mirror is a planar double-sided mirror, and the planar double-sided mirror is a galvanometer or a micro electro-controlled silicon glass. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the overall laser tunable device described in the first embodiment;

[0032] Figure 2 It is a schematic diagram of the etalon and the filter described in the first embodiment;

[0033] Figure 3 It is a schematic diagram of the overall laser tunable device described in the first embodiment;

[0034] Figure 4 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0035] Figure 5 Schematic diagram for calculating the optical path of the laser tunable device described in Embodiment 1;

[0036] Figure 6 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0037] Figure 7 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0038] Figure 8 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0039] Figure 9 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0040] Figure 10 Overall schematic diagram of the laser tunable device described in Embodiment 1;

[0041] Figure 11 Relationship diagram between the wavelength tunable range and the initial etalon angle when the laser (1550 nm) is restricted by the etalon cavity within the range of ±3°;

[0042] Figure 12 Analysis diagram of the tuning and mode hopping of the cavity mode and the cavity mode selector mode of the laser tunable device described in Embodiment 1;

[0043] Figure 13 Overall schematic diagram of the laser tunable device described in Embodiment 2;

[0044] Figure 14 Overall schematic diagram of the laser tunable device described in Embodiment 3;

[0045] Figure 15 Schematic diagram of the end mirror design described in Embodiment 4;

[0046] Figure 16 Schematic diagram of the end mirror design described in Embodiment 4;

[0047] Figure 17 Schematic diagram of the end mirror design described in Embodiment 4;

[0048] Figure 18 Schematic diagram of the end mirror design described in Embodiment 4;

[0049] Figure 19 Schematic diagram of the end mirror design described in Embodiment 4;

[0050] Figure 20 Schematic diagram of the end mirror design described in Embodiment 4;

[0051] Figure 21 Schematic diagram of the end mirror design described in Example 4;

[0052] Marking description: 1 - Light source module; 11 - Lens; 12 - Laser; 121 - Side of the laser without an anti-reflection coating; 122 - Side of the laser with an anti-reflection coating; 2 - Cavity mode selector; 21 - Etalon; 22 - Filter; 3 - Double-sided mirror; 41 - First mirror group; 411 - First mirror surface; 412 - Second mirror surface; 42 - Second mirror group; 421 - Third mirror surface; 422 - Fourth mirror surface; 5 - Laser output element; 51 - End mirror; 52 - Micro-spherical array mirror; 53 - Cylindrical mirror; 54 - Triangular prism; 55 - Grating mirror; 56 - Reflection grating; 6 - First driving and rotating component; 7 - Second driving and rotating component. Detailed implementation manners

[0053] The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the invention and are not used to limit the invention.

[0054] Example 1

[0055] This example discloses a laser tunable device, as Figure 1 shown, including: a light source module 1, a cavity mode selector 2, a double-sided mirror 3, a first mirror group 41, a second mirror group 42, and an end mirror 5. Among them, the light source module 1 is used to emit incident laser; the cavity mode selector 2 is arranged on the optical path of the laser. The cavity mode selector 2 has a frequency response of the mode selection mode, and the mode selection mode can make the frequency in the cavity mode selector align with one of the multiple cavity modes, so as to excite the laser marked as the selected cavity mode to emit laser preferentially over other cavity modes and change the optical path of the laser; the double-sided mirror 3 is arranged on the optical path of the laser. The double-sided mirror 3 is used to reflect the incident laser when rotating to change the reflection angle of the laser. When the double-sided mirror 3 rotates by an angle θ, the incident angle of the laser incident on the cavity film selector 2 after being reflected by the double-sided mirror 3 rotates by 2θ; the first mirror group 41 and the second mirror group 42 are respectively arranged on both sides of the double-sided mirror 3, and are used to reflect the laser reflected by the double-sided mirror 3 multiple times so that the emitted laser is parallel to the incident laser; the end mirror 5 is arranged on the output path of the emitted laser and is used to receive and output the laser.

[0056] In the above embodiment, as Figure 2 shown, the cavity mode selector 2 includes: an etalon 21, which has opposite partially reflecting surfaces defining multiple etalon modes and is used to change the optical path of the laser.

[0057] In the above embodiment, the cavity mode selector further includes: a filter 22, which is coated with a Fabry-Perot coating to form a filter. The filter is used to frequency-align with the mode selection mode selected by the cavity mode selector 2 and aligned with the cavity mode. The aligned frequency response is combined with the frequency response of the cavity mode selector to generate a combined frequency response that excites the selected cavity mode to emit laser preferentially over other cavity modes.

[0058] In the above embodiment, as Figure 1 shown, the first mirror group 41 includes: a first mirror surface 411 and a second mirror surface 412. The second mirror group 42 includes: a third mirror surface 421 and a fourth mirror surface 422. The first mirror surface 411 and the third mirror surface 421 are parallel, and the second mirror surface 412 and the fourth mirror surface 422 are parallel.

[0059] In the above embodiment, the cavity mode selector 2 is disposed between the first mirror group 41 and the double-sided mirror 3, or the cavity mode selector 2 is disposed between the second mirror group 42 and the double-sided mirror 3. Please refer to Figure 1 that is, the cavity mode selector 2 can be disposed at any position shown in 109, 117, 118, 120, 121.

[0060] In the above embodiment, as Figure 3 shown, the double-sided mirror 3 is fixed on the first driving rotating member 6. The first driving rotating member 6 is used to drive the double-sided mirror 4 to rotate relative to the first mirror group 41, the second mirror group 42, and the cavity mode selector 2. That is to say, the first mirror group 41, the second mirror group 42, the cavity mode selector 2, and the light source module 1 are all fixed.

[0061] In the above embodiment, both the first mirror group 41 and the second mirror group 42 are right-angled plane mirrors or right-angled triangular prisms. That is to say, the first mirror surface 411 and the second mirror surface 412 are perpendicular to each other, and the third mirror surface 421 and the fourth mirror surface 422 are perpendicular to each other.

[0062] In the above embodiment, the double-sided mirror 3 is a galvanometer mirror or a micro electro-controlled silicon glass.

[0063] Next, the present embodiment will be further explained in combination with the specific implementation process as follows:

[0064] Laser light is emitted from the light source module 1, reflected by the double-sided mirror 3, and then incident on the cavity mode selector 2. After the optical path in the cavity mode selector 2 is changed, the laser light is incident on the first mirror surface 411 and the second mirror surface 412 in sequence. At this time, when the double-sided mirror 3 rotates by an angle θ, the exit angle of the laser light after passing through the cavity mode selector 2 rotates by 2θ. Then, after the laser light is reflected on the second mirror surface 412, it is incident on the third mirror surface 421, the fourth mirror surface 422, and the double-sided mirror 3 in sequence, and finally is incident on the end mirror 5 for output.

[0065] As Figure 2As shown, the optical path difference of light passing through the etalon 21 can be written as:

[0066] Δ = n(CD + DE + EF) - (nCD + n′DJ) = n(DE + EF) - n′DJ (1)

[0067] Where n is the refractive index of the medium inside the etalon 212, n′ is the refractive index of the medium outside the etalon 21, and the refractive index in air is 1.

[0068] DE = EF = t / cosα (2)

[0069] Where α is the incident angle of the light on the etalon, and t is the thickness of the etalon.

[0070] DJ = DF sinγ = 2t·tanα·sinγ (3)

[0071] Where γ is the incident angle of the light outside the etalon 21.

[0072] Δ = 2nt / cosα - 2n′t·tanα·sinγ (4)

[0073] By Snell's law:

[0074] n′sinγ = nsinα (5)

[0075] Substituting formula (5) into formula (4), we get:

[0076] Δ = 2nt cosα = mλ = 2L e (6)

[0077] Where m is an integer, λ is the wavelength in vacuum, and we call L e the cavity length of the etalon, and the formula is:

[0078] L e = nt cosα (7)

[0079] In Figure 4 we find that when the two-sided mirror 3 rotates by an angle θ, the angle change of the laser incident on the etalon 21 is 2θ. Establish a coordinate system, as Figure 5 shown. Let the rotation fulcrum of the two-sided mirror 3 be the coordinate origin, and we get:

[0080] ab = H1 (8)

[0081] Where H1 is the z - coordinate distance of the light source.

[0082] bc = (-A + B1)sec2β (9)

[0083] Where A and B1 are the x and y coordinate distances of an edge of one of the mirror groups 4, and β is the initial angle of the double-sided mirror 3 (the initial angle is 45°, and the specific installation angle depends on the product design and installation conditions).

[0084] cd = 2Asec2β (10)

[0085] de = (-2A + B1 + B2)sec 2β (11)

[0086] Where B2 is the y coordinate distance of the other mirror group 4.

[0087] ef = 2Asec2β (12)

[0088] fg = [-A + B2 + (B1 + B2)sin 2β]sec 2β (13)

[0089] gP = H2 - 2(B1 + B2)(cosβ + sinβ)sin2β(cosβ - sinβ) (14)

[0090] Where H2 is the z coordinate distance of the end mirror 5.

[0091] As Figure 4 shown, H = H1 + H2, B = B1 + B2. Substituting formula (8) into (14) and adding them together, we obtain the laser cavity length formula as follows:

[0092] L = ab + bc + cd + de + ef + fg + gp = H + 2B cos 2β (15)

[0093] Taking the derivative of (15) can obtain the change in the optical path of the laser cavity, which is also an expression only related to cos 2θ, consistent with the change in the optical path of the etalon 21. At the same time, it can be found that the optical path in formula (15) is only related to the relative position of the mirror group 4 and the distance from the light source module 1 to the end mirror 51, and has nothing to do with the placement position of the light source module 1 or the double-sided mirror 3, or even the rotation fulcrum of the double-sided mirror 3. That is, there is a very large allowable error in the installation of the light source module 1 and the double-sided mirror 3.

[0094] As Figure 6 shown, it is a schematic diagram of another rotation direction of the double-sided mirror 3, and its principle is Figure 4 the same as that, and will not be elaborated here one by one.

[0095] Furthermore, in this embodiment, the position of the light source module 1 in the coordinate system is changed and recalculated. Although the optical path of each single optical path is different, the final added result remains unchanged. As Figures 7 - 10 shown, changing the rotation fulcrum of the double-sided mirror 3 will also have no effect on the optical path of the system.

[0096] Figure 7 and Figure 8 Describes the working optical path of the positive - angle rotation tuning after the rotation fulcrum of this embodiment changes from point O to point G. The laser is emitted from the laser 12, penetrates through the antireflection - coated side 122 of the laser, is collimated by the lens 11 and hits point P on the double - sided mirror 3. The double - sided mirror 3 rotates around point G to a new position forming an angle θ with the initial position (dotted line). The incident light 106 is reflected and passes through the cavity mode selector 2 and enters the first lens group 41. After being reflected by the first mirror surface 411 and the second mirror surface 412, it enters the second lens group 42. Similarly, after being reflected again by the third mirror surface 421 and the fourth mirror surface 422, it reaches point Q on the other reflecting surface of the double - sided mirror 3, is reflected again, and the outgoing light 113 hits the end mirror 5 and then returns to the light source module 100 along the original path to form a laser. If the end mirror is replaced with a total - reflection mirror, the output light is output from the other side 121 of the laser as 105.

[0097] Figure 9 and Figure 10 Describes the working optical path of the negative - angle rotation tuning after the rotation fulcrum of this embodiment changes from point O to point G. The laser is emitted from the bulk laser 12, penetrates through the antireflection - coated side 122 of the laser, is collimated by the lens 11 and hits point P on the double - sided mirror 3. The double - sided mirror 3 rotates around point G to a new position forming an angle θ with the initial position (dotted line). The incident light 106 is reflected and passes through the cavity mode selector 2 and enters the first group 41. After being reflected by the first mirror surface 411 and the second mirror surface 412, it enters the second lens group 42. Similarly, after being reflected again by the third mirror surface 421 and the fourth mirror surface 422, it reaches point Q on the other reflecting surface of the double - sided mirror 3, is reflected again, and the outgoing light 113 hits the end mirror 5 and then returns to the light source module 100 along the original path to form a laser. If the end mirror is replaced with a total - reflection mirror, the output light is output from the other side 121 of the laser as 105.

[0098] When using an air - cavity etalon, high - precision tuning can be achieved, but the cost is too high. When we use glass to make the etalon, the optical path difference of the etalon becomes:

[0099]

[0100] This then destroys the high - precision tuning. Although the difference in the incident angles between the outside and the inside of the etalon is very small, it still affects the synchronization between the cavity mode and the etalon mode.

[0101] The laser, in the form of wavelength and light intensity, is represented as an envelope of a series of continuous wavelengths on a coordinate graph. Usually, the central wavelength of the envelope is taken as the wavelength of the laser. In a laser device, there are usually multiple lasers with different wavelengths / frequencies, and we call these lasers with different wavelengths / frequencies cavity mode patterns. The cavity mode is defined by twice the cavity length, that is, the optical path length of a complete round trip in the cavity, which is equal to an integer multiple of the vacuum wavelength,

[0102] 2n0L=mλ (17)

[0103] where n0 is the refractive index in the cavity, m is an integer, and λ is the wavelength in vacuum.

[0104] According to the mathematical relationship between wavelength and frequency, we can obtain the frequency interval between adjacent cavity modes as:

[0105] Δv=c / 2n0L (18)

[0106] where c is the speed of light propagation in vacuum.

[0107] The cavity mode selector 2, that is, the etalon, also has the same relationship. Obviously, since the inner cavity length of the etalon 21 is much smaller than the cavity length of the entire laser tunable device, the mode spacing in the etalon 21 will be much larger than the cavity mode spacing. And there will be several cavity modes competing with each other in the envelope of an etalon mode. Then the cavity mode closest to the center frequency of the etalon mode will have an absolute advantage. Therefore, the frequency of the emitted laser is the frequency of the most advantageous cavity mode mentioned above. The filter 22 can ensure that only one etalon mode is excited at the same time. Then at this time, only one cavity mode will emit laser, that is, single longitudinal mode.

[0108] When the laser tunable device changes the cavity length, the frequency of each cavity mode will change. Similarly, changing the cavity length of the etalon 21 will also change the frequency of the etalon 21 mode. In the coordinate graph, it can be shown as the mode envelope or frequency moving left and right on the horizontal axis. As Figure 12 shown, we assume a cavity mode v q coincides with the etalon mode v f at the start of the laser operation. Then when the laser 12 is operating, both modes will move in the same direction, and at the same time, other cavity modes will also move together. When the change of the cavity mode is not synchronized with the change of the etalon 21 mode, it will be shown that one moves faster and the other moves slower, and all cavity modes will move at the same speed. After a period of time, when the difference between the cavity mode and the etalon 21 mode is at 1 / 2 of the longitudinal mode spacing Δv, other adjacent cavity modes (v q-1 or v q+1 ) will compete with the current emitting cavity mode, thus overwhelming the existing cavity mode and emitting laser of its own frequency, which is called mode hopping. Therefore, the tuning without mode hopping needs to satisfy:

[0109] |v′ q -v′ f |<Δv / 2 (19)

[0110] where v q ′ and v f ′ are the frequencies of the cavity mode and the etalon mode that were originally coincident after tuning, respectively.

[0111] Substitute the relationships between the two frequencies and the wavelengths into the above formula, and the following formula can be obtained through calculation:

[0112]

[0113] That is, mode hopping occurs when the difference between the cavity length change rate and the etalon change rate is less than the ratio of the wavelength to four times the cavity length. The tuning range can be calculated in the specific design according to this formula.

[0114] In addition to being affected as described above, the tuning range of the etalon itself is also affected by cosα. Because the cosine function itself has a range in mathematics, it is found through calculation that the influence of the etalon 21 on the tuning range is related to the initial angle of the etalon placement. There is the following relationship between the wavelength change and the etalon cavity length change when the etalon 21 is tuned,

[0115]

[0116] where Δλ is the wavelength tunable range and dα is the range of rotation of the internal angle of the etalon.

[0117] Taking the derivative of L e gives:

[0118] Δλ = -λtanα·dα (22)

[0119] Taking the derivative of formula (5) gives:

[0120]

[0121] Substituting equations (23) and (5) into equation (22) can solve for the variation of the tunable range at a specific wavelength within the angular tuning range of a specific dγ with respect to the initial angle γ of the etalon.

[0122] Figure 11 The figure shows the relationship between the limited tuning range of the 1550 nm laser and the initial angle of the etalon within the range of ±3° rotation of the double-sided mirror 3. It can be seen from the figure that the larger the initial angle, the larger the tuning range. However, in practical applications, the initial angle of the etalon should not be too large because it will affect the round-trip length of the complete light spot in the etalon. Therefore, the specific initial angle should seek a balance according to the specific design.

[0123] Embodiment 2

[0124] This embodiment discloses another laser tunable device. As Figure 13 shown, the difference from Embodiment 1 is that the first mirror group 41, the second mirror group 42, and the cavity mode selector 2 are fixed on the second driving rotating member 7, and the second driving rotating member 7 is used to drive the first mirror group 41, the second mirror group 42, the cavity mode selector 2, and the light source module 1 to rotate relative to the double-sided mirror 3.

[0125] The laser is emitted from the light source module 1, and after being reflected by the double-sided mirror 3, it is incident on the first mirror surface 311 and the second mirror surface 412 in sequence. At this time, the double-sided mirror 3 rotates by an angle θ, and the cavity mode selector 2 rotates by an angle 2θ. Then, after the laser is incident on the cavity mode selector 2, it is incident on the third mirror surface 421, the fourth mirror surface 422, and the double-sided mirror 3 in sequence, and finally is incident on the laser output element 5 for output.

[0126] Embodiment 3

[0127] This embodiment discloses another laser tunable device. As Figure 14 shown, the difference from Embodiment 1 is that the cavity mode selector 2 is arranged between the light source module 1 and the double-sided mirror 3. When the double-sided mirror 3 rotates by an angle θ, the cavity mode selector 3 rotates by an angle 2θ. Similarly, a driving rotating member can also be used to rotate and control the double-sided mirror 3 and the cavity mode selector 2, that is, the light source module 1, the first mirror group 41, the second mirror group 42, and the end mirror 5 all remain stationary.

[0128] The laser is emitted from the light source module 1, and after being incident on the cavity mode selector 2, it is incident on the double-sided mirror 3, the first mirror surface 411, the second mirror surface 412, the third mirror surface 421, the fourth mirror surface 422, and the double-sided mirror 4 in sequence, and finally is incident on the laser output element 5 for output.

[0129] Embodiment 4

[0130] This embodiment discloses another laser tunable device. As Figure 15 shown, the difference from Embodiment 1 is that the end mirror 5 is a total reflection mirror, so that the output laser returns to the light source module 1 along the original optical path and is output on the side 121 where the laser has no antireflection coating. Using a total reflection mirror is economical and practical.

[0131] For a Gaussian beam with a certain divergence angle of the reflected light, as Figure 16 shown, the total reflection mirror is a plane total reflection mirror, and a micro-spherical array mirror 52 is arranged on the surface of the total reflection mirror close to the double-sided mirror, which can compress the divergence of the Gaussian beam 204 in all directions to the maximum extent and return the beam along the original path 203.

[0132] AsFigure 17 As shown, the total reflection mirror is a curved surface reflection mirror, and its reflection surface has a certain curvature, which can compress the divergence of the Gaussian beam in one axial direction by 204.

[0133] As Figure 18 shown, the total reflection mirror is a plane total reflection mirror. A cylindrical lens 53 is provided on the side of the total reflection mirror close to the double-sided reflection mirror. The combination of the two makes the light beam pass through the cylindrical lens 53 to focus the light beam longitudinally, and then the total reflection mirror 51 placed at its focus passes back through the cylindrical lens 53 along the original path and becomes a parallel light beam 206 and returns.

[0134] As Figure 19 shown, the total reflection mirror is a plane total reflection mirror. The total reflection mirror is a triangular prism 54. An antireflection film is coated on the light-facing surface so that light can pass through the inside of the prism, and total reflection films are coated on the other two surfaces so that the incident light beam 208 is reflected multiple times inside the prism to concentrate the diverging light rays 207.

[0135] As Figure 20 shown, the total reflection mirror is a plane total reflection mirror. A grating reflection mirror 55 is provided on the side of the total reflection mirror close to the double-sided reflection mirror. The sawteeth thereon are used for multiple reflections of 209 to achieve the purpose of concentrating the diverging light beam 210.

[0136] As Figure 21 shown, the total reflection mirror is a plane total reflection mirror. A reflection grating 55 is provided on the side of the total reflection mirror far from the double-sided reflection mirror. The sawteeth on the grating 55 are used for multiple reflections of 211 to achieve the purpose of concentrating the diverging light beam 212.

[0137] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Therefore, any modifications, equivalent changes and decorations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A laser tunable device, characterized in that, Comprising: A light source module for emitting incident laser light; A cavity mode selector disposed on the optical path of the laser. The cavity mode selector includes a frequency response of a mode selection pattern, and the mode selection pattern can align the frequency in the cavity mode selector with one of a plurality of cavity modes, for exciting the cavity mode marked as the selected cavity mode to emit laser light preferentially over other cavity modes and changing the optical path of the laser; A two-sided mirror disposed on the optical path of the laser. The two-sided mirror is used to reflect the incident laser light when rotating to change the reflection angle of the laser. When the two-sided mirror rotates by an angle θ, the incident angle of the laser light incident on the cavity mode selector after being reflected by the two-sided mirror rotates by 2θ; A first mirror group and a second mirror group, respectively disposed on both sides of the two-sided mirror, for reflecting the laser light reflected by the two-sided mirror multiple times to make the output laser light parallel to the incident laser light; An end mirror disposed on the output path of the output laser light for receiving and outputting the laser light; The first mirror group includes: a first mirror surface, a second mirror surface, the second mirror group includes: a third mirror surface, a fourth mirror surface, the first mirror surface and the third mirror surface are parallel, and the second mirror surface and the fourth mirror surface are parallel; The cavity mode selector is disposed between the first mirror group and the two-sided mirror, or the cavity mode selector is disposed between the second mirror group and the two-sided mirror; The end mirror is a total reflection mirror, so that the output laser light returns to the light source module along the original optical path, passes through the lens and the laser in the light source module in sequence, and is output on the side of the laser where the anti-reflection coating is not applied; 2. The laser tunable device according to claim 1, characterized in that, The cavity mode selector includes: a Fabry-Perot etalon having relatively partial reflection surfaces defining a plurality of Fabry-Perot etalon modes, for changing the optical path of the laser; 3. The laser tunable device according to claim 2, characterized in that The cavity mode selector further includes: a filter. The Fabry-Perot etalon is coated to form the filter. The filter is used to align the frequency with the mode selection pattern selected by the cavity mode selector and aligned with the cavity mode. The aligned frequency response is combined with the frequency response of the cavity mode selector to generate a combined frequency response that excites the selected cavity mode to emit laser light preferentially over other cavity modes; 4. The laser tunable device according to claim 1, wherein Further includes a first driving and rotating component for driving the two-sided mirror to rotate relative to the first mirror group, the second mirror group, the cavity mode selector, and the light source module; 5. The laser tunable device according to claim 1, wherein Further includes a second driving and rotating component for driving the first mirror group, the second mirror group, the cavity mode selector, and the light source module to rotate relative to the two-sided mirror; 6. The laser tunable device according to claim 1, characterized in that, The cavity mode selector is disposed between the light source module and the two-sided mirror. When the two-sided mirror rotates by an angle θ, the cavity mode selector rotates by 2θ; 7. The laser tunable device according to any one of claims 4-6, characterized in that The first mirror group and the second mirror group are both right-angle plane mirrors or right-angle triangular prisms; 8. The laser tunable device according to claim 1, characterized in that A micro-spherical array mirror is disposed on the surface of the total reflection mirror close to the two-sided mirror; 9. The laser tunable device according to claim 1, characterized in that The total reflection mirror is a curved mirror; 10. The laser tunable device according to claim 1, wherein, A cylindrical mirror is disposed on the surface of the total reflection mirror close to the two-sided mirror; 11. The laser tunable device according to claim 1, wherein, The total reflection mirror is a triangular prism; 12. The laser tunable device according to claim 1, wherein, A grating mirror is disposed on the surface of the total reflection mirror close to the two-sided mirror; 13. The laser tunable device according to claim 1, characterized in that, A reflection grating is provided on a surface of the total reflection mirror that is away from the double-sided reflection mirror.

14. The laser tunable device according to claim 1, wherein, The double-sided reflection mirror is a planar double-sided reflection mirror, and the planar double-sided reflection mirror is a galvanometer or a micro electro-controlled silicon glass.

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