Large-range continuously tunable external cavity semiconductor laser without mode hopping

Abstract

The application provides a large-range continuously tunable external cavity semiconductor laser without mode hopping, which comprises a laser diode (1), a collimating lens (2), a polarization beam splitter (3), a narrow-band interference plate (4), a prism super high reflectivity film (5) and a piezoelectric module (6) arranged in sequence in an optical path, and the rotating axis of the prism super high reflectivity film (5) is located in the optical path of the laser and coincides with the rear surface of the piezoelectric module (6). The large-range continuously tunable external cavity semiconductor laser without mode hopping of the application utilizes the sensitivity of laser frequency to the rotation angle of the narrow-band interference plate, changes the interference plate angle and the cavity length at the same time, thereby realizing the high synchronization of the change of the interference plate transmission peak center frequency and the specific cavity mode frequency with the angle, realizing the laser with the laser output frequency without mode hopping and the continuous tunable output frequency with the rotation angle of the cavity mirror.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, specifically relating to a mode-skipping, wide-range, continuously tunable external cavity semiconductor laser. Background Technology

[0002] A semiconductor laser is a device that injects current into a semiconductor PN junction, generating stimulated emission through population inversion. Combined with an optical feedback structure, light is generated and amplified within the PN junction, ultimately producing a laser output. However, semiconductor lasers generally suffer from drawbacks such as unstable output laser light, large divergence angle, and large spectral linewidth. To optimize the performance of semiconductor lasers, external cavity semiconductor lasers extend the resonant cavity outside the laser, effectively reducing the spectral linewidth, improving beam quality, and decreasing the divergence angle. This results in a more stable and controllable output beam, meeting the needs of applications such as optical communication, lidar, and spectral analysis.

[0003] Existing interferometer external cavity semiconductor lasers, such as the one proposed in Chinese invention patent application CN 114899704 A, which is based on a pyramidal array external cavity mirror, involve outputting laser light from a semiconductor laser, collimating it with a collimating lens, and then projecting it onto the pyramidal array external cavity mirror to form a feedback laser. A resonant cavity is formed between the semiconductor laser tube and the external cavity mirror. An interferometer is placed between the collimating lens and the external cavity mirror, and the target wavelength is obtained by rotating its angle. Piezoelectric ceramics are bonded to the external cavity mirror, and the cavity length of the laser resonant cavity is changed by adjusting the voltage to fine-tune the laser. However, the center frequency of the transmission peak of the interferometer does not change simultaneously with the cavity mode frequency, which causes mode hopping and limits the continuously tunable frequency range.

[0004] Therefore, it is necessary to address the limitation that external cavity semiconductor lasers cannot be continuously tunable over a wide frequency range, promote the application and development of laser technology in various fields, improve the performance of related technologies, and facilitate progress in scientific research, industrial production, and other fields. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a mode-skipping, wide-range, continuously tunable external cavity semiconductor laser.

[0006] The idea behind this invention is to utilize the extremely high sensitivity of laser frequency to cavity length in an external cavity semiconductor laser. A device capable of changing the cavity length is set up, with the rotation axis positioned on the rear surface of a thick cavity mirror. By rotating the thick cavity mirror, the cavity length is changed, thereby altering the fixed cavity mode frequency. Simultaneously, a narrowband interferometer is used to assist in mode selection, causing the center position of the interferometer's transmission peak to move with the angle, highly synchronized with the change in the specific cavity mode frequency with the angle. This achieves a laser with non-mode-hopping output frequency and ensures continuous tunability of the output frequency with the rotation angle of the cavity mirror, solving the problem of continuous frequency tuning and ultimately realizing a laser with a wide range of continuously tunable frequencies.

[0007] Based on the above ideas, this invention provides a mode-skipping, wide-range, continuously tunable external cavity semiconductor laser. The laser includes a laser diode 1, a collimating lens 2, a polarizing beam splitter 3, a narrowband interferometer 4, and a prism-type high-intensity reflective film 5, which are sequentially arranged in the optical path. The laser is characterized by further including a piezoelectric module 6. The narrowband interferometer 4 is bonded to the front surface of the prism-type high-intensity reflective film 5, and the piezoelectric module 6 is bonded to the rear surface of the prism-type high-intensity reflective film 5. The piezoelectric module 6 has a thickness D. When the prism-type high-intensity reflective film 5 rotates, the rotation axis is located in the optical path of the laser and coincides with the rear surface of the piezoelectric module 6.

[0008] The coherent beam emitted by laser diode 1 is collimated into parallel light by collimating lens 2. The parallel light is then passed through polarizing beam splitter 3 to obtain horizontally polarized light or vertically polarized light with the same emission direction as laser diode 1. The horizontally polarized light or vertically polarized light is incident on narrowband interferometer 4 to obtain narrowband light. The narrowband light reaches the front surface of prism-type high-intensity reflective film 5 and is reflected back to laser diode 1. When the intracavity oscillation reaches the threshold, laser light is output through polarizing beam splitter 3.

[0009] In this invention, the thickness D of the piezoelectric module 6 satisfies the following relationship:

[0010]

[0011] Δλ=Δλ IF =λ0-λ'(ϕ)

[0012]

[0013] in, 5-rotation prism-type super reflective film The change in the wavelength of the cavity mode. Rotate the narrowband interferometer 4 The change in wavelength at the center position of the transmission peak of the interferometer. Rotate the narrowband interferometer 4 The wavelength at the center of the transmission peak of the interferometer. The transmission wavelength is when the narrowband interferometer 4 is perpendicular to the beam. L1 is the initial output wavelength of laser diode 1, L1 is the distance from the output light end face of laser diode 1 to the front surface of prism-type high-intensity reflective film 5 when the incident angle of the output light of laser diode 1 to prism-type high-intensity reflective film 5 is 0°, and D is the thickness of piezoelectric module 6. It is the incident angle of the prism-type super reflective film 5. It is the incident angle of narrowband interferometer 4. is the refractive index of narrowband interferometer 4.

[0014] In this invention, the initial wavelength of the laser diode 1 is matched with the center wavelength of the transmission peak of the narrowband interferometer 4.

[0015] The principle of the laser of this invention is to synchronously rotate the narrowband interferometer 4 and the prism-type high-intensity reflective film 5 to tune the center frequency of the transmission peak of the interferometer and the cavity mode frequency, thereby achieving wide-range continuous tunability. The specific implementation principle is as follows:

[0016] When the laser is incident perpendicularly on the front surface of the prism-type high-intensity reflective film 5, i.e., the incident angle is 0° (also referred to as the initial angle being 0° in this invention), let the thickness of the piezoelectric module 6 be... At this point, the cavity length is L1 (i.e., the distance from the output light end face of the laser diode to the front surface of the prism-type ultra-high intensity reflective film 5).

[0017] (1) Given the initial cavity length When the narrowband interference plate 4, the prism-type ultra-high intensity reflective film 5, and the piezoelectric module 6 rotate together at an angle of _____ At that time, the length of the cavity The resulting change in cavity length is .

[0018] (2) According to the fact that the frequency changes by c / 2L when the cavity length changes by half the wavelength, the resonant cavity jitter ΔL is related to the cavity mode frequency change. The relationship is: Thus, the cavity mode frequency change can be obtained. The relationship with the rotation angle θ is as follows: ,in It's frequency. It's the speed of light. It is the initial wavelength output by laser diode 1.

[0019] (3) Given The relationship between the change in cavity mode wavelength and the thickness of piezoelectric module 6 and its rotation angle θ can be obtained as follows: .

[0020] On the other hand, the rotation angle of the narrowband interferometer 4 (i.e., the incident angle of the narrowband interferometer). The standard formula for the relationship between wavelength variation and wavelength variation is: ,in The transmission wavelength is given by narrowband interferometer 4 when it is perpendicular to the beam, and the refractive index of narrowband interferometer 4 is given by [value missing]. The value is 2.

[0021] Therefore, in this invention, by selecting a piezoelectric module 6 with an appropriate thickness D, the change in transmission wavelength caused by the rotation angle of the interferometer is minimized when the interferometer and the rotating prism-type ultra-high intensity reflective film rotate synchronously. (Δλ) IF =λ0-λ'(ϕ))and the change in cavity mode wavelength caused by the rotation of the prism-type super-intensity reflective film 5 Equal or approximately the same (in this invention, "approximately the same" is understood as having an extremely small error and can be regarded as equal), thereby obtaining the effect of synchronous change of the center frequency of the transmission peak of the interferometer and the cavity mode frequency, solving the problems of small adjustable laser frequency range and discontinuous tunability caused by only changing the cavity length, and obtaining a laser with a large range of continuous tunability.

[0022] In another embodiment of the present invention, the thickness D satisfies the following relationship:

[0023] and ,in,

[0024]

[0025]

[0026] For prism-type super reflective film (5) rotation Time-cavity mode wavelength, Rotation of narrowband interferometer The wavelength at the center of the transmission peak of the interferometer. It is the incident angle of the prism-type super-strong reflective film (5). L1 is the incident angle of the narrowband interferometer (4), L1 is the distance from the output light end face of the laser diode (1) to the front surface of the prism-type high-intensity reflective film (5) when the incident angle of the prism-type high-intensity reflective film (5) is 0°, and D is the thickness of the piezoelectric module (6). The transmission wavelength when the narrowband interferometer (4) is perpendicular to the beam. is the refractive index of the narrowband interference sheet (4), and n is a natural number.

[0027] That is, by using the relationship between the rotation angle of the prism-type super-intensity reflective film and the corresponding cavity mode wavelength, a prism-type super-intensity reflective film of appropriate thickness is selected, so that the change in cavity mode wavelength caused by rotating the prism-type super-intensity reflective film is approximately the same as the change in transmission wavelength caused by rotating the interferometer.

[0028] The specific implementation principle is as follows:

[0029] Assuming that light is incident perpendicularly on the front surface of the prism-type ultra-high intensity reflective film 5, i.e., the initial angle is 0°, the thickness of the piezoelectric module is D, and the cavity length is L1.

[0030] (1) Initial cavity length , can be obtained

[0031] (2) When the prism-type super reflective film 5 rotates At that time, the length of the cavity Combining (1), the relationship between the rotation angle of the prism-type super-intensity reflective film 5 and the corresponding cavity mode wavelength can be obtained as follows:

[0032] In this invention, the operating wavelength of the laser diode 1 can be any wavelength. Preferably, from the perspective of ease of acquisition or economic saving, a 780 nm wavelength laser diode can be used. Those skilled in the art can also choose laser diodes with other operating wavelengths, such as 420 nm, 850 nm, and 1550 nm laser diodes.

[0033] In this invention, in order to achieve synchronous rotation of the narrow-band interference plate 4 and the prism-type high-intensity reflective film 5 bonded together, it can be accomplished by setting a piezoelectric ceramic 7, or by mounting the narrow-band interference plate 4 and the prism-type high-intensity reflective film 5 together on a high-precision rotating stage 8.

[0034] In a preferred embodiment of the present invention, a piezoelectric ceramic 7 is disposed on the rear surface of the piezoelectric module 6, and the rotation angle of the narrow-band interference plate 4 and the prism-type ultra-high intensity reflective film 5 is changed by the piezoelectric ceramic 7 and the piezoelectric module 6 together.

[0035] As an alternative implementation, a high-precision rotary stage 8 is used instead of the piezoelectric ceramic 7. The narrow-band interference plate 4, the prism-type high-intensity reflective film 5 and the piezoelectric module 6 are placed on the high-precision rotary stage 8. When the prism-type high-intensity reflective film 5 rotates, the rotation axis is located on the rear surface of the piezoelectric module 6 and is in the optical path.

[0036] This invention uses a rotating prism-type high-intensity reflective film 5 to change the cavity length, thereby changing the specific cavity mode frequency of the laser. At the same time, it uses a narrow-band interferometer to assist in mode selection, so that the center position of the transmission peak of the interferometer moves with the angle, which is highly synchronized with the change of the specific cavity mode frequency with the angle. This solves the problem of ultimately realizing a laser with a wide range of tunable frequencies. Attached Figure Description

[0037] Figure 1 A schematic diagram of a mode-free, wide-range, continuously tunable external cavity semiconductor laser.

[0038] Figure 2 This is a schematic diagram of the laser structure in Example 1;

[0039] Figure 3 This is a schematic diagram of the laser structure in Example 2;

[0040] Figure 4 The relationship between the rotation angle and the change in cavity mode frequency for prism-type high-intensity reflective films of different thicknesses.

[0041] Figure 5 The relationship between the rotation angle and the change in cavity mode wavelength for prism-type ultra-high intensity reflective films of different thicknesses;

[0042] Figure 6 This is a comparison diagram showing the relationship between the rotation angle of prism-type ultra-high intensity reflective films of different thicknesses and the cavity mode wavelength, and the relationship between the rotation angle of the interferometer and the transmission wavelength.

[0043] Among them, 1. Laser diode, 2. Collimating lens, 3. Polarizing beam splitter, 4. Narrowband interference plate, 5. Prism-type high-intensity reflective film, 6. Piezoelectric module, 7. Piezoelectric ceramic, 8. High-precision rotary stage. Detailed Implementation

[0044] The following examples are used to explain the technical solutions of the present invention in a non-limiting manner.

[0045] In this invention, for ease of explanation and not limitation, the direction toward the laser is referred to as "front" and the direction toward the piezoelectric module is referred to as "back".

[0046] Example 1

[0047] like Figure 1-2The schematic diagram of a mode-skipping, wide-range, continuously tunable external cavity semiconductor laser shown includes a laser diode 1, a collimating lens 2, a polarizing beam splitter 3, a narrowband interferometer 4, a prism-type high-intensity reflector 5, and a piezoelectric module 6, arranged sequentially in the optical path. The narrowband interferometer 4 is bonded to the front surface of the prism-type high-intensity reflector 5, and the piezoelectric module 6 is bonded to the rear surface of the prism-type high-intensity reflector 5, with the piezoelectric module having a thickness D. When the narrowband interferometer 4, the prism-type high-intensity reflector 5, and the piezoelectric module 6 rotate together, the axis of rotation is located in the optical path of the laser and coincides with the rear surface of the piezoelectric module 6.

[0048] The initial angle is defined as light incident perpendicularly onto the front surface of the prism-type high-intensity reflective film 5, at which point the incident angle is 0°, the piezoelectric module thickness is D, the cavity length is L1, and the operating wavelength is [missing information]. The interferometer operates at a wavelength of 780nm. By using a piezoelectric module in conjunction with piezoelectric ceramic 7, the angle between the incident light and the normals of the narrowband interferometer 4 and the prism-type ultra-high intensity reflective film 5 can be adjusted simultaneously.

[0049] During operation, the coherent beam output from laser diode 1 is collimated into parallel light by collimating lens 2. The parallel light is filtered out of the band after passing through narrowband interferometer 4, resulting in narrowband light. This narrowband light reaches the front surface of prism-type high-intensity reflective film 5 and is reflected in the same direction as the narrowband light. This reflected light returns to laser diode 1 after passing through narrowband interferometer 4 and polarization beam splitter 3. When the intracavity oscillation reaches the threshold, polarization beam splitter 3 outputs laser light. By using piezoelectric module 6 in conjunction with piezoelectric ceramic 7 to simultaneously adjust the angle between the incident light and narrowband interferometer 4 and the angle between the incident light and prism-type high-intensity reflective film 5, the center frequency of the transmission peak of the interferometer and the cavity mode frequency can be changed synchronously, achieving a wide range of continuously tunable output frequency.

[0050] By selecting an appropriate thickness for the piezoelectric module 6, the rotation of the narrow-band interferometer 4 and the prism-type ultra-high intensity reflective film 5 causes the center frequency of the transmission peak of the interferometer to change synchronously with the cavity mode frequency. Specifically, assuming that light is incident perpendicularly on the front surface of the prism-type ultra-high intensity reflective film 5, i.e., the initial angle is 0°, the cavity length is 10cm, and the working wavelength is 780nm, piezoelectric modules of different thicknesses are selected, namely D=20cm, D=22cm, D=24cm, D=25cm, and 28cm.

[0051] Figure 4 The relationship between the rotation angle of piezoelectric modules of different thicknesses and the change in cavity mode frequency is given by measurement, where the horizontal axis represents the change in the incident angle of the prism-type ultra-high intensity reflective film, and the vertical axis represents the change in cavity mode frequency.

[0052] Figure 5The relationship between the rotation angle and the change in cavity mode wavelength for piezoelectric modules of different thicknesses, obtained through measurement, is presented. The horizontal axis represents the change in the incident angle of the prism-type ultra-high intensity reflective film, and the vertical axis represents the change in cavity mode wavelength.

[0053] Figure 6 A comparative graph is presented showing the relationship between the rotation angle of prism-type super-intensity reflective films of different thicknesses and the cavity mode wavelength, and the relationship between the rotation angle of the interferometer and the transmission wavelength. The horizontal axis represents the change in the angle between the incident light and the prism-type super-intensity reflective film (interferometer), and the vertical axis represents the wavelength.

[0054] from Figure 6 It can be seen that, according to the calculations, the change in transmission wavelength occurs when the rotation angle of the interferometer (red solid line) is within the range of 0-14°. The result is 780nm - 774.3nm = 5.7nm. (From...) Figure 5 It can be seen that when the rotation angle is 14°, the change in cavity mode wavelength corresponding to the rotation angle of the 24mm piezoelectric module (green dashed line) is approximately 5.73nm. Similarly, it can also be seen that... Figure 6 The curve showing the relationship between the rotation angle of the 24mm thick piezoelectric module and the cavity mode wavelength (green dashed line) and the curve showing the relationship between the rotation angle of the interferometer and the transmission wavelength can also be seen. Within the range of 0-14°, they almost completely overlap, meaning that the changes in the center frequency of the transmission peak of the interferometer caused by the rotating narrow-band interferometer 4 and the prism-type ultra-high intensity reflective film 5 are approximately the same as those of the cavity mode frequency.

[0055] Therefore, when the cavity length is 10cm and the working wavelength is 780nm, a piezoelectric module with a thickness of 24mm is selected to rotate simultaneously with the interferometer. As the angle increases / decreases, the center frequency of the transmission peak of the interferometer and the cavity mode frequency increase / decrease simultaneously, overcoming the problem of continuous frequency tuning and enabling continuous tuning of the laser frequency over a wide range.

[0056] Example 2

[0057] The setup is the same as in Example 1, except that a high-precision rotating stage 8 is used instead of the piezoelectric ceramic 7. The narrow-band interference sheet 4, the prism-type ultra-high intensity reflective film 5, and the piezoelectric module 6, which are bonded together, are all mounted on the high-precision rotating stage 8, and it is ensured that when rotation occurs, the rotation axis is located on the rear surface of the piezoelectric module 6 and is in the optical path.

[0058] Similar to Example 1, a piezoelectric module 6 with a thickness of 24mm is selected. The angle between the incident light and the interferometer 4, as well as the angle between the incident light and the prism-type high-intensity reflective film 5, are adjusted by a high-precision rotating stage 8. This makes the position of the center of the transmission peak of the interferometer move with the angle and the frequency of the specific cavity mode change with the angle highly synchronized, thus overcoming the problem of continuous frequency tuning and enabling continuous tuning of the laser frequency over a wide range.

[0059] The mode-hopping-free, wide-range continuously tunable external cavity semiconductor laser of this invention achieves wide-range continuous tunability of the laser frequency. Compared with existing technologies, this invention overcomes the mode-hopping phenomenon caused by changes in laser frequency with cavity length (i.e., changes in cavity mode frequency). It innovatively utilizes the sensitivity of laser frequency to the rotation angle of a narrowband interferometer. By simultaneously changing the interferometer angle and cavity length, it achieves a high degree of synchronization between the center frequency of the interferometer's transmission peak and the frequency of a specific cavity mode as the angle changes. This results in a laser with a mode-hopping-free output frequency that ensures continuous tunability of the output frequency with the cavity mirror rotation angle, solving the problem of continuous frequency modulation and ultimately realizing a wide-range continuously tunable laser. The mode-hopping-free, wide-range continuously tunable external cavity semiconductor laser of this invention can meet the requirement of wide-range laser frequency tunability, thereby promoting the application and development of laser technology in various fields.

Claims

1. A mode-skipping, wide-range, continuously tunable external cavity semiconductor laser, the laser comprising a laser diode (1), a collimating lens (2), a polarizing beam splitter (3), a narrow-band interferometer (4), and a prism-type high-intensity reflective film (5) arranged sequentially in the optical path, characterized in that... The laser also includes a piezoelectric module (6), a narrowband interference plate (4) is bonded to the front surface of the prism-type high-intensity reflective film (5), and the piezoelectric module (6) is bonded to the rear surface of the prism-type high-intensity reflective film (5). The piezoelectric module (6) has a thickness D. When the prism-type high-intensity reflective film (5) rotates, the rotation axis is located in the optical path of the laser and coincides with the rear surface of the piezoelectric module (6). The coherent beam emitted by the laser diode (1) is collimated into parallel light by the collimating lens (2). The parallel light is then passed through the polarizing beam splitter (3) to obtain horizontally polarized light or vertically polarized light with the same emission direction as the laser diode (1). The horizontally polarized light or vertically polarized light is incident on the narrowband interferometer (4) to obtain narrowband light. The narrowband light is reflected back to the laser diode (1) after reaching the front surface of the prism-type high-intensity reflective film (5). When the oscillation in the cavity reaches the threshold, laser light is output at the polarizing beam splitter (3). The cavity length is changed by rotating the prism-type high-intensity reflective film (5), thereby changing the cavity mode frequency of the laser. At the same time, the mode selection is performed by adjusting the narrow-band interferometer, so that the center position of the transmission peak of the interferometer moves with the angle, which is highly synchronized with the change of cavity mode frequency with the angle.

2. The mode-skipping, wide-range, continuously tunable external cavity semiconductor laser according to claim 1, characterized in that... The thickness D satisfies the following relationship: ； Dl=Dl IF =λ0-λ'(ϕ); ； For prism-type super reflective film (5) rotation The change in the wavelength of the cavity mode. Rotate the narrowband interferometer (4) The change in wavelength at the center position of the transmission peak of the interferometer. Rotate the narrowband interferometer (4) The wavelength at the center of the transmission peak of the interferometer. The transmission wavelength when the narrowband interferometer (4) is perpendicular to the beam. L1 is the initial output wavelength of the laser diode (1), L1 is the distance from the end face of the laser diode (1) to the front surface of the prism-type high-intensity reflective film (5) when the incident angle of the laser diode (1) output light to the prism-type high-intensity reflective film (5) is 0°, and D is the thickness of the piezoelectric module (6). It is the incident angle of the prism-type super-strong reflective film (5). It is the incident angle of the narrowband interferometer (4). is the refractive index of the narrowband interference plate (4).

3. The mode-skipping, wide-range, continuously tunable external cavity semiconductor laser according to claim 1, characterized in that... The thickness D satisfies the following relationship: and ,in, ； ； For prism-type super reflective film (5) rotation Time cavity mode wavelength, Rotation of narrowband interferometer The wavelength at the center of the transmission peak of the interferometer. It is the incident angle of the prism-type super-strong reflective film (5). L1 is the incident angle of the narrowband interferometer (4), L1 is the distance from the output light end face of the laser diode (1) to the front surface of the prism-type high-intensity reflective film (5) when the incident angle of the prism-type high-intensity reflective film (5) is 0°, and D is the thickness of the piezoelectric module (6). The transmission wavelength when the narrowband interferometer (4) is perpendicular to the beam. is the refractive index of the narrowband interference sheet (4), and n is a natural number.

4. The mode-skipping, wide-range, continuously tunable external cavity semiconductor laser according to claim 1, characterized in that... Piezoelectric ceramics (7) are disposed on the rear surface of the piezoelectric module (6).

5. The mode-skipping, wide-range, continuously tunable external cavity semiconductor laser according to claim 4, characterized in that... When a high-precision rotary stage (8) is used to replace the piezoelectric ceramic (7), a narrow-band interference plate (4), a prism-type high-intensity reflective film (5) and a piezoelectric module (6) are placed on the high-precision rotary stage (8), and when the prism-type high-intensity reflective film (5) is rotated, the rotation axis is located on the rear surface of the piezoelectric module (6) and is in the optical path.

6. The mode-skipping, wide-range, continuously tunable external cavity semiconductor laser according to claim 1, characterized in that... The initial wavelength of the laser diode (1) is matched with the center wavelength of the transmission peak of the narrowband interferometer (4).

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