阅读说明：本技术 一种用于Littman结构的激光器腔体 (Laser cavity for Littman structure ) 是由 孙庆旭 朱兴邦 刘超 韩忠 朱云波 于 2021-09-07 设计创作，主要内容包括：本发明提供了一种用于Littman结构的激光器腔体,设置在腔体内的半导体增益芯片、固定设置在底座上的耦合镜和光栅,以及通过补偿单元固定到底座上的反射镜；腔体的腔长为Ld,补偿单元的长度为Ls,腔体在底座上的长度为Lb；当温度上升,底座膨胀,Lb增加,同时,补偿单元受到温度的影响,补偿单元的长度Ls也增加,抵消腔体腔长Ld的变化。采用本发明的技术方案：1、补偿单元安装于反射镜后,通过补偿单元的伸长及回缩实现腔体长度的补偿。2、补偿单元采用温度敏感材料,随温度的变化自身伸长或回缩,实现腔体长度的被动式补偿。(The invention provides a laser cavity for a Littman structure, which comprises a semiconductor gain chip arranged in the cavity, a coupling mirror and a grating which are fixedly arranged on a base, and a reflecting mirror which is fixed on the base through a compensation unit; the length of the cavity is Ld, the length of the compensation unit is Ls, and the length of the cavity on the base is Lb; when the temperature rises, the base expands, Lb increases, and meanwhile, the length Ls of the compensation unit also increases under the influence of the temperature, so that the change of the cavity length Ld of the cavity is counteracted. The technical scheme adopted by the invention is as follows: 1. the compensation unit is arranged behind the reflector, and the length of the cavity is compensated through the extension and retraction of the compensation unit. 2. The compensation unit adopts temperature sensitive materials, extends or retracts along with the change of temperature, and realizes the passive compensation of the length of the cavity.)

1. A laser cavity for a Littman structure, comprising: the semiconductor gain chip is arranged in the cavity, the coupling mirror and the grating are fixedly arranged on the base, and the reflecting mirror is fixed on the base through the compensation unit; the length of the cavity is Ld, the length of the compensation unit is Ls, and the length of the cavity on the base is Lb; when the temperature rises, the base expands, Lb increases, and meanwhile, the length Ls of the compensation unit also increases under the influence of the temperature, so that the change of the cavity length Ld of the cavity is counteracted.

2. The laser cavity of claim 1, wherein the compensation element is selected to have a suitable thermal expansion coefficient and a suitable length, the thermal expansion coefficient is selected to be related to the length of the cavity on the base and the thermal expansion coefficient of the base material, i.e., the length of the cavity on the base is Lb, the length of the compensation element is Ls, the thermal expansion coefficient of the base is a b, the thermal expansion coefficient of the compensation element is a s, and the compensation element is selected to satisfy the equation Ls x a s Lb x a b.

3. The laser cavity for a Littman structure as set forth in claim 2, wherein temperature compensation by the compensation unit is used for temperature stability of the cavity; the cavity length of the cavity is Ld, the length of the compensation unit is Ls, the length of the cavity on the base is Lb, the expansion coefficient of the base is alpha b, and the thermal expansion coefficient of the compensation unit is alpha s; when the ambient temperature variation is Δ T, due to thermal expansion and cold contraction, a length variation Δ L of the cavity on the base is Δ T × Lb × α b; the semiconductor gain chip, the coupling mirror, the grating and the reflector are all fixed on the base, the variation of the cavity length Ld is also delta L, the compensation unit is subjected to deformation displacement due to thermal expansion and cold contraction and meets the requirement that delta T multiplied by Ls multiplied by alpha s is delta L, at the moment, the cavity length variation caused by the thermal expansion and cold contraction of the base is offset by the displacement variation generated by the thermal expansion and cold contraction of the compensation unit, the stability of the cavity length is kept, and the stability of the output laser wavelength is further ensured.

Technical Field

The invention belongs to the technical field of laser cavity structures, and relates to a laser cavity for a Littman structure.

Background

The littman structure is a classical laser cavity structure of an external cavity laser, light emitted by a semiconductor gain chip is collimated to the surface of a grating through a lens, 1-level diffraction light is fed back to an active region of the laser according to the original path through a grating selection film, so that the gain of the selected mode in the inner cavity of the laser is amplified to obtain advantages in mode competition, and finally the gain is output as 0-level diffraction light of the grating, and laser tuning output is realized by changing the cavity length. The cavity is used as a precise optical system, a slight change of the cavity length causes a wavelength shift, and a mode hopping problem may occur, so that the temperature becomes an influence factor which is not negligible, and the following two aspects are mainly expressed: (1) the temperature change of the cavity causes the change of the cavity length, the drift of the output light wavelength occurs, and even the jump of the output light mode occurs. (2) The temperature of the cavity has gradient, and the structural member of the cavity deforms, so that the tuning range of the tunable laser light source is influenced.

In practical engineering applications, a typical littman external cavity semiconductor laser is shown in fig. 1, where fig. 1 includes: the grating comprises a reflector 1, a grating 2, a semiconductor gain chip 3, a coupling mirror 4 and a semi-transparent and semi-reflective film 5. The semiconductor gain chip generates spontaneous radiation light which is incident on the grating to generate diffraction and zero-order diffraction light output and is used as laser output or used for signal detection; the first-order diffracted light is reflected by the reflector, and the reflected light is fed back to the gain medium through the grating to generate laser oscillation, form light amplification and obtain laser. The laser output can be coupled out through zero-order reflected light or through a semi-transparent semi-reflecting film at one end of the semiconductor laser chip. The light loop among the reflector, the semi-transparent semi-reflective film and the grating forms a composite cavity, the cavity can generate a longitudinal mode, and the mode of laser in the cavity meets a standing wave equation: q × λ is 2L. Wherein q is the mode number of a single longitudinal mode and is an integer; λ is the wavelength of the laser; l is the optical cavity length of the composite cavity. In order to realize continuous mode-hopping-free tuning of laser, q in a standing wave equation is required to be constant, an extension line of a grating plane and an extension line of a reflector plane are intersected at one point, and when the reflector is driven by a displacement mechanism to rotate by taking the intersection point of the extension line of the grating plane and the extension line of the reflector plane as an origin, the rotation and the translation can be simultaneously carried out, so that the mode-hopping-free tuning is realized. As a precise optical system, when the external temperature changes, the cavity deforms due to expansion with heat and contraction with cold, so that the spectral characteristics, tuning range and reliability of laser output by the cavity are affected. The temperature change has two effects on the cavity, 1, the wavelength drift occurs in the temperature change of the cavity; 2. the temperature of the cavity has gradient, and the structural member of the cavity deforms, so that the tuning range of the tunable laser light source is influenced. To obtain stable laser output, the temperature of the cavity must be effectively controlled.

The invention is similar to the invention and is named as a patent (publication number is CN 111854813A) of a temperature self-compensation type extrinsic Fabry-Perot cavity and a manufacturing method, an extrinsic F-P cavity of the invention is shown as figure 2, and in the figure 2, a sapphire diaphragm 1, a silicon dioxide base 2, a vacuum cavity 3, a sapphire column 4, a silicon dioxide side wall 5 and a silicon dioxide base 6 are arranged on the sapphire column. When the temperature rises, the volume of the vacuum cavity 3 is increased due to thermal expansion, the silicon dioxide side wall 5 is lengthened and extends outwards, and the sapphire column 4 in the vacuum cavity 3 also expands inwards, so that the optical path change of reflected light caused by the temperature can be counteracted in a certain range, and the same is true when the temperature is reduced. The invention enhances the application temperature range of the extrinsic F-P cavity, reduces the cost and greatly reduces the workload of the optical modulation part.

The prior art generally adopts active temperature control, uses an active refrigeration and heating device, and adopts a temperature feedback control method to actively control the temperature of the whole cavity, and mainly has the following defects: (1) the active temperature control needs a refrigerating and heating device and a related driving circuit, and in order to realize the feedback control of the temperature, a temperature detection device needs to be added, so that the structure is complex, and the realization cost is high. (2) The active temperature control needs the cooperation of software and hardware, the algorithm is complex, and the realization difficulty is large.

Disclosure of Invention

Aiming at the problems, the invention provides a passive cavity temperature compensation method which can effectively solve the problems.

The technical scheme of the invention is as follows: a laser cavity for a Littman structure, comprising: the semiconductor gain chip is arranged in the cavity, the coupling mirror and the grating are fixedly arranged on the base, and the reflecting mirror is fixed on the base through the compensation unit; the length of the cavity is Ld, the length of the compensation unit is Ls, and the length of the cavity on the base is Lb; when the temperature rises, the base expands, Lb increases, and meanwhile, the length Ls of the compensation unit also increases under the influence of the temperature, so that the change of the cavity length Ld of the cavity is counteracted.

The compensation unit is selected from a material having a suitable thermal expansion coefficient and a length, where the selection of the material having the thermal expansion coefficient is related to the length of the cavity on the base and the thermal expansion coefficient of the material of the base, that is, the length of the cavity on the base is Lb, the length of the compensation unit is Ls, the thermal expansion coefficient of the base is α b, and the selection of the compensation unit satisfies the equation Ls × a s ═ Lb × a b.

In the above, the temperature compensation by the compensation unit is used for the temperature stability of the cavity; the cavity length of the cavity is Ld, the length of the compensation unit is Ls, the length of the cavity on the base is Lb, the expansion coefficient of the base is alpha b, and the thermal expansion coefficient of the compensation unit is alpha s; when the ambient temperature variation is Δ T, due to thermal expansion and cold contraction, a length variation Δ L of the cavity on the base is Δ T × Lb × α b; the semiconductor gain chip, the coupling mirror, the grating and the reflector are all fixed on the base, the variation of the cavity length Ld is also delta L, the compensation unit is subjected to deformation displacement due to thermal expansion and cold contraction and meets the requirement that delta T multiplied by Ls multiplied by alpha s is delta L, at the moment, the cavity length variation caused by the thermal expansion and cold contraction of the base is offset by the displacement variation generated by the thermal expansion and cold contraction of the compensation unit, the stability of the cavity length is kept, and the stability of the output laser wavelength is further ensured.

The technical scheme adopted by the invention is as follows: 1. the compensation unit is arranged behind the reflector, and the length of the cavity is compensated through the extension and retraction of the compensation unit. 2. The compensation unit adopts temperature sensitive materials, extends or retracts along with the change of temperature, and realizes the passive compensation of the length of the cavity. 3. The passive temperature compensation of the cavity is realized by utilizing expansion with heat and contraction with cold of the compensation material, the structure is simple, 4 is easy to realize, and the cost of the passive temperature compensation is low compared with that of an active temperature compensation scheme.

Drawings

Fig. 1 is a schematic diagram of a littman external cavity structure in the prior art.

FIG. 2 is a schematic diagram of a prior art extrinsic F-P cavity structure.

Fig. 3 is a schematic diagram of a chip structure of an external cavity laser according to the present invention.

In FIG. 3, 1-compensation unit, 2-mirror, 3-grating, 4-coupling mirror, 5-semiconductor gain chip, 6-cavity mount.

Detailed Description

In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

As shown in fig. 3, an embodiment of the present invention provides a passive temperature compensation chamber, which compensates for chamber length variation caused by temperature by using a compensation unit to offset chamber deformation caused by temperature, thereby ensuring temperature reliability of the chamber. A laser cavity for a Littman structure comprises a semiconductor gain chip arranged in the cavity, a coupling mirror and a grating which are fixedly arranged on a base, and a reflecting mirror which is fixed on the base through a compensation unit; the passive temperature compensation cavity adopts the compensation element to offset the cavity deformation caused by temperature. As shown in fig. 3, the semiconductor gain chip 5, the coupling mirror 4 and the grating 3 of the cavity are directly fixed on the base, and the reflector 2 is fixed on the base through the compensation unit 1. The cavity length of the cavity is Ld (neglecting the refractive index difference of different devices), the length of the compensation unit is Ls (neglecting the refractive index difference of the reflector and the compensation material), the length of the whole cavity on the base is Lb, the expansion coefficient of the base is ab, and the thermal expansion coefficient of the compensation unit is as. When the ambient temperature changes, the change amount is set to Δ T, the base expands or contracts due to thermal expansion and contraction, that is, Lb changes, and the change amount is set to Δ L, which satisfies the equation Δ L ═ Δ T × Lb × a b; because the semiconductor gain chip, the coupling mirror, the grating and the reflector are all fixed on the base, the variation of the cavity length Ld is also delta L; meanwhile, the compensation unit is also affected by temperature, Ls is also changed, and when the displacement variation of the compensation unit satisfies the equation Δ T × Ls × α s ═ Δ L, that is, the displacement variation of the compensation unit is equal to the cavity length variation, the deformation of the compensation unit cancels the variation of the cavity length Ld, and at this time, the passive displacement compensation of the compensation unit ensures the temperature stability of the cavity length, thereby ensuring the stability of the output laser wavelength. The compensation unit needs to select a material with a proper thermal expansion coefficient and a length thereof, which are directly related to the thermal expansion coefficient and the length of the base material, and needs to satisfy the equation Ls × a s ═ Lb × a b, so that the influence of temperature on the cavity length can be completely counteracted, and the cavity length Ld is ensured to be constant. Therefore, the temperature stability of the cavity can be ensured through the passive temperature compensation of the compensation unit.

The technical scheme adopted by the invention is as follows: 1. the compensation unit is arranged behind the reflector, and the length of the cavity is compensated through the extension and retraction of the compensation unit. 2. The compensation unit adopts temperature sensitive materials, extends or retracts along with the change of temperature, and realizes the passive compensation of the length of the cavity. 3. The passive temperature compensation of the cavity is realized by utilizing expansion with heat and contraction with cold of the compensation material, the structure is simple, 4 is easy to realize, and the cost of the passive temperature compensation is low compared with that of an active temperature compensation scheme.

The technical features mentioned above are combined with each other to form various embodiments which are not listed above, and all of them are regarded as the scope of the present invention described in the specification; also, modifications and variations may be suggested to those skilled in the art in light of the above teachings, and it is intended to cover all such modifications and variations as fall within the true spirit and scope of the invention as defined by the appended claims.