CN111740311B - Narrow linewidth tunable laser and preparation method thereof - Google Patents

Narrow linewidth tunable laser and preparation method thereof Download PDF

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CN111740311B
CN111740311B CN202010763790.4A CN202010763790A CN111740311B CN 111740311 B CN111740311 B CN 111740311B CN 202010763790 A CN202010763790 A CN 202010763790A CN 111740311 B CN111740311 B CN 111740311B
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waveguide
passive waveguide
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narrow linewidth
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CN111740311A (en
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魏思航
阳红涛
王任凡
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Wuhan Minxin Semiconductor Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1003—Waveguide having a modified shape along the axis, e.g. branched, curved, tapered, voids
    • H01S5/101—Curved waveguide
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers

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Abstract

The invention discloses a narrow linewidth tunable laser and a preparation method thereof, wherein a laser chip sequentially comprises a substrate layer, a lower waveguide layer and an upper waveguide layer from bottom to top; the lower waveguide layer and the upper waveguide layer are positioned on different planes and perform light energy exchange through vertical coupling; the lower waveguide layer is provided with an active gain waveguide and a lower passive waveguide which are connected in a butt joint mode, and the cavity length of the lower passive waveguide is prolonged by arranging a plurality of bent waveguides; the upper waveguide layer is provided with an upper passive waveguide and a micro-ring reflector, the upper passive waveguide and the lower passive waveguide are vertically coupled through a coupler, the micro-ring reflector is coupled and connected with the upper passive waveguide, and the upper passive waveguide is provided with a plurality of bent waveguides to prolong the cavity length. The narrow linewidth tunable laser not only has small size, tunability and narrow linewidth of a laser chip, but also has low cost and high stability.

Description

Narrow linewidth tunable laser and preparation method thereof
Technical Field
The invention relates to the technical field of lasers, in particular to a narrow linewidth tunable laser and a preparation method thereof.
Background
Because the coherent technology is suitable for long-distance transmission, the communication fields such as backbone networks and data center interconnection mainly adopt coherent optical modules with transmission rates of 400G and more than 400G. The coherent technique has severe requirements on the phase noise (i.e., line width) of the laser transmitter. As transmission bandwidth increases, the laser linewidth requirements also increase, for example, 400G coherent technology requires laser linewidths less than 100 kHz. In addition, in order to further expand the bandwidth by using the wavelength division multiplexing technology, the coherent technology is more prone to use a wavelength tunable light source. The current narrow linewidth light source technology mainly comprises an external cavity tunable laser technology and a silicon light tunable laser technology. Although both schemes can satisfy the 100kHz line width and wavelength tuning function, the two schemes have the defects of high cost, poor stability of external optical coupling parts, large size and the like, and are difficult to be applied on a large scale. The semiconductor laser chip with low cost and high stability, such as a DBR or DFB array, can solve the above difficulties, but because the equivalent cavity length of the semiconductor laser chip is short, the line width of an output signal is often larger than 300kHz, and the narrow line width requirement in the coherent technology cannot be met.
Theoretically, the cavity length of a semiconductor laser chip is increased to the centimeter magnitude, and an output signal with the line width of 100kHz can be obtained, but the size of the chip is 5-10mm no matter a straight waveguide or a bent waveguide is adopted. Compared with a silicon optical scheme narrow linewidth laser, on one hand, the size of the device is not obviously reduced, and on the other hand, the cost is not obviously improved due to the fact that the number of the devices produced on the wafer is small. The larger the size of the laser chip is, the more serious the warpage is, and the warpage caused by the size will seriously affect the end face coating and mounting process of the chip, resulting in the consequences of reduced yield of the chip, reduced reliability and the like.
Disclosure of Invention
In order to achieve the purposes of small size, tunability, narrow linewidth and low cost, the invention provides a small-size narrow linewidth laser chip, a laser provided with the small-size narrow linewidth laser chip and a method for preparing the small-size narrow linewidth laser chip.
The invention provides a small-size narrow linewidth laser chip based on vertical coupling and micro-ring reflection technologies, which sequentially comprises a substrate layer, a lower waveguide layer and an upper waveguide layer from bottom to top;
the lower waveguide layer is provided with an active gain waveguide and a lower passive waveguide which are connected in a butt joint mode, and the cavity length of the lower passive waveguide is prolonged by arranging a plurality of bent waveguides; the lower waveguide layer and the upper waveguide layer are positioned on different planes and perform light energy exchange through vertical coupling;
the upper waveguide layer is provided with an upper passive waveguide and a micro-ring reflector, the upper passive waveguide and the lower passive waveguide are vertically coupled through a coupler, the micro-ring reflector is coupled and connected with the upper passive waveguide, and the upper passive waveguide is provided with a plurality of bent waveguides to prolong the cavity length.
Further, the active gain waveguide is a semiconductor optical amplifier or a DFB laser.
Further, the laser chip comprises a plurality of upper passive waveguides distributed up and down, adjacent upper passive waveguides are vertically coupled through a coupler, the upper passive waveguide positioned at the lowermost layer is vertically coupled and connected with the lower passive waveguide through the coupler, the micro-ring reflector is of a closed-loop structure, and the micro-ring reflector is coupled and connected with the upper passive waveguide at the uppermost layer.
Further, the coupler is a grating assisted vertical coupler or 1/4 wavelength coupler.
Further, the grating of the grating assisted vertical coupler is located in the lower passive waveguide or the upper passive waveguide.
Further, wavelength tuning is achieved by thermal tuning or electrical injection of the micro-ring reflector and the grating assisted vertical coupler.
Further, the micro-ring reflector includes a single or a plurality of micro-rings.
Further, the core area of the upper passive waveguide is larger than that of the lower passive waveguide.
The invention also provides a small-size narrow linewidth laser, which comprises the small-size narrow linewidth laser chip.
The invention also provides a preparation method of the small-size narrow linewidth laser chip, which comprises the following steps:
epitaxially growing a lower passive waveguide layer and an SOA active region on the substrate, and completing the butt joint of the lower passive waveguide layer and the SOA active region by adopting a butt joint growth technology;
generating a grating structure in the lower passive waveguide layer;
corroding the lower passive waveguide region and the SOA active region to form an SOA waveguide structure and a lower passive waveguide structure with a plurality of bent waveguides;
protecting the SOA region by using a mask, growing an upper passive waveguide layer upwards, and finishing the vertical coupling of the two passive waveguides through a grating structure;
and etching the micro-ring structure and the upper passive waveguide structure with a plurality of bent waveguides by adopting an etching technology.
The invention has the beneficial effects that: the invention provides a small-size narrow linewidth laser chip based on vertical coupling and micro-ring reflection technologies, wherein an active gain waveguide of the laser chip is used for providing signal gain; the lower passive waveguide is used as an expansion cavity of the active gain waveguide, and the line width of an output signal is compressed; the upper passive waveguide exchanges optical signals with the lower passive waveguide by means of a vertical coupling technology, so that the cavity length is prolonged, and the signal line width is further compressed; the micro-ring reflector is coupled with the upper passive waveguide, so that the micro-ring reflector plays a role of a reflector on one hand, and the line width of the laser is compressed on the other hand; the lower passive waveguide and the upper passive waveguide are vertically coupled, and the cavity length is prolonged by arranging a plurality of bent waveguides on the plane where the waveguides are located, so that a three-dimensional structure is realized, the size of a laser chip can be reduced, and the line width of a signal is also compressed; meanwhile, the preparation process is compatible with the laser chip process, so that the method is suitable for batch production and reduces the cost.
Furthermore, the laser chip comprises a plurality of upper passive waveguides which are distributed up and down, and adjacent upper passive waveguides are vertically coupled and connected through a coupler, so that the cavity length of the device is further prolonged, and the line width is compressed; the wavelength tunable function is realized by carrying out thermal tuning or electrical injection on the micro-ring reflector and the grating auxiliary vertical coupler.
Furthermore, the stability of the output wavelength can be improved through the mode selection effect of the grating auxiliary vertical coupler; the size of the upper passive waveguide is increased, so that the core area of the upper passive waveguide is larger than that of the lower passive waveguide to increase the size of light spots of transmitted light, the divergence angle of light beams is reduced, poor light spots of the lower passive waveguide can be converted into optimized light spots of the upper passive waveguide, the divergence angle of light spots output by the device is smaller, the quality of the light beams is higher, and the coupling with an external optical fiber is facilitated.
Drawings
FIG. 1 is a perspective view of a small-size narrow linewidth laser chip of the present invention;
FIG. 2 is a top view of a small-size narrow linewidth laser chip according to the present invention;
FIG. 3 is a schematic view of the butt joint of the active waveguide and the passive waveguide according to the present invention;
FIG. 4 shows the output linewidth of devices of different designs of the present invention;
FIG. 5 is a microring reflection spectrum, FP cavity transmission spectrum and wavelength dependent coupling efficiency spectrum of the present invention;
FIG. 6 is a wavelength plot of the laser chip output at this point when the micro-ring reflection spectrum is aligned with the FP transmission spectrum;
fig. 7 is a flow chart of a method for fabricating a small-size narrow-linewidth laser chip.
In the figure: the optical fiber amplifier comprises a 1-semiconductor optical amplifier SOA, a 2-lower passive waveguide, a 3-upper passive waveguide, a 4-grating auxiliary vertical coupler, a 41-grating, a 5-micro-ring reflector, a 6-micro-ring thermal tuning metal electrode and a 7-grating thermal tuning metal electrode.
Detailed Description
The narrow linewidth tunable laser chip, the preparation method thereof and the laser of the present invention will be further described with reference to the accompanying drawings:
the invention provides a small-size narrow linewidth laser chip based on vertical coupling and micro-ring reflection technologies, wherein an active gain waveguide of the laser chip is used for providing signal gain; the lower passive waveguide is used as an expansion cavity of the active gain waveguide, and the line width of an output signal is compressed; the upper passive waveguide exchanges optical signals with the lower passive waveguide by means of a vertical coupling technology, so that the cavity length is prolonged, and the signal line width is further compressed; the micro-ring reflector is coupled with the upper passive waveguide, so that the micro-ring reflector plays a role of a reflector on one hand, and the line width of the laser is compressed on the other hand; the lower passive waveguide and the upper passive waveguide are vertically coupled, and the cavity length is prolonged by arranging a plurality of bent waveguides on the plane where the waveguides are located, so that a three-dimensional structure is realized, the size of a laser chip can be reduced, and the line width of a signal is also compressed; meanwhile, the preparation process is compatible with the laser chip process, so that the method is suitable for batch production and reduces the cost.
As shown in fig. 1 and 2, the small-size narrow-linewidth laser chip of the embodiment of the invention sequentially comprises a substrate layer, a lower waveguide layer and an upper waveguide layer from bottom to top; the lower waveguide layer and the upper waveguide layer are located at different planes and exchange light energy through vertical coupling.
The lower waveguide layer is provided with an active gain waveguide 1 and a lower passive waveguide 2, as shown in fig. 3, one end of the active gain waveguide 1 is connected with one end of the lower passive waveguide 2 in a butt joint mode, and the cavity length of the lower passive waveguide 2 is extended by arranging a bent waveguide in the lower waveguide layer. An active gain waveguide 1 for providing signal gain in the device. The active gain waveguide may be a semiconductor optical amplifier 1 or a DFB laser. The semiconductor optical amplifier SOA converts input carriers into photons, providing signal gain in the device. The lower passive waveguide 2 is used as an extended cavity of the SOA to compress the line width of an output signal.
The upper waveguide layer is provided with an upper passive waveguide 3 and a micro-ring reflector 5, one end of the upper passive waveguide 3 is vertically coupled and connected with the other end of the lower passive waveguide 2 through a coupler, the micro-ring reflector 5 is coupled and connected with the upper passive waveguide 3, and the upper passive waveguide 3 prolongs the cavity length through arranging a bent waveguide on the upper waveguide layer. The upper passive waveguide 3 is positioned on the upper layer of the lower passive waveguide 2, and the upper passive waveguide 3 exchanges optical signals with the lower passive waveguide 2 by means of a vertical coupling technology and is used for increasing the cavity length and further compressing the signal line width. The coupler can be a grating auxiliary vertical coupler 4 or 1/4 wavelength coupler, and can also be replaced by other couplers; preferably, the grating auxiliary vertical coupler 4, the grating 41 of the grating auxiliary vertical coupler can be located in the lower passive waveguide 2 or the upper passive waveguide 3, and the grating auxiliary vertical coupler enables the upper passive waveguide and the lower passive waveguide to exchange optical signals by means of a grating auxiliary vertical coupling technology, and can also play a role in grating mode selection. And the micro-ring reflector 5 has a higher Q value, is coupled with the upper passive waveguide 3 and plays a role of a reflector. It is emphasized that the micro-ring reflector is a closed-loop structure, which has the effect of increasing the effective cavity length in addition to tuning the wavelength. The micro-ring reflector with the closed-loop structure has an increased effective cavity length compared with a non-closed-loop reflector (such as a ring reflector), and further plays a role in compressing the line width of the laser. The micro-ring reflector 5 may comprise a single or a plurality of closed micro-rings.
The lower passive waveguide 2 and the upper passive waveguide 3 are vertically coupled, and the cavity length of the lower passive waveguide and the cavity length of the upper passive waveguide are prolonged by arranging bent waveguides on waveguide layers where the waveguides are located. Because the two waveguide layers are not positioned in one plane, the three-dimensional structure can increase the cavity length of the device without additionally increasing the chip size.
The resonant cavity of the laser chip comprises an SOA cavity, an optical cavity of a lower passive waveguide and an upper passive waveguide and an equivalent cavity of a micro-ring reflector. The purpose of narrow line width is realized by prolonging the total cavity length of the resonant cavity of the laser chip.
In the invention, light is generated from the SOA, then enters the lower passive waveguide, enters the upper passive waveguide through the vertical coupling structure, is coupled with the micro-ring reflector, and is reflected back to the upper passive waveguide after being coupled with a part of required wavelength in the transmission process of the micro-ring reflector after entering the micro-ring reflector, so that resonance is carried out in the resonant cavity. After the optical field in the resonant cavity is stabilized, light is emitted from the tail end of the upper passive waveguide.
In order to further increase the cavity length of the device, the laser chip can comprise a plurality of upper passive waveguides distributed up and down, adjacent upper passive waveguides are vertically coupled and connected through a coupler, one end of the upper passive waveguide positioned at the lowest layer is vertically coupled and connected with the other end of the lower passive waveguide 2 through the coupler, and the micro-ring reflector 5 is coupled and connected with the upper passive waveguide at the uppermost layer.
In the invention, two wavelength selection devices of the micro-ring reflector 5 and the grating auxiliary vertical coupler 4 exist, and in order to realize the function of wavelength tuning, the two wavelength selection devices can be realized by means of thermal tuning or electric injection and the like. For example, the reflectivity curve is shifted by heating the metal above the micro-ring reflector, changing the refractive index of the micro-ring waveguide, and the device outputs a wavelength signal at that location when the peak of the micro-ring reflectivity curve coincides with the longitudinal mode of the device FP. And if the temperature of the micro-ring waveguide is continuously increased, the device outputs a wavelength signal of the next FP longitudinal mode. When the micro-ring and the grating auxiliary vertical coupler are adopted for wavelength tuning, the tuning range can cover the whole wave band of C or L.
The invention firstly realizes the purpose of small size, and then expands the cavity length by vertical coupling of the multi-plane waveguide, the micro-ring reflector and the curved waveguide arranged in the plane waveguide, thereby realizing the purpose of narrow line width. The principle of narrow line width is as follows:
the line width v of the output signal of the device can be obtained by the line width formula of the laser chip:
Figure 903073DEST_PATH_IMAGE001
in the formula (I), the compound is shown in the specification,v 0 showing the output line width of a single longitudinal mode of the corresponding FP laser after the two ends of the SOA are plated with films,f ex the intensity of the feedback signal is represented, namely the intensity of the light returned to the SOA gain region by the passive waveguide,n w1 l w1 andn w2 l w2 is the optical cavity length of the passive waveguide,n r l r for the equivalent cavity length of the micro-ring reflector, the equivalent cavity length can be represented by the following formula:
Figure 85792DEST_PATH_IMAGE002
wherein k is the coupling coefficient of the straight waveguide and the micro-ring, and R is the radius of the micro-ring. When the coupling coefficient is small, the equivalent cavity length is far higher than the actual circumference of the micro-ring, but when the coupling coefficient is small, the transmission loss in the micro-ring cavity must be small.
The feedback coefficient can be visually found from the line width formulaf ex Increasing the length of the passive waveguiden w1 l w1 Andn w2 l w2 and increasing the equivalent cavity length of the micro-ringn r l r The laser linewidth can be significantly reduced. However, the use of common planar 2-dimensional waveguide structures to achieve a centimeter-length cavity length necessarily results in chip sizes that are also on the order of centimeters. In order to avoid the great increase of the chip size, the optical power of the lower passive waveguide and the upper passive wave are enabled by the vertical coupling technologyThe optical powers of the waveguides are coupled with each other, and a 3-dimensional waveguide structure is realized. Wherein, the grating can be positioned in the lower passive waveguide or the upper passive waveguide, and the grating periodΛSatisfies the following formula:
Figure 396688DEST_PATH_IMAGE003
in the formula (I), the compound is shown in the specification,β 2 is the propagation constant of the underlying passive waveguide,β 1 is the propagation constant of the upper passive waveguide,mthe formula is a positive integer and corresponds to the back coupling condition of the upper and lower passive waveguides. When the wavelength of light transmitted in the device meets the formula, the upper passive waveguide and the lower passive waveguide are coupled, and the coupling efficiency of the vertical coupler can reach more than 80%. Because the coupling efficiency is related to the wavelength, the structure has a certain mode selection effect at the same time, and the stability of the output wavelength is improved. By optimally designing the transmission mode of the upper passive waveguide, for example, increasing the waveguide size, improving the light spot size of transmitted light, and reducing the beam divergence angle, the poor light spot of the lower passive waveguide can be converted into the optimized light spot of the upper passive waveguide, so that the divergence angle of the output light spot of the device is smaller, the beam quality is higher, and the coupling of the device and an external optical fiber is facilitated.
According to the principle, the invention designs a small-size narrow linewidth laser chip which is a monolithic integrated device, all materials and structures can be grown and manufactured on an active material substrate (InP or GaAs) in a monolithic integration mode without involving the integration of active III-V materials and silicon-based waveguides, so that the process is simpler, the chip can be prepared by using a wafer-level chip process, the chip is suitable for mass production, and the cost is reduced. As shown in fig. 1 and 2, the overall length of the chip is 1.5mm and the width is 2 mm. Wherein:
the length of the semiconductor optical amplifier 1 is 900um, the width is 1.8um, and the end bending angle needs to be larger than 5 degrees to avoid reflection. The S0A gain spectrum peak is located near 1.55um, and the spectrum width is greater than 55 nm.
The lower passive waveguide 2 comprises 5 bent waveguides, but because the radius of the bent waveguides is larger than 300um and the relative refractive index difference between the waveguide medium and the surrounding medium is large, the loss does not exceed 0.4%. The first four of which serve the transmission function and the 5 th one of which serve the reflection avoidance function. The lower passive waveguide 2 and the active waveguide are connected in a butt joint mode, the thickness of the waveguide is about 0.4um, and the butt joint coupling loss does not exceed 10%. The total length of the underlying passive waveguide 2 will be greater than 7mm, as estimated by the structure.
The length of the grating vertical coupling structure is 500um, and the position is in front of the fifth curved waveguide. The optical signal of the lower passive waveguide 2 is coupled into the upper passive waveguide 3 by the grating diffraction effect, and the transmission direction is opposite. The interval between the two waveguides is about 0.4um, the mode propagation constant of the lower passive waveguide is 14um-1The propagation constant of the upper passive waveguide is 12um-1Therefore, according to the calculation formula of the grating period, the grating period is 0.238um, and the number of the gratings is about 2100. It can be concluded from fig. 5 that the coupling efficiency of the two passive waveguides is about 82% at 1.55019 um.
The width of the upper passive waveguide 3 is 1.9um, the thickness is about 0.8um, the upper passive waveguide 3 comprises two bent waveguides, and the loss does not exceed 0.4%. The total length of the upper passive waveguide 5 will be greater than 5mm, estimated from this structure.
The radius of the micro-ring reflector 5 is 500um, the width of the micro-ring waveguide is 1.9um, and the thickness of the micro-ring reflector is 0.8 um. The coupling coefficient of the micro-ring is 0.3um-1In the case of (1), the reflectivity is about 88%, at this time, the feedback coefficient of the device is about 0.45, the total length of the passive waveguide of the device is about 12mm, and the longitudinal mode line width of the InP-based 900um cavity length FP laser is normally less than 1MHz, which can be shown as the output line width of the device is about 10kHz according to fig. 4 (curve fex =0.45 k = 0.3).
When the micro-ring thermal tuning metal electrode 6 is thermally tuned, the refractive index of the waveguide changes, the reflection spectrum of the micro-ring in fig. 6 shifts to a long wavelength, while the transmission spectrum of the FP cavity remains unchanged. When the micro-ring reflection peak and the FP peak coincide, the laser wavelength changes. In order to maintain the coupling efficiency of the vertical coupling structure, the grating thermal tuning metal electrode 7 needs to be adjusted to maximize the coupling efficiency at the tuned wavelength. The coupler curves in fig. 5 show that other wavelengths have lower coupling efficiencies than the lasing wavelength, and thus the vertical coupling structure can maintain the wavelength stability of the device by using this wavelength dependent loss mechanism. After the optical signal is processed through the processes, the line width is compressed to be below 100kHz, and the optical signal is output by the upper passive waveguide. The waveguide on the upper layer has a larger core area relative to the waveguide on the lower layer, and the thickness and the width of the core area are closer, so that the emergent light has the characteristics of small divergence angle and high beam quality, and is more suitable for optical fiber coupling.
The invention also provides a small-size narrow linewidth laser, which comprises the small-size narrow linewidth laser chip.
The invention also provides a preparation method of the small-size narrow linewidth laser chip, as shown in fig. 7, comprising the following steps:
s1, epitaxially growing a lower passive waveguide layer and an SOA active region on the substrate, and completing the butt joint of the lower passive waveguide layer and the SOA active region by adopting a butt joint growth technology;
s2, generating a grating structure in the lower passive waveguide layer;
s3, corroding the lower passive waveguide area and the SOA active area to form an SOA waveguide structure and a lower passive waveguide structure with a plurality of bent waveguides;
s4, protecting the SOA area by using a mask, growing an upper passive waveguide layer upwards, and completing vertical coupling of two passive waveguides through a grating structure;
and S5, etching the micro-ring structure and the upper passive waveguide structure with a plurality of bent waveguides by adopting an etching technology.
The invention finally provides a preparation method of the C-band adjustable narrow linewidth laser chip, which comprises the following steps:
step 1: and selecting an InP substrate, and epitaxially growing an N-type InP lower limiting layer, an InGaAsP lower waveguide layer, an InGaAsP quantum well active region structure and a cover InP layer in sequence.
Step 2: according to the schematic diagram, the quantum well with the length of 900um is reserved, and the quantum well structures at other positions are removed. InP, InGaAsP core layer and InP cover layer are sequentially grown by adopting a butt joint growth technology to complete the butt joint of the lower passive waveguide and the SOA active region, and a grating structure with the period of 0.238um is formed by utilizing a partial holographic exposure technology
And step 3: adopting a BH laser process to manufacture a mesa structure, simultaneously corroding an active region and a lower passive waveguide region to finish the SOA waveguide structure and the lower passive waveguide structure, then growing P-N type InP to form a reverse joint, and finally removing a mask and growing about 1.4um P type InP to finish the SOA of BH. The BH laser structure may be replaced with a waveguide structure such as a ridge waveguide structure or a buried ridge waveguide structure.
And 4, step 4: and protecting the SOA region by using a mask, corroding other regions to be near 100nm above the lower passive waveguide, and then sequentially growing 300nm of InP, an upper passive waveguide core region of 800nm of InGaAsP and 300nm of InP. And etching about 700nm downwards by adopting an etching technology to finish the upper-layer passive waveguide and micro-ring structure.
And 5: and separating the metal electrode and the waveguide in the region outside the SOA by using a dielectric film or BCB and other materials to finish the structure in the schematic diagram, wherein the front end face is coated with a film with the reflectivity of 70-95%, the rear end face is coated with a film with the reflectivity of 5-50%, and the optical signal is output from the rear end face and is coupled into the optical fiber.
It will be understood by those skilled in the art that the foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included within the scope of the present invention.

Claims (9)

1. A narrow linewidth laser chip is characterized by comprising a substrate layer, a lower waveguide layer and an upper waveguide layer from bottom to top in sequence; the lower waveguide layer and the upper waveguide layer are positioned on different planes and perform light energy exchange through vertical coupling;
the lower waveguide layer is provided with an active gain waveguide and a lower passive waveguide which are connected in a butt joint mode, and the cavity length of the lower passive waveguide is prolonged by arranging a plurality of bent waveguides;
the upper waveguide layer is provided with an upper passive waveguide and a micro-ring reflector, the upper passive waveguide is vertically coupled with the lower passive waveguide through a coupler, the micro-ring reflector is coupled with the upper passive waveguide, and the upper passive waveguide is provided with a plurality of bent waveguides to prolong the cavity length;
the laser chip comprises a plurality of upper passive waveguides distributed up and down, adjacent upper passive waveguides are vertically coupled through a coupler, the upper passive waveguide positioned at the lowermost layer is vertically coupled with the lower passive waveguide through the coupler, the micro-ring reflector is of a closed-loop structure, and the micro-ring reflector is coupled and connected with the upper passive waveguide at the uppermost layer.
2. The narrow linewidth laser chip of claim 1, wherein the active gain waveguide is a semiconductor optical amplifier or a DFB laser.
3. The narrow linewidth laser chip of claim 1, wherein the coupler is a grating assisted vertical coupler or an 1/4 wavelength coupler.
4. The narrow linewidth laser chip of claim 3, wherein a grating of the grating assisted vertical coupler is located in the lower passive waveguide or the upper passive waveguide.
5. The narrow linewidth laser chip of claim 3, wherein wavelength tuning is achieved by thermal tuning or electrical injection of a micro-ring reflector and a grating assisted vertical coupler.
6. The narrow linewidth laser chip of claim 1, wherein the microring reflector comprises a single or multiple microrings.
7. The narrow linewidth laser chip of claim 1, wherein the core of the upper passive waveguide is larger than the core of the lower passive waveguide.
8. A narrow linewidth laser comprising the narrow linewidth laser chip of any one of claims 1 to 7.
9. A method of fabricating a narrow linewidth laser chip according to claim 1, comprising the steps of:
epitaxially growing a lower passive waveguide layer and an SOA active region of the semiconductor optical amplifier on the substrate, and finishing the butt joint of the lower passive waveguide layer and the SOA active region of the semiconductor optical amplifier by adopting a butt joint growth technology;
generating a grating structure in the lower passive waveguide layer;
corroding the lower passive waveguide area and the semiconductor optical amplifier SOA active area to form a semiconductor optical amplifier SOA waveguide structure and a lower passive waveguide structure with a plurality of bent waveguides;
protecting the SOA region of the semiconductor optical amplifier by using a mask, growing an upper passive waveguide layer upwards, and finishing the vertical coupling of two passive waveguides through a grating structure;
and etching the micro-ring structure and the upper passive waveguide structure with a plurality of bent waveguides by adopting an etching technology.
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