CN112864799A

CN112864799A - Branch cavity semiconductor tunable laser and preparation method thereof

Info

Publication number: CN112864799A
Application number: CN202011643736.2A
Authority: CN
Inventors: 郑婉华; 杜方岭; 王海玲; 王明金
Original assignee: Institute of Semiconductors of CAS
Current assignee: Institute of Semiconductors of CAS
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2021-05-28
Anticipated expiration: 2040-12-31
Also published as: CN112864799B

Abstract

The invention provides a semiconductor tunable laser with a branch cavity, which comprises: a first grating (1) having a first period; at least one second grating (5) and one third grating (7), each having a second period and a third period, located on a branch of one end of the first grating (1); a multimode interferometer (4) for connecting the first grating (1) and the at least one second grating (5) and the third grating (7); when the first grating (1) and the second grating (5) are subjected to mode selection, laser in a first wavelength range is obtained through a multi-mode interferometer (4); when the first grating (1) and the third grating (7) are subjected to mode selection, laser in a second wavelength range is obtained through the multi-mode interferometer (4); the first wavelength range is continuous with the second wavelength range. The invention can realize the connection of multiple tuning ranges by regional power injection and selective regional power injection, thereby realizing the output of a large wavelength range.

Description

Branch cavity semiconductor tunable laser and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductor laser, in particular to a branch cavity semiconductor tunable laser and a preparation method thereof.

Background

With the rapid development of the information age, a Wavelength Division Multiplexing optical network (WDM) is more and more important in modern society, and is an important path for solving the rapid increase of data. In WDM systems, a small number of tunable semiconductor lasers can be used to replace a large number of fixed wavelength semiconductor lasers, allowing a significant cost reduction. Tunable semiconductor lasers play an indispensable role in WDM systems. However, the mainstream of the currently commercially available tunable semiconductor Laser in the society is a traditional structure based on a Sampled Grating (SG-DBR) or Distributed Feedback Laser (DFB) array, which requires high-precision lithography such as electron beam exposure or holographic exposure and an active/passive integration technology based on multiple epitaxy, so that the cost of the tunable Laser is still a high problem so far, and a low-cost and large-range tunable Laser is still a scientific problem.

Disclosure of Invention

Technical problem to be solved

Aiming at the problems, the invention provides a branch cavity semiconductor tunable laser and a preparation method thereof, which are used for at least partially solving the technical problems of small tunable range, high cost and the like of the traditional tunable laser.

(II) technical scheme

One aspect of the present invention provides a split cavity semiconductor tunable laser, including: a first grating 1 having a first period; at least one second grating 5 and a third grating 7 having a second period and a third period, respectively, which are located on a branch of one end of the first grating 1; a multimode interferometer 4 for connecting the first grating 1 and at least one second grating 5 and a third grating 7; when the first grating 1 and the second grating 5 are in mode selection, laser in a first wavelength range is obtained by utilizing a vernier effect through the multi-mode interferometer 4; when the first grating 1 and the third grating 7 are in mode selection, laser in a second wavelength range is obtained by utilizing a vernier effect through the multi-mode interferometer 4; the first wavelength range is continuous with the second wavelength range.

Further, the laser further comprises, between the first grating 1 and the multimode interferometer 4: a phase adjustment region 2, on which there is electrical injection, for fine tuning of the phase.

Further, the laser further comprises, between the first grating 1 and the multimode interferometer 4: and a gain region 3 with electrical injection thereon for providing gain to the entire Y-cavity semiconductor tunable laser.

Further, the first grating 1, the phase adjusting region 2, the gain region 3, the at least one second grating 5 and the third grating 7 are electrically isolated from each other, so that partitioned electric injection is realized.

Furthermore, the whole laser is active, the material is a semiconductor epitaxial material, and the pumping mode is electric injection.

Further, the connection between the multi-mode interferometer 4 and the at least one second grating 5 and the third grating 7 is an arc waveguide or a straight waveguide.

Further, the multimode interferometer 4 is a multimode interference self-imaging coupling region.

The invention also provides a preparation method of the semiconductor tunable laser with the branch cavity, which comprises the following steps: s1, growing a silicon dioxide protective layer on the epitaxial wafer; s2, transferring the patterns to the epitaxial wafer in sequence by multiple times of photoetching or etching; s3, removing residual silicon dioxide, regrowing silicon dioxide to be used as an insulating layer, photoetching and etching the opening of the power injection window and growing P-surface metal; s4, photoetching and corroding metal to pattern electrodes to form electric isolation; s5, thinning, grinding and polishing the back of the epitaxial wafer; and S6, growing N-side metal on the back of the epitaxial wafer, and scribing and cleaving to obtain the branch cavity semiconductor tunable laser.

(III) advantageous effects

According to the branch cavity semiconductor tunable laser and the preparation method thereof, the two lasers are compounded together through the subarea power injection and the selective area power up, so that the respective tuning ranges of the two lasers can be connected together, the large-range tuning is realized on one laser, the design does not need secondary epitaxy, the design can be realized only by using a common photoetching technology, the manufacturing cost can be greatly reduced, and the experiment process is simplified.

Drawings

Fig. 1 schematically shows a schematic structural view of a branch cavity semiconductor tunable laser according to an embodiment of the present invention;

FIG. 2 schematically illustrates an optical field of light propagating in a non-gain InP waveguide according to an embodiment of the present invention;

FIG. 3 schematically illustrates a simulated structure of a multi-mode interferometer (MMI) according to an embodiment of the invention;

FIG. 4 schematically illustrates a light field propagation diagram for a multimode interferometer according to an embodiment of the invention;

FIG. 5 is a schematic diagram showing the relationship between the length of a multi-mode interferometer and the output power of any port according to an embodiment of the present invention;

FIG. 6 is a schematic diagram showing the relationship between the width of a multi-mode interferometer and the output power of any port according to an embodiment of the present invention;

FIG. 7 is a schematic diagram showing two grating reflection spectra vernier with periods of 55um and 65um, respectively, according to an embodiment of the present invention;

FIG. 8 is a schematic diagram showing two grating reflection spectra vernier with periods of 55um and 60um, respectively, according to an embodiment of the present invention;

fig. 9 schematically illustrates a flow diagram of a method of fabricating a branched cavity semiconductor tunable laser according to an embodiment of the present invention;

description of reference numerals:

1-a common grating zone; 8-an active region;

2-a phase adjustment zone; 9-gain waveguide P-type epitaxy;

3-a gain region; w 1-Ridge Width;

4-MMI region; w2-MMI region width;

5-a first grating zone; w3-MMI region length;

6-gain waveguide N-type epitaxy; w4-MMI region taper;

7-a second grating zone; w 5-gain region length.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.

An embodiment of the present disclosure provides a split cavity semiconductor tunable laser, please refer to fig. 1, including: a first grating 1 having a first period; at least one second grating 5 and a third grating 7 having a second period and a third period, respectively, which are located on a branch of one end of the first grating 1; a multimode interferometer 4 for connecting the first grating 1 and at least one second grating 5 and a third grating 7; when the first grating 1 and the second grating 5 are in mode selection, the mode selection is carried out by utilizing a vernier effect through the multi-mode interferometer 4 to obtain laser in a first wavelength range; when the first grating 1 and the third grating 7 are in mode selection, the multimode interferometer 4 is used for selecting the mode by utilizing the vernier effect to obtain laser in a second wavelength range; the first wavelength range is continuous with the second wavelength range.

Fig. 1 provides a Y-cavity semiconductor tunable laser, comprising: three sections of surface gratings with different periods are respectively a first grating 1 in a public area, a second grating 5 in a non-public area and a third grating 7. The first grating 1 is respectively combined with the second grating 5 and the third grating 7 to form a vernier effect for mode selection. When the first grating 1, the phase adjusting area 2, the gain area 3 and the multimode interferometer 4 are electrified, one of the second grating 5 and the third grating 7 is electrified in sequence (the second grating 5 and the third grating 7 cannot be electrified simultaneously), and two different tuning ranges which are connected end to end can be obtained by carefully designing the period of the three sections of surface gratings, so that a wavelength output in a large range can be obtained at a common output end.

When the semiconductor tunable laser is tested, the surface gratings with different periods need to be selectively powered up. The first grating 1 must be powered up, the second grating 5 and the third grating 7 select one to be powered up, after the test is finished, the other grating is powered up, and the first grating and the second grating cannot be powered up simultaneously. And finally, the wavelength tuning range of the Y-type cavity semiconductor tunable laser is the superposition of the two wavelength tuning ranges.

It should be noted that the semiconductor tunable laser includes not only a Y-cavity but also other branch cavities such as a claw cavity, that is, the non-common region includes not only the second grating 5 and the third grating 7, but also the fourth grating, the fifth grating, and so on. When the non-public area of the semiconductor tunable laser comprises more than two gratings, the first grating 1 is combined with the gratings in the non-public area in sequence to form a vernier effect for mode selection, so that a plurality of different tuning ranges which are connected end to end are obtained, and a large wavelength tuning can be obtained. The realization method comprises the steps of electrifying one of the gratings in the non-public area, then electrifying other gratings in the non-public area in sequence to respectively obtain lasers in different wavelength ranges, and designing the period of a plurality of surface gratings to realize the continuity of different wavelength ranges.

On the basis of the above embodiment, the laser further includes, between the first grating 1 and the multimode interferometer 4: a phase adjustment region 2, on which there is electrical injection, for fine tuning of the phase.

The process of fine tuning of the phase is mainly achieved by a precise sweep of the injection current for that region.

On the basis of the above embodiment, the laser further includes, between the first grating 1 and the multimode interferometer 4: and a gain region 3 with electrical injection thereon for providing gain to the entire Y-cavity semiconductor tunable laser.

The material of the gain region 3 consists essentially of five quantum wells of AlGaInAs, which provide gain to the entire laser by electrical injection.

On the basis of the above embodiment, the first grating 1, the phase adjusting region 2, the gain region 3, the at least one second grating 5 and the third grating 7 are electrically isolated from each other to realize the partitioned injection.

The electrical isolation may be performed by using a slot with a certain etching depth, or by using ion implantation, and in this embodiment, the electrical isolation is performed by etching the slot. The subarea power injection is used for realizing independent control of each area, so that coordination among the areas is convenient, and wavelength tuning in a large range can be realized.

On the basis of the above embodiment, the laser is entirely active, the material is a semiconductor epitaxial material, and the pumping mode is electrical injection.

The laser is integrally active, so that power loss caused by electrical isolation is compensated, the power of the whole laser is improved, the semiconductor epitaxial material has the advantages of wide gain range and low threshold current, the pumping mode of electrical injection is convenient to use, and high-precision control is easy to realize.

On the basis of the above embodiment, the connection between the multimode interferometer 4 and the at least one second grating 5 and the third grating 7 is an arc waveguide or a straight waveguide.

As shown in fig. 1, a 1 × 2 MMI region of the multi-mode interferometer 4 is used to connect the left common region and the right two gratings, and the connection between the MMI region and the second grating 5 and the third grating 7 is an arc, but not limited to an arc, and for example, a straight waveguide may be used for connection. The arc-shaped waveguide can increase the distance between the two waveguides and prevent the coupling between the waveguides; the straight waveguide has the technical effect of relatively low loss and can be selected according to actual requirements.

On the basis of the above embodiment, the size range of the multi-mode interferometer 4 is determined according to the used material and the required wavelength, for example, the width size range of the multi-mode interferometer 4 is 11-13um and the length size range is 190-210um according to the used material and the target wavelength.

The specific dimensions of the MMI region are determined by the magnitude of the injection current, depending on whether or not the electrical injection is to be performed. By sizing the MMI, a 1 × 2 optical path and minimal insertion loss can be achieved.

On the basis of the above embodiment, the multimode interferometer 4 is a multimode interference self-imaging coupling region.

The main working process of the multimode interferometer comprises the following steps: light entering the MMI from the common port can be split into multiple beams and enter different branches by multimode interference inside the MMI under proper dimensioning.

On the basis of the above-described embodiments, the period ranges of the first grating 1, the second grating 5 and the third grating 7 need to be determined according to the used material and the desired wavelength, for example, the period range of the first grating 1 is 55um, and the period range of at least one of the second grating 5 and the third grating 7 is 65um and 60 um.

The periods of the three different surface gratings are determined according to the wavelength range to be excited by the laser, and the designed periods of the three surface gratings can enable two wavelength tuning ranges to be connected together. The period of the first grating 1 is different from the periods of the second grating 5 and the third grating 7, so that different wavelength intervals can be realized, and the vernier effect can be used. In addition, the etching depth, etching width, periodicity, ridge width and ridge etching depth of the surface grating are all determined by the performance of the laser to be realized.

Another embodiment of the present disclosure provides a method for manufacturing a branch cavity semiconductor tunable laser according to the foregoing description, with reference to fig. 9, including: s1, growing a silicon dioxide protective layer on the epitaxial wafer; s2, transferring the patterns to the epitaxial wafer in sequence by multiple times of photoetching or etching; s3, removing residual silicon dioxide, regrowing silicon dioxide to be used as an insulating layer, photoetching and etching the opening of the power injection window and growing P-surface metal; s4, photoetching and corroding metal to pattern electrodes to form electric isolation; s5, thinning, grinding and polishing the back of the epitaxial wafer; and S6, growing N-side metal on the back of the epitaxial wafer, and scribing and cleaving to obtain the branch cavity semiconductor tunable laser.

The laser does not need secondary epitaxy and electron beam lithography, and can be realized by using a common photoelectron process. The main process comprises the following steps: growing silicon dioxide as a mask, and transferring the patterns to the epitaxial wafer in sequence by using a common photoetching and etching technology (according to the actual structure of the laser, the steps of growing the silicon dioxide, photoetching and etching need to be repeated for many times); removing residual silicon dioxide, regrowing silicon dioxide to be used as an insulating layer, opening an electric injection window through common photoetching and etching technologies and growing P-surface metal; performing common photoetching, and corroding metal to pattern electrodes to form electric isolation; thinning, grinding and polishing the back; and finally growing N-face metal.

When the laser is tested, the common grating, the gain region, the phase modulation region and the MMI region of the left common region are electrified (in fact, the MMI region can be electrified or not electrified, the power of the laser can be increased by electrifying, but the designed size is different from that under the condition of no electrifying). For the second grating 5 and the third grating 7 at the right end, one is electrified, and the other is not electrified. When light enters the non-injection grating area, no gain is lost, and the light can be consumed completely in the transmission process without forming feedback by designing enough length, so that the non-injection grating cannot generate effective mode selection. Therefore, when the charged common grating and the first grating or the second grating carry out vernier effect mode selection, the influence of the other grating is avoided. For example, when the common grating, the gain region, the phase modulation region, the MMI region and the first grating are subjected to power injection, the power injection of the second grating is not performed, after the test is finished, the power injection of the first grating is stopped, the power injection of the second grating is performed instead, and the test is continued. Therefore, the connection of two wavelength tuning ranges obtained by vernier effect can be realized by finely designing the period of three sections of surface gratings, so that a large-range continuous wavelength output is realized at a public end.

The present invention relates to a tunable laser of a semiconductor with a branch cavity and a method for manufacturing the same.

In a Y-cavity tunable semiconductor laser structure, an embodiment uses w2 ═ 190um, and w3 ═ 12.5 um. Fig. 2 is a graph of the optical field of light propagating in an InP waveguide without gain, where the light is gradually absorbed and lost, and propagates as far as about 200 um. Fig. 3 is a simulation structure diagram of the MMI used in the present embodiment. The structure simulation result is as shown in fig. 4, 55um is adopted in the period of the first grating 1, 60um is adopted in the period of the second grating 5, 65um is adopted in the period of the third grating 7, and the width of the slot in the grating area is 1-1.1 um. When the first grating 1, the phase adjusting region 2, the gain region 3 and the second grating 5 are charged and the third grating 7 is not charged, the light entering the third grating 7 is completely lost and feedback cannot be formed. Therefore, only two sections of gratings 1 and 5 play a role in selecting the mode, a single longitudinal mode can be selected by utilizing the vernier caliper effect, the single longitudinal modes with different wavelengths can be subjected to lasing by changing the currents of the first grating 1 and the second grating 5 according to the vernier effect, and the tuning range of the two sections of gratings in the period theory is larger than 36 nm. After the current scanning is completed, the power-up area is adjusted, the first grating 1, the phase adjusting area 2, the gain area 3 and the third grating 7 are subjected to electric injection, the second grating area 5 is not subjected to electric injection, and similarly, the light entering the second grating area 5 is completely lost, and feedback cannot be formed. Only two sections of gratings of the first grating region 1 and the third grating region 7 play a role in selecting a single longitudinal mode, a single longitudinal mode can be selected by utilizing a vernier caliper effect, the single longitudinal modes with different wavelengths can be subjected to lasing by changing the currents of the first grating region 1 and the third grating region 7 according to the vernier effect, and the used tuning range on the period theory is larger than 36 nm. FIG. 5 is a graph showing the relationship between the length of the MMI used and the output power of any port in the present embodiment; fig. 6 shows the relationship between the width of the MMI used and the output power of any port in this embodiment.

As can be seen from fig. 7 and 8, when the first grating 1 and the second grating region 5 perform the vernier effect, the coincidence peak of the initial position is about 1530 um; when the first grating 1 and the third grating region 7 perform a vernier effect, the coincidence peak of the initial positions is about 1560 um. When the first grating 1 and the second grating area 5 are scanned with current, the tuning position can be approximately 1555, and then the first grating 1 and the third grating area 7 are scanned with current, so that the tuning ranges of the first grating 1 and the third grating area are combined end to end, and thus, two sections of different wavelength tuning ranges are connected together, thereby greatly increasing the tunable range of light output from the first grating 1 end, and realizing the tuning in a large range. In this embodiment, no power is applied to the MMI region.

The preparation method of the Y-shaped cavity tunable semiconductor laser is explained by taking a preparation method of a semiconductor tunable laser of AlGaInP multi-quantum well with a wave band of 1.55um based on micro-nano periodic structure mode selection as an example. The embodiment comprises the following steps:

in step S1, a silicon dioxide passivation layer is grown to a thickness determined by the etching depth, and the silicon dioxide used in this embodiment is 300nm thick.

Step S2, finally transferring all patterns onto the epitaxial wafer by multiple photolithography and etching techniques, wherein step S1 is repeated multiple times, and the residual silicon dioxide is removed before each repetition.

And step S3, using silicon dioxide as a protective layer, and opening an electrode window on the ridge through photoetching and etching technologies.

And step S4, growing P-type metal, using photoresist as a protective layer, developing, corroding the metal, and patterning the electrode.

Step S5, thinning and polishing the back InP.

Step S6, an n-plane metal is grown and rapid thermal annealing is performed to alloy form ohmic contacts. And (4) scribing, cleaving, and performing tubulation test.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A split-cavity semiconductor tunable laser, comprising:

a first grating (1) having a first period;

at least one second grating (5) and one third grating (7), each having a second period and a third period, located on a branch of one end of the first grating (1);

a multimode interferometer (4) for connecting the first grating (1) and the at least one second grating (5) and the third grating (7);

when the first grating (1) and the second grating (5) are in mode selection, laser in a first wavelength range is obtained through the multi-mode interferometer (4); when the first grating (1) and the third grating (7) are in mode selection, laser in a second wavelength range is obtained through the multi-mode interferometer (4); the first wavelength range is continuous with the second wavelength range.

2. The branch cavity semiconductor tunable laser according to claim 1, further comprising between the first grating (1) and a multimode interferometer (4):

a phase adjustment region (2) with electrical injection for fine tuning of the phase.

3. The branch cavity semiconductor tunable laser according to claim 2, further comprising between the first grating (1) and a multimode interferometer (4):

and a gain region (3) with electrical injection thereon for providing gain to the entire Y-cavity semiconductor tunable laser.

4. The branch cavity semiconductor tunable laser according to claim 2, wherein the first grating (1), the phase adjustment region (2), the gain region (3), the at least one second grating (5) and the third grating (7) are electrically isolated from each other to realize partitioned injection.

5. The tunable laser of claim 2, wherein the laser is active as a whole, the material is semiconductor epitaxial material, and the pumping means is electrical injection.

6. The branch cavity semiconductor tunable laser according to claim 1, wherein the junction of the multimode interferometer (4) and the at least one second (5) and third (7) gratings is an arc waveguide or a straight waveguide.

7. The branch cavity semiconductor tunable laser according to claim 6, wherein the multimode interferometer (4) is a multimode interferometric self-imaging coupling region.

8. A method for preparing the branch cavity semiconductor tunable laser according to any one of claims 1 to 7, comprising the following steps:

s1, growing a silicon dioxide protective layer on the epitaxial wafer;

s2, transferring the patterns to the epitaxial wafer in sequence by multiple times of photoetching or etching;

s3, removing residual silicon dioxide, regrowing silicon dioxide to be used as an insulating layer, photoetching and etching the opening of the power injection window and growing P-surface metal;

s4, photoetching and corroding metal to pattern electrodes to form electric isolation;

s5, thinning, grinding and polishing the back of the epitaxial wafer;

and S6, growing N-side metal on the back surface of the epitaxial wafer, and scribing and cleaving to obtain the branch cavity semiconductor tunable laser.