CN107565381B - Distributed feedback semiconductor laser device and photonic integrated emission chip module - Google Patents

Abstract

the invention discloses a distributed feedback type semiconductor laser device and a photon integrated emission chip module. The grating of the device is formed by connecting two chirped gratings in series through a gain area without grating, or formed by connecting sampling gratings with chirped sampling periods in series through a gain area without grating; wherein, the electrode of the first chirp grating is composed of three electrodes which are mutually electrically isolated, the corresponding part of the middle electrode of the grating is a phase shift adjusting area, and the corresponding parts of the electrodes at two sides of the grating are side areas; the corresponding portion of the second chirped grating is either a passive region without gain or an active region controlled by one or more electrodes. The invention can continuously adjust the lasing wavelength of the laser to meet the requirements of ITU-T standard by changing the injection current or the proportion of the injection current of the side area and the phase shift adjusting area; when the second chirped grating structure is identical to the first grating structure, the laser has better single-mode characteristics and narrower line width.

Description

Distributed feedback semiconductor laser device and photonic integrated emission chip module

technical field

The invention belongs to the technical field of optoelectronics, and relates to optical fiber communication, photon integration, photoelectric sensing and other photoelectric information processing. The invention relates to a distributed feedback type semiconductor laser device whose wavelength can be finely adjusted within a certain range and a manufacturing method thereof.

Background technique

As the core device of optical fiber communication system, distributed feedback (Distributed Feedback, DFB) semiconductor laser has attracted worldwide attention due to its small size and simple structure. The refractive index of ordinary uniform grating semiconductor laser is modulated periodically and uniformly. On both sides of the Bragg wavelength of this laser, there are two modes with the same resonator loss and the lowest symmetrically, which is called the degeneracy of the two modes. To obtain good single-mode behavior, a quarter-wavelength (λ/4) true phase shift can be introduced at the center of the uniform grating to eliminate mode degeneracy and allow the laser to lase at its Bragg wavelength.

To process this real phase-shifted DFB semiconductor laser, the engraving of the grating needs to be controlled with nanometer precision. At present, only high-precision electronic writing equipment that has undergone special treatment can achieve such processing accuracy. This kind of high-precision electronic writing equipment is expensive, and it takes a lot of time to process and produce this kind of real phase-shifted uniform grating. Therefore, the production cost of real phase-shifted DFB semiconductor lasers is high, and it is not yet capable of large-scale industrial application.

In order to overcome this shortcoming, Professor Chen Xiangfei of Nanjing University proposed the method of replacing the real phase-shifted uniform grating with a uniformly sampled grating with equivalent phase shift to make distributed feedback semiconductor lasers used in optical fiber communication systems. The advantage of this method is that the equivalent phase-shifted sampling grating semiconductor laser with the same lasing performance as the real phase-shifted grating semiconductor laser can be obtained, but the processing accuracy required by the latter is one to two orders of magnitude lower than the former, so it can be greatly reduced. Difficulty and cost of processing.

However, whether it is an equivalent phase-shift sampling grating semiconductor laser or a real phase-shift grating semiconductor laser, due to various accidental factors in the production process, the lasing wavelength of the laser will deviate from the designed ITU-T standard. Therefore, the actual distributed feedback semiconductor laser requires a special tuning device, such as an electric heating device or changing the injection current, to adjust the lasing wavelength of the laser to the ITU-T standard. These special tuning devices will complicate the structure of the laser and degrade its performance.

On the other hand, due to the sharp increase in the demand for the transmission capacity of the optical communication network, the number of channels multiplexed by the Wavelength Division Multiplexing (WDM) system is increasing. This communication system needs to use lasers with different lasing wavelengths as light source. In order to reduce the resulting sharp rise in energy consumption and maintenance costs, photonic integration circuit (PIC) is an inevitable choice. If the electric heating device or the way of changing the injection current is still used to adjust the lasing wavelength of each unit laser to align with the ITU-T standard, then in addition to causing a serious imbalance in the output laser power of each unit laser, it will also cause the laser array structure Extraordinarily complex issue.

In fact, for the multi-wavelength semiconductor laser array made by the equivalent phase-shift sampling grating technology, the single-mode yield of the lasing wavelength of each unit laser can be guaranteed by introducing an equivalent phase shift, while the overall lasing wavelength The drift can be accomplished by adding an electric auxiliary heating device to the laser array chip as a whole. However, the study found that in such a laser array chip, the lasing wavelength of each unit laser fluctuates up and down with the ITU-T standard. Generally, it still often reaches the range of a few tenths of a nanometer, far exceeding that in dense wavelength division multiplexing communication systems. The requirements stipulated by ITU-T. This will lead to a serious drop in the yield of multi-wavelength semiconductor laser array chips.

Contents of the invention

Aiming at the above-mentioned shortcomings of semiconductor lasers in the prior art, the present invention proposes a new distributed feedback semiconductor laser structure.

Technical scheme of the present invention is:

A distributed feedback semiconductor laser device, the grating of the distributed feedback semiconductor laser device is formed by two chirped gratings connected in series through a gain region without a grating, or a sampling grating chirped by a sampling period (which is selected as the excitation The ±1-level sub-grating of the radiation channel is still a linear chirped grating) connected in series through the gain region without grating; the electrode of the first chirped grating is composed of three mutually electrically isolated electrodes, and the middle electrode of the grating corresponds to Part of it is a phase shift adjustment area, and the corresponding part of the electrodes on both sides is a side area; the corresponding part of the second chirped grating is a passive area without gain, or an active area controlled by one or more electrodes;

As a further improvement of the present invention, the two side regions of the first chirped grating have the same length;

As a further improvement of the present invention, the two side region electrodes of the first chirped grating can be connected together with wires to form the same side region electrode;

As a further improvement of the present invention, the second chirped grating can be exactly the same chirped grating as the first chirped grating;

As another improvement of the present invention, the corresponding part of the second chirped grating can be composed of three active regions controlled by mutually electrically isolated electrodes, that is, two side regions and an intermediate phase shift adjustment region;

As a further improvement of the present invention, the two side regions and the middle phase shift adjustment region corresponding to the second chirped grating are exactly the same as the first chirped grating;

As a further improvement of the present invention, the two side regions corresponding to the second chirped grating can be connected together with a wire to form the same side region electrode;

As a further improvement of the present invention, the electrodes of the four side region electrodes and the two intermediate phase shift adjustment regions of the laser of the present invention can be connected together with wires to form the total side region electrodes and the total phase shift adjustment region electrodes ;

The present invention also provides a distributed feedback semiconductor laser monolithic integrated array, the distributed feedback semiconductor laser monolithic integrated array is composed of the above-mentioned distributed feedback semiconductor laser device.

The present invention also provides a photonic integrated emission chip module, which consists of a laser monitor array, the above-mentioned semiconductor laser monolithic integrated array, a modulator array, a power equalizer array and a multiplexer, through selective area epitaxial growth or docking growth technology, sequentially The growth is integrated on the same epitaxial wafer.

The beneficial effects of the present invention are:

When the laser of the present invention is working normally, the first chirped grating of the laser can be continuously adjusted to lasing at different grating periods by changing the injection current in the side region and the intermediate phase shift adjustment region of the first chirped grating. Therefore, the lasing wavelength of the laser can be finely adjusted continuously. If the total injection current of the laser remains unchanged, the lasing wavelength of the laser can be finely regulated by changing the ratio of the injection current in the side region and the phase shift adjustment region, and the laser maintains a similar threshold value and lasing output power.

If the part corresponding to the second chirped grating is a passive feedback area or an active feedback area controlled by a single electrode, then the second chirped grating acts as a wide-spectrum reflector, which can convert the laser generated by this laser from the first The outer end face of a chirped grating is reflected, which greatly improves the laser output efficiency of the laser. At the same time, if the two chirped gratings of the laser are sampling gratings whose sampling period is linearly chirped, compared with linearly chirped gratings, while obtaining the same reflective (or transmissive) performance, the impact on the gratings is greatly reduced. Machining accuracy is required, so its manufacturing cost can be significantly reduced.

If the second chirped grating is the same three-electrode grating structure as the first chirped grating, when the three electrodes of the two gratings are all connected with the same current, due to the selection of the laser by the two chirped gratings The frequency and feedback functions are exactly the same, so the frequency selection effect of such a grating on the generated laser has been further strengthened, so the output laser has better single-mode characteristics, and the output laser has a narrower linewidth.

Description of drawings

Fig. 1 is the grating structure schematic diagram of the laser of the present invention when the second chirped grating is a passive grating;

Fig. 2 is the grating structure diagram of the laser of the present invention when the second chirped grating is an active grating controlled by a single electrode;

Fig. 3 is the grating structure diagram of the laser of the present invention when the second chirped grating is an active grating controlled by three electrodes;

Fig. 4 is a schematic diagram of the active region structure of the first chirped grating of the distributed feedback semiconductor laser of the present invention;

In the figure: 1. P electrode; 2. Ohmic contact layer; 3. P-InP layer; 4. Grating layer; 5. Upper confinement layer; 6. Active layer; 7. Lower confinement layer; 8. n-InP buffer layer; 9, n-InP substrate; 10, n electrode.

Fig. 5 is a schematic diagram of the functional structure of a multi-wavelength photonic integrated emission chip.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Embodiment one

This embodiment provides a distributed feedback semiconductor laser device, which is formed by connecting two chirped gratings in series through a gain region without a grating, or by connecting two sampling gratings with a sampling period chirped in series through a gain region without a grating ; The electrode of the first chirped grating is composed of three electrodes electrically isolated from each other, the corresponding part of the middle electrode of the grating is the phase shift adjustment area, and the corresponding part of the electrodes on both sides of the grating is the side area; the second chirped grating The corresponding portion of the grating is a passive region with no gain (as shown in Figure 1), or an active region controlled by one (as shown in Figure 2) or multiple electrodes (as shown in Figure 3). The structure of the active region of the first chirped grating of the distributed feedback semiconductor laser of the present invention is shown in FIG. 4 .

In this embodiment: the two side region electrodes of the first chirped grating can be connected together by wires to form the same side region electrode; the two side region electrodes of the first chirped grating can have the same length.

In this embodiment, the second chirped grating and the first chirped grating can be exactly the same chirped grating, and the corresponding electrodes and structures are also the same, and both have the same two side regions and a phase shift The composition of the adjustment area; the two side area electrodes of the second chirped grating can be connected together by wires to form the same side area electrode.

In this embodiment: the four side region electrodes of the two chirped gratings can be connected together by wires to form the same side region electrodes, and the two phase shift adjustment region electrodes of the two chirped gratings can be connected by wires together to form the same phase shift adjustment region electrodes.

In this embodiment, the electrodes of the adjacent phase shift adjustment regions, side regions, gain regions, and the second chirped grating can be separated by a certain distance, or by implanting helium ions, or by etching electrical isolation grooves, etc. way of galvanic isolation.

The realization principle of the fine adjustment of the lasing wavelength of the distributed feedback semiconductor laser device of the present invention is as follows:

Here, the first chirped grating in Figure 2 corresponds to the two side regions and the middle phase shift adjustment region with the same length, and the corresponding position of the second chirped grating is the active region controlled by a single electrode, and the adjacent middle phase The principle of finely adjusting the lasing wavelength of the distributed feedback semiconductor laser device of the present invention will be described by using the case where the electrodes of the shift adjustment region, the side region and the gain region are electrically isolated from each other.

Since each linear chirped grating can be regarded as a superposition of uniform gratings with continuously changing grating periods, when the injection current in the laser of the present invention is higher than the threshold value, if the side region and the middle phase shift of the first chirped grating are adjusted By injecting currents of different magnitudes into the region electrodes, different phase shifts can be introduced into the uniform gratings of different periods, which makes the lasing wavelength have the lowest threshold value at a certain period position of the grating, so this laser can produce lasers of this wavelength. laser. When changing the electrode injection current ratio (size) of the side region of the laser chirped grating and the middle phase shift adjustment region, the linear chirped grating can be induced to generate lasing at different grating period positions, and then the lasing wavelength of the laser can be finely adjusted .

Embodiment two

This embodiment provides a monolithic integrated array of distributed feedback semiconductor lasers, which is composed of the distributed feedback semiconductor laser device described in Embodiment 1.

The present embodiment also provides a photonic integrated emission chip module (as shown in Figure 5), which consists of a laser monitor array, the above-mentioned distributed feedback semiconductor laser monolithic integrated array, modulator array, power equalizer array and multiplexing Devices are sequentially grown and integrated on the same epitaxial wafer through selective area epitaxial growth or butt growth technology.

Embodiment three

This embodiment adopts a manufacturing method of a distributed feedback semiconductor laser and an array thereof, the steps of which are as follows:

(1) Epitaxial n-type InP buffer layer, 100nm thick undoped lattice-matched InGaAsP lower confinement layer, strained InGaAsP multiple quantum wells and 100nm thick p-type lattice-matched InGaAsP upper confinement layer on n-type InP substrate material Floor;

(2) The production method of the grating:

①The manufacturing method of the linear chirped sampling grating, using the method of double-beam holographic interference to expose through the sampling photoresist, transfer the chirped sampling grating pattern to the photoresist on the upper confinement layer, and then perform material etching, A required chirped sampling grating structure is formed on the upper part of the upper confinement layer.

②The manufacturing method of the linear chirped grating, using the method of high-precision electron beam writing, the linear chirped grating is recorded on the photoresist on the upper confinement layer, and then the material is etched to form the required chirped grating structure.

(3) After the grating is fabricated, the p-type InP layer and the p-type InGaAs ohmic contact layer are grown by secondary epitaxy. After the epitaxial growth is completed, the fabrication of the ridge waveguide is completed by using ordinary photolithography combined with chemical wet etching;

( ₄ ) Deposit a layer of 300nm thick SiO layer or organic BCB insulating layer around the ridge waveguide with plasma enhanced chemical vapor deposition process;

(5) Then use photolithography and chemical wet etching to remove the _SiO2 layer or organic BCB insulating layer above the laser ridge waveguide to expose its InGaAs ohmic contact layer;

(6) Using the method of magnetron sputtering, 100nm thick Ti and 400nm thick Au are respectively plated on the entire laser structure, combined with photolithography and chemical wet etching, the ohmic contact of InGaAs is exposed above the ridges A Ti-Au metal P electrode is formed on the layer;

(7) After thinning the entire laser wafer to 150 μm, a 500 nm-thick Au-Ge-Ni alloy is evaporated below the base material as the n-electrode;

(8) Then connect and lead each P electrode of the obtained laser chip side region, phase shift adjustment region, gain region and the second chirped grating with a gold wire to form each side region, phase shift adjustment region, and gain region and the P electrode of the second chirped grating; the simplified solution is that the P electrodes of all side regions of the laser chip are connected together with gold wires to become the total side region P electrodes, and the P electrodes of all phase shift adjustment regions are used The gold wires are connected together and lead out to become the P electrode of the overall phase shift adjustment area.

The manufacture of the multi-wavelength laser array chip composed of the unit distributed feedback semiconductor laser of the present invention, compared with the single wavelength distributed feedback semiconductor laser, only needs to make unused linear chirped gratings for each unit laser, and other The making process is exactly the same.

In summary, the grating of the distributed feedback type semiconductor laser device of the present invention consists of two linear chirped gratings (also can be the sampling grating of sampling cycle linear chirp, and the ± 1st order sub-grating that it is selected as the lasing channel is also linear Chirped grating) is connected in series through the gain area without grating; the electrode of the first grating is composed of three mutually isolated electrodes, the corresponding part of the middle electrode of the grating is the phase shift adjustment area, and the corresponding part of the electrodes on both sides of the grating is is the side region; the corresponding part of the second chirped grating can be a passive region without gain, or an active region controlled by one or three electrodes; the adjacent phase shift adjustment region, side region, The electrodes of the gain region and the second chirped grating are electrically isolated in some way. When different current densities are injected into the side region and phase shift adjustment region of the first chirped grating, a current-controlled real phase shift (or equivalent phase shift) can be introduced at a specific period of the corresponding chirped grating. By changing the injection current in the side region and phase shift adjustment region, the first chirped grating of the laser can be continuously adjusted to lasing at different grating periods, so that the lasing wavelength of the laser can be continuously adjusted to meet the requirements of ITU-T standards . Under the condition that the total operating current of the laser remains constant, the lasing wavelength of the laser can be finely regulated by changing the injection current ratio of the side region and the phase shift adjustment region, and the laser maintains a similar threshold value and lasing output power . At the same time, the second chirped grating acts as a broad-spectrum reflector, which can reflect most of the laser light generated by this laser from the outer end face of the first grating. Or, when the second chirped grating structure is exactly the same three-electrode grating junction as the first grating, when the three electrodes of the two chirped gratings are connected with the same current, the laser device will , the lasing laser has better single-mode characteristics and narrower linewidth.

The above is only the preferred mode of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Be the protection scope of the present invention.

Claims (9)

1. Distributed feedback type semiconductor laser device, it is characterized in that: the grating of described device is formed by two chirped gratings through the gain region without grating in series, or is by the sampling grating of two sampling period chirps through the gain region without grating The gain area is connected in series; the electrode of the first chirped grating is composed of three mutually electrically isolated electrodes, the corresponding part of the middle electrode of the grating is the phase shift adjustment area, and the corresponding part of the electrodes on both sides is the side area; The corresponding part of the second chirped grating is a passive area without gain, or an active area controlled by one or more electrodes; by changing the side area of the laser chirped grating and the middle phase shift adjustment area electrode injection current Ratio, triggering the linear chirped grating to generate lasing at different grating period positions, and then fine-tuning the lasing wavelength of the laser. 2. The distributed feedback semiconductor laser device according to claim 1, characterized in that: the two side region electrodes of the first chirped grating are connected together by wires to form the same side region electrode. 3. The distributed feedback semiconductor laser device according to claim 1, characterized in that: the two side regions of the first chirped grating have the same length. 4. The distributed feedback semiconductor laser device according to claim 1, characterized in that: the second chirped grating is the same chirped grating as the first chirped grating, and its corresponding electrodes and structures are also the same, Both are composed of identical two side regions and a phase shift adjustment region. 5. The distributed feedback semiconductor laser device according to claim 4, characterized in that: the two side region electrodes of the second chirped grating are connected together by wires to form the same side region electrode. 6. The distributed feedback semiconductor laser device according to claim 4, characterized in that: four side region electrodes of two chirped gratings are connected together with wires to form the same side region electrodes, and two chirped gratings The two phase shift adjustment area electrodes of the grating are connected together by wires to form the same phase shift adjustment area electrode. 7. The distributed feedback semiconductor laser device according to claim 1, characterized in that: each electrode of the adjacent phase shift adjustment region, side region, gain region and the second chirped grating passes through a certain distance, Either by implanting helium ions, or by etching an electrical isolation trench. 8. A monolithic integrated array of distributed feedback semiconductor lasers, characterized in that it is composed of the distributed feedback semiconductor laser device according to any one of claims 1 to 7. 9. A photonic integrated emission chip module, characterized in that: by laser monitor array, distributed feedback type semiconductor laser monolithic integrated array, modulator array, power equalizer array and multiplexer according to claim 8, through Selected area epitaxial growth or docking growth technology, which is sequentially grown and integrated on the same epitaxial wafer.