A semiconductor laser that realizes multi-wavelength lasing with a single device

Abstract

The present invention discloses a semiconductor laser that can achieve multi-wavelength lasing with a single device, which includes a laser region and an SOA region integrated at the light-emitting end of the laser. Both the laser region and the SOA region successively include a positive electrode layer, an electrical isolation layer, a grating layer, an active layer, a buffer layer, and a negative electrode layer. The grating layer is divided into a grating distribution region and a grating blank region, and the grating of the grating layer is obtained by superimposing a seed grating, a first sampling grating, and a second sampling grating. The positive electrode layer is separated by the electrical isolation layer into a grating electrode and a blank electrode. The grating electrode provides pump current for the grating distribution region, and the blank electrode provides transparent current for the grating blank region. By applying voltage to the SOA region, additional gain is provided for the laser, thereby increasing the output power of the laser region. The present invention meets the wavelength requirements of WDM, and can effectively solve the problems existing in the existing multi-wavelength semiconductor laser arrays, such as complex structure, difficult integration, high additional power consumption, inconvenience for use in dense wavelength division multiplexing systems, and special considerations required for realizing fast switching between different lasers or channels.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic technology, and particularly relates to a semiconductor laser that realizes multi-wavelength lasing with a single device. Background Art

[0002] At present, with the advent of the 5G era, wavelength division multiplexing technology is widely used in the field of optical communication, which poses higher requirements for light sources. A low-cost and high-performance monolithic integrated multi-wavelength laser has become the key. There are already various integrated multi-wavelength lasers on the market, such as tunable distributed Bragg reflector laser arrays, microdisk laser arrays, vertical cavity surface emitting laser arrays, parallel distributed feedback (DFB) laser arrays, and series DFB lasers.

[0003] Due to its characteristics such as stable mode, easy single-mode operation, and easy integration with other photonic devices, the DFB laser is considered an ideal light source for wavelength division multiplexing technology. The parallel DFB laser array is favored for its advantages in multi-wavelength applications. However, with the increase in the number of application wavelengths, it is inevitable to increase wavelength combiners such as multimode interferometers and arrayed waveguide gratings, which not only introduces additional losses but also increases the size of the device. Although the series DFB laser array can effectively reduce the use of wavelength combiners, in order to avoid mutual interference between series gratings, the wavelength interval between adjacent lasers needs to be taken very large, which is not conducive to use in a dense wavelength division multiplexing system. Summary of the Invention

[0004] The present invention provides a semiconductor laser that realizes multi-wavelength lasing with a single device, which can meet the wavelength requirements of WDM, and can also effectively solve the problems existing in existing multi-wavelength semiconductor laser arrays, such as complex structure, difficult integration, large additional power consumption, inconvenient for use in a dense wavelength division multiplexing system, and special considerations are required to achieve fast switching between different lasers or channels.

[0005] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A semiconductor laser that realizes multi-wavelength lasing with a single device includes a laser region and an SOA region integrated at the light output end of the laser;

[0007] Both the laser region and the SOA region sequentially include a positive electrode layer, electrical isolation, a grating layer, an active layer, a buffer layer, and a negative electrode layer;

[0008] The grating layer is divided into a grating distribution region and a grating blank region, and the grating of the grating layer is obtained by superimposing a seed grating, a first sampled grating, and a second sampled grating;

[0009] The positive electrode layer is separated into two parts by the electrical isolation. One part covers the grating distribution area in the grating layer, and the other part covers the grating blank area in the grating layer. The positive electrodes covering the grating distribution area and the grating blank area are respectively called the grating electrode and the blank electrode;

[0010] The grating electrode is used to provide a pump current for the grating distribution area, enabling the laser to resonate and amplify within the grating area;

[0011] The blank electrode is used to provide a transparent current for the grating blank area, avoiding power loss due to material absorption when the laser passes through the blank area;

[0012] The SOA area is used to provide additional gain for the laser by applying power to the SOA area, improving the output power of the laser area;

[0013] The active layer, buffer layer, and negative electrode layer provide gain, buffering, and a negative electrode for laser resonance.

[0014] To optimize the above technical solutions, the specific measures taken also include:

[0015] The above-mentioned grating layer uses the sampled Bragg grating technology, and the output of the seed grating is sampled twice using a first-order sampled grating and a second-order sampled grating to obtain equally spaced multi-wavelength light output;

[0016] Among them, the seed grating is used to confirm the 0th-order lasing wavelength;

[0017] The first-order sampled grating is used to determine the central wavelength at which the laser operates, and the REC technology is used to introduce an equivalent π phase shift to the central wavelength to achieve single-mode output of the light wave;

[0018] Based on the result of the first-order sampling, the second-order sampled grating performs periodic sampling to obtain the grating distribution area and the grating blank area, so as to obtain equally spaced multi-wavelength lasers;

[0019] The interval of the multi-wavelength laser is changed by modifying the period of the second-order sampled grating.

[0020] The above-mentioned 0th-order lasing wavelength λ 0 has a lasing position at 80 nm away from the gain center, and the central wavelength λ 1 is at the gain center.

[0021] The period of the above-mentioned seed grating Λ 0 is determined by the formula Λ 0 =λ 0 / 2n 0 ;

[0022] The period P of the first-order sampled grating1 From the formula 1 / P 1 = 2n 1 / λ 1 - 1 / Λ 0 to determine, and a π-phase shift is inserted into the first sampling grating;

[0023] The period P of the second sampling grating 2 is used to determine the wavelength interval Δλ of the multi-wavelength laser, and 1 / P 2 = 2n 2 / (λ 1 - Δλ) - 2n 1 / λ 1 ;

[0024] wherein, n 0 、n 1 and n 2 are the effective refractive indices corresponding to different wavelengths, and the effective refractive index can be obtained through the material dispersion coefficient.

[0025] The above-mentioned second sampling grating is a apodized grating with a duty cycle of 10%.

[0026] The above-mentioned active layer is a multi-quantum well structure.

[0027] The cavity length of the above-mentioned semiconductor laser is 5 mm, the length of the SOA region is 400 μm, and the waveguide bending angle of the SOA region is 7 degrees.

[0028] Both end faces of the above-mentioned semiconductor laser are AR coated, and the reflectivity of the AR coating is 0.5%.

[0029] The present invention has the following beneficial effects:

[0030] Effectively reduces the size of the traditional laser array, which is beneficial to the integration and low cost of optical chips. The grating of the laser is generated by superimposing a seed grating and two sampling gratings. Among them, the first sampling is used to determine the central wavelength of the laser operation, and then the second sampling is combined to obtain multiple wavelengths in the central band, so as to realize the output of 4 equally spaced wavelengths by a single laser. In addition, the first sampling uses the Reconstruction-Equivalent Chirp (REC) technology to introduce an equivalent π-phase shift to achieve single-mode output of light waves; then, by modifying the period of the second sampling grating, the wavelength interval of the output light can be arbitrarily changed; at the same time, combined with temperature and power tuning, only four such lasers are needed to cover the entire C band. And, to avoid the spatial hole burning effect, the second sampling grating uses the apodization technology to reduce the coupling coefficient of the optical field.

[0031] The multi-wavelength semiconductor laser of the present invention can achieve laser output with 4 evenly spaced wavelengths using a single laser. Compared with traditional laser arrays, it can effectively reduce the number of lasers used, avoid the problems of lasers and channel switching in the array, not only has a simpler structure, but also reduces the channel switching time. At the same time, compared with the parallel semiconductor laser array, the laser of the present invention can avoid the additional loss caused by multiplexing, and effectively improve the side mode suppression ratio of the output light; compared with the series laser array, the laser of the present invention can solve the problem of large lasing wavelength intervals between lasers under the same waveguide, which is beneficial to dense wavelength division multiplexing. Moreover, a single laser also has more advantages in terms of control, integration, packaging, etc. Description of the Drawings

[0032] Figure 1 is a schematic structural diagram of a multi-wavelength semiconductor laser;

[0033] Figure 2 is a schematic diagram of the grating after two samplings;

[0034] Figure 3 is a simulation diagram of the grating transmission spectrum after two samplings;

[0035] Figure 4 is a spectral test diagram of the multi-wavelength semiconductor laser. Detailed Embodiment

[0036] The following further describes the embodiments of the present invention in detail with reference to the drawings.

[0037] The present invention proposes a semiconductor laser that can achieve multi-wavelength output with a single laser. Only one laser can achieve 4-wavelength light output with equal intervals, which is equivalent to using a single laser to complete the work of 4 lasers in a traditional array. It not only has a simpler structure, but also reduces the channel switching time.

[0038] The following further describes in detail the technical solutions provided by the embodiments of the present invention with reference to the drawings.

[0039] Figure 1 is a schematic structural diagram of a semiconductor laser that can achieve multi-wavelength output with a single laser, including a laser region and an (semiconductor optical amplifier) SOA region integrated at the light output end of the laser;

[0040] Both the laser region and the SOA region sequentially include a positive electrode layer, electrical isolation, a grating layer, an active layer, a buffer layer, and a negative electrode layer;

[0041] The grating layer is divided into a grating distribution region and a grating blank region, and the grating of the grating layer is obtained by superimposing a seed grating, a first sampling grating, and a second sampling grating;

[0042] The positive electrode layer is separated into two parts by the electrical isolation, one part covering the grating distribution area in the grating layer and the other part covering the grating blank area in the grating layer; the two parts of the positive electrode can be energized separately without affecting each other.

[0043] For the convenience of subsequent introduction, the positive electrodes covering the grating distribution area and the grating blank area are respectively named the grating electrode and the blank electrode.

[0044] The cavity length of the laser is 5 mm, and the actual cavity length can be adjusted according to the grating etching depth and the sampled grating period, and no special limitation is made here;

[0045] Preferably, the SOA area integrated at the light output end of the laser has a length of 400 μm; and the waveguide in the SOA area is bent, and the bending angle is 7 degrees to reduce the reflection at the waveguide end face.

[0046] Furthermore, AR coating is performed on both ends of the semiconductor laser, and the reflectivity of the AR coating is about 0.5%.

[0047] The active layer is a multi-quantum well structure, providing gain for laser resonance, and the number of quantum wells can be adjusted as needed;

[0048] Figure 2 It is a schematic diagram of the grating structure of a semiconductor laser chip that realizes multi-wavelength output with a single chip. In the multi-wavelength laser of the present invention, the grating layer uses the sampled Bragg grating technology to sample the seed grating twice to obtain equally spaced multi-wavelength light output. Among them, the seed grating is used to confirm the 0th order lasing wavelength. The first sampled grating uses the REC technology to introduce an equivalent π phase shift to the central wavelength after the first sampling; the second sampled grating is based on the result of the first sampling and performs large-period sampling to obtain the grating distribution area and the grating blank area, and obtains multi-wavelength lasers with small intervals.

[0049] The seed grating is used to confirm the 0th order lasing wavelength, and the 0th order wavelength λ corresponding to the seed grating 0 should be about 80 nm away from the gain center to avoid the lasing of the 0th order wavelength.

[0050] The first sampled grating is used to determine the central wavelength at which the laser operates, and uses the REC technology to introduce an equivalent π phase shift to the central wavelength to achieve single-mode output of light waves;

[0051] The second sampled grating is based on the result of the first sampling and performs periodic sampling to obtain the grating distribution area and the grating blank area to obtain equally spaced multi-wavelength lasers;

[0052] The interval of the multi-wavelength lasers is changed by modifying the period of the second sampled grating.

[0053] The period of the first sampling grating is jointly determined by the required central wavelength and the period of the seed grating;

[0054] The period of the second sampling grating is jointly determined by the required wavelength interval and the period of the first sampling grating.

[0055] The period of the seed grating is determined by the formula Λ 0 = λ 0 / 2n 0 determined;

[0056] The central wavelength λ 1 should be taken near the gain center, and the period of the first sampling grating is determined by the formula 1 / P 1 = 2n 1 / λ 1 -1 / Λ 0 determined, and a π phase shift is inserted into the first sampling grating;

[0057] The wavelength interval Δλ is determined by the period P 2 of the second sampling grating, 1 / P 2 = 2n 2 / (λ 1 -Δλ)-2n 1 / λ 1 , so that Δλ can be changed by modifying P 2 . Where n 0 , n 1 and n 2 are the effective refractive indices corresponding to different wavelengths, and the effective refractive index can be obtained through the material dispersion coefficient.

[0058] Preferably, in order to cover as many of the second sampling periods as possible, the cavity length of the semiconductor laser needs to be increased.

[0059] However, increasing the cavity length of the semiconductor laser easily causes the spatial hole burning effect, resulting in multimode lasing.

[0060] The second sampling grating is a apodized grating with a duty cycle of 10%. The grating duty cycle is reduced to reduce the optical field coupling coefficient to counteract the spatial hole burning effect caused by the long cavity.

[0061] In a specific embodiment of the present invention, the gain center of the electroluminescence spectrum of the epitaxial wafer used for growth is approximately at 1555 nm. Therefore, the lasing wavelength corresponding to the seed grating is taken as 1635 nm (80 nm away from the gain center); the central wavelength after the first sampling is positioned near the gain center, thereby determining the grating period of the first sampling, and introducing a π phase shift using the REC technique; the wavelength corresponding to the second sampling is taken as 90 GHz different from the central wavelength, and the grating period of the second sampling is determined accordingly; finally, a multi-wavelength optical output with a central wavelength of 1550 nm and a spacing of 90 GHz is obtained.

[0062] Preferably, the above grating etching processes all adopt holographic exposure technology.

[0063] It should also be noted that the second sampling grating is a apodized grating, and the duty cycle is adjusted to 10%. The set value of the duty cycle can be modified according to the actual cavity length and the grating etching depth, and no special limitation is made here.

[0064] It should also be noted that the central wavelength and wavelength interval in the embodiments of the present invention can be adjusted according to actual requirements, and no special limitation is made here.

[0065] Figure 3 It is a simulation diagram of the grating transmission spectrum of a semiconductor laser that realizes multi-wavelength output with a single chip. The simulation of the grating transmission spectrum is based on the coupled mode theory, and the transmission properties of the grating after two samplings are simulated by means of the transfer matrix method.

[0066] Preferably, the parameters used in the simulation are all consistent with the actual wafer processing parameters, laser design parameters, etc.;

[0067] Furthermore, there are multiple mode transmittances in the simulated transmission spectrum that are lower than 10%, that is, these modes can resonate in the grating with a reflectivity of more than 90%, thereby obtaining optical outputs of multiple modes;

[0068] Furthermore, considering that the threshold gains of the respective modes are different, and the difference in the threshold gains between the modes increases as the position away from the central wavelength increases, only several modes near the central wavelength can actually obtain effective gain and lasing.

[0069] Figure 4 It is the spectrum diagram of the multi-wavelength semiconductor laser obtained by experimental testing.

[0070] Preferably, the experiment is carried out at 25 °C, and a Rigol current source is used to power the multi-wavelength semiconductor laser;

[0071] The specific power supply scheme is as follows: the SOA is powered with 80 mA, the grating electrode is powered with 150 mA, and the blank electrode is powered with 180 mA;

[0072] The output light of the multi-wavelength semiconductor laser is coupled into a spectrometer using a multimode lens-coupled optical fiber, and the Figure 4 spectral diagram shown is obtained by scanning. In the spectral diagram, the central wavelength lasered by the multi-wavelength semiconductor laser is approximately 1555 nm, and the side mode suppression ratio of the output light of four modes near the central wavelength exceeds 45 dBm, and the light of these 4 modes can be effectively utilized;

[0073] The optical wavelength intervals of the 4 modes are uniform, and the wavelength interval is approximately 90 GHz after actual measurement and conversion.

[0074] By increasing the current of the SOA, the output power of the multi-wavelength semiconductor laser can be effectively increased.

[0075] By changing the current of the grating electrode and the temperature of the experimental bench, the wavelength of the output light of the multi-wavelength semiconductor laser can be tuned.

[0076] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A semiconductor laser that realizes multi-wavelength lasing with a single chip, characterized in that, it includes a laser region and an SOA region integrated at the light-emitting end of the laser; both the laser region and the SOA region sequentially include a positive electrode layer, electrical isolation, a grating layer, an active layer, a buffer layer, and a negative electrode layer; the grating layer is divided into a grating distribution region and a grating blank region, and the grating of the grating layer is obtained by superimposing a seed grating, a first sampling grating, and a second sampling grating; the seed grating is used to confirm the 0th-order lasing wavelength; the first sampling grating is used to determine the central wavelength at which the laser operates, and the REC technology is used to introduce an equivalent π phase shift to the central wavelength to achieve single-mode output of light waves; the second sampling grating performs periodic sampling based on the result of the first sampling to obtain the grating distribution region and the grating blank region to obtain equally spaced multi-wavelength lasers; the interval of the multi-wavelength lasers is changed by modifying the period of the second sampling grating; the positive electrode layer is separated into two parts by the electrical isolation, one part covers the grating distribution region in the grating layer, and the other part covers the grating blank region in the grating layer. The positive electrodes covering the grating distribution region and the grating blank region are respectively called the grating electrode and the blank electrode; the grating electrode is used to provide a pump current for the grating distribution region so that the laser can resonate and amplify in the grating region; the blank electrode is used to provide a transparent current for the grating blank region to avoid power loss due to material absorption when the laser passes through the blank region; the SOA region is used to provide additional gain for the laser by applying power to the SOA region and improve the output power of the laser region; the active layer, the buffer layer, and the negative electrode layer provide gain, buffering, and a negative electrode for laser resonance.

2. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 1, characterized in that, The lasing wavelength λ of level 0 0 has a lasing position at 80 nm from the gain center, and the central wavelength λ 1 is at the gain center.

3. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 2, characterized in that, The seed grating Λ 0 has a period determined by the formula Λ 0 = λ 0 / 2n 0 ; The period P of the first sampling grating 1 From the formula 1 / P 1 = 2n 1 / λ 1 - 1 / Λ 0 is determined, and a π phase shift is inserted into the first sampling grating; The period P of the secondary sampling grating 2 determines the wavelength interval Δλ of the multi-wavelength laser, and 1 / P 2 = 2n 2 / (λ 1 -Δλ) - 2n 1 / λ 1 ; where n 0 , n 1 and n 2 are the effective refractive indices corresponding to different wavelengths, and the effective refractive index can be obtained through the material dispersion coefficient.

4. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 1, characterized in that, the second sampling grating is a apodized grating with a duty cycle of 10%.

5. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 1, characterized in that, the active layer is a multi-quantum well structure.

6. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 1, characterized in that, the cavity length of the semiconductor laser is 5 mm, the length of the SOA region is 400 μm, and the waveguide bending angle of the SOA region is 7 degrees.

7. A semiconductor laser that realizes multi-wavelength lasing with a single chip according to claim 6, characterized in that, both end faces of the semiconductor laser are AR coated, and the reflectivity of the AR coating is 0.5%.

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