A wavelength division multiplexing laser array and a wavelength interval correction method thereof

Abstract

This invention provides a wavelength division multiplexing (WDM) laser array and its wavelength spacing correction method, relating to the field of semiconductor optoelectronic device technology. It includes: N DFB laser channels; each DFB laser channel comprises a physical phase-shift grating, sequentially divided into a uniform grating segment A, a phase-shift modulation segment B, and a uniform grating segment C along the light propagation direction; segments A and C are of equal length, and segment B is located at the midpoint between segments A and C. This invention avoids the multi-level sub-grating mode competition problem and center wavelength shift problem of the sampling grating by employing a physical phase-shift grating; it actively controls the phase shift by independently changing the injection current or thermoelectrode of segment B in each channel, achieving continuous wavelength tuning without mode hopping and manufacturing error compensation; segment B utilizes an equivalent phase shift to increase the tuning region length, ensuring optimal side-mode suppression ratio while improving tuning efficiency, significantly reducing energy consumption and thermal crosstalk between multiple channels.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to a wavelength division multiplexing laser array and a method for correcting the wavelength spacing therebetween. Background Technology

[0002] With the rapid development of wavelength division multiplexing (WDM) optical communication systems, the demand for multi-wavelength light sources is becoming increasingly urgent. Monolithically integrated multi-wavelength distributed feedback laser arrays have become ideal light sources for WDM systems due to their advantages such as small size, low cost, low power consumption, and controllable wavelength.

[0003] Traditional uniform grating DFB lasers, without introducing a phase shift, generate a pair of symmetrical degenerate resonant modes on both sides of the stopband, leading to dual-mode lasing or unstable single-mode operation. To address this issue, a λ / 4 phase shift is typically introduced into the grating. Existing technologies have reported the fabrication of multi-wavelength DFB laser arrays using equivalent phase shift (EPS) or reconstruction-equivalent chirp (REC) techniques and sampling gratings. However, these methods rely on the approximation of the equivalent phase shift of the sampling Bragg grating, which presents the following problems: the equivalent phase shift of the sampling grating depends on higher-order sub-gratings; the lasing wavelength is sensitive to changes in the sampling period, resulting in a high risk of mode hopping; the tuning method is limited, typically requiring overall tuning or relying on complex multi-electrode configurations; and insufficient fabrication precision of the uniform grating's equivalent phase shift and the sampling grating itself leads to wavelength shift.

[0004] Achieving precise wavelength spacing is one of the core challenges for multi-wavelength DFB laser arrays. The lasing wavelength difference between adjacent channels and the grating period difference satisfy the Bragg relation. In the O-band (1310nm), a 100GHz frequency spacing corresponds to a wavelength spacing of approximately 0.57nm, and a grating period difference of only about 0.087nm. This scale is far smaller than the precision limit of current photolithography technology, and even electron beam lithography cannot completely guarantee error-free operation. On the other hand, in actual manufacturing, waveguide width processing errors can also cause center wavelength shifts. Therefore, relying solely on a pre-designed grating period to ensure wavelength spacing will inevitably result in significant wavelength deviations in actual manufacturing, severely affecting the array's wavelength uniformity and yield. Therefore, wavelength compensation is an essential core technology.

[0005] In existing technologies, the method of simultaneously tuning the wavelength of all channels by changing the overall chip temperature to compensate for manufacturing errors requires a large power consumption for overall heating. At the same time, for laser arrays, since the spacing between channels is very close, usually only tens of micrometers, thermal diffusion will cause serious thermal crosstalk between channels, resulting in inconsistent wavelength drift of each channel, which will disrupt the original wavelength spacing order. Summary of the Invention

[0006] This invention provides a wavelength division multiplexing laser array and its wavelength spacing correction method to solve the defect in the prior art where thermal diffusion leads to severe inter-channel thermal crosstalk.

[0007] On one hand, the present invention provides a wavelength division multiplexing laser array, comprising: N DFB laser channels monolithically integrated on the same semiconductor substrate; each DFB laser channel includes a physical phase shift grating, which is sequentially divided into a uniform grating A, a phase shift modulation segment B, and a uniform grating C along the light propagation direction; Segment A and segment C are of equal length, and segment B is located in the middle of segment A and segment C; The periods of the physical phase-shifting gratings in each channel are different and are distributed in an arithmetic sequence. Physical phase-shifting gratings are fabricated by electron beam lithography or nanoimprint lithography.

[0008] According to the wavelength division multiplexing laser array provided by the present invention, the total phase shift introduced by segment B is: , where n is a non-negative integer; the physical length of segment B is much smaller than the total cavity length of the laser, with an approximate ideal point phase shift.

[0009] According to the present invention, a wavelength division multiplexing laser array further includes an electrode structure comprising a first electrode, a second electrode, and a thermal electrode; segments A and C are jointly connected to the first electrode; segment B is separately connected to the second electrode; the thermal electrode is located above segment B, and the thermal electrode and the second electrode are physically isolated by an insulating layer; the first electrode and the second electrode are electrically isolated by ion implantation of a high-resistivity region or etching of an isolation trench.

[0010] According to the wavelength division multiplexing laser array provided by the present invention, a semiconductor optical amplifier is monolithically integrated after the C-segment; the substrate of the semiconductor optical amplifier is an InP substrate, and a thermoelectric cooler is integrated below the laser array.

[0011] This invention also provides a method for correcting the wavelength spacing of a wavelength division multiplexing laser array, comprising: By changing the chip temperature through a thermoelectric cooler integrated under the chip, the lasing wavelength of N DFB laser channels is shifted to the vicinity of the target band using the thermo-optic effect. By monitoring the spectrum of each channel in real time, the injection current of the second electrode or the thermoelectrode current of the B section of each channel is adjusted separately, and the lasing wavelength of each channel is finely adjusted independently to compensate for the wavelength deviation caused by the manufacturing error of the grating period, so that the channel spacing is restored to the design value. Amplifying current is injected into the semiconductor optical amplifier integrated after segment C to amplify the output optical power of the DFB laser; Based on the steady-state operation after compensation, a tuning signal is superimposed on segment B of the target channel to achieve rapid wavelength switching.

[0012] According to the wavelength division multiplexing laser array wavelength spacing correction method provided by the present invention, the step of shifting the lasing wavelength of N DFB laser channels as a whole to near the target wavelength band includes: The overall operating temperature of the chip is regulated by a thermoelectric cooler; Based on the operating temperature, the effective refractive index of the active region and grating region of all DFB laser channels is changed synchronously by utilizing the thermo-optic effect of semiconductor materials, so that the lasing wavelength of each channel drifts synchronously in the same direction and keeps the drift amount consistent, so that the whole falls into the preset target band range.

[0013] According to the present invention, a method for correcting the wavelength spacing of a wavelength division multiplexing laser array includes the following steps for compensating for wavelength deviations caused by grating period manufacturing errors: The actual lasing spectrum of each channel is acquired in real time, and the deviation between the actual wavelength of each channel and the design target wavelength is calculated. For each channel, adjust the second electrode injection current or thermistor current of its B segment according to the deviation. By adjusting the effective refractive index of section B, the phase shift angle introduced by section B is adjusted. Based on the resonance condition of the central phase-shifted DFB, the lasing wavelength is continuously drifted without mode skipping as the phase shift angle deviates from the design value until the wavelength deviation of each channel converges to the preset tolerance range, and the wavelength interval of adjacent channels is restored to the design value of an arithmetic sequence.

[0014] According to the wavelength spacing correction method for wavelength division multiplexing laser arrays provided by the present invention, the formula for the resonance condition is expressed as follows: , In the formula, δ is the detuning amount, and k is the grating coupling coefficient. Let B be the phase shift angle introduced in segment B, and L be the laser cavity length.

[0015] According to the wavelength spacing correction method for wavelength division multiplexing laser arrays provided by the present invention, the step of superimposing a tuning signal on the B segment of the target channel includes: After the wavelength spacing correction is completed and each channel is in steady state, for the target channel that needs to switch wavelengths, an alternating tuning signal corresponding to the target wavelength offset is superimposed on the DC bias current of its B segment. During dynamic tuning, the wavelengths of non-target channels remain locked, and the tuning heat of the target channel is only localized in the phase shift tuning region of that channel, without disrupting the overall wavelength grid order of the array.

[0016] The wavelength spacing correction method for a wavelength division multiplexing laser array provided by the present invention further includes: using the independent control capability of the grating width during grating fabrication by electron beam lithography or nanoimprint lithography to reduce the influence of waveguide width processing error on the center wavelength in advance; and combining the independent tuning of the phase shift angle of the B segment to collaboratively correct the composite wavelength offset caused by grating period error and waveguide width error, so that the wavelength deviation of each channel finally converges to a preset tolerance range.

[0017] This invention provides a wavelength division multiplexing (WDM) laser array and its wavelength spacing correction method. By employing a physical phase-shifting grating instead of the equivalent phase shift of a sampling grating, the multi-level sub-grating mode competition problem of the sampling grating is completely avoided. The phase-shifting grating of each channel has a three-segment structure (ABC), with segments A and C having the same length, and segment B located at the center of the cavity. This symmetrical structure ensures the optimal side-mode suppression ratio. Segment B simultaneously performs the dual functions of λ / 4 phase shift and wavelength tuning. The phase shift is actively controlled by independently changing the injection current of segment B in each channel, achieving continuous wavelength tuning without mode skipping and manufacturing error compensation. Segment B adopts a 90°+n×360° multi-period phase-shifting design, which significantly improves the tuning sensitivity while maintaining single-mode lasing. The grating is fabricated using EBL or NIL, and the grating width can be independently controlled, greatly reducing the influence of waveguide width on the center wavelength and further improving the accuracy of wavelength control. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a wavelength division multiplexing laser array provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a phase-shifting grating structure with multiple channels provided in an embodiment of the present invention; Figure 3 This is a top view schematic diagram of the overall structure of the integrated SOA provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the phase-shifting grating waveguide structure for integrated SOA provided in an embodiment of the present invention; Figure 5 This is a flowchart of a wavelength spacing correction method for a wavelength division multiplexing laser array provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] The following is combined Figures 1-5 This invention describes a wavelength division multiplexing laser array and its wavelength spacing correction method.

[0022] like Figures 1-5 As shown, an embodiment of the present invention provides a wavelength division multiplexing (WDM) laser array, comprising: N DFB laser (feedback laser) channels monolithically integrated on the same semiconductor substrate; the lasing wavelengths of the N channels are equally spaced, with adjacent channels having a wavelength spacing of 100 GHz or 200 GHz to adapt to the ITU standard wavelength grid of WDM systems; the semiconductor substrate is a (100) crystal orientation n-type InP substrate (i.e., indium phosphide). The substrate is a Phosphide (III-V compound semiconductor material). The active region of the N DFB laser channels is an InGaAsP multi-quantum-well structure with the emission peak located at 1310 nm. Each channel is arranged in a one-dimensional array along a direction parallel to the substrate surface, and the spacing between adjacent channels is adapted to the high-density integration requirements. In the prior art, the equivalent phase shift of the sampling grating depends on the higher-order sub-grating. The lasing wavelength is sensitive to the sampling period change, the risk of mode hopping is high, and the tuning method is single. Usually, it can only be tuned as a whole or rely on a complex multi-electrode configuration. The equivalent phase shift of the uniform grating and the insufficient processing accuracy of the sampling grating itself can easily lead to wavelength shift. However, in this embodiment, the fabrication is carried out by EBL (electron beam lithography) or NIL (nanoimprint lithography) combined with subsequent B-segment tuning, which constitutes a dual guarantee mechanism of "high-precision fabrication + active compensation".

[0023] Each DFB laser channel contains a physical phase-shifting grating, which is sequentially divided into a uniform grating segment A, a phase-shifting modulation segment B, and a uniform grating segment C along the light propagation direction; the periods of the phase-shifting gratings in the N DFB laser channels are all different, and are denoted as follows: , And it satisfies: , in, Let be the grating period of the i-th channel, i be the channel index, and N be the total number of DFB laser channels. The initial grating period, This represents the grating period increment between adjacent channels.

[0024] The physical phase-shifting grating is a non-sampling grating, unlike the equivalent phase-shifting or reconstructed-equivalent chirped gratings in general embodiments. It avoids the multi-level sub-grating mode competition problem, completely eliminating the drawbacks of sampling gratings, such as the sensitivity of the lasing wavelength to sampling period changes and the high risk of mode hopping. In general techniques, the equivalent phase shift of the sampling grating depends on higher-order sub-gratings, the lasing wavelength is sensitive to sampling period changes, and the risk of mode hopping is high; moreover, the tuning method is singular, usually only allowing overall tuning or relying on complex multi-electrode configurations. This embodiment uses a physical phase-shifting grating instead of the equivalent phase shift of the sampling grating, completely avoiding the multi-level sub-grating mode competition problem of the sampling grating. Furthermore, the insufficient fabrication precision of the uniform grating's equivalent phase shift and the sampling grating itself can easily lead to wavelength shift. This embodiment, fabricated using EBL or NIL, combined with subsequent B-segment tuning, constitutes a dual guarantee mechanism of "high-precision fabrication + active compensation."

[0025] Segment A and segment C are of equal length, and segment B is located at the midpoint between segments A and C. This symmetrical structure places the phase shift at the exact center of the cavity, with the defect mode located at the exact center of the grating stopband. This results in the largest threshold gain difference between the defect mode and the edge mode, achieving the optimal edge mode suppression ratio (SMSR). This overcomes the drawbacks of asymmetric phase shift schemes, which exacerbate the spatial hole burning effect and reduce the yield of single-mode modules. Since segment B is located at the exact center of the cavity, the light field distribution at this location has a specific symmetry, allowing small changes in phase shift to be efficiently converted into wavelength drift, further improving tuning efficiency.

[0026] The physical phase-shifting gratings of each channel have different periods, arranged in an arithmetic sequence; the common difference ΔΛ of the arithmetic sequence satisfies the Bragg relation. Where Δλ is the wavelength interval between adjacent channels. The effective refractive index of the grating region; in the O-band 1310nm, the wavelength interval corresponding to the 100GHz frequency interval is about 0.57nm, and the corresponding grating period difference is only about 0.087nm. This scale is much smaller than the precision limit of existing photolithography technology. It is difficult to guarantee the precision by simply relying on the preset period. Therefore, this embodiment introduces a subsequent tuning mechanism for compensation.

[0027] Physical phase-shifting gratings are fabricated using electron beam lithography or nanoimprint lithography. During fabrication, electron beam lithography and nanoimprint lithography can simultaneously and precisely control the grating period and grating width, reducing the center wavelength shift introduced by waveguide width processing errors to the nanometer level, significantly improving wavelength control accuracy. Electron beam lithography can achieve sub-10nm pattern resolution, ensuring the morphological accuracy of the phase-shifting grating, while nanoimprint lithography can maintain the consistency of the grating pattern over a large area, making it suitable for mass production.

[0028] The total phase shift introduced by segment B is Where n is a non-negative integer; the physical length of segment B is much smaller than the total cavity length of the laser to approximate the ideal point phase shift. The total phase shift is increased by an integer number of 360° cycles on the 90° base phase without changing the position of the lasing mode, ensuring stable single-mode lasing; at the same time, the longer physical length of segment B can increase the amount of phase shift angle change caused by unit current change, improving tuning sensitivity; the value of n is small to maintain single-mode lasing and a good side-mode suppression ratio, avoiding the reduction of mode selectivity due to the phase shift deviating from the ideal point phase shift caused by excessively long segment B; segment B adopts an equivalent λ / 4 phase shift design of 90° + n × 360°, allowing for a longer physical length of segment B without changing the essential function of phase shift, so that the effective refractive index change of segment B under unit current change can be converted into a larger phase shift angle change, thereby significantly improving tuning efficiency and reducing tuning power, while the shorter segment B makes the phase shift approximate the ideal point phase shift, further optimizing single-mode characteristics.

[0029] The feedback laser array also includes an electrode structure, which includes a first electrode, a second electrode, and a hot electrode; segments A and C are connected to the first electrode together; segment B is connected to the second electrode separately; the hot electrode is located above segment B, and the hot electrode and the second electrode are physically isolated by an insulating layer; the first electrode and the second electrode are electrically isolated by ion implantation of a high-resistivity region or etching of an isolation trench. The first electrode is used to inject a constant current to provide stable gain, the second electrode is used to inject a variable current to change the effective refractive index of segment B through carrier plasma effect, and the hot electrode is used to pass current to generate Joule heating to change the effective refractive index of segment B through thermo-optic effect; the insulating layer is made of SiO2 or SiN material, and its thickness is adapted to the balance requirements of electrical isolation and thermal conduction; the hot electrode covers at least the segment B region in the vertical direction to ensure that heat is effectively conducted to segment B; the insulating layer not only achieves physical isolation between the hot electrode and the second electrode, but also plays a role in regulating the heat conduction path. Since the thermal conductivity of the insulating layer is much lower than that of semiconductor materials, heat is mainly conducted downward in the vertical direction to segment B before lateral diffusion, which further limits the lateral diffusion range of heat and ensures that there is no significant thermal crosstalk when the spacing between adjacent channels is 20~30μm. This structure allows the channels to be arranged closely, realizing high-density integration. At the same time, the hot electrode is fabricated on the insulating layer, which is compatible with CMOS back-end processes, eliminating the need for additional complex process steps and reducing manufacturing costs.

[0030] Following segment C (i.e., the output direction of each DFB laser channel), a semiconductor optical amplifier (SOA) is monolithically integrated. The SOA has an independent third electrode, electrically isolated from the first and second electrodes of the DFB, which can amplify the power of the optical signal output by the DFB without changing its wavelength characteristics, ensuring that the power amplification, gain control, and wavelength tuning functions are independent and do not interfere with each other. The SOA and the DFB laser share the same waveguide structure and are fabricated in the same manufacturing process as the DFB laser through docking growth or selective region epitaxy. Since the SOA and the laser can be fabricated together in the same manufacturing process, with only differences in waveguide design, the amplification of the laser array's optical power can be achieved without additional manufacturing processes. The substrate of the semiconductor optical amplifier is an InP substrate, and a thermoelectric cooler is integrated below the laser array. SOA and DFB lasers share the same waveguide structure and are fabricated in the same manufacturing process as DFB lasers through docking growth or selective region epitaxy, achieving output optical power amplification without additional process steps; thermoelectric coolers are used to achieve overall coarse tuning of all channel wavelengths by changing the temperature of the entire chip; both end faces of the laser array are coated with antireflection coatings (AR / AR) to eliminate the influence of random end face phase, ensure the consistency of the initial phase of different batches of devices, and suppress mode competition caused by residual reflections in the cavity.

[0031] This invention also provides a wavelength spacing correction method for wavelength division multiplexing laser arrays, comprising: By changing the chip temperature using a thermoelectric cooler integrated beneath the chip, the lasing wavelengths of the N DFB laser channels are shifted to near the target wavelength using the thermo-optic effect. The steps include: The overall operating temperature of the chip is regulated by a thermoelectric cooler. Based on the operating temperature, the effective refractive index of the active and grating regions of all DFB laser channels is synchronously changed using the thermo-optic effect of the semiconductor material. This causes the lasing wavelengths of each channel to drift synchronously in the same direction, maintaining a consistent drift amount, and ensuring that the entire wavelength falls within the preset target band range. The refractive index temperature coefficient dn / dT of the thermo-optic effect is approximately 1~2×10⁻⁶. -4 / K, during the overall tuning process, the wavelength shift of each channel is basically consistent, which can avoid the disorder of spacing caused by thermal crosstalk between channels. Compared with the traditional overall heating scheme, this embodiment avoids the defects of large power consumption and severe thermal crosstalk between channels by localized B-segment tuning, and reserves the appropriate wavelength adjustment margin for subsequent independent fine tuning. The specific coarse tuning process is as follows: first, through TEC overall coarse tuning, the wavelength of each channel is moved to the vicinity of the target band by using the thermo-optic effect, and then enters the independent fine tuning stage, which effectively solves the problems of large power consumption and severe thermal crosstalk in the traditional overall heating scheme.

[0032] The ability to independently control the grating width during grating fabrication using electron beam lithography or nanoimprint lithography pre-emptively reduces the impact of waveguide width processing errors on the center wavelength. Traditionally, when using sampling gratings to fabricate DFB gratings, the use of low-resolution lithography techniques such as laser direct writing or contact exposure inevitably introduces errors in the grating width at the level of tens to hundreds of nanometers, thereby introducing a shift in the center wavelength on the order of 10 GHz to 100 GHz. In contrast, this embodiment uses a physical phase-shifting grating combined with EBL / NIL fabrication, introducing only nanometer-level waveguide width errors, minimizing the impact of waveguide width on the center wavelength, and significantly reducing the total amount of wavelength deviation that needs to be compensated for subsequently.

[0033] By monitoring the spectrum of each channel in real time, adjusting the injection current of the second electrode or the thermoelectrode current of segment B in each channel, and combining this with the independent tuning of the phase shift angle of segment B, the composite wavelength shift caused by grating period error and waveguide width error is synergistically corrected. The lasing wavelength of each channel is independently fine-tuned to compensate for wavelength deviations caused by grating period manufacturing errors, ensuring that the wavelength deviations of each channel converge to the preset tolerance range, thus restoring the channel spacing to the design value. The steps include: The actual lasing spectrum of each channel is acquired in real time, and the deviation between the actual wavelength of each channel and the design target wavelength is calculated. For each channel, adjust the second electrode injection current or thermistor current of its B segment according to the deviation. The specific compensation process is as follows: different bias currents are applied to segment B of each channel in sequence. Under the feedback of real-time spectral monitoring, the current of each segment B is adjusted so that the wavelength of each channel is accurately aligned with the preset equally spaced wavelength grid. The power consumption of each channel is extremely low during the compensation process, and the wavelengths of adjacent channels do not affect each other during the tuning process, and there is no thermal crosstalk.

[0034] By adjusting the effective refractive index of segment B, the phase shift angle introduced by segment B is adjusted. Based on the resonance condition of the central phase-shifted DFB (under the ideal condition that segment B is located at the exact center of the cavity and both ends are coated with antireflection films), the formula is expressed as: , In the formula, δ is the detuning amount, and k is the grating coupling coefficient. The phase shift angle introduced in segment B, where L is the laser cavity length. The design value of the phase shift angle is... ,when When δ < 0, the lasing wavelength undergoes a blue shift; when When δ>0, the lasing wavelength redshifts; during the tuning process, heat is mainly confined to the B segment and conducted to the substrate below through the insulating layer, with minimal lateral heat diffusion. Even when the spacing between adjacent channels is 20~30μm, there is still no significant thermal crosstalk. The tuning operations of each channel are independent of each other, and single-channel tuning will not affect the lasing wavelength and spacing stability of other channels. Even if there is a manufacturing error of ±0.02nm in the grating period prepared by EBL or NIL, it can be compensated by the B segment current tuning, and the wavelength deviation can be controlled within ±0.05nm, thus widening the manufacturing tolerance by several times.

[0035] The lasing wavelength is continuously and mode-free as it deviates from the design value with the phase shift angle until the wavelength deviation of each channel converges to the preset tolerance range, and the wavelength interval between adjacent channels is restored to the design value of an arithmetic sequence.

[0036] Injecting an amplification current into the SOA integrated after segment C amplifies the output optical power of the DFB laser. The gain medium of the SOA is the same as that of the active region of the DFB laser. After injecting the amplification current, the output light of the DFB can be amplified without introducing additional wavelength shift and without affecting the stability of the corrected wavelength spacing, thus meeting the application requirements of high-power laser arrays. The monolithic integration of the SOA and the DFB laser allows the entire device to have optical signal amplification function while maintaining a compact structure. Since the SOA and the laser can be fabricated together in the same manufacturing process, with differences only in waveguide design, the optical power amplification of the laser array can be achieved without additional manufacturing processes. This integration method avoids the losses caused by the coupling of discrete components and meets the application requirements of high-power laser arrays, such as long-distance transmission and optical switching systems.

[0037] Based on the steady-state operation after compensation, a tuning signal is superimposed on segment B of the target channel to achieve rapid wavelength switching. The steps include: After wavelength spacing correction is completed and each channel is in steady-state operation, for the target channel requiring wavelength switching, an alternating tuning signal corresponding to the target wavelength offset is superimposed on the DC bias current of its B segment. The response time of the variable current injected into the second electrode is ≤1ns, enabling nanosecond-level fast wavelength switching and adapting to the dynamic wavelength scheduling requirements of high-speed wavelength division multiplexing systems. The response time of the hot electrode tuning is approximately 1~100μs, with a wider tuning range, and can be used for static wavelength bias. The two tuning methods are physically isolated, independently controlled, and do not interfere with each other, and can work together. The hot electrode is used for static wavelength bias to provide coarse tuning. The second electrode is used for dynamic modulation to provide fine tuning and cover a wider wavelength range; the B-segment is extremely short and the tuning region is localized, resulting in extremely low tuning power consumption and no heat diffusion to adjacent channels, making it suitable for high-density integration; based on steady-state operation, this embodiment also supports multiple channels to coordinate tuning to cover a wider wavelength range. The wavelength of a specific channel is biased outside the target grid by the wide tuning capability provided by the thermal electrode, while the second electrode is responsible for fine locking. This combination of "slow tuning coarse sweep + fast tuning lock" makes the laser array not only suitable for fixed WDM systems, but also adaptable to optical network environments that require dynamic reconfiguration.

[0038] During dynamic tuning, the wavelengths of non-target channels remain locked, and the tuning heat of the target channel is only localized in the phase shift tuning region of that channel, without disrupting the overall wavelength grid order of the array.

[0039] In summary, the wavelength division multiplexing laser array and its wavelength spacing correction method provided by this invention, by using EBL or NIL to fabricate physical phase-shift gratings with different periods, can compensate for wavelength deviations within ±0.05nm even if there are manufacturing errors in the period (e.g., ±0.02nm) through B-segment current tuning, even if there are manufacturing errors in the period. This compensation mechanism greatly reduces the stringent requirements on grating writing accuracy and improves the yield. Taking a 1310nm, 100GHz spacing in the O-band as an example, the required grating period accuracy is approximately 0.12nm. The compensation mechanism in this embodiment can relax the manufacturing tolerance by several times. Using physical phase-shift gratings (non-sampling gratings), phase-shift gratings with different periods can be directly fabricated using EBL / NIL, resulting in extremely high processing accuracy. EBL / NIL can simultaneously and precisely control the grating period and grating width, introducing only nanometer-level errors to minimize the influence of waveguide width on the center wavelength, further improving wavelength control accuracy. Compensation can be achieved using phase-shift segment tuning. The symmetrical design, with equal lengths for segments A and C and segment B centered at half the cavity length, positions the phase shift at the cavity's exact center, placing the defect mode at the center of the stopband. This maximizes the threshold gain difference with the two side modes, resulting in the highest side-mode suppression ratio (SMSR). The total phase shift in segment B is 90° + n × 360°. The shorter segment B approximates an ideal point phase shift, further optimizing single-mode characteristics. The introduction of n × 360° does not alter the lasing mode position but allows for flexible design of segment B length to meet process requirements. Even a small increase in segment B length significantly improves tuning sensitivity (increased wavelength change per unit current) and reduces the absolute value of the required tuning current. The dual-layer tuning architecture—independent tuning of segment B (carrier injection / thermoelectrode) + overall TEC tuning—achieves both independent fine-tuning of each channel's wavelength and compensation for manufacturing errors, as well as coarse tuning of the overall wavelength. This tuning method is flexible and widely applicable. Furthermore, by utilizing the carrier injection effect to change the refractive index of segment B, tuning speeds can reach nanosecond levels, far faster than thermal tuning. The B-segment is extremely short and the tuning region is localized, resulting in extremely low tuning power consumption, high tuning efficiency, and no heat diffusion to adjacent channels, allowing for close-packed channel arrangement. An SOA is integrated after the C-segment to amplify the output optical power of the DFB laser, meeting the requirements of long-distance transmission and high-power applications. A dual-mode tuning mechanism is employed: carrier injection tuning (second electrode): high speed (nanosecond level), suitable for dynamic wavelength modulation; thermo-optical tuning (thermoelectrode): wide range (nm-level tuning can be achieved by optimizing thermoelectrode power), suitable for static wavelength bias and manufacturing error compensation. The two mechanisms are physically isolated and independently controlled, without interference, allowing for flexible selection of the tuning method according to application requirements. The heat generated by the thermoelectrode is mainly confined to the shorter B-segment and conducted downwards through the insulating layer, with minimal lateral heat diffusion; the spacing between adjacent channels can be as small as 20~30μm without significant thermal crosstalk, achieving high-density integration. The thermoelectrode is fabricated on top of the insulating layer, compatible with CMOS back-end processes, requiring no additional complex process steps.With a center wavelength of 1310nm (O band), it is suitable for wavelength division multiplexing systems, optical switching and optical communication applications.

[0040] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wavelength division multiplexing laser array, comprising N DFB laser channels monolithically integrated on the same semiconductor substrate, characterized in that: Each DFB laser channel includes a physical phase-shift grating, which is divided into a uniform grating A, a phase-shift modulation section B, and a uniform grating C along the light propagation direction. The lengths of segments A and C are equal, and segment B is located at the midpoint between segments A and C; The periods of the physical phase-shifting gratings in each channel are different and are distributed in an arithmetic sequence. The physical phase-shifting grating is fabricated by electron beam lithography or nanoimprint lithography.

2. The wavelength division multiplexing laser array according to claim 1, characterized in that, The total phase shift introduced by segment B is: , where n is a non-negative integer; the physical length of segment B is much smaller than the total cavity length of the laser, with an approximate ideal point phase shift.

3. The wavelength division multiplexing laser array according to claim 1, characterized in that, It also includes an electrode structure comprising a first electrode, a second electrode, and a thermal electrode; segments A and C are connected together to the first electrode; segment B is connected separately to the second electrode; the thermal electrode is located above segment B, and the thermal electrode and the second electrode are physically isolated by an insulating layer; the first electrode and the second electrode are electrically isolated by ion implantation of a high-resistivity region or etching of an isolation trench.

4. A wavelength division multiplexing laser array according to claim 1, characterized in that, A semiconductor optical amplifier is monolithically integrated after segment C; the substrate for the semiconductor optical amplifier is an InP substrate, and a thermoelectric cooler is integrated below the laser array.

5. A wavelength spacing correction method for a wavelength division multiplexing laser array, based on a wavelength division multiplexing laser array as described in any one of claims 1 to 4, characterized in that, include: By changing the chip temperature through a thermoelectric cooler integrated under the chip, the lasing wavelength of N DFB laser channels is shifted to the vicinity of the target band using the thermo-optic effect. By monitoring the spectrum of each channel in real time, the injection current of the second electrode or the thermoelectrode current of the B section of each channel is adjusted separately, and the lasing wavelength of each channel is finely adjusted independently to compensate for the wavelength deviation caused by the manufacturing error of the grating period, so that the channel spacing is restored to the design value. Amplifying current is injected into the semiconductor optical amplifier integrated after segment C to amplify the output optical power of the DFB laser; Based on the steady-state operation after compensation, a tuning signal is superimposed on segment B of the target channel to achieve rapid wavelength switching.

6. The wavelength spacing correction method for wavelength division multiplexing laser arrays according to claim 5, characterized in that, The steps to shift the lasing wavelength of all N DFB laser channels to near the target wavelength include: The overall operating temperature of the chip is regulated by a thermoelectric cooler; Based on the operating temperature, the effective refractive index of the active region and grating region of all DFB laser channels is changed synchronously by utilizing the thermo-optic effect of semiconductor materials, so that the lasing wavelength of each channel drifts synchronously in the same direction and the drift amount remains consistent, so that the whole falls into the preset target wavelength range.

7. The wavelength spacing correction method for wavelength division multiplexing laser arrays according to claim 5, characterized in that, The steps to compensate for wavelength deviations caused by grating period manufacturing errors include: The actual lasing spectrum of each channel is acquired in real time, and the deviation between the actual wavelength of each channel and the design target wavelength is calculated. For each channel, the second electrode injection current or the thermoelectric current of its B segment is adjusted according to the deviation amount. By adjusting the effective refractive index of section B, the phase shift angle introduced by section B is adjusted. Based on the resonance condition of the central phase-shifted DFB, the lasing wavelength is continuously drifted without mode skipping as the phase shift angle deviates from the design value until the wavelength deviation of each channel converges to the preset tolerance range, and the wavelength interval of adjacent channels is restored to the design value of an arithmetic sequence.

8. The wavelength spacing correction method for wavelength division multiplexing laser arrays according to claim 7, characterized in that, The formula for the resonance condition is expressed as follows: ， In the formula, δ is the detuning amount, and k is the grating coupling coefficient. Let B be the phase shift angle introduced in segment B, and L be the laser cavity length.

9. A wavelength spacing correction method for wavelength division multiplexing laser arrays according to claim 5, characterized in that, The steps for superimposing the tuned signal onto segment B of the target channel include: After the wavelength spacing correction is completed and each channel is in steady state, for the target channel that needs to switch wavelengths, an alternating tuning signal corresponding to the target wavelength offset is superimposed on the DC bias current of its B segment. During dynamic tuning, the wavelengths of non-target channels remain locked, and the tuning heat of the target channel is only localized in the phase shift tuning region of that channel, without disrupting the overall wavelength grid order of the array.

10. A wavelength spacing correction method for wavelength division multiplexing laser arrays according to claim 5, characterized in that, Also includes: The ability to independently control the grating width during grating fabrication using electron beam lithography or nanoimprint lithography reduces the impact of waveguide width processing errors on the center wavelength in advance. Combined with independent tuning of the phase shift angle in segment B, the composite wavelength shift caused by grating period error and waveguide width error is synergistically corrected, so that the wavelength deviation of each channel finally converges to the preset tolerance range.

Images