CN114825050B

CN114825050B - Cascade multi-wavelength integrated semiconductor laser and application thereof

Info

Publication number: CN114825050B
Application number: CN202210746215.2A
Authority: CN
Inventors: 奚燕萍; 李文; 陈洋俊
Original assignee: Rizhao Ai Rui Optoelectronics Technology Co ltd
Current assignee: Rizhao Ai Rui Optoelectronics Technology Co ltd
Priority date: 2022-06-29
Filing date: 2022-06-29
Publication date: 2023-02-03
Anticipated expiration: 2042-06-29
Also published as: CN114825050A

Abstract

The invention discloses a cascade multi-wavelength integrated semiconductor laser and application thereof, belonging to the field of semiconductor lasers. The invention forms multi-wavelength monolithic integration by cascading a plurality of wavelength lasers along the propagation direction of an optical field, thereby completing signal output and wave combination of the multi-wavelength lasers on the same optical path. An absorption region can be arranged between any two single longitudinal mode lasers in the cascade multi-wavelength integrated semiconductor laser, and the gain regions of the single longitudinal mode lasers can be different. Therefore, the optical path control mode in the optical subassembly or the optical module is greatly simplified, optical path control components such as a wave combiner, a filter plate and the like required by other existing schemes are omitted, the implementation cost is reduced, and the packaging process is simplified.

Description

Cascade multi-wavelength integrated semiconductor laser and application thereof

Technical Field

The invention relates to the field of semiconductor lasers, in particular to a cascade multi-wavelength integrated semiconductor laser and application thereof.

Background

With the rapid increase of emerging application requirements of cloud computing cloud storage, ultra-high-definition video and the like, an optical communication system gradually evolves towards a technical direction supporting larger transmission capacity and higher transmission rate, and the requirements provide higher requirements for the performances of chip integration design, high integration, miniaturization, low power consumption and the like of devices and module packaging. Different application systems have different requirements on the speed, wavelength and other properties of the light source. For example, the conventional 10G EPON local side OLT includes two transmitting chips, i.e., 10G 1577nm and 1.25g 1490nm semiconductor lasers, so as to be compatible with low-rate EPON while upgrading the rate. Similarly, when the existing gigabit PON is upgraded to the 10 gigabit PON, the hybrid PON Combo-PON is used as a solution with obvious advantages, and the GPON and the 10G PON are combined, and chips with different wavelengths of two technologies are integrated into the same optical module, namely, a 10G 1577nm semiconductor laser and a 2.5g 1490nm semiconductor laser, so that the technologies before and after upgrading coexist, and two optical signals are transmitted relatively independently. As another example, optical modules that include in-line fiber detection also typically have a need to integrate two optical source signals. Optical time domain reflection OTDR detection for fiber troubleshooting and maintenance generally sends a pulse light source of a certain wavelength to an optical fiber, and obtains attenuation information by measuring a return signal thereof, thereby indirectly measuring the loss of the optical cable and the fault position. In order to realize online monitoring while transmitting normal signals and avoid interruption of normal communication in the detection process, a pulse light source with a certain wavelength and signal light sources with different wavelengths are generally integrated into one optical module, and signals on the two wavelengths work simultaneously without mutual interference.

At present, there are several methods for integrating multiple downlink emitting chips, and the more common scheme is TO package the respective laser diode modules TO-CAN respectively and then perform subsequent packaging. As shown in FIG. 1, for example, two emission signal wavelengths need to be integrated, the lasing wavelength is first packaged independently ₁ LD of ₁ TO-CAN 101 and lasing wavelength λ ₂ LD of ₂ And a TO-CAN 102, which combines the two wavelengths by using a control element combination 103 of a space optical path and is coupled TO an output optical fiber 105 through a coupling lens 104. At present, the single-wavelength chips are respectively and independently packaged in TO, and then the filtering wave plate, the coupling lens and the like are used for realizing wave combination, so that the defects of large loss, large volume, complex packaging process and the like exist.

For multi-wavelength integration at the transmitting end, there are other wave-combining manners, such as Box packaging schemes, as shown in fig. 2, laser chips LD with different wavelengths are respectively and independently attached to a submount to form an array arrangement 201, then output light is collimated by respective collimating lenses 202, each channel is subjected to wave-combining by a spatial-optics-based wave combiner 203 such as Z-Block, and the light is converged and coupled to an optical fiber 207 by an isolator 204, an optical path adjusting Block 205, and a coupling lens 206. The scheme has the defects of large volume, complex structure, high cost, high difficulty and the like, and the active light collimation and coupling are required to be carried out for multiple times in the packaging process.

As shown in fig. 3, another type of integrated method based on a laser integrated array chip and a planar waveguide combiner (such as an arrayed waveguide grating AWG or a multimode interferometer MMI) is provided, and the

functions

201, 202, and 203 in fig. 2 are completed on one chip in this manner, but the scheme has the main defects that the difficulty in manufacturing the chip is high, an active and passive integration process is required, the yield of the chip is low, the loss of the combiner is large, and the like.

Disclosure of Invention

The invention forms multi-wavelength monolithic integration by cascading a plurality of wavelength lasers along the propagation direction (longitudinal direction) of an optical field, thereby completing signal output and wave combination of the multi-wavelength lasers on the same optical path. The application relates to the field requiring integration of multiple wavelengths, including but not limited to hybrid passive optical network systems, optical time domain reflection OTDR on-line detection, data communication wavelength division multiplexing systems, 5G wireless forwarding, laser radar Lidar and the like.

The invention provides a cascade multi-wavelength integrated semiconductor laser, which comprises at least two sections of single longitudinal mode lasers which are connected in series and have different light-emitting wavelengths, wherein the light-emitting wavelengths of the at least two sections of single longitudinal mode lasers are changed in an increasing manner along the semiconductor laser from a light-emitting end face; each section of single longitudinal mode laser comprises a grating for realizing single longitudinal mode output, and the light-emitting wavelength of each section of single longitudinal mode laser is out of the Bragg stop band of the grating of other sections of single longitudinal mode lasers.

Preferably, the grating is below or above the active area.

Preferably, an absorption region is arranged between any two single longitudinal mode lasers, the grating structure in the absorption region is the same as the grating structure in the single longitudinal mode laser on the shorter light emitting wavelength side in the single longitudinal mode lasers on two adjacent sides, and the absorption region applies a reverse bias voltage or does not apply a voltage.

Preferably, when the gain range of the same material can cover the working wavelength of each section of single longitudinal mode laser, the gain region of each section of single longitudinal mode laser adopts the same material and the same structure; otherwise, different materials and/or structures are adopted in the gain region of each section of the single longitudinal mode laser.

Preferably, each segment of the single longitudinal mode laser comprises an independent P electrode, and the N electrode of each segment of the single longitudinal mode laser is independent or shared.

Preferably, each section of the absorption region comprises an independent P electrode, and an N electrode of the independent P electrode is shared with the single longitudinal mode laser on the shorter wavelength emitting side in the single longitudinal mode lasers on two adjacent sides.

Preferably, all the absorption regions and the single longitudinal mode laser share an N electrode.

Preferably, the light-emitting end face is plated with an antireflection film; and plating a high-reflection film or an antireflection film on the end face close to the longest light-emitting wavelength, or keeping the end face in a cleavage state.

The invention also provides a 10G PON OLT based on the cascaded multi-wavelength integrated semiconductor laser, the cascaded multi-wavelength integrated semiconductor laser comprises two sections of single longitudinal mode lasers which are connected in series and have different light-emitting wavelengths, and the light-emitting wavelengths of the two sections of single longitudinal mode lasers are 1480-1500nm and 1575-1580nm respectively.

Preferably, the cascaded multi-wavelength integrated semiconductor lasers are packaged in a TO-CAN.

The invention also provides an OTDR detection optical module based on the cascade multi-wavelength integrated semiconductor laser, and the cascade multi-wavelength integrated semiconductor laser comprises two sections of modulation signal generation lasers and repetitive pulse detection signal generation lasers which are connected in series and have different light-emitting wavelengths.

The invention also provides a high-capacity data communication optical module which comprises the cascaded multi-wavelength integrated semiconductor laser.

The invention has the advantages that the longitudinal cascade integration mode ensures that each working wavelength can independently work under the condition of meeting the respective performance requirement; the optical path control mode in the optical subassembly or the optical module is greatly simplified, optical path control components such as a wave combiner and a filter plate required by other existing schemes are omitted, the implementation cost is reduced, and the packaging process is simplified.

Drawings

FIG. 1 is a wave combining mode of a separate TO-CAN transmitting terminal;

FIG. 2 shows a wave combining manner of Box package at the transmitting end;

fig. 3 is an integrated wave-combining mode of a laser integrated array chip and a planar waveguide wave-combiner;

4 (a) -4 (c) are sequentially cascaded multi-segment single longitudinal mode lasers along the propagation direction of the optical field according to the present invention;

fig. 5 (a) and 5 (b) are cross-sectional views of a two-wavelength direct modulation laser emitting chip in embodiment 1;

FIG. 6 is a gain/absorption spectrum of each region of the dual wavelength direct modulation laser transmitter chip in example 1;

fig. 7 is a schematic structural diagram of a cascaded multi-stage single longitudinal mode laser and a gain/absorption spectrum of each region in embodiment 2;

fig. 8 is a schematic structural view of embodiment 3.

Wherein: 101. LD ₁ TO-CAN；102、LD ₂ TO-CAN; 103. a control element combination of the spatial light path; 104. a coupling lens; 105. coupled to an output fiber; 201. array arrangement; 202. a collimating lens; 203. a combiner; 204. an isolator; 205. a light path adjusting block; 206. a coupling lens; 207. light is coupled to the optical fiber in a converging way; 501. an N-type electrode; 501-1, an N-type first electrode; 501-2, an N-type second electrode; 502. an N-type substrate; 503. a lower cladding; 504. a lower respective confinement layer; 505. a strained multi-quantum well active layer; 506. upper respective confinement layers; 507. a buffer layer; 508. a grating layer; 509. an upper cladding layer; 510. a ridge waveguide; 511. a P-side ohmic contact layer; 512. a P-type electrode; 512-1, a P-type first electrode,512-2, P type second electrode; 512-3, a P-type third electrode; 513. plating the front end face of the antireflection film; 514. a 1490nm gain section, 515, a first electrically isolated channel; 516. 1490nm absorption region, 517, a second electrically isolated channel; 518. 1577nm gain section; 519. plating the backlight end face of the high-reflection film; 520. a 1490nm segment grating; 521. a 1490nm absorption region grating; 522. grating in 1577nm band.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The invention provides a cascaded multi-wavelength integrated semiconductor laser, which is cascaded with a plurality of sections of single longitudinal mode semiconductor lasers with different working wavelengths along the propagation direction of an optical field. The working wavelength of each section is the lasing wavelength of each section.

As shown in fig. 4 (a) -4 (c), the cascaded multi-wavelength integrated semiconductor lasers are sequentially cascaded with multi-segment single longitudinal mode lasers along the direction of optical field propagation z. All the sections in the device work in a single longitudinal mode, and preferably, the side mode suppression ratio of the single longitudinal mode laser is more than 30dB, namely, only one main lasing wavelength is provided. The mode for realizing the single longitudinal mode work includes, but is not limited to, a gain coupling distribution feedback grating, a loss coupling distribution feedback grating, a refractive index coupling distribution feedback phase shift grating, a refractive index coupling distribution feedback uniform grating with an asymmetric end face, and the like. The grating layer that ensures single mode operation can be either below the active area (N-side grating) or above the active area (P-side grating).

The sections of the device are cascaded in order of magnitude of the operating wavelength, as shown in FIG. 4 (a), with a wavelength λ ₁ <λ ₂ <…<λ _n And n is an integer. The operating wavelength spacing of the segments may or may not be uniform, with the operating wavelength of each segment preferably being outside the bragg stop band of the grating of all other wavelength segments. The gain region material and structural design on the long wavelength side and the implant level are adjusted such that its material gain absorption curve is substantially transparent to short wavelengths.

The end face close to the side with the longest working wavelength can select a proper film coating mode according to application, such as a high-reflection film, an antireflection film or a state of maintaining cleavage; and the end face close to one side of the shortest working wavelength is plated with an antireflection film. Each segment has independent P-side electrode and N-side electrode, and can inject electric signal independently. Optionally, the N-side electrodes of the cascaded single-stage longitudinal mode lasers are combined and shared.

Alternatively, each different operating wavelength may employ an active region structure having a different gain spectral peak to provide sufficient gain for each operating wavelength, respectively. If the effective gain range of the material can cover different operating wavelengths of each segment, each segment can be designed with the same gain region.

Alternatively, as shown in fig. 4 (b), an electrodeless absorption region may be added between two adjacent sections of lasers, and this region retains the grating layer thickness, material and structure in the single longitudinal mode laser at the shorter wavelength emission side of the single longitudinal mode lasers at two adjacent sides. The length of the absorption section is 1/5 to 1/2 of the length of the laser on the same wavelength side.

The electrodeless absorbing region serves to absorb and feed back signals on the relatively short wavelength side so that it has a negligible minor effect on the adjacent relatively long wavelength operating band. Further, according to the backlight detection requirement, a reverse bias electrode can be added in the electrodeless absorbing region, i.e. the applied voltage of the P-side electrode is less than that of the N-side electrode, as shown in FIG. 4 (c). Alternatively, the absorbing region and the N-side electrode on the short wavelength side thereof may be combined and shared or all the segment N-side electrodes of the cascade may be combined and shared, depending on the application.

Optionally, the optical field confinement and the carrier confinement of the device are realized by a ridge waveguide mode or a Buried Heterojunction (BH) mode.

The growth material system of the device is not particularly limited, and an InP/InGaAsP material system, an InP/AlGaInAs material system, a GaAs/InGaAs material system, a GaAs/AlGaAs material system, or the like can be used, but not limited thereto.

It is worth noting that the individual wavelength values mentioned for each application in the following examples are the center wavelengths in the wavelength range required for each application, and thus the following example protection schemes are not limited to the mentioned wavelength values, but are applicable to any values in the wavelength range of the application.

Example 1

The existing various 10G PON OLTs need TO be compatible downwards, namely, the traditional low-speed ONU and the ONU with the 10G speed are simultaneously supported, a 10G 1575-1580nm laser and a 2.5G or 1.25G 1480-1500nm laser are respectively and independently packaged into a TO-CAN form, and then the TO-CAN form is combined with various filters TO carry out the integration of discrete devices in the OSA through the control of a spatial optical path, so that the wave combination of two wavelengths is completed.

In embodiment 1, the two wavelength lasers are monolithically integrated into the same device, and this scheme is to use two LDs separated in fig. 1 ₁ TO-CAN 101 and LD ₂ The chips with two wavelengths in the TO-CAN 102 are integrated into one chip in a single chip mode, packaged in the same TO-CAN and then directly coupled TO the optical fiber through the coupling lens, and space optical path elements of a transmitting part in the scheme of fig. 1 are omitted.

Referring to fig. 5 (a) and 5 (b), the optical field and carrier confinement of the integrated dual-wavelength direct modulation laser emission chip adopts a ridge waveguide mode, and the chip sequentially comprises an N-type electrode 501, an N-type substrate 502, a lower cladding 503, a lower respective confinement layer 504, a strained multiple quantum well active layer 505, an upper respective confinement layer 506, a buffer layer 507, a grating layer 508, an upper cladding 509, a ridge waveguide 510, a P-side ohmic contact layer 511, and a P-type electrode 512 from bottom to top along the growth direction x. The front end surface 513 coated with the antireflection film, the 1490nm gain section 514, the first electrical isolation channel 515, the 1490nm absorption region 516, the second electrical isolation channel 517, the 1577nm gain section 518 and the backlight end surface 519 coated with the high reflection film are sequentially arranged from left to right along the z direction of the light field propagation direction.

The active regions of the gain section 514 and the absorption region 516 are the same, i.e., the quantum well structure and material parameters are the same, and the gain peak is near 1490 nm. The gain section 518 has a different quantum well structure and material parameters than the gain section 514, with a gain peak around 1577 nm. The grating layer 508 in fig. 5 (a) is etched in fig. 5 (b) along the z-direction to form an index-coupled phase-shifting grating to ensure the single-mode operation of the 1490nm gain section 514 and the gain section 518, respectively, but with different grating periods. The 1490nm segment grating 520 has a period P1, the 1490nm absorption region 516 has a period P2, and the 1577nm segment grating 522 has a period P3. P1 and P3 are determined by the operating wavelengths of the 1490nm gain section 514 and 1577nm gain section 518, respectively. P2 can be chosen to be the same as P1, i.e. to retain a first order grating, chosen such that light is absorbed while returning a light signal in the-z direction; p2 may also be chosen equal to twice P1, the choice being such that the feedback light, while being absorbed, will be diffracted in other directions than the z-direction. Can play a role of isolating from a 1577nm section laser. From left to right in the z-direction, the bottom of the device comprises an N-type first electrode 501-1 and an N-type second electrode 501-2; the top of the device includes a P-type first electrode 512-1, a P-type second electrode 512-2, and a P-type third electrode 512-3. To illustrate the difference of main performance parameters in Z direction, fig. 5 (b) only shows the distribution of key layers in Z direction, mainly including an electrode layer, a strained multi-quantum well active layer (indicated by hatching), and a grating layer. Electrically isolating

channels

515 and 517 are formed in the interface region of each segment in fig. 5 (b) by etching the P-side ohmic contact layer 511 and part of the ridge waveguide 510 downward, thereby performing the electrical isolation function of each segment implantation. The other layers of fig. 5 (a) are uniformly distributed in the z-direction and are not shown in fig. 5 (b) accordingly.

The P-type first electrode 512-1 and the N-type first electrode 501-1 are forward biased, i.e., the voltage applied by the P-type first electrode 512-1 is greater than that of the N-type first electrode 501-1, thereby providing a pumping source for the 1490nm gain region. The P-type second electrode 512-2 and the N-type first electrode 501-1 are reversely biased, i.e. the voltage applied by the P-type second electrode 512-2 is smaller than that applied by the N-type first electrode 501-1, so as to form effective rapid absorption of a left side 1490nm signal. The P-type third electrode 512-3 and the N-type second electrode 501-2 are forward biased, i.e., the voltage applied to the P-type third electrode 512-3 is greater than that applied to the N-type second electrode 501-2, thereby providing a pumping source for the 1577nm gain region.

The working principle of the device is described as follows:

the 1490nm segment electrode injects a DC plus AC electrical signal under forward bias to produce 1490nm signal light through the gain section 514 and grating 520. The signal light is output leftward from the front facet 513 and rightward into the absorption region 516, and since 1490nm is still within the bragg reflection passband wavelength of the grating 521, the 1490nm signal is gradually reflected while being absorbed. Thus forming an equivalent wavelength-selective, low-reflection facet to the 1490nm cavity in the x-direction at the location of the first electrically isolated trench 515.

The 1490nm absorption region 516 adopts an independent electrode for applying reverse bias voltage, and the length of the region is 1/5 to 1/2 of the length of the laser with the same wavelength in the front section. The technical effect of selecting in this way has two: on one hand, carriers generated by 1490nm light absorption can be quickly pulled out of an active region, and the absorption region is prevented from being saturated, so that 1490nm light is prevented from entering the 1577nm gain region 518 and crosstalk is generated on the gain region; on the other hand, this section can have sufficient light absorption to generate sufficient backlight current when used as a backlight detector (MPD) for backlight detection of 1490nm signals.

The 1577nm segment electrodes inject a dc plus ac electrical signal under forward bias to produce 1577nm of signal light through the gain region 518 and grating 522. The signal light passes through the 1490nm absorption region 516 and the 1490nm gain region 514 in this order to the left, and is output from the front facet 513. While the 1577nm signal propagates to the left, the 1490nm active region material is almost transparent to 1577nm since it lies outside the reflection passband of the 1490nm grating and the 1577nm corresponding transition energy is much smaller than the band gap difference of the 1490nm gain region, and 1577nm can pass through the 1490nm segment with almost no or very low loss.

Fig. 6 illustrates the gain/absorption spectrum 601 of 1490nm gain region 514, the absorption spectrum 602 of 1490nm absorption region 516, and the gain/absorption spectrum 603 of 1577nm gain region 518, respectively. As shown, the operating wavelength of 1490nm segment 514 falls at point a on the gain/absorption curve 601, so that a larger operating gain is obtained at the operating wavelength, and a signal is output to the left from the light-exiting facet 513. After the 1490nm signal propagates to the right into the absorption region 516, the operating point is point B on the absorption curve 602 for the segment 516, at which point the 1490nm signal will experience a large absorption loss until the signal is almost completely absorbed in the segment, rather than entering the 1577nm gain region. The operating wavelength of the 1577nm band falls on the higher gain C point of the gain/absorption curve 603 of the band, and is substantially transparent or sees little absorption as it passes through the 1490nm absorption region, corresponding to point D on the graph. By further optimizing the 1490 active region structure, this absorption can be optimized to be nearly transparent. The 1577nm signal will then pass through the 1490nm segment in an almost transparent state, corresponding to operating point E on the figure.

In the mode, the 1490nm and 1577nm of the device are monolithically integrated together in a relatively independent working mode, and output on the same optical path, so that wave combination is completed in a compact and low-cost mode.

Example 2

In order to implement online OTDR detection, the optical module needs to integrate a signal wavelength and an OTDR wavelength, and in embodiment 2, the lasers with these two wavelengths are monolithically integrated on the same chip, so that the module integrating the OTD function is greatly simplified. In this embodiment, the transmission signal employs a direct modulation laser with a wavelength range of 1575-1580 nm; and the OTDR detection signal has a repetitive pulse generation laser with the wavelength range of 1640-1660 nm. This application may be other signal wavelengths and OTDR wavelengths depending on the actual detection scenario.

The device is longitudinally and sequentially cascaded with a 1577nm gain area, a 1577nm absorption area and a 1650nm gain area, wherein positive bias voltage is applied to the two gain areas, reverse bias voltage is applied to the absorption area, the left side is plated with an antireflection film to form a light-emitting end face, and the right side is plated with a high-reflection film to form a backlight end face. The schematic diagram of the three-stage structure and the gain or absorption spectrum of each stage are shown in FIG. 7. The gain spectrum 701 of the 1577nm segment provides sufficient gain (operating point a) for this segment, which transmits signal light out the left. This signal is reflected to the right by the absorption edge of the absorption region and thus has little effect on the 1650nm laser, which operates at point B of absorption line 702. The point C on the 1650nm gain spectrum 703 provides gain for the section, and the signal is transmitted to the left, passes through the point D on the left 702 and the point E on the left 701 in sequence in a transparent state or with low loss, and outputs a detection pulse from the light-emitting surface.

Example 3

In the application of high-capacity data communication such as 400G, 800G and the like, a direct current laser and external modulation scheme based on a wavelength division multiplexing system is adopted, output signals of all wavelength lasers are respectively coupled to a modulator and then are independently modulated, and finally a wave combiner is adopted for wave combination. At present, the industry mostly adopts the form that each channel wavelength laser is separated, and adopts the mode of space optical path coupling to carry out hybrid integration with subsequent modulation and wave-combining devices.

The integration mode provided by the invention can cascade lasers of various wavelength channels working by direct current, at the moment, P-side electrodes of various channels are independent, and N-side electrodes can be combined and shared. Taking two wavelengths as an example, the cascading manner is shown in fig. 8. According to the wavelength channel interval and considering the number of integrated channels, if the maximum wavelength range does not exceed 50 to 60nm, the same gain region design can be adopted, otherwise, the design of different gain regions of each channel needs to be considered.

The technical principles of the present invention have been described above with reference to specific embodiments. The description is made for the purpose of illustrating the principles of the invention and should not be construed in any way as limiting the scope of the invention. Based on the explanations herein, those skilled in the art will be able to conceive of other embodiments of the present invention without inventive effort, which would fall within the scope of the present invention.

Claims

1. A cascade multi-wavelength integrated semiconductor laser is characterized in that the cascade multi-wavelength integrated semiconductor laser comprises at least two sections of single longitudinal mode lasers which are connected in series and have different light emitting wavelengths, and the light emitting wavelengths of the single longitudinal mode lasers which are connected in series and have different light emitting wavelengths are changed in an increasing mode along the semiconductor laser from a light emitting end face; each section of single longitudinal mode laser comprises a grating for realizing single longitudinal mode output, and the light-emitting wavelength of each section of single longitudinal mode laser is out of the Bragg stop band of the grating of other sections of single longitudinal mode lasers; an absorption region is arranged between any two single longitudinal mode lasers, and the grating structure in the absorption region is the same as the grating structure in the single longitudinal mode laser on the shorter light-emitting side in the single longitudinal mode lasers on two adjacent sides; and the active region in the absorption region is the same as the active region in the single longitudinal mode laser at the shorter wavelength side in the single longitudinal mode lasers at two adjacent sides.

2. The cascaded multiwavelength integrated semiconductor laser of claim 1, wherein the grating is below the active region or above the active region.

3. The cascaded multiwavelength integrated semiconductor laser of claim 1, wherein the absorbing region has a reverse bias voltage applied or no voltage applied.

4. A cascaded multiwavelength integrated semiconductor laser as claimed in any of claims 1 to 3, wherein the gain region of the same material can cover the operating wavelength of each section of single longitudinal mode laser, and the gain region of each section of single longitudinal mode laser adopts the same material and the same structure; otherwise, different materials and/or structures are adopted in the gain region of each section of the single longitudinal mode laser.

5. The cascaded multiwavelength integrated semiconductor laser according to any of claims 1 to 3, wherein each of the segments of the single longitudinal mode lasers comprises a separate P-electrode, and the N-electrodes of each of the segments of the single longitudinal mode lasers are separate or common.

6. The cascaded multiwavelength integrated semiconductor laser of claim 3, wherein each segment absorbing region comprises a separate P-electrode, the N-electrode of which is shared with the shorter wavelength side of the two adjacent sides of the single longitudinal mode laser.

7. A cascaded, multiwavelength integrated semiconductor laser as claimed in claim 3, wherein all of the absorbing regions and the single longitudinal mode laser share an N electrode.

8. The cascaded multiwavelength integrated semiconductor laser as claimed in any of claims 1-3, wherein the exit facets are coated with an anti-reflection coating; and plating a high-reflection film or an antireflection film on the end face close to the longest luminescence wavelength, or keeping the cleavage state.

9. A 10G PON OLT comprising the cascaded multi-wavelength integrated semiconductor laser as claimed in any one of claims 1 to 8, wherein the cascaded multi-wavelength integrated semiconductor laser comprises two serially connected single longitudinal mode lasers with different emission wavelengths, and the emission wavelengths of the two single longitudinal mode lasers are 1480 to 1500nm and 1575 to 1580nm, respectively.

10. The 10G PON OLT of claim 9, wherein the cascaded multi-wavelength integrated semiconductor lasers are packaged in a TO-CAN.

11. An OTDR detection optical module, comprising a cascaded multi-wavelength integrated semiconductor laser according to any of claims 1 to 8, said cascaded multi-wavelength integrated semiconductor laser comprising two series-connected modulated signal generating lasers and repetitive pulse detection signal generating lasers having different emission wavelengths.

12. An optical module for high capacity data communication comprising a cascaded multi-wavelength integrated semiconductor laser as claimed in any one of claims 1 to 8.