CN110336184B

CN110336184B - A low noise SOA-PIN integrated photodetector

Info

Publication number: CN110336184B
Application number: CN201910638464.8A
Authority: CN
Inventors: 李洵; 董智星; 周玉兰; 王衡; 赵佳; 杜刘革; 王作佳; 黄卫平
Original assignee: Shandong University
Current assignee: Shanghai Manguang Information Technology Co ltd
Priority date: 2019-07-16
Filing date: 2019-07-16
Publication date: 2021-03-12
Anticipated expiration: 2039-07-16
Also published as: CN110336184A

Abstract

The invention discloses a low-noise SOA-PIN integrated optical detector, which sequentially comprises the following components in the signal light propagation direction: the SOA part and the PIN part share the same bottom electrode, the top of the SOA part and the PIN part is provided with an SOA top electrode and a PIN top electrode which are independently arranged, the total reflection mirror is positioned on the outer side of the PIN part, the SOA part comprises a grating space filter structure layer, and the direction of the grating space filter structure layer is along the propagation direction of signal light.

Description

SOA-PIN integrated optical detector with low noise

Technical Field

The invention relates to the technical field of photoelectric devices, in particular to a low-noise SOA-PIN integrated optical detector.

Background

With the demand of the internet for a proliferation of traffic and bandwidth, the demand for receivers in optical communication systems is increasing. Conventional optical receivers usually employ PIN photodiodes or Avalanche Photodiodes (APDs) as photodetectors, but they have difficulty meeting the requirements of current receivers for photodetectors. On the one hand, PIN has good bandwidth characteristics, but since it has no intrinsic gain, using PIN alone as a photodetector does not provide sufficient sensitivity for the receiver. On the other hand, an APD can provide an intrinsic gain, but the intrinsic gain is generated by an avalanche multiplication effect of an electrical domain, so that the gain bandwidth product of the APD has a certain upper limit, and in an optical communication system with a speed of 25Gb/s, 40Gb/s or higher, the APD is often unusable due to the limited bandwidth.

A better solution is to use a Semiconductor Optical Amplifier (SOA) as a preamplifier of a PIN photodetector to amplify an optical signal in advance, and then use the PIN to complete photoelectric conversion. However, this solution brings about significant problems as follows: firstly, the introduction of the SOA brings extra Amplifier Spontaneous Emission (Amplifier Spontaneous Emission) noise, which greatly reduces the signal-to-noise ratio of the detected signal in the PIN, thereby affecting the sensitivity characteristic of the receiver; secondly, the SOA as an additional discrete device makes more components in the receiver, the structure becomes more complex, and there may be a problem of large coupling loss between the SOA and the PIN.

To reduce the effect of noise, a filter is typically added to the optical receiver to filter out a portion of the out-of-band noise. The common filter is a band-pass filter, but no matter the filter is a band-pass filter or a low-pass, high-pass, band-stop filter, etc., the filters are all based on the spectrum filtering action, i.e., the signals are only screened on the wavelength level, the signals of the required wave band are left, and the signals of the unnecessary wave band are filtered, so that the effect of inhibiting the wide-spectrum noise is achieved. The spectrum filtering method has certain limitations, and cannot distinguish signals and noise at the same wavelength, the filtering effect (signal-to-noise ratio after filtering) completely depends on the pass band width and pass band characteristics of the filter, the narrower the pass band width and the better the pass band characteristics are, the more noise is filtered, but even if the pass band is sufficiently narrow, the noise in the pass band cannot be avoided, and the too-narrow pass band may cause signal distortion.

Disclosure of Invention

In order to solve the technical problem, the invention provides a low-noise SOA-PIN integrated optical detector so as to achieve the purposes of filtering noise and improving the signal-to-noise ratio.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a low-noise SOA-PIN integrated optical detector sequentially comprises the following components in the signal light propagation direction: the optical fiber signal transmission device comprises an SOA part, a PIN part and a total reflection mirror, wherein the bottom of the SOA part and the bottom of the PIN part share the same bottom electrode, the top of the SOA part is an SOA top electrode and the PIN top electrode which are independently arranged, the total reflection mirror is located on the outer side of the PIN part, the SOA part comprises a grating space filter structure layer, and the direction of the SOA part is along the transmission direction of signal light.

In the above scheme, the SOA part includes from bottom to top in proper order: the device comprises a bottom contact layer, a bottom electrode, a substrate layer I, a buffer layer, a flat coupling waveguide layer, a first respective limiting layer, a gain active layer, a second respective limiting layer, a spacing layer, a grating spatial filter structure layer, an etching stop layer, an upper cladding layer, a contact layer I and an SOA top electrode.

In the above scheme, the gain active layer includes a single quantum well layer wrapped by two barrier layers.

In the above scheme, the grating spatial filter structure layer includes a P-type grating waveguide layer and a P-type grating cover layer.

In the above scheme, the PIN part includes from bottom to top in proper order: the bottom contact layer and the bottom electrode, the substrate layer II, the N-type layer, the intrinsic absorption layer, the P-type layer, the contact layer II and the PIN top electrode.

In the above scheme, the thickness of the intrinsic absorption layer of the PIN portion is the same as the thickness of the N-type separate confinement layer, the gain active layer, and the P-type separate confinement layer of the SOA portion, and the centers of the two layers are aligned in the vertical direction. The purpose of such a structural design is to make the gain active region (i.e., the region where the optical field is largest in the transverse optical field distribution) in the SOA section and the absorption intrinsic layer (i.e., the region where the absorption efficiency is highest) in the PIN section on the same horizontal plane, which is advantageous in that it can be ensured that the light output from the SOA section is absorbed by the PIN section to the maximum extent.

In the scheme, the distance between the SOA top electrode and the PIN top electrode is 2-3 mu m.

In the above scheme, the grating spatial filter structure layer is a quarter-wavelength phase shift grating.

In the scheme, the integrated optical detector is a monolithic integrated device formed by sequentially carrying out two times of epitaxial growth on the SOA part and the PIN part.

In the above scheme, the reflectivity of the total reflection mirror is 100%.

The principle core of the low-noise SOA-PIN integrated optical detector spatial filtering provided by the invention is that the spatial distribution of signal light and noise in a grating structure is different, so that the spatial distribution of a signal light field in a device is converged at a PIN part, and a noise light field is uniformly distributed in the device, so that the signal-to-noise ratio of a signal detected by the PIN part is higher than the signal-to-noise ratio of an input signal, and the functions of filtering the noise, improving the signal-to-noise ratio and improving the sensitivity are achieved.

The grating spatial filter structure layer is a quarter-wavelength phase shift grating, and compared with a common first-order grating, the grating spatial filter structure layer is characterized in that a quarter-wavelength phase shift layer is inserted at the center of the grating, and the length L of the quarter-wavelength phase shift layer can be expressed as L (N +1/4) lambda_B/n_effWherein N is any positive integer, λ_BIs the Bragg wavelength, n_effIs the equivalent refractive index. The grating period Lambda of the quarter-wavelength phase shift grating meets the Bragg law Lambda/(2 n)_eff). The grating space filter structure can enable the wavelength to satisfy lambda ═ lambda_BThe coherent optical field has peak value distribution in the central phase shift area, and along with the increase of the reflection coefficient of the normalized grating, most coherent optical fields are concentrated in the adjacent area of the central phase shift area. For signals with off-center wavelengths or no coherence, the spatial distribution of the optical field will be hardly affected by the spatial filtering structure of the grating.

The end of the PIN portion was coated with a total reflection film having a reflectance of 100%. Such a structural design is due to the following considerations: as described above, the first-order bragg grating structure with quarter-wavelength phase shift can make the coherent signal light field have peak distribution in the central phase shift region, but if the grating structure with the ordinary quarter-wavelength phase shift region located in the center of the device is directly adopted, because the device is designed with a PIN photodetector capable of absorbing the light field in the phase shift region, if light enters from only one side, the light field distribution at both sides of the phase shift region is not symmetrical, and the effect of converging the light field by using the quarter-wavelength phase shift grating cannot be achieved. Because the devices usually adopt a single-side light feeding mode, in order to ensure the symmetry of the optical field distribution in the devices, the symmetrical structure of the quarter phase shift grating needs to be folded along the center, so that signal light is injected from a single side and is output from the same side after being reflected by the tail end of the device. In view of the above, the end of the PIN portion is coated with the total reflection film, so that the device becomes a double-folded one-eighth phase shift grating with the phase shift region at the end.

Due to the presence of the total reflection film, the phase shift condition to be satisfied by the length L 'of the PIN section in the propagation direction of the signal light becomes L' ═ N +1/4) λ_B/(2n_eff). The phase shift condition may be such that the coherent signal optical field, having a wavelength equal to the bragg wavelength, converges to a maximum extent to the PIN portion, while the noise (wavelength uniformly distributed over the entire spectrum and without coherence) optical field exhibits a substantially uniform spatial distribution within the device. The phase shift condition will therefore result in the device having the best noise characteristics, i.e. the signal detected in the PIN section will have the largest signal-to-noise ratio.

The SOA part also comprises an N-type flat coupling waveguide (SCW) layer, and the N-type flat coupling waveguide layer can enlarge the mode spot of guided light and reduce the optical field limiting factor so as to ensure the coupling efficiency of an input optical field.

In the SOA part, the material of the first substrate layer is N-type InP, and the doping concentration is about 3 multiplied by 10¹⁸cm^-3(ii) a The buffer layer is made of N-type InP with a thickness of 450-550 nm and a doping concentration of 1 × 10¹⁸cm^-3(ii) a The flat coupling waveguide layer is made of high-refractive-index N-type InGaAsP, the band gap wavelength of the flat coupling waveguide layer is 1130nm, the thickness range of the flat coupling waveguide layer is 450nm to 550nm, and the doping concentration of the flat coupling waveguide layer is 1 multiplied by 10¹⁸cm^-3(ii) a The material of the first respective confinement layer is N-type InGaAsP, the band gap wavelength of the first respective confinement layer is gradually changed from 980nm to 1250nm, the thickness of the first respective confinement layer is in the range of 225nm to 275nm, and the doping concentration of the first respective confinement layer is about 0.5 multiplied by 10¹⁸cm^-3(ii) a The gain active layer is a well layer wrapped by two barrier layersThe well layer is made of AlGaInAs, the working wavelength of the well layer is 1550nm, the thickness of the well layer is about 5nm, 1.3% of compressive strain is adopted, each barrier layer is made of AlGaInAs, the band gap wavelength of the barrier layer is 1250nm, the thickness of the barrier layer is 10nm, and 0.4% of tensile strain is adopted; the second respective confinement layer is made of P-type InGaAsP, the band gap wavelength of the second respective confinement layer is gradually changed from 1250nm to 980nm, the thickness range of the second respective confinement layer is 90nm to 110nm, and the doping concentration is about 0.2 multiplied by 10¹⁸cm^-3(ii) a The spacer layer is made of P-type InP with a thickness of 30nm and a doping concentration of about 0.3 × 10¹⁸cm^-3(ii) a The grating spatial filter structure layer consists of a grating waveguide layer and a grating covering layer, the grating waveguide layer is made of P-type InGaAsP, the band gap wavelength of the grating waveguide layer is 1260nm, the thickness range of the grating waveguide layer is 50nm to 60nm, and the doping concentration of the grating waveguide layer is about 0.5 multiplied by 10¹⁸cm^-3The grating covering layer is made of P-type InP with a thickness of 50nm and a doping concentration of about 0.7 × 10¹⁸cm^-3(ii) a The material of the etch stop layer is P-type InGaAsP, the band gap wavelength is 1100nm, the thickness is 10nm, and the doping concentration is about 0.7 multiplied by 10¹⁸cm^-3(ii) a The upper cladding layer is made of P-type InP with a thickness of 1700nm, and adopts a gradual doping mode with a doping concentration range of 0.7 × 10¹⁸cm^-3To 2X 10¹⁸cm^-3(ii) a The contact layer comprises a layer with a band gap wavelength of 1300nm, a thickness of 50nm and a doping concentration of more than 3 × 10¹⁸cm^-3The P-type InGaAsP material and a layer with the thickness of 150nm and the doping concentration of more than 3 multiplied by 10¹⁹cm^-3P-type InGaAs material.

In the PIN part, the substrate layer is made of N-type InP and has a doping concentration of about 3 × 10¹⁸cm^-3(ii) a The N-type layer is made of N-type InP, has a thickness of 450-550 nm and a doping concentration of 5 × 10¹⁷cm^-3(ii) a The absorption layer is made of undoped InGaAs and has the thickness of 580 nm; the P-type layer is made of P-type InP, has a thickness of 1530nm to 1870nm and a doping concentration of about 5 × 10¹⁷cm^-3(ii) a The contact layer comprises a layer with a band gap wavelength of 1300nm, a thickness of 50nm and a doping concentration of more than 3 × 10¹⁸cm^-3The P-type InGaAsP material and a layer with the thickness of 150nm and the doping concentration of more than 3 multiplied by 10¹⁹cm^-3P-type InGaAs material.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

(1) the invention provides a concept of spatial filtering, and the core idea of the concept is to filter noise by using the spatial distribution difference of signal light and noise in a grating spatial filtering structure. The concept of spatial filtering distinguishes signals and noise by using wavelength and also distinguishes signals and noise by using coherence and non-coherence, so that compared with spectral filtering, spatial filtering can discriminate signals and noise from more essential characteristics, thereby achieving better filtering effect and obtaining higher signal-to-noise ratio. Specifically, the device design provided by the invention comprises a grating spatial filtering structure which is essentially a quarter phase shift grating, according to the analysis, the distribution of signal light and noise in the grating spatial filtering structure is different, the signal light field can be converged in a quarter phase shift region (namely PIN part) to a great extent, and the noise light field is almost uniformly distributed in the device, so that the strength of the PIN part and the signal field can generate larger difference, and the effects of filtering noise and improving the signal-to-noise ratio are achieved.

(2) Simulation verification shows that compared with a structure that the SOA and the PIN are used as discrete devices in cascade connection, the SOA-PIN integrated optical detector provided by the invention has the advantages that for the same input signal light, the signal-to-noise ratio of a signal detected by the PIN part can be improved by 20dB to 40 dB; furthermore, when the signal light which has passed through the spectrum filtering is input into the grating space filtering structure without gain, the signal-to-noise ratio of the signal detected by the PIN part is still improved by about 18dB compared with the input signal, which proves that the space filtering effect is really due to the spectrum filtering effect under the reasonable structural design.

(3) The SOA-PIN integrated optical detector provided by the invention can simultaneously complete the functions of gain, detection and noise filtering required by an optical communication system receiver in a single device, wherein the gain is realized through the SOA part, the detection is realized through the PIN part, and the noise filtering is realized through a grating space filtering structure.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

Fig. 1 is a schematic perspective view of a low-noise SOA-PIN integrated optical detector disclosed in an embodiment of the present invention;

FIG. 2 is a left side view of a low noise SOA-PIN integrated optical detector as disclosed in an embodiment of the present invention;

FIG. 3 is a right side view of a low noise SOA-PIN integrated optical detector as disclosed in an embodiment of the present invention;

FIG. 4 is a top view of a low noise SOA-PIN integrated optical detector according to an embodiment of the present invention;

FIG. 5 is a diagram illustrating an optical field distribution of signals inside a detector according to an embodiment of the present invention;

FIG. 6 is a graph of the spatial distribution of the noise field inside a detector according to an embodiment of the present invention;

fig. 7 is a spectrum of a signal received by the PIN section.

In the figure, 1, a bottom contact layer and a bottom electrode; 2. a first substrate layer; 3. a buffer layer; 4. a slab coupling waveguide layer; 5. a first respective confinement layer; 6. a single quantum well gain active layer; 7. a second respective confinement layer; 8. a spacer layer; 9. a grating spatial filter structure layer; 10. an etch stop layer; 11. an upper cladding layer; 12. a first contact layer; 13. an SOA top electrode; 14. a second substrate layer; 15. an N-type layer; 16. an intrinsic absorber layer; 17. a P-type layer; 18. a second contact layer; 19. a PIN top electrode; 20. a total reflection mirror; m, SOA, parts; n, PIN part (a).

Detailed Description

The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

The invention provides a low-noise SOA-PIN integrated optical detector, as shown in FIG. 1, the specific embodiment is as follows: the optical detector shown in the present embodiment operates in the 1550nm band and includes, in the horizontal direction, an SOA section M, PIN section N and a total reflection mirror 20.

As shown in fig. 2, the SOA section includes, from bottom to top: the device comprises a bottom contact layer, a bottom electrode 1, a substrate layer I2, a buffer layer 3, a flat plate coupling waveguide layer (SCW layer) 4, a first respective confinement layer 5, a single quantum well gain active layer 6, a second respective confinement layer 7, a spacing layer 8, a grating spatial filter structure layer 9, an etch stop layer 10, an upper cladding layer 11, a contact layer I12 and an SOA top electrode 13.

In this embodiment, the substrate layer 2 is N-type InP with a thickness of 350 μm and a doping concentration of about 3 × 10¹⁸cm^-3。

The buffer layer 3 is made of N-type InP with a thickness of 500nm and a doping concentration of about 1 × 10¹⁸cm^-3And the refractive index is 3.17.

The flat coupling waveguide layer (SCW layer) 4 is made of N-type InGaAsP with band gap wavelength of 1130nm, thickness of 500nm and doping concentration of about 1 × 10¹⁸cm^-3And a refractive index of 3.3.

The material of the first respective confinement layer 5 is N-type InGaAsP, the band gap wavelength is gradually changed from 980nm to 1250nm, the thickness is 250nm, and the doping concentration is about 0.5 multiplied by 10¹⁸cm^-3And a refractive index of 3.2.

The single quantum well gain active layer 6 is composed of a well layer wrapped by two barrier layers, the well layer is made of AlGaInAs, the working wavelength is 1550nm, the thickness is 5nm, 1.3% of compressive strain is adopted, the refractive index is about 3.5, the two barrier layers are made of AlGaInAs, the band gap wavelength is 1250nm, the thickness is 10nm, 0.4% of tensile strain is adopted, and the refractive index is 3.3.

The material of the second respective confinement layer 7 is P-type InGaAsP, the band gap wavelength is gradually changed from 1250nm to 980nm, the thickness is 100nm, and the doping concentration is about 0.2 multiplied by 10¹⁸cm^-3And a refractive index of 3.2.

The spacer layer 8 is made of P-type InP with a thickness of 30nm and a doping concentration of about 0.3 × 10¹⁸cm^-3。

The grating spatial filter structure layer 9 consists of a grating waveguide layer and a grating covering layer, wherein the grating waveguide layer is made of P-type InGaAsP, the band gap wavelength is 1260nm, the thickness is 50nm, and the doping concentration is about 0.5 multiplied by 10¹⁸cm^-3The grating covering layer is made of P-type InP with a thickness of 50nm and a doping concentration of about 0.7 × 10¹⁸cm^-3. The period of the grating in the grating space filtering structure is 235nm, the corresponding Bragg wavelength is 1550nm, and the grating coupling coefficient is 7000m^-1。

The material of the etch stop layer 10 is P-type InGaAsP with a band gap wavelength of 1100nm, a thickness of 10nm and a doping concentration of about 0.7 × 10¹⁸cm^-3。

The upper cladding 11 is made of P-type InP with a thickness of 1700nm and adopts a gradual doping mode with a doping concentration range of 0.7 × 10¹⁸cm^-3To 2X 10¹⁸cm^-3。

The first contact layer 12 is composed of a layer with band gap wavelength of 1300nm, thickness of 50nm, and doping concentration greater than 3 × 10¹⁸cm^-3The P-type InGaAsP material and a layer with the thickness of 150nm and the doping concentration of about 3 x 10¹⁹cm^-3P-type InGaAs material. The contact layer 12 is directly connected with the top electrode of the SOA, and the top electrode of the SOA is made of conductive metal.

The top of the SOA part is etched into a ridge waveguide structure, so that the equivalent refractive index in the horizontal direction is in low-high-low distribution, meanwhile, the refractive index distribution from the buffer layer 3 to the second respective limiting layer 7 is in low-high-low distribution, so that the mode spot of guided light is concentrated in the central area of the gain active layer, the mode spot of guided light is enlarged through the SCW layer, and meanwhile, the optical field limiting factor is reduced, so that the coupling efficiency of an input optical field is ensured.

The SOA section vertical direction has a total thickness of 3415nm except the substrate, a length of 399.5 μm in the signal light propagation direction, and contains 1700 complete grating periods.

As shown in fig. 3, the PIN section includes, from bottom to top: a bottom contact layer and bottom electrode 1, a substrate layer two 14, an N-type layer 15, an intrinsic absorber layer 16, a P-type layer 17, a contact layer two 18, and a PIN top electrode 19.

The material of the second substrate layer 14 is N-type InP with a thickness of 350.4 μm and a doping concentration of about 3 × 10¹⁸cm^-3。

The N-type layer 15 is made of N-type InP with a thickness of 500nm and a doping concentration of about 1 × 10¹⁸cm^-3。

The material of the intrinsic absorber layer 16 is undoped InGaAs and has a thickness of 580 nm.

The material of the P-type layer 17 is P-type InP, and the thickness is 1735 nm.

The second contact layer 18 is formed by a layer with a thickness of 50nm and a doping concentration of more than 3 × 10¹⁸cm^-3And a layer of InGaAsP material with a thickness of 150nm and a doping concentration of about 3X 10¹⁹cm^-3P-type InGaAs material. The contact layer 18 is directly connected to the PIN top electrode, which is made of a conductive metal.

The total thickness of the PIN portion in the vertical direction except the substrate was 3015nm, and the length in the signal light propagation direction was 20.034 μm, which corresponds to the length of 170.5 grating half periods.

Specifically, the manufacturing steps of the SOA-PIN integrated photoelectric detector chip epitaxial wafer are that each layer structure of the PIN portion grows on the second substrate layer 14, then one side of the epitaxial wafer is etched, the etching thickness is 3415nm of the total thickness of the SOA portion except the substrate, and then each layer structure of the SOA portion grows in a butt joint mode in the etched area. This process is required to ensure that the bottom of the SOA section plate coupling waveguide layer (SCW layer) 4 is substantially at the same level as the bottom of the PIN section first buffer layer 15.

Growing a bottom contact layer on the bottom of the first substrate layer and the second substrate layer, and manufacturing a bottom electrode 1, wherein the bottom contact layer is made of InGaAs with the thickness of 150nm and the doping concentration of about 3 multiplied by 10¹⁹cm^-3The bottom contact layer is in direct contact with the bottom electrode, and the bottom electrode is made of conductive metal.

As shown in fig. 4, the SOA top electrode is manufactured above the first contact layer of the SOA part, the PIN top electrode is manufactured above the second contact layer of the PIN part, the two electrode areas are prevented from being adhered, and the two electrode areas are separated by 3 μm.

After the epitaxial wafer is cleaved, a total reflection mirror 20 is plated on the outside of the PIN part along the propagation direction of the optical signal.

To better illustrate the effects of the present invention, a numerical simulation verification example regarding the above-described embodiment is given below, and simulation conditions of the simulation verification example are shown in table 1:

table 1 simulation conditions of simulation verification examples

According to the simulation result obtained under the simulation condition, other characteristic parameters calculated according to the simulation result comprise the spatial distribution conditions of a signal light field and a noise field in the detector, which are shown in fig. 5 and 6; the spectrum of the signal received by the PIN section is shown in fig. 7. The signal-to-noise ratio of the PIN partial absorption region is about 45dB, the integral gain of the device is about 42dB, the bandwidth is about 25Gbps, and the sensitivity is about-36 dBm.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-noise SOA-PIN integrated optical detector is characterized by sequentially comprising the following components in the propagation direction of signal light: the optical fiber grating comprises an SOA part, a PIN part and a total reflection mirror, wherein the bottoms of the SOA part and the PIN part share the same bottom electrode, the tops of the SOA part and the PIN part are an SOA top electrode and a PIN top electrode which are independently arranged, the total reflection mirror is located on the outer side of the PIN part, the SOA part comprises a grating space filter structure layer, the direction of the grating space filter structure layer is along the propagation direction of signal light, and the grating space filter structure layer is a quarter-wavelength phase shift grating.

2. A low noise SOA-PIN integrated optical detector as claimed in claim 1, wherein the SOA section comprises, in order from bottom to top: the device comprises a bottom contact layer, a bottom electrode, a substrate layer I, a buffer layer, a flat coupling waveguide layer, a first respective limiting layer, a gain active layer, a second respective limiting layer, a spacing layer, a grating spatial filter structure layer, an etching stop layer, an upper cladding layer, a contact layer I and an SOA top electrode.

3. A low noise SOA-PIN integrated photodetector as claimed in claim 2, wherein said gain active layer comprises a single quantum well layer wrapped by two barrier layers.

4. A low noise SOA-PIN integrated photodetector as claimed in claim 2, wherein said grating spatial filter structure layer comprises a P-type grating waveguide layer and a P-type grating cladding layer.

5. A low noise SOA-PIN integrated optical detector as claimed in claim 2, wherein the PIN portion comprises, in order from bottom to top: the bottom contact layer and the bottom electrode, the substrate layer II, the N-type layer, the intrinsic absorption layer, the P-type layer, the contact layer II and the PIN top electrode.

6. A low noise SOA-PIN integrated photodetector as claimed in claim 5, wherein the intrinsic absorbing layer of the PIN section and the N-, gain-, and P-type confinement layers of the SOA section have the same thickness, and the centers of the two layers are aligned in the vertical direction.

7. A low noise SOA-PIN integrated photodetector as claimed in claim 1, wherein the SOA top electrode and the PIN top electrode are spaced apart by 2-3 μm.

8. The integrated low-noise SOA-PIN photodetector of claim 1, wherein the integrated photodetector is a monolithic integrated device formed by two epitaxial growths of the SOA portion and the PIN portion in sequence.

9. A low noise SOA-PIN integrated optical detector as claimed in claim 1, wherein the reflectivity of the total reflection mirror is 100%.