Dual-wavelength pump-probe system and method for silicon waveguide carrier lifetime characterization

Abstract

The application relates to a dual-wavelength pumping detection system and method for silicon waveguide carrier lifetime characterization, and belongs to the technical field of carrier dynamics characterization. The system adopts a dual-wavelength cooperative measurement architecture, the pumping light path is focused to irradiate the to-be-measured silicon waveguide from above the chip after polarization adjustment, power adjustment and time delay to excite free carriers; the normalized detection mechanism of the ratio of input reference and output signal is constructed by collecting the detection light before and after the to-be-measured silicon waveguide chip; meanwhile, the synchronous detection link is formed by using a modulation unit and a phase-locked detection unit, the influence of environmental noise, light source power fluctuation and coupling drift on the measurement result is effectively suppressed, the interference of pumping scattered light on the detection signal is reduced through the output end light filtering structure, and therefore the sensitivity, stability and repeatability of the silicon waveguide carrier lifetime measurement are significantly improved; the direct measurement of the carrier lifetime is realized by fitting the normalized transmission change curve under different time delays.

Description

Technical Field

[0001] This invention belongs to the field of silicon photonics chip testing and semiconductor carrier dynamics characterization technology, specifically relating to a dual-wavelength pump detection system and method for characterizing carrier lifetime in silicon waveguides. Background Technology

[0002] Silicon-based photonic integration technology has been widely applied in optical communication, optical interconnection, optical sensing, and on-chip information processing due to its advantages such as compatibility with CMOS processes, low manufacturing cost, and high integration density. In silicon waveguides and related devices, the generation, recombination, and diffusion behavior of charge carriers directly affect a series of key performance characteristics, including optical absorption loss, free carrier dispersion, modulation bandwidth, and nonlinear response. Therefore, studying the carrier lifetime in silicon waveguides is of great significance for understanding the device's physical mechanisms, optimizing process parameters, and reducing propagation loss.

[0003] Existing methods for measuring carrier lifetime mainly include microwave photoconductivity attenuation, time-resolved photoluminescence, and pump-probe methods. Among these, the pump-probe method has become an important tool for studying carrier dynamics due to its advantages such as high time resolution, applicability to micro / nano-scale structures, and non-contact measurement. However, existing techniques still have the following shortcomings when performing pump-probe measurements on silicon photonic chip waveguide structures:

[0004] On the one hand, the measurement objects are mostly bulk materials or large-area samples, making it difficult to adapt to on-chip structures such as silicon waveguides, grating couplers, or edge couplings; existing devices are mostly designed for bulk silicon or large-area semiconductor samples, lacking dedicated test schemes for on-chip integrated waveguides. On the other hand, in pump-probe measurements, coupling instability and light source fluctuations significantly affect measurement accuracy: the probe signal itself is weak, and the chip input / output coupling efficiency is easily affected by factors such as fiber position drift, environmental vibration, temperature changes, and light source power fluctuations, resulting in poor measurement repeatability and high noise levels. In addition, pump scattered light can directly contaminate the probe results—pump light illuminating the chip from above or scattering on the chip surface may enter the probe optical path, causing background interference to the probe signal and reducing the accuracy of phase-locked detection. Furthermore, existing schemes generally lack reference normalization and synchronous detection mechanisms, and do not set up input reference detectors or beam splitting reference channels, making it difficult to effectively suppress probe light source drift, coupling efficiency fluctuations, and systematic noise. Finally, existing systems typically measure carrier lifetime independently, which is not convenient for joint analysis with on-chip optical parameters such as waveguide propagation loss under the same platform or sample conditions, thus limiting in-depth research on the physical mechanisms of devices.

[0005] Therefore, there is an urgent need for a highly stable dual-wavelength pump-probe test system and method for silicon waveguide structures to achieve high-sensitivity and high-repeatability measurement of carrier lifetime, and to have good anti-drift and anti-noise capabilities. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-wavelength pump-probe test system and method for measuring carrier lifetime in silicon waveguides, which solves the problems of unstable coupling of silicon photonic chips, insufficient reference normalization, pump scattering light interference, and low carrier lifetime test accuracy in the prior art.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention relates to a dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, comprising:

[0009] The pump optical path is used to output pump light of the first wavelength and illuminate the test area of ​​the silicon waveguide chip under test in order to excite free carriers in the silicon waveguide under test.

[0010] The probe optical path is used to output probe light of the second wavelength and input it into the silicon waveguide chip under test to detect the waveguide transmission change caused by free carriers.

[0011] The chip coupling and sample carrier module is used to carry the silicon waveguide chip under test and realize the input coupling and output coupling between the probe light and the silicon waveguide chip under test;

[0012] The reference detection module is used to collect the probe light in front of the silicon waveguide chip under test as an input reference signal;

[0013] The detection output module is used to collect the detection light after passing through the silicon waveguide chip under test, and use it as the output detection signal;

[0014] The filtering and signal processing module is used to filter the output probe signal, and perform ratio normalization, synchronous detection and data acquisition processing based on the input reference signal and the output probe signal. It also extracts the probe light changes induced by free carriers and obtains the carrier lifetime of the silicon waveguide under test.

[0015] Preferably, the pump optical path includes:

[0016] The first polarization adjustment unit is used to adjust the polarization state of the pump light;

[0017] The first power adjustment unit is used to adjust the output power of the pump light;

[0018] A modulation unit is used to modulate the intensity of the pump light;

[0019] The mechanical delay unit includes short mechanical delay lines and a retroreflector respectively disposed before and after the modulation unit, which are used to adjust the propagation optical path of the pump light and form an adjustable time delay.

[0020] The pump focusing unit is used to focus the pump light from above the silicon waveguide chip under test onto the area under test.

[0021] Preferably, the detection optical path includes:

[0022] The second polarization adjustment unit is used to adjust the polarization state of the probe light;

[0023] The second power adjustment unit is used to adjust the output power of the probe light and divide the probe light into a reference probe branch and a measurement probe branch.

[0024] The probe light focusing unit is used to focus the probe light on the measurement probe branch onto the area to be measured;

[0025] The reference detection module is installed in the reference detection branch;

[0026] The chip coupling and sample carrying module and the detection output module are sequentially arranged on the measurement detection branch. The detection light on the measurement detection branch enters the silicon waveguide chip under test through the chip coupling and sample carrying module, and is then output by the silicon waveguide chip under test to the detection output module.

[0027] Preferably, the filtering and signal processing module includes a filtering unit disposed in front of the detection output module, and a normalization processing unit, a phase-locked detection unit, and a data acquisition unit connected to the reference detection module and the detection output module;

[0028] The ratio normalization unit is used to normalize the input reference signal and the output probe signal;

[0029] The phase-locked detection unit is used to perform synchronous phase-locked detection on the normalized output signal;

[0030] The data acquisition unit is used to acquire phase-locked loop detection results and output time-resolved transmission variation curves;

[0031] The reference signal of the data acquisition unit comes from the modulation frequency of the modulation unit.

[0032] Preferably, the pump light is selected from a band where the absorption coefficient of silicon material is higher than that of the probe light, and is used to excite free carriers in the silicon waveguide under test; the probe light is selected from a low-loss communication window band, and is used to propagate along the silicon waveguide under test and detect the transmission changes caused by free carriers.

[0033] Preferably, when the second power adjustment unit divides the probe light into a reference probe branch and a measurement probe branch, a small proportion of the probe light enters the reference probe module, and the remaining probe light enters the silicon waveguide chip under test, so as to achieve real-time normalization compensation for probe light power fluctuations and input coupling efficiency changes.

[0034] Preferably, the chip coupling and sample carrying module includes an input coupling structure, an output coupling structure, a sample stage, and a multi-dimensional fine-tuning mechanism for adjusting the relative positions of the input coupling structure, the output coupling structure, and the sample stage;

[0035] The input coupling structure and the output coupling structure are end-face coupling structures or grating coupling structures;

[0036] The sample stage is used to support the silicon waveguide chip under test.

[0037] The multidimensional fine-tuning mechanism is a five-dimensional or six-dimensional fine-tuning frame.

[0038] This invention also relates to a carrier lifetime measurement method implemented using the above-described dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, comprising the following steps:

[0039] S1. Output pump light of the first wavelength and probe light of the second wavelength, and adjust the polarization state and output power of the two lights;

[0040] S2. Pump light shines from above the silicon waveguide chip under test onto the test area, exciting free carriers in the silicon waveguide under test;

[0041] S3. The reference detection module collects the probe light in front of the silicon waveguide chip under test to form an input reference signal;

[0042] S4. The probe light is coupled into the silicon waveguide chip under test to detect the waveguide transmission change caused by free carriers. After coupling, the output light is filtered. The probe output module collects the coupled probe light to form the output probe signal.

[0043] S5. The filtering and signal processing module performs ratio normalization processing on the input reference signal and the output probe signal, and inputs the normalized signal into the phase-locked loop detection unit for synchronous detection. The data acquisition unit obtains the time-resolved transmission change curve, and the carrier lifetime of the silicon waveguide under test is obtained by fitting the time-resolved transmission change curve.

[0044] Preferably, in step S3, the probe light is divided into a reference probe branch and a measurement probe branch by the second power adjustment unit. A small proportion of the probe light enters the reference probe module, and the probe light in front of the silicon waveguide chip under test is collected by the reference probe module set on the reference probe branch.

[0045] Preferably, in step S2, before the pump light shines from above the silicon waveguide chip under test onto the test area, the relative time delay between the pump light and the probe light is scanned by changing the position of the short mechanical delay line; and the pump light is vertically irradiated onto the surface of the silicon waveguide chip under test by adjusting the return reflector.

[0046] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0047] 1. The dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, as disclosed in this invention, uses a pump light of a first wavelength to illuminate the test area of ​​the silicon waveguide chip under test to excite free carriers in the silicon waveguide under test. A probe light of a second wavelength is input and coupled to the silicon waveguide chip under test to detect the waveguide transmission change caused by free carriers. It is specifically designed for silicon waveguides and silicon photonic chip devices and realizes direct measurement of on-chip carrier lifetime.

[0048] 2. The dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, as disclosed in this invention, employs a reference probe module to collect the probe light in front of the silicon waveguide chip under test as the input reference signal, and a probe output module to collect the probe light after passing through the silicon waveguide chip under test as the output probe signal. The input reference signal is used as the comparison object for the output probe signal, and the power fluctuation of the probe light source and the fiber coupling efficiency drift are normalized in real time, which significantly improves the stability and repeatability of the measurement system.

[0049] 3. The dual-wavelength pump detection system for silicon waveguide carrier lifetime characterization disclosed in this invention uses a modulation unit to modulate the pump light and works in conjunction with a phase-locked detection unit for synchronous detection. This effectively suppresses environmental noise and asynchronous background interference, and significantly improves the signal-to-noise ratio of weak detection signals.

[0050] 4. The dual-wavelength pump detection system for silicon waveguide carrier lifetime characterization disclosed in this invention includes a filtering and signal processing module. This module includes a filter unit located in front of the detection output module, which can effectively filter out background contamination caused by pump light scattering and reduce the interference of pump scattered light on the detection results.

[0051] 5. The dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, as disclosed in this invention, incorporates a mechanical delay unit in the pump optical path. This unit allows for adjustment of the relative time delay between the pump and probe beams, facilitating the acquisition of time-resolved carrier decay curves and enabling the extraction of accurate carrier lifetime parameters.

[0052] 6. This invention supports carrier lifetime measurement under the same chip or similar process conditions, and can combine propagation loss testing of waveguides of different lengths, geometric parameters of waveguides with different structures, etching depth parameters, surface treatment conditions, and sidewall roughness and doping parameters obtained by auxiliary characterization to analyze the correlation between carrier lifetime, propagation loss and process conditions, providing a comprehensive characterization basis for the performance optimization of silicon photonic devices. Attached Figure Description

[0053] Figure 1This is a schematic diagram of a dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides.

[0054] Figure 2 This is a schematic diagram showing the interaction of pump light and probe light in the sample area of ​​the silicon waveguide chip under test.

[0055] Figure 3 This is a schematic diagram of the silicon waveguide coupling method for probe light input;

[0056] Illustration: 1-Filter unit, 2-Silicon waveguide chip under test, 3-Probe light focusing unit, 4-Second power adjustment unit, 5-Second polarization adjustment unit, 6-Second circular aperture, 7-Pump focusing unit, 8-Retrogressive mirror, 9-Modulation unit, 10-Short mechanical delay line, 11-First power adjustment unit, 12-First polarization adjustment unit, 13-First circular aperture, 14-Inverse conical mode conversion structure, 15-Silicon substrate, 16-Buried oxide layer, 17-Top device layer silicon. Detailed Implementation

[0057] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments. The following embodiments are used to illustrate the invention, but are not intended to limit the scope of the invention.

[0058] See attached document Figure 1 As shown, the dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, as disclosed in this invention, mainly includes a pump optical path, a probe optical path, a chip coupling and sample carrying module, a reference probe module, a probe output module, and a filtering and signal processing module. In this embodiment, the pump optical path preferably uses pump light with a wavelength of 780 nm, and the probe optical path preferably uses probe light with a wavelength of 1560 nm. The 780 nm pump light can be effectively absorbed by silicon material to excite electron-hole pairs in the silicon waveguide under test; the 1560 nm probe light is located in the near-infrared communication band, can propagate in the silicon waveguide under test, and exhibits a sensitive response to absorption changes caused by free carriers. This system employs the above dual-wavelength configuration, functionally distinguishing the pumping and probe processes, thereby facilitating the time-domain characterization of on-chip carrier lifetime.

[0059] The pump optical path is used to output pump light of a first wavelength and illuminate the test area of ​​the silicon waveguide chip under test to excite free carriers in the silicon waveguide under test. The pump optical path includes a first polarization adjustment unit 12, a first power adjustment unit 11, a modulation unit 9, a mechanical delay unit, and a pump focusing unit 7. After the pump light is adjusted into a circular beam by the first circular aperture 13, it enters the first polarization adjustment unit 12. The first polarization adjustment unit 12 uses a first half-wave plate to adjust the polarization state of the pump light. The first power adjustment unit 11 uses a first polarization beam splitter prism to adjust the output power of the pump light. The modulation unit 9 uses a mechanical shutter or chopper to periodically modulate the intensity of the pump light so that the subsequent phase-locked detection unit can use the modulation frequency as a reference frequency for synchronous detection. The mechanical delay unit includes short mechanical delay lines 10 and a retroreflector 8 respectively disposed before and after the modulation unit to adjust the propagation path of the pump light and form an adjustable time delay. The short mechanical delay lines 10 are used to change the propagation path of the pump light and further change the relative time delay between the pump light and the probe light reaching the test area. The pump focusing unit 7 uses a pump focusing objective lens. The pump light is focused from above the silicon waveguide chip under test and irradiated onto the test area through the pump focusing objective lens, thereby exciting free carriers in the silicon waveguide under test.

[0060] The aforementioned detection optical path outputs a second wavelength detection light and inputs it to the silicon waveguide chip under test (SWT) to detect changes in waveguide transmission caused by free carriers. Specifically, the detection optical path includes a second polarization adjustment unit 5, a second power adjustment unit 4, and a detection light focusing unit 3. After the detection light is adjusted into a circular beam with a circular cross-section by a second circular aperture 6, it enters the second polarization adjustment unit 5. The second polarization adjustment unit 5 uses a second half-wave plate to adjust the polarization state of the detection light. The second power adjustment unit 4 uses a second polarization beam splitter prism to adjust the output power of the detection light, dividing the detection light into a reference detection branch and a measurement detection branch. A smaller proportion of the detection light enters the reference detection module PD-in to acquire the input reference signal, while a larger proportion of the remaining detection light enters the input coupling structure and is input to the SWT chip 2. Through this beam splitting reference structure, the power change of the detection source can be monitored in real time, and the detection signal can be normalized in subsequent processing, thereby reducing the impact of source drift and coupling efficiency fluctuations on the measurement results. The probe light focusing unit 3 uses a probe focusing objective lens to focus the probe light onto the area to be measured.

[0061] In this embodiment, the chip coupling and sample carrying module includes an input coupling structure, an output coupling structure, a sample stage, and a multi-dimensional fine-tuning mechanism for adjusting the relative positions of the input coupling structure, the output coupling structure, and the sample stage. This mechanism carries the silicon waveguide chip under test (SWT) and enables input and output coupling between the probe light and the SWT. The input and output coupling structures are end-face coupling structures or grating coupling structures. The sample stage carries the SWT, and the multi-dimensional fine-tuning mechanism is preferably a five-dimensional or six-dimensional fine-tuning frame, used to adjust the relative positions of the input coupling structure, the output coupling structure, and the SWT to achieve high-precision alignment.

[0062] like Figure 3 As shown, the output coupling structure is an end-face coupling structure. In this embodiment, the input end also adopts an end-face input method. After being shaped by the input probe light focusing unit 3 in free space, the probe light enters the on-chip inverse conical mode field conversion structure 14 from the input end face of the chip under test, and then propagates into the silicon waveguide chip under test 2. After propagating through the silicon waveguide under test, the probe light is then exported from the chip output end face and transmitted to the probe output module PD-out through the output coupling structure. The end-face coupling structure can effectively match the external input beam with the on-chip waveguide mode, improving the stability and repeatability of the probe light input and output.

[0063] The coupling method of the probe light input silicon waveguide preferably combines end-face coupling with an inverse tapered mode conversion structure 14. The silicon waveguide chip under test is preferably an SOI structure, comprising, from bottom to top, a silicon substrate 15, a buried oxide layer 16, and a top device layer silicon 17; the inverse tapered mode conversion structure 14 and the silicon waveguide are continuously formed in the same device layer silicon. After the probe light enters from the chip input end face, it first enters a narrow tip region near the input end face, where the light field exhibits a large mode distribution; subsequently, as the inverse tapered mode conversion structure 14 gradually widens along the propagation direction, the light field gradually transitions from an extended mode to a propagation mode constrained by the on-chip silicon waveguide, and finally propagates into the standard silicon waveguide segment. Preferably, the standard silicon waveguide is a strip waveguide formed in the SOI device layer, with the inverse tapered mode conversion structure 14 integrally formed with it. The chip output also uses end-face coupling to guide the probe light propagating through the waveguide to the output detector.

[0064] See attached document Figure 1 As shown, the reference detection module uses a reference detector PD-in, which is set on the reference detection branch to collect the probe light in front of the silicon waveguide chip under test as the input reference signal.

[0065] The chip coupling and sample carrying module and the detection output module are sequentially arranged on the measurement detection branch. The detection light on the measurement detection branch enters the silicon waveguide chip 2 under test through the chip coupling and sample carrying module, and is then output by the silicon waveguide chip 2 under test to the detection output module. The detection output module uses an output detector PD-out to collect the detection light after passing through the silicon waveguide chip under test as the output detection signal.

[0066] The filtering and signal processing module is used to filter the output probe signal and perform ratio normalization, synchronous detection, and data acquisition processing based on the input reference signal and the output probe signal. It extracts the free carrier-induced probe light change and obtains the carrier lifetime of the silicon waveguide under test. Specifically, the filtering and signal processing module includes a filtering unit located before the probe output module, and a normalization processing unit, a phase-locked detection unit, and a data acquisition unit connected to the reference probe module and the probe output module. In this embodiment, to reduce background interference caused by pump light scattering, a filtering unit 1 is provided before the probe output module. The filtering unit is preferably a 1560 nm bandpass filter and / or a 780 nm cutoff filter. The probe light output from the chip output terminal first passes through the filtering unit to filter out stray light scattered by the pump light from above, and then is acquired by the output detector PD-out. This effectively improves the purity of the output probe signal and the accuracy of phase-locked detection. The reference probe module and the probe output module output the input reference signal and the output probe signal, respectively, which are both input to the filtering and signal processing module. The ratio normalization unit is used to normalize the input reference signal and the output detection signal to compensate for power fluctuations, coupling drift, and slow system drift of the detection light source. The normalized signal is then input to the phase-locked detection unit, which uses a lock-in amplifier to perform synchronous phase-locked detection on the normalized output signal. The lock-in amplifier references the modulation frequency of the mechanical shutter or chopper for synchronous phase-locked detection, thereby extracting the weak transmission change signal synchronized with the pump modulation frequency. The data acquisition unit uses a data acquisition card to acquire the phase-locked detection results, i.e., the normalized output signal at different delay positions, and outputs the time-resolved transmission change curve. The reference signal of the data acquisition unit comes from the modulation frequency of the modulation unit.

[0067] like Figure 2As shown, the pump light and probe light have different effects on the sample area of ​​the silicon waveguide chip 2 under test. The probe light propagates in the waveguide along the propagation direction of the silicon waveguide under test; the pump light is focused from above the chip under test onto a local area of ​​the waveguide test area, thereby exciting free carriers in that area. The irradiation area of ​​the pump light and the effective propagation area of ​​the probe light in the waveguide spatially overlap, allowing the free carriers excited by the pump light to modulate the transmission intensity of the probe light in that section of the waveguide. Specifically, after the pump light irradiates, a transient free carrier distribution is formed in the waveguide under test, and the free carrier absorption effect will cause the output intensity of the probe light to decrease; as the free carriers recombine, the transmission intensity of the probe light gradually recovers. By measuring this transmission recovery process under different pump-probe relative time delay conditions, the carrier lifetime information in the silicon waveguide under test can be obtained. In summary, this system is based on a dual-wavelength collaborative measurement architecture, using pump light to excite free carriers in the silicon waveguide chip under test, and characterizing the carrier recombination dynamics process by the transmission change of the probe light in the waveguide.

[0068] In a preferred embodiment, the silicon waveguide chip under test may further be provided with multiple sets of test structures for correlation characterization. These test structures include, but are not limited to, straight waveguides of different lengths, strip waveguides of different widths, ridge waveguides with different etching depths, waveguides under different surface treatment conditions, waveguides under different annealing conditions, and a pump-free reference waveguide fabricated using the same process as the waveguide under test. By obtaining carrier lifetime parameters, propagation loss parameters, structural size parameters, and process condition parameters on the same chip or chips from the same process batch, the correspondence between carrier lifetime and waveguide propagation loss, surface recombination, etching damage, sidewall roughness, and doping conditions can be further established.

[0069] Specifically, during carrier lifetime measurement, the data acquisition unit records the input reference signal output by the reference detection module. The output detection signal of the detection output module The position of the mechanical delay unit Pump light modulation frequency Pump power Detection of optical power and the structural parameters of the waveguide under test. The structural parameters include the waveguide length. Pump light and waveguide interaction length Waveguide width Top silicon thickness Etching depth waveguide cross-sectional area and waveguide exposed perimeter or effective surface perimeter .

[0070] When the mechanical delay unit adopts a retroreflective delay structure, the delay line displacement is... The corresponding relative delay time between pump light and probe light It can be obtained by the following formula:

[0071] ,

[0072] in, The refractive index of air, The speed of light in a vacuum. When the refractive index of air is approximately 1, the relative delay time can be approximately expressed as:

[0073] ,

[0074] At each delay time Below, the probe optical signals before and after the silicon waveguide chip under test are collected by the reference probe module and the probe output module, respectively. , The ratio is then normalized to obtain the normalized transmission signal. :

[0075] ,

[0076] Normalized transmission signal without pump light excitation As a benchmark, the relative transmission change induced by free carriers can be obtained:

[0077] ,

[0078] in, Indicates the delay time The normalized transmission signal change caused by pump light-induced free carriers, i.e. ; This represents the reference normalized transmission signal when not excited by pump light, i.e. ;therefore, This represents the relative transmission change induced by free carriers, used to characterize the magnitude of the change in probe light transmission intensity relative to the reference state after the pump light excites free carriers. The normalized transmission signal can be determined by the pump light in the off state, the negative delay state, or the long delay state after complete carrier recombination. Because free carriers are generated in a local region of the silicon waveguide after pump light irradiation, the free carrier absorption effect causes a transient change in the probe light transmission intensity. As carrier recombination occurs, the relative transmission change gradually recovers. The data acquisition unit performs data acquisition at different delay times... Record the changes to form a time-resolved transmission curve.

[0079] In one embodiment, when the carrier recombination process in the silicon waveguide under test is mainly dominated by a single recombination mechanism, the time-resolved transmission variation curve can be fitted using a single exponential model:

[0080] ,

[0081] in, The amplitude coefficient, This represents the position with zero delay between the pump and probe beams. For background bias, The carrier lifetime in the silicon waveguide under test is denoted as . When multiple recombination processes such as bulk recombination, surface recombination, defect-assisted recombination, or diffusion escape simultaneously exist in the silicon waveguide under test, the time-resolved transmission variation curve can also be fitted using a bi-exponential model:

[0082] ,

[0083] in, and These represent the characteristic time constants corresponding to different composite channels. and These represent the weights of the corresponding composite components. The equivalent carrier lifetime can also be obtained using an amplitude-weighted method, depending on the requirements.

[0084] ,

[0085] Therefore, the carrier lifetime parameters corresponding to each group of waveguide structures under test can be obtained. or equivalent carrier lifetime parameter .

[0086] In a preferred embodiment, the additional absorption coefficient caused by free carriers can also be calculated based on the normalized transmission signals before and after pumping. Let the effective interaction length corresponding to the pump light interaction region be... The change in the additional absorption coefficient induced by free carriers It can be represented as:

[0087] ,

[0088] When the change in transmission is small, the change in the additional absorption coefficient can be approximately expressed as:

[0089] ,

[0090] Given the known calibration parameters of the free carrier absorption cross-section or absorption coefficient of silicon material at the detection wavelength, the additional absorption coefficient change can also be used to estimate the pump-induced change in free carrier concentration. Specifically, the additional absorption caused by free carrier absorption can be expressed as:

[0091] ,

[0092] in, and These represent the free carrier absorption cross sections for electrons and holes at the detection wavelength, respectively. and These represent the changes in electron and hole concentrations induced by the pump light, respectively. Under the condition of approximately electron neutrality... At that time, we can obtain:

[0093] ,

[0094] By using the above method, while obtaining the carrier lifetime, it is possible to further obtain the trend of pump-induced free carrier concentration decay over time.

[0095] In a preferred embodiment, propagation loss test waveguides of different lengths are disposed on the silicon waveguide chip under test to obtain waveguide propagation loss parameters. For a length of... The The output power of a test waveguide was measured under the same input power and coupling conditions. Its output power can be expressed as:

[0096] ,

[0097] in, To input the probe light power, and These represent the coupling efficiency at the input and output ends, respectively. Let be the waveguide propagation loss coefficient. By fitting the output power of waveguides of different lengths, the influence of end-face coupling loss on the propagation loss extraction can be eliminated or reduced. Specifically, taking the natural logarithm of the above equation yields:

[0098] ,

[0099] Therefore, with For waveguide length When performing a linear fit, the negative of the slope is the propagation loss coefficient. The propagation loss coefficient can also be converted into a loss parameter in dB / cm:

[0100] ,

[0101] in, Units of length and The length units remain consistent. When using a base-10 logarithmic form, the output power of waveguides of different lengths can also be fitted:

[0102] ,

[0103] in, This is a constant term that includes input power and end-face coupling loss. From this, propagation loss parameters under different waveguide structures or different manufacturing conditions can be obtained. .

[0104] In a preferred embodiment, the carrier lifetime parameters measured in the same chip under test can be used. or With propagation loss parameters By performing the correlation analysis, we obtain the data set relating carrier lifetime, propagation loss, and process parameters:

[0105] ,

[0106] in, , , The first The width, silicon layer thickness, and etching depth of each waveguide test structure. This represents the propagation loss corresponding to the test structure. This represents the carrier lifetime corresponding to the test structure. and These represent the pump light power and probe light power during measurement, respectively. By comparing data sets from different test structures, it can be determined whether the shortened carrier lifetime is related to increased propagation loss, increased etching depth, increased waveguide sidewall area, or changes in surface treatment conditions.

[0107] Furthermore, body lifespan is known or obtained through auxiliary tests. In this case, surface recombination correlation parameters can also be estimated based on the equivalent carrier lifetime under different waveguide geometries. For a cross-sectional area of... The effective surface perimeter is The waveguide structure, whose equivalent carrier lifetime can be approximately expressed as:

[0108] ,

[0109] in, For the equivalent surface recombination velocity, Let be the geometric factor corresponding to the ratio of the waveguide's surface area to its volume. From this, we can obtain:

[0110] ,

[0111] By comparing different etching depths, waveguide widths, or surface treatment conditions This allows for the analysis of the impact of etching damage and surface recombination on carrier lifetime. It should be noted that the aforementioned... The surface composite characterization parameters are obtained based on the equivalent geometric model and are not limited to the only method for calculating surface density of states. In practical applications, they can be further calibrated by combining process calibration, surface passivation experiments, electrical tests, or microscopic morphology test results.

[0112] In a preferred embodiment, for waveguides fabricated under different etching conditions, the etching depth can be adjusted. Etching power, etching gas flow rate, etching time, sidewall angle, annealing temperature, and surface passivation conditions are recorded as process parameters and correlated with carrier lifetime. Propagation loss and equivalent surface recombination velocity Perform a corresponding analysis. When a group of waveguides simultaneously exhibits large propagation losses... Shorter carrier lifetime and a large equivalent surface recombination rate If the process conditions result in high sidewall scattering loss or surface defect recombination, it can be determined that the process conditions may introduce strong sidewall scattering loss or surface defect recombination. Conversely, if the waveguide exhibits lower propagation loss and longer carrier lifetime after annealing or surface treatment, it indicates that the process conditions are beneficial in reducing the effects of sidewall defects or surface recombination.

[0113] In a preferred embodiment, the sidewall roughness parameter can be obtained by scanning electron microscopy, atomic force microscopy, or process linewidth monitoring of the structure, and is expressed as root mean square roughness. Relevant length Or line width deviation Characterization. Doping concentration parameters can be obtained through wafer source parameters, process records, resistivity measurements, Hall effect measurements, or secondary ion mass spectrometry, and are expressed as doping concentration. or Characterization. The sidewall roughness parameters and doping concentration parameters, together with the carrier lifetime parameters and propagation loss parameters obtained by this system, are used to form a correlation data table:

[0114] ,

[0115] By comparing or fitting the aforementioned correlation data tables, the impact of different process factors on carrier recombination and optical transmission loss in silicon waveguides can be analyzed. The above correlation analysis does not require all parameters to be measured directly in a single measurement; rather, it allows the carrier lifetime parameters measured by this system to be combined with in-wafer loss testing, process monitoring structures, microscopic morphology characterization, and material electrical parameters, thereby providing a basis for the structural design, etching process optimization, and surface treatment process optimization of silicon photonic devices.

[0116] The carrier lifetime measurement method implemented using the aforementioned dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides includes the following steps:

[0117] S1. Output pump light of the first wavelength and probe light of the second wavelength, adjust the polarization state and output power of the two lights, and adjust the polarization state and power of the two lights through the corresponding half-wave plate, polarization beam splitter prism and variable attenuator to bring the system into the predetermined working state.

[0118] S2. After being modulated by the modulation unit 9, the pump light is irradiated from above the silicon waveguide chip under test to the test area, exciting free carriers in the silicon waveguide under test. At the same time, the relative time delay between the pump light and the probe light is changed by the short mechanical delay line 10 and the retroreflector 8. By changing the position of the short mechanical delay line 10, the relative delay between the pump light and the probe light can be scanned in the picosecond to nanosecond time range, thereby obtaining the complete attenuation trajectory of the free carrier-induced transmission change.

[0119] S3. The probe light is divided into a reference probe branch and a measurement probe branch by the second power adjustment unit. The probe light in front of the silicon waveguide chip under test is collected by the reference probe module set on the reference probe branch to form an input reference signal.

[0120] S4. The probe light is coupled into the silicon waveguide chip under test to detect the waveguide transmission change caused by free carriers. After coupling, the output light is filtered. The probe output module collects the coupled probe light to form the output probe signal.

[0121] S5. Under different delay time conditions, the input reference signal and output probe signal are simultaneously acquired. The filtering and signal processing module performs ratio normalization processing on the input reference signal and output probe signal. The normalized signal is then input to the phase-locked loop detection unit for synchronous detection. The data acquisition unit obtains the time-resolved transmission variation curve. Based on the obtained time-resolved transmission variation curve, a single-exponential or double-exponential model is used for fitting, thereby obtaining the carrier lifetime in the silicon waveguide under test. The single-exponential model is suitable for cases with a single dominant recombination process, while the double-exponential model is suitable for cases with multiple processes superimposed, such as surface recombination and defect-assisted recombination.

[0122] In a preferred embodiment, the silicon waveguide chip under test is a strip-shaped silicon waveguide chip formed on an SOI platform. The probe light is coupled to the waveguide under test through the input end face with the assistance of the on-chip inverse conical mode field conversion structure, and is coupled out through the output end face. The pump light is vertically irradiated from above the chip to the waveguide test area, so that free carriers are generated locally only in the irradiated area.

[0123] Supports the correlation between carrier lifetime τ and propagation loss α within the same chip or batch of samples. dBA comparative analysis was conducted on waveguide dimensions, etching depth, surface treatment conditions, etc., to provide a basis for process optimization.

[0124] The present invention has been described in detail above with reference to the embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides, characterized in that, It includes: The pump optical path is used to output pump light of the first wavelength and illuminate the test area of ​​the silicon waveguide chip under test in order to excite free carriers in the silicon waveguide under test. The probe optical path is used to output probe light of the second wavelength and input it into the silicon waveguide chip under test to detect the waveguide transmission change caused by free carriers. The chip coupling and sample carrier module is used to carry the silicon waveguide chip under test (SWT) and realize the input and output coupling of the probe light to the SWT. Specifically, it includes an input coupling structure and an output coupling structure. The input coupling structure and the output coupling structure are end-face coupling structures, and the input coupling structure is also combined with an inverse conical mode conversion structure. The probe light enters the on-chip inverse conical mode conversion structure from the input end face of the SWT, transitions into the SWT, propagates, and is then input-coupled to the SWT, propagating in the waveguide along the propagation direction of the SWT. After propagation in the SWT, the probe light is then exported from the chip output end face and transmitted to the probe output module through the output coupling structure. The pump light is focused from above the SWT and irradiates a local area of ​​the waveguide test region, exciting free carriers in this region. The irradiation area of ​​the pump light and the effective propagation area of ​​the probe light in the waveguide are spatially overlapped, so that the free carriers excited by the pump light modulate the transmission intensity of the probe light in this section of the waveguide. The reference detection module is used to collect the probe light in front of the silicon waveguide chip under test as an input reference signal; The detection output module is used to collect the detection light after passing through the silicon waveguide chip under test, and use it as the output detection signal; The filtering and signal processing module is used to filter the output probe signal, and perform ratio normalization, synchronous detection and data acquisition processing based on the input reference signal and the output probe signal to extract the probe light change induced by free carriers and obtain the carrier lifetime of the silicon waveguide under test. After the pump light is irradiated, a transient free carrier distribution is formed in the waveguide under test. The free carrier absorption effect will cause the output intensity of the probe light to decrease. As the free carrier recombines, the transmission intensity of the probe light gradually recovers. By measuring the transmission recovery process under different pump-probe relative time delay conditions, a time-resolved transmission change curve is obtained. The carrier lifetime of the silicon waveguide under test is obtained by fitting the time-resolved transmission change curve.

2. The dual-wavelength pump-detection system for silicon waveguide carrier lifetime characterization according to claim 1, characterized in that: The pump optical path includes: The first polarization adjustment unit is used to adjust the polarization state of the pump light; The first power adjustment unit is used to adjust the output power of the pump light; A modulation unit is used to modulate the intensity of the pump light; The mechanical delay unit includes short mechanical delay lines and a retroreflector respectively disposed before and after the modulation unit, which are used to adjust the propagation optical path of the pump light and form an adjustable time delay. The pump focusing unit is used to focus the pump light from above the silicon waveguide chip under test onto the area under test.

3. The dual-wavelength pump-detection system for silicon waveguide carrier lifetime characterization according to claim 1, characterized in that: The detection optical path includes: The second polarization adjustment unit is used to adjust the polarization state of the probe light; The second power adjustment unit is used to adjust the output power of the probe light and divide the probe light into a reference probe branch and a measurement probe branch. The probe light focusing unit is used to focus the probe light on the measurement probe branch onto the area to be measured; The reference detection module is installed in the reference detection branch; The chip coupling and sample carrying module and the detection output module are sequentially arranged on the measurement and detection branch.

4. The dual-wavelength pump-detection system for silicon waveguide carrier lifetime characterization according to claim 2, characterized in that: The filtering and signal processing module includes a filtering unit disposed in front of the detection output module, as well as a normalization processing unit, a phase-locked detection unit, and a data acquisition unit connected to the reference detection module and the detection output module. The ratio normalization unit is used to normalize the input reference signal and the output probe signal; The phase-locked detection unit is used to perform synchronous phase-locked detection on the normalized output signal; The data acquisition unit is used to acquire phase-locked loop detection results and output time-resolved transmission variation curves; The reference signal of the data acquisition unit comes from the modulation frequency of the modulation unit.

5. The dual-wavelength pump-detection system for silicon waveguide carrier lifetime characterization according to claim 1, characterized in that: The pump light is selected from a band where the absorption coefficient of silicon material is higher than that of the probe light, and is used to excite free carriers in the silicon waveguide under test; the probe light is selected from a low-loss communication window band, and is used to propagate along the silicon waveguide under test and detect the transmission changes caused by free carriers.

6. The dual-wavelength pump-detection system for silicon waveguide carrier lifetime characterization according to claim 3, characterized in that: The second power adjustment unit divides the probe light into a reference probe branch and a measurement probe branch. A small proportion of the probe light enters the reference probe module, while the rest enters the silicon waveguide chip under test, so as to achieve real-time normalization compensation for probe light power fluctuations and input coupling efficiency changes.

7. The dual-wavelength pump-detection system for characterizing carrier lifetime in silicon waveguides according to claim 1, characterized in that: The chip coupling and sample carrier module also includes a sample stage and a multi-dimensional fine-tuning mechanism for adjusting the relative positions of the input coupling structure, the output coupling structure and the sample stage. The sample stage is used to support the silicon waveguide chip under test; The multidimensional fine-tuning mechanism is a five-dimensional or six-dimensional fine-tuning frame.

8. A method for measuring carrier lifetime using the dual-wavelength pump-probe system for characterizing carrier lifetime in silicon waveguides as described in any one of claims 1 to 7, characterized in that, It includes the following steps: S1. Output pump light of the first wavelength and probe light of the second wavelength, and adjust the polarization state and output power of the two lights; S2. Pump light shines from above the silicon waveguide chip under test onto the test area, exciting free carriers in the silicon waveguide under test; S3. The reference detection module collects the probe light in front of the silicon waveguide chip under test to form an input reference signal; S4. The probe light is coupled to the sample carrier module input via chip coupling to the silicon waveguide chip under test. Specifically, the probe light enters the on-chip inverse conical mode field conversion structure from the input end face of the chip under test, transitions into the silicon waveguide chip under test, and propagates in the waveguide along the propagation direction of the silicon waveguide under test. The irradiation area of ​​the pump light and the effective propagation area of ​​the probe light in the waveguide are spatially overlapped, so that the free carriers excited by the pump light modulate the transmission intensity of the probe light in this section of the waveguide. The probe light detects the waveguide transmission change caused by the free carriers. After propagating through the silicon waveguide under test, the probe light is then output from the chip output end face. After coupling and output, it is filtered. The detection output module collects the coupled probe light to form an output detection signal. S5. The filtering and signal processing module performs ratio normalization processing on the input reference signal and the output probe signal, and inputs the normalized signal into the phase-locked loop detection unit for synchronous detection. After the pump light is irradiated, a transient free carrier distribution is formed in the waveguide under test. The free carrier absorption effect will cause the output intensity of the probe light to decrease. As the free carriers recombine, the transmission intensity of the probe light gradually recovers. By measuring the transmission recovery process under different pump-probe relative time delay conditions, the data acquisition unit obtains the time-resolved transmission change curve, and the carrier lifetime of the silicon waveguide under test is obtained by fitting the time-resolved transmission change curve. By combining propagation loss tests of waveguides of different lengths, geometric parameters of waveguides with different structures, etching depth parameters, surface treatment conditions, and sidewall roughness and doping parameters obtained from auxiliary characterization, the correlation between carrier lifetime, propagation loss, and process conditions is analyzed. Specifically: (1) The carrier lifetime parameters and propagation loss parameters measured in the same chip under test are compared. By performing the correlation analysis, we obtained a set of data relating carrier lifetime, propagation loss, and process parameters. , represented as: ， in, , , The first The width, silicon layer thickness, and etching depth of each waveguide test structure. This represents the propagation loss corresponding to the test structure. This represents the carrier lifetime corresponding to the test structure. and These are the pump light power and probe light power during measurement, respectively. The waveguide length; By comparing data sets from different test structures, the correlation between carrier lifetime and propagation loss, etching depth, waveguide sidewall area, and surface treatment conditions was determined. (2) The effects of etching damage and surface recombination on carrier lifetime are analyzed by comparing the equivalent surface recombination velocities under different etching depths, waveguide widths, or surface treatment conditions. The equivalent surface recombination velocity is expressed as: ， in, For the equivalent surface recombination velocity, For known lifespan or lifespan obtained through auxiliary tests, This refers to the carrier lifetime parameter; (3) For waveguides fabricated under different etching conditions, the etching depth is... Etching power, etching gas flow rate, etching time, sidewall angle, annealing temperature, and surface passivation conditions are recorded as process parameters and correlated with carrier lifetime. Propagation loss and equivalent surface recombination velocity Perform corresponding analysis: When a group of waveguides simultaneously exhibits large propagation loss Shorter carrier lifetime and a large equivalent surface recombination rate When the process conditions are such that the sidewall scattering loss or surface defect recombination is introduced, it is judged that the process conditions introduce strong sidewall scattering loss or surface defect recombination. When the waveguide after annealing or surface treatment exhibits low propagation loss and long carrier lifetime, it indicates that the process conditions are beneficial to reducing the influence of sidewall defects or surface recombination. (4) Using root mean square roughness Relevant length Line width deviation Doping concentration or For characterization, it is combined with carrier lifetime parameters and propagation loss parameters to form a correlation data table. , represented as: ， The correlation data tables are compared or fitted to analyze the impact of different process factors on carrier recombination and optical transmission loss in silicon waveguides.

9. The carrier lifetime measurement method according to claim 8, characterized in that: In step S3, the probe light is divided into a reference probe branch and a measurement probe branch by the second power adjustment unit. A small proportion of the probe light enters the reference probe module, and the probe light in front of the silicon waveguide chip under test is collected by the reference probe module set on the reference probe branch.

10. The carrier lifetime measurement method according to claim 8, characterized in that: Before the pump light in S2 shines on the test area from above the silicon waveguide chip under test, the relative time delay between the pump light and the probe light is scanned by changing the position of the short mechanical delay line; the pump light is vertically irradiated onto the surface of the silicon waveguide chip under test by adjusting the return reflector.

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