CN112909738A

CN112909738A - Two-dimensional on-chip sensor based on double grating feedback and design method

Info

Publication number: CN112909738A
Application number: CN202110074988.6A
Authority: CN
Inventors: 张浩然; 王涛; 王高峰
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2021-01-20
Filing date: 2021-01-20
Publication date: 2021-06-04

Abstract

The invention discloses a two-dimensional on-chip sensor based on double grating feedback and a design method thereof. This design has the characteristics of a conventional laser: low threshold, single longitudinal mode, small divergence angle, and because of the simple structure, the difficulty of preparation and integration is reduced, and the cost of mass production is reduced. Meanwhile, due to the particularity of the grating structure, the wavelength excited by the laser is related to the ambient refractive index, so that the design also has the function of detecting the ambient refractive index, the sensitivity reaches 221nm/RIU, and the quality factor reaches 4420RIU^‑1The method has important significance for rapid, real-time and accurate detection in the fields of environment, biology, medical treatment, chemistry and the like.

Description

Two-dimensional on-chip sensor based on double grating feedback and design method

Technical Field

The invention relates to design and application of an active sensing device, belongs to the crossing field of laser and sensing technologies, and particularly relates to a two-dimensional on-chip sensor design method based on double grating feedback.

Background

The one-dimensional sub-wavelength High Contrast Grating (HCG) is a compact optical element with a structure period smaller than the wavelength of incident light and sensitive to polarization, and the reflection spectrum characteristics of the HCG can be controlled by changing the structure parameters such as period, thickness and duty ratio, so as to generate rich physical phenomena such as rayleigh anomaly, resonance anomaly and broadband High reflection. The high-refractive-index material of the HCG is usually a semiconductor material with a refractive index greater than 2, and the low-refractive-index material of the HCG can be a working environment substance with a low refractive index such as gas and liquid, so that the grating can have excellent interactivity with the environment, and therefore, a sensor designed based on the HCG has good application potential no matter in a gas environment or a liquid/solution application scene, and is also one of hot spots of optical sensor design and research.

The superior performance of the HCG broadband high-reflection mirror provides a means for simplifying the design and reducing the size of a Vertical Cavity Surface Emitting Laser (VCSEL), so that the HCG-VCSEL has great success in the fields of 3D sensing, face recognition, environment detection, optical communication and the like. This type of laser generally has three parts, an upper mirror is formed by a suspended HCG and a small number of DBRs (distributed Bragg reflectors), a lower mirror is formed by a large number of DBRs, and a resonant cavity is formed by a middle filling layer with a thickness that is an integral multiple of half a wavelength. Although the size and difficulty of mirror epitaxial growth has been reduced to some extent compared to full DBR VCSELs, the growth challenges of suspended HCGs and the underlying DBR continue to impede their further development.

Laser Light, i.e. the Light Amplification by Stimulated Emission of Radiation, changes in the wavelength of the laser Light depend on the refractive index changes of the resonant cavity and the external environment under the condition that the shape of the cavity and the gain medium are not changed. The gain of the gain medium compensates the radiation loss and other losses in the state of stimulated radiation, so that the line width of the laser is very narrow and can be less than 1nm, and the laser has a very high quality factor.

Disclosure of Invention

Aiming at the characteristics that HCG in the prior art is sensitive to the change of the environmental refractive index and can provide broadband high reflection, and the laser has the advantages of high coherence and narrow linewidth output, the HCG and the laser are combined and applied to the optical sensor, so that the method has important significance for real-time, accurate and quick detection in the fields of environment, biology, chemistry and the like. Therefore, the invention provides a two-dimensional on-chip sensor based on double-grating feedback and a design method thereof, the structural characteristics and the abundant spectroscopy characteristics of the HCG can meet the interaction requirement of the sensor and a detected body, and can form a laser resonant cavity, the use of the HCG at two sides can reduce the size of a device and solve the problem that the traditional VCSEL is difficult to grow epitaxially on a dozen layers of DBRs, and meanwhile, the HCG structure with the same upper and lower parts is convenient for mass production and integration.

A two-dimensional on-chip sensor based on double grating feedback is of a sandwich structure, grating layers with the same structure are arranged on two sides, and a gain layer is clamped in the middle; F-P resonance is formed between the gratings on the two sides, and guided mode resonance exists in the horizontal direction, so that an Fano line type with asymmetric resonant cavity reflection spectrum is formed; the grating layer is a sub-wavelength high-contrast grating structure taking an external environment as a low-refractive index material, and provides broadband high-reflectivity for the direction perpendicular to the periodic variation of the refractive index; due to the structural design of the double-side grating, a Fabry-Perot resonant cavity is formed in the vertical direction, and light excited by pumping passes through the gain layer back and forth in the resonant cavity to obtain gain, so that stimulated emission light is amplified; since the whole device is of a sub-wavelength structure, guided mode resonance caused by high-order diffraction exists in the grating plane, so that the lasing wavelength is related to the change of the environmental refractive index. The pump light excites the gain medium to generate stimulated radiation after reaching the lasing condition; the change of the refractive index of the body to be measured can directly cause the movement of the resonant cavity mode.

The whole device of the invention can be completely exposed in the body to be tested; the object to be detected is a gaseous or liquid low-refractive-index flowable substance.

The grating layer is made of semiconductor material with refractive index of 2-3.6, such as silicon nitride, gallium arsenide, indium phosphide and the like; the grating layer is used as a top layer or a bottom layer reflector, and at least partial area of the reflector is provided with a sub-wavelength grating structure by means of dry etching, wet etching and the like; the upper and lower double grating periodicity change direction, structure parameter, periodicity are all the same, and the high refractive index strips are aligned.

The gain layer adopts organic gain doped in silicon dioxide such as Rhodamine (Rhodamine), DCM and derivatives thereof, or semiconductor gain such as quantum wells and quantum dots; the gain thickness is between 50nm and 500 nm.

The sensor uses laser wavelength to measure refractive index change, and the refractive index sensor usually uses sensitivity

And quality factor

The performance of the sensor is characterized, wherein, delta lambda is the shift of the peak position of the lasing spectrum, delta n is the change of the corresponding refractive index, and FWHM is the full width at half maximum of the lasing wavelength.

A design method of a two-dimensional on-chip sensor based on double grating feedback comprises the following steps:

the method comprises the following steps: calculating the reflectivity of HCG by simulation means such as RCWA (Rigorous Coupled Wave analysis), FDTD (Fine Difference Time domain) and FEM (Fine Element method), scanning the reflection spectrum under different structural parameters such as period, duty ratio and thickness, and respectively drawing the reflectivity maps of wavelength, period, duty ratio and thickness, thereby searching the structural parameters with proper spectral characteristics.

Step two: through single-period structure simulation, proper gain and spacer layer thickness are searched, and the resonant wave band of the resonant cavity is designed to be overlapped with a gain spectrum.

The invention has the advantages that: the invention innovatively applies the double-side HCG structure to realize the laser design, has the advantages of low threshold, single longitudinal mode, small divergence angle and the like as a laser, and as a refractive index sensor, the single longitudinal mode output brought by the laser greatly improves the signal-to-noise ratio of detection signals, and the narrow line width output greatly improves the quality factor of the sensor.

Drawings

Fig. 1 is a schematic structural diagram of a two-dimensional on-chip sensor with double grating feedback according to the present invention.

Fig. 2 is a schematic structural diagram of a two-grating feedback two-dimensional on-chip sensor according to an embodiment of the present invention.

Fig. 3(a) is a thickness scanning reflection spectrum of HCG in a two-dimensional on-chip sensor with double grating feedback according to the present invention.

FIG. 3(b) is a HCG high-resolution reflection spectrum with a period of 530nm, a duty cycle of 0.5 and a thickness of 230nm in the double-grating feedback two-dimensional on-chip sensor of the invention.

FIG. 3(c) is a plot of laser output curve and FWHM versus input for a two-dimensional on-chip sensor with dual grating feedback according to the present invention.

FIG. 3(d) is a line graph of peak wavelength and FWHM versus refractive index for a two-dimensional on-chip sensor with dual grating feedback according to the present invention.

Detailed Description

In order to make the technical solution, design method and device advantages of the present invention more clear, the present invention is further described in detail below by way of specific examples with reference to the accompanying drawings.

The invention provides a two-dimensional on-chip sensor with double grating feedback and a design method. The overall structure of the design is shown in fig. 1, wherein 4 of the upper grating layer 1 is a grating structure formed by etching, 5 is a grating support layer which is not etched, and of course, the thickness of 5 is determined by the design requirement of the device cavity and can be 0. Likewise, 10 in the lower grating layer 3 is a grating structure formed by etching, 9 is a grating support layer which is not etched, and 9 can also be 0, but 1 and 3 both have the same structural parameters. The gain layer 2 may be a silicon dioxide layer doped with organic matter such as rhodamine, or a semiconductor gain composed of quantum wells and quantum dots such as GaAlAs/InGaAsP, the gain layer 2 may have 6 and 8 spacer layers, which may protect the gain material and have the function of expanding the cavity length, and the gain layer 2 may have 6 and 8 also may be 0.

FIG. 2 is a schematic diagram showing a specific example of a structure in which the upper grating layer 1 and the lower grating layer 3 are both grating structures without the support layers 5 and 9 in FIG. 1, and the grating is made of Si with a refractive index of 2₃N₄The period Lambda is 530nm, the duty ratio F is 0.5, and the thickness T is 230 nm. The gain layer 2 is R6G (Rhodamine 6G) doped silicon dioxide, with no

spacers

6 and 8 as in fig. 1 above and below.

FIG. 3(a) is a thickness scan reflectance spectrum of the HCG structure of the example shown in FIG. 2 with a fixed period Λ 530nm and duty cycle F ═ 0.5, where the abscissa and ordinate are normalized using the period Λ, and the dashed black line in the figure is where the parameters used in this example are. FIG. 3(b) is a high resolution reflectance spectrum of the selected structure of this example, with a reflectance of greater than 99.5% over the wavelength range of 535nm to 585 nm. The absorption spectrum of the organic gain R6G is 512nm, the gain spectrum is 570nm, and the HCG reflection spectrum can better cover the gain wave band. FIG. 3(c) is a plot of the input-output curve and the FWHM versus input for the laser of this example, which has a lower threshold of about 17 μ J/cm²The FWHM decreases rapidly after the pump exceeds a threshold, about 0.05nm, and maintains a narrow linewidth output over a large range. FIG. 3(d) is a plot of the peak wavelength and FWHM of the sensor of this example as a function of refractive index for a sensitivity of 221nm/RIU and a quality factor FOM of 4420RIU^-1。

It should be understood that the above description is only for the purpose of simplicity and convenience of description and should not be taken as limiting the invention as it relates to the directional terms such as "upper" and "lower" and to the extent of "etc." "or" multiple ", but rather as a limitation on the specific direction or amount of the invention.

Finally, it is noted that this example is given to aid in further understanding of the invention, and that those skilled in the art will understand that: various alternatives and modifications are possible without departing from the invention and the scope of the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.

Claims

1. A two-dimensional on-chip sensor based on double grating feedback is characterized in that: the grating layer is of a sandwich structure, grating layers with the same structure are arranged on two sides, and a gain layer is clamped in the middle; F-P resonance is formed between the gratings on the two sides, and guided mode resonance exists in the horizontal direction, so that an Fano line type with asymmetric resonant cavity reflection spectrum is formed; the grating layer is a sub-wavelength high-contrast grating structure taking an external environment as a low-refractive index material, and provides broadband high-reflectivity for the direction perpendicular to the periodic variation of the refractive index; due to the structural design of the double-side grating, a Fabry-Perot resonant cavity is formed in the vertical direction, and light excited by pumping passes through the gain layer back and forth in the resonant cavity to obtain gain, so that stimulated emission light is amplified; since the whole device is of a sub-wavelength structure, guided mode resonance caused by high-order diffraction exists in the grating plane, so that the lasing wavelength is related to the change of the environmental refractive index.

2. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the double-side grating of the device is exposed to the working environment at the same time.

3. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the refractive index sensor works in an environment with a lower refractive index, namely is suitable for a gas environment and is also suitable for a liquid environment.

4. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the grating layer is made of a semiconductor material with a high refractive index of 2.0-3.6.

5. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the grating layer comprises a grating structure formed by etching and a grating support layer which is not etched.

6. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the two layers of grating layers have the same periodic variation direction of refractive index, structural parameters and period number, and the high refractive index strips are aligned.

7. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: the gain layer is composed of a light-emitting semiconductor or a medium doped with organic dye molecules; the thickness of the gain layer is 50 nm-500 nm.

8. The two-dimensional on-chip sensor based on double grating feedback of claim 1, wherein: and spacing layers are arranged on two sides of the gain layer.

9. The two-dimensional on-chip sensor based on double grating feedback of claim 5, wherein: the thickness of the unetched grating support layer is 0.

10. The design method of the two-dimensional on-chip sensor based on the double grating feedback as claimed in claim 1, the method comprises the following specific steps:

the method comprises the following steps: calculating the reflectivity of the HCG by a simulation means, scanning reflection spectra under different periods, duty ratios and thicknesses, and respectively drawing reflectivity spectrograms of wavelength, period, duty ratio and thickness so as to find out structural parameters with proper spectral characteristics;