WO2017069620A1

WO2017069620A1 - Photonic integrated circuit (pic), pressure sensing system comprising such a pic and method for pressure sensing using such a pressure sensing system

Info

Publication number: WO2017069620A1
Application number: PCT/NL2016/050718
Authority: WO
Inventors: Joost Cornelis Geluk
Original assignee: Technaton B.V.
Priority date: 2015-10-21
Filing date: 2016-10-19
Publication date: 2017-04-27
Also published as: NL2015640B1

Abstract

The invention relates to a photonic integrated circuit (PIC) for use in a pressure sensing system comprising an integrated photonic component (IPC), configured to be exposed to an external pressure and to generate a wavelength response based on deformation, wherein the wavelength response comprises a pressure-induced wavelength response and a temperature-induced wavelength response. The pressure sensing system further comprises an incoming waveguide for coupling a light source to an optical input of the IPC and an outgoing waveguide for coupling an optical output of the IPC to analysis means. The pressure sensing system further comprises temperature correction means, wherein the temperature correction means provide information relating to the temperature-induced wavelength response. The present invention further relates to a pressure sensing system comprising a PICas described above. The present invention further relates to a method for pressure sensing using a pressure sensing system as described above.

Description

Photonic Integrated Circuit (PIC), pressure sensing system comprising such a PIC and method for pressure sensing using such a pressure sensing system

Field of the Invention

The present invention relates to a bare die photonic integrated circuit. The present invention further relates to a pressure sensing system comprising the photonic integrated circuit as described above. The present invention also relates to a method for pressure sensing using the pressure sensing system as described above.

Background

Pressure sensing systems comprising semiconductor integrated circuits are known in the art. In U.S. Patent No. 7,207,227 a pressure sensing system is disclosed for detecting pressure without requiring direct mechanical contact, in which a cavity or recess is provided in a semiconductor substrate and a diaphragm or membrane, which can be deformed by pressure, covers the cavity. U. S. Patent No. 8,991,265 discloses a pressure sensing system including a flexible membrane deformable in response to pressure. The flexible membrane covers a cavity and includes a strain gauge thai- produces signals corresponding to an elastic deformation of the flexible membrane.

A disadvantage of the known semiconductor pressure sensing system is that using membranes as transducing element inherently involves nonlinearity and hysteresis in response. Also the thickness of the membrane needs to be customized to accommodate a certain pressure range.

Object of the Invention

An object of the invention is to provide a pressure sensing system to determine the pressure without the need for deforming the transducer elements.

A further object of the invention is to improve the sensitivity, selectivity, working range, accuracy, repeatability and hysteresis and/or the complexity in the readout.

Summary of the Invention

This object is achieved by a photonic integrated circuit (PIC) for use in a pressure sensing system comprising an integrated photonic component (IPC), configured to be exposed to an external pressure and to generate a wavelength response based on deformation, wherein the wavelength response comprises a pressure-induced wavelength response and a temperature-induced wavelength response. The pressure sensing system further comprises an incoming waveguide for coupling a light source to an optical input of the IPC and an outgoing waveguide for coupling an optical output of the IPC to analysis means. The pressure sensing system further comprises temperature correction means, wherein the temperature correction means provide information relating to the temperature-induced wavelength response. The PIC is made out of an optical conducting material. The optical conducting material has anisotropic thermal expansion properties or wherein means are provided for causing the optical conducting material to have anisotropic thermal expansion properties during use. Such means may comprise means for generating an appropriate electric field in the optical conducting material or the like. Applicant has found that advantageously an external pressure causing elastic deformation of the IPC can be determined based on the direct compressibility or deformability of the IPC, which in the above context translates into a varying wavelength response, such as a shifting wavelength as function of deformation. Applicant has observed that pressure sensing systems employing differences in wavelength resulting from a deformation of photonic material have great accuracy, low complexity and increased sensitivity in comparison with prior art membrane based systems. Furthermore, there is no longer a need for use of deforming transducer elements such as membranes. An important step, however, is to ensure the wavelength response is properly corrected for deformation caused merely by changing temperatures, which can also cause deformation of the IPC. Through experiments, Applicant has found that with the above pressure sensing system pressure sensing with relatively high resolution is possible.

An embodiment relates to the PIC as described above, wherein the IPC comprises an optical resonator. The resonance wavelength of the optical resonator can be advantageously used to determine the wavelength response related to the deformation of the IPC. In particular the temperature-induced wavelength response appears to be a linear function of the temperature. By means of example it is mentioned that during experiments with a prototype PIC, Applicant has observed a linear wavelength response versus the temperature of 77 pm/K for an optical ring resonator.

The optical resonator can be advantageously used with lasers to facilitate high-resolution optical spectrum analysis. An embodiment relates to the PIC as described above, wherein the temperature correction means comprises a temperature sensor located in close proximity to the IPC. Applicant has found that the temperature-induced wavelength response is roughly a factor 100 larger than the corresponding pressure-induced wavelength response. The temperature-induced wavelength response, however, has been found to be linear for typical operating temperature ranges. Advantageously, the wavelength response can thus be easily compensated for temperature or temperature changes.

An embodiment relates to the PIC as described above, wherein the optical conducting material is selected from a silicon-on-isolator (SOI), Indium Phosphide (InP), Lithium Niobate (Li bC ), a glass based compound, or a III-V semiconductor material.

An embodiment relates to the PIC as described above, wherein the optical resonator is selected from a ring resonator, a race track resonator, Fabry-Perot resonator, or an optical cavity.

An embodiment relates to the PIC as described above, wherein the IPC is elongated in a first longitudinal direction and the temperature correction means comprise an auxiliary IPC, wherein the auxiliary IPC is elongated in a second longitudinal direction with a nonzero angle a between the first and second longitudinal direction. Advantageously, in this embodiment there is no need to measure the temperature in 'real time' as the temperature-corrected wavelength response can be determined based on the wavelength response of the IPC and the wavelength response of the auxiliary IPC. In particular the use of anisotropic materials is advantageous in this respect.

An embodiment relates to the PIC as described above, wherein the nonzero angle a is determined based on the anisotropy of the optical conducting material. The nonzero angle a is chosen by a skilled person such that by using the anisotropic thermal expansion properties of the optical conducting material the pressure-induced wavelength response can be determined.

An embodiment relates to the PIC as described above, wherein the nonzero angle a is defined as 0° < a < 90°

An embodiment relates to the PIC as described above, wherein the IPC and the auxiliary IPC are race track resonators. Such race track resonators can be employed in particular in situations wherein the optical conducting material has anisotropic expansion properties. An embodiment relates to the PIC as described above, wherein the analysis means are configured for determining the external pressure based on a temperature-corrected wavelength response.

An embodiment relates to the PIC as described above, wherein the analysis means comprise an interferometer.

An embodiment relates to the PIC as described above, wherein the interferometer is selected from a Mach-Zehnder interferometer (MZI), Michelson interferometer, or a Sagnac interferometer.

Preferably, a three arms MZI is used to allow continuous phase sensing over multiple interference cycles.

An embodiment relates to the PIC as described above, wherein the is a bare die device.

An embodiment relates to the PIC as described above, wherein the light source comprises a laser which is arranged on or integrated with the integrated photonic component IPC.

An embodiment relates to the PIC as described above, wherein the analysis means are arranged on or integrated with the integrated photonic component IPC.

An embodiment relates to the PIC as described above, wherein the wavelength response is associated with an interference phase resulting from optical interference of light of the incoming and outgoing waveguides.

Moreover, the present invention relates to a pressure sensing system, comprising a PIC as described above, wherein the PIC is exposed in a measuring volume. The pressure sensing system further comprises a light source, wherein the light source is coupled to the incoming waveguide. The pressure sensing system further comprises analysis means, wherein the analysis means are coupled to the outgoing waveguide. The PIC is made out of an optical conducting material. The optical conducting material has anisotropic thermal expansion properties or means are provided for causing the optical conducting material to have anisotropic thermal expansion properties during use.

Moreover, the present invention relates to a method for pressure sensing using a pressure sensing system as described above, comprising the steps of

using the light source for providing light to the IPC,

determining a wavelength response of the IPC in response to deformation of the IPC caused by exposure to temperature and pressure of a fluid in the measuring volume, determining the pressure based on a temperature-correction of the wavelength response.

An embodiment relates to the method as described above, wherein the method further comprises the step of using a temperature sensor for obtaining temperature data to determine a temperature-induced wavelength response of the wavelength response.

Brief description of Drawings

The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown. They are intended exclusively for illustrative purposes and not to restrict the inventive concept, which is defined by the appended claims.

Figure 1 shows a schematic view of a pressure sensing system comprising a photonic integrated circuit (PIC) in accordance with an embodiment of the invention; Figure 2 shows a schematic view of a PIC in accordance with an embodiment of the invention;

Figure 3 shows a schematic view of a pressure sensing system comprising the photonic integrated circuit in accordance with an alternative embodiment of the invention; Figure 4 shows a characteristic temperature dependence of a measured wavelength response of a PIC in accordance with an embodiment of the invention; and Figure 5 shows a top view of a PIC in accordance with an embodiment of the invention.

Detailed Description of Embodiments

Figure 1 shows a schematic view of a pressure sensing system comprising a photonic integrated circuit (PIC). The pressure sensing system 1 comprises a carrier 3, wherein the PIC 2 is basically a bare die or a chip, mounted on the carrier 3. Furthermore, the PIC 2 is exposed in a measuring volume 9 of a fluid, such as water, oil, air, or any other appropriate liquid or gas. The measuring volume 9 may be a closed volume or an open volume in a fluid communication with an external source, such as an external volume or the environment surrounding the PIC 2.

In a preferred embodiment of the invention, the PIC 2 comprises a protection layer (not shown) for separating the PIC 2 from the measuring volume 9. The protection layer can, for example, be a coating or a thin glass-based layer. The PIC 2 is arranged to generate a wavelength response that is dependent on pressure and temperature in the fluid environment.

The pressure sensing system further comprises a light source 4, such as a laser. The light source 4 provides light to the PIC 2. The light source 4 can be arranged internally, on the carrier 3 or on the PIC 2, or externally, outside the housing with the fluid environment. The light source 4 can be connected via a waveguide or a glass fiber to an incoming waveguide of the PIC 2. The pressure sensing system 1 further comprises analysis means

5 for analyzing the wavelength response generated by the PIC 2, the PIC 2 generates an optical signal. The analysis means 5 comprise a wavelength measurement system, such as a Mach-Zehnder interferometer (MZI). The basic concept of a MZI is that one light path is split in two arms and recombined for optical interference. The interference phase observed at the output is dependent on wavelength and the optical path difference. Furthermore, the analysis means 5 can be arranged internally, on the carrier 3 or on the PIC 2, or externally, outside the measuring volume 9.

Typically, the analysis means 5 generate an electronic output signal associated with the measured wavelength response.

In a preferred embodiment of the invention, the analysis means 5 comprise a three arms MZI. The three arms MZI allows continuous phase sensing over multiple interference cycles. Advantageously, the optical configuration is simpler since a stable laser light source can be used and the phase can be determined via a simple algorithm from three photodiode responses, i.e. one in each arm of the three arms MZI.

Figure 2 shows a schematic view of a PIC 2 of the pressure sensing system of figure 1. The PIC 2, made out of an optical conducting material, comprises an integrated photonic component (IPC) 6 and incoming and outgoing waveguides 7', 7" optically coupled herewith. In close proximity to the IPC 6, the PIC 2 further comprises a temperature sensor 8. The IPC 6 can, for example, be an optical ring resonator, a Fabry- Perot resonator, an optical cavity, or any other kind of optical resonator.

During operation, light provided by the light source 4 (not shown) is guided to the IPC 6 via the waveguide 7'. A wavelength of the light is tuned until resonance occurs in the IPC 6 at a resonance wavelength. When a pressure is applied to the PIC 2, directly or indirectly, the resonance wavelength of the IPC 6 changes due to deformation of the IPC

6 which causes a change of a path length of light in the IPC 6. Such a resulting wavelength response, i.e., the change of the resonance wavelength, can be used to determine the pressure causing the deformation, under usage of a compensation for a temperature-induced wavelength response. The wavelength response, due to deformation of the IPC 6, is directly determined by the optical conducting material of the PIC 2, specifically by the refractive index of the optical conducting material.

In an embodiment of the invention, the resulting wavelength response is associated with an interference phase resulting from optical interference of light of the incoming and outgoing waveguides 7', 7" measured by an interferometer, preferably a MZI.

The temperature-induced wavelength response of the IPC 6 is roughly a factor 100 larger than a pressure-induced wavelength response of the IPC 6. At the same time the temperature-induced wavelength response has been found to be substantially linear in typical operating temperature ranges (see figure 3). Thus compensation for the temperature-induced wavelength response is possible by using temperature data measured by the temperature sensor 8 located in a close proximity of the IPC 6. The temperature sensor 8 can be a thermistor, thermocouple, resistance thermometer (RTD), or silicon bandgap temperature sensor.

Figure 3 shows a schematic view of a pressure sensing system comprising a photonic integrated circuit (PIC) according to an alternative embodiment of the invention. In this embodiment, the light source 4" is arranged on or integrated with the PIC 2. Also, the analysis means 5" is arranged on or integrated with the PIC 2 which comprises the IPC 6.

Figure 4 shows a temperature dependency of the measured wavelength of the IPC 6. Following experiments performed by Applicant, a linear behavior of the measured resonance wavelength of the IPC 6 versus the temperature was found. In a following step of a pressure measurement by means of the pressure sensing system described here, the linear behavior can be used to correct for the temperature-induced wavelength response using the temperature sensor 8. After correction for the temperature-induced response, the pressure-induced wavelength response due to deformation can be obtained, associated with a pressure that is applied to the pressure sensing system 1.

Experiments were conducted with a pressure sensing system using a ring resonator on a silicon-on-insulator (SOI) chip and a connecting fiber feed-through, allowing passive transmission measurements. The SOI chip was submerged in a water containing tank, in order to create a stable sensing environment. Figure 4 shows a schematic top view of the PIC 2. In this embodiment, it is specified that the optical conducting material is an anisotropic material with anisotropic thermal expansion properties during use. That is the optical conducting material has anisotropic thermal expansion properties or anisotropic thermal expansion properties are provided in the anisotropic material using appropriate excitation means.

The PIC 2 comprises an IPC 10, an auxiliary IPC 10', and incoming and outgoing waveguides l l ',l l ";12',12" optically coupled herewith. Both the IPC 10 and the auxiliary IPC 10' have an elongated shape, to enhance the interaction of the IPC with the anisotropic material in the direction of the elongation. The IPC 10 has a first longitudinal direction and the auxiliary IPC 10' has a second longitudinal direction, with a nonzero angle a between the first and second longitudinal direction of respectively the IPC 10 and the auxiliary IPC 10'.

In an embodiment of the invention, the resulting wavelength response is associated with an interference phase resulting from optical interference of light of the outgoing waveguides 11 ", 12" measured by an interferometer, preferably a MZI. That is, the wavelength response is associated with an interference phase shift resulting from relative changes in the optical path lengths between the interfering light paths.

Optionally, the anisotropy may be used to discriminate optical path length changes in modes of orthogonal polarization (TE and TM) in the waveguides of one or more MZI structure(s).

During operation, the different longitudinal directions in the anisotropic material will lead to different thermal dependencies of the wavelength responses of the IPCs 10, 10' . From comparison of both wavelength responses it is possible to correct the wavelength response for the temperature-induced wavelength response and thus calculate the pressure-induced wavelength response.

In a preferred embodiment of the invention, the nonzero angle a is chosen such that, the first and second longitudinal direction, defining the nonzero angle a, coincide with the, or two, main anisotropic directions in the anisotropic material.

The skilled person will furthermore understand that the above-described pressure sensing system 1 in principle can also be used as a contact pressure sensor, or a load sensor. Other alternatives and equivalent embodiments of the present invention are conceivable within the idea of the invention, as will be clear to the person skilled in the art. The scope of the invention is limited only by the appended claims.

Claims

1. Photonic Integrated Circuit, PIC, (2) for use in a pressure sensing system comprising

an integrated photonic component, IPC, (6), configured to be exposed to an external pressure and to generate a wavelength response based on deformation, wherein the wavelength response comprises a pressure-induced wavelength response and a temperature-induced wavelength response;

an incoming waveguide (7') for coupling a light source (4) to an optical input of the IPC (6);

an outgoing waveguide (7") for coupling an optical output of the IPC (6) to analysis means (5), and

temperature correction means, wherein the temperature correction means provide information relating to the temperature-induced wavelength response,

wherein the PIC (2) is made out of an optical conducting material, and either the optical conducting material has anisotropic thermal expansion properties or wherein means are provided for causing the optical conducting material to have anisotropic thermal expansion properties during use.

2. Photonic Integrated Circuit according to any one of the preceding claims, wherein the IPC (6) comprises an optical resonator.

3. Photonic Integrated Circuit according to any one of the preceding claims, wherein the temperature correction means comprise a temperature sensor (8) located in close proximity to the IPC (6).

4. Photonic Integrated Circuit according to claim 1, wherein the optical conducting material is selected from a silicon-on-isolator, SOI, Indium phosphide, InP, Lithium Niobate, LiNbC , a glass based compound, or a III-V semiconductor material.

5. Photonic Integrated Circuit according to claim 2, wherein the optical resonator is selected from a ring resonator, a race track resonator, Fabry-Perot resonator, or an optical cavity.

6. Photonic Integrated Circuit according to claim 1, wherein the IPC (10) is elongated in a first longitudinal direction and the temperature correction means comprise an auxiliary IPC (10'), wherein the auxiliary IPC (10') is elongated in a second longitudinal direction with a nonzero angle a between the first and second longitudinal direction.

7. Photonic Integrated Circuit according to claim 6, wherein the nonzero angle a is determined based on the anisotropy of the optical conducting material.

8. Photonic Integrated Circuit according to claim 7, wherein the nonzero angle a is defined as 0° < a < 90°.

9. Photonic Integrated Circuit according to any one of claims 6 - 8, wherein the IPC (10) and the auxiliary IPC (10') are race track resonators.

10. Photonic Integrated Circuit according to any one of the preceding claims, wherein the analysis means (5) are configured for determining the external pressure based on a temperature-corrected wavelength response.

11. Photonic Integrated Circuit according to any one of the preceding claims, wherein the analysis means (5) comprise an interferometer.

12. Photonic Integrated Circuit according to claim 7, wherein the interferometer is selected from a Mach-Zehnder interferometer (MZI), Michelson interferometer, a

Sagnac interferometer.

13. Photonic Integrated Circuit according to any one of the preceding claims, wherein the PIC (2) is a bare die device, preferably a semiconductor bare die device.

14. Photonic integrated circuit according to any one of the preceding claims 1 - 15, wherein the light source (4) comprises a laser which is arranged on or integrated with the integrated photonic component IPC (6).

15. Photonic integrated circuit according to any one of the preceding claims 1 - 14, wherein the analysis means (5) are arranged on or integrated with the integrated photonic component IPC (6).

16. Photonic integrated circuit according to any one of the preceding claims 1 - 14, wherein the wavelength response is associated with an interference phase shift due to relative changes in the optical paths lengths between the interfering light paths in the incoming and outgoing waveguides.

17. Pressure sensing system (1), comprising:

a PIC (2) according to any one of the preceding claims 1 - 16, wherein the PIC (2) is exposed in a measuring volume (9);

a light source (4), wherein the light source is coupled to the incoming waveguide (7', 11 ', 12');

analysis means (5), wherein the analysis means are coupled to the outgoing waveguide (7", 11 ", 12"), and

18. Pressure sensing system (1) according to claim 17, wherein the light source (4) comprises a laser which is arranged on or integrated with the integrated photonic component IPC (6).

19. Pressure sensing system (1) according to claim 17 or 18, wherein the analysis means (5) are arranged on or integrated with the integrated photonic component IPC (6).

20. Method for pressure sensing using a pressure sensing system according to any one of claims 17 - 19, comprising the steps of:

using the light source (4) for providing light to the IPC (6), determining a wavelength response of the IPC (6) in response to deformation of the IPC (6) caused by exposure to temperature and pressure of a fluid in the measuring volume (9),

determining the pressure based on a temperature-correction of the wavelength response.

21. Method according to claim 20, further comprising the step of using a temperature sensor for obtaining temperature data to determine the temperature-induced wavelength response of the wavelength response.