阅读说明：本技术 光学形状传感器、光学形状感测控制台和系统、以及光学形状感测方法 (Optical shape sensor, optical shape sensing console and system, and optical shape sensing method ) 是由 M·B·范德马克 A·H·范杜斯卓滕 E·G·范皮滕 G·W·T·霍夫特 于 2019-01-24 设计创作，主要内容包括：本发明涉及一种光学形状传感器(OS),包括：光纤(F2),其具有定义纵向方向的长度,所述光纤(F2)具有沿着所述光纤(F2)的所述长度延伸的至少两个纤芯(C21、C22)；光学耦合构件(OCM2),其被布置在所述光纤(F2)的近侧光纤端处,所述耦合构件(OCM2)具有第一远侧端面(OF2)和近侧第二端面(IF2),所述第一远侧端面被光学地连接到所述近侧光纤端,所述近侧第二端面在所述光纤(F2)的所述纵向方向上与所述第一远侧端面(OF2)间隔开,所述光学耦合构件(OCM2)被配置为将光耦合到所述纤芯(C21、C22、C23)中的每一个内。从所述光学耦合构件(OCM2)到所述近侧光纤端的过渡处的光学界面(OI)是部分反射并且大幅度透射的,其中,所述光学界面(OI)从所述近侧第二端面(IF2)远侧以这种距离被布置并且被配置为使得光在所述光学界面(OI)处以实质上不与在所述光学耦合构件(OCM2)的所述第二端面(IF2)处反射的光的反射强度分布交叠的反射强度分布被反射。(The invention relates to an optical shape sensor (OS) comprising: an optical fiber (F2) having a length defining a longitudinal direction, the optical fiber (F2) having at least two cores (C21, C22) extending along the length of the optical fiber (F2); an optical coupling member (OCM2) arranged at a proximal fiber end OF the optical fiber (F2), the coupling member (OCM2) having a first distal end face (OF2) optically connected to the proximal fiber end and a proximal second end face (IF2) spaced apart from the first distal end face (OF2) in the longitudinal direction OF the optical fiber (F2), the optical coupling member (OCM2) being configured to couple light into each OF the cores (C21, C22, C23). An Optical Interface (OI) at the transition from the optical coupling member (OCM2) to the proximal optical fiber end is partially reflective and substantially transmissive, wherein the Optical Interface (OI) is arranged at such a distance distally from the proximal second end face (IF2) and is configured such that light is reflected at the Optical Interface (OI) with a reflection intensity distribution that does not substantially overlap with a reflection intensity distribution of light reflected at the second end face (IF2) of the optical coupling member (OCM 2).)

1. An optical shape sensor comprising:

an optical fiber (F2) having a length defining a longitudinal direction, the optical fiber (F2) having at least two cores (C21, C22) extending along the length of the optical fiber (F2),

an optical coupling member (OCM2) arranged at a proximal fiber end OF the optical fiber (F2), the coupling member (OCM2) having a first distal end face (OF2) optically connected to the proximal fiber end and a proximal second end face (IF2) spaced apart from the first distal end face (OF2) in the longitudinal direction OF the optical fiber (F2), the optical coupling member (OCM2) being configured to couple light into each OF the cores (C21, C22),

an Optical Interface (OI) at the transition from the optical coupling member (OCM2) to the proximal optical fiber end, the Optical Interface (OI) being partially reflective and substantially transmissive, wherein the Optical Interface (OI) is arranged at such a distance distally from the proximal second end face (IF2) and configured such that light is reflected at the Optical Interface (OI) with a reflected intensity distribution that does not substantially overlap in time with the reflected intensity distribution of light reflected at the second end face (IF2) of the optical coupling member (OCM2), such that the Optical Interface (OI) is configured to serve as a starting position for all cores (C21, C22) of the shape reconstruction of the optical shape sensor.

2. The optical shape sensor according to claim 1, wherein the optical coupling means (OCM2) is a graded index (GRIN) lens (GRIN 2).

3. The optical shape sensor of claim 2, wherein the GRIN lens (GRIN2) has a pitch of k/4, wherein k is an odd integer greater than or equal to 1.

4. The optical shape sensor according to claim 3, wherein k is 3, 5 or 7.

5. The optical shape sensor according to claim 1, wherein the Optical Interface (OI) has an optical interface refractive index different from at least one of an optical fiber refractive index of the optical fiber (F2) and an optical coupling member refractive index of the optical coupling member (OCM 2).

6. Optical shape sensor according to claim 1, wherein the distal first end (OF2) OF the optical coupling member (OCM2) is fusion-bonded to the proximal optical fiber end, and the Optical Interface (OI) is provided at the fusion-bond.

7. Optical shape sensor according to claim 1, wherein the distal first end (OF2) OF the optical coupling member (OCM2) is connected to the proximal optical fiber end via an adhesive layer, and the Optical Interface (OI) is provided at the adhesive layer.

8. Optical shape sensor according to claim 1, wherein the ratio of the intensity of the light reflected at the Optical Interface (OI) to the intensity of the light incident on the Optical Interface (OI) is at 10^-6To 10^-5Within the range of (1).

9. Optical shape sensor according to claim 1, wherein the proximal end face (IF2) of the optical coupling member (OCM2) is configured to be connected to a distal end of a light supply patch wire (PC) supplying input light, wherein a foil (IM) is arranged at the proximal end face (IF2) of the optical coupling member (OCM2), the foil (IM) being configured to reduce reflection of light at the connection of the proximal end face (IF2) of the optical coupling member (OCM2) and the distal end of the light supply patch wire (PC).

10. An optical shape sensing console, comprising:

an Optical Interrogation Unit (OIU) configured to transmit input light into the optical shape sensor (OS) according to claim 1 and to receive in response to the input light an optical response signal from each of the fiber cores (C21, C22) of the optical shape sensor (OS),

a Shape Reconstruction Unit (SRU) configured to reconstruct a shape of the optical shape sensor (OS) from the optical response signal, wherein the Shape Reconstruction Unit (SRU) is configured to determine a starting position of shape reconstruction for each of the cores (C21, C22) from the optical response signal, wherein the Shape Reconstruction Unit (SRU) is configured to identify a respective peak (SP2) of a reflected intensity distribution of input light reflected at the Optical Interface (OI) in the optical response signal of the cores (C21, C22) and to determine a respective starting position for shape reconstruction from the peak (SP 2).

11. The optical shape sensing console as claimed in claim 10, wherein the shape reconstruction unit is further configured to align the determined starting positions for the cores (C21, C22) with respect to each other.

12. The optical shape sensing console as claimed in claim 11, wherein the shape reconstruction unit is configured to align the determined start positions using a phase recovery algorithm.

13. An optical shape sensing system comprising an optical shape sensor (OS) according to claim 1 and an optical shape sensing console (C) according to claim 10.

14. A method of optical shape sensing, comprising:

transmitting input light into the optical shape sensor according to claim 1,

receiving an optical response signal from each of the cores (C21, C22) of the optical shape sensor (OS) in response to the input light,

identifying in the optical response signal a respective peak (SP2) of a reflected intensity distribution of the input light reflected at the Optical Interface (OI),

determining a shape reconstruction starting position for each of the cores (C21, C22) from the peak (SP2), and

reconstructing the shape of the optical shape sensor (OS) starting from the shape reconstruction starting position.

15. Computer program comprising program code means for causing a computer to carry out the steps of the method as claimed in claim 14 when said computer program is carried out on the computer.

Technical Field

The present invention relates to the field of optical shape sensing. The present invention is applicable to interventional medical devices and interventional treatment procedures, in particular to minimally invasive medical procedures using optical interrogation techniques.

Background

In minimally invasive medical interventions, guidewires are used to advance catheters to a target region (e.g., guidewires are used to advance catheters to the heart during minimally invasive cardiovascular interventions). These procedures are typically guided using, for example, real-time X-ray imaging that depicts two-dimensional projection images of the catheter and guidewire. However, challenges with X-ray imaging include the 2D nature of the imaging and ionizing radiation that may be harmful to the patient and physician, as well as contrast agents that are toxic to the patient's kidneys. A more viable alternative is to use optical shape sensing technology that can provide three-dimensional shape information of the medical device without any harmful radiation. One way to achieve spatially sensitive bending and twisting using optical fibers is to combine multiple cores with fiber bragg gratings along their length. One possible arrangement may be three or more cores oriented in a helical configuration along the longitudinal fiber axis, including an additional straight core in the center of the helix.

In particular, an optical shape sensing guidewire is used in minimally invasive procedures, the optical shape sensing guidewire having an optical connector for facilitating backloading of a catheter over a proximal end of the guidewire. The guidewire may be advanced to the target region of the intervention prior to introduction of the diagnostic or therapeutic catheter. The guidewire is typically a filament that allows for loading of the catheter over the proximal end of the guidewire and advancement of the catheter over the guidewire to reach the target area.

To allow for post-loading, an optical connector for the guidewire is needed that is small enough to allow a standard catheter to be post-loaded onto the guidewire before re-establishing the optical connection of the shape sensing enabled guidewire with the optical shape sensing console.

For backloadable guidewires, optical connectors comprising one or more graded index (GRIN) lenses have been proposed, as described for example in WO2016/193051a 1. GRIN lenses are a promising option as optical coupling means in optical connectors due to their compactness and their inherently low surface reflection. In a conventional lens, the combination of the curved surface at any point on the surface and the refractive index of the lens material causes light to be refracted in a desired direction at a given point. The difference in refractive index between the glass material of the lens and the surrounding air is generally necessary for the function of a conventional lens, but as a disadvantage it also causes some of the incident light to be reflected. In the GRIN lens, in contrast to the conventional lens, the light beam is bent due to the refractive index distribution of the lens changing in the radial direction. The role of a GRIN lens is therefore not critically dependent on the refractive index difference between the lens material and any adjacent material along the optical path at the input or output end of the GRIN lens. This property serves to eliminate or at least largely suppress reflections in the optical path by avoiding any air-to-glass transition when a connection between two optical connectors is established. Low reflection is achieved when the indices of refraction are closely matched at any point along the optical path. The reflection should be made low because otherwise it would overwhelm the relatively weak optical response signal from each point of the sensing fiber during the shape sensing procedure.

One characteristic of GRIN lenses is the so-called pitch. The light beam entering the GRIN lens is continuously refracted due to the refractive index distribution in the radial direction of the GRIN lens, and the optical field inside the GRIN lens thus periodically changes with a period length along the light propagation axis. The pitch of a GRIN lens is defined as the geometric length of the GRIN lens divided by the period length. For example, if the pitch is 1/4 or 3/4 or 5/4, etc., a set of collimated beams may exit the GRIN lens at the output end face when the beams enter the GRIN lens from the core of the optical fiber at the input end face, and vice versa. When the GRIN lens should have a predetermined pitch, then the geometric length of the GRIN lens is determined based on the refractive index in the axial center of the GRIN lens and the numerical aperture of the GRIN lens.

In Optical Shape Sensing (OSS), for example, the strain in the four cores of a fiber optic sensor is measured and the 3D shape of the sensor is calculated from these measurements. In order to define the starting position for 3D shape reconstruction of the sensor, some method is needed to horizontally align the relative shape reconstruction starting positions of all cores of the multicore sensing fiber down to the micrometer. One possibility is to use a correlation method that uses reflection or rayleigh backscattering from a fiber bragg grating in the fiber. This method compares the current state of backscattering to a previously recorded reflection profile of the fiber, possibly a few millimeters apart, as a calibration. Another approach employs reflection at the index step (e.g., at the connector interface), especially when the connector is polished at a right angle. The refractive index step occurs exactly at the same location for all cores, a very useful property because it is independent of the calibration method. It would be reasonable to also use this principle for the connection of a backloadable guide wire, i.e. to use the refractive index step at the interface between the guide wire connector lens and the patch cord connector lens as a starting point for the shape reconstruction. However, this method has some problems. One problem arises from the necessity of a sterile barrier (e.g. foil) between the two connector ends of the patch cord and the guide wire, introducing two refractive index steps with two reflections that cannot be accurately separated at a short distance (short time delay). Another problem occurs during reconnection of the guidewire, particularly after post-unloading of the catheter on the connector. The connector will become contaminated or at least wet which changes the refractive index step at the interface and thus the intensity of the reflection. Yet another problem is that any reconnection of the backloadable guidewire will show a slightly different compression of the intermediate layer (e.g. the foil forming the sterile barrier), which again changes the reflection. Thus, the refractive index step at the interface between the two connectors is variable, rendering identification of this interface in the optical response signal from the fiber core difficult and the shape reconstruction of the shape sensor less accurate.

The object of the invention is to accurately measure the time delay in the signals in several channels (cores) simultaneously, down to the level of microns of the optical propagation delay. By using a suitable physical marker, such as a refractive index step common to all markers, the delay between signals in the channel can be discovered and fixed. In each individual channel there are other reflections that may interfere due to crosstalk and cause systematic or random errors in the measured delay. Although any reflections can be very sharp in the time domain, the measurements are done in discrete steps and a fourier transform of a limited sampling range is performed. This widens the reflection peaks in the time domain and the tails of those peaks originating from different reflections may start to overlap, leading to cross-talk in the measurement between given reflections. A typical step size may be 0.05mm and a typical sampling range may contain 64 steps (nodes) corresponding to an interval of 3.2 mm.

In addition to the in-channel crosstalk explained above, there may also be inter-channel crosstalk that must be considered similarly. This crosstalk is a result of optical coupling between different channels caused by imperfections in the optical device.

Disclosure of Invention

It is an object of the invention to provide an optical shape sensor allowing shape reconstruction with improved accuracy.

It is a further object of the present invention to provide an optical shape sensing console configured to reconstruct the shape of an optical shape sensor with improved accuracy.

Further, it is an object of the invention to provide an optical system comprising said optical shape sensor and said optical shape sensing console.

It is a further object to provide a method of optical shape sensing that allows shape reconstruction with improved accuracy.

According to a first aspect of the invention, there is provided an optical shape sensor comprising

An optical fiber having a length defining a longitudinal direction, the optical fiber having at least two cores extending along the length of the optical fiber,

an optical coupling member arranged at a proximal fiber end of the optical fiber, the coupling member having a first distal end face optically connected to the proximal optical fiber end and a proximal second end face spaced apart from the first distal end face in the longitudinal direction of the optical fiber, the optical coupling member being configured to couple light into each of the cores,

an optical interface at a transition from the optical coupling member to the proximal optical fiber end, the optical interface being partially reflective and substantially transmissive, wherein the optical interface is arranged at such a distance from the proximal second end face and configured such that light is reflected at the optical interface with a reflection intensity distribution that does not substantially overlap in time with a reflection intensity distribution of light reflected at the second end face of the optical coupling member.

The invention is based on the idea of providing an optical interface with a step of the refractive index at the location of the transition from the optical coupling member to the proximal optical fiber end in the optical shape sensor. Such an optical interface can be advantageously used as a starting position for all cores for shape reconstruction. Unlike the optical interface at the proximal end of the optical coupling member (i.e. at the interface between the optical shape sensor connector and the patch cord corresponding connector), the optical interface at the fiber/coupling member-transition is not subject to influences from the sterile barrier, pressure, etc. between the two connectors. Thus, the reflection at such an interface is stable and can be easily recovered in the optical response signals from all the cores. The time position of light reflection at such an optical interface in the optical response signal of the core can be reliably measured and the time delay in the response signal of the core can be adjusted to zero so that the relative starting positions of all cores of the fiber can be accurately aligned down to the micrometer level. The optical interface at the transition from the optical coupling member to the proximal optical fiber end is partially reflective, e.g. may provide less than-50 dB of reflection, and is substantially transmissive, e.g. the insertion loss at the optical interface may be less than 1 dB. Further in accordance with the present invention, the optical interface is sufficiently spaced from the proximal end face of the optical coupling member such that a reflected intensity profile of light reflected at a transition from the fiber to the coupling member does not substantially overlap in time with a reflected intensity profile of light reflected at the proximal end face of the coupling member. "substantially" also includes that there is no overlap at all, but may include a small negligible overlap, such that light reflection from the optical interface at the fiber/coupling member-transition is a well-discerned and suitable choice for the starting position for shape reconstruction.

The distance of the optical interface at the fiber/coupling member-transition from the proximal end face of the coupling member may be in the range of1 mm-5 mm or more. In this configuration, the reflected intensity peak of the reflection at the fiber/coupling member-transition is sufficiently separated in the time domain from the reflected intensity peak of the reflection at the proximal end face of the optical coupling member. In short, if, for example, at a certain intensity level of reflection, the Fourier transform requires 64 nodes of 0.05mm to determine the exact micron-sized reflection peak position, then the coupling member end faces should be separated by at least 3.2 mm.

Further, the optical interface at the transition from the optical coupling member to the proximal optical fiber end should be configured such that its optical reflection is not only sufficiently separated from other measured input light reflections in the time domain, but also has sufficient intensity per se and is therefore well distinguishable. This can be achieved by reducing the reflectivity at the proximal end face of the optical coupling member and/or by increasing the reflectivity at the optical interface at the transition from the optical coupling member to the proximal optical fiber end. Increasing or decreasing the reflectivity of the optical interface may be achieved by tuning the refractive index difference at the optical interface at the transition from the optical coupling member to the optical fiber end.

On the one hand, it is critical that the marker (the optical interface at the transition from the optical coupling member to the proximal fiber end) reflects higher than the shape sensing signal from the sensor so that it is clearly discernable. On the other hand, the tail of the marker reflection peak will overlap the sensor signal. Care must be taken that the shape sensing signal from the fiber sensor is not overwhelmed by the marker reflection. Typically, a marker signal of 15dB-20dB above the sensor signal is found to be suitable, the sensor signal is typically more than 25dB above the noise floor or rayleigh scattering, and the sensor signal is due to back reflection from the fibre bragg grating. It should be noted, however, that the known structure of the sensor signal allows it to be filtered out, so that the marker reflection peak can become visible at a level of 30 dB-40 dB above the residual filtered background.

Further embodiments of the optical shape sensor according to the invention will be described below.

In a preferred embodiment, the optical coupling means is a graded index (GRIN) lens, preferably having a pitch of k/4, where k is an odd integer greater than or equal to 1.

The GRIN lens is advantageous as an optical coupling means if the optical shape sensor is a backloadable optical shape sensor (e.g. a backloadable shape sensing enabled guide wire). 1/4, 3/4, 5/4 … …, the pitch of the GRIN lens is advantageous because on the one hand the marker optical interface forming the starting point for the shape reconstruction is then sufficiently spaced from the proximal end face of the GRIN lens that the intensity of the light reflection at the marker optical interface is well separated from the intensity of the light reflection at the proximal end face of the GRIN lens and on the other hand the GRIN lens with these pitches provides focusing of the collimated beam onto the proximal fiber end of the sensor fiber at the proximal end face.

The GRIN lenses may have a pitch of 5/4 or 7/4. If the GRIN lens has a pitch of 3/4, 5/4, or 7/4, a good compromise between a sufficiently large distance of the optical interface from the proximal end face of the GRIN lens (in one aspect) and keeping the GRIN lens aberration within a controllable range can be found. With these pitches, the numerical aperture and radial cross-section of the GRIN lens can remain substantially the same as with the 1/4 pitch GRIN lens. Further, within the range of pitches of the GRIN lenses mentioned above, the mechanical strength of the optical connector with the GRIN lenses may still be high, even when considering the very small diameter of the GRIN lenses in the backloadable version of the optical shape sensor. Typical diameters may be 0.2mm to 0.4 mm.

It is further important that the gradient index transition layer can be formed as a result of a fusion process that bonds the glass material and fibers of the lens. The thickness of this layer may typically be 10 nm-100 nm or even more, depending on the exact procedure. Such layers generally reduce the reflection intensity.

For good approximation, the refractive index n₀1, 472 GRIN lens with modal index n_ModalityThe reflection of the sharp transition between fibers 1, 451 is given by:

for a given value, this results in R being 5.1x10^-5This is quite high for the purposes of the present invention. The advantage of using a gradient index transition layer is that the reflection can be further reduced by a factor of 10-100 and in practical cases a factor of about 50 is found.

The ratio of the intensity of the light reflected at the Optical Interface (OI) to the intensity of the light incident on the Optical Interface (OI) may be from 10^-6To 10^-5Within the range of (1).

Further, the optical transition layer refractive index of the optical interface at the fiber/coupling member-transition may be different from at least one of the optical fiber refractive index of the optical fiber and the optical coupling member refractive index of the optical coupling member.

In this embodiment, the reflection of light at the marker optical interface is well-discerned due to the refractive index step between the marker optical interface and the proximal optical fiber end and/or between the marker optical interface and the refractive index of the optical coupling member. For example, the optical coupling member and the optical fiber may have the same or substantially the same refractive index, wherein in this case the marker optical interface may be provided by a thin layer of material between the optical fiber end and the distal optical coupling member end, the thin layer of material having a refractive index different from the refractive index of the optical fiber material and the optical coupling member material. This can be achieved, for example, by using an adhesive or bonding agent having a refractive index different from the refractive index of the optical fiber and the optical coupling member. In another example, the optical fiber may have a refractive index different from the refractive index of the optical coupling member, wherein in this case the optical fiber end may be fusion spliced to the optical coupling member, and then the fusion splice itself provides a step in the refractive index of the optical interface at the transition from the proximal optical fiber end to the distal end face of the optical coupling member.

Thus, in one embodiment, the distal first end of the optical coupling member may be fusion spliced to the proximal optical fiber end, and the optical interface is provided at the fusion splice.

In an alternative embodiment, the distal first end of the optical coupling member may be connected to the proximal optical fiber end via an adhesive layer, and the optical interface is provided at the adhesive layer.

If the proximal end face of the optical coupling member is configured to be connected to a distal end of the light supply patch wire supplying the input light, wherein a foil may be arranged at the proximal end face of the optical coupling member, the foil is configured to reduce reflection of light at the connection of the proximal end face of the optical coupling member and the distal end of the light supply patch wire.

This measure reduces the reflection intensity of the reflection at the proximal end face of the coupling member. The foil is preferably index matched to the optical coupling member on the shape sensor side and the corresponding optical coupling member on the patch cord side, such that it further reduces the reflection intensity of the reflection at the proximal end face of the optical coupling member relative to the reflection intensity of the reflection at the marker optical interface at the transition from the optical coupling member to the proximal optical fiber end. Thus, the reliability of the identification of the reflection peak of the reflection at the optical interface and thus the accuracy of the determination of the starting point for the shape reconstruction is further improved.

In particular, it is advantageous if the foil is compressible and/or elastic. The compressible foil may help to compensate for a tilting angle or bending of the proximal end face of the optical coupling member, which may be due to manufacturing tolerances. The inclination angle or curvature of the proximal end face of the optical coupling member and/or the distal end face of the corresponding optical coupling member may cause refraction at the proximal end face due to the air gap, which can be avoided by a compressible foil between the optical coupling member of the shape sensor connector portion and the corresponding optical coupling member connector portion.

According to a second aspect of the present invention, there is provided an optical shape sensing console comprising:

an optical interrogation unit configured to transmit input light into an optical shape sensor according to the first aspect and to receive an optical response signal from each of the cores of the optical shape sensor in response to the input light,

a shape reconstruction unit configured to reconstruct a shape of the optical sensor from the optical response signal, wherein the shape reconstruction unit is configured to determine a starting point for each of the shape-reconstructed cores from the optical response signal, wherein the shape reconstruction unit is configured to identify in the optical response signal a respective peak of a reflected intensity distribution of the input light reflected at the optical interface and to determine a starting position for shape reconstruction from the peak.

According to this aspect of the invention, the optical shape sensing console uses the peak of the reflected intensity distribution of the reflection at the optical interface at the fiber/coupling member transition in the optical response signal to determine a starting point for shape reconstruction with high accuracy. The shape reconstruction unit determines the relative starting position of the cores, e.g. in the time domain, from peaks in the optical response signals from all cores. The shape reconstruction unit may further align the relative start positions in the time domain by adjusting the delay between the determined relative start positions to zero. This can be done by using a phase recovery algorithm.

The shape reconstruction unit may then reconstruct the 3D shape of the optical shape sensor starting from the aligned starting position of the fiber cores.

According to a third aspect of the invention, there is provided an optical shape sensing system comprising an optical shape sensor according to the first aspect and an optical shape sensing console according to the second aspect.

According to a fourth aspect of the invention, there is provided a method of optical shape sensing, comprising:

the input light is transmitted into the optical shape sensor according to the first aspect,

receiving an optical response signal from each of the cores of the optical shape sensor in response to the input light,

identifying in the optical response signal a respective peak of a reflected intensity distribution of the input light reflected at the optical interface,

determining a shape reconstruction start position for each of the cores from the peaks, and

reconstructing a shape of the optical shape sensor starting from the shape reconstruction start position.

According to a further aspect of the invention, a computer program is provided comprising program code means for causing a computer to carry out the steps of the method according to the fourth aspect when said computer program is carried out on the computer.

The optical shape sensing console, optical shape sensing system and method of optical shape sensing according to the present invention have the same or similar advantages as indicated above with respect to the optical shape sensor. It shall be understood that the claimed method, the claimed console, the claimed system and the claimed computer program have similar and/or identical preferred embodiments as the claimed optical shape sensor, in particular as defined in the appended claims and as disclosed herein.

Drawings

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the following drawings

FIG. 1 shows a sketch of an optical shape sensing system including an optical shape sensor and an optical shape sensing console;

FIG. 2 shows a length of optical fiber for use in the optical shape sensor of FIG. 1;

FIG. 3 shows a cross-section of the optical fiber of FIG. 2;

FIG. 4 shows an embodiment of a fiber and GRIN lens arrangement;

FIGS. 5A-C show three GRIN lenses with different pitches;

FIG. 6A, B shows an optical fiber connected to a GRIN lens with a different pitch;

FIGS. 7A-D are graphs showing the intensity of optical response signals from four cores of an optical fiber;

fig. 8 illustrates an embodiment of a fiber and GRIN lens arrangement according to an embodiment of the present invention;

fig. 9 shows a schematic diagram of the reflected intensity distribution in the time domain from the fiber/GRIN lens arrangement according to fig. 4 on the shape sensor side in the case of an 1/4 pitch GRIN lens and in the case of a 3/4 pitch GRIN lens; and is

Fig. 10A, B shows two optical fibers each connected to a GRIN lens and an intermediate layer between the two GRIN lenses.

Detailed Description

Fig. 1 shows an optical shape sensing system 10 that may be used for minimally invasive medical procedures. The optical shape sensing system 10 includes an optical shape sensor OS and an optical shape sensing console C. The optical shape sensor OS may be connected to an optical shape sensing console C via a patch cord PC. The optical shape sensor OS and the patch cord PC may be connected to each other via an optical connection device OCD.

The optical shape sensor OS comprises an optical fiber having at least two cores extending along the length of the optical fiber. An example of an optical fiber 30 for use in an optical shape sensor OS is shown in fig. 2 and 3. The optical fiber 30 shown in fig. 2 and 3 is a multicore fiber having four cores 31, 32a, 32b, and 32 c. The core 31 is a central core extending along the central axis of the optical fiber 30. The cores 32a, 32b, and 32c are outer cores spirally surrounding the central core 31. Each core 31, 32a, 32b, 32c may be embedded in a cladding 34. The cores 31, 32a, 32b, 32c are protected by a coating 35 (not shown in fig. 2), for example a polymer coating. The three outer cores 32a, 32b, 32c are equidistant from each other in a cross-section perpendicular to the longitudinal direction of the optical fiber 30, as shown in fig. 3.

The outer diameter D of the coating 35 may be 200 μm. The outer diameter d of the cladding may be 125 μm. For example, the diameter of each core 31, 32a, 32b, 32c may be 6 μm. For example, the distance between each outer core 32a, 32b, 32c and the central core 31 may be 35 μm.

The cores 31, 32a, 32b, 32c may each have a fiber bragg grating along their length.

Referring again to fig. 1, the optical shape sensor OS may be configured as a backloadable guidewire GW. The proximal part PE of the guide wire GW has the function as a connector part for connecting with the distal end DE of the patch cord PC. The connector part of the guide wire GW must cooperate with a corresponding connector part of the patch cord PC. Since the guidewire GW is in direct contact with the patient, the guidewire GW must be sterile, while the patch cord and console C may not be sterile. The connector part of the guide wire GW and the corresponding connector part of the patch cord PC form an optical connection device OCD. Line B illustrates the barrier between the sterile side (guide wire GW) and the non-sterile side (patch cord PC, console C).

In a backloadable version of the guide wire GW or generally the optical shape sensor OS, the connection between the optical shape sensor OS and the patch cord PC depends on the connector part both comprising the optical coupling means. The coupling member may be configured as a graded index (GRIN) lens. An example of such an optical connection device OCD is shown in fig. 4. Fig. 4 shows an optical connector portion OC1 and an optical connector portion OC2, the optical connector portion OC1 may be a connector portion of a patch cord PC, and the optical connector portion OC2 may be a connector portion of the optical shape sensor OS in fig. 2. The optical connector portion OC2 includes an optical coupling member OCM2, which OCM2 may be configured as a GRIN lens GRIN2 connected to an optical fiber F2, and which optical coupling member OCM2 couples light into and out of the cores C21, C22, C23 of the optical fiber F2. The coupling member has a distal end face OF2 optically connected to the proximal optical fiber end OF the fiber F2 and a proximal end face IF2, the proximal end face IF2 being spaced apart from the distal end along the longitudinal direction LC OF the optical fiber F2.

The optical fiber F2 of the optical shape sensor OS may extend along the entire length of the guidewire GW to sense the optical shape of the guidewire during an interventional procedure. The optical fiber F2 may be a multicore fiber having cores C21, C22, C23. The fiber F2 may have more than three cores, for example, fiber F2 may be arranged like the fibers shown in FIGS. 2 and 3. In FIG. 4, the optical fiber core C22 is the central core relative to the longitudinal axis LC of the fiber F2.

The optical connector portion OC1, which in turn may be connected to the patch cord PC of the optical shape sensing console C as shown in fig. 1, includes an optical coupling member OCM1, which OCM1 may be configured to be connected to the GRIN lens GRIN1 of optical fiber F1, and which OCM1 couples light into and out of the cores C11, C12, C13 of optical fiber F1. The coupling member has a distal end face OF1 and a proximal end face IF1, said proximal end face IF1 being optically connected to the distal optical fiber end OF the optical fiber F1. Connector portion OC1 forms a corresponding connector portion to connector portion OC 2.

Fig. 4 shows an exemplary case of 1/4 pitch GRIN lens GRIN 2. The pitch will be described in more detail later.

The light beams from each OF the cores C11, C12, C13 enter the GRIN lens GRIN1 at the proximal end IF1 OF the GRIN lens GRIN1 and exit the GRIN lens GRIN1 as collimated beams at the distal end OF1 OF the GRIN lens GRIN 1. The collimating effect of the GRIN lens GRIN1 is due to the pitch of 1/4 of the GRIN lens GRIN 1. The collimated beam then enters an optical connector portion OC2 with optical coupling means OCM2, which optical coupling means OCM2 is here configured as a GRIN lens GRIN2 connected to an optical fiber F2. In fig. 4, the entire arrangement of GRIN lenses 1 and GRIN lens 2 has a pitch of 1/2. In view of the configuration of the GRIN lenses GRIN1 and GRIN2 as 1/4 pitch lenses in each case, the set of collimated light beams may enter and exit from the focal points of the cores C11, C12, C13 or C21, C22, C23 of the fibers F1, F2 from the connectors OC1 and OC2, and vice versa. It should be noted that the light beam from core C11 enters core C23 after having propagated through GRIN lens GRIN1 and GRIN2, i.e., the image of cores C11, C12, C13 is flipped at cores C21, C22, C23.

Due to its compactness and its mainly low surface reflection, GRIN lenses are a good choice in a backloadable version of the optical shape sensing technology in medical interventional devices. For example, light is not reflected or refracted at the air-glass transition, but is bent in a graded index profile, e.g., extending in a radial direction of the GRIN lens. This property serves to eliminate any air-to-glass transition when a connection is made, i.e., when the fiber and GRIN lens are fused, adhered, or otherwise connected to one another. Between connectors OC1 and OC2, a thin index matching intermediate layer IM (e.g., foil) may be disposed to reduce or eliminate reflection at the distal end OF1 OF GRIN lens GRIN1 and the proximal end IF2 OF GRIN lens GRIN 2. The same matching layer may have mechanically advantageous properties that are deformable (compressible). In general applications, it may be a fluid or a gel. It may be elastic and compressible thin within the scope of the invention and its applications. In this way, the matching intermediate layer IM is able to deform into any surface irregularities OF the connecting portion and provide a perfect mechanical and optical match between the surfaces OF1 and IF2 OF the optical coupling members OCM1 and OCM 2.

Fig. 4 shows a typical length L of, for example, 1.3mm and a typical diameter of, for example, 0.3mm for a GRIN lens. Referring to fig. 5A to 5C, fig. 6A and 6B, the physical principle of the GRIN lens will be explained in more detail.

GRIN lenses, or generally GRIN optical components, have a gradual, position-dependent change in refractive index that is used to control the propagation of light through the respective component. An important subset of GRIN optics consists of cylinders (also called GRIN rod lenses) with refractive index that changes only along the radial distance r. For example, GRIN rod lenses have an almost parabolic radial refractive index profile:

wherein g is a gradient constant, n₀Is the refractive index in the center of the GRIN-rod lens and r is the radial position with respect to the longitudinal central axis of the GRIN-rod lens. The light entering the GRIN-rod lens is continuously refracted and the optical field inside such GRIN-rod lens is thus periodically changed along the z-axis (cylinder axis) with the following period lengths

A common way to express the length of a GRIN-rod lens is with respect to the pitch P, which is the geometric length L of the GRIN-rod lens divided by the period length z_{Period of time}：

The geometric length L of a GRIN lens is proportional to its pitch P according to equation (3).

Fig. 5A shows a GRIN-rod lens having a pitch P of 0.25, fig. 5B shows a GRIN-rod lens having a pitch P of 0.5, and fig. 5C shows a GRIN-rod lens having a pitch P of1 in some examples.

GRIN rod lenses with a pitch P-1, 2, 3, 4, … image their front plane onto their rear plane and vice versa. GRIN rod lenses with a pitch P of 0.5, 1, 5, 2, 5, … also image the front plane onto the back plane, but the image is now reversed, as is the case with the GRIN lens arrangement in fig. 4 formed by both GRIN lenses GRIN1 and GRIN 2. Another commonly used pitch is P-1/4, 3/4, 5/4, …, for which GRIN-rod lenses collimate light from each point on their front plane at their back plane and vice versa.

Fig. 6A shows an example of a GRIN lens having a pitch of 3/4, and fig. 6B shows an example of a GRIN lens having a pitch of 5/4.

The numerical aperture of a GRIN-rod lens is defined by the refractive index at the center of the GRIN-rod lens and the refractive index at the outer boundary of the GRIN-rod lens:

where d is the diameter of the GRIN rod lens perpendicular to the cylinder axis (see fig. 1).

When the minimum required NA and the maximum diameter d are known, the GRIN rod lens can be designed with a gradient constant g:

when, in addition, the required pitch P is known, the GRIN rod lens must have a length L as follows:

when making the optical connector of the shape sensor OS in fig. 4 (like the optical connector OC2), the fiber F2 and the GRIN lens GRIN2 may be bonded to each other by a fusion process. Fusion splicing is a process in which an optical fiber F2 (fig. 4) or F (fig. 6A, 6B) and a GRIN lens GRIN2 (fig. 4) or GRIN lens GRIN (fig. 6A, 6B) are bonded end-to-end using heat. In other words, the fiber and GRIN lens are fused together because the materials of the fiber and GRIN lens are locally melted, similar to the soldering process. Alternatively, the method of bonding the fiber and GRIN lens to each other uses a thin layer of adhesive.

In optical shape sensing, strain is measured in the core C21, C22, C23 (fig. 4) of the fiber F2 (or in the four cores 31, 32a, 32b, 32C (fig. 2, 3) of the fiber 30). The strain in the core may be due to bending and/or twisting in the fiber. The optical shape sensing console C (fig. 1) has an optical interrogation unit OIU configured to transmit input light into the cores C21, C22, C23 of the optical fiber F2 of the optical shape sensor OS and receive optical response signals from each of the cores C21, C22, C23 (or 31, 32a, 32b, 32C) of the optical shape sensor OS in response to the input light. The optical response signals from each of the fiber cores are indicative of strain in the optical fiber F2 along the optical shape sensor OS. The optical shape sensing console C also includes a shape reconstruction unit SRU (fig. 1) configured to computationally construct the shape of the optical shape sensor OS from the optical response signals received by the optical interrogation unit OIU. Optical shape sensing enables 3D shape reconstruction of the optical shape sensor OS. Accurate shape reconstruction of the optical shape sensor OS requires a well-defined starting point or position down to the micrometer level along the optical shape sensor OS for 3D shape construction of the optical shape sensor OS. However, the optical response signal received from the core may have a relative delay in time from core to core, and it is difficult to recover the starting position for the shape reconstruction of all cores from the optical response signal of the core. In other words, the response signal received from the core only provides a relative starting position that may be different from core to core. Therefore, some methods are needed to align these relative start positions of all the cores of the optical shape sensor OS down to the micrometer level in order to obtain a shape reconstruction of the optical shape sensor that is as accurate as possible.

One possibility to align the relative starting positions of the cores may be to use reflection from a fiber bragg grating in fiber F2 or rayleigh backscattering in fiber F2. This method compares the current state of backscattering to a previously recorded reflection profile of the fiber, possibly a few millimeters apart, as a calibration. However, this approach is disadvantageous because such a calibration requires that during the calibration process it is necessary to have (temporary) physical markers that can be induced by e.g. pressure points, to accurately locate the relative physical positions of the associated segments of the different cores. This method is also disadvantageous because it can be time consuming.

Another possibility is to employ reflection OF the input light at the interface between the two GRIN lenses GRIN1 and GRIN2 in fig. 4 (i.e. the interface at the end OF1 OF GRIN lens GRIN1 and the end IF2 OF GRIN lens GRIN 2). The method has the following advantages: it is independent of any calibration method. In this method, the glass-air-glass index step is the basis for reflection at the optical interface between GRIN lens GRIN1 and GRIN 2. This step occurs exactly at the same position of all cores and alignment with respect to the starting position can be easily obtained.

In the latter approach, however, there are at least two problems, one of which is based on the necessity of having a sterile barrier (like an intermediate layer IM (fig. 4), e.g. foil) between the two connectors OC1 and OC2 of the patch cord PC and the guide wire GW when the latter is a backloadable guide wire. Further, at the interface between the two GRIN lenses GRIN1 and GRIN2 in fig. 4, the reflected intensity of the input light may vary strongly due to contamination of blood, variable pressure on the connection interface and due to the fact that the sterility of the connection of the two connectors OC1 and OC2 is fixed to the intermediate layer IM present to each other. Another problem is that the end faces OF1 and IF2 cannot be polished precisely at right angles to the optical axis, so that a variable air gap may exist. These conditions may prevent accurate recovery of such interfaces in the optical response signal from the core, as will be explained below.

Fig. 7A-D show examples of optical response signals received in response to input light from four cores, core 0 to core 3, in the arrangement of fig. 4 (with the optical fibers shown in fig. 2 and 3) when making a connection between two fibers F1 and F2 with 1/4 pitch GRIN lenses GRIN1 and GRIN 2. Core 0 represents the central core and cores 1, 2, 3 represent the outer cores of fiber F2.

FIGS. 7A-D show, for the cores, each of core 0, core 1, core 2, and core 3 shows the amplitude distribution of the optical response signal along the corresponding core of optical connectors OC1 and OC2 (FIG. 4) (nodes 4000 and 4200 in the time domain optical response signal). FP represents the reflection peak OF the reflection OF light at the optical interface between the two GRIN lenses GRIN1 and GRIN2 in fig. 4, i.e. at GRIN lens end faces OF1 and IF2 with an intermediate layer IM (foil) between them. Comparison of the reflection peaks FP between core cores 0, 1, 2, 3 reveals that the reflection peak FP of central core 0 is higher because the optical interface is at right angles to central core 0 and most of the reflected light is focused straight back into core 0 of fiber F1.

SP2 represents the reflection peak OF the reflection OF light at the optical interface between fiber F2 and GRIN lens GRIN2 in fig. 4 (i.e., at the distal end OF2 OF GRIN lens GRIN 2). As shown for core 0, in the case of GRIN lens GRIN2, which is an 1/4 pitch GRIN lens, reflection peaks FP and SP2 are separated from each other by approximately 27 indices (nodes). As can also be taken from fig. 7A-D, the reflection peak SP2 is higher than the reflection peak FP for the outer core 1-core 3, while the reflection peak SP2 is lower than the reflection peak FP for core 0.

SP1 represents the reflection peak of the reflection of light at the optical interface between fiber F1 and GRIN lens GRIN1 in fig. 4 (i.e., at the proximal end IF1 of GRIN lens GRIN 1). CTP represents a peak of the amplitude distribution of the optical response signal due to crosstalk from the outer core into the central core 0.

As is apparent from fig. 7A-D, for a backloadable optical shape sensor OS, the reflection at the optical interface between the optical fiber F2 and the GRIN lens GRIN2 may be useful to act as a common starting position for all cores used for shape reconstruction. This means that it is possible to measure the time position of the light reflection at the optical interface at the transition from the GRIN lens 2 of the optical shape sensor OS to the optical fiber F2 and to adjust the time delay between the cores to zero. At this point, the reflection of the optical interface is slight or can become slight, but is well visible and stable.

However, the tail of the reflected intensity profile of the reflection at the interface between the two GRIN lenses GRIN1 and GRIN2 can overlap with the reflected intensity profile of the reflection at the optical interface between fiber F2 and GRIN lens GRIN2, deteriorating the accuracy of the position (which in a typical system should be about 0.02 node distance or 1 micron propagation delay), with which the reflection peak SP2 can be measured. This overlap would therefore prevent accurate restoration of the starting position of each of the cores of fiber F2 due to reflection peak SP2 from the optical interface between fiber F2 and GRIN lens 2.

Thus, according to the present invention, the partially reflective and substantially transmissive optical interface at the transition from the GRIN lens GRIN2 to the proximal fiber end of optical fiber F2 should be arranged at such a distance distally from the proximal end-face IF2 of the GRIN lens GRIN2 and configured such that light is reflected at the optical interface at the transition from the GRIN lens GRIN2 to the optical fiber F2 with a reflected intensity profile that does not substantially overlap the reflected intensity profile of light reflected at the proximal end-face IF2 of the GRIN lens GRIN 2.

In accordance with the principles of the present invention, the length of GRIN lens GRIN2 is increased to pull reflection peaks FP and SP2 farther away from each other. However, in a backloadable version of shape sensing enabled guidewire GW, GRIN lens GRIN2 must have a small diameter. Given the numerical aperture of fiber F2, which is typically NA 0.21, and the typical field diameter of 70 microns for a 125 micron fiber sensor, this requires a fairly small focal length (1/4 pitch length) of1, 0-1, 5mm so that the light can be collimated within 0.25-0.40mm diameter of all cores with sufficiently low GRIN lens aberrations. These parameters are compatible with the most widely used guidewire diameters of 0.36mm, 0.46mm or 0.89 mm.

Therefore, for a given situation, lengthening of the GRIN lens GRIN2 should be accomplished without changing the numerical aperture and radial cross-section of the GRIN lens GRIN 2. This can be accomplished according to the present invention by using higher pitch lenses (such as 3/4 and 5/4 pitch GRIN lenses) that also produce collimated beams. Such GRIN lenses are a very good compromise between GRIN lens aberrations and sufficient separation of the reflection peaks FP and SP2, where the latter provides a more accurate restoration of the relative start positions of each core for shape reconstruction and for alignment of these relative start positions to find a common start position for shape reconstruction.

FIG. 8 illustrates an embodiment of an optical shape sensor OS configured according to the principles of the present invention. The optical shape sensor OS includes an optical connector OC2 having a GRIN lens GRIN2 with 3/4 pitch. In this way, the optical interface OI at the transition OF the proximal end OF the optical fiber F2 to the distal end face OF2 OF the GRIN lens GRIN2 is in a sufficient distance distally from the proximal end face IF2 OF the GRIN lens GRIN2 such that the reflection peak SP2 OF the reflected intensity distribution at the optical interface OI is well separated from the reflection peak FP OF the reflected intensity distribution at the proximal end face IF2 OF the GRIN lens GRIN 2. Also shown in fig. 8 are a fiber ferrule FF housing an optical fiber F2 and a tube or sleeve SL housing the fiber ferrule FF and GRIN lens 2 in a mechanically stable manner.

Fiber F2 may be fusion spliced to GRIN lens GRIN 2. In this case, the fusion joint may form an optical interface OI. The gradient index transition layer may be formed as a result of a fusion process that combines the glass material of the lens and the fibers. The thickness of this layer may typically be 10 nm-100 nm or even more, depending on the exact procedure. Such layers generally reduce the reflection intensity.

For good approximation, the refractive index n₀1.472 GRIN lens and method of making_ModalityThe reflection of the sharp transition between fibers of 1.451 is given by:

for a given value, this results in R being 5.1x10^-5This is quite high for the purposes of the present invention. The advantage of using a gradient index transition layer is that the reflection can be further reduced by a factor of 10-100 and in practical cases a factor of about 50 is found.

If the optical fiber F2 is connected to the GRIN lens GRIN2 by bonding them to each other, the optical interface OI may be formed by a layer of adhesive or bonding agent. It is also possible to use the GRIN lens of fig. 6B with a pitch of 5/4 as the GRIN lens GRIN2, or even higher GRIN lenses of 1/4 odd-times pitch could be used as the lens GRIN2 if the GRIN lens aberrations are not too high.

In general, the ratio of the intensity of the light reflected at the optical interface OI to the intensity of the light incident on the optical interface OI may be from 10^-6To 10^-5Within the range of (1).

Fig. 9 shows the optical response signals in the time domain from the arrangement in fig. 4 for 1/4-pitch GRIN lens 2 and 3/4-pitch GRIN lens 2. If the GRIN lens GRIN2 is a 1/4 pitch GRIN lens, the reflection peak FP from the optical interface between the two GRIN lenses GRIN1 and GRIN2 and the reflection peak of the optical interface at the transition from the fiber F2 to the GRIN lens GRIN2 do substantially overlap. The situation is much better with the arrangement according to fig. 8 using 3/4 pitch GRIN lens GRIN 2.

An advantageous effect of the optical shape sensor OS according to fig. 8 is that, as shown in fig. 9, the tails of the reflection peaks FP of the light reflected at the interface between the two GRIN lenses GRIN1 and GRIN2 have much less overlap with the reflection intensity distribution around the peak SP2 of the light reflected at the optical interface OI of the 3/4-pitch GRIN lens GRIN2, compared to the GRIN lens having 1/4 pitch ("SP 2(1/4 pitch") in fig. 9). The reflection peak SP2(3/4 pitch) is shifted from the reflection peak FP by a factor of 3 compared to the reflection peak SP2(1/4 pitch). As shown by the arrow V in fig. 9, the reflection peak FP is variable and unpredictable (depending on the compression of the foil, blood contamination, etc.) and therefore cannot be easily adjusted for its effect. This is for example different from the case with signals from fibre bragg gratings which are predictable and can be filtered out.

Also shown in fig. 9 is reflection peak SP1 at the optical interface between optical fiber F1 and GRIN lens GRIN1 with a pitch of 1/4. The use of higher pitch GRIN lenses 1 is not necessary because reflection peak SP1 is spaced further apart from reflection peak SP2(3/4 pitch) than reflection peak FP.

Thus, by using the 3/4-pitch GRIN lens GRIN2, the effect of the reflection peak FP of the reflection at the interface between the two GRIN lenses GRIN1 and GRIN2 on the reflection peak SP2 from the reflection at the optical interface OI is reduced and therefore the position of the peak SP2 of each core C21-C23 (or 31, 32a, 32b, 32C) can be measured with lower background and therefore more accuracy.

The accuracy of the determination of the reflection peak position of the reflection peak SP2 of the 3/4-pitch or 5/4-pitch GRIN lens GRIN2 can be further improved by increasing the height of the reflection peak SP2 relative to the reflection peak FP. This can be achieved by reducing the reflection peak FP by using an optimized intermediate layer IM for index matching or by polishing the end faces OF1 and IF2 OF the GRIN lenses GRIN1 and GRIN2 in fig. 4 at a small angle, as shown in fig. 10A and B. The layer IM (e.g., foil) may be thick and compressive enough to overcome the geometric differences introduced by the angular polishing OF the end faces OF1 and IF 2. Without foil IM, the light would exit GRIN lens GRIN1 at an angle polished by the angle OF end face OF 1. Since the orientation of the angle polishing cannot be exactly the same in both GRIN1 and GRIN2, a proper optical connection between the lenses will not be possible. By using compressible foil IM in the use of compressible foil IM in between the two lenses GRIN1 and GRIN2, the light is again straight out towards the second GRIN lens GRIN 2. In this way, the compressible foil achieves proper connection without requiring that the angle polish on both GRIN lens GRIN1 and GRIN2 be oriented in the same manner. Foil IM may be index matched to reduce reflection of light at end IF2 of GRIN lens GRIN 2.

An alternative or additional measure is to add a reflection peak SP2, which can be done by tuning the refractive index difference between the GRIN lens GRIN2 and the fiber F2, e.g. by selecting for these elements materials with sufficiently different refractive indices to provide a sufficient refractive index step at the optical interface OI, for the fused version (see above for n₀And n_Mode(s)Example) or by using a suitable adhesive providing a sufficient refractive index step at the optical interface OI, provided that the optical fiber F2 and the GRIN lens GRIN2 are bonded together. In general, the optical interface refractive index of the optical interface OI may be different from the optical fiber refractive index of the optical fiber F1 and the optical coupling memberAt least one of the optical coupling member refractive indices of OCM 2.

Referring again to fig. 1, the optical interrogation unit OIU is configured to transmit input light into the optical shape sensor OS and receive optical response signals from each of the fiber cores (e.g., C21, C22, C23) of the optical shape sensor OS in response to the input light. The received light for each channel or core is measured in output from the interferometer and thus both phase and intensity are measured. The shape reconstruction unit SRU is configured to reconstruct the shape of the optical shape sensor OS from the optical response signals, wherein the shape reconstruction unit SRU is configured to determine the starting position of each of the cores of the optical shape sensor used for shape reconstruction from the optical response signals. The shape reconstruction unit SRU is configured to identify or measure in the optical response signal the respective peaks SP2 of the reflected intensity profile of the reflection at the optical interface OI at the transition from the optical fiber F2 to the GRIN lens GRIN2 as described above and to determine from these peaks the relative starting position of each of the cores used for shape reconstruction.

The shape reconstruction unit SRU may further be configured to align the start positions of the cores for shape reconstruction, e.g. using a phase recovery algorithm for the interferometric signals of each channel to align the identified start positions of the cores for shape reconstruction.

In a method of optical shape sensing, input light is transmitted into the optical shape sensor OS, and an optical response signal from each of the fiber cores (e.g., C21, C22, C23) of the optical shape sensor OS is received in response to the input light. The shape of the optical shape sensor OS is reconstructed from the optical response signals. The corresponding peaks of the reflected intensity distribution of the light reflected at the optical interface OI (fig. 4, 8) are identified in the optical response signal. A shape reconstruction start position for each of the cores is determined from the peaks, and the shape of the optical shape sensor from the shape reconstruction start position is reconstructed.

The method may be performed by a computer program comprising program code means for causing a computer to perform the method as mentioned above when said computer program is run on a computer.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. Although specific measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage.

A computer program may be stored/distributed on a suitable non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

Any reference signs in the claims shall not be construed as limiting the scope.