Spectrally encoded probes

A novel endoscope, which can be a spectrally encoded endoscope (SEE) probe having forward-view, side-view, or a combination of forward and side views is provided herein. The SEE probe includes a light guiding component, a light focusing component, and a grating component. The probe is configured to forward a light such as a spectrally dispersed light from the grating component to a sample with no intermediate reflections between light guiding component and the grating component. A triangular grating, such as a staircase grating or an overhang grating may be used as the grating component.

FIELD OF THE DISCLOSURE

The present disclosure relates to endoscopes. More particularly, the disclosure exemplifies spectrally encoded endoscopic probes.

BACKGROUND INFORMATION

Medical endoscopic probes have the ability to provide images from inside the patient's body. Considering the potential damage to a human body caused by the insertion of a foreign object, it is preferable for the probe to be as small as possible. Additionally, the ability to image within small conduits such as small vessels, small ducts, small needles, cracks, etc., requires a small probe size.

One useful medical probe employs spectrally encoded endoscopy (“SEE”), which is a miniature endoscopy technology that can conduct high-definition imaging through a sub-mm diameter probe. In a SEE probe, broadband light is diffracted by a grating at the tip of an optical fiber, producing a dispersed spectrum of the different wavelengths (colors) on the sample. Light returned from the sample is detected using a spectrometer; and each resolvable wavelength corresponds to reflectance from a different point on the sample. Thus, a SEE probe encodes light reflected from a given point in the sample by wavelength. The principle of the SEE technique and a SEE probe with a diameter of 0.5 mm, i.e., 500 μm have been described by D. Yelin et al., in a publication entitled “Three-dimensional miniature endoscopy”, Nature Vol. 443, 765-765 (2006). Another similar example is described by G. Tearney et al., in “Spectrally encoded miniature endoscopy”, Opt. Lett., 27(6): p. 412-414, 2002. Imaging with SEE can produce high-quality images in two- and three-dimensions.

Spectrally-encoded endoscopy utilizes the ability of the diffraction grating that deflects incident light to a diffraction angle according to wavelength. When the deflected light hits an object, light is scattered by the object. Detecting the scattered light intensity at each wavelength is equivalent to detecting the intensity from the corresponding diffraction angle. Thus, one-dimensional line image of the object is obtained. A two-dimensional image is obtained by rotating the SEE probe. A three-dimensional image can be obtained by rotating and translating (moving linearly) the SEE probe. Moreover, when incorporated into a sample arm of an interferometer, the SEE probe can also acquire depth information from a sample (e.g., tissue). Typically, as the grating deflects the light, the incident light is usually bent with respect to the optical axis of the probe. In this way, no light goes straight with respect to the optical axis. As no light goes straight, it is not possible with conventional spectrally-encoded endoscopy configuration to view in a forward direction.

Current trend of the spectrally-encoded endoscopy employs side-view type, with a few examples exhibiting forward viewing characteristics. The front-view type consists of multiple components including lenses, spacer elements, prisms and gratings, which makes the probe design complicated. Examples of such designs can be found, for example, in C. Pitris et al., Optical Express Vol. 11 120-124 (2003) and U.S. Pat. No. 8,145,018, both of which disclose a dual prism configuration where a grating is sandwiched between two prisms (a “grism”). This grism directs spectrally dispersed light in the directions including the optical axis of the fiber. The grism consists of multiple components (grating, prisms) which need proper alignment. The need of a grism to construct a forward-view probe increases the cost, complexity of fabrication and size of the probe. Publication WO2015/116951 discloses another forward view endoscope where the angled reflective side surface makes the light incidence angle on the grating such that at least one of the wavelengths propagates parallel to the optical axis of the lens. However, these known designs of forward view SEE probes have drawbacks. First, this design may not allow for use of the full available aperture. A smaller aperture means a decreased achievable resolution.

Second, both designs need a reflective surface in the spacer. This is not particularly easy to fabricate considering the miniature size of the spacer. In particular, the alignment of the spacer and the GRIN lens poses challenges during fabrication.

Further, the illumination fiber is off-axis to the GRIN lens, which introduces additional difficulties in fabrication as well as optical aberrations. In some designs, a reflective coating is needed at least for the second reflective surface, which will introduce light loss and scattering in the system. This coating is also needed for the first reflective surface unless a lower refractive index epoxy is used. A lower reflective index epoxy usually requires special curing conditions, which poses additional concerns for mass production.

Accordingly, it can be beneficial to address and/or overcome at least some of the deficiencies indicated herein above, and thus to provide a new SEE probe having forward direction view and/or omnidirectional view, and an apparatus to use such a probe, e.g., for imaging in a small optics. It is also beneficial to provide a SEE probe having a lower cost and/or less complexity compared to prior known probes.

SUMMARY OF EXEMPLARY EMBODIMENTS

According to at least one embodiment of the invention, there is provided an apparatus comprising a spectrally encoded endoscopy probe comprising: a light guiding component; a light focusing component; and a grating component (e.g., a triangular grating) wherein the probe is configured for guiding a light from the light guiding component, through the light focusing component and to the grating component in the direction of the probe optical axis, and then forwarding a spectrally dispersed light from the grating component towards a sample with no intermediate reflections.

According to at least one embodiment of the invention, there is provided an apparatus comprising a probe that comprises: a light guiding component; a light focusing component; and a triangular grating component, wherein the probe is configured for guiding a light from the light guiding component, through the light focusing component and to the grating component in the direction of the probe optical axis, and then forwarding a diffracted light from the grating component towards a sample with no intermediate reflections.

According to yet other embodiments, there is provided a system comprising a light guiding component; a light focusing component; a grating component, a rotary element, one or more detection fibers, one or more detectors, and one or more processors configured to processes light from multiple diffracted orders and for a single color image based on that light. The probe may be configured for guiding a light from the light guiding component, through the light focusing component and to the grating component in the direction of the probe optical axis, and then forwarding a spectrally dispersed light from the grating component towards a sample with no intermediate reflections.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments disclosed herein describe SEE probes that can have good resolution in both the scanning direction and the spectral direction due to a fuller use of the diameter available. These embodiments also provide SEE probes without the need for one or more off-axis element in the design and also without the need for a mirror reflection element. The lack of off-axis elements and mirror reflections simplifies the manufacturing process and improves reliability of the probe. Further, due to the use of more limited accepting angles in the collection of reflected light, some embodiments of the SEE probes as provided herein can be designed such that the 0th order and −2nd order will not cause stray light in the system. This is especially true for many designs with substantially no transmitted 0th order light and the reflected 0th order light being at a very large angle.

A diagram of an exemplary embodiment of a SEE probe100according to the present disclosure is shown inFIG. 1. This exemplary SEE probe100includes an optical fiber10(light guiding component), a focusing lens12(light focusing component), a spacer14, and a diffraction grating16(grating component). Broadband light (or other electro-magnetic radiation) can be coupled or otherwise provided into the fiber10, and focused by the lens12. The light (or other electro-magnetic radiation) travels through the focusing lens12, the spacer14, and is incident on the grating16without any reflections therebetween. At the grating16, the light is diffracted according to its wavelength and incident angle. Each light (having a wavelength λ or a wavelength band Δλ) is focused on a unique spatial location on the tissue18(sample). As shown inFIG. 1, X1, X2, and X3are unique spatial locations of tissue18for wavelengths λ1, λ2, and λ3, respectively. Therefore, the light (or other electro-magnetic radiation) can be focused into a plane or line20, rather than onto a point. The plane or line20shown inFIG. 1is referred to as a spectrally-encoded line. One of the wavelengths in the light can propagate substantially parallel to the optical axis (Ox) of the lens12, shown as λ1inFIG. 1. Light (or other electro-magnetic radiation) reflected by the tissue18can be coupled or otherwise provided back to the fiber10or to a different fiber (not shown), and then the collected light can be delivered to a detector (not shown) that includes a spectrometer (not shown). At the spectrometer, the spectrum of the returning light (or other electro-magnetic radiation) can be read out as an electrical signal, which can then be used to generate a line image of the tissue using a computer or other digital processor (not shown). The exemplary SEE probe100can be scanned rotationally along the optical axis Ox of the lens as shown by the rotational arrow22, e.g., by rotating or oscillating the lens12or in other ways which should be understood to those having ordinary skill in the art.

As shown inFIG. 1and in other embodiments, no off-axis element is required to provide the forward-viewing design. There is no need for an off-axis element either between the light guiding component and the light focusing component or in any reflections/mirrors prior to the light hitting the grating. This can simplify the manufacturing process and/or improve reliability because alignment of the optics becomes easier compared to previously known SEE probes.

FIG. 2shows ray tracing of illumination and diffracted light according to one exemplary embodiment. InFIG. 2, the illumination fiber10is coaxial with focusing lens12. The lens12is shown inFIG. 2as a GRIN (graded index) lens for easy fabrication, but a ball lens or other shape of lens may also be used. This embodiment ofFIG. 2specifically optimizes the grating16so that the incident angle on the grating will be designed such that at one specific wavelength (e.g. blue, 415 nm), one of its diffraction orders (−1 order in this case) will propagate parallel to the optical axis like it is undiffracted (the diffraction angle is the same as the incident angle).

As shown inFIG. 2, after the focusing lens12, light passes through spacer14and then is incident upon the grating16with no reflection therebetween. The −1st diffraction order is shown inFIG. 3A. The 0th order will be reflected and is not shown.FIG. 3Bshows the −2nd diffraction order for the probe design shown inFIG. 2. Due to limited accepting angles of the detection fiber (e.g. NA=0.5), the 0th order (reflected) and the −2nd order diffracted at a larger angle usually will not cause stray light in the system. The field of view (FOV) can be extended by either increasing the wavelength range or by introducing higher diffraction orders. The FOV can also be extended by increasing the incident angle on the grating as explained later. Table 1 provides light propagation for the various orders at three different wavelengths with an incident angle θi=56.1°.

For the design shown inFIG. 2, the grating period is fixed at about 1 μm for convenience and a blue light (415 nm) was designed to be at the center of the FOV and the red light (800 nm) was designed to be at the edge of the FOV.FIG. 3Ashows an exemplary half-angle FOV that can be obtained with the probe design ofFIG. 2using the −1st diffraction order. In other embodiments, other light bands may be used, and other wavelengths or relative wavelengths can be defined as the center and the end of the FOV. Moreover, depending on the desired application, the grating can be designed so that diffractive others are tailored to occupy specific FOV angles.FIG. 3Bshows an exemplary half-angle FOV formed by the −2nd diffraction order for the probe design shown inFIG. 2.

In this manner, in the embodiment ofFIG. 2, due to limited accepting angles of the detection fiber (not shown), the 0th order and the −2nd order should not cause substantive stray light in the system.

The FOV can be extended by either increasing the wavelength range of the light or by using higher diffractive orders. For example, as shown inFIG. 3C, if the wavelength range is extended from 0.8 μm to 1 μm, the field of view (half angle) is increased from 30° to 43°, as compared toFIG. 3A. One potential issue here is the −2nd diffraction order of the blue light shown inFIG. 3B, which will interfere with the blue portion of the −1st diffraction order (e.g., 415 nm will be covering both center FOV and the FOV corresponds to 830 nm). At least two measures can be taken to address this issue. One is to design the grating to minimize the higher order diffraction efficiencies. The other one is to introduce one more detection fiber to specifically receive higher angle light, e.g. from 30 degrees to 43 degrees. For example, a filter can be introduced or the grating on the detection fiber can be designed such that the blue end wavelength will be filtered out.

In some embodiments, the focusing lens12can be a ball lens. The spacer14may be formed of a transparent material that supports the grating16. In other words, spacer material can be a support for grating16, for example, epoxy material used to align and fix the lens12to the grating16or a glass material may be used. Alternatively, spacer14may be just free space (air) between the lens12and grating16. In practice, spacer14may be a transparent wafer substrate on which a plurality of grooves are disposed to form the grating16.

FIG. 4shows a probe having a grating16designed to diffract +1storder light. As compared to the embodiment shown inFIG. 2, inFIG. 4, the light incident angle on the grating is changed from positive to negative. The diffraction order is also changed from −1stto +1stin this case. Similar to the case shown with reference toFIG. 2andFIG. 3A, both the 0th order and higher diffraction orders may not introduce stray light due to limited accepting angle from the detection fiber or lower efficiencies of the grating for higher orders of diffraction, or both. Table 2 provides light propagation angles for the first and second positive (+) diffractive orders at three different wavelengths.

Due to limited accepting angles of the detecting fiber (not shown), the 0th order and the +2ndorder will not cause stray light in the system using a probe of this embodiment. As in the previous embodiment, the FOV can be extended by either increasing the wavelength range or by using higher diffraction orders.

For the design shown inFIG. 4, the grating period is fixed at about 1 μm for convenience. For both designs (FIG. 2andFIG. 4), the blue light (415 nm) will be in the center FOV and the red light (800 nm) will be at the edge of the FOV. However as previously mentioned, other light bands may be used, and other wavelengths or relative wavelengths can be defined as the center and the end of the FOV.

FIG. 5shows an exemplary embodiment where the pitch of the grating is designed to define specific wavelengths as the center and the end of the FOV. As shown inFIG. 5, the center FOV is now covered by the red (800 nm) light instead of the blue light (415 nm). In this embodiment, the grating period was significantly increased, e.g. from about 1 μm to 2.5 μm. The design changed the wavelength polarity in the FOV. That is, as shown inFIG. 5the red light is in the center and the blue light is at the edge of the FOV. This can be of particular interest for several reasons. One is that the grating as well as the quantum efficiency of the detector usually has a higher efficiency in the red region. Since the center FOV is usually more important, there would be improved efficiency and/or resolution in this region. This reversed wavelength polarity design may also be particularly useful in a color SEE probe when using the second positive (+2) diffraction order because the +2nd diffraction order will have the blue wavelength in the center and the red wavelength at the periphery of the FOV. Moreover, for this long grating period design, several higher diffraction orders can coexist in the field of view as shown inFIG. 6A-6C.FIG. 6Ashows the field of view of the SEE probe shown inFIG. 5where the red (800 nm) wavelength is in the center of the FOV and the blue (415 nm) wavelength is as the edge of the FOV when using the +1st diffraction order.FIG. 6Billustrates the location of the various wavelengths in the FOV of the second (+2) diffraction order; andFIG. 6Cillustrates the location of the various wavelengths in the FOV of the fifth (+5) diffraction order. This phenomena is explained more in detail herein below.

For the long grating period design, several higher diffraction orders can coexist as illustrated inFIG. 6A-6Cand summarized in Table 3 for +1st, +2nd, +3rd, +4th, and +5th diffraction orders. In some embodiments, therefore, a grating is designed to particularly enhance the efficiencies of one or more of these higher diffraction orders.

Table 3 provides light propagation angles for the various orders for the embodiment shown inFIG. 5at three different wavelengths with an incident angle θi=56.1°.

As the +5th order shown in Table 3 can cover a much larger FOV compared to +1st order shown inFIG. 4, it is possible to design a system by using +5th order for side-view applications with a very coarse grating to begin with. This is particularly advantageous as a coarse grating is easier to fabricate and align than a fine-pitch grating.

An embodiment for color imaging using multiple order diffraction is possible using, for example, the structural design shown inFIG. 2. A probe as shown inFIG. 2is designed such that the incident angle is 81 degrees and the grating groove density is 0.1983 lines/mm. Light beams having center wavelengths of 415 nm, 498 nm, and 622.5 nm are diffracted in forward view direction in −6th, −5th, and −4th order, respectively. Using this probe, 3 monochromatic images are obtained for blue (415-475 nm, −6th order), green (498-570 nm, −5th order), and red (622.5-712.5 nm, −4th order) channels. The half-angle FOV is 29.3 degrees. By combining the 3 monochromatic images using known image processing algorithms, it is possible to obtain a forward view RGB color image of any region of interest scanned by the probe.

A side view probe is shown inFIG. 7. This probe is based on the +5th refractive order of the reversed wavelength polarity design shown inFIG. 5. The light incident angle on the grating is 390.8° and the FOV is 47°, (0.415 μm to 0.800 μm). The grating period, however, is 2.5 μm compared to 0.5 μm for other previously known side view designs.

Diffraction Grating Design

For clarity in the discussion of diffraction orders, the sign convention for the grating equation is provided and shown inFIGS. 8A and 8B. For the incident and the diffracted light, the light is rotated with respect to the grating surface normal. If the rotation of the diffracted light with respect to the normal is clockwise, the sign of the diffracted light is negative (negative angles), as illustrated inFIG. 8B. For the diffraction orders, the diffracted light is rotated with respect to the 0th order light and if the rotation of the diffracted light is counterclockwise with respect to the 0th order, the sign is positive (positive diffracted orders), as show inFIG. 8A.

According to the sign conventions defined inFIGS. 8A and 8B, the grating equation will take the form shown in the following Equation 1,
−nisin θi+ndsin θd=mGλ(1)
where m is the diffraction order (m=0, ±1, ±2, . . . ), G is the grating spatial frequency (unit: 1/μm), λ is the wavelength of the light in vacuum (unit: μm), niand ndare refractive indexes of the incident light and the diffracted light respectively, and −θiand θdare the incident angle and the diffracted angle as defined by the sign convention shown inFIGS. 8A and 8B.

For the forward view (front-view) design as described herein it means that at least one specific wavelength λ0, the incident angle and the diffracted angle satisfy Equation (2).
θi=θd(2)

Combining Equations 1 & 2, the requirement of the incident light angle can be derived such that Equation (3) is satisfied

The corresponding diffraction angle can thus also be derived from Equation (4):

sin⁢⁢θd=ni⁢m⁢⁢G⁡(λ-λ0)-nd⁢m⁢⁢G⁢⁢λ(ni-nd)⁢nd(4)
Then, the half FOV angle for the forward view probe is determined as: Δθ=θd−θi.

The inventors herein have explored possible light incident angles and their corresponding half FOV angles, as shown inFIG. 9. The calculation is based on Equations 3 and 4, where it is assumed the refractive index of refracted light nd=1 (air), λ0=0.415 μm (blue wavelength), and λ=0.8 μm (red wavelength). According to the plot shown inFIG. 9, it is clear that the half FOV angle will increase as the incident angle on the grating increases. When the incident angle on the grating is getting close to 90°, the resulting half FOV angle will range from 55° (for ni=1.5) to 70° (for ni=1.7) depending on the refractive indexes that the incident light encounters. The design of the grating16embodied byFIG. 2follows the plot shown inFIG. 9.

One solution space for the calculated light incident angle and the half FOV angle vs. −mG for different refractive indexes of the incident light is shown inFIG. 9. The refractive index that the diffracted light observes is assumed to be 1 (i.e., the diffracted light travels through air). These solutions cover the design embodied byFIG. 2.

Another solution space for the calculated light incident angle and the half FOV angle vs. mG for different refractive indexes of the incident light is shown inFIG. 10. The refractive index that the diffracted light observes is also assumed to be nd=1 and the refractive index that the incident light encounters is assumed to be ni=1.5. The plots ofFIG. 10are numerical solutions corresponding to the design of gratings embodied byFIGS. 4, 5 and 7. This solution space can be understood as the negative sign in Equation (3) is moved to the left side of the equation (i.e. product −1 on both sides of Equation (3)). The incident angle as well as the diffraction order is thus changing the sign.

The reversed polarity solution we observed in the embodiment exemplified byFIGS. 6A-6Ccan also be explained by Equation (3), i.e. the same light incident angle θi and the same grating constant G corresponds to one or more combinations of mλ0.

In some exemplary embodiments, the incident angle, grating constant (G), and half FOV angle are designed based on the results shown inFIGS. 9 and 10. Due to the symmetry, we only focus on the solutions shown inFIG. 9. If nd=1 (air), ni=1.5 (e.g., corresponding to epoxy OG603 used for our examples), m=−1, λ0=0.415 μm, G=1/μm, we have θi=56.1°. The design of the grating shown inFIGS. 4 and 5is based on these numbers outlined here.

As shown in Table 4, column A, if we increase the incident angle to 60.63°, the grating constant will be G=1.05/μm and the half FOV angle will be 32.78°. If we continue increasing the incident angle to 65.92°, the grating constant will be G=1.1/μm and the half FOV angle will be 36.62° (column B). If the incident angle is 71.12°, the grating constant will be G=1.14/μm and the half FOV angle will be 40.64° (column C). Lastly, when the incident angle is 81.00°, the grating constant for this case will be 1.19/μm and the half FOV angle will be 49.03° (column D).

Grating Formation

The gratings used in the probes of the various embodiments of this invention are triangular gratings. Triangular gratings are more generalized blazed grating, whose grating lines possess a triangular, sawtooth shaped cross section. The formed structure can be staircase like as shown inFIG. 11A.FIG. 11Ashows a staircase design according to the numerical solution for θi=56.1° and corresponding dimensions thereof of a 1 micron pitch. This staircase design is based on a typical blazed grating, but it is tailored to a specific wavelength to obtain specific results for given parameters nd=1 (air), ni=1.5, m=−1, λ0=0.415 μm, and G=μm. Triangular gratings of the type shown inFIG. 11Acan be molded with a master which has a complement shape (often times the grating itself) of the desired structure. The fabrication of the master is usually done with photolithography process as shown inFIG. 15orFIG. 16.

This specific design of the grating shown inFIG. 11Ais for the exemplary probe shown inFIG. 2. The staircase design includes embodiments where gratings have a sidewall of the staircase “steps” that are parallel to the optical axis Ox. It also includes staircase designs where the sidewall is not completely parallel, but has an overhang.

FIG. 11Bshows parameters to design a staircase grating, one method is to first optimize the half FOV angle with a reasonable light incident angle according to Equations 3-4. The results of the optimization will be the grating period Λ and the light incident angle θi with a known or expected half FOV angle. Then straight lines, i.e. lines parallel to the optical axis (and thus parallel to the incident light) and perpendicular lines to the parallel lines are drawn to form a staircase profile, hence the name for staircase grating.

The Rigorous coupled-wave analysis (RCWA) has been used to analyze the grating efficiency for the design shown inFIG. 11A. As used herein, grating efficiency refers to the ratio of the diffracted light energy to the incident light energy in a given wavelength (or wavelength region) at a given diffraction order. As understood by those skilled in the art, increasing the number of lines per unit distance (decreasing the pitch) of a grating increases the energy throughput. However, the intention here is design the grating in a manner that the diffraction efficiency is optimized for a specific wavelength at a specific diffraction odder. For the −1st order (negative first order diffraction), the average efficiency is about 30%. In some embodiments, the efficiency is further optimized using different diffraction orders or different pitch, as discussed elsewhere in the various embodiments. TE (transverse electromagnetic) analysis shows a higher diffraction efficiency than TM (transverse magnetic) analysis. As a comparison, the diffraction efficiency for the −2nd order (negative first order diffraction) is much lower for this type of staircase grating design. The diffraction efficiency for the −2nd order can be as low as, for example, less than 0.04 for the entire region and less than 0.02 from 500 to 800 nm. In other embodiments, the grating can be optimized of the −2nd order.

To better understand the energy allocation, the efficiencies were calculated for all the diffraction orders (reflected and transmitted) for both TE and TM modes. In the embodiments disclosed herein, there is no transmitted 0th order. Most of the light at the 0th order is the reflected 0th order for this case. Advantageously, the reflected 0th order light can then be reused for designing a probe with an enlarged FOV, as explained more in detail herein below.

Photolithography can be used to fabricate the grating as disclosed herein. The fabrication method falls into a larger catalog of so called “binary optics”, where several masks can be designed specifically to form the structure of interest as shown inFIG. 11B. In the RCWA analysis, grating design with 20 steps in the grating structure was simulated (FIG. 11B). Four masks used in the lithography and shown in this process, are able to provide 2^4=16 steps in the final design, which should be enough for some applications, where other applications would require a different fabrication method. A specific process that generates up to 2^N phase levels from N binary transmission masks can be used to create any grating structure.

The staircase grating design can be a starting point for further optimization. That is, the staircase design can be used when fine tuning the position of the point where two shorter edges of the triangle intersect, i.e. point P shown inFIG. 11B. The optimization can start with, for example, the position of the point P in the grating period Λ and then in the grating height d or vice versa. Once it reaches the local minimum in one direction, we can start searching for the local minimum in another direction. This process continues until the solution converges.

A merit function may be used for this optimization process. One possible merit function should include at least two parameters, one is the average diffraction efficiency for the desired diffraction order. The other one is the minimum diffraction required which, for one embodiment, ranges from approximately 0.4 (400 nm) to approximately 0.15 (800 nm). If needed, a penalty (or weighting) function can be also introduced to consider the 0th order or the higher orders diffractions.

In some embodiments, the grating can be a binary grating.FIG. 15depicts exemplary grating fabrication method steps for a binary grating.FIG. 16depicts exemplary grating fabrication method steps for a multi-step binary grating. In general, the most common process for the fabrication of diffractive binary optics involves photolithographic methods that are similar to those used for the fabrication of microelectronics. These methods are based on the use of photoresist deposited on a substrate, etching the photoresist with the use of a mask, and the removal of the photoresist to obtain the desired grating structure. As shown inFIGS. 15 and 16, a plural lithographic masks can be used depending on the desired number of etch levels, and therefore, the desired diffraction efficiency. The processing steps include: (1) placing a desired mask over a substrate coated with photoresist; (2) irradiating the mask with electromagnetic energy (transmitting portions of the mask allows light to expose the photoresist, so the photoresist is removed from the substrate); (3) etching the substrate areas without photoresist to a determined depth (binary step). During etching, the areas of the substrate with photoresist remain impervious to the etching process; (4) removing the remaining photo resist. These four initial steps form a basic binary structure as shown inFIG. 15. After the photoresist is removed to form the binary structure ofFIG. 15, the process can be continued form additional levels. Therefore, as illustrated inFIG. 16, the process may further include the steps of: (5) coating the binary structure with photoresist; (6) irradiating a new mask with electromagnetic energy (transmitting portions of the mask allows light to expose the photoresist, so the photoresist is removed from the substrate); (7) etching the substrate areas without photoresist to a determined depth (to from a second binary step). During etching, the areas of the substrate with photoresist remain impervious to the etching process; and (8) removing the remaining photo resist. These processes can be repeated until the desired number of levels is etched into the substrate.

Many different methods exist for the fabrication of diffractive microstructures. Apart from the above described lithographic techniques, direct machining, and replication (e.g., the previously described us of a “master”) are well known. The choice of fabrication technique is generally driven by a balance of the desired function and cost.

The fabrication of the master is usually done with photolithography as shown inFIG. 15and/orFIG. 16. However, for the special grating design shown inFIG. 14, due to the undercut the design cannot be fabricated as a typical blazed grating. Anisotropic etching or other etching methods that could result in undercut such as deep RIE (reactive-ion-etching) can used to create the master. It is worth noting that during fabrication the vertices of the triangle will be rounded and the edge of the triangle can deviate Slightly from a perfect straight line. The definition of staircase or triangular grating here should also include the results due to the fabrication limits/errors/defects when the vertices are rounded or the edges are bended.

Other embodiments may employ triangular gratings that are not staircase gratings per se. For example, the grating may be a triangular overhang grating. The optimization of this grating can be performed in a similar manner to that of the staircase grating. A binary grating design can also provide reasonable diffraction efficiencies with optimization. One issue associated with the binary grating is the higher efficiency for higher diffraction orders. Nevertheless, any type of triangular grating that can provide reasonable diffraction efficiencies with the specified grating period and incident angle may be used in the probes as described herein.

Thus, in some embodiments, the optimization of the grating can be described byFIGS. 12A and 12Bas well asFIGS. 13A and 13B. In these figures, probe refractive index, ni=1.5 and the diffracted space medium is presumed to have a refractive index of nd=1.0, and each of the parameters as shown can be optimized. In these optimizations, one edge of the triangle is assumed parallel to the probe axis Ox. The unknown “y” dimension as shown inFIGS. 13A and 13Bis thus calculated as the difference between the grating period Λ and product of the grating height h and tangent value of light incident angle θ.

One optimized grating design that is a triangular overhang is shown isFIG. 14. In this grating, where the refractive indices are defined as nd=1 and ni=1.5, the optimized design provides h=1 and a1=1. This grating provides a minimum efficiency of 65% from 400 nm to 800 nm and has an average efficiency of greater than 75% over the same range.

In some embodiments, the grating fabrication methods as described by B. Bai et al. (Appl. Opt. 2010 Oct. 1, 49(28):5454-64) may be used. Bai has described the fabrication and replication of the slanted overhanging grating couplers that can be realized using known microfabrication technologies, including EBL, RIE, RIBE, and UV replication.

In some embodiments, the fabrication methods as described by O. Barley et al. (Appl. Opt. 2012 Dec. 1 51(34) 8074-80) may also be used. Barley formed surface-relief resonance-domain diffraction gratings having deep and dense grooves. Barley used a process having the steps of “(a) recording a resonance-domain grating pattern in e-beam resist layer with e-beam lithography, (b) transferring the recorded spatial pattern to a fine metal mask, and (c) transferring the spatial pattern from the metal mask to the substrate of the resonance-domain grating using reactive ion etching (RIE) technology.” These and other fabrication methods are believed to be well within the knowledge of those skilled in the art to which the present invention pertains.

Increased FOV

As explained previously, for several embodiments, the 0th order is reflected. Thus, it is useful to reuse/recycle this 0th order light. The 0th order light can be reused to increase the FOV.FIG. 17illustrates an embodiment of a staircase grating configured to reuse the reflected 0th order light to increase the FOV. The −1st order light42exits the grating16as forward view light. The reflected 0th order light38is further reflected by, for example, a total internal reflection (TIR) sidewall or a reflective coating30, and the internally reflected 0th order light39will re-enter the system at a different angle, and re-interact with the staircase (blazed) grating16as a reflection40. For this design, the reflective surface30needs to be optically flat, i.e. fine-polished or injection molded. It is possible to introduce a mild curvature on this surface for injection molded parts to correct aberrations in the optical system, if necessary. As illustrated inFIG. 17, the −1st order light42exits the grating16parallel to the probe optical axis Ox, and serves as forward view light. On the other hand, the light of reflection40(reused 0th order) exits the grating at a negative angle with respect to the optical axis, and thus serves as side view light. Therefore, two detection fibers are preferably used with this embodiment ofFIG. 17, i.e. one for forward view and one for the side view light. Due to limited accepting angles, the 0th order and the −2nd order will not cause stray light in the system. On the contrary, when the grating is properly designed with an optimized sidewall30, the grating can use the 0th order to increase the FOV.

FIG. 18illustrates another grating having a sidewall surface32on the side thereof substantially parallel to the optical axis. Again, the grating sidewall surface32can have a mild curvature for aberration corrections. The 0th order reflected light38from the first surface of grating16will function as the incident light and interact with the sidewall surface32. The sidewall surface32can be formed as a second diffractive grating, which can diffract the 0th order reflected light38into diffracted light50and diffracted light52. The diffracted light50and52from the sidewall surface32(second grating) functions as the illumination for side view or even back view purposes, depending on the selected orders such as −1st, −2nd, etc. InFIG. 18, the light diffracted by the sidewall32is shown as −1st order light52and 0th order light50. However, the sidewall32(second grating) can also be designed to diffract specific desired orders of diffraction at desired angles of illumination. On the other hand, inFIG. 18, the original −1st order light42propagated parallel to the optical axis and serves as forward view light. Again, two detection fibers are preferably used for this system, i.e. one for forward view and one for side view (or back view).

A combination of the grating configurations shown inFIGS. 17 and 18can make possible an omni-directional SEE probe. An example of a grating configured to implement an omni-directional SEE probe is shown inFIG. 19. According toFIG. 19, the reflected 0th order light38reflected from the first surface of grating16will interact with a sidewall surface34. The sidewall surface34is designed as a second grating such that it will diffract the 0th order light38into diffracted light50for back view and will also reflect light39for side view purposes. The reflected light39will interact with the first surface of grating16again for side-view illumination. The diffracted light50from the sidewall surface34(second grating) functions as the illumination light for back view purposes, depending on the diffracted orders such as 0th, −1st, −2nd, etc. Three detection fibers are needed in the case ofFIG. 19, i.e. one for forward view, one for side view and one for back view. In this manner, a true omni-directional viewing probe can be provided with a minimum number of optical elements.

The designs shown inFIGS. 17-19provide an enlarged FOV with only one illumination fiber. It is possible to design the grating slightly differently to enlarge the half FOV coverage even further, by introducing one or more additional illumination fibers. One example is shown inFIG. 20, where a see probe200includes first and second illumination fibers10aand10b, first and second GRIN lenses12aand12b, and first and second gratings16aand16barrange within a common sheath210. According to the SEE probe200ofFIG. 20, 0° to 30° of the FOV is covered by the forward view design described above in in reference toFIG. 2. And 30° to 80° of the FOV is covered by a side view probe design, as the one described above in reference toFIG. 7(except with negative diffraction angles). As described above, for the forward view probe, the grating period can be 2.5 μm with an incident angle of 49.6. For the side view probe, the grating period is 0.5 μm with an incident angle of 25.4°. Binary grating is used here for both forward view and side view, which is optimized for highest diffraction efficiency at −1st order.

The inventors herein have simulated the imaging quality obtainable with the forward probe view design shown inFIG. 20. Calculated spot diagrams and the RMS wavefront errors have shown that the imaging quality is close to (but not at) the diffraction limit for the forward view probe. Thus, further optimization according to the methods provided herein will further optimize this grating to reach the diffraction limit. For the simulated side view probe ofFIG. 20, diffraction limited imaging can be achieved in the wavelength range centered around 0.63 μm.

A probe following the design ofFIG. 20has been made and tested. The side view probe section has a FOW with void space below 30°; this void space in the FOV is filled by the forward view probe design, as shown inFIG. 20. Tests performed by the inventors resulted in an acquired image being distorted. However, such distortions can be numerically corrected afterwards using known image processing algorithms. Due to the limit of the scanning motors, the inventors have been able to only scan an angle range of about 70°. A full circle can be scanned properly by modifying the motor and introducing a rotary junction. Table 5 summarizes the imaging wavelengths and FOV angles obtained with the configuration of the SEE probe200shown inFIG. 20.

An alternative grating design to the staircase grating design shown inFIG. 11is explained in reference toFIGS. 22A and 22B. This design is optimized for low reflectance and high transmitted diffraction.FIG. 22Adepicts a cutaway on the plane grating along the optical axis and perpendicular to grating plane. For this design,4002is the grating plane, and4001is the physical edge (shape) of the staircase grating. The optical axis (Ox) of the probe is shown as numeral4003and the forward direction light (diffracted light), which is parallel to the optical axis, is shown as arrow4004. The upper left part of the figure is the probe spacer material of refractive index (ni), where ni=1.5. The lower right part of the figure is assumed to be air or diffracted space medium with refractive index (nd), where nd=1.0. For this design, a wavelength range of 415 to 830 nm or a similar range is contemplated. The grating follows the equations (1) through (4) of the previously presented embodiments and for a specific wavelength λ0=415 nm. Reflected rays4006(a) and4006(b) with wavefront4008are the reflection caused by coupling of waves from the scatter at the upper ridges4010of the grating. Reflected rays4007(a) and4007(b) with wavefront4009are the reflection caused by scatter at the lower ridges4011of the grating. The grating shape is optimized such that the reflected wavefronts4008and4009interfere destructively, so that effects of the reflection will be low. For this optimization, optical path difference of rays4006(b) and4007(a) are calculated as explained below.

InFIG. 22B, it can be seen that as the beams4107and4106travel from the left, the path difference can be calculated with the paths from the equi-phase points,4111and4110. Path1of beam4107from point4111to point4112is
Path1=−niΛ cos θicos 2θitan γ  (5)

A is the pitch of the grating and is the inverse of grating constant G. In order to have destructive interference the path difference between the two rays or wavefronts must have path length equal to integral multiple of the wavelength and a half wavelength. This wavelength can be chosen independent of the forward propagating wavelength λ0=415 nm.
Path1−Path2=(k+½)Λ, [k=0,±1,±2, . . . ]  (7)

Angle γ is determined from Snell's law of refraction as:

Using these equations, one exemplary design is summarized in Table 6. For this embodiment, the shortest wavelength, 415 nm, is chosen for minimizing the reflection, thus maximizing the transmitted diffraction at that wavelength. The path difference is 622.5 nm which is 1.5 times the wavelength of 415 nm. Rigorous coupled wave analysis (RCWA) calculation for the grating of one example provide good efficiency for both TM and TE light. In this example, the efficiency of TE is approximately between 0.6 (400 nm) and 0.3 (800 nm). For TM light, the efficiency ranges approximately between 0.5 to slightly over 0.1.

Another exemplary embodiment of grating design for minimized reflection is explained usingFIGS. 12A and 12Bwhere the probe and the system can function, as previously described with reference toFIG. 2, in a forward view imaging mode. This design is optimized for low reflectance and high transmitted diffraction similar toFIG. 2, but also is optimized with blazed angle of the grating for higher diffraction efficiency.FIGS. 12A and 12Bdepicts a cutaway on the plane grating along the optical axis and perpendicular to grating plane. These figures are greatly enlarged to view a portion of the grating structure for ease of explanation. It is noted that the grating is shown as having locally flat surfaces and linearly defined edges, but the various embodiments of this invention may be applied to planer as well as slightly curved (concave or convex) surfaces.

For the design shown inFIG. 12A, 4402is the grating plane and4401is the physical shape (edge) of the step (staircase) grating. The optical axis Ox of the probe is shown as4403, and the forward direction light, which is parallel to the optical axis, is shown by4404. The plane of the embodiment shown inFIGS. 12A and 12Bis intentionally tilted by the blazed angle α on this grating to form blazed grating so that Snell's law of refraction applies to the beam4412to refract and diffract into the direction of beam4413. The equation for such condition is as follows:

sin⁢⁢α=ndni⁢sin⁡(θi-θd⁢⁢c+α)(9)
which is the same as:

The upper left part of the figure is the probe spacer material of refractive index, ni=1.5. The lower right part of the figure is assumed to be air or diffracted space medium with refractive index, nd=1.0. For this design, wavelength range of 415 to 830 nm is used. The grating follows the equations (1) through (4) of the previously presented embodiments, for a specific diffracted wavelength λ0=415 nm. And the blazed angle can be independently chosen for wavelengths other than λ0.

InFIG. 12A, reflected rays4406(a) and4406(b) with wavefront4408are the reflection caused by coupling of waves from the scatter at the upper ridges4410of the grating. Reflected rays4407(a) and4407(b) with wavefront4409are the reflection caused by scatter at the lower ridges4411of the grating. The grating shape is optimized such that the reflected wavefront4408and4409interfere destructively, so that effects of the reflection will be low. For this optimization, optical path difference of rays4406(b) and4407(a) are calculated as explained below.

As shown inFIG. 12B, as the beams4507and4506travel from the left, the path difference can be calculated with the paths from equi-phase points4514and4510.

Λ is the pitch of the grating and is the inverse of grating constant G. In order to have destructive interference, the path difference between the two rays or wavefronts must have path length equal to integral multiple of the wavelength and a half wavelength. Again, this wavelength can be chosen independent of the forward propagating wavelength λ0=415 nm.
Path1−Path2=(k+½)Λ, [k=0,±1,±2, . . . ]  (13)

Angle γ is determined from Snell's law of refraction at point4112, as:

Due to the configurations of the staircase gratings, grating steps and diffraction rays, only a few conditions exist, which must be satisfied to minimize the effects of reflection in the grating.

Using these equations, one example design is summarized in table 7 shown below. For this embodiment, the center wavelength, λc=622.5 nm, is chosen for minimizing the reflection, thus maximizing the transmitted diffraction at that wavelength in the forward direction. The path difference is 933.75 nm, which is 1.5 times the wavelength chosen. The center wavelength of λc=622.5 nm is also used for the blaze angle optimization, in order to increase the overall diffraction efficiency over all the wavelengths. Rigorous coupled wave analysis (RCWA) calculation for the grating of this embodiment using the design parameters of Table 7 provides an efficiency of approximately 0.4. The efficiency of a grating having this parameters this embodiment was also acceptable, having a higher TE with Emax=0 56 and a min=0.3 at 800 nm. TM has a similar maximum at blue λ and a min of 0.2 (at 800 nm). The overall diffraction efficiency over the full spectrum range for −1st order diffraction is higher than that for the grating described in reference to Table 6.

In this design, the field of view (FOV) can be extended by using additional orders of light (e.g., the the reflected 0th order. It is even possible to have an omni-directional probe design, as described above.

In this and other embodiments, a grating with a much larger period (e.g. Λ>1.5 μm) can be used in combination of higher diffraction orders (m>1) for side view probes with a larger FOV. In our design example, if we use the blazed grating to enhance the 5thorder diffraction, even with a grating period of 2.5 μm, it is possible to achieve a larger FOV of 47°.

Some embodiments provide a grating with a large overhang, as shown inFIG. 14. One particular advantage in the various embodiments of the invention as described herein is that the probe can have improved resolution compared to prior SEE probes in one or both of the scanning direction and the spectral spectral direction since these embodiments provide the ability to use the full diameter available on the probe.

Another particular advantage in the various embodiments of the invention is that, due to limited accepting angles of the detecting fiber or fibers, the 0thorder and the −2ndorder will not cause significant stray light in the system. This is especially true as for the many embodiments described herein having no transmitted 0thorder light. In many instances, the reflected 0thorder light is at a very large angle and will not significantly cause stray light. Advantageously, in some embodiments, the reflected 0thorder light can be reused (redirected) to increase the FOV angle of the probe. Further advantageously, the steps and blaze angle of the grating can be designed to minimize effects of the 0thorder reflected light by causing destructive interference of reflected light.

Imaging System

A system to acquire an image from the SEE probe according to an exemplary embodiment of the present disclosure is shown in the diagram ofFIG. 23. The system30ofFIG. 23includes, for example, a light source370, a detector/spectrometer380, a fiber optic rotary joint (FORJ)330, a probe302, and an image processing computer350. The light source370outputs light of broadband spectrum (or other electro-magnetic radiation). The range of the wavelength can be within the visible region, which is from 400 nm thorough 800 nm. However, other wavelengths may also be used. In the exemplary imaging system300, the light can be directly guided or otherwise provided into a fiber372, which can be called an illumination fiber. The illumination fiber372can be connected to the FORJ330, and further guided to (and/or associated with) another illumination fiber310, which is connected to the FORJ330within a sheath320. At the end of the illumination fiber310, the exemplary SEE probe302can be attached. The light scattered back from an object or sample (e.g., tissue) can be collected by the probe302and guided to a detection fiber312. The detection fiber312can be connected to another detection fiber382via the FORJ330. The detection fiber382can be connected to the detector/spectrometer380via a collimating optical384. The detector/spectrometer380can detect the intensity of selected wavelength. This exemplary function of detecting the selected wavelength can be performed by the spectrometer. By mechanically scanning the probe in a direction328perpendicular to the diffraction direction via a mechanical scanning unit contained within the FORJ330, it is possible to obtain a two-dimensional image of the object. The mechanical scan can be performed by, e.g., Galvo scanner or motor to rotate the probe together with the illumination fiber310and the detection fiber312. Computer350includes one or more microprocessors configured to control and operate the various parts of system300, and executes computer-executable instructions (program code) to reconstruct images based on signals obtained from detector/spectrometer330.

In some exemplary embodiments, instead of guiding the broadband light from light source370into the illumination fiber372, the light can first be dispersed to predetermined wavelength(s) λ1, λ2, . . . , λN. For example, the light with the wavelength λi (1≤i≤N) can be input into the illumination fiber372in a multiplexed manner. The input light is provided through the junction (FORJ330), illumination fiber310, probe302to the sample; and collected via the probe302, detection fiber312, junction (FORJ330), detection fiber382, and guided to the detector/spectrometer380. Optionally, in the case of imaging with light of individual wavelengths λi, the detector/spectrometer380can be or include a simple light intensity detector such as photo-detector because the input light has a wavelength of λi. By changing i from 1 to N, it is possible to obtain the one-dimensional line image, by using a simple intensity photodetector or a line sensor. By mechanically scanning the line, it is possible to acquire the two-dimensional image of the object.

The FORJ330can be optional. One role of the optional junction (FORJ330) can be to make the probe302, including the illumination fiber310and the detection fiber312, detachable. With this exemplary function, the probe302can be disposable and thus a sterile probe for human “in vivo” use can be provided every time an imaging operation is performed.

Various exemplary SEE probes as described and shown herein can deflect light along the reference axis, and facilitate forward viewing. The exemplary probe may be held stationary or it may be rotated, where the rotation of the probe is particularly useful for acquiring a two-dimensional front-view image as well as a color image.

For example, since the detection fiber312can be attached to the front-view type SEE probe, continuous rotation of the probe can cause the illumination fiber310and the detection fiber312to become tangled. Therefore, in some exemplary embodiments, it is possible that the probe can be rotated, e.g., +/−approximately 360 degrees back and forth. In other exemplary embodiments, the exemplary probe can be rotated +/−approximately 180 degrees back and forth. In further exemplary embodiments, other degrees of rotation can be used, such as, e.g., 90 degrees or 270 degrees of back and forth rotation.

According to various exemplary embodiments, a multi-cladding fiber can be utilized for both the illumination fiber310and the detection fiber312. Multi-cladding fiber can act as if it has different core diameters depending on a light propagating direction. Thus, such multi-cladding fiber can be used as the illumination fiber and the detection fiber. If the multi-cladding fiber is connected to a “rotary junction,” continuous rotation of the probe can be performed.

This exemplary imaging system300can be used with, for example, the exemplary probes as described in the various exemplary embodiments herein. The exemplary front-view SEE probes as described herein are categorized into two exemplary types. One type of probe can use an illumination fiber and a detection fiber. Another type of probe can use only one fiber, which may be, for example, a multi-cladding (double clad) fiber.

Certain aspects of the various embodiment(s) of the present invention can be realized by one or more computers that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a transitory or non-transitory storage medium to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer system, for example, is part of or attached to the imaging processor and can obtain and modify information received from the imaging detector and an optional second detector. For example, the computer system can be used to process the three different orders of light and create a color image based on the images from the three different orders.

Thus, the detector/spectrometer380can be connected to computer350which includes an imaging processor and one or more display units connected to the imaging processor via a high definition multimedia interface (HDMI). Optionally, a separate image server is another computer unit connected to the processor connected via an Ethernet cable or a wireless access point.

FIG. 24a schematic block diagram of a control and processing system applicable to the various embodiments of a SEE probe described herein. As shown inFIG. 24, the computer control system is representative of computer350shown inFIG. 23. InFIG. 24, the computer350includes central processing unit (CPU)401, a storage memory (RAM)402, a user input/output (I/O) interface403, and a system interface404. The computer350described byFIG. 24can issue a command that can be transmitted to the imaging system300via a user interface unit/arrangement403. A touch panel screen can be included as part of the user interface unit/imaging processor, but key board, mouse, joy-stick, ball controller, and foot pedal can also be included. The user can cause a command to be initiated to observe inside a lumen of the human body through the exemplary front-view SEE probe using the user interface unit/imaging processor. For example, when the user inputs a command via the user interface403, the command is transmitted to the central processing unit CPU401for execution thereby causing the CPU to issue a command via the system interface404to one or more of the light source370, detector/spectrometer380or FORJ330.

The CPU401is comprised of one or more processors (microprocessors) configured to read and perform computer-executable instructions stored in the storage memory402. The computer-executable instructions may include program code for the performance of the novel processes, methods and/or calculations disclosed herein.

The computer350functions as imaging processor that can be programmed to apply exemplary image processing such as noise reduction, coordinate distortion correction, contrast enhancement and so on. After or even during the image processing is performed, the data can be transmitted from the imaging processor to a display (not shown). A liquid crystal display (LCD) can be the display. The display can display, for example, the individual images obtained from a single color or a composite color image according to the various exemplary embodiments of the present disclosure. The display can also display other information than the image, such as the date of observation, what part of the human body is observed, the patient's name, operator's name and so on.

The CPU401is configured to read and perform computer-executable instructions stored in the Storage/RAM402. The computer-executable instructions may include those for the performance of the methods and/or calculations described herein. For example, CPU401may calculate the angular momentum or speed of rotation of the SEE probe, and can use that information (rotation speed or angular momentum) to operate the FORJ. In this manner, computer350can obtain a new set of images where their angular positions are corrected. Storage/RAM402includes one or more computer readable and/or writable media, and may include, for example, a magnetic disc (e.g., a hard disk), an optical disc (e.g., a DVD, a Blu-ray), a magneto-optical disk, semiconductor memory (e.g., a non-volatile memory card, flash memory, a solid state drive, SRAM, DRAM), an EPROM, an EEPROM, etc. Storage/RAM402may store computer-readable data and/or computer-executable instructions. The components of the processor may communicate via a bus.

The system I/O interface404provides communication interfaces to input and output devices, which may include a keyboard, a display, a mouse, a printing device, a touch screen, a light pen, an optical storage device, a scanner, a microphone, a camera, a drive, communication cable and a network (either wired or wireless).

The system I/O interface404also provides communication interfaces to input and output devices. The detector may include, for example a photomultiplier tube (PMT), a photodiode, an avalanche photodiode detector (APD), a charge-coupled device (CCD), multi-pixel photon counters (MPPC), or other. Also, the function of detector may be realized by computer executable instructions (e.g., one or more programs) recorded on a Storage/RAM402.

In an exemplary operation, the user can placed the exemplary SEE probe into a sheath, and then can insert such arrangement/configuration into a predetermined position of a human body. The sheath alone may be inserted into the human body in advance, and it is possible to insert the SEE probe into the sheath after sheath insertion. The exemplary probe can be used to observe inside human body and works as endoscope such as arthroscopy, bronchoscope, sinuscope, vascular endoscope and so on.

Definitions

In referring to the description, specific details are set forth in order to provide a thorough understanding of the examples disclosed. In other instances, well-known methods, procedures, components and circuits have not been described in detail as not to unnecessarily lengthen the present disclosure.

It should be understood that if an element or part is referred herein as being “on”, “against”, “connected to”, or “coupled to” another element or part, then it can be directly on, against, connected or coupled to the other element or part, or intervening elements or parts may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or part, then there are no intervening elements or parts present. When used, term “and/or”, includes any and all combinations of one or more of the associated listed items, if so provided.

Spatially relative terms, such as “under” “beneath”, “below”, “lower”, “above”, “upper”, “proximal”, “distal”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the various figures. It should be understood, however, that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, a relative spatial term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are to be interpreted accordingly. Similarly, the relative spatial terms “proximal” and “distal” may also be interchangeable, where applicable.

The term “about,” as used herein means, for example, within 10%, within 5%, or less. In some embodiments, the term “about” may mean within measurement error.

The term “substantially”, as used herein means that, within fabrication parameters and/or measurement error.

The terms first, second, third, etc. may be used herein to describe various elements, components, regions, parts and/or sections. It should be understood that these elements, components, regions, parts and/or sections should not be limited by these terms. These terms have been used only to distinguish one element, component, region, part, or section from another region, part, or section. Thus, a first element, component, region, part, or section discussed below could be termed a second element, component, region, part, or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the”, are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that the terms “includes” and/or “including”, when used in the present specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof not explicitly stated.

The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described exemplary embodiments will be apparent to those skilled in the art in view of the teachings herein. Indeed, the arrangements, systems and methods according to the exemplary embodiments of the present disclosure can be used with any SEE system or other imaging systems, and for example with those described in U.S. Pat. Nos. 6,341,036; 7,796,270; 7,843,572; 7,859,679; 8,045,177; 8,145,018; 8,780,176; and 8,812,087; and U.S. Patent Application Nos. 2008/0013960 and 2011/0237892; and PCT publications WO2015/116951 and WO2015116939, the disclosures of which are incorporated by reference herein in their entireties.