Technical Field

This application discloses an optomechanical apparatus for wide-angle optical applications .

Background art

Optomechanical systems are a sub-discipline of optical and mechanical engineering in which optics such as lenses , mirrors , fibers and prisms are integrated into mechanical structures , for example cells , housings , trusses , among others , to form an optical instrument .

Wide-angle optical applications become more attractive from the emerging necessity of the systems being able to accommodate and capture big scenario imaging, with large field of view ( FoV) . Wide-angle systems can be used in di f ferent application fields , li ke , autonomous driving, to measure the Time-Of-Flight ( TOF) , Transmit/Receive ( Tx/Rx ) , etc, patterns emission to deep field 3D cameras , image camera systems , fiber laser emission with high power, etc .

One of the main disadvantages of the previously described wide-angle systems resorts in the system si ze and the image aberrations caused by the optical lenses system and mechanical tolerance .

With current technical solution, it will be possible to overcome some of the mentioned problems , namely related to :

- Large Field Of View ( FOV) and High angular resolution systems that typically imply using signi ficantly large amount of photodetectors that must be installed in a predetermined and fixed position, often resulting in an overall large dimensioned system;

- in state-of-the-art LiDAR systems , the optical elements are usually installed close to heat sources ( electronic components ) , and, therefore , are signi ficantly af fected by this temperature gradient ;

- In wide-angle system lenses the optical aperture is small compared to the lens si ze ;

- Photodetectors arrangement without complex electronic system ( Layout and components ) .

Summary

The present invention describes an optomechanical apparatus to increase angular resolution and measurement range of LiDAR systems comprising : an optomechanical hollow tube ; a monocentric ball lens support , installed in one end of the optomechanical hollow tube ; a monocentric ball lens installed in the center of the monocentric ball lens support , crossing said support from one side to the other ; and a spherical hemisphere installed in the same end of the optomechanical hollow tube covering both the monocentric ball lens support and the monocentric ball lens ; wherein the monocentric ball lens comprises at least two types of material of di f ferent refractive index .

In a proposed embodiment of present invention, the monocentric ball lens comprises a smaller diameter than the hollow tube and the spherical hemisphere .

Yet in another proposed embodiment of present invention, the spherical hemisphere comprises a hollow dome shape with a uni form distribution of optical fibers throughout the interior surface of the hollow dome shape , which pierces its structural wall , providing a mechanical support and an optical connection of said optical fibers to the outside of the hollow dome shape .

Yet in another proposed embodiment of present invention, the monocentric ball lens comprises an inside portion, internal dual monocentric spherical hemisphere (Nl ) , with lower refractive index, and an outer portion, external dual monocentric spherical hemisphere (N2 ) , with higher refractive index .

Yet in another proposed embodiment of present invention, the internal dual monocentric spherical hemisphere (Nl ) comprises two identical monocentric spherical hemispheres bonded together .

Yet in another proposed embodiment of present invention, the external dual monocentric spherical hemisphere (N2 ) comprises an external portion and an internal portion, the external portion being located on one side of the monocentric ball lens support inside of the optomechanical hollow tube , and the internal portion being located on the oppos ite side of the monocentric ball lens support inside of the spherical hemisphere .

Yet in another proposed embodiment of present invention, the external portion of the external dual monocentric spherical hemisphere (N2 ) is adapted to capture incoming light beams inside of the optomechanical hollow tube and evenly reflect and distribute components of the light beams through the inner surface of the spherical hemisphere . Yet in another proposed embodiment of present invention, the optical fibers are adapted to ensure the connection and the correct light beam transmission between the inner surface of spherical hemisphere and an avalanche photodiode arrangement .

Yet in another proposed embodiment of present invention, the external portion and an internal portion of the external dual monocentric spherical hemisphere (N2 ) comprise nonidentical geometric formats bonded together and also bonded with the outer surface of the internal dual monocentric spherical hemisphere (Nl ) .

General Description

The present application describes an optomechanical apparatus that can be integrated in LiDAR systems , being used to measure the Time-Of-Fl ight ( TOF) , providing an increased angular resolution and measurement range . This solution was developed in order to improve the overall performance of LiDAR sensors , automotive integrated systems and wide-angle optical applications .

The technical solution herein disclosed allows to, within several alternatives :

- enable the accommodation of large FOV with angular resolution;

- increase the system' s optical aperture ;

- miniaturi ze the receiver system;

- isolate the optical path;

- increase the f lexibility on the photodetectors arrangement ; - increase the optical performance ;

- decrease the number of used optical elements on the system;

- increase the angular resolution;

- decrease signi ficantly the imaging optical aberrations ;

- decrease background light effects and arti facts ;

- control the incident optical power on APD (Avalanche Photodiode ) surface ; and

- provide an adaptive and flexible PCB ( Printed Circuit Board) .

The disclosed optomechanical apparatus herein described represents enormous advantages for a receptor sensor . This solution allows to , as previously anticipated, minimi ze the imaging optical aberrations , minimi ze the background light ef fects , simpli fy the wavelength filtering, isolate the path for the reflected light and allow a high ratio between system aperture and si ze of sensor .

From a generic operating point of view, a LiDAR sensor emits and receives light beams reflected from a target point . The target reflected light is transmitted through a glass cover to an opto-electro-mechanical system . The herein disclosed Opto-electro-mechanical system comprises a Optomechanical tube , a Monocentric Ball lens , Multi-mode Optical fibers or Waveguides , Avalanche Photodiodes , transimpedance ampli fiers ( TIA) and electronic/mechanical elements .

A Monocentric ball lens can be described as a ball shaped lens , which in the proposed solution, comprises at least two di f ferent materials . The selected materials can comprise a selection of adapted glass or polymers , or a combination thereof . The typical structure of these lens can accommodate a large FOV, miniaturi zation and high image quality . In the monocentric lens , the center of all refractive surfaces coincides with each other, and the image surface plane is f ormed/ref lected in a single hemisphere .

In the disclosed apparatus , the inside portion of the lens comprises a lower refractive index when compared with the external portion of said lens . Thus , when the light passes the first outer lens surface , due to the exiting refractive index di f ferences , it is refracted in a speci fic direction, that focus the entire light beam diameter in a locali zed spot . The diameter of the central material will define the final aperture of the system . For this system, only spherical aberration will perturb the performance , but this can be easily overcome resorting to the use of three additional lenses . The developed monocentric lens , depending on its design, can accommodate until 120 ° of FOV .

The Opto-electro-mechanical system will receive the target reflected light , which will be trans ferred from the outside to the inside of the housing system, by a glass cover .

The system acquires the light sources which additionally can pass through a narrow band wavelength filter in order to obtain a speci fic light wavelength beam, which will then propagate inside an optomechanical tube until it reaches the monocentric lens . This filter can be located inside the optical tube , or on the surface of the monocentric lens . The Optomechanical tube it is necessary to guide the captured light towards the system avoiding the loss of irradiance .

When the filtered light beam reaches the spherical monocentric lens , it is refracted on a speci fic spot of the opposite spherical hemisphere . At this opposite image spherical hemisphere plane , it is installed one additional hal f spherical concave hemisphere covering all the range of the refractive lens , which comprises an array set of multimode optical fibers arranged along the entire inner surface . The optical fibers are fixed and secured through a troughhole arrangement that allow the evenly distribution around all the inner surface of the outer hemisphere plane , providing a mechanical support to the fiber arrays and a light connection between the inside and the outside of the hemispherical plane .

When the refracted light is focused on these fibers , the light beam is propagated inside these optical fibers , until it reaches an arrangement of avalanche photodiodes (APD) .

At the end of the optical fiber path, an APD arrangement will receive the propagated optical light beam, transducing it into an electrical signal . Each optical fiber is terminated with a conventional state-of-the-art connector, for example , one of a FC or LC or SC fiber optical connector . The APD electrical signal is then classi fied as a di f ferential signal , and it is transmitted to the filter and ampli fication modules , which are composed by the TIA ampli fiers . There , the noise will be filtered, and the APD response signal ampli fied . The voltage output of the TIA ampli fier module it is acquired on a TDC ( Time Division Converter ) and analyzed .

Brief description of the drawings

For better understanding of the present application, figures representing preferred embodiments are herein attached which, however, are not intended to limit the technique disclosed herein . Fig. 1 - illustrates the overall view of proposed

Optomechanical apparatus (100) .

Fig. 2 - illustrates the proposed Optomechanical apparatus (100) in a longitudinal sectional view, where the numerical references are related to:

1) optomechanical hollow tube;

2) monocentric ball lens;

3) monocentric ball lens support;

4) spherical hemisphere with Optical Fiber connection points ;

5) optical Fibers / fiber array.

Fig. 3 - illustrates a tree-dimensional view of the lenses, where the numerical references are related to:

2) monocentric ball lens,

4) spherical hemisphere.

In this illustration it is possible to visualize the light beams color separation.

Fig. 4 - illustrates a longitudinal sectional view of the lenses and the hemisphere, where the numerical references are related to:

2) monocentric ball lens,

Nl) internal dual monocentric spherical hemisphere;

N2) external dual monocentric spherical hemisphere;

4) spherical hemisphere.

In this illustration it is possible to visualize the light beams color separation reflected in the hollow spherical hemisphere . Description of Embodiments

With reference to the figures, some embodiments are now described in more detail, which are however not intended to limit the scope of the present application.

As previously anticipated, the proposed optomechanical apparatus (100) comprises an optomechanical closed hollow tube (1) with a predetermined length, which in one of its ends comprises a monocentric ball lens support (3) circularly closing the entire end of said tube, and which further comprises a monocentric ball lens (2) in the center of said support (3) , preferably with a smaller diameter with regard to the inner diameter of the tube (1) . Along with the support (3) , the mentioned end of the tube (1) is additionally sealed with a spherical hemisphere (4) with a wider diameter than the diameter of the lens (2) , and inferior, or at least equal, to the inner diameter of the tube (1) . The spherical hemisphere (4) , having a hollow dome shape, incorporates a uniform distribution of optical fibers (5) throughout all its interior surface, which pierces the structural wall of the dome providing a mechanical support to the fiber array, allowing an optical connection of the fibers (5) to the outside of the structure the spherical hemisphere (4) . Thus, it is possible to guarantee the correct transfer of the optical light beams collected on the inner face of the spherical hemisphere (4) , reflected by the lens (2) , to the outside of the apparatus (100) .

In one of the proposed embodiments of present optomechanical apparatus (100) , the monocentric ball lens (2) is composed of at least two different materials, evenly distributed over each face of the lens, comprising one of a polymers and/or glass. Thus, the monocentric ball lens (2) inside portion, i.e., the internal dual monocentric spherical hemisphere (Nl) , is composed by a lower refractive index when compared with the external portion of said lens, external dual monocentric spherical hemisphere (N2) (higher refractive index) . As it is possible to perceive through the analysis of the figure 4, the monocentric ball lens (2) comprises several distinctive components. Particularly, and in one of the proposed embodiments, the ball lens (2) comprises and internal dual monocentric spherical hemisphere (Nl) and an external dual monocentric spherical hemisphere (N2) . The internal dual monocentric spherical hemisphere (Nl) is composed by two identical monocentric spherical hemispheres which are bonded together.

The external portion of the external dual monocentric spherical hemisphere (N2) of the lens (2) is considered to be the hemisphere which captures the light beams coming from the inside of the hollow tube (1) . The internal portion of the external dual monocentric spherical hemisphere (N2) of the lens (2) is located in the opposite hemisphere of the external portion, transferring the captured beams, diffracting them through the inner surface of the spherical hemisphere (4) where the optical fibers are evenly distributed .

The fact that the used materials in the lens (2) have different characteristics, results in that the inner portion (Nl) of the lens (2) comprises a lower refractive index when compared with the external portion (Higher refractive index) (N2) of said lens (2) .

This will originate that, when the light passes through the outer lens surface (Nl) , due to the existing refractive index differences, it will be refracted by the external lens surface (N2) in a specific direction of the spherical hemisphere (4) , focusing the entire light beam diameter in localized spots.

The optical fiber array, that ensures the connection and the correct light beam transmission between the spherical hemisphere (4) and the APD arrangement, in one of the proposed embodiments, incorporates multi-mode optical fibers with step index, each fiber (5) comprising a core of fused silica within a range of 50pm to 100pm and a cladding diameter of fluorine doped silica within a range of 125pm to 140. The numeric aperture of each fiber (5) will be comprising ranges between 0.12 and 0.26 and will terminated in one of a FC or LC or SC fiber optical connector, in order to ensure the connection to the APD arrangement.