Technical field

This application relates to an adaptive filtering module.

Background art

In optoelectronic instruments, it is possible to identify several sources of noise, originated at either the optoelectronic elements itselves and/or at the electronic system (s) surrounding it. Any random perturbation of the instrument, originated both intrinsically at any instrument component or externally, has the potential to generate noise on the detected signals. In fact, there are sources of noise that will always be present in an optoelectronic instrument and, in some cases, it is enough to critically affect the instrument performance. In optoelectronic instruments built to operate outdoors in an uncontrolled environment and comprising photodetectors, background radiation such as solar or artificial illumination is one of the most relevant noise sources. In such systems, the background radiation is also converted into an electrical voltage/current, along with the actual signal. If not properly controlled, the noise generated by background radiation may be so high that photodetectors may saturate or the signal may be camouflaged in the noise. This makes the instrument stop doing the main function it was designed for. Typically, the background radiation spans a wavelength range much wider than the emission bandwidth of the emitter, so optical filtering is a possibility to reduce out-of-band noise and, thus improve the performance of the instrument. In fact, the use of optical filters, typically Band-Pass filters (BPF) , to deal with noise, allows reaching higher signal/noise ratio and accommodating the working specifications. Optical filters with narrower pass-band mean that less noise generated from background radiation is added to the detected signals. However, the use of narrow filters also makes the system more sensitive to temperature changes. Since both the emission wavelength of the laser and the spectral properties of the filter change with temperature, it may happen that at a certain temperature the pass-band of the filter does not match the emission wavelength of the laser, so no signal can reach the photodetectors and the instruments stops working. Considering a scenario where a LIDAR instrument is placed outside a vehicle, which can move anywhere around the world under extreme harsh atmospheric conditions, controlling the internal temperature of the instrument is, perhaps, one of the biggest challenges. Being able to control it at all time under a tight range, e.g. ± 10°C, would be undoubtedly of highest interest for several reasons, but it is very challenging to achieve such narrow temperature of operation range. Moreover, it is well known that the refractive index of materials, not to mention coefficient of thermal expansion, nor others, the emission wavelength of laser diodes and the spectral properties of optical filters may change considerably with temperature. As an example, a change of about ten degrees Celsius (°C) on common high-power laser diode emitters may shift their emitting wavelength by a few nanometers. Hence, the effects of temperature on an optoelectronic system performance must be carefully addressed .

Document US8076958B2 discloses a signal preprocessing device which is integrated into a structure-borne sound sensor or into an acceleration sensor, for sensing structure-borne sound. Said device comprising at least one filter module having at least two BPFs . A method for operating said device is also disclosed, in which a filtering operation is carried out in which at least two frequency bands, which are at least to a certain extent part of the structure-borne sound spectrum, are transmitted.

Document US20030178555A1 discloses a filtering method and mechanism for scanners, including a regular visible light source and an infrared light source that are both turned on under a scanner. A transmission mechanism is provided for reciprocally placing a visible light filter plate and an infrared light filter plate in the scanner light path to filter light emitting from the regular visible light and infrared light source. Changing and switching between regular and infrared light scanning is done without warm up delay of the light source.

Summary

The present application discloses an adaptive filtering module comprising:

— a filtering apparatus, to be installed in the detection unit of an optoelectronic system; said filtering apparatus comprising at least two optical filters inserted in an indexing mechanism; each filter with specific optical parameters related to Central Wavelength, Full Wide at Half Maximum, temperature variation and angle of incidence performance; and

— a control unit comprising:

— a temperature module, adapted to monitor in real time data temperature values of the filtering apparatus, of the emission unit's light source and of the photodetectors of the detection unit's optoelectronic system;

— a database module adapted to store a list of filtering apparatus and the respective specifications related with the number of filters used, its relative positions, and their optical parameters ;

— a processing module provided with processing means configured to correlate in real-time the information collected by the temperature module and the data stored in the database module in order to actuate the indexing mechanism of the filtering apparatus .

In one embodiment of the adaptive filtering module, the filters of the filtering apparatus are of a band-pass filter, Long-Pass filter, Short-pass filter or Neutral Density filter type.

In another embodiment, the filters of the filtering apparatus are arranged in a single row of individual filters.

Yet in another embodiment, the filters of the filtering apparatus are arranged in more than one row.

Yet in another embodiment, the rows are parallel.

In another embodiment, the indexing mechanism of the filtering apparatus is of a linear type.

In another embodiment, the filters of the filtering apparatus are arranged in at least one wheel. Finally, in one embodiment, the indexing mechanism of the filtering apparatus is of a rotary type.

General Description

The present application is related to optoelectronic systems and, more specifically, to the necessity of filtering narrow spectral bands when using single-wavelength light source (s) - emitters -, to reduce noise in optoelectronic detectors. In order to achieve that it is proposed a multiple filter arrangement to minimize the effects of wavelength drift of the emitter - light source - caused by thermal oscillations. In the context of this description a filter can be of a BPF, Long-Pass filter, Short-pass filter or Neutral Density filter type.

The technology now developed can be integrated in any optoelectronic system, such as a LIDAR system, and can be applied in automotive, aeronautics, robotics or other electronic assemblies.

The present application intends to solve the problem associated with optoelectronic systems and the thermal wavelength shifts between the emission unit and the spectral properties of the optical filters used in the detection unit, in order to have the system working uninterrupted over a wide range of temperatures and with higher signal/noise ratio. In this context, it is an object of the technology now developed, to filter unnecessary photons - undesirable noise - on high sensitive optoelectronic systems. It is another object of the present technology to eliminate the typical use of a BPF with large Full Wide at Half Maximum wavelength (FWHM), which adds more noise to the detected signals to be able to accommodate the large range of working temperatures typically needed for the system. The proposed solution uses a set of predefined narrow filters to cover the range of working temperatures needed for the system, resulting in less undesirable photons/second arriving to the photodetector and enabling noise reduction. It is another object of the present technology to enhance objects detection/recognition, by using several narrower filters having their center wavelength (CWL) aligned with the emission unit's CWL.

In accordance with one aspect of the present application, the above and other objects can be accomplished by means of a multiple filter arrangement configured to automatically select a different filter according to the temperature of operation of the optoelectronic system. Therefore, it is proposed an adaptive filtering module adapted to perform a noise temperature dependence control in optoelectronic sytems. To accomplish that, in another aspect of the present application, the adaptive filtering module is comprised by a filtering apparatus and a control unit. The filtering apparatus comprises at least two optical filters, each with specific and predefined optical parameters related to CWL, FWHM, temperature variation and angle of incidence performance. The parameter's configuration of each of the individual filters is performed at the initial stage of operation, prior to the installation of the filtering apparatus in the detection unit of the optoelectronic system, and it is dependent on the working temperature range of the system. The filtering apparatus can be installed at any position along the detection unit: immediately before the receiving optics, immediately before the photodetectors or even embedded in the receiving optics. The filters can be arranged in the apparatus according to several designs, such as in a single row of individual filters, in more than one row of individual filters or disposed in a single or multiple wheel mechanism. Concerning to the first design, the single row arrangement allows for no filters overlapping and therefore highest transmissions may be achieved, being also the most straightforward scenario. However space may be a problem. The second and third approaches are more compact, however in a double raw design, for example, filters overlapping came into play and the total transmittance will be lower when comparing with the single row or wheel design. The mentioned designs are implemented by means of a linear or rotary indexing mechanisms, which represents the physical structure where the filters are inserted, ensuring its correct shift and position according to the noise temperature control performed at the control unit. In fact, the noise temperature control is achieved by automatically selecting which filter of the apparatus is to be used, according to the levels of noise allowed in the detection unit of the optoelectronic system, and the real working temperatures of the system - emission unit's light source, photodetectors and filtering apparatus - at each moment.

In accordance with another aspect of the present application, the control unit comprises temperature module, a database module and a processing module. The temperature module is configured to monitor in real-time data temperature values of the emitter unit's light source, photodetectors and filtering apparatus. The database module is used to store information related to working temperature ranges and respective emitting and detected wavelengths of the emitter and photodetectors. Besides that, it is used to store a list of all filtering apparatus and respective specifications, in particularly the number of filters and relative positioning to each other, as well as optical parameters - filtering characteristics - including temperature dependence. The processing module is provided with processing means configured to correlate in real-time the information collected by the temperature module and the data stored in the database module, in order to perform positioning control of the filters of the filtering apparatus. In this way, it is possible to automatically handle multiple filters exchange triggered by real-time temperature readings.

With this approach, the technology now developed allows for a designed noise temperature dependence control providing freedom of specifications' design of each of the individual filters embedded in the filtering apparatus. The main advantages arising from this are the following:

Improve signal/noise ratio on optoelectronic systems that need highly sensitive photodetectors;

Increase accuracy and stabilize signal detection vs. working temperature. Ultimately, avoid system stops working properly due to saturation or by lying out of the detection band;

It is compatible with other systems on which the working principles rely on narrow filtering and precise photo detection, especially if the system working temperatures range are required to be quite large, like it is typically in the case of systems for the automotive and aeronautic industries;

- is highly flexible in terms of further system developments (future new product generations), totally and easily configurable and updatable, by being always compatible with different or new emitters, detectors and filters, as long as their specifications are introduced/updated at the database module;

- Enhancement in objects detection/recognition, by using narrower filters with their center wavelength (CWL) aligned with the emitter CWL.

Brief description of drawings

For easier understanding of this application, figures are attached in the annex that represent forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

Figure 1 illustrates a conceptual diagram of the technology now developed, in which the reference numbers represent:

1 - optoelectronic system;

2 - emission unit;

3 - detection unit;

4 - photodetector;

5.1 - filtering apparatus placed in front of the receiving optics;

5.2 - filtering apparatus placed after the receiving optics ;

5.3 - filtering apparatus integrated in the receiving optics ;

6 - receiving optics;

7 - control unit;

8 - temperature module;

9 - database module;

10 - processing module;

14 - obstacle. Figure 2 illustrate a particular embodiment of the adaptive filtering module, wherein the filtering apparatus has a single row design and is placed after the receiving optics, in which the reference numbers represent:

1 - optoelectronic system;

2 - emission unit;

3 - detection unit;

4 - photodetector;

5.2 - filtering apparatus placed after the receiving optics ;

6 - receiving optics;

11.1-11.5 - filters;

14 - obstacle.

Figure 3 illustrate a particular embodiment of the adaptive filtering module, wherein the filtering apparatus has a double row design and is placed in front of the receiving optics, in which the reference numbers represent:

1 - optoelectronic system;

2 - emission unit;

3 - detection unit;

4 - photodetector;

5.1 - filtering apparatus placed in front of the receiving optics;

6 - receiving optics;

12.1- empty space;

12.2 to 12.6 - filters;

14 - obstacle.

Figure 4 illustrates the filtering apparatus with a wheel design, in which the reference numbers represent:

5 - filtering apparatus;

13 - filters of the wheel design. Description of Embodiments

Now, embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

It is developed an adaptive filtering module for noise temperature dependence control. In one embodiment, the module is integrated in an optoelectronic system (1), and is comprised by a filtering apparatus (5) and a control unit

(7) . As illustrated in figure 1, the filtering apparatus (5) can be integrated in the detection unit (3) in three different positions: immediately before (5.1) the receiving optics (6), immediately before (5.2) the photodetector (4), or even, eventually, embedded (5.3) in the receiving optics (6) . The control unit (7) comprises a temperature module

(8), a database module (9) and a processing module (10) . The temperature module (8) is configured to monitor in real-time data temperature values of the light source of the emission unit (2), photodetectors (4) and filtering apparatus (5) . The database module (9) is used to store information related to working temperature ranges and respective emitting and detected wavelengths of the emission unit (2) and photodetectors (4) . Besides that, it stores a list of all filtering apparatus (5) and respective specifications, in particularly the number of filters and relative positioning to each other, as well as filtering characteristics including temperature dependence. The processing module (10) is provided with processing means adapted to correlate in real time the information collected by the temperature module (8) and the data stored in the database module (9), in order to perform positioning control of the filters of the filtering apparatus (5) . In another embodiment, as illustrated in figure 2, the filtering apparatus (5) is placed immediately before (5.2) the photodetectors. Five filters of a BPF type, (11.1) to (11.5), are assembled in a single row which has five possible stationary positions - five indexer controllable positions - corresponding to each of the five BPF to place exactly in front of the photodetectors (4) . The filters are configured in the following manner,

11.1 - BPF: CWL=905nm; FWHM=13nm; %T>=90%;

11.2 - BPF: CWL=915nm; FWHM=15nm; %T>=90%;

11.3 - BPF: CWL=895nm; FWHM=15nm; %T>=90%;

11.4 - BPF: CWL=925nm; FWHM=15nm; %T>=90%;

11.5 - BPF: CWL=885nm; FWHM=13nm; %T>=90%,

and are assembled in the following order: BPF(11.5), BPF (11.3) , BPF (11.1) , BPF(11.2), BPF 11.4) . This filtering configuration and respective positioning is stored in the database module (9) . The temperature module (8) is responsible for monitoring in real-time the temperature of the light source of the emission unit (2), photodetectors

(4) and filtering apparatus (5) . By correlating the filtering apparatus configuration data, stored in the database module (9) with the monitoring data from the temperature module (8), the processing module (10) is able to perform positioning control of the filters of the filtering apparatus

(5) . Said control is performed actuating in a linear indexing mechanism included in the filtering apparatus (5) .

In another embodiment, as illustrated in figure 3, the filtering apparatus (5) is placed in front (5.1) of the receiving optics (6) . The schematic shows the six possible positions for the filters labelled (12.1) to (12.6) in a double row design, wherein both rows are parallel. Each row has three possible stationary positions aligned with the photodetectors (4), with three indexer controllable positions for each row. In this embodiment, five BPF are used with an empty position on the central position of the back row (12.1) . The filters (12.4), (12.2) and (12.3) are located by this order on the front row and the filters (12.6) and (12.5) are located, respectively, on the left and right extremities of the back row. The filters are configured in the following manner,

12.2 - BPF CWL=905nm; FWHM=19nm; %T>=90%;

12.3 - BPF CWL=915nm; FWHM=11nm; %T>=90%;

12.4 - BPF CWL=895nm; FWHM=11nm; %T>=90%;

12.5 - BPF CWL=905nm; FWHM=11nm; %T>=90%;

12.6 - BPF CWL=905nm; FWHM=11nm; %T>=90%.

The selective use of filtering combinations ( 12.3 ) & ( 12.5 ) or ( 12.4 ) & ( 12.5 ) is useful for reset the receiving part of the system in extreme unexpected case scenarios where photodetector saturation may occurred.

In yet another embodiment, as illustrated in figure 4, the filtering apparatus (5) has a wheel design, and the positioning control of the filters (13) is performed by control unit (7) actuating in a rotary indexing mechanism included in said apparatus (5) .

This description is of course not in any way restricted to the forms of implementation presented herein and any person with an average knowledge of the area can provide many possibilities for modification thereof without departing from the general idea as defined by the claims. The forms of implementation described above can obviously be combined with each other. The following claims further define the forms of implementation.