CN118104152A

CN118104152A - Optical communication terminal

Info

Publication number: CN118104152A
Application number: CN202180103239.XA
Authority: CN
Inventors: 秦宇
Original assignee: Shanghai Yuhang Optics Technology Co ltd
Current assignee: Shanghai Yuhang Optics Technology Co ltd
Priority date: 2021-10-12
Filing date: 2021-10-12
Publication date: 2024-05-28
Also published as: WO2023060451A1

Abstract

An optical communication terminal OCT (1) comprising an optical Telescope (TLA) adapted to enlarge the diameter of a light beam received from a light emitter unit (2A) of the optical communication terminal OCT and to reduce the diameter of the light beam received from an external optical flying platform of a light receiver unit (2B) for the optical communication terminal OCT, (1) wherein at least one central shielding coating (11) is provided on the surface of an optical component (10) of the optical receiver unit (2B) and adapted to suppress light backscattered and/or reflected by the optical Telescope (TLA) of the optical communication terminal OCT (1).

Description

Optical communication terminal

Technical Field

The present invention relates to an optical communication terminal for optical communication that uses a laser beam to transmit an optical communication signal or a quantum key for Quantum Key Distribution (QKD).

Background

A communication system includes two or more optical communication terminals that communicate with each other. These optical communication terminals are assembled on a fixed platform, a mobile platform or a manned or unmanned aerial vehicle. The communication link between the optical communication terminals may be an end-to-end connection or a network of optical communication terminals, some of which may act as relay stations. Optical communication is an addition and/or alternative to radio frequency based communication. Optical communications provide higher data rates than conventional radio frequency transmissions. Optical communication terminal OCT inherently supports low size, low weight, and low power (SWaP) compared to conventional radio frequency terminals. Accordingly, a large amount of data can be efficiently transmitted through the broadband channel of the optical communication terminal.

Fig. 1 schematically shows a communication system SYS comprising different types of terminals located on the ground, suitable for communicating with non-ground communication terminals integrated in different types of manned or unmanned aerial platforms. The telecommunications system may also include an inter-platform link. The high altitude platform systems HAPS may communicate with each other through the associated communication terminals. The aircraft may communicate directly with the ground terminals or indirectly through a relay communication terminal, as shown in fig. 1. The ground terminals may be located in fixed locations or may be integrated into a movable object or vehicle, such as a train, vehicle, etc. as shown in fig. 1. Communication between the handheld mobile user equipment UE and the ground terminal via a near-earth flying communication terminal is also possible, as shown in fig. 1. The flying platform in the communication system SYS may also provide a communication access point for any location on earth, even in case no land-based telecommunication network is available at the respective location.

Alignment of the optical communication terminal may be provided by the coarse pointing assembly CPA. The mirror of the coarse directing assembly serves as a beam directing structure. In a conventional coarse pointing assembly, the rotational axis of the mirror is positioned about its center of gravity to minimize the gravitational torque that the motor of the coarse pointing assembly must counteract. However, this configuration results in a large CPA structure. Furthermore, the optical surface of the mirror of the coarse pointing assembly and the receiving telescope are exposed for a long period of time during the non-operational phase of the optical communication terminal. This in turn increases the contamination rate of the photosensitive surface, resulting in reduced lifetime and performance of the device.

It is therefore an object of the present invention to provide an optical communication terminal for optical communication adapted to overcome the above-mentioned drawbacks of the conventional coarse pointing assembly of a mirror having a rotation axis at its center of gravity.

Disclosure of Invention

According to a first aspect of the present invention, the object is achieved by an optical communication terminal for optical communication, which uses a laser beam for transmitting an optical communication signal.

According to a first aspect of the present invention there is provided an optical coarse pointing assembly of an optical communication terminal adapted to establish and/or maintain an optical communication link between the optical communication terminal and an external optical flying platform, wherein the optical coarse pointing assembly has a CPA mirror adapted to reflect a light beam received from the external optical flying platform into a telescope of an optical head unit of the optical communication terminal and/or reflect a light beam received from a telescope of an optical head unit of the optical communication terminal into the external optical flying platform, wherein the CPA mirror of the optical coarse pointing assembly is pivotable about an elevation axis located offset from the centre of gravity of the CPA mirror.

An advantage of the optical coarse pointing assembly according to the first aspect of the present invention is that the size of the CPA structure is minimal, facilitating transportation of the optical communication terminal. Furthermore, the optically reflective surfaces of the CPA mirror and other optical components may be protected during non-operational phases of the task. The CPA mirror reduces the contamination rate of the photosensitive surface in its closed position and increases the operating life and performance of the optical communication terminal.

In a possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the CPA mirror is pivotable about the elevation axis by means of a controllable drive structure.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the pivoting angle of the CPA mirror about the elevation axis is adjustable by a control unit adapted to control the driving structure of the CPA mirror.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the controllable driving structure of the CPA mirror comprises a capstan driving structure or a gear driving structure.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the CPA mirror comprises a mirror body having a reflective optical surface layer, the reflective optical surface being located on a pivotable base element which is driven by a controllable driving structure of the CPA mirror.

In a possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the elevation axis is located at the lower edge of the mirror body of the CPA mirror.

In another possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the CPA mirror is pivotable about an elevation axis between a closed position and at least one open position. In the closed position, the telescope of the optical head unit is covered by the CPA mirror. In at least one open position, the light beam is reflected by the optical surface of the CPA mirror to establish and/or maintain an optical communication link between the optical head unit and the external optical flying platform.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the CPA mirror is lockable in the closed position by means of a controllable locking structure of the optical coarse pointing assembly.

This increases the safety of protecting the photosensitive surface from unwanted contamination.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the coarse pointing assembly is placed as a replaceable module in front of the telescope of the optical head unit of the optical communication terminal.

This facilitates mounting the coarse pointing assembly on an optical communication terminal.

In another possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the coarse pointing assembly is rotatable about an azimuth axis and/or an elevation axis to establish and/or maintain an optical communication link between the optical head unit and the external optical flying platform.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the optical surface layer of the mounted CPA mirror faces the front surface of the telescope of the optical head unit of the optical communication terminal.

In a possible embodiment of the optical rough finger assembly according to the first aspect of the invention, the optical surface layer of the CPA mirror is made of a highly reflective material, in particular gold.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the pivotable base element of the CPA mirror is made of a physically lightweight material, in particular aluminum or glass ceramics.

In a further possible embodiment of the optical coarse pointing assembly according to the first aspect of the invention, the CPA assembly is adapted to provide a basic angular movement of the light beam in the acquisition mode of the optical communication terminal to establish a communication link between the optical communication terminal and the external flying platform by controlling the position of a CPA mirror of said CPA assembly.

The present invention also provides a method for establishing and/or maintaining an optical communication link between an optical communication terminal and an external optical flying platform by pivoting a CPA mirror of an optical coarse-pointing assembly of the optical communication terminal about an elevation axis offset from the center of gravity of the CPA mirror.

Conventional laser communication terminals may use a shared telescope aperture to transmit and receive data and to track the laser beam. In the transmission path, a laser beam may be generated and coupled into a shared beam path, for example by a dichroic mirror. The transmitted light may be emitted through a telescope with an optical surface to widen the collimated transmitted laser beam to a target laser beam diameter. However, a portion of the transmitted light is backscattered or reflected into the optical system, which may cause self-blind effects, especially on extended tracking sensors. Since the emitted laser beam is typically many orders of magnitude more intense than the light received from an external counterpart communication terminal, this will have a negative impact on tracking and communication performance.

It is therefore another object of the present invention to provide an optical communication terminal to reduce self-blind effects caused by back-scattered and/or reflected light.

According to another aspect of the invention, this object is achieved by an optical communication terminal comprising an optical telescope adapted to enlarge the diameter of a light beam received from a light emitter unit of said optical communication terminal and to reduce the diameter of a light beam received from an external optical flying platform for an optical receiving unit of said optical communication terminal, wherein at least one central shielding coating is provided on a surface of an optical component of said light receiver unit and adapted to suppress light backscattered and/or reflected by said optical telescope of said optical communication terminal.

In a possible embodiment of the optical communication terminal according to the second aspect of the invention, the central shielding coating comprises a material that is opaque at least in a predetermined communication frequency range of the optical communication terminal.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the central shielding coating comprises an absorbing or reflecting material.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the central shielding coating comprises a circle having a predetermined radius.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the central shielding coating is arranged in the center of the optical component of the optical receiver unit.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the optical component comprises an optical lens of an optical receiver unit in the optical communication terminal.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the optical telescope in the optical communication terminal comprises an on-axis lens telescope without a central shielding.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the on-axis lens telescope comprises a single-piece optical lens or a plurality of lenses made of transparent material within a predetermined communication frequency range of the optical communication terminal.

In another possible embodiment of the optical communication terminal according to the second aspect of the invention, the material of the single-piece optical lens or the multi-piece optical lens is made of a homogeneous material.

In a possible embodiment of the optical communication terminal according to the second aspect of the invention, the material of the single optical lens or the plurality of optical lenses may comprise silicon or germanium.

In another possible embodiment of the optical communication terminal according to the second aspect of the invention, the optical telescope lens comprises an aspherical convex front surface and a spherical or aspherical concave rear surface.

In a possible embodiment of the optical communication terminal according to the second aspect of the present invention, the optical telescope lens is designed to enlarge the laser beam emitted by the optical emission unit of the transceiver and passing through the rear surface of the optical telescope lens, and to reduce the diameter of the laser beam received through the front surface of the optical telescope lens, wherein the reduced laser beam is output to the optical receiving unit of the transceiver through the rear surface of the optical telescope lens by the beam filtering unit.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, a central shielding coating is provided at a surface of the component of the optical receiving unit, adapted to shield the tracking sensor in the optical receiver unit of the transceiver of the optical communication terminal from light backscattered and/or reflected by the optical telescope of the optical communication terminal.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the central shielding coating provides an attenuation which depends on the ratio between the radius of the central shielding coating and the beam radius of the received light beam.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the side surface of the tapered portion of the optical telescope lens comprises a plurality of suppression steps adapted to suppress backscattered and/or reflected light.

In a further possible embodiment of the optical communication terminal according to the second aspect of the invention, the front surface of the telescope lens is adapted to receive the laser beam from the coarse pointing assembly of the optical communication terminal.

Conventional optical communication systems may use a shared telescope assembly to transmit and receive laser beams to reduce the size, weight, and power consumption of the optical communication terminal. The amplified laser light may be generated in an erbium doped fiber amplifier EDFA at the transmitter side. However, due to the physical nature of optical amplification in erbium doped fiber amplifiers, unwanted Amplified Spontaneous Emission (ASE) noise is generated in addition to the desired analog emission. The amplified light signal is directed towards the point-front assembly and to a dichroic beam splitter, which has the task of directing the transmitted light to the telescope assembly after reflection at the fine pointing assembly FPA. However, not all transmitted light is directed out of the telescope. A portion of the light is reflected back to the optical system. This may be due to non-ideal anti-reflection coatings and contamination of the telescope surface. The reflected light reaches the dichroic beam splitter and passes towards a receiving path where a filter may be present to reject the background light. These filters are centered around the receive wavelength and can suppress the transmitted light, however, amplified spontaneous noise generated by the boosted EDFA is present at the receive wavelength and can reach the high sensitivity tracking sensor through these filters. Thus, the tracking sensor may saturate, which does prevent the normal operation of tracking. In the worst case, the tracking sensor may even be damaged if the intensity of the transmitted light is too high. Another problem caused by the back-reflected ASE noise is that it may severely interfere with weak received communication signals.

It is therefore another object of the present invention to provide an optical transceiver capable of reducing Amplified Spontaneous Emission (ASE) such that the ASE noise no longer blinds the sensors provided to the receiver unit and/or such that the ASE noise does not interfere with the received communication signals.

According to a third aspect, the object is achieved by an optical transceiver of an optical communication terminal having an optical transmitter unit adapted to transmit optical communication signals in at least one predetermined communication frequency range and an optical receiver unit adapted to receive optical communication signals in the predetermined communication frequency range, wherein the optical transmitter unit comprises a laser diode adapted to generate a laser beam amplified by a boosted Erbium Doped Fiber Amplifier (EDFA) of the optical transmitter unit, wherein an amplification gain of the boosted EDFA is reduced to reduce spontaneous emission noise ASE amplified by a broadband EDFA generated by the boosted EDFA, wherein the reduced amplification gain of the boosted EDFA is compensated by a corresponding increase of an output power of the laser beam generated by the laser diode.

In a possible embodiment of the optical transceiver according to the third aspect of the invention, the optical transmitter unit is adapted to transmit the optical transmission signal at a predetermined transmission wavelength within a predetermined communication frequency range of the optical communication terminal.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical receiver unit is adapted to receive an optical reception signal of a predetermined reception wavelength within a predetermined communication frequency range of the optical communication terminal.

In a further possible embodiment of the optical transceiver according to the third aspect of the present invention, the optical transmission signal of the optical transmitter unit is provided to the telescope of the optical communication terminal through a pre-point assembly, a dichroic beam splitter and a fine pointing assembly.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical receiver unit of the optical communication terminal comprises at least one optical bandpass filter adapted to reject light outside the band of the reception filter centered around the reception wavelength of the optical receiver unit.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical bandpass filter of the optical receiver unit is adapted to suppress reflected light at the transmission wavelength of the optical transmitter unit of the optical communication terminal.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the EDFA-ASE noise generated by the boosted EDFA of the optical transmitter unit comprises a spectral overlap with the receive filter band of the at least one optical band-pass filter of the optical receiver unit of the optical communication terminal.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical reception signal passing through the optical band pass filter of the optical receiver unit is split by the beam splitter into a first optical signal provided to the optical receiver unit tracking sensor and a second optical signal provided to the optical receiver unit optical signal demodulator of the optical communication terminal through the single mode fiber and the EDFA pre-amplifier.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, in the calibration mode of the optical communication terminal, the adjustment of the amplification gain of the optical transmitter unit boost EDFA and the corresponding adjustment of the optical transmitter unit laser diode output power is performed by the control unit of the optical transmitter unit to reduce EDFAASE noise.

In another possible embodiment of the optical transceiver according to the third aspect of the invention, the telescope comprises an optical telescope lens made of a homogeneous material that is transparent in the communication frequency range of the optical communication terminal and has a high refractive index.

In still another possible embodiment of the optical transceiver according to the third aspect of the present invention, the optical telescope lens is designed to expand the laser beam emitted by the light emitter unit and entering through a rear surface of the optical telescope lens, and is designed to reduce a diameter of the laser beam received through a front surface of the optical telescope lens, wherein the reduced laser beam is output to the light receiver unit of the optical communication terminal through the rear surface of the optical telescope lens.

In another possible embodiment of the optical transceiver according to the third aspect of the invention, the optical telescope lens of the telescope comprises an aspherical convex front surface and a spherical or aspherical concave rear surface.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical telescope lens of the telescope is made of a homogeneous material. In a possible embodiment, such a uniform material may comprise silicon or germanium.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical telescope lens of the telescope comprises a conical portion and/or a cylindrical portion, wherein a side surface of the conical portion of the optical telescope lens comprises a plurality of suppressing steps adapted to suppress the backscattered or reflected optical signal.

In a further possible embodiment of the optical transceiver according to the third aspect of the invention, the optical receiver unit comprises at least one optical component having a central shading coating adapted to suppress light backscattered and/or reflected by the optical telescope of the optical communication terminal.

Optical communication terminals are sensitive to vibrations generated on the flying platform and mechanical forces exerted on the hardware. In addition, a transport space for transporting the optical communication terminal is very limited.

It is therefore another object of the present invention to provide an optical communication terminal which is adaptable to mechanical forces during transportation and which does not occupy much transportation space during transportation.

According to a fourth aspect, the present invention provides an optical communication terminal for transmitting an optical communication signal using a laser beam, the optical communication terminal comprising: an optical transceiver having a light emitter unit adapted to transmit optical communication signals in at least one predetermined communication frequency range and a light receiving unit adapted to receive optical communication signals in said predetermined communication frequency range, and an optical head unit having a telescope for collecting optical power and adjusting a laser beam diameter, wherein the telescope comprises a monolithic optical telescope lens made of a uniform material transparent in the communication frequency range and having a high refractive index.

In a possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens comprises a front surface and a rear surface.

In a preferred embodiment, the optical telescope lens comprises an aspherical convex front surface. In one possible embodiment, the optical communication terminal further comprises a concave rear surface that is spherical or aspherical.

In a possible embodiment of the optical communication terminal according to the fourth aspect of the present invention, the optical telescope lens is designed to expand the laser beam emitted by the light emitter unit entering through the rear surface of the optical telescope lens, and is further designed to reduce the diameter of the laser beam received through the front surface of the optical telescope lens, wherein the reduced laser beam is output to the light receiver unit through the rear surface of the optical telescope lens.

In a further embodiment of the optical communication terminal according to the fourth aspect of the invention, the homogenous material of the optical telescope lens may comprise a high thermal conductivity. In particular, when silicon is used as a uniform material, high thermal conductivity can be achieved.

In another possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the homogenous material of the optical telescope lens may comprise an absorption characteristic shielding optical signals having frequencies outside the predetermined communication frequency range to minimize optical noise in the optical receiver unit.

In another possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens can comprise at least one side surface having a circumferential rotationally symmetrical portion.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens can comprise a conical portion and/or a cylindrical portion.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the side surface of the tapered portion of the optical telescope lens may comprise a plurality of suppression steps adapted to suppress backscattered or reflected optical signals.

In another possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the homogeneous material of the optical telescope lens comprises silicon.

In another possible alternative embodiment, the uniform material of the optical telescope lens can include germanium.

In another possible alternative embodiment, the homogeneous material of the optical telescope lens may also comprise glass.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens is manufactured in a turning manufacturing process.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens may also be manufactured during grinding.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical telescope lens is manufactured in an additive manufacturing process.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical receiver unit may comprise a monolithic or composite filter and a beam splitter lens to provide the received optical signal to a tracking sensor of the optical transceiver.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the aspherical convex front surface of the optical telescope lens is adapted to receive a laser beam from the coarse pointing assembly CPA of said optical communication terminal.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the frame structure for mounting the optical transceiver and/or the optical head unit in the optical communication terminal is manufactured in an additive manufacturing process.

In another possible embodiment of the optical communication terminal according to the fourth aspect of the present invention, the optical head unit may comprise a pre-point assembly PAA, a fine pointing assembly FPA and/or a dichroic mirror CBS.

In a possible embodiment of the optical communication terminal, the dichroic mirror is designed to separate the received light beam and the light beam from the transmitting unit by means of respective wavelength characteristics.

In a further possible embodiment of the optical communication terminal according to the fourth aspect of the invention, the optical communication terminal is integrated in a mobile flying station comprising an aerial platform, an aeroplane or a drone or the like, or may be integrated in a ground station for providing tower-to-tower communication.

Features of different aspects of the invention may be combined with each other.

Drawings

Hereinafter, possible embodiments of the optical communication terminal according to the present invention are described with reference to the accompanying drawings.

Fig. 1 shows a communication system for transmitting communication signals using a communication terminal;

FIG. 2 shows a block diagram of a possible exemplary embodiment of an optical communication terminal OCT according to an aspect of the present invention;

FIG. 3 illustrates another exemplary embodiment of an optical communication terminal OCT in accordance with an aspect of the present invention;

FIG. 4 shows a block diagram of a possible exemplary embodiment of an optical communication terminal OCT according to an aspect of the present invention;

FIG. 5 shows a schematic diagram of a possible embodiment of an optical system within an OCT of an optical communication terminal according to an aspect of the present invention;

FIGS. 6A, 6B illustrate an exemplary embodiment of an optical telescope lens used in OCT of an optical communication terminal in accordance with an aspect of the present invention;

FIG. 7 shows a possible exemplary embodiment of an optical system with a coarse pointing assembly CPA of an optical communication terminal OCT according to an aspect of the present invention;

Fig. 8 shows a top view of an optical system implemented in an optical head unit of an optical communication terminal according to an embodiment of the present invention;

fig. 9 shows a top view of an optical system used in OCT of an optical communication terminal according to an aspect of the present invention;

FIG. 10 illustrates an exemplary embodiment of a filter and beam splitter lens used in OCT of an optical communication terminal in accordance with an aspect of the present invention;

FIGS. 11A, 11B, 11C illustrate an exemplary embodiment of a frame structure of an optical communication terminal OCT according to an aspect of the present invention;

FIGS. 12A, 12B illustrate possible exemplary embodiments of an optical coarse pointing assembly of an optical communication terminal according to one aspect of the present invention;

FIG. 13 is a schematic diagram illustrating the operation of an optical coarse pointing assembly of the optical terminal of FIGS. 12A and 12B;

FIGS. 14A and 14B illustrate operation of an optical communication terminal including a center shielding coating according to another aspect of the present invention;

fig. 15 shows the technical effect of a center shielding coating in a possible exemplary embodiment of an optical communication terminal; and

Fig. 16 shows a schematic diagram of a possible exemplary embodiment of an optical transceiver with reduced spontaneous emission noise of the EDFA amplification according to another aspect of the invention.

Reference number:

1 optical communication terminal

2 Transceiver

2A transmitter unit

2B receiver unit

3 Optical head unit

3A telescope lens

3B BS ACU

3C precision direction component

3D dichroic mirror

3E point front assembly

4 Coarse pointing assembly

4ACPA reflector

4B elevation shaft

4C lifting driving structure

4D azimuth driving structure

5 Electronic unit

6 Inhibition step

7 Beam splitter lens

7A lens

7B folding mirror prism

7C lens

7D beam splitter cube

8 Tracking sensor

9 Frame structure

10 Optical component

11 Masking coating

12 Folding mirror

13 Emitter and modulator unit with laser diode

14 Boost EDFA

15TX collimator

16 Beam splitter

17 Single mode optical fiber

18EDFA preamplifier

19RFE and demodulator

20 Control unit

Detailed Description

The Optical Communication Terminal (OCT) 1 can be used in a communication system SYS as shown in fig. 1. The optical communication terminal 1 may be integrated in a mobile flying station comprising a high-altitude platform, an aeroplane or a drone, etc., as shown in fig. 1. The optical communication terminal OCT may also be integrated in the ground station for providing tower-to-tower communication. The optical communication terminal 1 may be used to supplement or replace a radio frequency communication link between a base station and a mobile flying platform. The optical communication terminal 1 provides one or more broadband optical communication channels by transmitting or carrying modulated optical communication signals via at least one optical communication link OCL using a laser beam.

Fig. 2 shows a block diagram of an optical communication terminal 1 according to an aspect of the present invention. The optical communication terminal 1 includes an optical transceiver 2 and an optical head unit 3. The optical transceiver 2 has an optical transmitter unit 2A adapted to transmit optical communication signals in at least one predetermined communication frequency range. The optical transceiver 2 further comprises an optical receiver unit 2B adapted to receive optical communication signals within a predefined communication frequency range.

As shown in fig. 2, the optical communication terminal 1 further includes an optical head unit 3. The optical head unit 3 includes a telescope TLA, which is used to collect optical power and adjust the diameter of the laser beam. The telescope TLA of the optical head unit 3 may include a single-piece optical telescope lens 3A made of a uniform material transparent in the communication frequency range and having a high refractive index n. The optical telescope lens 3A of the telescope TLA in the optical head unit 3 may include a convex front surface FSUR and a concave rear surface RSUR. In the preferred embodiment, the convex front surface of the optical telescope lens 3A of the telescope TLA in the optical head unit 3 is constituted by an aspherical surface. The concave rear surface of the optical telescope lens 3A of the telescope TLA may include a spherical or aspherical concave rear surface. The telescope TLA of the optical head unit 3 is adapted to receive an incident communication signal carried via a laser beam, and the size of the diameter of the laser beam can be reduced to match the size of the optical components of the optical communication terminal 1. The optical telescope TLA of the optical head unit 3 is also adapted to operate as a beam expander that emits a laser beam. In this way, the aperture and the secondary collimating lens may be combined in a single component to reduce assembly and integration effort by minimizing the number of components required within the optical head unit 3 of the optical communication terminal 1.

In one possible embodiment, the optical telescope lens 3A may be made of silicon. Silicon includes a high refractive index n. Another advantage of using silicon is that silicon also has a high thermal conductivity. Furthermore, the absorption characteristics of silicon make it a good long-pass filter that can suppress visible wavelengths and other signals outside the transmission frequency range, thereby minimizing optical noise in the receiver system. In addition, silicon can protect sensitive receivers and tracking sensors from thermal damage and direct exposure to sunlight. Due to the strongly thermally conductive nature of silicon, the temperature can be kept uniform throughout the body of the lens, which contains a uniform refractive index. Furthermore, the high refractive index n of silicon may allow for shorter system lengths by maintaining a reasonable radius of curvature for the aperture of the optical telescope lens. The optical telescope lens 3A may be made of other uniform materials than silicon.

The optical telescope lens of the optical telescope of the optical head unit 3 is designed to expand the laser beam emitted by the light emitter unit 2A and entering through the rear surface RSUR of the optical telescope lens. The optical telescope lens is further designed to reduce the diameter of the laser beam received through the front surface FSUR of the optical telescope lens. Then, the reduced laser beam is output to the light receiver unit 2B of the optical transceiver 2 through the rear surface RSUR of the optical telescope lens. The uniform material of the optical telescope lens includes an absorption characteristic that shields an optical signal of a frequency outside a predetermined communication frequency range, in particular, visible light, to minimize optical noise in the optical receiver unit 2B.

The optical telescope lens 3A may include different shapes. Possible embodiments of the optical telescope lens 3A can comprise at least one side surface with a circumferential rotationally symmetrical portion. The optical telescope lens of the optical head unit 3 may also include a conical portion. In yet another possible embodiment, the optical telescope lens of the optical head unit 3 may also comprise a cylindrical portion.

In a preferred embodiment of the optical communication terminal 1 according to the invention, the side surface of the tapered portion of the optical telescope lens may comprise a plurality of suppression steps adapted to suppress any type of backscattered or reflected optical signals. The optical telescope lens can be manufactured in a manufacturing process. The manufacturing process may include a turning manufacturing process, a grinding process, or an additive manufacturing process.

Furthermore, in a possible embodiment, the frame structure for mounting the optical transceiver 2 and/or the optical head unit 3 of the optical communication terminal 1 may be manufactured in an additive manufacturing process. As shown in the block diagram of fig. 4, the optical head unit 3 may comprise different sub-units including a pre-dot assembly PAA, a fine-pointing assembly FPA, and a dichroic mirror CBS. The dichroic mirror CBS may be designed to separate the received light beam from the light beam received from the emitter unit assembly by their respective wavelength characteristics.

Fig. 3 shows a possible embodiment of an Optical Communication Terminal (OCT) 1 integrated in a frame structure. In the illustrated embodiment, the optical communication terminal 1 comprises a Coarse Pointing Assembly (CPA) 4 in front of the optical head unit 3. The optical head unit 3 is connected to an optical transmission and reception system 2 forming an optical transceiver. The optical transceiver 2 may also be integrated in the optical head unit 3. The optical transceiver 2 may also be connected to an electronic unit 5 of the optical communication terminal 1. The electronic unit 5 may comprise different electronic components including an FEC codec system or a terminal microcontroller TMC. The electronic unit 5 may also comprise an FPA/PAA controller FPC, an EPS and a supervising entity. The total length L of the optical communication terminal 1 includes the length L1 of the CPA 4, the length L2 of the optical head unit 3 and the integrated optical transceiver 2, and the length L3 of the electronic unit 5 within the frame, as shown in fig. 3.

Fig. 4 shows the optical head unit 3 of the optical communication terminal 1 in more detail. In the shown embodiment the optical head unit 3 comprises an integrated optical transmission and reception system 2, i.e. an optical transceiver 2. The optical communication terminal 1 can provide bidirectional communication in which data is transmitted in both directions at a high bit rate of more than 1 Gbps. Both transmit and receive paths share the same telescope TLA. Signal separation may be achieved by polarization and signal frequency. The rough alignment of the optical communication terminal 1 may be performed by a rough pointing assembly (CPA) 4. The coarse pointing assembly 4 is adapted to control and align the light beam for the reception and transmission of light. The coarse pointing assembly 4 may be used to provide the basic angular movement of the laser beam required for the acquisition mode and also to predict the relative movement between different optical communication terminals. The Coarse Pointing Assembly (CPA) 4 provides a relatively large angular range. In this way, the optical communication link OCL, and in particular the optical communication link that cooperates with the optical flying platform, can be established and maintained to accommodate large relative movements between two adjacent flying platforms or between the flying platform and the ground station with minimal impact on the beam quality of the laser beam. A Coarse Pointing Assembly (CPA) 4 is provided in front of the telescope TLA of the optical head unit 3. The telescope TLA of the optical head unit 3 is used to collect the optical power and adapt the diameters of the respective laser beams. In the optical communication terminal 1 according to the present invention, the telescope TLA of the optical head unit 3 may include a single piece of optical telescope lens 3A made of a uniform material. Furthermore, the optical telescope lenses 3A are transparent in the respective communication frequency ranges, and have a high refractive index n. The telescope TLA can be connected to a BS ACU unit 3B, as shown in fig. 4, which can be used as an alignment and calibration tool. The optical head unit 3 further includes a Fine Pointing Assembly (FPA) 3C, as shown in fig. 4. The optical head unit 3 further includes a dichroic mirror (CBS) 3D. In the embodiment shown in fig. 4, the optical head unit 3 includes a pre-spot assembly (PAA) 3E.

In the embodiment shown in fig. 4, the transceiver 2 is integrated in the optical head unit 3. The transceiver 2 includes an optical transmitter unit 2A and an optical receiver unit 2B. The optical transmitter unit 2A is adapted to transmit optical communication signals in at least one predefined communication frequency range. The optical receiver unit 2B is adapted to receive an optical communication signal within a predetermined communication frequency range. In the embodiment shown in fig. 4, the optical transmitter unit 2A comprises a transmitter and modulator, a boost EDFA and a transmission collimator. The generated optical signal is applied to the dichroic mirror 3D by the optical transmitter unit 2A through the pre-dot assembly 3E as shown in fig. 4.

In the embodiment shown in fig. 4, the optical receiver unit 2B includes at least one optical filter for receiving the optical communication signal from the dichroic mirror 3D. The optical receiver unit 2B further comprises a BS beam splitter 16 adapted to split the received optical beam into two signal components. The first split optical signal component is supplied to the preamplifier EDFA18 and the RFE and demodulation unit 19 of the optical receiver unit 2B. In the illustrated embodiment, the second split optical signal component is provided to a four-quadrant detector (4 QD) 8. A fine pointing function may be provided to mitigate high frequency interference in the common optical signal path. These disturbances may originate from various sources of vibration on the flying platform. In addition, for the ground communication terminal, the atmospheric turbulence can be corrected.

Fig. 5 shows a top view of an optical system within the optical communication terminal 1 according to the present invention. In the illustrated embodiment, it can be seen that the telescope TLA of the optical head unit 3 comprises in the illustrated exemplary embodiment a monolithic optical telescope lens 3A made of homogeneous material. The single-piece optical telescope lens 3A of the telescope TLA is transparent in a predetermined communication frequency range. Further, the optical telescope lens 3A of the telescope TLA has a high refractive index n. The optical telescope lens 3A is designed to expand the laser beam emitted by the light emitter unit 2A via the pre-spot assembly 3E, which enters through the rear surface RSUR of the optical telescope lens 3A. The optical telescope lens 3A of the telescope TLA is further designed to reduce the diameter of the laser beam received through the front surface FSUR of the optical telescope lens 3A. The reduced laser beam is output through the rear surface RSUR of the optical telescope lens 3A, and enters the light receiver unit 2B through the dichroic mirror 3D. In a possible embodiment, the optical telescope lens 3A of the telescope TLA is made in such a way that it forms a homogeneous body in one piece. This allows the optical system shown in fig. 5 to be adapted to mechanical vibrations or mechanical forces. Since the telescope TLA includes a single-piece optical lens, misalignment caused by mechanical force or vibration can be avoided. Furthermore, the optical system using the monolithic optical telescope lens 3A does not require complex interactions between different components such as different lenses or mirrors, thereby reducing complexity and increasing the elasticity and robustness of the optical system. Thus, the optical system having the single-piece optical telescope lens 3A can certainly operate more reliably because the different optical components are not dislocated or malfunctioning. In addition, the use of the monolithic optical telescope lens 3A can reduce the size of the optical system, and thus the optical head unit 3. In this way, the length and the overall size of the optical communication terminal 1 can be minimized, thereby saving transmission space. The optical telescope lens 3A of the telescope TLA includes a front surface FSUR and a rear surface RSUR, as shown in fig. 5. In a preferred embodiment, the front surface FSUR of the optical telescope lens 3A comprises an aspherical convex front surface. The rear surface RSUR is concave. The concave rear surface RSUR may include a spherical concave rear surface or an aspherical concave rear surface. The optical telescope lens 3A expands the laser beam emitted by the light emitter unit 2A, entering through the rear surface RSUR of the optical telescope lens 3A, and is also designed to reduce the diameter of the laser beam when received through the front surface FSUR. Then, the reduced laser beam is output through the rear surface RSUR of the optical telescope lens 3A, and supplied to the light receiver unit 2B of the transceiver 2. As shown in the embodiment of fig. 5, the uniform material of the optical telescope lens 3A may have an absorption characteristic that shields optical signals of frequencies outside the predetermined communication frequency range to minimize any type of optical noise in the optical receiver unit 2B of the transceiver 2.

As shown in the embodiment of fig. 5, the optical telescope lens 3A of the telescope TLA can comprise at least one side surface having a rotationally symmetrical portion around it. In the embodiment shown in fig. 5, the optical telescope lens 3A includes a conical portion. The optical telescope lens 3A can also comprise other shapes and forms, as explained in the context of fig. 11A, 11B, 11C. The conical portion of the optical telescope lens 3A comprises in a preferred embodiment a plurality of suppression steps adapted to suppress backscattered or reflected optical signals.

Fig. 6A shows a conical design of the optical telescope lens 3A with multiple suppression steps to suppress backscattered or reflected optical signals. Fig. 6A shows a front view, a side view and a perspective rear view of the optical telescope lens 3A of the telescope TLA.

Fig. 6B shows a view of another possible exemplary embodiment of an optical telescope lens 3A that can be used in an optical communication terminal 1 according to the present invention. In the embodiment of fig. 6A, the number N of suppression steps may vary depending on the use and size of the lens. In the illustrated embodiment, the optical telescope lens includes three (n=3) suppression steps 6-1, 6-2, 6-3 adapted to suppress backscattered or reflected optical signals. The front surface FSUR of the optical telescope lens 3A includes an aspherical convex front surface FSUR.

Fig. 6B shows another possible exemplary embodiment of an optical telescope lens 3A, which has not only a conical section but also a cylindrical section. The side surface of the tapered portion of the optical telescope lens 3A in fig. 6B may also include a suppressing step 6 to suppress the backscattered or reflected optical signal. The dimensions and lengths of the different parts of the optical telescope lens 3A can vary depending on the use case.

Fig. 7 shows a cross section of an optical system with a Coarse Pointing Assembly (CPA) in front. In the illustrated embodiment, the Coarse Pointing Assembly (CPA) includes an X/Y pointing system that includes a so-called Lissley prism pair.

Fig. 8 shows another top view of an optical system implemented in the optical head unit 3 of the optical communication terminal 1 according to the present invention. In the illustrated embodiment, the optical receiver unit 2B may comprise a monolithic optical filter and beam splitter lens 7 adapted to provide the received optical signal to a tracking sensor 8 of the optical transceiver 2. The optical filter and the beam splitter lens 7 may also be assembled from different components that may be glued together. It may comprise a first lens 7A, a folding mirror prism 7B, a lens 7C and a beam splitter cube 7D.

Fig. 9 shows different views of a possible implementation of the optical filter and the beam splitter lens 7. The telescope TLA of the optical head unit 3 is adapted to receive the incoming communication signals and to distribute the received power to the tracking and data sensor 8. The optical filter and the beam splitter lens 7 may be implemented by separate components, such as a lens and a beam splitter, which are combined into a single component. In this way, assembly and integration work can be reduced by further minimizing the number of parts required within the optical system of the optical communication terminal 1.

Fig. 10 shows different views of a frame structure for mounting the optical transceiver 2 and/or for mounting the optical head unit 3 of the optical communication terminal 1. In a preferred embodiment, the frame structure 9 as shown in fig. 10 may be manufactured in an additive manufacturing process. As shown in fig. 10, the frame structure 9 may hold the CPA4 in front of the optical head unit 3 and the electronic unit 5 of the optical communication terminal 1. The optical head unit 3 may in turn include a pre-spot assembly PAA, a fine pointing assembly FPA, and a dichroic mirror CBS.

Fig. 11A, 11B, 11C show cross-sections of different exemplary embodiments of an optical telescope lens 3A used in possible embodiments of an optical system of an optical communication terminal 1.

Fig. 11A shows an optical telescope lens 3A with only a conical cross section, which in a possible embodiment may comprise a side surface with a predefined number N of suppression steps 6.

Fig. 11B shows a possible embodiment of an optical telescope lens 3A comprising a conical portion and a cylindrical portion.

Fig. 11C shows another exemplary embodiment of an optical telescope lens 3A including only a cylindrical portion. In any case, the optical telescope lens 3A includes a convex surface FSUR and a concave surface RSUR, as shown in fig. 11A, 11B, 11C.

The optical telescope lens 3A can be made of different materials. In a preferred embodiment, the optical telescope lens 3A is made of silicon. Silicon has absorption characteristics to mask optical signals having frequencies outside of a predetermined communication frequency range. The predefined communication frequency range may be, for example, an infrared frequency range or a frequency band. In this way, optical noise in the optical receiver unit 2B is minimized. The communication frequency range or communication band may comprise one or more communication channels CH transmitting data in the same or opposite transmission directions.

Silicon Si comprises a relatively high refractive index n. Another advantage of using silicon is that silicon has a high thermal conductivity. In an alternative embodiment, the optical telescope lens 3A of the telescope may be made of germanium Ge. In another alternative, the optical telescope lens 3A of the telescope TLA can also be made of glass material. In a preferred embodiment, the optical telescope lens 3A is made of a single uniform and homogenous component.

The optical communication terminal 1 as shown in the block diagram of fig. 4 comprises a coarse pointing component 4. The coarse pointing assembly 4 may be mounted to the optical head unit 3 and is adapted to establish and/or maintain an optical communication link OCL between the optical communication terminal 1 and an external optical flying platform. In a preferred embodiment, the optical coarse pointing assembly 4 comprises a CPA mirror 4A, as shown in the schematic diagrams of fig. 12A, 12B and 13. The CPA mirror 4A is adapted to reflect a light beam received from an external optical flying stage or from another optical communication terminal OCT and/or to reflect a light beam received from the telescope TLA of the optical head unit 3 of the same optical communication terminal 1 to the external optical flying stage or the external optical communication terminal OCT. The CPA mirror 4A of the optical coarse directing assembly 4 is pivotable about an elevation axis 4B located offset from the center of gravity (CoG) of the CPA mirror 4A.

In one possible embodiment, the CPA mirror 4A is pivotable about the elevation axis 4B by a controllable elevation drive structure 4C of the optical coarse pointing assembly 4. In one possible embodiment, the controllable lifting drive structure 4C may comprise a winch drive structure, as shown in fig. 12B. In alternative embodiments, the lift drive structure 4C for the CPA mirror 4A may also comprise a gear drive structure. In the embodiment shown in fig. 12A, 12B, the coarse pointing assembly 4 further comprises an azimuth winch drive arrangement 4D for adjusting the azimuth angle.

The CPA mirror 4A comprises a mirror body with a reflective optical surface layer on a pivotable base element driven by a controllable driving structure 4C of the CPA mirror 4A. As shown in fig. 12A, 12B, in the preferred embodiment, the elevation axis 4B is located at the lower edge of the body of the CPA mirror 4A. The CPA mirror 4A is pivotable about an elevation axis 4B between a closed position and at least one open position. Fig. 12A, 12B show the CPA mirror 4A in an open position, wherein the light beam is reflected by the optical surface of the CPA mirror to establish or maintain an optical communication link OCL between the optical head unit 3 of the optical communication terminal 1 and an external optical flying platform, in particular another external optical communication terminal OCT, as shown in fig. 13. In the closed position, the telescope 3A of the optical head unit 3 is covered by the closed CPA mirror 4A. In the closed position, the CPA mirror 4A may in a possible embodiment also be locked by a controllable locking structure of the optical coarse pointing assembly 4. This provides additional protection to the optical surface from damage and contamination.

The coarse pointing assembly 4 is rotatable about an azimuth axis and/or an elevation axis 4B to establish or maintain an optical communication link OCL between the optical head unit 3 of the optical communication terminal OCT 1 and an external optical flying platform, in particular another optical communication terminal OCT 1. As shown in fig. 12A, 12B, 13, the optical surface layer of the CPA mirror 4A faces the front surface of the telescope 3A of the optical head unit 3 in the optical communication terminal 1. The optical surface layer of the CPA mirror 4A may in one possible embodiment be made of a highly reflective material, in particular gold. The optical surface layer is placed on the pivotable base element of the CPA mirror 4A. In a preferred embodiment the pivotable base element may be made of a physically lightweight material, in particular aluminium or glass ceramics.

The CPA assembly 4 of the optical communication terminal 1 is adapted to provide a basic angular movement of the laser beam in the acquisition mode of the optical communication terminal to establish an optical communication link OCL between the optical communication terminal 1 and an external flying platform or external optical communication terminal OCT. Furthermore, the basic angular movement of the optical laser beam may be controlled to compensate for the relative movement between the optical communication terminal 1 and the external flying platform or external optical communication terminal OCT to maintain the already established optical communication link OCL or external communication terminal OCT between the optical communication terminal and the external flying platform.

The CPA mirror 4A of the coarse directing assembly 4 serves as a laser beam directing structure. In the optical coarse pointing assembly 4 according to the present invention, the CPA mirror 4A is pivotable about an elevation axis 4B located offset from the center of gravity COG of the CPA mirror 4A. In one possible embodiment, the elevation axis 4B may be located at the lower edge of the CPA mirror 4A, as shown in the schematic diagrams of fig. 12A, 12B and 13. This unbalanced installation is possible because the coarse pointing assembly 4 operates in a microgravity environment. In a microgravity environment, this off-center configuration does not produce additional torque. The configuration of the optical coarse pointing assembly 4 as a pivotable CPA mirror 4A with an elevation axis 4B offset from the center of gravity CoG of the CPA mirror 4A allows for a compact form factor during transportation and commissioning of the optical communication terminal 1. Furthermore, the CPA mirror 4A protects the optical surfaces of the optical system from physical damage in its closed position and reduces possible contamination of the CPA mirror 4A and the telescope TLA of the optical head unit 3. In some cases, commissioning of the device may be associated with large vibrations and shocks, wherein the CPA structure according to the present invention may be fixed to avoid potential damage. In one possible embodiment, the scanning CPA mirror 4A, which is pivotable about the elevation axis 4B, may be secured with a locking structure. The offset center of gravity configuration of CPA mirror 4A provides a large amount of inertia about the rotational axis of elevation axis 4B, which can reduce the angular acceleration for a given torque. However, due to the lower height of the support structure for the elevation axis 4B, the moment of inertia about the azimuth axis is significantly reduced. This results in an increase in angular acceleration about the azimuth axis and a decrease in elevation axis acceleration. The positioning of the optical coarse pointing assembly 4 of the CPA mirror 4A pivotable about the elevation axis 4B at a position offset from the center of gravity CoG of the CPA mirror 4A increases the compactness of the structure and thus reduces the weight during transportation of the optical coarse pointing assembly 4 mounted to the optical communication terminal 1. In addition, the pivotable CPA mirror 4A may provide additional protection against physical damage or contamination.

Fig. 13 schematically shows the communication of two optical communication terminals 1,1 'over an optical communication link OCL, wherein the laser beam is reflected by a CPA mirror 4A, 4A'. In the schematic shown, the CPA mirrors 4A, 4A 'are in an open position and are arranged to maintain the optical communication link OCL between the optical head units 3 of the optical communication terminals 1, 1'. The coarse pointing assembly 4 is rotatable about an azimuth axis and an elevation axis 4B to maintain the optical communication link OCL between the optical head units 3 of the optical communication terminals 1, 1'. The CPA assembly 4 for each optical communication terminal 1,1 'is adapted to provide a basic angular movement of the optical laser beam in the acquisition mode of the optical communication terminal to establish an optical communication link OCL between the optical communication terminal 1 and an external optical communication terminal 1'. Further, the angular movement may be used to compensate for the relative movement between the optical communication terminal 1 and the external optical communication terminal 1' to maintain the optical communication link OCL established in the acquisition mode. The CPA mirror 4A comprises an angle relative to the front of the optical head unit 3, which angle is adjustable by a controllable driving structure. In a possible embodiment, the pivoting angle of the CPA mirror 4A about the elevation axis 4B is adjusted by a control unit of the optical communication terminal 1 adapted to control the driving structures 4C, 4D of the CPA mirror 4A. In one possible embodiment, the pivot angle may be continuously varied to cause substantial angular movement of the laser beam to establish and/or maintain the optical communication link OCL, as shown in FIG. 13. In one possible embodiment, the current pivot angle of the CPA mirror 4A relative to the front surface of the optical head unit 3 may also be notified to the external flying platform and/or the external optical communication terminal via the optical communication link OCL, so that the external flying platform or the external optical communication terminal may adjust its own pivot angle accordingly. This results in a more robust optical communication link OCL between the optical communication terminal 1 and the external flying platform.

The optical communication terminal 1 as shown in the block diagram of fig. 4 can transmit and receive data and track a laser beam using a shared telescope aperture. In the transmission signal path, a laser beam is generated and coupled into a shared (collimated) beam path by a dichroic mirror 3D. The transmitted light exits through telescope TLA to widen the collimated transmitted laser beam to the target beam diameter. In one possible embodiment, the optical surface of the telescope lens 3A may be coated with an anti-reflection coating to minimize any kind of back reflection into the receiver system of the transceiver 2. The optical system may be manufactured in a clean room environment to reduce backscatter caused by surface contaminants, such as dust particles. A small fraction (e.g. less than 0.5%) of the light is back-scattered or reflected into the optical system, which may cause self-blind effects, in particular on the tracking sensor 8 provided in the receiver unit 2B. Since the transmitted laser beam typically comprises an intensity that is many orders of magnitude higher than the light received from the opposite end. This may negatively impact tracking and communication performance.

Fig. 14A schematically illustrates the problem caused by back-reflected and back-scattered light, especially at a receiving sensor, such as the tracking sensor 8 of the receiver unit 2B. Rays may be emitted from the emitting arm and back reflected or backscattered at the telescope surface of the telescope lens 3A. The ray hitting the receiving sensor may cause a self-blinding effect. In the receiving arm, the light rays or beams pass through optical components 10-1, 10-2, 10-3, 10-4, such as optical filters and lenses. The amount of return light can be minimized by a high degree of cleanliness, which results in few scattering particles and special absorption measures, such as coatings or specific geometries on the telescope of the optical telescope TLA. If all potential reflecting surfaces in the telescope system TLA are curved, the returned light reaches the receiving sensor 8 of the receiver unit 2B only on a narrowly confined laser beam, as shown in fig. 14A. According to the optical communication terminal 1 of the second aspect of the present invention, at one of the optical surfaces of the optical component 10-i (e.g., the optical component 10-1 shown in fig. 14B) within the optical receiver unit 2B, such a narrow return beam will be blocked by a special spatial filter or central blocking coating 11. The at least one central barrier coating is adapted to reduce the return light by several orders of magnitude. At the same time, the at least one central shielding coating 11 only slightly reduces the received light power, for example by about 10% (0.5 dB). Fig. 14B shows an embodiment of an optical communication terminal 1 comprising at least one central shading coating 11 on the optical component 10.

According to a second aspect, the present invention provides an optical communication terminal 1 comprising an optical telescope TLA comprising at least one lens 3A adapted to enlarge the diameter of a light beam received from a light emitter unit 2A of the optical communication terminal and to reduce the diameter of a terminal from an external optical flying platform or a light receiver unit 2B for the optical communication terminal 1. In the optical communication terminal 1 as shown in the embodiment of fig. 14B, at least one central shielding coating 11 is provided on the surface of the optical component 10 of the optical receiver unit 2B. The at least one central shading coating 11 is adapted to suppress light backscattered and/or reflected by the lens 3A of the optical telescope TLA of the optical communication terminal 1. The center shielding coating 11 is provided on the surface of the optical component 10 of the light receiver unit 2B of the optical communication terminal 1. The central shielding coating 11 is composed of a material that is opaque in a predetermined communication frequency range of the optical communication terminal 1. The central masking coating 11 used on the front surface of the optical component 10 comprises an absorbing or reflecting material. In a preferred embodiment, the central shielding coating 11 may comprise a circle having a predetermined radius r. The center shielding coating 11 is provided at the center of the optical member 10 of the light receiver unit 2B. The optical component 10 in the optical communication terminal 1 may include an optical lens of the optical receiver unit 2B, for example. In the embodiment shown in fig. 14B, the optical telescope TLA of the optical communication terminal 1 includes an on-axis telescope lens 3A. The central shielding coating 11 is disposed in the center of the received-light signal path of the light receiver unit 2B. In one possible embodiment, the on-axis telescope lens 3A can comprise a monolithic optical lens. In alternative embodiments, the optical telescope TLA can include multiple pieces of optical lenses. The telescope lens 3A is made of a uniform material transparent in a predetermined communication frequency range of the optical communication terminal 1. In one possible embodiment, the material of the optical telescope lens 3A comprises a uniform material. In one possible embodiment, the homogeneous material of the telescope lens 3A can comprise silicon or germanium.

As shown in the embodiment of fig. 14B, the optical telescope lens 3A of the telescope TLA can include a front surface FSUR and a rear surface RSUR. In one possible embodiment, the front surface FSUR of the optical telescope lens 3A is an aspherical convex front surface. The rear surface RSUR may include a concave rear surface that is spherical or aspherical. The optical telescope lens 3A shown in the embodiment of fig. 14B is provided to expand the laser beam emitted by the light emitter unit 2A and passing through the rear surface RSUR of the optical telescope lens 3A, and is further designed to reduce the diameter of the laser beam received through the front surface FSUR of the optical telescope lens. Then, the reduced laser beam is output to the light receiver unit 2B via the folding mirror 12 and the dichroic mirror 3D through the rear surface RSUR of the optical telescope lens 3A.

As shown in fig. 14B, in the illustrated embodiment, a central shielding coating 11 is provided on the surface of the optical member 10-1 of the light receiver unit 2B. In the embodiment shown, the central shielding coating 11 is adapted to shield the tracking sensor 8 or any other optical sensor of the light receiver unit 2B of the optical communication terminal 1 from light backscattered and/or reflected by the optical telescope TLA.

The attenuation provided by the central masking coating 11 shown in fig. 14B depends on the ratio between the central masking radius r and the beam radius r of the back-reflected beam, as shown in fig. 15.

Fig. 15 shows the total power (watts) of the receiving sensor 8 at a transmit power of 1 watt. The radius of the central shroud is in millimeters. As can be seen from fig. 15, the energy or power reflected onto the tracking sensor 8 decreases with increasing shielding radius r. In another possible embodiment, the side surface of the conical portion of the optical telescope lens 3A shown in fig. 14B may comprise a plurality of suppression steps 6 adapted to further suppress backscattered and/or reflected light. The front surface FSUR of the telescope lens 3A may be adapted to receive a laser beam from the coarse pointing assembly 4 of the optical communication terminal 1, as shown in the block diagram of fig. 4.

Fig. 14B shows that the isolation between the transmitted laser beam and the tracking sensor 8 is about 60dB without providing a central shielding. Assuming a receive beam radius of 5mm and a further attenuation of 25dB, the loss in the receive beam can beA central masking coating 11 with a radius of 1.5mm is achieved. The illustrated embodiment allows the use of an on-axis telescope lens design despite potential back reflection and/or scattering effects. Different kinds of configurations of the telescope lens 3A can be used for this setting. Providing an on-axis lens telescope TLA provides advantages over off-axis lens telescopes or off-axis mirror telescopes. The on-axis lens telescope is easy to align, and in addition, the manufacturing cost is significantly reduced, and the size is more compact.

Fig. 16 shows a block diagram of the operation of the optical transceiver 2 according to another aspect of the present invention. According to a third aspect, the present invention provides an optical transceiver 2, the optical transceiver 2 having an optical transmitter unit 2A adapted to transmit optical communication signals in at least one predetermined communication frequency range and an optical receiver unit 2B adapted to receive optical communication signals in the predetermined communication frequency range. The optical transmitter unit 2A of the optical transceiver 2 according to the third aspect of the present invention includes a laser diode LD of the transmitter and modulation unit 13, as shown in fig. 16. The laser diode of the transmitter and modulation unit 13 is adapted to generate a laser beam which is amplified by the enhanced erbium doped fiber amplifier EDFA14 of the optical transmitter unit 2A. In the optical transceiver 2 according to the third aspect of the present invention, the amplification gain G of the boosted EDFA14 is reduced to reduce the broadband EDFA amplified spontaneous emission noise ASE generated by the boosted EDFA 14. The corresponding increase in the output power of the laser beam produced by the laser diode LD of the laser and transmitter modulation unit 13 compensates for the reduced amplification gain G of the boost EDFA 14. The amplified light is produced by an enhanced erbium doped fiber amplifier EDFA14 at the optical transmitter unit 2A and may be provided to a TX collimator 15, as shown in fig. 4. In addition to the desired stimulated emission, unwanted amplified spontaneous emission noise ASE is generated due to the physical nature of the optical amplification in the boosted EDFA 14. As shown in the block diagram of fig. 16, the amplified signal is directed to a pre-point assembly (PAA) 3E and then to a Dichroic Beamsplitter (DBS) 3D. The task of the Dichroic Beam Splitter (DBS) 3D is to direct the transmitted light to the telescope lens 3A of the optical telescope TLA after reflection at the Fine Pointing Assembly (FPA) 3A. Since not all of the transmitted light is directed out of the telescope TLA, part of the light is reflected back to the optical system. This may occur due to non-ideal anti-reflection coatings at the TLA surface of the optical telescope lens 3A and due to contaminants that may accumulate during the manufacturing process. The back reflected light reaches a Dichroic Beam Splitter (DBS) 3D and passes towards a receive path where an optical filter 10 may be provided to reject background light. The optical filters 10 are centered on a reception wavelength, for example 1565nm. The optical filters 10 suppress transmitted light at 1540nm, for example, however, ASE noise generated by the boost EDFA14 is still present at the receive wavelength, so it can pass through these optical filters 10 and can reach the high sensitivity tracking sensor 8 of the optical receiver unit 2B after the wavelength-independent intensity beam splitter IBS. To avoid saturation of the tracking sensor 8 with ASE noise, the amplification gain of the boost EDFA14 is automatically reduced to reduce the broadband EDFA-ASE noise generated by the boost EDFA 14. To compensate, the output power of the laser beam generated by the laser diode 13 is increased to the same extent. The suppression of the reverse reflection ASE noise also reduces interference with the relatively weak received communication signal in the Single Mode Fiber (SMF) 17 of the preamplifier EDFA 18 coupled to the receiver unit 2B.

The optical transmitter unit 2A is adapted to transmit an optical transmission signal at a predetermined transmission wavelength within a predetermined communication frequency range of the optical communication terminal 1. The optical receiver unit 2B is adapted to receive an optical reception signal of a predetermined reception wavelength within a predetermined communication frequency range of each optical communication terminal 1. The optical transmission signal of the optical transmitter unit 2A is supplied to the telescope TLA of the optical communication terminal 1 via a pre-point assembly (PAA) 3E, a Dichroic Beam Splitter (DBS) 3D, and via a Fine Pointing Assembly (FPA) 3C. In one possible embodiment, the optical receiver unit 2B of the optical communication terminal 1 comprises at least one optical bandpass filter BPF constituting an optical component 10 adapted to suppress light outside the reception filter band centered on the reception wavelength of the optical receiver unit 2B. The optical band-pass filter BPF of the optical receiver unit 2B is adapted to suppress reflected light at the transmission wavelength of the optical transmitter unit 2A of the optical communication terminal 1. The EDFA-ASE noise generated by the boosted EDFA14 of the optical transmitter unit 2A may include spectral overlap with the receive filter band of the at least one optical band-pass filter BPF of the optical receiver unit 2B within the optical communication terminal 1. The optical reception signal having passed through the optical band-pass filter BPF of the optical receiver unit 2B is divided by the Intensity Beam Splitter (IBS) 16 into a first optical signal supplied to the tracking sensor 8 of the optical receiver unit 2B and a second optical signal supplied to the optical signal demodulator 19 of the optical receiver unit 2B of the optical communication terminal 1 via the single mode optical fiber (SMF) 17 and the EDFA pre-amplifier 18, as shown in fig. 16.

In one possible embodiment, in the calibration mode of the optical communication terminal 1, the control unit 20 of the optical transceiver 2 may control the adjustment of the amplification gain of the boosted EDFA14 of the optical transmitter unit 2A and the corresponding adjustment of the output power of the laser diode 13 of the optical transmitter unit 2A to reduce the EDFA ASE noise. The ASE noise power from the boost EDFA14 is reduced so that it cannot blindly and does not interfere with the communication signal that might be implemented in the range of 43dbm of a 10Gbit/s system. The ASE power is suppressed by simultaneously increasing the optical power from the seed laser diode LD to reduce the gain G of the boost EDFA 14. For example, when the input power is 0dBm, the boosted EDFA14 needs to provide 30dB of gain in order to obtain +30dBm of output power from the boosted EDFA 14. If the input power is increased to +4dBm, the booster EDFA14 need only provide 26dB gain to achieve an output power of +30 dBm. The reduction in gain of the boosted EDFA14 results in different benefits. It reduces ASE noise power to reduce self-blindness of the tracking sensor 8. Furthermore, it reduces the interference between ASE noise and weak communication signals in the receiving side preamplifier EDFA 18. In addition, the boosted EDFA14 operating at lower gain consumes less electrical power, which eases the thermal management system, increases reliability and provides more structural integrity.

Claims

1. An optical communication terminal OCT, (1) comprising an optical Telescope (TLA) adapted to enlarge a beam diameter received from a light emitter unit (2A) of the optical communication terminal OCT (1) and to reduce a beam diameter received from an external optical flying platform for a light receiver unit (2B) in the optical communication terminal OCT (1), wherein at least one central shielding coating (11) is provided on a surface of an optical component (10) of the light receiver unit and adapted to suppress light backscattered and/or reflected by the optical astronomical Telescope (TLA) of the optical communication terminal OCT.

2. Optical communication terminal according to claim 1, wherein the central shielding coating (11) comprises a material that is opaque in a predetermined communication frequency range of the optical communication terminal OCT (1).

3. Optical communication terminal according to claim 1 or 2, wherein the central shading coating (11) comprises an absorbing material or a reflecting material.

4. An optical communication terminal according to any of claims 1 to 3, wherein the central shielding coating (11) comprises a circular shape with a predetermined radius r.

5. The optical communication terminal according to any one of claims 1 to 4, wherein the central shielding coating (11) is provided at the center of the optical component (10) of the optical receiver unit (2B).

6. The optical communication terminal according to any of claims 1 to 5, wherein the optical component (10) comprises an optical lens of an optical receiver unit (2B) of the optical communication terminal OCT (1).

7. Optical communication terminal according to any of claims 1 to 6, wherein the optical Telescope (TLA) of the optical communication terminal (1) comprises an on-axis lens telescope without a central shielding.

8. Optical communication terminal according to claim 7, wherein the on-axis lens Telescope (TLA) comprises a single piece optical lens (3A) or a plurality of pieces of optical lens made of a transparent material, which is transparent within a predetermined communication frequency range of the optical communication terminal OCT (1).

9. An optical communication terminal according to claim 8, wherein the material of the monolithic optical lens (3A) comprises silicon or germanium or other homogeneous material.

10. The optical communication terminal according to any of claims 7 to 9, wherein the optical telescope lens (3A) of the Telescope (TLA) comprises an aspherical convex Front Surface (FSUR) and a spherical or aspherical concave Rear Surface (RSUR).

11. The optical communication terminal according to claim 10, wherein the optical telescope lens (3A) is designed to enlarge a laser beam emitted by the optical transceiver unit (2A) and passing through a Rear Surface (RSUR) of the optical telescope lens (3A), and to reduce a diameter of the laser beam received through a Front Surface (FSUR) of the optical telescope lens (3A), wherein the reduced laser beam is output to the optical receiver unit (2B) through a Rear Surface (RSUR) of the optical telescope lens (3A) via a dichroic mirror (3D).

12. Optical communication terminal according to any of claims 1 to 11, wherein the central shielding coating (11) provided on the surface of the component (10) of the optical receiver unit (2B) is adapted to shield the tracking sensor (8) in the optical receiver unit (2B) of the optical communication terminal OCT (1) against light backscattered and/or reflected by the optical Telescope (TLA) of the optical communication terminal OCT (1).

13. Optical communication terminal according to any of claims 1 to 12, wherein the central shielding coating (11) provides a ratio attenuation depending on the central shielding radius r of the received light beam and the beam radius r.

14. The optical communication terminal according to any of the claims, wherein the side surface of the tapered portion of the optical telescope lens (3A) comprises N suppression steps adapted to suppress backscattered and/or reflected light.

15. Optical communication terminal OCT (1) according to any one of claims 10 to 14, wherein the Front Surface (FSUR) of the telescope lens (3A) is adapted to receive a laser beam from a coarse pointing assembly (4) of the optical communication terminal (1).