Generation of optical pulses with controlled orthogonal value distribution

Abstract

The present invention relates to a device for generating optical pulses, comprising a laser configured to output the optical pulses and a pulse driver configured to provide electrical pulses to the laser to drive the laser. In addition, the pulse driver is configured to provide the laser with the electrical pulses having amplitudes / intensities that obey a preset probability distribution, so that orthogonal values ​​of the optical pulses obey another preset probability distribution.

Description

Technical Field

[0001] The present invention relates to a device and a method for generating optical (laser) pulses with orthogonal values ​​having a certain preset probability distribution. Background Art

[0002] Communication and cryptography based on electromagnetic pulses, for example in the form of optical laser pulses, are gaining increasing interest. It is necessary to develop small, high-performance optical transmitters for classical and quantum optical communications and for generating quantum random numbers with a predefined distribution.

[0003] Many transmitters used in optical communications use lasers and external electro-optic modulators (such as phase or intensity modulators) to encode information onto pulses of laser light. For example, coherent optical communications use electro-optic modulators to encode information in electromagnetic field quadrature, which is measured at the receiving end using coherent detection.

[0004] The above quadratures, denoted as p and q, correspond to the two perpendicular components of the magnitude vector in optical phase space (e.g., and Among them, A and are the amplitude and phase of the optical pulse, respectively). In telecommunications, the two quadrature components are also called the in-phase and quadrature components of the electromagnetic field, respectively.

[0005] Electro-optic modulators are usually based on materials whose refractive index or absorption varies with an applied electric field. For example, modulators based on LiNbO3 or semiconductor waveguides are widely used in transmitters to induce amplitude (intensity) and phase modulation. However, they suffer from several limitations, such as: (1) high power consumption of the drive electricity, (2) large device size that limits the compactness of the transmitter, (3) instability over time due to fluctuations in the operating point, and (4) limited electro-optic bandwidth. Therefore, it is desirable to make transmitters that circumvent the need for electro-optic modulators, so that the unit has high performance, low cost, compactness, and robustness.

[0006] In addition to classical communication, some quantum communication schemes also rely on external electro-optical modulators. In addition, in quantum communication, the above limitations will be more severe due to the low signal-to-noise ratio of the system, which is a typical feature when weak light is transmitted over long distances. In these cases, the stability and fluctuations of the modulator will lead to very low performance.

[0007] Among all quantum communication technologies, Quantum Key Distribution (QKD) is one of the most mature technologies. QKD allows two parties to exchange keys, where the security of the keys is guaranteed by the principles of quantum physics. In standard QKD, the transmitter (Alice) sends a quantum signal to the receiver (Bob). QKD protocols can be divided into two groups, Discrete Variable Quantum Key Distribution (DV-QKD) and Continuous Variable Quantum Key Distribution (CV-QKD) protocols. In DV-QKD, the key is encoded by assigning discrete values ​​to the degrees of freedom of a single photon. For example, the BB84 DV-QKD protocol uses four polarization states to encode the key. In CV-QKD, the quantum signal corresponds to a weakly decaying pulse (weakly coherent state) with key information encoded by assigning orthogonal continuous values ​​to the electromagnetic field. For example, the GG02 CV-QKD protocol uses orthogonal optical coherent states modulated according to a random Gaussian distribution.

[0008] DV-QKD requires expensive single-photon technology and dedicated fiber channels, which greatly limits its application in real-world scenarios. CV-QKD removes the need for single-photon technology to measure the orthogonality of optical pulses by using coherent detection with a strong reference pulse, called a local oscillator (LO). One advantage of CV-QKD over DV-QKD is that its security is less affected when the quantum channel is transmitted in cooperation with a higher-power classical channel. CV-QKD implementations can be implemented using standard components developed for coherent optical communications, sharing hardware and channels with classical communications. To date, all CV-QKD implementations use cumbersome external electro-optical modulator schemes to modulate the phase and amplitude of optical pulses. Therefore, there is a need to improve CV-QKD transceivers, increase robustness, simplify schemes, reduce costs, and achieve higher bit rates.

[0009] In view of the above, an object of the present invention is to provide a device and method for generating optical pulses in communication and cryptography scenarios so as to alleviate the above problems. Summary of the invention

[0010] The present invention achieves the above-mentioned object by providing a device for generating optical pulses, the device comprising a laser configured to output the optical pulses (optical pulses, both terms are interchangeable in this article) and a pulse driver configured to provide electrical pulses to the laser to drive the laser. In addition, the (electrical) pulse driver is configured to provide the laser with the electrical pulses having an amplitude / intensity that obeys a preset probability distribution (in a timely manner, i.e., within a time repetition period / duty cycle of the electrical pulses) so that the orthogonal values ​​of the optical pulses obey another preset probability distribution.

[0011] According to an embodiment, the device comprises a control means configured to repeatedly operate the laser a) below the lasing threshold for a first preset time period and b) subsequently above the lasing threshold for a second preset time period so as to randomize the phase of the light pulses. The lasing threshold is represented by a certain threshold pump power or threshold current and is given by a certain state where the small signal gain is exactly equal to the resonant cavity loss.

[0012] Furthermore, the above object is achieved by providing a method for generating a first optical pulse having orthogonal values ​​of a preset probability distribution, the method comprising the steps of generating a first electrical pulse having an amplitude / intensity that obeys a probability distribution (e.g., a Rayleigh distribution) and driving a first laser by means of the generated first electrical pulse. In this method, driving the first laser comprises repeatedly driving the first laser a) below the laser threshold for a first preset time period and b) then above the laser threshold for a second preset time period, so that the phase of the first optical pulse output by the first laser based on the first electrical pulse is randomized in a sequence of continuous optical pulses (particularly, the phase may obey a uniform distribution).

[0013] The orthogonality depends on the amplitude (intensity) and phase of the optical pulses. According to the present invention, the distribution of the orthogonality is controlled by the configuration of a preset distribution of electrical pulses provided by an electrical pulse driver / generator. By repeatedly driving / operating the laser below and above the laser threshold, a continuous sequence of optical pulses with an approximately uniform distribution of optical phases can be achieved, i.e., a completely randomized phase with a uniform distribution that completely covers the entire range from 0 to 2 continuous radiation.

[0014] The pulse driver may be configured to provide electrical pulses to the laser that obeys a Rayleigh distribution, so that the amplitude (intensity) of the optical pulse also obeys a Rayleigh distribution. Combined with the phase of the optical pulse obeying a uniform distribution that is a Gaussian distribution, the orthogonal values ​​of the optical pulse result (each and Among them, A and The amplitude and phase of the optical pulse obey the Gaussian distribution.

[0015] Advantageously, by means of the embodiments of a device and a method thus provided, a high performance optical transmitter for classical and quantum communication purposes, and also for quantum cryptography applications, can be realized. The device can be used as part of a quantum random number generator and / or quantum key distribution / exchange system.

[0016] The device may also include a beam splitter and an unbalanced Mach-Zehnder Interferometer. In this embodiment, the pulse driver may be configured to generate and provide electrical pulses having not only a preset probability distribution but also electrical pulses having a probability distribution interleaved with electrical pulses having a constant / equal amplitude. The unbalanced Mach-Zehnder Interferometer is used to interfere with adjacent electrical pulses (one of which has the constant amplitude and the other has an amplitude according to the probability distribution). Thus, a reliable quantum random number generator with a preset distribution may be provided.

[0017] In addition, a system is provided, comprising a device according to one of the above embodiments, and further comprising a detector device (receiving end), configured to receive the optical pulse output by the laser and comprising a balanced detector means. For example, the detector means can be used to perform orthogonal measurement and thereby detect the random number code transmitted in the optical pulse output by the laser, and receive a quantum key.

[0018] For example, the detector means of the system may also include another laser (acting as a local oscillator, providing a reference signal / light pulse for measuring quadrature values) and / or a 90° optical hybrid for performing the quadrature measurement.

[0019] According to some embodiments, the system can operate as a quantum cryptography system, in particular, a continuously variable quantum key distribution (CV-QKD) system. In this case, the device operates as Alice (name) and the detector device operates as Bob (name). According to one of these embodiments, the device includes a beam splitter for splitting the optical pulses output by the laser, another laser used as a local oscillator for outputting relatively strong pulses with constant amplitude (relatively high amplitude) and another detector device for measuring orthogonal values. Optionally, in addition to the beam splitter and the other detector device, no other laser is provided, but the local oscillator is transmitted from Alice to Bob by means of relatively strong pulses of equal amplitude interleaved with pulses obeying the above-mentioned probability distribution, such as a Rayleigh distribution. In all these cases, the other detector device at the Alice end can have a similar construction to the above-mentioned detector device.

[0020] According to an embodiment, the device of the system comprises another detector device. The detector device of this embodiment may comprise a balanced detector and a 90° optical mixer for measuring the quadrature value of the optical pulse provided by the laser of the device by means of a reference pulse received from the Bob end. The laser optical pulse output by the laser of the device driven by the pulse driver is split by a beam splitter. One of the outputs of the beam splitter is provided to an attenuator and leaves the device, for example, via a circulator, to be received by the detector device of the system.

[0021] The other output of the beam splitter is fed to the other detector means provided at the device (Alice) end. The detector means of the system (i.e. Bob) comprises a local oscillator in the form of another laser, and another beam splitter for splitting the light emitted by the other laser. One of the outputs of the other beam splitter is used by a balanced detector at the Bob end to determine the quadrature at the Bob end, while the output of the other beam splitter (via one of the LO channels) is provided to the device for determining the quadrature at the Alice end.

[0022] In addition, a method for generating random numbers is provided herein. The method comprises the steps of the above method for generating light pulses with a predetermined probability distribution of orthogonal values. The uniform distribution of the phases of the light pulses output by the laser ensures randomness. The random numbers can be obtained by optical interference and subsequent measurement using an appropriate detector device.

[0023] For example, the optical pulses generated with Rayleigh amplitude distribution and approximately uniform random phase can be interfered by a reference laser (local oscillator) and detected by a balanced detector. In this case, the detected values ​​will be truly random (due to phase diffusion) and follow a Gaussian distribution. In addition, by interleaving optical pulses with constant amplitude and optical pulses with a Rayleigh distribution and interfering adjacent pulses using an unbalanced Mach-Zehnder interferometer, a Gaussian distributed QRNG (Quantum Random Number Generator) can be obtained. A QRNG with a specific distribution can be used for CV-QKD that requires random numbers with continuous values ​​following a specific probability distribution.

[0024] Thus, a method for generating random numbers is provided, comprising the steps of the method for generating light pulses with a predetermined probability distribution of orthogonal values ​​as described above, and further comprising:

[0025] generating a second electrical pulse comprising the first electrical pulse, subject to the probability distribution and interleaved with a third electrical pulse of equal amplitude;

[0026] driving said first laser to output said first light pulse by means of said generated second electrical pulse; and

[0027] Interfering adjacent ones of said generated second electrical pulses by means of an interferometer, in particular, by means of an unbalanced Mach-Zehnder interferometer.

[0028] The disclosed method thus allows simplifying or even avoiding electronic post-processing and thus enables higher random number generation rates to be obtained.

[0029] In addition, according to a specific embodiment, a quantum key distribution method for encrypting communication data is provided. According to one embodiment, a method for distributing a quantum key is provided, the method comprising the steps of the method for generating light pulses with a predetermined probability distribution of orthogonal values ​​as described above, and further comprising

[0030] A) at a transmitting end (Alice): generating a second electrical pulse having a constant amplitude; driving a second laser (used as a local oscillator) by means of the generated second electrical pulse to output a second optical pulse (reference optical pulse); splitting the first optical pulse to obtain a first part of the first optical pulse and a second part of the first optical pulse; splitting the second optical pulse to obtain a first part of the second optical pulse and a second part of the second optical pulse; measuring a quadrature value of the first part of the first optical pulse using the first part of the second optical pulse; multiplexing the second part of the first optical pulse and the second part of the second optical pulse to obtain a multiplexed optical pulse; attenuating the multiplexed optical pulse to obtain an attenuated multiplexed optical pulse; and transmitting the attenuated multiplexed optical pulse to a receiving end (Bob) (connected to the transmitting end through a communication channel);

[0031] as well as

[0032] B) At the receiving end: receiving the transmitted attenuated multiplexed optical pulses and measuring the orthogonal values ​​of the received attenuated multiplexed optical pulses, for example, by means of another beam splitter, a delay component, a 90° optical hybrid and a balanced detector (see also the detailed description below).

[0033] According to one embodiment, a method for distributing a quantum key is provided, the method comprising the steps of the method for generating light pulses with a predetermined probability distribution of orthogonal values ​​as described above, and further comprising:

[0034] A) At a transmitter (Alice):

[0035] generating a second electrical pulse comprising the first electrical pulse, subject to the probability distribution and interleaved with a third electrical pulse of equal amplitude;

[0036] driving said first laser to output said first light pulse by means of said generated second electrical pulse;

[0037] Splitting the first light pulse to obtain a first portion of the first light pulse and a second portion of the first light pulse;

[0038] measuring a quadrature value of the first portion of the first light pulse;

[0039] attenuating the second portion of the first light pulse to obtain an attenuated light pulse; and

[0040] Transmitting the attenuated optical pulse to a receiving end (connected to the transmitting end through a communication channel);

[0041] as well as

[0042] B) At the receiving end:

[0043] The quadrature value of the received attenuated optical pulse is measured, for example, by means of a further beam splitter, a delay element, a 90° optical hybrid and a balanced detector (see also the detailed description below).

[0044] In this embodiment, only a single (first) laser is used to reduce the complexity of the structure.

[0045] According to another embodiment, a second laser is used which behaves as a local oscillator (i.e. a true local oscillator) generated at the receiving end. According to this embodiment, a method for distributing a quantum key is provided, the method comprising the steps of the method for generating optical pulses with a predetermined probability distribution of orthogonal values ​​as described above, and further comprising

[0046] A) At a transmitter (Alice):

[0047] Splitting the first light pulse to obtain a first portion of the first light pulse and a second portion of the first light pulse;

[0048] attenuating the first portion of the first light pulse by an attenuator to obtain an attenuated light pulse; and

[0049] Transmitting the attenuated optical pulse, in particular, via a first circulator, to a receiving end (connected to the transmitting end via a communication channel);

[0050] as well as

[0051] B) At the receiving end:

[0052] generating reference light pulses by a second laser (acting as a local oscillator);

[0053] Splitting the reference light pulse to obtain a first part of the reference light pulse and a second part of the reference light pulse;

[0054] measuring a quadrature value of said attenuated optical pulse by means of said first portion of said reference optical pulse, in particular, received via a second circulator; and

[0055] Transmitting, in particular, transmitting the second part of the reference light pulse to the transmitting end via a second circulator;

[0056] as well as

[0057] C) at the transmitting end:

[0058] receiving a second portion of said reference light pulse, in particular via said first circulator; and

[0059] A quadrature value of the second portion of the first light pulse is measured by means of the received second portion of the reference light pulse.

[0060] All of the above-described embodiments of the apparatus of the present invention can be used to implement at least some of the steps of all of the above-described embodiments of the method of the present invention.

[0061] Other features and advantages of the present invention will be described with reference to the accompanying drawings. In the specification, reference is made to the accompanying drawings which are intended to illustrate preferred embodiments of the present invention. It should be understood that such embodiments do not represent the full scope of the present invention.

[0062] Figure 1 A schematically illustrates an embodiment of an apparatus for generating optical pulses having controlled distributed quadrature values, and Figure 1 B illustrates an apparatus for measuring quadrature values.

[0063] Figure 2 A Gaussian fit of measurements of values ​​of an orthogonality obtained from an apparatus according to the invention is shown.

[0064] Figure 3 An embodiment of a system for generating and detecting random numbers is schematically illustrated, including a laser, an unbalanced Mach-Zehnder interferometer, and a photodetector.

[0065] Figure 4 An embodiment of a continuously variable quantum key distribution (CV-QKD) system with a "transmitted local oscillator" as provided herein is illustrated.

[0066] Figure 5 Another embodiment of a CV-QKD system is shown.

[0067] Figure 6 An embodiment of a CV-QKD system with a "true local oscillator" is illustrated.

[0068] The present invention provides an apparatus and method for generating light / optical pulses with orthogonal values ​​obeying a probability distribution, which can be stably used in the context of communication and cryptography applications, in particular, can be stably used to generate random numbers. In addition, a system and method for generating and detecting light pulses are also provided.

[0069] Figure 1A and 1B illustrate an embodiment of the present invention. The optical pulses are generated by a laser. The laser may include a laser diode (LD) that provides single-mode operation and high modulation bandwidth. The laser is supplied with electrical pulses that drive the laser to a desired duty cycle below and above the laser threshold and obey a preset probability distribution. Each repetitive duty cycle consists of a first time period in which the laser is operated below the laser threshold and a second time period in which the laser is operated above the laser threshold. The duration of the electrical pulses may be less than 50% of the repetition period / cycle of the generated pulse train. The orthogonality of the electromagnetic field is defined as and Among them, A and are the amplitude and phase of the optical pulse, respectively. Therefore, the preset amplitude distribution for A and The desired distribution for p and q is obtained by combining the distributions of . In particular, it is possible to generate optical pulses with a preset amplitude distribution and an approximately uniformly distributed optical phase.

[0070] The laser is driven by electrical pulses provided by a pulse driver that supplies electrical pulses to the laser device. The laser is modulated from below the laser threshold to above the laser threshold by means of the pulse driver. For example, the laser device is first operated at a current at least about 30% below the threshold, for example, in the range of 50% to 30% below the threshold, to simultaneously produce strong cavity field decay and highly amplified spontaneous emission (ASE). This decays all previous coherence to negligible levels, while the ASE, itself a product of vacuum fluctuations, provides a shielding field with a truly random phase. The laser is then simply brought above the laser threshold, for example, until it is 10%, 20% or 30% above the laser threshold or even more, to rapidly amplify the cavity field to macroscopic levels, for example, to a peak power of tens of mV. This amplification is electrically increased in value and is therefore independent of the optical phase.

[0071] By modulating the laser from below the laser threshold to above, an optical pulse with a completely randomized phase is generated. For example, according to a specific example, the laser can include a laser diode emitting about 852nm and having a 36mA threshold. It can be electrically modulated at 100MHz using an electrical pulse of about 1ns duration. According to these instructions, a phase-randomized coherent light / optical pulse with a time width of 400ps and a peak power of 3.5mW can be generated. It should be noted that an optical frequency isolator can be placed right after the laser to avoid back reflections into the cavity of the same laser diode. The laser source can also be operated at other wavelengths, such as at about 1300 or 1500nm, which are beneficial to optical communication fibers.

[0072] The electrical pulses provided by the pulse driver follow the Figure 1 A is a preset distribution illustrated at the top. By appropriately choosing the temporal distribution of the electrical pulses for a given duty cycle, the amplitude distribution of the optical pulses, and therefore the distribution of the values ​​of the quadrature, can be controlled. It should be noted that a bias voltage can be added to the electrical signal to drive the laser from well below threshold to close to threshold. This bias allows the amplitude of the optical pulses to follow a desired distribution and allows the phase to be appropriately randomized.

[0073] For example, using a driving electrical pulse that follows a Rayleigh distribution can make the quadrature values ​​(p and q) follow a Gaussian probability distribution. In this case, the Gaussian distribution for the quadrature values ​​derives from the Rayleigh distribution of the phase and amplitude applied to the optical pulse by the electrical pulse, which is approximately uniformly distributed. Figure 2 Experimental results obtained by driving the laser with Rayleigh distributed electrical pulses are shown. The resulting distribution of the values ​​of the measured quadrature turns out to be close to Gaussian.

[0074] In detail, the measurement result is achieved by interfering with an external laser such as a continuous wave (CW) laser and measuring the interference result with a balanced detector BD (Balanced Detector). The balanced detector BD may include a photodiode for detecting laser pulses. The measurement is performed using a 2 nanosecond pulse with a repetition rate of 100 MHz. Optical pulses whose amplitude follows a Rayleigh distribution and whose phase follows an approximately uniform distribution can cause the orthogonal distribution to approximate a Gaussian distribution. The variance of the Gaussian distribution can be controlled by adjusting the variance of the Rayleigh distribution. In all other embodiments described herein and in the context, generating Gaussian distributed orthogonal optical pulses when using Rayleigh distributed electrical pulses is used only as an example. By changing the time distribution of the electrical pulses, other probability distributions (e.g., mixed Rayleigh distributions) are also possible.

[0075] Due to the phase diffusion process, the phase of the emitted light pulse is truly random and follows an approximately uniform distribution. The use of phase diffusion, combined with the control of the electrical signal distribution, allows the generation of quantum random numbers with a preset continuous distribution. For example, by using an external laser to measure quadrature, a quantum random number generator can be produced that provides random numbers following a Gaussian distribution.

[0076] Optical pulses provided by lasers can be transmitted via a communication (quantum) channel, for example, via an optical fiber or a waveguide. Figure 1 B can be used to obtain Figure 2The experimental results shown are received by a detector device. The detector device includes an external laser as a local oscillator LO (Local Oscillator) that outputs a reference light pulse, a 90° optical hybrid, and two balanced detectors BD. This scheme is called heterodyne detection, in which the orthogonal p and q of each pulse are measured simultaneously. Alternatively, homodyne detection can be implemented, in which both p and q of each pulse are measured by randomly shifting the phase of the local oscillator using an external modulator.

[0077] Figure 3 An embodiment of a system including an apparatus for generating and detecting random numbers is illustrated. The laser is again driven by an electrical pulse pattern in which electrical pulses of constant amplitude are interleaved between Rayleigh distributed pulses, e.g. Figure 3 The top row shows (pulses with constant amplitude and pulses that are part of a Rayleigh distribution alternating with each other).

[0078] The light pulses emitted by the laser are fed to a beam splitter. An unbalanced Mach-Zehnder interferometer can be used to interfere with adjacent light pulses. The interferometer consists of an input coupler that divides the power of the incoming light pulse equally into the two arms of the interferometer. The long arm allows the replicated pulse stream to be delayed by one period relative to the pulse in the short arm. The two pulse streams coherently interfere in the output coupler of the interferometer. It should be noted that, in general, in addition to providing a quantum random number generator, Figure 3 The illustrated device with the ability to modulate a distribution of orthogonal values ​​by controlling the electrical pulses driving the laser can also be used for classical and quantum communication applications (e.g., for building modulation-free and simple transceivers).

[0079] Figure 4 An embodiment of a continuously variable quantum key distribution (CV-QKD) system with a "transmitted local oscillator" is shown. At Alice's end, Figure 4 The system shown includes a first laser whose output quadrature values ​​obey a Gaussian distribution (signal pulses) and a second laser used as a local oscillator LO to generate equal-amplitude intense optical pulses (higher than the amplitude of the optical pulses output by the first laser). Typically, the optical power of the local oscillator is several orders of magnitude higher than the signal pulses provided by the first laser. The local oscillator pulses and the signal pulses are split using two independent beam splitters BS (Beam Splitters), and Alice uses one of the outputs of each beam splitter BS to measure the orthogonality at her station. For example, such measurements can be made by heterodyne detection using a 90° optical mixer and an unbalanced detector of a detector device. A delay component and a beam splitter BS are used to time-division multiplex the other outputs of the beam splitter BS. The optical pulses are attenuated using an optical attenuator ATT (Attenuator) at the output end of Alice to obtain the appropriate orthogonal variance required for the QKD protocol.

[0080] The attenuated pulse is sent through a quantum communication channel (e.g., a fiber link or free space) to Bob (another detector device at the receiving end), who also measures the quadrature value using a balanced detector BD and a 90° optical hybrid assembly (see also Figure 1 Alice and Bob's measurements result in correlated Gaussian data that can be used to derive the key. Several other techniques can be used to multiplex the output of the LO and the signal pulses before sending the signal over the communication channel, such as polarization, wavelength, or spatial multiplexing.

[0081] like Figure 4 In the configuration shown, the local oscillator output is transmitted from Alice to Bob ("transmitted local oscillator"). Alternatively, Bob can measure the quadrature using a third laser generated locally at his station. This scheme, called a "true local oscillator" or "local local oscillator", offers advantages in terms of security.

[0082] Figure 5 Another implementation of the CV-QKD scheme is shown, which can be used for both parties to obtain the key. This configuration only requires a single laser, so compared to Figure 4 The configuration shown in the figure simplifies the implementation. The laser driven by electric pulses consists of electric pulses that obey the Rayleigh distribution and are interleaved between equal-amplitude strong pulses (local oscillator). The orthogonal distribution of the optical pulses (per second pulse) generated by the electric pulses with Rayleigh distribution will be Gaussian. The optical pulses output by the laser are split using a beam splitter. Alice estimates the orthogonality by measuring one of the outputs. The other output is attenuated to adjust the variance of the orthogonality according to the requirements of the QKD protocol. The attenuated optical pulses are sent to Bob, who measures the orthogonality to obtain data related to Alice's measurement.

[0083] An implementation of a system including a "true local oscillator" that can be implemented with two lasers is for example Figure 6As shown in the figure. The laser at Alice's end generates orthogonal optical pulses with Gaussian modulation by driving the laser from below the laser threshold to above the laser threshold using the Rayleigh distribution of the electrical pulse. Then, the optical pulses generated by the laser are split using a beam splitter BS. Then, one of the outputs is attenuated to the desired variance set by the GG02 protocol and sent to Bob via port 1 of the circulator C1. At the Bob end, the optical pulse received via the quantum channel is input to port 2 of the circulator C2. Bob uses another laser (CW or pulse) as LO. The output of the LO is split using a beam splitter BS. One of the outputs of the beam splitter BS is used to measure the orthogonality of the input from Alice at port 3 of C2. The other output of the beam splitter BS is fed into port 1 of C2 and reaches Alice through the communication channel. Alice uses the incoming optical pulse from Bob through port 3 of C1. Both Alice and Bob can measure orthogonality by using, for example, heterodyne detection performed with a 90° level optical mixer and a balanced detector BD.

[0084] All previously discussed embodiments are not intended to be limiting but rather serve as examples to illustrate the features and advantages of the present invention. It should be understood that some or all of the above features may also be combined in different ways.

Claims

1. A device for generating optical pulses, comprising: a laser configured to output the light pulses; as well as, a pulse driver configured to provide electrical pulses to the laser to drive the laser; in, The pulse driver is configured to provide the electrical pulses with a desired duty cycle time distribution and with a controlled preset probability distribution amplitude to the laser, wherein the preset probability distribution amplitude of the electrical pulses is applied to the amplitude of the optical pulses so that the orthogonal values ​​of the optical pulses obey another preset probability distribution; The apparatus further comprises a control means configured to repeatedly operate the laser a) below a lasing threshold for a first preset time period and b) subsequently above the lasing threshold for a second preset time period so as to randomize the phase of the light pulses.

2. The apparatus of claim 1, wherein the pulse driver is configured to provide electrical pulses to the laser that obey a Rayleigh distribution.

3. The apparatus of claim 1, wherein the orthogonal values ​​of the optical pulses follow a Gaussian distribution.

4. The apparatus of claim 1 further comprising a beam splitter and an interferometer.

5. The apparatus of claim 4, wherein the interferometer is an unbalanced Mach-Zehnder interferometer.

6. A system comprising the apparatus of any one of the preceding claims, and further comprising a detector arrangement configured to receive the optical pulses output by the laser, and wherein the detector arrangement comprises a balanced detector means.

7. A system as claimed in claim 6, wherein the detector device further comprises a further laser and / or a 90° optical hybrid.

8. A system as claimed in claim 6 or 7, wherein the device further comprises a beam splitter, an attenuator and either a) another detector device or b) another laser and another detector device.

9. The system of claim 8, wherein: wherein the attenuator is configured to attenuate an output of the beam splitter of the apparatus, and wherein the apparatus further comprises a first circulator configured to provide the attenuated output to the detector means; as well as The detector arrangement comprises: a further beam splitter configured to receive light pulses from the further laser, and a second circulator configured to receive an output of the further beam splitter and provide it to the device; And among them the first circulator being configured to provide the output of the further beam splitter provided by the second circulator to the further detector arrangement of the apparatus, and The second circulator is configured to provide the attenuated output of the beam splitter of the device received via the first circulator to a balanced detector of the detector arrangement of the system.

10. The system of claim 9, wherein: The second circulator is configured to provide the attenuated output of the beam splitter of the device received via the first circulator to the balanced detector of the detector arrangement of the system through a 90° optical hybrid.

11. A method for generating light pulses having orthogonal values ​​of a predetermined probability distribution, comprising the following steps: generating a first electrical pulse obeying a probability distribution; as well as driving a first laser to output a first optical pulse by means of said generated first electrical pulse; wherein the first electrical pulse having a desired duty cycle time distribution and having a controlled preset probability distribution amplitude is provided to the first laser, wherein the preset probability distribution amplitude of the first electrical pulse is applied to the amplitude of the first optical pulse so that the orthogonal value of the first optical pulse obeys another preset probability distribution; as well as Driving the first laser includes repeatedly driving a) the first laser below a lasing threshold of the first laser for a first preset time period and b) subsequently above the lasing threshold for a second preset time period so as to randomize the phase of the output first light pulses. The method of claim 11 , wherein the probability distribution is a Rayleigh distribution.

13. A method for generating a random number, comprising the steps of the method according to claim 11 or 12, and further comprising: generating a second electrical pulse comprising the first electrical pulse, subject to the probability distribution and interleaved with a third electrical pulse of equal amplitude; driving said first laser to output said first light pulse by means of said generated second electrical pulse; as well as An interferometer is used to interfere with adjacent ones of the generated second electrical pulses.

14. The method of claim 13, wherein the interferometer is an unbalanced Mach-Zehnder interferometer.

15. A method for distributing quantum keys, comprising the steps of the method according to claim 11 or 12, and further comprising: A) At a transmitter: generating a second electrical pulse having a constant amplitude; driving a second laser to output a second optical pulse by means of said generated second electrical pulse; Splitting the first light pulse to obtain a first portion of the first light pulse and a second portion of the first light pulse; Splitting the second light pulse to obtain a first portion of the second light pulse and a second portion of the second light pulse; measuring the quadrature value of the first portion of the first light pulse using the first portion of the second light pulse; multiplexing the second part of the first optical pulse and the second part of the second optical pulse to obtain a multiplexed optical pulse; Attenuating the multiplexed optical pulses by an attenuator to obtain attenuated multiplexed optical pulses; as well as Transmitting the attenuated multiplexed optical pulse to a receiving end; as well as B) At the receiving end: receiving the transmitted attenuated multiplexed optical pulses; as well as The quadrature value of the received attenuated multiplexed optical pulse is measured.

16. A method for distributing quantum keys, comprising the steps of the method according to claim 11 or 12, and further comprising: A) At a transmitter: generating a second electrical pulse comprising the first electrical pulse, following the probability distribution and interleaved with a third electrical pulse of equal amplitude; driving said first laser to output said first light pulse by means of said generated second electrical pulse; Splitting the first light pulse to obtain a first portion of the first light pulse and a second portion of the first light pulse; measuring the quadrature value of the first portion of the first light pulse; attenuating the second portion of the first light pulse by an attenuator to obtain an attenuated light pulse; as well as transmitting the attenuated optical pulse to a receiving end; as well as B) At the receiving end: The quadrature value of the received attenuated light pulse is measured.

17. A method for distributing quantum keys, comprising the steps of the method according to claim 11 or 12, and further comprising: A) At a transmitter: Splitting the first light pulse to obtain a first portion of the first light pulse and a second portion of the first light pulse; attenuating the first portion of the first light pulse by an attenuator to obtain an attenuated light pulse; as well as Transmitting the attenuated multiplexed optical pulse to a receiving end; as well as B) At the receiving end: generating a reference light pulse by a second laser; Splitting the reference light pulse to obtain a first part of the reference light pulse and a second part of the reference light pulse; measuring a quadrature value of said attenuated optical pulse received via a second circulator by means of said first portion of said reference optical pulse; and, transmitting the second part of the reference light pulse to the transmitting end via a second circulator; as well as C) at the transmitting end: receiving the second portion of the reference light pulse; as well as A quadrature value of the second portion of the first light pulse is measured by means of the received second portion of the reference light pulse.

18. The method of claim 17, wherein: The attenuated multiplexed optical pulse is transmitted to the receiving end via a first circulator.

19. The method of claim 17, wherein: Receiving the second portion of the reference light pulse is performed via a first circulator.

20. The method of claim 18, wherein: Receiving the second portion of the reference light pulse is performed via the first circulator.

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