RU2805561C1 - Device for controlling phase shifts of radiation in integrated circuits based on asymmetric mach-zehnder interferometer - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention concerns a device for controlling the phase shifts of radiation in integrated circuits based on an asymmetric Mach-Zehnder interferometer. The device consists of an adjustable optical attenuator, made in the form of a splitter, two phase modulators and an X-coupler with two inputs and two outputs, an asymmetric Mach-Zehnder interferometer with a delay line in the long arm and a phase modulator in the short arm. The arms of the interferometer are connected in an X-shaped coupler, the beams from which are directed to external photodetectors located outside the chip.

EFFECT: reducing the size of systems, including optical communication devices based on photonic integrated circuits and devices for measuring the phase shift, increasing the contrast at the outputs of the device and eliminating the need to adjust the external circuit.

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Description

Field of technology to which the invention relates

The invention relates to devices for measuring phase shift (noise) in optical systems based on photonic integrated circuits.

Glossary

In order to ensure the sufficiency of disclosure of the invention and to ensure the possibility of conducting an information search in relation to the claimed technical solution, as well as to understand the essence of the claimed invention, below is a list of terms used in the description that do not limit the scope of legal protection. Terms:

A waveguide is a guiding channel in which an electromagnetic wave can propagate.

Interference is a redistribution of the intensity of electromagnetic waves as a result of the superposition (superposition) of several electromagnetic waves.

An interferometer is a measuring device whose operation is based on the phenomenon of interference.

A quantum network is a communication network in which transmitted data is protected by quantum cryptography methods.

Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects cannot be described independently. Quantum coherence is a quantum phenomenon consisting in the correlation, or consistency, of the movement of microparticles that form a given physical system. A qubit is the smallest unit of information in a quantum computer (analogous to a bit in a conventional computer).

A laser is a source of electromagnetic radiation with high temporal and spatial coherence.

Modulator is a device for converting electrical signals into the optical domain (electro-optical conversion).

X-shaped coupler is a device that combines the functions of a splitter and a combiner.

Splitter/combiner - a device for dividing/summing input signals. Photo detector is a device for converting optical signals into the electrical domain (optoelectronic conversion).

State of the art

GENERAL REVIEW

Photonic integrated circuits (PICs) are a multi-component optoelectronic device (monolithic or hybrid integrated circuit), manufactured on a single substrate and capable of performing the functions of generating, detecting and processing optical signals, and gradually occupying a place as the basis of the nomenclature of components of all optical systems.

Photonic integrated circuits provide a platform that allows the monolithic integration of multiple optical components performing different functions on a single chip. Photonic integrated circuits can be fabricated on multiple material platforms, each with advantages and disadvantages. In modern and future systems based on photonics, where many different elements are used, the logical solution is their integration on a chip. This is what integrated photonics does - a relatively new and actively developing global industry. The known advantages of photonic integrated circuits, such as compactness, speed, and energy efficiency, allow them to complement or replace both discrete photonics and microelectronics in many applications.

One of the main problems in the field of application of FIS is miniaturization, reduction in cost of devices while maintaining the ability to control the operating parameters of FIS components.

In addition, a significant reduction in the cost of technology and obtaining small dimensions of devices based on FIS will significantly expand their areas of application and move from niche applications to use in large-scale user markets. Such penetration of FIS-based systems is subject to the availability of technologies that allow the creation of compact systems with low cost, weight and power consumption that can be easily integrated into user devices. With the help of photonic integrated circuits, it is possible to replace bulk discrete components with a single chip, the dimensions of which will not exceed 20 × 20 × 1 mm ³ and a weight of 10 grams.

Frequency instability caused by spontaneous transitions, optical losses and technical noise associated with voltage drops, vibrations and temperature fluctuations in the laser cavity has a significant impact on the quality of photonic integrated circuit devices.

In electro-optical modulators, electronic devices used in various fiber optic communication applications, Mach-Zehnder interferometers have become widespread. Mach-Zehnder interferometers are built into photonic integrated circuits and provide broadband electro-optical amplitude and phase characteristics over the multi-gigahertz frequency range.

A Mach-Zehnder interferometer is a device that interferes with radiation divided into two parts passing through different optical paths. In optical telecommunications, it is used as an electro-optical modulator for phase and amplitude modulation of light.

As a technical solution that allows monitoring the value of the phase shift of a signal in an optical system based on a photonic integrated circuit, a “Device for monitoring phase shifts of radiation in integrated circuits based on an asymmetrical Mach-Zehnder interferometer” is proposed.

The proposed device makes it possible to control the operating parameters of optical components of photonic integrated circuits used, for example, in quantum telecommunications

During the patent search, documents were found that define the state of the art and are not considered particularly relevant in relation to the claimed invention, namely: “Phase noise meter for narrow-band lasers based on a Mach-Zehnder interferometer consisting of an rm fiber” (patent No. RU 2664692 C1 ) “Optical analyzer and method for reducing relative intensity noise in interferometric optical measurements using a continuously tunable laser,” patent No. US 20030112442 A1)

“Set for measuring RF phase noise using a fiber optic delay line” (R.F. phase noise test set using fiber optic delay line, patent No. US 4918373 A) The above technical solutions represent various options for devices for estimating the value of the phase shift (noise level) in optical systems.

As an analogue, we can highlight the technical solution “Optical analyzer and method for reducing relative intensity noise in interferometric optical measurements using a continuously tunable laser”, patent No. US 20030112442 A1, priority date 2001-08-28). According to the description, the solution is a heterodyne optical network analyzer and a method for characterizing a device to reduce the influence of relative intensity noise in interferometric optical measurements by subtracting the measured intensities of the first and second interference signals obtained from the optical interferometer.

The difference between this technical solution is the absence of an adjustable optical attenuator in the form of another Mach-Zehnder interferometer, in this scheme used to compensate for the difference in losses in the arms of the interferometer to achieve the greatest contrast at its outputs. In addition, the solution proposed in this patent involves the use of a reference laser, that is, heterodyning. The device proposed in this patent performs homodyning, that is, the signal itself interferes with itself.

As a prototype of the claimed invention, one can consider the technical solution disclosed in the patent “Phase noise meter for narrow-band lasers based on a Mach-Zehnder interferometer consisting of an RM fiber” (patent No. RU 2664692 C1, priority date 2017.10.12). The solution relates to devices for measuring phase noise using the frequency discriminator method, which is a Mach-Zehnder interferometer, and can be used to certify narrow-band, highly stable lasers used in communication lines, hydrophones, lidar systems, as well as in phase-sensitive reflectometry. The phase noise meter for narrowband lasers includes: an optical coupler that forms two channels: the first, which records instantaneous source power values, and the second, which records two interference signals; a polarizer in the second channel, generating linearly polarized radiation at the input to an unbalanced fiber Mach-Zehnder interferometer, made of a fiber-optic separating coupler (1×2) based on a fiber with preservation of the polarization state at the input of the interferometer, an additional fiber with preservation of the polarization state, introducing a phase difference, and a combining fiber-optic coupler (2×1) based on a fiber with preservation of the polarization state at the output of the interferometer; a polarization beam splitter located after the Mach-Zehnder interferometer, separating two interference signals from orthogonally polarized waves; three optical radiation receivers, two of which are located after the polarization beam splitter in the second channel, and one in the first channel; an analog-to-digital converter, which receives signals from all three receivers, and after it a digital signal processing unit for calculating the power spectral density of the phase noise by performing functions in the following order: normalizing the interference signal to instantaneous values of the signal proportional to the laser power, in order to compensation for relative laser intensity noise; high-frequency filtering to compensate for temperature instability; calculation of phase fluctuations and calculation of the power spectral density of phase noise. The technical result is to minimize the measurement error of phase noise of a narrow-band laser. This technical solution also differs in the absence of an adjustable optical attenuator in the form of another Mach-Zehnder interferometer, which in this design is used to compensate for the difference in losses in the arms of the interferometer to achieve the greatest contrast at its outputs.

The above technical solutions, like the claimed invention, are intended for measuring phase shift (noise) in optical systems based on photonic integrated circuits, however, the sequence of modulation of the initial signal of the above technical solutions differs significantly from that proposed in the present invention. In particular, the key difference between the proposed method and the prototype is the inclusion in the circuit of a component such as an optical attenuator, as well as the absence of a phase modulator in the interferometer.

The technical problem for which the present invention is intended is to measure the phase shift between the pulses transmitted by the device being measured, which requires assessing the quality of adjustment of the components of the device being measured. In this case, the length of the delay line in the used asymmetric Mach-Zehnder interferometer can be selected depending on the pulse repetition period. The proposed device can be used in the form of a separate chip, radiation to which is supplied externally, or located on the same FIS with the device being measured.

The technical result of the proposed solution is the miniaturization of optical systems, including optical communication devices based on photonic integrated circuits and phase shift measuring devices, reducing the influence of thermal fluctuations and acoustic influences on the results of measuring the phase shift (compared to discrete circuits), including due to the possibility of positioning device for monitoring phase shifts and the measured device on one level and eliminating the need to adjust the external circuit.

Disclosure of the Invention

To solve the problem and achieve the above technical result, a “Device for monitoring phase shifts of radiation in integrated circuits based on an asymmetrical Mach-Zehnder interferometer” is proposed.

The device for implementing this method consists of the following elements:

1. Optical attenuator 2, made in the form of a disconnector 1, two phase modulators 3 and 4, and an X-shaped coupler 5;

2. Asymmetrical Mach-Zehnder interferometer 6 with a delay line 7 in the long arm, a phase modulator 8 in the short arm, while the interferometer arms are connected in an X-shaped coupler 9, the beams from which are directed to external (located outside the chip) photodetectors 10 (one or both external photodetectors can be replaced by one or two photodetectors built into the chip, respectively).

The operation of the device is described as follows:

1. A beam of light is directed from the output of the measured circuit, located on the same FIS, through a waveguide to an adjustable Mach-Zehnder interferometer 2 to separator 1, enters phase modulators 3 and 4, and is connected in an X-shaped coupler 5.

2. Next, beams from the X-shaped coupler 5, depending on the phase difference, are sent in different proportions into two channels into the interferometer 6, where two successive pulses are interfered with. One beam goes along the delay line 7, the second goes through the phase modulator 8, then two beams (from the delay line 7 or the phase modulator 8) enter the X-shaped coupler 9, from where, depending on the phase difference, they arrive in different proportions at the photodetectors 10.

An asymmetrical Mach-Zehnder interferometer with arms of significantly different lengths makes it possible to measure the phase shift of two successive light pulses due to the difference in optical paths in the interferometer arms. The length of the delay line in the form of a longer waveguide in one of them is selected so that, at a given pulse repetition rate, the maximums of the envelopes of two successive pulses arrive simultaneously at the optical connector at the output of the device. The addition of an asymmetric Mach-Zehnder interferometer with an adjustable optical attenuator 2 is used to compensate for the difference in losses in the arms of the asymmetric Mach-Zehnder interferometer, which provides the greatest contrast (the ratio of the difference between the largest and smallest signals at the output to the smallest signal) and, therefore, increasing the accuracy of phase shift measurements by outputs of the scheme “Device for monitoring phase shifts of radiation in integrated circuits based on an asymmetrical Mach-Zehnder interferometer.”

To summarize, the description of the device can be presented as follows:

A device for monitoring phase shifts of radiation in integrated circuits based on an asymmetric Mach-Zehnder interferometer, consisting of an adjustable optical attenuator made in the form of a splitter, two phase modulators and an X-shaped coupler with two inputs and two outputs, an asymmetric Mach-Zehnder interferometer with a delay line in the long arm, by a phase modulator in the short arm, while the interferometer arms are connected in an X-shaped coupler, beams from which are directed to external photodetectors located outside the chip

The invention is disclosed and illustrated in the following drawings:

Fig. 1 - Schematic diagram of the device. The above figure schematically shows all the components of the device, showing the sequence of their arrangement. In this case, except for the sequence of arrangement of elements, there are no other requirements for the arrangement of elements.

Claims (1)

A device for monitoring phase shifts of radiation in integrated circuits based on an asymmetric Mach-Zehnder interferometer, consisting of an adjustable optical attenuator made in the form of a splitter, two phase modulators and an X-shaped coupler with two inputs and two outputs, an asymmetric Mach-Zehnder interferometer with a delay line in the long arm, by a phase modulator in the short arm, while the interferometer arms are connected in an X-shaped coupler, the beams from which are directed to external photodetectors located outside the chip.

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