Rec array tunable laser system for local oscillator light source in coherent systems

Abstract

The application discloses a REC array tunable laser system for a local oscillator light source in a coherent system, comprising a REC laser array, a waveguide beam splitter, an optical filter group, a wavelength detection module, a waveguide coupler, a photodetector, an intermediate frequency compensation module, a frequency measurement circuit, a wavelength switching control module and a TEC radiator. The REC array tunable laser system has the advantages of narrow linewidth and fast tuning compared with a conventional local oscillator light source. Based on the REC laser array, narrow linewidth lasers of different frequencies are outputted, and through the linkage control of the wavelength detection module, the frequency measurement circuit and the intermediate frequency compensation module, the micron-level adaptation of the coherent light wavelength and the signal light is realized, so that the constant output of the intermediate frequency signal is realized, and the problem of the intermediate frequency stability is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coherent communication, and particularly relates to a REC array tunable laser system for a local oscillator light source in a coherent system, and a high-precision REC (Reconstruction Equivalent Chirp) array tunable laser chip design for the local oscillator light source. BACKGROUND

[0002] With the rapid development of the information age, the increasing popularity of 5G technology has brought great convenience to human production and life, and the optical communication technology is also an important part of the 5G communication network. Laser communication technology taking light as the information carrier is also an important research direction to break through the existing high-speed communication bottleneck.

[0003] Space laser communication technology has the advantages of large communication capacity, good precision and reliability, fast transmission rate, and strong anti-electromagnetic interference, and has important strategic significance in many fields, which has attracted in-depth research by countries around the world. The communication terminal and the modulation mode are two important components of space laser communication technology, which have an important influence on the performance of space laser communication. With the development of space laser communication, the traditional intensity modulation / direct detection modulation has been unable to meet the rising demand for communication performance, and the coherent laser communication system has gradually become a better choice for space laser communication technology due to its high sensitivity, long relay distance, and multiple modulation modes.

[0004] In coherent laser communication, the stability of the intermediate frequency signal generated by the local oscillator light source and the signal light is crucial for subsequent information demodulation processing. The traditional tunable laser generally has the problems of complex process, high cost, and long tuning time. At the same time, after tuning and stabilization, changes in environmental parameters and other factors cause the wavelength of the tunable laser to change slightly. Taking a 200MHz intermediate frequency signal as an example, a 5MHz frequency shift of the 200MHz intermediate frequency signal generated by the coherent can cause a 5MHz frequency shift, which can interfere with subsequent information processing and achieve high-quality communication.

[0005] The reconstruction equivalent chirp technology can realize complex grating functions such as chirp structure, phase shift structure, period modulation grating, and apodized grating by using non-equidistant sampling Bragg grating structure, and reduce the precision requirement in the process of manufacturing, which is beneficial to large-scale laser array production and manufacturing. Based on the REC technology, various complex grating structures can be manufactured and the equivalent grating Bragg wavelength can be controlled with high precision, and a tunable semiconductor laser array with narrow linewidth, high precision, and high speed switching can be realized.

[0006] If a REC array is used to directly replace a traditional tunable laser to generate an intermediate frequency (IF) signal, the IF signal will be subject to random interference from both the signal light and the local oscillator light. Without adaptive feedback adjustment, this will cause a significant frequency shift. For example, coherently cohering a 1550nm signal light and a 1550.0016nm local oscillator light to generate a 200MHz IF signal will result in a wavelength difference of up to 0.04pm in practical applications, causing frequency jitter within a 5MHz range. Currently, there are no research results on using REC array tunable laser chips to realize local oscillator light sources at different wavelengths and control the output of stable IF signals through internal modules. Summary of the Invention

[0007] Technical problem solved: This invention discloses a REC array tunable laser system for local oscillator light source in a coherent system. By using a REC laser array to replace the traditional tunable laser as the local oscillator light source, and combining it with an internal control feedback module group, a wide range of coherent capabilities are achieved, and a stable intermediate frequency signal is output.

[0008] Technical solution:

[0009] A REC array tunable laser system for a local oscillator light source in a coherent system, the REC array tunable laser system comprising a REC laser array, a waveguide beam splitter, an optical filter bank, a wavelength detection module, a waveguide coupler, a photodetector, an intermediate frequency compensation module, a frequency measurement circuit, and a wavelength switching control module;

[0010] The REC laser array is used to output several lasers of different wavelengths at equal intervals. The output lasers are transmitted to one of the input terminals of the waveguide coupler via fiber waveguides.

[0011] The waveguide beam splitter is used to transmit the input signal light to the other input end of the optical filter bank and the waveguide coupler respectively with a preset splitting ratio;

[0012] The optical filter bank is connected to the wavelength switching control module via a wavelength detection module. The optical filter bank contains several waveguide channels, each allowing a wavelength of light to pass through that corresponds one-to-one with the wavelengths of several lasers in the REC laser array. The optical filter selects the corresponding channel based on the wavelength of the signal light, outputting the signal light to the wavelength detection module. The wavelength detection module detects the optical power of each channel and transmits the corresponding channel illumination information to the wavelength switching control module. The wavelength switching control module processes the channel values ​​input from the wavelength detection module and illuminates the corresponding lasers based on these values ​​to control the REC laser array, ensuring it operates in a channel that matches the signal light.

[0013] The waveguide coupler couples the local laser output by the REC laser array with the signal light, outputs the coherent intermediate frequency signal light, and the intermediate frequency signal light is transmitted to the photodetector through the optical fiber waveguide and converted into the corresponding intermediate frequency electric signal;

[0014] The frequency measurement circuit determines the frequency of the intermediate frequency electric signal output by the photodetector and outputs the measured frequency value to the intermediate frequency compensation module.

[0015] The intermediate frequency compensation module determines the laser that needs to be corrected in wavelength according to the channel value input by the wavelength switching control module, calculates the difference between the frequency value input by the frequency measurement circuit and the intermediate frequency standard value, and adjusts the lasing wavelength of the corresponding laser by changing the injection current of the phase shift region of the corresponding channel laser, so that the output light wavelength of the channel fluctuates within the tuning range and matches the signal light to stabilize the intermediate frequency value of the coherent signal.

[0016] Further, the REC array tunable laser system further comprises a TEC heat sink for dissipating heat from the REC laser array to maintain a constant temperature in the working environment.

[0017] Further, the laser array, waveguide beam splitter, optical filter group, wavelength detection module, waveguide coupler, photodetector, intermediate frequency compensation module, frequency measurement circuit, wavelength switching control module and TEC heat sink are integrated on the same chip.

[0018] Further, the REC laser array adopts a 64-wavelength laser array arranged in 8x8, the wavelength interval between adjacent lasers is 0.8nm, the wavelength interval between two adjacent lasers on the same waveguide is 6.4nm, and the output laser wavelength range is 1524.4-1571.6nm.

[0019] Further, the wavelength detection module and the optical filter group are connected one by one through a plurality of waveguides, and a micro photodetector is attached to the tail end of each waveguide inside the module.

[0020] Further, the wavelength detection module detects the power through the micro photodetector at the tail of the waveguide to determine the waveguide channel sequence number with the signal light, converts the electric signal generated by the channel light through the micro photodetector into sequence information through the built-in logic circuit, adds a data frame header, and then sends it to the wavelength switching control module.

[0021] The wavelength switching control module detects the frame header information after receiving the sequence information input by the wavelength detection module, determines the channel sequence value carried by the sequence information when detecting that the frame header is valid, controls the on-off of the corresponding channel of the REC laser array, lights up the corresponding laser, realizes the matching with the signal light wavelength, and outputs the local laser to the waveguide coupler for coherent effect.

[0022] Further, the wavelength switching control module is connected with each laser in the REC laser array one by one, and the lighting of each laser is independently controlled.

[0023] Further, the adjustment step of the intermediate frequency compensation module is 0.02 nm / mA.

[0024] Further, the frequency determination range of the frequency measurement circuit is 0-1000MHz; for high-frequency signals exceeding the frequency determination range, the high-frequency signals are removed through the internal protection circuit.

[0025] Further, the optical power of the intermediate frequency signal light is represented as:

[0026]

[0027] In the formula, E1 is an input signal light electric field, P1 is a signal light power, and ω1 is a signal light angular frequency, is a signal light phase changing with time, E2 is a local oscillator light electric field, P2 is a local oscillator light power, ω2 is a local oscillator light angular frequency, and ω IF =ω1-ω2 is an intermediate frequency, and the coherent signal power is amplified by times.

[0028] Beneficial effects:

[0029] First, the REC array tunable laser system for the local oscillator light source in the coherent system of the application can significantly improve the tunable range of the local oscillator light source from the characteristics of the REC laser array, and compared with the millisecond-level tuning time of the traditional tunable laser, the wavelength switching time of the REC laser array can reach tens of nanoseconds, which significantly improves the speed of tunable.

[0030] Second, the REC array tunable laser system for the local oscillator light source in the coherent system of the application is based on the REC technology, which can realize precise processing and manufacturing at a lower cost, has mature technology and is easy to integrate, and is suitable for large-scale production and application.

[0031] Third, the REC array tunable laser system for the local oscillator light source in the coherent system of the application realizes the automatic adaptation of the tunable light source and the signal light through the cooperation of the optical filter group, the wavelength detection module and the wavelength switching control module, without the need to know the specific wavelength value of the signal light in advance in the tuning range, which significantly improves the automation capability of the coherent system.

[0032] Fourth, the REC array tunable laser system for the local oscillator light source in the coherent system of the embodiment of the present application can effectively eliminate the negative effects of the intermediate frequency signal frequency fluctuation, feedback control the output constant intermediate frequency signal, and realize high-quality coherent communication. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structure schematic diagram of the REC array tunable laser system for the local oscillator light source in the coherent system of the embodiment of the present application;

[0034] Figure 2 is a schematic diagram of an 8*8 REC laser array of the embodiment of the present application;

[0035] Figure 3 is a schematic diagram of the connection structure of the 8*8 REC laser array and the intermediate frequency compensation module of the embodiment of the present application;

[0036] Figure 4 is a schematic diagram of the wavelength power spectrum of 64 channels of the REC laser array of the embodiment of the present application;

[0037] Figure 5 is a schematic diagram of the frequency spectrum of the 200MHz intermediate frequency signal generated by the coherent system without intermediate frequency compensation;

[0038] Figure 6 is a schematic diagram of the frequency spectrum of the 200MHz intermediate frequency signal generated by the coherent system without intermediate frequency compensation; DETAILED DESCRIPTION

[0039] The following embodiments can make the professional technical personnel more fully understand the present application, but do not limit the present application in any way.

[0040] Reference Figure 1 The embodiment discloses a REC array tunable laser system for a local oscillator light source in a coherent system, which comprises a REC laser array, a waveguide beam splitter, an optical filter set, a wavelength detection module, a waveguide coupler, a photodetector, an intermediate frequency compensation module, a frequency measurement circuit and a wavelength switching control module.

[0041] The REC laser array is used to output several kinds of equally spaced different wavelength lasers, and the output laser is transmitted to one input end of the waveguide coupler through an optical fiber waveguide.

[0042] The waveguide beam splitter is used to transmit the input signal light to the optical filter set and the other input end of the waveguide coupler respectively with a preset light splitting ratio.

[0043] The optical filter set is connected with the wavelength switching control module through the wavelength detection module, the optical filter set comprises a plurality of waveguide channels, and each waveguide channel allows the light wavelength corresponding to one of the plurality of lasers of the REC laser array to pass; the optical filter selects the corresponding channel according to the wavelength of the signal light, outputs the signal light to the wavelength detection module through the selected channel, detects the optical power of each channel by the wavelength detection module, and delivers the corresponding channel lighting information to the wavelength switching control module; the wavelength switching control module processes the channel value input by the wavelength detection module, and lights up the laser corresponding to the channel value to control the REC laser array to work in the channel matched with the signal light.

[0044] The waveguide coupler couples the local laser output by the REC laser array with the signal light, and outputs the coherent intermediate frequency signal light, which is transmitted to the photodetector through the optical fiber waveguide and converted into the corresponding intermediate frequency electric signal.

[0045] The frequency measurement circuit measures the frequency of the intermediate frequency electric signal output by the photodetector, and outputs the measured frequency value to the intermediate frequency compensation module.

[0046] The intermediate frequency compensation module determines the laser that needs to be wavelength corrected according to the channel value input by the wavelength switching control module, calculates the difference between the frequency value input by the frequency measurement circuit and the intermediate frequency standard value, and finely adjusts the lasing wavelength of the corresponding laser by changing the injection current of the phase shift region of the corresponding channel laser, so that the output light wavelength of the channel fluctuates within the tuning range and matches the signal light to stabilize the intermediate frequency value of the coherent signal.

[0047] For the convenience of description, only an 8x8 REC laser array is used to illustrate the technical scheme in this embodiment, and in actual application, the REC array tunable laser system of this embodiment can select any array combination and interval wavelength REC laser array as needed. When the total number of lasers of the REC laser array used is not 64, only the number of structural parts of other devices needs to be adaptively adjusted, for example, the number of channels of the optical filter set and the number of micro photodetectors of the wavelength detection module, and the control principle of the laser is the same.

[0048] In this embodiment, the 8x8 REC laser array is used to generate 64-channel laser with an interval of 0.8nm, covering the wavelength range of 1524.4-1571.6nm as the local light source, and output to the waveguide coupler to be coherent with the signal light, and the structure diagram is as shown in Figure 2 The wavelength and power spectrum diagram of the 64 channels of the laser is as shown in Figure 4 The waveguide beam splitter is used to deliver the input signal light to the optical filter set and the waveguide coupler at a splitting ratio of 10:90; the waveguide coupler is used to receive the signal light and the local light to be coherent, and the coherent relationship is as follows:

[0049] The input signal light can be expressed as:

[0050]

[0051] The expression of the local oscillator light output by the REC laser array is:

[0052]

[0053] wherein E1 is the input signal light electric field, P1 is the signal light power, ω1 is the signal light angular frequency, is the signal light phase varying with time, E2 is the local oscillator light electric field, P2 is the local oscillator light power, ω2 is the local oscillator light angular frequency, the signal light and the local oscillator light are coherently mixed in a 3dB waveguide coupler, and the light power expression of the two coherently mixed lights is:

[0054]

[0055] wherein ω IF = ω1- ω2 is the intermediate frequency, and the signal power is amplified by times after being cohered, thereby improving the detection sensitivity. The intermediate frequency signal is simultaneously disturbed by the signal light and the local oscillator light, and without adaptive feedback adjustment, a large frequency offset will be caused. The signal light with a wavelength of 1550 nm and the local oscillator light with a wavelength of 1550.0016 nm are cohered to generate an intermediate frequency signal with a frequency of 200 MHz. In actual application, the wavelength difference between the two light signals will fluctuate within 0.04 pm, so that the intermediate frequency signal frequency will fluctuate within 5 MHz. The photoelectric detector will detect the frequency-fluctuated intermediate frequency signal, and convert the light signal into an electric signal for processing by a frequency measurement circuit.

[0056] The optical filter set receives the signal light input by the waveguide beam splitter, and contains 64 channels, each of which allows the light wave with a wavelength corresponding to the center wavelength of one of the 64 lasers of the 8*8 REC laser array to pass through. The signal light is reflected to the corresponding wavelength channel in the optical filter set and transmitted to the wavelength detection module through the waveguide. The module is connected to the 64 channels of the optical filter set one by one, and the power is detected by the micro photoelectric detector at the tail of the waveguide to determine the waveguide channel number with the signal light. In this embodiment, 6-bit data is used to number the 64 channels, and 6’b000000-6’b111111 can cover 64 channel numbers. If channel 35 has signal light transmission, the wavelength detection module will generate 6’b100011, add a data frame header, and convert the electric signal generated by the channel light through the micro photoelectric detector into sequence information and transmit it to the wavelength switching control module through the built-in logic circuit.

[0057] The wavelength switching control module, after receiving the electrical signal input by the wavelength detection module, first detects the frame header information, and when detecting that the frame header is valid, judges the channel sequence value carried thereby, thereby controlling the switching of the corresponding channel of the REC laser array, lighting the laser corresponding thereto, realizing the matching with the signal light wavelength, and outputting the local laser to the waveguide coupler for the coherent effect.

[0058] The frequency measurement circuit, after receiving the intermediate frequency electrical signal input by the photodetector, measures the frequency value thereof, and the frequency measurement range thereof is 0-1000MHz, so as to satisfy different communication rates and the corresponding intermediate frequency signal frequencies. For high frequency signals exceeding the range, the internal protection circuit is used to remove the signals so as to maintain the normal operation of the module. In the case of normal operation, the frequency measurement circuit delivers the frequency value to the intermediate frequency compensation module. The intermediate frequency compensation module receives the signals from the wavelength switching control module and the frequency measurement circuit. First, the wavelength switching module is used to determine the laser which needs to be wavelength corrected. Then, the frequency measurement circuit is used to judge the difference between the laser and the intermediate frequency standard value. Taking the 1550nm output light generating a 200MHz intermediate frequency signal as an example, in the case of 5MHz frequency shift, the wavelength will change by 0.04pm. In the case of non-operation of the intermediate frequency compensation module, the frequency spectrum diagram of the 200MHz intermediate frequency signal changing with time is shown in Figure 5 . The intermediate frequency compensation module in the embodiment changes the injection current of the phase shift region of the corresponding channel laser, so as to realize the fine regulation of the wavelength. The wavelength changes with the phase shift region current at a rate of 0.02pm / uA. The connection structure diagram of the intermediate frequency compensation module and the 8x8 REC laser array is shown in Figure 3 . The 64 lasers are connected to the intermediate frequency compensation module one by one, and are independently controlled without interference. At the same time, the TEC radiator works at a constant temperature of 25℃, so as to exert the better performance of the laser and maintain the stable output. Then, the output wavelength of the laser is synchronized and adapted to the signal light under the regulation of the intermediate frequency compensation module, so as to eliminate the influence of the wavelength difference and the jitter, and realize the constant output of the intermediate frequency signal. The frequency spectrum diagram of the 200MHz intermediate frequency signal changing with time under the normal operation of the embodiment is shown in Figure 6 . The frequency value of the intermediate frequency signal can be effectively constant. At the same time, when the next wavelength signal light arrives, the wavelength detection module and the wavelength switching control module select the corresponding channel laser again, and enter the next round of intermediate frequency stable control.

[0059] In summary, the REC array tunable laser system for the local oscillator light source in the dry system of the embodiment can realize wide-range fast tunable laser output, intelligently light up the corresponding channels of the laser array, and well suppress the wavelength search drift jitter of the local oscillator light and the signal light, provide reliable technical support for stable intermediate frequency signal output and realize high-quality coherent communication.

[0060] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application shall be considered as falling within the protection scope of the present application.

Claims

1. A REC array tunable laser system for a local oscillator light source in a coherent system, characterized in that, The REC array tunable laser system comprises a REC laser array, a waveguide beam splitter, an optical filter set, a wavelength detection module, a waveguide coupler, a photodetector, an intermediate frequency compensation module, a frequency measurement circuit and a wavelength switching control module. The REC laser array is used to output several kinds of equally spaced different wavelength lasers, and the output laser is transmitted to one input end of the waveguide coupler through an optical fiber waveguide. The waveguide beam splitter is used to transmit the input signal light to the optical filter set and the other input end of the waveguide coupler at a preset splitting ratio. The optical filter set is connected with the wavelength detection module and the wavelength switching control module, and comprises several waveguide channels, each of which allows the passage of light wavelengths corresponding to the several lasers of the REC laser array; the optical filter selects the corresponding channel according to the wavelength of the signal light, and outputs the signal light to the wavelength detection module through the selected channel, and the wavelength detection module detects the optical power of each channel and transmits the corresponding channel lighting information to the wavelength switching control module; the wavelength switching control module processes the channel value input by the wavelength detection module, and lights up the laser corresponding to the channel value to control the REC laser array to work in the channel matched with the signal light; The waveguide coupler couples the local oscillator laser output by the REC laser array with the signal light, and outputs the coherent intermediate frequency signal light, which is transmitted to the photodetector through an optical fiber waveguide and converted into a corresponding intermediate frequency electrical signal. The frequency measurement circuit measures the frequency of the intermediate frequency electrical signal output by the photodetector and outputs the measured frequency value to the intermediate frequency compensation module. The intermediate frequency compensation module determines the laser that needs to be wavelength corrected according to the channel value input by the wavelength switching control module, calculates the difference between the frequency value input by the frequency measurement circuit and the intermediate frequency standard value, and finely adjusts the lasing wavelength of the corresponding laser by changing the injection current of the phase shift region of the corresponding channel laser, so that the output light wavelength of the channel fluctuates within the tuning range and matches the signal light to stabilize the intermediate frequency value of the coherent signal.

2. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The REC array tunable laser system further comprises a TEC heat sink for dissipating heat from the REC laser array to maintain a constant temperature in the working environment.

3. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 2, wherein, The laser array, waveguide beam splitter, optical filter set, wavelength detection module, waveguide coupler, photodetector, intermediate frequency compensation module, frequency measurement circuit, wavelength switching control module and TEC heat sink are all integrated on the same chip.

4. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The REC laser array adopts a 64-wavelength laser array arranged in an 8x8 array, the wavelength interval of adjacent laser channels is 0.8nm, the wavelength interval of two adjacent lasers on the same waveguide is 6.4nm, and the output laser wavelength range is 1524.4-1571.6nm.

5. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The wavelength detection module and the optical filter set are connected one-to-one through several waveguides, and a miniature photodetector is attached to the tail end of each waveguide inside the module.

6. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 5, wherein, The wavelength detection module detects power through a micro photoelectric detector at the tail of the waveguide to determine the waveguide channel number with signal light, converts the electric signal generated by the channel light through the micro photoelectric detector into sequence information through an internal logic circuit, adds a data frame header, and then delivers to the wavelength switching control module; After receiving the sequence information input by the wavelength detection module, the wavelength switching control module detects the frame header information, judges the channel sequence value carried by the sequence information when detecting the valid frame header, controls the on-off of the REC laser array corresponding to the channel, lights up the corresponding laser, realizes the matching with the signal light wavelength, and outputs the local laser to the waveguide coupler for coherent effect.

7. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The wavelength switching control module is connected with each laser in the REC laser array one by one, and independently controls the lighting of each laser.

8. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The adjustment step of the intermediate frequency compensation module is 0.02 nm / mA.

9. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The frequency determination range of the frequency measurement circuit is 0-1000 MHz; for high frequency signals exceeding the frequency determination range, the internal protection circuit removes the high frequency signals.

10. The REC array tunable laser system for a local oscillator light source in a coherent system of claim 1, wherein, The optical power of the intermediate frequency signal light is represented as: wherein E1 is the input signal optical electric field, P1 is the signal optical power, ω1 is the signal optical angular frequency, is the time-varying signal optical phase, E2 is the local oscillator optical electric field, P2 is the local oscillator optical power, ω2 is the local oscillator optical angular frequency, ω IF = ω1- ω2 is the intermediate frequency frequency, and the coherent post-signal power is amplified by a factor of 2.

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