OPTICAL MODULE, OPTICAL TRANSCEIVER, AND METHOD OF CONTROLLING INTENSITY OF LIGHT

An optical amplifier modulates first light with a first modulation signal having a first frequency, and modulates second light with a second modulation signal having a second frequency. A splitter splits the first light and the second light. A light reception unit outputs an electric signal indicating intensity of light acquired by adding the received first light and the received second light. An intensity detection unit extracts a first component having the first frequency and a second component having the second frequency included in the electric signal, and detects amplitude of each of the first and second components. An amplification control unit monitors intensity of the first light based on amplitude of the first component and intensity of the second light based on amplitude of the second component, and controls amplification of each of the first light and the second light in the optical amplifier.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2023-79239, filed on May 12, 2023, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to an optical module, an optical transceiver, and a method of controlling intensity of light.

BACKGROUND ART

In a digital coherent technique applied to optical communication, a wavelength tunable light source such as an integrable tunable laser assembly (ITLA) is mounted as a light source in an optical communication apparatus. Light being output from the ITLA is split toward a reception-side apparatus and a transmission-side apparatus. The transmission-side apparatus transmits an optical signal acquired by modulating input light in response to a data signal. The reception-side apparatus demodulates an optical signal being received from another communication apparatus or the like to an intensity signal by causing the optical signal to interfere with light to be input. In this case, a wavelength of light to be input to the transmission-side apparatus and a wavelength of light to be input to the reception-side apparatus are the same wavelength.

In such a configuration, processing such as stabilization (Japanese Unexamined Patent Application Publication No. 2008-244270) and amplification (Japanese Unexamined Patent Application Publication No. 2007-193209) of light to be supplied to the transmission-side apparatus and the reception-side apparatus, and modulation (Japanese Unexamined Patent Application Publication No. 2001-133824) of light by various modulation methods is performed.

SUMMARY

In this case, in general, it is possible to handle two wavelengths by using two wavelength tunable light sources having different wavelengths of output light from each other. In this case, it is required to keep intensity of light of each of the two wavelengths constant. When two different light sources are mounted, light intensity can be kept constant by the same method so far, however, the light source is strongly required to be small in size and low in power consumption, and it is required to integrate the two light sources. In this case, in a path guiding light from a light source for outputting light of two wavelengths to a transmission side and a reception side, a place where light of two wavelengths passes through the same path occurs. Thus, it becomes difficult to individually monitor intensity of light of two wavelengths.

The present disclosure has been made in view of the above-described circumstances, and an object of the present disclosure is to monitor intensity of light of two wavelengths being guided by the same path with a simple configuration.

An aspect of the present disclosure is an optical module including: an optical amplifier configured to modulate first light having a first wavelength with a first modulation signal having a first frequency and amplify the first light, and modulate second light having a second wavelength different from the first wavelength with a second modulation signal having a second frequency different from the first frequency and amplify the second light; a splitter configured to split the first light and the second light being output from the optical amplifier; a light reception unit configured to receive the first light and the second light being split by the splitter, and output an electric signal indicating intensity of light acquired by adding the received first light and the received second light; an intensity detection unit configured to extract a first component having the first frequency being included in the electric signal and a second component having the second frequency being included in the electric signal, and detect amplitude of the first component and amplitude of the second component; and an amplification control unit configured to monitor intensity of the first light, based on amplitude of the first component, monitor intensity of the second light, based on amplitude of the second component, and control amplification of each of the first light and the second light in the optical amplifier, based on a monitoring result.

An aspect of the present disclosure is an optical transceiver including: a receiver configured to receive a received first wavelength multiplexed optical signal by interfering with first light having a first wavelength, and output a data signal acquired by demodulating the received signal; a transmitter configured to modulate second light having a second wavelength different from the first wavelength in response to the data signal, and multiplex the modulated optical signal into a second wavelength multiplexed optical signal and output the multiplexed signal; a signal processing unit configured to transfer the data signal being output from the receiver to the transmitter; and an optical module configured to output the first light and the second light, in which the optical module includes an optical amplifier configured to modulate the first light with a first modulation signal having a first frequency and amplify the first light, and modulate the second light with a second modulation signal having a second frequency different from the first frequency and amplify the second light, a splitter configured to split the first light and the second light being output from the optical amplifier, a light reception unit configured to receive the first light and the second light being split by the splitter, and output an electric signal indicating intensity of light acquired by adding the received first light and the received second light, an intensity detection unit configured to extract a first component having the first frequency being included in the electrical signal and a second component having the second frequency being included in the electric signal, and detect amplitude of the first component and amplitude of the second component, and an amplification control unit configured to monitor intensity of the first light, based on amplitude of the first component, monitor intensity of the second light, based on amplitude of the second component, and control amplification of each of the first light and the second light in the optical amplifier, based on a monitoring result.

An aspect of the present disclosure is a method of controlling intensity of light, including: modulating first light having a first wavelength with a first modulation signal having a first frequency and amplifying the first light, and modulating second light having a second wavelength different from the first wavelength with a second modulation signal having a second frequency different from the first frequency and amplifying the second light; splitting the first light and the second light being modulated and amplified; receiving the first light and the second light being split, and outputting an electric signal indicating intensity of light acquired by adding the received first light and the received second light; extracting a first component having the first frequency being included in the electric signal and a second component having the second frequency being included in the electric signal, and detecting amplitude of the first component and amplitude of the second component; and monitoring intensity of the first light, based on amplitude of the first component, monitoring intensity of the second light, based on amplitude of the second component, and controlling amplification of each of the first light and the second light, based on a monitoring result.

EXAMPLE EMBODIMENT

Hereinafter, example embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference signs, and redundant description is omitted as necessary.

First Example Embodiment

An optical module according to a first example embodiment will be described. The optical module according to the first example embodiment is configured as a wavelength tunable light source module that outputs first light L1and second light L2having wavelengths different from each other.

FIG.1schematically illustrates a configuration of an optical transceiver1000using an optical module according to the first example embodiment. The optical transceiver1000includes a receiver1001, a transmitter1002, a signal processing unit1003, and an optical module100according to the present example embodiment.

The optical module100outputs the first light L1and the second light L2having different wavelengths from each other to the receiver1001and the transmitter1002, respectively. Hereinafter, a wavelength of the first light L1is represented by λ1. A wavelength of the second light L2is represented by λ2.

The receiver1001receives a wavelength multiplexed optical signal SIG1acquired by wavelength multiplexing an optical signal having the wavelength λ1from another optical transceiver or the like. The receiver1001selectively receives the optical signal having the wavelength λ1by causing the first light L1received from the optical module100to interfere with the wavelength multiplexed optical signal SIG1. Then, the receiver1001outputs a data signal DAT acquired by demodulating the received optical signal having the wavelength λ1to the signal processing unit1003.

The signal processing unit1003transfers the received data signal DAT to the transmitter1002. The signal processing unit1003is configured as a digital signal processor (DSP) for digital coherence. The DSP has a function of outputting the received signal as it is, so-called loopback. Thus, the received data signal DAT can be transferred to the transmitter1002by using loopback included in the signal processing unit1003. Further, for example, the signal processing unit1003may be connected to a host apparatus via a not-illustrated electrical connector, the signal processing unit1003may transfer an electric signal A from the host apparatus to the transmitter1002, and the signal processing unit1003may transfer an electric signal B from the receiver1001to the host apparatus.

The transmitter1002modulates the second light L2received from the optical module100, based on the data signal DAT, and wavelength multiplexes the modulated optical signal to a wavelength multiplexed optical signal SIG2. Then, the transmitter1002outputs the wavelength multiplexed optical signal SIG2to an optical transceiver or the like of a transmission destination.

As described above, the optical transceiver1000can convert the received optical signal having the wavelength λ1into an optical signal having the wavelength λ2.

Next, the optical module100will be described.FIG.2schematically illustrates a configuration of the optical module100according to the first example embodiment. The optical module100includes an optical amplifier1, an optical splitter2, a light reception unit3, an intensity detection unit4, and an amplification control unit5.

The optical amplifier1amplifies each of input first light L1and input second light L2. Further, the optical amplifier1modulates each of the first light L1and the second light L2in response to modulation signals M1and M2supplied from the amplification control unit5. Then, the optical amplifier1outputs the amplified and modulated first light L1and second light L2to the optical splitter2. Note that, the modulation signal M1is also referred to as a first modulation signal. The modulation signal M2is also referred to as a second modulation signal.

The optical amplifier1will be described in more detail.FIG.3illustrates the configuration of the optical module100according to the first example embodiment in more detail. InFIG.3, in order to illustrate propagation paths of each of the first light L1and the second light L2, a spread of a beam of the first light L1and second light L2is displayed.

The optical amplifier1includes a first optical amplification unit11that amplifies and modulates the first light L1, and a second optical amplification unit12that amplifies and modulates the second light L2.

The first optical amplification unit11amplifies the first light L1incident from a light source6with an amplification factor associated to a control signal CON1input from the amplification control unit5.

Further, the first optical amplification unit11modulates the first light L1in response to the modulation signal M1input from the amplification control unit5. In this example, the modulation signal M1is a sinusoidal signal having a frequency f1. The first light L1being amplified and modulated by the first optical amplification unit11is output to the optical splitter2as light whose intensity varies periodically at the frequency f1. Note that, the frequency f1is also referred to as a first frequency.

Intensity P1of the first light L1output from the first optical amplification unit11is expressed by the following equation as a function of a current I1applied to the first optical amplification unit11.

In the equation [1], r is amplitude of a modulation component to be superimposed, and F1is a function indicating a relationship between the intensity of the first light L1and the current I1. The function depends on a characteristic of an optical amplifier, and is derived in advance.

The second optical amplification unit12amplifies the second light L2incident from the light source6with an amplification factor associated to a control signal CON2input from the amplification control unit5.

Further, the second optical amplification unit12modulates the second light L2in response to the modulation signal M2input from the amplification control unit5. In this example, the modulation signal M2is a sinusoidal signal having a frequency f2. The second light L2being amplified and modulated by the second optical amplification unit12is output to the optical splitter2as light whose intensity varies periodically at the frequency f2. Note that, the frequency f2is also referred to as a second frequency.

Intensity P2of the second light L2output from the second optical amplification unit12is expressed by the following equation as a function of a current I2applied to the second optical amplification unit12.

In the equation [2], as in the equation [1], r is the amplitude of the modulation component to be superimposed, and F2is a function indicating a relationship between the intensity of the second light L2and the current I2. The function depends on a characteristic of an optical amplifier, and is derived in advance.

The optical splitter2splits the incident first light L1into an output port PT1and the light reception unit3. Further, the optical splitter2splits the incident second light L2into an output port PT2and the light reception unit3. Herein, a ratio of light reflected by the optical splitter2to the light reception unit3is denoted as γ, and a ratio of light transmitted through the optical splitter2and output to an outside of the optical module100is denoted as 1-γ.

Each of the output ports PT1and PT2is connected to another optical component by optical fibers F1and F2, respectively. Thus, for example, the first light L1is output to the receiver1001, and the second light L2is output to the transmitter1002.

The light reception unit3receives the first light L1and the second light L2being split by the optical splitter2. Then, the light reception unit3outputs a detection signal DET associated to intensity of light acquired by adding the first light L1and the second light L2to the intensity detection unit4. The light reception unit3can be configured by, for example, a photodiode. In this case, the light reception unit3outputs a current signal indicating the intensity of the light acquired by adding the first light L1and the second light L2to the intensity detection unit4as the detection signal DET.

The intensity detection unit4performs predetermined signal processing on the detection signal DET, and thereby detects the intensity of each of the first light L1and the second light L2. As described above, the detection signal DET is a signal in which a component of the intensity of the first light L1periodically varying at the frequency f1and a component of the intensity of the second light L2periodically varying at the frequency f2are superimposed on each other.

Therefore, signal intensity of the detection signal DET is expressed by the following equation.

In the equation [3], n is conversion efficiency of the light reception unit3. γ is a splitting ratio of light in the optical splitter2as described above.

FIG.4illustrates the intensity of the detection signal DET, and a signal component of the first light L1and a signal component of the second light L2included in the detection signal DET. In this way, the detection signal DET is a signal acquired by adding a signal component ηγP1of the first light L1and a signal component ηγP2of the second light L2. Note that, each of the signal component of the first light L1and the signal component of the second light L2is also referred to as a first component and a second component, respectively.

Therefore, by passing the detection signal DET through a frequency filter that passes only the signal component having the frequency f1, the intensity detection unit4can extract the signal component having the frequency f1being a variation component of the first light L1from the detection signal DET. Then, the intensity detection unit4outputs an amplitude signal SA1indicating amplitude A1of the variation component of the first light L1to the amplification control unit5.

Similarly, by passing the detection signal DET through the frequency filter that passes only the signal component having the frequency f2, the intensity detection unit4can extract the signal component having the frequency f2being a variation component of the second light L2from the detection signal DET. Then, the intensity detection unit4outputs an amplitude signal SA2indicating amplitude A2of the variation component of the second light L2to the amplification control unit5.

The amplification control unit5outputs the above-described modulation signals M1and M2to the first optical amplification unit11and the second optical amplification unit12of the optical amplifier1, respectively.

Further, the amplification control unit5controls the first optical amplification unit11by using the control signal CON1in such a way that amplitude of the variation component of the first light L1becomes constant, based on the amplitude signal SA1. The first optical amplification unit11adjusts a value of the current I1in response to the control signal CON1, and thereby can make the amplitude of the variation component of the first light L1constant.

Similarly, the amplification control unit5controls the second optical amplification unit12by using the control signal CON2in such a way that amplitude of the variation component of the second light L2becomes constant, based on the amplitude signal SA2. The second optical amplification unit12adjusts a value of the current I2in response to the control signal CON2, and thereby can make the amplitude of the variation component of the second light L2constant.

Next, the light source6will be described.FIG.3illustrates a configuration example of the light source6. The light source6is configured as a wavelength tunable light source being capable of outputting the first light L1and the second light L2having wavelengths different from each other. The light source6includes a laser element61and an external resonator62.

In the laser element61, a first stripe611and a second stripe612made of an active medium being arranged separately in parallel in a direction orthogonal to an extending direction are formed on the same substrate. Each of a high reflection film61A and a non-reflection film61B are formed on two end surfaces of the laser element61, respectively. The laser element61emits light LA1and light LA2being a laser beam having different wavelengths from each other to the external resonator62from the end surface of the first stripe611and the second stripe612on which the non-reflection film61B is formed. Each of paths of the light LA1and the light LA2illustrated inFIG.3indicates a trajectory of a beam center.

The external resonator62includes a first resonance unit621and a second resonance unit622. Further, a non-reflection film62A is formed on an end surface of the external resonator62where light is incident and emits. The first resonance unit621causes the light LA1being incident from the laser element61to resonate between the end surface of the laser element61and a reflection means in the first resonance unit621, and thereby emits the first light L1being laser light having a first wavelength to the optical amplifier1. The second resonance unit622causes the light LA2being incident from the laser element61to resonate between the end surface of the laser element61and a reflection means in the second resonance unit622, and thereby emits the second light L2being laser light having a second wavelength to the optical amplifier1.

Each of the first resonance unit621and the second resonance unit622may be configured as various resonators. Each of the first resonance unit621and the second resonance unit622may be configured as a resonator that selects a wavelength of resonating light by providing, for example, a wavelength filter including two ring waveguides. In this case, by providing a heater in the ring waveguide and changing a temperature of the ring resonator, a refractive index of the ring waveguide is adjusted, and thereby it is possible to control, to a desired wavelength, each of the first light L1and the second light L2resonating at the first resonance unit621and the second resonance unit622.

In the first resonance unit621and the second resonance unit622, an emission waveguide of each of the first light L1and the second light L2is inclined with respect to an emission end surface in order to further reduce a reflectance of the non-reflection film. Therefore, each of the first light L1and the second light L2is emitted in a direction inclined with respect to the emission end surface.

Further, as illustrated inFIG.3, a first lens7, an isolator8, and a second lens9may be disposed in the optical module100.

The first lens7and the isolator8are disposed between the optical amplifier1and the optical splitter2. Each of the first light L1and the second light L2emitted from the optical amplifier1in different directions from each other is incident on the first lens7while being diffused. The first lens7converts the first light L1and the second light L2into light beams parallel to each other. The first light L1and the second light L2that become the parallel light beams pass through the isolator8, and then are incident on the optical splitter2. As a result, even when the first light L1and the second light L2are reflected after passing through the isolator8and incident on the isolator8as reflected light, the reflected light is blocked by the isolator8. This makes it possible to prevent the reflected light from being incident on the optical amplifier1and the light source6.

The second lens9is disposed on an output side of the optical splitter2. The second lens9converges the first light L1and the second light L2being incident from the optical splitter2, and emits the first light L1and the second light L2toward the output ports PT1and PT2, respectively.

Next, feedback control of intensity of each of the first light L1and the second light L2will be described.FIG.5illustrates a flowchart of feedback control according to the first example embodiment.

The light reception unit3outputs the detection signal DET indicating intensity of light acquired by adding the first light L1and the second light L2.

The intensity detection unit4performs frequency separation on the detection signal DET, and thereby acquires the amplitude signal SA1for the first light L1and the amplitude signal SA2for the second light L2.

The intensity detection unit4calculates the amplitude A1of the signal component having the frequency f1of the first light L1from the amplitude signal SA1. Further, the intensity detection unit4calculates the amplitude A2of the signal component having the frequency f2of the second light L2from the amplitude signal SA2.

The amplification control unit5determines whether the amplitude A1falls within a predetermined range R1. Note that, the predetermined range R1is also referred to as a first range.

When the amplitude A1does not fall within the predetermined range R1, the amplification control unit5outputs the control signal CON1to the optical amplifier1in order to fall the amplitude A1within the predetermined range R1.

The optical amplifier1adjusts the current I1of the first optical amplification unit11in response to the control signal CON1.

The amplification control unit5determines whether the amplitude A2falls within a predetermined range R2. Note that, the predetermined range R2is also referred to as a second range.

When the amplitude A2does not fall within the predetermined range R2, the amplification control unit5outputs the control signal CON2to the optical amplifier1in order to fall the amplitude A2within the predetermined range R2.

The optical amplifier1adjusts the current I2of the second optical amplification unit12in response to the control signal CON2.

InFIG.5, the processing of steps S7 to S9 is performed after the processing of steps S4 to S6, but this is merely an example. The processing of steps S4 to S6 may be performed after the processing of steps S7 to S9 is performed first, or the processing of steps S4 to S6 and the processing of steps S7 to S9 may be performed in parallel.

As a result, the optical module100can perform feedback control in such a way that the intensity of each of the first light L1and the second light L2becomes a desired value.

Note that, the intensity of each of the first light L1and the second light L2can be continuously controlled by regularly or intermittently performing the feedback control constituted of the above-described steps S1 to S9.

Therefore, according to the present configuration, intensity of each of the first light L1and the second light L2can be controlled with high accuracy by feedback control.

Note that, in a case of monitoring light having two wavelengths as in the present example embodiment, it is also conceivable to provide two pairs of a light reception unit and an intensity detection unit, and monitor each piece of light having the two wavelengths by the two pairs. However, in this case, the number of components increases, and thus it leads to an increase in a size of an optical module and an increase in a manufacturing cost of the optical module.

In contrast, the optical module100has a simple configuration for monitoring intensity of each of the first light L1and the second light L2, based on light received by the single light reception unit3. As a result, the optical module can be decreased in a size, and the manufacturing cost can be reduced.

Second Example Embodiment

In the first example embodiment, feedback control based on a monitoring result of intensity of each of first light L1and second light L2has been described. Meanwhile, when an optical module is operated, first, feedforward control for performing initial setting of the intensity of each of the first light L1and the second light L2is performed. Then, in the present example embodiment, the feedforward control of the intensity of each of the first light L1and the second light L2will be described.

FIG.6schematically illustrates a configuration of an optical module200according to a second example embodiment. The optical module200has a configuration in which the amplification control unit5of the optical module100is replaced with an amplification control unit10.

When the feedforward control of the intensity of each of the first light L1and the second light L2is performed, the amplification control unit10outputs control signals CON1and CON2associated to target intensity to a first optical amplification unit11and a second optical amplification unit12, respectively. For this purpose, a correlation between a value of the control signal CON1, for example, a voltage, and the intensity of the first light L1must be recognized in advance. Similarly, a correlation between a value of the control signal CON2, for example, a voltage, and the intensity of the second light L2must be recognized in advance.

The correlation between a control signal and intensity of light can be held in advance as table information in the amplification control unit10, for example. The amplification control unit10can appropriately refer to table information TAB, and provide the control signals CON1and CON2associated to the target intensity to the first optical amplification unit11and the second optical amplification unit12, respectively.

Next, a feedforward control operation according to the second example embodiment will be described.FIG.7illustrates a flowchart of feedforward control according to the second example embodiment.

The amplification control unit10receives an instruction INS specifying the target intensity of each of the first light L1and the second light L2from an external apparatus or the like. The instruction INS may be given, for example, from a signal processing unit1003illustrated inFIG.1, or a not-illustrated control means provided in an optical module100or an optical transceiver1000.

The amplification control unit10refers to the table information TAB held in advance, and outputs the control signals CON1and CON2associated to the specified target intensity.

The first optical amplification unit11sets an initial value of a current I1in response to the control signal CON1. Similarly, the second optical amplification unit12sets an initial value of a current I2in response to the control signal CON2.

In steps S11 to S13, the current I1of the optical amplification unit1and the current I2of the second optical amplification unit12are set based on the instruction INS without monitoring the intensity of each of the first light L1and the second light L2. Thus, at this point of time, it is unclear whether the intensity of each of the first light L1and the second light L2becomes the target intensity.

Thus, by subsequently starting the feedback control described in the first example embodiment, the intensity of each of the first light L1and the second light L2can be set as a target value.

As described above, according to the present configuration, initial setting of intensity of each of the first light L1and the second light L2can be performed by feedforward control. Thereafter, the amplification control unit10performs feedback control of the intensity of each of the first light L1and the second light L2, and thereby it is possible to control the intensity of each of the first light L1and second light L2with high accuracy.

Other Example Embodiments

Note that, the present disclosure is not limited to the above-described example embodiments, and can be appropriately modified without departing from the spirit. For example, the configuration of the optical transceiver and the optical module described above is simplified for convenience of explanation, and it is needless to say that various other components may be included.

In the drawings referred to in the above example embodiments, transmission of a signal between components is represented by using an arrow, but this does not mean that the signal is transmitted only in one direction between two components, and bidirectional transmission of the signals can be made as necessary.

The configuration of the light source6described in the above-described example embodiment is merely an example. As long as the first light L1and the second light L2can be similarly output to the optical amplifier1, the configuration of the light source may be another configuration.