Control device for optical filters

Abstract

In order to further speed up the response speed of an optical filter in which transmission wavelength can be adjusted according to the temperature, the control circuit of the optical filter generates and outputs a signal that generates a power waveform having a leading pulse part and an attenuation part which is after the leading pulse part and in which attenuation proceeds exponentially to a predetermined value from a point lower than the height of the pulse part and higher than the predetermined value. Further, where a plurality of optical filters are provided and used while switching between the plurality of optical filters, the transmission wavelength can also be switched in a short time.

Description

[Technical Field]

[0001] This invention relates to a control technique for an optical filter whose transmission wavelength can be adjusted according to temperature. [Background technology]

[0002] In recent years, the expansion of video distribution services and cloud services has accelerated the construction of new data centers, while communication traffic in existing data centers has surged. The power consumption of network equipment that processes communication traffic within data centers continues to increase, and in order to achieve further scaling up and power saving in the future, it will be important to replace conventional electronic switch equipment, which converts optical signals into electricity for processing, with optical switch equipment that processes optical signals as light. On the other hand, in order to achieve overall network efficiency with optical switch equipment, it is desirable to set the wavelength of the variable optical filter included in the optical switch equipment to 50 microseconds or less.

[0003] Here, a variable optical filter is a filter that extracts a specific optical wavelength from among multiple optical wavelengths, and is a device that can select any optical wavelength by a control signal. As such a variable optical filter, ring-type optical filters using optical waveguides made of silicon (Si) or quartz (SiO2) are considered promising because they have high finesse (i.e., selectivity) and the wavelength can be varied by temperature control using a small heater. For example, Non-Patent Literature 1 reports a wavelength setting speed of 50 μs using a Si ring-type optical filter.

[0004] Furthermore, as one method of increasing speed, Non-Patent Document 2, for example, proposes improving the response speed by reducing the thickness of the cladding layer. However, from the standpoint of complicating the manufacturing process, it is undesirable to change manufacturing parameters such as the thickness of the cladding layer. Moreover, as one method of improving the response speed of optical filters manufactured using a standard manufacturing process, Non-Patent Document 3, for example, proposes the so-called "turbo pulse" method, which involves applying a rectangular voltage with instantaneous high power to rapidly heat the filter. It has been reported that this can reduce the response speed of optical filters called Mach-Zehnder type to less than 10 microseconds. However, Mach-Zehnder type optical filters have low finesse and low integration density, making them unsuitable for optical switch equipment for data centers. Furthermore, in ring-type optical filters, heating shifts the wavelength to the long-wave side, and conversely, cooling shifts the wavelength to the short-wave side. However, the "turbo pulse" method only speeds up the heating direction, and cannot speed up the cooling direction.

[0005] To address the problem of not being able to increase the speed in the cooling direction, a method has been proposed, for example, in Non-Patent Document 4, in which two ring-type optical filters are arranged in parallel and switched between using switches placed before and after the optical filters. In this way, when setting a wavelength shorter than the wavelength of the currently selected optical filter, the other optical filter, which is not currently selected and is waiting in an unheated state, can be heated using a "turbo pulse" to increase the speed.

[0006] However, Non-Patent Documents 3 and 4 use rectangular turbo pulses, and it was found that, as a characteristic of high-finesse optical filters, the response speed cannot be sufficiently fast at all wavelength settings. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] AL Liepvre, et al., "Fast Tunable Silicon Ring Resonator Filter For Access Networks," Proceedings of Optical Fiber Communication (OFC) 2015, Tu3E.5 (2015). [Non-Patent Document 2] O. Moriwaki, et al., "Fast Switching of 84 μs for Silica-based PLC Switch," Proceedings of OFC 2020, Th3B.5 (2020). [Non-Patent Document 3] H. Matsuura, et al., “Fast Frequency Tuning of Silicon-Photonic Thermo-optic MZI Filters using “Turbo Pulse” Method,” Proceedings of OFC 2018, M4H.2 (2018). [Non-Patent Document 4] R. Matsumoto, et al., "Design and verification of a LO bank enabled by fixed-wavelength lasers and fast tunable silicon ring filters for creating large scale optical switches," Optics Express 29 (24), 39930 (2021). [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Therefore, in one aspect, an object of the present invention is to provide a technique for increasing the response speed of an optical filter whose transmission wavelength can be adjusted according to temperature. [Means for solving the problem]

[0009] The control circuit of the optical filter according to the first aspect of the present invention generates and outputs a signal that generates a power waveform having a leading pulse portion and, after the pulse portion, a decay portion that exponentially decays from a level lower than the height of the pulse portion and higher than a predetermined value to the predetermined value, for a heater of the optical filter whose transmission wavelength can be adjusted according to temperature. The optical filter device according to the second aspect of the present invention includes: (A) the control circuit described above; (B) a plurality of optical filters whose transmission wavelengths can be adjusted according to temperature and each having a heater; (C) a first optical switch connected to the plurality of optical filters and capable of outputting input light to any one of the plurality of optical filters; and (D) a second optical switch connected to the plurality of optical filters and capable of outputting light from any one of the plurality of optical filters. The control circuit further selects any one of the plurality of optical filters, controls the first optical switch to output input light to the selected optical filter, controls the second optical switch to output light from the selected optical filter, and outputs the above signal for realizing a target transmission wavelength in the selected optical filter to the heater of the selected optical filter.

Brief Description of Drawings

[0010] [Figure 1] FIG. 1 is a diagram showing a configuration example of an optical filter device according to the first embodiment. [Figure 2] FIG. 2 is a diagram for explaining the state switching of an optical switch. [Figure 3] FIG. 3 is a diagram for explaining the path switching of an optical switch section. [Figure 4] FIG. 4(a) is a diagram for explaining temperature change and transmission wavelength change, FIGS. (b) and (c) are diagrams for explaining step input and step response, FIGS. (d) and (e) are diagrams for explaining turbo pulse input and its response, and FIGS. (f) and (g) are diagrams for explaining the input waveform and response waveform according to the embodiment. [Figure 5] FIG. 5 is a diagram showing the processing flow of a control circuit. [Figure 6]FIG. 6 is a diagram showing an example of a power waveform according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing an example of a power waveform according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing a configuration example of an optical filter device according to the second embodiment. [Figure 9] FIG. 9 is a schematic diagram showing variations of an optical filter.

Embodiments for Carrying Out the Invention

[0011] [Embodiment 1] A configuration example of an optical filter device according to this embodiment is shown in FIG. 1. The optical filter device 1000 according to this embodiment includes an optical circuit chip 600 and a control circuit 400. The optical circuit chip 600 includes optical filters 310 and 320, optical switch units 100 and 200, and a thermometer 500 that measures the temperature of the optical circuit chip 600. The control circuit 400 obtains temperature information from the thermometer 500 and controls the optical switch units 100 and 200 and the optical filters 310 and 320. The optical switch unit 100 is connected to the inputs of the optical filters 310 and 320. Input light (Input) is input, and according to an instruction from the control circuit 400, it outputs the input light to either the optical filter 310 or the optical filter 320. Also, the optical switch unit 200 is connected to the outputs of the optical filters 310 and 320, and according to an instruction from the control circuit 400, it outputs the output light from either the optical filter 310 or the optical filter 320. The optical switch unit 100 includes, for example, Mach-Zehnder interferometer type optical switches 110 to 130, and the optical switch unit 200 includes, for example, Mach-Zehnder interferometer type optical switches 210 to 230.

[0012] The optical filters 310 and 320 are, for example, ring-shaped optical filters, and their transmission wavelength can be adjusted according to the temperature. Each of them has a heater for temperature adjustment, which is not shown in Figure 1. The control circuit 400 alternately selects optical filter 310 and optical filter 320 when changing the transmission wavelength, and controls each of the optical switches 110 to 130 included in the optical switch unit 100 to output input light to the selected optical filter. Similarly, the control circuit 400 controls each of the optical switches 210 to 230 included in the optical switch unit 200 to output output light from the selected optical filter. Furthermore, the control circuit 400 outputs a signal waveform to the heater of the selected optical filter to achieve the target transmission wavelength with the selected optical filter, based on the temperature measured by the thermometer 500.

[0013] Optical switches 110 to 130 are 2-input, 2-output switches, as schematically shown in Figures 2(a) and (b), respectively, and in this embodiment, one input (represented by *) is not used. These optical switches can switch between a first state, as shown in Figure 2(a), where input in1 and output out1 are connected, and a second state, as shown in Figure 2(b), where input in1 and output out2 are connected. The inputs and outputs of these optical switches are interchangeable, and in optical switches 210 to 230 included in the optical switch unit 200, one output (represented by *) is not used.

[0014] Based on these basic operations, by switching the state of each optical switch in the optical switch units 100 and 200 shown in Figure 1 as shown in Figure 3(a), the input light passes through the optical filter 310 and outputs output light having a specific wavelength. By switching as shown in Figure 3(b), the input light passes through the optical filter 320 and outputs output light having a specific wavelength. Note that for optical switches 120 and 130, output out1 is terminated (denoted as x) so that no light is output when switched to the first state, and for optical switches 220 and 230, input in1 is terminated so that no light is input when switched to the first state. Specifically, as shown in Figure 3(a), by switching optical switch 110 to the first state, optical switch 120 to the first state, and optical switch 130 to the second state, input light is output to the optical filter 310. Furthermore, by switching the optical switch 230 to the second state, switching the optical switch 220 to the first state, and switching the optical switch 210 to the second state, the output light from the optical filter 310 is output.

[0015] Furthermore, as shown in Figure 3(b), by switching the optical switch 110 to the second state, the optical switch 120 to the second state, and the optical switch 130 to the first state, input light is output to the optical filter 320. Also, by switching the optical switch 230 to the first state, the optical switch 220 to the second state, and the optical switch 210 to the first state, output light from the optical filter 320 is output.

[0016] Furthermore, since the optical switches 120 and 130 and 220 and 230 are introduced to cut out leaked light and suppress crosstalk, functionally, if optical switches 110 and 210 are present, the optical filters 310 and 320 can be selected. Alternatively, the configuration of the optical switch sections 100 and 200 may be changed by adopting optical switches based on other methods.

[0017] While the state switching of each optical switch as described above is the same as in the conventional method, the control circuit 400 outputs a different signal waveform to the heater of the selected optical filter from among optical filters 310 and 320, which allows for high-speed setting of the transmission wavelength of the optical filter. Here, we will explain the key points of the signal waveform to be output to the heater of the optical filter using Figures 4(a) to (g). High-finesse optical filters, such as ring-type optical filters, require precise and high-speed control to adjust the temperature to the target temperature because the transmittance of light changes sharply even with a small temperature shift. As shown in the upper part of Figure 4(a), we attempt to raise the temperature to the target temperature in 10 to 100 μs, but as schematically shown in the lower part of Figure 4(a), the transmission wavelength band, indicated by the dotted line and represented by the horizontal triangle, gradually shifts in accordance with the temperature rise, and only when the target temperature (Target) is reached can the desired transmission wavelength band be obtained.

[0018] Figure 4(b) shows the results of applying a unit step input (also called a step function) to the heater of the optical filter, and Figure 4(c) shows the step response of temperature and the step response of transmittance to this step input. The vertical axis in Figure 4(b) represents normalized power. This normalized power is P / P0 [unit: none], which is the value obtained by dividing the power (electrical power) P [W] of Joule heat physically injected into the heater by the power P0 [W] that must be continuously injected to maintain the target temperature. In Figures 4(d) and (f), the vertical axis also represents normalized power. The vertical axis in Figure 4(c) represents the normalized temperature, with the starting temperature as 0 and the target temperature as 1, and the transmittance of light at the wavelength corresponding to the target temperature. The same applies to Figures 4(e) and (g). As can be seen, with step input, the target temperature is not reached even after 40 μs, so the transmittance does not increase. In other words, the response speed cannot be increased with step input.

[0019] In contrast, Figure 4(d) shows an example of a turbo pulse demonstrated using conventional technology. The turbo pulse shown in Figure 4(d) is created by adding a large initial pulse with a height exceeding 9 at normalized power to the step input. However, as shown in Figure 4(e), with such a turbo pulse, the temperature initially reaches the target temperature, but cannot maintain it, dropping before gradually converging back to the target temperature. When viewed in terms of transmittance, this results in large fluctuations, and is not stable even at 40 μs.

[0020] In contrast, this embodiment employs a novel power waveform as shown in Figure 4(f). This novel power waveform has a pulse portion with a very large height exceeding 15 in normalized power, and an attenuation portion that decreases exponentially from a point much lower than the height of the pulse portion, approaching a predetermined value (here, 1). The details will be explained later, but by employing such a special power waveform, as shown in Figure 4(g), the target temperature is reached in less than 10 μs and is maintained stably and sustainably, and the transmittance can be maintained at 1.0 in less than 10 μs. In other words, the response speed can be increased. If such a high-speed response is possible, even when multiple stages of optical filters are used to bring the transmission spectrum closer to an ideal rectangle, a target response time of 50 μs can be achieved, for example.

[0021] [Method 1 for generating power waveforms in Embodiment 1] This method will be explained using Figure 5. First, pre-shipment calibration is performed to configure various settings used during the operation of the optical filter device 1000 (Step S1).

[0022] First, a step input is applied to the heater of the optical filter included in the optical filter device 1000, and the temperature change ΔT(t) of the heater corresponding to the step input (i.e., the step response) is set to the final temperature ΔT ∞ The function U(t) divided by ΔT(t) / ΔT ∞Calculate it. And, assuming L[·] is the Laplace transform, calculate G(s)=L[U(t)]s. This corresponds to the transfer function for the input power waveform of the optical filter. And, U * (t)=L[1 - e -t / τ0 , and q * (t)=L -1 [U * (t) / G(s)]. Note that L -1 [·] is the inverse Laplace transform, 1 - e -t / τ0 is a function representing the target temperature change (for example, the temperature change in Fig. 4(g)), τ0 represents the time constant, and is a value corresponding to the target response speed (for example, a value of 50 μs or less). q * (t) represents the input waveform for obtaining the target temperature change. That is, this calculation inversely calculates the power waveform for obtaining the target temperature change based on the temperature response characteristics (step response above) of the heater.

[0023] In step S1, record the data of the power waveform q * (t) thus obtained in the non-volatile memory included in the control circuit 400. Also, obtain the temperature T0 of the optical circuit chip 600 from the thermometer 500, and at that time, also acquire the wavelength W0 with the best transmittance. Further, change the temperature of the optical circuit chip 600 and measure the wavelength with the maximum transmittance at multiple temperatures, and perform linear fitting to also acquire the rate of change of wavelength with respect to temperature change k = dW / dT [nm / K]. Also, when applying a power waveform obtained by multiplying q * (t) by x, obtain the temperature rise T x , and calculate the proportionality coefficient m = x / T * of q x (t) required to raise the temperature of the heater by 1K. Further, regard the heater of the optical filter as a resistor and obtain its resistance value R [Ω]. Also record the temperature T0, wavelength W0, k, m, and R thus obtained in the non-volatile memory.

[0024] After performing this pre-shipment calibration, when actually operating the optical filter device 1000, steps S3 to S13 in Figure 5 are repeated. Specifically, the control circuit 400 obtains the current temperature T1 from the thermometer 500 (step S3). Then, the control circuit 400 calculates the transmission wavelength W1 of the optical filter at temperature T1 (step S5). Here, W1 is calculated as W1 = k × (T1 - T0) + W0 [nm].

[0025] The control circuit 400 then determines whether the target wavelength W2 of the light to be output by the optical filter device 1000 has changed (step S7). If the target wavelength W2 has not changed, the process proceeds to step S13. On the other hand, if the target wavelength W2 has changed, the control circuit 400 selects the optical filter that has not been selected, rather than the one currently selected, and calculates the required temperature change ΔT from the target wavelength W2 (step S9). Specifically, it calculates ΔT = (W2 - W1) / k [K].

[0026] The control circuit 400 then instructs the optical switch units 100 and 200 to switch, calculates the applied waveform to obtain the temperature change amount ΔT, and outputs the signal of the applied waveform to the heater of the optical filter selected this time (step S11). Specifically, the power waveform P(t) = m × ΔT × q * The (t)[W] is calculated and output. Note that actual power sources are often voltage sources (E(t)) or current sources (I(t)), so the output may be converted to a voltage waveform or current waveform as shown below. E(t) = {P(t) × R} 1 / 2 [V] I(t) = {P(t) / R} 1 / 2 [A]

[0027] Then, the control circuit 400 returns to step S3 and repeats the process described above until the process is completed (step S13).

[0028] For example, q *Figure 6 shows a specific waveform example for (t)-1. In Figure 6, the vertical axis represents normalized power, and the horizontal axis represents time. Figure 6 also shows the waveform for a silicon ring-type optical filter heater. In this example as well, the waveform includes a pulse portion from 0 to approximately 5 μs and a decay portion from approximately 5 μs onward. In the decay portion, the value decreases exponentially. The pulse portion is provided to apply high power for rapidly heating the optical filter with the heater. In Figure 6, fine irregularities and curves that smoothly connect to the decay portion can be seen, but in reality, such fine waveforms are faster than the temperature response rate and are not important when viewed overall; they can be replaced with rectangular pulses without any problem. The decay portion is the part where the value decreases exponentially, and fine vibrations can be seen in Figure 6, but these vibrations are due to calculation errors and it is not actually necessary to reproduce such a vibrating waveform.

[0029] In the example above, the power waveform q * An example was shown in which (t) is calculated and the data is stored in non-volatile memory, but it is also possible to store the voltage waveform or current waveform. That is, the normalized voltage waveform v(t) and current waveform i(t) are as follows. v(t) = {q * (t) × R} 1 / 2 i(t) = {q * (t) / R} 1 / 2 Note that {m × ΔT} 1 / 2 By multiplying by this, the desired voltage waveform or current waveform can be obtained.

[0030] [Power waveform generation method 2 in Embodiment 1] This method provides a simple way to generate a desirable power waveform. Specifically, it assumes that a power waveform of the shape shown in Figure 7 will be output, and its parameters are stored in advance. When actually outputting the waveform, it is scaled according to the target wavelength.

[0031] As shown in Figure 7, there is a pulse section at the beginning with a width w1 and a height h1, followed by a decay section with an initial height h2 and asymptotically approaching 1 exponentially with a time constant τ2 (also written as τ2). A gap w2 may be provided between the pulse section and the decay section.

[0032] The pulse portion may be a rectangular pulse, or it may have a smooth, curved shape. However, the integral value Q [J] of the pulse portion is set to be expressed as Q = ξ × C × (T2 - T1), where C [J / K] is the heat capacity of the heater structure, ξ is a proportionality constant corresponding to the distance between the heater structure and the waveguide, T1 [K] is the temperature before heating, and T2 is the temperature corresponding to the target wavelength W2. The pulse width w1 is set according to the target response speed, and is, for example, in the range of 0.1 to 50 μs.

[0033] The attenuation is expressed as 1 + h2exp{-(t-w1-w2) / τ2}. Typically, h2 ≪ 1, for example, h2 is approximately 0.1. h2 is determined by the ratio of the ease of heating around the waveguide to the ease of heating over a wider area of ​​the substrate, and may differ in non-silicon photonics materials such as Silica PLC, InP, and SiN waveguides. The attenuation is necessary to counteract the slow changes required when heating the large heat capacity of the substrate, and its height h2 is proportional to the ratio of the ease of heating around the waveguide to the ease of heating that large heat capacity. For example, if the waveguide has a hollow structure (adiabatic structure) and the "large heat capacity" can be isolated, h2 will be zero. Even if the heat capacity of the "large heat capacity" is very large, h2 will approach zero. Conversely, if there is a relatively small "large heat capacity," such as an electrode or other structure, h2 will tend to increase. Furthermore, the time constant τ² is typically between 1 and 100 μs.

[0034] Each parameter of such a power waveform is determined by prior measurements. First, a pulse with appropriately selected pulse width w1 and height y is applied to the heater, and the time change of the transmitted wavelength through the optical filter is measured. There are various methods for this measurement, but for example, light containing various wavelengths (i.e., white light) is input to the optical filter, the output of the optical filter is spectrally analyzed with a spectrometer, each spectrally analyzed light is input to separate high-speed photodetectors to become an electrical signal, the waveform of each light is recorded with an oscilloscope, and the waveforms for each wavelength are displayed together with the time synchronized. Alternatively, the wavelength of a variable-wavelength monochromatic laser is input to the optical filter, the waveform is recorded in the same way, and then the wavelength of the laser light is slightly changed and the same measurement is performed, and the same measurement is repeated to achieve the same result. Since wavelength change and temperature change correspond, the wavelength change is converted to a temperature change, and if the maximum value Ty of the temperature change at pulse height y is taken, then it is calculated as ξ×C=w1×(y / Ty).

[0035] Furthermore, due to constraints of the control circuit, etc., a specific maximum pulse height y MAX If a pulse of a higher height is not possible, the maximum temperature difference T required for operation as an optical filter is specified. MAX Therefore, w1 = [ξ × C] / (y MAX / T MAX The pulse width w1 is determined according to the following. For hardware that can achieve a maximum voltage of about 10V using a silicon ring-type optical filter, w1 is typically a value of 1 to 5μs.

[0036] Next, ignoring the pulses mentioned above, we measure the temperature change ΔTp [K] of the optical filter when a certain power P [W] is steadily applied to the heater, and calculate P0 = P / ΔTp. Since the temperature change of the optical filter cannot be measured directly, we use the change in the transmission wavelength of the optical filter ΔW to calculate ΔTp = ΔW / k. This P0 is the power required to raise and maintain the temperature of the optical filter by 1 degree. Using this value, the height of the pulsed section normalized is h1 = ξ × C / (P0 × w1).

[0037] Furthermore, when the temperature change amount ΔT is required, the actual height of the pulse section is h1 × P0 × ΔT. As mentioned above, ΔT is calculated as ΔT = (W2 - W1) / k [K].

[0038] Next, a damping section with a shape defined by initial values ​​w2=0μs, h2=0.1, and τ2=20μs is added to the pulse section obtained earlier. Here, the value of h2 is normalized by P0. In this case, the damping section is 1+h2exp{-(t-w1-w2) / τ2}, but if the temperature change is ΔT, then when actually applied, it becomes P0×ΔT×{1+h2exp{-(t-w1-w2) / τ2}}.

[0039] Then, the time evolution of the transmission wavelength of the optical filter when a power waveform including pulse and attenuation portions is applied is determined, and optimization methods such as the steepest descent method are used to optimize the widths w1 and w2, pulse height h1, initial height h2 of the attenuation portion, and time constant τ2 so that the response speed is as fast as possible.

[0040] The widths w1 and w2, pulse height h1, initial height h2 of the attenuation section, time constant τ2, P0, and k obtained in this manner are recorded in the non-volatile memory of the control circuit 400.

[0041] When actually operating the optical filter device 1000, the same processing as steps S3 to S13 shown in Figure 5 is performed. However, in step S11, the height of the pulse portion is h1 × P0 × ΔT, and the power waveform P(t) is formed such that the attenuation portion is P0 × ΔT × {1 + h2exp{-(t-w1-w2) / τ2}}. When outputting as a voltage waveform or current waveform, R and m mentioned above are further recorded in non-volatile memory, and the waveform is transformed and output in the same manner as described above. E(t) = {P(t) × R} 1 / 2 [V] I(t) = {P(t) / R} 1 / 2 [A]

[0042] Alternatively, instead of calculating parameters for the power waveform, parameters for the current waveform or voltage waveform may be calculated and recorded in non-volatile memory. When operating the optical filter device 1000, the waveform may be formed and output according to these parameters for the current waveform or voltage waveform. In this case, the procedure described above as power waveform generation method 2 can be performed while setting the final applied voltage or current according to the equations E(t) and I(t) in the previous paragraph.

[0043] [Embodiment 2] In the first embodiment, the configuration allowed for the selection of either of two optical filters, 310 or 320. However, this configuration presents a problem in that it is difficult to accommodate high-frequency wavelength switching. Specifically, when switching the transmission wavelength, the optical filter must be switched. If the target optical filter has not sufficiently cooled naturally to ambient temperature, the transmission wavelength cannot be accurately adjusted. Therefore, it is undesirable to switch optical filters in less time than required for natural cooling.

[0044] In this embodiment, by using an integer N (3 or more) optical filters, it is possible to select a sufficiently naturally cooled optical filter from among N-1 optical filters other than the currently selected optical filter, thereby supporting high-frequency wavelength switching.

[0045] Figure 8 shows an example of the configuration of an optical filter device according to this embodiment. The optical filter device according to this embodiment includes an optical circuit chip 600b and a control circuit 400b. The optical circuit chip 600b includes a front-end optical switch unit 100b, a back-end optical switch unit 200b, N optical filters, and a thermometer 500 for measuring the temperature of the optical circuit chip 600b. The optical switch unit 100b has 1 input and N outputs and includes a group of optical switches that output input light to a selected optical filter. The optical switch unit 200b has N inputs and 1 output and outputs output light from a selected optical filter. The control circuit 400b sequentially selects optical filters from the first optical filter to the Nth optical filter, for example in a round-robin format, controls the optical switch unit 100b so that input light is output to the selected optical filter, and controls the optical switch unit 200b so that output light is output from the selected optical filter.

[0046] The control circuit 400b outputs the power waveform, voltage waveform, or current waveform described in the first embodiment to the selected optical filter. This not only enables high-speed response but also allows for high-frequency wavelength switching.

[0047] Furthermore, in the configuration of the optical filter device shown in Figure 8, even if the control circuit 400b uses a turbo pulse as shown in Figure 4(d), the response speed will be slower than in the first embodiment, but it will be able to handle high-frequency transmission wavelength switching.

[0048] [Other technical matters] The above explanation primarily focused on waveguides, optical switches, and optical filters manufactured from silicon, but the same approach can be applied to those manufactured from other materials.

[0049] Furthermore, while the structure of the optical filter was explained using a ring-type optical filter as an example, it is not limited to a single-ring ring-type optical filter as schematically shown in Figure 9(a), but may also be a two-stage ring-type optical filter as schematically shown in Figure 9(b). In addition, an optical filter using a Bragg grating as schematically shown in Figure 9(c) or a lattice filter as schematically shown in Figure 9(d) may also be used.

[0050] Although embodiments of the present invention have been described above, the numerical values ​​are merely examples and are not limiting. Furthermore, the power waveform, voltage waveform, or current waveform is set to enable the heater of the optical filter to respond quickly, and the shape of the waveform itself may change depending on the type of optical filter.

[0051] The embodiments described above can be summarized as follows:

[0052] According to an embodiment of the present invention, the control circuit for an optical filter generates and outputs a signal to a heater of an optical filter whose transmission wavelength can be adjusted according to temperature, which generates a power waveform having a leading pulse portion and an attenuation portion that follows the pulse portion and attenuates exponentially to a predetermined value from a point lower than the height of the pulse portion and higher than a predetermined value.

[0053] By outputting such a signal to the heater of the optical filter, the heater of the optical filter can reach the target temperature earlier than with the so-called turbo pulse used in conventional technology. This allows the target transmission wavelength to be set earlier, and light of the target wavelength to be output earlier.

[0054] Furthermore, it is preferable that the height of the pulse section and the predetermined value mentioned above are set according to the transmission wavelength to be set in the optical filter. The integral value of the pulse section may also be set according to the transmission wavelength to be set in the optical filter. In addition, a predetermined gap may be provided between the pulse section and the attenuation section for optimization purposes. The initial height of the attenuation section is sufficiently small, about 1 / 10 of the height of the pulse section.

[0055] Furthermore, the control circuit described above may generate the above signal by scaling a pre-prepared and standardized power waveform, current waveform, or voltage waveform based on the amount of temperature change required to change the transmission wavelength from the current temperature to the transmission wavelength to be set in the optical filter. In this way, it becomes possible to respond quickly to various temperatures, i.e., transmission wavelengths.

[0056] The pre-prepared and standardized power waveforms, current waveforms, or voltage waveforms mentioned above may be power waveforms defined by the height and width of the pulse portion, and the height and time constant at the start of attenuation of the attenuation portion, or current waveforms or voltage waveforms that generate such power waveforms. It is also acceptable to define the waveforms in such a simplified manner. Furthermore, parameters that specify the start time of the attenuation portion may also be defined.

[0057] On the other hand, the pre-prepared and standardized power waveforms, current waveforms, or voltage waveforms mentioned above may also be power waveforms calculated inversely based on the heater's temperature response characteristics (e.g., step response) to obtain a target temperature change in the heater, or current waveforms or voltage waveforms that generate such power waveforms. Even waveforms obtained through such calculations have pulse and attenuation sections as described above, enabling the realization of more favorable temperature changes.

[0058] Furthermore, the optical filter device according to an embodiment of the present invention includes (A) a control circuit having the features described above, (B) a plurality of optical filters, each having a heater and capable of adjusting the transmission wavelength according to the temperature, (C) a first optical switch connected to the plurality of optical filters and capable of outputting input light to any of the plurality of optical filters, and (D) a second optical switch connected to the plurality of optical filters and capable of outputting light from any of the plurality of optical filters. The control circuit described above further selects one of the plurality of optical filters and controls the first optical switch to output input light to the selected optical filter, controls the second optical switch to output light from the selected optical filter, and outputs the above signal to the heater of the selected optical filter to achieve the target transmission wavelength in the selected optical filter.

[0059] This approach not only improves the high-speed response of individual optical filters, but also allows for faster wavelength switching by switching from the currently selected optical filter to another, rather than continuing to use a single optical filter.

[0060] Furthermore, the control circuit described above may also sequentially select multiple optical filters in a round-robin manner. This allows for the priority selection of optical filters that have undergone natural cooling, and as the number of optical filters increases, it becomes possible to handle high-frequency wavelength switching.

[0061] Furthermore, an embodiment of the present invention provides a control method for an optical filter, which involves (A) generating and outputting a signal to the heater of an optical filter capable of adjusting the transmission wavelength according to the temperature, that generates a power waveform consisting of a leading pulse portion (for example, a signal for power, current, or voltage that generates only a pulse portion as a power waveform, as shown in Figure 7), and (B) generating and outputting a signal to the heater of the optical filter that generates a power waveform that, after the pulse portion, starts at a point lower than the height of the pulse portion and higher than a predetermined value and then exponentially decays to the predetermined value (for example, a signal for power, current, or voltage that generates a power waveform that decays exponentially after the pulse portion, as shown in Figure 7).

Claims

1. For a heater in an optical filter whose transmission wavelength can be adjusted according to temperature, The leading rectangular pulse section, Following the pulse section, there is an attenuation section that attenuates exponentially from a point lower than the height of the pulse section but higher than a predetermined value to the predetermined value. It generates and outputs a signal that produces a power waveform having the following characteristics. A control circuit for the aforementioned optical filter, A predetermined gap is provided between the pulse section and the attenuation section. Control device.

2. The height of the pulse portion and the predetermined value are set according to the transmission wavelength to be set in the optical filter. The control circuit according to claim 1.

3. For a heater in an optical filter whose transmission wavelength can be adjusted according to temperature, The leading pulse section, Following the pulse section, there is an attenuation section that attenuates exponentially from a point lower than the height of the pulse section but higher than a predetermined value to the predetermined value. It generates and outputs a signal that produces a power waveform having the following characteristics. A control circuit for the aforementioned optical filter, The aforementioned control circuit is The signal is generated from the result of scaling a pre-prepared and standardized power waveform, current waveform, or voltage waveform based on the amount of temperature change required to change the transmission wavelength from the current temperature to the transmission wavelength to be set in the optical filter. Control circuit.

4. The aforementioned pre-prepared and standardized power waveform, current waveform, or voltage waveform is: The power waveform is defined by the height and width of the pulse portion and the height and time constant of the attenuation portion at the start of attenuation, or the current waveform or voltage waveform that generates the power waveform. The control circuit according to claim 3.

5. The aforementioned pre-prepared and standardized power waveform, current waveform, or voltage waveform is: Based on the temperature response characteristics of the heater, the power waveform is calculated inversely to obtain a target temperature change in the heater, or the current waveform or voltage waveform that generates the power waveform. The control circuit according to claim 3.

6. A control circuit generates and outputs a signal that produces a power waveform for a heater of an optical filter whose transmission wavelength can be adjusted according to temperature, the signal having a leading pulse portion and a subsequent attenuation portion that starts lower than the height of the pulse portion but higher than a predetermined value and then exponentially attenuates to the predetermined value. Multiple optical filters, each having a heater, whose transmission wavelength can be adjusted according to the temperature, A first optical switch connected to the plurality of optical filters and capable of outputting input light to any of the plurality of optical filters, A second optical switch connected to the plurality of optical filters and capable of outputting light from any of the plurality of optical filters, It has, The aforementioned control circuit is The first optical switch is controlled to select any optical filter other than the currently selected optical filter from the plurality of optical filters, and to output input light to the selected optical filter, and the second optical switch is controlled to output light from the selected optical filter. The selected optical filter's heater is output with the signal necessary to achieve the target transmission wavelength for that optical filter. Optical filter device.

7. The control circuit sequentially selects the plurality of optical filters in a round-robin format. The optical filter device according to claim 6.

8. A signal is generated and output to the heater of an optical filter whose transmission wavelength can be adjusted according to temperature, producing a power waveform consisting of a leading rectangular pulse. A signal is generated and output to the heater of the optical filter, which produces a power waveform that, after a predetermined interval following the pulse portion, starts at a point lower than the height of the pulse portion but higher than a predetermined value and then exponentially attenuates to the predetermined value. A control method for the aforementioned optical filter.

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