Light source device

Abstract

A light source device (1) comprises: an optical integrated circuit (10) which has a substrate (11); an optical element (5a) which is formed on the substrate (11) and outputs measurement light having a predetermined wavelength; an output unit (6) which is formed on the substrate (11) and outputs the measurement light to the outside of the substrate (11); a light separation unit (21) to which a portion of the measurement light outputted from the output unit (6) is inputted, and which separates the portion of the measurement light into first light and second light at a predetermined separation rate, the separation rate changing monotonously in a predetermined wavelength region; a light detection unit (25, 26) which detects the first light and / or the second light; and a computation unit (9b) which computes the total light amount and centroid wavelength of the measurement light on the basis of at least the detection result of the light detection unit (25, 26).

Description

Light source device

[0001] One aspect of the present disclosure relates to a light source device.

[0002] For example, Patent Document 1 describes a light source device including a light source having a semiconductor optical amplifier and a resonator filter formed on a substrate.

[0003] Japanese Patent Application Laid-Open No. 2018-110158

[0004] In the light source device described in Patent Document 1, a part of the light from the light source is branched and input to a wavelength monitor. Also, the light output to the outside of the substrate is branched by a beam splitter, one of the branched lights is output as output light, and the other light is detected by a power monitor. The detection results by the wavelength monitor and the power monitor are used for feedback control. On the other hand, such a light source device is required to reduce loss.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a light source device capable of performing a wavelength monitor and a power monitor while reducing loss.

[0006] The light source device according to one aspect of the present disclosure is "[1] an optical integrated circuit having a substrate, an optical element formed on the substrate and outputting measurement light having a predetermined wavelength, an output unit formed on the substrate and outputting the measurement light to the outside of the substrate, and a part of the measurement light output from the output unit or a part of the measurement light branched on the optical path between the optical element and the output unit is input, and a light separation unit that separates the part of the measurement light into first light and second light at a predetermined separation ratio, the separation ratio being monotonically changed in a predetermined wavelength range, the light separation unit, a light detection unit that detects at least one of the first light and the second light, and an arithmetic unit that calculates the total light amount and the center wavelength of the measurement light based at least on the detection result of the light detection unit."

[0007] This light source device includes an optical separation unit that receives a portion of the measurement light output from the output unit, or a portion of the measurement light branched in the optical path between the optical element and the output unit, and separates the portion of the measurement light into a first light and a second light at a predetermined separation ratio. This separation ratio changes monotonically in a predetermined wavelength range. At least one of the first light and the second light is detected by an optical detection unit, and the total amount of light (optical power) and the centroid wavelength of the measurement light are calculated based at least on the detection result of the optical detection unit. This allows for wavelength monitoring and power monitoring while reducing losses. That is, for example, in the light source device described in Patent Document 1, a portion of the light from the light source is branched and input to the wavelength monitor, and another portion of the light from the light source is detected by the power monitor, which can lead to large losses and ultimately reduce the power of the output light. In contrast, this light source device calculates the total amount of light and the centroid wavelength of the measurement light based at least on the detection result of the optical detection unit, thus reducing losses. Therefore, this light source device allows for wavelength monitoring and power monitoring while reducing losses.

[0008] A light source device relating to one aspect of this disclosure may be [2] "the light source device according to [1], further comprising a control unit that controls the wavelength of the measurement light output from the optical element based on the centroid wavelength of the measurement light calculated by the calculation unit." In this case, the wavelength of the measurement light output from the optical element can be controlled based on the centroid wavelength of the calculated measurement light.

[0009] A light source device relating to one aspect of this disclosure may be [3] "the light source device according to [1] or [2], wherein the light separation unit is a wavelength separation coupler formed on the substrate, and a portion of the measurement light branched in the optical path between the optical element and the output unit is input to the wavelength separation coupler." In this case, the light separation unit can be realized using a wavelength separation coupler formed on the substrate.

[0010] A light source device relating to one aspect of this disclosure may be [4] "the light source device according to [3], wherein the wavelength separation coupler is a wavelength division multiplexing coupler." In this case, the light separation unit can be realized using a wavelength division multiplexing (WDM) coupler.

[0011] A light source device relating to one aspect of this disclosure may be [5] "the light source device according to [1] or [2], wherein the light separation unit is an optical filter disposed outside the substrate, and a portion of the measurement light output from the output unit is input to the optical filter." In this case, the light separation unit can be realized using an optical filter disposed outside the substrate.

[0012] A light source device relating to one aspect of this disclosure may be [6] "a light source device according to any one of [1] to [5], wherein the light detection unit comprises a first detector for detecting the first light and a second detector for detecting the second light." In this case, wavelength monitoring and power monitoring can be performed based on the detection results of both the first light and the second light.

[0013] A light source device relating to one aspect of this disclosure may be [7] "a light source device according to any one of [1] to [5], further comprising a wavelength filter formed on the substrate, which transmits light in a transmission range including at least a part of the predetermined wavelength range while blocking light outside the transmission range." In this case, it is possible to suppress the input of light having a peak in a wavelength range other than the predetermined wavelength range in which the separation rate changes monotonically to the light separation unit.

[0014] A light source device relating to one aspect of this disclosure may be a light source device according to any one of [1] to [7], wherein the light detection unit is formed on the substrate. In this case, the device can be miniaturized.

[0015] A light source device relating to one aspect of this disclosure may be [9] "a light source device according to any one of [1] to [8], further comprising a light source that outputs input light, wherein the optical element generates and outputs measurement light from the input light, and the light source is formed on the substrate." In this case, the device can be miniaturized.

[0016] According to one aspect of this disclosure, it is possible to provide a light source device that can perform wavelength monitoring and power monitoring while reducing losses.

[0017] This is a diagram illustrating the configuration of a light source device according to an embodiment. (a) shows the light input to the input unit, (b) shows the light output from the wavelength filter unit, and (c) shows the light output from the wavelength selection unit. (a) shows the wavelength detection unit of the first example, (b) shows the wavelength detection unit of the second example, and (c) shows the wavelength detection unit of the third example. This is a diagram illustrating an example of the transmittance of the light separation unit. This is a diagram illustrating a method for calculating the centroid wavelength. (a) shows the reference state, (b) shows the case where the centroid wavelength deviates from the reference state, and (c) shows another case where the centroid wavelength deviates from the reference state. This is a diagram illustrating an example of the relationship between the amount of deviation of the centroid wavelength and the amount of adjustment of the heater power. This is a diagram illustrating the configuration of a light source device according to the first modification. This is a diagram illustrating the configuration of a light source device according to the second modification. (a) shows the wavelength detection unit of the fourth example, and (b) shows the wavelength detection unit of the fifth example. This is a diagram illustrating the configuration of a light source device according to the third modification. This is a diagram illustrating the configuration of a light source device according to the fourth modification. This figure shows an example of the transmission characteristics of the WDM coupler shown in Figure 12. This is a configuration diagram of the light source device of the fifth modified example. This is a configuration diagram of the light source device of the sixth modified example. This is a configuration diagram of the light source device of the seventh modified example. (a) is a diagram showing the light input to the input section in the seventh modified example, (b) is a diagram showing the light output from the wavelength filter section, and (c) is a diagram showing the light output from the wavelength selection section.

[0018] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted.

[0019] The light source device 1 shown in Figure 1 is a light source device that outputs output light Lo to the outside, and is a light source device with a wavelength monitor that has the function of monitoring the wavelength and light intensity (optical power) of the output light Lo. In this example, the light source device 1 is configured as a tunable light source in which the wavelength of the output light Lo can be changed. A tunable light source can be used in wavelength division multiplexing (WDM) technology to realize high-capacity optical communication.

[0020] The light source device 1 is configured to include an optical integrated circuit 10. The optical integrated circuit 10 has a substrate 11, and is configured by fabricating various optical elements such as optical waveguides on the substrate 11. The substrate 11 is a semiconductor substrate formed of a semiconductor such as silicon. The light source device 1 includes a light source 2, an input unit 3, a wavelength filter unit 4, a wavelength selection unit 5, an output unit 6, a beam splitter 7, a wavelength detection unit 8, and a computer 9.

[0021] Light source 2 generates and outputs input light Li, which is input to input unit 3. In this example, light source 2 is a white light source that generates white light as input light Li, but it may also be a tunable light source or a wavelength-swept light source that can change the wavelength of input light Li.

[0022] The input section 3 is the part that inputs the input light Li to the optical waveguide of the optical integrated circuit 10, and is formed on the substrate 11. The light source 2 is optically connected to the input section 3 via optical elements such as a lens and an optical fiber, so that the input light Li is input to the input section 3.

[0023] The input light Li input to the input unit 3 is guided to the first waveguide 12 formed on the substrate 11. The wavelength filter unit 4 is provided in the first waveguide 12. The wavelength filter unit 4 transmits light in a predetermined wavelength range (in this example, wavelengths λ1 and above and λ2 and below) while blocking light outside that wavelength range. The wavelength filter unit 4 is configured, for example, by including a plurality of ring resonators.

[0024] The wavelength selection unit 5 is located at the end of the first waveguide 12 opposite to the input unit 3. That is, the wavelength selection unit 5 is formed on the substrate 11. The wavelength selection unit 5 is configured to include an optical element 5a having a wavelength selection function, and generates and outputs a measurement light LM having a predetermined wavelength from the input light Li that has passed through the wavelength filter unit 4. In this example, the optical element 5a is a plurality of ring resonators, but it may include any element capable of realizing the wavelength selection function, and may include a WDM coupler, a Bragg grating (FBG: Fiber Bragg Grating), a circulator, a Mach-Zender interferometer, an arrayed waveguide grating (AWG: Arrayed Waveguide Grating), or a vernier filter, etc.

[0025] The wavelength selection unit 5 further includes a heater 5b (temperature control element) for adjusting the temperature of the optical element 5a. The wavelength of the measurement light LM generated by the wavelength selection unit 5 changes according to the temperature of the optical element 5a. This is because the refractive index of the optical element 5a changes according to the temperature of the optical element 5a. Therefore, in order to keep the wavelength of the measurement light LM constant, it is necessary to adjust the amount of power applied to the heater 5b to keep the optical element 5a constant. Furthermore, the wavelength of the measurement light LM can be controlled by controlling the amount of power applied to the heater 5b to control the temperature of the optical element 5a. The drive of the heater 5b is controlled by the computer 9. Note that the wavelength selection unit 5 may also include an element that changes the refractive index by an electric field or magnetic field instead of the heater 5b. In this case as well, the wavelength of the measurement light LM can be controlled by controlling the drive of the element.

[0026] As shown in Figure 2(a), in this example, the input light Li input to the input unit 3 is white light with equal light intensity at each wavelength. As shown in Figure 2(b), the wavelength filter unit 4 outputs light with wavelengths λ1 to λ2. As shown in Figure 2(c), the wavelength selection unit 5 outputs measurement light LM having wavelengths included in the wavelength range of λ1 to λ2.

[0027] The first waveguide 12 is optically connected to the second waveguide 14 via a branch coupler 13, and the measurement light LM output from the wavelength selection unit 5 is guided to the second waveguide 14 via the branch coupler 13. The branch coupler 13 and the second waveguide 14 are formed on the substrate 11.

[0028] The output unit 6 is a part for outputting the measurement light LM to the outside of the optical integrated circuit 10 (substrate 11), and is formed on the substrate 11. The output unit 6 is provided at one end of the second waveguide 14 and outputs the measurement light LM propagating through the second waveguide 14 to the outside. The output unit 6 is composed of, for example, a spot size converter (SSC) or a grating coupler (GC). The output unit 6 is optically connected to the beam splitter 7 via optical elements such as a lens and an optical fiber so that the measurement light LM is input to the beam splitter 7.

[0029] The beam splitter 7 splits the measurement light LM output from the output unit 6 into the target light LB, which is a part of the measurement light LM, and the output light Lo, which is the remaining part of the measurement light LM. The target light LB is input to the wavelength detection unit 8. The output light Lo becomes the output light of the light source device 1. The beam splitter 7 is optically connected to the wavelength detection unit 8 via optical elements such as a lens and an optical fiber so that the target light LB is input to the wavelength detection unit 8. Details of the wavelength detection unit 8 will be described later.

[0030] Computer 9 is composed of, for example, a computer equipped with a processor such as a CPU and a storage medium such as RAM and ROM. Computer 9 functions as a control unit 9a that controls the light source 2, the wavelength selection unit 5, and the wavelength detection unit 8. Computer 9 also functions as a calculation unit 9b that performs predetermined calculations based on the signal output from the wavelength detection unit 8 to calculate the total light quantity and centroid wavelength of the measurement light LM. Computer 9 may also be electrically connected to a display unit that displays a GUI (Graphical User Interface) for control display and a GUI for displaying measurement results, and an input unit for inputting control parameters, etc. Computer 9 controls the heater 5b of the wavelength selection unit 5 based on the calculated centroid wavelength of the measurement light LM, and controls the temperature of the optical element 5a of the wavelength selection unit 5. As a result, the wavelength of the measurement light LM output from the optical element 5a is controlled to the desired wavelength.

[0031] The details of the wavelength detection unit 8 will be described with reference to Figure 3. The first example of the wavelength detection unit 8 shown in Figure 3(a) includes a light separation unit 21, a first detector 25 (photodetector), and a second detector 26 (photodetector). As described above, the wavelength detection unit 8 receives the target light LB, which is a part of the measurement light LM.

[0032] The light separation unit 21 separates the target light LB into a first light L1 and a second light L2 at a predetermined separation ratio. In this example, the light separation unit 21 is composed of an optical filter 21a that separates the target light LB by transmitting and reflecting it at a predetermined transmittance (separation ratio), thereby separating the target light LB into the first light L1, which is reflected light, and the second light L2, which is transmitted light. The optical filter 21a is located outside the substrate 11, not on the substrate 11. As shown in Figure 4, the transmittance of the light separation unit 21 increases linearly in a predetermined wavelength range (wavelengths λ1 to λ2 in this example). In this case, the optical filter 21a is an LRG (Linear Reflectance Gradient on the wavelength axis) filter. In the example in Figure 4, the transmittance (and reflectance) increases linearly in the wavelength range of wavelengths λ1 to λ2, and the transmittance (and reflectance) of light remains constant in wavelength bands other than this wavelength range (shorter wavelengths than wavelength λ1 and longer wavelengths than wavelength λ2). However, in wavelength bands other than the specified wavelength range (shorter wavelengths than wavelength λ1 and longer wavelengths than wavelength λ2), the transmittance (and reflectance) of light does not need to be constant.

[0033] Each of the first detector 25 and the second detector 26 is composed of, for example, an image sensor or a point sensor. The first detector 25 detects the first light L1 reflected by the light separation unit 21, and the second detector 26 detects the second light L2 that has passed through the light separation unit 21. The first detector 25 outputs a detection signal to the computer 9 representing the light intensity R of the first light L1 (reflected light) detected by the first detector 25. The second detector 26 outputs a detection signal to the computer 9 representing the light intensity T of the second light L2 (transmitted light) detected by the second detector 26. The sum of the light intensity R of the first light L1 and the light intensity T of the second light L2 corresponds to the total light intensity A (light power) of the target light LB. The total light intensity of the measurement light LM can be calculated based on the total light intensity A of the target light LB and the division ratio by the beam splitter 7.

[0034] The second example of the wavelength detection unit 8 shown in Figure 3(b) comprises only an optical separation unit 21 and a first detector 25, and does not include a second detector 26. In the second example, the optical separation unit 21 is movable between an incident position where the target light LB is incident on the optical separation unit 21 and a retracted position where the target light LB is not incident on the optical separation unit 21. In this example, when the optical separation unit 21 is in the incident position, the first light L1 transmitted through the optical separation unit 21 is detected by the first detector 25. In this case, the detection signal output from the first detector 25 when the optical separation unit 21 is in the incident position represents the amount of transmitted light T. Also, when the optical separation unit 21 is in the retracted position, the detection signal output from the first detector 25 corresponds to the total amount of target light LB A. The amount of reflected light R is calculated by subtracting the amount of light T from the total amount of light A. In the second example, the second light L2 reflected by the optical separation unit 21 is not detected.

[0035] Unlike the above example, the reflective configuration may be such that when the light separation unit 21 is located at the incident position, the first light L1 reflected by the light separation unit 21 is detected by the first detector 25. In this case, the detection signal output from the first detector 25 when the light separation unit 21 is located at the incident position represents the amount of reflected light R. The detection signal output from the first detector 25 when the light separation unit 21 is located at the retracted position corresponds to the total amount of target light LB A. The amount of transmitted light T is calculated by subtracting the amount of light R from the total amount of light A. In this case, the second light L2 that has passed through the light separation unit 21 is not detected.

[0036] The wavelength detection unit 8 of the third example shown in Figure 3(c) comprises a beam splitter 27, an optical separation unit 21, a first detector 25, and a second detector 26. The beam splitter 27 divides the target light LB into transmitted light and reflected light in a predetermined ratio. In this example, the optical separation unit 21 is positioned between the beam splitter 27 and the first detector 25, and is configured in a reflective arrangement where reflected light from the beam splitter 27 enters the optical separation unit 21. The detection signal output from the first detector 25 (detection signal of the first light L1) corresponds to the amount of transmitted light T. The sum of the detection signals output from the second detector 26 corresponds to the total amount of target light LB A. The amount of reflected light R is calculated by subtracting the amount of light T from the total amount of light A. In the third example, the second light L2 reflected by the optical separation unit 21 is not detected. In the third example, the light intensity T is calculated by considering the reflectance of the beam splitter 27 in relation to the detection signal output from the first detector 25. Specifically, for example, if the beam splitter 27 is a half-mirror, the light intensity T is represented by multiplying the value corresponding to the detection signal by the reciprocal of the reflectance (1 / 2). In addition, the total light intensity A is calculated by considering the transmittance of the beam splitter 27 in relation to the detection signal output from the second detector 26. Specifically, for example, if the beam splitter 27 is a half-mirror, the total light intensity A is represented by multiplying the value corresponding to the detection signal by the reciprocal of the transmittance (1 / 2).

[0037] Unlike the above example, the light separation unit 21 may be positioned between the beam splitter 27 and the second detector 26, in a transmission configuration where transmitted light from the beam splitter 27 enters the light separation unit 21. In this case, the detection signal output from the second detector 26 corresponds to the amount of transmitted light T. The detection signal output from the first detector 25 corresponds to the total amount of target light LB A. In the modified example of the third example, the amount of light T is calculated by considering the transmittance of the beam splitter 27 with respect to the detection signal output from the second detector 26. Specifically, for example, if the beam splitter 27 is a half mirror, the value corresponding to the detection signal multiplied by the reciprocal of the transmittance of 1 / 2 represents the amount of light T. The total amount of light A is calculated by considering the reflectance of the beam splitter 27 with respect to the detection signal output from the first detector 25. Specifically, for example, if the beam splitter 27 is a half mirror, the value corresponding to the detection signal multiplied by the reciprocal of the reflectance of 1 / 2 represents the total amount of light A. The amount of reflected light R is calculated by subtracting the amount of light T from the total amount of light A. In this case, the second light L2 that has passed through the light separation unit 21 is not detected. Thus, in any of the first to third examples, if at least two of the total amount of light A of the target light LB, the amount of light T of the transmitted light that has passed through the light separation unit 21, and the amount of reflected light R of the reflected light reflected by the light separation unit 21 can be detected, the total amount of light A, the amount of light T, and the amount of light R can be obtained by calculation.

[0038] Referring to Figure 5, the method for calculating the centroid wavelength of the target light LB (measurement light LM) will be explained. In Figure 5, the horizontal axis represents wavelength, and the vertical axis represents spectral intensity (in the case of the light spectrum) and transmittance (in the case of the light separation unit 21). The centroid wavelength is a weighted average of wavelengths, weighted by spectral intensity (luminance). That is, the centroid wavelength is the value obtained by dividing the integral of the product of the wavelength of light and the intensity of light at that wavelength over the entire wavelength range by the integral of the intensity of light over the entire wavelength range. The centroid wavelength of the target light LB is equal to the centroid wavelength of the measurement light LM.

[0039] The wavelength λ50% at which the amount of light T transmitted from the light separation unit 21 and the amount of light R reflected from it are equal is expressed by equation (1). If δλ is the deviation of the centroid wavelength λ of the target light LB from 50% of the wavelength λ, then the centroid wavelength λ is expressed by equation (2): λ = δλ + 50% of λ (2) In this case, the deviation amount δλ is calculated by equation (3). In this way, the centroid wavelength λ (shift amount δλ) of the target light LB can be calculated based on the wavelengths λ1 and λ2, the amount of transmitted light T transmitted through the light separation unit 21, and the amount of reflected light R reflected by the light separation unit 21.

[0040] The computer 9 (arithmetic unit 9b) calculates the total light intensity A and centroid wavelength λ of the target light LB based on the detection results of the first detector 25 and / or the second detector 26. As described above, the total light intensity of the measurement light LM can be calculated based on the total light intensity A of the target light LB, and the centroid wavelength of the measurement light LM is equal to the centroid wavelength λ of the target light LB. Therefore, it can be considered that the computer 9 calculates the total light intensity and centroid wavelength of the measurement light LM based on the detection results of the first detector 25 and / or the second detector 26.

[0041] The computer 9 (control unit 9a) controls the heater 5b of the wavelength selection unit 5 based on the calculated total light amount A and centroid wavelength λ of the target light LB (measurement light LM), thereby controlling the temperature of the optical element 5a of the wavelength selection unit 5. This controls the wavelength of the measurement light LM output from the optical element 5a to the desired wavelength. For example, if the centroid wavelength of the target light LB in the reference state shown in Figure 6(a) is λ0, and the centroid wavelengths of the target light LB when the centroid wavelength deviates from the reference state, as shown in Figures 6(b) and 6(c), are λA and λB, then the deviation amount Δλ of the centroid wavelength is expressed as Δλ = λA - λ0 and Δλ = λB - λ0, respectively. The computer 9 has in advance stored a relationship (slope Δλ / ΔP) between the deviation amount Δλ of the centroid wavelength and the adjustment amount ΔP of the heater 5b power, as shown in Figure 7, for example. Then, the computer 9 determines the amount of adjustment ΔP for the heater 5b power based on the centroid wavelength shift Δλ calculated based on the detection results of the wavelength detection unit 8 (first detector 25 / second detector 26) and the aforementioned relationship. The computer 9 adjusts the power of the heater 5b based on the determined adjustment amount ΔP. [Operation and Effects]

[0042] The light source device 1 includes an optical separation unit 21 that receives the target light LB, which is a part of the measurement light LM output from the output unit 6, and separates the target light LB into the first light L1 and the second light L2 at a predetermined separation ratio. The separation ratio monotonically changes in a predetermined wavelength range (wavelengths λ1 to λ2). Then, at least one of the first light L1 and the second light L2 is detected by the first detector 25 and / or the second detector 26, and based on at least the detection results of the first detector 25 and / or the second detector 26, the total light amount A (optical power) and the center wavelength λ of the target light LB (measurement light LM) are calculated. Thereby, wavelength monitoring and power monitoring can be performed while reducing losses. That is, for example, in the light source device described in Patent Document 1 above, since a part of the light from the light source is branched and input to the wavelength monitor and another part of the light from the light source is detected by the power monitor, the loss increases, and there is a possibility that the power of the finally output output light becomes small. In contrast, in the light source device 1, the total light amount A and the center wavelength λ of the target light LB are calculated based on at least the detection results of the first detector 25 and / or the second detector 26, so that the loss can be reduced. Therefore, according to the light source device 1, wavelength monitoring and power monitoring can be performed while reducing losses. Also, for example, in the light source device described in Patent Document 1 above, since the light output from a waveguide different from the waveguide that guides the output light is input to the wavelength monitor, the wavelength of the output light itself cannot be monitored, and there is a possibility that the wavelength of the output light changes due to external factors while the waveguide that guides the output light is guiding the light. In contrast, in the light source device 1, the target light LB, which is a part of the measurement light LM output from the output unit 6, is input to the wavelength detection unit 8, and the wavelength is monitored based on the detection result of the wavelength detection unit 8, so that the wavelength monitoring can be performed stably.

[0043] The computer 9 (control unit 9a) controls the wavelength of the measurement light LM output from the optical element 5a based on the calculated center wavelength λ of the target light LB. Thereby, the wavelength of the measurement light LM output from the optical element 5a can be controlled based on the calculated center wavelength λ of the target light LB.

[0044] The optical separation unit 21 is an optical filter 21a disposed outside the substrate 11, and the target light LB output from the output unit 6 is input to the optical filter 21a. Thus, the optical separation unit 21 can be realized using the optical filter 21a disposed outside the substrate 11.

[0045] A first detector 25 for detecting the first light L1 and a second detector 26 for detecting the second light L2 are provided as a light detection unit. Thus, wavelength monitoring and power monitoring can be performed based on the detection results of both the first light L1 and the second light L2.

[0046] A wavelength filter unit 4 is provided on the substrate 11, which transmits light in a predetermined wavelength range (wavelengths λ1 to λ2) while blocking light outside the wavelength range. Thus, it is possible to suppress light having a peak in a wavelength range other than the predetermined wavelength range where the separation rate changes monotonically from being input to the optical separation unit 21. For example, when the wavelength selection unit 5 is constituted by a ring resonator, since the wavelength selection unit 5 has resonance wavelengths at intervals of several tens of nm, when the input light Li which is white light is input to the wavelength selection unit 5, light having a peak in a wavelength range other than the target wavelength range (wavelengths λ1 to λ2) may also be guided to the second waveguide 14 (optical separation unit 21). By providing the wavelength filter unit 4, it is possible to suppress such light from being input to the optical separation unit 21. [Modification Example]

[0047] The light source device 1 of the first modification example shown in FIG. 8 does not include a beam splitter 7 but includes a branching coupler 31. The branching coupler 31 is provided in the second waveguide 14 and branches the measurement light LM propagating through the second waveguide 14 at a predetermined ratio. A part of the branched measurement light LM is output from the second output unit 31a as the target light LB and input to the wavelength detection unit 8. The remaining part of the branched measurement light LM is output from the output unit 6 as the output light Lo. Thus, in the first modification example, the target light LB which is a part of the measurement light LM branched in the second waveguide 14 (on the optical path between the optical element 5a and the output unit 6) is input to the wavelength detection unit 8. Also by such a first modification example, as in the above-described embodiment, wavelength monitoring and power monitoring can be performed while reducing loss.

[0048] As shown in the second modified light source device 1 in Figure 9, in the first modified example, the target light LB output from the second output unit 31a may be split by the beam splitter 32, one of the split target light LBs, the first branched light LB1, may be detected by the wavelength detection unit 8, and the other of the split target light LBs, the second branched light LB2, may be detected by the photodetector 33.

[0049] In the second modified example, the wavelength detection unit 8 may be configured as in the fourth example shown in Figure 10(a), or as in the fifth example shown in Figure 10(b). In the fourth example shown in Figure 10(a), the first light L1, which is transmitted light from the light separation unit 21, is detected by the first detector 25. In this case, the detection signal output from the first detector 25 corresponds to the amount of transmitted light T. The detection signal output from the photodetector 33 corresponds to the total amount of target light LB A. The amount of reflected light R is calculated by subtracting the amount of light T from the total amount of light A.

[0050] In the fifth example shown in Figure 10(b), the first light L1, which is reflected light from the light separation unit 21, is detected by the first detector 25. In this case, the detection signal output from the first detector 25 corresponds to the amount R of the reflected light. The detection signal output from the photodetector 33 corresponds to the total amount A of the target light LB. The amount T of the transmitted light is calculated by subtracting the amount R from the total amount A. With this second modification, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment.

[0051] The third modified light source device 1 shown in Figure 11 differs from the above embodiment in that it does not have a beam splitter 7 and has a third waveguide 34 positioned between the first waveguide 12 and the second waveguide 14. The third waveguide 34 is optically connected to the first waveguide 12 via a branch coupler 13a and optically connected to the second waveguide 14 via a branch coupler 13b. A portion of the measurement light LM is guided from the first waveguide 12 to the third waveguide 34 via the branch coupler 13a. A portion of the measurement light LM output from the third waveguide 34 is input to the wavelength detection unit 8 as the target light LB. Thus, in this third modified embodiment, the target light LB, which is a portion of the measurement light LM guided to the third waveguide 34 (branched on the optical path between the optical element 5a and the output unit 6), is input to the wavelength detection unit 8. With this third modified embodiment, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment.

[0052] The fourth modified light source device 1 shown in Figure 12 differs from the above embodiment in that it does not have a beam splitter 7, but does have a branching coupler 31. A portion of the measurement light LM branched by the branching coupler 31 is input to the light separation unit 21 as the target light LB. In this example, the light separation unit 21 is composed of a wavelength division multiplexing (WDM) coupler (wavelength separation coupler) 21b, which is formed on the substrate 11. The WDM coupler 21b separates the target light LB by branching it with a predetermined transmittance (separation rate, branching rate). As shown in Figure 13, the transmittance of the WDM coupler 21b increases linearly in a predetermined wavelength range (linear wavelength range). Therefore, by designing the WDM coupler 21b so that the wavelength range of the target light LB is included in the linear wavelength range, the WDM coupler 21b can function as the light separation unit 21. In this specification, light that propagates through the third waveguide 35 without being branched by the WDM coupler 21b is referred to as "transmitted light," and light that is branched by the WDM coupler 21b is referred to as "reflected light."

[0053] In the fourth modification, the first detector 25 and the second detector 26 are formed on the substrate 11. The first detector 25 and the second detector 26 are composed of, for example, germanium photodiodes. The first detector 25 detects the first light L1 that propagates without being branched by the WDM coupler 21b. The second detector 26 detects the second light L2 that has been branched by the WDM coupler 21b. The detection signal output from the first detector 25 corresponds to the amount of transmitted light T in the above embodiment. The detection signal output from the second detector 26 corresponds to the amount of reflected light R in the above embodiment. Therefore, even with this fourth modification, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment. Furthermore, in the fourth modification, the light separation unit 21 can be realized using the WDM coupler 21b.

[0054] The fifth modified light source device 1 shown in Figure 14 differs from the fourth modified example in that the light source 2 is formed on the substrate 11. In this case, the light source 2 is composed of, for example, a laser diode. With this fifth modified example, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment.

[0055] The sixth modified light source device 1 shown in Figure 15 differs from the fourth modified example in that the WDM coupler 21b is formed in the third waveguide 34. With this fifth modified example, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment.

[0056] The seventh modified light source device 1 shown in Figure 16 differs from the fourth modified example in that it includes a first optical amplifier 41, a resonator filter 42, and a second optical amplifier 43 instead of the light source 2 and wavelength selection unit 5. The first optical amplifier 41 is, for example, a semiconductor optical amplifier (SOA) and is provided at one end of the first waveguide 12. A highly reflective film is formed on the end face of the first optical amplifier 41 opposite to the said end. The resonator filter 42 is provided at the other end of the first waveguide 12. A mirror or reflector is formed on the end face of the resonator filter 42 opposite to the said end. The resonator filter 42 functions as an external resonator, and a measurement light LM of a specific wavelength, amplified by reciprocating between the highly reflective film and the reflector, is output to the second waveguide 14 via the branch coupler 13.

[0057] The resonator filter 42 is, for example, a ring filter including one or more ring-shaped waveguides. The resonant wavelength of the resonator filter 42 is determined according to the circumference of the ring, refractive index, etc. The resonant wavelength of the resonator filter 42 is included in the wavelength range (linear wavelength range) in which the separation ratio changes linearly in the optical separation unit 21.

[0058] The second optical amplification unit 43 is, for example, a semiconductor optical amplifier and is provided in the second waveguide 14. A portion of the measurement light LM propagating through the second waveguide 14 is branched by the branching coupler 31 and input to the optical separation unit 21 as the target light LB. The measurement light LM that propagates through the second waveguide 14 without being branched by the branching coupler 31 is amplified in the second optical amplification unit 43. The amplified measurement light LM becomes the output light Lo of the light source device 1. In this example, the wavelength filter unit 4 is provided in the second waveguide 14. Figure 17 shows the light spectrum at each part of the light source device 1.

[0059] The present invention is not limited to the above embodiments and modifications. In the above embodiments and each modification, the wavelength filter unit 4 may be provided in the second waveguide 14. In the above embodiments, the control unit 9a and the calculation unit 9b are configured by a single device (computer 9), but the control unit 9a and the calculation unit 9b may be configured by separate devices (e.g., computers). The transmission range through which the wavelength filter unit 4 transmits light does not have to coincide with the wavelength range in which the transmittance of the light separation unit 21 changes monotonically, but only needs to include at least a part of that wavelength range.

[0060] In the above embodiment, the transmittance (separation rate) of the light separation unit 21 increased linearly in a predetermined wavelength range. However, the transmittance of the light separation unit 21 only needs to change monotonically in a predetermined wavelength range; for example, it may decrease linearly, or it may increase or decrease in a manner other than linear.

[0061] 1...Light source device, 2...Light source, 4...Wavelength filter unit, 5a...Optical element, 6...Output unit, 9a...Control unit, 9b...Calculation unit, 10...Optical integrated circuit, 11...Substrate, 21...Optical separation unit, 21a...Optical filter, 21b...Wavelength division multiplexing coupler (WDM), 25...First detector (photodetector), 26...Second detector (photodetector).

Claims

1. A light source device comprising: an optical integrated circuit having a substrate; an optical element formed on the substrate and outputting measurement light having a predetermined wavelength; an output unit formed on the substrate and outputting the measurement light to the outside of the substrate; an optical separation unit that receives a portion of the measurement light output from the output unit, or a portion of the measurement light branched in the optical path between the optical element and the output unit, and separates the portion of the measurement light into first light and second light at a predetermined separation ratio, wherein the separation ratio changes monotonically in a predetermined wavelength range; a photodetection unit that detects at least one of the first light and the second light; and a calculation unit that calculates the total amount of light and the centroid wavelength of the measurement light based at least on the detection result of the photodetection unit.

2. The light source device according to claim 1, further comprising a control unit that controls the wavelength of the measurement light output from the optical element based on the centroid wavelength of the measurement light calculated by the calculation unit.

3. The light source device according to claim 1 or 2, wherein the light separation unit is a wavelength separation coupler formed on the substrate, and a portion of the measurement light that has been branched in the optical path between the optical element and the output unit is input to the wavelength separation coupler.

4. The light source device according to claim 3, wherein the wavelength separation coupler is a wavelength division multiplexer coupler.

5. The light source device according to claim 1 or 2, wherein the light separation unit is an optical filter disposed outside the substrate, and a portion of the measurement light output from the output unit is input to the optical filter.

6. The light source device according to any one of claims 1 to 5, wherein the light detection unit comprises a first detector for detecting the first light and a second detector for detecting the second light.

7. The light source device according to any one of claims 1 to 5, further comprising a wavelength filter formed on the substrate, which transmits light in a transmission range including at least a portion of the predetermined wavelength range while blocking light outside the transmission range.

8. The light source device according to any one of claims 1 to 7, wherein the light detection unit is formed on the substrate.

9. The light source device according to any one of claims 1 to 8, further comprising a light source that outputs input light, wherein the optical element generates and outputs measurement light from the input light, and the light source is formed on the substrate.

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