Light source device

Abstract

The present invention provides a light source device that can perform wavelength monitoring and power monitoring while reducing losses. [Solution] The light source device 1 comprises an optical integrated circuit 10 having a substrate 11, an optical element 5a formed on the substrate 11 that outputs a measurement light LM having a predetermined wavelength, an output unit 6 formed on the substrate 11 that outputs the measurement light LM to the outside of the substrate 11, an optical separation unit 21 that receives a portion of the measurement light LM output from the output unit 6 and separates a portion of the measurement light LM into a first light L1 and a second light L2 at a predetermined separation ratio, wherein the separation ratio changes monotonically in a predetermined wavelength range, an optical detection unit that detects at least one of the first light L1 and the second light L2, and a calculation unit 9b that calculates the total light amount and centroid wavelength of the measurement light LM based at least on the detection result of the optical detection unit.

Description

Technical Field

[0001] The present invention relates to a light source device.

Background Art

[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.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 losses.

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

Means for Solving the Problems

[0006] The light source device of the present invention is [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; an optical detection 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 optical 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] The light source device of the present invention may also 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] The light source device of the present invention may also be [3] "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, as described in [1] or [2]." In this case, the light separation unit can be realized using a wavelength separation coupler formed on the substrate.

[0010] The light source device of the present invention may also be [4] "the light source device described in [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] The light source device of the present invention may also be [5] "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, as described in [1] or [2]." In this case, the light separation unit can be realized using an optical filter disposed outside the substrate.

[0012] The light source device of the present invention may also be [6] "the light detection unit comprising a first detector for detecting the first light and a second detector for detecting the second light, as described in any of [1] to [5]." In this case, wavelength monitoring and power monitoring can be performed based on the detection results of both the first and second light.

[0013] The light source device of the present invention may also 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] The light source device of the present invention may also be [8] "the light detection unit is formed on the substrate and is the light source device according to any one of [1] to [7]." In this case, the device can be miniaturized.

[0015] The light source device of the present invention may also 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. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a light source device that can perform wavelength monitoring and power monitoring while reducing losses. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram showing the configuration of the light source device according to the embodiment. [Figure 2] (a) is a diagram showing the light input to the input section, (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. [Figure 3] (a) is a diagram showing the wavelength detection unit of the first example, (b) is a diagram showing the wavelength detection unit of the second example, and (c) is a diagram showing the wavelength detection unit of the third example. [Figure 4] This figure shows an example of the transmittance of the light separation section. [Figure 5] This is a diagram illustrating the method for calculating the center of gravity wavelength. [Figure 6] (a) shows a reference state diagram, (b) shows a case where the center wavelength deviates from the reference state, and (c) shows another case where the center wavelength deviates from the reference state. [Figure 7] It is a diagram showing an example of the relationship between the deviation amount of the center wavelength and the adjustment amount of the heater power. [Figure 8] It is a configuration diagram of the light source device of the first modification example. [Figure 9] It is a configuration diagram of the light source device of the second modification example. [Figure 10] (a) is a diagram showing the wavelength detection unit of the fourth example, and (b) is a diagram showing the wavelength detection unit of the fifth example. [Figure 11] It is a configuration diagram of the light source device of the third modification example. [Figure 12] It is a configuration diagram of the light source device of the fourth modification example. [Figure 13] It is a diagram showing an example of the transmission characteristics of the WDM coupler in FIG. 12. [Figure 14] It is a configuration diagram of the light source device of the fifth modification example. [Figure 15] It is a configuration diagram of the light source device of the sixth modification example. [Figure 16] It is a configuration diagram of the light source device of the seventh modification example. [Figure 17] (a) is a diagram showing the light input to the input unit in the seventh modification example, (b) is a diagram showing the light output from the wavelength filter unit, and (c) is a diagram showing the light output from the wavelength selection unit.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are 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 composed of an optical integrated circuit 10. The optical integrated circuit 10 has a substrate 11, and is composed of various optical elements such as optical waveguides fabricated 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 into 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 composed of, for example, 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, such as a WDM coupler, a Bragg grating (FBG), a circulator, a Mach-Zender interferometer, an arrayed waveguide grating (AWG), or a vernier filter.

[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 that outputs 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 lenses and optical fibers 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, wavelength selection unit 5, and 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 target light LB, which is a part of the measurement light LM, is input to the wavelength detection unit 8.

[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, the transmittance (and reflectance) of light does not need to be constant in wavelength bands other than the wavelength range specified (shorter wavelengths than wavelength λ1 and longer wavelengths than wavelength λ2).

[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 (optical 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 wavelength detection unit 8 of the second example 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 is incident on 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 is incident on 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 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 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 following can be detected: 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 light reflected by the light separation unit 21, 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).

number

number

[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, for example, as shown in Figure 7. 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 relevant relationship. The computer 9 adjusts the power of the heater 5b based on the determined adjustment amount ΔP. [Mechanism of Action and Effects]

[0042] The light source device 1 receives the target light LB, which is a part of the measurement light LM output from the output unit 6, and includes an optical separation unit 21 that separates the target light LB into a first light L1 and a second light L2 at a predetermined separation ratio. This separation ratio changes monotonically in a predetermined wavelength range (wavelengths λ1 to λ2). 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 the total light amount A (optical power) and centroid wavelength λ of the target light LB (measurement light LM) are calculated based at least on the detection results of the first detector 25 and / or the second detector 26. This allows wavelength monitoring and power monitoring to be performed while reducing losses. That is, for example, in the light source device described in Patent Document 1, 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, so losses are large and there is a risk that the power of the output light that is ultimately output will be small. In contrast, the light source device 1 can reduce losses because it calculates the total light quantity A and centroid wavelength λ of the target light LB based at least on the detection results of the first detector 25 and / or the second detector 26. Therefore, the light source device 1 can perform wavelength monitoring and power monitoring while reducing losses. Furthermore, in the light source device described in Patent Document 1, for example, the light output from a waveguide separate from the waveguide that guides the output light is input to the wavelength monitor, so it is not possible to monitor the wavelength of the output light itself, and there is a risk that the wavelength of the output light may change due to external factors while the light is being guided through the waveguide that guides the output 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 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 centroid wavelength λ of the target light LB. This allows the wavelength of the measurement light LM output from the optical element 5a to be controlled based on the calculated centroid wavelength λ of the target light LB.

[0044] The light separation unit 21 is an optical filter 21a located outside the substrate 11, and the target light LB output from the output unit 6 is input to the optical filter 21a. This makes it possible to realize the light separation unit 21 using an optical filter 21a located 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 photodetector. This allows wavelength monitoring and power monitoring to be performed based on the detection results of both the first light L1 and the second light L2.

[0046] A wavelength filter section 4 is formed on the substrate 11, which transmits light in a predetermined wavelength range (wavelengths λ1 to λ2) while blocking light outside that wavelength range. This prevents light with peaks in wavelength ranges other than the predetermined wavelength range, where the separation ratio changes monotonically, from being input to the optical separation section 21. For example, if the wavelength selection section 5 is configured as a ring resonator, the wavelength selection section 5 has resonant wavelengths at intervals of several tens of nanometers. Therefore, when input light Li, which is white light, is input to the wavelength selection section 5, there is a possibility that light with peaks in wavelength ranges other than the target wavelength range (wavelengths λ1 to λ2) will also be guided to the second waveguide 14 (optical separation section 21). By providing the wavelength filter section 4, it is possible to prevent such light from being input to the optical separation section 21. [Differentiation]

[0047] The first modified light source device 1 shown in Figure 8 does not have a beam splitter 7, but is equipped with a branch coupler 31. The branch coupler 31 is provided in the second waveguide 14 and branches the measurement light LM propagating in the second waveguide 14 at a predetermined ratio. A portion of the branched measurement light LM is output from the second output unit 31a as target light LB and input to the wavelength detection unit 8. The remaining portion of the branched measurement light LM is output from the output unit 6 as output light Lo. Thus, in the first modified example, the target light LB, which is a portion 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. Even with this first modified example, wavelength monitoring and power monitoring can be performed while reducing losses, similar to the above embodiment.

[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, is detected by the wavelength detection unit 8, and the other of the split target light LBs, the second branched light LB2, is 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 of reflected light R. The detection signal output from the photodetector 33 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. 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 amplifier 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 branch 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 branch coupler 31 is amplified in the second optical amplifier 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. [Explanation of Symbols]

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

Claims

1. An optical integrated circuit having a substrate, An optical element formed on the substrate that outputs measurement light having a predetermined wavelength, An output unit formed on the substrate for outputting the measurement light to the outside of the substrate, 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, is input to the optical separation unit, and the portion of the measurement light is separated into a first light and a second light at a predetermined separation ratio, wherein the separation ratio changes monotonically in a predetermined wavelength range. A light detection unit that detects at least one of the first light and the second light, A light source device comprising: a calculation unit that calculates the total amount of light and the centroid wavelength of the measured light based at least on the detection result of the light detection 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 claim 1 or 2, 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 claim 1 or 2, further comprising a wavelength filter portion 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 detection unit is formed on the substrate, as described in claim 1 or 2.

9. It further includes a light source that outputs input light, The optical element generates and outputs the measurement light from the input light. The light source is formed on the substrate, as described in claim 1 or 2.

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