JPH0549202B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical demultiplexer that separates a plurality of lights of different wavelengths propagating in the same optical waveguide, or This invention relates to an optical circuit that acts as an optical multiplexer for combining light.

(Prior art) The optical communication system currently in practical use is a unidirectional optical fiber that connects a light source that emits signal light and a photodetector that receives the signal light and converts it into an electrical signal. This is the simplest one-to-one format. However, this simple system is being further developed into network optical communication that connects one-to-many or multiple-to-multiple terminal devices. In this network optical communication, bidirectional communication between terminals is performed using only one optical fiber, and different types of signals (for example,
When transmitting (audio, image data, etc.) over a single optical fiber, one optical fiber transmits light of different wavelengths, and a signal is placed on each wavelength separately to create two-way communication or one-way communication. A wavelength division multiplex communication method that performs multiplex communication is used. This wavelength multiplexing communication requires an optical multiplexer that combines lights of different wavelengths into one optical fiber, and conversely, an optical multiplexer that separates lights of different wavelengths transmitted through one optical fiber into their respective wavelengths. A demultiplexer and an optical multiplexer/demultiplexer having both of these functions are used.

Conventionally, an optical circuit shown in FIG. 8 is known as an optical multiplexer/demultiplexer. The input terminal of the first optical fiber 1 that transmits light with a wavelength of 0.89 μm is connected to a focusing rod lens 2, a prism 3, and a dielectric multilayer film filter 4 that transmits only light with a wavelength of 0.89 μm and reflects light with other wavelengths. It is connected to the glass block 5 through.
A second optical fiber 6 transmitting light with a wavelength of 0.81 μm
The input terminal of the laser beam is similarly optically coupled to the glass block 5 via a focusing rod lens 7, a prism 8, and a filter 9 that transmits only light with a wavelength of 0.81 μm.
Then, the intersection of the optical axis of the first optical fiber system and the optical axis of the second optical fiber system is made to coincide on the surface of the glass block 5, and the light having a wavelength of 0.89 μm is merged.
Furthermore, a third filter 11 is coupled to the glass block 5 via a prism 10 to reflect only the light with a wavelength of 0.89 μm and the light with a wavelength of 0.81 μm. is reflected toward the focusing rod lens 12 and connected to the common terminal 13.
It is transmitted to the outside via . Further, light with a wavelength of 1.2 μm and light with a wavelength of 1.3 μm are input from the common terminal 13 and directed toward the third filter 11 . A mirror 14 that reflects both the light with a wavelength of 1.2 μm and the light with a wavelength of 1.3 μm is arranged behind the third filter 11, and the light with a wavelength of 1.2 μm and the light with a wavelength of 1.3 μm that have passed through the third filter 11 are arranged.
m light is reflected toward the fourth filter 15. This fourth filter 15 has a characteristic of transmitting only light with a wavelength of 1.2 μm and reflecting light of other wavelengths. Therefore, the light having a wavelength of 1.2 μm passes through the fourth filter 15, passes through the converging rod lens 16, and is output to the third optical fiber 17. On the other hand, light with a wavelength of 1.3 μm is reflected by the fourth filter 15, passes through the fifth filter 18 and the converging rod lens 19, and is transferred to the fourth optical fiber 2.
Output to 0.

Furthermore, an optical circuit shown in FIG. 9 is known as another optical multiplexer/demultiplexer. In this optical circuit, an optical fiber guide groove 31 and a filter guide groove 32 are formed on a silicon substrate 30, and an optical fiber 33 that acts as an input/output port is installed in each fiber guide groove 31, and an optical fiber 33 that acts as an input/output port is installed in each fiber guide groove 32. Dielectric multilayer filter 3 that transmits or reflects only light of a specific wavelength
4 is inserted perpendicularly to the substrate to perform optical demultiplexing and optical multiplexing.

(Problems to be solved by the invention) In the optical multiplexer/optical demultiplexer shown in FIG. 8 mentioned above,
Various optical elements such as microlenses, prisms, and filters are used, and the optical axes of these optical elements must intersect or coincide with each other to be mounted on the glass block, which requires high assembly precision, making it unsuitable for mass production. It was hot. In addition, the optical multiplexing and
In optical demultiplexers as well, multilayer filters must be individually installed in fine grooves with a width of several tens of micrometers, and the assembly work is similarly troublesome and mass production is poor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, to provide an optical circuit that can be manufactured without complicated assembly work, and that can be integrally integrated including a photodetector. be.

(Means for Solving the Problems) The optical circuit according to the present invention includes a core layer for propagating a light beam, a first cladding layer having a refractive index higher than the refractive index of the core layer, and a refractive index lower than the first cladding layer. second rate
A resonant reflective cladding portion having at least one pair of cladding layers, the first cladding layer being in contact with the core layer, and having strong reflection characteristics toward the core for light in one or more specific wavelength ranges. and formed by partially changing the film thickness or refractive index of at least one of the first cladding layer or the second cladding layer, and transmitting only light in at least one wavelength range of the light in the specific wavelength range. It is characterized by having a wavelength separation region that transmits light.

(Function) FIG. 1 is a diagram showing an example of a resonant reflection type optical waveguide which is the basic configuration of an optical circuit according to the present invention. A second cladding layer 41 having a low refractive index is formed on a semiconductor substrate 40 made of a high refractive material, and this second cladding layer 41
A first cladding layer with a high refractive index is formed on top to form a resonant reflective cladding, and a transparent dielectric layer with a refractive index lower than that of the first cladding layer is deposited on the first cladding layer 42 to direct a light beam. Core part 43 for propagation
form. The light to be transmitted is totally reflected at the interface between the core section 43 and the air layer, and is also reflected by the interference effect in the resonant reflection cladding between the core section 43 and the semiconductor substrate 40, and propagates within the core section 43. . The reflectance of the resonant reflective cladding for light propagating within the core is determined by the first and second cladding layers 42 and 41.
is determined depending on the refractive index and thickness of the core portion 43 and the wavelength of the light to be transmitted,
By appropriately selecting the film thickness and refractive index of each cladding layer constituting the resonant reflective cladding, a reflectance close to 1 can be achieved. Since the reflectance of this resonant reflective cladding is close to 1, but slightly less than 1, a very small amount of light is transmitted through the resonant reflective cladding and radiated to the substrate. The light emitted to this substrate results in radiation loss, but if a resonant reflective cladding that satisfies the optimal film thickness conditions is used, the reflectance becomes approximately 1 and the loss can be suppressed to a few dB/cm or less. For a detailed explanation on this point, please refer to Japanese Patent Application No. 61-206698, which was previously proposed by the applicant. On the other hand, the reflectance of this resonant reflective cladding varies depending on the thickness of each cladding layer and the wavelength of the propagating light, so by partially changing the thickness of each cladding layer, a high A loss region (high transmittance region) can be partially formed. Therefore, if the thickness of each layer of the resonant reflective cladding is partially changed to create a state of low reflectance (high transmittance) for a specific wavelength λ ₁ , only the light with wavelength λ ₁ in this region will be directed toward the substrate. is transmitted and radiated. On the other hand, for light with a different wavelength λ ₂ , this region does not have a low reflection condition (high loss condition), so most of the light with a wavelength λ ₂ is reflected by the resonant reflection cladding, and is reflected further on. Propagates to the waveguide. As described above, the optical circuit according to the present invention constructs a resonant reflective cladding by laminating a dielectric layer with a predetermined refractive index and thickness on a semiconductor substrate, and also controls the thickness of the cladding layer constituting this resonant reflective cladding. The function as an optical demultiplexer can be achieved by only partially changing the structure, thus eliminating the need for any complicated assembly work. Furthermore, by forming a photodetector and its related electronic circuit elements on a semiconductor substrate in advance and laminating a dielectric layer on this semiconductor substrate, it is possible to monolithically integrate an optical demultiplexer and a photodetector. become.

(Example) FIG. 2 is a diagram showing the configuration of an example of an optical circuit according to the present invention. Two photodetectors 51a and 51b and related electronic circuit elements (not shown) such as an amplifier are formed on the silicon substrate 50 in advance. These photodetectors 51a, 51b and their associated electronic circuit elements can be easily manufactured using known silicon planar technology. A second layer consisting of _two layers of SiO (refractive index 1.45), which is a low refractive index material, is formed on this silicon substrate 50.
A cladding layer 52 is formed, and this second cladding layer 5
2 is a light refractive index material layer on TiO ₂ layer (refractive index
2.3) A first cladding layer 53 consisting of the second cladding layer 52 and the first cladding layer 53 is formed.
constitutes a resonant reflective cladding. Furthermore, a core 54 made of _two SiO layers is formed on the first cladding layer 53.
form. These first and second cladding layers 53
52 and the core 54 can be formed by sputtering, vapor phase growth, electron beam evaporation, or the like. As mentioned above, the reflectance of the resonant reflective cladding for light propagating through the core 54 is determined by the thicknesses d ₁ and d ₂ of the first and second cladding layers 53 and 52 and the refractive indexes n ₁ and n ₂ of the core 54 . Determined by the thickness d _c and the refractive index n _c , the thickness d ₁ of the first cladding layer and the thickness d ₂ of the second cladding layer when giving the maximum reflectance (minimum loss) are given by the following formula for the TE mode. Given.

d ₁ λ/4n ₁ [1-(n _c /n ₁ ) ² + (λ/2n ₁ d _ce ) ² ] ^-1/2・(2N+1) ...(1) d ₂ dce/2(2M+1) ... ...(2) (M, N=0, 1, 2...) Here, λ represents the wavelength of the light to be propagated,
d _ce is the equivalent core film thickness considering the amount of electromagnetic field seeping out of the core. Under low-loss conditions (high reflectance), the electromagnetic field hardly seeps into the resonant reflective cladding, so if the refractive index of the cladding layer (air in this example) above the core is n _p , then the core 54
The equivalent film thickness d _ce can be approximately approximated by the following equation.

In this way, the propagation loss of the resonant reflective optical waveguide is
It changes depending on the film thickness of the resonant reflective cladding consisting of two layers. Next, the radiation loss characteristics of the TE fundamental mode with respect to the film thickness d ₁ of the first cladding layer 53 are calculated and shown in FIG. In this calculation, core 54
The thickness of the second cladding layer 52 was 4 μm, and the thickness of the second cladding layer 52 was 2 μm. In the figure, the horizontal axis is the first cladding layer 5
The film thickness d ₁ of No. 3 is shown, and the vertical axis shows loss (amount of light transmitted toward the substrate). The solid line shows the calculation results for light with a wavelength of 0.633 μm, the broken line shows the calculation results for light with a wavelength of 0.85 μm, and the dashed-dotted line shows the calculation results for light with a wavelength of 1.3 μm. Considering light with a wavelength of 0.633μm, d ₁ =0.088μm, 0.264μm, 0.44μ
A high reflectance state (low loss state) occurs near the three film thickness conditions of m, and loss occurs near these film thicknesses.
This results in a low radiation loss state of less than 1dB/cm. Also, d ₁ =
In the vicinity of 0.176μm and 0.352μm, there is a very large radiation loss state (high transmittance state) of several + dB/cm or more.
becomes. On the other hand, d ₁ =0.088μm, 0.264μm, 0.44μm
In the vicinity, light with a wavelength of 0.85 μm and 1.3 μm
Since it is almost in a high reflectance state even for wavelengths of light, under these film thickness conditions, it is in a highly reflective state for three wavelengths of light, and a resonant reflective waveguide can be constructed. Also, d ₁ =0.176μm, 0.352μm
Under the conditions of 0.85μm wavelength light and 1.3μm
Since it is highly reflective for light with a wavelength of 0.633 μm, under this film thickness condition, only light with a wavelength of 0.633 μm is transmitted toward the substrate, and light with other wavelengths is reflected by the interference reflection cladding and propagates within the core 54. It turns out. Furthermore, considering light with a wavelength of 0.85 μm, d ₁ =
High transmittance occurs near 0.23μm, while
It has a high reflectance state for light with a wavelength of 0.633 μm and light with a wavelength of 1.3 μm. Therefore, by setting d ₁ =0.23 μm, only light with a wavelength of 0.85 μm is transmitted. Further, under the film thickness condition of d ₁ =0.33 μm, the film exhibits a high transmittance state only for light of a wavelength of 1.3 μm, and a high reflectance state for light of other wavelengths. As a result, by setting d ₂ =0.33 μm, only light with a wavelength of 1.3 μm is transmitted, and light with other wavelengths is reflected by the resonant reflective cladding and guided within the core. In this way, by partially changing the thickness of the first cladding layer and forming a wavelength separation region in the resonant reflective waveguide that transmits only light of a specific wavelength, an optical demultiplexer separates only light of a specific wavelength. It will function as The first state that results in this high transmittance state
And the film thickness conditions of the second cladding layer are given by the following equation.

d ₁ λ/2n ₁ [1-(n _c /n ₂ ] ² + (λ/2n ₁ d _ce ) ² ] ^-1/
2 ×N ... (4) d ₂ dce / 2 × M ... (5) (N, M = 1, 2, 3 ...) Equations (1), (2) and equations (4), (5) The difference is that Equations (1) and (2) are odd multiples of a certain least common divisor, and Equations (4) and (5) are even multiples. Also, to create high loss conditions, it is not necessary to bring both d ₁ and d ₂ close to the values of equations (4) and (5) at the same time;
It is also possible to bring only one side closer together. Since the first cladding layer is usually thinner and easier to control, the thickness of the first cladding layer is varied.

In this example, wavelengths λ ₁ and λ ₂ from the incident end of the core 54
It is assumed that two wavelengths of light are input, and these wavelengths of λ ₁ and λ ₂ are demultiplexed, respectively. The film thickness of the second cladding layer 53 is partially changed, and the first wavelength separation region 55a transmits only the wavelength light of λ ₁ and reflects the wavelength light of λ ₂ , and the wavelength light of λ ₁ is reflected and the wavelength light of λ ₂ is transmitted. A second wavelength separation region 55b that transmits only wavelength light is formed. These first and second wavelength separation regions are connected to the photodetector 51
It is formed at a position corresponding to the formation position of a and 51b. These two wavelength separation regions 55a and 55b
Based on the results shown in FIG. 3, the films of the first and second cladding layers 53 and 52 were adjusted so that the other parts were in a high reflectance state (low loss state) for both wavelengths of λ ₁ and λ ₂ . Set the thickness condition. Both the wavelength lights λ ₁ and λ ₂ that are incident on the core 54 propagate within the core 54 while being repeatedly reflected, and the wavelength light λ ₁ passes through the first and second cladding layers 5 in the first wavelength separation region 55a.
The wavelength light of λ ₂ passes through the first and second cladding layers 53 and 52, respectively, in the second wavelength separation region 55b and is photodetected. vessel 51b
incident on .

Next, a specific example of the design will be explained.

Consider the case of splitting light with a wavelength of 0.78 μm and a wavelength of 0.89 μm. FIG. 4 shows the wavelength dependence of the TE fundamental mode loss when the thickness of the first cladding layer is set to 0.13 μm, 0.24 μm, and 0.27 μm, respectively. Here, the thickness d _c of the core was 4 μm, and the thickness d ₂ of the second cladding layer was 2 μm. In addition, the refractive index of each layer is determined by the material of the core and the first cladding layer being SiO ₂ , and the material of the second cladding layer being SiO 2 .
The material of the cladding layer was TiO ₂ , and the refractive index data for each material at each wavelength was obtained from the document Handbook of Optical Constance of Solids (published by Academic Press, 1985) and used. In the example of Figure 4, d ₁ = 0.13μm
Light with wavelengths of both 0.78 μm and _0.89 μm is guided in the _portion of
wavelength can be emitted to the substrate. At this time, the loss curve in Figure 4 is steep on the short wavelength side and gentle on the long wavelength side, so for example, at a wavelength of 0.78 μm,
When cascading 0.89μm duplexers, the wavelength is 0.78μ
By demultiplexing the light with a wavelength of m first, greater isolation can be achieved with respect to light with a wavelength of 0.89 μm. As a design example, for a wavelength of 0.78μm, the demultiplexer
With a radiation loss of 200 dB/cm, an isolation of 19 dB or more and a coupling efficiency to the photodetector of about 90% can be achieved.

In addition, in the loss characteristics shown in Figure 3, the range of film thickness d ₁ in which high radiation loss (high transmittance) can be obtained is very narrow, and in order to obtain a loss of 100 dB/cm or more, a highly accurate measurement of several angstroms is required. Film thickness control is required. Therefore, in order to expand the allowable range of film thickness accuracy, anti-reflection code layers 60a and 60b are provided between the second cladding layer 52 and the substrate 50, respectively, as shown in FIG. It becomes possible to expand the width.

FIG. 6 shows the characteristics when the anti-reflection coating layers 60a and 60b are provided. The horizontal axis shows the film thickness of the first cladding layer 53, and the vertical axis shows the radiation loss per unit length. The wavelength of the light used was 0.633μm,
The solid line shows the characteristics without the anti-reflection coating layer,
The broken line shows the characteristics when a TiO ₂ layer is used as the anti-reflection coating layer, and the dashed line shows the characteristics when C7059 glass with a refractive index of 1.52 is used as the anti-reflection coating layer. The materials and thicknesses of the first cladding layer, second cladding layer, and core are the same as those used in FIG. 3. As is clear from FIG. 6, by providing the anti-reflection coatings 60a and 60b between the substrate 50 and the second cladding layer 52, the allowable range of film thickness for obtaining high transmittance characteristics is expanded, and the film thickness can be controlled during the manufacturing process. becomes even easier.

In addition, in the loss curves shown in Figures 3 and 4, the high reflectance characteristic part (low loss characteristic part) becomes flat over a wide range with respect to the film thickness of the second cladding layer or the propagation wavelength, resulting in high transmittance. A steeper section (high-loss characteristic section) is extremely advantageous in terms of design, as it allows greater isolation when constructing a duplexer. In order to achieve this purpose, the resonant reflection cladding can be constructed from one set of two layers, a second cladding layer with a low refractive index and a first cladding layer with a high refractive index, to two sets of four layers or a multilayer structure. .

FIG. 7 shows an example in which the optical circuit according to the present invention is applied to coherent optical communication. When the optical circuit according to the present invention having a demultiplexing light-receiving integrated circuit element is applied to coherent optical communication signals, the light from the local oscillator (light source) and the signal light must be mixed before entering the photodetector. For this purpose, the optical circuit shown in FIG. 7 is suitable. Three transmission lines 101, 102, and 103 are formed on the incident side of the substrate 100. Signal lights with wavelengths λ ₁ ′ and λ ₂ ′ whose wavelength ranges are separated by some distance from each other are transmitted from an external transmission path such as an optical fiber to the first transmission path 1.
01. It is assumed that these lights of λ ₁ ' and λ ₂ ' are highly precisely wavelength-controlled and modulated to have a slightly broadened spectrum. Second transmission line 10
2, the frequency is controlled with high precision, and light with a wavelength λ ₁ close to the wavelength λ ₁ ' is incident. The first transmission line 101 and the second
When the optical directional coupler 104 is used to couple _the transmission _{line 102} of
Light beams of λ ₁ ′+λ ₂ ′+λ ₁ are outputted to the fourth and fifth transmission paths 105 and 106, respectively, as the striped light beams. These fourth and fifth transmission lines 105 and 10
Optical elements 107 and 108, which integrally form a wavelength separation region and a photodetector that transmit only the light of λ ₁ and λ ₁ ', are formed on the output side of the 6, respectively. Performs coherent detection of the ₁ ′ signal light.

On the other hand, since the optical element 108 formed in the transmission line 106 reflects the signal light of λ ₂ ' toward the core by the resonant reflective cladding, the signal light of λ ₂ ' is further guided and travels. This transmission line 106 is connected to a directional optical coupler 109.
The light of λ ₂ and the signal light of λ ₂ ' are mixed into a light flux of λ ₂ +λ ₂ ', and
Two photodetectors 110 and 11
Transmit to 1. Then, the beat signal of the signal light of λ ₂ is coherently detected by the two photodetectors 110 and 111. Generally, the signal lights λ ₁ ′ and λ ₂ ′ are λ ₁
And the intensity is several + dB or less than the light of λ ₂ , so
The intermediate frequency beat signals coherently detected by the photodetectors 107, 108, 110, and 111 contain extremely large DC components. Therefore, by using two photodetectors for each signal light, the DC component can be balanced and removed. If the optical circuit according to the present invention is applied to such optical communication, each transmission path and optical element can be integrally integrated on a silicon substrate.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the embodiments described above, a silicon substrate was used as the substrate, but a GaAs substrate, an InP substrate, or the like may also be used.

Further, in the above-described embodiment, the light is reflected and guided by the air layer and the resonant reflective cladding, but it is also possible to form a resonant reflective cladding on each side of the core to guide the light. Of course it is possible.

(Effects of the Invention) As explained above, according to the present invention, a low refractive index cladding layer and a high refractive index cladding layer are sequentially deposited on a substrate to form a resonant reflective cladding, and a low refractive index cladding layer is formed on the resonant reflective cladding. It is possible to form a core part by depositing a refractive index transparent dielectric layer, and partially change the film thickness of one of the cladding layers to form a wavelength separation region that transmits only light of a specific wavelength toward the substrate. can. As a result, it is possible to create an optical circuit that functions as an optical demultiplexer simply by forming a thin film, and no complicated assembly work is required except for the connection part with the optical fiber.

Further, if a semiconductor substrate such as silicon is used as the substrate, an optical waveguide, an optical branching path, and a photodetector can be monolithically integrated on the substrate.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an example of a resonant reflective optical waveguide used in the present invention, FIG. 2 is a diagram showing the configuration of an example of the optical circuit according to the present invention, and FIG. 3 is a diagram showing the film thickness of the first cladding layer. A graph showing the relationship between and radiation loss characteristics,
FIG. 4 is a graph showing the relationship between propagation wavelength and radiation loss characteristics, FIG. 5 is a diagram showing the configuration of a modified example of the optical circuit according to the present invention, and FIG. A graph showing the relationship between layer thickness and loss characteristics; FIG. 7 is a diagrammatic perspective view showing an example in which the optical circuit according to the present invention is applied to coherent optical communication;
FIGS. 8 and 9 are diagrams showing the configurations of conventional optical demultiplexers and optical multiplexers. 40... Semiconductor substrate, 41, 52... First cladding layer, 42, 53... Second cladding layer, 43,
54...Core part, 50...Silicon substrate, 51
a, 51b...Photodetector, 55a, 55b...Separation area, 60a, 60b...Non-reflection coat.

Claims (1)

[Claims] 1. A core layer for propagating a light beam, a first cladding layer having a refractive index higher than that of the core layer, and a second cladding layer having a lower refractive index than the first cladding layer.
A resonant reflective cladding portion having at least one pair of cladding layers, the first cladding layer being in contact with the core layer, and having strong reflection characteristics toward the core for light in one or more specific wavelength ranges. and formed by partially changing the film thickness or refractive index of at least one of the first cladding layer or the second cladding layer, and transmitting only light in at least one wavelength range of the light in the specific wavelength range. An optical circuit characterized by having a wavelength separation region that transmits light. 2. The optical circuit according to claim 1, further comprising a plurality of wavelength separation regions that individually transmit a plurality of light beams having different wavelengths. 3. At least one pair consisting of a semiconductor substrate, a first cladding layer, and a second cladding layer formed on the semiconductor substrate and having a refractive index lower than the refractive index of the first cladding layer.
a resonant reflective cladding portion having a strong reflection characteristic for light in one or more specific wavelength ranges, and a wavelength separation region that transmits only light in at least one of the specific wavelength ranges. a core layer that is formed on the first cladding layer and propagates light in the specific wavelength range, and the wavelength separation region is connected to the first cladding layer or the second cladding layer. At least 1 of the thickness or refractive index of the layer
An optical circuit characterized in that the optical circuit is formed by partially making the film thickness or refractive index different from that of the resonant reflective cladding part. 4 a semiconductor substrate; one or more photodetectors formed on the semiconductor substrate and having a photodetection region; a first cladding layer and a first cladding layer formed on the semiconductor substrate and the photodetector; a resonant reflective cladding portion having at least one pair consisting of a second cladding layer having a refractive index lower than that of the second cladding layer, and having strong reflection characteristics for light in one or more specific wavelength ranges; a cladding portion that is located on the detector and constitutes a wavelength separation region that transmits only light in at least one of the specific wavelength ranges; a core layer that propagates light in the resonant reflective cladding region, and the wavelength separation region is partially formed by changing at least one of the film thickness and refractive index of the first cladding layer or the second cladding layer to the resonant reflective cladding portion. An optical circuit characterized in that it is formed by making the film thickness or refractive index different from each other. 5. A semiconductor substrate, one or more photodetectors formed on the semiconductor substrate and having a photodetection region, a first cladding layer and a first cladding layer formed on the semiconductor substrate and the photodetector. a resonant reflective cladding portion having at least one pair consisting of a second cladding layer having a refractive index lower than that of the second cladding layer, and having strong reflection characteristics for light in one or more specific wavelength ranges; a cladding portion that is located on the detector and constitutes a wavelength separation region that transmits only light in at least one of the specific wavelength ranges; a core layer that propagates light in the wavelength range, and an anti-reflection coating layer formed between the photodetector and the cladding, and the wavelength separation region is formed between the first cladding layer or the second cladding layer. It is formed by partially making at least one of a film thickness and a refractive index different from the film thickness or refractive index of the resonant reflective cladding part, and the non-reflective coating layer allows the wavelength separation region to pass through the wavelength separation region. An optical circuit characterized in that the optical circuit is configured such that light enters the photodetector in a substantially non-reflective state.