WO2010079611A1

WO2010079611A1 - Optical transmission/reception module

Info

Publication number: WO2010079611A1
Application number: PCT/JP2009/050226
Authority: WO
Inventors: 弘幸尾崎; 智志西川; 正和高林; 政利片山; 喜市吉新
Original assignee: 三菱電機株式会社
Priority date: 2009-01-09
Filing date: 2009-01-09
Publication date: 2010-07-15
Also published as: CN102177455A; TW201027154A; JPWO2010079611A1; TWI402550B; CN102177455B; JP5279847B2

Abstract

An optical transmission/reception module which can ensure the transmission quality without providing a collimating optical device and a narrow-band filter. A fiber (7) with a grating which has a function of the narrow-band filter to block transmission of an optical signal in a band other than a narrow band containing a wavelength of 1310 nm, a narrow band containing a wavelength of 1490 nm, and a narrow band containing a wavelength of 1550 nm is used as an optical fiber for transmitting an optical signal with the wavelength of 1310 nm that has passed through WDM filters (4, 5) to a station and transmitting optical signals with the wavelengths of 1490 nm and 1550 nm transmitted from the station to the WDM filter (5).

Description

Optical transceiver module

The present invention is a subscriber-side optical line termination device of GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network System) that provides subscribers with Internet service with a maximum transmission rate of 1 Gbit / s using an optical fiber. The present invention relates to an optical transmission / reception module mounted in an (ONU: Optical Network Unit) and performing processing of converting an optical signal into an electrical signal and processing of converting an electrical signal into an optical signal.

The GE-PON system comprises a station-side Optical Line Terminal (OLT) installed at a center station, an optical branching unit for branching transmission lines up to 32 and a subscriber installed at a subscriber's premises. It consists of a side optical line termination device.

The downstream data / voice signal transmitted from the station-side optical line termination to the subscriber-side optical line termination is assigned a wavelength of 1490 nm, and the downstream analog video signal is assigned a wavelength of 1550 nm.

On the other hand, a wavelength of 1310 nm is allocated to the upstream data signal transmitted from the subscriber-side optical line terminal to the station-side optical line terminal.

Thus, the GE-PON system performs single-core bidirectional optical communication using wavelength division multiplexing (WDM) to which a plurality of wavelengths are allocated.

However, in the GE-PON system, it is necessary to provide a guard band in the optical wavelength band of the downstream data / voice signal and the optical wavelength band of the analog video signal. That is, in order to avoid transmission and reception of optical wavelengths other than those optical wavelength bands, it is necessary to use an optical transmission and reception module in which the subscriber-side optical line termination device is provided with a guard band.

As described above, it is necessary to use an optical transmission / reception module in which the subscriber-side optical line termination device is provided with a guard band. For example, in the transmission / reception module disclosed in Patent Document 1, a plurality of WDM filters are used. Single-core bidirectional optical communication is realized by separating and multiplexing wavelength optical signals. However, in this transmission / reception module, guards adjacent to the optical wavelength of the downstream data / audio signal and the optical wavelength of the analog video signal can be obtained only by simply connecting the lens coupling optical element between the WDM filter and the optical fiber. It can not be applied to the GE-PON system in which the band is provided.

Here, FIG. 14 is an explanatory view showing a filter characteristic by diffused light (divergence light) of the receiving module disclosed in Patent Document 1. As shown in FIG. The rectangular portions in FIG. 14 mean standard specifications.

As apparent from FIG. 14, when the narrow band filter in the optical transmission / reception module in the subscriber-side optical line terminal is made incident as diffused light, the diffused light of the optical transmission / reception module is a guard band (wavelength band λ1-α Through).

Here, when the guard band and the light wavelength of the data / voice signal or the light wavelength of the analog video signal are adjacent, the filter characteristics of the narrow band filter change depending on the angle of the incident light with respect to the narrow band filter. It is necessary to maintain the transmission quality by maintaining the filter characteristics of the band pass filter.

In order to maintain the filter characteristics of the narrow band filter and secure the transmission quality, a narrow band filter is provided by installing a collimating optical device or the like for converting diffused light output from the optical fiber into parallel light (collimator light). It is sufficient to adjust the angle of incident light with respect to.

For example, Patent Document 2 discloses a transmitting / receiving module in which a narrow band filter and a collimating optical device are installed.

Here, FIG. 15 is an explanatory view showing filter characteristics by parallel light of the transmission / reception module disclosed in Patent Document 2. As shown in FIG. The rectangular portions in FIG. 15 mean standard specifications.

As apparent from FIG. 15, guard bands in the wavelength bands (λ1−α), λ1, and (λ1 + α) are provided, and transmission and reception of unnecessary light wavelengths can be avoided.

Further, Patent Document 3 discloses a configuration in which a tilted fiber grating and a non-tilted fiber grating are combined as a low reflection and high transmission loss wavelength filter of 40 dB or more. It is not easy to obtain low reflection and high transmission loss characteristics of 40 dB or more with only tilted gratings, but combining inclined and non-tilted fiber gratings with transmission loss of about 20 dB results in low reflection and high transmission loss of 40 dB or more. It is believed that the characteristics can be obtained.

In addition, the structure of the optical transmission / reception module using such a fiber type wavelength filter is not reported until now.

Japanese Patent Publication No. 2003-524789 (FIG. 2a) JP-A-2005-260220 (Paragraphs [0009], [0010], FIG. 4) Patent No. 3612780

Since the conventional light transmitting / receiving module is configured as described above, if the collimating optical device is installed, it is possible to maintain the filter characteristics of the narrow band filter and secure the transmission quality. However, the number of parts increases as the collimating optics are installed. For this reason, there existed a subject that size reduction became difficult and member cost became high.

Also, in the wavelength filter using the conventional fiber grating, when the exposure intensity is increased to obtain a high transmission loss of about 20 dB with the inclined fiber grating, residual reflection in the Bragg reflection wavelength band or the loss wavelength band tends to occur, and low There is a problem that the reflection characteristic is lost.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to obtain an optical transmission / reception module capable of securing transmission quality without installing a collimating optical device or a narrow band filter. Do.

The optical transmitting and receiving module according to the present invention transmits the optical signal of the first wavelength band transmitted by the wavelength division multiplexing means to the station side, and the optical signals of the second and third wavelength bands transmitted from the station side. A fiber with a grating having the function of a narrow band filter for blocking transmission of optical signals in bands other than the first, second and third wavelength bands as an optical fiber for transmitting It is.

According to the present invention, the optical signal of the first wavelength band transmitted by the wavelength division multiplexing means is transmitted to the station side, and the optical signals of the second and third wavelength bands transmitted from the station side are wavelength separated. As an optical fiber to be transmitted to the multiplexing means is configured to use a fiber with a grating having the function of a narrow band filter that blocks transmission of optical signals in bands other than the first, second and third wavelength bands, The transmission quality can be secured without installing the mating optical device or the narrow band filter, and as a result, the size reduction and the cost reduction of the members can be achieved.

FIG. 2 is an explanatory view showing a configuration of an optical transmission and reception module according to Embodiment 1. It is explanatory drawing which shows a fiber grating characteristic. FIG. 8 is an explanatory view showing a configuration of an optical transmission and reception module according to a second embodiment. FIG. 13 is an explanatory view showing a configuration of an optical transmission and reception module according to a third embodiment. FIG. 18 is an explanatory view showing a configuration of an optical transmission and reception module according to a fourth embodiment. FIG. 18 is an explanatory view showing a configuration of a fiber grating for an optical transmission and reception module according to a fifth embodiment. 21 is a graph showing an example of spectrum measurement of the tilted fiber grating according to the fifth embodiment. 21 is a graph showing an example of spectrum calculation of the tilted fiber grating according to the fifth embodiment. 21 is a graph showing measurement results of transmission loss of a tilted fiber grating when the length of an optical fiber portion for stray light attenuation according to Embodiment 5 is changed. FIG. 16 is an explanatory view showing a configuration of a fiber grating for an optical transmission and reception module according to a sixth embodiment. It is a graph which shows the example of spectrum calculation of the inclined fiber grating by Embodiment 6. FIG. FIG. 21 is an explanatory drawing showing the configuration of a fiber grating for an optical transmission / reception module according to a seventh embodiment. FIG. 21 is an explanatory drawing showing a method of manufacturing a fiber grating for an optical transmission / reception module according to Embodiment 8. It is explanatory drawing which shows the filter characteristic by the diffused light of the conventional transmission / reception module. It is explanatory drawing which shows the filter characteristic by parallel light of the conventional transmission / reception module.

Embodiment 1
FIG. 1 is an explanatory view showing a configuration of an optical transmission / reception module according to a first embodiment of the present invention. The optical transmission / reception module shown in FIG. 1 is mounted on a subscriber-side optical line termination device.

In FIG. 1, the transmission module 1 converts an electrical signal, which is an upstream data signal, into an optical signal of 1310 nm wavelength (optical signal included in the first wavelength band), and outputs the optical wavelength to the WDM filter 4 It is.

When receiving an optical signal (optical signal included in the second wavelength band) having a wavelength of 1490 nm, which is a downstream data / voice signal from the WDM filter 4, the receiving module 2 converts the optical signal into an electrical signal. It is a receiving module.

When receiving an optical signal of 1550 nm wavelength (an optical signal included in the third wavelength band), which is a downstream analog video signal, from the WDM filter 5, the receiving module 3 converts the optical signal into an electric signal. It is a module.

In FIG. 1, the optical signal of the first wavelength band transmitted by the transmitting module 1 is an optical signal of 1310 nm, the optical signal of the second wavelength band received by the receiving module 2 is an optical signal of 1490 nm, by the receiving module 3 Although an example is shown in which the optical signal of the third wavelength band to be received is an optical signal of 1550 nm, this is merely an example, and the first, second, and third wavelength bands are other wavelength bands. It goes without saying that it is also possible.

The WDM filter 4 transmits the light signal of wavelength 1310 nm output from the transmission module 1 to the WDM filter 5 side, and reflects the light signal of wavelength 1490 nm transmitted through the WDM filter 5 to the reception module 2 side. It is a separation multiplex filter.

The WDM filter 5 transmits the optical signal of wavelength 1310 nm transmitted through the WDM filter 4 to the side of the fiber ferrule 6 and transmits the optical signal of wavelength 1490 nm output from the fiber ferrule 6 to the side of the WDM filter 4 while the fiber ferrule 6 is a second wavelength division multiplex filter that reflects the optical signal of wavelength 1550 nm output from the light source 6 to the receiving module 3 side. The WDM filters 4 and 5 constitute a wavelength demultiplexing means.

The fiber ferrule 6 is a housing member for housing the fiber 7 with a grating, and is provided on the right of the WDM filter 5 in the figure.

The fiber 7 with grating transmits the optical signal of wavelength 1310 nm transmitted through the WDM filter 5 and outputs it to the connector 8 side, while the optical signal of wavelength 1490 nm and 1550 nm incident from the connector 8 side (transmitted from the station side ) Is an optical fiber that transmits the optical signal to the WDM filter 5 side. The fiber 7 with grating has a band other than a narrow band (first wavelength band) including a wavelength 1310 nm, a narrow band (second wavelength band) including a wavelength 1490 nm, and a narrow band (third wavelength band) including a wavelength 1550 nm. And the function of a narrow band filter to block the transmission of the light signal.

The connector 8 is a connecting member to which one end of the fiber with grating 7 is connected and to which one end of a single mode fiber is connected. The other end of the single mode fiber is connected to the station side optical line termination device.

Next, the operation of the optical transmission and reception module according to the first embodiment will be described. First, an operation of the optical transmission and reception module in the subscriber-side optical line termination apparatus transmitting an upstream data signal to the station-side optical line termination apparatus will be described.

When receiving an electrical signal that is an upstream data signal, the transmission module 1 converts the electrical signal into an optical signal with a wavelength of 1310 nm, and outputs the optical signal to the WDM filter 4.

When the WDM filter 4 receives an optical signal of wavelength 1310 nm from the transmission module 1, the WDM filter 4 transmits the optical signal of wavelength 1310 nm to the WDM filter 5 side.

The WDM filter 5 transmits the light signal of wavelength 1310 nm transmitted through the WDM filter 4 to the fiber ferrule 6 side.

As a result, when an optical signal of wavelength 1310 nm is incident on the fiber ferrule 6, an optical signal of wavelength 1310 nm is transmitted in the fiber 7 with a grating and emitted from the connector 8 to a single mode fiber.

Next, the operation of the optical transmission / reception module in the subscriber-side optical line termination device receiving downstream data / voice signals and analog video signals from the station-side optical line termination device will be described.

An optical signal with a wavelength of 1490 nm, which is a downstream data / voice signal transmitted from the station-side optical line terminal, and an optical signal with a wavelength of 1550 nm, which is a downstream analog video signal, are transmitted through a single mode fiber. It is incident from.

As a result, optical signals of wavelengths 1490 nm and 1550 nm are transmitted through the fiber 7 with a grating, and emitted from the fiber ferrule 6 to the WDM filter 5.

When the WDM filter 5 receives an optical signal with a wavelength of 1490 nm and 1550 nm from the fiber ferrule 6, the WDM filter 5 separates the optical signal with a wavelength of 1490 nm and the optical signal with a wavelength of 1550 nm and transmits the optical signal with a wavelength of 1490 nm to the WDM filter 4 side The light signal of wavelength 1550 nm is reflected to the receiving module 3 side.

Receiving the optical signal of wavelength 1550 nm from the WDM filter 5, the receiving module 3 converts the optical signal of wavelength 1550 nm into an electrical signal, and outputs a downstream analog video signal which is an electrical signal.

The WDM filter 4 reflects the light signal of wavelength 1490 nm transmitted through the WDM filter 5 to the receiving module 2 side.

Receiving the light signal of wavelength 1490 nm from the WDM filter 4, the reception module 2 converts the light signal of wavelength 1490 nm into an electric signal, and outputs downstream data / voice signal which is an electric signal.

Here, the fiber with grating 7 utilizes a light-induced refractive index change in which the refractive index increases when ultraviolet light is irradiated to the optical fiber.

That is, when the fiber with grating 7 is irradiated with ultraviolet light to the optical fiber, a diffraction grating is formed in the core or cladding of the optical fiber, and the periodic refractive index changes.

As a result, since the grating-equipped fiber 7 can reflect only a specific light wavelength corresponding to the period, it is used as an optical fiber type device having the function of an optical filter (narrow band filter).

In addition, since the grating-equipped fiber 7 can directly form the diffraction grating in the optical fiber nondestructively, it can be manufactured at low cost. In addition, since optical characteristics such as center wavelength, bandwidth, and reflectance can be easily changed, it has an advantage that low loss, miniaturization, and high reliability can be obtained.

The grating-equipped fiber 7 implemented in the optical transceiver module of FIG. 1 transmits a narrow band optical signal including a wavelength 1310 nm, a narrow band optical signal including a wavelength 1490 nm, and a narrow band optical signal including a wavelength 1550 nm. However, it has the function of a narrow band filter for attenuating optical signals in bands other than the above three narrow bands.

Therefore, it is not necessary to dispose a narrow band filter inside as in the conventional optical transceiver module. As a result, there is no need to convert the light wavelength from divergence light into collimator light, so there is no need to arrange collimator optics as in the conventional light transmitting and receiving module.

In addition, the fiber 7 with a grating has an optical signal of a narrow band including a wavelength of 1310 nm, a narrow band including a wavelength of 1490 nm, and a band other than the narrow band including a wavelength of 1550 nm, energy diffused from the core in the fiber to the cladding Can be secured.

Here, FIG. 2 is an explanatory view showing a fiber grating characteristic. As apparent from FIG. 2, it is unnecessary in the GE-PON system in which guard bands of wavelength bands (λ 1 -α), λ 1, (λ 1 + α) are provided without installing narrow band filters and collimator optical devices. Transmission and reception of light wavelengths can be avoided. The rectangular portion in FIG. 2 means a standard specification.

As apparent from the above, according to the first embodiment, the optical signal of wavelength 1310 nm transmitted through the WDM filters 4 and 5 is transmitted to the station side, and the wavelengths 1490 nm and 1550 nm transmitted from the station side are transmitted. An optical fiber for transmitting an optical signal to the WDM filter 5 side includes blocking (reflecting) transmission of a narrow band including wavelength 1310 nm, a narrow band including wavelength 1490 nm, and a band other than a narrow band including wavelength 1550 nm It is comprised so that the fiber 7 with a grating which has a function of a band pass filter may be used. For this reason, transmission quality can be ensured without installing a narrow band filter and collimating optical equipment, and as a result, it is possible to achieve miniaturization and reduction in member cost.

Second Embodiment
FIG. 3 is an explanatory view showing the configuration of an optical transmission / reception module according to a second embodiment of the present invention. In FIG. 3, since the same reference numerals as in FIG. 1 described in the first embodiment indicate the same or corresponding parts, the description will be appropriately omitted.

The fiber ferrule 9 with a grating is a fiber ferrule which accommodates the part equivalent to the grating part in the fiber 7 with a grating of FIG.

One end of the optical fiber 10 is connected to the fiber with grating housed in the fiber ferrule 9 with grating, and transmits the optical signal of wavelength 1310 nm transmitted through the WDM filter 5 and outputs it to the connector 8 side. An optical signal (optical signal transmitted from the station side) of wavelengths 1490 nm and 1550 nm incident from the 8 side is transmitted and output to the WDM filter 5 side.

In the first embodiment described above, the fiber with grating 7 is connected between the fiber ferrule 6 and the connector 8. However, the grating length of the fiber with grating 7 is shortened by changing the refractive index. In the second embodiment, the grating portion is housed in the fiber ferrule 6. Specifically, it is as follows.

The fiber ferrule 9 with a grating shown in FIG. 3 is made to grating the core of the fiber in the fiber ferrule, noting that the grating length can be shortened to 1 / n ² when the refractive index change amount is multiplied by n. It is a thing.

As a result, it is possible to reduce the area of extra fiber length processing, that is, to shorten the length of the optical fiber 10, thereby enabling space saving of the subscriber-side optical line termination device. In addition, by shortening the fiber length, the direct material cost can be reduced.

Therefore, the optical transmission and reception module of the second embodiment exhibits the effect of being able to reduce the size and cost of the member more than the optical transmission and reception module of the first embodiment.

Embodiment 3
FIG. 4 is an explanatory view showing a configuration of an optical transmission and reception module according to a third embodiment of the present invention. In FIG. 4, the same reference numerals as in FIGS. 1 and 3 denote the same or corresponding parts, and therefore the description will be appropriately omitted.

The connector with grating 11 is a connector that accommodates a portion corresponding to the grating portion in the fiber with grating 7 of FIG. 1.

In the optical transmitting and receiving module according to the first embodiment, although the fiber 7 with a grating is connected between the fiber ferrule 6 and the connector 8, the grating length of the fiber 7 with a grating is shortened by the change of the refractive index. In the third embodiment, the grating portion of the fiber 7 with a grating is accommodated in the connector 8 by doing this. Specifically, it is as follows.

In the connector with grating 11 of FIG. 4, focusing on the fact that the grating length can be shortened to 1 / n ² when the refractive index change amount is multiplied by n, the grating of the core of the optical fiber in the connector 11 is made to grating A part is provided.

As a result, the area for extra fiber length processing can be reduced, and space saving of the subscriber-side optical line termination device can be achieved. In addition, by shortening the fiber length, the direct material cost can be reduced.

Therefore, the optical transmission and reception module of the third embodiment exhibits the effect of achieving the downsizing and the reduction of the member cost more than the optical transmission and reception module of the first embodiment.

Fourth Preferred Embodiment
FIG. 5 is an explanatory view showing a configuration of an optical transmission and reception module according to a fourth embodiment of the present invention. In FIG. 5, the same reference numerals as those in FIG. 1 denote the same or corresponding parts, and therefore the description will be appropriately omitted.

The receptacle 12 with grating is disposed on the right of the WDM filter 5 in the figure and connected to one end of a single mode fiber, and has an optical axis adjustment function with the optical module and a connection mechanism with an external connector. It is a module part.

Further, the receptacle 12 with a grating accommodates a portion corresponding to the grating portion in the fiber 7 with a grating in FIG. 1.

In the first embodiment, although the fiber 7 with a grating is connected between the fiber ferrule 6 and the connector 8, the grating length of the fiber 7 with a grating is shortened by changing the refractive index, Embodiment 4 stores the fiber 7 with a grating in a receptacle. Specifically, it is as follows.

The receptacle 12 with a grating shown in FIG. 5 is one in which the grating length can be shortened to 1 / n ² if the refractive index change amount is multiplied by n, and the grating is made in the core of the fiber in the receptacle. is there.

Therefore, the optical transmission and reception module of the fourth embodiment achieves the effect of being able to reduce the size and cost of the member more than the optical transmission and reception module of the first embodiment.

The Fifth Preferred Embodiment
FIG. 6 is an explanatory view showing a structure of a fiber grating for an optical transmitting and receiving module according to a fifth embodiment of the present invention.

As shown in FIG. 6, a clad 14 is provided to cover the core 13 in a concentric manner, and the core 13 has an inclined fiber grating portion 15 and an optical fiber portion 16 for attenuating stray light.

In the fifth embodiment, a tilted fiber grating is used as a wavelength filter. Below, the manufacturing method of the inclined fiber grating part 15 is demonstrated first. Optical fiber gratings are fabricated by ultraviolet light exposure to optical fibers. The optical fiber to be used is compatible with the optical fiber connected to the optical transceiver module from the outside (connector 8 side (see Fig. 1), incident side of transmitted light) and optical characteristics such as core diameter and numerical aperture. A model is desirable. If there is no optical compatibility, a connection loss occurs when the optical transceiver module and the external fiber are connected via an optical fiber connector or the like, which causes signal degradation. In the present embodiment, so-called photo in which the exposure sensitivity is enhanced by adding Ge and B (boron) instead of the silica glass-based fiber (composed of silica glass clad and Ge (germanium) doped core) used for optical communication Use sensitive fiber. Specifically, the cladding is the same quartz glass, and Ge and B are added to the core, and the mode field diameter, numerical aperture and cladding diameter are in the same specification as that of the external single mode fiber, using the mode The field diameter is about 10 μm, the numerical aperture is about 0.13, and the cladding diameter is 125 μm.

Before exposure of the fiber grating, after two weeks treatment in high pressure hydrogen (100 atm) atmosphere to enhance exposure sensitivity, the grating is formed by irradiating Nd-YAG laser (output 200 mW, wavelength 266 nm) did. The laser for exposure may use an excimer laser. The portion to be irradiated with ultraviolet light is exposed in a state in which the coating of the fiber is removed to expose the cladding and brought close to the phase mask.

The period of the phase mask is adjusted so that the wavelength of the 1.55 μm band is a Bragg wavelength, and the periodic structure of the mask is inclined at an angle θ (see FIG. 6) with respect to the vertical line in the longitudinal direction of the optical fiber. Set as you are. θ is defined in the range of more than −90 ° and less than 90 °.

In the inclined fiber grating portion 15, a transmission loss called cladding mode occurs on the short wavelength side of the Bragg wavelength. In a grating with a uniform period, the cladding mode loss has a periodic comb-like spectrum shape, but in a chirped grating whose period is changed in the grating, the spectrum shape is averaged into a broad spectrum shape.

In order to explain the optical characteristics of the fiber grating, a graph showing an example of spectrum measurement of the inclined fiber grating portion 15 in FIG. 7 is used. The fiber grating was obtained by using a photosensitive fiber, tilting the phase mask by about 3.1 degrees, exposing the grating length at 5 mm and the chirp amount at about 0.4 nm. FIG. 7 shows the spectrum of transmission loss and reflection. Although Bragg reflection is present at a wavelength of 1556 to 1557 nm, the reflection angle has a small value of −30 dB or less because the inclination angle is adjusted to a condition under which Bragg reflection becomes smaller. Since the reflection intensity is sufficiently small, no structure appears in the transmission loss spectrum at the above wavelength. The loss appearing on the shorter wavelength side than 1553 nm in the transmission loss spectrum is due to the cladding mode described above. Since the fiber grating is chirped, the comb-like spectral structure is averaged. The loss near 1555 nm is a spectral structure due to the reflection from the fundamental propagation mode to the high order LP11 mode, also called ghost grating. In the optical fiber before exposure, this mode has a large propagation loss and does not appear as a spectral structure. However, when the average refractive index of the core is increased by the exposure of the grating and the propagation loss is reduced, as shown in FIG. It will increase. Since the LP11 mode is attenuated in the fiber area where the grating is not exposed, it is considered that the reflection intensity does not originally increase, but residual reflection may occur due to the influence of the nonuniformity of the grating and the like. The structure with a reflection intensity of -25 dB appearing at wavelengths 1554 to 1555 nm in FIG. 7 is due to such residual reflection.

Since the Bragg reflection intensity and the transmission loss of the cladding mode and the ghost grating vary depending on the grating tilt angle, it is necessary to adjust the mask tilt angle at the time of exposure in order to obtain the desired characteristics. In particular, the Bragg reflection has the property of being sensitive to the grating tilt angle. As the fiber grating length increases, the transmission loss increases as the change in refractive index due to exposure increases, but the change in refractive index caused by exposure is determined by the characteristics of the fiber used. Therefore, in order to obtain the desired transmission loss, first assume an appropriate refractive index change inherent to the fiber used, and then perform exposure in consideration of the grating length that can obtain the required transmission loss. Do.

For use in the optical transmission / reception module for GE-PON, as the characteristics of the wavelength filter, the use wavelength λA in the wavelength 1310 nm band, the use wavelength λB in the 1490 nm band, the transmission loss is small at the use wavelength λC in the 1550 nm band, It is necessary that the transmission loss is large in the guard band (for example, the wavelength band λC-α) and low reflection in those wavelength bands.

The transmission / reflection spectrum (calculation result) of the fiber grating when the grating length is 50 mm, the inclination angle of the grating is 4.5 degrees, and the change in refractive index due to exposure is 2 × 10 ⁻³ is shown in the graph of FIG.

In order to realize the required transmission loss wavelength width (for example, 1.5 nm), a chirped grating is used. The amount of chirp, which is the difference between the maximum value and the minimum value of the Bragg wavelength of the fiber grating, was 2.7 nm. In addition, in order to reduce reflection, apodization processing is assumed in which the amount of change in refractive index is gradually reduced at both ends of the grating.

From Fig.8, the transmission loss at the used wavelength λC at 1552 nm is small, and the transmission loss at the guard band wavelength band (wavelength band λC-α) shorter than the used wavelength is 40 dB or more (Fig. 8 (a)) It can be confirmed that the reflection intensity is small (see FIG. 8 (b)), and it is understood that the required specifications are satisfied in calculation. Since the tilt of the grating in the fiber core is about 1.45 times the mask tilt angle, the mask tilt angle is 3.1 degrees at the time of fabrication. However, when the transmission spectrum of the fiber grating actually manufactured was measured, it became clear that the stray light which propagates a clad part arises in a grating part, and the problem to which a transmission loss becomes small arises. For this problem, we use the attenuation of the clad propagation light due to the loss at the fiber jacket interface and avoid the reduction of transmission loss by providing an optical fiber part for stray light attenuation at the end of the fiber grating. It has been found that it can be done, and it was confirmed by measurement that it is sufficient to provide an optical fiber part for stray light attenuation in order to obtain a transmission loss of 40 dB or more. FIG. 9 is a graph showing the results of measuring the transmission loss by changing the length of the stray light attenuating optical fiber portion 16 with respect to the same inclined fiber grating portion 15. It can be understood from FIG. 9 that in order to obtain the transmission loss of 40 dB or more, the stray light attenuating optical fiber portion 16 of 16 cm or more may be provided.

Therefore, in order to be used in the optical transmission / reception module for GE-PON, it is sufficient to adopt a structure in which the stray light attenuating optical fiber portion 16 having a length of 16 cm or more is attached to the aforementioned inclined fiber grating portion 15.

With regard to the reflection characteristics, a trial manufacture was performed in which the inclination angle was changed, and it was confirmed that the reflection intensity became minimum around 3.1 degrees. Good low reflection characteristics can be obtained by adjusting the inclination angle optimally and exposing the grating uniformly.

As described above, since the necessary wavelength characteristics are obtained in the wavelength region used in the optical transmission / reception module for GE-PON by the fiber grating described in the present embodiment, the operation of the example described in the first embodiment and the third embodiment Thus, it is possible to save the space of the subscriber-side optical line termination device.

Embodiment 6
FIG. 10 is an explanatory view showing a structure of a fiber grating for an optical transmitting and receiving module according to a sixth embodiment of the present invention.

As shown in FIG. 10, in this embodiment, as the fiber grating, the connection inclined fiber grating portion 17a (fiber group with first type grating) and the connection non-inclined fiber grating portion 17b (fiber group with second type grating) And two grating portions connected with each other are used. The same reference numerals as in FIG. 6 denote the same or corresponding parts, and therefore the description will be appropriately omitted.

As the optical fiber, the same photosensitive fiber as in the fifth embodiment is used. Below, the characteristic of each grating is explained.

The coupling inclined fiber grating portion 17a is manufactured to have an inclination angle at which the Bragg reflection becomes small, and to have a transmission loss of 12.5 dB or more due to the cladding mode. Further, the connection non-inclined fiber grating part 17b is manufactured at a position close to the connection inclined fiber grating part 17a with a period such that Bragg reflection occurs at the cladding mode loss wavelength of the connection inclined fiber grating part 17a. Finally, the coupling inclined fiber grating portion 17a, the coupling non-inclination fiber grating portion 17b, and the stray light attenuating optical fiber portion 16 are manufactured to be coupled in this order. The connection inclined fiber grating portion 17a is on the connection side with the outside (connector 8 side (see FIG. 1)). Although it is possible to expose each grating separately or to perform batch exposure using a phase mask on which two corresponding types of patterns are formed, it is preferable to perform batch exposure because the cost can be reduced.

The coupling non-inclined fiber grating portion 17b has a wavelength band in which the reflection intensity by Bragg reflection is large, and the center wavelength thereof is the Bragg wavelength. By making the wavelength band where the transmission loss of the connection inclined fiber grating part 17a is sufficiently large include the reflection wavelength band of the connection non-inclination fiber grating part 17b, the connection non-inclination no fiber grating part 17b viewed from the outside The intensity of the Bragg reflection can be reduced. If the transmission loss of the coupling inclined fiber grating portion 17a is small in the Bragg reflection wavelength band of the coupling non-inclined fiber grating portion 17b, the reflection intensity viewed from the outside at that wavelength becomes large.

As described above, in the state in which the intensity of the Bragg reflection of the connection non-inclined fiber grating part 17b viewed from the outside is reduced, the transmission loss of all the fiber gratings is the Bragg reflection wavelength band of the connection non-inclined fiber grating part 17b. In particular, as the wavelength filter used in the light transmitting / receiving module, the transmission blocking wavelength range may be included in the above-mentioned Bragg wavelength band because it becomes large. In addition, when the transmission blocking wavelength range is wide, the wavelength range can be expanded by chirping the grating.

As the relative relationship of the wavelength position, the transmission loss due to the cladding mode occurs at a shorter wavelength than the Bragg reflection, so the transmission blocking wavelength range included in the transmission loss wavelength band due to the Bragg reflection of the connection non-inclined fiber grating portion 17b is connected As described above, by setting the shorter wavelength side than the Bragg wavelength band of the inclined fiber grating portion 17a for the left side and preventing the Bragg reflection on the longer wavelength side than the Bragg wavelength band of the connected inclined fiber grating portion 17a. It is possible to reduce the intensity of the Bragg reflection of the coupling non-inclined fiber grating portion 17b viewed from the side. The Bragg reflection intensity of the coupling inclined fiber grating portion 17a is reduced by adjusting the inclination angle, so that it is possible to obtain wavelength filter characteristics in which the reflection intensity is small at all wavelengths.

In the desired transmission blocking wavelength range, the light transmission loss of the inclined grating in the connection inclined fiber grating portion 17a and the light transmission loss of the non-tiled grating in the connection non-inclined fiber grating portion 17b are L1 (dB) and L2 (L In the case of dB), it is necessary to satisfy “L1 ≧ 12.5, L1 + L2 ≧ 40” (first condition).

Let R1 (dB) and R2 (dB) be the light reflectances of the inclined gratings in the above transmission blocking wavelength range and the Bragg wavelength band of the inclined grating, and let the reflectance of the non-tilting grating in the transmission blocking wavelength range be R0 ( In the case of dB), it is necessary to satisfy the following equation (1) (second condition).

Then, the first and second conditions are satisfied, and the minimum value of the light transmission loss of the entire optical filter in the transmission blocking wavelength range is 40 dB or more, and the light reflectance is −25 dB or less over the entire wavelength band. In addition, it is possible to adjust the inclination angle and period of the inclined grating in the connection inclined fiber grating portion 17a and the optical fiber length of the stray light attenuating optical fiber portion 16.

For example, the connecting inclined fiber grating portion 17a has a length of 45 mm, the connecting non-inclined fiber grating portion 17b has a length of 10 mm, the phase mask inclination angle is 3.1 degrees, the chirp amount is 2.7 nm, and the refractive index change amount The calculation result of the optical characteristics of the coupled fiber grating when the apodization processing is performed is 1.2 × 10 ^-3 is shown in the graph of FIG. It can be seen that both the transmission loss (see FIG. 11 (a)) and the reflection (see FIG. 11 (b)) satisfy the above specifications (conditions). Although the apodization treatment has a sixth order super Gaussian shape, it may have a second order or fourth order super Gaussian shape.

In FIG. 11A, a large transmission loss of −40 dB or more is observed at a wavelength width of about 2 nm in the 1550 nm band, which is due to the Bragg reflection of the connection non-inclined fiber grating portion 17b as described above. On the other hand, the broad transmission loss from this wavelength band to the short wavelength side is due to the transmission loss of the cladding mode of the connection sloped fiber grating portion 17a, and the relative relationship between the wavelength positions of the two gratings is as described above. Know that Further, of the two types of reflection bands in the 1550 nm band shown in FIG. 11B, the Bragg reflection of the connection non-inclined fiber grating portion 17b transmits the cladding mode of the connection inclined fiber grating portion 17a on the short wavelength side. It is reduced by the loss. The long wavelength side is the Bragg reflection intensity of the coupling inclined fiber grating portion 17a, which is reduced by adjusting the inclination angle.

The fiber grating having such a connection structure can be manufactured because high transmission loss can be obtained with a short fiber length for the same amount of change in refractive index as compared with the case of one type of inclined fiber grating described in the fifth embodiment. Has the effect of facilitating In addition, since the amount of chirp per unit length of the tilted grating can be increased, there is an effect that low reflection characteristics can be easily obtained.

Seventh Embodiment
FIG. 12 is an explanatory view showing a structure of a fiber grating for an optical transmission / reception module according to a seventh embodiment of the present invention.

As shown in FIG. 12, in the present embodiment, as the fiber grating, the coupling first inclined grating portion 18 a and the coupling second inclined grating portion 18 b (fiber group with first type grating) and the coupling non-inclined fiber grating It is set as the structure which connected the part 17b (2nd type grating attached fiber group). Therefore, the inclined grating portion has a structure in which two types of

inclined grating portions

18a and 18b are connected. The same reference numerals as in FIG. 6 or FIG. 10 denote the same or corresponding parts, and therefore the description will be appropriately omitted.

As the optical fiber, the same photosensitive fiber as in the case of the fifth and sixth embodiments is used. Below, the characteristic of each grating is explained.

The inclined grating section is produced by connecting the first inclined grating section 18a for connection (first (inclined) grating) at an inclination angle at which the Bragg reflection becomes small, and the second inclined grating section for connection 18b (second (inclined) grating ) Are also made at the same inclination angle. In the first grating and the second grating, the transmission loss wavelength is made to overlap with the same period and the same amount of chirp, but the first grating has a smaller FBG (Fiber Bragg Grating) length, that is, Make the amount of chirp per unit length large. By doing this, the reflectance of the first grating can be made smaller than the reflectance of the second grating.

The coupling non-inclined fiber grating portion 17b and the stray light attenuating optical fiber portion 16 are manufactured in the same manner as in the sixth embodiment. The connection non-inclined fiber grating part 17b (non-inclined grating) is fabricated at a position close to the inclined grating part 18b with a period such that Bragg reflection occurs at the cladding mode loss wavelength of the inclined grating. Finally, the connecting first inclined grating portion 18a, the connecting second inclined grating portion 18b, the connecting non-inclined fiber grating portion 17b, and the stray light attenuating optical fiber portion 16 are manufactured to be connected in this order. The coupling first inclined grating portion 18 a is on the connection side with the outside. Although it is possible to expose each grating separately or collectively by using a phase mask on which three corresponding types of patterns are formed, it is preferable to collectively expose because the cost can be reduced.

The light transmission loss of the first inclined grating, the light transmission loss of the second inclined grating, and the light transmission loss of the non-tilted grating in the desired transmission blocking wavelength range are L11 (dB) and L21 (dB, respectively). And L2 (dB), it is necessary to satisfy "L11 ≧ 2.5, L11 + L21 ≧ 12.5, L2 ≧ 15" (third condition).

The light reflectivity of the first inclined grating in the transmission blocking wavelength range described above and the Bragg wavelength band of the first inclined grating is R11 (dB) and R12 (dB), respectively, and the Bragg reflection of the non-inclined grating Where R21 (dB) and R22 (dB) are the light reflectances of the second inclined grating in the transmission loss wavelength band according to and the Bragg wavelength band of the first and second inclined gratings, respectively. It is necessary to satisfy 2) and Formula (3) (fourth condition).

And while satisfying the said 3rd and 4th conditions, the minimum value of the light transmission loss as the whole optical filter in the said transmission blockage | prevention wavelength range is 40 dB or more, and light reflectivity becomes -25 dB or less over all the wavelength bands. Thus, it is possible to adjust the tilt angle and period of the grating and the optical fiber length for stray light attenuation.

For example, the length of the connecting first inclined grating portion 18a is 10 mm, the length of the connecting second inclined grating portion 18b is 35 mm, the length of the connecting non-inclined fiber grating portion 17b is 10 mm, and the phase mask inclination angle is 3 Assuming that the degree of chirp is 2.7 nm, the change in refractive index is 1.2 × 10 ^-3 , and the apodized treatment is the same as in the case of the sixth embodiment, both the transmission loss and the reflection have the above specifications ( Characteristics satisfying the condition) are obtained.

The fiber grating having such a connection structure can easily obtain low reflection characteristics as compared with the case of the two types of inclined fiber gratings described in the sixth embodiment, and has an effect of facilitating manufacture. This is because the first inclined grating can increase the amount of chirp per unit length of the inclined grating when considering the reflection characteristics of the entire wavelength filter, and therefore the reflection can be made low and the contribution of the reflection by the second inclined grating can be obtained. Is reduced by the transmission loss of the first tilted grating.

In the vicinity of the transmission blocking wavelength range, the transmission loss wavelength range of the tilted grating near the outer side needs to include the reflection wavelength range of the tilted grating on the inner side in order to have low reflection characteristics as the entire grating viewed from the outer side There is. Also, as the amount of chirp per unit length of the tilted grating is larger, it is easier to obtain a low reflective grating, but the transmission loss intensity also decreases. Therefore, for the tilted grating close to the outside, adjust the total chirp amount so that the transmission loss wavelength range is equal to or more than the reflection wavelength range of the tilted grating on the inner side, and the transmission loss intensity of 1 dB or more By adjusting the amount of chirp per unit length and the fiber grating length so as to have, the wavelength position is also adjusted so that the transmission loss wavelength range includes the reflection wavelength range of the inclined grating on the inner side, viewed from the outside Low reflection characteristics can be obtained as a whole.

Also, in order to reduce the reflection at the transmission loss wavelength of the outermost grating, for example, the following is performed. As shown in FIG. 7, since the transmission loss wavelength and the reflection wavelength are substantially the same wavelength, for example, the Bragg wavelength band of the first inclined grating and the Bragg wavelength band of the second inclined grating are at the same wavelength position. The Bragg wavelength band of the first tilted grating includes the Bragg wavelength band of the second tilted grating by setting the total chirp amount of the first tilted grating to be equal to or greater than the total chirp amount of the second tilted grating. The transmission loss wavelength band of the inclined grating can include the reflection wavelength band of the second inclined grating, and low reflection characteristics can be obtained as the entire grating viewed from the outside.

Such multiplexing of inclined gratings has the effect that low reflection characteristics can be more easily obtained when the multiplicity is further increased from two connections. At this time, the period is the same for each inclined grating, and the amount of chirp per unit length may be larger as the inclination grating is closer to the external connection side, and the total amount of chirp may be the same or more.

Embodiment 8
FIG. 13 is an explanatory drawing showing a method of producing a fiber grating used for an optical transmitter-receiver module according to Embodiment 8 of the present invention.

Although fiber gratings are produced by exposure to ultraviolet light, refraction of light occurs when ultraviolet light passing through the phase mask passes through the surface of the fiber cladding, so that the tilt angle of the structure actually exposed in the fiber is the phase mask Approximately 1.45 times the angle of inclination of the In addition, the light collecting effect of the cylindrical surface of the cladding may cause the structure of the grating to be nonuniform.

In the present embodiment, as shown in FIG. 13A, the periphery of the fiber (core 13 and cladding 14) on the dielectric plate 19 is filled with the ultraviolet light transmitting liquid 22 and a phase mask is formed by the irradiation ultraviolet light 21 for exposure. Expose through 20.

For example, when water is used as the ultraviolet light transmitting liquid 22, the refractive index of water is close to the refractive index of the fiber cladding, so the effect of refraction at the surface of the cladding 14 is reduced. As a result, the tilt angle of the structure actually exposed in the fiber falls at about 1.1 times the tilt angle of the phase mask 20. Although the adjustment accuracy of the tilt angle of the phase mask 20 is determined by mechanical tolerances, the tilt angle of the structure actually exposed in the fiber corresponds to that of the phase mask 20 in consideration of producing a fiber grating at a desired tilt angle. The smaller the ratio of the tilt angles, the more accurate the tilt angles of the structures actually exposed in the fiber can be. In this case, the angular accuracy can be improved by about 30%. In order to obtain low reflection characteristics, it is necessary to adjust the inclination angle to a desired size, and when the angle is deviated, the Bragg reflection intensity is increased, so that manufacturing of the low reflection characteristics is easy when the angle accuracy is improved. Have the effect of

The same angle accuracy improvement effect, as shown in FIG. 13 (b), installs a fiber (core 13, clad 14) in the groove 23g provided in the grooved dielectric plate 23, and applies the irradiation ultraviolet light 21 for exposure. It can also be obtained by exposure through the phase mask 20.

For example, when a groove is provided in a quartz glass plate as the grooved dielectric plate 23, there is no difference between the refractive index of the fiber cladding and the refractive index of the fiber cladding, so that no refraction of light occurs at the cladding surface. As a result, the tilt angle of the structure actually exposed in the fiber is the same as the tilt angle of the phase mask, and the angular accuracy of the grating can be further improved. The groove 23g provided in the grooved dielectric plate 23 does not have to completely match the shape of the fiber cladding, and the same effect can be obtained even if it is a V-shaped groove that can be easily formed, for example.

Although the present invention has been described in detail, the above description is an exemplification in all aspects, and the present invention is not limited thereto. It is understood that countless variations not illustrated are conceivable without departing from the scope of the present invention.

Claims

A transmission module (1) for transmitting an optical signal in a first wavelength band;
A first receiving module (2) for receiving an optical signal of a second wavelength band different from the first wavelength band;
A second receiving module (3) for receiving an optical signal of a third wavelength band different from the first and second wavelength bands;
The optical signal of the first wavelength band transmitted from the transmission module is transmitted, while the optical signals of the second and third wavelength bands are separated to obtain the optical signal of the second wavelength band. Wavelength division multiplexing means (4, 5) for outputting the light signal of the third wavelength band to the second reception module while outputting the signal to the reception module of
The optical signal of the first wavelength band transmitted by the wavelength division multiplexing means is transmitted to the station side, and the optical signals of the second and third wavelength bands transmitted from the station side are transmitted to the wavelength separation multiplexing means And a fiber with grating (7) having the function of a narrow band filter for blocking transmission of optical signals in bands other than the first, second and third wavelength bands while transmitting.
Optical transceiver module.
The optical transmission / reception module according to claim 1,
The wavelength demultiplexing and multiplexing means transmits the optical signal of the first wavelength band transmitted from the transmission module while transmitting the optical signal of the second wavelength band transmitted by the fiber with a grating. A first wavelength demultiplexing filter (4) to be reflected to the receiving module side,
The optical signal of the first wavelength band transmitted through the first wavelength demultiplexing filter and the optical signal of the second wavelength band transmitted by the fiber with a grating are transmitted, while transmitted by the fiber with a grating And a second wavelength demultiplexing filter (5) for reflecting the optical signal of the third wavelength band to the second receiving module side.
Optical transceiver module.
The optical transmission / reception module according to claim 1,
The fiber with grating secures a return loss amount by energy diffusing an optical signal of a band other than the first, second and third wavelength bands from an inner core to a clad.
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
A fiber ferrule (9) is provided between the wavelength demultiplexing / multiplexing means and the fiber with a grating, and a connector (8) is provided to connect one end of the fiber with a grating to one end of a single mode fiber. A grating length of a grating portion of a fiber is shortened by a change in refractive index, and the grating portion is accommodated in the fiber ferrule.
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
The fiber ferrule (6) is provided between the wavelength demultiplexing / multiplexing means and the fiber with grating, and a connector (11) is provided to connect one end of the fiber with grating to one end of a single mode fiber; The grating length of the grating portion of the attached fiber is shortened by the change of the refractive index, and the grating portion is accommodated in the connector.
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
It further comprises a receptacle (12) provided on the station side,
The grating length of the fiber with grating is shortened according to a change in refractive index, and the grating portion of the fiber with grating is accommodated in the receptacle.
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
The optical signal of the first wavelength band transmitted by the transmitting module is an optical signal of 1310 nm, the optical signal of the second wavelength band received by the first receiving module is an optical signal of 1490 nm, the second reception The optical signal of the third wavelength band received by the module is an optical signal of 1550 nm,
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
The grating-equipped fiber includes a grating-equipped fiber portion (15) having a grating tilted with respect to the traveling direction of transmitted light, and a stray light attenuating optical fiber portion (16) for attenuating stray light propagating in the cladding of the optical fiber. And are optically connected.
Optical transceiver module.
The optical transmission / reception module according to any one of claims 1 to 3, wherein
As the fiber with grating, at least two fiber portions with grating (17a, 17b, 18a, 18b) and an optical fiber portion for attenuating stray light (16) for attenuating stray light propagating in the cladding of the optical fiber are optically Connected to the
At least one or more of the at least two grating attached fiber portions are disposed on the incident side of the transmitted light as a first type of grating attached fiber group (17a, 18a, 18b) inclined with respect to the traveling direction of the transmitted light,
And the stray light attenuating optical fiber part is formed on the outgoing side of the transmitted light,
And at least one other one of the at least two grating attached fiber sections is formed as an angle of substantially orthogonal to the traveling direction of the transmitted light as the second type grating attached fiber group (17b), Characterized in that it is disposed between a seed grating attached fiber group and the stray light attenuating optical fiber part,
Optical transceiver module.
The optical transmission / reception module according to claim 9, wherein
The group of fibers with a first type of grating described above comprises a chirped grating,
And the transmission blocking wavelength range included in the transmission loss wavelength band due to Bragg reflection of the fiber group with the second type grating is on the shorter wavelength side than the Bragg wavelength band of the fiber group with the first type grating, and the fiber group of the first type grating It is characterized in that Bragg reflection does not occur on the longer wavelength side than the Bragg wavelength band,
Optical transceiver module.
The optical transceiver module according to claim 10, wherein
The group of fibers with the first type of grating comprises at least two or more optically connected chirped diffraction gratings (18a, 18b),
The chirp amount per unit length of the diffraction grating disposed on the most incident side of the transmitted light in the first type grating fiber group is larger than the chirp amount per unit length of the other grating fiber,
And, the transmission loss wavelength band of the fiber with a grating disposed on the most incident side of the transmitted light is configured to include the reflection wavelength band of another fiber with a grating,
Optical transceiver module.
The optical transceiver module according to claim 10, wherein
Optical transmission loss of the fiber group with the first type of grating and the fiber group of the second type with grating in the desired transmission blocking wavelength range included in the transmission loss wavelength band of the fiber group with the second type of grating by Bragg reflection Assuming that the light transmission loss is L1 (dB) and L2 (dB), respectively, “L1 12.5 12.5, L1 + L2 40 40” is satisfied,
Let R1 (dB) and R2 (dB) be the light reflectances of the first-type grating attached fiber group in the transmission-stop wavelength range and the Bragg wavelength band of the first-type grating group, respectively. Assuming that the reflectance of the fiber group with two gratings is R 0 (dB), the following equation (1) is satisfied,

Furthermore, for the inclination angle and period of the grating and for the stray light attenuation, the minimum value of the light transmission loss of the entire optical filter in the transmission blocking wavelength range is 40 dB or more, and the light reflectance is -25 dB or less over the entire wavelength band. Characterized in that the optical fiber length is adjusted,
Optical transceiver module.
The optical transceiver module according to claim 10, wherein
In the transmission blocking wavelength range, the light transmission loss of the diffraction grating disposed on the most incident side of the transmitted light in the group of fibers with the first type grating, and the most incident side of transmitted light in the group of the fibers with first type grating When let L11 (dB), L21 (dB), and L2 (dB) be the light transmission loss of the fiber with a grating excluding those placed in and the light transmission loss of the fiber group with a second type of grating, respectively. Satisfy L11 ≧ 2.5, L11 + L21 ≧ 12.5, L2 ≧ 15 ”,
The light reflectance of the diffraction grating disposed at the most incident side of the transmitted light in the group of fibers with first type grating in the transmission blocking wavelength range and the Bragg wavelength band of the group of fibers with first type grating is R11 (dB And R12 (dB),
Of the fiber group with type 1 grating in the transmission loss wavelength band of the fiber group with type 2 grating by Bragg reflection and in the Bragg wavelength band of the fiber group with type 1 grating, the one arranged closest to the transmitted light When the light reflectivity of the fiber with a grating excluding R is R21 (dB) and R22 (dB) respectively, the following Equation 2 and Equation 3 are satisfied,

Furthermore, the inclination angle of the grating, the period, and the chirp amount so that the minimum value of the light transmission loss of the entire optical filter in the transmission blocking wavelength range is 40 dB or more and the light reflectance in all wavelength bands is -25 dB or less. The optical fiber length for stray light attenuation is adjusted,
Optical transceiver module.