JP2003515185A - Stereo and stacked holographic gratings for wavelength division multiplexing (WDM) and spectroscopy - Google Patents

Abstract

(57) [Summary] A three-dimensional diffraction grating having a substrate and a photoactive layer has a structure formed in the photoactive layer. This structure operates to diffract an optical signal into two selected spectral bands. This grating can be formed in a high spread form suitable for separating individual signals from the composite signal of both spectral bands. Alternatively, the grating can be formed in a low-spreading type, which can separate the composite signal from each other. In another embodiment, the second structure is formed in a photoactive layer. Each structure is configured to operate in one of the spectral bands, thereby allowing the signals in each band to be diffracted independently of each other. In another embodiment, the structure can have a curvilinear profile that allows the diffracted beam to be formed or focused without the need for an external lens.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION

The present invention relates to chromatic dispersion and combination gratings for spectroscopy and data transmission applications, and more particularly can be used to multiplex (or demultiplex) spectrally split signals into a single optical fiber. It is about the lattice.

[0002]

BACKGROUND OF THE INVENTION

There are numerous fields of technology that require spatial division of multiple optical signals with different wavelengths or different spectral regions (ie, "wavelength regions") (eg, spectroscopy and communications). On the contrary, it is often necessary to combine a plurality of optical signals having different wavelengths or spectral regions into a composite signal and transmit the combined signal with one optical fiber. The former operation is called demultiplexing, the latter operation is called multiplexing, and the entire process is called wavelength division multiplexing (WDM).

An example of a situation in which a device is required is in the field of communication. The operating spectral range of a typical optical fiber is 1100 nm to 1700 nm, which is 1
It corresponds to the frequency range of 76 THz to 273 THz. Also, some fibers have a low spectral range from 800 nm or below. Some of the standard spectral bands for optical data communications are listed in Table 1.

[0004] Table 1. Frequency and band corresponding to spectral region     Spectral range [nm] Frequency [GHz] Bandwidth   Lowest highest lowest highest [THz] 760 900 390789.5 330000.0 60.8 970 990 306185.6 300000.0 6.2 1260 1360 235714.3 218382.4 17.3 1480 1600 2006 55.7 185625.0 15.1 1600 1650 185625.0 180000.0 5.6 1528 1561 1941 17.6 1897766.4 4.3

Although some of these bands have very large bandwidths, it is not possible to generate a single optical signal that can utilize the entire bandwidth of that band. A normal optical signal has a data signal modulated on a carrier frequency, and this carrier frequency is the center frequency of the optical signal. The highest modulation frequency achieved so far is 1
Although it is in the THz region, the actually feasible modulation frequency is about 100 GHz. Therefore, when an optical signal is generated only by the modulator in a certain spectrum band,
It uses only a small fraction of the available bandwidth. For example, 100G
When a signal having a bandwidth of Hz is transmitted in the band of 1260 nm to 1380 nm, only 0.58% of the available bandwidth is used.

One known solution to this problem is to multiplex signals with different center frequencies into a single optical fiber with a wider operating spectral range than the spectral range of the band. Divide the spectral region of the band into several non-overlapping channels that are wide enough to modulate a single signal at the desired frequency without extending the spectral region of the channel, and separate each of those channels After generating the optical signal of 1), these signals are multiplexed and sent to the transmission side of the optical fiber.

This combined optical signal is transmitted by one optical fiber and is demultiplexed at the opposite receiving end—that is, divided into individual signals corresponding to the original signals generated in each channel. .

After multiplexing a plurality of spectrally spaced signals in individual channels having a single spectral band to form a composite signal containing all individual signals of the signal within the spectral band It is also possible to further multiplex a plurality of such composite signals, each having a signal set in a different spectral band. For example, a first having a plurality of individual signals in the spectral band from 1260 nm to 1360 nm.
Forming a second composite signal having the composite signal and a plurality of individual signals in the spectral band from 1528 mn to 1561 nm (these two composite signals are formed by two independent multiplexing operations), and then a third multiplex signal. These two composite signals can be multiplexed into one fiber (sometimes referred to as a trunk fiber) by a conversion operation. Then, at the other end (reception side) of the trunk fiber, this signal is first demultiplexed into two composite signals, and then demultiplexed by two independent operations to form each composite signal. To get.

Up to now, the operations of multiplexing and demultiplexing have generally been performed by means of reflective relief diffraction gratings, which usually consist of lines etched on the surface of the reflector element. Is. Such a diffraction grating can be used as a device with high dispersion or low dispersion. In high dispersion reflective relief gratings, a sufficient angular division is provided between the signals of adjacent channels of a single spectral band, which allows the signals of these channels to be divided. On the other hand, low-dispersion reflective relief gratings provide a narrow angular division, which is suitable for spectral division of a wide spectrum composite signal in different spectral bands.

High-dispersion reflective relief gratings generally cannot be used for spectral splitting of composite signals (ie, individual signals) with broad spectral width. This is usually due to insufficient or no diffraction of one or both signals. For example, a high dispersion reflective relief grating could be used as an inverse multiplexer to position the incident signal (containing two composite signals) appropriately to diffract one composite signal into separate signals. When placed, the other composite signal will typically diffract at a relatively larger angle than the first composite signal, resulting in poor results.

When a low dispersion reflective relief grating is used to demultiplex an incident signal containing two composite signals in different spectral bands, the individual signals in the individual channels of each composite signal are typically Insufficient spacing is maintained for reception by individual receiving optical fibers or detectors.

Other types of gratings such as fiber Bragg gratings, free space gratings, echelle gratings used in spectroscopy applications also have various drawbacks.

[0013]

SUMMARY OF THE INVENTION

As described above, there is a need for improved diffraction gratings for multiplexing and demultiplexing signals having different wavelengths in optical communication systems.

First, the present invention uses a substrate for a first composite signal having a first spectral region and a second composite signal having a second spectral region; a photoactive layer laminated on the substrate; A three-dimensional diffraction grating having a structure formed in the photoactive layer, the structure providing an optical coupling device operable in the first and second spectral regions.

Secondly, the invention is used for multiplexing and demultiplexing a first composite signal having a first spectral region and a second composite signal having a second spectral region; a substrate; laminated on the substrate And a first structure formed in the photoactive matrix;
The first structure provides a stereoscopic diffraction grating operable in at least one of the first spectral region and the second spectral region.

Thirdly, the present invention is used for multiplexing and demultiplexing a first composite signal having a first spectral region and a second composite signal having a second spectral region, a substrate; And a first structure formed in the photoactive matrix.
The structure is operable in the first spectral region and has a second formed in the photoactive matrix.
The structure is one that provides a stereoscopic diffraction grating operable in the second spectral region.

Furthermore, the present invention provides a free space device for combining (multiplexing) spatially divided spectral components into a single light beam, and a plurality of spectral components carried in the form of a single light beam. It provides a means for improving the performance of a device for spatial division (demultiplexing) into individual light beams, each having one spectral component, using a suitably optimized stereoscopic grating. .

[0018]   The invention will now be described by way of example with reference to the following accompanying drawings.

[0019]

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1a, two composite optical signals 1 carried by a single fiber 12
Intended to be used to separate two composite optical signals 8a (eg spectral region 1528nm to 1561nm) and 18b (eg spectral region 1260nm to 1360nm) into a first spectral beam and a second spectral beam 24b. A related art, high dispersion imaging relief reflection grating 10 is shown. The spectral region of optical signal 18a is divided into n channels, each of the n channels carrying an individual optical signal having a unique center frequency. The n channels can be tightly separated within the spectral region of the optical signal 18a (ie, they may have a separation of 1 nm or less), as long as the channels do not overlap. Similarly, optical signal 18b includes m non-overlapping channels, each of the m non-overlapping channels carrying a closely separated individual optical signal within the spectral region of optical signal 18b.

Spectral beam 24a corresponds to composite optical signal 18a and is captured as optical signal set 29a by optical fiber bundle 14 whose structure is shown in FIG. 1b. Spectral beam 24b corresponds to optical signal 18b and is captured by second fiber optic bundle 15 as optical signal set 29b.

Referring now to FIG. 1b, the first bundle 14 of optical fibers is depicted in more detail. Optical fiber bundle 14 includes many individual optical fibers, 14a through 14n. The ends 60 of the optical fibers 14a to 14n are arranged in a linear array and receive the spectral beam 24a. The individual light components of the spectral beam 24a are combined into the composite optical signal 18
corresponding to the individual optical signals of a, diffracted by the grating 10 at slightly different angles,
The optical fibers 14a to 14n are positioned so that each receives one of this individual component. The optical fiber bundle 15 has a similar structure and includes a number of individual optical fibers 15a to 15m (not shown).
Is also in a position to receive the individual optical signals forming the optical signal 18b.

Referring again to FIG. 1a. A set of tightly separated spectral components within a single relatively narrow spectral band of composite signal 18a (eg, spectral beam 2
4a) is separated or demultiplexed with acceptable efficiency and image quality,
It is possible to construct the grating 10, which is a high dispersion relief reflection grating, but in practice
The grating 10 cannot be used to efficiently separate and image individual channels or optical signals in two spectral bands that are spectrally far apart from each other (ie, the spectral bands of the composite signals 18a and 18b). . Spectral beam 24b is substantially distant from spectral beam 24a when fiber 12 and fiber bundle 14 are positioned to efficiently separate the individual optical signals that together form composite optical signal 18a. Spectral beam 24b is generally diffracted with low efficiency.

One of the reasons for this is that in order to demultiplex the closely separated channels into separate receiving fibers (ie fibers 14a to 14n), the grating has to be in each spectral band (ie spectral beam 24a or 24b). This is because it has to provide an acceptable angular separation of the individual optical signals in the channel. The angular separation of the diffracted spectral beams (24a and 24b) increases in proportion to the grating dispersion. The grating configuration can be optimized to provide relatively efficient angular spread from the diffracted light in the individual channels of one of the spectral bands to be separated. A typical structure of the grid 10 is shown at 30 which is an enlarged view of the circle 32. The grating 10 comprises glass and a rigid support such as a highly reflective layer 36 with suitable periodic microstructures. One of ordinary skill in the art would appreciate Layer 3
The surface of 6 could be configured to diffract light efficiently in a single spectral band. However, the relatively large separation between the spectral regions of the two different spectral bands makes it very difficult to achieve the same performance in the two bands. If the grating is optimized for use in the spectral region of spectral beam 24a, spectral beam 24b will not be diffracted correctly (or not at all). Performing the reverse operation, the two sets of optical channels carried by the fiber sets 14 and 15 from two very distant bands of light are combined into a single fiber 1.
The same thing happens when you try to combine in 2. In addition to the difficulties associated with focusing in spectral bands that are far apart, it is also very difficult to ensure a large, polarization-independent effect.

A grating, such as grating 10, is configured to have low dispersion, and the spectral beam 24a
It may also be configured to provide a smaller and more efficient angular separation between the and 24b. This is useful for separating the composite signals 18a and 18b from each other,
The low dispersion grating cannot adequately separate the individual optical signals forming the composite signal 18a or composite signal 18b.

The use of related art grating 10 to separate spectral components from multi-wavelength signals has several other disadvantages.

First, although the exact location of the diffracted beams 24a, 24b is very dependent on the location of the grating 10, the grating 10 is typically very sensitive to ambient temperature, and the temperature changes. The angle direction of the lattice 10 may change. For example, if the grating 10 rotates x degrees, the positions of the diffracted beams 24a and 24b will move 2x degrees. Therefore,
It is necessary to position the grating 10 accurately with respect to the main fiber 12 and the branch fibers 14 and 15.

Second, grating 10 most often reflects and diffracts only some of the light in the desired direction contained in signals 18a and 18b. Typically, grating 10 has optical signals 18a and 1
The maximum amount of 8b is diffracted into the first diffraction order (ie order 1) and beam 24
a and 24b, and beams 24a and 24b are configured to sequentially form signals 29a and 29b. The remaining light of the signals 18a and 18b acts like a partial reflector (
Diffractive order 0, not shown) partially reflected by grating 10, diffracted in an undesired direction (ie, an order other than order 1, not shown), or partially absorbed by grating 10. Or scattered. The scattered light corresponding to one signal (ie, the spectral band 2 directed to the bundle 14 of fibers, for example)
4a) may be collected by individual fibers within the fiber bundle 15, but since fiber bundle 15 is intended to collect light in the spectral band 24b, it causes crosstalk between channels. . This can lead to signal degradation.

Third, the active surface of a reflective grating, such as that shown at 36 in FIG. 1, is not easy to protect. The molding of the active surface is exposed and can easily be soiled or damaged by routine handling. Typically, the grate 10 cannot be washed to remove dirt or other contaminants.

Fourth, the efficiency of the grating 10 as a function of wavelength exhibits extremely different performance for s- and p-polarized light. This can lead to large variations in efficiency when using plane polarized light and different polarization directions.

Referring now to FIG. 2, a three-dimensional diffraction grating 90 according to the present invention is shown. This grating includes the substrate 111, the cover glass 112, the first active diffraction layer 211a, and the second active diffraction layer 211a.
Of the active diffraction layer 211b. The active diffraction layer 211a is formed on one side of the substrate 111. Similarly, the active diffraction layer 211b is formed on one side of the cover glass 112. The active diffraction layers 211a and 212 are adhered together by a layer of photoadhesive 113.

The diffractive layers 211a, 211b were such that when the incident beam from the half-space 200 hits the grating 90, the diffracted beam of the selected diffraction order was such that the grating was completely transparent or partially transparent. In some cases, it can be configured to propagate in a half-space 222 that contains the transmitted light, and a transmit (or “transmit”) diffraction grating can be formed. Alternatively, the diffractive layers 211a and 211b are
When the incident beam from the half-space 220 strikes the grating 90, the diffracted beam of the selected diffraction order will contain half the reflected light if the grating was fully or partially reflective. It can be configured to propagate into the space 222 and a reflective diffraction grating can be formed.

The diffractive layers 211a and 211b may be formed of dichromated gelatin or any other material that can be configured to diffract an optical signal. When using dichromated gelatin or other optically active material, the grating creates alternating high and low refractive index regions in one or both diffractive layers. It may be formed by This is further described below with respect to diffraction grating 100.

When the grating 90 is configured as a reflective diffraction grating, either the substrate 111 or the cover glass 112 must be made of a material that is transparent at least in the operating spectral range. When the grating 100 is configured as a transmission diffraction grating, both the substrate 111 and the cover glass 112 must be made of a material that is transparent, at least in the operating spectral range.

Both the substrate 111 and the cover glass 112 can be made of filter glass to limit the spectral range of light that interacts with the active diffractive layers 211a and 211b. Filter glass can also be used to modify the spectral characteristics of the light diffracted by the grating 90. The filtering properties of the substrate 111 and the cover glass 112 further include one or more interference filters 114a, 114b, 114c, 114d made by thin layer technology (or another method), any of the surfaces of the substrate 111 and the cover glass 112. Can be further strengthened by adding on top of the combination. For example, if grating 100 is configured as a reflective transmission grating and light enters grating 100 from the cover glass 112 side, interference filters 114c and 114c.
Either one or both of d can be formed on the surface of the cover glass 112. When the grating 100 is configured as a transmission diffraction grating, the interference filter 114a
Either one or both of and 114b may be formed on the side surface of the substrate 111. The interference filters 114a, 114b, 114c, 114d may be used to modify the spectrum of the diffracted light to compensate for spectral variations in the intensity of the light and non-uniform spectral response of the detector. Alternatively, the EDFA (Erbium-Doped Optical Fiber Amplifier) spectral non-uniformity can be compensated when the system is used in an optical fiber communication system. In addition, selected or all surfaces of both the substrate and cover glass are covered with a thin antireflective coating 115a, 115b, 115c, 115d to reduce possible reflections on these surfaces. You can also

A preferred form of grid 90 has been described. The cover glass 112, the second optically active layer 211b, the adhesive layer 113, the interference filters 114a to 114d, and the antireflection coatings 115a to 115d are optional. In its simplest form, the grating according to the invention may consist solely of a substrate (ie substrate 111) on which an optically active signal layer (ie layer 211a) is formed. Board 1
11 is necessary to optically provide strong support to the active layer 211a. When using the substrate 111, the cover glass 112, along with the substrate 111, protects the grid 100 from damage during handling or cleaning.

The substrate 111 and cover glass 112 are shown as planar elements. One or both of these elements may have different shapes. For example, either or both elements may be prisms or curved to provide the desired optical function.

Referring now to FIGS. 3A, 3B, 3C, 3D, each figure illustrates the use of a cubic diffraction grating 100a, 100b, 100c, 100d, each made according to the present invention. Elements of grids 100a-100d that are identical to elements of grid 90 (FIG. 2) are identified by the same reference numbers. The structure of grating 100a is shown at 106, which is an enlarged view of circle 108. The grating 100a comprises a substrate 111, an optically active layer 211a and a cover glass 112.

As mentioned above, the optically active layer 211a may be a layer of dichromated gelatin or other optically active material. As shown, grating 100a has alternating high refractive index regions 109 and low refractive index regions 110. The alternating regions 109, 110 may take different shapes (including planes for some applications as shown at 106), and generally they need not be perpendicular to the plane of the grating 100. . In order to function efficiently as a diffraction grating, the position of the continuous region 109 with increased index of refraction must follow a pre-defined, almost periodic function, which in some cases is periodic. In some cases (ie evenly spaced). These areas must be oriented to ensure correct performance in the spectral range where grating 100a is required to diffract. Area 10
The shape and position of 9,110 form the "structure" of the grating, which controls the operation of the grating as a transmission or reflection grating. In FIG. 3A, grating 100a is configured as a low dispersion transmit diffraction grating. One of ordinary skill in the art will be able to select the structure of grating 100a to alternately form regions 109 and 110 and diffract light in the selected spectral region.

The efficiency of the grating 100a is not only a structural feature, but also the thickness T of the optically active layer 211a, the average refractive index of the optically active layer 211a, the refractive index of the alternating regions 109 and 111. The magnitude of the difference between, the state where the refractive index changes from low to high within a single period (ie the sharpness of the transition between regions 109 and 1110), and how this transition changes in different regions of the lattice. It also depends on other factors, including One of ordinary skill in the art will appreciate that all these parameters must be considered in order to obtain the required performance of grating 100. The diffraction effect is
Caused by the index of refraction between layers 109 and 110 in the optically active layer 211a of the grating (ie, the volume of the grating, as opposed to surface diffraction as in the case of the relief reflective grating 10 (FIG. 1) ). For this reason, grids such as grids 90 and 100 are
It is called a three-dimensional lattice.

With particular reference to FIG. 3B, as in FIG. 1, signals 18a and 18b are two sets of spectrally separated composite optical signals. The signal 18a is from 1528 nm to 1561
It may have a spectral region of nm. The signal 18b is from 1260 nm to 13
It may have a spectral region of 60 nm. (These areas are exemplary, and in fact other areas as listed in Table 1 can be used). Spectral beam 16 exits mains fiber 12 as a divergent signal corresponding to both signals 18a and 18b. The spectral beam 16 is collimated by the lens 102. The parallel signals hit the grating 100. Like the grating 10, the grating 100a converts the spectral beam 16 into spectral beams 24a and 24a.
b, diffracts into a series of spectral beams including 114. Spectral beam 114
Is a zero-order beam that propagates out of the grating 100 without being diffracted. Spectral beams 24a and 24b are first order diffracted beams and correspond to signals 18a and 18b, respectively. Spectral beams 24a and 24b are offset from each other and correspond to composite signals 18a and 18b, respectively. Spectral beam 24a is transmitted by lens 104 as a set of single wavelength signals 29a, which correspond to the individual signal sets that together form composite signal 18a, into a bundle of fibers 14 (n individual individual signals as in FIG. 2). Is composed of a set of fibers). Similarly, beam 24b is transmitted by lens 104 into a bundle of fibers 15 (m) as a set of single-wavelength signals 29b, which together correspond to the individual sets of signals forming composite signal 18b.
(Consisting of a set of individual fibers).

By appropriately configuring the structure, a three-dimensional lattice such as the three-dimensional lattice 90 (FIG. 2) can be formed to provide an efficient high dispersion lattice or an effective low dispersion lattice.
Further, a solid grating such as solid grating 90 may be configured as a transmission grating or a reflective grating. The next feature of a cubic grating, such as grating 90, relates to its operation as a high-dispersion or low-dispersion grating, or its transmission or transmission grating. (I) thickness of the active layer (ii) refractive index of the active medium of the grating (iii) period of the grating (iv) oblique angle of the diffractive structure to the surface of the grating (v) depth of modification of the refractive index (vi) ) Refractive index distribution throughout the diffractive microstructure (vii) Incident angle

Those skilled in the art will be able to select and configure these features to provide the desired degree of dispersion and transmission or reflection characteristics to the grating.

3A to 3D show several modes of operation of a stereoscopic diffraction grating. Elements in FIGS. 3A, 3C, and 3D that correspond to elements in FIGS. 3B and 1A are given the same reference numbers.

3A and 3B show how the diffraction gratings 100a and 100b are used as transmission diffraction gratings. In particular, grating 100a separates two composite signals having different spectral regions (ie, composite signals 18a and 18b) from one fiber (ie, fiber 12) into two or more fibers 40 and 42. It is a low dispersion grating suitable for.

Grating 100b separates (or combines) the individual signals in the two spectral bands into individual fibers in two separate fiber bundles (ie fiber bundle 14 (FIG. 2) and fiber bundle 15). It is configured as a high dispersion grating suitable for By properly configuring the features of the grating 100b, the spectral beams 24a and 24a
It is possible to control the angular separation of b so that the component signals of the composite signal 18a can be efficiently separated from each other and the component signals of the composite signal 18b can also be efficiently separated from each other.

Gratings 100c and 100d are reflective gratings configured as a low dispersion grating and a high dispersion grating, respectively, and operate similarly to gratings 100a and 100b, respectively.

The low dispersion gratings 100a and 100c are designed to be efficient over the spectral regions of two separate bands. Component signals (ie signals 18a and 18b
The relative position of the fibers receiving the

The high-dispersion gratings 100b and 100d have the advantage that they can be configured to more accurately separate the signals within two particular spectral regions. However, these gratings require a more accurate configuration than the low dispersion gratings 100a, 100d.

[0049]   The gratings 100a-100d provide improved performance over the grating 10.

First, since the gratings 100a and 100b are transmission gratings rather than reflection gratings, the gratings are either main fiber 12 and fibers 40 and 42, or fiber bundles 14 and 15.
Even if it physically moves against, the sensitivity to it is low.

Secondly, as described above, by properly selecting the thickness of the active layer, its index of refraction, and the region of variation of the index of refraction of the entire grating and its distribution, the efficiency of the grating 100 can be determined by the value and the spectrum. It is much more controllable in terms of characteristics. The diffraction efficiency inside a properly designed grating 100 is greater than 99%, far exceeding the efficiency of reflective gratings available in communication systems. As a result, the signal is stronger and the risk of crosstalk between channels is significantly reduced.

Third, as mentioned above, the surface of the grid 100 can be easily protected by a cover glass or other protective material.

Fourth, those skilled in the art will appreciate that the efficiency of the grating 100 diffracting the signals 18a, 18b is less sensitive to the polarization of the incident signal (ie the signals 18a, 18b) than the relief grating 10. Will be understood.

Fifth, the grating 100 can function as either a transmitter or a reflector, allowing the injection and collection of fibers with different spatial configurations. This increases the flexibility of the multiplexer and demultiplexer design.

Referring now to FIG. 4, another embodiment grid 200 made in accordance with the present invention.
It is shown. Lattice 200 includes lattices 100a to 100d (FIGS. 3A to 3D)
Used in the same way as. The grating 200 has two independent structures. One of ordinary skill in the art will be able to form two independent structures in the grating 200.

The first structure is a region 202 having a high refractive index and a region 2 having a low refractive index.
04, and is designed to diffract light in a relatively narrow region including the spectral region of the signal 18a. Thus, this first structure is, for example, about 1528.
It is configured to have a bandpass characteristic for diffracting light in the wavelength region between nm and 1561 nm.

The second structure has a region 206 having a high refractive index and a region 2 having a low refractive index.
No. 08, and has a bandpass characteristic for diffracting light in the spectral region between 1260 nm and 1360 nm of the signal 18b. Achieve best performance individually within each spectral band by configuring all parameters of two separate diffractive structures such as period, refractive index correction depth, and refractive index distribution across period and grating can do.

In operation, the grating 200 is used in the same manner as the grating 100a shown in FIG. 3B. The first and second structures of grating 200 operate independently of each other and diffract the portions of spectral beam 16 that correspond to signals 18a and 18b, respectively. Compared to the grating 100, the grating 200 can be configured as a high-dispersion grating, both structures operating in a single spectral region, so that each structure provides a more accurate diffraction of the spectral beam in its respective spectral region. It has the advantage that it can be formed as follows.

Although the grating 200 has only two structures, it is possible in practice to embed more than two structures in the grating to separate many different sets of signals, each having a different spectral region. The operation of each structure is independent of each other as long as the thickness T of the grating is sufficient (ie, the volume of the grating 200 is sufficient). One of ordinary skill in the art will be able to choose a T of sufficient thickness to allow independent operation of the two structures.

Similarly, if the three-dimensional diffraction grating consists of two bonded active layers, such as grating 90 (FIG. 2), each layer may contain multiple diffractive structures and perform separate tasks.
This further extends the functionality of the invention and allows the production of diffractive elements with very complex functionality.

5A, 5B, 5C, 5D show another embodiment of a cubic diffraction grating with two structures, such as grating 200.

FIG. 5A shows an application of a low dispersion stereo transmission grating 200a with two independent diffractive structures that separate or combine two separate spectral bands, and FIG. 5B separates the diffractive geometry of both spectral bands. The application of a high-dispersion grating 200b with two independent diffractive structures, which is controlled and controlled simultaneously to separate the communication channels in each band, is shown.

5C and 5D, like the transmission gratings 200a and 200b of FIGS. 5A and 5B,
Figure 2 shows a reflective cubic diffraction grating with two structures each performing the same function.

It becomes more efficient when the structure of the grating is arranged to operate in a relatively narrow area. That is, if one of the gratings 200a-200d is used in place of the grating 10, the input light from the signal 16 that hits the grating 200 within the particular bandpass region of the two structures will be more diffracted and passed through the lens 104. Branch line 14
, 15. The internal efficiency (efficiency for light entering the diffractive structure, which may be less than total incident light due to possible loss of light at the surface of the grating) depends on the characteristics of the grating, but from grating 200a 100 for each 200d structure
Can approach%. Therefore, the risk of crosstalk between channels can be further reduced compared to the grating 10. In the above case described with reference to FIG. 1b, where each of the fibers 14, 15 actually carries many signals and contains many fibers, the grating 2
The grating corresponding to 00 must be designed to diffract the wavelength over the relevant region.

Another advantage of the gratings 200a-200d is that light outside the designed operating regions of the two structures that are configured to operate in the spectral regions of the signals 18a and 18b will be outside those spectral regions. Is not to diffract the light. Such light may be generated by nearby light sources, and the gratings 200a-200d may also function as noise filters to reduce the transmission of such transient light.

Referring now to FIG. 6, another embodiment of a stereoscopic transmission diffraction grating 300 according to the present invention is shown. The grating 300 has a unitary structure, which is more clearly shown by the enlarged view 302 of the circle 304. As shown, the grating 300 has a high index region 306 and a low index region 308. The alternating regions have a curved cross-section rather than a planar cross-section, as opposed to the structure of gratings 100 and 200. The shapes of the regions 302 and 304 are such that the diffracted beam 24a
, 24b (first order diffracted beam corresponding to signals 18a, 18b as described above).

Signals 18 a and 18 b are transmitted along mains fiber 12 and diverge beam 310
Come out with. The diverging beam 310 strikes the grating 300, which diffracts light over a range of wavelengths, including the wavelengths of the signals 18a and 18b that are components of the signal 16 as described above. The structure of the grating 300 corresponds to the signals 18a and 18b, respectively.
, Diffracted beams 24a, 24b are selected to focus on the branch fibers 14, 15. The grating 300 does not focus the zero order beam 312 for any wavelength.

The grating 300 offers the advantage of not requiring the lenses 102 and 104 to collimate the signal 16 and focus the beams 24a, 24b. Grating 300 also provides other advantages of grating 100 of FIG. 2 over grating 10 of FIG.

In another embodiment of the grating according to the present invention (not shown), the advantages of the grating 300 are the advantages of the noise filtering and the high efficiency of the grating 200 by making two structures in the grating. Can be combined. One of the structures has a relatively narrow passband in the spectral region of the signal 18a and can be configured to focus the first order diffracted beam 24a. Similarly,
Another structure has a narrow passband in the spectral region of the signal 18b and can focus the first order diffracted signal 24b.

While these preferred embodiments of the present invention have been described in terms of separating (or demultiplexing) several signals having different wavelengths from a pair of composite signals (18a and 18b), embodiments do not It can also be used to combine (or multiplex) several individual signals in two different spectral bands into a composite signal pair transmitted on a single main fiber. Combined multi-wavelength signal.

The described embodiments can be modified or changed without departing from the scope of the invention, which is limited only by the appended claims.

[Brief description of drawings]

FIG. 1A shows a prior art high dispersion reflective grating used in a communication system.

FIG. 1B is an enlarged view of a bundle of trunk fibers consisting of multiple fibers that accommodate multiple communication channels.

[Fig. 2]   3 is an example of a three-dimensional diffraction grating according to the present invention.

FIG. 3A illustrates a low dispersion stereo transmission grating that splits (or combines) two individual spectral bands for use in an optical communication system from one fiber to two fibers (or vice versa).

FIG. 3B: High dispersion stereo transmission diffraction for splitting (or combining) multiple individual channels within a single spectral band for use in optical communication systems from one fiber to multiple fibers (or vice versa). Shows a grid.

FIG. 3C shows another low-dispersion stereoreflecting grating that splits (or combines) two separate spectral bands for use in an optical communication system from one fiber to two fibers (or vice versa). There is.

FIG. 3D is another high dispersion stereo that splits (or combines) multiple individual channels within a single spectral band for use in optical communication systems from one fiber to multiple fibers (or vice versa). A reflective diffraction grating is shown.

FIG. 4 shows another embodiment of a stereoscopic transmission diffraction grating with two individual diffractive structures for individually treating different spectral bands according to the present invention.

FIG. 5A   3 illustrates a three-dimensional diffraction grating incorporating multiple structures according to the present invention.

FIG. 5B   3 illustrates a three-dimensional diffraction grating incorporating multiple structures according to the present invention.

FIG. 5C   3 illustrates a three-dimensional diffraction grating incorporating multiple structures according to the present invention.

FIG. 5D   3 illustrates a three-dimensional diffraction grating incorporating multiple structures according to the present invention.

[Figure 6]   3 is a three-dimensional transmission diffraction grating in which a focusing force is mounted on the grating according to the present invention.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] January 2, 2002 (2002.1.2)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CR, CU, CZ, DE, DK , DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, J P, KE, KG, KP, KR, KZ, LC, LK, LR , LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, R O, RU, SD, SE, SG, SI, SK, SL, TJ , TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (19)

[Claims] 1. An optical combiner for use with a first and a second composite signal, wherein the first composite signal has a first spectral region and the second composite signal is a second spectral signal. A device having a spectral region, the device comprising: (i) a substrate; (ii) a photoactive layer attached to the substrate; and (iii) a structure formed in the photoactive layer, wherein And a structure operable in the second spectral region (a) including a stereoscopic diffraction grating. 2. The structure is configured to provide a first diffractive spectral beam corresponding to the first composite signal and a second diffractive spectral beam corresponding to the second composite signal. The apparatus of claim 1, wherein the first and second spectral beams have angular separation. 3. An entrance lens for receiving the first and second composite signals and providing first and second parallel signals corresponding to the first and second composite signals, The apparatus according to claim 1, wherein the first and second parallel signals are incident on the three-dimensional diffraction grating. 4. The first and second diffracted spectral beams are received and a first diffracted beam is received.
3. The apparatus according to claim 2, further comprising a focusing lens for focusing the first diffracted beam on the second light receiving element and focusing the second diffracted beam on the second light receiving element. 5. The device according to claim 4, wherein the first light receiving element is a first light receiving fiber, and the second light receiving element is a second light receiving fiber. 6. The structure comprises: (i) receiving a first incident spectral beam and a second incident spectral beam; and (ii) the first composite signal for providing the first composite signal. The apparatus of claim 1, configured to diffract an incident spectral beam, and (iii) diffract the second incident spectral beam to provide the second composite signal. 7. The first composite signal comprises a first set of composite signals that are tightly separated within the first spectral region, and the second composite signal is within the second spectral region. A second set of closely separated composite signals at the first set of receiving fibers for each of the composite signals in the first set of tightly separated composite signals. The second of the densely separated composite signal diffracted into one fiber in
The apparatus of claim 1, configured to diffract each of the composite signals in the second set of fibers into a fiber in a second set of receiving fibers. 8. The device of claim 1, wherein the structure has a curvilinear configuration. 9. A three-dimensional diffraction grating for multiplexing and demultiplexing first and second composite optical signals, said first composite optical signal having a first spectral region, said second composite optical signal. The optical signal has a second spectral region and the grating comprises: (a) a substrate; (b) a photoactive element attached to the substrate; and (c) a first formed in the photoactive element. A first structure operable in the first spectral region, and (d) a second structure formed in the photoactive element that operates in the second spectral region. Possible second structures. 10. The first structure is configured to diffract a spectral beam in the first spectral region, and the second structure is diffracted to a spectral beam in the second spectral region. The grid of claim 9 constructed. 11. A three-dimensional diffraction grating that multiplexes and demultiplexes first and second composite optical signals, the first composite optical signal having a first spectral region and the second composite optical signal. The optical signal has a second spectral region, and the grating is formed in: (a) a substrate; (b) a first photoactive element attached to the substrate; and (c) a photoactive element. A first structure, wherein the first and second structures are
A first structure operable in at least one of the spectral regions of. 12. The three-dimensional diffraction grating according to claim 11, wherein the substrate is made of optical fiber glass, and the optical fiber glass is transparent to at least one of the first and second spectral regions. . 13. The method of claim 11, further comprising a thin film filter coating on at least one side of the substrate, the thin film filter coating being operable to modify a spectral component of light incident on the grating. Or 12
The three-dimensional diffraction grating described in. 14. The stereoscopic diffraction grating of claim 11, 12 or 13 further comprising a thin film anti-reflective coating on at least one side of the substrate. 15. The three-dimensional diffraction grating according to claim 11, 12, 13 or 14, further comprising a second structure formed in the first photoactive element. 16. The stereoscopic diffraction grating according to claim 11, 12, 13, 14 or 15, further comprising a cover glass, wherein the first photoactive element is disposed between the substrate and the cover glass. . 17. The method further comprising a second photoactive layer attached to the cover glass and a light transmissive adhesive layer coupling the first photoactive element to the second photoactive element. The three-dimensional diffraction grating described in. 18. The three-dimensional diffraction grating of claim 11, 12, 13, 14 or 15, wherein the cover glass is bonded to the first photoactive element using a light impermeable adhesive. 19. The three-dimensional diffraction grating according to claim 16, 17 or 18, wherein the cover glass is opaque in at least one of the first and second spectral regions.