KR20010033579A - An integrated optical transceiver - Google Patents

Abstract

A laser cavity formed between the first and second feedback elements 3 and 7; Wavelength selection means in the laser cavity, i.e., diffraction grating 4, for measuring the wavelength of the laser beam; An optical receiver 10; One of the feedback elements (3) partially transmittable at the laser beam wavelength to allow the transceiver to emit radiant energy at the laser beam wavelength; 10. An integrated optical transceiver comprising a wavelength selecting means (4) arranged to receive light through a feedback element different from the laser beam wavelength in the optical receiving means (10) and to transmit light of the selected wavelength.

Description

Integrated Optical Transceiver {AN INTEGRATED OPTICAL TRANSCEIVER}

Multi-wavelength optical communication networks can significantly increase transmission capacity, also improve the system's flexibility and allow for more flexible and novel management planning. Most of the problems with the realization of the cost efficiency of such systems are in the acquisition of stable multi-wavelength transceivers and detector devices with accurate channel wavelength definition and low temperature sensitivity. The latter can preserve the registration of the wavelength, thus allowing communication of other devices in different parts of the system operating at different temperatures. The wavelength selective injection feedback (DFB) device used in the conventional method has difficulty in obtaining accurate temperature control, and lacks the problem of lack of manufacturing wavelength definition and high coupling loss when trying to couple a channel into a single output. It is implicated.

The integration of active or passive wavelength selection devices in a laser or detector structure for constructing an integrated multi-wavelength transmitter or receiver device capable of transmitting or detecting a majority of wavelengths is proposed at the same time. In addition, such wavelength selection devices can be formed in the laser cavity to allow laser vibrations on most wavelength channels. The wavelength selection device used in such an arrangement is a grating based on a typical integrated structure consisting of a lens or mirror to always perform the required beam manipulation.

The present invention is directed to improving the above devices for providing an integrated multi-wavelength transceiver.

FIELD OF THE INVENTION The present invention relates to integrated optical transceivers, and more particularly, to transceivers used as cavity demultiplexer resonators for use in optical communication systems.

The invention is described in detail in the form of embodiments in accordance with the accompanying drawings.

1 is a schematic diagram showing a first embodiment of an integrated optical transceiver according to the present invention.

2 is a schematic diagram illustrating a second embodiment of an integrated optical transceiver according to the present invention.

According to a first aspect of the present invention, there is provided a laser cavity provided between a first and a second feedback element; Wavelength selection means within the laser cavity for detecting the laser beam wavelength of the laser cavity; At least one feedback element which is at least one feedback element partially transmitted and received at the laser beam wavelength to allow the transceiver to emit radiation energy of the laser beam wavelength; SUMMARY OF THE INVENTION An object is to provide an integrated optical transceiver which is arranged for transmitting light of a selected wavelength and receiving light through one feedback element and which is comprised of a laser beam wavelength in the light receiving means and another wavelength selecting means.

Such a transceiver can detect data input from one or a set of wavelength groups and simultaneously transmit data to other wavelengths or to different wavelength groups.

The wavelength selecting means determines the laser beam wavelength as part of the laser cavity and the selected wavelength transmitted to the light receiving means, thereby determining both the wavelength transmitted by the transceiver and the wavelength received by the transceiver.

Another aspect according to the invention is provided as part in combination with the transceiver.

Another aspect of the invention is apparent from the following detailed description and the appended claims in the specification.

Single wavelength transmission and calibration transceivers are described below, but the described arrangement may extend the number of arbitrary wavelength channels.

1 shows an optical chip 1 in which a transceiver, such as a silicon-insulator chip, is formed. An integrated waveguide 2, such as a silicon lip waveguide, is faceted at one end of the waveguide 2 towards the wavelength selection means 4, such as a transmission grating formed by a series of narrow shallow grooves 4A etched on the surface of the silicon chip. It extends from the first feedback element 3, such as a partially smooth semi-reflective (AR) coating forming a. Another waveguide 5 is formed on the chip 1 at a position for receiving light at a selected angle from the transmission grating 4, and through an optical amplifier 6, such as a semiconductor laser amplifier chip, through a laser amplifier 6. Is led to a second feedback element 7, such as the high reflective (HR) coated side of. In the described embodiment, the grating consists of a linear array of chirped periodic apertures to focus light transmitted therethrough.

Light traveling along the waveguide 2 toward the transmission grating 4 is dispersed into the silicon layer as indicated by the dotted line 8 so that the light leaves the waveguide 2. The light leaves the transmission grating 4 in the form of an interference pattern generated by the chirp period aperture of a linear array structure composed of gratings by a well known method, with different positions (i.e. An axis in the orthogonal direction and an axis parallel to the waveguide 2), each of which consists of light of a particular wavelength or wavelength band.

Wave guide (5) is positioned to receive a selected wavelength of λ _1, the wavelength λ ₁ is the wavelength transmitted by the transceiver. These wavelengths are AR-coated in well-known methods (3) and HR coatings ( 7) amplified in the laser cavity formed between them, so that the AR coating is only partially reflected, and this part of the light is transmitted from the transceiver through the AR coating 3 so that the output of the transceiver becomes wavelength λ ₁ . .

In addition, another waveguide 9 is provided on the chip at a selected angle to receive light of the second wavelength λ ₂ from the transmission grating 4, which transmits this to the detector 10, such as a photodiode.

The required spacing between waveguides 5 and 9 receiving wavelengths λ ₁ and λ ₂ , respectively, is typically on the order of 10-20 microns, depending on the dimensions and the geometry of the arrangement.

Thus, the transmission grating serves to manage the light of the second wavelength λ ₂ received by the transceiver at the photodiode 10, in part via the semi-reflective coating 3.

The wavelength selective structure 4 is integrally integrated as part of the laser cavity formed between the semi-reflective coating side 3 and the high reflective coating side 7 of the semiconductor laser amplifier chip 6. The grating 4 is used to set the wavelength related to the data transmitted and received on the same chip. The grating 4 sets the transmitted wavelength of the laser by acting as part of the laser cavity and as a wavelength selective filter. At the same time, the grating 4 acts as a band pass filter to allow the detector 10 to be irradiated in the correct range of wavelengths.

Thus, the wavelength selection of the grating 4 allows the form of a closed cavity against laser oscillation at one wavelength λ ₁ and also allows free detection of the other wavelength λ ₂ at the detector. The detector 10 is physically part of the laser resonator, but is separated from the laser resonator in the wavelength region. The photodiode 10 at the end of the waveguide 10 acts as a remarkably efficient absorber and prevents vibrational patterns at wavelengths.

1 is a diagram illustrating an embodiment of the transceiver. The data at wavelength λ ₂ are connected in the device and demultiplexed by the grating structure 4 to illuminate the detector 10. As described above, the embodiment in FIG. 1 is incorporated into the chirp focus grating 4 to perform both demultiplexing and focusing.

FIG. 2 shows another embodiment using a mirror 11 that is etched, aimed and focused on a silicon chip in addition to the reflective grating 12.

The laser beam wavelength of the laser is determined by the grating demultiplexer by providing wavelength selective feedback at λ ₁ in the optical amplifier 6.

It is managed by the mirror 11 and the grating 4 at the detected wavelength λ ₂ detector 10 received by the device. Thus, the grating 4 is contained within the laser cavity and multiplexes and demultiplexes the laser beam wavelengths radiated from the wavelengths of the input data during each period. This separates the detector 9 and constitutes a laser cavity between the highly reflective coated side 7 of the laser at the partially semi-reflective coated side 3 of the chip via the grating demultiplexer 12.

If the wavelengths λ ₁ and λ ₂ are significantly different, the antireflective coating 3 should be designed to have a low value (ie less reflection) for the detected wavelength λ ₂ in order to improve the coupling efficiency, It should be designed to have a high value (ie somewhat high reflection) with respect to the transmitted wavelength λ ₁ in order to reduce the hold.

The transceiver described above has many distinct advantages.

The inclusion of a passive grating demultiplexer eliminates any wavelength registration problem between the transmitted and detected wavelengths of the transceivers located in different parts of the system. This is due to the fact that the wavelengths detected and transmitted are set by the same passive demultiplexer device. For example, as in the above embodiment, the laser light emitted at λ ₁ is very precisely defined and manufactured with high immunity, i.e., a demultiplexer machine produced by a lithography process that allows a grating directed to submicron accuracy. It is determined by the academic structure. Thus, these wavelengths are automatically coupled to the detected wavelengths of other transceivers as they use the same demultiplexer but the laser and detector wavelengths are exchanged. Since the passive demultiplexer is effectively the same in both cases, the wavelength will be the same and will automatically adjust itself accordingly.

Inclusion of the grating element causes laser oscillation at a particular wavelength defined by the grating. These wavelengths can be set very accurately (better than 0.05 nm), while on the one hand they must be designed to be narrow enough to allow for reduction of the chirp and to disperse the disadvantages, on the other hand, stable and linear light It should be designed to be wide enough to allow current response (averaging output mode hopping effect).

Further, by thinning the waveguide 5 incorporating a laser into the grating, i.e., reducing the height and / or width of the waveguide 5, the waveguide thus approaches the grating 4 or 12 and is coupled within the laser. The spectral line width of the light can be reduced.

In addition, the transceiver can reduce the temperature sensitivity. The temperature dependence is due to two factors:

i) thermal expansion to change the grid pitch. The thermal expansion coefficient of silicon is 4.6 x 10 ^-8 K ^-1 and for typical device designs this value causes a change in the emitted laser wavelength of 0.7 nm in the temperature range -40 to 85 ° C.

ii) change in refractive index with temperature: this changes the operating wavelength of the grating. The refractive index with temperature for Si is 1.86 x 10 ^-4 K ^-1 . For typical device designs, this value leads to an approximate 9 nm wavelength change.

Thus, the resulting wavelength change with refractive index is on the order of magnitude larger than the corresponding change due to thermal expansion. But. Even the 9nm shift in the stable 125 ° C temperature range due to the coefficient variation is significantly smaller than the values used in conventional methods such as Fabry-Perot lasers.

In addition, wavelength variations with temperature due to active (laser) elements in device performance can be avoided as the wavelength is set by the passive grating device.

The resulting reduction in wavelength shift with temperature in combination with the reduction in the emitted laser line-width significantly reduces the resistance required at the channel wavelength. For example, in transceiver device operations with wavelengths of 1310 nm and 1550 nm, an approximate 100 nm channel width is required if the existing Fabry-Perot laser is operated without any temperature stabilization. This can be reduced to 10 nm if the transceiver described above is applied to the same laser.

As the end of the detector waveguide 9 becomes thinner, i.e., to increase the width of the waveguide mode as it approaches the gratings 4 and 12, the wavelength of the input data in the 9 nm range is increased by decreasing the height and / or increasing the width. The variation can be less than 1 dB in terms of channel loss. For example, the waveguide 9 can be tapered from a standard 4 micron width to 20 microns due to the extension of the detector response to allow for any changes in the emitted laser wavelength due to temperature.

In large channel separations such as 1310 nm to 1550 nm described above, it is difficult to obtain the required channel separation within the free spectral range (FSR) of the grating. To overcome this, the grating should be designed to operate outside the FSR, but in this case crosstalk with any external mode can be avoided or reduced. To ensure this, the device does not show a wavelength related to the potential interference mode at the input of the waveguide 9.

In addition, the transceiver described above provides another waveguide on a chip to receive other wavelengths within another laser cavity as described above or to receive other wavelengths within another detector as described above. It should be designed to transmit and / or receive one or more wavelength bands. For example, in a waveguide with an approximate 4 micron width, about 10 microns of space, more than 32 waveguides in the focal plane of the grating are allowed as the transceiver transmits 16 wavelengths and receives 16 wavelengths. It is possible to form.

In addition, the arrangement of the transceivers described above facilitates two possible methods for monitoring the light emitted from the laser. The first method is to sample light in a laser cavity using a grating. The grating should be designed to perform with a finite ratio of laser power in a small but lower or higher order diffraction mode. It can be coupled to another tap-off waveguide 13 and to another photodiode 14 (see FIG. 2). By accurate design, this higher order mode of spatial separation should be different from the modes of emitted and detected wavelengths λ ₁ and λ ₂ to allow for well separated waveguides in the focal plane.

The second method is based on monitoring the power emitted from the back side 7 of the laser amplifier 6. It is reflected from an angled mirror and coupled to the appropriate detector. In this case, the laser amplifier 6 must be fixed away from the chip edge to allow space for the mirror and the detector formed on the chip.

It is clear that the wavelength λ ₂ detected in order to maximize the receiver sensitivity of the transceiver should preferably coincide with the peak of the diffraction profile produced by the gratings 4, 12.

In addition, in the design of the AR coating 3, the receiver by reducing the laser cavity loss by increasing the reflectivity for the wavelength λ ₁ (requirement for reducing the laser threshold current) and the reflectance for the wavelength λ ₂ by reducing the receiver It is clear that a compromise must be reached between the need to increase the sensitivity of the circuit (the need to reduce the coupling loss to the input data).

For example, an AR coating with a reflectivity of about 20% (at both wavelengths) results in a coupling loss of 1 dB (i.e., a 1 dB reduction in sensitivity) compared to a coating with 0% reflectivity for received power. . The corresponding increase in laser threshold current will be about 30% compared to the use of HR coatings with 80% reflectivity.

As described above, the transceiver described above is preferably formed of a silicon-insulator (SOI) chip. SOI chips facilitate the integration of various elements of a transceiver and require relatively low manufacturing costs. Details of the SOI chips and rib waveguides formed therein are described in WO95 / 08787.

Methods for mounting elements such as photodiode detectors on SOI chips are described in GB2307786A and pending GB9702559.7 (ed. Number GB2315595A). The thin end rib waveguide structure is described in pending 9702579.7 (ed. Number GB2317023A).

Methods of producing transmission and reflection gratings on the surface of optical chips by electron beam or lithography techniques are well known and are not described in detail. The transmission grating 4 is typically configured in the form of a shallow groove with very few microns (ie 0.2 microns) in depth and height, and several microns in length. The period is chirped and typically varies from very few microns to several microns.

Reflective grating 12 typically consists of a deeply etched structure such that the reflective surface is 5-20 microns wide, with a spacing of about 5-20 microns, and the grating typically has a length of about 500 microns.

In addition, the mirror 11 is formed by extending all the passages through the light guide layer to be deeply etched and having a width of several hundred microns to several millimeters. Preferably, as shown in FIG. 3, the mirror is a concave lens for aiming and focusing light, and also has a reflective coating such as a coating of aluminum to be applied. As described above, the gratings and mirrors can be processed fairly accurately using known lithography etching processes, ie within an accuracy of about 0.2 micron. The above accuracy is repeated so that the transceiver can be manufactured with exactly combined transmit and receive wavelengths.

Claims (22)

A laser cavity formed between the first and second feedback elements; Wavelength selection means in the laser cavity for measuring the laser beam wavelength of the laser cavity; Light receiving means, which is at least one feedback element transmitted in part at the laser beam wavelength to allow the transceiver to emit radiation of the laser beam wavelength; And a wavelength selecting means different from the laser beam wavelength in the laser receiving means, arranged to receive light through one feedback element and to transmit light of the selected wavelength. 2. An integrated optical transceiver as set forth in claim 1, wherein said wavelength selecting means comprises a diffraction grating. 3. The apparatus of claim 2, further comprising: a first optical waveguide disposed to transmit and receive light at and from a grating at a first one of the angles corresponding to the laser beam wavelength received from the grating; And a second optical waveguide disposed to receive light from the grating at a second one of the angles corresponding to the selected wavelength received from the grating. 4. The integrated optical transceiver as set forth in claim 3, wherein said second waveguide has a width receiving end for receiving light in an angle range from a diffraction grating and a narrower transmission portion for transmitting light at the light receiving means. . 5. An integrated optical transceiver as claimed in claim 2, 3 or 4, wherein the diffraction grating is formed of an optical chip consisting of a transmission grating or a reflective grating formed by a series of recesses at the surface of the chip. In any of the preceding claims, the wavelength selection means is arranged to determine the laser beam wavelength and the selected wavelength with an accuracy of 10 nm or less regardless of temperature change. In any of the preceding claims, one of the feedback elements is comprised of a semi-reflective coating. 8. The integrated optical transceiver of claim 7, wherein the semi-reflective coating is more transmittable at the selected wavelength than the laser beam wavelength. The integrated optical transceiver of any of the preceding claims, wherein the other of the feedback elements consists of a highly reflective coating and is preferably arranged to reflect at least 80% of the light of the laser beam wavelength. The integrated optical transceiver as set forth in any one of the preceding claims, wherein the wavelength selecting means and the laser cavity are arranged such that the transceiver is capable of transmitting light at a majority of the laser beam wavelengths. The integrated optical transceiver as set forth in any one of the preceding claims, wherein the wavelength selecting means and the light receiving means are arranged to enable the transceiver to detect light at a majority of the selected wavelengths. 12. An integrated optical transceiver as claimed in claim 3, 10 or 11, wherein the majority of the optical waveguides are arranged to receive respective laser beam wavelengths or selected wavelengths from the light selection means. 13. The integrated optical transceiver of claim 12, wherein the receiving ends of the majority of waveguides are separated from each other by 20 microns or less, preferably 10 microns or less from each other. The integrated optical transceiver of any of the preceding claims, wherein one or each laser beam wavelength and one or each selected wavelength are arranged to be selected so as not to interfere with each other. An integrated optical transceiver as set forth in any of the preceding claims, characterized in that it is arranged with output monitoring means arranged to monitor the light transmitted through the other of the feedback element to monitor the power of emitted radiant energy. 4. The output power of the radiated energy of claim 3, wherein the diffraction grating is arranged to diffract light at the laser beam wavelength in a higher or lower order diffraction mode than received by the first optical waveguide. And output monitoring means for receiving the laser beam wavelength in a higher or lower order diffraction mode to monitor the power. 8. An integrated optical transceiver as set forth in any of the preceding claims, wherein said light receiving means is comprised of a photodetecting diode. The integrated optical transceiver of any of the preceding claims, wherein the integrated optical transceiver is integrated on a silicon-insulator chip. An integrated optical transceiver as claimed in any of the preceding claims, having a channel width of 10 nm or less. An integrated optical transceiver substantially as described by the accompanying drawings. The pair of transceivers of any of the preceding claims, wherein the laser beam wavelength of one transceiver is consistent with a selected wavelength of the other transceiver. 23. The device of claim 22, wherein the wavelength selection means of each transceiver consists of diffraction gratings each formed with the same accuracy, the laser beam wavelength and the selected wavelength of each transceiver being measured by essentially the same means and thus automatically coupled to each other. A pair of transceivers, characterized in that.