Milestone-Proposal:First Fiber Bragg Grating Demonstration at Communications Research Centre Canada in 1978

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Docket #:2019-07

This Proposal has been approved, and is now a Milestone

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Year or range of years in which the achievement occurred:


Title of the proposed milestone:

First Demonstration of a Fibre Bragg Grating, 1978

Plaque citation summarizing the achievement and its significance:

In 1978, researchers at the Communications Research Centre Canada were the first to observe photo-induced change of refractive index in glass optical fibres and demonstrate writing permanent refractive index gratings that act as very selective optical filters. Fibre Bragg Gratings of this type are easily integrated into fibre optic systems and have revolutionized the design of optical communications and sensor systems.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?

IEEE Ottawa Section

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Ottawa Section
Senior Officer Name: Winnie Ye, Section Chair

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Ottawa Section
Senior Officer Name: Winnie Ye, Section Chair

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Ottawa Section
IEEE Section Chair name: Winnie Ye, Section Chair

Milestone proposer(s):

Proposer name: Branislav Djokic
Proposer email: Proposer's email masked to public

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Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

Communications Research Centre (CRC) Canada, 3701 Carling Avenue, Ottawa (Nepean), Ontario K2K 2Y7, Canada, (Coordinates: 45.345196, -75.880435 )

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The site of the Communications Research Centre (CRC) Canada where the discovery was made.

Are the original buildings extant?


Details of the plaque mounting:

The plaques in two Canadian official languages, English and French, will be mounted outside of the CRC building so that they are easily accessible to the public.

How is the site protected/secured, and in what ways is it accessible to the public?

The Communications Research Centre (CRC) Canada is an agency of the Government of Canada and has on-site security. The site is accessible to the public by public and private transportation and on foot.

Who is the present owner of the site(s)?

The Government of Canada

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

In 1978, CRC researchers were the first to observe photosensitivity (photo-induced change of refractive index) in glass optical fibres and demonstrate that the phenomenon can be used to write permanent refractive index gratings that act as very selective in-line optical filters.

  • The work prompted many other inquiries into the cause of the photo-induced change of refractive index, i.e., photosensitivity, and its dependence on the wavelength of the light.
  • The Fiber Bragg Gratings that can be fabricated using this technique act as very selective optical filters and have since played an important role in optical communications and sensor systems.

Prior to this discovery, it was very difficult to fabricate high-quality fiber-compatible optical filters. The Fiber Bragg grating addressed this limitation handily.

The literature, e.g., [6], acknowledges that "Much additional work by many individuals took place before FBGs became a commercial reality." However, Hill et al's discovery is widely acknowledged to be the origin of this important optical technology.

This pioneering work has been widely recognized by the optics profession:

  • In 1991, Hill was elected to Fellowship in the Optical Society of America (OSA) for his efforts pertaining to fused fiber optical couplers, photosensitivity in fibers, novel fiber-based devices and nonlinear effects in fibers.
  • Hill was the 1995 recipient of the Manning Principal Award for the discovery of photosensitivity in optical fibers as well as the many commercial applications his work led to.
  • At the 1996 Optical Fiber Communications Conference, Hill was awarded the John Tyndall Award sponsored by the Institute of Electrical and Electronics Engineers (IEEE), the Lasers and Electro-Optics Society (LEOS) and the Optical Society of America. The award was presented for the discovery of photosensitivity in optical fibers and its application to Bragg gratings used in device applications in optical communications and sensor systems."
  • In 1998, Hill was awarded the inaugural Medal for Outstanding Achievement in Applied Photonics from the Canadian Association of Physicists (CAP) and the National Optics Institute (INO).
  • Hill was also awarded the Rank Prize in Optoelectronics in 2002 as one of four scientists recognized for creating and developing Fiber Bragg gratings.

What obstacles (technical, political, geographic) needed to be overcome?

Prior to this discovery, it was very difficult to fabricate high-quality fiber-compatible optical filters. The Fiber Bragg grating addressed this limitation handily.

A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. It is a periodic perturbation of the refractive index along the fiber length which is formed by exposure of the core to an intense optical interference pattern. This creates a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector. [4], [9] Today, FBGs have found applications in the fields of telecommunications, sensors, and fiber lasers. [8]

The first formation of permanent gratings in an optical fiber was demonstrated by Ken Hill et al. in 1978 at the Communications Research Centre (CRC), Ottawa, Ontario, Canada. This is supported by [1]-[9], unanimously. Initially, the gratings were fabricated using a visible laser propagating along the fiber core. [9]

There has been considerable interest in the theoretical study and fabrication of optical waveguide filters for light-wave communications. A motivation for the work presented in [1] was the improvement in the data-transmission capacity of light-wave communication links that results from the implementation of wavelength-division-multiplexed (WDM) systems. The waveguide filters can provide the accurate frequency discrimination required to separate the individual channels. Such filters can provide a further improvement of communication channel capacity if they are used as external reflectors to control the oscillation modes of the source. The resulting narrow oscillation line widths increase the potential channel packing density and reduce the effects of dispersion on each channel in high capacity WDM single-mode fiber links. [1]

Tailoring of the filter response for specific applications can be accomplished by implementing the appropriate longitudinal aperiodic perturbation of the waveguide structure. Experimental work in this area was restricted to the demonstration of simple band-stop filters or linearly chirped filters in planar waveguides. These structures have proven difficult to apply in practical form because of both their mode mismatch with optical fibers and their high optical loss. The loss presently limits the effective length of the filter structures fabricated in such waveguides to approximately 1 cm. The complexity of the response characteristic that can be synthesized was thus similarly limited. Other approaches to overcome these limitations of planar waveguide filters were desirable. [1]

Hill et al. reported in [1] the fabrication of tunable high-quality optical-waveguide filters with low scattering loss and the potential for extremely high-frequency selectivity. The standing wave pattern that resulted exposed the fiber and formed the periodic perturbation that comprises the filter. This photosensitive phenomenon was not reported previously and occurred to a greater or lesser extent in fibers other than of the type they used, Ge-doped silica-core fiber with numerical aperture (NA) in the range 0.1 - 0.2 and core diameter 2.5 µm. The photosensitivity was greatest for the larger Ge dopant concentration. Filters with effective lengths limited not by fiber loss but by the coherence time of the argon-ion laser (~0.1 µsec) can be fabricated in these fibers. [1]

To test the effectiveness of a number of these fiber reflection filters, the authors used each of these in place of the output reflector of an argon-ion laser and they were able to obtain stable continuous wave oscillation on the 488.0-nm line consistently. This demonstration represented the first reported distributed feedback (DFB) oscillation of a gas laser operating in the visible region of the spectrum. [1]

Hill et al. have utilized this phenomenon to form high-quality long-length reflection filters in fibers. They showed that these filters, whose reflectivity can reach nearly 100% of the light launched in the core, can be used as distributed feedback structures to replace the output reflector of an argon -ion laser. The filters have many potential applications, for example, in laser mode control and as synthesized filters with tailored response characteristics for use in high-capacity wavelength-multiplexed light-wave communication systems. The photosensitivity of the fiber guides found use as a storage mechanism and in wavelength-selective switches and couplers.

They pointed out that filters for these spectral regions can be made by different spatial-frequency techniques using two sources in the visible if adequate photosensitivity is not present in the infrared for direct writing. [1]

In [2], Hill et al. described in detail the experimental techniques used to produce and characterize these high-spectral resolution devices. The measurement of the filter characteristics showed that the filters can be made extremely narrow band (<200 MHz). This result was expected, since the filters were formed over long lengths of fiber and were accurately characterized as length-limited Bragg distributed-feedback waveguide filters. Moreover, these devices can be made with multiple rejection bands. An attractive feature of these structures was that they were readily tunable by mechanical strain. These characteristics, together with the compatibility of the devices with optical-fiber systems, made these filters of considerable interest as wavelength-selective devices for optical communications for use, most notably, in wavelength-multiplexed lightwave-communication systems. [2]

The authors demonstrated the formation of very-narrow-band reflection filters in an optical fiber by utilizing the photosensitivity of the fiber core. The filters were characterized as length-limited Bragg filter structures. Desired response characteristics can be obtained through the filters' capability to be overwritten to produce complex responses. These filters were used in a variety of devices useful for optical communications. [2]

A decade later, Gerald Meltz and colleagues demonstrated a flexible transverse holographic inscription technique where the laser illumination came from the side of the fiber. [3] This technique used the interference pattern of ultraviolet laser light to create the periodic structure of the fiber Bragg grating. [9] In [3], they cited the first Fiber Bragg Grating (FBG) demonstration, which motivated their research:

“In 1978, Hill et al.1,2 reported the formation of refractive-index gratings in germanosilicate fiber by sustained exposure of the core to the interference pattern of oppositely propagating modes of 488- or 514.5-nm argon-ion laser radiation. Subsequent investigations by Lam and Garside3 showed that the grating strength increased as the square of the writing power, which suggested a two-photon process as the cause of the index changes. This Letter presents the first results to our knowledge that show that in-fiber Bragg gratings can also be formed by illuminating the core from the side of the fiber with coherent UV radiation that lies in the 244-nm germania oxygen-vacancy defect band.4-6 This intense absorption band, which is ~35 nm wide, coincides with the second harmonic of both blue-green argon-ion laser lines used in previous research.” [3]

In [4], Hill et al, demonstrated a new FBG method based on fabrication of a phase mask grating:

“Certain optical fiber waveguides exhibit the property of photosensitivity’ which is a practical means for photoinducing1 permanent refractive index changes in the core of those fibers. Photosensitivity is not restricted to fiber structures: it has also been detected in several types of planar glass structures. A photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass. In this letter, we describe a nonholographic method for writing Bragg retroreflectors, in photosensitive optical fiber or planar waveguide structures. The essence of the method is to fabricate a phase mask grating. In conclusion, we have reported a simple method for fabricating high quality Bragg gratings in photosensitive optical waveguides, using low coherence lasers suitable for industrial environments. The spatial phase masks in the photolithographic Bragg grating imprinting apparatus apparently do not sustain damage in use. The combination of phase mask photoimprinting with single-pulse writing of in-fiber Bragg gratings14 could yield high-performance, low-cost devices.”

A detailed overview, with 102 references, of the beginnings of photosensitivity and fiber Bragg grating (FBG) technology by Hill and Meltz is presented in [5]. The basic techniques for fiber grating fabrication, their characteristics, and the fundamental properties of fiber gratings were described. The many applications of fiber grating technology were tabulated and selected applications described. Fiber grating technology and its applications were briefly reviewed. It was shown that the technology has a broad range of applications. The most promising applications have been in the fields of lightwave communications and optical fiber sensors which are based on the existence of photosensitivity in silica optical fibers and optical waveguides. However, this technology could be extended to other types of applications with the discovery of large photosensitivity in different material systems. [5]

In a highly acclaimed book by J. W. Goodman, “Introduction to Fourier Optics” [6], which has an outstanding number of 23635 citations as per Google Scholar, this discovery is described as follows:

“In 1978, Hill and coworkers [154] at the Communications Research Centre of Canada obtained some surprising experimental results while studying the nonlinear properties of a special fiber using blue light. They hypothesized and later proved that the phenomenon they were observing was caused by the writing of a relatively permanent, photoinduced index grating in the glass fiber itself. This was the birth of a new technology now known as Fiber Bragg Gratings (FBGs).“

The pioneering work by Hill et al., presented in [1], is still widely recognized and quoted in different fields, such as spectroscopy and bio-medical applications. This is illustrated by two recent papers, one on dual-comb spectroscopy published in Science in 2017 [7] and the other on femtosecond inscription of fiber Bragg gratings published in 2019 [8]:

“Dual-comb spectroscopy is generally very attractive for molecular spectroscopy, as well as asynchronous optical sampling, distance measurements, and fiber Bragg grating sensing [1].” [7]

“Fiber Bragg gratings (FBGs) were first demonstrated in the late 70's by Hill et al. [1]. Today, FBGs have found applications in various fields such as telecommunications, sensors, and fiber lasers.” [8]

What features set this work apart from similar achievements?

The literature, e.g., [6], acknowledges that "Much additional work by many individuals took place before FBGs became a commercial reality." However, Hill et al's discovery is widely acknowledged to be the origin of this important optical technology.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.


[1] K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication,” Appl. Phys. Lett., vol. 32, no. 10, pp. 647–649, 1978. Google Scholar: Cited by 2971.

[2] B. S. Kawasaki, K. O. Hill, D. C. Johnson, and Y. Fujii, “Narrow-band Bragg reflectors in optical fibers,” Opt. Lett., vol. 3, pp. 66–68, 1978. Google Scholar: Cited by 283.

[3] G. Meltz, W. W. Morey, and W. H. Glenn, “Formation of Bragg gratings in optical fibers by a transverse holographic method,” Opt. Lett., vol. 14, pp. 823–825, 1989. Google Scholar: Cited by 2657.

[4] K. O. Hill, B. Malo, F. Bilodeau, D. C. Johnson, and J. Albert, “Bragg gratings fabricated in monomode photosensitive optical fiber by UV exposure through a phase mask,” Appl. Phys. Lett., vol. 62, no. 10, pp. 1035–1037, 1993. Google Scholar: Cited by 1396.

[5] K. O. Hill and G. Meltz, “Fiber Bragg Grating Technology Fundamentals and Overview”, Journal of Lightwave Technology, vol. 15, no. 8, pp. 1263 – 1276, August 1997. Google Scholar: Cited by 2928.

[6] J. W. Goodman, “Introduction to Fourier Optics”, Roberts and Company Publishers; 3rd Edition, Dec. 2004. Google Scholar: Cited by 23635. (W H Freeman & Co; 4th Edition, May 1 2017)

[7] S. M. Link, D. J. H. C. Maas, D. Waldburger, U. Keller, “Dual-comb spectroscopy of water vapor with a free-running semiconductor disk laser”, Science, vol. 356, no. 6343, pp. 1164–1168, 16 June 2017. Google Scholar: Cited by 91.

[8] A. Halstuch, A. Shamir, and A. A. Ishaaya, “Femtosecond inscription of fiber Bragg gratings through the coating with a Low-NA lens”, Optics Express, vol. 27, no. 12, pp. 16935-16944, 2019. Google Scholar: Cited by 91.

[9] Fiber Bragg Grating, Wikipedia

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to Please see the Milestone Program Guidelines for more information.

Media:Ref_1_Hill.pdf Media:Ref_2_Hill.pdf Media:Ref_3_Meltz.pdf Media:Ref_4_Hill_Phase_Mask.pdf Media:Ref_5_Hill_Meltz_JLT-1997-1263.pdf Media:Ref_6_Book_p400_pg_10_2.pdf Media:Ref_7_Link_Science_2017.pdf Media:Ref_8_Halstuch_Opt_Exp_2019.pdf

(The full text of these references have been supplied to the staff of the IEEE History Center for support.)

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